Synthesis and characterization of amphiphilic graft copolymers based on poly(styrene-co-maleic anhydride) with oligo(oxyethylene) side chains and their GPC behavior

A series of amphiphilic graft copolymers were synthesized based on poly(styrene-co-maleic anhydride) (SMAs) (backbone copolymers) and methoxypolyethylene glycols (MPEGs) (grafts) in this study. Selection of proper reaction conditions using p-toluenesulfonic acid (PTSA) as catalyst and toluene as solvent in the present research can prevent crosslinking reactions which may occur due to the presence of di-functional polyethylene glycol in the commercial MPEGs. The structures and compositions of the graft copolymers were determined by gel permeation chromatography (GPC) and 1H NMR analysis. It is noteworthy that the GPC behavior of these graft copolymers follows the rule of thumb for GPC, i.e. the higher molecular weight copolymers have lower retention volumes. This is very different from the GPC behavior of similar graft copolymers reported previously in the literature. Also, differential scanning calorimetry (DSC) characterization shows that there are two transition temperatures for some of these amphiphilic copolymers owing to the existence of another aggregation phase of MPEG grafts.