EFFECT OF CHAIN-END GROUP HYDROPHOBICITY ON SURFACE AGGREGATION STRUCTURE OF POLY(STYRENE-BLOCK-4-VINYLPYRIDINE) SYMMETRICAL DIBLOCK COPOLYMER FILMS

Proton-terminated polystyrene-block-poly(4-vinylpyridine) (P(St-b-4VP) -H) and 3,3,3-trifluoropropyldimethylsilane-terminated polystyrene-blo ck-poly(4-vinylpyridine) (P(St-b-4VP)-C2CF) symmetric diblock copolyme rs were synthesized by a living anionic polymerization. Differential s canning calorimetry (DSC) measurements revealed that both diblock copo lymers were in a microphase-separated state in the bulk. The results o f X-ray photoelectron spectroscopy (XPS) measurements revealed that in the case of the P(St-b-4VP)-H film, the surface weight fraction of po ly(4-vinylpyridine) (P4VP) decreased drastically on annealing at 432 K for 90 h in order to minimize the magnitude of the free energy at the air-polymer interface, whereas in the case of the P(St-b-4VP)-C2CF fi lm, the surface P4VP weight fraction was almost the same as the bulk v alue even after annealing at 423 K for 90 h. Also, scanning force micr oscopy observations (SFM) were in good agreement with the XPS results. These results clearly indicate that the surface molecular aggregation state of the hydrophobic-hydrophilic diblock copolymer film can be co ntrolled by the hydrophobicity of the chain end groups. (C) 1998 Elsev ier Science Ltd. All rights reserved.