US 20040116647 A1
The invention herein disclosed comprises the use of oxazolidines, nitroalcohols, nitroamines, aminonitroalcohols, imines, hexahydropyrimidines, nitrones, hydroxylamines, nitro-olefins and nitroacetals to serve as hardeners and/or as catalysts for curing phenolic resins. The hardeners and catalysts described in the invention can be applied in any application where phenolic resins are used, including but not limited to adhesives, molding, coatings, pultrusion, prepregs, electronics, composites, fire resistant, and flame-retardant end uses.
1. A cured phenolic resin comprising:
a. a phenolic compound;
b. an aldehyde; and
c. a curing agent selected from the group consisting of oxazolidines, nitroamines, aminonitroalcohols, imines, hexahydropyrimidines, nitroalcohols, nitrones, hydroxylamines, nitro-olefins and nitroacetals.
2. The cured phenolic resin of
3. The cured phenolic resin of
4. A phenolic resin curing agent selected from the group consisting of oxazolidines, nitroalcohols, nitroamines, aminonitroalcohols, imines, hexahydropyrimidines, nitrones, hydroxylamines, nitro-olefins, nitroacetals and combinations thereof.
6. The curing agent composition of
7. A curing agent composition comprising a nitroaminoalcohol having the following structures:
8. The curing agent composition of
10. The curing agent composition of
11. The phenolic resin curing agent of
12. The phenolic resin curing agent of
13. The phenolic resin curing agent of
14. The phenolic resin curing agent of
15. The phenolic resin curing agent of
16. The phenolic resin curing agent of
17. The phenolic resin curing agent of
18. The phenolic resin curing agent of
19. The phenolic resin curing agent of
20. The phenolic resin curing agent of
21. The phenolic resin curing agent of
22. The phenolic resin curing agent of
23. The phenolic resin curing agent of
24. The phenolic resin curing agent of
25. The phenolic resin curing agent of
26. The phenolic resin curing agent of
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29. The phenolic resin curing agent of
 1. Field of the Invention
 The invention is directed toward compositions which are useful as hardeners and/or catalysts for novolac and resole phenolic resins.
 2. Description of the Prior Art
 Phenolic resins can be broadly divided into two general classes: novolacs and resoles. Novolac resins are generally characterized as being formaldehyde deficient. That is to say that the ratio of formaldehyde to phenolic groups is <1. Resole resins are generally characterized as being formaldehyde rich. That is to say that the ratio of formaldehyde to phenolic groups is >1. Both novolacs and resoles may incorporate a variety of phenolic compounds, alone or in combination, including but not limited to phenol, resorcinol, bisphenols, phloroglucinol, cresols, alkyl phenols, phenol ethers, tannins, and lignins. Similarly, other aldehydes may be substituted in whole or in part for formaldehyde, including but not limited to acetaldehyde, propionaldehyde, cyclohexanedicarboxaldehydes, benzaldehydes, furfural, and other aryl or heterocyclic aldehydes.
 Novolac resins are usually cured (crosslinked, hardened) through the use of formaldehyde, formaldehyde-donating hardener compounds, or formaldehyde equivalent compounds. Hexamethylenetetramine (hexa) and paraformaldehyde are often used commercially to cure novolac resins. In addition to a source of formaldehyde, heating and the presence of a catalyst are usually employed to accelerate the rate and extent of curing. Catalysts may include inorganic bases such as sodium or potassium hydroxide, Lewis acids such as zinc chloride, or amines such as triethylamine.
 Resoles, being formaldehyde rich, do not require additional formaldehyde to cure. Heat alone or heating in the presence of a catalyst—usually an acid—are all that are required.
 The invention herein disclosed comprises the use of oxazolidines, nitroalcohols, nitroamines, immes, aminonitroalcohols, hexahyudropyrimidines, nitrones, hydroxylamines, nitro-olefins and nitroacetals to serve as hardeners and/or as catalysts for curing phenolic resins. These hardeners include both completely new compositions as well as known compounds found to have unexpected activity. The hardeners are effective in curing a wide range of phenolic resins, including novolacs and resoles. Through the judicious selection of these hardeners, used either alone or in various combinations, it is possible to advantageously vary the processing parameters of these phenolic resin systems. Lower curing temperatures, controlled curing rates, and reduced post-cure cycles are advantageous improvements as compared to standard hexa-cured novolac or acid-catalyzed resole systems. These process improvements and reduction in cycle time have obvious economic benefits.
