Polycaprolactone-Based Block Copolymers. IV. Interfacial Activity in Poly(Vinyl Chloride) Containing Polyblends

The substantial difference in the T sub g of poly(vinyl chloride) (PVC) and poly( epsilon -caprolactone) (PCL) offers a sensitive method of locating a polystyrene (PS)--PCL diblock in PVC or in PS /PVC polyblends. When mixed with PVC, these diblocks are dispersed as individual molecules in equilibrium with micelles. The equilibrium position depends on the composition of the diblock; when PCL is the major component, molecular dissolution of PVC is enhanced. A 50/50 PS--PCL diblock, each block of which is of a higher molecular weight than the related homopolymer, is located mainly at the PS/PVC interface, as shown by the essentially unchanged T sub g of the PVC matrix and a sub-T sub g assigned to the external layer of the PVC phases plasticized by the PCL blocks of the copolymer. Blocks longer than the associated homopolymer chain clearly enhance the mutual anchoring of the PS and PVC phases. Since PS and PVC are intrinsically brittle polymers, their melt blending in the presence of properly designed PS--PCL diblocks gives rise to fragile materials. Graphs, Photomicrographs. 33 ref.--AA