Polymerization of polar monomers

Qualitative information is available on several other vinyl monomers including acrylonitrile [157—159], methacrylonitrile [160], tert.- 

The progress of the reaction with methylmethacrylate depends somewhat on initiator, temperature and solvent. Investigations have been carried out using fluorenyllithium [167, 168, 170], phenylmagnesium bromide [171, 172], butyllithium [173] and 1,1-diphenylhexyllithium [174] in toluene solution with or without the presence of ethers. Product analysis shows that two basic reactions occur with the monomer both with magnesium compounds [171, 175] and with butyllithium [176], viz. 

It is not certain if reaction (20) goes to completion. Reaction (19) leads to prop ation whereas (20) does not. The relative importance of the two steps will depend on initiator, solvent and temperature, but insufficient evidence is available to discuss variations systematically. Multiple attack on the monomer is possible at high initiator monomer ratios but is not likely to be important under polymerization conditions. Metallation of the monomer has been suggested to occur with butyllithium. It seems unlikely to occur in this system and the butane detected in the hydrolysis products of the reaction can come from other sources. Reaction (20) is not the only source of initiator loss as indicated by fractionation of the 

Experiments on termination with tritiated acetic acid [168] showed that all except the fraction of lowest molecular weight would add a proton with at least 80% efficiency. It seems reasonable to suppose that these chains would also be reactive towards monomer, but the shorter chains apparently do not propagate at all or if they do so it is with low efficiency. This leads to the suggestion [168] that the shorter chains are pseudo-terminated by intra-molecular complexing, e.g. 

Such chains might have a small probability of propagating by dissociation of the complex, but could also lead to the cyclic ketone above in a true termination reaction, or in the reaction with tritiated acetic acid. In the 

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In recent years homoleptic lanthanide(III) tris(amidinates) and guanidinates have been demonstrated to exhibit extremely high activity for the ring-opening polymerization of polar monomers such as e-caprolactone and trimethylene... 

Copolymerizations of nonpolar monomers with polar monomers such as methyl methacrylate and acrylonitrile are especially comphcated. The effects of solvent and counterion may be unimportant compared to the side reactions characteristic of anionic polymerization of polar monomers (Sec. 5-3b-4). In addition, copolymerization is often hindered by the very low tendency of one of the cross-propagation reactions. For example, polystyryl anions easily add methyl methacrylate but there is little tendency for poly(methyl methacrylate) anions to add styrene. Many reports of styrene-methyl methacrylate (and similar comonomer pairs) copolymerizations are not copolymerizations in the sense discussed in this chapter. 

Traditional Ziegler-Natta and metallocene initiators polymerize a variety of monomers, including ethylene and a-olefins such as propene, 1-butene, 4-methyl-1-pentene, vinylcyclo-hexane, and styrene. 1,1-Disubstituted alkenes such as isobutylene are polymerized by some metallocene initiators, but the reaction proceeds by a cationic polymerization [Baird, 2000]. Polymerizations of styrene, 1,2-disubstituted alkenes, and alkynes are discussed in this section polymerization of 1,3-dienes is discussed in Sec. 8-10. The polymerization of polar monomers is discussed in Sec. 8-12. 

On the other hand, the anionic polymerization of polar monomers appears to be very complicated. This is due to the functional groups which give rise to physical interactions (e.g. association), as well as chemical side reactions (e. g. termination... 

Various types of well-defined block copolymers containing polypropylene segments have been synthesized by Doi et al. on the basis of three methods (i) sequential coordination polymerization of propylene and ethylene 83-m>, (ii) transformation of living polypropylene ends to radical or cationic ones which initiate the polymerization of polar monomers 104, u2i, and (iii) coupling reaction between iodine-terminated monodisperse polypropylene and living polystyrene anion 84). In particular, the well-defined block copolymers consisting of polypropylene blocks and polar monomer unit blocks are expected to exhibit new characteristic properties owing to the effect of microphase separation. 

Polymerization of polar monomers by metallocene catalysts is an open field of research in which investigations are just beginning. 

The importance of the electrophilic character of the cation in organo-alkali compounds has been discussed by Morton (793,194) for a variety of reactions. Roha (195) reviewed the polymerization of diolefins with emphasis on the electrophilic metal component of the catalyst. In essence, this review willattempt to treat coordination polymerization with a wide variety of organometallic catalysts in a similar manner irrespective of the initiation and propagation mechanisms. The discussion will be restricted to the polymerization of olefins, vinyl monomers and diolefins, although it is evident that coordinated anionic and cationic mechanisms apply equally well to alkyl metal catalyzed polymerizations of polar monomers such as aldehydes and ketones. 

