- AMER CHEMICAL SOC
A series of hyperbranched polylactides (HB-PLLAs) with different branching densities were prepared by the self-polycondensation of AB(2)-type macromonomers (degree of polymerization of polylactides (n) = 5.0, 8.4, 19, 29, and 42). The high-molecular-weight HB-PLLAs (M-w = 4.95 x 10(4)-1.47 x 10(5)) were prepared in good yields. Molecular characterizations of the HB-PLLAs were meticulously performed by size-exclusion chromatography at 25 degrees C using a system equipped with multiangle laser light scattering (SEC-MALS) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as the eluent. The z-averaged root-mean-square radius of gyrations (< S-2 >(1/2)(z)) of the HB-PLLAs in HFIP at 25 degrees C were much smaller than those of the linear PLLA with the corresponding weight-average molecular weight (M-w), supporting the presence of the branched architectures. The M-w dependence of < S-2 >(1/2)(z) of the HB-PLLAs was determined to follow the equations < S-2 >(1/2)(z) (nm) = 2.5 x 10(-1)M(w)(0.37) for n = 8.4, < S-2 >(1/2)(z) (nm) = 1.8 x 10(-1)M(w)(0.40) for n = 19, < S-2 >(1/2)(z) (nm) = 1.6 x 10(-1)M(w)(0.41) for n = 29, and < S-2 >(1/2)(z) (nm) = 1.1 x 10(-1)M(w)(0.44) for n = 42 in HFIP at 25 degrees C. A comparison of the experimental and theoretical results with respect to their dimensional properties indicated that the HB-PLLAs assume randomly branched architectures (i.e., a hyperbranched structure). The DSC and X-ray diffraction measurements suggested that the crystallization was remarkably suppressed by the introduction of the branched architecture.
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