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

摘要

This article reports on studies regarding the photoisomerization kinetics and self-assembly behaviors of two photoresponsive diblock copolymers, poly(4-acetoxystyrene)-blockpoly[ 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 ~1.14. The diblock copolymers exhibited moderate thermal stability, with thermal decomposition temperatures greater than 343.3 °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.