Interplay of macromolecular architecture and flow in polymer crystallization

Abstract

Processing flow can accelerate crystn. by orders of magnitude compared to the quiescent case, allowing lowcost, high-vol. manufg. Flow can also induce highly oriented crystal morphologies that allow simple polymers to attain exceptional properties. Among synthetic polymers, semicryst. polyolefins are the dominant materials due to their vast importance to quality of life worldwide. The architecture of the longest, slowest relaxing chains profoundly affects the kinetics and morphol. of flow-induced nuclei; and the "long chains" can exert strong effects even at low concn. This talk focuses on the importance of long-chain branching. We have examd. model binary blends of well-defined, H-polymer chains at low concns. in a matrix of entangled polyethylene chains. A new class of model branched polyethylenes is synthesized having H architecture with a "strut" that is free of short chain branching and "arms" that have a few percent short chain branching. Transient measurements of flow-induced crystn. in these binary blends reveal the effects of precisely tailored H-shaped polyethylenes on the nucleation and growth of polymer crystals.