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Effects of glassy, rubbery, and semicrystalline blocks on the mechanical response of polyolefin block copolymers.

作者:Lim, Lisa Sun.
30

The overall focus of this thesis is to understand the effects of glassy, semicrystalline, and rubbery blocks on the tensile mechanical properties of polyolefin block copolymers. Given the breadth of available materials from combining these three blocks, it is impractical both in logistical and economic senses to employ a purely empirical approach, i.e. investigating all possible polymer permutations, in search for the optimal block copolymers. Rather a firm understanding of the contribution of each block to the resultant mechanical properties would facilitate the design, a priori, of block copolymers synthesized for specific applications.; The tensile mechanical behavior of polyolefin block copolymers comprised of glassy, rubbery and semicrystalline blocks has been investigated and the results are described within this thesis. Polycyclohexylethylene (C) is the glassy block, poly(ethylene-alt-propylene) (P) is the rubbery block and the semicrystalline block is polyethylene (E). The block copolymers investigated consist of AB-type with glassy-semicrystalline and glassy-rubbery blocks and ABC-type with glassy-rubbery-semicrystalline blocks.; To investigate the failure mechanism of glassy-semicrystalline block copolymers, mechanical testing in the context of the following factors was explored: (1) chain architecture, (2) block sequence, (3) grain alignment, and (4) the amount of central block-bridging structures. The AB-type glassy-rubbery block copolymers were found to have similar tensile mechanical response to other thermoplastic elastomers (TPEs). The mechanical properties of these glassy-rubbery block copolymers were discussed in the context of the following factors: (1) chain architecture, (2) microstructure morphology, (3) chain entanglements, and (4) block sequence. The mechanical behavior of ABC-type glassy-rubbery-semicrystalline block copolymers was studied in the context of their: (1) crystallization behavior, (2) elasticity and cyclic deformation, (3) permanent deformation and set, and (4) tensile mechanical behavior with respect to chain entanglements and block sequence.; Collectively, these model block copolymers help us to understand the effects of glassy, rubbery and semicrystalline blocks on the tensile mechanical behavior of polyolefin block copolymers and provide us with the ability to control the modulus, tensile strength, and elasticity of polymeric materials. The ability to tailor the sequence, molecular weight, and composition of each block provides us with predictive tools to better design block copolymers for novel applications.

作者单位University of Minnesota.

页码223 p.

总页数223

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中图分类TB3;TQ02

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