In the course of structural study of aliphatic polyesters, the crystal structure of polyglycolide, the simplest polyester of the type -[-(CH2),-CO-O-],-was determined by interpretation of the X-ray diffraction patterns of the fibers. The crystallographic data are: a = 5.22 A, b = 6.19 A, c (fiber axis) = 7.02 A, theorthorhombic space group Pcrnn-Di;.Two molecular chains pass through the unit cell. The crystal structure was determined by the help of two dimensional and three dimensional FOURIER syntheses. The planar zig-zag chain molecules form a sheet structure parallel to the ac plane and have not the polyethylene type arrangement. High density of the crystallite, 1.69 g/cm3, namely the tight molecular packing and the close approach of the ester groups might stabilize the crystal lattice and contribute to the high melting point of this polymer. ZUSAMMENFASSUNG:I m Verlauf von Strukturuntersuchungen an aliphatischen Polyestern wurde die Kristallstruktur von Polyglykoliden, dem einfachsten Typ der allgemeinen Zueammensetzung -[-(CH&-CO-0-I,,durch Rontgenbeugung an Fasern bestimmt. Die kristallogaphischen Daten sind: a = 5,22A, b = 6,19A, c (Faserachse) = 7,02A, Raumgruppe P c m n -D~~ (orthorhombisch). Die Einheitszelle wird von zwei Molekiilketten durchsetzt. Die Kristallstmktur wurde mit Hilfe von zwei-und dreidimensionalen F o u m q n t h e s e n bestimmt. Die planar und im Zickzack angeordneten Molekiilketten bilden Schichten parallel zur ac-Ebene ; diese Anordnung entspricht nicht dem Polyiithylentyp. Die hohe Dichte der Kristallite (1,69 g/cm3), die durch die dichte Packung der Molekiile und die enge Nachbarschaft der Estergruppen bedingt ist, konnte das Gitter stabilisieren und so zum hohen Schmelzpunkt dieses Polymeren beitragen.
The ring-opening polymerization of glycolide was reported in the previous paper 1). Polymer characteristics, especially stability property, are presented in this paper.Melting point of polyglycolide was 227 to 230°C. It was constant in the region of the reduced viscosity of larger than 0.07.Specific gravity of polyglycolide depends upon crystallinity. The value of its perfect crystal was 1.707, calculated from the result of X-ray diffraction. The result of X-ray analysis was analogous to that of recent 1iteratures2s3). The specific gravity in the amorphous state was about 1.50. Amorphous sample can be made from the melt by quenching and was flexible and transparent. The specific gravity in the normal condition was 1.50 t o 1.60.Polyglycolide sheet was made successfully by the following way. Glycolide-lactide copolymer (92.5/7.5 mole-%) was obtained through ring opening polymerization, using antimony trifluoride as catalyst. It was
Polyglycolide is the simplest aliphatic polyester. Patents say that fibers and films with a high melting point and high strength can be made from this polymer 13). Recently, some of its properties were rep~rtedq,~), but polymerization behavior and detailed polymer property, especially its stability, have been obscure as yet.The ring-opening polymerization of glycolide and the property of polyglycolide have been studied in detail. The tensile yield strength of the stabilized sheet made from glycolide-lactide copolymer was about 17,000 psi, the value being larger than those of all commercial plastics. In this paper, the results of the ring-opening polymerization of glycolide are presented. ' The glycolide was prepared through the elimination of sodium chloride from sodium monochloroacetate. The monomer was purified by recrystallization to obtain a melting point above 83°C. The process we have studied is as follows. A. HomopolymerizationBulk polymerization with various catalysts was carried out in a sealed ampule under reduced pressure. The adequate polymerization condition was to heat a t 17OoC. for 10 hrs., or to heat a t 17OoC. for 2 hrs., then a t 230°C. for 0.5 hrs.Anionic polymerization catalysts such as potassium hydroxide, pyridine, and potassium carbonate gave brittle and highly colored polymers in low yield.Polymers were also prepared by using protonic acids such as sulfuric acid and phosphoric acid to yield brittle and highly colored polymers in high yield. 262
SynopsisVarious monomer addition methods were applied to the emulsion CO-polymerization of vinyl acetate and butyl acrylate of which polymerization reactivities are very different from each other. The grafting efficiency and homogeneity of copolymer were determined by the fractionation and measurement of dynamic viscoelasticity of emulsion polymers. A s the content of the second fraction of acetone-soluble part increased and that of the third fraction decreased, then the homogeneity of the copolymer increased. In this ease, only one dynamic loss peak existed near OOC. The result showed that homogeneous copolymers were obtained by continuous monomer addition methods and heterogeneous copolymers were obtained by initial addition of total monomers or stepwise monomer addition methods. Homogeneity of copolymer had great influence on various properties, e.g., hardness and adhesive properties. Film hardness was the lowest for homogeneous copolymer and it was the highest for heterogeneous copolymer. Homogeneous copolymer was best for adhering plywood and poly(viny1 chloride). It is remarkable that copolymers of vinyl acetate and butyl acrylate with very different properties were obtained by changing only the monomer addition methods.
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