Ortho-Substituted Ortho-Cresol Novolac Resins as an Epoxy Resin Curing Agent

A series of ortho-substituted ortho-cresol novolac resins were synthesized and used as curing agents for epoxy resins. The chemical structures of different ortho-substituted ortho-cresol novolac resins were investigated by many measurements, such as FT-IR, ¹H NMR, and ¹³C NMR. The results indicated that the ortho-cresol novolac resin with the needed proportion of ortho-substitution was synthesized through the adjustment of the reaction conditions. The studies on the curing kinetics of ortho-cresol novolac epoxy resin cured by different ortho-cresol novolac resins showed that the activation energy was reduced with an increase in the proportion of ortho-ortho methylene bridges.     

Co-condensates of resorcinols and methylol compounds for adhesive resins

A proton magnetic nuclear resonance study was performed on co-condensation reactions of resorcinol, 5-methylresorcinol and 2,5-dimethylresorcinol with methylol compounds, including ortho- and para-methylolphenol, N-methylol-caprolactam, methylol-N,N-diethylurea, methylolurea and N,N′-dimethylolurea. Spectral assignments, reaction kinetics and composition of products are discussed. The reaction in melt (120°C) with methylolphenols occurs as co-condensation in the presence of all catalysts studied. In resorcinols C4C6 substitution is favored. The rate constants of methylol disappearance clearly indicate the preferable influence of acid and alkaline catalyst (not zinc acetate) on para-methylol. The reaction with N-containing methylol compound does not give any co-condensate in the presence of alkaline catalyst. The optimum conditions for co-condensation mainly depend on reactivity of co-reagents with formaldehyde and stability of methylol compound. The quantitative amount of co-condensate with methylolcaprolactam can be obtained in melt-condensation (70°C) in the presence of acid catalyst. Because of the higher reactivity of urea, the reaction in melt (100°C) in the presence of acid catalyst does not lead to quantitative co-condensation. The condensation of methylol compound or resorcinols with formaldehyde can be avoided substantially by performing the reaction in aqueous solution at lower temperature.     

13C NMR study on the structure of ZnO-catalyzed phenol–urea–formaldehyde resin during its synthesis process

The structure of ZnO-catalyzed phenol–urea–formaldehyde (PUF) resin at different synthesis stages was analyzed by liquid ¹³C nuclear magnetic resonance spectroscopy. The results showed that the general structure of ZnO-catalyzed PUF resin was almost the same as the control PUF resin. Addition reaction between phenol and formaldehyde mainly occurred at the first stage. Total methylol groups amount between phenols of the control resin was a little lower than that of the ZnO-catalyzed PUF resin. Co-condensation and self-condensation reaction occurred at the second stage. The preparation method of ZnO-catalyzed PUF resin favored the co-condensation reaction between phenol methylol groups and urea units, while self-condensation reaction dominated the control resin at the second stage. Formaldehyde completely reacted for both the control and ZnO-catalyzed PUF final resin. The total amount of methylol and methylene groups between urea units and phenols, respectively, was almost the same for the two final resins. The total quantity of methylol groups between phenols represented a continuing downward trend from the first stage to the final stage, and the amount of methylol group (p-Ph–CH₂OH) of ZnO-catalyzed PUF resin was 30% more than that of the control resin. Total co-condensed methylene groups amount of ZnO-catalyzed PUF resin was greater than that of the control resin, which indicated that ZnO could make the urea units well incorporated into the co-condensed PUF resin.     

Boron-modified phenolic resins for high performance applications

A boron-modified phenolic resin (BPR) that flows at usable processing temperatures was prepared from the solvent-less reaction of triphenyl borate (TPB) and paraformaldehyde (PF). The reaction of TPB and PF was performed at three different resinifying temperatures, 130, 120 and 90 °C. The BPR produced at 90 °C melted upon reheating, which indicated promising processing applications for this resin. ¹H and ¹³C NMR spectra of resins from the three resinifying temperatures had the same pattern of absorptions. Substitution of methylol groups occurred at the ortho and para positions of the ester phenyl rings (4.86-4.75 ppm). Aromatic, methylene and ether linkage protons were assigned at about 7.45-6.74, 4.93-3.36 and 5.30-4.91 ppm, respectively. The synthesis of BPR from the reaction phenolic resins, produced under basic conditions (resoles) and boric acid was not feasible. The reactivity of the resoles species with each other is more favorable than that with boric acid.     

Size-exclusion Chromatography of Urea-Formaldehyde Resins

Samples of urea-formaldehyde resin have been investigated by means of size-exclusion chromatography systems: (A) Zorbax PSM packing with either pure N,N-dimethylacetamide (DMA) eluant or DMA+0.1 mol dm^?3 LiNO₃ eluant; (B) Styragel packing with DMA eluant. In addition to separation by size-exclusion, adsorption/partition and hydrodynamic effects were observed. The influence of reaction time and conditions on the production of large soluble aggregates was investigated briefly.     

