Dynamic mechanical properties of concentrated solutions of polymethyl methacrylate in diethyl phthalate

Abstract

The real ( J′) and imaginary ( J″) components of the complex compliance have been measured between 0.05 and 2400 cycles/sec. for two solutions of a fractionated polymethyl methacrylate with molecular weight 2.16 × 10 6. The temperature ranges were from −44° to 5° at a concentration of 20 % and from −30° to 45° at 30 %. The method of reduced variables gave superposed curves for J′ and J″ except for a low temperature anomaly in the 30 % solution and a high temperature anomaly in the 20 % solution near the maximum in J″. The temperature dependence of the relaxation times followed the WLF form of equation. The glass transition temperature of the 30 % solution was determined refractometrically to be −62°, from which the fractional free volume at this point is calculated to be 0.020. The relaxation and retardation spectra are similar in shape and magnitude to those found earlier for a series of poly- n-butyl methacrylate solutions in the same solvent. The monomeric friction coefficient in dyne-sec./cm. is 10 −6.99 and 10 −5.74 at 25°C. for the 20% and 30% solutions, respectively, the concentration dependence being consistent with that observed in the butyl polymer and corresponding to proportionality to e 25 c , where c is grams polymer per cubic centimeter solution. The average degree of polymerization between entanglement coupling points, calculated in several ways, is also consistent with the concentration dependence observed for the butyl polymer (proportional to c −2.3). Compared at equal temperatures and concentrations in monomoles per cubic centimeter, the methyl polymer has a friction coefficient 5 times larger than and an entanglement spacing 0.7 as large, respectively, as, those of the butyl polymer in the same solvent.