Poly vinyl cinnamate

Some typical properties of some commercial EVOH polymers (Soamol— Nippon Gohsei) are given in Table 14.2. 

As is to be expected, the table shows that as the humidity is increased, causing swelling and an increase in the interchain separation, so the oxygen permeability increases. Also, as expected, the percentage increase is greater the higher the vinyl alcohol content. 

Because of the excellent gas barrier properties, EVOH is of interest as a packaging material. However, because of its high water absorption it is usually used as an internal layer in a co-extruded film, sheet, bottle or tube. For example, the system HDPE-EVOH-EVA may be used as a barrier film for packaging cereals, and the system polystyrene-EVOH-polystyrene for packaging coffee and cream, whilst the system polystyrene-EVOH-polyethylene has the additional advantage of heat scalability. 

In the case of EVOH being used as an interlayer with polyethylene or polystyrene, it is necessary to use additional adhesive layers such as an ethylene-vinyl acetate-maleic anhydride terpolymer (e.g. Orevac— Atochem). 

While EVOH is of interest primarily for food packaging applications attention is now being turned to non-food outlets such as automotive fuel tanks, floor heating pipes and toothpaste tubes. 

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Poly(vinyl cinnamate) Resists. Dichromated resists exhibit numerous shortcomings which include lot-to-lot variabiUty of the components, aging of the formulated resists in solution and in coated form, poor process stabiUty (due to a sensitivity to variations in temperature and humidity), and intrinsically low photosensitivity requiring long exposure times for adequate insolubilization. 

Fig. 4. Chemistry of poly(vinyl cinnamate) negative-acting resist. Initial light absorption by the photosensitizer is followed by energy transfer to produce a pendant cinnamate group in a triplet electronic state. This combines with a second cinnamate on another polymer chain, forming a polymer—polymer...

Poly(vinyl cinnamate) is not used in the traditional areas of plastics technology but its ability to cross-link on exposure to light has led to important applications in photography, lithography and related fields as a photoresist. 

As with poly(vinyl alcohol), poly(vinyl cinnamate) is prepared by chemical modification of another polymer rather than from monomer . One process is to treat poly(vinyl alcohol) with cinnamoyl chloride and pyridine but this is rather slow. Use of the Schotten Baumann reaction will, however, allow esterification to proceed at a reasonable rate. In one example poly(vinyl alcohol) of degree of polymerisation 1400 and degree of saponification of 95% was dissolved in water. To this was added a concentrated potassium hydroxide solution and then cinnamoyl chloride in methyl ethyl ketone. The product was, in effect a vinyl alcohol-vinyl cinnamate copolymer Figure 14.8)... 

Figure 1 Left illustration of the application of a mask to produce different samples . Right FT-IR images of the carbonyl band of poly(vinyl cinnamate), showing different levels of crosslink density as revealed from a decrease in conjugated carbonyls. Reproduced from Rafferty et al. [9], Copyright 2002, with permission from the Society for Applied Spectroscopy.

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). 

A successful example of sensitization is found in the case of poly(vinyl cinnamate) (7). 

Typical photosensitizer (PS) Poly(vinyl cinnamate) (PVCn)... 

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. 

Since it does not staffer dark reactions, poly(vinyl cinnamate) (PVCi) is one of the most excellent and practically Important photosensitive polymers and has been widely lnvestlgated(1). Recently, it was found that a more highly photosensive polymer than PVCI was obtained by the separation of clnnamoyloxy group through -CH2-CH2-O-from the main chain of the vinyl polymer(2). The fact means that by... 

The Excited States of Poly(vinyl cinnamate) and their Photochemical Reactivities. The photochemical reaction of PVCi is believed to be Intermolecular crosslinking of the polymer chains by the formation of the four-membered ring from the central double bonds of cinnamoyl-oxy groups( ), and it is known that many experimental results from the photochemical reaction are interpreted well(6) if we can postulate that the reaction is the concerted cycloaddition according to the Woodward-Hoffmann s rule(lB). This means that the four-membered ring... 

Analyses of the Electronic Transitions of Poly(vinyl cinnamate). The concerted cycloaddltlon of clnnamoyloxy group is essentially the reaction of the central double bond. Therefore, we can expect to obtain the clearer image than that hitherto considered in the photochemical reaction if the contributions of the central double bond for the excited states are calculated quantitatively. It is known that the state functions of PPP model can be rewritten to the linear combinations of LE and CT(charge transfer) functions of MIM method(7 ) when we use the same atomic orbitals as the base functions(i ). Using the technique, the state functions in Table 2 are rewritten and the results are collected in Table 3- The relationship between these two methods is illustrated in Fig.1 (b),(c). 

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