Phenolic oligomers

Phenolic oligomers are prepared by reacting phenol or substituted phenols with formaldehyde or other aldehydes. Depending on the reaction conditions (e.g., pH) and the ratio of phenol to formaldehyde, two types of phenolic resins are obtained. Novolacs are derived from an excess of phenol under neutral to acidic conditions, while reactions under basic conditions using an excess of formaldehyde result in resoles. 

This chapter emphasizes the recent mechanistic and kinetic findings on phenolic oligomer syntheses and network formation. The synthesis and characterization of both novolac- and resole-type phenolic resins and dieir resulting networks are described. Three types of networks, novolac-hexamethylenetetramine (HMTA),... 

MATERIALS FOR THE SYNTHESIS OF NOVOLAC AND RESOLE PHENOLIC OLIGOMERS... 

The molecular weights and molecular weight distributions (MWD) of phenolic oligomers have been evaluated using gel permeation chromatography (GPC),23,24 NMR spectroscopy,25 vapor pressure osmometry (VPO),26 intrinsic viscosity,27 and more recently matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).28... 

The most widely used molecular weight characterization method has been GPC, which separates compounds based on hydrodynamic volume. State-of-the-art GPC instruments are equipped with a concentration detector (e.g., differential refractometer, UV, and/or IR) in combination with viscosity or light scattering. A viscosity detector provides in-line solution viscosity data at each elution volume, which in combination with a concentration measurement can be converted to specific viscosity. Since the polymer concentration at each elution volume is quite dilute, the specific viscosity is considered a reasonable approximation for the dilute solution s intrinsic viscosity. The plot of log[r]]M versus elution volume (where [) ] is the intrinsic viscosity) provides a universal calibration curve from which absolute molecular weights of a variety of polymers can be obtained. Unfortunately, many reported analyses for phenolic oligomers and resins are simply based on polystyrene standards and only provide relative molecular weights instead of absolute numbers. 

Phenolic networks, 411 Phenolic-novolac-cured systems, 415 Phenolic novolac-epoxy networks, flame retardance of, 415 Phenolic oligomers, 375... 

Under carefully selected reaction conditions, the polyetherification of an u)-phenol oligomer with an a, o)-di(electrophilic) oligomer produces unexpectedly pure ABA triblock copolymers(11). while the polyetherification of an a, u)-di(electrophilic) oligomer with an a, u)-di (nucleophilic) oligomer represents a new method for the synthesis of perfectly alternating (AB) block copolvmers(9-12.22). 

These are produced by carbonizing foams made from various binders and micro-spheres. The binders include polyurethane1), resol1121 and novolac39) phenolic oligomers, and epoxy oligomers39), while glass 38), carbon 39), and ceramic 18) micro-spheres fillers have been used for carbonized foams. 

Table 15. Properties of carbonized syntactic foams (Novolac phenolic oligomer and carbon microspheres) S9)...

Several other types of multicomponent ol otiKric foams have been proposed Foams based on mixtures of resol phenolic oligomers with novolac oligomers with urea oligomers 2—44) polycarboxamides with polyacrylonitrile with polystyrene ... 

The temperature dependence of Tj (Fig. 13) points to a noticeable effect of the nature of adsorbent (phenolic oligomer) on the properties of adsorbed water. Firstly, the value of Ti (1-1.2 s) is nearly half that of free water (in 0.5 1). Secondly, relaxation curves sharply differ in 20- and 400-oersted fields. In the 20-oersted field the dependence Ti = f (T) is stepwise and the steepest part is observed near temperatures corresponding to the phase transition water - ice . The authors suggest that the minimum observed between 0 to -2 °C is connected with the dispersion of the relaxation time distribution. In order to confirm this assumption a classical relaxation analysis using deuterated water and the temperature dependence of longitudinal relaxation time is required. 

Such a marked variation of dielectric properties does not occur in sorbed (or desorbed) samples of monolithic phenol oligomers. Therefore, for monolithic plastics, sorption of air moisture is a secondary phenomenon, in relation to dielectric properties, whilst for plastic foams it is a primary one. 

The linear bi- and tri-phenolic oligomers formed in the condensation of p-tert-butylphenol and formaldehyde i.e. the precursors to calixarenes) have been shown to form intermolecular associated dimers even at concentrations lower than 10 These have been called hemicalixarenes (see ref. 1, pp. 53-54) and presumably play a significant role in the proclivity of the linear oligomers to form cyclic oligomers. 

The benzyl radical presumably participates ala) in an intermolecular oxidative coupling of another antioxidant, 4,4.-isopropylidenebis(2-methyl-6-tert-butyl-phenol). The resulting phenolic oligomer is further oxidized and forms the more complex product XLVIII via intramolecular C—0 bonding50. ... 

Phenolic oligomers [(-l-)-catechin and (—)-epica-techin] in soaking water from lentils, white beans and black beans, and in food by-products (almond peels)... 

Epoxy resin coatings are cured by copolymerization with acrylic, polysulfide, polyurethane, polyamine, polyamide, amino, and phenolic oligomers. 

In the presence of alcohols, the reactive species is a carbenium ion (4), formed from the hemiacetal (5) (Eq. 7). Efforts to synthesize model compounds continue the work started by Bender and coworkers. A series of new dimeric and trimeric compounds, derived from o-cresol, have been synthesized and their structures determined by IR, NMR, and elemental analysis. Additional homologues of p-cresol have been prepared by Kammerer and Niemann, to study the melting behavior of a wide range of methylene-bridged phenol oligomers. Prepolymer formation, namely novolac production, has been studied in batch and continuous flow reac-... 

Structure of glyoxal-phenol oligomers supported by NMR data (Ramires et at., 2010a). 

For phenol-formaldehyde molar ratios with a formaldehyde surplus of 1 1.2 to 2.5, resoles are created under alkaline condensation for a formaldehyde deficiency of 1 0.5 to 0.9, novolacs are created under acid condensation. During the formation of phenol oligomers, both acid and alkaline catalysis eliminate water as a condensation product. Figure 1.1. 

Nitrile rubber adhesives have been used to bond medium-to-high polarity rubbers with polyamide substrates. In an early work, nitrile rubber in solvent was treated with 10-20 parts of phosphoric acid at 50-100°C and subsequently neutralized. In more recent work, acrylic acid, methacrylic acid, dicumyl peroxide and phenol ether were added to a mixture of nitrile and formaldehyde-phenol oligomer to give a mbber-to-polyamide adhesive. 

Complementary HPLC-MS has also applied to structure elucidation in other polymers including polyethylene terephthalate [10], phenol oligomers [11], phosphoric acid containing polyarylene ethers [12], isocyanates [13], polyurethanes [14], polyamindoamine dendrimers [15], N-isopropyl acrylamide [16], oligo-(phenylene-vinylene) dimer [13], polyetherether ketone [17] and carbon blacks [18]. 

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