Comparative Equilibrium Studies on the Sorption of Metal Ions with Macroporous Resins Containing a Liquid Ion-Exchanger

Abstract

The distribution of five metal ions (M ^m+) including Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) between dilute sulfate solutions and macroporous resins containing di(2-ethylhexyl) phosphoric acid (D2EHPA, HR) was investigated. Experiments were carried out as a function of aqueous pH, D2EHPA concentration in the resin phase, and temperature. The equilibrium data were numerically analyzed. It was shown that the sorption reaction could be described by assuming the formation of metal complexes with a general composition MR _m (HR) _n in the resin phase. For several systems a change of complex stoichiometry with temperature was observed and discussed. The apparent thermodynamic data for the formation of these complexes were also calculated.     

Curing properties of high-Ortho phenol-formaldehyde resins with co-catalysis

In this study, sodium carbonate (Na₂CO₃) was used as a catalyst to prepare high-ortho phenol-formaldehyde (HOPF) resin, and ester and carbonate curing accelerators were used to increase its curing rate. The physicochemical properties of the prepared resins and the mechanism of curing acceleration were investigated. The results showed that, with the addition of Na₂CO₃, the ortho/para ratio of methylol groups increased from 7.257 to 27.800. The gel time of the cure-accelerated HOPF resins decreased from 620 to 240 s as compared with PF resin. The bonding strength of plywood bonded with the cure-accelerated HOPF resins were all above 0.70 MPa. The curing acceleration was caused by the carbonate ions rather than the metal ions, and a temporary incorporation mechanism apparently occurred for the ester accelerators. The prepared phenolic resin had fast curing rate, low curing temperature, high thermal stability, and favorable mechanical performance, which has potential for industry applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47229.     

Structural analysis of phenolic resole resins

The chemical structure and cure characteristics of a group of phenolic resole resins were studied by means of three major analytical techniques. In particular, the effects on structure and reactivity of formaldehyde/phenol ratio and the type of reaction catalyst used were studied. Gel permeation chromatography was used to determine resin molecular weight distributions, and NMR, to determine chemical structural features. In this connection a selective oxidation procedure, converting free methylol groups to adehydes, has allowed unambiguous determination of methylene ether bridge structures to be made from the NMR data. The F/P ratio in a resole largely determines the type of molecular structures which are formed. However, triethylamine as a catalysts tends to favor methylene ether bridge formation, whereas sodium hydroxide favors methylene bridges. The rate and direction of subsequent thermal cure of the resoles prepared is shown by differential scanning calorimetry to depend markedly on the type of catalyst present during the curing stage. The DSC curing curves are interpreted in the light of the structural information provided by NMR.     

13C Nuclear Magnetic Resonance Studies of Phenol-Formaldehyde Resins 1 - Model Compounds

High resolution ¹³C n.m.r. data are presented for a series of model compounds generated by the acid catalysed reaction of either phenol or cresol with formalin. The pure compounds prepared for this study allow unambiguous identification of features associated with ortho-ortho, ortho-para and para-para linked moieties, and hence allow analysis of the sequence structure in the typical resin. To aid assignment of the spectra a comparison is made between the predictions of the spectra using simple additivity relationships and the experimentally observed shifts. It is found that the differences between theory and experiment vary systematically with structure, and averaged correction factors are presented for various characteristic structures.     

Synthesis,Characterization and Glass Reinforced Composites of Acetone-Formaldehyde - Resorcinol Resins

Abstract

Acetone-Formaldehyde (AF) resin having methylol groups ([sbnd]CH₂OH) has been prepared and condensed with resorcinol (R) in the presence; of alcoholic alkali catalyst at varying ratios of AF:R; 1:1, 1:1.5 and 1:2. The resultant AF-R resins were characterized by elemental analysis, IR spectral studies, number average molecular weight (Mn) estimated by non-aqueous conductometric titration and thermogravimetry. The curing study of AF-R resins with Hexamethylenetetramine (HMTA) was monitored by Differential Scanning Calorimetry (DSC) and kinetic parameters were evaluated. The glass reinforced composites based on AF-R-HMTA system have also been prepared and characterized.     

