Influence of fluorocarbon chains on the crystallization behaviors of aliphatic polyurethanes

The aliphatic polyurethanes were synthesized from either hexamethylene diisocyanate (HDI) and 2,2,3,3-tetrafluoror-1,4-butanediol or HDI and 1,4-butandiol. The crystallization behaviors of the aliphatic polyurethanes were characterized using differential scanning calorimetry, wide-angle X-ray diffraction, and polarized optical microscopy. The effects of fluorocarbon chains on the solubility behavior, microstructure, thermal transition property, crystal morphology, and crystallization behaviors were investigated. The fluorinated polyurethane exhibited a lower viscosity, higher solubility in organic solvents, smaller fraction of ordered hydrogen-bonded carbonyls, and lower transition temperatures than the corresponding fluorine-free polyurethane. The wide-angle X-ray diffraction measurements reflected change of crystal structure with the (CF2)2 moieties in place of (CH2)2 moieties. Polarized optical microscopy also revealed that the polyurethanes exhibited a variety of spherulitic texture. The isothermal crystallization process of the polyurethanes was described by the Avrami analysis. The result showed that the Avrami exponent (n) was around 2.5, which suggested the growth of crystal might be spherulite growth corresponding to homogeneous (thermal) nucleation and diffusion control. The crystallization activation energy was estimated to be −130.9 kJ/mol for the fluorinated polyurethane and −276.9 kJ/mol for the fluorine-free polyurethane from Arrhenius form. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009