Influence of supramolecular interaction type on photoresponsive azopolymer complexes : a surface relief grating formation study

Abstract

The influence of the supramolecular interaction type—hydrogen bonding, proton transfer, and pure ionic bonding—on photoresponsive behavior, particularly surface relief grating (SRG) inscription, has been investigated using a homopolymer with an ambient temperature glass transition (Tg). To this end, poly(dimethylaminoethyl methacrylate) (PDMAEMA or PDM) of relatively high molecular weight (42K) was complexed at various azo/DM molar ratios with dimethylaminoazobenzene derivatives functionalized by hydroxyl (azoOH) or carboxylic acid (p-methyl red or azoCOOH) groups, and quaternized PDM (PDMQ) was complexed at equimolar ratio with a sulfonated analogue (methyl orange or azoSO3), and the structural and thermal properties of these complexes were determined. SRG inscription on spin-coated films was found to be possible because complexation increases the Tg above ambient. The efficiency of SRG inscription on spin-coated films, which increases with azo content, is highest for the purely ionic azoSO3/PDMQ complex despite its very high Tg, while the proton transfer azoCOOH/PDM complexes, involving ionic and H-bonding with acid-salt structures, show somewhat more efficient SRG inscription than do the purely hydrogen-bonded azoOH/PDM complexes, and this despite some azoCOOH crystallization at the highest molar ratios. These findings clarify the comparative effectiveness of different supramolecular bond types on SRG inscription and provide a useful guide for the design of supramolecular photoresponsive polymers for SRG applications.