Strengthening And Toughening Of Poly(Propylene Carbonate)Using Non-isocyanate Urethane

Derived from the copolymerization of CO₂ and propylene,poly?propylene carbonate??PPC?has displayed excellent biodegradability,biocompatibility as well as water/oxygen barrier,making an ideal alternative for traditionalnon non-biodegradable polymers.However,as amorphous aliphatic polycarbonate,PPC suffers from poor mechanical and thermal properties,which greatly hinder its application in many fields.Physical blending is widely used to modify polymers,but phase separations occurs owing to the poor intermolecular interaction between PPC and other polymers.Toward this end,reactive unsaturated urethane?USU?and furan-based polyurethanes?NIPU?have been rationally designed and synthesized via non-isocyanate routes.The hydrogen bondings can be formed between the carbonate unites in the main chain of PPC and urethanes?hydrogen bonding and amido bond moiety?,which both enchance the intermolecular interactions and serve as physical crosslinking points.In this regard,strengthening and toughening of PPC could be simultaneously achieved by melt blended with USU or NIPU.More details are listed as below:USU was synthesized by the reaction of 3-aminopropanol and cyclic carbonate obtained from the coupling reaction between glycidyl methacrylate and CO₂.For comparision,saturated urethane?SU?was synthesized via a similar route except that cyclic carbonate was hydrogenated.Furthermore,the modified PPC were prepared via melt blending with USU or SU.According to their FTIR spectra,the disaperance of the signals corresponding to the alkene groups indicates the radical polymerization of USU occurred during blending.Therefore,the hydrogen bonding between PPC and urethane moieties can serve as cross linking points.When USU loading was less than 8 wt%,the tensile strength of USU modified PPC could maintain above 30 MPa,which was closed to pure PPC?35.6 MPa?.And when USU loading was 8 wt%,the elongation at break increased by 5.3 times,and the strength decreased by 15.8%.Besides,the breaking energy improved with the increasing USU loading.However,the strength of SU modified PPC decreased significantly with a higher content of SU,showing only plasticizing effect.Novel furan-based no-isocyanate polyurethanes?NIPU1 and NIPU2?were quantitatively synthesized from 5-hydroxymethylfurfural,CO₂ and diamines.Furthermore,the resultant NIPUs were melt blended into PPC.According to the differential scanning calorimeter?DSC?results,both the glass transition temperature?T_g?of PPC/NIPU1 blend and PPC/NIPU2 blend increased by 7?,which resulted from the tangle of chains and the hydrogen bonding interaction.And the strength increased above 1 times.When NIPU1 loading was 5 wt%,the strength of PPC/NIPU1 increased by 103.7%,and the elongation at break increased by 46%comparing to pure PPC.When NIPU2 loading was 5 wt%,the strength and the elongation at break increased by 83%and 27%contrasting to pure PPC,respectively.According to the breaking energy calculated from stress-strain curves,NIPUs could also toughen PPC effectively.