Guolin Lu

A novel poly(N-vinylcaprolactam)-based well-defined amphiphilic graft copolymer synthesized by successive RAFT and ATRP

A series of well-defined amphiphilic graft copolymers consisting of a hydrophobic poly(tert-butyl acrylate) (PtBA) backbone and hydrophilic poly(N-vinylcaprolactam) (PNVCL) side chains were synthesized via the combination of reversible addition–fragmentation chain transfer (RAFT) polymerization, atom transfer radical polymerization (ATRP), and the grafting-from strategy without any polymeric functional transformation. RAFT homopolymerization of tert-butyl 2-((2-bromopropanoyloxy)methyl)acrylate (tBBPMA) was first performed to give a well-defined Br-containing PtBBPMA backbone with a low polydispersity (Mw/Mn = 1.22). PNVCL side chains were grown from the backbone via straightforward ATRP of N-vinylcaprolactam using CuBr/Me6Cyclam as the catalytic system in 1,4-dioxane to afford the target PtBA-g-PNVCL amphiphilic graft copolymers with narrow molecular weight distributions (Mw/Mn ≤ 1.32). The self-assembly behavior of these graft copolymers in aqueous media was studied by fluorescence spectroscopy and transmission electron microscopy (TEM), and furthermore, their thermo-responsive behavior was investigated by UV-vis and dynamic light scattering (DLS). Finally, the hydrophobic PtBA backbone was selectively hydrolyzed into a hydrophilic PAA backbone without affecting PNVCL side chains in the acidic environment to provide PAA-g-PNVCL graft copolymers.

Poly(acrylic acid)-graft-poly(N-vinylcaprolactam): a novel pH and thermo dual-stimuli responsive system

Stimuli-responsive polymers have undoubtedly been of great interest in the past few decades due to a variety of potential applications in biomedical territory. Herein, we report a novel dual-stimuli responsive double hydrophilic graft copolymer system, poly(acrylic acid)-g-poly(N-vinylcaprolactam) (PAA-g-PNVCL), which could respond to changes in pH and temperature simultaneously. In our design, poly(acrylic acid) (PAA) was selected as a pH-sensitive moiety, whereas poly(N-vinylcaprolactam) (PNVCL) could be regarded as a thermo-sensitive one. The responsiveness of PAA-g-PNVCL to pH and temperature by itself was demonstrated in detail primarily: dynamic light scattering (DLS), fluorescence spectroscopy, and transmission electron microscopy (TEM) were employed to examine its pH-induced micellization behavior; 1H NMR, DLS, and TEM were employed to examine its thermo-induced micellization behavior. Finally, its responsiveness to the combination of both stimuli was studied by UV-vis test.

Constructing well-defined star graft copolymers

This review highlights representative efforts to construct well-defined star graft copolymers over the past decade. Star graft copolymers, consisting of multiple arms connected to a central core as the backbone, and branched side chains grafted from the arms, possess a more complex topological architecture than traditional graft copolymers and star polymers bearing linear arms. According to the distinction of grafting density, star graft copolymers can be divided into typical star graft copolymers with loosely grafted side chains, and star brush polymers with densely grafted side chains. For the synthesis of both types, there are great difficulties in achieving precise control over their topology, microstructure, and composition. Especially for the preparation of star brush polymers, their high grafting densities and steric hindrance also bring more challenges. Through the combination of two tactics for preparing star polymers, the diverse strategies employed in synthesizing graft copolymers, and a great variety of controlled/living polymerization techniques, a series of star graft polymers has been obtained. Thanks to the giant size and high compactness of star brush polymers, the unique hierarchical self-organization behavior of these highly branched star polymers will pave the way for their potential use in the fields of drug delivery, bio-catalysis, super soft elastomers, and templates for hybrid nanomaterials, acting as unimolecular micelles.

Synthesis of PPEGMEA-g-PMAA densely grafted double hydrophilic copolymer and its use as a template for the preparation of size-controlled superparamagnetic Fe3O4/polymer nano-composites

