The effect of branching on the physical properties of 73/27 4-hydroxybenzoic acid/2-hydroxy-6-naphthoic acid

The 73/27 4-hydroxybenzoic acid (HBA)/2-hydroxy-6-naphthoic acid (HNA) copo lyester was prepared by the inclusion of two crosslinkable oligomers. These systems were synthesized by melt polymerization and characterized using di fferential scanning calorimetry, thermogravimetric analysis, polarized opti cal microscope and wide-angle X-ray diffraction. The transition from thermo plastic to thermosetting character occurred when 10wt% or above of oligomer was added to the 73/27 HBA/HNA random mixture. The melt rheology of the HB A/HNA copolyesters containing two oligomers was investigated. The copolyest ers displayed an increase in complex viscosity and transition from liquid-l ike to solidlike behavior as the oligomer content increased, and finally th ere was no melting transition when the oligomer content reached 10wt%. Shea r storage modulus measured by a dielectric mechanical analysis decreased sl ightly with increasing oligomer content. An adhesive test using an aluminum sheet revealed an increase in the lap shear strength up to 5wt% of oligome r content without a significant reduction in shear storage modulus. On the other hand, the 73/27 HBA/HNA containing 10wt% oligomer displayed a dramati c decrease in lap shear strength. Copyright (C) 1999 John Wiley & Sons, Ltd .