Propene-hexene copolymers crystallize in a new polymorphic form of isotactic polypropylene when the concentration of hexene is higher than nearly 10-15 mol %. The hexene units are included in the crystals, inducing an increase of density that allows crystallization of 3-fold helical chains in a trigonal unit cell according to the space group R3c or Rc, where the helical symmetry of the chains is maintained in the crystal lattice. The structure of this new form is similar to those of isotactic polybutene and polystyrene and does not crystallize in polypropylene homopolymer because it would have too low density. The crystal structure of isotactic polypropylene is therefore no longer an exception to the principles of polymer crystallography, but the new structure represents the fulfillment of these principles and indicates that the packing of polymer molecules is mainly driven by density.
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http://dx.doi.org/10.1021/ja0572957 | DOI Listing |
Angew Chem Int Ed Engl
December 2024
Department of chemistry, University of California, Riverside, Riverside, CA, 92521, USA.
Sulfated zirconium oxide (SZO) catalyzes the hydrogenolysis of isotactic polypropylene (iPP, M=13.3 kDa, Đ=2.4,
Angew Chem Int Ed Engl
January 2025
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY, 14853, USA.
Polymer stereocomplex formation represents a promising research area as it can improve thermal and mechanical properties of co-crystallized polymer strands of opposite chirality. Polymers that form stereocomplexes commonly feature high stereoregularity and usually require sourcing from enantiopure monomer building blocks. Herein, we report the in situ polyether stereocomplex formation from racemic epoxide monomers, i.
View Article and Find Full Text PDFSoft Matter
June 2024
School of Materials Science and Engineering, Tianjin University, Tianjin 300072, P. R. China.
The dimension or entanglement of polymer chains is crucial to chain dynamics, and the polymer chains can be diluted and disentangled in a solution by reducing the interaction with each other. This letter addresses the role of solution concentration in the crystal transition of isotactic polybutene-1 (iPB-1) with low molecular weight crystallized from solution. It turned out that the transition of iPB-1 obtained from the higher concentration of the solution is faster than that obtained from the lower one.
View Article and Find Full Text PDFMacromol Rapid Commun
August 2024
CAS Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China.
This communication reports an effective strategy helping address the long-troubling melt processing issue of isotactic polybutene-1 (i-PB) caused by its extremely slow II-I crystal phase transition. The solution lies in a facile synthesis of i-PB containing H-shape long-chain-branching structures (LCB-i-PB) by applying a so-called ω-alkenylmethyldichlorosilane copolymerization-hydrolysis (ACH) chemistry to butene-1 polymerization with Ziegler-Natta or metallocene catalysts. It is evident that the H-shape LCB structures effectively enhance chain entanglements of i-PB and induce an over-the-board acceleration of the overall melt crystallization process including nucleation, form II crystallization, and form II-form I phase transition.
View Article and Find Full Text PDFMacromol Rapid Commun
July 2024
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing, 100029, P. R. China.
The II-I phase transition of isotactic poly(1-butene) (iPBu) leads to improved mechanical performance. However, this will take several weeks and increase storage and processing costs. In this work, shear forces are introduced into the supercooled iPBu melt, and the effects of isothermal crystallization temperature (T) and shear temperature (T) on crystallization and phase transition are explored.
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