A process for preparing homopolymers and copolymers of addition polymerizable monomers, or mixtures of such monomers, and the resulting polymer, wherein the process comprising contacting said monomer or mixture under high monomer conversion polymerization conditions with a catalyst composition comprising: a) a catalyst system comprising a Group 3-10 metal complex; and c) a silane, or hydrocarbylsilane corresponding to the formula: JjSiH4-j or AnJjSiH4-(n+j) wherein: J is C1-40 hydrocarbyl, A is a C2-20 alkenyl group, n is 1 or 2, and j is 0 or 1; wherein the polymer comprises from 0.1 to 100 long chain branches per 10,000 carbons, and at least some of which comprise a silane branching center.