Metal-free Synthesis Of Polyester Diol And Polyester-based Polyurethane

With the growing concern on depletion of oil resources and the mushrooming awareness of environmental conservation,it is emerging as a global consensus to develop and use renewable and biodegradable polymer materials.Recently,the ring-opening copolymerization(ROCOP)of epoxides and anhydrides has gained increasing attention as a promising route to polyesters,owing to the mild reaction conditions as well as the diversity and sustainability of monomers.Polyesters with high molecular weight are expected to be ideal substitutes for the traditional non-degradable polymers in a wide range of applications such as packaging and agricultural mulch films in order to solve the white pollution problem,while polyester polyols with low molecular weight can be used for the preparation of high-performance polyester-based polyurethanes.Up to now,organometallic complexes with high catalytic activity and excellent controllability have represented the most investigated catalysts for ROCOP of epoxides and anhydrides,but the resultant polymeric products may suffer from coloring problem and the potential biological toxicity.In this dissertation,organocatalysts composed of thioureas and organic bases have been explored as non-metallic catalysts for ROCOP of epoxides and anhydrides.Using water as an efficient initiator,polyester diols with completely alternating structure and controllable molecular weight(M_n=2.0?10.8 k Da)were prepared.Furthermore,one-pot synthesis of polyester-based polyurethanes was achieved via tandem step-growth polymerization between in-situ formed polyester diols and diisocyanates.The details and results are listed as follows:1.With propylene oxide(PO)and phthalic anhydride(PA)as modal substrates for ROCOP,the effects of the structure of thioureas and organic bases,the ratio of thioureas/organic bases,the amount of initiators as well as the reaction temperature were investigated.The experimental results indicated that all thiourea/organic base pairs are quite effective for ROCOP,affording polymeric products with completely alternating structures,but thiourea can not catalyze the ROCOP alone.Instead,it activates PO as a hydrogen bonding donor and therefore significantly improves the catalytic activity of organic bases.Moreover,the combination of organic base with strong basicity like 1,8-diazabicyclo[5.4.0]undec-7-ene(DBU)and thiourea with strong electron donor effect like 1,3-diisopropylthiourea(TU-1)shows the best catalytic activity.Under the reaction condition of 90°C,TU-1/DBU/PO/PA=1/1/500/100,the conversion of PA reaches 99%within 2 h with a turnover frequency(TOF)of 45 h^-1.Besides,the molecular weight of the product has linear relationship with the conversion of PA when water serves as the initiator,which is indicative of living polymerization feature.Importantly,the polyesters are terminated with hydroxyl groups.The molecular weight of the products can be precisely controlled by regulating the amount of water,and polyester diols with average molecular weight ranging from 2.0 k Da to 9.5 k Da have been successfully synthesized.2.Polyester diol with target average molecular weight of 2.0 k Da has been successfully synthesized with full conversion of PA under the polymerization condition of 80°C,TU-1/DBU/PO/PA/H₂O=1/1/500/100/10.Then,isophorone diisocyanate(IPDI)was added to react with the above polyester diol via tandem catalysis of TU-1/DBU,enabling the one-pot synthesis of polyester-based polyurethane.Furthermore,the monomer scope has been expanded by using epoxides including ethylene oxide,propylene oxide,1,2-butylene oxide,1,2-epoxycyclohexane,allyl glycidyl ether,and anhydrides including phthalic anhydride,succinic anhydride,cis-1,2,3,6-tetrahydrophthalic anhydride,cis-5-norbornene-endo-2,3-dicarboxylic anhydride,as well as diisocyanates including hexamethylene diisocyanate,isophorone diisocyanate,1,3-bis(isocyanatomethyl)cyclohexane,4,4'-diphenylmethane diisocyanate.In all cases,polyester-based polyurethanes with diverse functionality have been successfully synthesized in one-pot process by tandam catalysis of TU-1/DBU.