Preparation and characterization of aromatic polyimides derived from 4,4′-oxydiphthalic anhydride and 4,4′-diaminodiphenylmethane with different alkyl substituents

Studies of Formation Mechanism, Structure, and Properties of Network Copolymers Obtained by Cocuring of Rolivsan Thermosetting Resins with Aromatic Diamines

Rolivsan thermosetting resins (ROLs) demonstrate high glass-transition temperatures and excellent processability. In our work, high-temperature properties of ROLs were significantly improved using a novel technique for structural and chemical modification of microheterogeneous network polymers. This technique involves, among other procedures, cocuring of rolivsan resins with aromatic diamines (ADA). The most noticeable increase in storage moduli and glass transition temperatures (Tg) of these copolymers was achieved when ROLs were modified with 10-15 wt.% of ADA and the resulting blends were subjected to thermal treatment in air in the temperature range 180 to 320°C for several hours. FTIR, 13С NMR spectroscopy, and dynamic mechanical and thermal analyses were used for studying the structure and properties of the obtained products. It was demonstrated that the mechanism of formation of ROL-ADA copolymers includes the following high-temperature reactions: (i) three-dimensional radical copolymerization of unsaturated ROL components and (ii) cleavage of heat-sensitive methacrylate crosslinking units inside the polymer network. The second process is accompanied by formation of pending units of methacrylic acid and methacrylic anhydride, which participate in condensation reactions with ADA.

Combination of polymerization and polycondensation in the synthesis, chemical modification, and cure of rolivsan thermosetting resins

Rolivsan thermosetting resins (ROLs) attract constant attention due to their epoxy-like high processability; at the same time, their high-temperature performance is much better than that of epoxy resins and bismaleimides. Development of these materials involves a nontrivial approach to synthesis of thermostable resins; this approach is based on introducing a new structure-forming tool, that is, 1-arylethanol group. The present article demonstrates the important role of polycondensation in rolivsan chemistry. ROLs consist of (di)vinylaromatic ethers and thermosensitive monomeric and oligomeric (di)methacrylates, which are formed after a series of acid-catalyzed reactions between di-secondary aliphatic-aromatic diols, such as bis-[4-( α-hydroxyethyl)phenyl] ether, and unsaturated carboxylic acids, such as methacrylic acid. The process of ROL cure is a combination of polymerization and polycondensation. In the course of this process, in the temperature range from 140°С to 170°С, the initial densely cross-linked ROL-copolymer is formed as a result of three-dimensional radical copolymerization of highly unsaturated components. Post-cure of ROLs in the 200–300°С temperature interval leads to structural rearrangement (polycondensation). Cured ROLs demonstrate morphology typical of thermosets; they consist of highly cross-linked spherical microdomains that are weakly bound by less densely cross-linked polymer interlayers. Thermocatalytic transformations of rolivsans modified by small amounts of additives (epoxies and aromatic diamines) were used in the development of a new approach to synthesis of heat-resistant thermosetting resins via high-temperature polycondensation in interdomain layers (which are used as a peculiar kind of microreactors).

Novel polycondensation method of improving high-temperature properties of microheterogeneous rolivsan copolymers modified by inserting epoxy and imide bridges between spherical microdomains

Rolivsan thermosetting resins (ROLs) (low-viscosity solvent-free compositions including (di)vinylaromatic ethers and thermosensitive (di)methacrylates) were modified by low amounts of polyfunctional compounds (epoxy resins (ERs) and aromatic diamines (DAs)). Thermochemical transformations in modified ROLs give novel glassy densely cross-linked copolymers with increased high-temperature strength and thermo-oxidative stability. It was revealed that copolymers obtained at different ROLs/ERs and ROLs/DA mixing ratios (which were varied over a wide range) and different heat treatment regimes have various compositions, cross-link densities, chemical, topological, and morphological structures. Structural features of these copolymers were studied by Infrared spectroscopy, dynamic mechanical, thermal, and elemental analyses; the temperature dependences of flexural strength were also obtained. Morphological pattern of the cured ROLs is typical of microheterogeneous polymers where spherical highly cross-linked microdomains (polymer grains) with high Tg are weakly bound by less densely cross-linked defective (intergrain) polymer layers with lower Tg. On the basis of the data obtained in the studies of thermochemical transformations in ROLs/ERs and ROLs/DA blends, the new approach to improving thermal stability and heat resistance of thermosetting resins was developed. We suggest using intergrain layers in microheterogeneous cross-linked polymers as “microreactors” which include target polyfunctional compounds for various high-temperature polymerization and polycondensation reactions.