Graft copolymer thermoplastic elastomers, structure

Thermoplastic elastomers (TPE), 9 565-566, 24 695-720 applications for, 24 709-717 based on block copolymers, 24 697t based on graft copolymers, ionomers, and structures with core-shell morphologies, 24 699 based on hard polymer/elastomer combinations, 24 699t based on silicone rubber blends, 24 700 commercial production of, 24 705-708 economic aspects of, 24 708-709 elastomer phase in, 24 703 glass-transition and crystal melting temperatures of, 24 702t hard phase in, 24 703-704 health and safety factors related to, 24 717-718... 

Thermoplastic elastomers are often multiphase compositions in which the phases are intimately dispersed. In many cases, the phases are chemically bonded by block or graft copolymerization. In others, a fine dispersion is apparently sufficient. In these multiphase systems, at least one phase consists of a material that is hard at room temperature but becomes fluid upon heating. Another phase consists of a softer material that is rubberlike at RT. A simple structure is an A—B—A block copolymer, where A is a hard phase and B an elastomer, eg, p oly (styrene- -elastomer- A styrene). 

In contrast, thermoplastic elastomers vulcanize by a physical cross-linking, that is, by formation of hard domains in a soft matrix. Here, hard and soft refer to glass transition temperatures relative to application temperatures. The properties of these thermoplastic elastomers follow directly from their structures. All thermoplastic elastomers (TPEs, plastomers) are copolymers with long sequences of hard and soft blocks. They can be block polymers, segment polymers, or graft polymers. 

These structures are illustrated in Figure 1.3. Through the leadership of Amos and others, polymer blends and grafts found uses as rubber-toughened plastics, which include high-impact polystyrene (HiPS) and acrylonitrile-butadiene-styrene (ABS) plastics. As further illustrated in Table 1.1, block copolymers containing a water-soluble block and an oil soluble block became important as surfactants through the work of Lunsted, while other block copolymers, composed of elastomer and plastic blocks, were useful as thermoplastic elastomers. 

Multiphase or multicomponent polymers can clearly be more complex structurally than single phase materials, for there is the distribution of the various phases to describe as well as their internal structure. Most polymer blends, block and graft copolymers and interpenetrating networks are multiphase systems. A major commercial set of multiphase polymer systems are the toughened, high impact or impact modified polymers. These are combinations of polymers with dispersed elastomer (rubber) particles in a continuous matrix. Most commonly the matrix is a glassy amorphous thermoplastic, but it can also be crystalline or a thermoset. The impact modified materials may be blends, block or graft copolymers or even all of these at once. 

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