Next Article in Journal
Unmanned Aircraft Systems Risk Assessment Based on SORA for First Responders and Disaster Management
Previous Article in Journal
Current Status and Future Developments of Micromegas Detectors for Physics and Applications
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Applied Sciences
Volume 11
Issue 12
10.3390/app11125359
applsci-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Characteristics of Polycarbonate Soft Segment-Based Thermoplastic Polyurethane

by
Chien-Hui Wu
1,2,
Chin-Wen Chen
1,2,
Po-Han Chen
1,2,
Yi-Shin Chen
1,2,
Fu-Sheng Chuan
2,3,* and
Syang-Peng Rwei
1,2,*
1
Institute of Organic and Polymeric Materials, National Taipei University of Technology, Taipei 10608, Taiwan
2
Research and Development Center for Smart Technology, Taipei 10608, Taiwan
3
Department of Fashion and Design, Lee Ming Institute of Technology, New Taipei City 243, Taiwan
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2021, 11(12), 5359; https://doi.org/10.3390/app11125359
Submission received: 28 April 2021 / Revised: 7 June 2021 / Accepted: 7 June 2021 / Published: 9 June 2021
Browse Figures
Versions Notes

Abstract

:
The pre-experiment of the present study revealed that polyurethane (PU) synthesized using poly (hexamethylene carbonate) glycol (PHC) has high melt viscosity and is difficult to process. Therefore, poly (trimethylene carbonate) glycol (PTC) was employed to synthesize a PU product with low melt viscosity. First, four types of thermoplastic polyurethane (TPU) were formed through one-step solvent-free synthesis. TPU is presented in the format “TPU-X-Y,” with X representing the polyol (PTC or PHC, around 1000 molecular weight) and Y the chain extender (1,3-propane diol [PDO] or 1,4-butane diol [BDO]) used. The TPU was synthesized using a fixed molar ratio of (isocyanate):(polyol):(chain extender) = 2:1:1 and compared. The results indicated that chain entanglement often occurred among the long carbon chains of PHC. The synthesized TPU employed a property of PTC, namely converting polarity into reverse polarity in high temperatures, to resolve the high melt viscosity of TPU of the PHC series, which causes processing difficulties. The synthesized TPU-PTC-PDO exhibited favorable molecular arrangements. Given its polarity, TPU-PTC-PDO has outstanding tensile properties (strength at break: 41.10 ± 10.78 MPa; 100% modulus = 6.73 ± 0.12 MPa), making processing at lower temperatures (180 or 190 °C) feasible. With the inclusion of PTC, the synthesized polycarbonate TPU exhibits the advantages of polycarbonate and is suitable for a wide range of applications.

Graphical Abstract

1. Introduction

Early polyurethane (PU) synthesis methods involved synthesis in organic solvents. Dimethylformamide (DMF), a frequently used solvent, poses environmental risks, is detrimental to liver function, and reduces fertility. Other common solvents, including methyl ethyl ketone (MEK), toluene, and cyclohexanone, are highly volatile, nonenvironmentally friendly, and harmful to human health. Therefore, scientists have employed novel environmentally friendly synthesis methods such as waterborne polyurethane (WPU) [1,2], which uses cationic, anionic, and nonionic emulsifiers [3,4,5] to disperse PU micelles in water. However, the micelle size used for WPU must be moderate to achieve proper dispersion and prevent deposition in water. Micelle size is directly related to molecular weight; thus, the molecular weight of micelles used for WPU must be of limited size. If excessively large micelles are used for WPU, the mechanical strength of the resulting products will be weaker than that of those created using traditional solvent-based PU synthesis methods [6]. Scientists have also employed solvent-free PU synthesis methods [7,8] that do not require organic solvents and do not involve volatile organic compounds (VOCs) in product processing, making them environmentally friendly. Because solvent-free methods involve bulk polymerization, the synthesized product has a higher molecular weight and stronger mechanical strength than PU produced using WPU or traditional synthesis methods. In addition to exhibiting various advantages, solvent-free methods require little time for synthesis given their reaction speed. One-shot solvent-free PU synthesis is commonly used in industrial production. However, relatively few studies have compared solvent-free PU with solvent-based and waterborne PU. The present study investigated one-shot solvent-free PU synthesis and conducted an in-depth discussion of its properties.
Aliphatic, cyclic-aliphatic, and aromatic isocyanates are isocyanate monomers commonly applied in one-shot solvent-free PU synthesis. Because the reaction properties of aromatic isocyanates are more favorable than those of aliphatic and cyclic-aliphatic isocyanates, aromatic isocyanates are commonly used in industrial fields [9]. Among aromatic isocyanates, 4,4″-methylene diphenyl diisocyanate (MDI) has replaced the commonly-used toluene diisocyanate (TDI), which has been listed as a restricted substance because of the extremely harmful effects of VOCs on human health. MDI is not volatile and has favorable reaction properties and outstanding symmetry; moreover, high tacticity in the hard segment enhances the tensile strength and hardness of PU [10,11].
Polyols commonly used for PU synthesis include polyester, polyether, and polycarbonate polyols. In particular, polycarbonate-polyol-synthesized PU exhibits the excellent mechanical properties of polyester and the hydrolytic stability of polyether. The various advantages of carbonate groups in polycarbonate polyols have been mentioned in the literature [12]. Functional groups in polycarbonate polyols are rigid functional groups, which engender a high glass transition temperature (Tg) and increased plasticity in the synthesized PU. Consequently, polycarbonate PU has higher mechanical strength and greater Young’s modulus than do polyester or polyether PU made of a similar recipe [13]. Because carbonate groups have one more O atom than ester groups do, polycarbonate PU is more resistant to hydrolysis and oxidation than polyester or polyether PU [14]. Furthermore, the high polarity of carbonate groups results in polycarbonate PU having excellent wearability [15,16], enabling its application in the coating, binder, elastomer, and foaming material fields [17,18,19].
PU is a class of segmented copolymers composed of soft and hard segments. The soft segment is usually polyols, and the hard segment includes the diisocyanate and the chain extender. Due to the immiscibility of hard and soft segments, micro-phase separation occurs. The properties of the micro-phase separation copolymers are directly related to their two-phase microstructure, with the hard segments possessing more hydrogen bonds acting as physical crosslinks, for the flexible soft segments, and provide the material with high modulus and elastomeric properties [20,21].
The present study aimed to synthesize a solvent-free thermoplastic PU (TPU) with mechanical properties suitable for widespread application. Bifunctional monomers were selected to ensure the polymerization of a thermoplastic linear polymer. MDI was employed as the isocyanate, and polycarbonate polyol with a molecular weight of 1000 was adopted as the polyol. Two common bifunctional monomers, 1,3-propane diol (1,3-PDO) and 1,4-butane diol (1,4-BDO), were used as chain extenders. One-shot solvent-free PU synthesis was performed to polymerize polycarbonate-based TPU. The present study discusses the TPU’s properties. In the pre-experiment, three common commercial polyols, poly (butylene adipate) glycol (PBA, polyester type, Mn = 1000 g/mole), poly (tetramethylene ether) glycol (PTMG, polyether type, Mn = 1000 g/mole), and poly (hexamethylene carbonate) glycol (PHC, polycarbonate type, Mn = 1000 g/mole) were adopted to synthesize the TPU and their melt flow of index (MI) was verified and their molecular weight tested by GPC measurement (as listed in Tables S1 and S2). The results of the MI tests revealed that TPU-PHC-BDO has the lowest MI value of the three types of TPUs, so we did the experiments to discuss this phenomenon in the present study. To our knowledge, in-depth analysis of this problem has yet to be conducted. The current researchers observed the molecular structures and hypothesized that longer main carbon chain lengths result in chain entanglement, enabling the polymer to retain its melt strength in the melt state. However, the resulting poor flowability causes processing difficulties, thereby limiting the polymer’s applications. The previous experiment aimed to design a polycarbonate TPU with low melt viscosity to increase the application of polycarbonate TPU. Scholars have noted that trimethylene carbonate (TMC) has a high polar attraction in low-temperature environments. However, its polarity decreases under high temperatures, resulting in reverse polar attraction [22,23]. TMC can be synthesized into poly (trimethylene carbonate) glycol (PTC), comprising repeating units of TMC. Because PTC is not commercially available, we referenced a patented method and used TMC to synthesize PTC [24]. We attempted to design a TPU comprising repeating units of MDI-PTC-PDO and polymer chains with high tacticity. Because the polymer chains have high polar attraction, the TPU will have favorable mechanical strength under room temperature and good flowability in the melted state.
Accordingly, a series of experiments were designed to synthesize four types of TPU using MDI with two types of polycarbonate polyols and two types of chain extender (i.e., PDO or BDO). First, the TPUs were used to test the initial hypothesis. Subsequently, spectral structure analysis, mechanical property analysis, flowability analysis, and thermal property analysis were performed to verify whether chain entanglement reduced the flowability of PHC-synthesized TPU and whether the designed MDI-PTC-PDO has high mechanical properties and low melt viscosity.

