Cyclodextrins in polymer synthesis: free radical polymerization of cyclodextrin host-guest complexes of methyl methacrylate or styrene from homogenous aqueous solution

Abstract

The polymerization of methylated β-cyclodextrin (m-β-CD) 1 : 1 host-guest compounds of methyl methacrylate (MMA) (1) or styrene (2) is described. The polymerization of complexes 1 a and 2 a was carried out in water with potassium peroxodisulfate (K2S2O8)/sodium hydrogensulfite (NaHSO3) as radical redox initiator at 60°C. Unthreading of m-β-CD during the polymerization led to water-insoluble poly(methyl methacrylate) (PMMA) (3) and polystyrene (4). By comparison, analogously prepared polymers from uncomplexed monomers 1 and 2 in ethanol as organic solvent with 2,2′-azoisobutyronitrile (AIBN) as radical initiator showed significantly lower molecular weights and were obtained in lower yields in all cases. Polymerization of m-β-CD complexed MMA in water, initiated with 2,2′-azobis(N,N ′-dimethyleneisobutyroamidine) dihydrochloride, occurred much faster than the polymerization of uncomplexed MMA in methanol under similar conditions. Furthermore, it was shown, that the precipitation polymerization of complexed MMA from homogeneous aqueous solution can be described by equations (Pn–1 ∝ lsqb;Irsqb;0.5) similar to those for classical polymerization in solution.