Urea-based Polymer Materials:Synthesis And Properties Of Polyisocyanurates And Poly(urea Carbonate)s

Compared to traditional petroleum-based polymers,biobased polymers are more suitable materials fitting with the national strategy on sustainable development since they are the way to reduce the dependence on nonrenewable fossil feedstocks.Urea is an important biobased feedstock for chemical industry.Therefore,the exploitation and the utilization of urea-based polymer is an essential part of sustainability,by which biobased materials could be diversified further and could be more potential in the substitution of conventional petroleum-based polymers.In this dissertation,important urea derivatives,such as bis(2-carboxyethyl)isocyanurate(BCI)and dihydroxyalkyl urea,together with some other biobased monomers were applied in the preparation of new ureabased polymers which are namely polyisocyanurates and poly(urea carbonates).The properties of the obtained polymers were studied as well.(1)Bis(2-carboxyethyl)isocyanurate(BCI)was esterified and its dimethyl ester(BCMI)was reacted with di(2-hydroxyhexyl)urea to form the isocyanurate-ring-containing polymer poly(isocyanurato urea ester)(PICUE-6)via transesterification polymerization.Poly(isocyanurato ester amide)PICEA-6 and poly(isocyanurato amide)PICA-6 were prepared in the same way from 6-amino-1-hexanol and hexamethylenediamine,respectively.All the polyisocyanurates exhibit excellent thermal stability.The glass transition temperatures of PICUE-6,PICEA-6 and PICA-6 are detected to be 52.4,82.8 and 110.6 °C,respectively.Only PICA-6 has melting peak on the differential scanning calorimetry(DSC)curve and the melting temperature is found to be 250 °C,which is obviously higher than most of biobased polymers exploited so far.The limit oxygen index(LOI)values of PICUE-6 and PICEA-6 are 24.0%,which indicates the flame retardancy for these two polymers.(2)Poly(urea carbonate)s(PUCs)were prepared from di(2-hydroxyalkyl)ureas and dimethyl carbonate(DMC).The products in the early stage of polymerization were linear PUC but by further reaction under the catalysis of the organic super base 1,5,7-Triazabicyclo[4.4.0]dec-5-ene(TBD),the urea group attacked the carbonate group to form allophanate cross-linker.The formation of allophanate was verified by a small-molecular model reaction.The allophanate cross-linker is not static but dynamic since it is able to perform a reversible transesterification with free hydroxyl group in the polymer systems.The dynamic cross-linkers ensure keeping the 3-dimentional network of polymers while realizing the reprocessibility of polymers.The results in our work showed that for the final PUC products,the relationship between viscosity and temperature fits with the Arrhenius Equation,as well as the swelling experiments and reprocessing experiments all verify the formation of vitreous materials.The PUC vitrimers exhibit excellent mechanical properties.The tensile strength of PUC-4 and PUC-6 is quite similar to conventional commodity polymers,the values are 8.6 and 15.1 MPa,respectively.And for the elongation at break,the values are over 80%,which preliminarily indicates that both vitrimers are tough materials.