One-Pot Synthesis of Poly(vinyl alcohol) (PVA) Copolymers via Ruthenium Catalyzed Equilibrium Ring-Opening Metathesis Polymerization of Hydroxyl Functionalized Cyclopentene

Abstract

Well-defined poly(vinyl alcohol-alt-propenylene) (4) was synthesized in one-pot reaction via equilibrium ring-opening metathesis polymerization (ROMP) or acyclic diene metathesis (ADMET) of nonprotected 3-cyclopentene-1-ol (2) and 1,6-heptadiene-4-ol using (1,3-bis(2,4,6-trimethylphenyl)-2-midazolidinylidene)dichloro(phenylmet hylene)(tricyclohexylphosphine)ruthenium (6) and (1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)dichloro(o-isoprop oxyphenylmethylene)ruthenium (7) metathesis catalysts. The activation enthalpy and entropy of the equilibrium ROMP were determined as ΔH = -6.2 kcal mol^(-1) and ΔS = -18.9 cal mol^(-1) K^(-1). The observed thermodynamic parameters were supported by computational studies. The calculated ring strain energy for 2 (-6.8 kcal mol^(-1) is comparable with the observed activation enthalpy for its equilibrium ROMP reaction catalyzed by 6 or 7. The cis:trans olefinic bond ratio analysis indicated a 20:80 cis:trans selectivity. The hydrogenation of 4 resulted in poly(vinyl alcohol-alt-propylene) (11) in high yield. Because of the similar ring strain energies of cyclopentene (1) and 2, the equilibrium copolymerization results in a polymer having randomly distributed dyads. In general, it means that the polymer formed contains approximately 50% alternating polymer, 25% 3, and 25% 4 homopolymer dyads as expected for a random polymerization.