Study On The Synthesis And Properties Of Thermoreversible Non-Isocyanate Polyurethane Based On Bio-Based Dimer Fatty Acid

Non-isocyanate polyurethane(NIPU)is a new type of green material whose synthetic precursor replaces toxic isocyanates.Ammonolysis of cyclic carbonates to obtain polyhydroxyurethane(PHU)is currently the most promising synthetic scheme.In addition,the use of petroleum-based raw materials is considered unsustainable,so it is important to find renewable raw materials to prepare and process PHU.This paper progresses layer by layer,starting from thermoplastic PHU to prepare a new type of fully bio-based strong matrix resin,to the research on the dynamic reversibility and reprocessing of thermosetting neat PHU network and PHU network composites,and finally using the synergy of multiple dynamic bonds to modify the problem of generally high relaxation activation energy of PHU network.1.In Chapter 2,diglycerol and dimer acid(DA)are used as precursors for the solvent-and catalyst-free synthesis of fully biobased non-isocyanate polyurethanes to replace toxic isocyanates and petroleum-based reactants.Linear polyhydroxy(amide-urethane)s(L-NIPHAUs)were synthesized via the melt aminolysis copolymerization between diglycerol dicarbonate(DGDC)and diamino-telechelicoligoamides(DAPAhs)from DA and hexamethylenediamine(HDA)with"rigid and flexible"properties.Their synthesis,crystallinity and nanophase separation behavior were studied.DA oligoamide segments,as a"rigid and flexible"component of segmented L-NIPHAUs,their crystallinity,low T_g,low T_m and appropriate diglycerol bis(hydroxyurethane)segments enhance the crystallization behavior of L-NIPHAUs.They are the materials with strong and tough mechanical properties(σ_b up to 12.12 MPa,ε_b up to858%).And the huge polar difference between the long non-polar side chains and the hard segments,which is like a"barrel brush"effect,results in an excellent nanophase separation behavior.This enables the enrichment of non-polar side chains on the surface of the materials,which greatly improves the hydrophobicity of L-NIPHAUs with obvious low surface energy characteristics and good solvent resistance.2.In Chapter 3,this matrix was continued to be used,and a series of dynamic cross-linked neat PHAU networks with crystalline structure and PHAU/HEC_X composites were prepared without solvent and catalyst by introducing cross-linking points containing tertiary amine structures.First,the interface and covalent bonding between the matrix and hydroxyethyl cellulose(HEC)are verified.Even if a large number of hydroxyl groups are introduced,the non-polar side chains are enriched on the surface of the material due to the cross-linked network,showing high hydrophobicity(>90°).And we unexpectedly found that this composite network has a wide temperature damping effect of 141°C,which has the leading damping effect in the PHU field so far.The high hydrogen bond density introduced by the amide bonds in DAPA segments and HEC results in a crystalline structure in the network.After a temperature change,they undergo phase transition behavior in the cross-linked network.This provides a significant contribution to PHAU’s thermally responsive dynamic chemistry,stress relaxation and reprocessing capabilities.The phase transition of crystallization in the network is also responsible for the high losses in the initiation of the motion of the molten segments.Especially with the introduction of HEC,the crystalline phase transition becomes more difficult,which explains its wide temperature range damping phenomenon.The loss of motion of the two major segments in the network,glass transition and crystalline phase transition,together endow the polymers with shape memory function.3.In Chapter 4,we synthesized a series of linear unsaturated polyesters cyclocarbonate terminated polyester(t-CC-PHE-x:y)by a novel ring-opening method of cyclocarbonate with carboxyl group without vacuum distillation and solvent.After a simple molecular weight control and curing reaction of the t-CC-PHE-x:ys with DAPAhs,a series of PHUs with different-OH/ester and-OH/urethane components(PHEU-x:ys)were synthesized.With the increase of ester bonds,although the initiation temperature and relaxation time(τ*)of network topological rearrangement increased,the dynamic response E_a of the material decreased significantly,from 112 k J/mol to 62 k J/mol.Conversely,by introducing a large number of dynamic-OH/urethane bonds into PHEU-x:ys,the rearrangement initiation temperature andτ*of the material are greatly reduced.This is of great significance for the preparation of dynamic polyester networks.Due to the increase of-OH/ester bonds in the system,the side reactions of-OH/urethane bonds are relatively reduced after repeated reprocessing,and the reprocessing efficiency of the networks is greatly increased from 68.3%to 81.7%.At the same time,PHEU-x:ys also have good solvent resistance and comprehensive performance.