Dielectric relaxation and other properties of syndiotactic and isotactic poly(methyl methacrylate)

Abstract

The dielectric properties of s-PMMA and i-PMMA have been determined over a wide range of temperature and frequency. The complex plane method was used to represent the data. For s-PMMA in the glass phase the single relaxation process observed could be represented as a circular arc. Above the glass temperature, two dispersions were observed and each could be represented by a circular arc. For i-PMMA only one relaxation process was observed above the glass temperature. This process could be represented by a skewed circular arc whose parameters are similar to those of many other polymers. Below the glass temperature a relaxation process is observed; however, evidence is considered to show that it is the same process as the one above the glass temperature but one that disappears with decreasing temperature. The magnitude of the effective dipole moment for each process in s-PMMA and i-PMMA is treated from the point of view of Kirkwood. The necessary structural details are obtained from infra-red measurements previously reported. The variation of the effective moment with temperature is treated as a variable segment length of a polymer chain whose assumed structure is consistent with the infra-red evidence. The dielectric β-process in s-PMMA is shown to be equivalent to the mechanical β-process in the same polymer. X-Ray evidence is considered to show that the decrease in the glass temperature with increased bulkiness of the side chain is indeed due to an increase in the chain-chain separation.