Thermoplastic Superelastomers Based on Poly(isobutylene)-<i>graft</i>-Poly(<scp>l</scp>-lactide) Copolymers: Enhanced Thermal Stability, Tunable Tensile Strength, and Gas Barrier Property
Jeong Suk Yuk, Eunbi Mo, Suhyun Kim, Haemin Jeong, Hyeonji Gwon, Nam‐Kyun Kim, Young‐Wun Kim, Jihoon Shin
Abstract
A mechanically adjustable reinforced thermoplastic superelastomer system, with tunable gas-permeability, was developed. The superelastomer is based on a graft copolymer structure, using commercial butyl rubbers (or poly(isobutylene- co -isoprene), P(IB- co -I)) and l - or d, l -lactide (LLA or LA) derived from renewable feedstocks, by a “grafting from” controlled polymerization. First, hydroxyl-functionalized PIB (PIB- g -(OH)) macroinitiators were prepared through epoxidation using an economical alternative to m -chloroperoxybenzoic acid and ring-opening reaction. Second, PIB-based graft copolymers with end-hydroxylated poly(lactide) as hard side-chains, PIB- g -(P(L)LA–OH)s, were synthesized to target f P(L)LA of 0.18–0.45, to achieve mechanical reinforcement and an additional gas barrier. They were subsequently acetylated with an acetic anhydride to produce PIB- g -(P(L)LA–Ac)s with improved thermal stability. The well-defined molecular structures indicated controlled P(L)LA lengths, and the resulting superelastomers demonstrated improved thermal stability with increased T d,5%; microphase-separated structures having spherical and/or elongated features; thermoplastic behaviors proved by T ODT, which were much lower than the resulting T d,5%; and superior and adjustable mechanical characterizations, proving to control elastomeric-to-ductile properties. An oxygen permeability value as low as 27 mL mm m –2 day –1 atm –1 was achieved by increasing f P(L)LA to 0.45, comparable to polyethylene terephthalate. The partially biodegradable and processable gas barrier films based on these PIB- g -PLLA thermoplastic superelastomers have great potential for the flexible packaging of food and medical products.