Synthesis and aggregation behavior of grafted maleic acid copolymers

Grafted SMA containing poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether) (SMA-PEG) and its hydrophobically modified products poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether & dodecyl) (SMA-PEG+C(12)) and poly(styrene-co-maleic anhydride)-g-(dodecyl) (SMA-C(12)) were prepared using a single batch method. Their adsorption and rheology behavior was investigated using equilibrium surface tension and rheological techniques. The adsorption parameters, saturation surface excess concentration (Γ(max)), and the minimum area (A(min)) of these copolymers were evaluated. The results show that Γ(max) increased and A(min) correspondingly decreased with increasing hydrophobicity. Aggregation standard free energy of SMA-PEG+C(12) and SMA-C(12) suggested that increased hydrophobicity enhanced the tendency for aggregation to occur. The distinctive differences in the macroscopic appearance were shown by aqueous samples of the copolymers. The samples of SMA-M behaved as Newtonian fluids at all concentrations (from 1.0 wt% to 20.0 wt%), indicating that there were no macromolecular chain entanglements or interactions between aggregates in solution. For SMA-PEG+C(12), at concentrations above 10.0 wt%, the presence of cross-links between aggregates is presumed to be the reason for the viscoelastic behavior. Solid-like elastic behavior could occur at low concentration (5.0 wt%) of SMA-C(12), suggesting the formation of networks by inter-chain aggregation of the hydrophobic dodecyl chains.