Irreversibility of stretching‐induced local conformational changes as verified through an FTIR dichroism study for PVC

Abstract

The dichroic behaviour of 615 and 637 cm À1 bands of the IR spectrum of poly(vinyl chloride) (PVC) has been analysed through FTIR measurements on PVC ®lms stretched to various elongation ratios. By comparing the evolution both of the dichroic ratios and of the relative absorbance of those bands in the perpendicular direction to that of stretching, the occurrence of local chain orientation related to the conformational change GTTG À TTA GTGTTT at mmr isotactic tetrads can be differentiated from the normal orientation of syndiotactic sequences, so con®rming earlier proposals that the above conformational change takes place when stretching PVC.

Stereochemical microstructure dependence of physical properties of poly(vinylchloride) (PVC). Principles and some recent correlations

“…I. Actually, as demonstrated by a FTIR dichroism study (19 ) of the samples no appreciable orientation of chains occurs u p to A = 1.1. This allows the strong decrease of intensity observed in Fig Stretching degree Fig.…”

“…Loss of heterotactic triad content us conversion (0) and loss of isotactic triad content us increase of syndwtadic triad content (0) ofPVC after substitution reaction with NaMBT. in the case of the polymer series utilized for Tg. Besides, we designed a parallel study of the space charge distribution in films of the same polymer after stretching to various degrees, so a s to make the mmr under GTTGTT conformation adopt the more stable GTGTTT conformation (19). By doing that, we sought to prove the extent to which each of the two conformations is particularly sensitive to charge accumulation compared to the remaining structures, as suggested by the above quoted results (1 0).…”

“…A = final stretched length/initial unstretched length). A s described elsewhere (19) the only microstructural change during stretching up to A no greater than 1.3 consists mainly of gradually removing the permanent GTTG'TT conformations of mmr by exchanging them for GTGTTT conformations in an irreversible way.…”