Effects of reactive diluents in curing of epoxies as revealed by model reactions

Summary The tertiary amine induced oligomerization of diglycidyl ether of bisphenol A (DGEBA) containing epoxide-based diluents as well as the model reaction with phenyl glycidyl ether (PGE) itself were investigated. The oligomer products obtained were separated by HPLC. The structure of these oligomers was elucidated by spectroscopic methods. Reactive diluents such as phenyl glycidyl ether and cyclohexyl glycidyl ether (CHGE) influence the cure time and the network formation of the final crosslinked product.     

AlCl3/促进剂协同催化1-癸烯齐聚制备聚α-烯烃合成油

以三氯化铝为催化剂、过渡金属氯化物MCl₃（VCl₃、CrCl₃和TiCl₃）为促进剂,催化1-癸烯齐聚制备了具有高黏度指数的聚α-烯烃（PAO）合成油,系统研究了促进剂的作用机制和齐聚反应条件对齐聚反应活性和PAO性能和结构的影响。结果表明：VCl₃和CrCl₃的加入能明显增加1-癸烯齐聚反应收率和齐聚物的黏度指数。过渡金属氯化物通过双氯桥结构与三氯化铝形成双金属化合物,通过双金属间的协同效应,改变三氯化铝的吸电子能力来增加其催化活性。通过核磁氢谱（¹H NMR）和核磁碳谱（¹³C NMR）分析,确定了AlCl₃/MCl₃催化1-癸烯齐聚遵循阳离子聚合机制,1-癸烯齐聚物中主要的不饱和双键为三取代和双取代内烯烃。过渡金属氯化物促进剂可以调整优势反应途径从而改变齐聚产物的分布。     

Polymerization of p-cresyl glycidyl ether catalyzed by imidazoles

Summary The clear dependence between the age of mixtures of p-cresyl glycidyl ether and imidazoles and their subsequent rates of polymerization at elevated temperatures show that low molecular weight products formed by the reaction of p-cresyl glycidyl ether with imidazoles catalyze the polymerization of p-cresyl glycidyl ether much more efficiently than imidazoles by themelves.Especially in the reaction mixture of p-cresyl glycidyl ether with 1-methyl imidazole is 1,3-bis (4-methylphenoxy)-propanol-2 in high yield formed. This product is one of the most responsible for the acceleration of the polymerization in aged mixtures since it was found to accelerate considerably the polymerization of p-cresyl glycidyl ether when used as a cocatalyst with imidazoles.The isopropanol derivative accelerates the polymerization more efficiently than isopropanol.On the other hand, the isopropanol derivative is formed only to an insignificant extent when 2-ethyl,4-methylimidazole is used instead of 1-methylimidazole.     

Curing of epoxy resins with dicyandiamide

Summary The reaction behaviour of tertiary amine accelerated epoxy-dicyandiamide systems was studied using phenyl glycidyl ether and the diglycidyl ether of bisphenol A. N,N-dimethyl-benzylamine was applied as accelerator. The solvent, N,N-dimethylformamide, was used to obtain homogeneous reaction mixtures. The influence of the solvent on the reaction was investigated. Depending on reaction conditions the formation of oligomerization products was followed by HPLC measurements.     

