Phenolic resoles

Helmut Orth first reported the use of laetones to accelerate phenolic resole cure in 1957 [161]. A year later, Orth discovered that this effect could be extended to aliphatic esters as well [162], Despite the dramatic nature of the acceleration seen, Orth s observations were not applied in industry for a decade. In 1967, Sumitomo and BASF applied esters to soil grouting and wood uses [133,163, 164]. Neither of these applications were commercially successful, however, and commercial success would not occur until 1980 when Borden introduced ester-cured sand binders for foundry [165]. This technology was highly successful in UK and spread to the US, where it was applied immediately to foundry in 1981 and eventually to wood products in 1990 [119,166-173]. Esters are capable of reducing the gel times of resoles from several weeks to less than 30 s at room temperature. Both gaseous and liquid esters are applicable [119,166]. 

The mechanism of this reaction has been studied by several groups [133,174-177]. The consensus is that interaction of ester with the phenolic resole leads to a quinone methide at relatively low temperature. The quinone methide then reacts rapidly leading to cure. Scheme 11 shows the mechanism that we believe is operative. This mechanism is also supported by the work of Lemon, Murray, and Conner. It is challenged by Pizzi et al. Murray has made the most complete study available in the literature [133]. Ester accelerators include cyclic esters (such as y-butyrolactone and propylene carbonate), aliphatic esters (especially methyl formate and triacetin), aromatic esters (phthalates) and phenolic-resin esters [178]. Carbamates give analogous results but may raise toxicity concerns not usually seen with esters. 

Condensation reactions of hydroxymethyl groups on phenolic resoles and amines on melamine take place between pH 5 and 6 (Fig. 7.33). Only selfcondensations of hydroxymethyl substituents occur under strongly acidic or basic conditions. 

Alkaline phenolic resin, ester hardened. The binder is a low viscosity, highly alkaline phenolic resole resin (1.2 to 1.7%). The hardener is a liquid organic ester (18 to 25%). Sand is mixed with hardener and resin, usually in a continuous mixer. The speed of setting is controlled by the type of ester used. Low sand temperature slows the cure rate, but special hardeners are available for cold and warm sand. In 24 h compression strength can reach 4000 kPa (600 psi). 

The addition of a surfactant to liquid phenol resol oligomers affects the dispersity of the gas bubbles in the resin droplets and thus can increase the yield of hollow microspheres33,34 ... 

Binders for copper clad laminates consist of a solution of phenolic resol (part A) and of a composition obtained from a drying oil modified resol, hexamethylene-tetraamine and BPA/DC monomer or prepolymer [142, 143]. 

This paper reports on radical polymerization of MMA in phenolic resol and confirmation of the structure by measurement of d3mamic mechanical properties, scanning electron microscopy, and tensile tests, then the damping ability of these vinyl compound/phenolic IPNs is evaluated. 

Phenolic resol was synthesized by the usual procedure (See Scheme 1.) 1 mol of phenol, 1.2 mol of formaldehyde, and 0.04 mol of ammonia were heated at 70 C with vigorous stirring for 3 hours, then dehydration was carried out under vacuum. 

MMA polymerization was conducted at 70°C in phenolic resol, as shown in Scheme 2. The reaction product was poured into a large volume of methanol to precipitate the poly (methyl methacrylate) (PMMA). This was separated and washed several times with methanol, then dried at reduced pressure. 

The phenolic resol curing reaction and dimethacrylate polymerization were conducted at 170°C for 90 minutes, yielding vinyl compound/phenolic IPN. (See Scheme 3.)... 

Method 1 Poly (ethylene glycol) dimethacrylate (23G), and phenolic resol (PR) were mixed at 50°C for 10 minutes and dicumyl peroxide (DCP) was added. The polymerization and phenolic curing reactions then took place simultaneously at 170°C for 90 minutes in 200mm x 10mm x 1.5mm stainless steel mold. This product was called IPN 1. 

Method 2 First, 23G was polymerized at 70°C for 60 minutes, then the product, poly 23G, was ground finely. Poly 23G particle size was about 7.9 x 10 m in diameter. PR and the finely-powdered poly 23G were mixed at 50°C for 10 minutes and suspended in phenolic resol, then cured at 170°C for 90 minutes. This product was called IPN 2. 

Figure 1 shows time-conversion curves of MMA polymerization in phenolic resol by using various initiators. 

When BPO was used, MMA did not polymerize, and a long induction period resulted when DCP was used. However, even in phenolic resol, MMA polymerization proceeded when certain kinds of initiator were used, such as AIBN. 

Figure 2 shows time-conversion curves of MMA polymerization in phenolic resol compared with that in toluene. In phenolic resol, MMA polymerization proceeded more rapidly. However, there was a short induction period. These results suggest that by selecting the appropriate initiator, vinyl compound/phenolic IPNs can be expected. 

