Calorimetric investigation of polymerization reactions. IV. Curing reaction of polyester fumarate with styrene

The curing reaction of polyester fumarate with styrene was investigated with a differential scanning calorimeter (DSC) operated isothermally. The change in rate of cure was followed over the whole range of conversion. The rate of cure is accelerated by the gel effect to about ten to fifty times the rate of model copolymerization of diethyl fumarate with styrene. This autoacceleration is much enhanced for systems with higher crosslinking densities and at lower temperatures. The results confirm that both termination and propagation steps of the curing reaction are controlled by diffusion of polymeric segments and monomer molecules over almost the whole range of conversion. The final extent of conversion is short of completion for isothermal cure and even for postcure of polyester fumarate with styrene because of crosslink formation. The final conversion of isothermal cure decreases with increasing crosslinking density and shows a maximum with increasing reaction temperature. This temperature dependency of the final conversion is caused by the difference in the activation energies for two propagation rate constants k_pf and k_ps, which were evaluated to be 7–10 and 5–8 kcal/mole, respectively, for the intermediate stage of the curing reaction.     

Kinetics of Photocationically Curable Formulations Involving Glycerol Diglycidyl Ether and Phenyl Glycidyl Ether

Kinetic analysis of formulations based on glycerol diglycidyl ether and phenyl glycidyl ether were carried out in the presence of sulfonium salt as initiator at 35 mW cm^?2using photo differential scanning calorimeter and the final conversion was found to increase with an increase in phenyl glycidyl ether content. The effects of formulation monomer ratios at three different temperatures were studied. The variations in the observed kinetic parameters can be related to increase in mobility of reactive species with temperature, distance of counter ion from the propagating cationic center, as well as extent of crosslinking reaction which controlled the course and duration of the reaction. The applicability of autocatalytic kinetic model was also evaluated and the system underwent early gelation and the activation energy decreased with an increase in phenyl glycidyl ether content. Analysis of stable photocured films containing glycerol diglycidyl ether and phenyl glycidyl ether showed better thermal stability than rigid films obtained with glycerol diglycidyl ether.     

Acceleration mechanisms in curing reactions involving model systems

The mechanisms involving some of the most common accelerators in the curing reactions of epoxy resins have been investigated by use of model systems. Phenyl glycidyl ether was used as a model compound. The characterization of the reaction products was mainly carried out by High-Performance-Liquid-Chromatography and by preparative methods. Special attention was paid to the oligomerization reactions of the oxirane ring in the presence of tertiary amines. Three different types of oligomers depending on phenyl glycidyl ethers are discussed. The mechanisms of multifunctional accelerators such as imidazoles or phenol-MANNICH-base-compounds are much more difficult. The extraordinary interaction of imidazoles depends on the formation of different oligomers. Furthermore, the cleavage of the imidazole ring was observed. It is possible that the glycidyl ether oligomerization plays an important role in understanding the network structure. Some aspects of the accelerating effect of tertiary amines in the curing of glycidyl ethers with acid anhydrides were likewise discussed. The results obtained using these model reactions may be applied to influence the curing process in commercial epoxy resin systems.     

含介晶结构单元化合物改性环氧树脂E—51／DDM固化体系的动态力学行为

合成和表征了含有介晶结构单元的单环氧官能团化合物4-(4'-甲基基苯甲酰氧基)苯基缩水甘油醚(MPEP),以一定比例的MPEP加入到环氧树脂E-51/4,4'-二氨基二苯基甲烷(DDM)固化体系,获得了一系列在高分子链上悬挂介晶结构单元的固化网络结构,并对其动态力学行为进行了表征,侧链上介晶结构单元的引入使固化体系的交联密度降低,链段柔顺性增加,表现为与未加MPEP的体系相比,含有介晶结构单元的体系的玻璃化温度和动态模量下降,而且MPEP的加量越大,玻璃化温度和动态模量下降幅度越大.     

