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AbstractA theoretical study is carried out on the flexibility of aromatic polyamidoacids and polyimides containing planar cycles connected by different types of joints. It is shown that such polymer chains may be considered as a sequence of linear links joined at some angles with free rotation about the links. An expression for the mean square end-to-end distance for some types of these chains is given. An experimental investigation of the flexibility of some polyamidoacids obtained by polycondensation is also performed. The intrinsic viscosity is measured in θ-solvent. The molecular weight is determined by light scattering. The agreement between experimental and theoretical values of (h02/M)1,2 for polyaminoacids is satisfactory thus justifying the use of the suggested theoretical approach for study of the flexibility of insoluble polyimides.

AbstractThe energy of the geometric isomerisation of butene-2 was calculated, using different sets of semi-empirical nonbonded interaction potentials. Of the potential functions studied, those suggested by the authors and used by Scheraga were quite successful in reproducing the experimental result.

AbstractThe theory of well defined superstructures formed in binary mixtures of diblock copolymers with different molecular weights and composition in a strong segregation limit has been developed. Three types of binary mixtures were considered: a mixture of two cylinder-forming block copolymers; a mixture of cylinder- and lamellae-forming block copolymers; and a mixture of two lamellae-forming block copolymers. The formation (conditions and the thermodynamic characteristics) of mixed lamellar and cylindrical superstructures and their thermodynamic stability were investigated. It was shown that in the case of non-isomorphous block copolymers the change in mixture composition leads to a first-order phase transition from one morphology of the superstructure to another, i.e. to real phase segregation (each phase remains microphase segregated). The theory was compared with experimental data. The possibility of the formation of cylindrical domains in the mixture of two lamellae-forming block copolymers was predicted.

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AbstractA theoretical study was made of regular conformations of polyisocyanate molecules with different side groups using semiempirical conformation analysis. Quantum chemical calculations were made for small molecular fragments, in order to determine internal rotation barriers around bonds of the framework and distribution of local charges. Conformation analysis was carried out of larger chain segments dependent on two and four angles of internal rotation. Polymers with R = CH3, C3H7, C4H9and C7H7 (tolyl ring) side groups were examined. Regular conformations were found all for the polymers examined, which are spirals with parameters close to parameters of the helical structure found by X-ray analysis for polybutylisocyanate.

AbstractA computer has been used to model the behaviour of macromolecules of differing rigidities. A chain not intersecting itself has been used as the model on a cubic lattice. The solvent quality has been accounted for by incorporating forces of attraction (or repulsion) between each pair of chain units coming close together. Calculations have been made for chains with a rotation-isomeric mechanism of flexibility and with a mechanism described by persistent flexibility. Rigidization of the chain, regardless of the mechanism of flexing, reduced the energy of attraction (increased the temperature) corresponding to the θ point.

AbstractA chain model in a cubic lattice has been used to examine the effect of flexibility and the mechanism of the latter on local density and the micro-structure of macromolecules in solutions. The average number of intramolecular collisions, the distribution of loops, the average length of the rigid and of colliding parts, the distribution by length in “good” and “poor” solvents, have been calculated. The mode by which intramolecular collisions are realized in the various mechanisms of chain flexing has been analysed. The local density and the steric micro-structure of flexible chains are determined by the behaviour of short chain parts several bonds long. Where it is difficult for the chains to fold up, a small local density is typical, also a cross-shaped position of the interacting parts, and a slight dependence of the geometrical and thermodynamic characteristics on solvent quality. The existence of mobile reinforcements inside the chains results in an appearance of folding structure centres in solvents near the θ point, of large local densities in flexible chains, of an θ-temperature depending on rigidity, and of a larger dependence of internal characteristics of the chain on solvent quality. Intramolecular pseudo-crystals will also appear in the fairly rigid macromolecules in “poor” solvents near the θ-point.

AbstractThe classical, semi-empirical conformation analysis has been used to examine the local conformations in the ladder polyphenyl- and polymethyl-silsesquioxanes. The most probable valence angles at the oxygen atoms and the internal rotation angles were determined within the likely range of conformation parameters. Assuming that a fluctuating mechanism of flexibility exists, the persistant length of the examined polymers has been assessed.

AbstractBy simulation of polymer chains using a computer a study has been made of different characteristics of macromolecules adsorbed on a plane surface. As a model we took a self intersecting chain on a simple cubic lattice. The first unit of the chain is constrained to an adsorbing surface, and when any other chain units get onto the surface an energy gain ϵ results. The analysis covered flexible chains where there is equiprobability of trans- and gauche-isomers, and also stiffer chains with a preferred trans-configuration. The amounts of units adsorbed at the surface were calculated as well as the length of adsorbed and loop-like segments, the adsorbing layer thickness, the chain lengths and the areas covered on the surface by polymers with varying degrees of polymerization for different ϵ values. It is shown that in the region of polymer-surface energies below a critical level the number of polymer-surface contacts is small, irrespective of the length of the chain, whereas with energy values exceeding the critical level the number of contacts increases linearly with increasing numbers of chain units. In addition there is a redistribution of trans- and gauche-isomers in adsorbed and nonadsorbed parts of the macromolecules. Rigidization of the polymer chain increases the number of units in contact with the surface, and there is a sharpening of the transition from the nonadsorbed to the adsorbed state. The calculated adsorptive layer thicknesses characterized by the mean height of a chain end over the adsorbing surface are large in the pre-critical region, and depend on the molecular weight of the polymer chain, while in the post-critical region, on the other hand, the layer thickness is not a function of the chain length, and is small. It was found that the root mean square radius of inertia for an entire chain 〈R2〉 is invariably proportional to MW, and varies relatively little with ϵ. At the same time the radius of inertia of the adsorbed part of a macromolecules is near zero in the region of low polymer-surface interaction energies, and approximates 〈R2〉 in cases where the energies exceed a critical level.

