Studies on formaldehyde condensation resins. XII. Gelation theory for tetrafunctional amino resins

General kinetic equations for the gelation reaction of tetrafunctional amino monomer with formaldehyde are formulated according to Case's gelation theory. The ratio of the rate constant of the condensation reaction to that of the addition reaction is evaluated by applying a theoretical kinetic equation to the experimental measurements. The ratio of the rate constant for addition of an imino group to that for an amino group is also determined by combining the kinetic equation, stoichiometric relation, and expression for the gel point. The total yield of resin, the yield of sol, and the number-average molecular weight of the sol fraction are discussed.     

Studies on the thermal decomposition of thermosetting aniline-formaldehyde resins

The thermal decomposition of different aniline-formaldehyde (A-F) resins (1:1, 1:2. 1:3, 1:4 and 1:5) is studied in nitrogen and oxygen atmospheres. Values for the apparent reaction order, activation energy, pre-exponential factor are evaluated for different stages of decomposition. The validity of the linear kinetic compensation law is observed. The apparent activation energy values are higher in a nitrogen atmosphere than in an oxygen atmosphere and the higher value of the activation energy for the 1:5 A-F resin compared with the other A-F resins may be attributed to its larger cross-link density.     

Studies on formaldehyde condensation resins. XIII. Gelation of acetoguanamine–formaldehyde resin

The gelation reaction of acetoguanamine with formaldehyde was investigated in the light of the gelation theory for tetrafunctional amino resins described in the previous paper. The gel time and extents of reaction of formaldehyde, amino groups, and imino groups varied with the molar ratio in the feed, but values of K (the ratio of the rate constant for condensation to that for addition) and k (the ratio of the rate constant for addition of the imino group to that of the amino group) were nearly constant. When the catalyst concentration was increased, the gel time, extents of reaction of each functional group, and the values of K and k varied; in particular K increased markedly. From the results of varying the molar ratio and concentration of acidic catalyst, it was found that the number of methylol groups per molecule of acetoguanamine at the gel point was influenced by the reaction conditions but the number of methylene linkages per molecular of acetoguanamine was nearly constant at about 0.6, regardless of reaction conditions. The number-average molecular weights up to the gel point varied with the reaction conditions, but at the gel point they were all nearly constant at about 385.     

Catalytic activity of anion-exchange resins modified with metal-porphine in oxidative reactions of phenols

Anion-exchange resins modified with metal-porphine (M-Pr) have been investigated to develop a solid catalyst in the oxidative reaction of phenols by O2 in air. Co-Pr, which is easily prepared and separable from the reaction mixture, has been proved to accelerate the oxidative reaction of phenols such as 3,5-di-tertbutyl-4-hydroxyanisole. The resulting main oxidative products were identified to be quinones by using the GC-MS method.     

Physical gelation of water‐borne thermosetting resins by percolation theory—Urea‐formaldehyde,melamine‐urea‐formaldehyde,and melamine‐formaldehyde resins

Percolation and effective‐medium theories are applied for calculating the connectivity threshold of colloid particles of given shapes, observed during the physical gelation, distinguished from chemical gelation, of aminoplastic resins. The rigidity threshold, being the critical solid fraction at which a rigid network is first formed, was also calculated. For that purpose, it was assumed that the central forces that act between the colloidal particles and aggregates were not alone, thus corresponding to the case of physical gelation. It was shown that the observed change of morphology exhibited by such particles and aggregates as a function of time, from elongated to spherical, significantly delays the gel point. Consequently, the latter occurs only after a rather high fraction of solid phase (typically from 30 to 60%) is formed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 971–978, 2008     

Chemistry of novolac resins. II. Reaction of model phenols with hexamethylenetetramine

