Methylmethacrylate, anionic polymerization

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

The anionic polymerization of methylmethacrylate at room temperature (originally called group transfer polymerization) [75-77] has provided a means for preparing star poly(methylmethacrylate) via the block polymerization with ethyleneglycoldimethacrylate ... 

The anionic graft polymerization of vinyl monomers onto carbon fiber or graphite powder initiated by metalized carbon fiber has been investigated. The metalation of polycondensed aromatic rings of a carbon fiber surface was achieved by treatment of the carbon fiber with BuLi in Ar,Ar,Ar, AT -tetramethylethylenediamine. The anionic polymerization of methylmethacrylate and styrene was reported. No grafting was observed when carbon fiber was treated simply with BuLi in THF or toluene [44,45]. 

Considerable information is available on the stereoregular anionic polymerization of methacrylates from the detailed studies by Goode, Owens, Fellmann, Snyder and Moore (76). These workers have found that the polymerization of methylmethacrylate produced either isotactic, syndiotactic or stereo block polymers. 

The formation of syndiotactic polymethylmethacrylate is the result of the prefered chain configuration in the free anionic polymerization, similar to the formation of syndiotactic structure by the free radical polymerization of methylmethacrylate. Bawn, James and North (77)... 

Acrylic Macromers. Thus far we have shown applications of SFC to the characterizations of monomers and crosslinkers. The next couple applications will focus upon the analysis of oligomeric methacrylates, specifically methacrylate macromers. Methacrylate macromers are frequently used as building blocks for larger architecturally designed polymers. Unfortunately, macromers far exceed the capability of GC and do not possess a chromophore for HPLC analysis. Hatada et. al. has used packed column SFC to analyzed the stereoisomers of oligomeric methylmethacrylate (MMA) prepared by anionic polymerization (13). 

Equation (26) is the ideal copolymer composition equation suggested [203] early in the development of copolymerization theory but which had to be abandoned in favour of eqn. (23) as a general description of radical copolymerization. Only in this particular case are the rates of incorporation of each monomer proportional to their homopolymerization rates. It was shown that the reactivity of a series of monomers in stannic chloride initiated copolymerization followed the same order as their homopolymerization rates [202] and so eqn. (26) could be at least qualitatively correct for carbonium-ion polymerizations and possibly for reactions carried by carbanions. This, in fact, does not seem to be correct for anionic polymerizations since the reactivities of the ion-paired species at least, differ greatly. The methylmethacrylate ion-pair will, for instance, not add to styrene monomer, whereas the polystyryl ion-pair adds rapidly to methylmethacrylate [204]. This is a general phenomenon no reaction will occur if the ion-pair is on a monomer unit which has an appreciably higher electron affinity than that of the reacting monomer. The additions are thus extremely selective, more so than in radical copolymerization. There is no evidence that eqn. (26) holds and the approximate agreement with eqn. (25) results from other causes indicated below. 

In Figure 10.29 another spectrum is reported, namely the MALDl-TOF spectrum of a copolymer containing units of a-methylstyrene (A) and units of methylmethacrylate (B). The sample is a reference material denoted SRM1487, and it was obtained by anionic polymerization using a bifunctional initiator, namely the dimer of a-methylstyrene (sodiirai salt). The most intense peaks are between... 

Electron withdrawing substituents in anionic polymerizations enhance electron density at the double bonds or stabilize the carbanions by resonance. Anionic copolymerizations in many respects behave similarly to the cationic ones. For some comonomer pairs steric effects give rise to a tendency to alternate [378]. The reactivities of the monomers in copolymerizations and the compositions of the resultant copolymers are subject to solvent polarity and to the effects of the counterions. The two, just like in cationic polymerizations, cannot be considered independently from each other. This, again, is due to the tightness of the ion pairs and to the amount of solvation. Furthermore, only monomers that possess similar polarity can be copolymerized by anionic mechanism. Thus, for instance, styrene derivatives copolymerize with each other. Styrene, however, is unable to add to a methyl methacrylate anion [379-381], though it copolymerizes with butadiene and isoprene. In copolymerizations initiated by n-butyllithium in toluene and in tetrahydrofuran at —78°C, the following order of reactivity with methyl methacrylate anions was observed [382]. In toluene the order is diphenylmethyl methacrylate > benzyl methacrylate > methyl methacrylate > ethyl methacrylate > a-methylbenzyl methacrylate > isopropyl methacrylate > t-butyl methacrylate > trityl methacrylate > a,a -di-methylbenzyl methacrylate. In tetrahydrofuran the order changes to trityl methacrylate > benzyl methacrylate > methylmethacrylate > diphenylmethyl methacrylate > ethyl methacrylate > a-methylbenzyl methacrylate > isopropyl methacrylate > a,a -dimethylbenzyl methacrylate > t-butyl methacrylate. 

