The infra-red absorption characteristics of syndiotactic poly(methyl methacrylate) from 1050 cm −1 to 1300 cm −1

Abstract

There are five (i.e. v 1 to v 5) infra-red absorption peaks associated with the ester group of s-poly(methyl methacrylate) while simple esters (i.e. methyl acetate) exhibit only one. These multiple absorption peaks do not arise because of specific intermolecular interactions because they persist in dilute solution. The multiple absorption peaks do arise because of specific intramolecular interactions because they disappear in copolymers of styrene. The implication being that a single ester group can be found in either one of two or perhaps four different rotational positions, each position is to be associated with a different force constant. The absorption characteristics could be described by the sum of seven Lorenz type dispersion functions each associated with a single absorption peak. From the Lorenz parameters the variation of integrated intensity (which is related to the population density in each environment) can be determined as a function of temperature. The integrated intensity was independent of temperature for all four peaks below the glass temperature: above the glass temperature they varied with temperature. However, the sum of the integrated intensities for peaks v 1 and v 2 as well as v 3 and v 4 was found to be independent of temperature over the entire experimental range. The implication is that the ester group can rotate from the environments associated with v 1 to v 2 or from v 4 to v 3 only above the glass temperature. Further experimental evidence indicates that the high temperature population distribution can be supercooled to room temperature. In addition, the dilute solution behaviour near room temperature is similar to the behaviour above the glass temperature for the solid polymer. The location, relative intensity, polarization and sensitivity to polymer chain tacticity indicates that peaks v 6, v 7 may be associated with a planar zig-zag arrangement of the backbone carbon atoms.