Fumiyuki Hamada

Estimation of thermodynamic interactions between polyethylene and n-alkanes by means of melting point measurements

SummaryThe thermodynamic interaction parameters for linear polyethylene-n-alkanes were investigated with n-C6H14, n-C7H16, n-C8H18, n-C18H38, and n-C32H66 as diluents, by determining the melting temperatures of polyethylene in its mixtures with n-alkanes. It follows that, with increasing the number of carbon atom in n-alkanes, the entropy parameterψ1 increases, the enthalpy parameterκ1 remains approximately equal to zero, and the free energy parameterχ1 decreases and approaches to zero. The change of the interaction parameters with the number of carbon atom in n-alkanes were discussed byPrigogines theory.ZusammenfassungDie thermodynamischen Wechselwirkungsparameter für das System lineares PolyÄthylen/n-Alkane wurden durch die Schmelzpunktsmessungen von PolyÄthylen in den Mischungen mit n-Alkanen bestimmt. Die als Verdünnungsmittel verwandten n-Alkane waren n-C6H14, n-C7H16, n-C8H18, n-C18H38 und n-C32H66. Es wurde gefunden, da\ mit steigender Zahl der Kohlenstoffatome in den n-Alkanen der Entropieparameterψ1 zunimmt, wÄhrend der Enthalpieparameterκ1 annÄhernd Null bleibt. Der Parameter der freien Energieχ1 nimmt ab und nÄhert sich Null. Die VerÄnderung der Wechselwirkungsparameter von der Zahl des Kohlenstoffatome in den n-Alkanen wurden nach der Prigogineschen Theorie diskutiert.

Effect of solvent on single crystal formation from dilute polyethylene solution: I. Surface free energy of single crystals estimated from kinetic theory

SummaryWith fractionated linear polyethylene, single crystals were prepared isothermally from dilute solutions in various solvents asn-octane,n-hexadecane, decaline, tetralin, toluene,p-xylene and diphenyl ether, which differed in the size and the thermodynamic properties. The fold length of lamellae was plotted against the crystallization temperature. For tetralin,p-xylene and toluene systems, their observed points lay nearly on the same curve, but for other solvent systems, the relation was obviously not independent of the kind of solvent from which the single crystals were formed. To discuss the effect of solvent on single crystal formation from dilute solution, the end surface free energy of single crystal was estimated from the equation based on the kinetic theory. It was pointed out that more regularly folded single crystals may be formed with solvent having larger thermodynamic interaction parameter and larger molar volume.ZusammenfassungDie Arbeit gilt der Frage, wie weit die Morphologie von Polyäthylen-Einkristallen vom Lösungsmittel beeinflußt wird. Hierzu werden solche Einkristalle unter isothermen Bedingungen aus Lösungen von fraktioniertem Linearpolyäthylen inn-Oktan,n-Hexadecan, Dekalin, Tetralin, Toluol,p-Xylol und Diphenyläther dargestellt. Zwischen den aus der röntgenographischen Kleinwinkelstreuung ermittelten Faltungslängen der Lamellen und den Kristallisationstemperaturen besteht bei Tetralin,p-Xylol und Toluol ein einfacher Zusammenhang. Die anderen untersuchten Lösungsmittel zeigten dagegen einen spezifischen Einfluß.Zur Diskussion wurde die freie Oberflächenenthalpie der Einkristalle abgeschätzt. Es wurde gezeigt, daß um so regelmäßiger gefaltete Einkristalle entstehen können, je größer der thermodynamische Wechselwirkungsparameter und das Molvolumen der verwendeten Lösungsmittel sind.

Thermodynamics of oligomer blends of poly(methylphenylsiloxane) and polystyrene

Abstract Heats of mixing to infinite dilution ΔH M (∞), excess volumes V E and cloud-point curves were experimentally determined for an upper critical solution temperature type of system, the poly(methylphenyl-siloxane)/polystyrene oligomer blend. ΔH M (∞) was positive and V E negative. Florys equation-of-state theory with modified combining rules was applied to this system. The theory with the positive value of the exchange enthalpy parameter reproduced the experimental thermodynamic properties except for the location of the maximum point in the cloud-point curves.

