Trifunctional resins

Tactix 742 is a tris-(hydroxyphenyl) methane based epoxy, which can be cured for 3 h at 177°C using 38 phr DDS and postcured for 2 h at 250°C with a Tg of 299°C to give composites ideal for components near high heat zones such as aircraft engine nacelles. 

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Another significant use of 3-methylphenol is in the production of herbicides and insecticides. 2-/ f2 -Butyl-5-methylphenol is converted to the dinitro acetate derivative, 2-/ f2 -butyl-5-methyl-4,6-dinitrophenyl acetate [2487-01 -6] which is used as both a pre- and postemergent herbicide to control broad leaf weeds (42). Carbamate derivatives of 3-methylphenol based compounds are used as insecticides. The condensation of 3-methylphenol with formaldehyde yields a curable phenoHc resin. Since 3-methylphenol is trifunctional with respect to its reaction with formaldehyde, it is possible to form a thermosetting resin by the reaction of a prepolymer with paraformaldehyde or other suitable formaldehyde sources. 3-Methylphenol is also used in the production of fragrances and flavors. It is reduced with hydrogen under nickel catalysis and the corresponding esters are used as synthetic musk (see Table 3). 

An example of the importance of free-volume availabiUty on cross-linking has been reported in the evaluation of a trifunctional derivative of an ahphatic isocyanate which contains an aromatic ring, y -tetramethylxyUdene diisocyanate (TMXDI) [2778-42-9] C 4H N202, as a cross-linking agent for hydroxy-functional resins (15). 

Rather similar are the 5.5-dimethylhydantoin derivatives shown in Figure 26.18 (b, e). These resins are said to eonfer improved weathering resistance but also exhibit higher water absorption. Another trifunctional material is p-glycidyl-oxy-A,A/-diglycidylaniline. This has been recommended for adhesive systems in conjunction with benzophenonetetracarboxylic acid dianhydride, which is a room temperature curing agent in this case. 

Triethylene diamine (TEDA), 230, 231 Triethyl phosphate (TEP), 354 Trifluoroactic anhydride, 78 Trifhioromethanesulfonic acid, 334 Trifunctional monomers, 14 Triglyceride content, in resins, 60 Trihydroxymethylphenol curing process, 410... 

The functionality of precursors varying between/ = 2 and/ = 6 is considered to be low (Figure 5.2). Polyurethane networks prepared from bifunctional telechelics and trifunctional triisocyanates, diepoxide (f = 2)-diamine (f = 4) systems, diepoxide if = 4)-cyclic anhydride (/ = 2) systems, phenol (/ = 3)-formalde-hyde if = 4) resins, or melamine (/ = 6)-formaldehyde (/ = 2) resins are in this category. 

Baekeland recognized that the trifunctional phenol would produce network polymers and therefore used difunctional ortho- or para-substituted phenols to produce linear paint resins. Linear thermoplastic products are formed by alkaline or acid condensation of formaldehyde with phenol derivatives such as /r-cresol (structure 4.81). 

A solventless PMR resin became known under the designation LARC 160 (15), which could be processed as a hot melt. An exchange of MDA in PMR-15 with a liquid isomeric mixture of di- and trifunctional amines (Jeffamine 22) provided a mixture of monomeric reactants which was tacky at room temperature. In the presence of 3% methanol the resin could be processed via a hot melt process. Unfortunately, the cured resin was inferior with respect to thermal oxidative stability in comparison to PMR-15. 

For example, novolacs are phenolic resins obtained by the condensation of phenol (trifunctional monomer) and formaldehyde (bifunctional monomer), using a stoichiometric excess of phenol so that formaldehyde is completely consumed without leading to gelation. In a second step, instead of directly adding the necessary formaldehyde, the polymer network is formed by reaction with hexamethylenetetramine (a condensation product of formaldehyde and ammonia usually called hexa), through a complex set of chemical reactions (Chapter 2). 

Trifunctional (meth)acrylate fluorine-containing cyclic and acyclic silane compounds have been prepared that form photocurable resin compositions. Coatings from these resins are anti-fouling and resist organic stains from oil mist and fingerprints without detracting from surface mar resistance. 

Fig. 9a and b. TBA spectra for a series of isothermal cures showing changes in (a) the relative rigidity and (b) the logarithmic decrement vs. time. Gelation and vitrification are evident in the 80, 125 and 150 °C scans, but only vitrification is observed in the 200 and 250 °C scans. The system studied was a trifunctional epoxy resin, XD7342 [triglycidyl ether of tris(hydroxyphenyl)-methane, Dow Chemical Co.], cured with a tetrafunctional aromatic amine, DDS (diamin iphenyl sulfone, Aldrich Chemical Co.)... 

The functionality may vary with reaction conditions. For example, in base-catalyzed copolymerization of phenol and formaldehyde, both monomers are bifunctional at ambient temperature, but phenol becomes trifunctional if the temperature is raised sufficiently. Copolymerization at ambient temperature can produce essentially linear, liquid, resole-type "prepolymers" of low molecular weight. Upon acidification and heat-curing, methylene and ether crosslinks formed by the now trifunctional phenol units transform the polymer into an insoluble resin [7] (see next page). The original Bakelite was such a "thermosetting" product. 

The graphite composite fabricated from this resin and cured at 390 °C indicated that the molecular weight increased but crosslinking efficiency was low. The result was improved by use of a trifunctional amine to achieve increased crosslinking density. 

Keywords silicone resin network, masonry protection, building material, natural stone impregnation, silicone coating of mineral substrates, structure-effect principle of trifunctional silicones... 

There is reason to believe that the molecular structure of crosslinked trifunctional silanes/siloxanes may also influence the durability of the resulting silicone resin network [14, 40 - 42]. Allowance must be made here for the fact that such considerations are models in nature and also that we still do not have adequate knowledge of the molecular principles of fully condensed silicone resin networks [15]. 

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