Hexakis(methoxymethyl)melamine Research Articles

Novel halogen-free flame retardant thermoset from a hybrid hexakis (methoxymethyl) melamine/phosphorus-containing epoxy resin cured with phenol formaldehyde novolac

This paper describes the curing behaviours, thermal properties and flame-resistance of a novel halogen-free epoxy hybrid thermoset, prepared by the curing reaction of hexakis (methoxymethyl) melamine (HMMM), a phosphorous- containing epoxy resin (EPN-D) with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) group and phenol formaldehyde novolac (n-PF). The resultant thermosets showed high glass-transition temperatures (Tg, 123-147°C) as determined by thermal mechanical analysis (TMA), excellent thermal stability with high 5 wt% decomposition tempera- tures (Td,5% ≥ 308°C) and high char yields (Yc ≥ 39.4 wt%) from the thermogravimetric analysis (TGA). All the cured EPN- D/HMMM/n-PF hybrid resins achieved the UL 94 V-0 grade with high limited oxygen indices (LOI > 45.7). It is found that phosphorous and nitrogen elements in the cured EPN-D/HMMM/n-PF hybrid resins had a positive synergistic effect on the improvement of the flame retardancy.

Preparation and properties of epoxy/phenol formaldehyde novolac/hexakis(methoxymethyl)melamine hybrid resins from in situ polymerization

AbstractBased on the self‐condensation of hexakis(methoxymethyl)melamine (HMMM), the condensation between HMMM and phenol formaldehyde novolac resin (n‐PF), and the addition reaction of diglycidyl ether of biphenyl A (DGEBA) and n‐PF, a homogeneous, transparent hybrid thermoset was prepared via in situ polymerization of DGEBA, n‐PF, and HMMM. No phase separations were observed even for the DGEBA/n‐PF/HMMM hybrid thermoset containing 40 wt % HMMM. These hybrid thermosets had high glass‐transition temperatures (98–127°C from differential scanning calorimetry and 111–138°C from dynamic mechanical analysis), excellent thermal stability with high 5 wt % decomposition temperatures (>322°C), high char yields (>24 wt %), and improved flame retardancy with high limited oxygen indices (>28.5). The excellent overall properties of these hybrid resins may lead to their applications in high‐performance “green” electronic products. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Halogen‐free flame retardant epoxy resins from hybrids of phosphorus‐ or silicon‐containing epoxies with an amine resin

AbstractEpoxy–melamine hybrid resins were obtained from in situ polymerization of siliconized (SE500) and phosphorylated (PE690) epoxy resins with hexakis(methoxymethyl)melamine (HMMM). The hybrid resins having HMMM contents less than 15 wt % exhibited high transparency and homogeneity. The compatibilities between SE500 and melamine as well as that between PE690 and melamine were poor than the compatibility between general bisphenol‐A epoxy and melamine. Incorporation of HMMM altered the degradation mechanisms and enhanced the thermal stability of the epoxy resins, especially for PE690 based resins. Excellent flame retardant property was observed with the hybrid resins because of the SiN and PN synergisms of flame retardation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1071–1077, 2006

Preparation and properties of crosslinkable waterborne polyurethanes containing aminoplast

In order to improve the water swelling, thermal/mechanical and adhesion properties of waterborne polyurethane (WBPU), a series of the crosslinkable WBPUs containing hydrophilic ionic component, dimethylol propionic acid (20 mole%), were prepared by in-situ polymerization using a cross-linker hexakis (methoxymethyl) melamine (HMMM). Effects of the HMMM content (2, 4, and 6 wt%) and curing temperature on these properties of the crosslinked WBPUs samples were investigated. All properties were found to increase with increasing HMMM content. It was found that the optimum curing temperature of the WBPU films and adhesives was near 120°C, which was not dependent on the HMMM content.

