Phenolic resins bearing maleimide groups: Synthesis and characterization

Novel phenolic novolac resins, bearing maleimide groups and capable of undergoing curing principally through the addition polymerization of these groups, were synthesized by the polymerization of a mixture of phenol and N‐(4‐hydroxy phenyl)maleimide (HPM) with formaldehyde in the presence of an acid catalyst. The polymerization conditions were optimized to get gel‐free resins. The resins were characterized by chemical, spectral, and thermal analyses. Differential scanning calorimetry and dynamic mechanical analysis revealed an unexpected two‐stage curing for these systems. Although the cure at around 275°C was attributable to the addition polymerization reaction of the maleimide groups, the exotherm at around 150 to 170°C was ascribed to the condensation reaction of the methylol groups formed in minor quantities on the phenyl ring of HPM. Polymerization studies of non‐hydroxy‐functional N‐phenyl maleimides revealed that the phenyl groups of these molecules were activated toward an electrophilic substitution reaction by the protonated methylol intermediates formed by the acid‐catalyzed reaction of phenol and formaldehyde. On a comparative scale, HPM was less reactive than phenol toward formaldehyde. The presence of the phenolic group on N‐phenyl maleimide was not needed for its copolymerization with phenol and formaldehyde. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 641–652, 2000     

Flame‐retardant epoxy resins from o‐cresol novolac epoxy cured with a phosphorus‐containing aralkyl novolac

A novel phosphorus‐containing aralkyl novolac (Ar‐DOPO‐N) was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) first with terephthaldicarboxaldehyde and subsequently with phenol. The chemical structures of the synthesized compounds were characterized with Fourier transform infrared, ¹H and ³¹P NMR, and elemental analysis. Ar‐DOPO‐N blended with phenol formaldehyde novolac was used as a curing agent for o‐cresol formaldehyde novolac epoxy, resulting in cured epoxy resins with various phosphorus contents. The epoxy resins exhibited high glass‐transition temperatures (159–177 °C), good thermal stability (>320 °C), and retardation on thermal degradation rates. High char yields and high limited oxygen indices (26–32.5) were observed, indicating the resins' good flame retardance. Using a melamine‐modified phenol formaldehyde novolac to replace phenol formaldehyde novolac in the curing composition further enhanced the cured epoxy resins' glass‐transition temperatures (160–186 °C) and limited oxygen index values (28–33.5). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2329–2339, 2002     

Introducing flexibility in urea–formaldehyde resins: Copolymerization with polyetheramines

Adhesives obtained by copolymerizing urea, formaldehyde, and difunctional polyetheramine with different molecular weights (230, 600, 900, and 2000 g mol⁻¹) are presented as a more resilient alternative to conventional urea–formaldehyde resins. Urea and polyetheramine contents were varied and the resulting resins characterized by FTIR, ¹³C‐NMR, and TGA. These resins were used for production of agglomerated cork panels, an application that demands that the binder system is flexible. Polyetheramine with molecular weight 900 g mol⁻¹ yielded the most promising agglomerated cork panel, with remarkable flexibility, good tensile strength, and with the E1 formaldehyde content specification for wood‐based panels used in construction, according to European Standard EN 12460‐5. These new thermoset adhesives have demonstrated to be capable of being used in systems where conventional formaldehyde‐based resins do not perform well due to inherent high rigidity. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1834–1843     

Phenol‐urea‐formaldehyde cocondensed resol resins: Their synthesis,curing kinetics,and network properties

Several phenol‐urea‐formaldehyde (PUF) cocondensed resol resins were synthesized by different procedures. The curing kinetics and network properties of these PUF resins were examined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). A kinetic study indicated that the activation energy values of PUF resins are generally higher than those of phenol‐formaldehyde (PF) resins during curing processes, but the curing rates of PUF resins are faster than those of PF resins. The pH values of PUF systems have a significant influence on the rate constants, although they affect the activation energy very slightly. Moreover, the dependence of activation energy on the conversion showed that there are more individual reactions with different activation energies occurring during the curing processes in PUF resins than in PF resins. The decomposition of methylene ether bridges to form methylene bridges probably occurs at high temperature in PUF resins. DMTA data indicated that the network rigidity of PUF resins is slightly lower than that of PF resin. The gel point and T_{tan δ2} transition measured by DMTA were consistent with the kinetic results obtained from the DSC data, but they were also related to the physical and mechanical properties of the network, especially with regard to the T_{tan δ2} transition. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1929–1938, 2003     

