The epoxy–polycarbonate blends cured with aliphatic amine—I. Mechanism and kinetics

Reaction mechanism of the PC–epoxy blends cured by aliphatic amine has been investigated by varying PC contents in the blends. The transamidation reaction tends to convert nearly all the carbonates into N-aliphatic aromatic carbamates even at ambient temperature before normal curing. The remaining amine proceeds the normal curing with epoxy at a higher temperature (80°C). For the PC–epoxy/aliphatic amine blend containing 6 wt % PC, the yielded N-aliphatic aromatic carbamate further reacts with amine to produce the urea structure. The urea undergoes substitution reaction with the hydroxyl formed from the normal curing to give the N-aliphatic aliphatic carbamate. For the blend containing 12 wt % PC, the N-aliphatic aromatic carbamate converts into the N-aliphatic aliphatic carbamate via two different routes. For the blend containing lower molecular weight of the aliphatic amine, the N-aliphatic aromatic carbamate reacts with hydroxyl to form the N-aliphatic aliphatic carbamate directly. For the blend containing higher molecular weight of aliphatic amine, the N-aliphatic aromatic carbamate decomposes into the aliphatic isocyanate accelerated by the presence of the residual oxirane. The isocyanate formed then reacts with hydroxyl to yield the N-aliphatic aliphatic carbamate. The activation energy (E_a) and preexponential factor (A) of the PC–epoxy/POPDA blends decrease with the increase of the PC content. Kinetic study by thermal analysis by the method of autocatalyzed model is able to correctly predict oxirane conversion vs. time relationship for the neat epoxy/aliphatic amine and the PC–epoxy/aromatic amine systems because the dominant reaction is the normal curing reaction between amine and oxirane. The model fails to predict the PC–epoxy/aliphatic amine system because the system is complicated by several other reactions besides the normal curing reaction. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2169–2181, 1997     

Microwave-mediated one step synthesis of tri- and tetracyclic heterocyclic molecules

Abstract

Tricyclic and tetracyclic compounds related to vasicine and batracyclin, respectively, have been synthesized via condensation of dicarboxylic acids (aliphatic acid, homophthalic acid, and aromatic acid) with diamines (aliphatic, aminobenzyl amine, and aromatic amine) under solvent-free condition.     

High resolution solid‐state 13C‐NMR study of as‐cured and irradiated epoxy resins

This article presents the effects of strong ionizing radiations on the physico‐chemical modifications of aliphatic or aromatic amine‐cured epoxy resins based on diglycidyl ether of bisphenol A (DGEBA). Such epoxy resins have a considerable number of applications in the nuclear industrial field and are known to be very stable under moderate irradiation conditions. Using extensively high resolution solid‐state ¹³C‐NMR spectroscopy we show that the aliphatic amine‐cured resin (DGEBA‐TETA) appears much more sensitive to gamma rays than the aromatic amine‐cured one (DGEBA‐DDM). On the one hand, qualitative analyses of the high resolution solid‐state ¹³C‐NMR spectra of both epoxy resins, irradiated under similar conditions (8.5 MGy), reveal almost no change in the aromatic amine‐cured resin whereas new resonances are observed for the aliphatic amine‐cured resin. These new peaks were interpreted as the formation of new functional groups such as amides, acids and/or esters and to alkene groups probably formed in the aliphatic amine skeleton. On the other hand, molecular dynamics of these polymers are investigated by measuring the relaxation times, T_CH, T_1ρH and T_1C , before and after irradiation. The study of relaxation data shows the formation, under irradiation, of a more rigid network, especially for the aliphatic amine‐cured system and confirms that aromatic amine‐cured resin [DGEBA‐4,4′‐diaminodiphenylmethane(DDM)] is much less affected by ionizing radiations than the aliphatic amine‐cured resin [DGEBA‐triethylenetetramine(TETA)]. Moreover, it has been shown that the molecular modifications generated by irradiation on the powder of the aliphatic‐amine‐cured resin appear to be homogeneously distributed inside the polymers as no phase separations can be deduced from the above analyses. Copyright © 2001 John Wiley & Sons, Ltd.     

Molecular engineering of pyroelectric polysiloxane Langmuir-Blodgett superlattices: synthesis,film preparation and pyroelectric properties

