Liquid crystalline elastomers based on diglycidyl terminated rigid monomers and aliphatic acids. Part 1. Synthesis and characterization

Abstract

Liquid crystalline elastomers (LCEs) were prepared by reacting rigid-rod mesogenic epoxy monomers with aliphatic diacids of variable length. The influence of acid and nature of epoxy monomer on the mechanism of network growth was investigated through DSC, FT-IR, MALDI, 1 H and 13 C NMR and rheological experiments. Depending on the nature of epoxy monomer, different mechanisms of network growth occurred, which were responsible for the formation of elastomers with different extent of branching.Clearing temperatures, enthalpies and entropies, and the nature of mesophases were also analyzed through DSC and X-ray diffraction, carried out on unstrained elastomers. It was found that both the rigid-rod mesogens and the aliphatic portions of carboxylic acids contribute to stabilize the mesophase. Moreover, upon stretching, all the LCEs exhibited the polydomain-to-monodomain transition, which is typical of this class of materials. q

Liquid crystalline elastomers based on diglycidyl terminated rigid monomers and aliphatic acids. Part 2. Mechanical characterization

“…Elastomers were synthesized from epoxy monomers PHBHQ and DOMS by reaction with carboxylic acids of general formula HOOC-(CH 2 ) n -COOH, with n comprised between 4 and 8, as it has been described in Part 1 [7]. In this paper, we have investigated on the mechanical properties of the systems obtained by reacting DOMS and PHBHQ with adipic acid (AA) and decanedioic acid (SA), respectively (DOMS-AA, PHBHQ-AA, DOMS-SA and PHBHQ-SA systems), whose thermal properties and mesophases are reported in Table 1.…”

“…In smectic phases, a stack of identical flat layers, parallel to each other, can be identified. In such phases, the inner maxima are related to the spacing of the smectic layers, d [7]. At this point the sample is opaque, indicating the existence of a 'polydomain' microstructure.…”

“…From the diameter of the outer maxima, calculations of the average intermolecular distance, D, i.e. the average distance between the long axes of adjacent molecules, can be done [7]. The inner diffraction ring is indicative of a smectic phase.…”

“…In Part 1 of this work we have reported the synthesis and characterization of two groups of LCEs obtained by reacting rigid-rod epoxy terminated molecules, namely p-bis(2,3-epoxypropoxy)-a-methylstilbene (DOMS) and 4 0 -(2,3-epoxypropoxy)phenyl-4-(2,3-epoxypropoxy)benzoate (PHBHQ), with aliphatic acids of general formula HOOC-(CH 2 ) n -COOH, with n comprised between 4 and 8 [7]. The curing reactions were investigated by DSC, FT-IR, rheological experiments, MALDI-TOF, NMR, and we found that, in the case of DOMS, the systems grow with a high degree of branching, giving rise to smectic A elastomers.…”

Synthesis and Properties of New Liquid Crystals as Curing Agents for Epoxy Resins

“…These include varying the epoxy resin curing agent functional group ratio, using a difunctional epoxy prepolymer with a different average chain length, and varying the molecular size of the difunctional curing agent, [3][4][5].…”