Synthesis of azobenzene‐containing polymers via RAFT polymerization and investigation on intense fluorescence from aggregates of azobenzene‐containing amphiphilic diblock copolymers

Abstract

The well-defined azobenzene-containing homopolymers, poly(6-(4-phenylazophenoxy)hexyl methacrylate (AHMA)) (PAHMA), were synthesized via reversible addition fragmentation chain transfer polymerization (RAFT) in anisole solution using 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) as the RAFT agent and 2,2'-azobisisobutyronitrile (AIBN) as the initiator. The first-order kinetic plot of the polymerization and the linear dependence of molecular weights of the homopolymers with the relatively low polydispersity index values (PDIs≤ 1.25) on the monomer conversions were observed. Furthermore, the amphiphilic diblock copolymer, poly(6-(4-phenylazophenoxy)hexyl methacrylate (AHMA)}-b-poly(2-(dimethylamino)ethyl methacrylate (DMAEMA)) (PAHMA-b-PDMAEMA), was prepared with the obtained PAHMA as the macro-RAFT agent. The structures and properties of the polymers were characterized by 1 H NMR and GPC, respectively. Interestingly, the amphiphilic diblock copolymers in chloroform (CHCl 3 ) solution (PAHMA 23 -b-PDMAEMA 97 (4 X 10 -5 M, M n(GPC) 18,400 g/mol, PDI = 1.48) and PAHMA 28 -b-PDMAEMA 117 (6 X 10 -5 M, M n (GPC) = 19,300 g/mol, PDI = 1.51) exhibited the intense fluorescence emission at ambient temperature. Moreover, the fluorescent intensity of PAHMA-b-PDMAEMA in CHCl 3 was sensitive to the ultraviolet irradiation at 365 nm, which increased within the first 10 min and later decreased when irradiation time was prolonged to 30 min or longer. The well distributed, self-assembled micelles composed of azobenzene-containing amphiphilic diblock copolymers, (PAHMA-b-QPDMAEMA)s (QPDMAEMA is quaternized PDMAEMA), in the mixed N,N-dimethyl formamide (DMF)/H 2 O solutions were prepared. Their fluorescent intensities decreased with the increasing amount of water.