N. P. Bessonova

Thermoelasticity of segmented polyurethanes

Various diphenylmethane diisocyanate-containing polyurethanes whose soft blocks differ in polarity and crystallizability have been investigated using deformation and scanning calorimetry to ascertain the contribution of different types of intermolecular interaction to elasticity of polyurethane elastomers.The phase composition of polyurethanes being investigated and its dependence on mechanical action have been analyzed on the basis of scanning calorimetry data. By measuring the mechanical work and thermal effect during extension (λ=1–3.5) deformation dependences of internal energy changes and the ratio of energy and entropy changes have been determined as well as energy contributions have been calculated. The data obtained for different temperatures demonstrate that a decrease in the fraction of energy changes is largely due to hard block structurization in the course of re-building the network of hydrogen bonds during deformation.

Thermodynamics of the deformation of segmented polyurethanes with various hard block contents II. Stress softening and mechanical hysteresis

The thermodynamics of stress-softening and hysteresis in PBUs with different compositions were studied using deformational calorimetry, and the intramolecular energy contribution of the soft blocks was established. It is shown that differing from filled elastomers, the softening and hysteresis losses of PBU, like those of a typical TEP, are accompanied by energy absorption reflecting intermolecular change in the hard domains. Increased hard block content increases energy changes, whereas increasing the temperature produces the reverse effect. The dependence of the deformation mechanism of PBU on the hard block content, temperature and mechanical history is discussed.

Crystallization of microphase-separated block copolymers with two crystallizing blocks

Statistical poly block copolymers of polyamide with polyethyleneoxide are investigated. The regularities governing the formation of their phase structure depending on the composition, temperature, and prehistory of the system are established. The character of crystallization of both blocks is shown to be due to their mutual solubility in the melt. Some peculiarities of microphase crystallization in PA/PEO block copolymers are revealed. It is found that, depending on the character of phase separation in the system, a PEO block may be crystallized either unimodally or in two well-separated temperature ranges.

Thermodynamics of the deformation of segmented polyurethanes with various percentages of hard block I. The initial deformation

The thermodynamic analysis of the uniaxial stretching of the polybutadiene polyurethanes of various compositions and mechanical history was carried out using deformation calorimetry. The initial small strain deformation was found to result from the volume elasticity of the hard phase. Samples containing up to 50% of the hard block behave like typical thermoelastoplastics, which are characterized by the “plastic-to-rubber” transition and large reversible deformations. More rigid samples behave similar to typical solid crystalline polymers aboveTg.

Thermodynamic behavior and mechanisms of deformation of phase-separated multiblock copolymers as revealed from deformation calorimetry

Abstract The thermodynamic analysis of the uniaxial stretching of block copolymers of various chemical compositions and hard block contents was carried out using a deformation calorimetry method. It was found that the initial small deformations result from the volume elasticity of the hard phase, independent of its content and chemical nature. The intramolecular energy contributions of soft blocks to the deformation thermodynamics were estimated. It was shown that the hard block contributions depend on their content and degree of sample stretching. The samples were divided into two groups with respect to their thermodynamic behavior.

Study of temperature transitions in solid poly(oxymethylene) by thermal analysis methods

Poly(oxymethylene)s with different molecular mass and chemical structure were studied using DSC, dynamic mechanical relaxation, thermomechanical analysis, and thermogravimetry.Molecular mobilities of two types were found in the amorphous phase of poly(oxymethylene). Unconstrained chains of poly(oxymethylene) soften at −70°C and then amorphous chains with different restraints from the crystalline phase are successively activated in a wide temperature interval.

Deformation calorimetry of polyurethane block-copolymers

A thermodynamic analysis of the uniaxial stretching of polyurethanes of various compositions and mechanical histories was carried out by using deformation calorimetry. The initial small strain deformations were found to result from the volume elasticity of the hard phase. The intramolecular energy contributions of the soft blocks were estimated. The hard block contributions were shown to depend on their content and on the degree of sample stretching. The predominant role of the soft component is proved to be manifested only in softened samples with a hard block content not exceeding 30%. The thermodynamics of the softening and hysteresis phenomena were studied. The dependence of the deformation mechanism on the hard block content and mechanical history is discussed.ZusammenfassungMittels Deformationskalorimetrie wurde eine thermodynamische Analyse der einachsigen Dehnung von Polyurethanen verschiedener Zusammensetzung und mechanischer Vorgeschichte durchgeführt. Für die anfänglichen geringen Stauchungsverformungen wurde festgestellt, daß sie der Volumenelastizität der Hartphase entstammen. Es wurde der intramolekulare Energiebeitrag der Soft-Blöcke geschätzt. Der Beitrag der Hart-Blöcke hängt von ihrem Gehalt und vom Dehnungsgrad der Probe ab. Die dominierende Rolle der Soft-Komponente macht sich ausschließlich in weichgemachten Proben mit einem Hart-Blockgehalt von weniger als 30% bemerkbar. Weiterhin wurde die Thermodynamik des Weichmachens und Hysterese-Erscheinungen untersucht.Es erfolgt eine Besprechung der Abhängigkeit des Deformationsmechanismus vom Hart-Block-Gehalt und der mechanischen Vorgeschichte.