Catalytic and ortho-directing effect of Zn2+, Mg2+, Ba2+, and Ca2+ metal hydroxides on the preparation of phenolic-formaldehyde resin

A one step method was employed to prepare PF (phenol-formaldehyde) resin adhesive from phenol and formaldehyde with Zn²⁺, Mg²⁺, Ba²⁺, and Ca²⁺ hydroxides as catalysts, and the physicochemical properties of the resulting polymeric material were analyzed. The viscosity of the liquid adhesive decreased at intermediate catalyst concentrations, while the polymerization rate decreased at the highest concentrations; no clear pattern could be observed between catalyst concentration and solid content. Differential scanning calorimetry (DSC) performed on the PF resin catalyzed by Ba²⁺ showed that the polymer had a curing exothermic peak at around 110?°C, while the initial curing temperatures of PF resins were affected by the type of metal hydroxide used, and were in the order Ca²⁺?<?Mg²⁺ <control sample. FTIR spectroscopy was used to monitor the degree of ortho/para substitution during the synthesis of PF resin with Ba²⁺, Ca²⁺, and Mg²⁺ hydroxides. The highest ortho/para ratio was achieved with Ba²⁺ at a concentration of 0.45?wt.%, which also resulted in the most significant increase in the polymerization rate for the formation of PF resin.     

Chitosan phosphate induced better thermal characteristics to cotton fabric

Chitosan phosphate was prepared and applied at different concentrations with and without low formaldehyde N‐methylol finishing agent (resin) to cotton fabrics. Chitosan phosphate was characterized by FTIR, nitrogen content, and phosphorus content. The so‐treated fabrics were monitored for thermogravimetric analysis (maximum decomposition temperature and residue contents after decomposition), nitrogen content, phosphorus content, tensile strength, and elongation at break. Results indicate that extent of reaction of chitosan phosphate with the cotton fabric relies on concentration of the former; increasing the concentration of the resin has practically no effect on this reaction though the resin functions as a chemical bridge between the chitosan phosphate and the cotton fabric. On the other hand, the nitrogen of the resin and the phosphorus of chitosan undergo synergetic effect and enhance the thermal properties of the treated cotton. Strength properties display higher values in the presence than in the absence of chitosan phosphate when the latter was used along with the resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2021–2026, 2007     

Quantitative 13C n.m.r. characterization of aqueous formaldehyde resins: 1. Phenol-formaldehyde resins

Phenol-formaldehyde (PF) resins which had experienced a variety of reaction conditions and/or ageing conditions were quantitatively characterized by ¹³C n.m.r. Under the specific conditions of this study, the phenol para position was favoured for reaction over the ortho position on a per site basis, particularly for condensation reactions. Increasing the reaction temperature from 23°C (14 days reaction) to 80°C (3 h reaction) did not alter the type of resin structure. Ageing PF resins resulted in extensive condensation and a drastic reduction in para-substituted methylol and hemiformal groups. This apparently contributes to a sharp reduction in the reactivity of these resins for reactions requiring methylol substituents on the ring.     

13C‐NMR study on cure‐accelerated phenol–formaldehyde resins with carbonates

Both liquid‐ and solid‐state ¹³C‐NMR spectroscopies were employed to investigate the cure‐acceleration effects of three carbonates [propylene carbonate (PC), sodium carbonate (NC), and potassium carbonate (KC)] on liquid and cured phenol–formaldehyde (PF) resins. The liquid‐phase ¹³C‐NMR spectra showed that the cure‐acceleration mechanism in the PC‐added PF resin seemed to be involved in increasing reactivity of the phenol rings, while the addition of both NC and KC into PF resin apparently resulted in the presence of ortho–ortho methylene linkages. Proton spin‐lattice rotating frame relaxation time (T_1ρH) measured by solid‐state ¹³C‐CP/MAS‐NMR spectroscopy was smaller for the cure‐accelerated PF resins than for that of the control PF resin. The result indicated that cure‐accelerated PF resins are less rigid than the control PF resin. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 841–851, 2000     

Phenol/cresol-formaldehyde resin characterization and contribution to product hardness

Lot-to-lot variations in a phenol/cresol-formaldehyde resin were fully characterized. Resin property-product hardness relationships were examined to elucidate the cause of variable hardness in product insulators and to establish acceptance criteria for the resin. A high methylol content (?CH₂OH), determined by quantitative carbon-13 nuclear magnetic resonance (¹³C-NMR), and a narrow molecular weight distribution (MWD), determined by size exclusion chromatography, were found necessary for resin to produce insulator meeting the minimum Shore D durometer specification of 40.     

13C‐NMR study on cure‐accelerated phenol‐formaldehyde resins with carbonates

Both liquid‐ and solid‐state carbon‐13–nuclear magnetic resonance (¹³C‐NMR) spectroscopies were used to investigate the cure acceleration effects of three carbonates (propylene carbonate, sodium carbonate, and potassium carbonate) on liquid and cured phenol‐formaldehyde (PF) resins. The liquid‐phase ¹³C‐NMR spectra showed that the cure acceleration mechanism in the propylene carbonate‐added PF resin seemed to be involved in increasing reactivity of the phenol rings, whereas the addition of both sodium carbonate and potassium carbonate into PF resin apparently resulted in the presence of ortho–ortho methylene linkages. Proton spin‐lattice rotating frame relaxation time (T_1ρH) measured by solid‐state ¹³C cross polarization/magic‐angle spinning NMR spectroscopy was smaller for the cure‐accelerated PF resins than that of the control PF resin. The result indicated that the cure‐accelerated PF resins are less rigid than the control PF resin. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1284–1293, 2000     

