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

The synthesis of essentially random methacrylic acid (MAA) copolymers is re ported. Precursor copolymers of styrene (ST) or 2,3-dimethylbutadiene (DMB) and a tert-butyldimethylsilylmethacrylate comonomer were synthesized initi ally by free-radical solution polymerization, followed by silyl deprotectio n to yield the desired amorphous MAA copolymers. The infrared characterizat ion of these copolymers is discussed with particular emphasis placed on the effect of temperature and composition on hydrogen bonding, the formation o f anhydrides at elevated temperatures, and quantitative measurements, leadi ng to an estimation of the dimensionless equilibrium constant describing th e self-association of MAA moieties. Comparisons are made to low molecular w eight analogues and previous studies on ethylene-co-methacrylic acid copoly mers. An important experimental finding is that the number of hydrogen-bond ed carboxylic acid dimers that are formed at equilibrium is a strong functi on of chain stiffness.