 The hardeners and catalysts described in this invention can be applied in any application where phenolic resins are used, including but not limited to adhesives, molding compounds, foundry materials, abrasives, friction materials, insulation, laminates, coatings, pultrusion, prepregs, electronics, composites, fire resistant, and flame-retardant end uses.
 The invention includes novel curing agents, i.e., hardeners and catalysts, drawn from a wide variety of existing and new oxazolidines, nitroalcohols, nitroacetals, nitro-olefins, nitroamines, hexahydropyrimidines, aminonitroalcohols, nitrones, hydroxylamines, and imines, as described below. The hardeners and catalysts are selected from the group consisting of pyrrolidine/2-Methyl-2-nitro-1,3-propanediol (PYRR/NMPD), diethylamine/2-Methyl-2-nitro-1,3-propanediol (DEA/NMPD), 2-furfural/2-Methyl-2-nitro-1,3-propanol (FUR/NMP), vanillin-isopropylhydroxylamine (IPHA) nitrone, 2-Methyl-2-nitro-1,3-propanediol-bis-diethylamine (NMPD-bis-DEA), Cyclohexanedicarboxaldehyde diimine (CHDA-A), 2-dimethylamino-2-hydroxymethyl-1,3-propanediol (DMTA), dimethylamine-2-Methyl-2-nitro-1,3-propanediol (DMA-NMPD), bis-(2-nitroisobutoxy)methane (NMP acetal), 5-nitro-5-hydroxymethyl-1,3-bis(isopropyl)hexahydropyrimidine (PYRIM) and formaldehyde-based nitrones from hydroxylamine, including hydroxylamine (HA), N-isopropylhydroxylamine (IPHA), N-propylhydroxylamine (PHA), hydroxylamines N-ethylhydroxylamine (EHA), N-t-butylhydroxylamine (tBuHA), and N-benzyl hydroxylamine (N-BzHA).
 Oxazolidines Zoldine® ZT-55 and ZT-65 (5-hydroxymethyl-1-aza-3,7-dioxabicyclo[3.3.0]octane), Bioban® CS-1246 (5-ethyl-1-aza-3,7-dioxabicyclo[3.3.0]octane), Bioban® CS-1135 (4,4-dimethyl-1-oxa-3-azacyclopentane), Amine CS-1991™ (5-methyl-1-aza-3,7-dioxabicyclo[3.3.0]octane), Zoldine® BBA (3-ethyl-2-isopropyl-1-oxa-3-azacyclopentane), and Bioban® N-95 (mixture of ZT, 5-hydroxymethoxymethyl-1-aza-3,7-dioxabicyclo[3.3.0]octane, and higher hydroxyalkoxymethyl oligomers), nitroalcohols tris(hydroxymethyl)-nitromethane (TN), 2-methyl-2-nitropropanol (NMP), and 2-methyl-2-nitro-1,3-propanediol (NMPD), and the hydroxylamines N-isopropylhydroxylamine (IPHA), N-ethylhydroxylamine (EHA), N-propylhydroxylamine (PHA), and N-t-butylhydroxylamine (tBuHA) were all obtained from Angus Chemical Company. The β-methyl-β-nitrostyrene, N,N-diethylhydroxylamine (DEHA), diethylamine (DEA), dimethylamine (DMA), isopropylamine (IPA), hexamethylenetetramine (HEXA), N-cyclohexylhydroxylamine (N-CyhexHA), N-benzylhydroxylamine (N-BzHA), hydroxylamine (HA), and common acids, bases, lab reagents and solvents were all commercial samples obtained from Aldrich Chemical Company. Formcel™ was obtained from Celanese. Durez PF novolac resin Varcum 29-607, Plenco PF novolac resin 13360, and Dynea PRF novolac resin 1204 were all commercially available materials. Other materials were synthesized as indicated below.
 GC Analyses:
 GC analyses were performed using a Hewlett Packard Model 5890A gas chromatograph with FID detector on a 30 meter×0.25 mm 1μ film DB-5 column.
 DSC Analyses:
 DSC analyses were performed using a TA Instruments Model Q100 differential scanning calorimeter. The DSC scans were run from 25° C. to 400° C. at ΔT=10° C./minute with a nitrogen flow of 50 cc/minute. Samples were prepared by dissolving the resin and hardener components in excess ethanol, then removing the solvent under vacuum at room temperature. Non-hermetic, aluminum sample pans were used. A small hole was punctured in the top before crimping.
