Isocyanate crosslinking in two‐component waterborne coatings

Two‐component isocyanate curing films (2C NCO) yield a unique combination of properties, such as excellent mechanical and chemical resistances and very good film formation. For waterborne 2C NCO curing applications, dedicated polyols and polyisocyanates have been developed. Film properties such as drying rate, hardness development and conversion of isocyanate groups were found to depend strongly on the hydroxyl group content of the polyol, and with that the amount of polyisocyanate crosslinker which is added to a formulation. Tack‐free time of a film does not, however, correlate to the conversion of isocyanate groups and, hence, to crosslink density. The crosslink density and chemical resistances increase with hydroxyl group content, although not all chemical resistances increase (coffee resistance) along this trend. This is explained with hydrolysis of isocyanates resulting in more hydrophilic urea links. Due to early vitrification of the curing film, diffusion of crosslinker and, hence, mixing of polyol and crosslinker are impaired. As a result, with increasing hydroxyl group concentration, an increasing part of the crosslinker cannot react with hydroxyl groups and can only undergo hydrolysis. © 2018 Society of Chemical Industry     

Novel water-dispersible glycidyl carbamate (GC) resins and waterborne amine-cured coatings

Water-dispersible glycidyl carbamate (GC) functional resins were synthesized and crosslinked using a water-dispersible amine to form coatings. GC functional resins are synthesized by the reaction of an isocyanate functional compound with glycidol to yield a carbamate (urethane) linkage (–NHCO–) and reactive epoxy group. The combination of both functionalities in a single resin structure imparts excellent mechanical and chemical properties to the coatings. Previous studies on the development of GC coatings have focused on solvent-borne coating systems. In this study, GC resins were modified by incorporating nonionic hydrophilic groups to produce water-dispersible resins. To determine the influence of the content of hydrophilic groups on dispersion stability, aqueous dispersions were made from a series of hydrophilically modified GC resins and characterized for particle size and dispersion stability. The composition of a typical, dispersed GC resin particle was predicted using Monte Carlo simulations. Stable GC dispersions were used to prepare amine-cured coatings. The coatings were characterized for solvent resistance, water resistance, hardness, flexibility, adhesion, and surface morphology. It was observed that GC resins were able to be dispersed in water without using any surfactant and by minimal mixing force (hand mixing) and produced coating films with good properties when crosslinked with a compatible waterborne amine crosslinker.     

2-甲基咪唑封闭型水性多异氰酸酯的合成及表征

将基于TDI的多异氰酸酯与二羟甲基丙酸(DMPA)反应,再用三乙胺(TEA)中和成盐及2-甲基咪唑(2-MI)封端后,制得一种水分散性封闭多异氰酸酯(WBI)。研究了封闭时间对封闭率的影响,采用FT-IR对封闭反应过程进行跟踪,通过TGA、DSC研究了其解封温度。结果表明,封闭反应的适宜条件为:2-MI与—NCO物质的量比为1.1～1.2∶1;反应温度60℃;反应时间2.5 h,解封温度为125.6～137.8℃。将WBI作为涂料固化剂可明显改善漆膜性能。     

PAPI的封闭与性能研究

以苯酚为封闭剂,对PAPI(多苯基多异氰酸酯)进行封闭。用二月桂酸二丁基锡为催化剂,有效地降低了PPAPI(封闭的PAPI)的脱封温度。以PPAPI为交联剂制备聚氨酯胶片,测试所得聚氨酯胶片的拉伸强度、断裂伸长率、撕裂强度、邵氏硬度等性能,讨论硫化温度、硫化时间、催化剂用量等各种因素对聚氨酯胶片性能的影响。     

高效无甲醛封端型WPU抗皱整理剂的研制

以异佛尔酮二异氰酸酯(IpDI)、聚醚二元醇(PEG-1000)为主要原料,以异丙醇为稀释剂、亚硫酸氢钠为封端剂,合成了封端型水性聚氨酯。通过探讨异氰酸酯指数(R值)、预聚温度、预聚时间、封端剂、封端温度和封端时间等因素对封端型水性聚氨酯性能的影响,得到最佳合成工艺。     

