Preferred silicon-containing polymers (referred to herein as polysilazanes) are alkoxy silyl substituted silazanes and siloxazanes of the formula: Z???A wherein Z is a silazane or siloxazane polymer and A is an alkoxy silyl group of the formula: ???X???R1???Si(R2)n(OR3)3-n wherein: X is bonded to a silicon atom of Z and is either 0 or ???NR4 wherein R4 is a member selected from the group consistin