Pressure-volume-temperature properties of polymethacrylates: anomalous behaviour in the melt

Abstract

Pressure-volume-temperature measurements have been performed for a series of polymethacrylates. Samples of poly(ethyl methacrylate) that have been pressed and quenched show densification between 100 and 150°C which disappears up to 200°C. Samples which have been heated above 200°C appear not to show this effect on reheating. Densifications similar to the above are also observed for the propyl and butyl polymethacrylates. Densification is not seen for poly(methyl methacrylate) nor for polyacrylates. Several other initial observations were made using other techniques. D.s.c. peaks are seen in this region which depend on the thermal history. The rheology is very dependent on thermal history. Some small changes in X-ray patterns are produced by thermal treatments. These observations could be interpreted as suggesting that polymethacrylates can be partially crystalline.