Chemistry of Resins

A comprehensive survey of the chemistry of natural resins relevant to art historical and archaeological contexts is given in Mills and White (1994 95-128) and is not repeated here. Rather, those aspects of structure and chemistry relating to molecular transformation and to the composition of aged resins encountered in archaeological contexts will be emphasized. 

Isoprene (2-methylbuta- 1,3-diene [Structures 7.1a and 7.1b]) is a C5 unit. Structure 7.1a shows the full structural formula where each line between the atoms represents two shared electrons in a covalent bond. In the case of more complex molecules, skeletal structures are used, as in Structure lb, where carbon atoms are normally represented by an intersection of bonds. Carbon-hydrogen bonds are not shown, although all other atoms (O, N, P and so on) are indicated. 

The term terpenoid is now the preferred generic name for this class of natural products. Many thousands of individual terpenoid molecules are known, 

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As with the other aminoplastics, the chemistry of resin formation is incompletely understood. It is, however, believed that under acid conditions at aniline-formaldehyde ratios of about 1 1.2, which are similar to those used in practice, the reaction proceeds via p-aminobenzyl alcohol with subsequent condensation between amino and hydroxyl groups (Figure 24.10). 

A brief investigation of the potential thermal and photo-lytical chemistry of resins 3 and 5 was undertaken. It was prompted by a report of the observation of site-site isolation on irradiation of 18% cross linked 3 (22). This is in contrast to soluble CpCo(C0)2 which forms di- and trinuc.lear clusters under the same conditions ( 33, 34). Similar apparent prevention of the formation of higher nuclear species was noted in the decarbonyla-tions of CH2Fe(C0)2H (22) and CH2Cgi(C0) 3H (M = Cr, Mo, W) (35), and in the catalytic activity of CfoCpTiCp (25). However, these species are all supported by a relativelyTiLghly cross linked polymer, and there was ample indication that lesser crosslinking enables "bimolecular" reactions of active centers (36,37,38,39). 

Aminoquinolines, 21 185, 199 Amino resins, 16 409. See also Amino resins and plastics coating resins, 7 96-98 formaldehyde in, 12 121 Amino resins and plastics, 2 618-652 chemistry of resin formation,... 

Wagner H (1973) The Chemistry of Resin Glycosides of the Convolvulaceae Family. In Bendz G, Santensson J (eds) Medicine and Natural Sciences. Chemistry in Botanical Classification. Academic Press, New York, p 235 12. Mannich C, Schumann P (1938) Uber Jalapenharz und dessen Hauptbestandteil, das Con-volvulin. Arch Pharm Ber Dtsch Pharm Ges 276 211... 

Sukh Dev 1983 Chemistry of resinous exudates of some Indian trees. Proc Indian Nat Sci Acad 49(A) 359-385... 

Fig. 5. Chemistry of cyclized mbbei—bis-a2ide negative acting resist, (a) Preparation of cyclized mbber resin from polyisoprene (b) photochemistry of aromatic bis-a2ide sensiti2ers. The primary photoproduct is a highly reactive nitrene which may combine with molecular oxygen to form oxygenated products, or may react with the resin matrix by addition or insertion to form polymer—polymer linkages.

Epoxy Resins. The chemistry of epoxy resin adhesives is quite varied. However, the most widely used is that formed from the reaction of 4,4 -isopropyhdene diphenol (bisphenol A) [80-05-7] and epichlorohydrin [106-89-8] C H CIO. This epoxy resin is more commonly known as... 

Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

Ion-exchange resins are categorized by the nature of functional groups attached to a polymeric matrix, by the chemistry of the particular polymer in the matrix, and by the porosity of the polymeric matrix. There are four primary types of functionaHty strong acid, weak acid, strong base, and weak base. Another type consists of less common stmctures in specialty resins such as those which have chelating characteristics. 

Gopolymerization. The chemistry of the resin matrix, the type and degree of porosity, the particle size, and the particle size distribution are estabhshed in the copolymerization step. Formulations and operating procedures must be strictiy foHowed. Reaction vessels must be weH designed. Mistakes made during copolymerization are rarely corrected during functionalization. 

As a family of resins originally developed in the early twentieth century, the nature and potential of phenoHc resins have been explored thoroughly to produce an extensive body of technical Hterature (1 8). A symposium sponsored by the American Chemical Society commemorated 75 years of phenoHc resin chemistry in 1983 (9), and in 1987 the PhenoHc Mol ding Division of the Society of the Plastics Industry (SPI) sponsored a conference on phenoHcs in the twenty-first century (1). 

This reaction, cataly2ed by uv radiation, peroxides, and some metal catalysts, eg, platinum, led to the production of a broad range of alkyl and functional alkyl trihalosilanes. These alkylsilanes have important commercial value as monomers and are also used in the production of sihcon fluids and resins. Additional information on the chemistry of sihcon hahdes is available (19,21—24). 

Propenylphenoxy compounds have attracted much research. BMI—propenylphenoxy copolymer properties can be tailored through modification of the backbone chemistry of the propenylphenoxy comonomer. Epoxy resins may react with propenylphenol (47,48) to provide functionalized epoxies that may be low or high molecular weight, Hquid or soHd, depending on the epoxy resin employed. Bis[3-(2-propenylphenoxy)phthalimides] have been synthesized from bis(3-rutrophthalimides) and o-propenylphenol sodium involving a nucleophilic nitro displacement reaction (49). They copolymerize with bismaleimide via Diels-Alder and provide temperature-resistant networks. 

Thermoplastic composites can be classified according to use, cost, performance, or processing methods. In the following discussion of the chemistry of the resin systems utilized in composites, three classes are considered ... 

Resins for advanced composites can be classified according to their chemistry typical resins are polyaryletherketones, polysulfides, polysulfones, and a very broad class of polyimides containing one or more additional functional groups (Table 2) (see also Engineering plastics). 

The chemistry of melamine has been reviewed (63,64). Melamine, although moderately basic, is better considered as the triamide of cyanuric acid than as an aromatic amine (see Cyanuric AND ISOCYANURIC AClDs). Its reactivity is poor in nearly all reactions considered typical for amines. In part, this may be a result of its low solubiUty (see Amino resins and plastics). 

MARTIN, R. w.. The Chemistry of Phenolic Resins, John Wiley, New York (1956)... 

Chemistry of rosin. All three types of rosin consist primarily of C20 mono-carboxylic diterpene resin acids, the most common of which have the molecular formula C20H20O2. In addition, rosins contain small amounts of neutral and other acidic components (e.g. fatty acids in tall oil rosin). The neutral components of rosins are diterpene alcohols, hydrocarbons and aldehydes, and their contents generally vary between 5 and 15 wt%. 

Thepreparadonof resin-bound nitroalkenes via a micro wave-assisted Knoevenagel reacdon of resin-bound nitroacedc acid v/ith aryl and alkyl subsdnited Mdehydes is reported. The potendiil of these resin-bound nitroalkenes for apphcadon in combmatorlM chemistry is demonstratedby a Diels-Alder reacdon v/ith 2,3-dimethylbutadienefScheme 8 9) Iris Mso used for one-pot three-component tandem [4t-2 /[3t-2 reacdons v/ith ethyl vinyl ether and styrene... 

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