Investigation of the amorphization process of partially crystalline polymers by hydrostatic weighing in an inert liquid

Abstract

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.

Phase Diagrams Semicrystalline Polymer–Liquid Revisited: Isotactic Polypropylene-Dibutyl Phthalate and Other Systems

“…20 using the method of stepwise isothermal amorphization in the immersion liquid. [19] It is seen that in the case of LDPE, T m is close to the endotherm maximum T max , whereas for i-PP, T m is considerably shifted toward the end of the curve, T f . The fraction of crystallites that are subjected to pure melting (it takes place at the constant temperature of the sample, T m , while the temperature of the DSC crucible can be higher) corresponds to the relative [19] are shown.…”

“…We use the term "destruction of crystallites" to emphasize that changing the polymer degree of crystallinity with temperature is a reversible thermomechanical process independent of the presence [5] or absence [19,20] of a low MW liquid. Its mechanism, based on a gradual pullout of polymer backbones due to excessive stress in the amorphous regions, was first proposed by Alfrey and Mark.…”

“…Its melting temperature, T m D 176.4 § 1.1 C, was determined from the kinetic experiments on hydrostatic weighing using the method of quasiequilibrium stepwise isothermal amorphization in the immersion liquid [19]. …”

Electrochemical Properties and Electropolymerization of Tetrakis(para-aminophenyl)porphyrin in Dichloromethane

“…Анализ полученных результатов позволяет сказать, что пленка является одним из видов высокомолекулярных соединений, которые плавятся в широком интервале температур, а именно, частично кристаллическим медленно кристаллизующимся полимерам. [37][38][39] …”

Phase equilibrium of a semicrystalline polymer-liquid system: Isotactic polypropylene-dibutylphthalate

“…Use of the term crystallite destruction in this case emphasizes the fact that the change in the degree of polymer crystallinity with a change in temperature is a reversible thermomechanical process both in the pres ence of liquid [7] and in its absence [19,20]. 1 Only the last crystallites, unbound by passage chains, are destroyed thermally, e.g., melts, [9].…”