By following the copolymerization of a model polyurethane system, HTP B D /2,6 (or 2.4)-TD I /B DO, by optical microscopy, it was found that initial reactant incompatibility was the key factor in determining the final morphology of bulk sample. Based on this finding and the esults from the previous paper, models are proposed to describe the morphology during polymerization of this particular polyurethane system for several hard segment compositions where both macro-phase separation and micro-phase separation of reactants can occur during polymerization. The copolymerization of one seemingly compatible system, PPO-EO/MDl/BDO, which has been previously studied and commercially produced, was also followed by optical microscopy. In the size range which can be detected with an optical microscope using conventional optics, no heterogeneities were observable at the beginning of this reaction but phase separation was evident later in the reaction and can be xplained by the presence of micro-phase separation of reactants. Globule and spherulite formation and the presence of multiple T 9 's and Tm's observed by previous workers can be explained by the two levels of heterogenities present during polymerization.

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