Diversity of polymer gels and the main factors determining the properties of gels and related solid polymers

This paper is a survey of the authors’ main results on the properties and structure of polymer gels of diverse nature that are related to the ideas of S.P. Papkov and G.V. Vinogradov. The properties of physical and chemical gels of various compositions and structures and of solid polymers prepared on their basis are considered in relation to the polymer concentration and thermodynamic quality of a solvent during gel preparation. It is demonstrated that the conditions of gel synthesis affect the dependence of the elastic modulus of the gel on the volume fraction of the solvent in it. The properties of the gels based on model chemical networks for soft- and stiff-chain polymers are compared.     

高分子立构复合结晶的研究进展

立构复合结晶是高分子结晶中的一种普遍现象,也是不同高分子之间共结晶的特殊形式.互为立体异构高分子在共混物和立体嵌段共聚物中可形成立构复合结晶.由于这种独特的链凝聚结构,立构复合结晶材料与相应的同质结晶材料的性能显著不同,立构复合结晶通常可提高高分子材料的熔点、耐热性、结晶能力、结晶度、机械力学性能、耐溶剂性能等.通过立构复合结晶,可使一些非晶或难结晶的高分子转变为可结晶或高结晶度的状态,从而实现材料性能的转变.因此,互为立体异构高分子之间的立构复合结晶为聚合物材料的性能优化和调控提供了有效的途径.文献已报道了多类可立构复合结晶的聚合物体系,包括脂肪族聚酯、脂肪族聚碳酸酯、聚甲基丙烯酸酯、聚酰胺和聚酮等.本文根据聚合物化学结构的不同,针对文献已报道的可立构复合结晶的高分子体系,综述了其立构复合结晶的形成条件、结构特征与物理性质.     

Solution properties of ion-containing polymers in polar solvents

The placement of ionic groups within the molecular structure of a polymer produces marked modification in physical properties. A large number of studies have been performed on these ion-containing polymers, but few have focused on the effects of anion–cation interactions (i.e., counterion binding or ionization) on hydrodynamic volume, especially as the molecular structure of the solvent and nature of counterion are varied. In this study changes in hydrodynamic volume are followed through reduced viscosity measurements as a function of the abovementioned molecular parameters. The dilute solution properties of various polyelectrolytes that contain sulfonate and carboxylate groups were investigated as a function of the counterion structure, charge density, molecular weight, and solvent structure. The polymeric materials were selected because of their specific chemical structure and physical properties. In the first instance a (2-acrylamide-2 methylpropanesulfonic acid)-acrylamide-sodium vinyl sulfonate terpolymer was synthesized and subsequently neutralized with a series of bases. Viscometric measurements on these materials indicate that the nature of the cation affects the ability of the polyelectrolyte to expand its hydrodynamic volume at low polymer levels. The magnitude of the molecular expansion is shown to be due in part to the ability of the counterion to dissociate from the backbone chain, which, in turn, is directly related to the solvent structure. The changes in solution behaviour of these inomers lend support for the existence of ion pairs (i.e., site binding) and ionized moieties on the polymer chains. Measurements performed in a variety of solvent systems further confirm this interpretation. In addition, and acrylamide-sodium vinyl sulfonate copolymer was partially hydrolyzed with sodium hydroxide to study the effect of varying the charge density at a constant degree of polymerization and counterion structure. The results show that the charge density has a significant effect on the magnitude of the reduced viscosity and dilute solution behaviour. These observations, made in aqueous and nonaqueous solvents, are related to the interrelation of hydrodynamic volume, counterion concentration, and site binding. Again the controlling factor is the degree of site binding of the counterion onto the polymer backbone. Finally, we observe that the increased hydrodynamic volume affects viscosity behavior beyond the polyelectrolyte effect regime. If the average charge density on the macromolecule is relative high and/or the molecular weight is large (≥ 10⁶) sufficient intermolecular interactions will occur to produce rapid changes in reduced viscosity.     

An investigation of the interconnection between topological characteristics of physical and chemical networks of anhydride adamantane-containing epoxy polymers

The interconnection between topological characteristics of chemical and physical networks of adamantane-containing epoxy polymers of anhydride curing is studied. It is shown that the introduction of adamantane fragments into the network of an epoxy polymer by different methods affects the glass-transition point and stress-strain properties. The changes in polymer properties depending on the concentration of modifying agents are analyzed during comparison of the frequency parameters of the networks of chemical bonds and engagements within a cluster model of the structure of the polymer amorphous state.     