AbstractThe Monte Carlo method has been used to examine the equilibrium characteristics of flexible chain concentrations in model lattices. Considered were the specific volume of the chain units and the reactions of random ones coming close together. The concentration effects have been considered by dividing all of the space into cubes of edges l = 5−21 long in which the periodic limiting conditions permit the formation of n chains composed of N = 16−121 units each. The studied concentration range was c=nN/l3, which varied from zero to c ≅0·7. The existence of forces of repulsion between chain units (a good solvent has been found to give rise to a mean square radius of inertia and number of intermolecular contacts in each of the chains which approached those for a separate chain in a θ solvent as the concentration increased). The same effect also applies to forces of attraction between chain units. In the concentration range c⩾ck, in which the intramolecular chain characteristics almost cease to change, there is overlapping of macromolecular coils when ck ∼[ν]θ−1, in which [ν]θ−intrinsic viscosity of the dilute θ solution. For the inter-chain unit energy of reaction at the θ point there is no concentration dependence of the geometrical and thermodynamic characteristics of separate macromolecules.

AbstractThe Monte Carlo method has been used to calculate equilibrium characteristics of model flexible copolymer chains differing as to the combination of blocks, but having identical compositions and contour lengths. The number of units was in all 64, and the number of microblocks varied from 2 to 64. Energies of homo- and hetero-contacts between pairs of attracted units varied within wide limits. Given equality of the homo- and hetero-contact energies the chain was a homopolymer containing “tagged” sections of varying length, which made it possible to determine the hierarchy of interactions in the polymer coils, namely, the extent to which the characteristics of a particular chain section are influenced by other sections positioned at various distances away from the former section along the chain. Local densities of units have been calculated, i.e. the number of intrachain contacts between units of a particular sort and between units belonging to different components. The structure of multiblock copolymers in selective solvents has been analyzed, and the conclusion formed that the copolymers must contain a number of quasi-globular chain sections (blocks) alternating with uncoiled blocks. Conditions under which globularized blocks merge into a single tangled clot-like formation are examined.

AbstractThe local conformations of stereoregular polymethacrylate (PMA) chains have been examined. The mean square dipole moment <μ2> and the correlation parameter g=<μ2>/nm2 for n→α (n is the degree of polymerization; m-dipole moment of the monomer unit) has been calculated for these and the stereoirregular chains. The isotactic PMA chains are mainly in the tg (or gt) conformation (60–80% of the monomer units), but a noticeable proportion (40-20%) have a tt conformation which serves as contact between them. The monomer units of the syndiotactic PMA chains have mainly the tt conformation (75–80%) with a participation of (about 20%) gg conformations. Up to 7% of the monomer units take on a gt and tg conformation. Values of g are greater than 1 over the whole range of admissible energy parameters where the chains are stereo-regular. The value is near the experimental in the case of all other chains and is obtained only by assuming strong hindrance to rotation of the pendant side group.

AbstractThe general theory of the conformational transition on adsorption of the individual macromolecule on a solid surface is developed. The statistical sum of the macromolecule on the surface is constructed by the method of generating functions. It is shown that change in the equilibrium state of the chain from the free to adsorbed on a rigid adsorbent comes about for a certain critical adsorption energy of the units, i.e. has the character of a phase transition (for N → ∞). An equation is constructed relating the critical adsorption energy to the characteristics of the chain and adsorbent. The order of the phase transition is analyzed and it is shown that it is determined by the distribution function of the lengths of the loops formed by the free chain relative to the virtual surface drawn through it, the geometric equivalent of the adsorbent. An expression is obtained for the order of the phase transition including the dimensionality of the free volume and adsorbent (the number of measurements according to which the extent of the adsorbent is infinite) and the exponent in the dependence of the size of the free chain on the degree of polymerization. The possibility of diverse phase transitions on adsorption of the macromolecules is shown.

AbstractLocal conformations of stereospecific PMMA chains have been investigated. For these chains and for atactic PMMA we calculated the mean square dipole moment 〈μ2〉 and the correlation factor g=(μ/nm2)n→∞. In the case of isotactic PMMA chains the share of tt conformations amounts to 75% of the monomer units, and in the syndio chains the amount of tt conformations is increased up to 90%. Vaues of g calculated for the isotactic and atactic chains over the entire interval of values permissible for the energy parameters that may be reconciled with experimental findings are obtainable only if it is assumed that there is a regular alternation of the directions of dipole moments of side polar groups (pendants), the rotation angle being x = 0 and 180°; in the syndio chains the probability of there being an alternation of the directions of dipole moments of the pendants 12

AbstractA theory for the conformations of comb-like polymers in solution has been developed by the scaling method. The local conformational structure and dimensions of such macromolecules have been studied over a wide range of change in solvent quality and solution concentration. The characteristic feature of the behaviour of solutions of comb-like and other branched macromolecules is the existence of a quasi-globular regime for semidilute solutions. In this regime, discrete macromolecules overlap, but their internal regions, close to the comb-like axes, are segregated.

AbstractThe liquid-crystal superstructures formed by diblock copolymers at arbitrary concentrations have been considered by the method of scaling. Analytical expressions have been obtained for the free energies of the superstructures and a diagram of states has been constructed for the system with the copolymer composition and concentration as coordinates. Transitions between the various morphologies with changes in concentration or under the effect of an external field are discussed.

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