Thermodynamic Rigidity Research Articles

Dynamic Monte Carlo Simulations of Strain-Induced Crystallization in Multiblock Copolymers: Effects of Asymmetric Block Rigidity.

Thermoplastic elastomers such as polyether-b-polyamides (or -polyesters), polyurethanes (or with -urea) and olefin block copolymers are commonly processed through a stretching process for achieving high elasticity and high toughness in their products, while the size diversity of semicrystalline microdomains of hard blocks appears as the key factor. By means of dynamic Monte Carlo simulations of strain-induced crystallization of locally concentrated and diluted crystallizable blocks alternatingly connected with noncrystallizable blocks in diblock and tetrablock copolymers, we have studied the size diversity of semicrystalline microdomains presumably raised by local concentration fluctuations of crystallizable blocks and found the dilution effects to persist from diblock to tetrablock copolymers. In the present work, we continued to study the effects of asymmetric block rigidity between crystallizable and noncrystallizable blocks on strain-induced crystallization of concentrated and diluted crystallizable blocks in diblock copolymers. The results showed that when crystallizable blocks hold higher thermodynamic rigidity than noncrystallizable blocks, the large semicrystalline domains become larger and the small semicrystalline domains become more, enhancing their size diversity. However, asymmetric kinetic rigidity has little effect. Our observations imply that industrial stretching processing could enhance the toughness of semicrystalline thermoplastic elastomers when their crystallizable blocks hold a higher thermodynamic rigidity relative to noncrystallizable blocks. Our integrated approach paved the way for a better understanding of the structure-property relationship in thermoplastic elastomers.

Amphiphilic molecular brushes with regular polydimethylsiloxane backbone and poly-2-isopropyl-2-oxazoline side chains. 1. Synthesis, characterization and conformation in solution

The samples of molecular brushes with a polydimethylsiloxane backbone and side chains of poly-2-isopropyl-2-oxazoline have been synthesized. Regular polydimethylsiloxane with undecene tosylate groups in every fourth siloxane unit was used as a macroinitiator. Two prepared samples are characterized by the same grafting density of side chains, but their different length and copolymer molar mass, 400,000 and 710000 g⋅mol−1. Solution behavior study revealed that macroinitiator and its precursor are flexible-chain polymers and macroinitiator’s thermodynamic rigidity is similar to one of polydimethylsiloxane. It was shown that the conformation of the graft copolymer molecules in a selective solvent resembles a polymer star because of the backbone of molecular brushes is strongly folded and shielded from the solvent by the side chains. The thermoresponsiveness of the synthesized molecular brushes in aqueous solutions has been demonstrated.

The interaction of DNA with piperazine derivatives of benzoimidazophthalazine

The interaction of DNA molecule with new synthetic compounds, piperazine derivatives of benzo[4,5]imidazo[1,2-a]phthalazine, was investigated by the spectral, hydrodynamic and optical methods. The thermodynamic parameters of the interaction and the stoichiometry of the complexes were determined by spectrophotometric titration. A mode of binding and structure of the complexes were determined by analyzing the changes in the intrinsic viscosity and the optical anisotropy of the macromolecule upon complexation. It is shown that an increase in the intrinsic viscosity and the optical anisotropy with a small content of the ligand in the complex is caused by the increase in the thermodynamic rigidity of macromolecules upon the formation of the complex. Increase of the contour length of the macromolecule in the complex does not occur, that indicates nonintercalative mode of binding the piperazine derivatives of benzoimidazophthalazine with DNA.

Persistence length of dendronized polymers: the self-consistent field theory.

We present numerical results for the thermodynamic rigidity and induced persistence length of dendronized polymers with systematically varied topology of their grafts obtained by the Scheutjens-Fleer self-consistent field method. The results were compared to predictions of an analytical mean-field theory. The two approaches have marked different predictions. In particular, the analytical theory predicts that the induced persistence length and the effective segment aspect ratio of dendronized polymers are increasing functions of the degree of branching of their side chains, whereas numerical calculations provide evidence of the opposite dependences. This discrepancy is argued to be due to the ability of side chains to repartition from the compressed to the dilated regions of a curved bottle brush, which is accounted for by the numerical, but not by the analytical method. The difference is most crucial in the light of the expected ability of dendronized polymers to have a liquid crystalline ordering in semi-dilute solutions.

