Poly(hydroxyl urethane)s with Double Decker Silsesquioxanes in the Main Chains: Synthesis, Shape Recovery, and Reprocessing Properties
3,13-Di(cyclic carbonate) double decker silsesquioxane, a new difunctional polyhedral oligomeric silsesquioxane (POSS), was successfully synthesized. By using this POSS macromer, the organic–inorganic poly(hydroxyl urethanes) (PHUs) were synthesized with POSS cages in the main chains. Compared to the neat PHU, the organic–inorganic PHUs displayed improved thermomechanical properties. The organic–inorganic PHUs were microphase-separated, and the main-chain POSS cages were self-assembled into the nanodomains in the size of 10–30 nm. It was found that the POSS nanodomains acted as the nano-cross-linking points of physically cross-linked networks. Although the linear organic–inorganic PHUs were soluble in common organic solvents, they were capable of displaying the thermomechanical properties similar to cross-linked PHU elastomers. Owing to the physical cross-linking, the organic–inorganic PHUs were endowed with shape memory properties. In the meantime, the organic–inorganic PHUs can be reprocessed at elevated temperature; the tensile mechanical strength can be recovered up to 90%. The reprocessing properties resulted from the transcarbamoylation reaction of hydroxyurethane structural units other than the disintegration of POSS nanodomains at elevated temperature. The reprocessing properties can be utilized to program the original shapes of shape memory polymers.
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