Tohru Kawai

Crystallization of filled Nylon 6 II. Isothermal crystallization

SummaryIsothermal crystallization kinetics from the melt of nylon 6 containing various amounts of untreated glass beads and Aerosil (series GB and A) and aminosilane-treated glass beads (series GBA) was studied by DSC method. Treatment of experimental data in terms of Kolmogorov-Avrami equation has shown that time exponentn is relatively insensitive to presence of GBA filler, whereas it was found to decrease gradually with increasing filler content in samples of GB and A series to value as low as 0.5 for sample A–67. Nucleation free energy was the same in pure nylon 6 and filled samples of GBA series, but dropped suddenly in samples of GB series when mean interparticle separation x decreased below “critical” value ξcrit =(5–10) x 10−6 m. Taking into account the concomitant drop of equilibrium melting temperature, it was concluded that these effects are a consequence of specific structural change in polymer phase accompanying transition into a “boundary state”. Temperature dependence of polyer crystallization rate in highly filled samples of A series at small supercoolings was found to obey them=4 law, which is characteristic of transformations in strained media. Experimental data seem to be consistent with the idea that the postulated strain energy might originate from negative capillary pressure between high-surface energy solid particles wette d by polymer melt. Quantitative analysis of overall crystallization rate dependence on interparticle distance x has shown that ξcrit may be identified with change of growth morphology from a three-dimensional to a two-dimensional one, while slowing down of growth rate at lower values of ξ was attributed to increase of nucleation free energy due to increasing contribution from capillary forces.

Conformational effects on complex formation in polymeric systems and matrix polymerization

Abstract Kabanov et al. reported that a complex could be formed between poly-L-lysine (I) and poly(acrylic acid) (II) which stabilizes the α-helix of I. In order to confirm this important result, the complex formation between I and various dicarboxylic acids of different chain lengths has been examined. Glutaric acid, whose extended chain length coincides with the distance between the adjacent amino groups of the I chain in the α-helix form was found to stabilize the α-helix. The structures of the complexes of I with oligo-and poly(acrylic acid)s were also studied by ORD in aqueous solutions and by x-ray analysis in the crystalline state. The results showed that the β-structure is preferred over the α helical conformation. This might be attributable to the fact that the distance between the neighboring carboxylic groups along II is shorter than that between the adjacent amino group of I in the α-helical form but coincides with the distance in the β-structure. On the basis of the structural information obt...

Crystallization during polymerization with special reference to synthetic polypeptides

Abstract In order to pursue the possibilities of the extended chain crystals formed in the course of polymerization, kinetics of the heterogeneous polymerization of L-and DL-alanine NCA in acetonitrile and the morphologies of the resultant polymers were studied. Electron microscopy revealed that the fibers formed in the beginning of polymerization thickened as the polymerization proceeded and that the growth mechanism of the polypeptide crystals is quite similar to that of polyoxymethylene crystals during the polymerization of trioxane in cyclo-hexane. X-ray diffraction patterns and IR spectroscopy revealed that the growing chain molecules, when they attained a certain degree of polymerization (DP = -3 to 4) beyond which they lost solubility in the system, crystallized into the form of ribbon-like fibers in which molecules, with the β-conformation, were aligned perpendicularly to the fiber axis. As the growing chains attained a critical length by further polymerization, they began to take the α-helical co...

Crystallization of polypeptides during polymerization

Abstract In order to pursue the possibilities of formation of extended chain crystals in the course of polymerization, kinetics of the heterogeneous polymerization of L- and DL-alanine N-carboxy anhydride (NCA) initiated by butylamine in acetonitrile and the morphologies of the resultant polymers were studied. The fibers formed in the beginning of polymerization thickened as the polymerization proceeded. The growing chain molecules, lost solubility in the system when they attained a degree of polymerization of 3 to 4 and crystallized in the form of ribbon-like fibers in which molecules with the β-conformation were aligned perpendicularly to the fiber axis. As the growing chains attained a critical length by further polymerization, they began to take the α-helical conformation. The crystals grew successively thereafter, taking the α-helical conformation through addition of the monomer molecules onto the reactive chain ends. Possible mechanisms are proposed for the nucleation and the subsequent growth of the crystals in the course of polymerization. The polymerization of NCAs of glycine and β-alanine has also been studied. The polymer precipitated in the form of spherulites consisting of ribbon-like crystalline units. The molecules in the ribbon-like crystals were arranged antiparallel, forming a hydrogen-bonded sheet. Homopolymerizations of other NCAs and copolymerizations were also examined in the same heterogeneous system.

A note on microfibrils in polyethylene

Abstract The results of diffraction (low-angle scattering of X-rays and electrons) and electron microscopy study show a significant qualitative coincidence in studies of the morphology of oriented polyethylene films obtained from polyethylene single crystal mats. The morphology approximates the ideal description of a microfibrillar structure. In certain cases a quantitative coincidence of the periods of alternation of densities along and across the texture (when comparing visible images and average periodicity from the data of X-ray diffraction study) is also obtained.