Biodegradable core-shell materials via RAFT and ROP: Characterization and comparison of hyperbranched and microgel particles

Article abstract of DOI:10.1021/ma1027092

Two methodologies for synthesizing novel, degradable, core cross-linked copolymer particles were investigated and the molecular properties of the resultant polymers were compared. The first approach was to synthesize hyperbranched poly(ε-caprolactone-co-N,N-dimethylamino-2-ethyl methacrylate (PCL-co-PDMAEMA) by combining metal-catalyzed ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and reversible addition-fragmentation chain transfer polymerization (RAFT) of N,N-dimethylamino-2-ethyl methacrylate. First, the hyperbranched core was prepared via ROP copolymerization of ε-CL and branching agent 4,4-bioxepanyl-7,7-dione (BOD). This polymerization was initiated using the hydroxyl moiety of the bifunctional initiator 4-cyano-1-hydroxypent-4-yl dithiobenzoate (ACP-RAFT) which resulted in reactive pendent RAFT groups located on the polymer chains. The hyperbranched structure was confirmed by GPC-MALLS and NMR. Subsequent chain extension of this hyperbranched macromolecule with DMAEMA using RAFT chemistry yielded water-soluble nanoparticles. The second method involved the synthesis of core-cross-linked-shell particles (CCS) by the arm-first route. Linear arms of DMAEMA were synthesized using ACP-RAFT and subsequently used as macroinitiator for the ROP of ε-CL and BOD to form a degradable microgel that was water-soluble. Once again, molecular structure was analyzed by ¹H NMR, ¹³C NMR, and GPC and molecular size by TEM. Finally, GPC-MALLS was used to qualitatively investigate the different cross-link densities of the degradable core by the two different methodologies. Thus, we demonstrate two synthetic approaches for constructing water-soluble, degradable core-shell nanoparticles that exhibit varying degrees of cross-linking by combining RAFT and ROP.