Irina O. Plyusnina

Combining epoxy oligomers with various functionality and thermoplastic modifiers enables targeted regulation of the architecture of polymer networks and the phase structure of composites. A comprehensive interference–microscopic approach is proposed for studying phase equilibria, diffusion characteristics, and structure formation kinetics in the ternary system thermoplastic polyurethane (TPU)–trifunctional epoxy oligomer (Tactix)–difunctional epoxy oligomer (DGEBA) cured with 4,4′-diaminodiphenylsulfone (DDS). It may provide control of the morphology of epoxy compounds in a narrow concentration range without changing the chemical nature of the components. The TPU–Tactix–DGEBA system is found to be thermodynamically compatible over a wide temperature range. A ternary diagram is constructed, serving as a concentration map of the final morphologies. Four topological regions were experimentally identified and described. It has been shown that the addition of Tactix (more than 30 vol.%) accelerates the onset of thermodynamic incompatibility and shifts the point of phase separation to lower conversion levels (from 22% to 15%). It was established that the average domain size of the dispersed phase (from 0.15 to 0.6 µm) is controlled by the relationship between the time to reach thermodynamic incompatibility and the kinetic inhibition of diffusion as conversion increases. The proposed approach demonstrates the possibility of precisely altering the morphology of epoxy compounds within a narrow concentration range (within 10 vol.%) without altering the chemical nature of the initial components.

The effect of polypropylene glycol (PPG) on the phase structure formation and deformation properties of a photocurable system based on bisphenol-A 10-ethoxylate dimethacrylate (BPADMA) was studied. Optical interferometry established the complete compatibility of the components before polymerization, and the critical PPG concentration predicted as corresponding to the center of the phase inversion region (28 vol.%) was determined. SEM confirmed the formation of the predicted phase structure, characterized by interpenetrating continuous phases. FTIR spectroscopy showed that the introduction of PPG has virtually no effect on the conversion degree (92.3% for neat BPADMA and 91.5% for BPADMA–PPG blend prepared by volume). The enhanced deformation capacity and reduced compressive resistance are attributed to the formed phase structure.

Qualitative and quantitative aspects of the formation of various types of phase structures, sizes and compositions were considered. For the studied polycaprolactone–epoxy resin/4,4′-diaminediphenylsulfone system, a phase diagram characterized by amorphous separation with a lower critical solution temperature was constructed and its evolution was traced with increasing conversion degree of epoxy groups. A method is proposed for determining the temperature–concentration parameters that determine the type of phase structure of composite materials, based on the optical interferometry method. All types of phase structures and features of structure formation in the phase reversal region and at its boundaries have been studied using optical and scanning electron microscopy methods. The dimensions of the structural elements were determined and their correlation with the temperature and concentration regimes of the system’s curing was established. The composition of phases in cured compositions was studied using FTIR spectroscopy, DSC and scanning electron microscopy. It is shown that by varying the temperature–concentration parameters of curing reactive thermoplastic systems, it is possible to specifically regulate the type of phase structure, phase sizes and their composition, which determine the operational properties of the material.

Preparation of hydrophobic coatings is still a challenge for researchers in various fields of science. One of the easiest ways consists of the use of special modifiers. However, usually such modifiers are poorly compatible with organic polymeric matrixes, which leads to segregation of modifiers and deterioration of coating properties. In this work, we have synthesized a number of organosilicon copolymers and studied their compatibility with epoxy matrix and hydrophobic efficiency. It was shown that the increase of phenyl-containing units leads to increase of compatibility but decreases hydrophobic efficiency. Addition of small amounts of such modifiers into commercial epoxy paint material can lead to an increase of contact angle of the final coating from 63 to 87° without deterioration of other physico-mechanical properties. These results open new perspectives in preparation of organosilicon hydrophobic modifiers with directed properties for fields of application such as paints and coating materials.

Currently, there is no quantitative approach for the phase structure of cured thermoplastic systems modified with thermoplastic predicting. To solve this problem, we carried out the first stage of the study on a model polycaprolactone–epoxy oligomer (PCL–DGEBA) system. Using differential scanning calorimetry (DSC), refractometry and optical interferometry, a phase diagram for PCL–DGEBA mixtures was constructed, and the Flory–Huggins interaction parameters of PCL–DGEBA mixtures were calculated. The structure of PCL–DGEBA mixtures with different PCL content was analyzed by optical microscopy. The change in the structure formation mechanism with increasing PCL concentration was shown. The diffusion coefficients are calculated by the Motano–Boltzmann method. The values of the apparent activation energy of the viscous flow PCL and of self-diffusion of DGEBA are determined. The obtained data will be used for the in situ curing kinetics and phase equilibria in the diffusion zone investigations in order to develop a quantitative method for predicting the phase structure of cured systems.