PHASE-BEHAVIOR OF A SUBSTITUTED POLY(PARA-PHENYLENE) - POLY(PARA-2,5-DIDECYL-P-PHENYLENE)

The thermal behavior of poly(para-2,5-didecyl-p-phenylene) has been in vestigated by differential scanning calorimetry and real time X-ray di ffraction. Poly(para-2,5-didecyl-p-phenylene) is a semicrystalline mat erial that crystallizes in a layered structure. The system exhibits tw o thermal transitions in the investigated temperature range. The first one, occurring at lower temperatures, provokes a reduction of the lay ered spacing accompanied by an appreciable disordering of the lateral side chains. Above the first transition the material is shearable, hig hly viscous, and birefringent. Thus, we have associated this transitio n to the formation of a layered mesophase. The higher temperature tran sition exhibits a twofold endothermic DSC peak and is characterized by the disappearance of X-ray diffracted intensity. At temperatures abov e the second transition the system presents the characteristics of an isotropic melt. Consequently, we have associated this transition with the complete disordering of the polymeric backbones. By following an a ppropriate thermal treatment it has been shown that the twofold shape of the endotherm characterizing the higher temperature transition can be changed into a single endotherm. This effect has been interpreted a s being due to the kinetics of main-chain ordering. This ordering seem s to proceed by the initial growth of domains with a high level of ord er followed by the subsequent increase of these domains through the in clusion of less ordered material. (C) 1998 John Wiley & Sons, Inc.