Selectively Degradable Core Cross-Linked Star Polymers

Abstract

A range of selectively degradable core cross-linked star (CCS) polymers were synthesized via a combination of atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP) using the “arm first” method. The multifunctional initiator 2-hydroxyethyl 2‘-methyl-2‘-bromopropionate was used to synthesize degradable poly(ε-caprolactone) (PCL) and nondegradable polystyrene (PSt) and poly(methyl methacrylate) (PMMA) macroinitiators which were subsequently cross-linked to generate CCS polymers. By using nondegradable (divinylbenzene (DVB), ethylene glycol dimethacrylate (EGDMA)) and degradable (4,4‘-bioxepanyl-7,7‘-dione (BOD), 2,2-bis(ε-caprolactone-4-yl)propane (BCP)) monomers to cross-link the different macroinitiators, a range of CCS polymers were synthesized where either the arm or the core domain can be selectively degraded. PCL/DVB and PCL/EGDMA arm-degradable CCS polymers were synthesized under various conditions to determine the optimal reaction conditions with hydrolysis yielding DVB and EGDMA cores, for which the hydrodynamic diameter was determined. Hydrolysis of PCL/PMMA/EGDMA miktoarm CCS polymer resulted in CCS polymer with a reduced number of arms, whereas PSt/BOD core-degradable CCS polymer yielded the original linear PSt arms upon hydrolysis. PCL/BOD and PCL/BCP fully degradable CCS polymers were also synthesized and shown to be completely degradable upon hydrolysis of the ester linkages to generate small-chain acid units.