Phase separation in benzoxazine/epoxy resin blending systems

Enlarging dynamic asymmetry in situ by controlling the polymerization sequence is known to be a good way to obtain phase separation structures in benzoxazine (BZ)/epoxy resin (ER) blending systems. In this paper, the possible reactions in BZ/ER blends were studied using model components. The results indicated that once phenolic hydroxyl groups (OH) were produced by the polymerization of BZ resin, the copolymerization between BZ and ER resin was unavoidable, which was unfavorable for the phase separation of the BZ/ER system. If ER could polymerize before BZ, the copolymerization between BZ and ER is expected to be suppressed by the lack of phenolic OH, and the dynamic asymmetry between ER and BZ could thus be enlarged, both of which are favorable for phase separation. In the following studies, a series of ER resins having different molecular weights (Mn) were used to study the possibility of phase separation in the BZ/ER systems. The turbidity observation, dynamic mechanical analysis and scanning election microscope experiments indicated that if the Mn of ER >= 4370 g mol(-1), phase separation could take place with the polymerization of BZ resin and different morphologies could be observed by varying the ER content.