Sustainable polymers can overcome the limitations of petroleum sourced materials due to their renewable feedstocks, biodegradability, recyclability, and nontoxic nature. The renewably sourced polymer polylactide is commercially produced, but its use is limited by its brittle nature. Consequently, reactive melt blends of end-functionalized polylactide and renewably sourced conjugated soybean oil were investigated. End-functionalized polylactide and conjugated soybean oil reacted in the melt to produce compatibilizers that reduced the droplet diameter, yielding blended materials with improved elongation to break over the parent polylactide homopolymer. Additionally, polyisoprene, a potentially sustainable polymer, was investigated as a macroinitiator for tough polylactide graft polymers. Two methods were investigated to synthesize the polyisoprene macroinitiator: post-polymerization functionalization and isoprene copolymerization with a hydroxyl functionalized monomer. To this end, Conjugated polyisoprene was synthesized by a ruthenium hydride catalyst post-polymerization and subsequently functionalized with a hydroxyl containing maleimide through a facile Diels-Alder reaction. The post-polymerization functionalized conjugated polyisoprene produced well defined polylactide graft copolymers. Furthermore, the hydroxyl containing monomer 2-methylenebut-3-en-1-ol was copolymerized with isoprene in both reversible addition-fragmentation transfer controlled radical and emulsion polymerization schemes. In spite of Diels-Alder side reactions, the copolymerizations produced macroinitiators for polylactide graft polymer synthesis. Polylactide graft polymers made from polyisoprene macroinitiators gave microphase separated, potentially tough materials.