Polypseudorotaxanes between α-cyclodextrin and poly(propylene glycol)-b-poly(ethylene glycol)-b-poly(propylene glycol) copolymers studied by MALDI-TOF mass spectrometry

• Reverse Pluronics (RP) were characterized by MALDI-TOF mass spectrometry.
• RP composition is almost unchanged in precipitated complexes with α-cyclodextrin.
• Blocks of up to 20 propylene glycol units did not prevent RP complexation.
• Abundance of RPs with short poly(ethylene glycol) is increased in the supernatant.

MALDI-TOF mass spectrometry is used to show that formation of solid polypseudorotaxanes between α-cyclodextrin (α-CD) and poly(propylene glycol)–poly(ethylene glycol)–poly(propylene glycol) block copolymers (PPG–PEG–PPG, Reverse Pluronics) is a block length selective process. A comparison of copolymer composition matrices of neat Reverse Pluronics 10R5 and 17R4 and of the copolymers in their precipitated complexes with α-CD shows that the distribution with respect to an absolute PPG content is not affected by the complexation, which means that complexation occurs with Reverse Pluronics generally, not just with the fraction of copolymers with at least one outer block short or completely absent and that α-CD can slide even over block of 20 PG. Nevertheless, the complexation is a selective process with respect to PEG as copolymers with shorter PEG blocks are more abundant in the supernatant while the content of PPG remains almost unchanged for both Reverse Pluronics.

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