Synthesis of a bifunctional epoxy monomer containing biphenyl moiety and properties of its cured polymer with phenol novolac

A new type of epoxy resin containing a 4,4′‐biphenylene moiety in the backbone (Bis‐EBP) is synthesized and confirmed by elemental analysis, infrared spectroscopy, and ¹H‐nuclear magnetic resonance spectroscopy. In addition, to evaluate the influence of the 4,4′‐biphenylene group in the structure, an epoxy resin having a 1,4‐phenylene group in place of the 4,4′‐biphenylene moiety (Bis‐EP) is synthesized. The cured polymer obtained through the curing reaction between the new biphenyl‐containing epoxy resin and phenol novolac is used for making a comparison of its thermal and physical properties with those obtained from Bis‐EP and bisphenol‐A (4,4′‐isopropylidenediphenyl)‐type epoxy resin (Bis‐EA). The cured polymer obtained from Bis‐EBP shows markedly higher fracture toughness of 1.32 MPa m^1/2, higher glass transition temperature, lower moisture absorption, and higher thermal decomposition temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 690–698, 1999     

Preparation and epoxy curing of p‐nonylphenol/dicyclopentadiene adducts

Phenol/dicyclopentadiene adducts were prepared from the BF₃‐catalyzed reaction of p‐nonylphenol and dicyclopentadiene at molar ratios of 2 : 1 and 3 : 2. These dicyclopentadiene‐derived novolac products contain tricyclodecane and multiple phenol functionalities. In curing with diglycidyl ether of bisphenol A, the polymer properties were compared with those cured with formaldehyde novolac or Jeffamine D‐400 amine. When p‐nonylphenol/dicyclopentadiene adducts were mixed with other commercially available curing agents such as Jeffamine D‐400 amine, the tricyclodecane functionality was introduced into the resulting epoxy network. The flexibility of the cured resin was improved due to the presence of the tricyclodecane moiety in the polymer structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2196–2206, 1999     

Synthesis of a novel epoxy resin containing pyrene moiety and thermal properties of its cured polymer with phenol novolac

A new epoxy resin containing the pyrene moiety in the backbone (3) was synthesized and confirmed by gel permeation chromatography and field‐desorption mass spectroscopy and infrared spectroscopy. In addition, to evaluate the influence of the pyrene moiety on the structure, epoxy resins having an anthrylene moiety (5) and having a phenylene moiety (7) were synthesized. The cured polymer obtained through the curing reaction between 3 and phenol novolac was used for making a comparison of its thermal properties with those obtained from 5, 7, and bisphenol‐A (4,4′‐isopropylidenediphenyl)‐type epoxy resin (Bis‐EA). The cured polymer obtained from 3 showed a higher glass transition temperature, lower coefficient of linear thermal expansion, lower moisture absorption, and markedly higher anaerobic char yield at 700°C of 37.6 wt %, which might be attributed to the higher aromaticity of 3 containing the pyrene moiety. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 528–535, 2000     

Low dielectric thermoset. I. Synthesis and properties of novel 2,6‐dimethyl phenol‐dicyclopentadiene epoxy

A 2,6‐dimethyl phenol‐dicyclopentadiene novolac was synthesized from dicyclopentadiene and 2,6‐dimethyl phenol, and the resultant 2,6‐dimethyl phenol‐dicyclopentadiene novolac was epoxidized to 2,6‐dimethyl phenol‐dicyclopentadiene epoxy. The structures of novolac and epoxy were confirmed by Fourier transform infrared spectroscopy (FTIR), elemental analysis, mass spectroscopy (MS), nuclear magnetic resonance spectroscopy (NMR), and epoxy equivalent weight titration. The synthesized 2,6‐dimethyl phenol‐dicyclopentadiene epoxy was then cured with 4,4‐diaminodiphenyl methane (DDM), phenol novolac (PN), 4,4‐diaminodiphenyl sulfone (DDS), and 4,4‐diaminodiphenyl ether (DDE). Thermal properties of cured epoxy resins were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), dielectric analysis (DEA), and thermal gravimetric analysis (TGA). These data were compared with those of the commercial bisphenol A epoxy system. Compared with the bisphenol A epoxy system, the cured 2,6‐dimethyl phenol‐ dicyclopentadiene epoxy resins exhibited lower dielectric constants (～3.0 at 1 MHz and 2.8 at 1 GHz), dissipation factors (～0.007 at 1 MHz and 0.004 at 1 GHz), glass transition temperatures (140–188°C), thermal stability (5% degradation temperature at 382–404°C), thermal expansion coefficients [50–60 ppm/°C before glass‐transition temperature (T_g)], and moisture absorption (0.9–1.1%), but higher modulus (～2 Gpa at 60°C). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2607–2613, 2003     

