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Sheng Li

Sheng2011

Current Position: Research Investigator, DuPont Central Research & Development

Adviser: Prof. R.A. Register

Undergraduate Institution: Massachusetts Institute of Technology

Project Title: Development of Novel Semicrystalline Ethylene-a-Olefin Block Copolymers

            In semicrystalline block copolymers, formation of solid-state morphology can be driven either by block incompatibility or by crystallization of one or more of the blocks.  Depending on the block interaction strength, a wide array of solid-state morphologies may be observed, ranging from spherulitic to confined crystallization within preexisting microphase-separated domains.
            The Dow Chemical Company recently developed a novel chain shuttling polymerization process to economically produce olefin block copolymers with alternating amorphous and semicrystalline chain segments.  In particular, a class of high-octene/long-block-length polyolefins was found to exhibit solid-state morphological characteristics that may be consistent with confined or templated crystallization from a microphase-separated melt.  
            In this project, we aim to examine the melt and solid-state morphologies of these novel olefin block copolymers using scattering and microscopy techniques.  The material characterization data obtained will allow us to correlate microscopic structural information to macroscopic material properties and to shed light on some of the unusual solid-state characteristics exhibited by this class of olefin block copolymers.
            Furthermore, the olefin block copolymers synthesized via chain shuttling are characterized by a most probable distribution in block lengths and number of blocks per chain.  We will investigate the effects of polydispersity and multiblock architecture on the block copolymer phase diagram, with specific attention paid to the phase behavior near the order-disorder transition.  Through these studies, we will better understand the influence these complexities have on the phase behavior of block copolymers.