13 - Other Thermoplastic Elastomers

Abstract

This chapter explores the properties and synthesis processes of the star block copolymer, thermoplastic elastomers (TPEs) based on interpenetrating networks (IPNs), and TPE Based on polyacrylates. Star-branched, radial, or multi-arm star copolymers are copolymers consisting of a core and arms held together by, or emanating from, the core. Besides the chemical nature of the constituents, the properties of star copolymers mainly depend on two structural factors––namely, on the molecular weight of the arms and the number of arms. There are two major synthetic routes to star copolymers-––namely, (1) arm-first method and (2) core first method. Besides these two major methods, several other methods have been reported in the literature. An interpenetrating polymer network is defined as a combination of two polymers in network form, at least one of which is synthesized and/or cross-linked in the immediate presence of the other. The chapter explains that a thermoplastic IPN contains physical cross-links in both polymers, rather than covalent cross-links. Thermoplastic IPNs are prepared by shearing or mixing either of the two polymers, or by polymerization of one or both of the polymers, or by the ionization of an ionomer component. At any rate, the final product has some kind of dual phase continuity. Poly (alkyl acrylates) with low glass transition temperature have better heat and oxygen resistance than polydienes and are suitable replacement for them in the central block of the triblock copolymer. Although there are several possible routes for the preparation of fully acrylic triblock copolymers, the simplest method appears to be a two-stage process using difunctional anionic initiators. The chapter states that the most favorable situation is the initiation of MMA by living poly (t-BA) anions.