Synthesis of porous supports containing N‐(p‐hydroxyphenyl)‐ or N‐(3‐4‐dihydroxybenzyl) maleimide‐anchored titanates and application as catalysts for transesterification and epoxidation reactions

N‐(p‐acetoxyphenyl)maleimide and N‐(piperonyl)maleimide were polymerized in suspension to give macroporous supports. After deprotection of the p‐acetoxyphenyl and of the piperonyl groups, resins with pendant p‐hydroxyphenyl and catechol units were obtained. These results illustrate a very easy and convenient way to synthesize phenol and catechol containing supports. Polymer‐supported transesterification and epoxidation catalysts were obtained by immobilization of Ti(OiPr)₄ and TiCl₄. These catalysts were efficient for both reactions and could be recycled several times although some titanium leaching (≤ 20%) was observed in each case. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2879–2886, 2000     

Synthesis of polymers bearing 1,3‐benzoxazine moiety in the side chains from poly(allylamine) and their crosslinking behaviors

A polymer bearing 1,3‐benzoxazine moiety in the side chain was synthesized successfully from poly(allylamine) based on a stepwise strategy consisted of three steps: (1) treatment of poly(allylamine) with salicylaldehyde to convert the amino group in the side chain into the corresponding o‐(iminomethyl)phenol moiety, (2) reduction of the o‐(iminomethyl)phenol to obtain the corresponding o‐(aminomethyl)phenol moiety, and (3) formation of 1,3‐benzoxazine moiety by the reaction of the o‐(aminomethyl)phenol with formaldehyde. The content ratio of benzoxazine moieties and o‐(aminomethyl)phenol moieties in the polymer were tunable by varying amount of formaldehyde. The presence of o‐(aminomethyl)phenol moieties exhibited a significant promoting effect on the crosslinking reaction. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation and characterization of crosslinked poly(N,N‐diethylacrylamide‐co‐2‐hydroxyethyl methacrylate) resins and their application as support in solid‐phase peptide synthesis

Novel hydrophilic and thermosensitive poly(N,N‐diethylacrylamide‐co‐2‐hydroxyethyl methacrylate) resins were prepared by inverse suspension polymerization with N,N′‐methylenebis(acrylamide) as a crosslinker. The effects of chemical composition and degree of crosslinking on the polymerization were investigated. The polymer resins were characterized by elemental analysis, infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. The thermosensitivity of the crosslinked resins was demonstrated by their lower critical swelling temperatures. The swelling and deswelling volume of the beads in water varied depending on the molar fraction of the N,N‐diethylacrylamide. These beads swelled extensively in a variety of common solvents. They had high loadings of functional hydroxyl groups and were used as supports in the solid‐phase synthesis of an oligopeptide. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1681–1690, 2003     

Nuclear magnetic relaxation in polyolefin resins

Nuclear magnetic resonance (NMR) spin–lattice relaxation times (T₁) in various polyethylene and polypropylene resins were measured at 20 MHz and at temperatures of 130–490 K. At each temperature and for all resins, only a single value of T₁ was found, which was consistent with the occurrence of rapid spin diffusion throughout the protons attached to the polymer chains. The data were analyzed for the estimation of activation energies corresponding to molecular motion causing spin–lattice relaxation. Two well‐defined minima were found for log_e(T₁) plotted as a function of temperature for all of the polypropylene resins. Single very broad minima were found for all of the polyethylene samples. In contrast, the free induction decay signals from all of the resins following single radio‐frequency pulses were observed to contain a rapidly decaying component followed by a much more slowly decaying signal. These components were used to estimate the amount of rigid component present in the solid resins at room temperature. Samples of one high‐density polyethylene and one low‐density polyethylene were irradiated with γ radiation up to a 500‐kGy dose to examine the effects of crosslinking on the NMR relaxation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 572–584, 2002; DOI 10.1002/polb.10116     

Characterization of novolac resins based on p-tert-butylphenol by PMR spectroscopy

The direct silylation of tert-butylphenol formaldehyde resins with N,O-bis(trimethylsily)acetamide (BSA) has allowed a more complete analysis of these resins to be made with proton magnetic resonance (PMR) spectrometry. A quantitative determination of mixtures of the monomer, dimer, trimer, and tetramer may be carried out at 100 MHz.     

