Temperature-Responsiveness of A-B-A Block Telomers at Solid-Liquid Interfaces.
Macroinitiators were prepared by coupling disuccinimidyl ester of 4,4'-azobis(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 could be dispersed monomolecularly. The telomers dispersed in water were aggregated by raising the temperature above 32 degrees C due to a coil-globule transition 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 might 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 PSt in the air-in-water system was dependent on temperature; that is, with the increase in temperature the contact angle of air bubbles largely decreased and leveled off above the coil-globule transition temperature (Tc). Correspondingly, 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 Tc. These phenomena were attributed to the changes in hydrophobicity of the telomer layer below and above the Tc. The usefulness of macroinitiators in preparing various kinds of block telomers which have responsiveness to external stimuli was strongly suggested. Copyright 1999 Academic Press.