Synthesis And Properties Investigation Of Chain-folding Polyurethane

Donor-Acceptor structure is a kind of non-covalent bonds intramolecularly or intermolecularly like hydrogen bond.Because of the difference of electric charge density,Donor group and Acceptor group interact with each other.In this work we synthesized the polyurethane with Donor group and Acceptor group in its main chain and studied the secondary micro-structure and the influence of structures on the performance of polyurethane.We also discussed the recovery of Donor-Acceptor structure in the cycle of stretch-recovery-annealing.We chose naphthalene and imide acting as Donor and Acceptor group respectively.Firstly,ethanolamine and 1,5-Naphthalene diisocyanate were added to the flask and we got the naphthalene chain extender with hydroxyl group in its both sides.Similarly,we used ethanolamine and Pyromellitic dianhydride as reactants and got the imide chain extender with hydroxyl group in its both sides.Because of the difference of activity between amino and hydroxyl group,the synthesis of these two chain extenders is easy and the product is very pure without any post-processing.Then we synthesized polyurethane in prepolymerization-chain extension ways.In the chain extension step we added the chain extenders above-mentioned in turn and got the polyurethane with Donor group and Acceptor group in its main chain alternately named AD-PU.Otherwise we also synthesized the polyurethanes with only Donor group or Acceptor group named D-PU or A-PU,without Donor group or Acceptor group in the main chain named BDO-PU,and the blends of A-PU and D-PU named A-PU+D-PU.On the one hand,when Donor group and Acceptor group interact the material will change its color to orange-red.So our AD-PU has the deepest orange-red color.We used UV-vis absorption spectrum to test the AD-PU film and found that the characteristic peak of AD-PU is highest.That is to say that when the Donor group and the Acceptor group exist in the same chain the intensity of Donor-Acceptor interaction is best.So because of the influence of Donor-Acceptor interaction the fluorescence emission peak of AD-PU is weaker than D-PU and A-PU+D-PU.Besides we found that the intramolecular Donor-Acceptor interaction hold a leading post when contrast with the intermolecular.Then we calculate the coefficients of Donor-Acceptor structure using Benesi-Hilbrand equation and found that one Donor group interact with one Acceptor.The Single Molecule Force Spectroscopy showed that the chain of AD-PU is self-folding when existed in dilute solution.And on the other,we studied the mechanical property and the recovery ratio after break of AD-PU film.The result says that AD-PU has the biggest breaking elongation(1200%).And the tensile stress(35MPa)and shape recovery ratio(95%)are greater than the other polyurethanes.Contrasted with other polyurethanes without DonorAcceptor interaction,the tensil stress increases 48%;the breaking elongation increases 28%.So we can say that the Donor-Acceptor interaction can endow the polyurethane with excellent mechanical property and can also promote the shape recovery ability.At last we studied the damage and the self-healing of the Donor-Acceptor microstructure in the cycle of stretch-recovery-annealing.The UV-vis absorption spectrum shows that the Donor-Acceptor structure will be ruined when stretching and the can partly recover when sample is released.If we put the released sample in a high temperature environment the Donor-Acceptor structure can recover to its original level.That is to say the Donor-Acceptor structure is a kind of reversible structures.And because of the reversibility of micro-structure AD-PU has outstanding mechanical property and shape stability.