Methyl methacrylate conversion dependence

Fig. 56. Dependence of specific refractive index increment on conversion of monomers to polymer for a styrene/acrylonitrile/methyl methacrylate terpolymer in methyl ethyl ketone at 20 °C and 436 nm. (a) - partial azeotrope, (b) terpolymer with composition distribution163 ...

Since Schultz (7) found that ultimate conversion depended considerably on temperature (in a highly polymerized methyl methacrylate system), similar effects would be expected in the postirradiation-heating of the PVC-styrene system. Such effects have indeed been found. Figure 4 shows the effect of heating temperature on the conversion level at two different radiation doses. No increased conversion is found for a temperature higher than 75 °C. This seems to indicate that a more or less definite melting point of the partially polymerized mixture exists. When this temperature is reached during the postirradiation treatment, the reaction runs to a point of termination and is unaffected by further temperature increases. 

Early studies of the free radical polymerization of methyl methacrylate did not show a solvent influence (18, 22, 23, 24) and consequently no solvent dependent influence of the conversion on the tacticity (23). A solvent dependence on stereocontrol in methyl methacrylate polymerization was however found by Watanabe and Sono (25) as early as 1962. Apparently, their paper has been overlooked. A literature search and a recalculation of most of the published data showed solvent influences on stereocontrol to be the rule and not the exception (6). Later experimental data on methyl methacrylate in about 50 solvents (7) and in 14 solvents (8) confirmed the earlier findings of Watanabe and Sono (25). 

Fig. 17. Dependencies of average composition of copolymer of styrene with methyl methacrylate on the weight conversion of reacted monomers p at the initial compositions x = 0.6 (7) and x = 0.35 (2). The curves are calculated experimental data, obtained by means of NMR and UV spectroscopy, are depicted by dark and P open circles, respectively [305]...

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. "... 

Acres and Dalton (1963a) also studied the emulsion polymerization of methyl methacrylate initiated by Co y radiation using a recording dilatometer. Only the conversion-time curves were measured with constant dose rate, varying monomer concentration, and with constant monomer concentration at different dose rates. Except at the lowest monomer concentration a clear gel effect was observed, with linear rates up to that point. The linenr rates increased with increasing monomer concentration up to about 0.4 mol/liter and then leveled oif. The dependence of the rate, before the gel effect, on the dose rate was 0.4 and, unlike their findings with styrene, not dependent on the monomer concentration. Their results were consistent with those of Hummel ei al. that methyl methacrylate follows, with y radiation, the generally accepted Smith-Ewart Case 2 kinetics except for the marked gd effect. 

These values for styrene at 50° C. are to be compared with those determined in solution or bulk, which are in the range (0.5 to 3) X 10 liters mole sec. . In methyl methacrylate polymerizations, k( is particularly strongly aflFected by conversion. The gel effect in bulk polymerization of this monomer has been determined by Robertson (53) and Benough and Melville (3). Robertson showed the decrease of kt to start at conversions as low as 5% in certain systems. In emulsion polymerization of methyl methacrylate, the low value of kf causes the gel effect to occur from very early in the reaction on, as demonstrated by Zimmt (71). The dependence of k on viscosity of the medium has been determined by Benson and North (9), who found that for methyl methacrylate, k( decreases by a factor of about 100 when the viscosity is increased from a very low value to about 200 centipoises. 

The free radical polymerization of styrene initialized by iniferter is influenced by chemical binding of iniferter on the surface of the silica." This reaction is used for grafting the polymer onto the surface of the silica. A similar approach is used when carbon whisker is incorporated during the graft-polymerization of methyl methacrylate. Depending on how the whisker is prepared, surface conversion can be increased up to twelve times compared to a polymerization with no whisker present. The addition of graphite to the poly esterification reaction doubles the molecular weight of the polymer. ... 

Deviations from ideal kinetics due to size-dependence and diffusion control of termination produce relatively weak effects at low conversions. However, at high conversions these effects are very significant in most radical polymerizations. Thus, instead of the reaction rate falling with time, as would be expected from Eq. (6.24) since the monomer and initiator concentrations decrease with conversion, an exact opposite behavior is observed in many polymerizations where the rate of polymerization increases with time. A typjgal example of this phenomenon is shown in Fig. 6.10 for the polymerization of methyl methacrylate in benzene solution at 50°C (Schulz and Haborth, 1948). An acceleration is observed at relatively high monomer concentrations and the curve for the pure monomer shows a drastic autoacceleration in the polymerization rate. This type of behavior observed under isothermal conditions is referred to as the gel effect. It is also known as the Tromsdorff effect or Norrish-Smith effect in honor of the early researchers in this field. ... 

Two-part reactive methyl methacrylate adhesives (MMAs) vary depending on formulation but typically have between 40-60% reactive VOC components, which results in greater than 99.5% conversion. Therefore, VOC emissions are typically less than 0.5%. These products are off-ratio tolerant compared to other systems and have no off-gassing issues. These products do have a distinct odor. 

Living polymerizations do not have either transfer or termination reactions, that is, the active chain carrier remains bound to an individual polymer chain up to the yield determined by the monomer-polymer equilibrium. The ionic ends of the living polymer can thus be used to produce block polymers of defined structure. This ability, however, depends on the polarity of the growing macroanion and the monomer to be added on. To a first approximation, the polarity can be described in terms of what is known as the e values of the two monomers. Electron-poor monomers have high e values and electron-rich monomers have strongly negative e values (see also Section 22.2.5). For example, the poly(methyl methacrylic anion) (monomer e = 0.40) starts the polymerization of acrylonitrile e = 1.20), but not that of styrene e = —O.SO). Conversely, however, the poly(styryl anion) can start the polymerization of methyl methacrylate. 

The stereocontrol of the free radical polymerization of a monomer at a given temperature is still weakly dependent on the solvent. In this case, however, there is a linear relationship between activation enthalpy differences and the corresponding activation entropy differences for each of the possible six differences of the total four possible elementary steps of a first-order Markov statistics (Figure 20-8). These relationships are each independent of the solvent used, and, so, also, of conversion. The straight lines are parallel to each other, that is, the compensation temperature is independent of the kind of diad formation occurring. The stereocontrol for methyl methacrylate at this temperature of about 60° C is therefore independent of the solvent used. 

---