Rates of epoxy−amine reactions in thermoset/thermoplastic blends with different thermoplastic concentrations were studied. The selected thermoset system was bisphenol A diglycidyl ether cured with 4,4‘-methylenebis[3-chloro-2,6-diethylaniline] in the presence of various concentrations of polyetherimide (PEI) (10−64 wt %). As the initial systems are homogeneous, the rate constants for the epoxy−amine neat system and the rate constants of the blends are the same, the addition of PEI in the epoxy−amine system leads only to a dilution of reactive groups during this first step. But due to the epoxy−amine reaction, a liquid−liquid phase separation occurs at a given conversion (in the range 0.2−0.4). At the same time and for PEI concentrations equal or higher than 30 wt %, a sudden increase of the reaction rate is observed from experimental results. Comparison between blends based on PEI and polystyrene (PS) shows that after phase separation the reaction rate of the PS blend was higher than the PEI blend due to a faster phase separation process for the PS blend. Estimations of the new dilution ratio of the two phases have been made through glass transition temperature measurements. Modeling of the kinetics of the epoxy−amine reaction in each phase of a 48 wt % PEI blend have been made. The increase of the reaction rate at phase separation can be explained by the formation of an epoxy−amine-rich phase with a faster reaction rate. Modeling permits to predict that gelation in this phase occurs at a conversion close to 0.6.

The phase separation process in a thermoplastic-modified epoxy system was studied using rheological dynamic analysis (RDA) and differential scanning calorimetry (DSC). Transmission electronic microscopy (TEM) was used to get direct representation of morphologies at different times during the phase separation process. The selected thermoset system was bisphenol A diglycidyl ether (DGEBA) cured with 4,4‘-methylenebis[3-chloro,2,6-diethylaniline] (MCDEA) in the presence of various compositions of polyetherimide (PEI), 10−64 wt %. As rheology is a signature of connectivity, the rheological behavior at phase separation was found to be greatly dependent on the initial concentration of PEI. Experimental results showed that when PEI concentration was lower than 10−15 wt %, phase separation induced a rapid decrease of the viscosity. For concentrations close to the phase inversion composition, a rheological behavior characteristic of a bicontinuous morphology appeared with a strong dependence on frequency. When PEI concentration was higher than 30 wt %, phase separation led to a gradual increase in viscosity. A large interdependence between morphology and initial composition was exhibited. Modeling of the rheological behavior using kinetic parameters and the relationship between viscosity and mass average molar mass was in good agreement with the experimental results.

Methyl methacrylate (MMA)/N,N-dimethyl acrylamide (DMA) gradient copolymers with various chemical composition were synthesized by nitroxide-mediated controlled radical polymerization (NMP). Molecular weight (MW) characterization via gel permeation chromatography demonstrated that these materials were made in a “controlled” manner. The reactivity ratios values r 1(MMA) = 2.36 and r 2(DMA) = 0.33 were experimentally determined using the linear least-squares numerical method, results in good agreement with the literature. Characterization of the glass transition temperature, T g, by differential scanning calorimetry (DSC) of gradient copolymers exhibited one T g, with a value intermediate to the T g of pure poly(methyl methacrylate) (PMMA) and poly(N,N-dimethyl acrylamide) (PDMA). In contrast, di- and triblock copolymers made of poly(n-butyl acrylate) (PBA) as central block and PMMA/PDMA gradient copolymer as external block yielded two T g, one corresponding to the T g of PBA and the other intermediate to the T g of PMMA and PDMA, indicating microphase separation which was confirmed by dynamic mechanical analysis and TEM observations of films of di- and triblock copolymers showing lamellae structure.