Methyl methacrylate solvent effects

Tsai, F.-J. Torkelson, J. M., "Microporous Poly(methyl methacrylate) Membranes Effect of a Low-Viscosity Solvent on the Formation Mechanism," Macromolecules, 23, 4983 (1990). 

Glusker, D. L. Galluccio, R. A. Evans, R. A. The mechanism of the anionic polymerization of methyl methacrylate, in. Effects of solvents upon stereoregularity and rates in fluorenyUithium-initiated polymerizations. 7. Am. Chem. Soc. 1964, 86, 187-196. 

The auto-acceleration effect appears most marked with polymers that are insoluble in their monomers. In these circumstances the radical end becomes entrapped in the polymer and termination reactions become very difficult. It has been suggested that, in thermodynamic terms, methyl methacrylate is a relatively poor solvent for poly(methyl methacrylate) because it causes radicals to coil while in solution. The termination reaction is then determined by the rate at which the radical ends come to the surface of the coil and hence become available for mutual termination. 

There are probably several factors which contribute to determining the endo exo ratio in any specific case. These include steric effects, dipole-dipole interactions, and London dispersion forces. MO interpretations emphasize secondary orbital interactions between the It orbitals on the dienophile substituent(s) and the developing 7t bond between C-2 and C-3 of the diene. There are quite a few exceptions to the Alder rule, and in most cases the preference for the endo isomer is relatively modest. For example, whereas cyclopentadiene reacts with methyl acrylate in decalin solution to give mainly the endo adduct (75%), the ratio is solvent-sensitive and ranges up to 90% endo in methanol. When a methyl substituent is added to the dienophile (methyl methacrylate), the exo product predominates. ... 

Monodispersed poly (methyl methacrylate-ethyleneglycol dimethacrylate) is prepared by a multistep swelling and polymerization method. When a good solvent such as toluene is applied as a porogen, the seed polymer severely affects the pore structure, whereas no effects are observed with poor solvents, such as cyclohexanol, as a porogen, in comparison with the conventional suspension polymerization (68,69). 

The results of chain transfer studies with different polymer radicals are compared in Table XIV. Chain transfer constants with hydrocarbon solvents are consistently a little greater for methyl methacrylate radicals than for styrene radicals. The methyl methacrylate chain radical is far less effective in the removal of chlorine from chlorinated solvents, however. Vinyl acetate chains are much more susceptible to chain transfer than are either of the other two polymer radicals. As will appear later, the propagation constants kp for styrene, methyl methacrylate, and vinyl acetate are in the approximate ratio 1 2 20. It follows from the transfer constants with toluene, that the rate constants ktr,s for the removal of benzylic hydrogen by the respective chain radicals are in the ratio 1 3.5 6000. Chain transfer studies offer a convenient means for comparing radical reactivities, provided the absolute propagation constants also are known. 

A superficially related dependence of on the medium has been observed by Norrish and Smith working with methyl methacrylate, and by Burnett and Melville with vinyl acetate. Rates in poor solvents are high, and determination of by the rotating sector method reveals what appears to be a decrease in kt in the poor solvents. This apparent decrease in kt accounts for the increased rate of polymerization. Actually, precipitation of the polymer seems to be responsible for the effect. The growing radicals become imbedded in precipitated droplets, presumably of very small size. The termination reaction is suppressed owing to isolation of the chain radical in one droplet from that in another. This gel effect is fairly common in systems yield-... 

Polymerizations conducted in nonaqueous media in which the polymer is insoluble also display the characteristics of emulsion polymerization. When either vinyl acetate or methyl methacrylate is polymerized in a poor solvent for the polymer, for example, the rate accelerates as the polymerization progresses. This acceleration, which has been called the gel effect,probably is associated with the precipitation of minute droplets of polymer highly swollen with monomer. These droplets may provide polymerization loci in which a single chain radical may be isolated from all others. A similar heterophase polymerization is observed even in the polymerization of the pure monomer in those cases in which the polymer is insoluble in its own monomer. Vinyl chloride, vinylidene chloride, acrylonitrile, and methacryloni-trile polymerize with precipitation of the polymer in a finely divided dispersion as rapidly as it is formed. The reaction rate increases as these polymer particles are generated. In the case of vinyl chloride ... 