Synthesis and crosslinking reaction of polyacetylenes substituted with benzoxazine rings: Thermally highly stable benzoxazine resins

Novel polyacetylenes, poly( 1 ) and poly( 2 ) substituted with benzoxazine rings were synthesized by the polymerization of the corresponding acetylene monomers 1 and 2 using Rh catalysts, [(nbd)RhCl]₂, and (nbd)Rh⁺B^–Ph₄ (nbd = 2,5‐norbornadiene). The polymers were heated at 250 °C under N₂ to obtain the corresponding polybenzoxazine resins, poly( 1 )′ and poly( 2 )′ possessing polyacetylene main chains via the ring‐opening polymerization of the benzoxazine moieties. The polyacetylene backbones were maintained after crosslinking reaction at 250 °C, which were confirmed by Raman spectroscopy. The benzoxazine resins were thermally highly stable as evidenced by differential scanning calorimetry and thermogravimetric analysis. The surface of poly( 1 )′ film became hydrophilic compared to that of poly( 1 ), while the surfaces of poly( 2 ) and poly( 2 )′ films showed almost the same hydrophilicity judging from the water contact angle measurement. Poly( 1 )′ and poly( 2 )′ exhibited refractive indices smaller than those of poly( 1 ) and poly( 2 ). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1884–1893     

N‐methylolmaleimide–benzene photoadduct: A novel monomer for the synthesis of functionally modified polyimides

A novel polycyclic dihydroxy diimide monomer was synthesized through the photocycloaddition of N‐methylolmaleimide to benzene and the reaction of maleimide–benzene photoadduct with formaldehyde. The monomer, which evolved formaldehyde at about 165 °C, was subsequently used to prepare low molecular weight polyamineimides and polyurethaneimides. Soluble polyamineimides, prepared with three different aromatic diamine monomers, exhibited initial decomposition temperatures between 277 and 329 °C and glass‐transition temperatures between 180 and 219 °C. An aliphatic polyamineimide prepared from 1,6‐hexanediamine was insoluble and had glass‐transition and initial decomposition temperatures of 225 °C and 294 °C, respectively, with prior loss of formaldehyde from end groups. Polyurethaneimides prepared with two aromatic diisocyanates showed loss of formaldehyde in the approximate range of 160–169 °C followed by loss of CO₂ and glass‐transition temperatures of 219 and 233 °C. Attempts to prepare polyamideimides resulted in oligomers with a low nitrogen content. Attempts to prepare polyesterimides were unsuccessful. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2645–2651, 2000     

Acceleration of amine/epoxy reactions with N‐methyl secondary amines

Kinetic studies established that the monomethylation of a primary amine leads to significantly higher reaction rates with glycidyl ethers. The relative rates for approximately 25 amines were determined in an alcohol solvent under pseudo‐first‐order conditions (excess epoxy). The rates were referenced to aniline. For the aliphatic amines, reactivity consistently increased upon going from a primary amine to the corresponding N‐methyl secondary amine. This acceleration effect was not seen for aniline. The enhanced reactivity was also seen in curing systems, both with pure methylated amine curing agents and with complex mixtures obtained from the partial methylation of polyamines. Economically viable partially methylated amine curing agents were obtained by the reductive alkylation of commercial polyamines with formaldehyde and by the reaction of monomethylamine with 3‐(N‐methylamino)propionitrile in the presence of hydrogen and a hydrogenation catalyst. Although actual cure performance is based on a complex combination of several factors, the acceleration due to monomethylation could be a useful tool for enhancing amine/epoxy curing reactions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 921–930, 2000     

Synthesis of α‐maleimide‐ω‐dienyl heterotelechelic poly(methyl methacrylate) and its cyclization by the intramolecular Diels–Alder reaction

