Synthesis of nanosized "cored" star polymers

A synthetic approach to nanosized "cored" star polymers is reported. A 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin core was functionalized with four 2,2,6,6-tetramethylpiperidinyl-l-oxy (TEMPO) initiating groups. Four-armed star copolymers of styrene and 4-hydroxystyrene were synthesized and functionalized with 3,5-di(3-buten-1-oxy) benzyl bromide groups but exhibited poor solubility. As an alternative, 5,10,15,20-tetrakis(3′,5′-dihydroxyphenyl)porphyrin was functionalized with 2-bromo-2-methylpropionyl groups capable of initiating atom transfer radical polymerization (ATRP). Copolymerization of the core initiator with l-but-3-enyl-4-vinylbenzene and styrene at low conversion produced soluble eight-armed star block copolymers. Through the ring-closing metathesis (RCM) reaction, the alkene groups of the polymer were intramolecularly cross-linked. The ester groups linking the cross-linked polymer arms to the porphyrin core were hydrolyzed, producing a "cored" star polymer with a molecular weight of approximately 20 kDa and a polydispersity index (PDI) of 1.5.