Thermally stimulated current study on flexible siloxane-modified epoxy sheets

Copolymers prepared from the epoxy resin of ALBIFLEX and PMPS oligomer were evaluated with IR, ¹H-and ¹³C NMRs for structural determinations. The flexible epoxy resin as a model compound was examined by TSC with variations on the operational parameters t_p and V_p. Transitions denoted as T_g,δ, T_g,γ, T_g,β, T_g,α and T_g,ρ in increasing order of temperature were observed for these copolymers. As an example, ESAF-7430 copolymer showed these transitions at −138, −84, 26, 87, and 110 °C, respectively. Each transition except the T_g,ρ at 110 °C, has been correlated to a segment in the copolymeric structure. The result indicates that TSC provides clear molecular transitions at the temperature of the transition. The molecular transition of the grafted PMPS-siloxane segment in an epoxy matrix appeared at the −45 °C region as a broad, nearly flat peak as it filled the concave part of the TSC curve of the unmodified resin. The flexibility that the modified copolymers retained may be attributed to these sub-T_g transitions as observed in the TSC spectrum.