2. Materials and Methods

2.1. Materials

The 4,4′-methylene diphenyl diisocyanate (MDI), 1,4-butanediol (BDO), and 1,3-propanediol (PDO) were provided by Lidye Chemical Co., Ltd., Taoyuan, Taiwan. TMC was purchased from Sun Chemical Technology Co., LTD., Shanghai, China. PHC (Mn = 1000 g/mole, OHV = 112.3 mg KOH/g) was purchased from Tosho, Tokyo, Japan. Dibutyltin dilaurate (DBTDL or T12) was purchased from Alfa Aesar, Harverhill, MA, US. Dimethylacetamide (DMAC, 99.8%), N,N-dimethylformamide (DMF, 99.8%), and Nafion NR50 were purchased from Sigma-Aldrich, St. Louis, MO, US. Methylene chloride (CH2Cl2, 99.8%) was purchased from Chem Seal, Richardson, TX, US. Methanol (99.8%) was purchased from JT Baker, Loughborough, LEI, UK.

2.2. Poly (TMC) Glycol Synthesis

TMC was subjected to monomer-based cationic ring-opening polymerization to synthesize PTC, with Nafion NR50 as the catalyst [22]. First, TMC (10 g) was dissolved in CH2Cl2 (20 mL) in a three-necked bottle. Nafion NR50 (2 g) was added, and a condenser was fixed to the bottle to reflux the volatile CH2Cl2. Mechanical stirring was then performed, and the mixture was left to react in a dry nitrogen environment for 24 h at 25 °C. Figure 1 presents the synthesis process.
After the reaction was completed, the product was instilled into a methanol/deionized water mixture (v/v = 9:1) for polarity separation. PTC sediment was collected from the bottom of the mixture and placed in a vacuum oven to remove excess water and solvent. PTC was subsequently subjected to nuclear magnetic resonance, and an automatic titrator was employed to determine the hydroxyl value (OHV). The hydroxyl value was then inputted into an equation to calculate a molecular weight (ASTM E 1899-02). Each batch of PTC had an OHV of 88.5–96.1 mg KOH/g.

2.3. TPU Synthesis

Polyol (PTC or PHC) and a chain extender (PDO or BDO) were placed in a 100 °C vacuum oven for 4 h to remove water. MDI was placed in a 60 °C convection oven for 2 h for melting. As presented in Table 1, TPU was synthesized using isocyanate, polyol, and a chain extender at a 2:1:1 mole ratio. Polyol and the chain extender were then extracted, evenly mixed utilizing a mechanical stirrer, and placed in an oven at 100 °C. The products were removed, added with MDI and T12 (catalyst), and subjected to machine mixing. After being mixed to a sticky state, the product was placed on an iron Teflon plate and placed in a 120 °C oven for 3 h. The baked lumpy TPU was subjected to tests, one of which involved using redissolved TPU as a coating material for mechanical property testing and dynamic mechanical analysis (DMA). The TPU was named in the TPU-X-Y format, with X and Y representing the polyol and chain extender used. For example, in TPU-PTCD-PDO, PTCD, and PDO represent the used polyol and chain extender, respectively. Figure 2 [25,26,27,28,29] displays the synthesis process. However, TPU copolymers in Figure 2 were ideal chemical structures for one unit cycle due to each lengthy polymer structure. Therefore, Figure 2 cannot show the random structure completely. Because the TPU used one-step synthesis in the research, MDI should react with BDO and polyols under an irregular state, and therefore the TPUs had the random hard segment repeat units. Scheme 1b in the manuscript was a suitable expression [26].

2.4. Instruments

2.4.1. Fourier Transform Infrared Spectroscopy

The Perkin Elmer Spectrum One Fourier transform infrared (FT-IR) (Waltham, MA, USA) spectrometer was set to the attenuated total reflectance mode to compare the TPU and polyol FT-IR spectrum and elucidate their chemical structures and verify the synthesized TPU. The testing conditions were set as 16 scans, the testing range 4000–650 cm−1, and the resolution 16 cm−1.

2.4.2. 1H Nuclear Magnetic Resonance

1H nuclear magnetic resonance (1H NMR) was performed using the Bruker AVANCE-III 300 MHz spectrometer (Billerica, MA, USA) to elucidate the chemical structure of the polyol and TPU and to verify the successful synthesis of the PTC. The polyol and TPU samples were dissolved in deuterated chloroform and deuterated dimethyl sulfoxide, respectively, and scanned 32 times at room temperature.

2.4.3. Gel Permeation Chromatography

The Malvern Panalytical Viscotek GPCmax VE-2001(Malvern, WOR, UK) was used to test the number-average molecular weight (Mn), weight-average molecular weight (Mw), and polydispersity index (PDI) of the TPU. The testing conditions were set as the DMF mobile phase, mobile speed of 1 mL/min, and a 300 mm × 810 mm column dimension.

2.4.4. Thermogravimetric Analysis

The Hitachi STA 7200 (Tokyo, Japan) was adopted for the pyrolysis analysis of polyol and TPU under a nitrogen environment at 35–600 °C, with the temperature increasing at 10 °C/min. The test results were analyzed to determine the initial decomposition temperature (Tdi) and the 5% weight loss temperature (Td 5wt%), and the differential thermogravimetry (DTG) curve was employed to label the maximum decomposition rate of temperature in the highest peak (Tmax).

2.4.5. Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) was performed on the polyol and TPU using the Hitachi SIINT SII X-DSC7000 (Tokyo, Japan). The resulting Tm and Tg curves were then analyzed. The polyol and TPU testing temperatures ranged from −80 to 150 °C and −80 to 215 °C, respectively, both of which were increased or decreased at 10 °C/min. Two heating–cooling cycles were performed, and the results of the second heating were adopted for DSC.

2.4.6. Dynamic Mechanical Analysis (DMA)

DMA was performed using the Hitachi DMS 6100 (Tokyo, Japan) in the tension mode. The specimens were 20 mm × 10 mm in size; the range of the testing temperature was −100 to 100 °C, increasing at 5 ° C/min; and the analysis was conducted at 1 Hz and deformation was 0.1 mm to collect the storage modulus (E′) and loss tangent (Tan δ).

2.4.7. Tensile Testing Machine

The tensile testing machine used was the Cometech A2 Universal (Taichung, Taiwan) with 500 kg load cell. The test was no preload. Dumbbell samples (size: length 33 mm, width 6 mm and thickness 0.32 mm) were employed as the specimen scale for ASTM D412-C tensile testing, and the gauge length was 33 mm. Each formulation was tested three times from the same batch. The stretching speed was 500 mm/min, and testing was performed under room temperature to obtain tensile strength, elongation at break, and modulus at 100% and 300% deformation.

