High Equilibrium Rigidity Research Articles

Surface active monomers: from micellar solution properties to molecular characteristics

Hydrodynamic methods and light scattering were used in the studies of solutions of a surface active monomer 11-acryloyloxyundecyltrimethylammonium bromide (AUTA-Br) and its polymers in 0.05 M NaCl. Aqueous solutions of AUTA-Br monomer in the concentration range of 4 to 16 CMC contain individual molecules and near-spherical AUTA-Br aggregates. The pAUTA-Br polymers possess rather high equilibrium rigidity (11.8 nm). This high value of equilibrium rigidity found for pAUTA-Br macromolecules is apparently caused by two factors: the presence of a bulky side substituent in each AUTA-Br monomer unit and incomplete suppression of electrostatic interactions between neighboring monomer units in the backbone.

The effect of side chain length on hydrodynamic and conformational characteristics of polyimide-graft-polymethylmethacrylate copolymers in thermodynamically good solutions

Samples of graft-copolymers with polyimide backbones and poly(methyl methacrylate) side chains synthesized by ATRP of methylmethacrylate on polyimide macroinitiator are investigated by 1H NMR, GPC, static and dynamic light scattering, sedimentation, and viscosimetry in chloroform and ethyl acetate solutions. Hydrodynamic and conformational behavior of graft-copolymers is well-described by the wormlike spherocylinder and Porod wormlike chain models. Samples of graft-copolymers have high equilibrium rigidity, the Kuhn segment length grows from 20 to 95 nm with the lengthening of side chains. The equilibrium rigidity and hydrodynamic diameter of the investigated graft-copolymers depend on the molar mass M of side chains as M 0.7.

Optical and Conformational Properties of LC Cellulose Derivatives in Dilute Solutions

To analyze the influence of structure of the cellulose derivatives on the mesomorphic behavior it was carried out the investigation of their molecular properties in dilute solutions. Flow birefringence and intrinsic viscosity of cellulose derivatives were studied. The optical anisotropy and equilibrium rigidity of polymer chain were determined. The investigated cellulose derivatives are characterized by the high equilibrium rigidity. It was established that their molecules have the conformation of a kinetically rigid coil. It was shown that the values and sign of flow birefringence and correspondingly the optical anisotropy of monomer units depends on the structure of side substitutes and are influenced by the solvent nature and thermodynamical quality of polymer solution.

Investigation of macromolecules exhibiting the structure of a once-broken rod by molecular optics. 2. Synthesis and investigation of three-block copolymers: poly(γ-benzyl L-glutamate)-poly(methyl methacrylate)-poly(γ-benzyl L-glutamate)

The copolymer is considered to be a flexible polymer coil bonded at its ends to helical sequences of poly(benzyl glutamate) (PBG) exhibiting high equilibrium rigidity. Solutions of copolymer samples were investigated in DMF at 25 o C by light scattering, flow birefringence, and viscometry. Their compositions, molecular weights, intrinsic viscosities, radii of gyration, second virial coefficients, and optical anisotropy were investigated. The molecular weights and optical anisotropy of the copolymer components were calculated. It was shown that the introduction of a long flexible PMMA joint into the rigid PBG molecule does not change the equilibrium rigidity of PBG

Hydrodynamic and conformational properties of molecules of rigid chain polynaphthoylene imidoquinazoline

Translational diffusion and the viscosity of ten samples of rod-like polynaphthoylene imidoquinazoline in 96% H 2SO 4 have been investigated. Equations of the Mark-Kuhn-Houwink type have been obtained [ ν] = 2.82 × 10 −4 M 1.40±0.05, D = 4.23 × 10 −5 M −0.80±0.02. It is shown that the hydrodynamic behaviour of the polynaphthoylene imidoquinazoline molecules in 96% H 2SO 4 may be adequately described by a model of the streamed worm-like spherocylinder with a high equilibrium rigidity A = (1300±300) × 10 −8 cm and hydrodynamic diameter of the chain d = (20±5) × 10 −8 cm.

