Crosslinking of dextran with some selective Cl-, P- and N-containing functional substances in aqueous solutions

Crosslinking reactions of Dextran (Dx) (M-n of 5.0X10(5) and 2.0X10(6) g mol(-1)) with some selective Cl-, P- and N-containing functional monomers such as epichlorohydrin (ECH), phosphorus oxychloride (POCl3) and N,N'-methylenebisacrylamide (MBAM) as well as with Co-60-gamma -irradiation were carried out in the basic aqueous solutions (2.8 N NaOH) at 25-50 degreesC. The optimum conditions of the effective swelling and crosslinking for the each system studied were found. Some swelling parameters such as initial rate of swelling (R-S, %min(-1)), crosslink density (rho, g ml(-1)), equilibrium swelling (S-eq, %) and average molecular weight of crosslinked fragments (M-e, g mol(-1)) for the Dx/crosslinker (CL) systems studied were determined by using of kinetic methods and well known Flory-Rehner equation. A substantial difference of these parameters observed fur the various Dx/CL systems was explained by the effect of nature and concentration of crosslinking agents on the mechanism of crosslinking and swelling processes. It was shown that R-S and rho values increase while the S-eq and M-e values decrease depending on the nature of CLs: in the following raw. gamma -ray-ECH-MBAM-POCl3. Concentration of MBAM does not influence the initial rate of swelling while effect of CL concentration is strongly advented in the Dx/ECH and Dx/POCl3 systems. Effectiveness of CLs is also confirmed by TGA analysis of crosslinking polymers. The formation of unsaturated crosslinked fragments, which are easily polymerized or photocyclodimerized as affected of u.v.-irradiation, was confirmed by Fourier transform infrared (FT-IR) spectroscopy. General scheme and proposed mechanism of crosslinking reactions in the Dx/CL systems was also described. (C) 2001 Elsevier Science B.V. All rights reserved.