 Gel Time Determinations:
 The gel times of resin formulations were determined by the manual hot plate method.
 A hot plate is preheated to 160° C. A small sample of the resin formulation is placed on the hot surface, and a timer is started. The sample melts and is “stroked” with a spatula until the gel point is reached—i.e., the thickening melt no longer “threads” as the spatula is stroked through it. At this point the timer is stopped. The elapsed time is recorded as the gel time. Reported values are averages of multiple determinations.
 PYRR/NMPD: 2-Methyl-2-nitro-1,3-propanediol (NMPD; 27.02 g, 0.20 moles) and pyrrolidine (14.22 g, 0.20 moles) were charged to a 250 mL flask. The mixture was stirred at room temperature under a nitrogen blanket. After about 30 minutes, an exotherm to about 40° C. was observed, and the pale yellow solution became turbid. When the exotherm subsided, the reaction mixture was heated at 60° C. for 3 hours, then at 70° C. for 12 hours. The product mixture was diluted with an equal volume of ethanol and toluene, then the solvents were removed by rotary evaporation to azeotrope off the water. The yield of PYRR/NMPD as a clear, amber oil was 33.92 g. GC analysis indicated the presence of 13 area % of unreacted NMPD.
 DEA/NMPD: NMPD (13.52 g, 0.10 moles) and diethylamine (DEA; 10.34 mL, 7.31 g, 0.10 moles) were charged to a 100 mL flask. The mixture was stirred at room temperature to give a clear, yellow solution. The solution was stirred at room temperature under a nitrogen blanket for 6 days. The solution was then diluted with an equal volume of toluene, and the solvent was removed by rotary evaporation to azeotrope off the water. A yellow oil was isolated. Some white crystals of unreacted NMPD separated from the product on standing at room temperature. The NMPD was removed by filtration. The yield of DEA/NMPD as a clear, yellow oil was 12.45 g. GC analysis showed the oil contained <3 area % of NMPD.
 FUR/NMP: Nitroethane (NE; 7.51 g, 0.10 moles), 2-furfural (19.22 g, 0.20 moles), and tetrahydrofuran (THF; 50 mL) were charged to a 250 mL flask. Amberlyst A-21 ion exchange resin (10 g) was then added. After stirring at room temperature under a nitrogen blanket for 2 weeks, the reaction mixture was filtered. The resin was washed on the filter with THF and the washings were combined with the filtrate. The solvent was removed by rotary evaporation to give 16.46 g of dark brown oil. GC/MS analysis indicated that the product was a mixture of ca. 14 area % of unreacted 2-furfural, ca. 55 area % of FUR/NMP product, and ca. 11 area % of the nitro-olefin. The crude product mixture was purified by chromatography on a silica gel column (Merck, Grade 9385, 230-400 mesh). The column was eluted with methylene chloride to remove first the nitro-olefin, and then the purified FUR/NMP product. The yield of FUR/NMP as an amber oil was 11.26 g. GC analysis indicated that all of the nitro-olefin had been removed.
 Vanillin-IPHA Nitrone: Vanillin (30.43 g, 0.20 moles), isopropylhydroxylamine (IPHA; ANGUS lot 5-H-93; 15.02 g, 0.20 moles) and methanol (50 mL) were charged to a 500 mL flask. The mixture was stirred at room temperature under a nitrogen blanket to give a clear, yellow solution. After a few minutes, a slow exotherm began, with a temperature of ca. 45° C. being reached in about 20 minutes. Shortly after the exotherm began to subside, crystalline solids began to separate from the reaction mixture. The reaction slurry was allowed to stir at room temperature overnight. The white crystalline solid product was isolated by filtration. The product was washed on the filter with a total of 100 mL of isopropanol. After drying, the yield of vanillin-IPHA nitrone product was 34.00 g. MP=178-179° C.
 NMPD-bis-DEA: NMPD (ANGUS lot ZD-06024; 27.08 g, 0.20 moles) and DEA (41.2 mL, 29.13 g, 0.40 moles) were dissolved with stirring in 40 g of distilled water in a 250 mL flask. An exotherm to about 45° C. occurred over about 10 minutes. The turbid reaction mixture solution was stirred at room temperature overnight. The reaction mixture was saturated with sodium chloride, then the layers were separated. The aqueous layer was extracted twice with equal volumes of ether. The extracts were combined and were dried over anhydrous magnesium sulfate. After filtering, the solvent was removed from the solution to give a quantitative yield of NMPD-bis-DEA as a clear yellow liquid product. GC analysis showed the product contained <3 area % of NMPD.
