A.Ye. Grishchenko

The optical anisotropy of the molecules of some polymethacrylate esters in the solid state and in solution

IT IS known that the optical anisotropy of polymethacrylates and polyacrylates is dependent on the length and structure of the side radicals [1, 2]. In the present work, by means of photoelastic and flow birefringence measurements, a study was made of the optical properties of some polymethacrylates differing in the length of the side group. Poly-n-octylmethacrylate (P-n-OMA), a polymer in which the mass of the side groups constitutes three quarters of the total mass of the macromolecule, was studied in greatest detail.

Photoelastic effect in swollen polydimethylsiloxane

Abstract Studies of the photoelasticity of the gels of certain chain polymers [1–3, 13, 14] have shown that at high concentrations ( c [ n ] > 1) the birefringence on stretching is composed of effects due to the intrinsic segment anisotropy ( α 1 − α 2 ) i and microform anisotropy ( α 1 − α 2 ) fs of the molecular chain: ( α 1 − α 2 ) = ( α 1 − α 2 ) i + ( α 1 − α 2 ) fs . In contrast to the rigid molecules of cellulose derivatives [3,14], the intrinsic anisotropy ( α 1 − α 2 ) i of the flexible polyvinylacetate chains (PVA) [13] is closely dependent on specific features of the environment and may differ widely in different solvents. The present work deals with the photoelasticity of polydimethylsiloxane, a chain polymer with high rigidity but differing from PVA in the absence of long side groups in the molecule and in the small anisotropy of the bonds in the molecular chain [4].

Birefringence of swollen non-Gaussian polymeric networks☆

Abstract On the basis of the statistics of non-Gaussian chains, an expression has been obtained for the way in which the reduced value of the coefficient of photoelasticity depends on the network-average molecular weight and the volumetric degree of swelling of the polymer. Poly- p -methylstyrene networks have been investigated experimentally as a function of the degree of swelling and the number of crosslinks in unit volume. A comparison between theory and experiment gives the possibility of assessing the thermodynamic rigidity.

The photoelastic effect in swollen polymers—III. Polyvinylacetate☆

EXPERIMENTS on swollen films of polystyrene [1] and natural rubber [2] have shown tha t in solvents with refractive indices differing from that of the dry polymer the segmental shape effect (micro-shape effect) plays an important part [3]. However the influence of this can be evaluated in the case of polymers with a large, intrinsic anisotropy, such as polystyrene and rubber. In the present work the s tudy of the segmental shape effect was extended to a polymer with a molecul~ of small intrinsic anisotropy.

Structural changes in polyethylene induced by small deformations

Abstract Anisotrophy in thermal conductivity and small-angle light scattering have been measured with films made of high-density polyethylene. Polyethylene deformation obeys different mechanisms in the regions of small ( 1·2) elongations. Deformation of polyethylene is of a complex, orientational-deformational character with participation of different molecular and supermolecular structures. Measurement of anisotropy in thermal conductivity in dependence on degree of elongation has been developed as a new method for determining the orientation function of macromolecular chains in deformed polymer films.

Study of the structure and molecular mobility of crystalline polyethylene by the methods of photo-elasticity and torsion pendulum☆

The authors have studied the temperature dependence of birefringence and the phase difference between stress and birefringence of PE films in a sinusoidal mechanical field. PE films with different degrees of crosslinkage and different degrees of extension were studied. It was found that the phase difference ϕ between stress σ and birefringence δn changes sign from positive to negative in the temperature region 40–70°C. The results are interpreted in terms of the biphasic PE model containing an amorphous phase with positive optical anisotropy and the crystalline phase with negative anisotropy.

Hydrodynamic and optical properties of polyvinylstearate molecules in solution

Abstract The viscosity, light-scattering, diffusion, sedimentation and flow birefringence of polyvinylstearate (PVS) solutions were investigated. The optical anistropy and thermodynamic rigidity of the molecular chains of PVS have been determined. A regular rise in the equilibrium rigidity of the main chain accompanying lengthening of the side radical has been confirmed by comparing the properties of PVS with those of other vinyl polymers.

A study of the photoelastic properties of segmented polyurethanes

The photoelastic effect of oligo-oxyethylene blocks in films of segmented polyurethanes of various MMs has been studied. Complicated time dependences of birefringence, when the load was applied and then removed, were found. It was shown that this is connected with the 2-phase morphology of these polymers. Comparison of the experimental values of their optical anisotropy with those calculated from a valency-optical scheme permitted an estimate of the thermodynamic rigidity of the chain.

Structure and properties of epoxide-amine molecular networks☆

Mechanical testing and photo-elasticity have been used to study the epoxideamine molecular networks representing the product of the interaction of the diglicidyl ether of resorcinol with metaphenylenediamine and aniline. The temperatures of the α transitions have been determined as a function of the average network molecular weight Mc. It is shown that the networks studied represent the superposing of structures with both positive and negative values of differences in their main polarizibilities. The thermodynamic rigidity of the molecular chains of the branches of the network is evaluated. It is shown that fall in the half-with of the α-process with rise in Mc is apparently associated with decline in the relative role of the small scale relaxation mechanisms.

The study of relaxational properties of molecular networks of polyoctafluoroamyl methacrylate by photoelasticity and torsion pendulum methods

Abstract The time dependencies of photoelasticity and the temperature dependencies of the mechanical properties of films of copolymers of octafluoroamyl methacrylate with ethylene glycol dimethacrylate have been studied. Three regions of mechanical loss were found. The transition at 170° is related to local processes in side groups. The main α-maximum of relaxation is due to segmental mobility; the λ-maximum at 120–150° is determined by cooperating processes of segmental mobility: the α-process is satisfactorily described by a bimodal distribution of relaxation times. The dimensions of kinetic units and the activation energies of fast and slow α-relaxation processes have been determined. The mean size of the kinetic units of the α-process is increased with increasing concentration ν of ethylene glycol dimethacrylate, affecting the degree of crosslinking of the copolymer network.