Changes in molecular relaxations and network properties of a triaromatic liquid crystal epoxy resin with nonterminal functional groups

Abstract

AbstractTwo types of liquid crystal epoxy precursors and corresponding epoxy‐amine networks are investigated in this paper. The epoxy groups are non‐terminal in one of the monomers (NTEM) and terminal in the other one (MU22). Both monomers contain the same mesogen and exhibit liquid crystal properties. Structural differences between the carbon chains affect physical properties of the monomers and the products of curing, which involves a typical diamine—DDM (4,4′‐diaminodiphenylmethane). Phase transition temperatures, conditions of the curing reaction and glass transition temperatures in the cured products are determined through differential scanning calorimetry (DSC), optical observations (POM) and broadband dielectric spectroscopy (BDS). The modification of the carbon chains affects the phase transition temperatures, dielectric response, and the glass transition in the cured products. The dielectric response of NTEM monomer reveals two relaxation processes (β and γ) associated with molecular motions of polar groups in the mesogen (β‐process) and in the carbon chains (γ‐process). In contrast, MU22 only displays a similar β‐process. A segmental α‐process related to structural reorientation (connected with glass transition) appears in both cured products, but in NTEM the glass transition temperature is significantly lower. Local relaxations in the epoxy networks match the corresponding processes in their respective precursors.