I.N. Shtennikova

Conformation and physical properties of polyisocyanates in solution

Abstract Hydrodynamic, dynamo-optical and electro-optical properties of aromatic (ArIC) and aliphatic (AlIC) polyisocyanates in solution have been investigated. Experimental data show that ArIC in solution has the statistical coil conformation. The flexibility of the chain corresponds to that of typical molecules of synthetic polymers. In contrast, the optical properties of AlIC solutions in nonpolar solvents indicate that the molecular shape resembles a weakly bending rod, while the molecular chain is characterized by a high degree of intramolecular orientational order. Application of the theory of hydrodynamic and optical properties of wormlike (persistent) chains to the experimental data permits calculation of the optical anisotropy, dipole moment and persistence length of the AlIC molecules. The values obtained are similar to those for synthetic polypeptides in the α-helical conformation. The data show that the most probable conformation of AlIC in nonpolar solvents is the planar cis chain.

Influence of the molecular weight (m.w.) on the hydrodynamic properties and optical anisotropy of ladder polyphenylsiloxane

(2) Changes of the ECM0 content from 0 to 100% in the copolymer were found to raise the glass temperature by more than 70%. (3) Copolymers with a 20-30% content of ECMO units were found not to crystallize. A decrease of the ECMO content produced crystallization of the copolymers due to the THF units present, and an increase of crystallization due to Che ECMO present. (4) A correlation was found to exist between the results of dynamic, mechanical and dilatometric measurements. Translated by K. A. ALLEY REFERENCES

Dynamooptical and electrooptical behaviour, rigidity, and molecular conformation of polyisocyanates in solutions☆

IT I

Molecular conformations, hydrodynamics and optics of ladder polymers

only quite recently that the polymerization [1, 3] and copolymerization [4, 5] of monoisocyanates has been found possible. Soon after this the unusual properties of solutions of aliphatic polyisocyanates, namely their high intrinsic viscosity [1, 6, 7] and the very large dil~ole moment of their molecules [8] were discovered. Analysis of the hydrodynamic [6-8] and dielectric [8] characteristics led to conclusions indicating the great extension and rigidity of the molecular chains of polyalkylisocyanates, and also to the conclusion that the molecules in solution had a conformation close to the straightrod. In view of these special conformational features it is reasonable to assume that the internal structure of polyisocyanate molecules will be characterized by regularity in arrangement and in orientational ordering. One of the best methods of detection and of making a quantitative study of the intramolecular ordering in rigid-chain polymers is by joint investigation of the dynamooptical and electrooptical behaviour of their solutions [9]. This paper describes the use of this method applied to samples of ID-butyland p-tolyl isocyanates. On the basis of experimental results conclusions are reached regarding the optical anisotropy, dipole moments, rigidity and probable conformation of the molecules under investigation.

Rotary friction, dipole moments, conformation and rigidity of polybutylisocyanate molecules in solution

Abstract 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.

Intramolecular liquid-crystal order in polymers with chain side groups

Experimental data on the dependence of the rotatory diffusion coefficients and dipole moments on molecular weight and the theory of hydrodynamic properties and of the size of wormlike chains were used for determining the main conformational characteristics of the polyisocyanate chain S is the number of molecular units in a segment, λ is the length of the projection of the monomer unit on the axis of the molecule, and μo is the dipole moment of the monomer unit. The values of S and λ agree with those found previously by hydrodynamic methods. It was shown that the flat cis-structure of the polyisocyanate chain corresponds to values of λ = 2 × 10−8cm andμo = 1·8D. Analysis of experimental data indicates that dimensions of “geometrical” and “electrical” segments in the PBIC chain are identical.

The sedimentation, diffusion and viscosity of polybutyl isocyanate solutions☆

Abstract Hydrodynamic, optical and electro-optical properties of solutions of polyphenyl methacrylic esters of cetyl and nonyl oxybenzoic acids and of random copolymers of the C 16 ester with cetyl methacrylate have been investigated. Experimental data show that the molecules of these polymers exhibit intramolecular orientationalpolar order of a mesomorphic type in which the side-chains form a mobile liquid-crystalline structure. The intramolecular mesomorphic state is due to the side chain radical containing groups capable of forming thermotropic nematic liquid crystals.

Conformational properties of hydroxypropylcellulose—II. Flow birefringence and optical anisotropy of hydroxypropylcellulose macromolecules

The progressive diffusion D, sedimentation coeffecient S0, intrinsic viscosity [η] and the molecular weights M of a number of polybutyl isocyanate (PBI) fractions were measured over a wide range of M. The experimental results were used to determine the structural parameters of the PBI molecular chain on the theoretical basis that this could be regarded as rigid, ellipsoidal, stretched and coiled persistent chains. The projection of the monomer chain unit on the molecular axis gave γ=2±0·1 A and represents a flat cis-configuration of the chain. The persistent length a of the PBI molecule was determined from the results of progressive diffusion using the progressive friction theory for coiled chains in the range of larger M; it was found to be 500A. The PBI molecular conformations were found to be similar to a slightly bent rod only in the range of small M (less than 4 × 104), while the best model for describing the hydrodynamic properties at larger M was the coiled chain.

Hydrodynamic and optical behaviour of polyester molecules of alkoxybenzoates and their dependence on molecular weight

Abstract The flow birefringence of solutions of hydroxypropylcellulose (HPC) in dimethylacetamide and tetrachloroethane has been investigated over a wide range of molecular weights. Comparison of the experimental dependence of shear optical coefficient [η]/[η] on molecular weight with the theoretical dependence for rigid wormlike chains made it possible to determine the equilibrium rigidity of HPC molecules. The segment length thus determined is in good agreement with the evaluation of rigidity from viscometry and diffusion data. The optical anisotropy of HPC molecules, ( α − α 2 ) = 500 × 10 −25 cm 3 and the degree of their intramolecular orientational-axial order were determined.

Conformational and optical properties of (acetoxypropyl)cellulose molecules in solutions

Abstract A study of progressing diffusion, sedimentation, viscosity and flow birefringence of phenylmethacrylyl ester fractions of cetyl- (C 16 ) and nonyloxybenzoic acids (C 9 ) in tetrachloromethane indicates that the equilibrium rigidity of the main chain of C 16 ( S = 22) and C 9 ( S = 16) polyester molecules, determined from hydrodynamic results somewhat exceeds the rigidity of molecules of a similar structure but without these side groups. A reduction in birefringence for C 16 and C 9 polyesters with an increase of molecular weight was observed experimentally. This abnormal variation in the optical anisotropy of macromolecules is, apparently, the consequence of a reduction in the orientation order in macromolecular side chains.