Reactions in aminosilane-epoxy prepolymer systems. II. Reactions of alkoxysilane groups with or without the presence of water

The hydrolysis and reactions of alkoxy silane groups have been studied on a model compound (TA) prepared from 2 mol of phenyl glycidyl ether and 1 mol of aminopropyl triethoxy silane. At low (40°C) and high (140°C) temperatures, the monomer conversion and the evolution of the molecular mass are followed by size exclusion chromatography (SEC). During the same reaction time, the evolution of the functional groups, hydroxyl CH? OH, ethoxy ? O? C₂H₅, and siloxane Si? O? Si, is observed by FTIR spectroscopy. Without the presence of water, reactions between hydroxyl and ethoxy silane lead to gelation at the end of the reaction. A by-product, probably a cyclic tetramer is also formed. After the hydrolysis, the reaction of the model compound is quite different. The product of reaction is always soluble, even after a treatment at high temperatures, and the evolution of the molecular mass versus the reaction time seems to correspond to the condensation giving a dead cyclic tetramer. From this study it is evident that the curing cycle has a great influence on the properties of the interface of a composite based on a epoxy matrix.     

Curing of epoxy-anhydride formulations in the presence of imidazoles

Differential scanning calorimetry was used to study the reaction of isomethyltetrahydrophthalic anhydride with phenyl glycidyl ether and the curing kinetics of diglycidyl ether of diphenylolpropane in the presence of imidazoles. The deformation-strength characteristics of cured epoxy polymers were determined.     

Optically clear simulataneous interpenetrating polymer networks based on poly(ethylene glycol) diacrylate and epoxy. II. Kinetic study

Simultaneous interpenetrating polymer networks (SINs) based on diglycidyl ether of bis-phenol A (DGEBA) and poly(ethylene glycol) diacrylate (PEGDA) in weight ratios of 100/0, 50/50, and 0/100 were blended and cured simultaneously by using benzoyl peroxide (BPO) and m-xylenediamine (MXDA) as curing agents. A kinetic study during SIN formation was carried out at 45, 55, 63, and 70°C. Concentration changes for both the epoxide and C?C bond were monitored with FTIR. A rate expression for DGEBA cure kinetics was established with a model reaction of phenyl glycidyl ether (PGE) and benzylamine. Experimental results revealed that lower rate constants and higher activation energy for the SIN were found, compared with those for the constituent DGEBA and PEGDA network formation. A model of network interlock was proposed to account for this phenomenon. During simultaneous cure of DGEBA and PEGDA, the interlock (mutual entanglement) between DGEBA and PEGDA networks provided a sterically hindered environment, which subsequently increased the activation energy and reduced cure rates for both DGEBA and PEGDA. © 1993 John Wiley & Sons, Inc.     

An analysis of the substitution effects involved in diepoxide-diamine copolymerization reactions

The relative reactivity of the functional groups present in aromatic amine and diepoxide monomers has been investigated by gel permeation chromatography. The ratio of rate constants for the consumption of the secondary and primary amine hydrogens involved in the reaction between aniline and phenyl glycidyl ether has been calculated to equal approximately 0.5. In the case of the reaction between N-methy aniline and diglycidyl ether of bisphenol A (DGEBA) the rate constant ratio for the consumption of the first and second epoxide groups in the DGEBA molecule is also approximately 0.5. In contradiction to previously published data these results suggest that substitution effects are unimportant for aromatic amines as well as DGEBA. Furthermore, etherification side reactions, consuming epoxide groups at the expense of the amine–epoxide reaction, also appear to be insignificant.     

Just a near attack conformer for catalysis (chorismate to prephenate rearrangements in water,antibody, enzymes,and their mutants)

Standard free energies for formation of ground-state reactive conformers (DeltaGN degrees ) and transition states (DeltaG) in the conversion of chorismate to prephenate in water, B. subtilis mutase, E. coli mutase, and their mutants, as well as a catalytic antibody, are related by DeltaG = DeltaGN degrees + 16 kcal/mol. Thus, the differences in the rate constants for the water reaction and catalysts reactions reside in the mole fraction of substrate present as reactive conformers (NACs). These results, and knowledge of the importance of transition state stabilization in other cases, suggest a proposal that enzymes utilize both NAC and transition state stabilization in the mix required for the most efficient catalysis.     

