Novel Well-defined Polystyrene-block-Poly(lactide-co-glycolide) Block Copolymers

Abstract

A facile preparation of polystyrene-block-poly(lactide-co-glycolide) PS-b-PLGA block copolymers was reported in detail. Well-defined PS-b-PLGA block copolymers were successfully obtained via living anionic polymerization and ring-opening polymerization. First, hydroxyl-terminated linear polystyrenes were prepared by living anionic polymerization. The resulting polymers were used as macroinitiators for ring-opening copolymerization of lactide and glycolide in the presence of the 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a catalyst in dichloromethane at ambient temperature. Transesterification and formation of DBU-initiated polymers were minimized by optimizing the catalyst concentration. Three block copolymers were synthesized in various molecular weights from 5000 g/mol to 33600 g/mol with low polydispersity. The formation of well-defined PS-b-PLGA block copolymers was followed by nuclear magnetic resonance spectroscopy and size-exclusion chromatography. Thermal properties of the block copolymers were investigated by thermal gravimetric analysis and differential scanning calorimetry. The morphology of the block copolymers was investigated using small-angle X-ray scattering in the bulk and via grazing incidence small-angle X-ray scattering as well as atomic force microscopy in thin film demonstrating organized nanostructures with uniform domain sizes. Overall, this manuscript describes an expanded polymer toolbox for PLGA-based polymers for next-generation lithography applications.

Keywords

• block copolymers
• polystyrene
• polyester
• morphology
• phase separation

Thanks

The author graciously thanks Prof. Marc Hillmyer (UMN), Prof. Frank Bates (UMN), and Dr. Joshua Speros (BASF) for helpful discussion as well as for their financial support. SAXS and GISAXS data were obtained at the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory. Parts of this work were carried out in the Characterization Facility, University of Minnesota.

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