This anionic polymerization is evidently of a living type as the unterminated polymer can be co-polymerized with either other masked disilenes bearing different functional groups or methylmethacrylate (MMA) to yield a block co-polymer [35]. Furthermore, it was found that the relationship between molecular weight and the degree of monomer conversion is linear, which is a necessary condition for a living polymerization [36]. 

Thus poly-(methylmethacrylate) was obtained by anionic polymerization using 2-methyl butylchloride Grignard reagent ([a] > = 1.39°). The optical rotatory power of the resulting isotactic polymer was found to be too strong in regard to what could be expected from the sole functional end groups of the polymer [24]. 

Several examples of ion-selective electrodes with ionophores covalently attached to a self-plasticized polymeric matrix have been reported in the literature. For instance, a Ca-selective electrode with the ionophore attached to a methylmethacrylate-co-decyl methacrylate backbone was developed recently [91]. Ion exchangers such as the dodecacarborane anion have been anchored to the polymeric backbone, with grafted dodecarborane showing greatly improved retention in the polymeric phase [88],... 

The polymerization of olefinic compounds like acrylonitrile, vinyl chloride, styrene, methylmethacrylate can be initiated by anion. The mechanism, in general, can be given as... 

Copolymerizations initiated by lithium metal should give the same product as produced from lithium alkyls. Usually the radical ends produced by electron transfer initiation have so short a lifetime they can have no influence on the copolymerization. This is true for instance in the copolymerization of isoprene and styrene (50). The product is identical if initiated by lithium metal or by butyllithium. With the styrene-methylmethacrylate system, however, differences are observed (79,80,82). Whereas the butyllithium initiated copolymer contains no styrene at low conversions, the one initiated by lithium metal has a high styrene content if the reaction is carried out in bulk and a moderate one even in tetrahydrofuran. These facts led O Driscoll and Tobolsky (80) to suggest that initiation with lithium occurs by electron exchange and that in this case the radical ends are sufficiently long-lived to produce simultaneous radical and anionic reactions at opposite ends of the chain. Only in certain rather exceptional circumstances would the free radical reaction be of importance. Some of the conditions required have been discussed by Tobolsky and Hartley (111). The anionic reaction should be slow. This is normally true for lithium based catalysts in hydrocarbon solvents. No evidence of appreciable radical participation is observed for initiation by sodium and potassium. The monomers should show a fast radical reaction. If styrene is replaced by isoprene, no isoprene is found in the copolymer for isoprene polymerizes slowly by free radical initiation. Most important of all, initiation should be slow to produce a low steady concentration of radical-anions. An initiator which produces an almost instantaneous and complete electron transfer to monomer produces a high radical concentration which will ensure their rapid mutual termination. 

This asymmetric end has the alkoxy group of alkyl vinylethers by cationic polymerization, phenyl group of styrene when either anionically or cationicaiiy polymerized, the vinyl group of butadiene under anionic catalysts to poly-1,2-butadiene, the ester and methyl of methylmethacrylate under anionic catalysis and the methyl of propylene by cationic catalysis. 

Anion-exchange resin useful for the extraction of copper from esters has been obtained by the amination of methylmethacrylate — DVB copolymer with hydrazine or guanidine Acryloyl chloride undergoes spontaneous polymerization with polyethylenepolyamine at room temperature to give an anion-exchange resin with high capacity and selectivity for bivalent metal ions... 

Polymerizations of methylmethacrylate initiated by organo-magnesium compounds also give rise to stereoregular products, although the active centre is almost certainly a covalent entity. Nevertheless, considerable similarities exist between these and conventional anionic systems. This is also true of polymerizations of alkyl vinyl ketones initiated by zinc and magnesium alkyls, and progress in this area has also been reported recently. ... 

The condensation method begins with molecular units, and the particles are built-up by a process of nucleation typical example is the preparation of polymer lattices, in which case the monomer (e.g., styrene or methylmethacrylate) is emulsified in water using an anionic or nonionic surfactant (e.g., sodium dodecyl sulphate or alcohol ethoxylate). A polymeric surfactant is also added to ensure the long-term colloid stabiHty of the resulting latex. An initiator such as potassium persulphate is then added and, when the temperature of the system has increased, initiation occurs that results in formation of the latex [polystyrene or poly(methylmethacrylate)]. 

Gonzalez M, Elizalde LE, Saldivar E. Synthesis of block copolymer poly(dimethylsiloxane-b-methylmethacrylate) by anionic ring opening polymerization and ATRP. 2 US -... 

Hyperbranched and comb polymers have also been used as surface active additive. Ariura et al. synthesized by combination of anionic and cationic polymerization a monodispersed hyperbranched polystyrene [73]. The authors proved by combination of DSIMS and neutron reflectivity the preferential surface enrichment of the branched protonated macromolecules when blended with its deuterated linear polystyrene counterparts with the same molar mass. Other systems involving the segregation of the branched macromolecules in binary blends were demonstrated such as in polyamide [74] or poly (methylmethacrylate) [75]. 

---