Epoxide/amine

The use of chiral shift reagents, e.g. tris-[3-(trifluoromethyl)- or -(hepta-fluoropropyl)-hydroxymethylene)-d-camphorato)]europium, praseodymium, or ytterbium, in the determination of optical purities of chiral alcohols, ketones, esters, epoxides, amines, or sulphoxides, or in the separation of n.m.r. signals of internally enantiotopic protons e.g. PhCHjOH), has been described. 

J. Klee u. H.H. Horhold, Mitteilbl. Chem. Ges. DDR 36, 225-233 (1989) (Epoxid-Amin-Additionspoly-mere). 

The amine-cured DGEBA epoxies utilized as matrices for filament wound composites generally form exclusively from epoxide-amine addition reactions (1). 

The nature of the cure reactions in these epoxies can be confirmed by monitoring the epoxide consumption via near infra-red spectroscopy for a series of epoxide-amine mixtures containing a range of amine contents. A plot of % epoxide consumption vs. amine concentration for DGEBA-T403 epoxies is illustrated in Fig. 2. This plot confirms that the DGEBA-T403 epoxy system forms exclusively from epoxide-amine addition reactions, because (i) 100% epoxide consumption is attained at the stoichiometric amine concentration associated with exclusive epoxide-amine addition cure reactions and (ii) extrapolation of this plot to zero amine content indicates there is no epoxide consumption i.e. there are no epoxide homopolymerization reactions. 

In the 177-300 °C temperature range studied, epoxide isomerization, oxidation and homopolymerization can occur followed by complex degradation reactions. There have been numerous studies on the homopolymerization of epoxides including the effects of catalysts, alcohols, cure temperature and epoxide-amine ratio on the... 

Schechter 55) proposed that the catalytic effect of hydroxyl groups on the epoxide-amine addition reaction involved a termolecular activated complex formed in the concerted reaction of amine, epoxide and hydroxyl. Smith 57) suggested a modified mechanism in which the same activated complex is formed in a bimolecular reaction between an adduct formed from epoxide (E) and the proton donor (HX), and the amine ... 

Another aspect that has not been taken into account in the kinetic models discussed so far is the occurrence of ether-forming reaction through epoxide homopolymerisation or reaction with hydroxyl groups. In the system TGDDM with an initial DDM concentration less than the stoichiometric level the overall conversion of epoxide is greater than that expected for epoxide-amine addition 89, 97 98). 

In practice the epoxide-amine cure is often accelerated by the addition of catalysts such as boron trifluoride complexes, and the boron trifluoride-ethylamine adduct (BFE) is widely used for this purpose. In addition to catalysing the epoxide-amine reactions, BFE can initiate homopolymerisation of epoxide. The accelerating effect of BFE is illustrated by DSC scans for the TGDDM/DDS/BFE system in Figure 12. The multiple-peaked exotherm associated with the BFE-catalysed TGDDM/DDS cure indicates that the kinetics of this system are more complex than those for the cure with amine alone. For this system the overall heat of reaction was found to decrease with increasing BFE concentration 89). For DDS alone Q0 was about 110 kJ per mole epoxide while the value for BFE alone was 75 kJ/mole, and the DDS/BFE values were between these limits. It appears that the proportion of epoxide homo-polymerisation relative to amine or hydroxyl addition increases with increasing BFE concentration. 

The cure kinetics of some epoxy resin powder coating composition were reported by Olcese et al.108). These were mixtures of BADGE resins with DICY and an epoxide-amine adduct or an imidazole as accelerator, together with TiOz and plasticisers. Data from DSC scans were analysed using Eq. (2-12) to obtain the apparent activation energy, E. Also Eq. (2-13) and (2-13 a) were used to obtain estimates of E and order... 

In the case of epoxide-amine reactions, p-hydroxyalkylamihe should be generated where a hydrogen bond between the free electron pair of nitrogen and secondary hydroxy group can be formed (Eq. (35)) ... 

It is worth pointing out that the stoichiometry between epoxy group and NH function has always been controlled furthermore, the curing conditions have been defined in order to have an epoxide-amine reaction as complete as possible 40 °C for 12 h, then at Tg + 30 °C for 24 h. 13C and 15N NMR [64]... 

Let us consider the variation of the composition in a two-component system (R + H), e.g., unsaturated polyester-styrene or epoxide-amine. Are density measurements capable of detecting such a variation ... 