 CHDA-bis-IPHA nitrone: Cyclohexanedicarboxaldehyde (CHDA; mixture of 1,4 and 1,3 isomers; Dow XUR-YM-2002108630; 14.02 g, 0.10 moles) and IPHA (ANGUS lot CEC200101840-54; 15.02 g, 0.20 moles) were stirred under nitrogen with 25 g of methanol in a 250 mL flask. An exotherm to ca. 50° C. ensued as the IPHA dissolved. The exotherm quickly cooled, resulting in a clear colorless solution. The solution was stirred at room temperature for several days. The solvent was removed from the solution by rotary evaporation. Toluene was added to the resulting paste, then the mixture was subjected to rotary evaporation again to remove water as an azeotrope. The resulting CHDA-bis-IPHA nitrone was an off-white solid. The yield was 23.3 g (92%). Because it was a mixture of isomers, the product exhibited a broad melting range of 130-140° C.
 The product could be recrystallized from 10:1 toluene—isopropanol to give more discrete isomer fractions having narrower melting ranges.
 CHDA-A: This adduct was made by the reaction of CHDA with an excess of aqueous ammonium hydroxide solution.
 DMTA: This aminoalcohol was made by the reductive methylation of TN by a modification of the method described in U.S. Pat. No. 2,363,466.
 DMA-NMPD: NMPD (ANGUS lot ZD-06024; 13.57 g, 0.10 moles) was dissolved in aqueous DMA (40 wt. %, 12.6 mL, 4.53 g, 0.10 moles) with stirring at room temperature under nitrogen. Within about 30 minutes the solution became very turbid and darker yellow in color. After 5 days at room temperature the reaction mixture was a white, waxy solid. The product was slurried with methanol and toluene, then the solvents were removed by rotary evaporation. The yield of off-white DMA-NMPD was 15.4 g (95%). MP was 73-77° C. GC analysis showed about 4 area % of NMPD.
 NMP acetal: This compound was prepared according to the method described in U.S. Pat. No. 2,415,046.
 PYRIM: TN (15 g, 0.1 moles), IPA (12 g, 0.2 moles), and 36 wt. % aqueous formaldehyde (7 mL, 0.1 moles) were mixed in a flask. The mixture was cooled in an ice bath to avoid loss of the amine. It was then stirred at room temperature for 30 minutes, then it was kept at 5° C. overnight. The solid product that separated was isolated by filtration and dried in air for 4 hours. The yield of 5-nitro-5-hydroxymethyl-1,3-bis(isopropyl)hexahydropyrimidine (PYRIM) as a tan solid was 22 g (91%). MP=116-117° C.
 FORMALDEHYDE-BASED NITRONES: Formaldehyde-based nitrones from hydroxylamine (HA), IPHA, PHA, EHA, tBuHA, and N-benzylHA were all prepared by the general procedure described below:
 IPHA (7.51 g, 0.10 moles; ANGUS lot CEC200101840-54) was dissolved in 15 g of methanol, then Formcel™ (55 wt. % formaldehyde in methanol; 5.45 g, 0.10 moles; Celanese lot T-2529 (Jan. 11, 2001)) was added. The clear colorless solution was stirred at room temperature for a few minutes. GC analysis showed complete conversion to the nitrone. The resulting solution was 31 wt. % in nitrone.
 PF RESOLE RESIN RS20020437871: A resin kettle was charged with phenol (47 g, 0.5 moles), aqueous formaldehyde (37 wt. %, 80 mL, 32.06 g, 1.0 mole) and 100 mL of 4 N sodium hydroxide solution. The solution was stirred under nitrogen. An exotherm to ca. 60° C. was observed upon mixing. This subsided over about 1 hour. The reaction mixture was stirred at room temperature overnight. The reaction mixture was then heated at 90-95° C. for 1 hour. After cooling to room temperature, the mixture was brought to pH 7 with hydrochloric acid. During this neutralization the temperature of the reaction mixture was kept at ca. 15° C. by cooling the kettle in ice water. After neutralization, the reaction mixture was allowed to settle. The upper, aqueous layer was decanted from the lower, resole layer. The resole was diluted with ca. 400 mL of acetone, and the solution was dried over anhydrous magnesium sulfate. The dried solution was filtered, then the solvent was removed by rotary evaporation at room temperature. The yield of resole as a clear brown liquid was 39.0 g.