Imidazole catalysis in the curing of epoxy resins

The high catalytic activity of imidazoles and particularly of 2-ethyl-4-methylimidazole (EMI) for the curing of epoxy resins and the properties of the resulting resins prompted this study concerned with the nature of the curing reaction. Epon 828 epoxy resin and the model compound phenyl glycidyl ether were used as starting materials with EMI, 2-methylimidazole, and dimethylbenzylamine as catalysts. During the curing of the resin at 50°C., the decrease in the infrared absorption of the epoxy band with time is accompanied by a decrease in the intensity of the imine band of the imidazole moiety, indicating its reaction with the epoxy group and its incorporation into the resin. The measurement of the residual epoxy content after curing for 24 hr. at 50 and 140°C. showed that the imidazoles were not more efficient in completing the epoxy reaction than dimethylbenzylamine. In the experiments with phenyl glycidyl ether the rate of reaction of the epoxy group with EMI was faster than the rate of polymerization, proving that the imidazole becomes permanently attached to the polymer chain. These results also suggest that the true catalytic species is not EMI but some addition product thereof. In comparative rate measurements the compound formed from equimolar quantities of EMI and phenyl glycidyl ether was found to be an excellent catalyst. The NMR analysis of the 1:1 and 1:2 adducts of EMI and phenyl glycidyl ether has shown that the second mole of phenyl glycidyl ether reacts with the ring nitrogen in the 3 position and not with the hydroxyl group of the mono adduct. By forming the bis adduct in this way the imidazole molecule acts as a crosslinking agent and at the same time introduces an alkoxide ion which can initiate further polymerization. It is very likely that this crosslinking is the process that leads to the superior physical and chemical properties (high heat deflection temperature, resistance to chemicals and oxidation) of the resins prepared with imidazoles as catalysts.     

Curing of epoxy resins with dicyandiamide

Summary The mechanism of the epoxy resin curing with dicyandiamide was studied using the model phenyl glycidyl ether and different substituted dicyandiamides. Some reaction products were isolated by HPLC and characterized by FTIR and Carbon-13 NMR spectroscopy. A reaction pathway is proposed discussing the formation of cyclic structures, carbonyl groups and oligomerization products of the glycidyl ether.     

Novel polyurethane coating technology through glycidyl carbamate chemistry

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.     

Analysis of thermal oligomerization mechanism of styrene by field desorption mass spectrometry

Field desorption mass spectra of normal and deuterated styrene oligomers synthesized in several alkylbenzenes were measured. Analysis of the mechanism of thermal oligomerization was carried out by identifying the molecular species in the reaction system using field desorption mass spectra. As a result, the existence of several kinds of molecular species was confirmed. The minor molecular species originated from dissolved oxygen, from the cleavage of solvent radicals to which oxygen was attached, or from H–D exchange in the oligomerization of deuterated styrene. The major molecular species originated from radical telomerization of solvents and styrene dimers, from the recombination termination reaction, and from the cage reaction between initiating radicals. Field desorption mass spectrometry was found to be useful for analyzing the mechanism of styrene oligomerization as well as characterizing the oligomers.     

Kinetics and mechanism of oligomerization of cardanol using acid catalysts

The kinetics and mechanism of oligomerization of cardanol over acid catalysts were studied. GPC results showed the formation of a mixture of oligomers such as dimer, trimer, tetramer, etc. IR spectra of the products of oligomerization showed a decrease in the intensity of the double bond absorption band at 1630 cm^?1 and the disappearance of terminal vinyl bands at 895 cm^?1 and 907 cm^?1. ¹H NMR spectra showed drastic changes in the unsaturated proton resonance signals at 5.5δ with respect to saturated protons at 0.2–2.5δ. The ratio of resonance integrals of unsaturated to saturated protons decreased from 1 : 6.5 to 1 : 20 after oligomerization. GPC studies showed that the rate of formation of the dimer, trimer, tetramer, etc. follow an identical path and that the individual oligomers are formed in the same weight percentage at any time during the reaction. A kinetic scheme is proposed to explain this phenomenon. Kinetic studies showed that the oligomerization reaction follows first order kinetics with respect to the monomer concentration and the rate constant is K = 6.6 × 10^?5s^?1. A probable mechanism for the oligomerization of cardanol is proposed.     

Suppression of Problematic Compound Oligomerization by Cosolubilization of Nondetergent Sulfobetaines