Hydrodynamic and dynamo-optical properties and conformation of cyanoethyl cellulose molecules in solution

Translational diffusion, velocity sedimentation and viscosity in acetone as well as flow birefringence (FB) and viscosity in cyclohexanone have been investigated for cyanoethyl cellulose (CEC) with degree of substitution 2.6 in the range of M = (24.5−317) × 10 3. The dependences of [ν], S o and D o on M were obtained. The value of the hydrodynamic constant is A 0 = 3.27 × 10 −10 erg deg −1 mol − 1 3 . According to hydrodynamic data, the equilibrium rigidity of CEC molecules is characterized by the length of the Kuhn segment A = 240 − 350 A ̊ and the coefficient of hindrance to intramolecular motion σ = 4.5-5.4. The hydrodynamic diameter of the chain is 8–14 Å. According to the FB data, the value of A is 260 Å. This value is in agreement with hydrodynamic data. The high value of optical anisotropy of the monomer unit, a | - a ⊥ = 17.8 × 10 −25 cm 3, is in agreement with the structure and anisotropy of the substituting groups, and the investigation of orientation angles of FB leads to the conclusion that, apart from high equilibrium rigidity, CEC in solution is characterized by considerable kinetic chain flexibility. The data for CEC are compared with the characteristics of other cellulose esters and ethers.

Optical anisotropy and rigidity of molecules polycyclohexanamide, polycaprolactam and their copolymers

Flow birefringence (FB) has been applied to solutions of a number of samples of polycyclohexanamide (PCHA), polycaprolactame (PCL) and their copolymers in sulphuric acid. Analysis of experimental data on FB by using Kuhn's equation leads to the length of the statistical segment for PCL (18Å) and for PCHA (133Å). High equilibrium rigidity of the PCHA chain is due to the “crankshaft” conformation, characteristic of all para-aromatic and para-cycloaliphatic polyamides. The shape of the curve of copolymer rigidity vs composition corresponds to additive flexibilities of the components of the copolymer.

The optical anisotropy and rigidity of the molecules of polycyclohexanamide, polycaprolactam and their copolymers

The flow-birefringence of a number of samples of polycyclohexanamide, polycaprolactam and copolymers of the two, in solution in sulphuric acid, has been investigated. Analysis of these measurements, using Kuhn's formula, gives the length of the statistical segment of polycaproamide as A=18 A ̊ , and of polycyclohexanamide as A=133 A ̊ . The high equilibrium rigidity of the polycyclohexanamide chain is explained by the “crankshaft” conformation characteristic of all para-aromatic and para-cycloaliphatic polyamides. The shape of the curve of the dependence of the flexibility of the copolymers on composition, corresponds to additivity of the flexibilities of the components.

Diffusion of poly- p-phenyleneterephthalamide in concentrated sulphuric acid

The translational diffusion of poly- p-phenyleneterephthalamide molecules of different molecular weights in 96% H 2SO 4 has been investigated with the aid of a new experimental technique. The diffusion coefficients D are not concentration dependent in dilute solutions, and show marked sensitivity to the length of macromolecules. The molecular weights of the specimens M obtained from the diffusion coefficients D in the light of the theory of translational friction of persistent chains are practically equal to those calculated in terms of a Tsvetkov-Klenin hydrodynamic parameter of A 0=3·78 × 10 −10 erg/deg. A slight divergence of the M values in question from those determined by the method of flow birefringence could stem from polydispersity of the specimens and from inconstancy of A 0. In the range of M=(4·−45) × 10 3 examined in this investigation relationships have bee found between the diffusion coefficients D and the intrinsic viscosity [η] and M: D=4·0 × 10 −5 M −0.80, [ η]=2·5 × 10 −5 M 1.7 M ⩽ 10,000) and [ η]=1·7 × 10 −2 M 1.0 ( M>20,000). In the light of a joint analysis of the diffusion and viscosimetric data a conclusion is reached as to the high equilibrium rigidity of poly- p-phenyleneterephthalamide molecules and as to their hydrodynamic properties in 96% H 2SO 4 which approximate to those of another rigid chain polymer, poly- p-benzamide, in the same solvent.

