Methyl methacrylate polymerization temperature

Fig. 3. Conversion curves of methyl methacrylate polymerization. Temperature 323 K., initiator AIBN at concentrations (mass %) of , 0.3 O, 0.4 Q, 0.5. Original results [35, 41] redrawn according to ref. 4.

Schultz (7) has studied the methyl methacrylate polymerization, which is interesting to compare with effects noted in the poly (vinyl chloride)-styrene graft polymerization. When his polymerizations were carried out well below the glassy transition temperature, the conversions reached limiting values. Monomer present in the system functioned as a plasticizing agent, allowing polymerization to occur up to the point... 

Terpolymers made from two different olefins and CO are known. They were first described in Brubaker s initial patent and involved the free radical initiated terpolymerization of CO and C2H with another olefin such as propylene, isobutylene, butadiene, vinyl acetate, diethyl maleate or tetrafluoroethylene More recently, in another patent, Hammer has described the free radical initiated terpolymerization of CO and C2H with vinyl esters, vinyl ethers or methyl methacrylate 26Reaction temperatures of 180-200 °C and a combined pressure of 186 MPa were employed. Typically a CO QH4 olefin molar ratio of 10 65 25 was observed in the terpolymers. In other patents, Hammer 27,28) has described the formation of copolymers with pendant epoxy groups by the free radical initiated polymerization of CO, QH4, vinyl acetate and glycidyl methacrylate. Reaction conditions similar to those stated above were employed, and a typical CO C2H vinyl acetate glycidyl methacrylate molar ratio of 10 65 20 5 was observed in the product polymer. 

The most favorable conditions for reactive processing of monolithic articles are created when the frontal reaction occurs at a plane thermal front. For example, a frontal process can be used for methyl methacrylate polymerization at high pressure (up to 500 MPa) in the presence of free-radical initiators. The reaction is initiated by an initial or continuous local increase in temperature of the reactive mass in a stationary mold, or in a reactor if the monomer is moving through a reactor. The main method of controlling the reaction rate and maintaining stability is by varying the temperature of the reactive mass.252... 

The key problems in a polymerization CSTR are the determination and characterization of micro- and macromixing, and the possibility of multiple steady states due to the exothermic nature of the reactions. Recent studies of CSTRs for bulk or solution free-radical polymerization indicate the possibility of multiple steady states due to the large heat evolution and difficult heat transfer that are characteristic of the reactors. Furthermore, even in simple solution polymerization (for example, in methyl methacrylate polymerization in ethyl acetate solvent), autocatalytic kinetics can lead to runaway conditions even with perfect temperature control for certain combinations of solvent concentration and reactor residence time. In practice, the heat evolution can be an additional source of autocatalytic behavior. 

Fig. 3.2. Methyl methacrylate polymerization initiated by hydrogen peroxide in methanol at room temperature. Sketch of the phase state in the beginning of the reaction as a function of the monomer concentration at constant hydrogen peroxide concentration 109)...

Polystyrene and poly(methyl methacrylate) polymerizations are typical of homogeneous bulk chain-growth reactions. The molecular weight distributions of the products made in these reactions are broader than predicted from consideration of classical, homogeneous phase free-radical polymerization kinetics because of autoacceleration (Section 6.13.2) and temperature rises at higher conversions. 

Better results were obtained in the methyl methacrylate polymerization reactions (Scheme 12). 153-156 showed high catalytic activity with a strong dependence on the ionic radius of the center metal. The lanthanum complex 154 was the most active catalyst and initiated the polymerization without any cocatalyst. Addition of small amounts of AlEts as cocatalyst increased the yield significantly. Polymerization initiated by 154 depended on the temperature and a low temperature (—78°C) was required to afford almost quantitative yields. The resulting polymers were basically syndiotactic and exhibited high molar masses and narrow polydispersities. The catalytic reaction with the lanthanum compound 157 showed no increase of catalytic activity but led to a larger fraction of atactic poly(methyl methacrylate). Moreover, the catalytic activity of all utilized initiators was solvent dependent. 153, 155, and 156 only showed catalytic activity by the addition of a cocatalyst. 153 afforded lower yield after changing the solvent from toluene into THF. 

The propagation rates for methyl methacrylate polymerization in polar solvents like tetrahydrofu-ran or dimethylformamide are lower than the rates of initiation [203]. There is no evidence, however, that more than one kind of ion pairs exist [204-206]. The ion pairs that form are apparently craitact-ion pairs [203]. Furthermore, based on the evidence, the counterions are more coordinated with the enolate oxygen atoms of the carbonyl groups than with the a-carbons. As a result, they exert less influence on the reactivity of the carbanions [203]. The amount of solvation by the solvents affects the reaction rates. In addition, intramolecular solvation from neighboring ester groups on the polymer chains also affects the rates. In solvents like dimethylformamide, tetrahydrofuran, or similar ones [203], the propagating chain ends-ion pairs are picmred as hybrid intermediates between two extreme structures. This depends upon the counterion, the solvent, and the temperature [203] ... 

The free-radical polymerization of vinyl chloride, like methyl methacrylate, is temperature-dependent, with the degree of syn-diotacticity and crystallinity increasing with decreasing temperature (Fordham et al. 1959). A tentative value for the activation energy difference between isotactic and syndiotactic propagations was calculated as 0.6 kcal/mole. As indicated before, the theoretical calculations gave 1.4-1.9 kcal/mole for the difference. In view of the approximate nature of these two sets of calculations, the results are in reasonable agreement. 

Summaiy In this short review, selected experimental approaches for probing the mechanism and kinetics of RAFT polymerization are highlighted. Methods for studying RAFT polymerization via varying reaction conditions, such as pressure, temperature, and solution properties, are reviewed. A technique for the measurement of the RAFT specific addition and fragmentation reaction rates via combination of pulsed-laser-initiated RAFT polymerization and j,s-time-resolved electron spin resonance (ESR) spectroscopy is detailed. Mechanistic investigations using mass spectrometry are exemplified on dithiobenzoic-acid-mediated methyl methacrylate polymerization. 

Fig. 4. Temperature dependence of the contribution of disproportionation to the overall termination process, S, for a methyl methacrylate polymerization at ambient pressure (selected references Refs. 305-308).

It is commonly assumed that, in suspension polymerization, heat transfer between polymerizing drops and the continuous phase is rapid and both phases have the same temperature. However, Lazrak and Ricard [115] showed that, with methyl methacrylate polymerization, the internal temperature of drops could be... 

In the free radical polymerization proeess, conducted usually at elevated temperatures, these effects are insignificant and the reaction usually leads to the formation of atactic polymer only. However, in some cases, like, for example, in free radical polymerization of methyl methacrylate at temperature below 0°C one obtains a crystalline polymer with syndiotactic structure, as it was proven by the high resolution nuclear magnetic resonance spectroscopy. These results confirm the rule that according to which the degree of stereoregularity decreases with increasing temperature. 

Fox and Schneckof carried out the free-radical polymerization of methyl methacrylate between -40 and 250 C. By analysis of the a-methyl peaks in the NMR spectra of the products, they determined the following values of a, the probability of an isotactic placement in the products prepared at the different temperatures ... 

The reaction of ACPC with linear aliphatic amines has been investigated in a number of Ueda s papers [17,35,36]. Thus, ACPC was used for a interfacia] polycondensation with hexamethylene diamine at room temperature [17] yielding poly(amide)s. The polymeric material formed carried one azo group per repeating unit and exhibited a high thermal reactivity. By addition of styrene and methyl methacrylate to the MAI and heating, the respective block copolymers were formed. 

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