Photochemical isomerization of azobenzene incorporated in poly(N,N-dimethyl-4-vinylphenethylamine-block-styrene) diblock copolymer by cross linkage

• Published in: Polymer (Guilford) 1997-11, Vol.38 (23), p.5755-5760
• Main Authors: Se, Kazunori, Kijima, Masato, Fujimoto, Teruo
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; p,p′-bis(chloromethyl) azobenzene; photochemical isomerization; Physicochemistry of polymers; poly (N,N-dimethyl-4-vinylphenethylamine-block-styrene); Polymers and radiations; Properties and characterization
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/S0032-3861(97)00132-8

Photochemical isomerization of p,p′-bis(chloromethyl) azobenzene (CAB) was investigated in poly-(N,N-dimethyl-4-vinylphenethylamine-block-styrene) block copolymer [P(PTA-b-St)]. The P(PTA-b-St) was prepared by anionic living polymerization. Both ends of CAB were attached to amino groups of the PPTA in the P(PTA-b-St) by quaternization in order to permit cross-linked films. When the films were irradiated with u.v. light (300 nm < λ1 < 380 nm), CAB underwent photoisomerization from the trans to the cis form. The photoisomerization did not proceed in a first-order kinetics. Hence, irradiation time-dependence of the results was analysed by the Kohlraush-Williams-Watts equation. The resultant values of parameter α, trans fraction at equilibrium (Ce) and a half-life period (Γ1/2), remained constant from 15°C to 30°C, but discontinuously changed at approximately 30°C which is close to the glass transition temperature (Tg) of PPTA. Therefore, the films were first irradiated with u.v. light at 60°C for 2h, resulting in a 28% content of cis form in CAB. Subsequently, when the films were irradiated with visible light (420nm< λ2) at 20°C for 2 h and 90°C for 2 h, the cis content of CAB changed to 21% and 0%, respectively. The retention and deletion of the cis form was controlled by an alternation of the thermal motion of PPTA above and below the Tg of PPTA in the P(PTA-b-St) block copolymer.