4-Vinyl cinnamic derivatives

TABLE I, . Synthesis and caracteristies of 4-vinyl cinnamic derivatives. ... 

The photosensitivity of poly(vinyl cinnamate) derives from the reactivity of the einnamoyl group. Cinnamic acid is a naffirally occurring compound (found in oil of cinnamon, from which it derives its name) and is readily synthesized. Its photosensitivity has long been known, though little use was made of this property until Mink and co-workers, while reviewing the literature in search of a potential cross-linking reaction, found it to be the only solid state photodimerization that was known at the... 

The first system, introduced as Kodak KPR resist in 1956, was based on poly(vinyl cinnamate) derivatives as resins and organic solvents like cellosolve acetate UV exposure brings about crosslinking, after which the unexposed parts can be developed with the original solvent of the resist. A second system, which was introduced for printed circuits in 1960, was based on derivatives of polyfisoprene) rubber as a resin and a bis-azide sensitizer. Upon UV exposure, crosslinking occurs and Nj is evolved. 

V. M. Kozenkov, V. G. Chigrinov, and H.-S. Kwok, Photoanisotropic effects in poly(vinyl-cinnamate) derivatives and their applications. Molecular Crystals and Liquid Crystals 409, 251 (2004). 

Photocrosslinking. The second class of photopolymer chemistry that is used in some commercial products is based on the reaction of unsaturated moieties attached to an organic polymer. These photopolymer materials include the [2+2] cycloaddition of the ethylenic groups in poly(vinyl cinnamate) polymers and in the newer styryl pyridinium (10) and thiazolium (77) derivatives of poly(vinyl alcohol). The main advantage of this chemistry is that, unlike free-radical photopolymerization, they are insensitive to the presence of oxygen. This photopolymer mechanism is principally used in applications employing a washout development process (e.g. resists). 

Photo-crosslinking and the reverse process of photodissociation of pre-existing crosslinks relies on a cycloaddition reaction (and on the reverse dissociation of the cyclic adduct). For example, derivatives of vinyl cinnamic acid can form crosslinks which are dissociated by irradiation with short wavelength light (e.g. 254 nm produced by low-pressure mercury arcs). In this process the polymer chains become separated, and the polymer itself is then soluble in organic solvents. 

Cinnamates occupy an important place in the history of photochemistry. Schmidt and his co-workers [18] used the solid state photochemistry of cinnamic acid and its derivatives to develop the idea of topochemical control of photochemistry in the crystalline state. Minsk [19] developed poly(vinyl cinnamate) as the first polymer for photoimaging. The cinnamate chromophore is still commonly incorporated in photopolymers of all types, including LC polymers, to enable them to be photochemically cross-linked [20], and a number of reports of the photochemistry of such MCLC and SCLC polymers are summarized below. 

In the presence of photosensitizers, this polymer was found by Tsuda to cross-link at a considerably faster rate than does poly(vinyl cinnamate) [160]. He showed that the cross-linking reaction also results in formation of cyclobutane derivatives. The cross-linking is illustrated on 3-furfurylacrylic ester ... 

Most of these azide polymers photocross-link at a faster rate than does poly(vinyl cinnamate), when exposed to light of 260 pm. In addition, they responded well to photosensitization. Also, it was observed [50] that the 4-isomer of azidophthalate shows greater speed increase than does the 3-isomer. In general, the poly(vinyl alcohol) derivatives were reported to exhibit higher cross-linking speeds than do other azide functionalized polymers [176]. 