水性聚氨酯固化剂研究应用进展

介绍了聚氨酯亲水改性的4种方法,即非离子、阳离子、阴离子和混合改性。在亲水改性基础之上又讨论了封闭型水性异氰酸酯的封闭机理、封闭剂种类及特点。阐述了水性聚氨酯固化剂在双组分涂料中的应用问题及发展趋势。     

Preparation and Characterization of Blocked PAPI with Sodium Bisulfate

Abstract

In this work sodium bisulfate was used as a blocking agent to block polymethylene polyphenylisocyanate (PAPI). The particle size distribution rate and the factors influencing the stability of the blocked isocyanate emulsion were studied by varying the stirring speed. Furthermore the blocked isocyanate was characterized using a variety of methods. In order to determine the best stirring speed for preparing blocked isocyanate, a laser particle size analyzer and thermo gravimetric analysis were used to the measure particle size distribution rate and the stability of the blocked isocyanate emulsion, respectively. Experimental results show that blocked rate was 96.77%, and that the blocked isocyanate emulsion dispersion was best, and had the greatest stability, at the stirring speed of 400 r/min. Different solvents were used to wash the blocked isocyanate emulsion and the freeze-dried product. Analysis by XPS, FTIR, DSC and TGA were used to characterize the blocked products, and the blocked isocyanate was also quantitative analyzed. Results from XPS, FTIR, DSC and TGA analytical methods were able to qualitatively analyze the various components of products. Combining these results with the quantitative analysis the blocked rate of instrument analysis was found to be 86.18%. This was lower than the value of 96.77% for the blocked rate measured by chemical analysis. This work could provide a reference for researchers to distinguish the components of blocked isocyanates and provide an instrument analysis method for measuring the blocked rate.     

Self-crosslinkable graft copolymer with blocked isocyanate and other functionalities: synthesis, reactivity and application to thermoset coatings

Novel self-crosslinkable graft copolymers with complementary reactive groups, that is, a pendant blocked isocyanate in the first segment and a hydroxyl group in the second segment, were developed. In order to incorporate isocyanate functionality, m-isopenyl-,-dimethyl benzyl isocyanate (TMI) was (copolymerized with n-butyl acrylate (nBA) by radical polymerization in solution. Subsequently, a part of the isocyanate was reacted with 2-hydroxyethyl acrylate (HEA) in order to incorporate a polymerizable double bond into the copolymer molecule. After blocking the remaining isocyanate groups with methyl ethyl ketone (MEK) oxime, the polymerizable prepolymer was copolymerized with methacrylates, including hydroxyl monomers, to form the graft copolymer. Another process of preparing the graft polymer was also carried out; TMI/nBA copolymer was reacted with MEK oxime to block about 70% of isocyanate groups, then poly(ol)polymer such as poly(ester)resin was added. After the grafting reaction was completed, remaining NCOs were blocked by MEK oxime. Furthermore, by incorporating neutralizable functionalities such as carboxyl or tertiary amino groups to the second segment of the graft copolymer, self-dispersible (self-stabilized) aqueous coating vehicles were prepared. MEK oxime blocked tertiary isocyanate from TMI in the present graft polymers exhibits fairly lower deblocking temperature comparing to the similar products derived from IBM (isocyanatoethyl methacrylate) or isophorone diisocyanate-hydroxyethyl acrylate (IPDI-HEA) adduct, and hence it is possible to produce coatings curable at a lower temperature (100–120 °C) while retaining satisfactory storage stability. Owing to this curability the coatings are applicable to the products made of plastics such as components of automotives etc. Possible application to waterborne coatings is also described.     

