Spin-label investigation of the dynamic behavior of stearic acid additivesin poly(vinyl chloride)

Three kinds of spin label compounds having a DOXYL-radical substituent at d ifferent positions df the hydrocarbon chain of stearic acid were added to t he poly(vinyl chloride) (PVC) including dioctyl phthalate (DOP) as plastici zer, and the order parameter (S) of each radical in PVC resin was determine d by the ESR measurement. The values of S which is a parameter of dynamic s tate of spin label compounds in PVC decreased by increasing the quantity of DOP added to PVC. Similarly, the values of S decreased by increasing the t emperature. The decrease of S may be explained by the, decrease of rigidity of PVC resin, due to the addition of DOP and the increase of the temperatu re. The half-decrease temperature of the order parameter (T-S1/2) for each radical decreased by increasing the quantity of DOP added to PVC and by dec reasing the density (d) and the glass transition temperature (T-g) of PVC r esin. The stable structures for each interaction model (PVC/stearic acid ad ditive model, PVC/DOP model) were estimated by molecular orbital (MO) calcu lation.