Phase structure and thermal stability of crosslinked polyurethane elastomers based on well-defined prepolymers

Taking advantage of the DSC method, general procedures were presented for qualitative and quantitative evaluation of the phase separation degree and the crystalline phase content in polyurethane elastomers with well-defined structures. Those elastomers were obtained not only in a typical one-step method but also in the prepolymer method with the use of urethane oligomers with controlled molecular weight distribution (MWD). Prepolymers with well defined chain structures and narrow distributions of their molecular weights (MWD) (M) over bar (w)/(M) over bar (n) = 1.1-1.3 were produced in a multistage method, i.e., in step-by-step polyaddition of 2,4- and 2,6-TDI with polyoxyethylenediols or with polycaprolactonediols of varied molecular weights. Isocyanate oligomers obtained at individual stages were then crosslinked with triethanolamine, whereas hydroxyl-terminated oligomers were crosslinked with 4,4',4"-triphenytmethane triisocyanate (Desmodur RE). The obtained polyurethane elastomers were found to be char-acterized by the presence of five phases: soft phase consisted of flexible polyol-type segments, crystalline phase made of soft segments, crystalline and amorphous hard phase made of hard segments, and intermediate phase, which was a composition of the soft and hard segments. The polyurethanes obtained out of prepolymers with defined MWD were characterized by better phase separation of the soft segments and increased structural order inside the hard phase as well as by better thermal stability than polyurethanes obtained from the typical one-step method. The structural effects were also discussed on the thermal properties of the synthesized elastomers as analyzed by the TG and DTA methods. (c) 2007 Wiley Periodicals, Inc.