Web Release Date: January 25,
Synthesis and Self-Assembly in Bulk of Linear and Mikto-Arm Star Block Copolymers Based on Polystyrene and Poly(glutamic acid)
and
Laboratoire de Chimie des Polymères Organiques, CNRS, ENSCPB-Université Bordeaux 1, 16 Avenue Pey Berland, 33607 PESSAC, France, and Institut Charles Sadron, CNRS, UPR 22, 6 Rue Boussingault BP 40016 F-67083 Strasbourg Cedex, France
Received September 14, 2007
Revised Manuscript Received December 5, 2007
Abstract:
Both AB linear-type and AB2 miktoarm star-type amphiphilic block copolymers based on polystyrene
(PS) as A block and poly(glutamic acid) (PGA) as B block were obtained by a four-step synthetic approach
combining (i) atom transfer radical polymerization of styrene and (ii) chemical modification of the bromo end
groups of ATRP-derived precursors into many or twice as many primary amino groups, followed by (iii) ring-opening polymerization of 
-benzyl-L-glutamate N-carboxyanhydride and (iv) a final step of hydrolysis. The
self-assembly properties in bulk of these linear PS-b-PGA and miktoarm star PS-b-(PGA)2 block copolymers
were subsequently investigated by different analytical means, including Fourier transform infrared spectroscopy
(FTIR), wide and small-angle X-ray scattering (WAXS and SAXS) and atomic force microscopy (AFM). FTIR
analysis revealed that the PGA block systematically adopted a rodlike 
-helix conformation, even for degree of
polymerization as low as 18. The very high immiscibility between PS and PGA blocks (conformational asymmetry)
drove all of these rod-coil block copolymers to self-assemble in a hexagonal in lamellar (HL) morphology in
the nanometer size range, whatever their composition and architecture. In addition, WAXS and SAXS results
evidenced the effect of the macromolecular architecture on the local organization of PGA helices: the linear
block copolymers showed an internal lamellar structure with PGA helices stacked, inter-digitated or folded
depending on the weight fraction of the rodlike PGA blocks, whereas miktoarm stars exhibited a stacked
microstructure, independently of the PGA content.
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