Synthesis and Self‐Assembly of Amphiphilic Block Copolymers from Biobased Hydroxypropyl Methyl Cellulose and Poly(l‐lactide)

Abstract

A series of well‐defined hydroxypropyl methyl cellulose‐block‐poly(l‐lactide) (HPMC‐b‐PLLA) diblock copolymers are synthesized via UV‐initiated thiol‐ene click reaction of thiol‐terminated HPMC with different block lengths and allyl‐terminated PLLA, using 2,2‐dimethoxy‐2‐phenylacetophenone as photocatalyst. The former is obtained by coupling the reducing aldehyde endgroup of short chain HPMC with the amine group of cysteamine, and the latter by ring‐opening polymerization of l‐lactide in the presence of allyl alcohol. Fourier transform infrared (FT‐IR), nuclear magnetic resonance (1H NMR), and diffusion ordered spectroscopy NMR confirm the successful coupling of both blocks. The molar mass of the resulting copolymers ranges from 7000 to 12 800 g mol−1 as determined by size exclusion chromatography. The copolymers are able to self‐assemble in aqueous medium, yielding micelles of 50–100 nm with core–shell structure as evidenced by dynamic light scattering, transmission electron microscopy, and 1H NMR. The critical micelle concentration of copolymers ranges from 0.12 to 0.15 mg mL−1. Last but not the least, the copolymers exhibit thermoresponsive behavior with a lower critical solution temperature around 80 °C. image