PREPARATION AND CHARACTERIZATION OF POLYELECTROLYTE COPOLYMERS CONTAINING METHYL-METHACRYLATE, AND 2-HYDROXYETHYL METHACRYLATE .2. POLYMERS BASED ON DIMETHYLAMINOETHYL METHACRYLATE

Co- and terpolymers containing dimethylaminoethyl methacrylate (DMAEMA), methyl methacrylate (MMA), and 2-hydroxyethyl methacrylate (HEMA) were prepared by solution polymerization, and characterized by dilute solution viscometry and proton and carbon-13 nuclear magnetic resonance spectroscopy. Polymers were prepared containing 75, 60, 40, 25, and 10 mol % DMAEMA but with differing levels of MMA and HEMA. Polymer solutions were titrated under nitrogen to obtain variations of pKb with alpha (the extent of protonation of the DMAEMA residue). From these experiments, we were able to show that, as expected, the cooperative nature of the ionization process decreased as the level of DMAEMA in the polymer was reduced from 75 mol % to 10 mol %. By comparing polymers containing similar amounts of DMAEMA monomer, we were also able to show that base strength increased with the polarity of the uncharged portion of the polymer, in other words, that polymers containing higher levels of HEMA were stronger bases than polymers containing higher levels of MMA. This effect was rationalized by assuming that higher contents of the more polar HEMA monomer facilitated the coil expansion that accompanied the process of ionization, thus increasing charge separations at corresponding values of alpha and increasing base strength.