Preparation and properties of crosslinkable waterborne polyurethanes containing aminoplast(I)

A series of crosslinkable, waterborne polyurethanes (I-WBPUs) were prepared by in-situ polymerization using isophorone diisocyanate (IPDI)/poly(tetramethylene oxide) glycol (PTMG,Mn=2,000)/ dimethylol propionic acid (DMPA)/ethylene diamine (EDA)/triethylamine (TEA)/aminoplast [hexakis(methoxymethyl)melamine (HMMM)] as a crosslinking agent. Typical crosslinkable, waterborne polyurethanes (B-WBPUs) blended from WBPU dispersion and aqueous HMMM solution was also prepared to compare with the I-WBPUs. The crosslinking reaction between WBPU and HMMM was verified using FTIR and XPS analysis. The effect of the HMMM contents on the dynamic mechanical thermal, thermal, mechanical, and adhesion properties of the I-WBPU and B-WBPU films were investigated. The storage modulus (E′), glass transition temperatures of the soft segment (Tgs) and the amorphous regions of higher order (Tgh), melting temperature (Tm), integral procedural decomposition temperature (IPDT), residual weight,T10% andT50% (the temperature where 10 and 50% weight loss occurred), tensile strength, initial modulus, hardness, and adhesive strength of both I-WBPU and B-WBPU systems increased with increasing HMMM content. However, these properties of the I-WBPU system were higher than those of the B-WBPU system at the same HMMM content. These results confirmed the in-situ polymerization used in this study to be a more effective method to improve the properties of the WBPU materials compared to the simple blending process.

Synthesis and flexibility–hardness of polymer coatings based on melamine with mesogenic groups

Liquid crystalline (LC) monomers that have mesogenic groups and hydroxyl end groups were synthesized and reacted with hexakis(methoxymethyl)melamine (HMMM) to form the mesogen-linked HMMM. The mesogen-linked HMMM was cross-linked with polyester resin on electro-galvanized steel sheets as substrates to study their potential utilities as coatings. The coatings consisting of the polyester resin and mesogen-linked HMMM showed a superior combination of film hardness and flexibility when compared to that of the coatings consisting of polyester resin and neat HMMM.

Condensation of Substituted Phenols with Hexakis(methoxymethyl)melamine: Synthesis, Characterization, and Properties of Substituted 2,4,6-Tris[3,4-dihydro-1,3-(2H)-benzoxazin-3-yl]-s-triazine Derivatives

Condensation of hexakis(methoxymethyl)melamine (HMMM) with 2,4-disubstituted and 4-substituted phenols in refluxing p-xylene catalyzed by dinonylnaphthalenedisulfonic acid (DNNDSA) gives substituted 2,4,6-tris[3,4-dihydro-1,3-(2H)-benzoxazin-3-yl]-s-triazine derivatives (1−4). These tris(benzoxazine) derivatives are characterized by infrared, 1H and 13C NMR, mass spectroscopy, and elemental analysis. Differential scanning calorimetry (DSC) studies suggest thermal cross-linking reactions of benzoxazines made from 4-substituted phenols but not for the one made from a 2,4-disubstituted phenol.

A New Class of Organic−Inorganic Sol−Gel Materials for Second-Order Nonlinear Optics

A new class of organic/inorganic sol−gel second-order nonlinear optical (NLO) materials based on the prepolymer of hexakis(methoxymethyl)melamine (HMM) and an alkoxysilane dye (ASD) has been investigated. The NLO-active alkoxysilane dye containing nitroazobenzene was incorporated into the melamine matrixes with a weight ratio of 1:1. This organic−inorganic composite (HMM/ASD) was formed via sol−gel reaction of the respective components. The optically clear (HMM/ASD) sample exhibits large second-order optical nonlinearity (d33 = 40 pm/V) after poling and curing at 220 °C for 30 min. The poled/cured HMM/ASD sample has better temporal stability at 100 °C compared to that of the poled/cured ASD, due to its higher cross-linking density. This is confirmed by dielectric relaxation results indicating that the molecular mobility associated with the glass transition was suppressed remarkably for the cured HMM/ASD sample. Furthermore, the second harmonic generation (SHG) relaxations of these NLO-active sol−gel materials were studied via biexponential function curve-fitting.

13C-NMR studies of commercial and partially self-condensed hexakis(methoxymethyl)melamine (HMMM) resins

13C-nuclear magnetic resonance (NMR) spectroscopy was employed to study the linkages in three commercial fully methylocated melamine-formaldehyde (HMMM) resins and their partially self-condensed resins by acid catalysis, in order to probe the structures linking melamine units. Distortionless enhancement by polarization transfer (DEPT) experiments show that the partially self-condensed resins contain both methylene ether and methylene linkages between melamine units. The extent of these linkages were estimated by quantitative 13C-NMR spectroscopy using inverse gated decoupling techniques. The results show that the ratios of methylene ether and methylene linkages to the triazine moiety vary from resin to resin. © 1996 John Wiley & Sons, Inc.