The synthesis of heterotelechelic poly(methyl methacrylate) (PMMA) containing α‐maleimide‐ω‐dienyl end‐groups and its subsequent intramolecular cyclization are described. The anionic polymerization of methyl methacrylate was carried out with 3‐tert‐butyldimethylsilyloxypropyl‐1‐lithium and 5‐bromo‐1,3‐pentadiene as the initiator and terminator, respectively, to synthesize α‐hydroxy‐ω‐dienyl‐PMMA. The introduction of the maleimide group to the α chain end by the reaction of the sodium salt of the polymer with N‐(3‐chloromethylphenyl)‐maleimide or N‐(3‐bromomethylphenyl)‐maleimide was not successful because of the nucleophilic addition of alkoxide to the carbon carbon double bond of the maleimide group. When 4,4′‐bismaleimidediphenylether was allowed to react with the alkoxide, the aimed α‐maleimide‐ω‐dienyl‐PMMA was obtained in a good yield. Ring closure by the intramolecular Diels–Alder reaction was carried out by the heating of the dilute polymer solution in tetrahydrofuran. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 237–246, 2000     

Alkyne‐containing phthalonitrile resins: Controlling mechanical properties by selective curing

An alkyne‐containing multiple aromatic ether‐linked phthalonitrile has been synthesized and characterized. The oligomeric phthalonitrile monomer was prepared from the reaction of an excess amount of bisphenol A with 4,4′‐dibromotolane in the presence of K₂CO₃ in a N,N‐dimethylformamide/toluene solvent mixture, followed by end‐capping with 4‐nitrophthalonitrile in a two‐step, one‐pot reaction. After being cured in the presence of bis(4‐[4‐aminophenoxy]phenyl)sulfone, the polymeric properties of the alkyne‐ and non‐alkyne‐containing oligomeric phthalonitrile resins were compared. Rheometric measurements and thermogravimetric analysis showed that the alkyne‐containing oligomeric phthalonitrile resin had better mechanical properties than an analogous non‐alkyne‐containing resin cured under identical conditions and exhibited excellent thermal and oxidative properties. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4774–4778     

Advanced flame‐retardant epoxy resins from phosphorus‐containing diol

Phosphorus‐containing epoxy systems were prepared from isobutylbis(hydroxypropyl)phosphine oxide (IHPO) and diglycidyl ether of bisphenol A (DGEBA). Diethyl‐N,N‐bis(2‐hydroxyethyl) aminomethyl phosphonate (Fyrol 6) could not be incorporated into the epoxy backbone by a reaction with either epichlorohydrin or DGEBA because intramolecular cyclization took place. The curing behavior of the IHPO–DGEBA prepolymer with two primary amines was studied, and materials with moderate glass‐transition temperatures were obtained. V‐0 materials were obtained when the resins were tested for ignition resistance with the UL‐94 test. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3510–3515, 2005     

Synthesis of polypeptides from activated urethane derivatives of α‐amino acids

A series of activated urethane‐type derivatives of α‐amino acids were synthesized and applied to polypeptide synthesis. The urethane used herein, N‐(4‐nitrophenoxycarbonyl)‐α‐amino acids 1 , were synthesized by N‐carbamoylation of γ‐benzyl‐L ‐glutamate, β‐benzyl‐L ‐aspartate, L ‐leucine, L ‐phenylalanine, and L ‐proline, with 4‐nitrophenyl chloroformate. When 1 was dissolved in N,N‐dimethylacetamide (DMAc) and heated at 60 °C, it was smoothly converted into the corresponding polypeptides with releasing 4‐nitrophenol and carbon dioxide. Spectroscopic analyses of the obtained polypeptides revealed that they were comparable with the authentic polypeptides synthesized by the ring‐opening polymerizations of amino acid N‐carboxyanhydrides (NCAs). Besides the successful polycondensations of a series of 1 , their polycondensations of 1a and other 1 were also successfully carried out to obtain the corresponding statistic copolypeptides. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2525–2535, 2008     

Effect of phenol and derivatives on atom transfer radical polymerization in the presence of air

