Surface enrichment in polymer blends involving hydrogen bonding

A phenolic polysiloxane, poly(4-ethenylphenolmethylsiloxane) (PEPS), that c ontains the phenolic hydroxyl group as a hydrogen-bond donor has been synth esized via hydrosilylation followed by hydrolysis. It was blended with a nu mber of hydrogen-bond acceptors of different strengths, including poly(4-vi nylpyridine) (PVPy) (strong), poly(vinylpyrrolidione) (PVPr) (strong), poly (dimethylacrylamide) (PDMA) (moderate), and poly(styrene-co-acrylonitrile) (PSAN) (weak). All blends were miscible in the bulk, as indicated by a sing le DSC T-g, and were shown to be homogeneous by optical microscopy. XPS mea surements demonstrated that all PEPS blends had surface enrichment in PEPS, which has a lower surface energy. AFM images showed that the surface morph ology in PVPy/PEPS, PVPr/PEPS, and PDMA/PEPS blends did not differ from tha t in the bulk, whereas the PSAN/PEPS blend exhibited a different surface st ructure that consisted of PSAN covered with a thin layer of PEPS. Depth pro filing by SIMS was in agreement with the XPS analysis. The results indicate d that (1) surface enrichment in hydrogen-bonding polymer blends is governe d by the interplay between the difference in the surface energy of the cons tituents and the bulk thermodynamics and (2) hydrogen-bonding interactions reduce surface enrichment.