CBE Seminar: Karthika Madathil

Properties of Triblock Copolymer Thermoplastics with Interaction-Tuned Polymer Additives

Abstract

Thermoplastics based on block copolymers (BCPs) are used in a wide range of commercial products. The mechanical properties of these materials depend on the architecture and composition of the BCP. Over the past several decades, a vast number of studies have shown that mechanical properties can be tailored by tuning the BCP architecture and composition, or by introducing non-covalent interactions through comonomers in one of the blocks. Relatively fewer works have used polymeric additives to tailor mechanical properties of BCPs due to the limited miscibility of most polymer blends. In this talk, I will show that the structure and mechanics of poly(styrene-b-ethylene butylene-b-styrene) (SEBS) can be tailored with linear random copolymers of poly(methyl methacrylate-co-cyclohexyl methacrylate) (PrC). The PrC additive has a slightly attractive interaction with polystyrene, and this enthalpic compatibility can overcome the conformational penalties that arise from mixing with the polystyrene block of SEBS. The SEBS/PrC blends have an ordered lamellar morphology with continuous rubbery and glassy domains for a very broad range of PrC molecular weights and loadings. Consequently, the PrC additives can improve the strength and modulus in these materials without impacting toughness. For comparison, linear polystyrene (PS) additives are miscible with SEBS only for low molecular weights and loadings, leading to a narrow process window for potential improvements to mechanical properties. Significantly, PrC additives with moderate molecular weights can improve the thermal stability of SEBS, while the PS additives (which are only miscible at low molecular weights) tend to depress the glass transition temperature of the styrenic domains and compromise the mechanical properties at elevated temperatures. These results show that the PrCs are suitable additives to tailor the mechanical properties of styrenic block copolymers, which is one of the largest sectors of the BCP industry, over a broad temperature range.

Bio

Karthika Madathil is a PhD candidate in Chemical Engineering at the University of Tennessee, Knoxville, advised by Professor Gila Stein. Her current research focusses on understanding the effects of thermodynamics and processing methods on the structure of block copolymer systems, with the goal of designing materials with tailored functionality and mechanical performance. She has a bachelor degree from Visvesvaraya National Institute of Technology, India, and a masters degree from Arizona State University, both in Chemical Engineering.