Poly(l-lactide)-block-poly(ethylene oxide)-block-poly(l-lactide) triblock copolymers (PLLA-b-PEO-b-PLLA) were
fractionated in terms of the number of LLA units by liquid
chromatography at the critical condition (LCCC) of PEO
block. The fractionated samples were identified using
MALDI-TOF mass spectrometry. The dependence of the
LCCC retention of the diblock and triblock copolymers
on the degree of polymerization of PLLA block(s) follows
Martin's rule very well. Unlike the case of PEO-b-PLLA
diblock copolymer reported earlier (Lee, H.; et al. Macromolecules
1999, 32, 4143), however, a splitting of the
elution peaks containing the same number of LLA units
was found. The peak splitting was ascribed to the different
length distributions of PLLA blocks at the two ends of the
PEO block. From the relative intensities of the peaks, the
split peaks were assigned to different isomeric structures
of the PLLA blocks. From these results we conclude that
the interaction of the triblock copolymers with the stationary phase is affected by the distribution of the interacting
blocks at the two ends of the center PEO block, in addition
to the total number of LLA units in the triblock copolymer.
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