Synthesis and characterization of polystyrene–poly(ethylene oxide)–heparin block copolymers

Abstract

AbstractA procedure for the preparation of new block copolymers composed of a hydrophobic block of polystyrene, a hydrophilic spacer‐block of poly(ethylene oxide) and a bioactive block of heparin was investigated. Polystyrene with one amino group per chain was synthesized by free radical oligomerization of styrene in dimethylformamide, using 2‐aminoethanethiol as a chain transfer agent. This amino group was used in the coupling reaction with amino‐telechelic poly(ethylene oxide) to produce an AB type diblock copolymer with one amino group per polystyrene (PSt)–poly(ethylene oxide) (PEO) chain. The amino‐semitelechelic oligo‐styrene was converted into the isocyanate‐semitelechelic oligo‐styrene using toluene 2,4‐diisocyanate and subsequent coupling with H2N–PEO–NH2 afforded AB type block copolymers with terminal amino groups. The coupling of PSt–PEO–NH2 with heparin was performed in a DMF–H2O mixture, first by activating the heparin carboxylic groups with EDC at pH 5.1–5.2 and subsequently reacting the activated carboxylic groups with the amino groups of the PSt–PEO–NH2 at pH 7.5. Depending on the molecular weights of the diblock copolymer used 25–29% w/w heparin was incorporated. These polymers will be further evaluated for their blood‐compatibility.