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A single crystal of 25,26,27,28-tetrahydroxycalix[4]arene molecular complex with n-hexane was grown by slow evaporation of a solution in n-hexane allowing a complete elucidation of its structure. For the first time a 25,26,27,28tetrahydroxycalix[4]arene molecular complex with toluene was obtained. In addition, its thermal stability was studied. The kinetic sorption curves of acetone, acetonitrile, nhexane, and toluene saturated vapors within 25,26,27,28-tetrahydroxycalix[4]arene were derived experimentally. It was shown that the kinetic sorption curve of acetonitrile saturated vapor within 25,26,27,28-tetrahydroxycalix[4]arene has a distinct peak corresponding to the 1:1 stoichiometry. It was suggested that the structural reorganization of 25,26,27,28-tetrahydroxycalix[4]arene provides transport of acetonitrile molecules into the molecular crystal and subsequent complexation with the formation of a thermodynamically stable hexagonal structure. A conclusion was drawn that the high thermal stability of 25,26,27,28-tetrahydroxycalix[4]arene solvates is due to strict compliance with the shape and size of the "guest" molecule and "host" cavity size.

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The potential of hydrostatic weighing of partially crystalline polymers in an inert liquid during the study of their amorphization and crystallization processes over a broad temperature range was demonstrated using the low-density polyethylene-polymethylsiloxane system as an example.Professor Kirill Evgen'evich Perepelkin was, at a minimum, an extraordinary being among domestic (Soviet and Russian) polymer scientists studying problems of chemical fiber technology. The scope of his scientific interests was exceptionally broad. However, the relationships of the properties of natural and synthetic polymers to their structure and the formation conditions of the latter practically constantly interested him. Therefore, the two articles on this theme that are published below by representatives of the Ivanovo school of polymer chemists, some of whom had the pleasure of conversing personally with Kirill Evgen'evich, have become by a twist of fate a symbol of our parting with this remarkable person and scientist.Hydrostatic weighing [1, 2] is a method aimed at studying structure transformations in partially crystalline polymers that are due to the temperature and thermodynamically active liquids under the condition that the polymer remains in the solid phase during the course of the experiment and does not contain fractions that are soluble in the given liquid in the studied temperature range. The practical capabilities of the method were published earlier [1-3].Obviously replacing a liquid that is thermodynamically active relative to the polymer by a thermodynamically inactive one will automatically fulfill the insolubility condition regarding fractions of any molecular weight. Therefore, it becomes possible to measure the weight in the liquid of a polymer that exists also in the liquid phase, i.e., the melt.Such an experiment is interesting from two viewpoints. First, the true temperature of full amorphization (melting of the last crystals) of a partially crystalline polymer can be determined as the intersection of the temperature dependences of the solid and liquid (melt) polymers. Second, the nature and extent of structural transformations of the polymer matrix related to the change of its molecular packing density can be judged from the time dependences of the polymer density at a constant temperature.Herein the amorphization of low-density polyethylene (LDPE) in polymethylsiloxane PMS-20 medium is examined as an example of the practical implementation of these capabilities.The subject of the study was LDPE (15083-020 grade, GOST 16377-77) with melt index 1.32 ± 0.2 g/10 min (IIRT-5M instrument, 190°C, load mass 2.16 kg) as disks (20.0 ± 0.2 mm diameter, 3.0 ± 0.1 mm thickness) prepared by pressing granules at 160°C followed by cooling in air.

Hydrostatic weighing of a polymer in an immersion liquid using low-density polyethylene as an example was used to show that a condition for the lack of recrystallization of partially crystalline polymers upon annealing is the attainment at this temperature of thermomechanical equilibrium that determines the ratio of the amounts of macromolecule elementary units existing in amorphous and crystalline regions during the crystallization of these polymers. A basis was found for the viewpoint that the Gibbs-Thomson equation is applicable only for estimating the dimensions of the last (not bonded to each other by connecting chains) crystallites disappearing at the true melting point.It is commonly thought in discussing crystallization processes of polymers with flexible chains from the melt, their additional crystallization (melting-recrystallization) during annealing, and complete melting [1-8] that these polymers are biphasic (crystalline and amorphous phases) and thermodynamically non-equilibrated (metastable).The experimentally observed manifestations of the metastability of partially crystalline polymers are: -a lower melting point (mp) than the equilibrium value ( 0 m T ) characteristic of ideal crystals; -a dependence of the mp on the heating rate and the thermal history of the sample; -additional spontaneous crystallization with a decrease of the glassification temperature of amorphous regions to the ambient temperature.Additional crystallization was clearly evident during successive stepwise heating of a partially crystalline polymer undergoing hydrostatic weighing in an immersion liquid. Additional crystallization of low-density polyethylene (LDPE) pressed at 160°C and crystallized in air at room temperature (mp = 111.2 ± 0.4°C) was distinctly observed in the range 58.5-110.2°C with such a heating regime [9]. Apparently only amorphization occurred in the range 29.3-58.5°C. Anyway, preliminary storage of the sample in a differential scanning calorimeter cell for 1 h at 40°C was accompanied by a decrease of its heat of fusion (ΔH m ) by 6% [glassification temperature (T g ) of this LDPE sample was about -53°C].Strictly speaking, these results were expected and agreed completely with existing concepts about the thermal behavior of partially crystalline polymers. However, the problem is that if the postulates of Gibbs regarding phase equilibria are strictly adhered to [10], then such polymers should be viewed as monophasic microheterogeneous metastable liquids in which the ratio between the amount of macromolecule elementary units located in the amorphous regions and crystallites is determined by the thermomechanical equilibrium conditions [11].Such treatment of the monophasic state of partially crystalline polymers differs in principle from that proposed earlier [3, p. 326] in that the amorphization process of such polymer liquids is considered to be a first-order phase transition complicated by a three-dimensional strain deformation relative to regions with long-range three-dimensional ordering in the space aro...

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