Phase separation process in poly(ε-caprolactone)−epoxy blends (PCL−epoxy) cured by 4,4‘-diaminodiphenyl sulfone (DDS) was investigated by OM and SEM. The blend compositions higher than the critical point exhibit macrophase separation by the spinodal decomposition (SD) mechanism of the epoxy and results in the epoxy particles being dispersed in the matrix. These epoxy particles grow larger gradually and connect to each other to give macrophase epoxy domains with irregular shape. After that, two more stages of microphase separations take place via a nucleation and growth (NG) mechanism and result in smaller epoxy particles being dispersed in the matrix. Blend compositions lower than the critical point exhibit the SD or NG mechanisms of PCL, but the microphase separation is observed only within the epoxy matrix. These phase separation mechanisms can be illustrated successfully by the phase diagram constructed by the spinodal and binodal curves. Hydrogen bonding between protons from the epoxy with carbonyls from PCL has been investigated by FTIR. The mixing free energy reduction by the hydrogen bonding can contribute to the LCST behavior rather than the UCST behavior predicted by the Flory−Huggins equation based on only nonpolar interactions.

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Transesterification has been investigated in poly(-caprolactone) (PCL)-epoxy blends. In the hot melt process, the hydroxyl on diglycidyl ether of bisphenol-A (DGEBA) monomers is too low to give a noticeable transesterification reaction. In the postcure process, model reactions reveal that the hydroxyls from a ring-opening reaction are able to react with the esters of PCL. In the meantime, the PCL molecular weight decrease and its distribution becomes broader. Nuclear magnetic resonance spectra reveal that fraction of the tertiary hydroxyls converts to secondary hydroxyls. In the cured DGEBA-3,3Ј-dimethylmethylene-di(cyclohexylamine)-PCL blend, a homogeneous morphology is achieved. PCL segments are grafted onto the epoxy network after postcuring and result in the lower T g observed in the differential scanning calorimetry thermogram. A higher transesterification extent also results in broader transition peaks by dynamic mechanical analysis.

In the Bisphenol A base polycarbonate−Bisphenol A base epoxy blend system, the carbonate group can react with epoxide in the presence of a tertiary amine. The transesterification reactions convert the original aromatic/aromatic carbonate of PC to aromatic/aliphatic and aliphatic/aliphatic carbonates. IR spectroscopy shows an unknown major structure formed during the later stages of the transesterification reaction. The unknown structure was investigated by a model reaction using diphenyl carbonate and phenyl glycidyl ether leading to the formation of 4-(phenoxymethyl)-1,3-dioxolan-2-one (PMD), which has been identified by IR, UV, 1H NMR, 13C NMR, and mass spectroscopy. The mechanism of forming the cyclic carbonate is proposed to proceed through a zwitterion and a nucleophile attack of the aromatic/aliphatic or the aliphatic/aliphatic carbonate group.