T. Yakushiji et al., DESIGN OF THERMORESPONSIVE SURFACES FOR T EMPERATURE-REGULATED HYDROPHOBIC CHROMATOGRAPHY AND SEPARATION OF STEROIDS, Kagaku kogaku ronbunshu, 24(2), 1998, pp. 205-210
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.