Zhao B (2004) A combinatorial approach to study solvent-induced self-assembly of mixed poly (methyl methacrylate)/polystyrene brushes on planar silica substrates effect of relative grafting density. Langmuir 20 11748-11755... 

The sodium naphthalene polymerization of methyl methacrylate is carried out in benzene and tetrahydrofuran solutions. Which solution will yield the highest polymerization rate Discuss the effect of solvent on the relative concentrations of the different types of propagating centers. 

Copolymerizations of nonpolar monomers with polar monomers such as methyl methacrylate and acrylonitrile are especially comphcated. The effects of solvent and counterion may be unimportant compared to the side reactions characteristic of anionic polymerization of polar monomers (Sec. 5-3b-4). In addition, copolymerization is often hindered by the very low tendency of one of the cross-propagation reactions. For example, polystyryl anions easily add methyl methacrylate but there is little tendency for poly(methyl methacrylate) anions to add styrene. Many reports of styrene-methyl methacrylate (and similar comonomer pairs) copolymerizations are not copolymerizations in the sense discussed in this chapter. 

The stereoselective polymerization of various acrylates and methacrylates has been studied using initiators such as atkyllithium [Bywater, 1989 Pasquon et al., 1989 Quirk, 1995, 2002]. Table 8-12 illustrates the effects of counterion, solvent, and temperature on the stereochemistry of the anionic polymerization of methyl methacrylate (MMA). In polar solvents (pyridine and THF versus toluene), the counterion is removed from the vicinity of the propagating center and does not exert an influence on entry of the next monomer unit. The tendency is toward syndiotactic placement via chain end control. The extent of syndiotacticity... 

TABLE 8-12 Effect of Counterion, Solvent, and Temperature of Polymerization of Methyl Methacrylate... 

For (c), a macromonomer that has a pendant group accustomed to the solvent is used as a comonomer in the dispersion polymerization of a monomer that composes the particle. The surface of resulting particles is covered with the pendant group and consequently stabilized by a steric stabilization effect (14,15). In this sense the macromonomer is a kind of stabilizer that shows its effect through polymerization, and it could be called as a stabilizer formed in situ. A copolymer of macromonomer and particle-composing monomer, which joins the polymer particle, is much more effective for dispersion than a soluble stabilizer. With the dispersion polymerization of methyl methacrylate, which uses a macromonomer composed of an oligo-oxazoline pendant group, it is possible to cut the amount of stabilizer used to one-tenth or less compared to the oxazoline homopolymer stabilizer (16). 

Fig. 16a-

Fig. 30a-d. Polymerization of methyl methacrylate by high speed stirring of polyethylene oxide solution, a) effect of monomer concentration on polymerization rate (PEO 4 g/100 ml, stirring speed 30000 rpm. b) effect of monomer (MMA) concentration on intrinsic viscosity of reaction mixture (PEO 4 g/100 ml, stirring speed 30000 rpm, solvent benzene, c) effect of PEO concentration on polymerization rate, d) effect of PEO concentration on intrinsic viscosity of reaction mixture (Stirring speed 30000 rpm)... 

Dispersion polymerizations of methyl methacrylate ntUizing poly(l,l,-dihydroper-fluorooctyl acrylate) as a steric stabilizer in snpercritical CO2 were carried out in the presence of helium. Particle size and particle size distribution were found to be dependent on the amonnt of inert helium present. Particle sizes ranging from 1.64 to 2.66 pm were obtained with varions amounts of helium. Solvatochromic investigations using 9-(a-perflnoroheptyl-p,p-dicyanovinyl)julolidine indicated that the solvent strength of CO2 decreases with increasing helium concentration. This effect was confirmed by calcnlations of Hildebrand solubility parameters (Hsiao and DeSimone, 1997). 

Fig. 2. Polymerizations of tert-butyl methacrylate ( BMA) (A) and methyl methacrylate (MMA) (B) initiated with (TPP)AlMe (1, X=Me) [monomer]o/[l (X=Me)]o=100, [1 (X= Me)]o=17.8 (A) and 19.6 (B) mM, CH2CI2 as solvent, room temperature. Effect of trimethy-laluminum (Me3Al) ([Me3Al]o/[2]o=3.0) on the rate of polymerization...

---