Influence of aryl substituents on the thermal and solubility behavior of poly(p-phenylene terephthalate) and poly(p-phenylene terephthalamide)

The substitution of poly(p-phenylene terephthalate) and poly(p-phenylene terephthalamide) with phenyl and biphenylyl substituents (4-biphenylyl and 2-biphenylyl) in the terephthalic acid unit lowers the melting temperatures and crystallization tendency and increases the solubility. The melting temperatures of the polyesters are in the range of 285–350°C. Melting of the polyamides occurs between 440–490°C. The polyamides begin to decompose in the same temperature range. In polyesters as well as in polyamides the 2-biphenylyl substituent was found to be more effective in decreasing the crystallinity, lowering the melt transition temperatures and increasing the solubility.