2.4.8. Parallel-Plate Rheometer

Rheological property testing was performed using the Anton Paar Physica MCR-301 (Graz, Austria) under the oscillation testing mode. A cone plate (diameter: 25 mm; cone angle: 1°) served as the upper plate. The testing height was 55 microns; the deformation was 1%; temperatures 180, 190, and 200 °C; and angular frequencies 1–500 rad/s. The data of 40 locations were collected. The experimental results were used to determine the complex viscosity and discuss the processing properties of the TPU.

3. Results and Discussion

3.1. FT-IR Structure Elucidation

The FT-IR spectrums of polyols and TPU were compared, indicating a successful synthesis (Figure 3). First, the stretching vibration peak of –OH, –CH, –C=O, and –C–O– was observed at 3500, 2940, 1740, and 1250 cm−1, respectively. In Figure 3a, because PTC repeating units consist of more carbonate functional groups, the peak absorbance of the carbonate characteristic is higher. In Figure 3b, because the PHC repeating unit consists of more –CH groups, the peak absorbance of the –CH characteristic is higher [30,31].
The FT-IR spectrum of the synthesized TPU revealed a sharp –NH stretching vibration peak at 3300 cm−1, a curved –NH stretching vibration peak at 1530 cm−1, and no –NCO stretching vibration peak at 2300 cm−1. This suggests a successful reaction between the –OH functional groups of polyols and the chain extender with the –NCO functional group of diisocyanate, creating urethane functional groups. Furthermore, the stretching vibration peak of the MDI aromatic ring was observed at 1600 cm−1, confirming synthesis success [32].
In the TPU spectrum, free carbonyl groups and H-bonded carbonyl groups were observed at 1740 and 1700 cm−1, respectively [33,34]. Figure 4 reveals the number of H-bonds; Figure 4b,d and Table 2 indicate that the PHC-synthesized TPU had more H-bonds because the repeating units in PHC consist of more –CH groups. Accordingly, the soft chain segments of the PHC-synthesized TPU were easily turned, enabling facile interaction, and H-bonds are commonly observed between or inside the structures of molecular chains [35]. By contrast, PTC repeating units comprise more carbonate functional groups, which are rigid and not easily turned, resulting in fewer interactions with hard chain segments. A comparison between the performance of TPU-PTC-PDO and TPU-PTC-BDO in Figure 4a,c and Table 2 revealed that the TPU-PTC-PDO contained more H-bonds, indicating more favorable molecular chain orientation and suggesting an increase in interaction force between molecular chains. Because the TPU was synthesized using one-step synthesis, the molecular chains were randomly arranged. The main structures of PTC and PDO in TPU-PTC-PDO both consist of three C atoms, which increase the regularity of molecular chains and facilitates the formation of H- and polar bonds. The BDO structure of TPU-PTC-BDO contains four C atoms, whereas the polyol contains three C atoms, resulting in the molecular chains formed by randomly arranged TPU monomers having less regularity in arrangement, thus preventing the occurrence of intermolecular interactions (H-bonds and polar bonds).

3.2. 1H NMR Resonance Structure Elucidation

For the two polyols, 1H NHR structural elucidation was performed. In Figure 5a, the peaks at PTC δ = 4.24 and 3.74 ppm represent the methyl protons next to the carbonate and alcohol groups, respectively; the peaks at δ = 2.06 and 1.92 ppm represent the remaining methyl protons. Similarly, the peaks at PHC δ = 4.09 and 3.61 respectively represent the methyl protons next to the carbonate and alcohol groups; the peaks at δ = 1.65, 1.54, and 1.38 ppm represent the remaining methyl protons [36,37].
1H NMR structural elucidation was performed to verify the chemical structure of the TPU. In Figure 5b, the peak at δ = 9.5 ppm represents the N–H bond in the urethane group, the peaks at δ = 7.3 and 7.05 ppm represent the H-atom on the MDI benzene ring, and the peak at δ = 3.75 ppm represents the methylene group (Ar–CH2–Ar) between the two MDI benzene rings. In the TPU-PTC-PDO spectrum, the peak at δ = 4.11 ppm represents the methyl group next to the urethane group′s carbonate group; the peak at δ = 1.92 ppm represents the remaining methyl group. In the TPU-PHC-PDO spectrum, the peak at δ = 4.01 ppm represents the methyl group next to the carbonate group and the urethane group; the peak at δ = 1.94 ppm represents the methyl group in the middle of the PDO, and the peaks at δ = 1.54 and 1.27 ppm represent the remaining methyl groups on the PHC. In the TPU-PTC-BDO spectrum, the peak at δ = 4.11 ppm represents the methyl group next to the carbonate group and the urethane group; the peak at δ = 1.92 ppm represents the methyl group in the middle of the PTC, and the peak at δ = 1.68 ppm represents the remaining methyl groups on the BDO. Finally, in the TPU-PHC-BDO spectrum, the peak at δ = 4.01 ppm represents the methyl group next to the carbonate group and the urethane group, and the peaks at δ = 1.55 and 1.28 ppm represent the remaining methyl groups. In sum, the characteristic peaks indicate the successful synthesis of TPU [14,38,39].

3.3. Gel Permeation Chromatography Analysis

The TPU copolymers using the same chain extender had similar molecular weights (Table 3). The number-average molecular weights of TPU-PTC-BDO and TPU-PHC-BDO were comparable (between 75,000 and 78,000 g/mole). The number-average molecular weights of TPU-PTC-PDO and TPU-PHC-PDO were also similar, both between 107,000 and 121,000 g/mole. Moreover, the PDI values of the TPU samples were lower than 2. These results suggest that the TPU PDI values are in a reasonable range, with a synthesis quality sufficient and suitable for processing. Moreover, the TPU using PDO as a chain extender had a higher molecular weight than the TPU using BDO as a chain extender during synthesis, reflecting that BDO has a more considerable steric hindrance than does PDO.

3.4. Decomposition Properties

A typical TPU is thermally unstable. Thus, thermogravimetric analysis was used to measure the decomposition characteristics of the copolymers. Figure 6a,b displays the thermogravimetry (TG) and differential thermogravimetry (DTG) curves for the TPU copolymers. The TG curves of TPU-PTC-PDO and TPU-PTC-BDO revealed three distinct regions of weight loss, which are reflected in three peaks on the DTG curve. This result implies that both copolymers possess at least three significant stages of decomposition. However, the TPU-PHC-PDO and TPU-PHC-BDO presented only two significant stages of decomposition. Typical TPU is composed of hard and soft segments, which usually represent two stages of decomposition. The first stage is related to the hard segments, and the second to the soft segments. The temperatures of initial decomposition (Tdi) for the TPU copolymers were approximately 220 to 260 °C (Table 4), possibly due to the decomposition of urethane segments caused by MDI and a chain extender, or by MDI and a polyol [40]. Subsequently, the decompositions of the TPU exhibited obvious differences at 5 wt% of weight loss (Td 5wt%). The temperatures of Td 5wt% for TPU-PHC-PDO and TPU-PHC-BDO herein were higher than those of TPU-PTC-PDO and TPU-PTC-BDO. This result may be due to the effect of the decomposition of soft segments. To confirm the decomposition properties of polyol monomers, their decomposition temperatures were also examined (Figure 6c,d). As may be observed from Figure 6c, the temperature regions of decomposition for the PTC and PHC were respectively from 180 to 325 °C and from 200 to 400 °C. Furthermore, the decomposition temperature of the maximum rate (Tmax) for the PHC was 367.1 °C, obviously exceeding that of the PTC. Therefore, the Td 5wt% of the TPU-PHC copolymers were higher than those of the TPU-PTC copolymers because the decomposition temperature of PHC is higher than that of PTC [41,42]. The TPU-PTC copolymers (i.e., TPU-PTC-PDO and TPU-PTC-BDO) on the TG curve presented their first and second shoulder peak from 270 to 375 °C and from 375 to 470 °C, which are reflected in the two peaks on the DTG curve, as shown in Figure 6a,b. The decomposition of the region was possibly related to the decomposition of soft polycarbonate segments (PTC), including the decomposition, cyclization, and re-decomposition for the cyclic compounds [43]. The decomposition of the TPU-PHC copolymers (i.e., TPU-PHC-PDO and TPU-PHC-BDO) presented only one shoulder peak between 400 and 500 °C, which was related to the decomposition of soft polycarbonate segments (PHC), which also involves cyclization and re-decomposition of the cyclic compounds. The PHC polyol on the DTG curves displays a Tmax peak at 300 to 400 °C; therefore, the TPU-PHC presented only one shoulder peak. The Td 5wt% of the TPU-PTC copolymers was lower than that of the TPU-PHC copolymers, but their decomposition properties were sufficient to withstand the processing temperature. The TPU-PHC samples also had favorable processability, which is investigated in the section on rheological behavior.

