The potentiometric titration, intrinsic viscosity, and 13 C NMR have been measured under various conditions to investigate the dissociation behavior of poly(2-methyleneglutaric acid) (PMGA), which has a charge density twice that of poly(acrylic acid) (PAA). The titration curves show that PMGA exhibits an apparent one-step dissociation similar to PAA, remarkably different from those of poly(maleic acid), poly(fumaric acid), and poly(itaconic acid), all having the same average charge density. The electrostatic interaction of PMGA does not level off at degrees of dissociation (R > 0.5), and the negative logarithm of the intrinsic dissociation constant (pK 0 ) of PMGA is 4.20 ( 0.05, similar to that of PAA. The intrinsic viscosity of a PMGA solution containing 0.05 N NaCl increases linearly with R. It has been shown from 13 C NMR measurements that the carboxyl groups on the side chain of PMGA dissociate preferentially in the region of R < 0.4. The electrostatic work required to remove H + from the rod surface calculated from a smeared charge model is in good agreement with the experimental data of PMGA, only for R e 0.5. The dissociation of carboxyl groups of PMGA in R > 0.5 is strongly depressed because of the decrease of the dielectric constant of water.

ABSTRACT:We examined preparation method of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMeA) with narrow molecular weight distributions (MWDs), over a wide range of molecular weight. The PAA and PMeA were prepared by anionic polymerization of I-butyl acrylate (TBA) and t-butyl methacrylate (TBMA) in the presence of LiCI [Teyssie et al., Macromolecules, 20, 1442 (I 987)], followed by two-step hydrolysis with Si(CH 3 )sl and HBr. The samples obtained were thoroughly characterized by means of size exclusion chromatography, 1 H NMR spectroscopy, vapor pressure osmometry, and light scattering for the PTBA and PTBMA, and poly(methyl acrylate) and poly(methyl methacrylate) prepared by the reaction of the PAA and PMeA with diazomethane, respectively. The characterization revealed that PAA and PMeA with narrow MWD can be prepared over the wide range of the molecular weight, 2 x 10 3 -8 x !0 5 . Potentiometric titration of the PAA and PMeA with different molecular weights was carried out in the aqueous solution at 25°C. It was found that the potentiometric titration curve of PMeA strongly depends on the molecular weight, while that of PAA does not. The dependence was observed only in the conformational transition region of the PMeA chain from compact to extended forms.KEY WORDS Poly(acrylic acid)/ Poly(methacrylic acid)/ Anionic Polymerization/ Narrow Molecular Weight Distribution / Dissociation Properties / Conformational Transition / Molecular Weight Dependence / Light Scattering / Polyelectrolyte is a macromolecule with many ionizable groups along a polymer backbone. The polyelectrolyte shows remarkably characteristic solution behavior different from non-ionic polymers and low molecular weight electrolytes but remains one of the least-understood condensed materials. Although bulk properties such as osmotic pressure and viscosity have been intensively studied for many years, understanding of the solution behavior of polyelectrolytes is lacking. This problem is especially critical because of the fundamental importance of many prototypical polyelectrolytes such as DNA. From an experimental point of view, challenge should be addressed to prepare well-defined polyelectrolytes to carry out several basic measurements.Poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMeA) are representative synthetic vinylic polyelectrolytes with weak acid functions at every second carbon atom in the main chain. The latter is well-known to show conformational transition from compact to extended form in a low degree of dissociation (oc). 1 -5 While there has been vast literature of the studies on their solution behavior, the samples which have been used so far are not necessarily well-defined from a viewpoint of molecular weight distribution (MWD). It was also pointed out that PAA samples with the MW higher than 106, prepared by radical polymerization, contain branching. 6 One noteworthy study in elucidation of the physical properties of the vinylic polyelectrolyte solution was carried out by Nagasawa and his co-workers in 1977. 7...