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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Analysis and Characterization".

Deadline for manuscript submissions: closed (20 December 2020) | Viewed by 28992

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Prof. Dr. Andreas Kandelbauer

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Center for Process Analysis & Technology (PA&T), School of Applied Chemistry, Reutlingen University, Alteburgstrasse 150, 72762 Reutlingen, Germany
Interests: advanced materials; bio-based materials; silicon-containing polymers; composite materials; surface technology; thermoanalysis; process analytics; reaction kinetics
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Prof. Günter Lorenz

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1. Center for Process Analysis & Technology (PA&T), School of Applied Chemistry, Reutlingen University, Alteburgstrasse 150, 72762 Reutlingen, Germany
2. Reutlingen Research Institute (RRI), Reutlingen University, Alteburgstrasse 150, 72762 Reutlingen, Germany
Interests: niche polymers; polymer chemistry; reactive extrusion; biomaterials; silicon-containing polymers

Special Issue Information

Dear Colleagues,

Silicones are modern chemical specialties that can be customized in many ways to provide specific material properties. Silicones are therefore indispensable in many branches of industry. The market research institute Ceresana has investigated the rapidly growing plastics market and discovered that global sales of silicones have grown by an average of 4.2% per year since 2008. In 2016, sales reached 15.5 billion US dollars. It is predicted that the silicone market will continue to grow by an average of 4.0% per year until 2024. The most important representatives are silicone elastomers, silicone oils, and silicone resins.

Compared to classical organic compounds, silicones have unusual properties. In particular, they are characterized by thermal stability up to 470 K (197 °C) and above. They exhibit excellent water repellency, physical properties that are largely independent of temperature, high gas permeability, pronounced surface and interfacial activity, good dielectric properties, high radiation resistance, especially to UV light, good sliding and lubricating properties, and good damping properties. In addition, silicones have a high physiological compatibility, making them suitable not only for technical applications but also in the field of medical devices. Over the next eight years, the demand for silicones in the automotive industry is expected to grow at a similar rate as in the electrical and electronics industry.

The aim of this Special Issue is to highlight the progress and fundamental aspects for the synthesis, characterization, properties, and application of silicon-containing polymers, as well as their copolymers, composites, and nanocomposites.

Articles covering the following aspects of silicone-chemistry and technology are highly welcome:

Novel synthetic procedures for silicone-containing polymers
Novel silicone rubbers, silicone oils, silicon-containing polymers and polymer blends or co-polymers with silicone containing polymers
Novel silicone-based materials and processing strategies
Characterization techniques, novel analytical approaches and testing methods
Applications of silicone-polymers

Prof. Andreas Kandelbauer
Prof. Günter Lorenz
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

silicones
silicone oil
silicone rubber
inorganic-organic hybrid materials
silicon-containing polymers
polysiloxanes

Published Papers (8 papers)

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Research

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10 pages, 19387 KiB

Open AccessArticle

Chemical Imaging of Single Anisotropic Polystyrene/Poly (Methacrylate) Microspheres with Complex Hierarchical Architecture

by Alexandra Wagner, Stefanie Wagner, Jan-Erik Bredfeldt, Julia C. Steinbach, Ashutosh Mukherjee, Sandra Kronenberger, Kai Braun, Andreas Kandelbauer, Hermann A. Mayer and Marc Brecht

