Abstract
A range of modified amine- and anhydride-cured epoxy systems based upon diglycidyl ether of bisphenol A was produced, through the systematic incorporation of moieties termed functional network modifiers (FNMs) that serve to change the network structure in controlled ways. Here, the chosen FNM was trimethylolpropane triglycidyl ether (TTE). The resulting materials were characterized by Fourier transform infrared spectroscopy, thermal analysis, dielectric spectroscopy and measurements of direct current conduction. A progressive reduction in the glass transition temperature of the modified samples was seen with increasing TTE, which is interpreted in terms of changes in the network architecture of the resin. The molecular origins of the dielectric γ and β relaxation processes are proposed. The observed increase in conduction seen exclusively with increasing TTE content in the amine-cured systems is considered in terms of the chemistry of the FNMs, variations in free volume, changes in molecular dynamics and residual unreacted groups retained from the curing reaction. Specifically, we relate the observed increase in conduction to the presence of unreacted amine groups.
Highlights
Epoxy resins are thermosetting polymers, which are widely used in diverse applications including dielectric materials, adhesives and fiber-reinforced composites
Tg is often considered to be closely related to the free volume in the system [3,18,32,33] and, In the case of amine curing, epoxide groups react preferentially with primary amines, such that the data presented in Table 1 could be related to changes in this factor that result from unreacted amine hydrogens will, in the form of secondary amines, tend to be located between (a) the choice of hardener; and (b) the incorporation of the triglycidyl ether (TTE) functional network modifier
Inclusion of the functional network modifiers (FNMs) modifies the chemical reactions that occur during curing. Such that, again, the invariance in DC conductivity with composition seen in the former material set we suggest that during amine-curing of systems containing the FNM, increased indicates that composition-related variations in molecular dynamics is unlikely to be the source of the homopolymerization occurs, which serves to consume epoxide groups
Summary
Epoxy resins are thermosetting polymers, which are widely used in diverse applications including dielectric materials, adhesives and fiber-reinforced composites. In the with OH groups in the system, forming ether links in a process termed etherification, albeit that if case of anhydride cured systems, in addition to the two terminal epoxide groups of the resin, OH the OH group originates from the backbone of the resin, the reaction is commonly referred to as groups react in the anhydride initiation process. These OH groups are found on the backbone of the homopolymerization (Figure A1). The impact of changes in the network architecture on charge transport is considered
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