Optically active photochromic polymers with three-arms star structure by atom transfer radical polymerization

Atom Transfer Radical Polymerization has been applied for the first time to synthesize optically active, photochromic methacrylic polymers having three-arms star structure, starting from a central core of C3 symmetry that can be used to investigate the conformational origin of chirality in this class of synthetic materials. By just changing the duration of the polymerization process, star-shaped macromolecules with distinct average chain lengths, low polydispersity values and well defined end-groups have been obtained. The so obtained polymers, fully characterized by spectroscopic and thermal techniques, exhibit relevant specific optical rotations and chiroptical properties with respect to the reference monomeric model compound, as well as to the related linear derivatives previously investigated. This behaviour is attributed to the stiffness of aromatic core, which limits the free movement of one chain end, thus favouring the macromolecules to assume a more elevated conformational rigidity with respect to the linear samples of comparable average chain length.