Polymers 2021, 13(9), 1438; https://doi.org/10.3390/polym13091438 - 29 Apr 2021

Cited by 1 | Viewed by 2909

Abstract

Monodisperse polystyrene spheres are functional materials with interesting properties, such as high cohesion strength, strong adsorptivity, and surface reactivity. They have shown a high application value in biomedicine, information engineering, chromatographic fillers, supercapacitor electrode materials, and other fields. To fully understand and tailor particle synthesis, the methods for characterization of their complex 3D morphological features need to be further explored. Here we present a chemical imaging study based on three-dimensional confocal Raman microscopy (3D-CRM), scanning electron microscopy (SEM), focused ion beam (FIB), diffuse reflectance infrared Fourier transform (DRIFT), and nuclear magnetic resonance (NMR) spectroscopy for individual porous swollen polystyrene/poly (glycidyl methacrylate-co-ethylene di-methacrylate) particles. Polystyrene particles were synthesized with different co-existing chemical entities, which could be identified and assigned to distinct regions of the same particle. The porosity was studied by a combination of SEM and FIB. Images of milled particles indicated a comparable porosity on the surface and in the bulk. The combination of standard analytical techniques such as DRIFT and NMR spectroscopies yielded new insights into the inner structure and chemical composition of these particles. This knowledge supports the further development of particle synthesis and the design of new strategies to prepare particles with complex hierarchical architectures. Full article

(This article belongs to the Special Issue Silicon-Containing Polymers)

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22 pages, 6400 KiB

Open AccessArticle

Synthesis of an Addition-Crosslinkable, Silicon-Modified Polyolefin via Reactive Extrusion Monitored by In-Line Raman Spectroscopy

by Steffen Ulitzsch, Tim Bäuerle, Mona Stefanakis, Marc Brecht, Thomas Chassé, Günter Lorenz and Andreas Kandelbauer

Polymers 2021, 13(8), 1246; https://doi.org/10.3390/polym13081246 - 12 Apr 2021

Cited by 6 | Viewed by 2304

Abstract

We present the modification of ethylene-propylene rubber (EPM) with vinyltetra-methydisiloxane (VTMDS) via reactive extrusion to create a new silicone-based material with the potential for high-performance applications in the automotive, industrial and biomedical sectors. The radical-initiated modification is achieved with a peroxide catalyst starting the grafting reaction. The preparation process of the VTMDS-grafted EPM was systematically investigated using process analytical technology (in-line Raman spectroscopy) and the statistical design of experiments (DoE). By applying an orthogonal factorial array based on a face-centered central composite experimental design, the identification, quantification and mathematical modeling of the effects of the process factors on the grafting result were undertaken. Based on response surface models, process windows were defined that yield high grafting degrees and good grafting efficiency in terms of grafting agent utilization. To control the grafting process in terms of grafting degree and grafting efficiency, the chemical changes taking place during the modification procedure in the extruder were observed in real-time using a spectroscopic in-line Raman probe which was directly inserted into the extruder. Successful grafting of the EPM was validated in the final product by ¹H-NMR and FTIR spectroscopy. Full article

(This article belongs to the Special Issue Silicon-Containing Polymers)

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37 pages, 9167 KiB

Open AccessArticle

Influence of Hard Segment Content and Diisocyanate Structure on the Transparency and Mechanical Properties of Poly(dimethylsiloxane)-Based Urea Elastomers for Biomedical Applications

by Natascha Riehle, Kiriaki Athanasopulu, Larysa Kutuzova, Tobias Götz, Andreas Kandelbauer, Günter E. M. Tovar and Günter Lorenz

Polymers 2021, 13(2), 212; https://doi.org/10.3390/polym13020212 - 9 Jan 2021

Cited by 18 | Viewed by 4479

Abstract

The effect of hard segment content and diisocyanate structure on the transparency and mechanical properties of soft poly(dimethylsiloxane) (PDMS)-based urea elastomers (PSUs) was investigated. A series of PSU elastomers were synthesized from an aminopropyl-terminated PDMS (

{\bar{M}}_{n}

: 16,300 g·mol⁻¹ [...] Read more.

