Current Position: Senior R&D Engineer, Shockwave Medical
Undergraduate Institution: Indian Institute of Technology, Bombay
Ph.D. Thesis Research:
The miscibility between two distinct polymer species in a block copolymer is quantified by the interaction strength (characterized by the Flory interaction parameter χ). Chemical incompatibility between the blocks that make up the block copolymer drives “microphase separation”, leading to domains rich in one specific species. This microphase separation in the melt results in non-homogeneity in composition, adversely affecting the chemical properties and consequently, the performance of the polymer.
Synthesis of random copolymers provides a flexible method to tune the interaction strengths between block copolymer moieties. ArB random copolymers will exhibit smaller χ (or interaction energy density coefficient, X) upon mixing with homopolymer C provided the solubility parameter (δ) of C lies between those of A and B; and the ArB composition can be varied continuously. Thus, by incorporating another polymeric species into one of the blocks of a block copolymer, one can conveniently tune the interblock interactions through the random block’s composition.
My project aims to study the miscibility of polyisoprene (PI), with an aim of identifying ethylene-based random copolymer species with an adequately low χ against PI to be miscible with PI in melt to sufficiently high molecular weights. PI (synthetic equivalent of natural rubber) is chosen as the material of interest because of its wide-spread applications, particularly in tire manufacture. The presence of hydrogenated polybutadiene improves the thermo-oxidative stability and lowers the gas permeability of polyisoprene. Styrene, with its elevated solubility parameter, is expected boost rubber compatibility at relatively low levels of incorporation. Thus, narrow distribution random copolymers of butadiene and styrene with negligible down-chain gradient synthesized via anionic polymerization followed by selective catalytic hydrogenation are chosen as candidates for miscibility with PI, which itself can be synthesized using living anionic polymerization. A series of well-defined near-symmetric “block-random” copolymers of PI and PBrPS (PB is polybutadiene and PS is polystyrene) with varying molecular weights and random block compositions will be synthesized and selectively hydrogenated catalytically such that only the butadiene units are saturated, leaving the styrene and isoprene units unsaturated. The mixing thermodynamics – via the measurement of the temperature at which polymer transitions from an ordered state with segregated domains to a disordered state (the order-disorder transition temperature, TODT) using small-angle X-ray scattering (SAXS) or Dynamic Mechanical Thermal Analysis (DMTA), will be examined. In addition, the mixing behavior of PI with other random copolymers of substituted styrene (methyl styrene and tert-butyl styrene) and butadiene species will be investigated using the same procedure. The polymerization chemistry of the substituted styrene-butadiene random copolymers is expected to be identical to that of the styrene-butadiene random copolymers due to their chemical similarity.