Post-functionalization Of Polymers Research Articles

Synthesis of Dendronized Polymers on the Au(111) Surface.

Dendronized polymers (DPs) consist of a linear polymeric backbone with dendritic side chains. Fine-tuning of the functional groups in the side chains enriches the structural versatility of the DPs and imparts a variety of novel physical properties. Herein, the first on-surface synthesis of DPs is achieved via the postfunctionalization of polymers on Au(111), in which the surface-confinement-induced planar conformation and chiral configurations were unambiguously characterized. While the dendronized monomer was synthesized in situ on Au(111), the subsequent polymerization afforded only short, cross-linked DP chains owing to multiple side reactions. The postfunctionalization approach selectively produced brominated polyphenylene backbone moieties by the deiodination polymerization of 4-bromo-4″-iodo-5'-(4-iodophenyl)-1,1':3',1″-terphenyl on Au(111), which smoothly underwent divergent cross-coupling reactions with two different isocyanides to form two types of DPs as individual long chains.

Tetracyanobutadienyl-Based Nonlinear Optical Dendronized Hyperbranched Polymer Synthesized via [2+2]Cycloaddition Polymer Postfunctionalization.

Dendronized hyperbranched polymers (DHPs) can provide advantages for both hyperbranched polymers and dendrimers, making them a promising structure platform for high-performance second-order nonlinear optical (NLO) materials. Herein, a new A3 +B2 -type DHP (HP2) is reported through facile and efficient [2+2]cycloaddition polymer postfunctionalization, in which tetracyanobutadienyl-based moieties are introduced as the main chromophores while isophorone-bridged moieties serve as the isolation chromophores. Benefiting from this unique hyperbranched structure design, the measured second-harmonic generation coefficient of HP2 can reach up to 96.6pmV-1 with high thermal stability, making it a good material candidate for second-order NLO applications.

Advanced Surfaces by Anchoring Thin Hydrogel Layers of Functional Polymers

Surface design and engineering is a critical tool to improve the interaction of materials with their surroundings. Immobilization of soft hydrogels is one of the attractive strategies to achieve surface modification. The goal of this review is to provide a comprehensive overview of the different strategies used for surface tethering of hydrogel layers via crosslinking immobilization of pre-fabricated functional polymers. In this strategy, crosslinkable polymers are first prepared via various polymerization techniques or post-functionalization of polymers. Afterwards, the crosslinkable polymers are attached or tethered on the surfaces of substrates using a variety of approaches including photo-crosslinking, click reactions, reversible linkages, etc. For each case, the principles of hydrogel tethering have been explained in detail with representative examples. Moreover, the potential applications of the as-modified substrates in specific cases have also been addressed and overviewed.

Seeing the Light: Advancing Materials Chemistry through Photopolymerization.

The application of photochemistry to polymer and material science has led to the development of complex yet efficient systems for polymerization, polymer post-functionalization, and advanced materials production. Using light to activate chemical reaction pathways in these systems not only leads to exquisite control over reaction dynamics, but also allows complex synthetic protocols to be easily achieved. Compared to polymerization systems mediated by thermal, chemical, or electrochemical means, photoinduced polymerization systems can potentially offer more versatile methods for macromolecular synthesis. We highlight the utility of light as an energy source for mediating photopolymerization, and present some promising examples of systems which are advancing materials production through their exploitation of photochemistry.

Biodegradable brush-type copolymer modified with targeting peptide as a nanoscopic platform for targeting drug delivery to treat castration-resistant prostate cancer

Well-defined amphiphilic tumor-targeting brush-type copolymers, poly(oligo(ethylene glycol) monomethyl ether methacrylate-co-G3-C12)-g-poly(ε-caprolactone) (P(OEGMA-co-G3-C12)-g- PCL), were synthesized by the combination of ring-opening polymerization (ROP), reversible addition-fragmentation transfer (RAFT) polymerization and polymer post-functionalization, in which G3-C12 was castration-resistant prostate cancer (CRPC) targeting peptide. The obtained polymers were then employed for the targeted treatment of CRPC by delivering a hydrophobic anticancer drug (bufalin, BUF). Polymerizable monomer, 3-((2-(methacryloyloxy)ethyl)thio)propanoic acid (BSMA) and PCL-based macromolecular monomer (PCLMA) were synthesized at first. RAFT polymerization of OEGMA, BSMA, and PCLMA afforded amphiphilic brush-type copolymers, P(OEGMA-co-BSMA)-g-PCL. Post-functionalization of the obtained polymers with G3-C12 led to the formation of the final amphiphilic targeting brush-type copolymers, P(OEGMA-co-G3-C12)-g- PCL. In aqueous media, P(OEGMA-co-G3-C12)-g-PCL self-assembles into micelles with a hydrodynamic diameter (Dh) of ∼66.1±0.44nm. It was demonstrated that the obtained micellar nanoparticles exhibited good biocompatibility and biodegradability. Besides, BUF-loaded micellar nanoparticles assembled from P(OEGMA-co-G3-C12)-g-PCL, BUF-NP-(G3-C12), showed a controlled drug release in vitro and improved anticancer efficacy both in vitro and in vivo.

