Impact of Macromonomer Molar Mass and Feed Composition on Branch Distributions in Model Graft Copolymerizations.

Graft polymers are useful in a versatile range of material applications. Understanding how changes to the grafted architecture, such as the grafting density ( z ), the side-chain degree of polymerization ( N sc ), and the backbone degree of polymerization ( N bb ), affect polymer properties is critical for accurately tuning material performance. For graft-through copolymerizations, changes to N sc and z are controlled by the macromonomer degree of polymerization ( N MM ) and the initial fraction of the macromonomer in the feed ( f MM 0 ), respectively. We show that changes to these parameters can influence the copolymerization reactivity ratios and, in turn, impact the side-chain distribution along a graft polymer backbone. Poly((±)-lactide) macromonomers with N MM values as low as ca. 1 and as high as 72 were copolymerized with a small-molecule dimethyl ester norbornene comonomer over a range of f MM 0 values (0.1 ≤ f MM 0 ≤ 0.8) using ring-opening metathesis polymerization (ROMP). Monomer conversion was determined using 1 H nuclear magnetic resonance spectroscopy, and the data were fit with terminal and nonterminal copolymerization models. The results from this work provide essential information for manipulating N sc and z while maintaining synthetic control over the side-chain distribution for graft-through copolymerizations.