Nanocomposites of Poly(hydroxyurethane)s with Multiwalled Carbon Nanotubes: Synthesis, Shape Memory, and Reprocessing Properties

Poly(hydroxyurethane)s (PHUs) are synthesized via non-isocyanate approaches and could be the potential alternatives of conventional polyurethanes. It is of importance to investigate the structure-property relationship of PHUs. In this work, we investigated the PHU nanocomposites containing multiwalled carbon nanotubes (CNTs). First, CNTs were functionalized with poly(acryloyl carbonate), a polymer bearing 6-membered cyclic carbonate groups (denoted PA6CC) via the surface reversible addition-fragmentation chain transfer polymerization approach. Thereafter, the PA6CC-grafted CNTs were dispersed in the mixtures of 6-membered bicyclic carbonate (6BCC) and tris(2-aminoethyl)amine. By initiating the curing reaction, the nanocomposites were successfully obtained with the content of CNTs up to 11 wt %. The morphological investigation showed that CNTs were well dispersed in the PHU matrix; the CNTs preserved good integrity. The PHU nanocomposites displayed a series of improved thermomechanical properties in terms of glass transition temperatures (T-g's), tensile mechanical properties, and thermal conductivity. Compared to plain PHU thermoset, the PHU nanocomposites possessed enhanced dielectric constants and low dielectric loss. Owing to the introduction of CNTs, the nanocomposites displayed improved shape memory properties. It was found that the nanocomposites preserved reprocessing properties at elevated temperatures as plain PHU. The reprocessing properties bestowed the shape memory materials with reprograming ability of original shapes.