Sequence-Controlled Copolymers Prepared via Entropy-Driven Ring-Opening Metathesis Polymerization.

A new general synthetic approach to sequenced macromolecules was developed and applied to the synthesis of polymers comprising lactic acid (), glycolic acid (), and ε-caprolactone ()-derived monomer units. The new method employs entropy-driven ring-opening metathesis polymerization (ED-ROMP) to prepare copolymers with embedded sequences and controlled molecular weights. Cyclic macromonomer precursors were prepared by ring-closing metathesis of ethylene glycol ()-linked sequenced oligomers bearing terminal olefins. ED-ROMP of the resulting macrocycles using Grubbs' second generation catalyst yielded , , , and ( = octenedioc acid; = hexenedioc acid). Hydrogenation produced the saturated sequenced copolymers. Molecular weight was well-controlled and could be adjusted by varying the monomer-to-catalyst ratio. s of 26-60 kDa were obtained (dispersities = 1.1-1.3). The methodology proved general for three different sequences and two olefinic metathesis groups.