Hydroxy radicals reaction with monomers

The transient radicals produced in reactions of hydroxy radicals with vinyl monomers in aqueous solution have been detected directly by EPR43 439 or UV spectroscopy,440-441 These studies indicate that hydroxy radicals react with monomers and other species at or near the diffusion-controlled limit ( Table 3.7). However, high reactivity does not mean a complete lack of specificity. Hydroxy radicals are electrophilic and trends in the relative reactivity of the hydroxy radicals toward monomers can be explained on this basis/97... 

Grant et a/.397 examined the reactions of hydroxy radicals with a range of vinyl and a-methylvinyl monomers in organic media. Hydroxy radicals on reaction with AMS give significant yields of products from head addition, abstraction and aromatic substitution (Table 3.8) even though resonance and steric factors combine to favor "normal tail addition. However, it is notable that the extents of abstraction (with AMS and MMA) arc less than obtained with t-butoxy radicals and the amounts of head addition (with MMA and S) are no greater than those seen with benzoyloxy radicals under similar conditions. It is clear that there is no direct correlation between reaclion rale and low specificity. 

Sulfate radical anion may be converted to the hydroxyl radical in aqueous solution. Evidence for this pathway under polymerization conditions is the formation of a proportion of hydroxy end groups in some polymerizations. However, the hydrolysis of sulfate radical anion at neutral pi I is slow (k— 107 M"1 s 1) compared with the rale of reaction with most monomers (Ar=l08-109 M 1 s 1, Table 3.7)440 under typical reaction conditions. Thus, hydrolysis should only be competitive with addition when the monomer concentration is very low. The formation of hydroxy end groups in polymerizations initiated by sulfate radical anion can also be accounted for by the hydration of an intermediate radical cation or by the hydrolysis of an initially formed sulfate adduct either during the polymerization or subsequently. 

In contrast to most other oxygen-centered radicaLs e.g. benzoyloxy (3.4.2.2.1), hydroxy (3.4.2.3)1, t-butoxy radicals and other r-alkoxy radicals (3.4.2.1.2) show relatively high regiospecificity in reactions with carbon-carbon double bonds (Table 3.8). Nonetheless, significant amounts of head addition are observed with the halo-olcfins, simple alkcncs, vinyl acetate and methyl acrylate. " Head addition is generally not observed with 1,1-disubstituted monomers. The exception is vinylidene niioride" where head addition predominates (Section... 

The transient radicals produced in reactions of hydroxy radicals with vinyl monomers in aqueous solution have been detected directly by or UV... 

Emulsion breakers are made from acrylic acid or methacrylic acid copolymerized with hydrophilic monomers [148]. The acid groups of acrylic acid and methacrylic acid are oxalkylated by a mixture of polyglycols and polyglycol ethers to provide free hydroxy groups on the molecule. The copolymers are made by a conventional method, for example, by free radical copolymerization in solution, emulsion, or suspension. The oxalkylation is performed in the presence of an acid catalyst, the acid being neutralized by an amine when the reaction is complete. 

Features of the free-radical initiation processes are similar for both the homopolymerization of functionalized monomers and copolymerization of the latter with conventional monomers. Common chemical initiators were applied. Azo-bis(isobutyro nitrile) was mostly used in bulk polymerization. No interference with phenolic hydroxy groups was observed in polymerization of 2-hydroxybenzo-phenoiKs, acetophenones, salicylates and of their derivatives [47]. The most rigorous eliinination of oxygen from the reaction mixture was necessary to achieve polymerization of monomeric hindered phenolic antioxidants or derivatives of 2-(2-hydroxyphenyl)benzotriazole [48]. An oxygen-free atmosphere is also an advantage for aromatic amines. A higher initiator level and/or increased temperature appear to be necessary to achieve normal polymerization rates with (D-functionalized monomers [46]. 

Polyelectrolytes and soluble polymers containing triarylamine monomers have been applied successfully for the indirect electrochemical oxidation of benzylic alcohols to the benzaldehydes. With the triarylamine polyelectrolyte systems, no additional supporting electrolyte was necessary [91]. Polymer-coated electrodes containing triarylamine redox centers have also been generated either by coating of the electrode with poly(4-vinyltri-arylamine) films [92], or by electrochemical polymerization of 4-vinyl- or 4-(l-hydroxy-ethyl) triarylamines [93], or pyrrol- or aniline-linked triarylamines [94], Triarylamine radical cations are also suitable to induce pericyclic reactions via olefin radical cations in the form of an electron-transfer chain reaction. These include radical cation cycloadditions [95], dioxetane [96] and endoperoxide formation [97], and cycloreversion reactions [98]. 

In the above condensation resist designs, the phenolic resin offers a reaction site as well as base solubility. Self-condensation of polymeric furan derivatives has been utilized as an alternative crosslinking mechanism for aqueous base development (Fig. 126) [375]. The copolymer resist is based on poly[4-hydroxy-styrene-co-4-(3-furyl-3-hydroxypropyl)styrene], which was prepared by radical copolymerization of the acetyl-protected furan monomer with BOCST followed by base hydrolysis. The furan methanol residue, highly reactive toward electrophiles due to a mesomeric electron release from oxygen that facilitates the attack on the ring carbons, readily yields a stable carbocation upon acid treatment. Thus, the pendant furfuryl groups serve as both the latent electrophile and the nucleophile. Model reactions indicated that the furfuryl carbocation reacts more preferentially with the furan nucleus than the phenolic functionality. 

The radical concentration [R ] was determined from the area under the integrated ESR spectrum by use of the relation calibrated with the spectrum for 4-hydroxy-2,2,6,6-tetramethylpiperidin-I-oxyl of known concentration dissolved in either the monomer or mixtures of monomer and solvent. The polymerization rate —d[M]/dt was determined from the extent of polymerization after a given time. The values obtained for [R ] and —d[M]/dt were substituted into Eq. (7-1) to evaluate kp. When [R ] changed with reaction time, kp was estimated from the relation... 

Side groups can be introduced by polymer-modification reactions for example, a hydroxy group can be converted to halides, tert-amino, nitro, sulfane, and disulfane groups and to heterocyclic units [107]. Acrylic monomers, with C = C double-bond containing side groups, can be used for radical and anionic crosslinking. 

Condensation reactions between hydroxyethyl cellulose or carboxy methyl hydroxy-ethyl cellulose provides potentially useful textile sizing resins.Starch materials have been treated with MA to obtain starch with maleate half-ester residues, with a substitution degree of 0.01-3.00. Styrene monomer is grafted onto the maleate/fumarate residues, with high efficiency, using standard free-radical initiators. 

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