Josef Baldrian

Structural modifications of hexagonal crystalline polyoxymethylene. Infra-red and X-ray study

Abstract Infra-red spectra and X-ray diagrams of polyoxymethylene samples prepared in various ways, of trioxanedioxolane copolymers and of a polyoxymethylene-polydioxolane blend were obtained. With hexagonal crystalline polyoxymethylene (HCPOM), it is possible to prepare two forms, A and B, differing in their infrared spectra; with copolymers, the maximum attainable content of form A rapidly decreases with increasing content of oxyethylene units in the chain. Form A could not be prepared in the polyoxymethylene-polydioxolane blend. Infra-red spectra of the two forms, A and B, of HCPOM differ in the vibrational interactions of neighbouring chains; these interactions are large in form A and small in form B. The possible structures of the A and B forms of HCPOM are discussed.

Solvent induced crystallization of syndiotactic poly(methyl methacrylate) relation to the formation of polymer aggregates in solution

SummarySolutions of syndiotactic (s) poly (methyl methacrylate) (PMMA) and samples of solid s-PMMA prepared from these solutions were studied by NMR and infrared (IR) spectroscopy and by wide-angle X-ray scattering (WAXS). IR spectra of s-PMMA films obtained from o-dichlorobenzene solutions by evaporation of solvent at room temperature have shown that the ordering of polymer chains which exists in aggregates of s-PMMA in o-dichlorobenzene is preserved in the solid state. s-PMMA prepared in this way is characterized as partly crystalline by WAXS. When o-dichlorobenzene is evaporated at elevated temperatures at which the aggregates of s-PMMA are decomposed, or if solid s-PMMA is obtained from solutions in which aggregation does not take place, the obtained solid polymer is amorphous.

The effect of crystallinity and of the type of crystalline structure on the thermally initiated oxidation of hydrolytic polymers of caprolactam

Abstract Under conditions where the rate of oxidation is not diffusion-controlled, the rate of oxidation of hydrolytic polymers of caprolactam is proportional to the amorphous fraction and independent of the nature of the crystalline phase. Sufficiently thin samples used for oxidation and prepared by cutting may be obtained only in a comparatively narrow crystallinity range: the cutting procedure reduces the crystallinity of highly crystalline polymers to 44% while, for samples with crystallinity of 26%, the content is raised to 37%. In all cases, the molecular weight of the polymer decreases.

Effect of swelling on the structure of oriented polyamide 6

Abstract The effect of swelling on the structure of polyamide 6 fibres was studied by means of small-angle and wide-angle X-ray scattering. The wide-angle data show that only the amorphous phase undergoes swelling. Changes in the scattering contrast caused by such preferential sorption are in agreement with the increased ‘apparent density’ of liquids in the amorphous phase. Due to the fact that the increase in the long period corresponds to the amount of the liquid sorbed, swelling is virtually one-dimensional. If there is an interfibrillar non-crystalling phase, its content is very low, or its structure is not accessible to molecules of the swelling agent. The elongation of intrafibrillar amorphous interlayers due to swelling is reflected in changes in the small-angle four-point diagram. The changes suggest that swelling causes narrowing of the distribution of distances between crystallites in fibrils, increases the angle between crystalline layers and the fibre axis and reduce waviness of crystalline-amorphous interfaces.

1H nuclear magnetic resonance characterization of internal motions in the amorphous phase of low-density polyethylene

Abstract 1 H nuclear magnetic resonance (n.m.r.) spectra of low-density polyethylene, static and with magic-angle rotation (MAR), were measured in the range 270–385 K. The amorphous component of the static 1 H n.m.r. spectrum was obtained by subtraction of the crystalline component based on crystallinity determination by X-ray and infra-red methods. The amorphous line is narrowed by more than an order of magnitude by MAR, proving the spatially anisotropic character of internal motion. The temperature dependence of the MAR n.m.r. linewidth corresponds to δE = 7.5 kcal mol −1 , which is ascribed to rapid small-scale conformational motions. The static amorphous lineshape could be fitted by the convolution of the MAR n.m.r. line with an orientation-dependent dipolar broadening function by adjustment of a single parameter A 0 characterizing the width of the dipolar broadening. The amorphous lineshape can be described by assuming the presence of only a single amorphous phase. The relation of A 0 to the rigid lattice second moment, as a measure of spatial hindrance, is discussed and the length of the flexible subchain is estimated.

The solid-liquid equilibria in the system polyoxyethylene/phenol

Abstract The solid-liquid (S-L) phase diagram and the X-ray diffractogram of a mixture of polyoxyethylene ( M = 2000) with phenol suggest the existence of a crystalline compound consisting of one molecule of phenol and two monomeric units of polyoxyethylene. The congruent melting point of this compound lies at 302.6 K. From an analysis of the phase diagram based on the theory of association equilibria, we have found that in the liquid phase: (1) the bond between phenol and polymer is very strong; (2) there exists a whole spectrum of association complexes containing different numbers of phenol molecules bound onto the macromolecule; and (3) the maximal number of bound phenol molecules is higher than in the crystalline compound.