Addition of chlorosulfonyl isocyanate to C==C bonds in cis-1,4-polyisoprene and reaction of the adduct with NaOH resulted in the formation of a water-soluble polyelectrolyte with N-sulfate and carboxylate groups. The polyelectrolyte showed anticoagulant activity and it was found, just as with heparin, that the activity was related to molecular weight and N-sulfate content.
Chemical transformation of functional groups in polymers has often been used as a method to prepare polymers with specific properties (1). Polymer-analogous reactions with polydienes have been described (2,3) and recently we reported on the chemical modification of polyisoprenes (43). By addition of chlorosulfonyl isocyanate (CSI) to C% bonds, modified polyisoprenes were obtained with N-chlorosulfonyl p-lactam and 0, y-unsaturated N-chlorosulfonyl carbonamide groups. A second-step modification by reaction with NaOH resulted in the formation of water-soluble polyelectrolytes with anticoagulant activity (5-7).are presented which give information about the chemical structure of the modified polymers.This article deals with the modification of cis-l,4-polyisoprene and results
ExperimentalSolutions of cis-l,4-polyisoprene (Cariflex IR 307, cis content more than 96%) in toluene (0.2M) were added to stirred solutions of CSI in the same solvent. Reactions were carried out at 0 or 20°C in a nitrogen atmosphere. After 1 hr the solid cis-l,4-polyisoprene-CSI adducts were isolated and washed with diethylether. Polyelectrolytes were synthesized from these adducts by heating with 2M NaOH for 1 hr. Subsequently they were precipitated by pouring the alkaline solutions in ethanol.More experimental details have been published elsewhere (43).
Results and DiscussionThe reaction of cis-l,4-polyisoprene with CSI (Scheme I) leads to the formation of a modified polymer with predominantly structure a, whereas structure b is also formed (43). It was found that with a 50% molar excess of CSI, addition takes place to an extent of 65% at 20°C (Table I , exp. 1). The degree of addition decreases by lowering the temperature, as can be seen from the results of exp. 2. The effect of a prolonged reaction time (6 hr) is supposed to be of minor importance, because an increase of the reaction time (exp. 3) does not lead to an increase of the degree of addition (cf. also the results of exps. 5 and 6). The effect of an increase of the CSI:cis-l,4-polyisoprene molar ratio, on the other hand, is apparent, as can be seen from the results of exps. 3 and 4.
Gamma irradiation of aqueous solutions of a synthetic heparinoid polyelectrolyte results in the formation of hydrogels, varying in water content and mechanical strength. The equilibrium water content and the mechanical strength of the hydrogels are dependent on the initial polyelectrolyte concentration, the molecular weight of the polyelectrolyte, the percentage of double bonds in the polyelectrolyte and the radiation dose.The polyelectrolyte hydrogels do not deplete Antithrombin Ill from blood and there is no activation of factor XII according to an in vitro kallikrein generation test. However, in a very sensitive test for factor XII activation (contact promoted shortening of the thrombotest) a slight activation of this factor was observed.
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