3.5. Phase Transition Regions

The morphology of TPU presents a two-phase microstructure because the two dissimilar segment types are incompatible. Therefore, DSC thermograms of TPU are likely to display four transition regions as both phases crystallize. However, the structure and concentration of the hard and soft segments and the molecular weights and types of soft segments all influence the phase transition regions in DSC thermograms [44,45,46]. Therefore, not all phase transition regions are displayed on DSC thermograms. Figure 7a indicates the DSC thermograms of TPU-PTC and TPU-PHC with PDO and BDO, respectively.
TPU-PHC copolymers had a phase transition region at 0–30 °C, which corresponds to the glass transition temperature of soft segments (Tgs). On the other hand, the glass transition temperatures of hard segments (Tgh) for the TPU-PTC and TPU-PHC copolymers were 100–160 °C. Thus, none of the samples exhibited a significant soft segment crystallization because of the effect of copolymer synthesis, though the PHC presented a melting temperature at approximately 42.2 °C (Figure 7b). Furthermore, the glass transition temperature of hard segments (Tgh) and the melting temperature were not apparent on the thermograms because of the low content of hard segments. These results indicate that the TPU-PTC and TPU-PHC copolymers are amorphous copolymers [47,48].
Dynamic mechanical analysis (i.e., DMA) can clearly determine the phase transition temperature and modulus of polymers. Chain extenders and polyols affect the Tgs of TPU. As Figure 8a indicates, the TPU storage modulus dropped by two to three orders between −25 and 50 °C, indicating the Tgs. In addition, the peak of the loss tangent (Figure 8b) is affected by the Tgs of the TPU. The TPU copolymers using the BDO chain extender presented lower Tgs than did the TPU with PDO (Table 5). In addition, the TPU copolymers with PHC soft segments displayed lower Tgs than did the TPU with PTC. These results are attributed to the soft segments and chain extenders of long carbon chains having more conformations. Furthermore, the TPU-PTC-BDO had the lowest value of Tan δ, indicating it has low levels of damping behavior under the action of external force. By contrast, the TPU-PHC-PDO had the highest energy loss. This result suggests that the TPU-PTC-BDO is suitable for resisting external forces, whereas the TPU-PHC-PDO is suitable for recoil-resistant materials.
Figure 8a shows that the storage modulus (E′) of TPU-PTC-BDO decreased rapidly between 50–75 °C. However, this decrease was not observed for TPU-PHC-BDO. The length of the plateau was associated with molecular mass, chain entanglement, and degree of crosslinking [49]. Because TPU-PTC-BDO and TPU-PHC-BDO have a similar molecular weight, the difference should probably be attributed to PHC molecular structure units having longer carbon chain lengths. That is, the long carbon chains entangled, enabling TPU-PHC-BDO to retain its main structure strength at high temperatures. Furthermore, FT-IR results suggested weaker intermolecular force in TPU-PTC-BDO, which causes its main structure to break up at temperatures between 50 and 75 °C, resulting in the intermolecular forces collapsing and the storage modulus significantly decreasing. This result is presented in Figure 8b, indicating that the Tan δ of TPU-PTC-BDO increased dramatically between 50 and 75 °C. In a glassy state, the TPU-PTC copolymers possess more carbonate groups so that the polymer chains are restricted in mobility, contrary to the TPU-PHC copolymers that own the long carbon chains [50].

3.6. Tensile Strength

The molecular weight of a polymer is a key factor affecting its tensile strength. As mentioned in Section 3.3, the TPU copolymers using the same chain extender had comparable molecular weights. Thus, the molecular weight can be ignored in the analysis of tensile strength. As Table 6 indicates, the TPU had high elongations at break (above 460%), and both the TPU-PHC-PDO and TPU-PHC-BDO had moderate strain at break. However, the TPU-PHC-BDO and TPU-PTC-PDO differed considerably in terms of the strain at break. The results are possibly affected by hydrogen bonding. According to the FT-IR results in Section 3.1 (Scheme 1a), the TPU-PHC-BDO and TPU-PHC-PDO had strong intermolecular hydrogen bonds in the TPU-PTC-BDO; because the regularity of the molecular chains was poor (atactic) and the intermolecular attraction weak, poor strength resulted. Notably, TPU-PTC-PDO uses an odd-numbered polyol and chain extender to cause regular molecular chains (isotactic), stacking well, and more secondary bonds (such as hydrogen bonds, benzene π−π stacking, and dipole–dipole interactions) (Scheme 1b). Both of the copolymers had the same number of the hydrogen bonds per unit in Scheme 1b, and whereas we can see that Scheme 1b focuses on the blue and red squares in the soft segments, TPU-PTC-PDO could have possible dipole–dipole force (δ+ to δ−) and TPU-PTC-BDO does not (δ− to δ−). More dipole interactions for TPU copolymers can drive better mechanical strength. According to the literature, the storage modulus increases with dipole interactions under a glassy state [51]. We also saw this phenomenon in this study, and Figure 8a in the manuscript revealed that the storage modulus of TPU-PTC-PDO was higher than TPU-PTC-BDO., It can be compared to Scheme 1b to prove that TPU-PTC-PDO has more dipole interactions than TPU-PTC-BDO. Thus, it has a high tensile strength close to TPU-PHC-BDO and TPU-PHC-PDO (Table 6). The regularity of molecular chains also affected the stretching process. As is shown in Figure 9a,b, the stress of the TPU samples presented a rapid rise at approximately 300% of elongation, except in the case of TPU-PTC-BDO. This was because TPU-PTC-BDO is an odd-numbered carbon chain (a long chain of three carbons) corresponding to an even-numbered carbon chain (a short chain of four carbons), and it cannot be arranged regularly after stress as is expected in strain-induced crystallization [52,53,54,55]. Therefore, the intermolecular hydrogen bonding effect for the TPU-PTC-BDO was lower than for other samples. Accordingly, the TPU-PTC-BDO presented the lowest stress but the highest elongation.

3.7. Rheology Testing of Complex Viscosity

The complex viscosity of the TPU using the PTC polyol was much lower than that of the TPU using PHC (Figure 10). This result is attributed to the considerable reduction in the interaction of the polarity of PTC polyol at high temperatures, and intermolecular attraction is lost [22,23]. The master curves obtained from time–temperature superposition also revealed the same trend (Figure 11). Remarkably, the storage modulus of the TPU using the PTC polyol plummeted in the high-temperature region (at a lower angular frequency). However, the soft segments of the PHC resulted in chain entanglement, with more interactions existing in the hard chain segments, which were extremely attractive. Therefore, it can reliably support the main structure and maintain the melt strength at high temperatures; for this reason, it will be slightly challenging to process and require higher processing temperatures. However, the urethane group is prone to decomposition under a long-term high-temperature environment. Thus, attention should be paid to the processing time of TPU-PHC samples. Furthermore, the viscosity of TPU-PTC-PDO at 180 °C was slightly lower than that of the TPU-PHC samples at 200 °C. Therefore, the low viscosity of TPU-PTC-PDO facilitates processing. From an energy usage perspective, the suitable processing temperature of TPU-PTC-PDO is lower than that of TPU-PHC samples. Accordingly, the tensile strength of TPU-PTC-PDO was similar to that of the TPU-PHC samples, and it had favorable fluidity at high temperatures. These results indicate that TPU-PTC-PDO can be applied in coating or precision injection, which may expand the future usage of polycarbonate TPU elastomer.

