Construction And Properties Of Urathane-type Sustainable Materials With Special Urethane Bonds

Polyurethane(PU)has excellent mechanical properties(high modulus,high strength,wear resistance,low temperature resistance),and is widely used in construction,transportation,aviation,electronics and other fields.Meanwhile,with the requirement of sustainable polymer materials,the detachable bonding of polyurethane hot melt adhesive,the recyclability of polyurethane,the preparation and high performance of bio-based polyurethane,and non-isocyanate polyurethane are all widely studied.This thesis utilizes the reversibility of blocked isocyanates to prepare TPU hot melt adhesives that can be disassembled at low temperature,thermally reversible self-healing polyurethanes with high flexibility and high healing efficiency,and bio-based healable/recyclable polyurethanes with multiple reversible mechanisms.A high-performance isocyanate polythiourethane was prepared by the addition of a highly selective and highly selective cyclic thiocarbonate to a hydrogen bond-rich dimer acid polyamide.The main contributions of this thesis are as follows:First,the bonding and disassembly of polyurethane hot melt adhesives often rely on melting process.However,this melting temperature is often too high,which leads to application limitations in the electronic field.We hope to introduce groups with strong electron-withdrawing inducing effect into the blocking agent to reduce the deblocking temperature.A nitro-containing bisphenol chain extender,which is also a blocking agent(DNBPA),was synthesized by direct nitration.MDI and PTMG-1000 were used as monomers,and a thermoplastic polyurethane containing thermally reversible urethane bonds was prepared and used in hot melt adhesives.Through the model compound method,it was confirmed that the deblocking ability of DNBPA-blocked isocyanates is strong,which is reflected in the lower deblocking temperature(97 ℃),high deblocking conversion rate and rate constant,and low activation energy,indicating that the strong inductive effect can effectively reduce the decapsulation temperature.After that,DNBPA was introduced into the TPU hot melt adhesive.The DSC desealing temperature of PU-DNBPA was97 ℃,the softening point was only about 120 ℃,and a high melt flow index could be achieved at low temperature.The introduction of DNBPA into the molecular chain can realize the deblocking of the molecular chain at a lower temperature,thus giving the TPU hot melt adhesive a lower disassembly temperature.Second,in order to avoid waste caused by the destruction of polyurethane due to internal stress,self-healing polyurethane was developed.However,it is still a challenge to prepare polyurethanes with high healing efficiency and maximum retention of their properties.In this research,we proposed a new scheme suitable for industrial production of self-healing polyurethane.A self-healing polyurethane(DiO-c-PU)was successfully synthesized using diacetyl oxime as the chain extender and triethanolamine as the crosslinking agent.Oxime-blocked isocyanates deblock at a higher temperature and regenerate at lower temperature,thereby achieving thermal reversibility and self-healing due to the concise and efficient thermal reversible reaction of oxime urethanes.FT-IR and DSC experiments confirmed that the oxime urethanes in the polyurethane deblocks efficiently at around 90℃,and re-blocks after the temperature is lowered.The process can be cycled at least three times.Microscopic observation confirmed that the cracks disappeared within 60～90min at 90℃.Tensile test shows that the synthetic DiO-c-PU has a self-healing efficiency of over 94%at 90℃for 1.5 h,which is more efficient.From the results,it appears that DiO-c-PU has good self-healing properties.Thirdly,bio-based,healable,and recyclable polyurethane materials conform to the sustainability of the polyurethane industry.By introducing dynamic covalent bonds,the cross-linked polyurethane can perform network rearrangement,thereby realizing self-healing and reprocessing.In this work,a self-healing/renewable polyurethane based on bio-based vanillin and tyrosine was successfully synthesized solvent-freely and catalysts-freely.Due to two different thermal reversible mechanisms,metathesis of imines and deblocking/re-blocking of phenolic urethanes,the PU obtained considerable self-healing efficiency and renewability.At 120℃,the surface scratches almost completely disappear within 90 minutes,and the tensile strength can be restored to～95%within 2 h.After remolded for 5 times,the chemical structure,glass transition temperature,deblocking behavior,tensile strength,elongation at break and gel content didn’t change significantly.Both the environmental friendliness of bio-based raw materials and the renewability of the obtained polyurethane materials meet the requirements of sustainability.Forthly,non-isocyanate polyurethanes(NIPUs)have been extensively studied for their potential sustainability.However,the low reactivity of five-membered ring carbonates with amines and uncontrollable side reactions at high temperatures always affect the molecular weight,thereby sacrificing the performance of NIPU.Although cyclothiocarbonates greatly improve reactivity,the polymerization product lacks sufficiently strong hydrogen bonds,resulting in severely insufficient properties.In this work,a bisphenol-S cyclic thiocarbonate and different amino-terminated dimer-acid polyamides(DAPAs)were used to prepare non-isocyanate polythiourethanes(SPTU-DAs).Wherein,bisphenol-S acts as hard segment due toπ-πpackage,and plentiful hydrogen bonds introduced by DAPA units induce crystallization and nanophase separation.Both of them endow the NIPUs with high mechanical performance.Meanwhile,active cyclic thiocarbonate,instead of cyclic carbonate,ensures rapid synthesis under mild conditions without side reactions.The experimental results of DSC,WAXD and DMA confirmed the existence of crystallization of SPTU-DAs.The resulting thermoplastic polythiourethane has a maximum strength of more than 10 MPa,which is stronger than that of the cross-linked non-isocyanate polythiourethane reported previously.It is of key significance to obtain high performance of non-isocyanate polythiourethanes.