Surface-Initiated Group Transfer Polymerization Mediated by Rare Earth Metal Catalysts

A graft-to strategy of poly(vinylphosphonates) on dopazide-coated gold nanoparticles using in situ catalyst activation

A modular synthetic pathway for poly(diethyl vinylphosphonates) grafting-to gold nanoparticles is presented. Utilising an azide-dopamine derivative as nanoparticle coating agent, alkyne-azide click conditions were used to covalently tether the polymer to gold nanoparticles leading to stable and well distributed colloids for different applications.

Design, Synthesis and Actual Applications of the Polymers Containing Acidic P-OH Fragments: Part 2-Sidechain Phosphorus-Containing Polyacids

Macromolecules containing acidic fragments in side-groups—polyacids—occupy a special place among synthetic polymers. Properties and applications of polyacids are directly related to the chemical structure of macromolecules: the nature of the acidic groups, polymer backbone, and spacers between the main chain and acidic groups. The chemical nature of the phosphorus results in the diversity of acidic >P(O)OH fragments in sidechain phosphorus-containing polyacids (PCPAs) that can be derivatives of phosphoric or phosphinic acids. Sidechain PCPAs have many similarities with other polyacids. However, due to the relatively high acidity of −P(O)(OH)2 fragment, bone and mineral affinity, and biocompatibility, sidechain PCPAs have immense potential for diverse applications. Synthetic approaches to sidechain PCPAs also have their own specifics. All these issues are discussed in the present review.

Application of poly(vinylphosphonic acid) modified poly(amidoxime) in uptake of uranium from seawater

To enhance the anti-biofouling properties and adsorption capability of poly(amidoxime) (PAO), vinylphosphonic acid (VPA, CH2[double bond, length as m-dash]CH-PO3H2) was polymerized on poly(acrylonitrile) (PAN) surface by plasma technique, followed by amidoximation treatment to convert the cyano group (-C[triple bond, length as m-dash]N) into an amidoxime group (AO, -C(NH2)[double bond, length as m-dash]N-OH). The obtained poly(vinylphosphonic acid)/PAO (PVPA/PAO) was used as an adsorbent in the uptake of U(vi) from seawater. The effect of environmental conditions on the anti-biofouling property and adsorption capability of PVPA/PAO for U(vi) were studied. Results show that the modified PVPA enhances the anti-biofouling properties and adsorption capability of PAO for U(vi). The adsorption process is well described by the pseudo-second-order kinetic model and reached equilibrium in 24 h. Adsorption isotherms of U(vi) on PVPA/PAO can be well fitted by the Langmuir model, and the maximum adsorption capability was calculated to be 145 mg g-1 at pH 8.2 and 298 K. Experimental results highlight the application of PVPA/PAO in the extraction of U(vi) from seawater.

Allyl group-containing polyvinylphosphonates as a flexible platform for the selective introduction of functional groups via polymer-analogous transformations

Polyvinylphosphonates are highly promising candidates for (bio)medical applications as they exhibit a tunable lower critical solution temperature, high biocompatibility of homo- and copolymers, and a broad foundation for post-synthetic modifications. In this work we explored polymer-analogous transformations with statistical polyvinylphosphonates comprising diethyl vinylphosphonate (DEVP) and diallyl vinylphosphonate (DAlVP). The C[double bond, length as m-dash]C double bonds were used as a starting point for a cascade of organic transformations. Initially, the reactive moieties were successfully introduced via bromination, epoxidations with OXONE and mCPBA, or thiol-ene click chemistry with methyl thioglycolate (6). The obtained substrates were then employed in a variety of consecutive reactions depending on the introduced functional motif: (1) the brominated substrates were converted with sodium azide to enable the copper-mediated alkyne-azide coupling with phenylacetylene (1). (2) The epoxides were reacted with sodium azide for an alkyne-azide click coupling with 1 as well as small nucleophilic compounds (phenol (2), benzylamine (3), and 4-amino-2,1,3-benzothiadiazol (4)). Afterwards the non-converted allyl groups were reacted with thiochloesterol (5) to form complex polymer conjugates. (3) An acid-labile hydrazone-linked conjugate was formed in a two-step approach. The polymeric substrates were characterized by NMR, FTIR, and UV/Vis spectroscopy as well as elemental analysis and gel permeation chromatography to monitor the structural changes of the polymeric substrates and to prove the success of these modification approaches.

Brush-like polymers: design, synthesis and applications

With the development of controlled polymerisation, almost all polymerisation strategies have been successfully transplanted to surface-initiated polymerisation. The resulting polymer brushes have emerged as an effective tool for surface functionalization and modulation of the surface properties of materials. To meet various demands it is possible to tailor a material surface with polymer brushes that have diverse dimensionalities, morphologies and compositions. The crowded environment within polymer brushes as well as the stretched conformation of polymer chains sometimes provide unique physicochemical properties, which lead to the delicate creation of inorganic-organic hybridised nanostructures, anti-fouling coatings, biomedical carriers, and materials for use in lubrication, photonics and energy storage. So far, challenges remain in the high-precision synthesis and topological control needed to realize extended applications of polymer brushes. In this Feature Article, we highlight the topology, potential application prospects and various synthetic protocols, particularly for recently established methods, for the efficient synthesis of polymer brushes, as well as their benefits and limitations.