{\bar{M}}_{n}

: 16,300 g·mol⁻¹), which was prepared by ring chain equilibration of the monomers octamethylcyclotetrasiloxane (D₄) and 1,3-bis(3-aminopropyl)-tetramethyldisiloxane (APTMDS). The hard segments (HSs) comprised diisocyanates of different symmetry, i.e., 4,4′-methylenebis(cyclohexyl isocyanate) (H₁₂MDI), 4,4′-methylenebis(phenyl isocyanate) (MDI), isophorone diisocyanate (IPDI), and trans-1,4-cyclohexane diisocyanate (CHDI). The HS contents of the PSU elastomers based on H₁₂MDI and IPDI were systematically varied between 5% and 20% by increasing the ratio of the diisocyanate and the chain extender APTMDS. PSU copolymers of very low urea HS contents (1.0–1.6%) were prepared without the chain extender. All PSU elastomers and copolymers exhibited good elastomeric properties and displayed elongation at break values between 600% and 1100%. The PSUs with HS contents below 10% were transparent and became increasingly translucent at HS contents of 15% and higher. The Young’s modulus (YM) and ultimate tensile strength values of the elastomers increased linearly with increasing HS content. The YM values differed significantly among the PSU copolymers depending on the symmetry of the diisocyanate. The softest elastomer was that based on the asymmetric IPDI. The elastomers synthesized from H₁₂MDI and MDI both exhibited an intermediate YM, while the stiffest elastomer, i.e., that comprising the symmetric CHDI, had a YM three-times higher than that prepared with IPDI. The PSUs were subjected to load–unload cycles at 100% and 300% strain to study the influence of HS morphology on 10-cycle hysteresis behavior. At 100% strain, the first-cycle hysteresis values of the IPDI- and H₁₂MDI-based elastomers first decreased to a minimum of approximately 9–10% at an HS content of 10% and increased again to 22–28% at an HS content of 20%. A similar, though less pronounced, trend was observed at 300% strain. First-cycle hysteresis among the PSU copolymers at 100% strain was lowest in the case of CHDI and highest in the IPDI-based elastomer. However, this effect was reversed at 300% strain, with CHDI displaying the highest hysteresis in the first cycle. In vitro cytotoxicity tests performed using HaCaT cells did not show any adverse effects, revealing their potential suitability for biomedical applications. Full article

(This article belongs to the Special Issue Silicon-Containing Polymers)

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18 pages, 5560 KiB

Open AccessArticle

Optimizing the Process Efficiency of Reactive Extrusion in the Synthesis of Vinyltrimethoxysilane-Grafted Ethylene-Octene-Copolymer (EOC-g-VTMS) by Response Surface Methodology

by Steffen Ulitzsch, Tim Bäuerle, Thomas Chassé, Günter Lorenz and Andreas Kandelbauer

Polymers 2020, 12(12), 2798; https://doi.org/10.3390/polym12122798 - 26 Nov 2020

Cited by 11 | Viewed by 2721

Abstract

Thermoplastic polymers like ethylene-octene copolymer (EOC) may be grafted with silanes via reactive extrusion to enable subsequent crosslinking for advanced biomaterials manufacture. However, this reactive extrusion process is difficult to control and it is still challenging to reproducibly arrive at well-defined products. Moreover, high grafting degrees require a considerable excess of grafting reagent. A large proportion of the silane passes through the process without reacting and needs to be removed at great expense by subsequent purification. This results in unnecessarily high consumption of chemicals and a rather resource-inefficient process. It is thus desired to be able to define desired grafting degrees with optimum grafting efficiency by means of suitable process control. In this study, the continuous grafting of vinyltrimethoxysilane (VTMS) on ethylene-octene copolymer (EOC) via reactive extrusion was investigated. Successful grafting was verified and quantified by ¹H-NMR spectroscopy. The effects of five process parameters and their synergistic interactions on grafting degree and grafting efficiency were determined using a face-centered experimental design (FCD). Response surface methodology (RSM) was applied to derive a causal process model and define process windows yielding arbitrary grafting degrees between <2 and >5% at a minimum waste of grafting agent. It was found that the reactive extrusion process was strongly influenced by several second-order interaction effects making this process difficult to control. Grafting efficiencies between 75 and 80% can be realized as long as grafting degrees <2% are admitted. Full article

