Characterization of Poly(l-lactide)-block-Poly- (ethylene oxide)-block-Poly(l-lactide) Triblock Copolymer by Liquid Chromatography at the Critical Condition and by MALDI-TOF Mass Spectrometry

Abstract

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.

Electrospray ionization mass spectrometry of the non-covalent complexes of ammonium ions with high molar mass polyethers

“…The sample is a complex mixture of various copolymer distributions, since the initiating block was a disperse PEG 8 kDa sample. Lee et al [34] demonstrated the successful separation of the copolymer distributions of a PLA-block-PEG-block-PLA triblock copolymer (of approximately the same molar mass) by LC at critical conditions. The application of such a separation in our MS method could provide the necessary deconvolution and allow the generation of more detailed information on the copolymer structures.…”

Mass spectra of copolymers

“…The MALDI–TOF spectra of the LCCC fractions display a smaller number of peaks with respect to the MALDI–TOF spectrum of the whole sample. In the case of diblock copolymers, the decrease (and the associated simplification) is very strong (Lee et al, 2000), whereas in the case of triblock copolymers, the decrease is less pronounced (Lee et al, 2001). Lee et al analyzed a triblock LA/EO/LA copolymer (LA = lactic acid, EO = ethylene oxide), and Figure 18 reports the MALDI spectrum of an LCCC fraction (Lee et al, 2001).…”

“… MALDI spectrum of an LCCC fraction of a triblock LA/EO/LA copolymer. Reproduced from Lee et al (2001) with permission from American Chemical Society (copyright 2001). …”

Polymer characterization by combining liquid chromatography with MALDI and ESI mass spectrometry

“…LCCC and SEC combined off-line with MALDI MS detection have been applied to the characterization of poly(propylene glycol) [40] poly(L-lactide)-block-poly (ethylene oxide)-block-poly(L-lactide) triblock copoolymers [41] polyamides-6 [42], and poly(propylene oxide)s [43].…”