Study On Synthesis Of Tetramethyl Xylylene Diisocyanate

The tetramethyl xylylene diisocyanate(TMXDI)is a low poison diisocyanate with both aliphatic and aromatic isocyanates characteristics.The elastomer made from TMXDI has the properties of softness,high strength,adhesion,flexibility,and the advantages of yellowing resistance,acid resistance and durability.There are plenty of methods to create TMXDI such a as phosgene,isocyanate,replacement,isocyanate and carbamate pyrolysis and the carbamate pyrolysis is the most suitable way.In this paper,the technological conditions for the preparation process of TMXDI by thermal decomposition of carbamate are studied.TMXDI can be synthesized by thermal cracking of tetramethyl xylylene diurethane(TMXDU).First,we introduces the way to prepare TMXDU using methyl carbamate(MC)and1,3-diisopropenyl benzene(DIPEB)as raw materials.The melting point of the product is129-131oC,which can be identified by using IR and 1H-NMR the structure of TMXDU.Through orthogonal experiment and single factor experiment,effects of reaction temperature,reaction time,raw materials proportioning,and catalyst dosage on TMXDU yield are investigated.The optimum reaction conditions are reached at reaction temperature of 130 oC,time period of 7 hours and the ratio of 10 between NMCand NDIPEBwhich leads to the results that TMXDU yield can reach 87.6% with the sulfuric acid dosage for DIPEB of 3%(mole percentages).Second,we studied the optimum conditions about synthesis of tetramethyl xylylene diisocyanate(TMXDI)by cracking tetramethyl xylylene diurethane(TMXDU).The density of the product is 1.073g/mL,and the refractive index is 1.5112 which was identified by using IR and 1H-NMR the structure of TMXDI.Through orthogonal experiment and single factor experiment,effects of pyrolysis temperature,feeding rate,and catalyst dosage on TMXDI yield are investigated.The optimum reaction conditions are reached with pyrolysis temperature of 305oC,feeding rate of 0.3g/min,and reaction pressure 0.07 Mpa which leads to the results that TMXDI yield can reach 56.9% with the ZnO for TMXDU of 1.0%(mole percentages).