It is proposed that the reactions of hexamethylenetetramine (HMTA) with 2,4-xylenol and with 2,6-xylenol occur by different pathways. The rate of reaction and the final product distribution depend on the initial xylenol : HMTA ratio and are different in the two systems. Measured by HMTA consumption, with 2,4-xylenol the reaction rate increased with increasing xylenol : HMTA ratios, whereas with 2,6-xylenol the rate of reaction decreased with increasing 2,6-xylenol : HMTA ratio. In systems which contain both 2,4- and 2,6-xylenol, a strong preference for reaction of the HMTA with the ortho site of 2,4-xylenol was noted. This preference was apparent even in mixtures in which 2,6-xylenol was present in greater amounts than 2,4-xylenol. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1389–1398, 1997     

Computer simulation of the formation of polymer networks

Complex crosslinked polymer structures can be quite easily modeled with the aid of computers. BTOSYM's implementation of an algorithm that has been developed by Eichinger and his co-workers over the last few years is described. This algorithm allows us to model both random (as in sulfur-cured rubber) and site-specific (as in end-linked silicones) crosslinking reactions. The simulation method provides detailed information on gel points, cycle rank, modulus of elasticity and other characteristics of the networks as they are formed. Illustrative results obtained with the program are presented.     

Addition reactions of thiophenols with dihydro- and tetrahydropyridinecarbonitriles. A comparison with reactions of phenols

p-Chlorothiophenol reacts with 1-methyl-1,2,5,6-tetrahydropyridine-X-carbonitriles ( 1 , X = 4, 6 , X = 3) and with 1-methyl-1,Y-dihydropyridine-3-carbonitrile (7, Y = 6, 8 , Y = 4) to give the anticipated addition products. Geometric isomers were formed from 6 , but not from 1 , and the stereochemistry of the products has been determined. The chemistry of the reactions with p-cresol was quite different. No reaction occurred with 6 or 7 , while 8 gave a 6-(2-hydroxy-5-methylphenyl)- derivative, analogous to the unexpected product obtained previously from 1 .     

Kinetics of the metal-catalyzed condensations of phenols and polyflavonoid tannins with formaldehyde

The rate constants and free energies of activation of Zn²⁺ -accelerated and Cr³⁺ -retarded condensations of resorcinolic A rings of polyflavonoid wattle tannins, as well as of the model compounds resorcinol and catechol with formaldehyde, were determined. A quantitative indication of the effect of strong metallic ion catalysts on phenol/aldehyde reactions was obtained. Second-order kinetics have been found to fit these metallic ion-catalyzed reactions. The dependence of the tannin/formaldehyde reaction on the concentration of Zn²⁺ and Cr³⁺ under acid and alkaline reaction conditions has been investigated and the respective catalytic coefficients determined. In the presence of the metallic ions used the reaction proved to be considerably less sensitive to variations of OH-concentration, hence of pH.     

Novel thermal curing reaction of oxetane resins with polyfunctional phenols

The thermal curing reaction of polyfunctional oxetanes (oxetane resins) such as tris[4‐(3‐ethyloxetane‐3‐yl)methoxyphenyl]methane (TEOMP) and 1,3,5‐tris(3‐ethyl‐3‐oxetanylmethoxy)benzene with certain polyfunctional phenols was performed in bulk with quaternary onium salts as catalysts. The reaction proceeded smoothly at 180–220 °C and produced insoluble gel products, and the rate of gel production increased with the reaction temperature. The rate of the addition reaction of TEOMP with 3,3′,5,5′‐tetrachlorobisphenol A was also measured by IR spectroscopy, and the rate of reaction was proportional to the product of the oxetane concentration and the catalyst concentration in the film state. Furthermore, the glass‐transition temperatures and 5 and 10 wt % weight‐loss temperatures of the resulting gel products were confirmed with differential scanning calorimetry and thermogravimetric analysis, and the glass‐transition temperatures and 5 wt % weight‐loss temperatures were 127–162 °C and 323–351 °C, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2028–2037, 2005     

Organic xerogels based on condensation of different m-substituted phenols with formaldehyde

