Crosslinking with malonate blocked isocyanates and with melamine resins

Automotive clearcoats with improved acid etch resistance are being formulated using a combination of a dialkyl malonate blocked polyisocyanate, a melamine crosslinker, and an acrylic polyol,^1,2 These coatings contain lower levels of melamine crosslinker compared to conventional acrylic/HMMM systems and show excellent acid etch resistance. We explored the reaction mechanism of this complex crosslinking system and found explanations for the good chemical resistance properties. Presented at the 25th International Waterborne, High-Solids, and Powder Coatings Symposium, February 18–20, 1998, New Orleans, LA. Science Rd., Norwalk, CT 06852; E-mail: AlexHe@Kingindustries.com and Wblank@Kingindustries.com.     

Crosslinking reactions during processing of silane modified polyethylenes

A study of the crosslinking reactions in silane modified polyethylenes has been completed. Crosslinking of ethylene-vinyl trimethoxy silane copolymers during high temperature melt processing has been investigated using melt rheological and infrared spectroscopic techniques. Two environmental factors are shown to influence crosslinking formation, namely oxidation of the polymer and the presence of di-n-butyl-tin dilaurate, a condensation catalyst. These are believed to initiate high temperature crosslink formation via different non-interacting mechanisms. It is deduced that silane crosslink formation as a result of oxidation is due to intramolecular interaction of oxidised polyethylene and pendant methoxy silane branches. Observation of a hydrogen bonded silanol intermediate species is consistent with this hypothesis.     

Crosslinking reactions of ethylene vinyl silane copolymers at processing temperatures

The crosslinking reactions of ethylene vinyltrimethoxy silane (EVS) copolymers at processing temperatures have been studied. Samples were heated in inert atmosphere with or without water at 130–350°C. The crosslinking reactions were followed by determination of the gel content and by analyzing the structural changes using FT-IR. As expected, no gel could be observed in pure EVS after treatment in nitrogen, whereas 30% was obtained if the nitrogen was presaturated with water. Addition of a catalyst, dibutyltindilaurate, increased the reaction rate considerably and a final gel content of 70–75% was obtained above 300°C. In contrast, neither water nor catalyst was needed for the formation of gel in a terpolymer of EVS containing butylacrylate as well. During heat treatment the acrylate units formed carboxylic acid, and blends of EVS and an ethylene acrylic acid (EAA) copolymer were therefore used as a model to study the reactions in detail. Despite absence of water these blends started to form gel at low temperatures, 150–200°C. This could mainly be related to internal production of water due to reaction between carboxylic groups leading to anhydride. Both cyclic and noncyclic anhydrides were detected by FT-IR analysis. A larger amount of EAA in the EVS–EAA blend increased the rate of gel formation and decreased the onset temperature, but no corresponding change in the formation of noncyclic anhydride was observed. Another kind of crosslink, formed by reaction between carboxylic acid and silanol groups, can possibly be one explanation to this behavior.     

The chemistry of lipid peroxidation metabolites: Crosslinking reactions of malondialdehyde

Malondialdehyde reacts readily with amino acids to form adducts containing vinylogous amidine linkages. Crosslinking reactions between nucleic acid bases, and amino acids induced by malondialdehyde also have been investigated. The physical data obtained for the adducts provide structural information on the possible mode of crosslinking of proteins and nucleic acids induced by this lipid metabolite.     

Study of deblocking and crosslinking reactions of a blocked isocyanurate cationomer

Summary A cationic adduct of a partly blocked hexamethylene isocyanurate and N-methyldiethanolamine was prepared and applied as a crosslinker in one-pack water-borne polyurethane system. The deblocking and crosslinking reactions were followed by FTIR, TGA and DSC techniques. Deblocking started at about 100°C, while at higher temperatures urethane, allophanate, and urea linkages were formed. The efficiency of the cationic crosslinker was evaluated by determining the insoluble part of the crosslinked polyurethane ionomer films. Films of a good solvent resistance were obtained using 15 wt% of the cationic crosslinker and 0.05 wt% of a catalyst at 130°C.     

Crosslinking cotton cellulose with aldehydes

The relative effectiveness of several aldehydes in crosslinking cellulose of cotton fabric was determined using a pad-dry-cure treatment and a treatment by immersion in a solution at room temperature. Aldehydes ranked in the same order of ability to crosslink in both treatments. Factors related to crosslinking ability are discussed. The aldehydes crosslinking to the greater extent hydrated readily in water because the aldehyde group was activated or because cyclic hydrates could be formed.     

