e integer; and from about 1 to about 15% by weight of a polysiloxane crosslink additive having the general formula ##STR8## wherein each R1, R'1, R2, R'2, R3 and R'3 is H or a substituted or unsubstituted hydrocarbon group, wherein at least three of said R or R' groups are --CH???CH2, and n is a positive integer; and curing said mixture to provide a crosslinked polysiloxane having a cone penetrati