A series of well-defined amphiphilic densely grafted copolymers, containing polyacrylate backbone, hydrophobic poly(methoxymethyl methacrylate) and hydrophilic poly(ethylene glycol) side chains, were synthesized by successive atom transfer radical polymerization. Poly[poly(ethylene glycol) methyl ether acrylate] comb copolymer was firstly prepared via the grafting-through strategy. Next, poly[poly(ethylene glycol) methyl ether acrylate]-g-poly(methoxymethyl methacrylate) amphiphilic graft copolymers were synthesized via the grafting-from route. Poly(methoxymethyl methacrylate) side chains were connected to the polyacrylate backbone through stable C–C bonds instead of ester connections. The molecular weights of both the backbone and the side chains were controllable and the molecular weight distributions were in the range 1.38–1.42. Poly(methoxymethyl methacrylate) side chains were selectively hydrolyzed under mild conditions without affecting the polyacrylate backbone to obtain the final product, poly[poly(ethylene glycol) methyl ether acrylate]-g-poly(methacrylic acid) densely grafted double hydrophilic copolymer. Finally, these double hydrophilic copolymers were used as templates to prepare superparamagnetic Fe3O4/polymer nano-composites with narrow size distributions via an in situco-precipitation process, which were characterized by FT-IR, TGA, DLS and X-ray diffraction in detail. The size of the nano-composites can be controlled in a certain range by adjusting the length of the poly(methacrylic acid) side chains and the weight ratio of copolymer to Fe3O4 nano-particle used.

One-step preparation of fluorographene: a highly efficient, low-cost, and large-scale approach of exfoliating fluorographite.

Fluorographene, a cousin of graphene, not only inherits the excellent mechanical properties of graphene but also has great unique application potential in high-performance devices and materials, such as lubricating agents, digital transistors, nanocomposites, and energy-storage devices. However, large-scale preparation of fluorographene remains a great challenge. Herein, an easy-operating, highly scalable, and low-cost approach was reported for the preparation of fluorographene using commercially available fluorographite as the starting material. In this procedure, fluorographite turned into few-layer fluorographene through a rapid exfoliation process with Na2O2 and HSO3Cl as exfoliating agents. The whole preparation process was performed in air and without heating, sonication, and protective gas. The obtained fluorographene was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, (19)F nuclear magnetic resonance spectroscopy, X-ray diffraction, thermogravimetric analysis, atomic force microscopy, and transmission electron microscopy, and it possesses a hexagonal polycrystalline structure. Fluorographene and fluorographite were employed as cathode materials of the primary lithium battery, and it was found that the specific discharge capacity of the battery using fluorographene was improved remarkably compared to that using fluorographite. Cyclic voltammetry results also showed that specific capacitances of fluorographene were dozens of times higher than that of fluorographite. It is clear that electrochemical properties of fluorographene are significantly improved against fluorographite.

tBHBMA: a novel trifunctional acrylic monomer for the convenient synthesis of PAA-g-PCL well-defined amphiphilic graft copolymer

A series of well-defined amphiphilic graft copolymers, consisting of a hydrophilic poly(acrylic acid) (PAA) backbone and hydrophobic poly(e-caprolactone) (PCL) side chains, was synthesized by the combination of reversible addition–fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP). A new acrylate monomer containing a ROP initiation group, tert-butyl(2-((4-hydroxybutanoyloxy)methyl)acrylate), was first prepared using tert-butyl acrylate as the starting material, and it was homopolymerized by RAFT in a controlled way to give a well-defined homopolymer bearing ROP initiation group in every repeating unit. This homopolymer directly initiated ROP of e-caprolactone to provide well-defined poly(tert-butyl acrylate)-g-poly(e-caprolactone) graft copolymers via the grafting-from strategy without post-polymerization functionality transformation. Finally, the hydrophobic poly(tert-butyl acrylate) backbone was selectively hydrolyzed in an acidic environment without affecting the PCL side chains to afford poly(acrylic acid)-g-poly(e-caprolactone) amphiphilic graft copolymers possessing the hydrophilic PAA backbone and equally distributed hydrophobic PCL side chains. The self-assembly behavior of the obtained amphiphilic graft copolymers and pH-sensitivity of the resultant micelles were investigated by fluorescence spectroscopy, DLS, and TEM. DSC and XRD analysis showed the crystallization behavior of poly(acrylic acid)-g-poly(e-caprolactone) graft copolymers.

(PAA-g-PS)-co-PPEGMEMA asymmetric polymer brushes: synthesis, self-assembly, and encapsulating capacity for both hydrophobic and hydrophilic agents

