Diallyl phthalate ester polymerization esters

The most common conformal coatings are derived from polyurethanes, acrylics, and epoxies the more special formulations for high-temperature performance are based on silicones, diallyl-phthalate esters, and polyimides. An example of a vapor deposited conformal coating is Parylene. It is obtained by vapor deposition of p-xylylene, which is formed as a transient by dehydrogenation of p-xylene at high temperature, and polymerization on the surface of the object to be coated. Because p-xylylene monomer is not stable, it is advantageous to work with the cyclic dimer, di-p-xylylene (paracyclophane), which, upon heating under reduced pressure, will produce the transient monomer which converts to the polymer at low temperatures. 

The extent of cyclization decreases quite sharply as one goes to ring sizes of 7 or more atoms. However, contrary to expectations, the extent of cyclization is still quite significant for many monomers. Thus the extent of cyclization (measured as the percent of monomer units that are cyclized) is 15-20% for diallyl esters giving ring structures containing up to 17 atoms [Holt and Simpson, 1956]. The polymerization of o-diallyl phthalate yields a polymer with more than 40% cyclization [Eaton et al., 1989 Matsumoto et al., 1980],... 

Esters of allyl alcohol, e.g., diallyl phthalate, are used as bifunctional polymerization monomers and can be prepared by simple esterification of phthalic anhydride with allyl alcohol. Several acrylic esters, such as ethyl or methyl acrylates, are also widely used and can be made from acrylic acid and the appropriate alcohol. The esters are more volatile than the corresponding acids. 

In this chapter, procedures for the polymerization of allyl acetate and related monocarboxylates of diallyl carbonate types, of diallyl phthalates, and of diallyl esters of other dicarboxylic acids are discussed. 

The study of unconjugated diolefin polymerizations is usually considered quite difficult because complex, three-dimensional networks are set up at very low conversion. Such cross-linked materials are generally intractable. The situation is quite different in the case of diallyl esters, especially in the case of diallyl phthalates. Both diallyl o-phthalate and diallyl m-phthalate may be converted to prepolymers, which are soluble in a variety of solvents. These two prepolymers are commercially availabe. When dissolved in their respective monomers and heated in the presence of typical initiators, such solutions are converted to cross-linked resins. Most of the shrinkage related to the conversion of monomers to pol)mers has taken place when the pre-polymer was formed originally. Therefore solutions containing relatively high levels of diallyl o-phthalate prepolymer shrink little on polymerization. 

For this reason, only di- and triallyl monomers have achieved commercial significance, and then only the esters. Since the cross-linked polymer occurring in this polymerization involves the side chains containing ester groups, they are also sometimes referred to industrially as polyesters. The di- and triallyl ester monomers are produced by the reaction of allyl alcohol with acids, acid anhydrides, or acid chlorides. Examples of monomers are diallyl phthalate (1) from phthallic anhydride, and triallyl cyanurate (II) from trichloro-5-triazine ... 

Unsaturated polyesters are produced from a mixture of esters made from unsaturated fatty acids, cross-linked vinyl monomer, and various polyols. The mixture is polymerized to form a cross-linked resin, with styrene monomer being used as a common vinyl cross-linking agent. Methacrylate esters, diallyl phthalate, a-methyl styrene, and vinyl toluene have also been used for this purpose. Certain dibasic unsaturated acids (or derivatives), such as... 

Diallyl Phthalate n (diallyl o-phthalate, DAP). In the monomeric form, DAP is a colorless liquid ester with a viscosity about equal to that of kerosene, widely used as a crosslinking monomer for unsaturated polyester resins, and as a polymerizable plasticizer for many resins. If polymerizes easily, either gradually or rapidly, increasing in viscosity until it finally becomes a clear, infusible solid. The name DAP is used for both the monomeric and polymeric forms. In the partly polymerized form, DAP is used in the production of thermosetting molding powders, casting resins, and laminates. 

The condensation of an alcohol with an acid to give an ester with water as a by-product is a classical way to make polymers (Table 17.1,1). In alkyd resin cooking (Section 13.4), it was mentioned that additional reactions are those between anhydride and alcohol or epoxide and between free acid and alcohol and esters (transesterification). The simple polyester with its repeating dyadic structure can be dissolved in styrene (about 70 parts polyester to 30 parts styrene) and polymerized at room temperature by a free-radical route using a redox couple. (Methyl ethyl ketone peroxide plus cobalt naphthenate would be typical.) Glass-reinforced boat hulls and automobile bodies are made from such systems. In some cases, monomers more expensive than styrene can be justified. Methyl methacrylate, triallyl cyan-urate, and diallyl phthalate have been suggested by various sources. Flammability... 

Swem and Jordan [60] prepared the allyl esters of caproic, caprylic, pelargonic, capric, lauric, myristic, palmitic, and stearic acids. Attempts to bulk polymerize the compounds with 0.5% of dibenzoyl peroxide resulted in only a slight lowering of the monomers iodine numbers, indicating very limited polymer formation. Copolymers with diallyl o-phthalate seemed to form with 1-20% of allyl esters. These copolymers were insoluble in acetone, amyl acetate, benzene, and acetic acid. 

---