Crosslinking of mixtures of diglycidylether of bisphenol‐A with 1,6‐dioxaspiro[4.4] nonan‐2,7‐dione initiated by tertiary amines: III. Effect of hydroxyl groups on network formation

BACKGROUND: Blends of epoxy resin oligomers, diglycidylether of bisphenol‐A (DGEBA), and a bislactone, 1,6‐dioxaspiro4.4]nonan‐2,7‐dione (s(γBL)), were anionically copolymerized using two tertiary amines as anionic initiators. Their curing rheology and gelation behaviour were studied to provide a more comprehensive knowledge of the curing of these previously studied systems. RESULTS: The activation energy for gelation was found to be similar to that previously measured using differential scanning calorimetry and appeared to increase in the presence of the bislactone. The reaction rate during copolymerization of DGEBA with s(γBL) was slower than DGEBA homopolymerization alone because the alkoxide attack on the epoxide is faster than the reaction of the carboxylate ion and the epoxy group. The effect of the initiator type on the gel conversion was small and was presumably due to differences in the kinetic chain length caused by amine regeneration from the quaternary amine. For the same initiator and at a constant ratio of DGEBA/s(γBL), an increase in the hydroxyl concentration of the DGEBA oligomer raised the gel conversion. For a DGEBA oligomer with low hydroxyl levels, an increase in the concentration of s(γBL) increased the gel conversion; however, for a DGEBA oligomer with high hydroxyl levels, increasing s(γBL) concentration decreased the gel conversion. CONCLUSION: These results are interpreted in terms of the effect of initiation rate and chain transfer rate on the kinetic chain length. The glass transition temperature of the gel was found to be controlled by the fraction of the aliphatic s(γBL) and the amount of plasticizing sol in the matrix. Copyright © 2009 Society of Chemical Industry