Anionic Polymerization of MMA and Renewable Methylene Butyrolactones by Resorbable Potassium Salts

Three resorbable potassium salts of hydride (K[H]), enolate Me2C=C(O'Pr)OK (K[E]), and allyl K[1,3-(SiMe3)(2)C3H3] (K[A]) have been investigated for controlled anionic polymerization of methyl methacrylate (MMA) and its cyclic analogs, naturally renewable methylene butyrolactones including alpha-methylene-gamma-butyrolactone (MBL) and gamma-methyl-alpha-methylene-gamma-butyrolactone (MMBL). When used alone at ambient temperature in toluene, these salts exhibit no (K[H]) to low (K[A]) to modest (K[E]) polymerization activity. Mixing of K[H] and Al(C6F5)(3) leads to the formation of an ate'' complex, K+[HAl(C6F5)(3)](-), which has been structurally characterized by X-ray diffraction; this complex has a high polymerization activity producing atactic PMMA, but addition of another equiv of Al(C6F5)(3) further enhances both the rate and the efficiency of the polymerization, now producing syndiotactic PMMA with a narrow molecular weight (MW) distribution of 1.04. The K[H]/2Al(C6F5)(3) system also exhibits high activity for polymerization of (M) MBL. In sharp contrast, addition of Al(C6F5)(3) to K[A] shuts down the polymerization at various temperatures. The most active, controlled, and syndioselective polymerization system in this series is K[E]/2Al(C6F5)(3). Accordingly, the polymerization control and kinetics of this most effective system have been examined in more detail. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2008-2017, 2011