Some important trends of the structure-property relationships in this field are well illustrated by a comparison of some stoichiometric, fully cured epoxide-amine networks (Table 10.6). 

Nonstoichiometric systems or incompletely cured stoichiometric systems behave as if they were internally plasticized systems. The modulus variation with cure conversion (x), for a typical stoichiometric epoxide-amine network, is shown in Fig. 11.8. 

Figure 11.8 Shape of isothermal, low-frequency, modulus variations against cure conversion for a stoichiometric epoxide-amine system. (1) vitrification (2) antiplasticization decreasing with conversion.

A comparison of results obtained for several networks based on the same epoxide-amine pair, but with variable amine/epoxide molar ratios, and thus variable crosslink densities, is shown in Table 11.3 (Tcharkhtchi et al., 1998). Havriliak-Negami and Perez models cannot be distinguished from one another by the quality of the fit of experimental curves, within experimental uncertainty. From a mathematical point of view, the Havriliak-Negami model is better than the Perez model because it has less parameters to fit (four parameters against five). In contrast, physical arguments could favor the Perez model, for which the parameters have a physical interpretation. 

For grafting onto , a wide variety of surface chemistries is available (Table 1). This makes it a versatile approach that can be applied on many different types of surfaces. Frequently, polymers incorporating thiol [85] or disulfide groups [86] are tethered to noble metal surfaces, but there are many other appropriate reactive pairs, such as carboxy-amine [87], epoxide-hydroxy [88] or epoxide-amine... 

Figure 2.8 Covalent immobilization can be achieved by linking either amino or acid groups of the enzyme with epoxides, amines, or aldehyde groups on the carrier, in addition, sugar residues can be coupled to the carrier.

This method has been applied to polyether triol-diisocyanate as well as polyether diol-trimethylolpropane-diisocyanate systems 142). The application of the branching theory enables to deal with systems involving groups of unequal and dependent reactivities. Determination of the substitution effect within amino groups in the epoxide-amine reactions is explained in a recent review143>). 

Subsequently, other workers including O Neill and Cole (4 and Dannenberg (5 ) showed that Reactions 2 and 3 proceed to the exclusion of Reaction 4. The reactivity of a particular epoxide-amine system depends on the influence of the steric and electronic factors associated with each of the reactants. It has been known for some time that hydroxyls play an important role in the epoxide-amine reaction. For example, Shechter et al. ( ) studied the reaction of diethylamine with phenylglycidyl ether in concentrated solutions. They showed that acetone and benzene decreased the rate of reaction in a manner consistent with the dilution of the reactants, but that solvents such as 2-propanol, water, and nitromethane accelerated the reaction (Figure 3). They also found that addition of 1 mol of phenol to this reaction accelerated it to an even greater extent that addition of 2-propanol or water. 

These mesoporous mixed titania-silica oxides are hydrophilic materials and are excellent catalysts for epoxidations of olefins, allylic alcohols and a,jff-unsaturated ketones with alkyl hydroperoxides in non-aqueous media [37]. Their performance can be improved even further by adding organic or inorganic bases to neutralize acid sites present on the surface [38,39], The latter cause side-reactions, especially with acid sensitive epoxides. Amine addition was particularly effective and led to the development of a mesoporous Ti-Si mixed oxide containing surface-tethered tertiary amino groups as an active, selective, and recyclable catalyst for the epoxidation of allylic alcohols [38]. 

T. Mika Cll) has reviewed the chemistry of curing agents and how these influence the properties of the cured resins. Compounds such as phenol and boron trifluoride are effective accelerators for epoxide-amine reactions, while solvents usually slow down this same reaction due the lower concentration of reactants and/or to specific hydrogen bond interactions. 

In this paper we address the area of the structure-property relations of epoxy matrices, with specific emphasis on amine-cured epoxides. In attempts to correlate the structure-property relations of amine-cured epoxides, there have been a number of studies on the mechanical properties of these glasses as a function of epoxide amine ratios and the chemical structure of the constituent epoxide and amine monomers.(1-15) Generally, there is no direct correlation between the chemistry of the epoxide and amine monomers and the mechanical properties of epoxies with the exception that as the distance between crosslinks becomes shorter, these glasses become more brittle.(1,10,15) Also, for a specific amine-cured epoxide system, the Tg is always highest for the fully reacted, highest crosslink density glass.(3,6,9,12,... 

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