Methyl methacrylate polymerization rate

Data illustrating the relationship of the initial rate to the concentration of monomer at fixed initiator concentration are given in Table X for styrene in benzene and for methyl methacrylate polymerized at various concentrations in the same solvent. If the efficiency / of utilization of primary radicals is independent of the monomer concentration, the quantity given in the last column should be... 

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... 

Previous studies on paraffins, rhodamine dyes, and l,3-bis(N-carbozoyl) propane excimers have concluded that there is a relationship between km and polymer viscosity and free volume [103-105], Indeed, this dependence has been investigated in the context of decreasing free volume during methyl methacrylate polymerization [83,84], It has been shown that the nonradiative decay processes follow an exponential relationship with polymer free volume (vf), in which kra reduces as free volume is decreased [see Eq. (5)]. Here, k. represents the intrinsic rate of molecular nonradiative relaxation, v0 is the van der Waals volume of the probe molecule, and b is a constant that is particular to the probe species. Clearly, the experimentally observed changes in both emission intensity and lifetime for/ac-ClRe(CO)3(4,7-Ph2-phen) in the TMPTA/PMMA thin film are entirely consistent with this rationale. 

The rate of the thermally initiated methyl methacrylate polymerization amounts to only about 1 % of the rate measured with styrene. It can be increased by the presence of heavy metal atoms [16] which can change the multiplicity of the diradical and thus also its reactivity. 

Another example of the matrix effect can be demonstrated by methyl methacrylate polymerization. Orlova et al. [65] postulated association of the growing radical with a molecule of the poly(methylmethacrylate) matrix. Propagation continues along the matrix at a reduced rate [66], yielding a... 

Norrish and Smith [29] and later Tromsdorff et al. [30] described a polymerization of methyl methacrylate, the rate of which increased from a certain conversion. The number of monomers of similar behaviour was extended by methyl acrylate [31 ], butyl acrylate [32] and other acrylates [33] and methacrylates [34], and vinyl acetate. The effect was explained by the reduction of the termination rate caused by hindered macroradical mobil-ity in viscous medium it was called the gel effect, or the Norrish-Tromsdorff effect. The gel effect is clearly manifested in radical polymerizations of weakly transferring monomers in bulk. It is significant also in the presence of a good solvent. The gel effect is suppressed by the presence of poor solvents++ and by... 

Rate behavior of this kind is observed for many other olefinic monomers. As an example, Figure 10.4 shows the rate of methyl methacrylate polymerization also to be first order in monomer and about half order in initiator. However, the mechanism in Example 10.3 is by no means universal. In outline, others involve ... 

Polyethylene glycol in the synthesis of materials. PEG has been used as a solvent in polymerization reactions. It was found to facilitate easy removal of the metal catalyst in transition metal mediated living radical polymerization (Figure 8.10). Products from this type of polymerization are usually heavily contaminated with intensely coloured copper impurities. In the case of methyl methacrylate polymerization the reaction rate was higher than in conventional organic solvents, but for styrene the reaction was slower than in xylene. 

In the photopolymerization of methacrylamide by benzoin methyl ether, chain-transfer to monomer has been found to be important, and benzalde-hyde is reported to be an inefficient photoinitiator of methyl methacrylate polymerization unless benzophenone and triethylamine are present. Acetophenone has been found to sensitize the cycloaddition of maleic anhydride to 7-oxabicyclo[2.2.1]heptan-5-one-2,3-dicarboxylic anhydride, , a-hydroxy-acetophenone derivatives have been found to be non-yellowing initiators, and h.p.l.c. has been used to determine residual carbonyl photoinitiators in u.v.-cured resins. In the emulsion-polymerization of methyl methacrylate using an aromatic ketone and a continuous or intermittent laser, the former conditions were found to be similar to those under continuous u.v. irradiation. The dependence of the polymerization rate and average chain-length on the absorbance of the initiator used in the photoinitiated polymerization of vinyl monomers has been studied. Interestingly, irrespective of all conditions, maximum conversion is observed when initiator absorbance is 2.51. "... 

More satisfactory data have been obtained for methyl methacrylate polymerization using soluble allylic compounds such as Cr(7r-C3115)3 or Cr(7r-2Me—C3 H4 )3 [229]. With these catalysts the rate relationship in the early stages of reaction is... 

Table 3. Initiator polymerization rate, initiation rate, and derived k /k, values for methyl methacrylate polymerization in various solvents at 30 °C14)...

PMMA was first produced commercially in the UK and in Germany in the early 1930s. Monomer methyl methacrylate polymerizes readily under ambient conditions and is therefore supplied with an inhibitor (up to 0.1 per cent of hydro-quinone). After removal of the inhibitor, free radical pol) merization with peroxides or azodi-isobutyronitrile at 100°C is employed commercially. Oxygen slows the rate of polymerization and leads to the formation of peroxides so is excluded by allowing nitrogen into the reaction vessel. Shrinkage between monomer to polymer is high at around 20 per cent. 

The phase diagrams of the ternary systems allow one to make a direct comparison between emulsion and microemulsion polymerization processes just by varying the surfactant concentration, as shown by Gan and coworkers [84,91,127]. Figure 8 represents the polymerization rate conversion curves for methyl methacrylate polymerization at different surfactant concentrations. 

There were attempts at controlling steric placement by a technique called template polymerization. An example is methyl methacrylate polymerization in the presence of isotactic poly(methyl methacrylate). The presence of template polymers, however, only results in accelerating the rates of polymerizations. 

The propagation rates for methyl methacrylate polymerization in polar solvents like tetrahydrofuran or dimethylformamide are lower than the rates of initiation.There is no evidence. 

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 ... 

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] ... 

Figure 5.10 Adaptive dynamic optimization of a semibatch methyl methacrylate polymerization, Cycle 1 conversion (actual and predicted), initiator flow-rate policy and predicted average...

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. 

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