Diblock copolymer-azobenzene complexes through hydrogen bonding: Self-assembly and stable photoinduced optical anisotropy

摘要

We have demonstrated the preparation of a series of photoaddressable supramolecular block copolymers by mixing a carboxy-terminated azobenzene derivative, 6-[4-(4′-cyanophenylazo)phenyloxy]hexanoic acid (AZO), and two polystyrene-b-poly(4-vinylpiridine) (PS-b-P4VP) block copolymers. AZO can be selectively attached to the P4VP block of PS-b-P4VP through hydrogen bonding interactions. The assembly of AZO with vinylpyridine group-containing polymers was initially investigated on a model system composed of P4VP homopolymer and AZO. Homogeneous liquid crystalline materials were obtained for ratios of AZO to vinylpyridine repeating unit, x, lower or equal to 0.50. Mixtures with higher x resulted in heterogeneous materials showing clear macrophase separation. Accordingly, a series of hydrogen-bonded complexes of PS-b-P4VP and AZO, PS-b-P4VP(AZO)x, with x = 0.25 and x = 0.50 were prepared. Lamellar and spherical morphologies were observed for the complexes based on PS24-b-P4VP9.5 (Mn,PS = 24,000, Mn,P4VP = 9500) and PS24-b-P4VP1.9 (Mn,PS = 24,000, Mn,P4VP = 1900), respectively. Photoinduced orientation of the azobenzene units was obtained in films of P4VP(AZO)x and PS-b-P4VP(AZO)x with x = 0.25 and 0.50 by using 488 nm linearly polarized light and characterized through birefringence and dichroism measurements. This investigation shows a versatile and less laborious approach to azobenzene-containing polymer materials with low chromophore content, of interest in optical application. © 2013 Wiley Periodicals, Inc.