Provided is a method comprising reacting the anionic living end of a polymer that is end capped with a steric hindering compound with a carbonyl-containing compound to produce a polymer with a homolytically cleaveable group. An engineered plastic may then be produced by adding the polymer containing a homolytically cleavable group to a solvent comprising at least one vinyl monomer; (b) optionally adding at least one additional inert solvent; (c) optionally adding additives selected from the group consisting of extender oils, modifiers, and antioxidants; and (d) initiating polymerization of the at least one vinyl monomer by the use of an initiator and/or heat, wherein a free radical is produced from the polymer containing a homolytically cleavable group.