Modification And Functionalization Of Halloysite Nanotubes Via Living Ring Open Metathesis Polymerization

Since Grubbs discovered the olefin metathesis reaction providing a new method for the formation of C=C bond, ring-opening metathesis polymerization (ROMP) was developed. The functional group has little effect on ROMP since ROMP is a double bond cracking-reconstruction process. Owing to its functional group tolerance and its well-control on the chain segment size and sequence, ROMP is often used as an effective way to prepare functional materials.Surface grafting modification is a commonly used method to functionalize and modify the inorganic substrate materials. Among the grafting approaches of "grafting to","grafting through" and "grafting from","grafting from" is widely utilized because of its high grafting density. In order to graft well-defined and uniform polymer brush on the surface of substrate materials,"grafting from" is often combined with living polymerization such as ionic polymerization, living radical polymerization, coordination polymerization and ROMP. Compared with other surface grafting methods, surface initiated ring-opening metathesis polymerization (SI-ROMP) has more advantages of versatility, effectiveness, and functional group tolerance.Herein, halloysite nanotubes (HNTs) as the substrate were functionalized with di-functional block copolymer via SI-ROMP.In this work, four functional norbornene-based monomers were synthesized first, which were the monomer M1with sugar pendant and the monomers M2-M4with nitrogen-atom pendant groups. These four monomers were successfully synthesized and the purity was more than95%from the results of Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (1H NMR).Then, four norbornene-based monomers were polymerized respectively via ROMP using Grubbs2nd generation catalyst (G2) as an initiator. Based on the homopolymerization, ROMP copolymerization of M1and M3were performed. The conversion of Ml was82%after2h polymerization time calculated by1H NMR, and polymer molecular weight (Mn) and molecular weight distribution index (PDI) of the resulted polymer P(M1) were Mn=3.28×104, PDI=1.72measured by a gel permeation chromatograph (GPC). Among the nitrogen-atom pendant monomers M2-M4, the ROMP of M3was controlled very well. The conversion of M3was98%after8h polymerization time, and Mn and PDI of the resulted polymer P(M3) were Mn=3.28×104, PDI=1.72measured by GPC. The homopolymerization of M1-M4and copolymerization of M1and M3were all living polymerization. In addition, it is better to polymerize M3first in copolymerization of Ml and M3.Surface initiated ring-open metathesis polymerization (SI-ROMP) on HNTs has been carried out:(ⅰ) the anchoring of a norbomenyl monolayer to the surface using the-OH groups on HNTs surface;(ⅱ) the attachment of the Grubbs2nd generation catalyst on the surface using the norbomenyl groups;(ⅲ) the copolymerization of M3and Ml added sequentially to prepare the copolymer brush containing the sugar chain segment and the nitrogen-atom chain segment (HNTs-P(M3M1)). The anchor, initiator and functional monomers were grafted onto HNTs from the results of FT-IR and thermo gravimetric analysis (TGA).To endow the polymer brushes with magnetic property, Fe3+was first attached through the coordination of nitrogen-atom along polymer chains. Then Fe3+was reduced into Fe0to form nano-particles in water phase. The resulting HNTs-P(M3M1)-Fe has magnetic property characterized by an outer placed magnet, and the particles on HNTs-P(M3M1)-Fe were uniform examined by transmission electron microscopy (TEM).