The influence of alkylene spacers on conformational and thermal properties of poly (aryl methacrylates)

The effect of introducing alkylene spacers on the thermal and conformational properties of poly(aryl methacrylates) has been studied. Poly(2‐phenylethyl‐1‐methacrylate) (PPEMA) and poly(4‐phenylbutyl‐1‐methacrylate) (PPBMA) samples of narrow poly‐dispersities and covering a very broad range of molecular weights were produced by free radical solution polymerization, followed by fractionation. These materials were studied by a combination of differential scanning calorimetry, light scattering, and viscometry measurements to allow evaluation of their glass transition temperatures (T_g) and characteristic ratios (C_∞). These results are compared with literature data available for poly(phenyl methacrylate) (PPMA), which has no alkylene spacer, and poly(benzylmethacrylate) (PBMA), which has a methylene spacer. A progressive decrease in T_g is observed as the length of the alkylene spacer is increased, reflecting the enhancement of side group (local) flexibility. C_∞ decreases substantially on going from PPMA to PBMA but then increases on going to PPEMA and PPBMA. This behavior is attributed to the fact that while side group flexibility increases for the materials with longer alkylene spacers, and this would be expected to decrease C_∞, the side group size is progressively increasing. Larger side groups generally increase C_∞ of polymethacrylates. Thus the observed C_∞ behavior for these polymers reflects both the size and flexibility of the substituents. © 1994 John Wiley & Sons, Inc.