Epoxy polymers based on functional adamantane derivatives

The main routes for modification of epoxy polymers with functional adamantane derivatives consisting of four saturated cycles are considered. It is shown that the high thermodynamic stability and rigidity of adamantane structure define a complex of properties of epoxy polymers and materials, as compared to the known polymers based on acyclic epoxy resins.

Investigations of the structure and conformations of star-shaped polymers with fullerene branching centers: Polystyrenes with different structures and functionalities of the C60 centers in toluene

The structure of regular star-shaped polystyrenes in deuterated toluene with single (C60) and double (C60-C60) branching centers and different numbers of arms (f = 6, 12, 22) has been investigated using small-angle neutron scattering. For functionalities f = 6 and 12, the thermodynamic rigidity and sizes of arms are larger than the corresponding characteristics of the linear polystyrene precursor; however, for f = 22, the situation reverses: the flexibility increases, the arms are compressed, and the radius of gyration of the stars decreases. The stars transform into dense spherical aggregates, the behavior of which is inconsistent with the Benoit and Daoud-Cotton theories for structures with a high functionality and Gaussian arms. This is explained by the competition between the structuring effect of the fullerene branching center on the solvent and by the reverse effect of the arms playing the role of defects in an ordered layer of the solvent around the fullerene.

Molecular properties of modified chitosan containing a quaternary amino group

A homologous series of the chitosan derivative N-[(2-hydroxy-3-trimethylammonium)pro-pyl]chitosan in a 0.33 M CH3COOH + 0.2 M CH3COONa mixture is studied via viscometry and static and dynamic light scattering. The molecular masses of the homologous series are determined, and the scaling relationships for the intrinsic viscosity, translational-diffusion coefficient, and hydrodynamic radius of molecules are derived. For the mentioned polymer-solvent system, the mean hydrodynamic invariant is estimated as A0 = (3.4 ± 0.1) × 10−15 kg m2/(s2 deg mol1/3). The equilibrium thermodynamic rigidity of modified chitosan chains is found to be 20 ± 2 nm. This value, like the parameters of the scaling relationships, suggests that the chitosan derivative under investigation belongs to the class of rigid-chain polymers. It is shown that, in the selected mixed solvent, the molecules of the modified chitosan are more compact than molecules of its nonmodified analog having close degrees of polymerization.

Cellulose Acetate Sulfate as a Lyotropic Liquid Crystalline Polyelectrolyte: Synthesis, Properties, and Application

The optimal conditions of cellulose acetate sulfate (CAS) homogeneous synthesis with the yield of 94–98 wt.% have been determined. CAS was confirmed to have an even distribution of functional groups along the polymer chain. The polymer was characterized by an exceptionally high water solubility (up to 70 wt.%). The isothermal diagrams of its solubility in water-alcohol media have been obtained. CAS aqueous solutions stability, electrolytic, thermal, and viscous properties have been defined. The main hydrodynamic characteristics such as intrinsic viscosity, Huggins constant, and crossover concentration have been evaluated. The parameters of polymer chain thermodynamic rigidity have been calculated. The formation of liquid crystalline structures in concentrated CAS solutions has been confirmed. CAS was recommended to be used as a binder for the medicinal forms of activated carbon and carbon sorbent for water treatment, hydrophilic ointment foundation.

Optical anisotropy of molecules of pyromellite-dianilic amido acid polyesters

The optical anisotropy of molecules of pyromellite-dianilic amido acid polyesters has been studied by the method of flow birefringence. Positive flow birefringence, which depends on the isomeric composition of the repeating unit, is detected. The thermodynamic rigidity of pyromellite-dianilic amido acid polyester molecules is calculated in terms of the valence-optical scheme. On passage from 100% para isomers of pyromellite-dianilic amido acid polyesters to macromolecules with a predominant content of meta isomers, optical anisotropy and equilibrium rigidity decrease by a factor of ∼2.