 The objective of this work was to explore the potential for hardeners (methylene donors) and catalysts/accelerators to cure PF and PRF novolac resins. Hexamethylenetetramine (hexa) was used as the baseline for comparison since it is the hardener used most extensively in this industry.
 Specific Examples of the Classes of Hardeners Cited in the Data
 The data (see Table 1 below) showed that the behavior of both of the PF novolac resins evaluated (Durez 29-607 and Plenco 13360) gave essentially the same performance with the various hardeners/catalysts tested. This indicated that the variations in cure behavior were a function of the hardener/catalyst and not of the resin. It was therefore reasonable to expect that a given hardener or catalyst would give similar performance with any PF novolac.
 The PRF resin (Dynea 1204) by virtue of its resorcinol content was more reactive than the PF novolac resins. This is a well-known property. The purpose for including it here was to determine the differences in performance between PF and PRF resins with these new hardeners/catalysts.
 Overall, with PF novolacs, the oxazolidines (OX), nitroalcohols (NA), nitro acetals (NAc), nitrones (NIT) and the aminonitroalcohols (ANA) appear to act as methylene (formaldehyde) donors. The nitroolefins (NO) are incorporated, but not as effectively as the methylene donors.
 The hydroxylamine IPHA is not capable of acting as a methylene donor. However, it exhibits catalytic activity when paired with other methylene donors such as TN and ZT, by lowering the curing onset and peak temperatures compared to the corresponding formulations without IPHA.
 Paraformaldehyde is more typically used than hexa as a hardener in PRF novolac resin formulations. Hexa was used here, however, to better allow comparisons of the new hardeners/catalysts with the PF novolac resins.
 Because of its resorcinol content, the PRF novolac resin generally exhibits higher reactivity than PF novolacs and its reactivity with OXs and ANAs in this study are different. For example, CS-1135 reacted vigorously and exothermally with the PRF novolac upon mixing at room temperature. TN and NMP acetal were more reactive with the PRF novolac than in the PF resins.
 In contrast, the ANAs appeared to be much poorer methylene donors here. The 3° amine groups present in the ANAs appear to act as catalysts in the PF novolac formulations, but this catalytic activity is overshadowed by the higher reactivity already provided by the resorcinol groups.
 In order to demonstrate the utility of this invention, a series of formulations were prepared by dissolving a commercially available PF novolac resin (Varcum 29-607 available from Durez Corp.) in ethanol along with the hardener/catalyst system to be evaluated. The solvent was then removed in a vacuum oven at ambient temperature. The resulting solid resin formulation was evaluated using a differential scanning calorimeter (DSC; TA Instruments Model Q100) to observe curing onset and peak temperatures and heats of curing for the curing events taking place. The DSC scans were run at ΔT=10° C./minute from 25° C. to 400° C. Hexamethylenetetramine (hexa) was used as a baseline since it is the hardener most commonly used in the industry. The results of these DSC analyses are shown in the below Table 2.
 The DSC results using hexa as the hardener show two exothermic curing events of nearly equal heat emission (measured as joules per gram, J/g). The ANGUS hardeners CS-1135 oxazolidine and the new nitroaminoalcohols DEA/NMPD and PYRR/NMPD showed dramatic lowering in the peak temperatures of both of the curing events. Significant cost savings may be realized through the use of lower mold temperatures allowed by using the hardeners of the invention. The combination of ZT-55 oxazolidine with new nitroaminoalcohol PYRR/NMPD resulted in almost all of the curing event taking place at <200° C. Advantageously, this provides cost savings through the elimination or dramatic reduction in the need for thermal post-curing. Oxazolidines ZT-55, CS-1991, and CS-1246, nitroalcohol TN, vanillin-IPHA nitrone, and the formulation of TN with ZT-55 all showed essentially all of the curing taking place in the 180-230° C. range. A further advantage indicated in these results is improved resin pot life at intermediate temperatures to allow for blending, resin transfer to molds, etc., followed by rapid cure at higher mold tempertures.
 Unexpectedly, the HAs of the invention have been shown to have a catalytic/accelerator effect on other methylene donors. Further, the function and utility of nitrone (NIT) intermediates as curing agents was unexpected. The ability of HAs to improve upon the performance of hexa is a truly novel and significant breakthrough.
