Reprocessing, shape recovery and dielectric properties of nanocomposites of Polyhydroxyurethane with barium Titanate

Poly(N-vinyl pyrrolidone) (PVPy) chains were grafted onto the surfaces of barium titanate (BaTiO3) nanoparticles via the surface-initiated living/controlled radical polymerization of N-vinyl pyrrolidone. The PVPy-grafted BaTiO3 nanoparticles were then incorporated into a crosslinked polyhydroxyurethane (PHU) which was derived from bis(six-membered) cyclic carbonate and a triamine ( i.e., Jeffamine T400). It was found that BaTiO3 nanoparticles were uniformly dispersed into the PHU matrix. The generation of nanocomposites resulted that the glass transition temperatures (Tg's) and mechanical properties were significantly enhanced. In the meantime, the nanocomposites had the dielectric properties superior to control PHU; the shape memory properties of the materials were significantly improved in terms of response, fixity of transient shape and recovery of the original shapes. Thanks to transcarbamoylation of hydroxyurethane structural units, the crosslinked nanocomposites can be reprocessed at elevated temperature. It was found that dibutyltin dilaurate (DBTDL) was an effective catalyst to decrease the Arrhenius activation energy of the dynamic reaction; the reprocessing of the nanocomposites can be carried out at the temperature as low as 120 degrees C.