The effect of nanoconfinement on methyl methacrylate polymerization: Tg, molecular weight, and tacticity

The effect of nanoconfinement on the free radical polymerization of methyl methacrylate (MMA) is investigated using differential scanning calorimetry, gel permeation chromatography, and 1H nuclear magnetic resonance. Both hydrophobic and hydrophilic 13 nm-diameter controlled pore glasses (CPG) are used for polymerization under nanoconfinement. The number-average and weight-average molecular weights increase under nanoconfinement because the onset of autoacceleration shifts to shorter times, whereas the polydispersity index at full conversion decreases relative to the bulk value. The tacticity changes from syndiotactic-rich triads for the bulk PMMA to a higher percentage of isotactic-rich triads in hydrophilic pores; the data are described by the first-order Markov model. In addition to the changes in molecular weight and tacticity, the glass transition temperature increases for both pore surfaces compared with the bulk, but the increase in hydrophilic pores is more pronounced.