Synthesis and characterization of positively charged amphiphilic water soluble polymers based on poly(N-isopropylacrylamide)

The synthesis and characterization of new water-soluble shear-responsive polymers based on N-isopropylacrylamide (NIPAM) is reported. These copolymers are synthesized using a two-steps procedure: (a) synthesis of the precursors by radical copolymerization in aqueous solvent between NIPAM and an amine-containing monomer N,N-[(dimethylamino)propyl]methacrylamide (MADAP) and (b) modification of the macromolecular backbone by reaction between MADAP units and alkylbromide. From kinetic studies performed during copolymerization, the reactivity ratios of the two monomers were determined in media of different ionic strength (rNIPAM=0.6 and rMADAP=0.6−1.3). Under these conditions, it was shown that the composition and the distribution of NIPAM and MADAP units into the macromolecular backbone remain approximately constant until 80% of conversion. For all the copolymers, in the composition range 0–25 mol% of MADAP units, an effective control of the molar mass is reported with the concentration of the reducing agent involved in the redox initiator. Finally, a quantitative alkylation procedure of MADAP units is described in chloroform using an inactive base and a large excess of alkylbromide.