Infrared characterization and determination of self-association equilibrium constants for methacrylic acid copolymers

The synthesis of essentially random methacrylic acid (MAA) copolymers is reported. Precursor copolymers of styrene (ST) or 2,3-dimethylbutadiene (DMB) and a tert-butyldimethylsilylmethacrylate comonomer were synthesized initially by free-radical solution polymerization, followed by silyl deprotection to yield the desired amorphous MAA copolymers. The infrared characterization of these copolymers is discussed with particular emphasis placed on the effect of temperature and composition on hydrogen bonding, the formation of anhydrides at elevated temperatures, and quantitative measurements, leading to an estimation of the dimensionless equilibrium constant describing the self-association of MAA moieties. Comparisons are made to low molecular weight analogues and previous studies on ethylene-co-methacrylic acid copolymers. An important experimental finding is that the number of hydrogen-bonded carboxylic acid dimers that are formed at equilibrium is a strong function of chain stiffness.