Mean‐field‐theory for polymers in mixed solvents. Thermodynamic and structural properties

Theoretical aspects of polymers in mixed solvents are considered using the Edwards Hamiltonian formalism. Thermodynamic and structural properties are investigated and some predictions are made when the mixed solvent approaches criticality. Both the single and the many chain problems are examined. When the mixed solvent is near criticality without solute, addition of a small amount of polymers shifts the criticality towards either enhanced compatibility or induced phase separation depending upon the value of the parameter describing the interaction asymmetry of the solvents with respect to the polymer. The polymer‐solvent effective interaction parameter increases strongly when the solvent mixture approaches criticality. Accordingly, the apparent excluded volume parameter decreases and may vanish or even become negative. Consequently, the polymer undergoes phase transition from a swollen state to an unperturbed state or even takes a collapsed configuration. The effective potential acting on a test chain in strong solutions is calculated and the concept of Edwards screening discussed. Structural properties of ternary mixtures of polymers in mixed solvents are investigated within the Edwards Hamiltonian model. It is shown that the effective potential on a test chain in strong solutions could be written as an infinite series expansion of terms describing interactions via one chain, two chains etc. This summation can be performed following a similar scheme as in the Ornstein‐Zernike series expansion.     

Dynamics of grafted star-branched polymers. A Monte Carlo study

Monte Carlo simulations of simple models of star-branched polymers were carried out. The model chains were confined to simple cubic lattice and consisted of f = 3 branches of equal length and the total number of polymer segments as well as the density of grafted chains on the surface were varied. The chains have had one arm end attached to an impenetrable plate. The simulations were performed by employing the set of local micromodifications of the chain conformations. The model chains were athermal, i.e. good solvent conditions were modeled, the excluded volume effect was present at the model. The density of grafted chains on the surface was varied from a single chain up to 0.3. The static and dynamic properties of the system were studied. The influence of polymer concentration as well as the polymer length on static and dynamic properties of the system studied was shown. The relation between the structure and short-time dynamics (relaxation times) was discussed.     

Star-branched polymers in an adsorbing slit: a Monte Carlo study

A coarse-grained model of star-branched polymer chains confined in a slit was studied. The slit was formed by two parallel impenetrable surfaces, which were attractive for polymer beads. The polymer chains were flexible homopolymers built of identical united atoms whose positions in space were restricted to the vertices of a simple cubic lattice. The chains were regular star polymers consisted of f = 3 branches of equal length. The chains were modeled in good solvent conditions and, thus, there were no long-range specific interactions between the polymer beads-only the excluded volume was present. Monte Carlo simulations were carried out using the algorithm based on a chain's local changes of conformation. The influence of the chain length, the distances between the confining surfaces, and the strength of the adsorption on the properties of the star-branched polymers was studied. It was shown that the universal behavior found previously for the dimension of chains was not valid for some dynamic properties. The strongly adsorbed chains can change their position so that they swap between both surfaces with frequency depending on the size of the slit and on the temperature only.     

The Structure of Star-Branched Chains in a Confined Space

Summary. We studied the properties of a simplified model of star-branched polymers confined in a slit formed by two parallel and impenetrable surfaces. The chains were built of identical united atoms (segments) whose positions were restricted to vertices of a simple cubic lattice. The polymer excluded volume and polymer segment-surface contact interactions were also introduced into the model. The properties of the model chains were determined by means of Monte Carlo simulations with a Metropolis-type sampling algorithm based on local changes of chain’s conformation. The structure of star-branched chains was investigated and the influence of the confinement and the temperature on the chain dimensions and structure was studied. It was shown that for chains in the adsorbing slits their sizes do not exhibit a universal behavior contrary to confined athermal polymers. The polymers in narrow slits at higher temperatures still exhibited features of a three-dimensional chain. It was also shown that chains in small slits and at low temperatures were fully adsorbed at one of the surfaces but could also switch the surface rapidly.     