Next, pol3nnerization and curing reactions were conducted simultaneously. Table I shows the results of the reactions. By using various vinyl compounds and initiators, poljnnerization of over 90% and condensation conversion over 80% was obtained (as measured by IR spectrum of the cured materials). Figure 3 shows typical IR spectra of dimethacrylate and phenolic resol IPN. Reaction conversion was calculated from the peak of C-C double bond, methylol, and carbonyl groups. 

Dynamic mechanical properties of IPN 1, IPN 2, poly 23G and cured phenolic resol (CPR) were examined, in order to investigate IPN structure. 

Polymerization of 23G proceeds in a way different from the curing reaction of phenolic resol. A cross-linking reaction between 23G and phenolic resol cannot be considered because there... 

Figure 5 shows the influence of IPN component ratio on Tg. Each sample was of IPN 1 type, prepared by the simultaneous method. Increasing the amount of 23G lowered the Tg of the IPN. This result also suggests that these IPNs show a good ability to mix. The Tg of IPN containing 70% of 23G was shown to be about 0 C, just like IPN 2 synthesized by the sequential method. The structure of 70%-23G-IPN can be considered to be cured phenolic resol in a continuous poly 23G phase. So, the loss tangent peak of IPN 2 at 0°C was attributed to the structure of 23G rich IPN such as 70%-23G-IPN. 

From the results of the previous section, it is considered that IPN 1 has properties of both poly 23G and cured phenolic resol. 

Properties of vinyl compound/phenolic IPN were discussed and the following conclusions drawn. MMA radical polymerization proceeded rapidly in the presence of phenolic resol. Poly (ethylene glycol) dimethacrylate, 23G, and phenolic resol IPNs were synthesized by simultaneous radical polymerization and phenolic resol curing reaction. These IPNs had a structure of poly 23G chains and cured phenolic resol chains so well entangled with each other that the whole acted as a single phase. This type of IPN is considered to... 

Epoxy-phenoUc High molecular weight epoxy resins cross-linked with phenolic resole resins Good Very good Most widely used system Universal gold lacquer for three piece cans Shallow drawn cans... 

Figure 5-18. Dynamic mechanical behavior during the chemical cure of a phenolic resole resin at 125 °C. The noise at the beginning of the experiment results from the rapid evolution of moisture, which causes some bubbles to form. [From J. Rose, MS Thesis, University of Connecticut, Storrs, CT (2001).]...

Another noteworthy aerospace adhesive was developed during the mid-1950s. It was a combination of a phenolic resole and an epoxy resin that had a use temperature ranging up to 260 C (500 F) as shown by the last entry in Table I. The formulation consisted of the following (parts by weight (pbw)) ... 

Solid diglycidyl ether of bisphenol A (n=2-3) Phenolic resole (A-stage)... 

The adhesive is manufactured in tape form by a hot-melt process. It is a tacky solid at room temperature. The integrity is maintained by using a finely woven glass fabric scrim as the carrier. This process is an excellent example of the compromises required in the technology of formulation. Some of the high-temperature performance that is expected from the phenolic resole is sacrificed for the improved bond strength and toughness afforded from the epoxy resin. The filler is added to make the thermal coefficient of expansion of the cured adhesive more metallic in nature. Dicyandiamide is the... 

Compared with phenolic resol resins, novolacs are of only minor importance as paint binders. Novolacs are, however, still very important as binders for basic dyes in printing inks. 

Figure 2 Rate of polymerization as a function of pH for phenolic resols of different molar ratios at 120°C (old concept).

Figure 3 Schematic relationship of gel time to pH for phenolic resols (new concept).

The resin is an alkaline phenolic resol solution, which reacts with a liquid ester. The resin and the ester produce an unstable complex, causing gelilication. The complex disintegrates and causes cross-polymerisation of the resin, producing a salt and an alcohol. 

ALKALINE PHENOLIC Resol - Alkaline phenol-formaldehyde resin 1. Gas hardened (alkaline phenohc cold- box) 2. Self-setting (alkaline phenohc no bake) Gas hardened with methyl formate vapour - low Cold-set with esters - low Formaldehyde Phenol Methyl formate Formaldehyde Phenol Esters ... 

ALKALINE PHENOLIC Resol - Alkaline phenol Formaldehyde resin 1. Gas hardened 2. Self-setting Particulate matter - soot fiom the inconqrlete combustion of carbon based resins Carbon oxides Formaldehyde Phenol, cresols and xylenols Aromatics Odom may be a problem... 

Bakelite 100 is a phenolic resole from Bakelite GmbH The following are products of Shell Chemicals ... 

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