Methyl methacrylate radical polymerization

There are some indications that the situation described above has been realized, at least partially, in the system styrene-methyl methacrylate polymerized by metallic lithium.29 29b It is known51 that in a 50-50 mixture of styrene and methyl methacrylate radical polymerization yields a product of approximately the same composition as the feed. On the other hand, a product containing only a few per cent of styrene is formed in a polymerization proceeding by an anionic mechanism. Since the polymer obtained in the 50-50 mixture of styrene and methyl methacrylate polymerized with metallic lithium had apparently an intermediate composition, it has been suggested that this is a block polymer obtained in a reaction discussed above. Further evidence favoring this mechanism is provided by the fact that under identical conditions only pure poly-methyl methacrylate is formed if the polymerization is initiated by butyl lithium and not by lithium dispersion. This proves that incorporation of styrene is due to a different initiation and not propagation. 

Canadian researchers published two papers on the modeling of methyl methacrylate radical polymerization, which is characterized by a pronounced gel effect. 

Ohtani, H., Tanaka, M., and Tsuge, S., Pyrol3 is-Gas Chromatographic Study of End Groups in Poly(methyl methacrylate) Radically Polymerized in Toluene Solution with Benzoyl Peroxide as Initiator, J. Anal Appl Pyrolysis, 15,167,1989. 

Bulk Polymerization. This is the method of choice for the manufacture of poly(methyl methacrylate) sheets, rods, and tubes, and molding and extmsion compounds. In methyl methacrylate bulk polymerization, an auto acceleration is observed beginning at 20—50% conversion. At this point, there is also a corresponding increase in the molecular weight of the polymer formed. This acceleration, which continues up to high conversion, is known as the Trommsdorff effect, and is attributed to the increase in viscosity of the mixture to such an extent that the diffusion rate, and therefore the termination reaction of the growing radicals, is reduced. This reduced termination rate ultimately results in a polymerization rate that is limited only by the diffusion rate of the monomer. Detailed kinetic data on the bulk polymerization of methyl methacrylate can be found in Reference 42. 

Polymerizations conducted in nonaqueous media in which the polymer is insoluble also display the characteristics of emulsion polymerization. When either vinyl acetate or methyl methacrylate is polymerized in a poor solvent for the polymer, for example, the rate accelerates as the polymerization progresses. This acceleration, which has been called the gel effect,probably is associated with the precipitation of minute droplets of polymer highly swollen with monomer. These droplets may provide polymerization loci in which a single chain radical may be isolated from all others. A similar heterophase polymerization is observed even in the polymerization of the pure monomer in those cases in which the polymer is insoluble in its own monomer. Vinyl chloride, vinylidene chloride, acrylonitrile, and methacryloni-trile polymerize with precipitation of the polymer in a finely divided dispersion as rapidly as it is formed. The reaction rate increases as these polymer particles are generated. In the case of vinyl chloride ... 

Since radical polymerizations are generally carried out at moderately high temperatures, most of the resulting polymers are highly atactic. This does not mean that there is a complete absence of syndiotacticity. There is a considerable difference in the extent of syndiotacticity from one polymer to another. Thus, methyl methacrylate has a much greater tendency toward syndiotactic placement than vinyl chloride. Whereas the poly(vinyl chloride) produced at the usual commerical polymerization temperature ( 60°C) is essential completely atactic, that is, (r) (m) 0.5, this is not the case for poly(methyl methacrylate). The polymerization of MMA, usually carried out at temperatures up to 100°C, yields polymers with appreciable syndiotacticity—(r) is 0.73 at 100°C. The difference is a consequence of the fact that MMA is a 1,1-disubstituted ethylene, leading to greater repulsions between substituents in adjacent monomer units. 

The ruthenium indenylidene Schiff base complexes XXVIIIa and XXVIIId, synthesized by Verpoort, were evaluated in atom-transfer radical polymerization of methyl methacrylate. The polymerization was initiated by ethyl 2-bromo-2-methyl-... 

