AbstractA dilatometer is described to study the temperature dependence of density (ρ) of solid and semiliquid polymers and the following linear relations have been established. Atactic poly(vinylisobutyl ether) (25–90°C): ρ = 0.9166 − 7.15 × 10−4×T. Isotactic poly(vinylisobutyl ether) (25–70°C): ρ = 0.9184 − 7.13 × 10−4×T. Poly(n‐butyl methacrylate) (90–150°C): ρ = 1.0622 − 8.41 × 10−4×T. Poly(dimethyl siloxane) (30–51°C, using Lipkins pycnometer): ρ = 0.9846 − 8.81 × 10−4×T; where ρ is in g.cm−3, temperatureTis in Celsius, and the linearity correlation coefficientris better than 0.9998. Their volume–temperature plots are also linear. As the plots of polyn‐butyl methacrylate curved slightly near its glass transition (20°C), the quadratic equation ρ = 1.0402 − 4.79 × 10−4×T− 1.46 × 10−6×T2(standard deviation = 1.57 × 10−3) has been suggested for the entire range of 30–150°C scrutinized in this study. The data have been utilized to derive thermal expansivity and some equation‐of
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