THE ROLE OF POLYMER ARCHITECTURE IN STRENGTHENING POLYMER-POLYMER INTERFACES - A COMPARISON OF GRAFT, BLOCK, AND RANDOM COPOLYMERS CONTAINING HYDROGEN-BONDING MOIETIES

A series of styrene-d(8)/4-hydroxystyrene graft and block copolymers h as been prepared by ''living'' radical and anionic techniques for use in interfacial strengthening studies at the polystyrene/poly(2-vinylpy ridine), PS/PVP, interface. The following copolymers in which A and B segments represent poly(styrene-d(8)) and poly(4-hydroxystyrene), resp ectively, have been prepared: poly(A-graft-B), poly(B-graft-A poly(B-b lock-A-block-B), poly(A-block-B-block-A-block-B-block-A). The poly(4-h ydroxystyrene) segments were obtained by ''living'' radical polymeriza tion of 4-acetoxystyrene or anionic polymerization of 4-methoxystyrene , followed by conversion to the phenolic derivative. In general, the a mphiphilic copolymers when placed at the PS/PVP interface acted as int erfacial reinforcers but were susceptible to the formation of micropha ses such as lamellae or micelles, and therefore the measured fracture toughness depended on both the copolymer/homopolymer interfacial stren gth and the toughness of the copolymer phase structure itself. The pen tablock copolymer showed better strengthening behavior than the triblo ck copolymer especially at very low areal chain density. The strengthe ning ability of the graft copolymers was found to depend on the length s of the polystyrene, PS, and poly(4-hydroxystyrene), PS(OH), segments . In both graft and block copolymers the PS(OH) segments were found to resist pull-out from the bulk PVP even at low degrees of polymerizati on (N-PS(OH)) = 29). The H-bonding interaction between the phenolic an d pyridyl groups combined with the severe immiscibility of poly(4-hydr oxystyrene) and polystyrene is the most likely cause for pull-out resi stance.