Anhydride curing of epoxy resins via chain reaction

In contrast to common curing reactions, the anhydride curing of epoxies follows a living anionic chain growth. The resulting consequences of this mechanism, i.e. (1) DP_n = a[M_o]/[I_o], (2) first-order kinetics and (3) Poisson chain-length distribution were tested with the phenyl glycidyl ether/phthalic acid anhydride system, using l-methyl imidazole. Overall agreement was found and the observed deviations could be explained with a modified Poisson process. Conformational properties of the resins were measured by static and dynamic light scattering and by viscometry. These were compared with the quantities of a corresponding branched system prepared with a mixture of phenyl glycidyl ether and bisphenol-A diglycidyl ether. Typical deviations to smaller dimensions were observed at high molar masses as a result of increasing branching.     

The relative reactivity of primary and secondary amine hydrogen atoms of aromatic amines with epichlorohydrin and N- and O-glycidyl compounds

The relative value of the rate constants for the reactions between the secondary and primary amine hydrogen atoms of 3-trifluoromethylaniline with epichlorohydrin, and of aniline with phenyl glycidyl ether and with some N-alkyl-N-glycidylanilines were determined by HPLC analysis. Values ranged from 0.14 to 0.24 and are in agreement with the findings of earlier workers for the reactions of aromatic amines with O-glycidyl compounds but in direct conflict with the claim of a recent publication. The value for the reaction between 3-trifluoromethylaniline and epichlorohydrin was unaffected by the nature of the catalyst, which covered a wide range of strengths and steric requirements.     

2-乙基-4-甲基咪唑固化环氧树脂体系动力学模型

由2-乙基-4-甲基咪唑(2,4-EMI)固化双酚A二缩水甘油醚型环氧树脂(DGEBA)的等温差示扫描量热(DSC)实验结果发现固化反应分两阶段进行,催化聚合反应有一诱导期.由DSC测试结果求得催化聚合反应的速率常数.从反应机理出发,以诱导期为边界,建立两阶段的微观固化动力学模型.从扩散的角度在模型中引入临界固化度(αc)和扩散因子,进一步建立扩散控制固化动力学模型,对不同2,4-EMI含量和固化温度(Tc)的体系,计算得到αc.研究发现扩散因素对固化动力学影响较大,固化反应前期由化学动力学控制,后期由扩散因素控制;αc主要由体系的玻璃化转变决定,Tc越高,体系玻璃化转变时对应的固化度越大,cα越大.     

Reaction of glycidyl phenyl ether with imines: A model study of latent hardeners of epoxy resins in the presence of water

The hydrolyses of several imines and their reactions with glycidyl phenyl ether were examined under highly humid conditions as a model study for the development of water‐initiated hardeners for epoxy resins. Diethyl ketone‐based imines were hydrolyzed more efficiently than methyl isobutyl ketone‐based imines. The reactions of glycidyl phenyl ether with the imines depended on their hydrolysis rates and the basicity of the amines generated from them. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 971–975, 2002     

Kinetic analysis of the phenyl-shift reaction in β-O-4 lignin model compounds: a computational study

The phenyl-shift reaction for the β-radical of phenethyl phenyl ether (PhCH(2)C?HOPh, β-PPE) is an integral step in the pyrolysis of PPE, which is a model compound for the β-O-4 linkage in lignin. We investigated the influence of natural occurring substituents (hydroxy, methoxy) on the reaction rate by calculating relative rate constants using density functional theory in combination with transition state theory, including anharmonic correction for low-frequency modes. The phenyl-shift reaction proceeds through an oxaspiro[2.5]octadienyl radical intermediate and the overall rate constants were computed invoking the steady-state approximation (its validity was confirmed). Substituents on the phenethyl ring have only little influence on the rate constants. If a methoxy substituent is located in the para position of the phenyl ring adjacent to the ether oxygen, the energies of the intermediate and second transition state are lowered, but the overall rate constant is not significantly altered. This is a consequence of the dominating first transition from reactant to intermediate in the overall rate constant. In contrast, o- and di-o-methoxy substituents significantly accelerate the phenyl-migration rate compared to β-PPE.     

