Solution polymerization of MMA

A new rate model for free radical homopolymerization which accounts for diffusion-controlled termination and propagation, and which gives a limiting conversion, has been developed based on ft ee-volume theory concepts. The model gives excellent agreement with measured rate data for bulk and solution polymerization of MMA over wide ranges of temperature and initiator and solvent concentrations. 

Figure 2. Isothermal polymerization of methyl methacrylate in a CSTR (1 5). a. Predicted steady-state monomer conversion vs. reactor residence time for the solution polymerization of MMA in ethyl acetate at 86 °C. h. Steady-state and dynamic experiments for the isothermal solution polymerization of MMA in ethyl acetate (solvent fraction O.k) ( ) steady states,...

Figure 7.3 shows the evolution of the oscillating reactor and jacket temperatures and the estimated product of UA obtained during the solution polymerization of MMA in ethyl acetate [11]. 

Wang et al. (2002) compared various in situ polymerization methods for the preparation of PMMA/clay nanocomposites. It was found that the particular preparative technique that is used has a large effect on the type of nanocomposites (in terms of nanoclay dispersion) that may be obtained. Solution polymerization of MMA only yields intercalated nanocomposites regardless of the presence of polymerizable double bond in the intergallery region. On the other hand, emulsion, suspension, and bulk polymerization can yield either exfoliated (with intergallery double bond) or intercalated (without double bond present) nanocomposites. 

Studies in the photoinitiation of polymerization by transition metal chelates probably stem from the original observations of Bamford and Ferrar [33]. These workers have shown that Mn(III) tris-(acety]acetonate) (Mn(a-cac)3) and Mn (III) tris-(l,l,l-trifluoroacetyl acetonate) (Mn(facac)3) can photosensitize the free radical polymerization of MMA and styrene (in bulk and in solution) when irradiated with light of A = 365 at 25°C and also abstract hydrogen atom from hydrocarbon solvents in the absence of monomer. The initiation of polymerization is not dependant on the nature of the monomer and the rate of photodecomposition of Mn(acac)3 exceeds the rate of initiation and the initiation species is the acac radical. The mechanism shown in Scheme (14) is proposed according to the kinetics and spectral observations ... 

Photoinitiation of polymerization of MMA and styrene by Mn(facac)3 was also investigated, and it was shown that the mechanism of photoinitiation is different [33] from that of Mn(acac)3 and is subject to the marked solvent effect, being less efficient in benzene than in ethyl acetate solutions. The mechanism shown in Schemes (15) and (16) illustrate the photodecomposition scheme of Mn(facac)3 in monomer-ethyl acetate and monomer-benzene solutions, respectively. (C = manganese chelate complex.)... 

The ion-pair complex formed by the interaction of hydroxobis(8-quinolyloxo) vanadium (V) [VOQ2OH] and /i-butyl amine is also effective in photoinitiation of polymerization of MMA in bulk and in solution [40]. The quantum yield of initiation and polymerization determined are equal to 0.166 and 35.0, respectively. Hydroxyl radical ( OH) is reported to be the initiating radical and the following photoreaction is suggested ... 

In this short initial communication we wish to describe a general purpose continuous-flow stirred-tank reactor (CSTR) system which incorporates a digital computer for supervisory control purposes and which has been constructed for use with radical and other polymerization processes. The performance of the system has been tested by attempting to control the MWD of the product from free-radically initiated solution polymerizations of methyl methacrylate (MMA) using oscillatory feed-forward control strategies for the reagent feeds. This reaction has been selected for study because of the ease of experimentation which it affords and because the theoretical aspects of the control of MWD in radical polymerizations has attracted much attention in the scientific literature. 

For purposes of simulation and illustration we have chosen a batch reactor, solution polymerization of methylmethacrylate (MMA). Kinetic data were taken from Schmidt and Ray (1981) and thermodynamic data from Bywater (1955). We do not here consider the influence of diffusion control on the termination or other rate processes because such effects may be small when in a solution which is siifHciently dilute or when the polymer is of low molecular weight. 

In 1962, Kimura, Takitani and Imoto (1) found that an aqueous solution of starch could easily polymerize methyl methacrylate (MMA) and about a half of polymerized MMA grafted on starch. This novel polymerization was called as "uncatalyzed polymerization". Since then, a lot of macromolecule was applied, instead of starch, and many of them were effective to initiate the radical polymerization of MMA. 

Our kinetic studies have concentrated on the polymerization of MMA in organic solution using solid potassium persulfate and a phase transfer catalyst. 

