Self-assembly and aggregation of ATRP prepared amphiphilic BAB tri-block copolymers contained nonionic ethylene glycol and fluorescent 9,10-di(1-naphthalenyl)-2-vinyl-anthracene/1-vinyl-pyrene segments

Abstract

Two novel amphiphilic BAB-type block copolymers, ADN-PEG3400-ADN and Py-PEG3400-Py containing deep blue and bluish-green fluorescent moieties were prepared using atom transfer radical polymerization (ATRP) (where, ADN=poly(9,10-di(1-naphthalenyl)-2-vinylanthracene), Py=poly(1-vinyl pyrene) and PEG3400=poly(ethylene glycol) with Mn=3400g/mol). The GPC number averaged molecular weights (MW) of the block copolymers were Mn=9600 and 13,800g/mol, respectively, based on polystyrene MW standards. The PEG3400 segment has a melting temperature (Tm peak) at 64–65°C, whereas the glass transition temperatures (Tg midpoint) of the ADN and Py segments were found to be 230°C and 193°C, respectively, and are similar to their respective homopolymers indicating complete microphase segregration. The photoluminescence (PL) emission of the copolymers ADN-PEG3400-ADN exhibited two maxima at 423.5nm and 441.5nm while Py-PEG3400-Py has a maximum at 488.5nm. Both copolymers form individual spherical micelles with diameter from 30 to 90nm for Py-PEG3400-Py and 40–160nm for ADN-PEG3400-ADN. The micelles, however, transform into cross-linked pearl-necklace-like aggregates at polymer concentrations above 1000ppm, which may be attributed to the physical cross-linking between adjacent spherical micelles caused by the PEG3400 segments.