4. Conclusions

The present study synthesized PTC and performed one-step solvent-free synthesis to synthesize two types of polycarbonate TPU (TPU-X-Y, X = PTC or PHC, Y = PDO or BDO) to explore differences in properties between TPU consisting of chains of odd-numbered and even-numbered carbon atoms. The results indicated that pyrolysis occurred in at least one segment in the TPU of PHC polyol. However, such pyrolysis may have been caused by two types of cracking behaviors, given that the pyrolysis temperatures of PHC and TPU hard segments are similar (Td ranges between 275 and 400 °C) and that PHC had adequate heat tolerance (Td 5wt% = 293.5–294.1 °C). However, because PTC consists of more carbonate groups, the pyrolysis temperature of PTC was lower than that of the TPU hard segments (Td = 251.7 °C). Accordingly, three-phase pyrolysis occurs in the TPU of PTC polyol (phase one: 220–315 °C; phase two: 295–385 °C, and phase three: 395–485 °C). The heat tolerance of the TPU of the PTC series was lower than that of the TPU of the PHC series (Td 5wt% = 243.5–270.4 °C). Therefore, when processing materials containing TPU of the PTC series, the temperature must be maintained below pyrolysis temperature to prevent pyrolysis and avoid material deterioration. The DSC and DMA results revealed the Tg of all the synthesized TPU to be 13.2–16.9 °C. In particular, chain entanglement often occurs in TPU of the PHC series, given the long carbon chain in the PHC group. This increases the TPU of the PHC series to levels closer to that of the TPU of the PTC series while retaining a constant storage modulus at 50–90 °C. Given the occurrence of chain entanglement between molecules, TPU of the PHC series exhibited outstanding tensile properties (tensile strength at break: around 38 MPa). By contrast, the high regularity of molecule arrangements in TPU-PTC-PDO generates immense polarity, thereby substantially enhancing its tensile properties (tensile strength at break: 41.1 ± 5.6 MPa). The rheology experiment revealed that TPU of the PTC series had high melt viscosity (TPU-PHC-PDO: 5.58 × 103 Pa·s at 200 °C at 1 rad/s, TPU-PHC-BDO: 3.16 × 103 Pa·s at 200 °C at 1 rad/s); this was due to entanglement between TPU molecular chains. In high-temperature environments, the polarity of TPU-PTC-PDO decreases, whereas the flowability increases. In low-temperature environments, the flowability of TPU-PTC-PDO is suitable for processing applications (2.51 × 103 Pa·s at 180 °C at 1 rad/s). The low-temperature processing of TPU-PTC-PDO conserves energy and saves costs; the material exhibits adequate flowability and mechanical properties under room temperature, thus boosting the potential for precision injection applications. The experimental results indicate that the synthesized TPU is suitable for a wide range of applications and exhibits the various advantages of carbonate TPU. Table 7 can show clearly the main results of these TPU copolymers to compare their advantages and disadvantages.

Supplementary Materials

The following are available online at https://www.mdpi.com/article/10.3390/app11125359/s1, Table S1 describes the composite of TPU copolymers, and Table S2 displays Mn, Mw, PDI, and MI of TPU copolymers.