Structural Rigidity of Aromatic Polyamides with Bulky Lateral Substitutions

In the present study the effect that controlled structural modifications have on the physical and conformational properties of a series of isomeric aromatic polyamides synthesized with different bulky pendant lateral groups was investigated. Physical properties of the aromatic polyamides such as thermal properties were determined by differential scanning calorimetry. Structural changes were determined by Fourier transform infrared spectroscopy, density and fractional free volume ( FFV). Light scattering and dynamic-mechanical analysis were used to characterize the thermodynamic and kinetic rigidity. Vogel's model was applied to evaluate kinetic rigidity in polyamide chains and the results were compared with physical properties data. It was found that there was a relationship between Tg and the conformational entropy determined by the structure which indicates that the higher the level of rigidity in the polyamide the higher the value of Tg. For kinetic rigidity, it was found that the relaxation time at infinite temperature Bα , was very close to the value 5 x 10-12 s, reported for other amorphous glassy materials. There was also a relationship between the activation energy of the glass transition U∞ and FFV, which is determined by the presence or absence of the bulky functional groups, indicating that the smaller the FFV, the higher the energy required for the glass transition to take place.

Molecular characteristics and surface layer structure of poly(siloxane imides)

The effects of spontaneous ordering of molecular chains of poly(siloxane imide) block copolymers in the surface layers of thin films on glass and gold supports have been studied by the oblique polarized beam and photoelasticity methods. The effective thermodynamic rigidity of molecular chains of the block copolymers (the statistical segment length) has been found to be A = 10.4 × 10−7 cm. The orientational ordering of molecular chains in poly(siloxane imide) surface layers is characterized by small values of the orientational order parameter (S 0 ∼ 0.007). This finding is explained by the microphase separation of the block copolymers. The evaporated gold layer contributes to the effect of surface birefringence owing to formation of the ordered system composed of islets—clusters of gold atoms.

The effect of solvent nature upon the optical anisotropy of poly-(1-trimethylsilyl-1-propyne)

Optical properties of poly-(1-trimethylsilyl-1-propyne) in solvents with different refractive indices and optical anisotropies have been studied by the dynamic birefringence method. An optical shape-effect has been detected in solvents characterized by refractive indices n s different from those of dry polymer n k. It was revealed that this effect is an effect of the macromolecule segment shape; this allowed us to estimate thermodynamic rigidity of the molecular chains under study ( A = 82 × 10 −8 cm). It has been found that the optical shear coefficient of the studied polymers solutions in anisotropic solvents exceeds considerably the same parameter in an isotropic solvent. It has been shown that this difference is caused by the solvent anisotropic molecules orientation by the axis of maximal polarizability along the macromolecule backbone. The assumption that the solvent molecules orientation order with respect to chain molecules does not depend on the chain molecule thermodynamic rigidity allowed us to obtain independent estimate of the sizes of static segments of the macromolecules under study (98 × 10 −8 cm).

Water vapor sorption by fibers of aromatic polyamides

Isotherms of water vapor sorption by fibers of aromatic polyamides of several types have been obtained in a wide range of relative pressures (p/p s from 0 to 0.8–0.9). It has been shown that different values of moisture sorption determined from sorption isotherms correlate with molecular and structural characteristics, such as the thermodynamic rigidity of macromolecules, the integral specific surface area with respect to an inactive sorbate (krypton), the average off-orientation angle, and the phase state of the structure. It has been speculated that a difference in the moisture sorption of the test fibers is primarily related to their phase structure, particularly, to the prevalence of either a mesophase or crystalline order.

Effect of solvent nature on the optical anisotropy of poly(1-trimethylsilyl-1-propyne) molecules

The optical properties of poly(1-trimethylsilyl-1-propyne) solutions in solvents possessing optical anisotropy have been studied with dynamic birefringence measurements. In solvents characterized by refractive indexes different from the refractive index of a dry polymer, the optical form effect has been discovered. This effect is determined by the shape asymmetry of a macromolecular segment and its rigidity. Estimates showed that the length of the statistical segment, which characterizes the thermodynamic rigidity of the macromolecular chains under study, is 82 × 10−8 cm. The shear optical coefficient for solutions of the test polymer in an anisotropic solvent is markedly higher than the corresponding value in an isotropic solvent. This difference is related to the orientation of anisotropic solvent molecules along the main chain of a macromolecule by their highest polarizability axis. Under the assumption that the orientational order of solvent molecules relative to chain macromolecules is independent of the thermodynamic rigidity of chain molecules, the size of the statistical segment of the macromolecules in question has been independently estimated as 98 × 10−8 cm.