Cure-reaction kinetics of amine-blocked polyisocyanates with alcohol using hot-stage Fourier transform infrared spectroscopy

Cure reaction between a series of N-methylaniline-blocked polyisocyanates, based on 4,4′-methylenebis(phenyl isocyanate), poly(tetrahydrofuran) and several substituted N-methylanilines, and n-decanol has been studied. The solid-state isothermal cure reaction was carried out using hot-stage FTIR spectroscopy, in the temperature range of 125–145°C. The urea carbonyl absorption band of blocked polyisocyanate moiety was used to monitor the conversion of blocked polyisocyanate into polyurethane. Kinetic and thermodynamic parameters were calculated using normalized conversion curves. The overall order of cure reaction, for each of the blocked polyisocyanates was found to be first order. Based on the results of kinetics and reaction conditions used in this study, the elimination-addition (S_N¹) mechanism was suggested for the cure reaction between N-methylaniline-blocked polyisocyanates and n-decanol. The effect of substituents present in the blocking agents on the cure reaction of N-methylaniline-blocked polyisocyanates was investigated and found that the cure reaction of N-methylaniline-blocked polyisocyanates was retarded by electron-donating substituents and facilitated by electron withdrawing substituents. The observed high negative entropy of activation value supports the formation of a four-centered, intramolecularly hydrogen-bonded ring structure during transition state of the cure reaction. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Unique waterborne systems based on TMXDI (meta) aliphatic isocyanate and TMI (meta) unsaturated isocyanate

TMXDI (meta) aliphatic isocyanate and TMI (meta) unsaturated isocyanate have been formulated into unique waterborne polymer systems. Poly(urethane) dispersions based on TMXDI (meta) aliphatic isocyanate are characterized by very low volatile organic component (VOC) levels as no solvents are required, excellent toughness and flexibility, high solids capability and low viscosity. Acrylic latexes modified with TMI (meta) unsaturated isocyanate are characterized by higher hardness levels with little loss of flexibility, and improved chemical and solvent resistance when compared to non-modified systems. Application areas for these coatings include automotive isocyanatoethylmetacrylate (OEM) and refinish, as well as trade sale paints.     

Synthesis and dissociation of amine‐blocked diisocyanates and polyurethane prepolymers

Substituted N‐methylanilines are shown to act as blocking agents for toluenediisocyanate. N‐methylaniline‐, N‐methyl‐p‐anisidine‐ and N‐methyl‐p‐nitroaniline‐blocked toluene diisocyanates have been prepared and characterized by FTIR, ¹H NMR and ¹³C NMR spectroscopies, and nitrogen content analysis. A new method for determining the minimum deblocking temperature of the blocked isocyanate is described. The method has advantages in that it can be used to find the minimum deblocking temperature of even non‐volatile blocking agents. The minimum deblocking temperature of the adducts is found to be in the following order: N‐methyl‐p‐anisidine–TDI adduct < N‐methyaniline–TDI adduct < N‐methyl‐p‐nitroaniline–TDI adduct. The anilines exhibit the same trend when they block a polyurethane prepolymer prepared using polypropylene glycol of molecular weight 2000 g mol^?1 and tolylene‐2,6‐diisocyanate. The deblocking temperatures are lower in the case of blocked prepolymers than in the blocked adducts. The blocked adducts and prepolymers are reacted with pyromellitic dianhydride (PMDA) in dimethylpropylene urea (DMPU) and the evolution of carbon dioxide is monitored to study the completion of imidization. The reaction time is in accordance with the deblocking ability of the adducts. The regeneration of the blocking agent is confirmed by gas chromatography. © 2002 Society of Chemical Industry     

对硝基苯酚封闭多亚甲基多苯基多异氰酸酯的研究

异氰酸酯作为木材胶粘剂的主要组分,需要对反应活性较高的-NCO基团进行封闭,以保证胶粘剂的适用期。采用对硝基苯酚封闭多亚甲基多苯基多异氰酸酯(PAPI),研究了投料比、加料方式、反应温度和反应时间等对封闭反应的影响,并分别采用二正丁胺法定量测定-NCO含量、FT-IR法跟踪检测-NCO、DSC法测定封闭物的解封温度。结果表明:对硝基苯酚可以用作-NCO的封闭剂;采用滴加PAPI的加料方式,当封闭剂过量10%(相对于PAPI中-NCO的物质的量而言)、反应温度为100℃和封闭反应10h时,封闭物的解封温度为106.1～112.94℃。     

