Thermal expansion of poly(oxy-2,6-dimethoxy-1,4-phenylene)

The thermal expansion coefficient of poly(oxy-2,6-dimethoxy-1,4-phenylene), PPOO, was measured from 150 to 500 K, using a thermomechanical analyzer connected to a computer for the data handling. Poly(oxy-2,6-dimethyl-1,4-phenylene), PPO, and some brominated poly(oxy-2,6-disubstituted-1,4-phenylene)s were studied as reference materials. The apparent glass transition temperatures of the high molar mass polymers were 456 K for PPOO and 487 K for PPO, and the changes in cubic thermal expansion coefficients at T_g were 6,01 · 10^?4 K^?1 for PPOO and 4,23 · 10^?4 K^?1 for PPO. The activation of the β-relaxation was found for PPOO at 260 K and attributed to the hindered torsional oscillations of the backbone phenylene groups. Another transition was found at 160 ? 170 K and interpreted as the γ-relaxation due to the oscillatory motion of the methoxy groups. Reasons for the differences in the thermal expansion behaviour of PPOO and PPO are discussed.