A wide range of linear and cyclic polysiloxanes substituted with side chains containing carboxylic acid groups have been synthesized and characterized in terms of their Langmuir/Langmuir-Blodgett (LB) film properties and their pyroelectric activity. The effects on these properties of varying the degree of side-group substitution, the length of aliphatic side groups, the incorporation of polar aromatic side groups and the deposition conditions utilized during the preparation of multilayer assemblies have been investigated. These materials form stable Langmuir layers at the air-water interface which can be transferred onto substrates such as glass and aluminium-coated glass. The alternate layer LB deposition technique, in which each polysiloxane layer is co-deposited in an alternating stacking sequence with monolayers of a monomeric aliphatic amine compound, has been used to fabricate macroscopically polar films which display a temperature-dependent electric polarization, the ‘pyroelectric effect’. Data are presented here for both linear and cyclic substituted polymer backbones showing that both systems provide useful insight into the pyroelectric behaviour of organic materials. Trends in the relationships between the pyroelectric activity and (1) the chemical structure of the materials and (2) the structure of the acid/amine superlattice have been identified and indicate that the optimum pyroelectric coefficient is observed for a linear copolysiloxane compound substituted with a polar aromatic pendant side group. Indeed, the pyroelectric coefficient measured for this material is ∼10μCm⁻² K⁻¹ which is currently the highest value reported for an LB assembly to our knowledge.     

Studies in some new initiator systems for vinyl polymerization. III. Amine–halogen systems as redox initiators

Amine–halogen redox systems are very efficient initiators of polymerization of a number of vinyl monomers in benzene media and are rather inefficient initiators in aqueous media. A large number of aliphatic amines and a few aromatic amines have been used. Among the halogens, chlorine and bromine are very effective. Iodine initiates with a few amines only. Endgroups incorporated are halogen and amine totalling an average of nearly one per chain in the case of polymerization in benzene media and 0.5–0.7 per chain in polymerization in aqueous media. In the light of endgroup results, a mechanism of initiation through halogen and amine radicals has been suggested.     

Transformations of 5,6,7,8-tetrafluoro-2-ethoxycarbonylchromone under the action of primary amines

5,6,7,8-Tetrafluoro-2-ethoxycarbonylchromone in aprotic polar solutions formed by nucleophilic aromatic ipso-substitution 7-alkyl(aryl)amino-5,6,8-trifluorochromones. This transformation in ethanol depended on the reactivity of the acting amine: with stronger nucleophiles, aliphatic amines, an opening of the γ-pyrone ring occurred, with aromatic amines 7-monosubstituted chromones were the main products, and the open-chain esters formed in lesser amount.     

Adhesive strength of fullerene-doped epoxyamine compositions

Dependence of adhesive strength of model gluing epoxide compositions glass-binder-glass hardened with aliphatic and aromatic amine hardeners on the fullerene additive content is studied. When aromatic amine is used as a hardener of epoxy-diane resin, addition of fullerenes does not affect the adhesive strength. On the contrary, when aliphatic amine hardener is used, the increase of adhesive strength as compared to nondoped composition was 400%. Use of a mixture of aliphatic and aromatic hardener leads to substantial synergism of their effect on strength properties of the fullerene-doped compositions.     

Polyepoxide-water interactions: Influence of the chemical structure of the network

We have investigated the influence of the chemical structure of polyepoxide networks on the sorption behaviour and water-induced changes of viscoelastic and mechanical properties. The β relaxation was found to be unaffected by the presence of adsorbed water for an anhydride and an aromatic amine based polyepoxide. The anhydride based network shows better behaviour in a water environment than the aromatic amine based network in terms of plasticisation, reversibility of the degradation and loss of mechanical properties. This has been attributed to (i) a smaller crosslinking density, leading to a smaller specific volume in the glassy state and thus a smaller water uptake and (ii) a strong interaction between water and tertiary amines in epoxide-aromatic amine networks. This interaction, probably of electrostatic nature, would result from the delocalization of the doublet of the nitrogen atom. The results are critically compared to the literature on aliphatic amine based polyepoxides, where the dependence of the β relaxation on the water content is proposed to be related to the electron-donating ability of the aliphatic chain.     

Catalyst-free chemoselective N-tert-butyloxycarbonylation of amines in water

[Structure: see text] Catalyst-free N-tert-butyloxycarbonylation of amines in water is reported. The N-t-Boc derivatives were formed chemoselectively without any isocyanate, urea, N,N-di-t-Boc, and O/S-t-Boc as side products. Chiral amines, esters of alpha-amino acids, and beta-amino alcohol afforded optically pure N-t-Boc derivatives. Amino alcohol and 2-aminophenol afforded the N-t-Boc derivative without oxazolidinone formation. Selectivity was observed during competition of aromatic amine vs aliphatic amine, amine vs amino acid ester, amine vs amino alcohol, and primary amine vs secondary amine.     

Homogeneous ion-exchange membranes of improved flexibility

Poly(styrenesulfonic acid) ion-exchange membranes having various degrees of porosity and flexibility have been prepared by using aliphatic and aromatic esters of p-styrenesulfonic acid. The membranes formed from the aliphatic ester monomers were found to exhibit an increase in water uptake, permeability, and flexibility with increase in the size of the alcohol group of the ester monomer. With membranes formed from the phenyl and β-naphthyl ester monomers the reverse trend was indicated. The flexibility of the membranes formed from the aromatic ester monomers was much greater than that obtained with the aliphatic esters.