13C‐NMR studies of commercial and partially self‐condensed hexakis(methoxymethyl)melamine (HMMM) resins

13C‐NMR studies of commercial and partially self‐condensed hexakis(methoxymethyl)melamine (HMMM) resins

Enhanced reactivity of melamine–formaldehyde resins by fractionation. Crosslinking at ambient temperature

AbstractA commercial hexakis(methoxymethyl)melamine (HMMM) resin was fractionated (1) by crystallization of the hexane–soluble fraction from hexane and (2) by partitioning the hexane–soluble and hexane–Insoluble fractions between alumina and various solvents. Crystallization afforded hexakis(methoxymethyl)melamine (1) of 90 to 95% purity. Partitioning afforded 12 fractions with altered proportions of polar and nonpolar species; the least polar fraction was spectroscopically and chromatographically similar to the crystallized material. Relative reactivities of certain fractions were estimated by 1H NMR studies of the rates of reaction with neopentyl alcohol in the presence of catalytic amounts of p‐toluenesulfonic acid (p‐TSA). It was found that the reactivity of fractions, rich in less‐polar species, was substantially greater than that of the commercial HMMM resin, whereas reactivity of fractions, rich in polar species, was less. Reactivity was especially enhanced by removal of all active hydrogen species, notably those containing NH groups. A practical consequence of this result was that fully formylated and alkylated melamine resins could crosslink with polyols at substantially lower temperatures than the commercial HMMM resin, which contained NH groups. Therefore, room‐temperature crosslinking was feasible.

Liquid crystalline acrylic copolymers for high‐solids enamel coatings

AbstractCarboxyl functional liquid crystalline (LC) acrylic copolymers were synthesized and were compared with carboxyl functional control copolymers of M̄n about 5000–15,000. Both types were crosslinked with a hexakismethoxymethyl melamine (HMMM) resin at 150°C, a temperature below the clearing points of the LC copolymers. Birefringent phases were visible in the crosslinked films made from LC polymers. FT‐IR indicated the presence of unreacted COOH in all crosslinked materials. Unreacted COOH groups in crosslinked LC copolymers appeared only slightly higher than those in crosslinked amorphous copolymers. The potential utility of these LC copolymers as binders for thermosetting coatings was assessed. Variables studied were HMMM content, the length of PHBA grafts, Tg and M̄n of the acrylic copolymer backbone, and functionality. Optimum LC copolymers have low backbone Tg (<O°C) and low functionality (< 7.5 mol %). Cured films of such copolymers have both high hardness (> 35 KHN), high impact resistance (> 80 in. ib), excellent adhesion, and good solvent resistance.

Curing relations of hexakis(methoxymethyl)melamine and its combinations with acrylic polymers

AbstractThe curing of hexakis(methoxymethyl)melamine (HMM) alone and in blends with functionally substituted acrylic polymers was monitored by means of torsional braid analysis, infrared spectroscopy, weight change, and analysis of the volatile by‐products. HMM alone, when heated with a strong acid catalyst, forms thermoset condensation polymers which evidently have the same methylene‐bridged structure as conventional melamine‐formaldehyde resins; the major elimination product is methylal. When HMM is blended with an acrylic polymer containing methacrylic acid units, the acrylic chains are crosslinked by elimination of methanol and formation of methylene ester linkages between the acid groups and the melamine. The crosslinking reaction proceeds with or without strong acid catalysis and is many times faster than the self‐condensation of HMM. Acrylic polymers containing primary hydroxyl groups (derived from 2‐hydroxyethyl methacrylate) also undergo acid‐catalyzed reaction with HMM, and at a rate so much faster than analogous carboxylated polymers, that storage stability of the catalyzed resin becomes a serious problem. If a weaker catalyst, such as phthalic anhydride, is used, the curing reaction is very much slower. In order to develop the maximum number of new linkages, according to any of the experimental criteria, all of these systems must be heated for longer times, or at higher temperatures, than are customarily used in thermosetting resin technology. Thus the known utility and durability of such acrylic/melamine resins are achieved with only a fraction of the total number of crosslinks which are potentially capable of formation.