DESIGN OF THERMORESPONSIVE SURFACES FOR T EMPERATURE-REGULATED HYDROPHOBIC CHROMATOGRAPHY AND SEPARATION OF STEROIDS

The purpose of this study is to elucidate the effect of molecular arch itecture of grafted polymers on the temperature-responsive hydrophilic /hydrophobic alterations of poly(N-isopropylacrylamide) (PIPAAm)-modif ied surfaces as well as the interaction with hydrophobic steroids. In particular, we focus on the effect of freely mobile PIPAAm chains intr oduced onto PIPAAm looped chain grafted surfaces. For this purpose, we prepared following two types of PIPAAm-modified surfaces; 1) looped c hain grafted surfaces using poly (IPAAm-co-N-acryloxysuccinimide), 2) PIPAAm terminally-grafted surfaces using residual active eater groups on the looped chain grafted surfaces. Temperature-responsive surface p roperty changes were evaluated by means of dynamic contact angle measu rements. Different temperature-responsive surface wettability changes were observed for these surfaces. Surface wettability changed drastica lly at 305 K for the surface with freely mobile PIPAAm chains, the tem perature corresponds to the LCST of PIPAAm in water. However, the PIPA Am looped chain grafted surface showed a lower transition temperature than the surface immobilized freely mobile PIPAAm chains. The differen ce in graft architecture also influenced the retention behavior of ste roids with different hydrophobicities. At higher temperature, separati on of steroids on both surfaces was accomplished in aqueous media. The surface with freely mobile PIPAAm chains showed a longer retention ti me than the PIPAAm looped chain grafted surface. This is due to a stro nger hydrophobic interaction between the surface with freely mobile PI PAAm chains and steroid molecules. Consequently, PIPAAm graft architec ture on the surface strongly influenced both wettability changes and i nteraction with steroids in response to temperature changes. These res ults suggest that we could regulate temperature-responsive hydrophobic interactions with solutes by designing PIPAAm molecular architecture on the surface of chromatography matrix.