(This article belongs to the Special Issue Silicon-Containing Polymers)

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13 pages, 2095 KiB

Open AccessArticle

A Process Analytical Concept for In-Line FTIR Monitoring of Polysiloxane Formation

by Julia C. Steinbach, Markus Schneider, Otto Hauler, Günter Lorenz, Karsten Rebner and Andreas Kandelbauer

Polymers 2020, 12(11), 2473; https://doi.org/10.3390/polym12112473 - 25 Oct 2020

Cited by 17 | Viewed by 3607

Abstract

The chemical synthesis of polysiloxanes from monomeric starting materials involves a series of hydrolysis, condensation and modification reactions with complex monomeric and oligomeric reaction mixtures. Real-time monitoring and precise process control of the synthesis process is of great importance to ensure reproducible intermediates and products and can readily be performed by optical spectroscopy. In chemical reactions involving rapid and simultaneous functional group transformations and complex reaction mixtures, however, the spectroscopic signals are often ambiguous due to overlapping bands, shifting peaks and changing baselines. The univariate analysis of individual absorbance signals is hence often only of limited use. In contrast, batch modelling based on the multivariate analysis of the time course of principal components (PCs) derived from the reaction spectra provides a more efficient tool for real-time monitoring. In batch modelling, not only single absorbance bands are used but information over a broad range of wavelengths is extracted from the evolving spectral fingerprints and used for analysis. Thereby, process control can be based on numerous chemical and morphological changes taking place during synthesis. “Bad” (or abnormal) batches can quickly be distinguished from “normal” ones by comparing the respective reaction trajectories in real time. In this work, FTIR spectroscopy was combined with multivariate data analysis for the in-line process characterization and batch modelling of polysiloxane formation. The synthesis was conducted under different starting conditions using various reactant concentrations. The complex spectral information was evaluated using chemometrics (principal component analysis, PCA). Specific spectral features at different stages of the reaction were assigned to the corresponding reaction steps. Reaction trajectories were derived based on batch modelling using a wide range of wavelengths. Subsequently, complexity was reduced again to the most relevant absorbance signals in order to derive a concept for a low-cost process spectroscopic set-up which could be used for real-time process monitoring and reaction control. Full article

(This article belongs to the Special Issue Silicon-Containing Polymers)

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16 pages, 3868 KiB

Open AccessArticle

Controlled Drug Release by the Pore Structure in Polydimethylsiloxane Transdermal Patches

by Barbara Mikolaszek, Jurgita Kazlauske, Anette Larsson and Malgorzata Sznitowska

Polymers 2020, 12(7), 1520; https://doi.org/10.3390/polym12071520 - 8 Jul 2020

Cited by 15 | Viewed by 3737

Abstract

The use of polydimethylsiloxanes (PDMS) as a drug carrier in transdermal adhesive patches is limited and there is insufficient data on the polymer structure and diffusivity, especially when additives modify the matrix. PDMS films with liquid additives (10% w/w): silicone oil (SO), polyoxyethylene glycol (PEG) or propylene glycol (PG) were prepared and indomethacin (IND; 5% w/w) was incorporated as a model active substance. The microstructure of the PDMS matrix and its permeability to water was investigated and correlated to the kinetics of the in-vitro IND release from the film. Three microscopic techniques were used to characterize in detail the microstructure of PDMS films: scanning electron microscopy, fluorescent microscopy and atomic force microscopy. PDMS films with hydrophilic PEG or PG showed different two-phase structures. A two-fold increase in steady-state flux of IND and increased water transport in the presence of PEG was attributed to the pore-like channels created by this polar solvent in the PDMS matrix. This effect was not observed in the films with PG, where only discontinuous droplet-like structures were visible. All additives significantly changed the tensile parameters of the films but the effects were not very pronounced. Full article

(This article belongs to the Special Issue Silicon-Containing Polymers)

