Alternating copolymers with glycyl-glycine and alanyl-alanine side-chain pendants: synthesis, characterization and solution properties

A series of chiral alternating copolymers based on glycyl-glycine attached styrenic monomer (VG) and alanyl-alanine tethered maleimide (MA) are synthesized through reversible addition-fragmentation chain transfer (RAFT) polymerization. The alternating sequential arrangement of the two monomers along the synthetic copolymer chain is systematically established through 1H and 13C NMR spectroscopic investigation. The thermal as well as chiroptical characteristics of the copolymers are also studied. Interestingly, the copolymers show unusual luminescence characteristics in different organic solvents under UV light irradiation, whereas in the solid state they emit blue, green and red fluorescence as witnessed from the corresponding fluorescence microscopy micrographs. Furthermore, after successful Boc group removal, the deprotected copolymers show pH-dependent solubility variation in aqueous solution with an almost invariant transition pH with respect to varying chain lengths of the polymers. Thus, the strategy reported herein offers a notable direction to fabricate various dipeptide-based sequence-controlled polymers with promising applications.