The Effects of (macro)molecular Structure on Hydrophilic Surface Modification of Polypropylene Membranes Via Entrapment.

Entrapment of a variety of ethyleneoxide-containing substances from nonpolar solutions into polypropylene (PP) microfiltration membrane surface for hydrophilic modification was studied. The results from gravimetric weight gain, surface characterization by contact angle measurements and ATR-IR spectroscopy, water flux measurements and protein adsorption revealed that poly(ethylene glycol)s (PEGs) were ineffective, while many nonionic amphiphilic substances, especially some tri-block copolymers of poly(ethyleneoxide) (PEO) and poly(propylene oxide) (PPO) were very effective for PP surface modification. The relationship between modifier structure and architecture and entrapment behavior was investigated by studying the micellization of the amphiphilic modifiers in nonpolar solutions via pyrene-probe fluorescence and (1)H NMR spectroscopy. We observed that the balanced structure of nonionic tri-block (macro)molecules tended to promote the formation of reverse micelles. For the most efficient polymeric modifiers, the lowest reverse critical micelle concentration (RCMC) had been observed. We conclude that a block copolymer structure and architecture promoting the self-association in the nonpolar solvent is the basis for a high modification efficiency, and that reverse micelles are involved in the entrapment modification performed at concentrations above RCMC. A different mechanism has been deduced for amphiphilic modifiers with low molar mass. This work provides more comprehensive insights in surface entrapment as a easy to perform physical surface modification method for polymeric materials.