Block and Graft Copolymers Chemistry Department and Polymer Materials and Interfaces Laboratory Virginia Polytechnic Institute and State University. Blacksburg. VA 24061 Multiphase polymer systems have received widespread attention in recent years, especially since the rate of appearance of new polymer types has diminished considerably. The new multiphase materials may be obtained in the form of blends, block and graft copolymers, or "interpenetrating" networks, all of which are usually characterized by the presence of two or more polymeric phases in the solid state. Such materials are, therefore to be distinguished from composite materials such as fiber- and particulate-filled thermoplastics and thermosets. The considerable number of recent collective works, dealing with multiphase polymer systems attests to their growing impact on current materials technology and these will be reviewed. Within the last decade, the relatively poor economics of new nolvmer and cooolvmer " . . nroduction counled to the need for new cost-effective materials for specific applications, has generated wide interest in . nolvmer blends or allovs. Unfor" tunately, most homopolymer pairs are immiscible with one another and give rise to low strength materials due to the lack of interfacialadhesion between thk separate phases. Block and graft copolymers, while being more expensive than simple blends and certainly more restricted in their range of composition, do offer several advantages over blends. First, the different segments are covalently bonded together, thereby eliminating the interface problem. Second, the molecular architecture can be accurately controlled to produce novel materials. Third, block or graft copolymers can be used to strengthen blends of immiscible polymers by sewing as "emulsifiers," which encourage physical connections between the phases, and thus improve the interfacial adhesion and load transferring capability of the components.
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Block Copolymers Block co~olvmersare now an i m ~ o r t a n area t of ~ o l v m e r science. Al;hoigh block polymers have been known ior some time ( I ) , it was not until uolvurethane materials were developed (2) that their potentiaibegan to be appreciated. Initial investigations of these block copolymers showed that they were s