T he free radical initiated polymerization of polar monomers containing pendant nitrile and carbonyl groups—e.g., acrylonitrile and methyl methacrylate—in the presence of metal halides such as zinc chloride and aluminum chloride, is characterized by increased rates of polymerization (2, 3, 4, 5,10, 30, 31, 32, 33, 34, 53, 55, 65, 66, 75, 76, 77, 87). Imoto and Otsu (30, 33, 34) have attributed this effect to the formation of a complex between the polar group and the metal halide. The enhanced reactivity of the complexed monomer extends to copolymerization with uncomplexed monomers, such as vinylidene chloride, which are readily responsive to... 

Without the third component no activity at all was observed. They proposed a mechanism similar to the one given by Yasuda et al. [216, 217] for polymerization of methylmethacrylate by lanthanocenes which are isoeleetronie with alkylzirconocenium ions. The role of the third component in this mechanism is not very clear. Nevertheless polymerization of polar monomers by metallocene catalysts is an open field of research and investigations are just beginning. 

Monomer reactivity is a broad concept, and it can not always be limited only to reactions of the double or triple bonds of a vinyl or acetylene group. Weakly polar monomers, such as styrene or butadiene, react almost exclusively by their double bonds. The anionic polymerization of polar monomers, such as a, /S-unsaturated esters and nitriles, is accompanied by many side reactions. A fairly large amount of oligomers and side products are formed, and these may affect the active centres, thus indirectly modifying propagation. 

For further elucidation of the initiation mechanism in polymerizations of polar monomers with organometals, a method for determining the instantan-neous concentrations of active centres has to be found, as well as an initiating system acting without side reactions. 

Interfacial Phenomena in Emulsion Polymerization of Polar Monomers... 

Comparison of published tota on vinylacetate polymerization kinetics, for which a steady-state period is typical (13), to the kinetics of variation of the number of particles which decreases during the process up to a factor of 40 (14), permits us to conclude that there is no correlatlonbetween the rate and the number of particles. This conclusion was supported by Medvedev et al. ( ) in the case of emulsion polymerization of methylm hacrylate. We deduce from the above data that the emulsifier concentration itself does not determine either the total surface of the disperse phase or the mmber of particles during polymerization of polar monomers. 

Sanchez-Barba, L.F., Hughes, D.L., Humphrey, S.M. et al. (2005) New bis(allyl)(diketiminato) and tris(allyl) lanthanide complexes and their reactivity in the polymerization of polar monomers. Organometallics, 24,3792. 

The lower stability of smaller particles which follows from tbe DLVO theory may be one of the factors affecting limited fiocculation of particles during polymerization of polar monomers. The importance of this factor... 

The restricted adsorption of anion-active emulsifier during polymerization of polar monomers (vinyl acetate) has also been reported in other work. Breitenbadi eX ul. (1970) established that in the case of polymerization initiated hy a,forming interface. The polymerization rate was found to depend on emulsifier concentration to the power of 0.1. 

It was established by Yeliseyeva and Bakaeva (1968) that in the polymerization of polar monomers (MA) the decrease of emulsifier adsorption depends on tbe structure of the latter and for some types of emulsifiers may reach limiting values. This was observed in tbe polymerization ofMA in the presence of a mixed type of emulsifier, partially sulfurated with sulfuric acid oxyethylated alkylphenol (emulsifier C-I0 ). Its adsorption on the particle surface increases with the initial concentration and reaches > 100% filling of the adsorption layer, conditionally corresponding to 0.3S nm per molecule. Stable, concentrated latexes with small particles are formed. Therefore, emulsifier adsorption and the mechanism ctf particle formation associated with it depends not only on monomer polarity but also on the chemical structure of the emulsifier. 

When using more active emulsifiers of the C-10 type (Yeliseyeva, 1966) the effective rate and the equilibrium value of adsorption increase in the polymerization of polar monomers, which reduces the intensity of the processes of initial flocculation. Moreover, in this case the charge density is not the only stabilizing factor it is su(f>lemented by the enthalpy factor which arises from hydration of oxyethylenic chains of emulsifier molecules. The presence of these emulsifiers creates conditions that enable tbe obtain-ment of polar polymer latexes of high stability. 

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