Preparation of small and photoresponsive polymer nanoparticles by intramolecular crosslinking of reactive star azo-polymers

Four-arm star azo-polymers with molecular weight control are prepared using the high selectivity of olefin cross-metathesis between acrylates and terminal olefins in the presence of multifunctional acrylates as the selective chain transfer agent. These reactive star azo-polymers are readily converted, by two different intramolecular crosslinking reactions of the end acrylate groups in dilute solution, to the new types of polymeric nanoparticles that exhibit distinct photoresponsive performance. Furthermore, the size and morphology of two types of polymeric nanoparticles show interesting and circular transformations when azo chromophore in nanoparticles underwent trans-cis-trans or cis-trans-cis isomerization cycles.