Methacrylic acid polymerization solvent effects

It was reported that, in the contrast to acrylic acid, methacrylic acid does not exhibit any template effect under conditions described. However, template effect appears if a solvent such as water or methanol is added, and also at higher temperatures of polymerization. 

Solvents influence the rate of free-radical homopolymerization of acrylic acid and its copolymerization with other monomers. Hydrogen-bonding solvents slow down the reaction rates. Due to the electron-withdrawing nature of the ester groups, acrylic and methacrylic ester polymerize by anionic but not by cationic mechanisms. Lithium alkyls are very effective initiators of a-methyl methacrylate polymerization yielding stereospecific polymers.Isotactic poly(methyl methacrylate) forms in hydrocarbon solvents. Block copolymers of isotactic and syndiotactic poly(methyl methacrylate) form in solvents of medium polarity. Syndiotactic polymers form in polar solvents, like ethylene glycol dimethyl ether, or pyridine. This solvent influence is related to Lewis basicity in the following order ... 

Copolymerization. Acrylic and methacrylic acids readily copolymerize free radically with many vinyl monomers. This versatility results from a combination of their highly reactive double bonds and their miscibility with a wide variety of water- and solvent-soluble monomers. Reactivity ratios derived from copolymerizations with many monomers are tabulated in many books on polymerization, for example in Wiley s Polymer Handbook (14) (see also Wiley s Database of Polymer Properties). Q and e values are parameters that may be established for a monomer based on a large number of reactivity ratios with other monomers. These parameters are associated with interactions between the monomer and the growing chain via resonance (Q) and polar effects (e). 

Polymerization Processes. A variety of processes are used commercially to homopolymerize and copolymerize acrylic acid and methacrylic acid. On the basis of economics and environmental considerations, water is generally the preferred industrial solvent or polymerization medium. However, the choice of process is usually dictated by the requirements of the polymer to be produced. As already indicated, pH influences the rate of polymerization. Comonomers and molecular weight of the polymer to be produced also have a profound effect on the tsqje of polymerization process that can be used and on the type of product obtained. The contents of Table 2 indicate the change from water-soluble to alkab-soluble emulsions and ultimately emulsion polsrmers is dependent on the comonomers in copolymers of acryUc and methacryUc acids. This transition from water-soluble polymer to emulsion polymer as the acidic monomer is decreased depends on the hydrophobicity of the comonomer. Introduction of divinyl monomers causes transition to gel materials in all compositions. The gels may vary from highly swollen to tightly bound copolymers, depending on the cross-linker level. 

Effect of the Reaction Medium. Since the transition state in propagation is relatively nonpolar and the propagation reaction is chemically controlled (up to high monomer conversions of 80%), there is weak solvent influence on the propagation rate coefficients. Extensive studies have been carried out, which mainly confirm this small influence of the solvent on the propagation rate coefficient (141-143). Larger effects in solvents have only been observed for specific monomers, eg, EHMA (144), vinyl acetate (145), vinyl benzoate (146), or specific solvents like supercritical CO2 (147-151). Furthermore, the values for the polymerizations of methacrylic acid and acrylic acid in water are significantly affected by the monomer concentrations (152-154). In the case of the solvent effects on EHMA, where hr, falls between 580 L mol s... 

In many cases, azobis(isobutyronitrile) (AIBN) is employed as radical initiator. The polymerization conditions, in particular solvent, depend mainly on both, solubility of the starting sf monomers and choice of comonomer. To give just a few examples, copolymers of dodecafluoroheptyl methacrylate with methacrylic acid could be synthesized in dioxane due to the solubilizing effect of methacrylic acid [66], copolymers of sfMA-H2F8 and sfMA-H2F4 with styrene could be prepared in toluene [35], and copolymerizations of i/methacrylates with butyl acrylate, hydroxy-butyl acrylate, and styrene were performed using tert-butyl peroxyacetate as initiator in methyl amyl ketone [31]. 

In the liquid state, solvents have a significant effect on the stereoregularity of poly (methacrylic acid) prepared with y-radiation [76]. In a given solvent (methanol, 1-propanol, and isopropanol were the only solvents considered in this work) the percentage of syndiotactic polymer increases with decreasing polymerization temperature. At a fixed temperature, syndiotacticity increases as the bulkiness of the solvent increases. In I-propanol, at a given temperature, the fraction of syndiotactic triads increases as the monomer concentration decreases. Polymers with as high as 95% syndiotactic character have been prepared [76]. 

In contrast to these relatively weak influences of many solvents, water has a pronounced impact on aqueous radical polymerization. It is frequently found that the polymerization rates of water-soluble monomers in aqueous solutions are higher than in organic solvents." PLP-SEC studies into different systems (methacrylic acid (MAA)" acrylic acid (AA)," A-isopropyl acrylamide," acrylamide, and A-vinyl pyrrolidone revealed a huge solvent effect on kp. Figure 1.2 demonstrates this effect on the example of A-vinyl pyrrolidone. 

Fig. 22. Polymerization of methacrylonitrile (MAN) with the living prepolymer of methy] methacrylate (MMA) (2)-methylaluminum bis(2,6-di-tert-butyl-4-methylphenolate) (3e) system [MAN]o/[2]o=50, [2]o=22.6 mM, CH2CI2 as solvent, rt, initial ratios of 3e to 2=3.0 ( ), 4.0 (A), and 10 ( ). Effect of the amount of Lewis acid 3e on the rate of polymerization...

Fig. 6.25. Effect of the percentage of 1-propanol in the porogenic mixture on the porous properties of monolithic polymers (Reprinted with permission from [64], Copyright 1998 American Chemical Society). Reaction conditions polymerization mixture ethylene dimethacrylate 16.00 wt.%, butyl methacrylate 23.88 wt.%, 2-acrylamido-2-methyl-l-propanesulfonic acid 0.12 wt.%, ternary porogen solvent 60.00 wt.% (consisting of 10 wt.% water and 90 wt.% of mixtures of 1-propanol and 1,4-butanediol), azobisisobutyronitrile 1 wt.% (with respect to monomers), polymerization time 20 h at 60°C.

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