Four samples of organic xerogels have been prepared by polycondensation of different m-substituted phenols (3-aminophenol, m-cresol, phenol and resorcinol) with formaldehyde and subsequent drying. From the set of tested solvents, n-butanol has been chosen as the most suitable one. The reactivity of the m-substituted phenols was ascertained in the order phenol < m-cresol < resorcinol < 3-aminophenol. Phenol and m-cresol did not completely react with formaldehyde during polycondensation reactions. The used type of m-substituted phenol strongly influenced the properties of the final material (the appearance of the organic xerogels, the values of densities and shrinkage after drying, the amount of humidity released during drying and the carbon yield after pyrolysis). The pyrolytic process has been evaluated by TG–MS as three-step process. The first step was characterised as volatile substances loss (n-butanol and water) and mostly CO₂ evolution, the second step as evolution of the rest volatiles and the beginning of the carbonisation processes, whilst during the third step merely carbonisation reactions occurred. On the basis of all considered results, 3-aminophenol has been evaluated as the most appropriate precursor for carbon xerogel preparation. It is cheap and the most reactive; it exhibited the lowest values of density, shrinkage and humidity content as well as relatively high carbon yield.     

Formation of formal compounds in reaction of dimethyl phenols with formaldehyde

Formaldehyde was reacted with both 2,4-dimethylphenol(2,4-xyenol) and 2,6-dimethylphenol(2,6-xylenol), which are model compounds of monofunctional phenols, and the reaction products were subjected to HLC analysis to elucidate details of the formation process and bonding manner of a formal group, which can greatly affect the performance of phenol–formaldehyde resins. As a result, formal compounds of dimethylphenols were successfully separated by HLC. It was further found, as a result of tracing the reactions by HLC, that the formation of a formal group occurs at either position of the ortho and para positions, and that methylol compounds were formed following formation of the formal compounds. Furthermore, as a result of NMR analysis as well as consideration of solvation on the basis of the relative elution volumes of the nonacetylated and acetylated reaction products it was found that the formal group was added to the phenol nuclei.     

Cyclometallation reactions XII. On the effect of various leaving groups on internal metallation reactions with alkylmanganese complexes

The interaction of azobenzene and MnR(CO)₅ (R  Me, Et, CH₂Ph, CH₂-C₆Me₅, COCF₃, COCH₂C₆F₅, COCH₂OPh, Ph or C₆F₅) affords M$\text{n(C}{}_6\text{H}{}_4\text{NN}$Ph)-(CO)₄, together with a binuclear complex Mn₂(CO)₆(C₁₂H₁₀N₂) in some cases. The metallation reaction is shown to proceed most readily with Mn-(CH₂Ph)(CO)₅; with this reagent, the metallated complexes M$\text{n(C}{}_6\text{H}{}_4\text{CH}{}_2\text{P}$Me₂)-(CO)₃[PMe₂(CH₂Ph)] (two isomers) and M$\text{n(C}{}_6\text{H}{}_4\text{CH}{}_2\text{A}$sMe₂(CO)₄ have been obtained on treatment with EMe₂(CH₂Ph) (E  P and As, respectively).     

Computer simulation of network formation via crosslinking copolymerization

The topology of networks formed by radical crosslinking copolymerization is strongly dependent on the type of crosslinker chosen. By a series of computer simulations, the influence of the relative reactivities of crosslinker and monomer on the network properties was investigated. Basic condition of the simulation is the postulation of a diffusion process control of the polymerization reaction. The resulting networks are analyzed with respect to cycle rank, loop formation, dangling ends, sol fraction and crosslinker molecules reacted only by one double bond. The results of the computer simulations indicate that the reactivity of the crosslinker decisively affects the properties of the network. Particularly the cycle rank, which determines the elastic properties of the network, is influenced strongly by the reactivity of the crosslinker. A change of the cycle rank of approximately one decade was observed. The influence of the reactivity was found to be most important in the region where the reactivity of the crosslinker is less than the reactivity of the monomer.