An Approach to New Polymeric Materials via Blocks, Grafts and Blends

Abstract

There are at least four ways to formulate a polymeric material with unique properties: (1) develop new monomers, (2) develop new methods and techniques of polymerization, (3) combine existing monomers in such a way that the resulting material has certain superior properties, and (4) combine existing polymers in unusual ways to achieve new and useful properties. Thermoplastic elastomers are ordered, block copolymers of the general structure A-B-A, where A is a thermoplastic polymer segment and B is an elastomeric polymer segment. The thermoplastic elastomers are composed of “hard” and “soft” segments which exhibit rigid properties and elastomeric properties at one and the same time. A two-phase system is formed, with the center segment phase constituting a continuous three-dimensional elastomeric network and the dispersed end segment phase serving as multi-junction points for the ends of the center segment. Choice of monomers, block length, the weight fractions of A and B, and the segment arrangement are crucial in achieving elastomeric performance. Block copolymers having segment arrangements such as A-B, or B-A-B do not exhibit the tensile behavior characteristic of thermoplastic elastomers, since for a continuous network to exist both ends of the elastomer segment must be immobilized in the non-elastomeric domains.