NOTES. Shisb Kebab Structures Formed on Needle-Like Polyoxymetbylene Crystals

Transcription

1 JOURNAL OF POLYMER SCIENCE: Polymer Ph- Edition VOL. 13 (1975) NOTES Shisb Kebab Structures Formed on Needle-Like Polyoxymetbylene Crystals Needle-like crystals of polyoxymethylene (POM) prepared in our laboratory14 by a cationic polymerization of trioxane in cyclohexane are slender hexagonal single crystals6 consisting of extended-chain molecules. Crystal overgrowth of polymers on these particular crystals was of interest and initial experiments were carried out by cooling polymer solutions in the presence of the needles. This note reports briefly on the finding that shish kebab structures, very similar to those generated in flowing solutions,- are formed on the needle-like crystals under static conditions. This growth habit occurs with the same kind of polymer (i.e., POM) and also with polyethylene WE). The POM crystals were prepared as described The needles, obtained as radial structures, were separated by boron trifluoride (BF3) etching. eg The length of the needles ranged from 20 to 80 pm and the thickness from 1 to 3 pm. POM used for the overgrowth was Delrin 150X (diacetate, h& = 1.57 X 106, from E. I. du Pont de Nemours & Co.) and POM diacetate (mu = 5.4 X 10 ) prepared according to a patented method.l0 The PE used was Sholex 6150 (au = 5.2 X 10 ;from Showa Denko Co.). Over-crystallization was carried out as follows. With POM, 0.2 g of POM diacetate, either Delrin or the sample prepared in this laboratory, was dissolved under dry argon in 50 ml dimethylformamide (DMF), in a 100-ml flask immersed in an oil bath. At the boiling point (152OC), the needles (0.2 g) were suspended and the solution waa allowed to cool without stirring. The crystallization apparently started at around 12OoC, when the rate of cooling was ca. 0.WoC/ min. Another run was made using bromobenzene (b.p., 156OC) in place of DMF. The stability of the needle-like crystals in solvents was remarkable,2s3 the crystals being hardly affected in boiling DMF or bromobenzene, which easily dissolved ordinary POM. The bulk of the aggregate obtained was filtered and washed with acetone. A similar procedure was used for overgrowth of PE. A 0.2 g/50 ml solution of Sholex was prepared in boiling xylene and, after addition of 0.2 g of needles, the solution was cooled at the similar rate. Crystallization was observed from ca. 100OC. Figures la and 1b show scanning electron micrographs (Japan Electron Optics Laboratory) of the original (BF3-treated) needle-like crystals and the needles upon which Delrin overgrew from DMF solution, respectively. The binary structure developed looks very similar to the shish kebabs usually obtained by stirring polymer solutions, although it is much larger in scale. Polarizing microscopy ( Ortho-Pol, E. Leitz) with a test plate revealed the molecular orientation in the overgrown layers to be parallel with that in the needles (or with the direction of the lengh of needles). It is obvious that the prism faces of needle-like crystals furnished the substrate and the layer-like overgrowth proceeded radially in the presence of no more turbulance than could have been caused by convection. Molecular chains were perhaps folded in the layers. Upon heating in the microscope attachment (at 4-6OC/min), the overgrown POM layers appeared to melt at around 176OC, while the needles were stable until melting, with extensive decompoeition and sublimation, was obeerved at OC. The same morphology was reproduced with the true POM di-acetate. A similar structure was also obtained with bromobenzene as the solvent. Surprisingly, the same type of overgrowth occurred with polyethylene, as is shown by the scanning electron micrograph in Figure lc and the polarized micrograph in Figure 2a. Consequently lattice mismatch between the two polymer crystals seemed to have little effect on the epitaxy, and the molecular orientation of the substrate POM determined that of the overgrown PE layers. However, the PE layers were piled more irregularly. The binary structure was examined by subjecting the aggregate to a severe BF3 etching treatment (i.e., 20 cc BF3 gas for a 100-ml sample in cyclohexane). As shown in Figure 2b, the needles originally existed along the center 1975 by John Wiley & Sons, Inc. 1461

2 1462 NOTES (b) Fig. 1 (continued)

3 NOTES (C) Fig. 1. Scanning electron micrographs of needle-like POM crystale; (a) original (BF3-treated); (b) with POM (diacetate, Delrin) over-crystallized; and (c) PE (Sholex) over-crystallized. (a) Fig. 2 (continued)

4 1464 NOTES Fig. 2. Polarized micrographs of POM/PE shish kebabs; (a) before (i.e., same as Fig. 1 (c)); and (b) after aelective etching of POM cores. shish kebab structures have been eelectively removed, thus leaving only the shell of very fragile piles of overgrown PE layere. The PE appeared to melt around 131OC. In summary, the needle-like crystals furnished a good substrate for both POM and PE and shish kebab structures were formed without mechanical agitation. The Occurrence of such structures was quite abundant in all cases studied. By analogy the present results are suggestive for Fig. 3. Trannmiaaion electron micrograph of polymethylene crystals from dilute xylene solution.

5 NOTES 1465 the growth mechanism of similar structures under flow, which is still a matter of controveray." The original interpretation,8 accounting for the presence of some slender core, seems to be the most likely. Mechanical flow would not be essential for the growth of layere, however, if a suitable substrate were already present. Figure 3 shows an electron micrograph (from an earlier study in our laboratory) of shish kebab crystals which appeared when polymethylene (of extremely high molecular weight, prepared from diazomethane) was recrystallized from a dilute xylene solution at 86.5OC without intentional stirring. That ahish kebab structures appear incidentally during solution crystallization was also pointed out long ago.i2 The authore thank Mr. S. Mitauhashi for the help with the electron microscopy of Figure 3 and valuable discussions. References 1. M. Iguchi, Ann. Meet. Soc. Fiber Sci. Tech., Japan, June 1973 (Tokyo), preprint p M. Iguchi, Brit. Polym. J., (1973). 3. M. Iguchi and I. Murase, J. Cryst. Growth, 24/ (1974). 4. M. Iguchi, I Murase, and K. Watanabe, Brit. Polym. J., 6.61 (1974). 5. M. Iguchi and I. Murase, Makromol Chem., in press. 6. S. Mitauhashi, Bull. Textile Res. Inst. (Japan), 66.1 (1963). 7. A. J. Pennings and A. M. Kiel, Kolloid-2.2. Polymere, 205,160 (1965). 8. A. J. Pennings, J. M. A. A. van der Mark, and A. M. Kiel, Ibid., 237,336 (1970). 9. M. Iguchi and I. Murase, 23rd Polymer Discussions, Soc. High-Polymers, Japan, Oct (Tokyo), preprint p S. D. Nogare, J. 0. Punderaon, S. H. Jenkins, F. C. Starr, W. P. Langsdorf, and G. S. Stamatoff, Japan Pat. S to E. I. du Pont de Nemoure & Co. (1958). 11. T. Nagasawa, Y. Shimamura, and T. Matsumura, 22nd Polymer Discussions, SOC. High- Polymers, Japan, Nov (Tokyo), preprint-i, p D. C. Baasett and A. Keller. Phil. Mag., 7,1553 (1962). Research Institute for Polymere and Textiles, 4 Sawatari, Kanagawa-ku. Yokohama 221, Japan Received January 16,1975 Revised March 17,1975 M. ICUCHI I. MURASE. Permanent address: Central Research Laboratory, Sumitomo Chemical Co., Ltd., 2-40 TSUkahara, Takatauki 569, Osaka, Japan.