Cosolvent fractionation of PMOXA-b-PDMS-b-PMOXA: Bulk separation of triblocks from multiblocks

Challenges regarding the synthesis, purification, and characterization of the amphiphilic triblock copolymer poly(2-methyl-2-oxazoline)-block-polydimethylsiloxane-block-poly(2-methyl-2-oxazoline) (PMOXA-b-PDMS-b-PMOXA) are herein illustrated and discussed. A block copolymer (BCP) library was synthesised by cationic ring-opening polymerisation of 2-methyl-2-oxazoline on broadly and narrowly dispersed PDMS macroinitiators. The crude BCPs were fractioned by a newly developed cosolvent fractionation technique. With this it is possible to remove the side products of chain-transfer reactions, intrinsic to the polymerisation of 2-oxazolines. The obtained fractions were characterized by nuclear magnetic resonance, gel permeation chromatography and light scattering, revealing that the cosolvent fractionation separates multiblock copolymers from triblock copolymers. Self-assembly of the individual polymer fractions showed that the cosolvent fractionation is essential to yield polymersome forming triblock copolymers.