DECONVOLUTION OF SCANNING CALORIMETRIC SIGNALS OBTAINED FOR AQUEOUS MIXTURES OF POLY(OXYPROPYLENE) OLIGOMERS

High-sensitivity differential scanning calorimetric (HSDSC) data obtai ned for mixtures of poly(oxypropylene) (POP) oligomers, of different m olecular masses, in aqueous solution have been deconvoluted using a pr eviously reported mass action thermodynamic model of aggregation (Arms trong, J.; et nl. J. Phys. Chem. 1995, 99, 4590) to investigate polyme r aggregation/phase separation in these mixed systems, The data shows that POP oligomer solutions will phase separate at well defined temper atures as the POP solution is warmed. The data obtained shows no scan rate dependence which prompts the hypothesis that phase separation is adequately described by a nucleation and growth mechanism, It is concl uded that the nucleation step is observable by HSDSC while the growth phase is calorimetrically silent. The model derived parameters indicat e that the: phase transitions occurring at the lower temperature are o nly slightly modified compared to those values obtained for the respec tive single-polymer solutions, whereas the higher temperature transiti ons are markedly altered, A descriptive model is proposed which is use d to explain the obtained results. Essentially the model suggests that the higher molecular mass component, which phase separate at lower te mperatures, aggregates and phase separates independently of the lower molecular mass component. However, depending upon the molar ratio of t he two components, the lower molecular mass component will, at the app ropriate temperature; either join the already existing high molecular mass component aggregates or will form separate aggregate nuclei.