Dual‐Curing of Waterborne Urethane‐Acrylate Coatings by UV and Thermal Processing

A waterbased dual‐cure urethane‐acrylate oligomer has been synthesized by polycondensation of monomers bearing hydroxyl, isocyanate and acrylate groups. To obtain a stable aqueous dispersion, carboxylate groups were grafted on the oligomer chain and the isocyanate groups were protected by a blocking agent. After water release by a brief heating, the dry films were cured either by a short UV exposure in the presence of a photoinitiator to induce the polymerization of the acrylate double bonds, or by heating up to 150 °C to release the isocyanates and promote the polycondensation by reaction with the hydroxyl groups, but mainly by a combination of UV and thermal cure. Both processes have been followed quantitatively by infrared spectroscopy to evaluate the influence of the temperature on the reaction rate and on the cure extent. The newly developed waterbased dual‐cure coatings were found to be quite resistant to accelerated weathering because of their aliphatic structure and their high crosslink density. Their light stability was substantially improved by the addition of a hydroxyphenyltriazine UV absorber and a hindered amine radical scavenger.

Thermal curing of the dual‐cure waterborne PUA formulation at a temperature of 150 °C.     

Effect of crosslinking on mechanical and viscoelastic properties of semiinterpenetrating polymer networks composed of poly(vinyl chloride) and isocyanate crosslinked networks

Semiinterpenetrating polymer networks (SIPNs) of PVC/isocyanate/poly‐triol were prepared by premixing small (150 μm dia.) porous (30% voids) unplasticized PVC particles, 10% by weight of isocyanate, and a triol at different OH/NCO mol ratios. Three types of isocyanates (methylene bis‐phenyl diisocyanate (MDI), oligomeric MDI isocyanates (PAPI), and toluene diisocyanate (TDI) prepolymer/polytriol) were used. Two‐roll milling was followed by hot‐press curing. The tensile, flexural, and impact strengths increased when small amounts of crosslinked isocyanate networks were created in PVC. The isocyanate/polyol hydroxyl stoichiometry was varied, and the effects of crosslinking on the tensile, impact, and flexural strengths of PVC/isocyanate/triol SIPNs were examined. The strength increments were greater when the OH/NCO mole ratio went from 0 to 0.25, than when it went from 0.25 to 1.0. In many cases, increasing OH/NCO mol ratio from 0.5 to 1.0 decreased tensile, impact, and flexural strengths. Both PAPI and MDI (30% NCO content) gave bigger improvements in the these mechanical strengths than the TDI (only 9.7% NCO). These SIPN blends exhibited lower tan δ peak temperatures and a single distinct loss modulus, E″, peak values at lower temperatures than those of PVC that had been exposed to the same processing temperatures. Substantial amounts of isocyanate networks exist in SIPN phases according to DMTA studies. The OH/NCO ratio did not generally correlate with the decreases in the glass transition temperatures in these three sets of blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1402–1411, 2000     

2,4,6-三氯苯酚封闭PAPI的研究

以2,4,6-三氯苯酚作为多亚甲基多苯基多异氰酸酯(PAPI)的封闭剂制备可低温解封的封闭异氰酸酯。讨论了nOH/nNCO、反应温度和反应时间对PAPI封闭反应的影响,并对封闭产物进行了FT-IR、1H-NMR、13C-NMR和DSC分析。结果表明,当nOH/nNCO为1.1、温度为80℃、时间为3 h时,封闭效果较好;加入催化剂可缩短封闭反应时间;封闭产物的初始解封温度约为80℃。     

Synthesis and characterization of diethylene glycol monobutyl ether—Blocked diisocyanate crosslinkers

Typically blocked isocyanate systems are used to obtain the performance of two component polyurethane (PU) system in a one-component mixture. In this study four types of isocyanates namely, hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI) and toluene diisocyanate (TDI) were blocked with diethylene glycol monobutyl ether (DEGMBE). Elimination of the isocyanate groups and the formation of urethane bonds were studied by FTIR spectroscopy and titration methods. Thermal dissociation of blocked diisocyanates was analyzed by DSC and TGA techniques.     