In Sect. 1.3, photoinitiation by means of donor—acceptor complexes was described. In some cases, these complexes may play an important role even without the contribution of light energy. In the presence of aliphatic amines and CCI4, methyl methacrylate is polymerized at temperatures 300 K. In polar solvents (7V,7V-dimethy formamide, dimethylsulphoxide, chloroform), interaction of aliphatic amines as donors with methyl methacrylate as acceptor produces complexes [91] which yield initiating radicals with CC14 [92]... 

At first, methyl methacrylate (MMA) polymerization was used as a model reaction system. However, phenolic derivatives are well known as antioxidants and inhibitors for radical polymerization (lU), so such a reaction would not be expected to occur. However, by proper choice of vinyl compounds and initiators, it was found that such polymerization is possible, and that a variety of IPNs can be produced. 

Systems Where Radical Desorption is Negligible. Styrene and methyl methacrylate emulsion polymerization are examples of systems where radical desorption can be neglected. In Figures 4 and 5 are shown comparisons between experimental and theoretical conversion histories in methyl methacrylate and styrene polymerization. The solid curves represent the model, and it appears that there is excellent agreement between theory and experiment. The values of the rate constants used for the theoretical simulations are reported in previous publications (, 3). The dashed curves represent the corresponding theoretical curves in the calculation of which gel-effect has been neglected, that is, ktp is kept constant at a value for low viscosity solutions. It appears that neglecting gel-effect in the simulation of styrene... 

Another example of the macroinitiator approach to making block copolymers is shown in Scheme 8.4. Since methyl methacrylate (MMA) polymerization cannot effectively be initiated by TEMPO-based alkoxyamine initiators, a poly(methyl methacrylate) macroinitiator (XIII) was prepared using conventional free radical polymerization [16]. However, the azo initiator was functionalized with a TEMPO-based alkoxyamine. Since the main mechanism of termination during bulk MMA polymerization is by radical coupling, most of the MMA polymer chain-ends are functionalized with alkoxyamine groups. 

Thus the values shown in Table 1.8 are for standard conditions and represent just one of a series of ceiling temperatures for various monomer concentrations above which polymer formation is not favoured. Thus, in a bulk polymerization reaction the ceiling temperature may change with conversion in such a way that complete conversion is not achieved. For example, if methyl methacrylate is polymerized at 110°C the value of [M]c calculated from the above equation is 0.139M and this will be the monomer concentration in equilibrium with the polymer. The polymer, when removed from the monomer, will have the expected ceiling temperature as given in Table 1.8 and will depolymerize only if there is a source of free radicals to initiate the depolymerization (Section 1.4.1)... 

Similarly, the variation of kp with solvent in methacrylate polymerization can be explained on the assumption that the complexed radical is either inactive or less reactive. Since methyl methacrylate has no aromatic ring in itself, it seems to be possible to estimate the stability constants for the complex formation of the poly (methyl methacrylate) radical end with aromatic solvents. However, since the variation of kp in methyl methacrylate polymerization with solvent is too small, the determination of Ks with significant figures is impossible. Accordingly, it is difficult to estimate the unpurturbed kpo value for methyl methacrylate and thus difficult to estimate the stability constant of the complex in aromatic solvents. 

Phenoxyl radicals (Ph-0 ) are known not to iiutiate radical polymerization in most cases (2) and may be RTCP catalysts if they can activate Polymer-I. Based on this idea, we attempted to use phenol derivatives as catalysts, thus extending the element of the catalyst to O (Figure 1). Notably, the phenols include common antioxidants for foods and resins and natural compounds such as vitamins (Figure 1). Their commonness (hence cheapness) and environmental safety may be highly attractive for practical applications. In this paper, we will present the results of the styrene and methyl methacrylate (MMA) polymerizations, along with a mechanistic study. 