Numerous small organic compounds exist in equilibrium among monomers, soluble oligomers, and insoluble aggregates in aqueous solution. Compound aggregation is a major reason for false positives in drug screening, and even soluble oligomers can interfere with structural and biochemical analyses. However, an efficient way to manage the equilibrium of aggregation‐prone compounds, especially those involved with soluble oligomers, has not been established. In this study, solution NMR spectroscopy was used as a suitable technique to detect compound oligomers in equilibrium, and it was demonstrated that cosolubilization of nondetergent sulfobetaines (NDSBs) can largely suppress compound oligomerization and aggregation by shifting the equilibrium toward the monomers. The rotational correlation time was obtained from the ratio of the selective and nonselective longitudinal NMR relaxation times, which directly and quantitatively reflected the apparent sizes of the compounds in the equilibrium. The rotational correlation time of the aggregation‐prone compound SKF86002 (1 mM ) was substantially reduced from 0.31 to 0.23 ns by cosolubilization of 100 mM NDSB195. NDSB cosolubilization allowed us to perform successful structural and biochemical experiments with substantially fewer artifacts, which represents a strategy to directly resolve the problematic oligomerization and aggregation of compounds.     

Controlling Product Composition of Metathesized Triolein by Reaction Concentrations

Triolein was used as a model material to investigate the effect of concentration on self metathesis of vegetable oils. The metathesis reaction using Grubbs' second generation catalyst (used at a level of 2.5?mol?% of triolein) was carried out at 38?°C using dichloromethane as the solvent. The products from three reaction concentrations were investigated: neat, 10 and 20?mmol/L. The products from the reactions were separated by column chromatography and the fractions were characterized by ¹H-NMR, ¹³C-NMR, MS and FTIR. Mono-cyclic and multi-cyclic triacylglycerol-based compounds and different level aliphatic triacylglycerol-like oligomers were produced, but the compositions of the products were found to be significantly controlled by the reaction concentrations. Cyclic compounds were favorably produced at lower reaction concentrations, whereas, linear oligomers were favorably produced at higher reaction concentrations. Cyclic compounds were formed mainly from adjacent fatty acid chains on the glycerol backbone. In the neat reactions, only linear oligomers were produced. The trans/cis ratios increased as concentration was increased.     

端乙酸酯基GAP的合成与性能研究

以1,4-丁二醇为引发剂,三氟化硼乙醚络合物为催化剂,使环氧氯丙烷发生开环聚合制得环氧氯丙烷均聚物（PECH）,PECH经叠氮化形成端羟基叠氮基缩水甘油醚聚合物（GAP）,然后再以1-甲基眯唑为催化剂,用乙酸酐将GAP酯化成端乙酸酯基GAP（ETGAP）。用FT—IR、DSC等方法研究了ETGAP的结构和性能。ETGAP的玻璃化转变温度为-65．36℃,热分解温度为251．02℃,黏度小,可用作含能增型剂。     

Analysis of the cure kinetics of epoxy/imidazole resin systems

The reaction kinetics for the cure of epoxy resins with imidazoles were determined from Fourier transform infrared spectroscopy and differential scanning calorimetry studies. The diglycidyl ether of bisphenol A and phenyl glycidyl ether were cured with various concentrations of 2-ethyl-4-methyl-imidazole ranging from 4.0 to 100.0 mol %. The first step in the curing process is the formation of epoxide/imidazole adducts. These adducts initiate the etherification reaction which crosslinks the resin. The kinetics were determined and confirmed for both the adduct and the etherification reactions as a function of the imidazole concentration. A model was developed and used to predict the concentrations of the unreacted epoxide groups and the reaction products for a wide range of imidazole concentrations and cure temperatures.     

Thermal and dyeing properties of acrylonitrile-glycidyl methacrylate copolymers

The copolymerization of acrylonitrile (AN) with glycidyl methacrylate (GMA) has been investigated in tetrahydrofuran (THF). The reactivity ratios were estimated and the thermal behaviour of the homo- as well as the copolymers, both in air, and under nitrogen atmosphere was investigated using differential thermal analysis (DTA) and thermogravimetry (TG) techniques. GMA was found to initiate the nitrile oligomerization reaction in the copolymers upon heating. The dyeing ability, as well as the colour fastness towards UV light have also been investigated. It was found that the copolymers showed better affinity towards basic dyes compared to homopolyacrylonitrile. This affinity increases with increasing the GMA content in the copolymer.     

Zur oligomerenbildung bei der thermischen polymerisation von styrol

It is shown that in thermal polymerization of styrene four dimers and six trimers are formed by parallel occurring oligomerization reactions. With increasing temperature the rate of oligomerization increases more rapidly than the rate of polymerization. The relativ yields of the different oligomers depend on temperature, too.     