Synthesis,characterization, and properties of a novel epoxy resin containing both binaphthyl and biphenyl moieties

A new epoxy resin containing both binaphthyl and biphenyl moieties in the skeleton (BLBPE) was synthesized and confirmed by electrospray ionization mass spectroscopy, ¹H‐nuclear magnetic resonance spectroscopy, and infrared spectroscopy. To evaluate the combined influence of two moieties, one epoxy resin containing binaphthyl moiety and another containing biphenyl moiety were also synthesized, and a commercial biphenyl‐type epoxy resin (CER3000L) was introduced. Thermal properties of their cured polymers with phenol p‐xylene resins were characterized by differential scanning calorimetry, dynamic mechanical, and thermogravimetric analyses. The cured polymer obtained from BLBPE showed remarkably higher glass transition temperature and lower moisture absorption, as well as comprehensively excellent thermal stability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Development of a DOPO‐containing melamine epoxy hardeners and its thermal and flame‐retardant properties of cured products

In this study, a novel Schiff base of melamine used as flame‐retardant curing agent for epoxy resins, was synthesized via condensation reaction of 4‐hydroxybenzaldehyde with melamine, followed by the addition of 9,10‐dihydro‐9‐oxa‐10‐phosphaphen‐anthrene 10‐oxide (DOPO) to the resulting imine linkage. The structure of DOPO‐containing melamine Schiff base (P‐MSB) was characterized by Fourier transformed infrared spectroscopy, ¹H‐nuclear magnetic resonance (¹H‐NMR) and ³¹P‐NMR. The compound (P‐MSB) was used as a reactive flame retardant in o‐cresol formaldehyde novolac epoxy resin (CNE) to prepare flame‐retardant epoxy resins for electronic application. The thermal and flame‐retardant properties of the epoxy resins cured by various equivalent ratios phenol formaldehyde novolac (PN) and P‐MSB were investigated by the nonisothermal differential scanning calorimetry, the thermogravimetric analysis, and limiting oxygen index test. The obtained results showed that the cured epoxy resins possessed high T_g (165°C) and good thermal stability (T_5%, 321°C). Moreover, the P‐MSB/CNE systems exhibited higher limiting oxygen index (35) and more char was maintained in P‐MSB/CNE systems than that in PN/CNE system and the effective synergism of phosphorus–nitrogen indicated their excellent flame retardancy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and properties of new novolacs based on heteroatom‐bridged phenol derivatives

We describe the synthesis and properties of new novolacs prepared by addition‐condensation of heteroatom‐bridged phenol derivatives and formaldehyde. The trifluoroacetic acid‐catalyzed polymerization of equimolar amounts of bis(4‐methoxyphenyl) ether ( 1a ) and formaldehyde proceeded homogeneously to afford the polymer ( 2a ) in 49% yield (M_n 2600, M_w/M_n 1.8). From the FTIR, ¹H‐NMR, and ¹³C‐NMR spectra of 2a , it was evident that the polymer had methylene moieties‐bridged repeating units in the polymer backbone. A higher molecular weight novolac ( 2a ′) (yield 99%, M_n 16,600, M_w/M_n 12.9) could be prepared by using an excess of formaldehyde. Bis(4‐methoxyphenyl) sulfone novolac ( 2b ) (M_n 1300, M_w/M_n 1.2) and bis(4‐methoxyphenyl) sulfide novolac ( 2d ) (M_n 1200, M_w/M_n 1.9) were also prepared. However, the polymerization of bis(4‐hydroxyphenyl) sulfone ( 1c ) did not proceed, even when it was attempted under various reaction conditions. From TGA, the temperatures at 10% loss in weight (T₁₀) for 2a , 2a ′, and 2b were found to be 413, 430 and 393°C, respectively. These results suggested that heteroatom‐bridged novolacs based on phenol derivatives have good thermal stability than other organosoluble polymers; moreover, these novolacs could be expected to function as processable materials, polymer blends for engineering plastics, etc. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Novolac epoxy resins and positron annihilation

