The synthesis and properties of isotactic-atactic polystyrene graft copolymers

Abstract

RECENT studies of the properties of graft copolymers has enabled certain general characteristics of this class of polymers to be explained.We have shown previously [1-5] on the example of graft eopolymers of the amphipathic type that their structural and thermomechanical properties are a distinctive combination of the properties of the two components. At the same time the solubility of these eopolymers is considerably reduced and this is explained by the mutual screening effect of the components [3, 6]. In our work in this field the graft eopolymers studied were obtained from components differing widely both in chemical nature and physical properties (for example polystyrene-polyacrylic acid and polystyrenepolyvinylalcohol grafts, etc. [1-6] and moreover in these systems one of the polymeric components was a polymer with a rigid chain and a glass temperature (Tg) above its decomposition temperature. Furthermore both homopolymers were non-crystalline systems of irregular structure [3-6]. I t was of interest to s tudy the properties of a graft copolymer consisting of chains of the same chemical nature but possessing different structures. Copolymers of crystalline, isotactie (main chain) and amorphous, atactic (side chains) polystyrene were chosen for the present work. I t is known that in ordinary, atactic polystyrene the high-elastic state is covered by a temperature interval of 50 ° (Tg90°; T m 140°). For crystallized, isotactic polystyrene, with the same chemical structure but a different spatial arrangement of the asymmetric carbon atoms in the backbone (dd or ll) the total absence of the high-elastic state is characteristic, but on the other hand the melting point (230 ° ) is high. On conversion to the amorphous state, when heated above its T~ (90°), this polymer again acquires the properties of a rigid plastic [7]. On grafting on to crystalline, isotactic polystyrene ataetic polystyrene chains, with their characteristic random sequence of asymmetric carbon atoms, the production of a graft copolymer with a well defined high-elastic region while maintaining a high melting point would be expected [5]. Such a graft copolymer would also provide a suitable model for the s tudy of the structural properties