Author Contributions

Conceptualization, C.-H.W. and F.-S.C.; methodology, C.-H.W., F.-S.C., and S.-P.R.; formal analysis, C.-H.W. and C.-W.C.; data curation, P.-H.C. and Y.-S.C.; writing—original draft preparation, C.-H.W.; writing—review and editing, C.-W.C.; supervision, S.-P.R.; All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministry of Science and Technology of Taiwan, grant number MOST 109-2634-F-027-001-.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Liang, H.; Liu, L.; Lu, J.; Chen, M.; Zhang, C. Castor Oil-Based Cationic Waterborne Polyurethane Dispersions: Storage Stability, Thermo-Physical Properties and Antibacterial Properties. Ind. Crop. Prod. 2018, 117, 169–178. [Google Scholar] [CrossRef]
  2. Feng, Z.; Wang, D.; Zheng, Y.; Zhao, L.; Xu, T.; Guo, Z.; Hussain, M.I.; Zeng, J.; Lou, L.; Sun, Y.; et al. A Novel Waterborne Polyurethane with Biodegradability and High Flexibility for 3D Printing. Biofabrication 2020, 12, 035015. [Google Scholar] [CrossRef] [PubMed]
  3. Liang, H.; Feng, Y.; Lu, J.; Liu, L.; Yang, Z.; Luo, Y.; Zhang, Y.; Zhang, C. Bio-Based Cationic Waterborne Polyurethanes Dispersions Prepared from Different Vegetable Oils. Ind. Crop. Prod. 2018, 122, 448–455. [Google Scholar] [CrossRef]
  4. Bullermann, J.; Friebel, S.; Salthammer, T.; Spohnholz, R. Novel Polyurethane Dispersions Based on Renewable Raw Materials—Stability Studies by Variations of DMPA Content and Degree of Neutralisation. Prog. Org. Coat. 2013, 76, 609–615. [Google Scholar] [CrossRef]
  5. Ji, X.; Wang, H.; Ma, X.; Hou, C.; Ma, G. Progress in Polydimethylsiloxane-Modified Waterborne Polyurethanes. RSC Adv. 2017, 7, 34086–34095. [Google Scholar] [CrossRef] [Green Version]
  6. Xiao, Y.; Fu, X.; Zhang, Y.; Liu, Z.; Jiang, L.; Lei, J. Preparation of Waterborne Polyurethanes Based on the Organic Solvent-Free Process. Green Chem. 2016, 18, 412–416. [Google Scholar] [CrossRef]
  7. Feng, Y.; Liang, H.; Yang, Z.; Yuan, T.; Luo, Y.; Li, P.; Yang, Z.; Zhang, C. A Solvent-Free and Scalable Method To Prepare Soybean-Oil-Based Polyols by Thiol–Ene Photo-Click Reaction and Biobased Polyurethanes Therefrom. ACS Sustain. Chem. Eng. 2017, 5, 7365–7373. [Google Scholar] [CrossRef]
  8. Lu, X.; Fang, C.; Sheng, X.; Zhang, L.; Qu, J. One-Step and Solvent-Free Synthesis of Polyethylene Glycol-Based Polyurethane As Solid–Solid Phase Change Materials for Solar Thermal Energy Storage. Ind. Eng. Chem. Res. 2019, 58, 3024–3032. [Google Scholar] [CrossRef]
  9. Nagy, L.; Nagy, T.; Kuki, Á.; Purgel, M.; Zsuga, M.; Kéki, S. Kinetics of Uncatalyzed Reactions of 2,4′- and 4,4′-Diphenylmethane-Diisocyanate with Primary and Secondary Alcohols. Int. J. Chem. Kinet. 2017, 49, 643–655. [Google Scholar] [CrossRef]
  10. Joshi, M.; Adak, B.; Butola, B.S. Polyurethane Nanocomposite Based Gas Barrier Films, Membranes and Coatings: A Review on Synthesis, Characterization and Potential Applications. Prog. Mater. Sci. 2018, 97, 230–282. [Google Scholar] [CrossRef]
  11. Zhang, L.; Huang, J. Effects of Hard-Segment Compositions on Properties of Polyurethane–Nitrolignin Films. J. Appl. Polym. Sci. 2001, 81, 3251–3259. [Google Scholar] [CrossRef]
  12. Petrović, Z.S.; Ferguson, J. Polyurethane Elastomers. Prog. Polym. Sci. 1991, 16, 695–836. [Google Scholar] [CrossRef]
  13. Kang, S.-Y.; Ji, Z.; Tseng, L.-F.; Turner, S.A.; Villanueva, D.A.; Johnson, R.; Albano, A.; Langer, R. Design and Synthesis of Waterborne Polyurethanes. Adv. Mater. 2018, 30, 1706237. [Google Scholar] [CrossRef] [PubMed]
  14. Wang, J.; Zhang, H.; Miao, Y.; Qiao, L.; Wang, X.; Wang, F. Waterborne Polyurethanes from CO 2 Based Polyols with Comprehensive Hydrolysis/Oxidation Resistance. Green Chem. 2016, 18, 524–530. [Google Scholar] [CrossRef]
  15. Chang, M.-T.; Lee, J.-Y.; Rwei, S.-P.; Wu, W.-Y.; Chiang, W.-Y.; Chang, S.-M.; Pan, Y.-H. Effects of NCO/OH Ratios and Polyols during Polymerization of Water-Based Polyurethanes on Polyurethane Modified Polylactide Fabrics. Fibers Polym. 2017, 18, 203–211. [Google Scholar] [CrossRef]
  16. Jofre-Reche, J.A.; Fuensanta, M.; Yáñez-Pacios, A.; Colera, M.; Rodriguez, F.; Iglesias, I.; Costa, V.; Martín-Martínez, J.M. Improvement in Adhesion, Abrasion Resistance, and Aging of Polyurethane Coatings Prepared with Polycarbonate Diol for Internal Pipelines. J. Mater. Civ. Eng. 2017, 29, 06017009. [Google Scholar] [CrossRef]
  17. Golling, F.E.; Pires, R.; Hecking, A.; Weikard, J.; Richter, F.; Danielmeier, K.; Dijkstra, D. Polyurethanes for Coatings and Adhesives—Chemistry and Applications. Polym. Int. 2019, 68, 848–855. [Google Scholar] [CrossRef]
  18. Zhang, H.; Chen, Y.; Zhang, Y.; Sun, X.; Ye, H.; Li, W. Synthesis and Characterization of Polyurethane Elastomers. J. Elastomers Plast. 2008, 40, 161–177. [Google Scholar] [CrossRef]
  19. Zhang, H.; Fang, W.-Z.; Li, Y.-M.; Tao, W.-Q. Experimental Study of the Thermal Conductivity of Polyurethane Foams. Appl. Therm. Eng. 2017, 115, 528–538. [Google Scholar] [CrossRef]
  20. Foks, J.; Janik, H.; Russo, R.; Winiecki, S. Morphology and Thermal Properties of Polyurethanes Prepared under Different Conditions. Eur. Polym. J. 1989, 25, 31–37. [Google Scholar] [CrossRef]
  21. Jiang, L.; Ren, Z.; Zhao, W.; Liu, W.; Liu, H.; Zhu, C. Synthesis and Structure/Properties Characterizations of Four Polyurethane Model Hard Segments. R. Soc. Open Sci. 2018, 5, 180536. [Google Scholar] [CrossRef] [Green Version]
  22. Brodin, A.; Jacobsson, P. Dipolar Interaction and Molecular Ordering in Liquid Propylene Carbonate: Anomalous Dielectric Susceptibility and Raman Non-Coincidence Effect. J. Mol. Liq. 2011, 164, 17–21. [Google Scholar] [CrossRef]
  23. Schneider, U.; Lunkenheimer, P.; Brand, R.; Loidl, A. Broadband Dielectric Spectroscopy on Glass-Forming Propylene Carbonate. Phys. Rev. E 1999, 59, 6924–6936. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  24. DiCosimo, R.; Drysdale, N.E.; Sunkara, H.B. Process to Make Poly(Trimethylene Carbonate) Glycol. U.S. Patent 8252885, 28 August 2012. [Google Scholar]
  25. Mattia, J.; Painter, P. A Comparison of Hydrogen Bonding and Order in a Polyurethane and Poly(Urethane−urea) and Their Blends with Poly(Ethylene Glycol). Macromolecules 2007, 40, 1546–1554. [Google Scholar] [CrossRef]
  26. Kumagai, S.; Motokucho, S.; Yabuki, R.; Anzai, A.; Kameda, T.; Watanabe, A.; Nakatani, H.; Yoshioka, T. Effects of Hard- and Soft-Segment Composition on Pyrolysis Characteristics of MDI, BD, and PTMG-Based Polyurethane Elastomers. J. Anal. Appl. Pyrolysis 2017, 126, 337–345. [Google Scholar] [CrossRef]
  27. Lin, W.; Qu, J.-P. Enhancing Impact Toughness of Renewable Poly(Lactic Acid)/Thermoplastic Polyurethane Blends via Constructing Cocontinuous-like Phase Morphology Assisted by Ethylene–Methyl Acrylate–Glycidyl Methacrylate Copolymer. Ind. Eng. Chem. Res. 2019, 58, 10894–10907. [Google Scholar] [CrossRef]