Mean-field theory of ordering in polymer systems with orientational-deformation interactions

On the basis of the mean-field method (single-chain approximation), expressions were derived for the free energy of a chain with dipolar orientation-deformation interactions of Gaussian subchains with a fixed mean-square length. In terms of this approach, the systems experience a second-order phase transition from the isotropic state to an ordered state. The Curie point and the dipole and quadrupole order parameters were related to the thermodynamic chain bending rigidity. The types and characteristics of transitions in anisotropic lattice models with dipolar orientational interactions were compared with those in continuous models with quadrupole interactions in terms of the mean-field approximation (Maier-Saupe theory). The short-and long-range orientational order in single-chain models (mean molecular field) and the corresponding multichain models (with local intrachain interactions of subchains) were compared. A comparison of the orientational correlation functions in single-chain and multichain models composed of flexible segments of a fixed length and rigid elements showed their qualitative equivalence as applied to the description of the statistical properties of chains in polymer systems with dipolar orientational-deformational interchain interactions, especially in the case of high chain ordering. Owing to the long-range fluctuation instability in two-dimensional multichain systems, the results of the mean-field theory are applicable only to parts of systems with finite sizes (domains).

Fragments of Heterocyclic Copolyamide Phase Diagrams

Fragments of a ternary phase diagram of the system heterocyclic copolyamide—DMAA/LiCl—precipitant (H2O and isobutanol) are obtained. The temperature—concentration boundary of the phase transition for sulfuric-acid solutions of the heterocyclic copolyamide in the region of the existence of isotropic and anisotropic phases is determined. A hypothesis is advanced concerning the relatively high thermodynamic rigidity of the copolyamide molecules, close to the rigidity of PABI but less than the rigidity of PPTA.

Equilibrium Rigidity of Polyorganophosphazene Molecules

The optical anisotropy and orientation angles of polyorganophosphazene (PPhPh) molecules with different lengths and side-chain structures have been investigated by flow birefringence and viscosimetry methods. Quantum-chemical calculations of the optical anisotropy per monomer unit within the polymer fragments with different conformations were carried out. It was shown that both short-range and long-range interactions (i. e. the structure of the polymer backbone and steric interactions between side chains) influenced the conformation of the PPhPh molecules and should be taken into account for the determination of the thermodynamic rigidity value A. The experimental value of A, (50 ± 5)·10–8 cm, obtained by different methods, adequately corresponds to the structure and observed physical parameters of the PPhPh molecules. Molecules of this class of polymers are not rigid chains in a common way (A > 150·10–8 cm), but alternating double bonds of their backbones bring about some increase in the equilibrium rigidity. It can be assumed that, for this class of polymers, the mesogeneity on a molecular level is defined by the strong interactions of fluorine-containing side chains rather than by the rigidity of their backbones.

Effect of Single-Charged Anions of Different Nature on the DNA Molecule Conformation in Water–Salt Solutions

Methods of intrinsic viscosity (η) and beam flow birefringence were used to study the effects of some single-charged ions (F–, Cl–, Br–, I–, NO–2, NO–3, ClO–4, SCN–, CH3COO–) on the size and thermodynamic rigidity of a DNA molecule in aqueous solutions of sodium salts in a broad interval of ionic strength μ when temperature T is changed. It has been shown that the close interactions in a macromolecule and the resulting DNA persistent length a are independent of the type of the salt anion over the whole interval of μ. On the contrary, the specific volume of the DNA molecule in solution, proportional to the ηvalue, is quite sensitive to the anionic composition of the solvent, which is due to the effect of anions and their hydration on the long-range interactions in the macromolecule. The presence of polyatomic and halide anions is manifested differently in the η value of DNA. Possible factors responsible for the observed effect and the role of structural alterations of water upon anion hydration are discussed.

Polysaccharide Film Technologies: Interfacial Order and Chain Thermodynamic Rigidity

Polysaccharide Film Technologies: Interfacial Order and Chain Thermodynamic Rigidity

Huggins viscometric constant of semirigid and rigid-chain aromatic polyamides

The absolute values of the Huggins viscometric constant for semirigid- and rigid-chain aromatic polyamides are high, but not very high in comparison to the values for flexible-chain polymers. The Huggins viscometric constant virtually does not change with some, at least two-fold, change in the molecular weight of semirigid- and rigid-chain polyamides, which is similar to the results known for flexible-chain polymers. Either the thermodynamic rigidity of the macromolecules or the thermodynamic affinity between polymer and solvent as a function of the nature of the solvent have the predominant effect on the values of the Huggins viscometric constant in solutions of aromatic polyamides.