Synthesis of novel cylindrical bottlebrush polypseudorotaxane via inclusion complexation of high density poly(ε-caprolactone) bottlebrush polymer and α-cyclodextrins

Abstract

Poly(ε-caprolactone) (PCL) macromonomers (MMs) with norbornenyl end groups were synthesized viaring-opening polymerization (ROP) of ε-caprolactone using stannous 2-ethylhexanoate (Sn(Oct)₂) as catalyst. Then ring-opening metathesis polymerization (ROMP) of these MMs was carried out using the highly active, fast-initiating ruthenium olefin metathesis catalyst (H₂IMes)(pyr)₂(Cl)₂RuCHPh to form high molecular weight (M_n = 420–1346 kDa) and high density PCL bottlebrush polymers. The inclusion complexation of the prepared PCL bottlebrush polymers and α-cyclodextrins (α-CDs) afforded the novel bottlebrush polypseudorotaxanes with a length of 350 ± 50 nm and a width of 50 ± 10 nm. The formation of bottlebrush polypseudorotaxane was confirmed by nuclear magnetic resonance (NMR) spectroscopic analysis, X-ray diffractogram analysis and dynamic light scattering (DLS) measurements. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the bottlebrush polypseudorotaxane displays higher thermal stability and weaker melting and crystallization behavior in comparison to its PCL bottlebrush precursor. Transmission electron microscopy (TEM) revealed that the resultant bottlebrush polypseudorotaxanes possess a unique elongated cylindrical morphology.