 The question of use levels is somewhat complicated. Hexa is used as a hardener at levels of from about 3% to as much as 15 or 20% based on resin weight. The use level depends upon the end use application, the cured resin properties desired in that application, and the processing conditions to be used.
 Similarly, the ANGUS-based hardeners/methylene donors disclosed herein (OX, NA, NIT, ANA, NAm, NAc, PYRIM) can be used at different levels to achieve different processing behaviors and end use properties. As a guideline for use, we have assembled a table of “formaldehyde equivalents” for hexa and the various methylene donors we have disclosed. This table enables a user to determine how much of a chosen hardener is needed to provide the same equivalents of formaldehyde that would be provided by a given amount of hexa. In general, these new ANGUS-based hardeners would be expected to be used at from about 0.1 wt. % to as much as 75 wt. % based on resin weight.
 It should be noted that the objective of this invention was not only to discover new hardeners and catalysts that can be cured at lower temperatures than hexa-based formulation. In a broader sense, the objective was to discover new hardeners and catalysts that would lead to broader control over the processing of phenolic resins. Low temperature cure and/or a reduction in post cure baking time are certainly of value in terms of energy savings and increase in throughput. But an increase in pot life stability of a resin system can also provide significant benefits to an end user. Examples include injection molding, filament winding, and pultrusion applications in which the resin is often a melt rather than a solution. In these applications the ability to provide a resin formulation that will not advance while in the melt but will rapidly cure at an elevated cure temperature will result in more consistent parts, less resin waste, and less machine down-time to clean out advanced resin.
 Finally, the hardeners and catalysts discovered in this invention can be used in any of the applications in which phenolic resins are used, including, molding compounds, foundry materials, abrasives, friction materials, insulation, adhesives, coatings, prepregs, electronics, laminates, filament winding, pultrusion, composites, and fire resistant and flame-retardant end uses.
 A broader variety of hardeners/catalysts were evaluated alone and in combination. The results obtained in the comparative survey remain valid as shown in Table 3.
 In addition, the following observations can be made:
 Oxazolidines (OX)
 The ability of an oxazolidine to act as a methylene donor is a function of its structure.
 Oxazolidines derived from aldehydes other than formaldehyde show low activity (Zoldine BBA).
 Bis-oxazolidines such as ZT and CS-1991 are poorer methylene donors than mono-oxazolidines such as CS-1135. They have a greater affinity for formaldehyde. It is expected that mono-oxazolidines in which the N—H was replaced by N—R would also be poorer methylene donors.
 While N-95 has a higher formaldehyde equivalent weight than ZT, it has comparable reactivity. The additional formaldehyde content is not in a more active form.
 CS-1135 and CS-1991 are more effective methylene donors than hexa by DSC, and CS-1135, CS-1991, and CS-1246 showed shorter gel times than a hexa formulation containing the same formaldehyde equivalent.
 The combination of an oxazolidine (ZT) with a nitroalcohol (TN) did not improve performance. No synergy was realized.
 The combination of oxazolidines with hydroxylamines (HA) seemed to result in a lowering in the temperature of the second curing event seen by DSC, but had little positive effect on the initial curing events. This behavior was corroborated by the lack of improvement in gel times. Both N-alkyl and N,N-dialkyl HAs showed similar performance.
 The 3° amine DMTA showed DSC performance similar to HAs.
 The combination of ANAs with OX improved both DSC performance and gel time, but used in combination with HAs were similar to HAs alone.
 The combination of OXs with NAs and HAs showed improved DSC and gel time performance when OX was the predominant methylene donor.
 Aminonitroalcohols (ANA)
 The ANAs DEA-NMPD AND PYRR-NMPD had lower DSC cure onset and peak temperatures and shorter gel times than the hexa baseline formulation.
 The combination of the ANA DEA-NMPD with the nitroalcohol (NA) TN had lower DSC cure onset and peak temperatures and shorter gel time than the hexa baseline formulation. Poorer results were obtained with DMA-NMPD.
 The DSC performance of ANAs in the presence of HAs was better than with ANAs alone.
 Formulations containing ANAs, NAs, and HAs had better DSC and gel time performance than ANA-NA or ANA-HA formulations.
 Overall, ANAs appear to act as both catalysts by virtue of their Mannich base 3° amine group and as methylene donors through both their nitroalcohol group and their Mannich base group.
