Solution properties of amylose tris(3,5-dimethylphenylcarbamate) and amylose tris(phenylcarbamate): Side group and solvent dependent chain stiffness in methyl acetate, 2-butanone, and 4-methyl-2-pentanone

摘要

Five amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) samples ranging in weightaverage molecular weight M _w from 1.7 × 10 ~4 to 3.4 × 10 ~5 were studied by light and small-angle X-ray scattering, sedimentation equilibrium, and viscometry in methyl acetate (MEA), 2-butanone (MEK), and 4-methyl-2-pentanone (MIBK) at 25 °. Seven amylose tris(phenylcarbamate) (ATPC) samples whose M _w ranges between 2 × 10 ~4 and 3×10 ~6 were also investigated in MEK at 25 °. The radii of gyration, particle scattering functions, and intrinsic viscosities determined as a function of M _w were analyzed in terms of the cylindrical wormlike chain model mainly to determine the Kuhn segment length λ ~(-1) and the contour length h (or the helix pitch) per residue. While the obtained h values (0.36-0.38 nm) of ADMPC are quite insensitive to the solvents, the λ ~(-1) value not only is 1.5-3 times larger than that of ATPC in the corresponding solvent but also significantly increases with an increase of the molar volume of the solvent, and it reaches 73 nm in MIBK, which is the highest value for previously investigated phenylcarbamate derivatives of polysaccharides. This high stiffness is most likely due to the steric hindrance of the solvent molecules H-bonding with the NH groups of the polymer.