Model random polyampholytes from nonpolar methacrylic esters

Copolymerizations of nonpolar methacrylic esters followed by functional group conversions were employed to produce random polyampholytes. Random terpolymers of Solketal methacrylate (SMA):tert-butyl methacrylate (tBMA): N,N-dimethylaminoethyl methacrylate (DMAEMA) were prepared from 80:10:10 and 54:23:23 mol % mixtures of monomers by RAFT polymerization in 1,4-dioxane. The terpolymers were treated with iodomethane to convert the DMAEMA units to quaternary ammonium ions and then with concentrated aqueous HCl/1,4-dioxane to convert the SMA units to glyceryl methacrylate units and the tBMA units to methacrylic acid units. 1H NMR analyses of the unreacted monomers in reaction mixtures after partial polymerization and compositions of the terpolymers calculated from reactivity ratios support random structures for the terpolymers. ¹H NMR analyses of the polymers support complete conversions of the nonpolar monomer units in the terpolymers to ionic and hydrophilic monomer units in the polyampholytes. SEC analyses gave M_w/M_n = 1.3-1.4 for terpolymers having DP_n< 300 andM_w/M_n> 3 for terpolymers having higher DP_n SEC analyses of the derived polyampholytes gave M_w/M_n=2.2-3.2 for all samples. Isoelectric points of polyampholytes were determined by potentiometric titrations and measurements of aqueous solution viscosity as a function of pH.