A.V. Volokhina

The flow birefringence and conformation properties of poly-p-phenylenoxadiazole molecules in solutions☆

Abstract The flow birefringence (FBR) of sulphuric acid solutions of poly- p -phenyleneoxadiazole (PPOD) samples having various mol.wt. has been determined. The characteristic angles of orientation [χ/g] increase with the mol.wt. M as a linear function of M[η]([η]-intrinsic viscosity). The proportionality factor is slightly larger than the theoretical value for rigid kinetic molecular chains; this can be explained by some polydispersity in the samples. The given FBR [n]/[η] changes with the M in accordance with the theory for kinetically rigid coiled chains. The analysis of this dependence gave the length of the Kuhn segment as A ≈ A which is twice that got earlier from the hydrodynamic data. Barrier σ to internal rotation inthe PPOD chains is about 1·5 according to FBR, which is close to that got earlier for aromatic polyamides but much lower than that typical for flexible-chain polymers.

The hydrodynamic and conformational properties of poly-p-phenyleneoxadiazole in solutions☆

The diffusion coefficients D and intrinsis viscosities [η] have been measured for 23 poly-p-phenyleneoxadiazole specimens in sulphuric acid. Molecular weights of the specimens have been calculated from the experimental values of D and [η] for different theoretically possible values of the hydrodynamic parameter A0. It is shown that the experimental data agree well with theories of translational friction and intrinsic viscosity of vermicular chains when values of the molecular parameters are as follows: A0 = 3·6 × 10−10 erg/deg, monomer unit length ψ = 7·2 A, Kuhn segment length A ≈ 100 A, hydrodynamic diameter of the molecular chain d ≈ 6 A. Relationships determining the dependence of D on MDη and of [η] on MDη are adduced.

Dynamic birefringence and molecular rigidity of poly-p-benzamide in solution☆

The flow birefringence (FBR) of solutions in sulphuric acid of a number of poly-p-benzamide (PPBA) specimens have been investigated and the intrinsic viscosities [n] of the same solutions have been measured. The characteristic values of FBR [n] and of the angles of orientation [x/g] have been determined for the solutions investigated. The molecular weight, M, has been calculated for all the PPBA specimens studied from a comparison of the values of [x/g] and [n]. The relationships obtained, [n]=1.6 × 10−5 × M1.7 and Dr=2 × 2015 × M2.7, indicate that the conformation of PPBA molecules in solution is approximately rod-like. By use of the theory of the optical a nisotropy of persistent chains, quantitative data about the equilibrium rigidity of PPBA molecules been otained from a comparison of the characteristic values of [n] and [x/g]. It is shown that the number of monomeric links in the statistical chain segment of PPBA, S, is 320 and the corresponding length of the segment, A, is 2000 A.

Flow birefringence and rigidity of molecules of aromatic copolyamides of para-structure☆

The authors have studied the flow birefringence and characteristic viscosities in sulphuric acid solution of a number of samples of copolyamides containing poly-p-phenylene terephthalamide and poly-p-benzamide units. From the experimental dependence of the reduced bierfringence [n]/[n] on the length of the chain using the Tsvetkov theory of flow birefringence for kinetically rigid vermiform chains, they determine the length of the Kuhn segment A = (520±60) × 10−10 m and the optical anisotropy of the monomer unit Δa=80 × 10−31m3 of the copolymers. The value of A obtained reasonably matches the theoretical for the structural model with weak hindrance of rotation.

Dynamic birefringence and molecular conformation of aromatic polyamide hydrazide in solutions

A study was made of flow birefrngence (FB) in solutions of several samples of para-aromatic polyamide hydrazide (PPAH) in DMSO and intrinsic viscosities [η] of these solutions measured. Using characteristic values of [ξ/g] of angles of orientation and values of [η], molecular weights M of the samples studied were determined. Using the theory of optical anisotropy of persistent chains the length of the Kuhn segment A=800 A of the molecular chain of PPAH was determined from the dependence of [n]/[η] on M ([n] being the characteristic value of FB). A somewhat lower value, compared with the length of the segment of the para-aromatic polyamides, may be explained by the fact that in molecular chains of PPAH a small proportion of ammide groups is in cis-configuration.

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 Kuhns formula, gives the length of the statistical segment of polycaproamide as A=18A, 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.

The conformational and optical characertistics of some aromatic copolyamides from flow birefringence data

Abstract Flow birefringence and characteristic orientation in sulphuric acid solutions of homologous series of 3 aromatic polyamides have been studied. The values of the structurally-conformational parameters of the molecules of the above polyamides were determined from the dependence of the optical coefficient of shear using the birefringence theory for persistent chains. The results obtained are explained in the content of the proposed molecular models, by the simultaneous action of the structural and deformational mechanisms of flexibility in polyamide chains.

Copolymerization of α-piperidone with ε-caprolactam and α-pyrrolidone☆

Abstract A study has been made of the increase in polymerizability of α-piperidone in the presence of lactams with different degrees of strain in the ring. It is shown that the degree of conversion of piperidone to polymer increases as the concentration of caprolactam in the monomer mixture or the reaction temperature are increased. Separation of the copolymers as precipitates also brings about increase in the proportion of piperidone in the copolymer. On the other hand, when piperidone is copolymarized with the less strained lactam α-pyrrolidone there is no activation effect. These results can be explained on the basis of the thermodynamics of copolymerization of lactams.

Specifics of the thermal oxidative decomposition and burning of fabrics from fibre mixtures

ConclusionsIt has been shown that on introducing up to 12% by wt. PCA into a fibre from a mixture of two polymers (PPTA and PCA), a marked increase in the fire-protective characteristics of the fibre is observed.Differences have been established in the mechanism of fire-protective action of the phosphorus-containing combustion retarder for materials from a mixture of cellulosic fibre and PPTA and fabrics from a mixture of cellulosic fibre and a fibre from a mixture of PPTA and PCA.

Water vapor sorption and structural features of mixed fibres from rigid-chain copolymers

ConclusionsSorption isotherms for vapors of an active and an inactive sorbate have been measured for fibres prepared from mixtures of two rigid-chain copolyamides.It has been shown that the investigated mixed fibres have low specific surface values (with respect to the inert sorbate). The experimental values of water vapor sorption for these are less than those calculated by an additive scheme, the greatest decrease being observed at a content of 10% by wt. of the second rigid-chain component (CA) in the mixture.Ideas about interpolymer interactions which are displayed in extreme form at a definite composition of the mixed fibre (at a CA content of 10%) have been proposed to explain the nonadditive change in water vapor sorption by the mixed fibres.