Synthesis and improved mechanical properties of twin‐mesogenic epoxy thermosets using siloxane spacers with different lengths

Abstract

A series of twin-mesogenic epoxy resins with siloxane (di-, tri-, and tetra-siloxane) chain spacers of different lengths were successfully synthesized. Results showed that the melting point of the twin-mesogenic epoxy monomers decrease by more than 50 C due to the change of siloxane spacer length. In particular, the tri-and tetra-incorporated siloxane twin-mesogenic epoxy monomers showed a liquid crystalline (LC) phase below 100 C during the cooling process. Epoxy thermosets with isotropic and smectic (S m ) LC phases were then prepared using an aromatic amine and the dependence on curing temperature was investigated. Furthermore, the relationship between the ordered network chain structure and mechanical properties was investigated. Results were compared with isotropic and S m LC phases. The tensile strain and fracture energy in the S m type LC thermosets increased without a decrease in the tensile modulus, and this occurred in all systems irrespective of siloxane spacer length. The maximum value of the fracture energy (283 kJ m −2 ) reached by LC thermosets with increased spacer lengths was twice as large as that using the alkyl chain spacer (144 kJ m −2 ).

Epoxy resin composites with commercially available graphene: toward high toughness and rigidity

“…Furthermore, the fracture energy calculated from the area under the stress-strain curves is employed to study the toughness of EP composites. 30 The fracture energy of ATCG-PVP/EP-0.2 composite is increased to 3.6 kJ m À2 (56.5% higher than the corresponding value for pure EP), indicating the remarkable improvement in toughness. Dose the PVP surfactant play the role of toughening agent in EP composites?…”

Fracture toughness of highly ordered liquid crystalline epoxy thermosets achieved by optimized composition of curing agents

“…This is attributed to the induced molecular orientation in the networked epoxy polymer chains. Frequently used mesogenic backbone structures include biphenyl, 4–7 terphenyl, 8 stilbene, 9–20 azomethine, 21–36 ester, 37–49 ketone, 50 and azo 51,52 . In an earlier study, we reported a remarkable improvement in both the thermal and mechanical properties.…”

“…This is attributed to the induced molecular orientation in the networked epoxy polymer chains. Frequently used mesogenic backbone structures include biphenyl, [4][5][6][7] terphenyl, 8 stilbene, [9][10][11][12][13][14][15][16][17][18][19][20] azomethine, [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] ester, [37][38][39][40][41][42][43][44][45][46][47][48][49] ketone, 50 and azo. 51,52 In an earlier study, we reported a remarkable improvement in both the thermal and mechanical properties.…”

Advances in Liquid Crystalline Epoxy Resins for High Thermal Conductivity

“…Mesogenic groups and flexible chains exist between epoxy groups [ 19 ]. In addition, the twin mesogenic epoxy monomer has a structure in which a flexible chain exists between the mesogenic groups [ 24 ]. The properties of LCE tend to depend on the flexibility of the mesogenic group and spacer attached to the epoxy group; therefore, the structure and properties of the mesogenic group are important factors affecting the thermal conductivity of LCE [ 25 , 26 ].…”