Preparation And Study Of Polyurethanes With Reprocessing And Shape Memory

Because the reprocessing materials have excellent manifestation on security,lifetime,environmental compatibility and repeatability,it always takes up important position in material research.Many reprocessing materials not only repair themselves but also have excellent shape memory properties.Moreover,the strength,hardness,rigidity,wear resistance and impact resistance of polymer materials can be effectively improved when the reprocessing polymer materials are introduced with modifiers.In this thesis,the reprocessing and shape memory properties of the materials are studied respectively.1.A commercial novolac epoxide was used to react with carbon dioxide(CO₂)to obtain a novel five-membered cyclic carbonate.This novel novolac epoxide-based five-membered cyclic carbonate(NE5CC)was successfully utilized to prepare polyhydroxyurethane(PHU)thermoset.To improve the thermomechanical properties of the PHU thermoset,nanocrystalline cellulose(NCC)was used as the modifier.To facilitate dispersion of the modifier,the surface of NCC was functionalized with poly(N-vinylpyrrolidone)(PVPy).The functionalized NCC(NCC-PVPy)was prepared via the surface-initiated reversible addition-fragmentation chain transfer(RAFT)polymerization of N-vinylpyrrolidone(NVP).It was found that NCC-PVPy was readily dispersed in PHU matrix in the form of single nanocrystals.The nanocomposites of PHU with NCC displayed the enhanced glass transition temperatures and improved mechanical properties.In the meantime,the nanocomposites had good shape recovery properties;the nanocomposites can be reprocessed at elevated temperature.The reprocessing properties can be utilized to reprogram the original shapes of the shape memory nanocomposites.2.Polythiourethanes(PTUs)crosslinked with dynamic disulfide bonds were synthesized via a non-isocyanate approach.First,a difunctional five-membered cyclic trithiocarbonate(1)was synthesized via the reaction of diglycidyl ether of bisphenol A(DGEBA)with carbon disulfide(CS₂).Second,the step-growth polymerizations of 1 with?,?-diamino poly(propylnene oxide)s with various molecular weights were carried out to obtain a series of linear poly(mercapto thiourethane)s.These linear poly(mercapto thiourethane)s were readily crosslinked with disulfide bonds,which were generated via radical coupling reaction with the side mercapto groups.These crosslinked PTUs can be tailored into the materials from thermosetting plastics to crosslinked elastomers,depending on the molecular weights of?,?-diamino poly(propylene oxide)s.More importantly,these crosslinked PTUs displayed excellent reprocessing properties at elevated temperatures,which was attributed to the metathesis reaction of dynamic disulfide bonds.