Polymer Stereochemistry

A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (10 July 2018)

Special Issue Editor

Department of Chemistry and Biology, Salerno University, 84084 Fisciano SA, Italy
Interests: polyolefin synthesis; structure–reactivity relationships in homogeneous Ziegler–Natta catalysis; polyinsertion catalysis aimed to asymmetrically synthesise chiral intermediates

Special Issue Information

Dear Colleagues,

In the mid-1950s, the chemical world was startled by the announcement of prof. Natta that stereoregular polymers of α-olefins can be formed with Ziegler catalysts. About 30 years later, the discovery of the methyluminoxane as a powerful cocatalyst provided a wide armoury of homogeneous polyinsertion catalysts for the synthesis of new polymeric materials with finely tuned structures. Furthermore, the growing interest in green chemistry, even in the field of macromolecular science, involved monomers from renewable sources bearing asymmetric centres enabling them to give different stereoregular polymers. The aim of this Special Issue is to collect papers describing both the synthetic aspects concerning the production of stereoregular polymers and the relationship between stereoregularity and physical properties. We also welcome works dealing with the steroregularity related to the behaviour of the so-called smart materials as well as both experimental and theoretical studies on the stereocontrol mechanisms.

Prof. Leone Oliva
Guest Editor

Manuscript Submission Information

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Keywords

  • Stereoregular polyolefins
  • Asymmetric monomer
  • Optically active polymer
  • Stereoselective catalysis
  • Ziegler–Natta catalyst
  • Structure–properties relationship

Published Papers (4 papers)

