SynopsisA procedure for the preparation of new block copolymers composed of a hydrophobic block of polystyrene, a hydrophilic spacer-block of poly(ethy1ene oxide) and a bioactive block of heparin was investigated. Polystyrene with one amino group per chain was synthesized by free radical oligomerhtion 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(ethy1ene oxide) to produce an AB type diblock copolymer with one amino group per polystyrene (PSt)-poly(ethy1ene oxide) (PEO) chain. The amino-semitelechelic oligestyrene was converted into the isocyanatrsemitelechelic oligo-styrene using toluene 2,4diisocyanate and subsequent coupling with H,N-PEO-NH, afforded AB type block copolymers with terminal amino groups.The coupling of PSt-PEO-NH, with heparin was performed in a DMF-H,O mixture, first by activating the heparin carboxylic groups with EDC at pH 5.1-52 and subaequently reading 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. Thew polymers will be further evaluated for their blood-compatibility.
The reaction of mixtures of pivalolactone (PVL), alkanediols, and dimethyl terephthalate (DMT) was investigated in a two-stage melt process. NMR measurements (XH, 13C,-, 1H-13C) indicated that poly(ether ester)s had been formed. Apart from a significant amount of ether bonds, the copolymers contained practically no PVL sequences, which was also observed using a model system consisting of bis-(hydroxybutyl) terephthalate and PVL. From the results of the model study it was concluded that ring opening of PVL had occurred by attack on the /3-carbon atom, followed by alkyl-oxygen bond scission, thus leading to the formation of ether bonds. Furthermore, it was found that propagation through successive attacks on PVL had not taken place; instead the formed carboxylic acid end groups reacted with hydroxyl groups, resulting in isolated PVL units in the polymeric chains. In this paper also data are presented about the effect of the catalyst and of the type of lactone on the copolymer synthesis.
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