Kinetic studies on light-induced cationic ring-opening reactions on 2,3-epoxypropyl phenyl ether

Light-induced cationic ring-opening reactions of 2,3-epoxypropyl phenyl ether (phenyl glycidyl ether, PGE) in acetone, methanol and bulk were studied. Cations are produced by electron transfer from excited sensitizers (anthracene, An; 9,10-phenanthrenequinone, PQ; benzophenone, BP) or from photolytically cleaved sensitizer (benzoin isoproyl ether, BIPE) to diphenyliodonium hexafluorophosphate. With excess of acetone and methanol, addition reactions take place resulting in 2,2-dimethyl-4-phenoxymethyl-1,3-dioxolane and 1-methoxy-3-phenoxy propan-2-ol as main products. The efficiency of the sensitizers taken from the quantum yields of PGE conversion, follows the order An ? BIPE > PQ > BP in acetone and An ～ BP > BIPE ? PQ in methanol. Unlike bulk polymerization, in these addition reactions no steady-state concentration of cations exists and the reaction accelerates with time. When alcohol is added in only small proportions, the initial addition reactions goes over into a linear oligomerization. The relatively higher basicity of methanol over PGE influences the nature of the active center, and the course of reaction depends on methanol concentration. Kinetic expressions, which account for all possible types of active centers, have been derived to express the rate of PGE reactions in methanol.     

Selective cleavage of the linear ether bond in benzyl glycidyl ether and triphenylmethyl glycidyl ether by potassium alkalide as two-electron-transfer reagent

The linear ether bond was exclusively cleaved in benzyl glycidyl ether and triphenylmethyl glycidyl ether under the influence of K⁻, K⁺(15-crown-5)₂ (1), whereas the strongly strained three-membered oxacyclic ring remained undisturbed. Potassium glycidoxide and benzylpotassium were found as the primary reaction products of benzyl glycidyl ether with 1. Subsequently, benzylpotassium reacted with benzyl glycidyl ether giving the next potassium glycidoxide molecule and bibenzyl. Benzyl phenyl ether was used as a model compound to explain the mechanism of bibenzyl formation. The reaction of triphenylmethyl glycidyl ether with 1 resulted in potassium glycidoxide and stable triphenylmethylpotassium. After treating with a quenching agent a new glycidyl ether or glycidyl ester was obtained from potassium glycidoxide. These results were found when the reaction occurred at the excess of glycidyl ether. In another case, i.e. at the excess of 1 further reactions took place with the participation of potassium anions and various new compounds were observed in the reaction mixture after benzylation or methylation. Thus, the method of substrates delivery influences the course of studied processes in a decisive way.     

Synthesis of Novel Glycidol Copolymers with Pendant Alkene and Hydroxyl Groups

A series of linear poly glycidol copolymers, tethering with both alkene and hydroxyl groups, were prepared by a combination of anionic ring-opening polymerization （ROP） using specific reactions of ethoxy ethyl glycidyl ether （EEGE） and allyl glycidyl ether （AGE） firstly, and subsequently removal of the protection group of glycidol in EEGE to achieve the linear copolymer pendant with both hydroxyl groups and double bonds. The EEGE/AGE monomer reactivity ratio is measured to be 3.30/1.13. The chemical compositions of the as-synthesized polymers were characterized by tH NMR and GPC, and the glass transition temperatures （Tg） of as-synthesized polymers were determined by DSC. The final copolymers have abundant double bonds and hydroxyl as side groups. Furthermore, the ratio of the double bonds to hydroxyl groups can be controlled by the ratio of the starting materials in a wide range.     