A very simple empirical kinetic model of the acid‐catalyzed cure of urea–formaldehyde resins

The hot pressing operation is the final stage in MDF (medium density fiberboard) manufacture; the fiber mat is compressed and heated up to promote the cure of the resin. The aim of the investigations is to study the curing reactions of UF (Urea–Formaldehyde) resins as commonly used in the production of MDF, and to develop a simplified kinetic model. This investigation has combined Raman spectroscopy to study the reaction cure and ¹³C‐NMR for the quantitative and qualitative characterization of the liquid and still uncured resin. Raman spectroscopy was found very interesting for the study of the resin cure and permitted to obtain kinetic data as the basis for a simple empirical model, considering a homogeneous irreversible reaction of a single kind of methylol group and ureas with rate constants depending on their degree of substitution. Although these results can provide a better understanding of the composition and the cure of an UF resin, several issues remain open, such as the influence of the reversibility of the reactions taking place during the curing process as well as the possible formation of cyclic groups in the resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5977–5987, 2006     

The curing of UF resins studied by low‐resolution 1H‐NMR

A series of UF resins and one MUF resin were studied by low‐resolution ¹H‐NMR. The mobility of the resin during curing could be followed by measuring the spin‐spin relaxation time (T₂) with curing time. The relative curing behavior was similar to that found by traditional gel time measurements. In addition, extra features in the T₂ plots with curing time showed at what point the bulk of the condensation reactions took place. The speed of cure was also related to the chemical groups in the liquid resin, and it was found that the linear methylol groups were mainly responsible for the curing speed of the resins. By studying the curing with different hardener levels and glue concentrations it was found that a UF resin is more sensitive to the glue mix concentration than an MUF resin. A cured resin was also studied after curing to investigate postcuring effects. Water seemed to play the biggest role in the postcure, with substantial amounts present immediately after cure, which decreased with curing time and aging. For the low mol ratio resins studied here further curing reactions did not seem to play a major role in the post curing phenomenon. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 754–765, 2000     

Accelerated cure of phenol–formaldehyde resins: Studies with model compounds

2‐Hydroxymethylphenol (2‐HMP) and 4‐hydroxymethylphenol (4‐HMP) were used as model compounds to study the reactions that occur during cure of phenol–formaldehyde (PF) resin to which cure accelerators (ethyl formate, propylene carbonate, γ‐butyrolactone, and triacetin) have been added. The addition of cure accelerators significantly increased the rate of condensation reactions. The cure accelerators were consumed during the reaction, indicating that they do not act as true catalysts. Major dimeric and trimeric reaction products were isolated and their structures determined. The results are consistent with a mechanism in which the hydroxymethyl group of 2‐HMP (or 4‐HMP) is first transesterified by the cure accelerator. The ester group is then displaced by reaction with the negatively charged ortho or para position of a second molecule (S_N2 mechanism) or is converted to a reactive quinone methide intermediate, which subsequently reacts with the negatively charged ortho or para position of a second molecule (quinone methide mechanism). When accelerators were added to the reaction mixture, the self‐condensation of 2‐HMP was faster than that of 4‐HMP. As is well documented in the literature, the exact opposite is true without added accelerators. This result would seem to indicate that the phenolic oxygen helps activate the esterified ortho‐hydroxymethyl group. The number and nature of crosslinks in a PF resin cured with added cure accelerator might be different than those in a PF resin cured without an added cure accelerator. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3256–3263, 2002     

The Coagulation of Finely-Divided Ion Exchange Resins and the Use of the Coagulated Material for Rapid Ion Removal

Abstract

Finely-ground ion exchange resin particles remove ions from solution much more rapidly than the conventional-size beads. Such finely-divided solids form suspensions when added to aqueous solutions. A method was required for rapidly removing such suspensions once ion adsorption had occurred, and to this end it is shown that the particles (-400 mesh) can be completely coagulated within a few minutes by the addition of suspensions of oppositely-charged solids. Thus anion exchange resins are coagulated by cation exchange resins (200 to 400), montmorillonite (200), kaolin (30), charcoal (10), silica (10), and glass (5), the figures representing arbitrarily defined relative coagulating abilities. Coagulating power is shown to increase markedly with decreasing particle size. Most suitable for ion removal is a mixed finely-divided resin formed by coagulation of anionic and cationic resins from pure water. The mixed resin, when added to 1 liter of 3 × 10^?4 M sodium phosphate solution removes all the phosphorus within 2 min, and when added to 1 liter of 2.5 × 10^?4 M calcium chloride, removes over 90% of the calcium within 3 min.