Morphology and enzymatic degradation of poly(L-lactic acid) single crystals

被引:202
作者
Iwata, T [1 ]
Doi, Y [1 ]
机构
[1] RIKEN, Inst Phys & Chem Res, Polymer Chem Lab, Wako, Saitama 35101, Japan
关键词
D O I
10.1021/ma980008h
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
Lamellar single crystals of poly(L-lactic acid) (PLLA) were grown from a 0.05% solution of p-xylene at 90 degrees C. The hexagonal, truncated-lozenge and lozenge-shaped single crystals with spiral growth were prepared simultaneously, and these crystals were relatively stable under conditions of electron bombardment. The hexagonal and lozenge-shaped crystals gave well-resolved electron diffractograms from which the reciprocal lattice parameters a* = 0.935 nm(-1), b* = 1.626 nm(-1), and gamma* = 90 degrees could be determined, and these lattice parameters corresponded with those of the alpha structure of PLLA fibers. Accordingly, the hexagonal crystal was considered as pseudo-hexagonal symmetry, but actually with orthorhombic packing of the PLLA chains; i.e., the ratio of the a and b cell parameters is quite equal to root 3. The enzymatic degradation of PLLA single crystals with a proteinase-K from the mold Tritirachium album in 50 mM Tris-HCl buffer at pH 8.5 and 37 degrees C was investigated by means of transmission electron microscopy, atomic force microscopy, high-performance liquid chromatography, and gel permeation chromatography. Enzymatic degradation progressed from the edges of lamellar crystals to yield a rounded shape without decreasing the molecular weights and lamellar thicknesses. it has been concluded that the single crystals were enzymatically hydrolyzed at the disordered chain-packing region of crystal edges rather than chain-folding surfaces of single crystals. As the degradation time increased, in a rare case the diamond holes were observed on the crystal surfaces of lozenge-shaped single crystals.
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页码:2461 / 2467
页数:7
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