Oligomerization of 1-hexene with bimetallic catalysts based on titanium or zirconium derivatives and organoaluminum compounds

The oligomerization of 1-hexene at 20° C in the presence of various bimetallic systems obtained by reaction of titanium (IV) and zirconium (IV) derivatives with organoaluminum compounds has been studied. The transition metal, the nature of its substituents, and that of those attached to aluminum, strongly affect the catalytic activity. Oligomerization only proceeds with systems which contain Ti or Zr reduced forms. Two series of low molecular weight oligomers are formed, C_6n and C_6n+2. Each is composed of both saturated and unsaturated hydrocarbon homologues. The large amount of saturated products after hydrolysis shows that aluminum metal alkyls are either involved in the propagation or are very efficient transfer agents.     

Polymerization of p-cresyl glycidyl ether catalyzed by imidazoles I. The influence of the imidazole concentration,the reaction temperature,and the presence of isopropanol on the polymerization

The polymerization of p-cresyl glycidyl ether catalyzed by imidazoles has been investigated as a model reaction for the polymerization of technical epoxy resins. The dependence of oligomer yield on time, temperature, and imidazole concentration, the distribution of the polymerization degrees, and the influence of isopropanol have been studied. The reaction rate and the average degree of polymerization are affected by the presence or absence of a secondary nitrogen on the imidazole, i.e., different results are obtained when 2-ethyl, 4-methyl imidazole (EMI) or 1-methyl imidazole (1-MIA) are used. 1-MIA seems to be “precursor” of the catalyst rather than a catalyst by itself. The comparisons of CGE polymerizations catalyzed by 1-MIA in the absence and presence of isopropanol show only quantitative differences: The polymerization in the presence of isopropanol is faster, and the average degree of polymerization is shifted to higher values. The activation energies of CGE polymerizations catalyzed by different imidazoles have been determined.     

Oligomerization of α-octene catalyzed by zeolites

The oligomerization of octene-1 was studied in the presence of zeolites of different structural types (e.g., Y, Beta, ZSM-12, and ZSM-5). It was shown that at 150–200°C, wide-pore zeolite catalysts Y, Beta, and ZSM-12 exhibit high catalytic activity in the reaction. The conversion of catalyzed octene can be as high as 96%, and the yield of oligomers is 88–100 wt %. Zeolite ZSM-5 at 150–180°C has low activity and mainly catalyzes the isomerization of octene-1. As the temperature rises to 250°C, low molecular weight oligomers resulting from the cracking process are the main products of this reaction. The activity and selectivity of zeolite catalysts in the oligomerization of octene-1 are conditioned by their acidic properties and structural characteristics, as well as by the reaction conditions. It was revealed that the main oligomerization products are octene dimers having an alkylnaphthene structure and containing unsaturated hydrocarbons with tri- and tetra-substituted double bonds in amounts of 2.2–3.2%. The properties of the octene oligomers synthesized in the presence of zeolite Beta are similar to the characteristics of hydrogenated poly-α-olefins, the oligomerization of which was performed on AlCl₃ complexes.     

乙烯齐聚合锆系催化剂研究进展

综述了锆系催化体系的特点和研究进展,并对各种配体对催化活性和选择性的影响进行了分析比较。在乙烯齐聚合的催化体系中,不同有机铝对催化乙烯齐聚合的活性和选择性有较大的影响。在锆系催化剂中加入第三组分对乙烯齐聚物的相对分子质量分布有明显的调变作用。     

Epoxy resin curing by dicyandiamide using model compounds

Summary The reaction behaviour of different accelerated homogeneous epoxy-dicyandiamide systems was studied using phenyl glycidyl ether as a model and as solvent N,N-dimethylformamide. N,N-dimethylbenzylamine, imidazole, 2-methylimidazole were applied as accelerator. The reaction course was followed by HPLC and ¹³C-NMR measurements. A reaction mechanism involving a tautomerisation of dicyandiamide depending on temperature is suggested.