Allyl monomers

Allyl monomers, such as allyl acetate (see Chapter 10), are often known to give 1 1 alternating copolymers with However, several polyfunc- 

Schildknecht explored copolymerization of triallyl cyanurate (TAC) and triallyl isocyanurate (TAIC) with MA. The red-colored acetone solution of the TAC-MA copolymer could be neutralized with aqueous sodium hydroxide to give a white opaque microgel dispersion. The dispersion could be used to cast free films. 

Using high-energy radiation, dimethylallyl has been copolymerized with MA to give crosslinked materials.These materials were suggested as possible ion-exchange resins. 

Allyl alcohol is known to copolymerize with MA to give equimolar copolymers with lactone and carboxylic acid groups (see Chapter 10). Allyl maleate or fumarate, with free-radical initiation, will also copolymerize with 

giving nonequimolar copolymers potentially useful in detergent com-positions/  

Diallyl monomers find significant use in cyclopolymerization (Section 4.4.1). Transfer to monomer is of greater importance in polymerizations of allyl than it is in diallyl monomers. This might, in part, reflect differences in tlie nature of the propagating species [e.g. a secondary alkyl (115) v.v a primary alkyl radical (116)]. Electronic factors may also play a rolc.  

The polymerizability of allyl monomers is thought to be directly related to the abstractabilily of a-hydrogens.  

---

The monomer can also be copolymerized with acrylamide. Because of the high chain-transfer rate of aUyflc radicals, the molecular weights tend to be lower than for acryflc polymers. These polymers are sold either as a viscous solution or a dry powder made by suspension polymeriza tion (see Allyl monomers AND POLYPffiRS). 

In this article, mainly monoallyl compounds are described. DiaHyl and triaHyl compounds used as monomers are covered in the article entitled Allyl MONOMERS AND POLYMERS and also in the hterature (36,37). 

Transfer to monomer is of particular importance during the polymerization of allyl esters (113, X=()2CR), ethers (113, X=OR), amines (113, X=NR2) and related monomcrs.iw, 8, lb2 The allylic hydrogens of these monomers arc activated towards abstraction by both the double bond and the heteroatom substituent (Scheme 6.31). These groups lend stability to the radical formed (114) and are responsible for this radical adding monomer only slowly. This, in turn, increases the likelihood of side reactions (i.e. degradative chain transfer) and causes the allyl monomers to retard polymerization. 

Hydrophobic polymers with some hydrophilic groups can be obtained with an emulsion polymerization technique. Suitable monomers are nitrogen-containing acrylics and methacrylics allyl monomers such as dimethylamino-ethyl methacrylate, dimethylaminopropyl methacrylamide, diethylamino-ethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate and nitrogen-containing allyl monomers (e.g., diallylamine and N,N-diallyl-cyclohexylamine) [225,226]. 

In radical chain polymerisation of allylic monomers (containing the chemical allyl group CH2 = CR-CH3, like propylene, isobutylene,...), a transfer on the monomer can occur leading to a very stable allyl radical unable to propagate the chain. Thus radical chain polymerisation of such monomers, especially propylene is not feasible, as a competition exists between the propagation rate and the high rate of transfer on the monomer (see, Figure 22). 

The activity of transition metal allyl compounds for the polymerization of vinyl monomers has been studied by Ballard, Janes, and Medinger (10) and their results are summarized in Table II. Monomers that polymerize readily with anionic initiators, such as sodium or lithium alkyls, polymerize vigorously with allyl compounds typical of these are acrylonitrile, methyl methacrylate, and the diene isoprene. Vinyl acetate, vinyl chloride, ethyl acrylate, and allylic monomers do not respond to these initiators under the conditions given in Table II. 

Thus, a semilogarithmic plot of the gel time as a function of 1/T should be linear, with the slope corresponding to the apparent activation energy. We have determined the gel times for a temperature range of 25°-50° C for a thiol-ene system consisting of stoichiometrically equivalent amounts of a trifunctional thiol, trimethylolpropane tris(2-mercaptoacetate), and a trifiinctional allyl monomer, triallyl isocyanurate. In this system, we also added 0.31% by weight of hydroquinone, to prevent premature polymerization, and 1.0% by weight of a commercial photoinitiator, Esacure TZT. 

Apparently, the driving force for the ring opening is the relief of the strain in the spiro system and the formation of the stable carbonate double bond. The double ring opening is probably a concerted process from the initial radical addition product to the open-chain radical. Even though the spiro compound XI is an allyl monomer, it does copolymerize with a wide variety of comonomers. 

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... 

This is proved by the observation that the rate of decomposition of persulphate drops to the same low value as when allyl acetate is added in the absence of alcohol. On addition of allyl acetate, the sulphate ion radicals react with the allyl monomer rather than with the alcohol, so that no alcohol radicals are formed and reaction (VII) cannot take place. Formaldehyde is only formed in the absence of allyl acetate. It should be noted that Bartlett and Nozaki (24) could not confirm these observations. 

---