Relations Entre Structure Chimique Et Propriétés Mécaniques Dans Les Réseaux Époxydes

Abstract

Relationships existing between chemical structure and the dynamic mechanical properties of epoxide networks are reviewed. This paper is focused on different model networks, prepared by the reaction between amines and DGEBA or DGEBD diepoxide monomers in stoichiometric proportions. The limit glass transition temperature, Tg, , is shown to depend mainly on molecular flexibility of network chains and on crosslink density. Frequency dependence of Tg, obeys the time-temperature superposition principle and can be described by a WLF-type equation. However, the coefficients C1 and C2 in this equation depend on the molecular characteristics of the network, in agreement with free volume concepts. Values of elastic modulus well above Tg reflect mostly the influence of crosslink density. Surprisingly to some extent, application of rubber elasticity theory to these densely crosslinked systems yields very reasonable average network chain molecular weights Mc. In the glassy region, the mechanical relaxationsp and y are shown to originate from motions of -CH2-CHOH-CH2-0-epoxide groups and of -(CH2)4-groups, respectively. Motions responsible for the @-relaxation appear at the same temperature, whatever the network characteristics may be. On the other hand, both amplitude and broadening of the p-relaxation loss peak are functions of crosslink density, From a practical viewpoint, these two characteristics influence markedly the plastic behavior of the networks and their elastic modulus at room temperature as well.

Thiol−Yne Photopolymerizations: Novel Mechanism, Kinetics, and Step-Growth Formation of Highly Cross-Linked Networks

“…The T g in polymer networks is primarily determined by the stiffness of the polymer backbone and the cross-link density. ( 40 ) Both DDY and BDDVE possess similarly nonrigid, saturated, nonfunctionalized backbones, which are presumably of similar stiffness. The observed increase in glass transition temperature is thus attributed to the higher cross-link density of PETMP/DDY.…”

“…The T g of the more completely reacted PETMP/DDY network is ∼70 °C higher than the PETMP/BDDVE network. The T g in polymer networks is primarily determined by the stiffness of the polymer backbone and the cross-link density . Both DDY and BDDVE possess similarly nonrigid, saturated, nonfunctionalized backbones, which are presumably of similar stiffness.…”

Free volumes and structural relaxations in diglycidyl ether of bisphenol-A based epoxy–polyether amine networks

“…[3][4][5] One of the outstanding features of epoxy-amine networks is the ease of tunability of the network architecture by varying the crosslink density and/or the exibility of chains between crosslinks. 6 Some of the common methods used to systematically vary the crosslink density of epoxy-amine networks are controlling the extent of cure, 7,8 altering the stoichiometric ratios of epoxy and amine, 9,10 using a mixture of monoamines and primary diamines, [11][12][13][14][15] and using aliphatic epoxy resins and diamines instead of conventional aromatic co-monomers 16 etc.…”

Intermolecular interactions on amine‐cured epoxy matrices with different crosslink densities. Influence on the hole and specific volumes and the mechanical behavior

“…Thus, the molecular structure of epoxy matrices can be changed in a continuous and controlled mode, from that corresponding to a linear polymer to that for a highly crosslinked polymer. [1][2][3][4][5][6][7][8][9] Working at epoxy/amine stoichiometric ratio, full reacted networks can be obtained avoiding lateral chains and secondary reactions. Selecting amines with a similar chemical structure, the change in the chemical composition of the system is minimal, and hence the chain flexibility between crosslink points can be retained.…”

“…Several works have been published studying epoxy/amine mixtures trying to understand the effects of different variables on their final behavior of this kind of polymers. [1][2][3][4][5][6][7][8][9][10][11][12] However, most of them have been focused on the effects of the network architecture on their thermal and mechanical behavior and not on the microstructure of the generated networks. The chemical composition, architecture and packing density, chemical interactions, and local mobility of the networks obtained after curing processes are important variables to be analyzed because of their influence on the elastic and fracture properties, 4,5,7,9,[11][12][13] and besides, on the diffusion processes of small molecules through these matrices.…”