Four kinds of epoxy resins: cresol novolac, tris-hydroxyphenylmethane, tetramethylbiphenol, and bisphenol A, were cured with phenol novolac epoxy resins. Characteristics of these epoxy compounds were studied by the positron annihilation lifetime (PAL) technique. Glass transition temperatures, thermal expansion coefficients, and volume of intermolecularspace holes among polymer chains were obtained from the lifetime, τ₃, of the long-lived component of ortho-positronium. It was revealed that, at the glass transition temperature, T_g, the volume of the hole created among polymer chains expanded 1.4 times the volume at room temperature. The smaller flexural modulus of tris-hydroxyphenylmethane than that of the other samples was explained by the volume of intermolecular-space holes obtained from τ₃. Aging effects were seen in the data of the intensities, I₃, of ortho-positronium, which became smaller after heating the samples above T_g. I₃ and τ₃ were strongly affected by the density of cross-linkings, and their chemical structures. The larger the density of cross-linkings, the smaller I₃ and higher T_g were obtained. Epoxy compounds with the higher water-absorption rates had larger intermolecular-space holes. © 1993 John Wiley & Sons, Inc.     

Modification of Nylon 6 by phenol‐containing polymers

A crystalline polymer, Nylon 6, was selectively blended with various amorphous polymers containing phenolic moieties. It was found that moisture absorption by the amide group in Nylon 6 could effectively be reduced by blending with p‐Cl‐novolac at ratios as low as 2 phr (part per hundred resin). Blends of Nylon 6 with vinylphenol homopolymer and its copolymer with styrene also showed reduced moisture uptakes, but the effect was less dramatic than that of the p‐Cl‐novolac blend at all blend ratios. Novolac content in excess of 5 phr shows little additional advantage in moisture reduction. Thermal transitions of blends of Nylon 6 with poly(vinyl phenol), its copolymer, and p‐Cl‐novolac were also investigated. At a blend ratio of 5 phr, p‐Cl‐novolac caused a larger increase in glass transition temperature than the other two blends. The melting temperatures of the blends were little influenced by low levels of the amorphous polymer incorporation, but broader melting endotherms in the differential scanning calorimetry scans were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 295–300, 1999     

Interpolymer complexes and miscible blends of poly(N-vinyl-2-pyrrolidone) with novolac resin and the effect of crosslinking on related behaviour

The formation of complexes between poly(N-vinyl-2-pyrrolidone) (PVP) and novolac resin in various solvents was studied. Interpolymer complexes were formed in methanol, ethanol, 2-butanone, cyclohexanone and N,N-dimethylformamide (DMF). However, only polymer blends were obtained in N-methyl-2-pyrrolidone. The nature of the solvent has a profound influence on the degree of interpolymer association. The formation of 1/1 and 2/1 ([novolac]/[PVP]) interpolymer complexes in DMF solution was shown by measurements of reduced viscosity, conductivity and clear point. Differential scanning calorimetry revealed the single-phase nature of both the blends and the complexes of uncured novolac/PVP. The complexes had higher glass transition temperatures than those of the blends with the same composition, and the strength of the interactions between the components in the complex is much higher than that in the blend. The driving force in the formation of the interpolymer complexes between novolac and PVP is the hydrogen-bonding interaction between the hydroxyl of the novolac and the proton-accepting groups of PVP. Both the blends and the complexes were cured with 15 wt% hexamethylenetetramine relative to novolac content. The cured novolac/PVP blends were only partially miscible, but significant amounts of complex still existed in the cured complexes. Fourier transfer infrared spectroscopy revealed that the interaction between the components was rather strong for both the uncured and cured blends.     