THE CURING BEHAVIOR OF DIGLYCIDYL-4, 5-EPOXYCYCLOHEXANE-1,2-DICARBOXYLATE

The curing behavior of diglycidyl-4, 5-epoxycyclohexane-1, 2-dicarboxylate with m-phenylenediamine has been studied by using torsional braid analysis. It is shown that the whole curing processproceeds in two stages, that is, curing reaction at temperatures below 100℃mainly occurs at the ali-phatic epoxy rings, whereas a rapid increase in reaction rate of the remaining cycloaliphatic epoxy ringoccurs only at temperatures above 130℃. Between the temperature range from 100℃to 130℃, the"full reaction" of the aliphatic epoxy rings is approximated, while the reaction rate of the cycloaliphaticepoxy ring begins to increase gradually. The maximum glass transition temperature (T_(g∞)) of the systemdoes not emerge before 220℃. The apparent activation energy is 13 .2 kcal/mole.     

Study of photopolymers. XXX. Syntheses of new di(meth) acrylate oligomers by addition reactions of epoxy compounds with active esters

Some dimethacrylate oligomers were synthesized by new addition reactions of 2,2-(4-hydroxyphenyl)propane diglycidyl ether (BPGE) or glycidyl methacrylate (GMA) with phenyl methacrylates such as phenyl methacrylate (PMA), 4-nitrophenyl methacrylate (NPMA), 2,4-dichlorophenyl methacrylate (DCPMA), 4-methoxyphenyl methacrylate (MPMA), and (4-cinnamoyloxy)phenyl methacrylate (CIPMA) using tetrabutylammonium bromide as a catalyst at 120°C. The other new dimethacrylate or diacrylate oligomers were also prepared by the addition reactions of GMA or glycidyl acrylate with active esters such as di(S-phenyl)thioisophthalate (PTIP), di(4-nitrophenyl)isophthalate (NPIP), di(4-nitrophenyl)adipate (NPAD), and di(4-nitrophenyl)sebacate (NPSB) under similar reaction conditions. Furthermore, the rates of photochemical reaction of the obtained dimethacrylate oligomers were measured with 3 mol % of various photosensitizers such as benzoin iso-propyl ether (BIPE), 2-ethylanthraquinone (EAQ), and benzophenone (BP). The rate of photochemical reaction of BPGE-DCPMA oligomer was higher than those of BPGE-PMA, BPGE-NPMA, and BPGE-MPMA oligomers using BIPE as a photosensitizer. However, the photochemical reactivity of the unsensitized BPGE-CIPMA was almost the same as that of the sensitized BPGE-DCPMA. On the other hand, when EAQ was used as a photosensitizer, GMA-PTIP oligomer showed much higher reactivity than GMA-NPAD, GMA-NPSB, and GMA-NPIP oligomers. Also it was shown that the activity of EAQ as a sensitizer was higher than BIPE and BP in the photochemical reaction of BPGE-DCPMA oligomer.     

Oligomerization of Substituted Phenyl Glycidyl Ethers with Tertiary Amine

The oligomerization of substituted phenyl glycidyl ethers was studied kinetically in the presence of dimethylbenzylamine using toluene or dioxane as a solvent. The infrared spectra of the resultant oligomers suggest that the reaction products have the internal carbon-carbon double-bond un-saturation, which is confirmed by the catalytic hydrogenation. The molecular weights of the oligomers also suggest that γ-phenoxy allyl alcohol produced by the initial reaction step, in which the γ-proton of phenyl glycidyl ether is attracted by a base, amine, reacts with other phenyl glycidyl ether and thus proceeds further, yielding the oligomer. The value of the reaction constant ρ is obtained positive for this reaction, which indicates that electron-withdrawing substituents of phenyl gylcidyl ethers increase the rate of oligomerization. A kinetic analysis shows that the proposed reaction sequence accounts for all the characteristics of the polymerization including sigmoidal shapes of monomer consumption curves, reaction rates, and induction periods.