Fluorescence Studies on Self-association of Biodegradable Pyrene-labeled Poly(L-lysine) Grafted with Poly(caprolactone)

The biodegradable amphiphilic graft copolymer (PolyLysPy-PCL) containing hydrophilic pyrene end-labeled poly(L-lysine) (PolyLysPy) backbone and hydrophobic polycaprolactone (PCL) side chains was synthesized by the amide condensation of PolyLysPy and PCL. PolyLysPy was prepared from ring-opening polymerization of N-epsilon-benzyloxycarbonyl-L-lysine N-carboxyanhydride (Lys(Z)-NCA) initiated by 1-pyrenemethylamine and followed by removing the side-chain protective groups. PCL was prepared from the enzymatic ring-opening polymerization of epsilon-caprolactone by a porcine pancreas lipase. The structures and number-average molecular weights (Mn) of the graft copolymer and its precursors were confirmed and investigated by the H-1 NMR measurement. The self-assembly of the graft copolymer in water/DMSO mixture solution was examined by fluorescent signals assigned to the pyrene moiety. The increase in the grafting percent of PCL to a PolyLysPy polymer backbone can facilitate the self-assembly by the hydrophobic interaction of associated PCL grafts.