Preparation and Self-Assembly of Stimuli-Responsive Azobenzene-Containing Diblock Copolymers through Microwave-Assisted RAFT Polymerization

This article reports on studies regarding the photoisomerization kinetics and self-assembly behaviors of two photoresponsive diblock copolymers, poly(4-acetoxystyrene)-block-poly[6-(4-methoxy-azobenzene-4'-oxy) hexyl acrylate] (poly (StO(54)-b-Cazo(9)) and poly(StO(54)-b-Cazo(5))), which dissolved in a THF/H2O solution through two-step reverse additionfragmentation transfer polymerization. We examined the effect of heating methods (i.e., conventional and microwave heating) on the polymerization kinetics of a 4-acetoxystyrene-based macrochain transfer agent (StO macro-CTA). The kinetics studies on the homopolymerization of StO by using microwave heating demonstrated controllable characteristics with relatively narrow polydispersities at similar to 1.14. The diblock copolymers exhibited moderate thermal stability, with thermal decomposition temperatures greater than 343.3 degrees C, suggesting that the enhancement of the thermal stability was due to the incorporation of azobenzene segments into block copolymers. Poly (StO(54)-b-Cazo(9)) showed lower photoisomerization rate constants (k(t) = 0.039 s(-1)) compared with Cazo monomer (k(t) = 0.097 s(-1)). Micellar aggregates with a mean diameter of approximately 238.3 nm were formed by gradually adding water to the THF solution (water content510 vol %), and are shown in SEM and TEM images of the diblock copolymer. The results of this study contribute to the literature regarding the development of photoresponsive polymer materials. (c) 2014 Wiley Periodicals, Inc.