Allyl acetate polymerization

An especially interesting case of inhibition is the internal or autoinhibition of allylic monomers (CH2=CH—CH2Y). Allylic monomers such as allyl acetate polymerize at abnormally low rates with the unexpected dependence of the rate on the first power of the initiator concentration. Further, the degree of polymerization, which is independent of the polymerization rate, is very low—only 14 for allyl acetate. These effects are the consequence of degradative chain transfer (case 4 in Table 3-3). The propagating radical in such a polymerization is very reactive, while the allylic C—H (the C—H bond alpha to the double bond) in the monomer is quite weak—resulting in facile chain transfer to monomer... 

In the polymerization of vinyl acetate, chain transfer to the acetate portion of the monomer is an important aspect of the process (see Chapter 7 of this volume). In the case of the allyl acetate polymerization, chain transfer to the acetate moiety is considered negligible as compared to the degradative chain-transfer process [14, 15]. 

In the 1952 paper mentioned above [3], Gilman reported on the formation of lithium dimethylcuprate from polymeric methylcopper and methyllithium. These so-called Gilman cuprates were later used for substitution reactions on both saturated [6] and unsaturated [7, 8, 9] substrates. The first example of a cuprate substitution on an allylic acetate (allylic ester) was reported in 1969 [8], while Schlosser reported the corresponding copper-catalyzed reaction between an allylic acetate and a Grignard reagent (Eq. 2) a few years later [10]. 

It is reported that methyl acrylate, allyl acetate, vinyl acetate and dimethyl maleate give only low yields of oligomers with butyllithium under all experimental conditions (31). Furukawa and coworkers (32) confirm that vinyl acetate will not polymerize and that n-butyl-vinyl-ether will not either. High polymers can be formed from isopropyl acrylate (39) in toluene at —70° and from t-butyl acrylate (65). The reported failure of methyl acrylate and butyl acrylate to yield high polymers could reflect a genuine difference in behaviour connected with the side group or. could simply result from failure to choose the most favourable conditions for polymerization. Vinyl acetate can be polymerized by lithium metal (49) but co-polymerization experiments suggest that the polymer is formed by a radical mechanism. 

In the polymerization of allyl acetate, transfer to monomer produces an unreactive radical which fails to re-initiate growth of the polymer chain. Bartlett and Tate (31) compared the rates of polymerization for the unlabelled monomer and.the deuterated monomer CH2 CH-CD2 0-CO CH3. The deuterated monomer polymerized more rapidly giving a product of higher molecular weight. These observations suggest that the rate of polymerization and the molecular weight of the polymer are controlled by the reaction... 

Bartlett, P. D., and K. Nozaki Polymerization of allyl compounds. III. The peroxide-induced copolymerization of allyl acetate with maleic anhydride. J. Amer. chem. Soc. 68, 1495 (1946). 

Bartlett and Tate (14) studied the polymerization of allyl acetate and allyl-l-d acetate and found that the rate of poly-... 

A similar association phenomena has been proposed (3) in the methyl methacrylate-zinc chloride system. The formation of org tilled mobile monomer arrays has been suggested to account for the accelerated polymerization of methyl methacrylate in the presence of aluminum bromide (87) and allyl alcohol and allyl acetate in the presence of zinc chloride (55, 87). 

Russian workers have proposed that the increased activity of allyl acetate and allyl alcohol in free radical or gamma ray initiated polymerization in the presence of zinc chloride may be connected with the decreased degradative chain transfer with complexed monomer or the activation of the stabilized allyl radical in the complexed monomer—i.e., the conversion of degradative chain transfer to effective transfer (55, 87). However, these explanations have been partially rejected as inadequate. 

Deactivating chain transfer to monomer is quite common in polymerization of allyl monomers [40-42], Allyl radicals such as that of allyl acetate are resonance-stabilized, with the result that polymerization rates and molecular weights remain low. Moreover, with chain transfer as the dominant termination mechanism, the termination rate is first order in free radicals. This lets the free-radical population become proportional to the initiator concentration and leads to a polymerization rate that is first order rather half order in initiator and zero order in monomer. 

It has been suggested that free-radical polymerization would be a useful way to react an equimolar mixture of allyl acetate and methyl methacrylate. Is this a good idea (Allyl acetate e — —1.07, Q = 0.24 methyl methacrylate e = 0.40, Q = 0.78). 

It is also to be expected that pressure will affect the rate of chain transfer reactions to monomer, polymer, and solvent. In the polymerization of allyl acetate, where degradative chain transfer to monomer occm s, the rates of the propagation and transfer reactions increase by about the same amoimt for a given increase in pressure (17). The transfer reaction becomes less degradative—i.e., the allyl acetate radicals become more reactive—as pressure is increased. 

In the presence of benzoyl peroxide, allyl acetate gives poor yields of polymer of low molecular weight. The deuterium-labeled ester, CH CHCD2OAC, polymerizes 2 to 3 times as fast as the 01 dinary ester, and gives polymer of about twice the molecular weight. How do you account for these facts ... 

With regard to radical polymerization some controversial results have also been obtained. Thus Mondvai and co-workers [138] have shown that o-dinitro benzene was a stronger retardant of radical polymerization of methyl methacrylate than other isomers. On the contrary Hammond and Bartlett [139] found that o-6initrobenzcne was a weaker retardant than other isomers of polymerization of allyl acetate. 

Chain transfer to monomer was described earlier in general terms for vinyl monomers [cf. Eq. (6.138)]. Such reactions are particularly favored with allylic monomers such as allylic acetate which have the structure CH2=CH-CH2X with a C-H bond alpha to the double bond described as an allylic C-H. The propagating radical in the polymerization of such monomers is very reactive, while the allylic C-H bond in the monomer is quite weak, resulting in facile chain transfer to monomer ... 

Figure 1. Dependence of the percentage of hh linkage on polymerization tempera-ture in bulk polymerizations. Key O, allyl acetate and , methallyl acetate. (Reproduced, with permission, from Ref. 21. Copyright 1981, J. Polym. Sci.

The polymerization of allyl esters of saturated monobasic acids, e.g., allyl acetate and allyl laurate, yields linear thermoplastic polymers containing 5-20 monomer units per molecule. These homopolymers and copolymers with vinyl monomers such as vinyl acetate, vinyl chloride, and vinylidene cliloride have been used as thermoplastic adhesives and plasticizers. 

Bulk Polymerization of Allyl Acetate in Sealed Tubes. 298... 

In this chapter, procedures for the polymerization of allyl acetate and related monocarboxylates of diallyl carbonate types, of diallyl phthalates, and of diallyl esters of other dicarboxylic acids are discussed. 

Over a fivefold variation of the peroxide concentration, at a constant polymerization temperature, the MW of poly(allyl acetate) remains virtually constant at 1300 (i.e., DP = 13) (Litt and Eirich foimd the degree of polymerization to be 20-25 in their work). 

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