Preparation and characterization of graft copolymers of polyacrylamide and polyethylenimine

Condensation grafting of polyethylenimine (PEI) onto poly(acrylamide-co-acrylic acid) (PAM-co-AA) with 1.5 and 10wt.% acrylic acid (AA) contents was investigated. The grafting was accomplished by a two-step reaction mechanism involving: (i) the conversion of AA into acid chloride (AC) using thionyl chloride (SOCl2); and (ii) the condensation of AC on PAM with amine on PEI to form graft copolymer. A FTIR technique was used to confirm the reactions by observing the appearance of AC vibration at 1800cm−1 and amide vibration at 1550cm−1. The condensation reaction was fast in formamide (FAM) solution, and the degree of grafting (d.g.) was a weak function of temperature. The AA content of PAM, the molecular weight (MW) of PEI, and the ratio of [PEI]0/[PAM]0 were three major factors in determining the d.g. and the chain structure. The graft copolymers with the d.g. of 0.1–1.7 were obtained. Based on the experimental data and theoretical analysis, the possible structures of the graft copolymer chains were postulated and discussed.