Polymer Science, Series C最新文献

The aqueous solutions of star-shaped four-arm poly(2-alkyl-2-oxazolines) and poly(2-alkyl-2-oxazines), in which the upper rim-functionalized calix[4]arene acts as a branching center, are studied by static and dynamic light scattering and turbidimetry. It is shown that at low temperatures in aqueous solutions of these polymer stars aggregates are formed as a result of interaction of hydrophobic calix[4]arene cores and formation of hydrogen bonds between dehydrated monomer units of arms. The process of aggregation dominates upon heating of the solutions. Varying the mode of arm attachment to a core causes a change in its configuration. The values of the phase transition temperature decrease when comparing polymers with the lower rim-functionalized core with polymers in which arms are attached to the upper rim of calix[4]arene.

Aqueous solutions of linear poly(2-ethyl-5,6-dihydrooxazine) and eight-armed star-shaped poly(2-isopropyl-2-oxazoline) have been studied by light scattering and turbidimetry. The influence of the duration of annealing at temperatures above the phase separation temperature on the behavior of the solutions has been analyzed. It has been shown that the characteristics of linear polymer solutions do not vary in the studied annealing time interval. The cloud point of star polymer solutions also does not depend on the annealing time. However, significant changes have been observed at the microscopic level, namely, irreversible aggregation due to the interaction of hydrophobic segments of poly(2-isopropyl-2-oxazoline) arms formed during annealing at a high temperature.

This review addresses recent achievements in the field of producing photonic-crystalline structures from polymer core/shell particles. The synthesis of polymer particles, in which a core is formed by hard crosslinked polymers and a shell is based on thermoplastic polymers or elastomers, offers the way to create the so-called stimuli-responsive (or “smart”) photonic crystals. Main principles underlying the self-assembly of polymer particles into periodic colloidal structures are considered. Elastic large-area 3D structures can be formed by the self-organization of core/shell particles under their compression at high temperatures. Prospects for the application of smart photonic-crystalline films are also highlighted.

Studies on free-radical micellar polymerization of ionogenic amphiphilic monomers have been analyzed. Major types of the monomers and features of their polymerization in the micellar state have been described. Approaches to the analysis of kinetic features and mechanism of micellar polymerization have been considered; the applicability of the Morgan–Kaler microemulsion model to the description of quantitative features of micellar polymerization has been shown.

New amphiphilic ABA-type molecular brushes of mixed block–graft topology, where the central block B is a molecular brush with a hydrophobic polyimide backbone and hydrophilic side chains of poly(methacrylic acid) and A blocks are peripheral hydrophobic chains of poly(methyl methacrylate), have been synthesized. For the synthesis of the copolymers, an approach based on a combination of atom transfer radical polymerization (ATRP) and click chemistry in the variant of Cu(I)-catalyzed azide–alkyne cycloaddition was proposed. To implement the proposed approach, a procedure was developed for the synthesis of heterofunctional polyimide macroinitiators containing ATRP-initiating groups in each unit and terminal alkynyl groups capable of participating in the “click” reaction. Further, the synthesis of well-defined block–graft ABA molecular brushes was carried out using such initiators. First, peripheral poly(methyl methacrylate) chains were synthesized in a controlled mode using ATRP, followed by their functionalization with azide groups. Then, using the click chemistry approach, these chains were grafted to the terminal alkynyl groups of the heterofunctional initiator. The hydrophilic side chains were introduced into block B using the “grafting from” ATRP method in several steps through the intermediate formation of a regularly grafted prepolymer with poly(tert-butyl methacrylate) side chains. At the last step, as a result of selective acid hydrolysis of the side-chain ester groups in block B, amphiphilic multicomponent brushes with hydrophilic poly(methacrylic acid) units in the side chains were obtained. The possibility of sequential and simultaneous ATRP and click reaction has been examined.

This contribution was focused on the developing of an improved method for preparing hypercrosslinked polystyrene by bridging styrene-0.5% DVB copolymer with monochlorodimethyl ether (MCDE) up to 100, 150, 200 and 300% via Fidel–Crafts reaction. The modification comprises both the reduction in the consumption of the catalyst, SnCl₄, and the complete substitution of SnCl₄ with the more active and less expensive catalyst, FeCl₃. Reducing the SnCl₄ quantity from 1.0 to 0.1 mol per one mole of the ether leads to the formation of hypercrosslinked networks which exhibit a quite good swelling in non-solvents, rater low apparent density, and a noticeable pore volume, but, surprisingly, to a dramatic reduction in the measured inner surface area. The latter finding could be explained by the formation in the networks with very narrow pores which remain inaccessible to the testing argon atoms. The situation changes cardinally if the reaction mixture is additionally provided with oxalyl chloride (0.5 mol per mol of the ether) which reacts with methanol at the moment of its formation during the reaction of the ether with polystyrene. The latter reaction proceeds so violently that it is possible to reduce the amount of SnCl₄ by a factor of at least 13 or diminish the essential portion of FeCl₃ by a factor of 30, compared to the recommended previously 0.3 mol FeCl₃ per one mole of the MCDE.

Recent advances in controlled atom transfer radical polymerization are reviewed. Polymerization techniques carried out in the presence of small catalyst amounts, as well as air oxygen traces, are addressed. Particular attention is given to processes occurring under the action of light and near UV radiation. Latest achievements of Atom Transfer Radical Polymerization in the modification of solid surfaces of inorganic substrates and organic polymers by grafting polymer chains are analyzed. Potential of the method for synthesizing conjugates with proteins and nucleic acids, which are of interest as biosensors and target drug delivery agents, is also demonstrated.

The review addresses the synthesis of copolymers with the controlled distribution of monomer units (random, gradient, block-random, block-gradient, multiblock copolymers) by reversible deactivation radical polymerization and the ways of purposeful variation in the sequence of units in macromolecules during the synthesis. The effect of chain microstructure on the properties of these copolymers is discussed.

The review addresses modern approaches to the synthesis of mechanically tough polymer hydrogels which are based on the concept of double networks. Various types of double networks, such as covalently crosslinked networks; hybrid networks, in which one network is crosslinked by covalent bonds and another network is crosslinked by labile dynamic bonds; and networks that are constructed using labile bonds in each network, are considered. Double networks consisting of one polymer network and one supramolecular network, nanocomposite double networks, and multicomponent (three-component, four-component, etc.) networks are described. Advantages and disadvantages of new approaches to designing mechanically tough double networks are considered.

Approaches to the synthesis of polymer composite materials filled with graphene and its derivatives, methods of introducing graphene and its functionalized forms into polymer matrices, and effect of fillers on the electrophysical, mechanical, and electrorheological properties and the structure of the materials are considered. Research trends that can promote the integration of polymer composites with graphene and graphene derivatives into innovative world-class products and in the everyday life are indicated.