On connection between conformational and thermodynamic properties of poly-2,4-dimethylstyrene in various solvents

Abstract

The unperturbed chain dimensions K θ of polydimethylstyrene (PDMS) in 12 solvents were determined by the Stockmayer-Fixman procedure. It was found that the value of K θ decreased monotonously with increasing solvent power (i.e. with increasing the exponent a in the relation [η] = K η M a ) The unperturbed chain dimensions in θ-solvent were obtained by extrapolation of log K θ to a = 1 2 . They are equal to 0·064. Analysis of data obtained both in aromatic and non-aromatic solvents showed that the decrease of the unperturbed chain dimensions was proportional to the product ( βN s): K θ 1,3 = K θ. a = 1 2 1 3 (1 – 2·5 × 10 21 βN s) (β is the excluded volume of the chain units and N s is the mean number of the absorbed solvent molecules). The values of N s were determined by light scattering in the series of mixed solvents. In the non-aromatic solvents, the unperturbed chain dimensions decrease with increase of the density of the molecular packing. It is suggested that interaction of neighbouring bulky side groups of the polymer chain is decreased by the solvent and this replaces the potential energy minimum of the chain in the direction of more folded conformations.