The bulk properties of a copolymer are directly affected by monomer sequence, yet efficient, scalable, and controllable syntheses of sequenced copolymers remain a defining challenge in polymer science. We have previously demonstrated, using polymers prepared by a step-growth synthesis, that hydrolytic degradation of poly(lactic-co-glycolic acid)s is dramatically affected by sequence. While much was learned, the step-growth mechanism gave no molecular weight control, unpredictable yields, and meager scalability. Herein, we describe the synthesis of closely-related sequenced polyesters prepared by entropy-driven ring-opening metathesis polymerization (ED-ROMP) of strainless macromonomers with imbedded monomer sequences of lactic, glycolic, 6hydroxy hexanoic, and syringic acids. The incorporation of ethylene glycol and metathesis linkers facilitated synthesis and provided the olefin functionality needed for ED-ROMP. Ring-closing to prepare the cyclic macromonomers was demonstrated using both ring-closing metathesis and macrolactonization reactions. Polymerization produced macromolecules with controlled molecular weights on a multigram scale. To further enhance molecular weight control, the macromonomers were prepared with cis-olefins in the metathesis-active segment. Under these selectivity-enhanced (SEED-ROMP) conditions, first-order kinetics and narrow dispersities were observed and the effect of catalyst initiation rate on the polymerization was investigated. Enhanced living character was further demonstrated through the preparation of block copolymers. Computational analysis suggested that the enhanced polymerization kinetics were due to the cis-macrocyclic olefin being *

The hydrolytic behavior and physical properties of a polymer are directly related to its constituent monomer sequence, yet the scalable and controllable synthesis of sequenced copolymers remains scarcely realized. To address this need, an enhanced version of entropy-driven ring-opening metathesis polymerization (ED-ROMP) has been developed. An unprecedented level of control is obtained by exploiting the kinetic and thermodynamic differences in the metathesis activity of cis- and trans-olefins embedded in large, unstrained macrocycles. First-order rate kinetics were observed, and polymer molecular weights were found to be proportional to catalyst loading. Computational analysis suggests that incorporation of a cis-olefin into the monomer backbone both introduces a thermodynamic driving force and increases the population of metathesis-active conformers. This approach offers a generally applicable method for enhancing living character in ED-ROMP.

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The extent to which small changes in monomer sequence affect the behaviors of biological macromolecules is studied regularly, yet the dependence of bulk properties on small sequence alterations is underexplored for synthetic copolymers. Investigations of this type are limited by the arduous syntheses required, lack of scalability, and scarcity of examples of polymer systems that are known to exhibit sensitive sequence/property dependencies. Our group has previously explored the hydrolysis behaviors of a library of sequenced poly(lactic-co-glycolic acid)s and found a strong correlation with the L−G sequence. To investigate the degree to which properties are dominated in this system by relatively short-range sequence changes, we have incorporated precisely sequenced and mildly "scrambled" L−G oligomers into cyclic macromonomers and subjected them to entropy-driven ring-opening metathesis polymerization, a method that we have recently shown produces polymers with molecular weight control and sequence preservation. The resulting polymers, which have identical composition and molecular weight, were hydrolyzed. Molecular weight decrease, mass loss, thermal behaviors, and film/surface characteristics were monitored to reveal stark differences in degradation behaviors despite the confinement of errors within a short segment. Article pubs.acs.org/Macromolecules

Linker segments in sequence controlled polyester backbones significantly affect thermal, mechanical and degradation properties.