Synthesis and properties of novel 4,4′‐biphenylene‐bridged flame‐retardant cyanate ester resin

The bisphenol‐containing 4,4′‐biphenylene moiety was prepared by the reaction of 4,4′‐bis(methoxymethyl) biphenyl with phenol in the presence of p‐toluenesulfonic acid. The bisphenol was end‐capped with the cyanate moiety by reacting with cyanogen chloride and triethylamine in dichloromethane. Their structures were confirmed by Fourier transform infrared spectroscopy, ¹H‐NMR, and elemental analysis. Thermal behaviors of cured resin were studied by differential scanning calorimetry, dynamic mechanical analysis, and TGA. The flame retardancy of cured resin was evaluated by limiting oxygen index (LOI) and vertical burning test (UL‐94 test). Because of the incorporation of rigid 4,4′‐biphenylene moiety, the cyanate ester (CE) resin shows good thermal stability (T_g is 256°C, the 5% degradation temperature is 442°C, and char yield at 800°C is 64.4%). The LOI value of the CE resin is 42.5, and the UL‐94 rating reaches V‐0. Moreover, the CE resin shows excellent dielectric property (dielectric constant, 2.94 at 1 GHz and loss dissipation factor, 0.0037 at 1 GHz) and water resistance (1.08% immersed at boiling water for 100 h). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of novel phosphorus-containing epoxy hardeners and thermal stability and flame-retardant properties of cured products

Two novel flame-retardant curing agents for epoxy resins, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-containing 4-[(phenylamino)methyl]phenol (P-Ph) and DOPO-containing Mannich-type bases (P-DDS-Ph), were synthesized by the condensation of 4-hydroxybenzaldehyde with 4-aminophenol and DDS, respectively, followed by the addition of DOPO to the resulting imine linkage. Chemical structures of these materials were characterized with FTIR, ¹H-NMR spectra, ³¹P-NMR spectra, and elemental analysis. The thermal properties and flame retardancy of o-cresol novolac epoxy resin (CNE) cured with different contents of the phosphorus-containing compounds were investigated by nonisothermal differential scanning calorimetry, thermogravimetric analysis, and limiting oxygen index (LOI). The obtained results showed that more char was formed while containing lower contents of the phosphorus-containing compounds in the P-Ph/CNE and P-DDS-Ph/CNE indicating their excellent flame retardancy. Moreover, the P-DDS-Ph/CNE exhibited higher T_g (224°C) and better thermal stability (T_10%, 330°C) than that of P-Ph/CNE. Therefore, the developed P-DDS-Ph/CNE may be potentially used as environmentally preferable products in electronic fields. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Study on a parameter to express glass‐forming relationship of phenolic–novolac resin

Chemoviscosity and glass‐forming ability of commercial phenolic–novolac resin are investigated at hexamethylenetramine (HMTA) curing agent content weight from 6 to 9%. We propose a parameter, M_k, which is based on chemoviscosity change rate and T_g0 of uncured liquid resin, to predict glass‐forming ability of the fully cured phenolic–novolac resin. It is found that M_k has a negative linear relationship with T_g∞, and the lower M_k represents the better glass‐forming ability of initial phenolic–novolac uncured liquid resin while the higher T_g∞ represents the better glass‐forming ability of fully cured resin. Further more, M_k establishes a kinetic glass‐forming relationship between liquid uncured and fully cured phenolic–novolac resin in terms of comparing with T_g∞. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Effect of Phenol/Formaldehyde Stoichiometry on the Modification of Epoxy Resin Using Epoxidized Novolacs