A series of well-defined amphiphilic asymmetric polymer brushes containing hetero side chains, hydrophobic polystyrene (PS) and hydrophilic poly(ethylene glycol) (PEG), was synthesized by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP). The well-defined polyacrylate-based backbones (Mw/Mn ≤ 1.22), PtBBPMA-co-PPEGMEMA, were first prepared by RAFT copolymerization of tert-butyl 2-((2-bromopropanoyloxy)methyl)acrylate (tBBPMA), which bears a Br-containing ATRP initiating group and a poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) macromonomer. The reactivity ratios determined by Fineman–Ross and Kelen–Tudos methods showed that both monomers tended to form random copolymers. The density of the Br-containing ATRP initiating group could be well tuned by the feeding ratio of comonomers. ATRP of styrene was directly initiated by PtBBPMA-co-PPEGMEMA without polymeric functionality transformation to afford well-defined (PtBA-g-PS)-co-PPEGMEMA polymer brushes (Mw/Mn ≤ 1.26) via the grafting-from strategy. The pendant tert-butoxycarbonyls in the backbone were selectively hydrolyzed to carboxyls for providing (PAA-g-PS)-co-PPEGMEMA polymer brushes. Both polymer brushes with the exact same side chains, but different backbones, self-assembled into large compound micelles and bowl-shaped micelles in aqueous media, respectively. This is a direct and strong example to address the importance of the properties of the backbone of a graft copolymer on its self-assembly behavior. Interestingly, different from common spherical micelles, which can just solubilize hydrophobic compounds within their core, the large compound micelles formed by (PtBA-g-PS)-co-PPEGMEMA polymer brushes can encapsulate hydrophilic Rhodamine 6G and hydrophobic pyrene separately or simultaneously.

Synthesis of α-helix-containing PPEGMEA-g-PBLG, well-defined amphiphilic graft copolymer, by sequential SET-LRP and ROP

A series of well-defined polypeptide-based amphiphilic graft copolymers containing hydrophilic poly(poly(ethylene glycol) methyl ether acrylate) (PPEGMEA) backbone and hydrophobic poly(gamma-benzyl-L-glutamate) (PBLG) side chains was synthesized by succes

SET-LRP synthesis of novel polyallene-based well-defined amphiphilic graft copolymers in acetone

A series of polyallene-based well-defined amphiphilic graft copolymers consisting of hydrophobic poly(6-methyl-1,2-heptadiene-4-ol) (PMHDO) backbone and hydrophilic poly(2-(dimethylamino)ethyl acrylate) (PDMAEA) side chains, was synthesized by the combination of living coordination polymerization and single-electron transfer living radical polymerization (SET-LRP). A double-bond-containing PMHDO backbone with pendant hydroxyls was prepared via [(η3-allyl)NiOCOCF3]2-initiated living coordination polymerization of a hydroxyl-containing allene derivative, 6-methyl-1,2-heptadiene-4-ol (MHDO). The pendant hydroxyls in the homopolymer were then treated with 2-chloropropionyl chloride to provide the PMHDO-Cl macroinitiator. Finally, the target PMHDO-g-PDMAEA well-defined graft copolymers were constructed through the grafting-from technique via SET-LRP of 2-(dimethylamino)ethyl acrylate (DMAEA) in acetone, a nonpolar solvent, initiated by the macroinitiator using CuCl/Me6TREN as catalytic system. The narrow molecular weight distributions (Mw/Mn ≤ 1.18) and kinetics experiment showed the controllability of SET-LRP graft copolymerization of DMAEA. The critical micelle concentrations (cmc) of PMHDO-g-PDMAEA amphiphilic graft copolymers in aqueous solution were determined by fluorescence probe technique and the dependence of cmc on pH or salinity were also investigated. Micellar morphologies were visualized using transmission electron microscopy.

The first amphiphilic graft copolymer bearing a hydrophilic poly(2-hydroxylethyl acrylate) backbone synthesized by successive RAFT and ATRP

A series of well-defined amphiphilic graft copolymers consisting of a hydrophilic poly(2-hydroxyethyl acrylate) (PHEA) backbone and hydrophobic polystyrene side chains were synthesized by the combination of reversible addition–fragmentation chain transfer (RAFT) polymerization, atom transfer radical polymerization (ATRP), and the grafting-from strategy. A new acrylate monomer containing an ATRP initiating group, 2-hydroxyethyl 2-[(2-chloropropanoyloxy)methyl]acrylate, was first prepared via a four-step procedure using 2-hydroxyethyl acrylate as a starting material. This monomer was then RAFT homopolymerized to give a PHEA-based homopolymer bearing a Cl-containing ATRP initiating group in every repeating unit with a narrow molecular weight distribution (Mw/Mn = 1.08). This homopolymer directly initiated the ATRP of styrene to afford the desired well-defined poly(2-hydroxyethyl acrylate)-graft-polystyrene graft copolymers (Mw/Mn ≤ 1.30) containing a hydroxyl in every repeating unit of the backbone without polymeric functionality transformation. The self-assembly behavior of the amphiphilic graft copolymers obtained was investigated by dynamic light scattering and transmission electron microscopy.