Biodegradable Core−Shell Materials via RAFT and ROP: Characterization and Comparison of Hyperbranched and Microgel Particles

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 1 H NMR, 13 C 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.