Methacrylic acid polymerization constants

Pojman et al. found an unusual mode of propagation when there are large amounts of bubbles 45), In studying fronts of methacrylic acid polymerization, they observed convection that periodically occurred under the front at the same time as the front deformed and undulated. The period of convection was about 20 seconds and remained constant during the entire front propagation. 

Table 8.2 Rate constants " for template polymerization of methacrylic acid.

Figure 8.13. Template polymerization of methacrylic acid along with poly(N-vinylp5nrolidone). Termination rate constant as a function of [T o/[M]o.

The radical polymerization in aqueous solution of a series of monomers—e.g., vinyl esters, acrylic and methacrylic acids, amides, nitriles, and esters, dicarboxylic acids, and butadiene—have been studied in a flow system using ESR spectrometry. Monomer and polymer radicals have been identified from their ESR spectra. fi-Coupling constants of vinyl ester radicals are low (12-13 gauss) and independent of temperature, tentatively indicating that the /3-CH2 group is locked with respect to the a-carbon group. In copolymerization studies, the low reactivity of vinyl acetate has been confirmed, and increasing reactivity for maleic acid, acrylic acid, acrylonitrile, and fumaric acid in this order has been established by quantitative evaluation of the ESR spectra. This method offers a new approach to studies of free radical polymerization. 

To synthesize water-soluble or swellable copolymers, inverse heterophase polymerization processes are of special interest. The inverse macroemulsion polymerization is only reported for the copolymerization of two hydrophilic monomers. Hernandez-Barajas and Hunkeler [62] investigated the copolymerization of AAm with quaternary ammonium cationic monomers in the presence of block copoly-meric surfactants by batch and semi-batch inverse emulsion copolymerization. Glukhikh et al. [63] reported the copolymerization of AAm and methacrylic acid using an inverse emulsion system. Amphiphilic copolymers from inverse systems are also successfully obtained in microemulsion polymerization. For example, Vaskova et al. [64-66] copolymerized the hydrophilic AAm with more hydrophobic methyl methacrylate (MMA) or styrene in a water-in-oil microemulsion initiated by radical initiators with different solubilities in water. However, not only copolymer, but also homopolymer was formed. The total conversion of MMA was rather limited (<10%) and the composition of the copolymer was almost independent of the comonomer ratio. This was probably due to a constant molar ratio of the monomers in the water phase or at the interface as the possible locus of polymerization. Also, in the case of styrene copolymerizing with AAm, the molar fraction of AAm in homopolymer compared to copolymer is about 45-55 wt% [67], which is still too high for a meaningful technical application. 

To prepare water-soluble polymers employing CCT, it is necessary to modify the polymerization conditions.312 439 Use of a standard batch reaction leads to hydrolysis of catalyst, changing the catalyst level over the course of the polymerization, yielding a mixture of products and poor control of the reaction. A feed or starved-feed process that adds catalyst over the course of the reaction maintains a constant catalyst level and high conversion. The approach can be applied to a range of monomers such as methacrylic acid, 2-aminoethyl methacrylate hydrochloride, 2-hy-droxyethyl methacrylate, 2-methacryloxyethyl phos-phoryl choline, glycerol monomethyl methacrylate, and 3- O-methacryloyl-1,2 5,6-di- O-isopropylidene-D-glucofuranose. 

Takeuchi and co-workers (18) coupled combinatorial techniques with molecular imprinted polymers to develop sensors for triazine herbicides. The library consisted of a 7 x 7 array containing different fractions of monomers methacrylic acid (MAA) and 2-(trifluoromethyl)acrylic acid (TFMAA) with constant concentrations of the imprint molecules ametryn or atrazine. After UV-initiated polymerization, the products from the sensor library were characterized by HPLC measurement of herbicide concentration. The receptor efficiency was observed to vary with monomer type the atrazine receptor efficiency increased with MAA composition and the ametryn receptor was enhanced by increased fractions of TFMAA. Although only monomer concentration was varied in the hbraries, the authors conclude that the CM synthetic approach would be usefiil in analyzing other variables such as solvent, cross-linking agent, and polymerization conditions to produce optimum molecularly imprinted polymer sensors. 

Monomers which have been successfully polymerized using ATRP include styrenes, acrylates, methacrylates, and several other relatively reactive monomers such as acrylamides, vinylpyridine, and acrylonitrile, which contain groups (e.g., phenyl, carbonyl, nitrile) adjacent to the carbon radicals that stabilize the propagating chains and produce a suf cientiy large atom transfer equilibrium constant. The range of monomers polymerizable by ATRP is thus greater than that accessible by nitroxide-mediated polymerization, since it includes the entire family of methacrylates. However, acidic monomers (e.g., methacrylic acid) have not been successfully polymerized by ATRP and so also halogenated alkenes, alkyl-substimted ole ns, and vinyl esters because of then-very low intrinsic reactivity in radical polymerization and radical addition reactions (and hence, presumably, a very low ATRP equilibrium constant). 

In a study of the polymerization of methacrylic acid in a solvent system consisting of water, dioxane, and ethanol, it was shown that at constant dielectric strength, the rate of polymerization increases with the concentration of water. On the other hand, at a constant concentration of water, the rate of polymerization was not significantly changed as the dielectric constant of the reaction medium was varied [39]. The ionic strength of the medium also seems to have, at best, only a slight influence on the rate of polymerization [38]. 

The polymerization of itaconic acid seems not to have been studied very extensively, although industrial applications in copolymer systems appear to be of considerable interest. In view of the work of A. Katchalsky and coworkers [38] on the effect of pH on the polymerization of acrylic acid and methacrylic acid, analogous research on pH effects on itaconic acid reactions has been carried out to a limited extent [95, 96]. Typically, with a persulfate initiator in an aqueous solution at 50°C, the monomer is converted to an extent of 85-90% to its homopolymer within 35-45 hr. In the pH range of 2.3-3.8, the rate of polymerization is constant. As the pH increases, the rate becomes progressively slower and stops completely at a pH of 9. Generally, the last 5-10% of the monomer seems to be difficult to convert to polymer. 

Table 4 Rate constants of elementary processes for methacrylic acid template polymerization Temp. kp k,...

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