Electrophilic condensation polymerization

Most of the compounds in this class have been prepared from preexisting crown ether units. By far, the most common approach is to use a benzo-substituted crown and an electrophilic condensation polymerization. A patent issued to Takekoshi, Scotia and Webb (General Electric) in 1974 which covered the formation of glyoxal and chloral type copolymers with dibenzo-18-crown-6. The latter were prepared by stirring the crown with an equivalent of chloral in chloroform solution. Boron trifluoride was catalyst in this reaction. The polymer which resulted was obtained in about 95% yield. The reaction is illustrated in Eq. (6.22). 

Even general AB-type monomers, affording polyamide, polyester, polyether, and so on, undergo chain-growth condensation polymerization if the polymer end group becomes more reactive than the monomer by virtue of the change of substituent effects between the monomer and polymer. Both the resonance effect and inductive effect of the nucleophilic site on the reactivity of the electrophilic site at the para and meta positions of the monomer are applicable, respectively. 

The chain-growth condensation polymerization leading to aromatic polyether can be applied to the synthesis of a well-defined poly(ether sul-fone) by the condensation polymerization of 25, which is different from other monomers for chain-growth condensation polymerization in that the nucleophilic site and electrophilic site are on each benzene ring connected with an electron-withdrawing group, a sulfonyl group (Scheme 94). In the polymerization of 25 in the presence of an initiator and 18-crown-6 in sulfolane at... 

The telechelica,(i -bis(2,6-dimethylphenol)-poly(2,6-dimethylphenyl-ene oxide) (PP0-20H) [174-182] is of interest as a precursor in the synthesis of block copolymers [175] and thermally reactive oligomers [179]. The synthesis has been accomplished by five methods. The first synthetic method was the reaction of a low molecular weight PPO with one phenol chain end with 3,3, 5,5 -tetramethyl-l,4-diphenoquinone. This reaction occurred by a radical mechanism [174]. The second method was the electrophilic condensation of the phenyl chain ends of two PPO-OH molecules with formaldehyde [177,178], The third method consists of the oxidative copolymerization of 2,6-dimethylphenol with 2,2 -di(4-hydroxy-3,5-di-methylphenyl)propane [176-178]. This reaction proceeds by a radical mechanism. A fourth method was the phase transfer-catalyzed polymerization of 4-bromo-2,6-dimethylphenol in the presence of 2,2-di(4-hy-droxy-3,5-dimethylphenyl)propane [181]. This reaction proceeded by a radical-anion mechanism. The fifth method developed was the oxidative coupling polymerization of 2,6-dimethylphenol (DMP) in the presence of tetramethyl bisphenol-A (TMBPA) [Eq. (57)] [182],... 

The rate equation with strongly acidic catalysts is also second order in silanol and first order in catalyst (75). The mechanism is proposed to proceed via protonation of silanol, followed by an electrophilic attack of the conjugate acid on nonprotonated silanol. The condensation processes outlined in reactions 16a and 16b for sulfonic acids is also an applicable mechanism for the acid catalysis. The condensation polymerization in emulsion catalyzed by dodecylbenzenesulfonic acid is second order in silanol, but the rate has a complex dependence on sulfonic acid concentration (69). This process was most likely a surface catalysis of the oil-water interface and was complicated by self-associations of the catalyst-surfactant. 

Another advantage of this method is that no catalyst is needed for the addition reaction this means that the base-catalyzed polymerization of the electrophilic olefin (i.e., a,j8-unsaturated ketones, esters, etc.) is not normally a factor to contend with, as it is in the usual base-catalyzed reactions of the Michael typCi It also means that the carbonyl compound is not subject to aldol condensation which often is the predominant reaction in base-catalyzed reactions. An unsaturated aldehyde can be used only in a Michael addition reaction when the enamine method is employed. 

Plywood and particle board are often glued with cheap, waterproof urea-formaldehyde resins. Two to three moles of formaldehyde are mixed with one mole of urea and a little ammonia as a basic catalyst. The reaction is allowed to proceed until the mixture becomes sympy, then it is applied to the wood surface. The wood surfaces are held together under heat and pressure, while polymerization continues and cross-linking takes place. Propose a mechanism for the base-catalyzed condensation of urea with formaldehyde to give a linear polymer, then show how further condensation leads to cross-linking. (Hint The carbonyl group lends acidity to the N—H protons of urea. A first condensation with formaldehyde leads to an inline, which is weakly electrophilic and reacts with another deprotonated urea.)... 

You saw a carbonyl addition reaction forming a polymer right at the beginning of the chapter—the polymerization of formaldehyde. If an amine is added to formaldehyde, condensation to form imines and imine salts occurs readily. These intermediates are themselves electrophilic so we have the basis for ionic polymerization—electrophilic and nucleophilic molecules present in the same mixture. Reaction with a second molecule of amine gives an aminal, the nitrogen equivalent of an acetal. 

In this paper, we shall discuss, first by a polymerization of unsaturated side-groups (side-chains), second by the polymer-analogous condensation of suitable functional groups, third by ring-closures (cyclization) via electrocyclic reactions and, fourth by cyclization via electrophilic substitution reactions. 

Comparison of empirical formulas indicates that compounds II and III are isomeric, and correspond to an apparent trimer of isophorone I minus two molecules of water. This circumstance suggests that the carbonyl group of I is a center of C-C bond formation by way of aldol condensation followed by elimination of the resulting alcohol. Predictably, enone I should be prone to polymerize under alkaline conditions due to its two electrophilic carbons and three potential carbanionic centers (see Scheme 55.1). 

Aldehydes can methylolate phenols with an acid as a catalyst and therefore function as latent electrophiles in the negative resist design based on condensation (Fig. 125) [150]. The methylolated phenolic resin is expected to dissolve more slowly in aqueous base than its precursor resin and therefore this process could be exploited in negative imaging. Furthermore, the methylolated phenol can undergo further condensation with phenol. If the phenol is polymeric, the second reaction results in crosslinking, lowering the dissolution rate even further. 

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 biosynthesis of the proanthocyanidins is believed to proceed by addition of an electrophilic extension unit derived from a flavan-3,4-dioP or a flavan-3-oP to a nucleophilic starter unit, most likely a flavan-3-ol, with sequential addition of further chain-extension units. Although the genetics of interflavanyl bond formation in the proanthocyanidin polymerization process are not yet defmed, " the search for the elusive condensing enzyme continues unabated. ... 

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