Stereocomplexation in novel degradable amphiphilic block copolymer micelles of poly(ethylene oxide) and poly(benzyl α-malate)

The ring-opening polymerization of 5-(S)-[(benzyloxycarbonyl)methyl]-1,3- dioxolane-2,4-dione (l-malOCA) and 5-(R)-[(benzyloxycarbonyl)methyl]-1,3- dioxolane-2,4-dione (d-malOCA) from poly(ethylene oxide), PEO, macroinitiators using 4-methoxypyridine as the catalyst is reported. The self-assembly of these polymeric amphiphiles was shown to proceed most efficiently by a solvent switch methodology from THF to nanopure H ₂O. Variation of the block lengths revealed that, as expected, larger block copolymers led to increased micelle dimensions as determined by dynamic light scattering (DLS) and transmission electron microscopy (TEM) and longer hydrophobic blocks led to increased micelle stabilities as determined by measurement of the critical micelle concentration (CMC). Furthermore, the self-assembly of equimolar mixtures of PEO-b-P(l-BMA) and PEO-b-P(d-BMA) resulted in micelles of increased sizes by both DLS and TEM analysis. These micelles also have a CMC value of 5.53 × 10 ^-3 g L ^-1 which is markedly lower than micelles formed from either enantiopure block copolymer (CMC values = 1.23 × 10 ^-2 g L ^-1 and 9.78 × 10 ^-3 g L ^-1 for micelles formed from PEO-b-P(l-BMA) and PEO-b-P(d-BMA) respectively).