Surface-Mediated Construction of an Ultrathin Free-Standing Covalent Organic Framework Membrane for Efficient Proton Conduction

As a new class of crystalline porous organic materials, covalent organic frameworks (COFs) have attracted considerable attention for proton conduction owing to their regular channels and tailored functionality. However, most COFs are insoluble and unprocessable, which makes membrane preparation for practical use a challenge. In this study, we used surface-initiated condensation polymerization of a trialdehyde and a phenylenediamine for the synthesis of sulfonic COF (SCOF) coatings. The COF layer thickness could be finely tuned from 10 to 100 nm by controlling the polymerization time. Moreover, free-standing COF membranes were obtained by sacrificing the bridging layer without any decomposition of the COF structure. Benefiting from the abundant sulfonic acid groups in the COF channels, the proton conductivity of the SCOF membrane reached 0.54 S cm^-1 at 80 °C in pure water. To our knowledge, this is one of the highest values for a pristine COF membrane in the absence of additional additives.

C–H Bond Activation of Silyl-Substituted Pyridines with Bis(Phenolate)Yttrium Catalysts as a Facile Tool towards Hydroxyl-Terminated Michael-Type Polymers

Herein, silicon-protected, ortho-methylated hydroxy-pyridines were reported as initiators in 2-aminoalkoxy-bis(phenolate)yttrium complexes for rare earth metal-mediated group-transfer polymerization (REM-GTP) of Michael-type monomers. To introduce these initiators, C−H bond activation was performed by reacting [(ONOO)tBuY(X)(thf)] (X = CH2TMS, thf = tetrahydrofuran) with tert-butyl-dimethyl-silyl-functionalized α-methylpyridine to obtain the complex [(ONOOtBuY(X)(thf)] (X = 4-(4′-(((tert-butyldimethylsilyl)oxy)methyl)phenyl)-2,6-di-methylpyridine). These initiators served as functional end-groups in polymers produced via REM-GTP. In this contribution, homopolymers of 2-vinylpyridine (2VP) and diethyl vinyl phosphonate (DEVP) were produced. Activity studies and end-group analysis via mass spectrometry, size-exclusion chromatography (SEC) and NMR spectroscopy were performed to reveal the initiator efficiency, the catalyst activity towards both monomers as well as the initiation mechanism of this initiator in contrast to commonly used alkyl initiators. In addition, 2D NMR studies were used to further confirm the end-group integrity of the polymers. For all polymers, different deprotection routes were evaluated to obtain hydroxyl-terminated poly(2-vinylpyridine) (P2VP) and poly(diethyl vinyl phosphonate) (PDEVP). Such hydroxyl groups bear the potential to act as anchoring points for small bioactive molecules, for post-polymerization functionalization or as macroinitiators for further polymerizations.

Lewis Pair-Mediated Surface-Initiated Polymerization

We present the first example of surface-initiated polymerization mediated by Lewis pairs for the synthesis of polymer brushes on planar substrates. The method enables the rapid grafting polymerization from the self-assembled monolayer or surface-attached macroinitiators, furnishing linear polymer brushes and bottle-brush brushes. Both homopolyester and block copolyester brushes can be synthesized via this versatile approach. This work not only opens up new opportunities for the application of Lewis pair-mediated polymerization but also enriches the surface-initiated polymerization on different surfaces.

Metal-Catalyzed Group-Transfer Polymerization: A Versatile Tool for Tailor-Made Functional (Co)Polymers

Accommodating the increasing demand for tailor-made polymers is a major goal in polymer chemistry. Therefore, the investigation of polymerization techniques, which allow the precise synthesis of macromolecules is of exceptional interest. Ionic or controlled radical polymerization are capable living-type methods for the generation of uniform polymers. However, even these approaches reach their limits in certain issues. In the last decades, group-transfer polymerization (GTP) and especially metal-catalyzed GTP have proven to give access to a plethora of tailor-made homo- and copolymers based on α,β-unsaturated monomers. Thereby, GTP has established its potential in the development of functional and smart polymers. This concept article highlights the most significant progress in metal-catalyzed GTP with a focus on functional (co)polymers including different polymeric architectures and microstructures.

Direct functionalization of cellulose nanocrystals with polymer brushes via UV-induced polymerization: access to novel heterogeneous visible-light photocatalysts

An efficient and facile strategy for the preparation of polymer brushes on cellulose nanocrystals via photopolymerization is reported.

Ultrathin free-standing polymer membranes with chemically responsive luminescence via consecutive photopolymerizations

A facile and general strategy for the preparation of chemically responsive ultrathin free-standing polymer membranes is demonstrated via UV-induced photopolymerizations.

