Synthesis and evaluation of modified urethane dimethacrylate resins with reduced water sorption and solubility.

Melamine/formaldehyde crosslinkers: characterization, network formation and crosslink degradation

Mesoporous melamine resins have been prepared using hexamethoxymethyl melamine (HMMM) as monomer and block-co-polymer Pluronic F127 as template. At acidic conditions, HMMM condenses into melamine resins, replicating the mesophases formed by the block-co-polymer template. The template can be removed by solvent extraction, yielding mesoporous melamine resins with surface areas of up to 258 m2/g and pore diameters of 7.8 nm. At a HMMM/F127 weight ratio of 1:1 an ordered mesoporous melamine resin is observed exhibiting a 2d hexagonal arrangement of cylindrical pores. The simplicity of the synthesis of these mesoporous films allows the large scale production of the materials, for example, in the form of free-standing films.

Mesoporous Melamine Resins by Soft Templating of Block-co-Polymer Mesophases

Aqueous dispersion adhesives of anionic polyurethanes which have high heat resistance and low activation temperature, even when employed without addition of a crosslinker. The polyurethane is the reaction product of an isocyanate terminated polyurethane prepolymer, and a chain extender. The polyurethane prepolymer is the reaction product of a polyol component and a diisocyanate component, the polyol component including: a sulfonated polyester polyol, a hydroxy carboxylic acid of the formula: (HO)xR(COOH)y wherein R represents a straight or branched, hydrocarbon radical containing 1 to 12 carbon atoms, and x and y represent values from 1 to 3, and a low molecular weight aliphatic diol having a molecular weight of from 60 to 400.

Aqueous polyurethane dispersion adhesive compositions with improved heat resistance

Nano-structure phosphorus-containing polyurethane dispersions: synthesis and crosslinking with melamine formaldehyde resin

The 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.

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

The mechanism of cure has been studied in coating systems comprising blends of ammonium salts of acrylic acid–acrylic ester copolymers and alkoxymethylmelamines. Experiments were conducted both on the resin components themselves and on model compounds having analogous chemical structures. Curing of the resin begins with loss of ammonia to regenerate free carboxyl groups, rather than loss of water to form amides. The alkoxy group is eliminated, and ester crosslinks are formed between the carboxyl and the methylolmelamine. Base binding studies on cured films show that the extent of crosslinking depends on the exact composition of the resin system and the presence or absence of an acidic catalyst. These variables can be adjusted to provide essentially quantitative crosslinking in the cured coating, as shown by the complete disappearance of unreacted carboxyl groups.

Crosslinking reactions of acrylic polymers containing carboxyl groups with melamine resins

Copolymers of ethylene and vinyl acetate having grafted thereon a mixture of a major proportion of one or more acrylic acid esters and a minor proportion of an ethylenically unsaturated comonomer containing a cure-site for sulfur vulcanization, and the vulcanized elastomers obtained therefrom, are disclosed.

Sulfur vulcanizable ethylene-vinyl acetate copolymer elastomers

Vulcanizable elastomeric compositions are disclosed which are the reaction products of 80 to 90 mole percent of a mixture of thiodiethanol and one or more aliphatic or cycloaliphatic diols and 20 to 10 mole percent of an aromatic or cycloaliphatic dicarboxylic acid wherein the diol content is at least 50 mole percent thiodiethanol and about 1 to 10 mole percent of a diol providing pendant allylic unsaturation.

Vulcanizable elastomers derived from thiodiethanol

Static and dynamic properties were studied in a series of polyurethane elastomers as a function of selected compositional variables such as curative system, curative level, catalyst level, and curing temperature A number of physical properties including swelling ratio, density, glass transition temperature, stress–strain behavior, and thermal conductivity were also measured on these elastomers The selected variables affect dynamic mechanical properties as well as heat buildup A good correlation was noted between the loss modulus and the heat generation The loss modulus and the heat generation decrease with decreasing curative level The elastomers cured with a mixture of triol and diamine give lower loss modulus and heat buildup than those cured with diamine alone These responses are believed due to the increase in covalent crosslinks The observed low heat generation of the elastomer cured with 02 phr azelaic acid as a catalyst level was also attributed to the high crosslink density The curing temperature, in the range investigated, appears to have very little effect on the properties Thus, the choice of formulation variables, especially the use of diamine–triol blends, provides an effective means of minimizing heat generation in dynamic applications of polyurethane elastomers

Viscoelastic properties and heat generation in urethane elastomers

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