Development of crystallinity in a polyurethane containing mesogenic units. 1. Morphology and mechanism

This work extends prior studies of a polyurethane containing mesogenic moieties. Opticaland thermal methods reveal that this polyurethane exhibits monotropic mesomorphic behavior. Two distinctcrystallization mechanisms and crystal morphologies are identified, one arising from the isotropicmelt and producing a spherulitic texture and the other arising from the mesophase and producing a threadedtexture. A combination of thermal analysis, X-ray diffraction, and dynamic rheological studies reveals thatcrystals grown from the mesophase are readily perfected to a higher melting form by annealing whereasspherulitic crystals are less amenable to perfection. The development and perfection of the crystallinestate were also found to be dependent on polyurethane molecular weight.