 Nitroalcohols (NA)
 NAs alone are weak methylene donors in PF novolac resin formulations.
 The combination of NAs with HAs did show improved DSC and gel time performance although these formulations did not perform better than the hexa baseline formulation.
 The combination of NAs with amines (Am) showed improved DSC performance with DMTA but not with DEA. It can be surmised that stronger base strength gives better performance.
 The imine (Im) CHDA-A in combination with the NA TN gave better DSC performance and shorter gel times than the hexa baseline formulation.
 Combinations of nitroamines (NAm) with NA gave DSC and gel time results that were similar to those obtained with ANAs and NAs. Performance was better than with the hexa baseline formulation.
 Nitroamines (NAm)
 The low DSC curing onset and peak temperatures observed with NMPD-bis-DEA confirmed the hypothesis that the Mannich base groups of both the ANAs and NAms act as both catalysts and as methylene donors. Performance was better than hexa baseline.
 NMPD-bis-DEA is effective in generating low DSC cure temperatures and short gel times even at catalytic concentrations (1-2%).
 Hexahydropyrimidines (PYRIM)>
 PYRIM are effective methylene donors.
 Formulations of PYRIM with HAs gave better DSC and gel time performance than the hexa baseline formulation.
 Formulations of PYRIM with HAs and NAs gave better DSC and gel time performance than the hexa baseline formulation.
 Nitrones (NIT)
 NIT derived from IPHA and CHDA or vanillin are methylene donors and are about as effective as NAs.
 The performances of the IPHA nitrones of CHDA or vanillin are not improved by formulation with NAs or ANAs.
 The formaldehyde nitrones of EHA, PHA, IPHA and tBuHA all gave better DSC performances than the hexa baseline formulation.
 The DSC performances of the formaldehyde-IPHA and the formaldehyde-PHA nitrones were comparable to those of the TN-IPHA and TN-PHA formulation. This strongly supports the intermediacy of nitrones in NA-HA formulations.
 Nitroolefins (NO)
 NOs are incorporated at high reaction temperatures.
 Formulation of NA with NO gives DSC performance comparable to the NA alone. No synergy was observed.
 Formulations of NO with both NA and HA gave DSC and gel time results that were comparable to NA-HA formulations. No synergy was observed.
 Nitroacetals (NAc)
 The DSC performance of NAcs were comparable to those of NAs.
 Hydroxylamines (HA)
 The performance of this class of compounds is discussed in combination with the other classes. HA alone was not effective in curing PF novolac.
 Imines (Im)
 CHDA-A alone was comparable in performance to TN.
 CHDA-A was effective in improving the DSC and gel time performance of NA formulations. Performance was better than hexa baseline.
 Hexa-Based Formulations (Am)
 HAs were found to be effective methylene transfer agents even in hexa formulations. This is a completely novel and unexpected result, but it does fit the performance of HAs seen above.
 IPHA in particular appears to perform catalytically with hexa. Formulations containing a fixed level of hexa with 5.0, 2.5, and 1.0% of IPHA all gave the same gel time.
 PHA, DEHA, and N-CyhexHA were less effective than IPHA, but were still improved over the baseline hexa formulation.
 Formulations of NAm with hexa were only marginally improved over the baseline hexa formulation.
 PF resole resins are made with an excess of formaldehyde. Hence, they do not require a methylene donor to effect curing. Typically, they are cured by heat alone, or with heat and an acid catalyst.
 The data shown above indicated that HAs were effective methylene transfer agents. Since resole resins are formaldehyde rich, it begged the question to determine whether HAs could effectively cure resole resins via similar methylene group transfer.
 In order to evaluate the effects of the HAs alone, a resole resin was synthesized free of residual acid or base.
 The results of this preliminary study (Table 4) showed the following:
 IPHA increased the gel time of the resole resin. Gel time increased with increasing IPHA concentration.
 OX increased the gel times of the resole resin. The less reactive ZT gave longer gel time than the more reactive CS-1135. This is probably a function of base strength.
 TN gave a gel time intermediate between ZT and CS-135. The addition of IPHA to TN actually increased gel time further.
 Resole resin catalyzed with oxalic acid had a shorter gel time than the uncatalyzed resin.
 The gel times for oxalic acid—IPHA formulations increased in gel time, with longer gel time at higher IPHA concentration.
 However, this increased gel time behavior, although unexpected, may actually be of great benefit: it may be a means of effectively improving the working pot life of resole resin formulations without impairing their performance.