Preparation of core–shell attapulgite particles by redox-initiated surface reversible addition–fragmentation chain transfer polymerization via a “graft from” approach

Polymethyl methacrylate layer was grown uniformly from attapulgite by using surface-initiated reversible addition–fragmentation chain transfer polymerization via redox initiation system.

Bypassing the lack of reactivity of endo-substituted norbornenes with the catalytic rectification-insertion mechanism

The novel rectification–insertion mechanism for the polymerization of polar norbornenes: making alternating copolymers from a single monomer.

The catalytic 1,2-insertion polymerization of polar norbornenes (NBEs) leads to the formation of functional rigid macromolecules with exceptional thermal, optical and mechanical properties. However, this remarkable reaction is plagued by the low reactivity of the polar monomers, and most notably of those bearing a functional group in endo position. We have examined the polymerization mechanism of NBEs bearing one or two CO₂Me groups either in exo or endo position catalyzed by the so-called naked allyl Pd⁺ SbF₆^– catalyst (1). Although endo dimethyl ester of 5-norbornene-2,3-dicarboxylic acid (NBE(CO₂Me)₂) is polymerized by 1, two endo units are never inserted consecutively along the polymer chain. Indeed, 1 is a tandem catalyst which not only catalyzes the insertion of the monomer but also the isomerization of endo and exo isomers. Thus, the polymerization of endo monomers proceeds via a novel mechanism, coined rectification–insertion mechanism, whereby half of the endo monomers are rectified into exo ones prior insertion, leading to the formation of an alternating endo–exo copolymer using an endo only feedstock. With this mechanism, the lack of reactivity of endo norbornenes is bypassed, and the polymerization of predominantly endo polar NBEs bearing a variety of functionalities such as esters, imides, acids, aldehydes, alcohols, anhydrides, or alkyl bromides proceeds with catalyst loadings as low as 0.002 mol%.

Self-assembly of nano/micro-structured Fe3O4 microspheres among 3D rGO/CNTs hierarchical networks with superior lithium storage performances

Nano/micro-structured Fe3O4 microspheres among three-dimensional (3D) reduced graphene oxide (rGO)/carbon nanotubes (CNTs) hierarchical networks (the ternary composite is denoted as rGCFs) have been synthesized using a facile, self-assembled and one-pot hydrothermal approach. The rGCFs composite exhibits superior lithium storage performances: initial discharge and charge capacities of 1452 and 1036 mAh g(-1), respectively, remarkable rate capability at current densities from 100 mA g(-1) to 10 A g(-1) and outstanding cycling performance up to 200 cycles. The highly enhanced electrochemical performances of rGCFs depend heavily on the robust 3D rGO/CNTs hierarchical networks, the stable nano/microstructures of active Fe3O4 microspheres and the positive synergistic effects of building components. The systematic structure characterizations and electrochemical investigations provide insightful understanding towards the relationship between structure/morphology and lithium storage performances, which may pave the way for the rational design of composite materials with desirable goals.

Surface coordination polymerization of ethylene by hydrozirconation-immobilized metallocene

Hydrozirconation on vinyl-terminated substrates (silicon wafer and nanosilica sphere) is employed as an efficient way for immobilization of zirconocene catalyst through Zr-C bonds, which is applied in surface coordination ethylene polymerization producing surface-tethered polyethylene (PE). The formation of Zr-C σ bond induced by hydrozirconation provides an initiator precursor for growing a layer of PE covalently linked onto substrates. The results from SEM, AFM, and TEM show that the surface polymerization is controlled by hydrozirconation. Surface pattern or core-shell structure with crystalline PE coating can be formed, when silicon wafer is selectively functionalized with vinyl-groups or vinyl-modified nanosilica is applied. It is believed that hydrozirconation for the synthesis of zirconocene initiator can be a versatile route to prepare polyolefin hybrid materials.

Rare earth metal-mediated group-transfer polymerization: from defined polymer microstructures to high-precision nano-scaled objects

Poly(2-isopropenyl-2-oxazoline) (PIPOx) and poly(2-vinylpyridine) (P2VP) have been efficiently synthesized using bis(cyclopentadienyl)methylytterbium (Cp2YbMe) as catalyst. The polymerizations of 2-isopropenyl-2-oxazoline (IPOx) and 2-vinylpyridine (2VP) follow a living group-transfer polymerization (GTP) mechanism, allowing a precise molecular-weight control of both polymers with very narrow molecular-weight distribution. The GTP of IPOx and 2VP occurs via N coordination at the rare earth metal center, which has rarely been reported previously. The relative coordination strength of different monomers at the ytterbium center is determined by copolymerization investigations to be in the order of DEVP > MMA > IPOx > 2VP. In combination with living cationic ring-opening polymerization, PIPOx is converted to molecular brushes with defined backbone and poly(2-oxazoline) side chains using the grafting-from method.