Four polymerization examples are presented here to illustrate both available sensitivity, experimental difficulties, and hopefully some interesting aspects of the polymerization processes. The first two examples are the semi-continuous emulsion polymerization of methyl methacrylate (MMA) and styrene, respectively. The third example is a batch charged copolymerization of butyl acrylate (BA) with MMA. The fourth example is a semi-continuous solution polymerization of an acrylic system. In this last example aliquots were taken manually and analyzed at 29.7°C under static conditions. No further polymerization occurred after the samples were cooled to this temperature. 

We have conducted a graft copolymerization of MM A onto FVA making use of potassium persulfate (KPS) in three different ways with water-swollen PVA film containing KPS and with PVA solutions containing KPS in H20 and DMSO. The polymerization of MMA proceeds heterogeneously in the two former cases and homogeneously in the latter case. 

Figure 6. Polymerization of MMA in benzene solution at 30° C. (A), Left-hand expression of Equation 12 (B), 1 /P , plotted against [S] / [Af]...

Figure 7. Polymerization of MMA at 50°C. in benzene, toluene, and xylene solution and at 60°C. in chloroform solution Top left-hand expression of Equation 12 plotted against [S]/[M]...

The thermodynamic excluded volume effect should be also reflected as a solvent effect on gelation. That is, a more delayed gelation is expected in a good solvent than in a poor solvent this was the case in the solution polymerization of DAP in various solvents [75,76]. In this connection, Walling [3] has reported the solvent effect on the gelation in the copolymerization of MMA with EDMA, but the result was contrary to our expectations. So, we will discuss this subject in more detail later. 

The photoreduction of aromatic ketones by tertiary amines is reported [38] to proceed at rates which are substantially faster than those observed for the corresponding photoinduced hydrogen abstraction from, e.g. alcohols. A limit case is given by fluorenone, the photoreduction of which does not occur in alcohol, ether or alkane solution, but readily takes place in the presence of amines, tertiary amines being the most effective [39,40]. Xanthone has also been reported to be easily photoreduced by iV,A-dimethylaniline [41], but not by 2-propanol [42]. However, the oxidation of tertiary amines photosensitized by fluorenone and xanthone is much less efficient than when sensitized by benzophenone, apparently because of lower rates of hydrogen abstraction [43]. Fluorenone/tertiary amine systems have been used successfully to photoinitiate the polymerization of MMA, St, MA and AN [30,38,44] and rather similar results have been obtained in the photoinitiated polymerization of MA by the benzophenone/EtsN system [45]. Thus, the great variety of substrates participating in exciplex formation has been readily extended to polymer-based systems. 

Copolymers of 2-vinyl fluorenone with MMA [poly(2VF-co-MMA)s], containing 2VF units in a wide range of compositions, have been used as photoinitiating systems in combination with Et3N, or indole-3-yl acetic acid (lAA), in the polymerization of MMA in benzene solution [30,38] and compared with fluorenone (FLO) and 2-methyl fluorenone (2MF). 

Free and polymer-bound 2-benzyloxy-thioxanthone exhibit similar flash photolysis behaviour and the same photoreduction quantum yield in the presence of 2-(A, AT-diethylamino) ethanol. This clearly shows that the polymeric nature does not appear to affect photophysical properties of the thioxanthone moiety. The photoinitiated polymerization of MMA in benzene solution, using BOTX and poly(StX-co-St) in combination with 2-(MA -dieffiylamino) ethanol, indicates that the polymer-bound chromophore seems to operate in the same way and with similar efficiency as the free photoinitiator, at least in conditions of dilute chromophore concentration. 

Copolymers of MBA with styrene [poly(MBA-co-St)] containing variable amounts of MBA co-units, have also been applied [107] to the UV initiated polymerization of MMA in benzene solution. 

TaWe 19. Effect of the composition of poly(MBA-co-St)s on the photoinitiated polymerization of MMA in benzene solution [107]... 

Indeed, photophysical studies by laser flash photolysis combined with the determination of MMA polymerization rate (Rp) in toluene solution, have allowed evaluation of the triplet state lifetime of the above systems, as well as their relative quantum yields of initiation ( j) and a-cleavage ( ). As reported in Table 22, 3, values for poly(MBA) and poly(MBVE) are appreciably lower than those for MBI and MBEE, respectively. On this basis, the polymeric photoinitiators would be expected to display lower activity than the models in the polymerization of acrylic monomers. On the contrary, poly(MBA) and poly(MBVE), together with the related copolymers, show higher values of Rp and hence i, in the UV initiated polymerization of MMA in toluene solution. These findings, therefore, confirm the previously obtained results in film matrix, where a HDDA/BA equimolar mixture was used as curing formulation (Table 21). 

TaUe 22. Rate of polymerization and relative quantum yields in the polymerization of MMA in toluene solution [110]... 

---