V.N. Tsvetkov

Determination of the composition and study of the compositional inhomogeneity of copolymers by means of a polarizing diffusometer

(1) Polyl ,2 ,4and poly-l ,3 ,4-oxadiazoles have been synthes ized by in t ramolecular polyheterocycl izat ion. (2) I t is shown exper imenta l ly t h a t polyl ,3 ,4-oxadiazoles are more hea t res is tant t h a n polyl ,2 ,4-oxadiazoles of corresponding s t ructure . (3) I t is shown b y calculat ion b y the molecular orbitals m e th o d t h a t the u-electron sys tem of the isolated 1,3,4-oxadiazole ring is more stable t h an the u-electron sys tem of the 1,2,4-oxadiazole ring, and the 1,3,4-oxadiazole-phenyl ring sys tem has a higher energy of conjugat ion t h a n the 1,2,4-oxadiazole-phenyl system. Translated by E. O. PHILLIPS

Flow birefringence of graft copolymer solutions

Abstract An homologous series of methyl methacrylate-styrene graft copolymers with a wide range of contour lengths has been obtained by grafting on to a backbone polymer made polydisperse by artificial means. As the length of the molecules is increased the reduced birefringence at first increases linearly (with a change in sign), in agreement with the requirements of the theory of flow birefringence in solutions of shortchain molecules of finite thickness, and then it reaches a limiting value. Estimations of the ratio of the persistent length of the molecule to its thickness, from the results of optical and hydrodynamic measurements, are in good agreement.

Shape effects in graft copolymer macromolecules

A study is made of the concentration dependence of the shape effect for methyl methacrylate-styrene copolymers in dioxan, and the macro- and microshape effects are isolated. Despite the considerable length of the segment A for the main chain of the macromolecule, the macroshape effect is much greater than that of the microshape, owing to the considerable thickness of the molecule. The shape asymmetry of the macromolecule p=1·9 (coiling degrees), while that of the statistical segment ps is < 1·5. The latter finding agrees with the estimated value of A/d≈1 based on measurement of the viscosity and dynamic birefringence in the absence of shape effects (bromoform).