Abstract
Polyurethanes based on 4,4'-diphenylmethane diisocyanate (MDI), 1,4-butane diol (BDO) and polypropylene oxide diol (PPO) form a segmented random copolymer which phase separates into hard and soft segment domains. The morphology of the hard segment (MDI/BDO) domains has been the object of considerable research because of the large influence of these domains on the mechanical properties of the material. A number of models based on wide and small angle x-ray and DSC studies ranging from highly ordered crystallites to paracrystalline domains have been proposed. In this study STEM and TEM imaging coupled with microdiffraction has revealed the presence of two distinct crystal structures with different morphologies.
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