Abstract
We show how the self-assembly of miktoarm star copolymers can be controlled by modifying the side chains of their polypeptide arms, using A(2)B and A(2)B(2) type polymer/polypeptide hybrids (macromolecular chimeras). Initially synthesized PS2PBLL and PS2PBLL2 (PS, polystyrene; PBLL, poly(epsilon-tert-butyloxycarbonyl-L-lysine)) miktoarms were first deprotected to PS2PLLHCl and PS2PLLHCl2 miktoarms (PLLHCl, poly(L-lysine hydrochloride)) and then complexed ionically with sodium dodecyl sulfonate (DS) to give the supramolecular complexes PS2PLL(DS) and PS2(PLL(DS))(2). The solid-state self-assemblies of these six miktoarm systems were studied by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and small- and wide-angle X-ray scattering (SAXS, WAXS). The side chains of the polypeptide arms were observed to have a large effect on the solubility, polypeptide conformation, and self-assembly of the miktoarms. Three main categories were observed: (i) lamellar self-assemblies at the block copolymer length scale with packed layers of a-helices in PS2PBLL and PS2PBLL2; (ii) charge-clustered polypeptide micelles with less-defined conformations in a nonordered lattice within a PS matrix in PS2PLLHCl and PS2PLLHCl2; (iii) lamellar polypeptide-surfactant self-assemblies with beta-sheet conformation in PS2PLL(DS) and PS2(PLL(DS))(2) which dominate over the formation of block copolymer scale structures. Differences between the 3- and 4-arm systems illustrate how packing frustration between the coil-like PS arms and rigid polypeptide conformations can be relieved by the right number of arms, leading to differences in the extent of order.