Dilatometric measurements on poly(4-methyl-1-pentene) glass and melt transition temperatures, crystallization rates, and unusual density behavior

Dilatometers were used to measure the volume‐temperature curves of seven poly(4‐methyl‐1‐pentene) (PMP) samples between −30 and +270°C., and to measure crystallization rates on one sample between 220 and 236°C. A glass transition temperature of 18–29°C. was found, and the crystalline melting point was found to be 250°C. The value of dV/dT above and below the glass temperature was used to measure the degree of crystallinity. The results indicate that the crystalline PMP is less dense at room temperature than the amorphous polymer. However, because of different rates of expansion, the normal positive volume change on melting is observed. A density value of 0.828 ± 0.002 g./ml. at 20°C. is calculated for the PMP crystal.