Novel synthesis of photocrosslinkable polymers

A new preparative route to photocrosslinkable polymers in which the polymers are produced directly from the polymerization of vinyl monomers having photocrosslinkable groups has been investigated. The photosensitive resins thus produced have higher sensitivity and resolution than conventional photosensitive resins. The monomers were synthesized from the esterification of vinylphenols or vinyl β-chloroethyl ether with cinnamic acid, β-styrylacrylic acid, and their homologs, and from the etherification of vinyl β-chloroethyl ether with hydroxychalcones. Homopolymerizations of these monomers and their copolymerizations with other comonomers were investigated with the use of both radical and ionic initiators. It is shown that radical polymerization of the monomers gave soluble polymers only at low conversion. Anionic initiators did not initiate polymerization. Cationic polymerization imparted soluble polymers in high yield, except for the monomers bearing cyano groups, which generally gave insoluble polymers. Infrared and NMR spectroscopic investigation of the cationically obtained soluble polymers and comparative investigation by cationic polymerization of model compounds indicated that polymerization of the monomers proceeds through the vinyl double bond without affecting the photosensitive unsaturated bond. Thus, linear photocrosslinkable polymers with an intact photoreactive group may be produced by cationic polymerization. In general, these polymers have uniform structure and modifiable physical properties depending on the monomer used. The polymer thus obtained from β-vinyloxyethyl cinnamate has been shown to have excellent properties for use as a photo-resist.     

Demixing in athermal mixtures of colloids and excluded-volume polymers from density functional theory

We study the structure and interfacial properties of model athermal mixtures of colloids and excluded volume polymers. The colloid particles are modeled as hard spheres whereas the polymer coils are modeled as chains formed from tangentially bonded hard spheres. Within the framework of the nonlocal density functional theory we study the influence of the chain length on the surface tension and the interfacial width. We find that the interfacial tension of the colloid-interacting polymer mixtures increases with the chain length and is significantly smaller than that of the ideal polymers. For certain parameters we find oscillations on the colloid-rich parts of the density profiles of both colloids and polymers with the oscillation period of the order of the colloid diameter. The interfacial width is few colloid diameters wide and also increases with the chain length. We find the interfacial width for the end segments to be larger than that for the middle segments and this effect is more pronounced for longer chains.     

Photoradical ageing of polymers

The general laws of photoradical ageing of various carbon-chain and heterogeneous-chain polymers caused by reactions of electronically excited radicals have been considered. Information is given on mechanisms, efficiency, and kinetic features of these processes; also the occurrence of photoradical chain processes. It is shown that reactions of electronically excited macroradicals can be made use of in directed changes in the structure and properties of polymers.     

Macromolecule-metal complex interactions as precursors for the catalytic chemical modification of polymers

Chemical modification of polymers via catalysis has recently emerged as an area of increasing importance in macromolecular chemistry. It provides an efficient synthetic route for the production of novel polymers with desirable physical properties and functional groups which are often inaccessible by conventional polymerization techniques. Diene-based polymers and copolymers are ideal for chemical modification because of the technological importance associated with the parent materials and the reactivities of the double bonds in the polymer chain. In employing organometallic catalysts for such modifications, it has been found that the ligand environment of the catalyst as well as the functionality of the polymer has a profound effect on the nature of the macromolecule-metal complex interaction and the resulting polymer modification. The importance of the macromolecule metal complex interactions and the design of appropriate catalyst systems is illustrated for the hydrogenation, hydroformylation/hydroxymethylation and hydrosilylation of a number of polymers.     

脂肪族聚酯及共聚酯的生物降解性研究

以酯交换法或直接缩聚法合成了一系列脂肪族聚酯，经二异氰酸酯(HDI)扩链得到含氨酯键的聚酯及共聚酯，用DSC、X射线衍射等分析表征了聚酯及共聚物的结构和性能。用土埋试验、CO2释放试验和黑曲霉降解试验着重研究了这些聚合物的生物降解性，详细讨论了聚酯结构、组成及聚酯分子量对生物降解性的影响。     

Modified polyurethanes as a new type of thromboresistant polymers

New thromboresistant polymers are prepared via the physical modification of polyurethanes with water-soluble inert compounds. It is shown that the removal of water-soluble compounds from the polymer surface favors its self-purification without any dramatic changes in the conformation of proteins and in the structure of blood components. As a result, the time of whole-blood clotting on the polymer surface is higher by factor of 2.5–2.8 at a content of a low-molecular-mass modifier of 2 wt %.     

Fluorocarbon associative polymers

Fluorocarbon associative polymers modified along the backbone or at the extremities by hydrophobic groups are reviewed with respect to their association and rheological properties in aqueous solutions. Above a threshold concentration corresponding to the formation of a reversible network structure, the solutions behave as physical gels. In this review, it is shown that the viscoelasticity of fluorocarbon associative polymer gels is enhanced with respect to that of hydrocarbon analogues. For polymers substituted at the extremities (telechelics), significant progresses have been made in recent years concerning the microstructure, the phase behavior and the rheology of the gel state. Telechelics in solutions are forming multiconnected structures, which dynamical features are in good agreement with those of transient network models.     