  28. Tien, Y.I.; Wei, K.H. High-Tensile-Property Layered Silicates/Polyurethane Nanocomposites by Using Reactive Silicates as Pseudo Chain Extenders. Macromolecules 2001, 34, 9045–9052. [Google Scholar] [CrossRef]
  29. Velankar, S.; Cooper, S.L. Microphase Separation and Rheological Properties of Polyurethane Melts. 2. Effect of Block Incompatibility on the Microstructure. Macromolecules 2000, 33, 382–394. [Google Scholar] [CrossRef]
  30. Zhang, Y.; Liang, R.; Xu, J.; Shen, L.; Gao, J.; Wang, X.; Wang, N.; Shou, D.; Hu, Y. Efficient Induction of Antimicrobial Activity with Vancomycin Nanoparticle-Loaded Poly(Trimethylene Carbonate) Localized Drug Delivery System. Int. J. Nanomed. 2017, 12, 1201–1214. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  31. Shen, Z.; Zhang, J.; Zhu, W.; Zheng, L.; Li, C.; Xiao, Y.; Liu, J.; Wu, S.; Zhang, B. A Solvent-Free Route to Non-Isocyanate Poly(Carbonate Urethane) with High Molecular Weight and Competitive Mechanical Properties. Eur. Polym. J. 2018, 107, 258–266. [Google Scholar] [CrossRef]
  32. Niemczyk, A.; Piegat, A.; Sonseca Olalla, Á.; El Fray, M. New Approach to Evaluate Microphase Separation in Segmented Polyurethanes Containing Carbonate Macrodiol. Eur. Polym. J. 2017, 93, 182–191. [Google Scholar] [CrossRef]
  33. Jofre-Reche, J.A.; García-Pacios, V.; Costa, V.; Colera, M.; Martín-Martínez, J.M. Role of the Interactions between Carbonate Groups on the Phase Separation and Properties of Waterborne Polyurethane Dispersions Prepared with Copolymers of Polycarbonate Diol. Prog. Org. Coat. 2015, 88, 199–211. [Google Scholar] [CrossRef]
  34. Fuensanta, M.; Jofre-Reche, J.A.; Rodríguez-Llansola, F.; Costa, V.; Iglesias, J.I.; Martín-Martínez, J.M. Structural Characterization of Polyurethane Ureas and Waterborne Polyurethane Urea Dispersions Made with Mixtures of Polyester Polyol and Polycarbonate Diol. Prog. Org. Coat. 2017, 112, 141–152. [Google Scholar] [CrossRef]
  35. Yilgor, I.; Yilgor, E. Structure-Morphology-Property Behavior of Segmented Thermoplastic Polyurethanes and Polyureas Prepared without Chain Extenders. Polym. Rev. 2007, 47, 487–510. [Google Scholar] [CrossRef]
  36. Bao, J.; Shi, G.; Tao, C.; Wang, C.; Zhu, C.; Cheng, L.; Qian, G.; Chen, C. Polycarbonate-Based Polyurethane as a Polymer Electrolyte Matrix for All-Solid-State Lithium Batteries. J. Power Sources 2018, 389, 84–92. [Google Scholar] [CrossRef] [Green Version]
  37. Hyun, H.; Kim, M.S.; Khang, G.; Lee, H.B. Ring-Opening Polymerization of Trimethylene Carbonate by Poly(Ethylene Glycol) in the Presence of HCl·Et2O as a Monomer Activator. J. Polym. Sci. Part A Polym. Chem. 2006, 44, 4235–4241. [Google Scholar] [CrossRef]
  38. Feula, A.; Tang, X.; Giannakopoulos, I.; Chippindale, A.M.; Hamley, I.W.; Greco, F.; Buckley, C.P.; Siviour, C.R.; Hayes, W. An Adhesive Elastomeric Supramolecular Polyurethane Healable at Body Temperature. Chem. Sci. 2016, 7, 4291–4300. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  39. Kuran, W.; Sobczak, M.; Listos, T.; Debek, C.; Florjanczyk, Z. New Route to Oligocarbonate Diols Suitable for the Synthesis of Polyurethane Elastomers. Polymer 2000, 41, 8531–8541. [Google Scholar] [CrossRef]
  40. García-Pacios, V.; Iwata, Y.; Colera, M.; Miguel Martín-Martínez, J. Influence of the Solids Content on the Properties of Waterborne Polyurethane Dispersions Obtained with Polycarbonate of Hexanediol. Int. J. Adhes. Adhes. 2011, 31, 787–794. [Google Scholar] [CrossRef]
  41. Orgilέs-Calpena, E.; Arán-Aís, F.; Torró-Palau, A.M.; Orgilέs-Barceló, C. Sustainable Polyurethane Adhesives Derived from Carbon Dioxide. Polym. Renew. Resour. 2016, 7, 1–12. [Google Scholar] [CrossRef]
  42. Ma, L.; Song, L.; Wang, H.; Fan, L.; Liu, B. Synthesis and Characterization of Poly(Propylene Carbonate) Glycol-Based Waterborne Polyurethane with a High Solid Content. Prog. Org. Coat. 2018, 122, 38–44. [Google Scholar] [CrossRef]
  43. Cipriani, E.; Zanetti, M.; Brunella, V.; Costa, L.; Bracco, P. Thermoplastic Polyurethanes with Polycarbonate Soft Phase: Effect of Thermal Treatment on Phase Morphology. Polym. Degrad. Stab. 2012, 97, 1794–1800. [Google Scholar] [CrossRef]
  44. Hesketh, T.R.; Bogart, J.W.C.V.; Cooper, S.L. Differential Scanning Calorimetry Analysis of Morphological Changes in Segmented Elastomers. Polym. Eng. Sci. 1980, 20, 190–197. [Google Scholar] [CrossRef]
  45. Lin, M.-F.; Shu, Y.-C.; Tsen, W.-C.; Chuang, F.-S. Differential Scanning Calorimetry Analysis of Silicon-Containing and Phosphorus-Containing Segmented Polyurethane. I—Thermal Behaviors and Morphology. J. Appl. Polym. Sci. 2001, 81, 3489–3501. [Google Scholar] [CrossRef]
  46. Shu, Y.-C.; Lin, M.-F.; Tsen, W.-C.; Chuang, F.-S. Differential Scanning Calorimetry Analysis of Silicon-Containing and Phosphorus-Containing Segmented Polyurethane. II Annealing Effect. J. Appl. Polym. Sci. 2001, 81, 3502–3513. [Google Scholar] [CrossRef]
  47. Ma, Z.; Hong, Y.; Nelson, D.M.; Pichamuthu, J.E.; Leeson, C.E.; Wagner, W.R. Biodegradable Polyurethane Ureas with Variable Polyester or Polycarbonate Soft Segments: Effects of Crystallinity, Molecular Weight, and Composition on Mechanical Properties. Biomacromolecules 2011, 12, 3265–3274. [Google Scholar] [CrossRef] [Green Version]
  48. Andronova, N.; Albertsson, A.-C. Resilient Bioresorbable Copolymers Based on Trimethylene Carbonate, l-Lactide, and 1,5-Dioxepan-2-One. Biomacromolecules 2006, 7, 1489–1495. [Google Scholar] [CrossRef]
  49. Eckstein, A.; Suhm, J.; Friedrich, C.; Maier, R.-D.; Sassmannshausen, J.; Bochmann, M.; Mülhaupt, R. Determination of Plateau Moduli and Entanglement Molecular Weights of Isotactic, Syndiotactic, and Atactic Polypropylenes Synthesized with Metallocene Catalysts. Macromolecules 1998, 31, 1335–1340. [Google Scholar] [CrossRef]
  50. Kim, B.K.; Lee, S.Y.; Xu, M. Polyurethanes Having Shape Memory Effects. Polymer 1996, 37, 5781–5793. [Google Scholar] [CrossRef]
  51. Li, Y.; Chen, J.; Cai, P.; Wen, Z. An Electrochemically Neutralized Energy-Assisted Low-Cost Acid-Alkaline Electrolyzer for Energy-Saving Electrolysis Hydrogen Generation. J. Mater. Chem. A 2018, 6, 4948–4954. [Google Scholar] [CrossRef]
  52. Wang, F.; Chen, S.; Wu, Q.; Zhang, R.; Sun, P. Strain-Induced Structural and Dynamic Changes in Segmented Polyurethane Elastomers. Polymer 2019, 163, 154–161. [Google Scholar] [CrossRef]
  53. Christenson, E.M.; Anderson, J.M.; Hiltner, A.; Baer, E. Relationship between Nanoscale Deformation Processes and Elastic Behavior of Polyurethane Elastomers. Polymer 2005, 46, 11744–11754. [Google Scholar] [CrossRef]