Improving the anticancer activity of α-hederin by physically encapsulating it with targeted micelles assembled from amphiphilic block copolymers

Alfa-hederin (Hed) is regarded as a promising drug in cancer therapy especially in drug-resistant cancers. However, its reduced anticancer activity caused by protein absorption limits its wide clinical applications. The purpose of this study was to develop diblock copolymer-based micelles as an integrated platform for targeted delivery of Hed to overcome its intrinsic drawbacks. Amphiphilic diblock copolymers, poly(epsilon-caprolactone)-b-poly(oligo(ethylene glycol) monomethyl ether methacrylate-co-RGD) (PCL-b-P(OEGMA-co-RGD)) consisting of hydrophobic PCL, hydrophilic POEGMA and targeting peptide (RGD) were fabricated via the combination of ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP), and polymer post-functionalization. Hed-containing targeting micellar nanoparticles, Hed-NP-RGD, were obtained via the co-micellization of PCL-b-P(OEGMA-co-RGD) and Hed, showing hydrodynamic diameter 108 ± 1 nm and zeta potential −4.10 ± 0.15 mV. In vitro experiments demonstrated that Hed-NP-RGD possessed superior anti-proliferative and cellular apoptosis in comparison with that of free Hed possibly due to the assumption that the presence of polymeric micelles protected Hed molecules from absorption by proteins and tumor-targeting effect.

Visible Light Photocatalytic Thiol–Ene Reaction: An Elegant Approach for Fast Polymer Postfunctionalization and Step-Growth Polymerization

An elegant approach for fast polymer postfunctionalization and step-growth polymerization (via addition reaction) under aerobic condition was developed from visible light photocatalytic thiol–ene “click” reaction, employing Ru(bpy)3Cl2 as photoredox catalyst and p-toluidine as redox mediator. The nature of the photoredox catalysts, thiol substrates, and solvents were extensively investigated for this reaction with two types of alkene polymers: polybutadiene and poly(allyl methacrylate)s. The use of N-methyl-2-pyrrolidone as the solvent and p-toluidine as redox mediator remarkably improved the reaction rates and limited the formation of side products. Finally, this highly efficient thiol–ene reaction was employed for the synthesis of polymers by step-growth addition polymerization.

Sequential control over thiol click chemistry by a reversibly photoactivated thiol mechanism of spirothiopyran.

A novel photocontrolled thiol click chemistry based on spirothiopyran and maleimide is reported. Upon irradiation with λ=365 nm light, the spirothiopyran can isomerize to the open merocyanine form, a thiophenolate group, which can rapidly react with maleimide. The unreacted MC will readily isomerize back to the starting spirothiopyran, which can be repeatedly photoactivated as needed. Thus, this reversible photoactivated thiol confers spatiotemporal sequential control on the thiol-maleimide reaction using only one type of photochemical reaction. Polymer post-functionalization and hydrogel building with subsequent multipatterning using different maleimide molecules in a temporal sequential manner indicate that this photocontrolled Michael addition reaction can modulate the specific chemical events in a sequence.

Photoredox catalyst-mediated atom transfer radical addition for polymer functionalization under visible light

A facile method for post-functionalization of polymers with side olefin groups was developed by visible light-mediated atom transfer radical addition (ATRA) employing a photoredox catalyst, fac-Ir(ppy)3.

Facile Synthesis of Thermally Stable Poly(N-vinylpyrrolidone)-Modified Gold Surfaces by Surface-Initiated Atom Transfer Radical Polymerization

Well-controlled polymerization of N-vinylpyrrolidone (NVP) on Au surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP) was carried out at room temperature by a silanization method. Initial attempts to graft poly(N-vinylpyrrolidone) (PVP) layers from initiators attached to alkanethiol monolayers yielded PVP films with thicknesses less than 5 nm. The combined factors of the difficulty in the controllable polymerization of NVP and the instability of alkanethiol monolayers led to the difficulty in the controlled polymerization of NVP on Au surfaces. Therefore, the silanization method was employed to form an adhesion layer for initiator attachment. This method allowed well-defined ATRP polymerization to occur on Au surfaces. Water contact angle, X-ray photoelectron spectroscopy (XPS), and reflectance Fourier transform infrared (reflectance FTIR) spectroscopy were used to characterize the modified surfaces. The PVP-modified gold surface remained stable at 130 °C for 3 h, showing excellent thermal stability. Thus, postfunctionalization of polymer brushes at elevated temperatures is made possible. The silanization method was also applied to modify SPR chips and showed potential applications in biosensors and biochips.

Double click reaction strategies for polymer conjugation and post-functionalization of polymers

Double click reaction strategies, which are a combination of different type of click reactions, allow the preparation of polymers with various topologies and the post-functionalization of polymers, which cannot be easily achieved by using only one click reaction. The most studied click reaction combinations may be listed as the Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC)–Diels–Alder, and the CuAAC–nitroxide radical coupling reactions for polymer–polymer conjugation and the CuAAC–Diels–Alder, or the CuAAC–thiol-ene reactions for post-modification of polymers.

Reactive patterning via post-functionalization of polymer brushes utilizing disuccinimidyl carbonate activation to couple primary amines

Polymer brushes provide an exceptional route to surface functionalization due to their chemical and mechanical robustness, lack of large-area defects, and high density of functional groups. In spite of these benefits, the synthetic difficulty and complex surface structure associated with polymer brushes have hindered their utilization for constructing multifunctional, patterned surfaces. In this contribution we describe the use of a rapid and highly efficient polymer brush post-functionalization technique as a facile method for controlling surface functionality of polymer brushes. Poly(2-hydroxyethyl methacrylate) (PHEMA) brushes are post-functionalized via activation with N,N′-disuccinimidyl carbonate (DSC) and subsequent coupling to molecules containing α-amine moieties. This post-functionalization effectively tailors surface energy resulting in water contact angles ranging from 40° to 100° using different conjugate molecules. Furthermore, the solvent tolerance, insensitivity to reactant concentration, and rapid reaction time of the aminolysis reaction enable surface energy patterning of the polymer brushes through the use of “reactive” soft lithography. Finally, these surface energy patterns could be “developed” by exposure to gold nanoparticle solutions to yield surfaces with patterned nanoparticle density.