A composition comprising:(i) a crosslinkable thermoplastic resin;(ii) an organic peroxide crosslinking agent; and(iii) a linear polyorganosiloxane having the following recurring unit: ##STR1## wherein R is a saturated aliphatic or aromatic group and each R can be alike or different;a is about 5 to about 100;b is about 1 to about 1000; and the polyorganosiloxane is terminated at the [CH.sub.2 ].sub.a end with --CH.dbd.CH.sub.2 or hydrogen and at the ##STR2## end with--[CH.sub.2 ].sub.a --CH.dbd.CH.sub.2 or hydrogen provided that at least one --CH.dbd.CH.sub.2 is present.