Journal
JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY
Volume 51, Issue 3, Pages 672-686Publisher
WILEY
DOI: 10.1002/pola.26419
Keywords
block copolymers; living polymerization; polyethylene (PE); polyolefins; Ziegler-Natta polymerization
Categories
Funding
- Natural Sciences and Engineering Research Council (NSERC) of Canada
- Canada Research Chair
- Canadian Foundation for Innovation (CFI)
- Ontario Ministry of Training, Colleges, and Universities
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We demonstrate, in this article, the facile synthesis of a broad class of low-polydispersity ethylene-norbornene (E-NB) copolymers having various controllable comonomer composition distributions, including gradient, alternating, diblock, triblock, and block-gradient, through living''/quasiliving E-NB copolymerization facilitated with a single Pd-diimine catalyst (1). This synthesis benefits from two remarkable features of catalyst 1, its high capability in NB incorporation and high versatility in rendering E-NB living'' copolymerization at various NB feed concentrations ([NB](0)) while under an ethylene pressure of 1 atm and at 15 degrees C. At higher [NB](0) values between 0.42 and 0.64 M, E-NB copolymerization with 1 renders nearly perfect alternating copolymers. At lower [NB](0) values (0.11-0.22 M), gradient copolymers yield due to gradual reduction in NB concentration, with the starting chain end containing primarily alternating segments and the finishing end being hyperbranched polyethylene segments. Through two-stage or three-stage living'' copolymerization with sequential NB feeding, diblock or triblock copolymers containing gradient block(s) have been designed. This work thus greatly expands the family of E-NB copolymers. All the copolymers have controllable molecular weight and relatively low polydispersity (with polydispersity index below 1.20). Most notably, some of the gradient and block-gradient copolymers have been found to exhibit the characteristic broad glass transitions as a result of their possession of broad composition distribution. (C) 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 672-686
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