Synthesis And Characterization Of Polyurethane Elastomer Based On Meta-xylylene Diisocyanate

Polyurethane is a kind of unique polymer material with a wide range of hardness and can be used in a great many fields such as foams,coatings,adhesives,thermoplastic elastomers and so on.In this article,polyurethane elastomers and prepolymers are prepared by using m-xylylene diisocyanate(XDI)as the key monomers.The effects of the types of chain extenders,oligomer diols and the isocyanate index(R)on the properties of materials were studied.The relationship between structure and properties of XDI-based polyurethane elastomers were investigated.By adjusting the isocyanate index(R)and the types of oligomer diols and chain extenders,eight kinds of XDI polyurethane elastomers were prepared by one-step batch feeding method.It was found that the molecular weight of XDI polyurethane elastomers were affected by the R value,the types of oligomer glycol and chain extender.The highest molecular weight of elastomer was achieved when polycarbonate diol(PCD-2000)was used as oligomer diol and hydroquinone dihydroxyethyl ether(HQEE)as chain extender with R=1.01.The number-average molecular weight was 48200,weight-average molecular weight was 131300 and molecular weight distribution index was 2.72.The storage modulus and glass transition temperature(T_g)of the HQEE chain-extended elastomers are higher than those of the1,4-butanediol(BDO)chain-extended material.The elastomers prepared by PCD-2000 diol exhibited the highest storage modulus and T_g,followed by the materials prepared by polycaprolactone(PCL-2000),and the lowest prepared by polytetramethylene ether glycol(PTMEG-1000).The temperatures of 5%weight loss of the elastomers based on PCD-2000,PTMEG-1000 and PCL-2000 were all above 320?,which indicated that XDI polyurethane elastomers had good thermal stability.Rheological analysis showed that the composite viscosity(?*)of the elastomers decreased and the storage modulus(G')decreased with the increase of temperature or frequency.The process of preparation of low free XDI polyurethane prepolymer was established.The effects of feed ratio,reaction temperature,reaction time and distillation temperature on the NCO value of the product were discussed.The structure and dynamic viscosity of the prepolymer were analyzed by infrared spectroscopy and rotational viscometer.The results show that when glycerol triacetate is used as solvent,the molar ratio of raw materials is 4:1,the reaction temperature is 60?,and the distillation temperature is 100?,the NCO values of the prepolymers prepared by PCD-2000 and PTMEG-1000 were 3.35%and 5.87%,respectively,which were closest to the theoretical values(3.53%and 6.10%).Viscosity analysis showed that the viscosity of the prepolymers decreased with the increase of temperature.The viscosity of the prepolymers prepared by PTMEG-1000 at 50?and 90?was 783 cp and 168 cp,indicating that the prepolymer had excellent processability.Eight kinds of polyurethane elastomers were prepared by prepolymer method using low free polyurethane prepolymers as the key materials and BDO or HQEE as chain extenders respectively.The results show that when polyurethane elastomers were prepared by low-free XDI-PTMEG-1000 polyurethane prepolymers,the highest molecular weight of elastomer was achieved when HQEE was used for chain extension and R=1.03.The number-average molecular weight was 49000,weight-average molecular weight was 100800 and molecular weight distribution index was 2.06.The molecular weight distribution of polyurethane elastomers prepared by low free XDI polyurethane prepolymers were narrower.The storage modulus and T_g of the HQEE chain-extended XDI polyurethane elastomers are higher than those of the BDO chain-extended material.The temperature of 5%weight loss of polyurethane prepared with low free XDI-PCD-2000 polyurethane prepolymers were above 320?,and the temperature of elastomers prepared by low free XDI-PTMEG-1000 polyurethane prepolymers were above 335?,all of which had good thermal stability.