Local Chain Conformation Research Articles

Viscoelastic study of the conformational transition of poly(methacrylic acid) in dilute aqueous solution

AbstractThe dynamic viscosity of dilute aqueous solution of poly(methacrylic acid) (PMA) was measured over the frequency range 2–500 kHz for various degrees of ionization. The relaxation spectrum calculated from the viscosity exhibits a conformational relaxation spectrum in the short‐time region and a rotational one in the long‐time region. The former is fitted by the Zimm theory over the entire range of ionization, including the transition from a compact structure to an open one. The conformational relaxation time begins to increase at the midpoint of the transition region, but the rotational relaxation time increases very markedly in the initial stage of the transition.The present and previously reported experimental findings are interpreted in terms of the assumption that the compact structure is stabilized by short‐range methyl–methyl bonding as well as “long‐range” methyl–methyl bonding (bonding between methyl groups spatially close but remotely connected along the chain contour). In the initial stage of the transition, the latter primarily break up, resulting in expansion of overall chain dimensions, and subsequently the former are destroyed, resulting in the change in local chain conformation.

Application of infrared spectrometry to the study of some polymer problems

AbstractInfrared spectroscopy has been applied as a major tool for the investigation of a number of polymer problems. The major products of thermal degradation (300°C.) of polymonochlorotrifiuoroethylene and copolymers with vinylidene fluoride have been Identified and are considerably different depending upon whether or not degradation occurs in nitrogen or oxygen. A mechanism based on random chain cleavage has been proposed for both the homopolymer and copolymer system. A method has also been developed for the determination of the vinylidene fluoride content in vinylidene fluoride‐monochlorotrifluoroethylene copolymers by measuring the —CH— stretching absorption of the —CH2CF2— units in solid films. Absolute values of —CH2CF2‐ content have been determined by high‐resolution NMR and melting point techniques. It has been shown that the intensity of the —CH— stretching absorptions is dependent on the local chain conformation about the —CH2— unit. In another problem the “hardness” of polyethylene waxes has been found to be dependent, on the degree of branching as measured by the methyl absorption at 1378 cm.−1. Molecular weight has been shown to have little effect on the hardness.