Thus, one should expect similar behavior for transition metal enolates where there is significant covalent character to the M-O (or M-G) bond. This section will focus on polymerization of (meth)acrylate esters by group 4 metallocene (or the related group 3 and lanthanocene ") initiators where the mechanism of this process is analogous to the classical GTP process. Of course, the polymerization of (meth)acrylates by other transition metal complexes has been reported frequently in the literature however, in many cases the mechanisms of these processes are less well understood or involve free radical or other forms of initiation. Recent examples of other transition metal-mediated methyl methacrylate (MMA) polymerization processes that may proceed via a GTP or anionic mechanism are given. " "- " ... 

If more than one monomer species is present in the reaction medium, a copolymer or an interpolymer can result from the polymerization reaction. Whether, however, the reaction products will consist of copolymers or just mixtures of homopolymers or of both depends largely upon the reactivity of the monomers. A useful and a simplifying assumption in kinetic analyses of free-radical copolymerizations is that the reactivity of polymer radicals is governed entirely by the terminal monomer units. " For instance, a growing polymer radical, containing a methyl methacrylate terminal unit, is considered, in terms of reactivity, as a poly(methyl methacrylate) radical. This assumption, not always adequate, can be used to predict satisfactorily the behavior of many mixtures of monomers. Based on this assumption, the copolymerization of a pair of monomers involves four distinct growth reactions and two types of polymer radicals. 

The ruthenium(II) complexes interact with CCI4 and are oxidized in the process to become Ru(III) and radicals CCl3 that add to molecules of methyl methacrylate. The polymerization proceeds via repetitive additions of methyl methacrylate molecules to the radical species that are repeatedly generated from the covalent species with carbon-halogen terminal groups [226]. Suwamoto also reported [226] that addition of a halogen donor, PhsC-Cl aids the shift of the equilibrium balance to dormant species. The reaction of polymerization can be illustrated as follows ... 

Bezuglyi and co-workers have published information on the reactivity of anion radicals and dianions of some a- substituted 9,10-anthraquinones generated electrochemically. The ions from the substituted anthraquinones will polymerize styrene whereas methyl methacrylate will polymerize only in the presence of ions from the unsubstituted anthraquinone. This idea has been used by Miertus et al. for the polymerization of acrylonitrile initiated by electrolytically prepared radical anions of benzephenone and 2,2 -bipyridyl. Funt and Hsu have extended this... 

Calculated Decay Constants for All Radicals (Atr), for Poly(Methyl methacrylate) Radicals (it ), for Change of A Radicals to S Radical (A i), Ratios of Rate Constants of A - S and S - A, and Reaction Order of Decay of A Radical in Various Polymeric Systems at 65°C... 

The creative technique of pyrene fluorescene intensity measurements was proposed to investigate the particle nucleation mechanisms involved in the OAV microemulsion polymerization [45], The experimental data show that microemulsion droplets are the major particle nucleation loci for the polymerization system with the more hydrophobic styrene as the monomer. This is followed by the flocculation of the latex particles with the remaining droplets. In contrast, the free radical polymerization taking place initially in the continuous aqueous phase (homogeneous nucleation) plays an important role in methyl methacrylate microemulsion polymerization. The computer simulation work of Mendizabal et al. [46] also led to the conclusion that the extent of homogeneous nucleation increases with increasing the solubility of monomer in water. 

DEPN-mediated methyl methacrylate (MMA) polymerization, obtaining low-polydispersity polymers. The polymer chain end on the DEPN side has a strong tendency to possess a styrene or AN terminal unit rather than an MMA terminal unit (the MMA terminal radical adds to styrene or AN monomer much faster than it combines with DEPN), suppressing the decomposition. 

Benzyl thionobenzoate (58) is believed to be ineffective as a transfer agent in MMA polymerization because of an unfavorable partition coefficient. Poly(methyl methacrylate) radical (PMMA ) is a much better radical leaving group than benzyl radical. Analogous benzyl thiocarbonylthio compounds (e.g., benzyl dithiobenzoate or dibenzyl trithiocarbonate) are also ineffective as RAFT agents in MMA polymerization. 

---