The reaction was successfully applied to both electron-rich and electron-poor 4-nitrophenyl carboxylates among them, the conversion of the electron-deficient esters was found to be faster and more efficient. Many functional groups are tolerated on both the side of the carboxylic ester (halo, keto, formyl, ester, cyano, nitro and protected amino groups, heterocyclic and a,-unsaturated carboxylic esters) and of the alkene (electron-rich alkyl-substituted alkenes, electron-poor acrylate derivatives, trimethylvinylsilane as an ethylene surrogate). The cinnamate derivatives could become particularly useful substrates, since the availability of the synthetically equivalent vinyl halides is rather limited. In analogy to conventional Mizoroki-Heck chemistry, linear (Zi)-substituted alkenes are predominantly but not exclusively obtained. Selected examples are shown in Table 4.1. 

Nearly all uses and appHcations of benzyl chloride are related to reactions of the active haUde substituent. More than two-thirds of benzyl chloride produced is used in the manufacture of benzyl butyl-phthalate, a plasticizer used extensively in vinyl flooring and other flexible poly(vinyl chloride) uses such as food packaging. Other significant uses are the manufacture of benzyl alcohol [100-51-6] and of benzyl chloride-derived quaternary ammonium compounds, each of which consumes more than 10% of the benzyl chloride produced. Smaller volume uses include the manufacture of benzyl cyanide [140-29-4], benzyl esters such as benzyl acetate [140-11-4], butyrate, cinnamate, and saUcylate, benzylamine [100-46-9], and benzyl dimethyl amine [103-83-8], and -benzylphenol [101-53-1]. In the dye industry benzyl chloride is used as an intermediate in the manufacture of triphenylmethane dyes (qv). First generation derivatives of benzyl chloride are processed further to pharmaceutical, perfume, and flavor products. 

Lignin has a complex structure that varies with the source, growing conditions, etc. This complex and varied structure is typical of many plant-derived macromolecules. Lignin is generally considered as being formed from three different phenylpropanoid alcohols— coniferyl, coumaryl, and sinapyl alcohols, which are synthesized from phenylalanine via various cinnamic acid derivatives and commercially is sometimes treated as being composed of a Cg repeat unit where the superstructure contains aromatic and aliphatic alcohols and ethers, and aliphatic aldehydes and vinyl units. 

As a rule, alkynes react in bromo- and iodofluorinations by monoaddition because vinylic a./f-halofluorides as electron-deficient alkenes are generally less reactive. However, some aryl-conjugated alkenes, such as cinnamate or stilbene derivatives 3 or 5, respectively,184 may also be halofluorinated by hydrogen fluoride/pyridine/A-halosuccinimide reagent.185... 

Although benzophenone derivatives have found application in a number of photopolymerization processes (10), these have usually involved cross-linking reactions induced by energy transfer from photo-exdted benzophenones to groups (e.g. cinnamate) attached to the polymer chains. In such cases, the benzophenones act as sensitisers and not as photoinitiators. An e>fample in which hydrogen abstraction by photoexdted benzophenone has been utilized for photoinitiation is the ultra-violet induced grafting of styrene on to polyethylene (8,45). Recently, extensive studies concerned with photoinitiation of vinyl polymerization by benzophenone derivatives in homogeneous media have been carried out, and are described in detail below. 

Introduction of these photocrosslinkable structures in macro-molecular chains can be performed by esterification of hydroxyla-ted polymers with cinnamoyl chloride. Cellulose Q).condensation products (4, ) and mainly poly(vinyl alcohol) have Been treated( by this method. Other chemical modifications have been studied as ester interchange of poly(vinyl acetate) 7) and Knoevenagel reaction on polyesters (8). Very few results on the synthesis of such photocrosslinkable polymers by polymerization have been reported. Therefore free radical polymerization of cinnamic acid vinyl derivatives did not lead to the expected polymers, but to insolubilization reactions. Howewer cationic procedure can be a good way in some cases since Kato et al. could polymerize by this way with high yields p-vinyl phenylcinnamate (9) and B-vinyloxyethyl cinnamate (10). 

Early studies of solid-state polymerization of vinyl derivatives have been reviewed (5). The initial discussions of the topochemicrd principle 0 were replete with examples from the photocycloaddition of cinnamic acid derivatives. 

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