Thermodynamics of poly(dimethylsiloxane) solutions

Improved expressions for thermodynamic excess functions for mixtures of a non-polar polymer and a solvent are presented on the basis of modification of the combining rules of mixing which were assumed by Flory in the equation-of-state theory of pure fluids and their solutions. The modified theory assumes that the number of external degrees of freedom is non-additive with respect to the segment fraction and that the sizes of the core volumes of segments in pure liquids and solution are different. This theory can reproduce the experimental results of the interaction parameter χ and the excess volume of mixing, which the Flory theory failed to reproduce. Direct comparisons of the modified combining rules with experimental results is satisfactory.

Small-angle X-ray scattering from heparin in solution

SummaryX-ray small-angle scattering fron heparin in solution was measured, and compared with theoretical curves based on various nolecular models. Good agreement was obtained for the model consisting of α-D-glcosamine in the 4C1 conformation and α-L-iduronate in the 1C4 conformation. It was suggested that the helical conformation is maintained even in solution, at least in part. The helix pitch was estimated to be 0.75–0.85 nm.

Theoretical consideration on the number of external degrees of freedom and its application to poly(dimethylsiloxane) solutions

SummaryThe Flory theory of polymer solution was modified by assuming the non-additivity of the number of the degree of external freedom for a binary mixture and applied the modified Flory theory to poly (dimethylsiloxane)-solvent systems. This theory can reproduce the experimental results of the interaction parameter χ and the excess volume of mixing, which the Flory theory failed to reproduce.

Thermodynamic study on heat of mixing of polyisobutylene with ethylbenzene

SummaryThe heat of mixing of polyisobutylene with ethylbenzene was measured from 18.2 to 69.2° C with a Tian-Calvet twin micro-calorimeter, and the exchange enthalpy parameter X12 in Florys theory was estimated. The X12 obtained was discussed also in comparison with the one based on Manzini model. Further combining with osmotic pressure data, temperature dependence of the entropy parameter Q12 was referred.

Scattering functions of poly(amino acid) in helix-coil transition

Abstract Scattering functions of poly(amino acid) in the helix-coil transition region have been calculated on the basis of the Zimm-Bragg theory, to examine the effects of the helical content on the scattering function and on the cross-section factor, from which the radius of gyration of the cross section and the mass per unit length of the helical sequence can be obtained. The molecule is assumed to contain only one α-helical sequence of any length, leaving unfolded coils at the chain ends. The statistical mechanical averages of the interference among scattering units, apart from the interference within the helical sequence, are approximated by the expansion in terms of the even moments up to the eighth moment, which are calculated by the generator matrix method based on the conformation energies computed for poly ( l -alanine). The scattering function at intermediate angles varies systematically according to the variation of the helical content, demonstrating the sensitivity of intermediate-angle scattering to the conformational changes in the helix-coil transition. The comparison of the Guinier plots of the cross-section factors, calculated from the scattering functions at various helical contents, has indicated that the radius of gyration of the cross section of the helical sequence can be determined accurately from the plots even when the coil content is as much as 30%, and that the mass per unit length is determinable to within an error of 6% unless the coil content exceeds 10%.

Theory of tagged polymer method in small-angle X-ray scattering

SummaryIt was shown that the conformation of a single polymer chain in concentrated solutions and in undiluted state can be estimated from the small-angle X-ray scattering of “randomly tagged polymer” mixed in the systems. The randomly tagged polymer means the polymer containing heavy atoms at randomly selected positions along the molecule. The excess scattering of the tagged polymer is obtained by subtracting the scattering of the untagged polymer solution (or bulk) from that of the mixture solution (or bulk) containing the tagged and untagged polymers. The excess scattering obtained in this way contains the contributions of some undesirable “cross terms” of the scattering amplitude. The method for the experimental evaluation of these terms and the conditions under which these terms are negligible are discussed. It was found that the cross terms can be neglected when the contrast in scattering power between the tagged and untagged scattering units is sufficiently large, and the number of the tags per tagged molecule is not so small.The distribution of the tags in the tagged molecules was also taken into consideration. By averaging the theoretical scattered intensity over all possible positions of the tags, it was found that the excess scattering is practically proportional to the scattering function of the untagged polymer when the number of the tags per tagged molecule is not so small. Experimental verification of this theory was shown.It was also shown experimentally that the conformational change, which may be caused by the effect of the tags, can be eliminated by the extrapolation of the results obtained for a series of tagged polymers with various tag contents to zero tag content.