Crosslinking and decomposition reactions of epoxide‐functionalized polynorbornene. II. Impact of reactions on mechanical properties

Low dielectric constant materials are critical to meeting the demand for continual reduction in feature sizes and increase in interconnect density required for future high‐speed microelectronic devices. Polymers based on functionalized norbornenes are inherently attractive for these applications as they exhibit good electrical properties such as a low dielectric constant and appealing mechanical properties. Although polynorbornenes inherently possess properties that are attractive for microelectronics packaging, films of these polymers are not solvent‐resistant. Solvent‐resistant crosslinked films can be attained by generation of acid species to promote cationic crosslinking of epoxide side groups. This article is the second part of a two‐part study investigating the crosslinking of a copolymer of decyl norbornene and epoxide norbornene. In the first part of this study, it was proposed that epoxide decomposition reactions are also possible at cure temperatures greater than 160°C. This decomposition mechanism results in the complete loss of crosslinkable epoxide groups while leaving the norbornene backbone intact. Although crosslinking and decomposition reactions have independent mechanisms, both reactions directly affect the level of crosslinking. In this part of the study, the solvent swelling behavior, tensile modulus, elongation to break, and residual stress were investigated for polymer films cured under various conditions to validate the proposed mechanisms. The trends observed with these properties are consistent with the counteracting nature of epoxide crosslinking and decomposition reactions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1020–1029, 2004     

用TMPTA加速EPDM的交联反应过程

采用三羟甲基丙烷三丙烯酸酯（ＴＭＰＴＡ）作共交联剂,研究其对ＥＰＤＭ的过氧化物硫化行为、力学性能及老化性能的影响。结果表明,ＴＭＰＴＡ可降低混炼胶料的粘度,缩短正硫化时间,提高交联效率,改善力学性能,提高耐老化性能等。     

用TMPTA加速EPDM的交联反应过程

采用三羟甲基丙烷三丙烯酸酯作共交联剂,研究其对ＥＰＤＭ的过氧化物流化行为、力学性能及老性能的影响,结果表明,ＴＭＰＴＡ可降低混炼胶料的粘度,缩短正硫化时间,提高交联效率,改善力学性能,提高耐老化性能等。     

Crosslinking reactions and swelling behavior of matrices based on N-acryloyl-TRIS(hydroxymethyl)aminomethane

Summary In this study, new hydrogels in rod shape were prepared from N-acryloyl-TRIS(hydroxymethyl)aminomethane (NAT) using ethylene glycol dimethacrylate (EGDMA) or N,N’methylenebisacrylamide (BIS) as crosslinking agent, dimethylformamide (DMF) as solvent and benzoyl peroxide (BPO) as initiator. In most cases, 2-hydroxyethyl methacrylate (HEMA), acrylamide (Aam) or acrylic acid (Aac) were used as co-monomers. The polymeric matrices obtained by free radical polymerization exhibited different properties by changing crosslinker, crosslinker concentration, co-monomer and initial NAT/co-monomer mole ratio. Besides, hydrogels from HEMA, Aam and Aac with BIS in absence of NAT were prepared under the same experimental reaction conditions in order to compare the properties of these products with those synthesized from NAT and the respective co-monomers. Some of the final products were selected to perform urea release assays, conducted through swelling-controlled release. Urea was chosen as “model” plant fertilizer agent.     

Crosslinking reaction of rubber with aldehydes

The reactions of rubber with aldehydes have previously been studied in latex or in solutions and the reaction products formed by cyclization, condensation, or addition, have been reported. In the present study, solid-state reactions of rubber with aldehydes were carried out. It was found that crosslinked rubbers may be obtained by press curing in the presence of aldehydes with acidic catalysts. Polychloroprene and Hypalon especially undergo these reactions without a catalyst or with a small amount of catalyst. In the experiments using various aldehydes, some improvements in the properties of the crosslinked rubber were observed when aldehydes such as paraformaldehyde or α-polyoxymethylene were used. Some Lewis acids such as SnCl₂·2H₂O were found to be more effective catalysts than the above, and it was found that organic acids such as p-toluenesulfonic acid could also be used. The curing seemed to be an ionic reaction. The physical properties of the crosslinked rubber are similar to these of sulfur-cured rubbers.     