ABSTRACT

Unmodified epoxy resins based on bisphenol A exhibit brittleness and low elongation after cure. This article reports the results of a study for improving the properties of epoxy resin by blending with suitable thermosets. Hybrid polymer networks of diglycidyl ether of bisphenol A (DGEBA) resin with epoxidized phenolic novolac resins (EPN) containing phenol and formaldehyde in different stoichiometric ratios were prepared by physical blending. The modified epoxy resins were found to exhibit improved mechanical and thermal properties compared to the neat resin. DGEBA resins containing 2.5 to 20 wt% of epoxidized novolac resins (EPN) prepared in various stoichiometric ratios (1:0.6, 1:0.7, 1:08, and 1:0.9) between phenol and formaldehyde were cured using a room temperature amine hardener. The cured samples were tested for mechanical properties such as tensile strength, modulus, elongation, and energy absorption at break. All the EPNs are seen to improve tensile strength, elongation, and energy absorption at break of the resin. The blend of DGEBA with 10 wt% of EPN-3 (1:0.8) exhibits maximum improvement in strength, elongation, and energy absorption. EPN loading above 10 wt% is found to lower these properties in a manner similar to the behavior of any filler material. The property profiles of epoxy–EPN blends imply a toughening action by epoxidized novolac resins and the extent of modification is found to depend on the molar ratio between phenol and formaldehyde in the novolac.     

Time–temperature–transformation cure diagrams of phenol–formaldehyde and lignin–phenol–formaldehyde novolac resins

In this study, the time–temperature– transformation (TTT) cure diagrams of the curing processes of several novolac resins were determined. Each diagram corresponded to a mixture of commercial phenol–formaldehyde novolac, lignin–phenol–formaldehyde novolac, and methylolated lignin–phenol–formaldehyde novolac resins with hexamethylenetetramine as a curing agent. Thermomechanical analysis and differential scanning calorimetry techniques were applied to study the resin gelation and the kinetics of the curing process to obtain the isoconversional curves. The temperature at which the material gelled and vitrified [the glass‐transition temperature at the gel point (_gelT_g)], the glass‐transition temperature of the uncured material (without crosslinking; T_g0), and the glass‐transition temperature with full crosslinking were also obtained. On the basis of the measured of conversion degree at gelation, the approximate glass‐transition temperature/conversion relationship, and the thermokinetic results of the curing process of the resins, TTT cure diagrams of the novolac samples were constructed. The TTT diagrams showed that the lignin–novolac and methylolated lignin–novolac resins presented lower T_g0 and _gelT_g values than the commercial resin. The TTT diagram is a suitable tool for understanding novolac resin behavior during the isothermal curing process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of tetrafunctional epoxy resins and their modification with polydimethylsiloxane for electronic application

High-performance tetrafunctional epoxy resins were synthesized by reacting a suitable tetraphenols which were obtained by the condensation of appropriate dialdehyde with phenol followed by epoxidation with a halohydrin. The structure of the synthesized tetraphenols was confirmed by infrared (IR), mass spectra (MS), and nuclear magnetic resonance (NMR) spectroscopy. Dispersed silicone rubbers were used to reduce the stress of the synthesized tetrafunctional epoxy resin cured with phenolic novolac resin for electronic encapsulation application. The dynamic viscoelastic properties and morphologies of neat rubber-modified epoxy networks were investigated. The thermal mechanical properties and moisture absorption of encapsulants formulated from the synthesized tetrafunctional epoxy resins were also studied. The results indicate that a low-stress, high glass transition temperature (T_g), and low-moisture-absorbing epoxy resin system was obtained for semiconductor encapsulation application. © 1996 John Wiley & Sons, Inc.     

Synthesis of aralkyl novolac epoxy resins and their modification with polysiloxane thermoplastic polyurethane for semiconductor encapsulation

A series of phenol‐based and naphthol‐based aralkyl epoxy resins were synthesized by the condensation of p‐xylylene glycol with phenol, o‐cresol, p‐cresol, or 2‐naphthol, respectively, followed by the epoxidation of the resulting aralkyl novolacs with epichlorohydrin. The incorporation of stable dispersed polysiloxane thermoplastic polyurethane particles in the synthesized epoxy resin's matrix was achieved via epoxy ring‐opening with the isocyanate groups of urethane prepolymer to form an oxazolidone. The mechanical and dynamic viscoelastic properties of cured aralkyl novolac epoxy resins were investigated. A sea‐island structure was observed in all cured rubber‐modified epoxy networks via SEM. The results indicate that a naphthalene containing aralkyl epoxy resin has a low coefficient of thermal expansion, heat resistance, and low moisture absorption, whereas phenol aralkyl type epoxy resins are capable of imparting low elastic modulus result in a low stress matrix for encapsulation applications. Modification of the synthesized aralkyl epoxy resins with polysiloxane thermoplastic polyurethane have effectively reduced the stress of cured epoxy resins, whereas the glass transition temperature was increased because of the formation of the rigid oxazolidone structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1905–1916, 1999     

