Poly(styrene-b-vinylphenyldimethylsilanol) and its blends with homopolymers

Block copolymers of vinylphenyldimethylsilanol (VPDMS) and styrene were syn thesized by living anionic polymerization of vinylphenyldimethylsilane and styrene with sec-butyllithium as initiator in THF at -78 degrees C, followe d by an oxygen insertion reaction via oxyfunctionalization, in part or all, with. dimethyldioxirane. The resulting silanol group (=Si-OH) at the 4-pos ition of the styrene copolymer acts as a hydrogen bond donor, thus enhancin g miscibility with polymers containing hydrogen bond accepting groups. The block copolymers containing varying amounts of silanol groups and their ble nds with poly(n-butylmethylmethylacrylate) (PBMA), poly(vinylpyrrolidone) ( PVPr), and poly(vinylpyridine) (P4VPy) were characterized by temperature mo dulated differential scanning calorimetry (MDSC) and Fourier transform infr ared spectroscopy (FTIR). In blends with PBMA, the PVPDMS block is miscible with PBMA when it contains about 11-33% silanol groups, and the polystyren e blocks retain their identity as separate domains. These observations sugg est microphase separation as the dominant mechanism. However, at higher sil anol contents, the T-g results indicate the presence of three different dom ains and are indicative of a microphase-macrophase separation mechanism. Th e block copolymer containing 21% VPDMS units, PVPDMS-21, forms transparent films when blended with PVPr at all ratios; again, the PS blocks are unaffe cted, and the T-g results conform to the predictions of a microphase separa tion mechanism. There is also a positive deviation of the T-g of the mixed phase from the calculated weight-average value as a result of strong hydrog en bonding between the silanol and amide carbonyl groups. The interaction b etween pyridine and silanol group results in a large shift in the -OH stret ching frequency (Delta v = 223 cm(-1)), indicative of strong intermolecular hydrogen bonding interaction which is evidenced also by the presence of th e pyridinium structure in the FTIR spectra. The strong interaction is respo nsible for microphase separation as the dominant mechanism in morphological development with a large synergistic T-g effect. On the basis of spectrosc opic and T-g results, the relative strength of intermolecular hydrogen bond ing in the blends can be ranked in the order P4VPy > PVPr > PBMA. The stren gth of the intermolecular hydrogen bonding between the homopolymer and the silanol containing block, in relation to the self-association of silanol gr oups, governs the mechanisms of morphological development, i.e., microphase separation versus microphase-macrophase separation.