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Research

10 pages, 1059 KiB  
Article
Substituent Effects of Phenyl Group on Silylene Bridge in Stereospecific Polymerization of Propylene with C1-Symmetric Ansa-Silylene(fluorenyl)(amido) Dimethyl Titanium Complexes
by Huajin Wang, Yanqing Li and Zhengguo Cai
Polymers 2018, 10(10), 1075; https://doi.org/10.3390/polym10101075 - 28 Sep 2018
Cited by 2 | Viewed by 2806
Abstract
A C1-symmetric (methylphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (1) and (diphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (2) were synthesized and characterized by 1H NMR, element analysis, and X-ray crystal analysis. The coordination mode of the fluorenyl ligand to the titanium [...] Read more.
A C1-symmetric (methylphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (1) and (diphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (2) were synthesized and characterized by 1H NMR, element analysis, and X-ray crystal analysis. The coordination mode of the fluorenyl ligand to the titanium metal is an η3 manner in each complex. These complexes were applied for propylene polymerization using dried modified methyaluminoxane (dMMAO) as a cocatalyst under different propylene pressures in a semi batch-type method. The catalytic activity was strongly dependent on the structure of the complex and the propylene pressure, where complex 1 exhibited the highest activity (600 kg mol−1·h−1) under a propylene pressure of 8.0 atm to produce high molecular weight polypropylene. The polypropylenes obtained were syndiotactic-rich with an rr value of 0.50, indicating that the silylene bridge was not efficient for the isospecificity of a constrained geometry catalyst (CGC). The mechanical properties of the resulting polymers depended on their microstructure. Full article
(This article belongs to the Special Issue Polymer Stereochemistry)
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12 pages, 5766 KiB  
Article
Maleic Anhydride-Grafted Isotactic Polybutene-1 and Modified Polyamide 6
by Yongxian Zhao, Chen Ma, Shijie Cheng, Wei Xu, Yuejuan Du, Yansong Bao and Zuojie Xiao
Polymers 2018, 10(8), 872; https://doi.org/10.3390/polym10080872 - 05 Aug 2018
Cited by 8 | Viewed by 4408
Abstract
Maleic anhydride (MAH)–divinyl benzene (DVB) multi-monomer melt-grafting onto isotactic polybutene-1 (iPB-1) was carried out in a torque rheometer. The effects of dicumyl peroxide (DCP), MAH, and DVB concentrations, and temperature, on the reaction, were investigated. The optimized conditions were 170 °C, DVB/MAH = [...] Read more.
Maleic anhydride (MAH)–divinyl benzene (DVB) multi-monomer melt-grafting onto isotactic polybutene-1 (iPB-1) was carried out in a torque rheometer. The effects of dicumyl peroxide (DCP), MAH, and DVB concentrations, and temperature, on the reaction, were investigated. The optimized conditions were 170 °C, DVB/MAH = 4:6 (mass ratio). DVB as a comonomer enhanced the grafting degree (Gd) and grafting efficiency (Ge) of iPB-g-MAH better than styrene. The initiator DCP had little effect on Gd as its concentration over 0.2 phr, but the grafts’ melt flow rate (MFR) increased significantly, and relative molecular weight decreased remarkably with increased DCP concentration. With increasing Gd, the contact angle of grafts with water decreased, and there was a larger crystallization rate. The study of iPB-1 and iPB-g-MAH (Gd = 1.5%)-modified polyamide 6 (PA6) showed that iPB-g-MAH had an obviously toughening effect on PA6. With increasing iPB-g-MAH concentration, the blends of impact strength and elongation at break increased obviously, tensile strength decreased slightly, and MFR decreased prominently, which greatly slowed the processing degradation of PA6. The properties of iPB-1/PA6 blends deteriorated. Both DSC curves and SEM micrographs confirmed that PA6/iPB-g-MAH blends had much better compatibility than PA6/iPB. The reason was that the anhydride group in iPB-g-MAH reacted with amide group in PA6 to improve the compatibility between two phases, and iPB-g-MAH is an excellent modifier for PA6. Full article
(This article belongs to the Special Issue Polymer Stereochemistry)
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8 pages, 1756 KiB  
Article
Assignment of Regioirregular Sequences in the 13C NMR Spectrum of Syndiotactic Polypropylene
by Roberta Cipullo, Antonio Vittoria and Vincenzo Busico
Polymers 2018, 10(8), 863; https://doi.org/10.3390/polym10080863 - 04 Aug 2018
Cited by 2 | Viewed by 5812
Abstract
The 13C NMR microstructure of a polypropylene (PP) sample is a fundamental source of information on its properties, and also a ‘fingerprint’ of the catalytic species used to produce it. Likely due to a much greater technological importance, isotactic polymers (i-PP) have [...] Read more.
The 13C NMR microstructure of a polypropylene (PP) sample is a fundamental source of information on its properties, and also a ‘fingerprint’ of the catalytic species used to produce it. Likely due to a much greater technological importance, isotactic polymers (i-PP) have been more thoroughly investigated that syndiotactic ones (s-PP). In this paper, we report the first full assignment of regioirregular sequences in s-PP samples made with two well-known molecular catalysts, namely a Cs-symmetric (cyclopentadienyl)(fluorenyl) ansa-zirconocene and a fluxional bis(phenoxyimine)Ti species. The results shed more light on the mechanism of chain propagation at the two catalysts, and open the door to the investigation of more elusive cases like the formation of s-PP blocks in the presence of multi-sited heterogeneous Ziegler-Natta systems. Full article
(This article belongs to the Special Issue Polymer Stereochemistry)
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10 pages, 3203 KiB  
Article
A Study of the Pressure-Induced Solidification of Polymers
by Xiuru Liu, Linji Zhang, Chaosheng Yuan, Ru Jia, Chunguang Shao, Mingyou Wang and Shiming Hong
Polymers 2018, 10(8), 847; https://doi.org/10.3390/polym10080847 - 01 Aug 2018
Cited by 5 | Viewed by 3131
Abstract
By using a self-designed pressure-jump apparatus, we investigated the melt solidification behavior in the rapid compression process for poly-ethylene-terephthalate (PET), polyether-ether-ketone (PEEK), isotactic polypropylene (iPP), high-density polyethylene (HDPE), and the living polymer sulfur. The experimental results clearly show that crystallization could be inhibited, [...] Read more.
By using a self-designed pressure-jump apparatus, we investigated the melt solidification behavior in the rapid compression process for poly-ethylene-terephthalate (PET), polyether-ether-ketone (PEEK), isotactic polypropylene (iPP), high-density polyethylene (HDPE), and the living polymer sulfur. The experimental results clearly show that crystallization could be inhibited, and some melts were solidified to the full amorphous state for PET, PEEK, and sulfur. Full amorphous PEEK that was 24 mm in diameter and 12 mm in height was prepared, which exceeded the size obtained by the melt quenching method. The bulk amorphous sulfur thus obtained exhibited extraordinarily high thermal stability, and an abnormal exothermic transition to liquid sulfur was observed at around 396 K. Since the solidification of melt is realized by changing pressure instead of temperature and is not essentially limited by thermal conductivity, it is a promising way to prepare fully amorphous polymers. In addition, novel properties are also expected in these polymers solidified by the pressure-jump within milliseconds. Full article
(This article belongs to the Special Issue Polymer Stereochemistry)
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