Physical aging of epoxy resin blended with poly(ether sulfone): Effect of poly(ether sulfone) molecular weight

The physical aging process of 4-4'-diaminodiphenylsulfone (DDS) cured diglycidyl ether bisphenol-A (DGEBA) blended with various molecular weights of poly(ether sulfone) (PES; M-n = 28,600, 10,600, and 6,137) was studied by DSC. For DGEBA/DDS system blended with a low MW PES-3 (M-n = 6,137), no phase separation of the polymer blend and only one enthalpic relaxation process due to physical aging was observed. Since the high MW PES-1 (M-n = 28,600) had a T-g close to that of fully cured DGEBA/DDS, the fully cured DGEBA/DDS/PES-I blend had a broader glass transition than a neat DCEBA/DDS system. However, the DSC results showed two enthalpic relaxation processes due to the physical aging of PES-rich and cured epoxy-rich phases as the material was aged at 155 degreesC (30 degreesC below T-g). Since the T(g)s of PES-1-rich and epoxy-rich phases overlapped with each other, the enthalpic relaxation processes corresponding to each phase coupled to each other in the earlier stage of physical aging. The medium MW PES-2 (M-n = 10,600) has a much lower T-g than that of fully cured DGEBA/DDS, two well separated TgS were observed for the cured DOEBA/DDS/ PES-2 blend, indicating the cured epoxy was immiscible with PES. Aging the polymer blend at 155 degreesC (24 degreesC below T(g)1 of the PES-2-rich phase and 53 degreesC below T-g2 OF the epoxy-rich phase) produced two well separated relaxation processes due to PES-2-rich and epoxy-rich phases. The experimental results suggested that aging the polymer blend at a suitable temperature would improve the phase separation between PES-1-rich and epoxy-rich phases.