Methacrylate systems

Very similar variations in average copolymer composition with conversion have recently been observed in the styrene methyl methacrylate system by both Johnson et al ( and by Dionisio and O Driscoll (. The reason for the variation may be due to a viscosity effect on propagation rate constants QO). 

Werner (1980) has studied devolatilization in corotating twin-screw extruders when the volatile component was stripped from the polymeric solution by applying a vacuum to the system. Rough estimates of the equilibrium partial pressure of the volatile component in the feedstream for each of the systems studied by Werner indicate that this pressure was less than the applied pressure, which means that bubbles could have been formed. Figure 17 shows the influence of the externally applied pressure on the exit concentration for a methyl methacrylate-poly(methyl methacrylate) system of fixed concentration. Note that the exit concentration decreases as the pressure is decreased, but seems to approach an asymptotic value at the lowest pressures studied. Werner also reported that at a fixed flow rate and feed concentration the exit concentration did not vary with screw speed (over the range 150-300 min" ), which also suggests that ky alay, is independent of screw speed. Figure 18 is a plot of data obtained by Werner on an ethylene-low-density poly(ethylene) system and also shows that decreases in the applied pressure result in decreases in the exit concentration, but here a lower asymptote is not observed. 

The behavior of the system is somewhat similar to that of methyl methacrylate (Figure 11). Hence, it may be possible to describe both systems in terms of a pronounced gel effect at conversions higher than 25 to 30%, as generally accepted for the methyl methacrylate system. 

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. 

Our results of investigations in the MMA-BA system should be of general relevance at least to the acrylate-methacrylate system. 

Figure 2. Variation of the total monomer conversion with reaction time for the LS-(methyl methacrylate) system at 50°C in different media V, water X, water-dioxane 1 1 O, dioxane A, water—methanol 1 1 and , methanol.

D. Price, L.K. Cunliffe, K.J. Bullett (formerly Pyrah), T.R. Huh, G.J. Milnes, J.R. Ebdon, B.J. Hunl, and P. Joseph, Thermal behavior of covalently bonded phosphonate flame retarded poly(methyl methacrylate) systems. Polym. Adv. Technol., 19 (6), 710-723 (2008) and previous references therein. 

Fracture Surface Morphology and Phase Relationships of Polystyrene/Poly(methyl Methacrylate) Systems... 

Fig. 3. a) Polymerization quantum yield of the thioxanthone — diphenyliodonium-chloride — methyl methacrylate system vs. diphenyliodoniumchloride concentration (X = 365 nm, I bs = 5xl0 7 ein-stein 1"1 s in acetonitrile/water 90 vol%, [MMA] = 1 moll-1) b) Plot corresponding to Eq. (12b)... 

METHACRYLIC SYSTEM. Methyl methacrylate purchased from Merck and 1,1,1-trimethylol propane trimethacrylate (TRIM) supplied by Degussa, used as crosslinker, were dried over molecular sieves but not otherwise purified, so that they still contained 15 ppm and 100 ppm methylethylhydroquinone, respectively. The initiator of radical polymerization was azobisisobutyronitrile (AIBN). 

By setting the temperature of the reaction medium at 60 C from the beginning of the IPN formation, the PUR synthesis is accelerated, and that of the methacrylic system begins after the usual inhibition period. The competition between the two processes can still favour the complete formation of PUR before appreciable radical copolymerisation may have taken place, though the kinetic curves may change or even cross. For this reason, a second factor, the content of PUR catalyst, is varied too with less stannous octoate, the formation of the first network is more or less delayed, even at 60 C, and counterbalances to some extent the effect of temperature. In such a case, the conversion of the methacrylic phase may proceed further before higher or even post-gel conversions are reached for polyurethane. Thus, IPNs in which both networks have been formed more or less simultaneously, are obtained by this... 

Figure 5. Small-angle X-ray scattering data fix>m a polymerized cubic phase in the DDAB / water / methyl methacrylate system. The abscissa is s=2 sin 0 / X, in A l, where 6 is half the scattering angle and X (=1.54A) is the wavlength of the radiation used. The vertical lines give the theoretical peak positions for an Im3m lattice with a lattice parameter of 1ISA. The maximum at s =...

Figure 6a. A transmission electron micrograph of a polymerized cubic phase in the DDAB/water/methyl methacrylate) system. The dark regions correspond to PMMA and the light regions to void. Magnification is l.OOO.OOOx.

By far the most used systems are matrices based on methacrylate, methacrylamide and styrene and the most common crosslinkers are ethyleneglycol dimethacrylate and divinylbenzene. Methacrylamide based species are the most hydrophilic and styrene ones the most hydrophobic, with the methacrylate systems falling in between. This therefore provides quite a wide choice and imprinted polymers with high mechanical stability and chemical inertness, suitable for example in HPLC applications, are readily achievable. To some extent the chemical nature of the matrix is of less importance than its morphology, and in this respect the type and level of crosslinker used, together with the nature and proportion of the porogen are more crucial (see later). All of these experimental parameters are of course inter-dependent. 

The first extensive review on organomagnesium compounds and their complexes as polymerization initiators was published in 1968 [8], Most of the work in the 1980s was directed toward the development of living systems, based on organomagnesium initiators methyl methacrylate systems. These efforts were rewarded with only limited success. 

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