Temperature-responsiveness of A-B-A block telomers at solid-liquid interfaces

Macroinitiators were prepared by coupling disuccinimidyl ester of 4,4'-azob is(cyanovaleric acid) with poly(N-isopropylacrylamide) (PIPA), which had an amino group at its end. Styrene was telomerized with the initiators in THF . When the styrene content in the A-B-A block telomer obtained (PIPA-b-PSt- b-PIPA) was high, the telomer formed an irreversible aggregation resulting in microspheres, whereas the telomer with a much shorter styrene block coul d be dispersed monomolecularly, The telomers dispersed in water were aggreg ated by raising the temperature above 32 degrees C due to a coil-globule tr ansition of PIPA moieties. The PIPA-b-PSt-b-PIPA could be strongly adsorbed to polystyrene (PSt) solid surfaces to form a layer, and the PSt blocks mi ght lay on the PSt surface and the PIPA blocks might direct to the solution phase. The contact angle of air bubbles on the surface of telomer-coated P St in the air-in-water system was dependent on temperature; that is, with t he increase in temperature the contact angle of air bubbles largely decreas ed and leveled off above the coil-globule transition temperature (T-c). Cor respondingly, the amount of protein Concanavalin A adsorbed to the telomer layer deposited on the PSt surface increased gradually with an increase in temperature and leveled off above the T-c. These phenomena were attributed to the changes in hydrophobicity of the telomer layer below and above the T -c. The usefulness of macroinitiators in preparing various kinds of block t elomers which have responsiveness to external stimuli was strongly suggeste d. (C) 1999 Academic Press.