Dynamic mechanical properties of concentrated solutions of poly- n-butyl methacrylate in diethyl phthalate

Abstract

The real ( J′) and imaginary ( J″) components of the complex compliance have been measured between 10 and 2400 cycles/sec. for four solutions of a fraction of poly- n-butyl methacrylate with molecular weight 3.05 × 10 6. The solvent was diethyl phthalate. The temperature range for each polymer concentration was as follows: 30%, −49° to 0°; 40.3%, −49° to 25°; 50%, −15° to 47°; 60%, −44° to 40°C. The method of reduced variables gave superposed curves for J′ and J″ except for a low-temperature anomaly in the 60% solution and a high-temperature anomaly in each solution near the maximum in J″. The temperature dependence of relaxation times followed an equation of the WLF form in each case. The value of α f (thermal expansion of free volume derived from the WLF equation) ranged from 2.2 to 2.8 × 10 −4 deg. −1. The glass transition temperatures, T g , of the 50% and 60% solutions were determined refractometrically as −67° and −46°, respectively; f g (fractional free volume at T g from the WLF equation) was 0.024 for both. The high-temperature reduction anomaly was resolved by a treatment used earlier for several undiluted methacrylate polymers, formally equivalent to assuming a dissociation of entanglement points with increasing temperature; the apparent heat of dissociation was 2.1 kcal./mole for all four solutions. The relaxation and retardation spectra are similar in shape except for differences in time scale and in magnitude. The monomeric friction coefficient ζ 0 at 0°C. ranges from 10 −6.28 for the 30% to 10 −2.90 for the 60% solution, and is closely represented by the equation ζ 0 = 5.8 × 10 −10 e 24 c , where c is grams polymer per cubic centimeter solution. From the relative magnitudes and positions of the retardation spectra near their maxima, the average degree of polymerization between entanglement points is concluded to be proportional to c 2.3.