Conformation of aromatic polyamide molecules in solutions

Using experimental results concerning the equilibrium rigidity of molecules of some aromatic polyamides (PA) a study was made of the possible structure of poly- p-benzamide (PBA) and other aromatic PA molecules with phenyl rings incorporated in the para-position in the molecular chain. It was shown that a unique high equilibrium rigidity of molecules of these polymers is due to the co-planar trans-structure of amide groups resulting in a conformation of molecular chain similar to the shape of a “crankshaft”. Equilibrium chain rigidity evaluated using this model is in satisfactory agreement with experimental results. It was shown that the main factors determining the equilibrium rigidity of PBA molecules is the inequality of bond angles between carbon and nitrogen atoms of the amide group and deviations from the coplanar structure during the heat motion of the molecular chain.

On conformation of molecules of aromatic polyamides in solutions

On the basis of experimental data concerning the equilibrium rigidity of molecules of aromatic polyamides, possible structures of molecules of poly-ϱ-benzamide (PPBA) and other aromatic polyamides with phenyl rings included in the chain in the para position have been considered. It is shown that extremely high equilibrium rigidity of these polymer molecules is due to the coplanar trans-structure of their amide groups leading to a “crankshaft”-like conformation of the chain. The equilibrium rigidity of the chain estimated with the aid of this model is in good agreement with experimental data. It is shown that the main factors determining the equilibrium flexibility of the PPBA molecules are the inequality of valence angles at carbon and nitrogen atoms of the amide group and also a departure from coplanarity of the amide group due to thermal motion of the chain.

The physical properties of rigid chain polymer molecules in solution

Various features of the chemical structure of a polymer that can give rise to a high equilibrium rigidity of its molecular chains (interaction of side groups, the presence of rings in the main chain, a ladder structure, conjugation in the chain etc.) are outlined. It is shown how study of the hydrodynamic and optical properties of dilute solutions of a polymer enables quantitative information on the equilibrium flexibility of its molecules to be obtained. It is characteristic of chain molecules with high equilibrium rigidity that they also have high kinetic rigidity. The latter gives rise to a number of unique properties of rigid chain polymers that are essentially different from the properties of flexible chain polymers (high briefringence of solutions in mechanical and electrical fields, low frequency dispersion of dielectric polarization, the Kerr effect etc.). Study of the non-equilibrium dielectric and electro-optical properties of solutions of rigid chain polymers using appropriate theories, enables substantial information to be obtained on intramolecular mobility, optical anisotropy and on the magnitude and direction of the dipole moments of polar groups in the polymer molecules.

Molecular conformations, hydrodynamics and optics of ladder polymers

Hydrodynamic (diffusion, sedimentation, viscosity), dynamo-optical and electro-optical properties of several ladder polysiloxanes with different substituents in the side groups have been investigated. In accordance with the theories of hydrodynamic properties of worm-like chains, the equilibrium rigidity of the main chain of these macromolecules was evaluated quantitatively. High equilibrium rigidity of ladder polysiloxanes is a direct consequence of the double-chain structure of their molecular chains. Values of reduced birefringence in electrical and mechanical fields in solutions of ladder polysiloxanes increase with molecular weight but tend to a limit, which is characteristic for semirigid macromolecules. Birefringence in an electrical field for solutions of all ladder polymers investigated is by two orders higher than the value of electro-optical effect in polymers with flexible chains and its sign (negative) coincides with that of flow birefringence. In a variable (sinusoidal) field in the region of high frequencies, strong frequency dependence of birefringence is characteristic for all samples. Unique electrooptical properties in constant and variable fields prove that, in contrast to polymers with flexible chains, highly organized orientational long-range order exists in ladder macromolecules, moreover, it is not only an axial order but also a polar one. The occurrence of long-range correlation in the orientation of polar groups and bonds of the molecular chain gives rise to high total moment of the macromolecule, which is responsible for its rotation in an electrical field. The direction of this dipole moment coincides with the long axis of the molecule since the Kerr effect is of the same sign as flow birefringence.