Dynamics of star branched polymers in a matrix of linear chains — a Monte Carlo study

A simple cubic lattice model of the melt of 3-arm star-branched polymers of various length dissolved in a matrix of long linear chains (n₁ = 800 beads) is studied using a dynamic Monte Carlo method. The total polymer volume fraction is equal to 0,5, while the volume fraction of the star polymers is about ten times smaller. The static and dynamic properties of these systems are compared with the corresponding model systems of isolated star-branched polymers and with the melt of linear chains. It has been found that the number of dynamic entanglements for the star polymers with arm length up to 400 segments is too small for the onset of the arm retraction mechanism of polymer relaxation. In this regime dynamics of star-branched polymers is close to the dynamics of linear polymers at corresponding concentration and with equivalent chain length. The entanglement length for star polymers appears to be somewhat larger compared with linear chains.     

Segmented polymers — A new class of doped non-conjugated polymers with enhanced electrical conductivity

A new class of segmented non-conjugated dopable polymers, built up from short conjugated blocks connected with flexible chains (spacers), has been proposed. After the redox reaction of doping these polymers exhibit properties similar to those of the fully conjugated polymers and increase considerably their electrical conductivity. A solid state polymer effect has been observed. It has been found that the conjugated building units (biphenyl, diphenyl ether and 1,3,4-oxadiazole) do not interact with the dopant when included in a low molecular weight substance. When these units are incorporated in a polymer chain they change their reactivity and the polymer can be doped. The doping process takes place only when the polymer is in the solid state and the nature of this phase is of considerable importance. The phenomenon observed, i.e. doping of non-conjugated polymers with segmented structure could be explained with a favourable arrangement of the conjugated blocks in the solid phase, leading to enhanced π-π - interaction (equivalent to extended conjugation). By the collective interaction of several conjugated blocks with the dopant the polymer is partially oxidized and charge carriers are formed. The result is enhanced electrical conductivity.     

Gradient polymers and copolymers

Gradient polymers are two component polymeric systems in which the concentration of one component varies in a continuous way from one side to the other in systems with plane-parallel geometry. Such systems can be obtained from an amorphous polymeric matrix by diffusing into another monomer creating a gradient of concentration, which is fixed by, for example, photo-polymerization. Properties of such systems with plane-parallel geometry are discussed. Paricular attention is given to the systems with cylindrical geometry in which the gradient of the second polymer varies from the center to outside. This class of gradient polymers has a great practical application as gradient optical polymeric fibers and multifocal lenses. An interesting and new class of gradient polymers are systems systems consisting of semicrystalline polymeric matrices in which a gradient of structure is created by appropriate thermal treatment and an amorphous polymer gradient is formed by diffusion of a monomer and its subsequent polymerization. The structural, thermal and mechanical properties are discussed mainly for a model system consisting of polyethylene and polystyrene. The polymeric gradient systems, consisting of an oriented semicrystalline polymer and amorphous gradient polymer, are discussed showing that the structurally gradient matrices and amorphous polymer offer a great variety of factors which can influence the properties of multicomponent gradient polymers. Recently obtained gradient copolymers in which the chemical composition varies from one end to the other a macromolecule are presented. It is shown how such macromolecules can be obtained with different type of changes of the composition. The unusual properties of gradient copolymers are discussed considering their mechanical and thermal properties as well their specific behaviour as compatibilizers. © 1998 John Wiley & Sons, Ltd.     

Recent progress on cyclic polymers: Synthesis,bioproperties, and biomedical applications

Polymer topologies exert a significant effect on its properties, and polymer nanostructures with advanced architectures, such as cyclic polymers, star‐shaped polymers, and hyperbranched polymers, are a promising class of materials with advantages over conventional linear counterparts. Cyclic polymers, due to the lack of polymer chain ends, have displayed intriguing physical and chemical properties. Such uniqueness has drawn considerable attention over the past decade. The current review focuses on the recent progress in the design and development of cyclic polymer with an emphasis on its synthesis and bio‐related properties and applications. Two primary synthetic strategies towards cyclic polymers, that is, ring‐expansion polymerization and ring‐closure reaction are summarized. The bioproperties and biomedical applications of cyclic polymers are then highlighted. In the end, the future directions of this rapidly developing research field are discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1447–1458