Crosslinking of poly(vinyl chloride) with bismaleic compound. I. Crosslinking mechanism

Crosslinked poly(vinyl chloride) (PVC) was obtained by using bismaleic compound (BMC). Styrene, as auxiliary crosslinker, can markedly promote the crosslinking course. After having carefully studied the gelling behavior of PVC in crosslinking, and the reactivity of styrene and BMC with PVC, the crosslink mechanism was suggested. The main crosslink reaction is the bridging of bismaleic compound between PVC macroradicals, which were created by thermal degradation of PVC and disproportionation of PVC with initiator radicals and styrene radicals. The first step of crosslink reaction was the BMC grafting on PVC macroradicals. Then styrene copolymerizes with active center bearing on bismaleic compound to propagate graft chain, which make bridging reaction easier to take place. At last, PVC^* reacted with another double bond possessed by grafted BMC to form network structure     

Crosslinking cotton with formaldehyde in phosphoric acid

Cotton print cloth was treated with a solution of formaldehyde in concentrated orthophosphoric acid (a strong cellulose swelling agent). The treatment produces a crosslinked cotton with extremely high wet wrinkle recovery and moisture absorptivity, and very low dry wrinkle recovery. The variations in physical properties are explained in terms of crosslink distribution throughout the fiber and specifically by differences in interlamellar and intralamellar crosslinking. Data on the chemical and physical properties of the fabric as well as electron micrographs of fiber cross-sections are presented and compared or contrasted with data from similar treatments employing other solvents such as water (a moderate swelling agent), acetic acid (a weak swelling agent), and sulfuric acid (a solvent which restricts crosslinking to the periphery of the fiber). Although the treatment causes extensive fiber swelling, it produces very little change in crystallinity and no change in crystal lattice type. Also discussed are the effects of combining this wet crosslinking and conventional dry-cure crosslinking with methylol amides in a two-stage process, in which the wet crosslinking is used either as a pretreatment or as an aftertreatment.     

含硫交联剂水性聚氨酯的制备及其性能

以β-巯基乙醇和1,3,5-三丙烯酰基六氢-1,3,5-三嗪(TAT)为原料,合成了一种含硫三官能度的交联剂STAT,将其与三羟甲基丙烷(TMP)反应,合成了水性聚氨酯SPU1~6,进一步进行成膜处理,得到胶膜WPU1~6。利用衰减全反射红外(ATR-FTIR)、热重分析、X射线衍射和电子拉力试验机分别对水性聚氨酯胶膜结构、热性能和力学性能进行了表征,进一步探讨了S-TAT含量对聚氨酯性能的影响。结果表明,随着S-TAT含量的增大,胶膜的结晶度和软段的玻璃化温度均先增加后降低,胶膜在水中的吸液率先降低后升高,胶膜的拉伸强度、断裂伸长率和弹性模量均增加;当n(S-TAT)∶n(TMP)=3∶2时,胶膜WPU4的结晶度增加到24.91%,软段的玻璃化温度增加到-36.36℃,在水中的吸液率降低到7.34%;当n(S-TAT)∶n(TMP)=5∶0时,胶膜WPU6的拉伸强度为19.8 MPa,断裂伸长率为399%,弹性模量为39.80 MPa。     

Cross-linking of acetate fibres with blocked diisocyanate

Conclusions We have thus demonstrated that acetate fibres may be chemically modified by incorporating the adduct of tolylene diisocyanate, ethylene glycol and phenol in the spinning solution, with subsequent heat treatment of the spun fibre. The chemical modification takes place chiefly by reaction of the isocyanate groups with hydroxyls on the cellulose acetate. It has been established that fibres produced in this way have improved wet properties, a lower crease tendency and increased stability to light, heat and chemical agents.All-Union Scientific-Research Institute for Synthetic Fibres (VNIIV). Translated from Khimicheskie Volokna, No. 4, pp. 61–64, July–August, 1969.     