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14 pages, 1622 KiB

Open AccessArticle

Hyperbranched Polycarbosiloxanes: Synthesis by Piers-Rubinsztajn Reaction and Application as Precursors to Magnetoceramics

by Huayu Zhang, Lei Xue, Jianquan Li and Qingyu Ma

Polymers 2020, 12(3), 672; https://doi.org/10.3390/polym12030672 - 17 Mar 2020

Cited by 16 | Viewed by 3314

Abstract

Silicon-containing hyperbranched polymers (Si-HBPs) have drawn much attention due to their promising applications. However, the construction of Si-HBPs, especially those containing functional aromatic units in the branched backbones by the simple and efficient Piers-Rubinsztajn (P–R) reaction, has been rarely developed. Herein, a series of novel hyperbranched polycarbosiloxanes were prepared by the P–R reactions of methyl-, or phenyl-triethoxylsilane and three Si–H containing aromatic monomers, including 1,4-bis(dimethylsilyl)benzene, 4,4′-bis(dimethylsilyl)-1,1′-biphenyl and 1,1′-bis(dimethylsilyl)ferrocene, using B(C₆F₅)₃ as the catalyst for 0.5 h at room temperature. Their structures were fully characterized by Fourier transform infrared spectroscopy, ¹H NMR, ¹³C NMR, and ²⁹Si NMR. The molecular weights were determined by gel permeation chromatography. The degrees of branching of these polymers were 0.69–0.89, which were calculated based on the quantitative ²⁹Si NMR spectroscopy. For applications, the ferrocene-linked Si-HBP can be used as precursors to produce functional ceramics with good magnetizability after pyrolysis at elevated temperature. Full article

(This article belongs to the Special Issue Silicon-Containing Polymers)

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Review

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17 pages, 417 KiB

Open AccessReview

The Influence of Filler Particles on the Mechanical Properties of Maxillofacial Prosthetic Silicone Elastomers: A Systematic Review and Meta-Analysis

by Aparna Barman, Farah Rashid, Taseef Hasan Farook, Nafij Bin Jamayet, James Dudley, Mohd Firdaus Bin Yhaya and Mohammad Khursheed Alam

Polymers 2020, 12(7), 1536; https://doi.org/10.3390/polym12071536 - 12 Jul 2020

Cited by 10 | Viewed by 4643

Abstract

Although numerous studies have demonstrated the benefits of incorporating filler particles into maxillofacial silicone elastomer (MFPSE), a review of the types, concentrations and effectiveness of the particles themselves was lacking. The purpose of this systematic review and meta-analysis was to review the effect of different types of filler particles on the mechanical properties of MFPSE. The properties in question were (1) tensile strength, (2) tear strength, (3) hardness, and (4) elongation at break. The findings of this study can assist operators, technicians and clinicians in making relevant decisions regarding which type of fillers to incorporate based on their needs. The systematic review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 26 original articles from 1970 to 2019 were selected from the databases, based on predefined eligibility criteria by two reviewers. The meta-analyses of nine papers were carried out by extracting data from the systematic review based on scoring criteria and processed using Cochrane Review Manager 5.3. Overall, there were significant differences favoring filler particles when incorporated into MFPSE. Nano fillers (69.23% of all studies) demonstrated superior comparative outcomes for tensile strength (P < 0.0001), tear strength (P < 0.00001), hardness (P < 0.00001) and elongation at break (P < 0.00001) when compared to micro fillers (30.76% of all studies). Micro fillers demonstrated inconsistent outcomes in mechanical properties, and meta-analysis of elongation at break argued against (P < 0.01) their use. Current findings suggest that 1.5% ZrSiO₄, 3% SiO₂, 1.5% Y₂O₃, 2–6% TiO₂, 2–2.5% ZnO, 2–2.5% CeO₂, 0.5% TiSiO₄ and 1% Ag-Zn Zeolite can be used to reinforce MFPSE, and help the materials better withstand mechanical degradation. Full article

(This article belongs to the Special Issue Silicon-Containing Polymers)

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