封闭型异氰酸酯胶粘剂的研制

以聚乙二醇（PEG）、甲苯-2,4-二异氰酸酯（TDI）等为原料制得阳离子水性聚氨酯,异氰酸酯用丁二酮肟进行封闭制备封闭型异氰酸酯胶粘剂,探讨了阳离子水性聚氨酯溶液的固含量、TDI的封闭,解封以及封闭型异氰酸酯的用量对产品性能的影响.结果表明：30%的阳离子水性聚氨酯溶液加入溶液质量15%左右的封闭型异氰酸酯的胶粘剂对金属的粘接效果较好.     

New copolymers of N,N-dimethylacrylamide with blocked isocyanates for oligonucleotide immobilization in DNA microarray technology

A family of copolymers of N,N-dimethylacrylamide containing blocked isocyanate functionalities is presented. The copolymers were characterized by DSC, GPC and ¹H NMR. Calorimetric analysis showed for any composition broad endothermal phenomena followed by a stronger exothermal peak, which can be attributed, respectively, to the deblocking and subsequent reaction of generated NCO groups.Characterization of glass slides coated with these polymers was done by contact angle measurements and atomic force microscopy. While the former method revealed minimal differences with formation of moderately hydrophilic surfaces, microscopic images showed a more homogeneous coating formation for the copolymer structure with 50% molar of blocked isocyanate. The efficiency of the coated substrates in the immobilization of amino functionalized oligonucleotides was successfully assessed through binding tests and analysis by confocal fluorescence microscopy.Finally, some model microarrays were fabricated by spotting and hybridization with complementary, fluorescently labelled targets was carried out. It resulted in surfaces coated with copolymers which show well defined circular spots with a fluorescence intensity higher than that obtained by slides treated by silanization, and based on the same immobilization chemistry.     

相转移催化法NaHSO3封闭异氰酸酯反应速率的研究

以亚硫酸氢钠固体粉末为封闭剂,丙酮为溶剂对多亚甲基多苯基异氰酸酯（PAPI）进行封闭反应。考查了在不同温度下异氰酸根浓度（-NCO％）随时间变化的情况,并进行了动力学分析,计算出不同温度下的反应动力学常数。     

Synthesis and characterization of reactive blocked‐isocyanate coupling agents from methyl ethyl ketoxime,ethyl cellosolve/ε‐caprolactam blocked aromatic and aliphatic diisocyanates

A series of water‐dispersible blocked polyisocyanates were synthesized from toluene 2,4‐diisocyanate (TDI), isophorone diisocyanate (IPDI), dimethylol propionic acid, methyl ethyl ketoxime (MEKO), ethyl cellosolve (EC), and ?‐caprolactam (CL). The physical properties, such as the viscosity, pH, and storage stability, of the blocked‐polyisocyanate adducts were measured. All aqueous dispersions of the blocked polyisocyanates showed good storage stability. The prepared blocked polyisocyanates were characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, and thermogravimetric analysis techniques. The FTIR confirmed that the ? NCO groups of the original TDI and IPDI molecules were completely blocked by the blocking agents. The thermal analysis measurements revealed that both the blocked TDI‐ and IPDI‐based polyisocyanates started to deblock at about 55–85°C. Compared to the CL‐blocked polyisocyanates, the MEKO‐ and EC‐blocked polyisocyanates had lower thermal dissociation temperatures and faster deblocking rates. We also found that the initial deblocking temperatures of the TDI‐based adducts were lower than those of the IPDI‐based adducts. The water resistance and tensile properties of the composite films from the blocked‐polyisocyanate crosslinkers and hydroxyl–polyurethane emulsion (HPUE) matrix were studied. The tensile strength increased and the elongation at break were lower in the composites compared to the pure HPUE film. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011