Polypseudorotaxane-based multiblock copolymers prepared via in situ ATRP of NIPAAm initiated by inclusion complex having a feeding ratio of 4 β-CDs to ferrocene containing initiator

Unexpected Polypseudorotaxanes Formed from the Self-assembly of β-Cyclodextrins with Poly(N-isopropylacrylamide) Homo- and Copolymers

“…The preparative pathways of PNIPAAm homo- and copolymers and their self-assembly with β-CDs are shown in Scheme . As our previous report suggested, while using PPRs self-assembled from the Fc-containing ATRP initiator FTB with four β-CDs to initiate the in situ ATRP of NIPAAms to end-cap themselves into the corresponding low-number CD-threaded PRs, the attached PNIPAAm blocks were found to be not bulky enough as end-capping stoppers and the threaded β-CDs could move outward and slip off the flank PNIPAAm blocks . To further highlight the self-assembly behavior and crystal structure created from the self-assembly of PNIPAAm with β-CDs, one PNIPAAm copolymer and two homopolymers were synthesized.…”

“…However, the XRD pattern of F40N4CD was evidently different from that of F4CD and its main diffraction peaks appeared at 10.5, 12.9, and 19.7°. Taking into account our result using the in situ ATRP of NIPAAm to end-cap PPRs self-assembled from the Fc-containing ATRP initiator FTB with four β-CDs into the corresponding PRs with attached PNIPAAm oligomers as bulky stoppers, these results clearly indicated that β-CDs are indeed self-assembled with PNIPAAm in an aqueous solution to create a new matched over-fit crystal structure compared with the matched tight-fit β-CD–PPG PPRs via a manner of main-chain inclusion complexation.…”

“…As seen, the spectrum of β-CD exhibits multiple C1, C4, and C6 resonance peaks for its less symmetrical cyclic conformation in the uncomplexed crystal state, which leads to strong splitting for all of the C 1 –C 6 resonances. However, all of the carbon resonance peaks of β-CD incorporated in F40N4CD are featured by reduced splitting upon forming a PPR as previously reported. , In comparison with the spectra of PPRs obtained from Br–TEG–Fc–TEG–Br-β-CD PPR as the initiator for the in situ ATRP of NIPAAm, these threaded β-CDs in F40N4CD hold a relatively lower symmetrical cyclic conformation. Nevertheless, even considering the contribution of uncomplexed β-CDs, this less symmetrical conformation suggested that the self-assembly of β-CDs would be confined to the flank PNIPAAm blocks instead of the central initiator block to form PPR, and the inward movement of threaded β-CDs along the PNIPAAm blocks would be a time-consuming process …”

“…Meanwhile, both FTB and F40N showed no diffraction peaks as a small noncrystalline molecule and an amorphous polymer, respectively. The XRD pattern of F4CD self-assembled from FTB with four β-CDs displayed the characteristic tunnel-type crystal diffraction peaks at 11.7 and 17.8°, considerably different from those of β-CD, but the same as those previously reported. ,, Furthermore, this pattern resembled those of PPR samples synthesized using F4CD as the initiator for the in situ ATRP of NIPAAm . However, the XRD pattern of F40N4CD was evidently different from that of F4CD and its main diffraction peaks appeared at 10.5, 12.9, and 19.7°.…”

“…Recently, aiming to prepare PR-based multiblock copolymers possessing a small number of threaded CDs to depress the intermolecular hydrogen-bond interactions and to lessen the channel-like crystal structure enhancing the mobility of these threaded CDs along a polymeric chain, a bifunctional ferrocene (Fc)-containing atom transfer radical polymerization (ATRP) initiator was prepared and subsequently self-assembled with four β-CDs per initiator to give PPRs, followed by in situ ATRP of NIPAAms to end-cap themselves into the corresponding PRs with attached PNIPAAm oligomers as bulky stoppers . This was based on the assumption that fully stretched PNIPAAm blocks would be thicker enough as bulky end-capping stoppers in the cross-sectional area of a polymeric chain compared with PPO and PDMS or PSi according to the findings of Yuan, et al and our studies. − , After finishing the ATRP followed by 7 days of dialysis for purification, about half of the added β-CDs were still entrapped on the polymeric chain.…”