The various phenolic compounds in conjunction with Cu(II) or Cu(I)‐N,N,N′,N″,N″‐pentamethyl diethylenetriamine (PMDETA) complexes are used to initiate atom transfer radical polymerization (ATRP) of methyl methacrylate, styrene, and methyl acrylate in the presence of a limited amount of air at temperatures in the range of 80–110 °C. Meanwhile, an effort is directed toward the elucidation of the role of phenol and derivatives in ATRP catalyzed by Cu(II)/PMDETA. The catalytic sequence involves the formation of Cu(I) by electron transfer from phenol to Cu(II); Cu(I) so formed can then react in two distinctly different ways: with organic halide to form a propagating radical or with oxygen to form copper salt in its higher oxidation state; and regeneration of Cu(I) by excess phenol. Such regeneration of Cu(I) would be expected to lead to polymerization as a result of the consumption of oxygen and phenol as well. The phenols with electron releasing groups tended to increase the conversion of the polymerization. In this respect, sodium phenoxide, a more effective additive was found, whereas p‐nitro phenol was the least effective. The obtained polymers displayed the common features of a controlled polymerization such as molecular weight control and low polydispersity index value (M_w/M_n < 1.5). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 351–359, 2004     

Phosgene‐free synthesis of polypeptides: Useful synthesis for hydrophobic polypeptides through polycondensation of activated urethane derivatives of α‐amino acids

We report a useful synthetic method of polypeptides using a series of urethane derivative of α‐amino acids (l ‐leucine, l ‐phenylalanine, l ‐valine, l ‐alanine, l ‐isoleucine, l ‐methionine), which are readily synthesized by N‐carbamoylation of tetrabutylammonium salts of α‐amino acids with diphenyl carbonate. Heating these urethane derivatives in N,N‐dimethylacetamide in the presence of n‐butylamine successfully gave the corresponding polypeptides with well‐defined structures through polycondensation with the elimination of phenol and CO₂. The matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry investigation showed that the resulting polypeptides had an n‐BuNH₂‐incorporated initiating end and an amino group at propagating end. These results strongly indicated that primary amines served as an initiator in this polycondensation system. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3726–3731     

Oligomeric cyanate ester resins: Application of a modified Ullmann synthesis in the preparation of thermosetting polymers

New multiple aromatic ether containing oligomeric cyanate ester resins have been synthesized using a modified Ullmann reaction. The oligomeric monomers were prepared by reacting resorcinol and 1,3‐ or 1,4‐dibromobenzene in the presence of potassium carbonate and a catalytic amount of a copper(I) complex in a N,N‐dimethylformamide/toluene mixture. The hydroxyl terminated intermediates were end‐capped with the cyanate moiety by reaction with cyanogen bromide in the presence of triethylamine in dry acetone. The oligomeric cyanate ester monomers are liquid at room temperature, which enhance their processability to polymeric networks. The thermo‐oxidative properties were determined for the new cyanate ester polymers as well as their storage modulus. The length of the aromatic ether spacer between the terminal cyanate ester groups was varied to investigate the effect of changing the spacer length on the properties of the material. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4559–4565, 2006     

Ring‐opening polymerization of six‐membered cyclic carbonates initiated by ethanol amine derivatives and their application to protonated or quaternary ammonium salt‐functionalized polycarbonate films

Ring‐opening polymerization (ROP) of monofunctional neopentylglycol carbonate (NPGC) with or without bifunctional di(trimethylolpropane) carbonate (DTMPC), which are derived from available corresponding alcohols, affords linear polycarbonates or covalently‐linked polycarbonate networks, respectively. A series of available ethanol amine derivatives having the different numbers of 2‐hydroxylethyl arms (N,N,N’,N’‐tetrakis(2‐hydroxyethyl)ethylenediamine, triethanolamine, N‐methyldiethanolamine or N,N‐dimethylethanolamine) initiates the ROP of NPGC to afford star‐shaped, telechelic, or linear polycarbonates bearing tertiary amines with well‐controlled molecular weights and relatively narrow polydispersities Furthermore, the copolymerization of NPGC and DTMPC in the presence of these initiators readily gives tertiary amine‐modified polycarbonate films with well transparency and flexibility. These amino groups are easily converted to ammonium salts by protonation with acids, while the quaternization with benzyl bromide is strongly affected by the steric hindrance of these amines. N‐Methyldiethanolamine or N,N‐dimethylethanolamine residues in these films react easily with benzyl bromide to give quaternary ammonium salt‐functionalized films. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 487–497