Miscibility,crystallization behavior and specific intermolecular interactions in thermosetting polymer blends of novolac epoxy resin and polyethylene glycol

Thermosetting polymer blends of novolac epoxy resin (EPN) and polyethylene glycol (PEG) were studied. The miscibility and crystallization behavior of the blends before curing reaction were investigated by polarized optical microscopy and differential scanning calorimetry (DSC). Overall uncured blend compositions were homogeneous in amorphous state. Single composition‐dependent glass‐transition temperature (T_g) for each blend could be observed, and the experimental T_g's of blends with EPN content ≥40 wt% could be explained well by the Gordon–Taylor equation. Thermal properties of blends cured with 4,4′‐diaminodiphenylmethane were also determined by DSC. The capability of PEG to crystallize in cured blends was different from that in uncured ones because of the topological effect of highly crosslinking structure. On the basis of Fourier transform infrared spectroscopy results, it was judged that there were intermolecular hydrogen‐bonding interactions between EPN and PEG in both cured and uncured blends. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Phenolic‐epoxy matrix curable by click chemistry—synthesis,curing, and syntactic foam composite properties

Alkyne functional phenolic resin was cured by azide functional epoxy resins making use of alkyne‐azide click reaction. For this, propargylated novolac (PN) was reacted with bisphenol A bisazide (BABA) and azido hydroxy propyloxy novolac (AHPN) leading to triazole‐linked phenolic‐epoxy networks. The click cure reaction was initiated at 40–65°C in presence of Cu₂I₂. Glass transition temperature (Tg) of the cured networks varied from 70°C to 75°C in the case of BABA‐PN and 75°C to 80°C in the case of AHPN‐PN. DSC and rheological studies revealed a single stage curing pattern for both the systems. The cured BABA‐PN and AHPN‐PN blends showed mass loss above 300°C because of decomposition of the triazole rings and the novolac backbone. Silica fiber‐reinforced syntactic foam composites derived from these resins possessed comparable mechanical properties and superior impact resistance vis‐a‐vis their phenolic resin analogues. The mechanical properties could be tuned by regulating the reactant stoichiometry. These low temperature addition curable resins are suited for light weight polymer composite for related applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41254.     

Some structure-property relationships in polymer flammability: Studies of phenolic-derived polymers

The investigation of the thermal degradation of the char-formaing phenol–formaldehyde resins is conducted to provide information for the systematic design of high temperature flame-resistant phenolics. Three different processes of curing are used: (1) Formaldehyde or s-trioxane is reacted with m-substituted phenol–formaldehyde oligomers under acidic conditions to give the methylene bridged-novolac resins. (2) Phenol and m-substituted phenols are reacted with CH₂O under basic conditions and then heated to give the methylene bridged resol resins. (3) p-Terephthaloyl chloride and m-and p-substituted novolac oligomers are reacted to give cured resins with ester linkages. The evaluation of the effect of various substituents indicates that the oxygen index (OI) increases from about 33 for unsubstituted phenolics to about 75 for meta-halogen substituted phenolics. The evaluation of the effect of various crosslinking agents shows that the OI for CH₂O-cured phenolics is 75 as compared to 50 for the trioxane cured phenolics and to 40 for the terephthaloyl chloride cured phenolics. A set of phenolic copolymers with different weight percentage content of halogen substituted phenols are synthesized as novolacs and resols. The results surprisingly indicate no increase of OI for the cured novolac copolymers, whereas the increase is observed for the cured resol copolymers. The activation energy for the thermooxidative degradation of the cured novolacs is about 12–15 kJ/mol lower as compared to that of the curd resols.