Star polymers with both temperature sensitivity and inclusion functionalities

We designed and synthesized novel star poly(N-isopropylacrylamide) (star-PNIPAm) and star-PNIPAm with cyclodextrin (CD) end groups (star-PNIPAm-CD) by atom transfer radical polymerization (ATRP). In the synthesis, β-CD-core with 21 initiation sites, heptakis[2,3,6-tri-O-(2- chloropropionyl)]-β-cyclodextrin (21Cl-β-CD), was first synthesized by the reaction of β-CD with 2-chloropropionyl chloride (CPC). Then, 21-arm star-PNIPAm (PDI = 1.03) was synthesized by ATRP of N-isopropylacrylamide (NIPAm) initiated via 21Cl-β-CD. Finally, a star-PNIPAm-CD (PDI = 1.02) was synthesized by ATRP of a monovinyl β-CD (GMA-EDA-β-CD) initiated via star-PNIPAm. The obtained star-PNIPAm and star-PNIPAm-CD were characterized by means of SEC/MALLS, NMR, IR, and DSC. By using 8-anilino-1-naphthalenesulfonic acid ammonium salt hydrate (ANS), 1-adamantanamine hydrochloride (ADA-NH ₃Cl), and ibuprofen sodium salt (ibuprofen-Na) as guest molecules, thermal sensitivity and inclusion behaviors of the star polymers were investigated by fluorescence spectrophotometer and DLS. It is found that the star polymers can combine both thermal sensitivity of PNIPAm and inclusion behavior of β-CD. Interestingly, the star polymers can self-assembly to form nanosized aggregates in aqueous solution above their LCSTs. The self-assembly behavior shows molecular recognition capability. And formation and dissociation of the nanosized aggregation can change reversibly by changing temperature above and below the LCST.