  54. Cui, X.; Li, W.; Yan, D. Investigation on Odd-Odd Nylons Based on Undecanedioic Acid: 1. Synthesis and Characterization. Polym. Int. 2004, 53, 1729–1734. [Google Scholar] [CrossRef]
  55. Cui, X.; Liu, Z.; Yan, D. Synthesis and Characterization of Novel Even–Odd Nylons Based on Undecanedioic Acid. Eur. Polym. J. 2004, 40, 1111–1118. [Google Scholar] [CrossRef]
Applsci 11 05359 g001 550
Figure 1. PTC synthesis.
Figure 1. PTC synthesis.
Applsci 11 05359 g001
Applsci 11 05359 g002 550
Figure 2. Synthesis route of TPU copolymers.
Figure 2. Synthesis route of TPU copolymers.
Applsci 11 05359 g002
Applsci 11 05359 g003 550
Figure 3. FT-IR spectrum of (a) PTC, TPU-PTC-PDO, and TPU-PTC-BDO; and (b) PHC, TPU-PHC-PDO, and TPU-PHC-BDO.
Figure 3. FT-IR spectrum of (a) PTC, TPU-PTC-PDO, and TPU-PTC-BDO; and (b) PHC, TPU-PHC-PDO, and TPU-PHC-BDO.
Applsci 11 05359 g003
Applsci 11 05359 g004 550
Figure 4. C=O characteristic deconvolution peaks of (a) TPU-PTC-PDO, (b) TPU-PHC-PDO, (c) TPU-PTC-BDO, and (d) TPU-PHC-BDO.
Figure 4. C=O characteristic deconvolution peaks of (a) TPU-PTC-PDO, (b) TPU-PHC-PDO, (c) TPU-PTC-BDO, and (d) TPU-PHC-BDO.
Applsci 11 05359 g004
Applsci 11 05359 g005 550
Figure 5. 1H NMR resonance spectrum of (a) polyols and (b) TPU.
Figure 5. 1H NMR resonance spectrum of (a) polyols and (b) TPU.
Applsci 11 05359 g005
Applsci 11 05359 g006a 550Applsci 11 05359 g006b 550
Figure 6. Decomposition curves of (a) TPU-TG, (b) TPU-DTG, (c) polyols-TG, and (d) polyols-DTG.
Figure 6. Decomposition curves of (a) TPU-TG, (b) TPU-DTG, (c) polyols-TG, and (d) polyols-DTG.
Applsci 11 05359 g006aApplsci 11 05359 g006b
Applsci 11 05359 g007 550
Figure 7. Second heating DSC thermograms of (a) TPU and (b) polyols.
Figure 7. Second heating DSC thermograms of (a) TPU and (b) polyols.
Applsci 11 05359 g007
Applsci 11 05359 g008 550
Figure 8. TPU (a) storage modulus curve and (b) tangent delta curve.
Figure 8. TPU (a) storage modulus curve and (b) tangent delta curve.
Applsci 11 05359 g008
Applsci 11 05359 sch001 550
Scheme 1. (a) TPU-PHC copolymers had strong intermolecular hydrogen bonds; (b) the regularity of the molecular chains in TPU-PTC copolymers.
Scheme 1. (a) TPU-PHC copolymers had strong intermolecular hydrogen bonds; (b) the regularity of the molecular chains in TPU-PTC copolymers.
Applsci 11 05359 sch001
Applsci 11 05359 g009 550
Figure 9. Stress–strain curve of TPU when the chain extender is (a) PDO or (b) BDO.
Figure 9. Stress–strain curve of TPU when the chain extender is (a) PDO or (b) BDO.
Applsci 11 05359 g009
Applsci 11 05359 g010 550
Figure 10. TPU rheology testing (complex viscosity vs. angular frequency) at (a) 180 °C, (b) 190 °C, and (c) 200 °C.
Figure 10. TPU rheology testing (complex viscosity vs. angular frequency) at (a) 180 °C, (b) 190 °C, and (c) 200 °C.
Applsci 11 05359 g010
Applsci 11 05359 g011 550
Figure 11. Master curve obtained from time–temperature superposition of (a) TPU-PTC-PDO, (b) TPU-PHC-PDO, (c) TPU-PTC-BDO, and (d) TPU-PHC-BDO.
Figure 11. Master curve obtained from time–temperature superposition of (a) TPU-PTC-PDO, (b) TPU-PHC-PDO, (c) TPU-PTC-BDO, and (d) TPU-PHC-BDO.
Applsci 11 05359 g011
Table
Table 1. Composite of TPU copolymers.
Table 1. Composite of TPU copolymers.
TPU-X-YMole Ratio = [A]:[B]:[C] a
TPU-PTC-BDO2:1:1
TPU-PHC-BDO2:1:1
TPU-PTC-PDO2:1:1
TPU-PHC-PDO2:1:1
a: [A] = diisocynate; [B] = polycarbonate diol; [C] = chain extender.
Table
Table 2. Ratios of the intensities of the IR bands at 1740 and 1700 cm−1 in the ATR-IR spectra of the polycarbonate TPUs.
Table 2. Ratios of the intensities of the IR bands at 1740 and 1700 cm−1 in the ATR-IR spectra of the polycarbonate TPUs.
TPU-X-Y1740 cm−1 Intensity (%)1700 cm−1 Intensity (%)
TPU-PTC-PDO67.532.5
TPU-PHC-PDO47.252.8
TPU-PTC-BDO73.526.5
TPU-PHC-BDO54.245.8
Table
Table 3. Number-average molecular weight (Mn), weight-average molecular weight (Mw), and PDI of TPU copolymers.
Table 3. Number-average molecular weight (Mn), weight-average molecular weight (Mw), and PDI of TPU copolymers.
TPU-X-YMn (g/mole)Mw (g/mole)PDI
TPU-PTC-BDO77,000137,0001.78
TPU-PHC-BDO75,000139,0001.85
TPU-PTC-PDO120,000226,0001.88
TPU-PHC-PDO107,000204,0001.91
Mn: number-average molecular weight; Mw: weight-average molecular weight; PDI: polydispersity index (Mw/Mn).
Table
Table 4. Characteristic temperatures of decomposition.
Table 4. Characteristic temperatures of decomposition.
Polyol or TPU-X-YTdi a (°C)Td 5wt% b (°C)Tmax c (°C)Ts1 d (°C)Ts2 d (°C)
PTC182.2212.0251.7--
PHC205.0242.0367.1--
TPU-PTC-PDO224.3243.5263.9322.8438.8
TPU-PHC-PDO260.5293.5350.8444.8-
TPU-PTC-BDO247.7270.4298.1344.5441.0
TPU-PHC-BDO261.8294.1343.9448.3-
a: Tdi: temperature of initial decomposition; b: Td 5wt%: decomposition temperature of 5 wt% of weight loss; c: Tmax: temperature of the maximum rate; d: Ts1 & Ts2: first and second shoulder peaks on the DTG curve.
Table
Table 5. Peak of loss tangent response to the Tgs of TPU.
Table 5. Peak of loss tangent response to the Tgs of TPU.
TPU-X-YTgs (°C)
TPU-PTC-PDO5.73
TPU-PHC-PDO5.15
TPU-PTC-BDO1.08
TPU-PHC-BDO0.81
Table
Table 6. Mechanical properties of the TPU copolymers.
Table 6. Mechanical properties of the TPU copolymers.
TPU-X-YElongation at Break
(%)		Modulus at 100%
Deformation (MPa)		Modulus at 300%
Deformation (MPa)		Tensile Strength
(MPa)
TPU-PTC-PDO571.6 ± 27.26.73 ± 0.1215.18 ± 0.1941.1 ± 10.8
TPU-PHC-PDO466.6 ± 11.84.92 ± 0.0313.68 ± 0.0337.9 ± 16.9
TPU-PTC-BDO613.3 ± 25.55.62 ± 0.078.19 ± 0.0313.4 ± 0.8
TPU-PHC-BDO482.2 ± 21.75.86 ± 0.1814.30 ± 0.2737.9 ± 10.8
Table
Table 7. TPU main results and properties.
Table 7. TPU main results and properties.
TPU-X-YTdi (°C)Tensile Strength (MPa)Complex Viscosity (Pa·s) at 180 °C at 1 rad/s
TPU-PTC-PDO224.341.1 ± 10.82.51 × 103
TPU-PHC-PDO260.537.9 ± 16.91.45 × 104
TPU-PTC-BDO247.713.4 ± 0.81.49 × 103
TPU-PHC-BDO261.837.9 ± 10.81.24 × 104
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Wu, C.-H.; Chen, C.-W.; Chen, P.-H.; Chen, Y.-S.; Chuan, F.-S.; Rwei, S.-P. Characteristics of Polycarbonate Soft Segment-Based Thermoplastic Polyurethane. Appl. Sci. 2021, 11, 5359. https://doi.org/10.3390/app11125359

AMA Style

Wu C-H, Chen C-W, Chen P-H, Chen Y-S, Chuan F-S, Rwei S-P. Characteristics of Polycarbonate Soft Segment-Based Thermoplastic Polyurethane. Applied Sciences. 2021; 11(12):5359. https://doi.org/10.3390/app11125359

Chicago/Turabian Style

Wu, Chien-Hui, Chin-Wen Chen, Po-Han Chen, Yi-Shin Chen, Fu-Sheng Chuan, and Syang-Peng Rwei. 2021. "Characteristics of Polycarbonate Soft Segment-Based Thermoplastic Polyurethane" Applied Sciences 11, no. 12: 5359. https://doi.org/10.3390/app11125359

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop