B.A. Rozenberg

Reaction-induced phase separation in modified thermosetting polymers

Thermosetting polymers are frequently used in formulations, including rubbers, thermoplastic polymers or oils, etc, in an amount of the order of 2–50 wt% with respect to the thermoset. This extra component, called the modifier, may initially be immiscible or may phase-separate during cure. This last process, i.e the reaction-induced phase separation, is the subject of this review. A thermodynamic description of the process is made, using the Flory-Huggins equation at two approximation levels, i.e. a quasi-binary approach and a multicomponent treatment taking polydispersity of constituents into account. Thermodynamic factors affecting the phase separation process are thus established. Nucleation and growth (NG) and spinodal demixing (SD) are considered as possible phase separation mechanisms. Factors promoting one or the other process are discussed. The control of morphologies generated is analyzed on the basis of thermodynamic and kinetic arguments. Ideas for obtaining particular morphologies enhancing particular properties are put forward.

Oriented Liquid Crystalline Network Polymers

Liquid crystalline network polymers (LCNP’s) were discovered about 20 years ago [1–3], simultaneously with liquid crystalline polymers of linear type (LCP’s). Nevertheless, we can state now that LCP’s have been studied considerably better than LCNP’s. The results of these investigations are documented in numerous books and reviews [3’10]. Formation of highly oriented, macroscopically uniform LCP’s under influence of external mechanical, electric or magnetic fields and fixation of chain orientation at cooling of polymers below glass transition temperature allows one to obtain films, fibers or molded plastics with high degree of anisotropy of physical characteristics and outstanding mechanical properties, thermal and chemical stability. LCP’s also exhibit interesting optical properties revealed under the action of electric or magnetic fields. These properties are perspective for the development of new type of materials for recording, displaying and storing information [8,11]. So, if the usefulness and opportunities of LCP’s application now is understood quite well, the revealing of LCNP’s potentials are only in a progress.

Morphology control at phase separation of curing multicomponent thermosets

The process of phase separation in the course of the thermoset curing reaction is considered. Clarification of the role of kinetic factors in such processes is the focus of the article, and the need in a kinetic theory for cure reaction-induced phase separation (CRIPS) is substantiated. An adequate nonequilibrium approach proposed previously is given further development. A new CRIPS model with equilibrium boundary conditions is introduced.

Effect of the chemical structure of oligomer rubbers on the phase equilibrium in epoxy-rubber systems

Abstract A study was made of the phase condition of systems consisting of ED-20 epoxyresin and oligomer rubber. It was shown that the addition of polar groups to an oligobutadiene molecule improves compatibility with the epoxy component. Experimental results may be described within the framework of the Flory-Huggins theory. Upper critical temperatures of solution in the systems studied were calculated. It was found that oligobutadienes containing functional groups with a clearly expressed ability to associate show unusual behaviour.

On the relation between the glass transition temperature of network epoxide polymers and their chemical structure

Abstract The glass transition temperature increments have been calculated for some network epoxide and amine chain fragments. It has been found that the glass transition temperature is unambiguously predetermined by the chemical structure of the polymer.

Concerning the nature of molecular movement in epoxy-amine network glassy polymers

Abstract The NMR impulse method has been used to study the relaxation properties of a number of model epoxy-polymers based on the diglycidyl ether of resorcinol with various concentrations of crosslinks, degrees of branching and with crosslinking fragments of various types. During glass formation, molecular movement in the network polymers is accomplished by segments of at least two types: node with adjacent chain fragments and chain fragments respectively.

The mechanism of decay of active centres in polymerization of trioxan in solution

As a result of kinetic and spectrophotometric studies of the polymerization of trioxan with B+A− salts as catalysts (where B+ = Ph3C+, CH3CO+ or CH3OCH2+, and A− = SbCl6− or SbF6−) it has been found that termination of the growing chains involves both physical and chemical processes the ratio of the two being dependent on the structure of the active centres and on the conditions of polymerization.

Synthesis of silver nanoparticles with polystyrylcarboxylate ligands

Silver nanoparticles stabilized by polystyrylmonocaboxylate ligands with varied chain lengths are synthesized via the low-temperature reduction of silver polystyrylmonocaboxylate with triethylamine. Silver nanoparticles have small dimensions, narrow size distributions, high stability, and ability to redisperse in nonpolar solvents. The kinetic features of the reaction are studied via high-performance liquid chromatography; UV, visible and IR spectroscopy; and transmission electron microscopy. It is shown that the reduction of silver occurs in the cores of reverse micelle species organized by diphilic macromolecules of silver polystyrylmonocarboxylates.

Synthesis and free-radical polymerization of water-soluble acrylamide monomers

Water-soluble acrylamide monomers N-(hydroxymethyl)acrylamide, N-(hydroxymethyl)methacrylamide, N,N-diethanolacrylamide, N,N-diethanolmethacrylamide, N,N-methylethanolacrylamide, and N,N-methylethanolmethacrylamide have been synthesized and characterized. The kinetics and thermodynamics of the free-radical polymerization of these monomers and of the model compounds N-isopropylacrylamide and acrylamide have been studied by the methods of isothermal and scanning calorimetry. The structure and the solubility of the said polymers in water and organic solvents have been investigated and their molecular-mass characteristics and temperatures of glass transition (T g) and melting (T m) have been examined by DSC, liquid chromatography, 1H NMR and IR spectroscopy, and chemical analysis of functional groups. Hydrogels and amphiphilic network polymers based on acrylamide monomers have been prepared and characterized.

Synthesis of a macromonomer based on ɛ-caprolactone and 2-hydroxyethyl methacrylate

The mechanism of forming the macromonomer based on ɛ-caprolactone and 2-hydroxyethyl methacrylate under the effect of dibutyltin dilaurate has been investigated. The molecular-mass characteristics and the functional-type distribution of the macromonomer have been determined. It has been established that, as the concentration of the methacrylic component is increased, the contribution of side reactions related to its anionic polymerization rises. It has been shown that macromonomers with caprolactone backbones and terminal methacrylic and hydroxyl groups may be obtained. A method has been proposed for the purification of polymerization products from low-molecular-mass impurities, such as dimethacrylates and diols.