Crosslinking of styrene-butadiene rubber with polyurethanes bicapped with benzyocyclobutene

Summary A polyurethane prepared from 1,9-nonanediol and toluene-2,4-diisocyanate with M_n=11,840, was capped on both ends in a reaction with 4-(benzocyclobutenyl) methanol. The polyurethane was used to crosslink styrene-butadiene rubber through Diels-Alder reactions on the benzocyclobutene functionality. The synthesis and characterization of 4-(benzocyclobutenyl) methanol, a molecule not reported previously, is presented. The crosslinking reaction was carried out on intimate mixtures of the telechelic polyurethane and SBR at elevated temperature and pressure. Various physical properties of the crosslinked material were studied.Work done at the Department of Chemistry, University of Akron, Akron, OH 44325, USA     

Crosslinking and decomposition reactions of epoxide functionalized polynorbornene. Part I. FTIR and thermogravimetric analysis

The miniaturization of microelectronic devices has created a demand for new low‐dielectric‐constant materials to be used as insulating layers between metal interconnects. In this study, a functionalized polynorbornene consisting of a copolymer of decyl norbornene and epoxide norbornene has been investigated as a low‐temperature curing dielectric. Polynorbornenes possess properties that are attractive for microelectronics packaging; however, films of these polymers must be crosslinked in order to obtain the solvent resistance and low solvent swelling necessary for multilayer applications. Crosslinking of these materials was achieved by acid‐catalyzed cationic crosslinking of epoxide side groups. The reactions that occurred during higher temperature curing of epoxy functionalized norbornene films were studied using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis. Epoxide crosslinking and epoxide decomposition reactions were identified and studied as a function of temperature and time. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 568–577, 2003     

Crosslinking of PVC formulations treated with UV light

Typical wire and cable formulations of plasticized Poly(vinyl chloride) were prepared with three different stabilizer systems: Ca/Zn (2:1 or 1:1) and dibasic lead phthalate. The mixtures contained trimethylolpropane trimethacrylate (TMPTMA) as crosslinking agent and a UV photoinitiator (Irgacure 819). Mixtures were dry‐blended, then roll‐milled and to finally hot‐pressed at 180°C to obtain sheets of 1 and 1.5 mm thickness. Small specimens (3 × 3 cm) were irradiated with UV light for up to 10 days while monitoring changes at different time intervals. The presence of TMPTMA in the samples, as expected, influenced the storage modulus (E′) and gel content percentage, specifically for the thinner samples. These results indicated that UV irradiation produced surface crosslinking. The samples with crosslinking agent also reached higher carbonyl index values. The Ca/Zn formulations showed higher mechanical properties with respect to the Pb ones, thus suggesting that during the stabilization period of the Ca/Zn mixtures, an effective crosslinking was promoted. Irregular behavior was observed during the last days of treatment for both types of formulations, thereby suggesting an optimum irradiation time for this procedure. J. VINYL. ADDIT. TECHNOL. 12:49–54, 2006. © 2006 Society of Plastics Engineers.     

Crosslinking of elastomeric vinylidene fluoride copolymers with nucleophiles

The monomer sequence CF₂CF(CF₃)CH₂CF₂CF₂CF(CF₃) has been identified by ¹⁹FNMR as the selectively base-sensitive site of poly(vinylidene fluoride/hexafluoropropylene). Similar studies of other vinylidene fluoride (VF₂) copolymers with either tetrafluoroethylene (TFE) or perfluoro(methyl vinyl ether) (PMVE) show that the generalized base-sensitive site of VF₂ copolymers which contain one or more perfluorinated monomers can be formulated as: Depending on the nature of A, treatment with bases can lead to elimination of HF or the elements of CF₃OH. In perfluoro(methyl vinyl ether)-containing copolymers a major pathway of elimination from the intermediate carbanion involves loss of ^?OCF_3, which decomposes to COF₂ and ^?F. With benzylamine, COF₂ was efficiently trapped as dibenzylurea by the excess base. The structural unit of PMVE is therefore substantially degraded when such copolymers are subjected to basic curatives. The use of PMVE in fluoroelastomer technology is therefore reserved for TFE-based ultra-high performance perfluoroelastomers, and for peroxide-curable hydrofluoroelastomers designed for excellent low-temperature service. The relative reactivity of HFP-VF₂-HFP and TFE-VF₂-TFE sites toward basic nucleophiles was determined in solution at room temperature. Whereas the two sites undergo HF elimination with similar ease, subsequent nucleophilic attack on the formed unsaturation by unreacted base or another nucleophile clearly differentiates these two sites. This differential reactivity is consistent with the differing vulcanization rates and vulcanizate stabilities of poly(VF₂/HFP) and poly(VF₂/HFP/TFE).