Study On Kinetics Of Alcohol-Isocyanate Reaction

Reaction between isocyanate and alcohol is the key step of polyurethane foaming.Despite numerous researches on the reaction of phenyl-isocyanate and alcohol,theories on such reaction mechanism and kinetics have been developed and reaction in ether solvents similar to industrial foaming environment is rarely studied.High performance liquid chromatography(HPLC)was applied in this thesis to investigate reactions of p-toluene isocyanate(PTI)and n-propanol in triglyme solvent with/without amine catalyst,and explore the effect of conditions on kinetics,mechanism and reaction pathway.Regardless of the concentration of catalyst,a lower initial molar ratio of alcohol to PTI(r=n(OH)0/n(NCO)0)leaded to significant amount of by-product urea,which means traditional dibutylamine titration was not applicable,while HPLC could track the reaction.apart from N,N'-di(p-tolyl)urea,no other by-products formed according to material balance calculations.During catalytic reaction,linear relationships existed between original concentration of alcohol,isocyanate and catalyst and the second-order reaction rate constant k.In non-catalytic process,a lower initial reaction rate was observed,various factors affected and the reaction rate constant turned out to be random.After the effect of reaction conditions on kinetics was investigated,reaction pathway was proposed as follows,Reaction(2)determined the generation of main product carbamate under catalytic circumstances,while reaction(1)controlled in non-catalytic condition.