Initiator Moiety Research Articles

An anchor for help: a cross-linking moiety for block copolymer membrane stabilization for ultrafiltration applications in water.

Block copolymer membranes are an exciting class of materials used to separate small contaminants from water. Covalent cross-linking of the membrane matrix is one approach to alleviate stability issues, which limit their application nowadays. In the current work, membranes from amphiphilic block copolymers are manufactured and cross-linked using a UV-active radical initiator moiety.

Rapid Characterization of Polymer Materials Using Arc Plasma-Based Dissociation-Mass Spectrometry

Fingerprinting spectra of polymer materials containing information of monomers' molecular weight and detailed structure, constituents, and sequences were obtained by a direct analytical process using arc plasma-based dissociation (APD)-mass spectrometry. The thermal arc plasma generated using a simple arc discharge device induces the dissociation of the polymeric backbone, producing mass spectra with strong regularity within seconds. The molecular weight of the repeating unit was revealed by equal intervals between peak series and protonated monomer ions in the mass spectra. Meanwhile, lots of secondary fragment ions were produced to provide abundant structural information. For polyethers, it is even possible to decipher (read) the "sequence" directly from their spectra. Polymers composed of isomers or only differing in their initiator moieties were easily distinguished with their characteristic APD mass spectra. The spectra were highly reproducible according to the results of similarity calculation. Unlike pyrolysis mass spectrometry, in the APD device, polymers in liquid, solid, powder, and crude samples can be analyzed directly without any pretreatment, and the regular spectra are easier to interpret. Compared with other direct analytical methods, more structural informative spectra can be acquired owing to the high energy, high temperature, and unique chemical reactivity of arc plasma. Thus, this technique is promising to be a valuable tool in rapid elucidation of polymer materials.

Synthesis of uniform polymer microspheres with “living” character using ppm levels of copper catalyst: ARGET atom transfer radical precipitation polymerisation

The first example of activators regenerated by electron transfer atom transfer radical polymerisation (ARGET ATRP) under precipitation polymerisation (PP) conditions is reported. This new method for polymer synthesis (called ARGET ATRPP) requires only very low levels of metal catalyst for success, a distinctive feature that enables the production of uniform polymer microspheres under reversible-deactivation radical polymerisation control. The influence of the polymerisation conditions (monomer concentration, reaction time, initiator and catalyst concentrations) on the polymerisations and microsphere products were investigated and optimised. The ARGET ATRPP methodology was used to prepare polymer microspheres with narrow particle size distributions and mean particle diameters in the micron-size range, under dilute monomer conditions (2%) whilst using very low copper catalyst concentrations (down to 1.7 ppm). The “living” characteristics of the polymer microspheres enabled poly(methyl methacrylate) brushes to be grafted-from the microspheres directly without the need for any additional surface functionalisation step to immobilise initiator moieties.

Preparation and Evaluation of 2 m Long Open Tubular Capillary Columns of 50 μm Internal Diameter for Separation of Peptides in Liquid Chromatography

A 2 m long open tubular column with a copolymer layer fabricated on the inner surface of silica capillary of 50 μm id has been prepared. A ligand with a terminal halogen was bound to the capillary inner surface via silanol-isocyanate reaction and an initiator moiety was introduced by reacting with the terminal halogen. Then a thick layer of linear copolymer chains was generated on the inner surface of capillary by reversible addition-fragmentation transfer polymerization of styrene and N-phenyl acrylamide. The resultant open tubular column exhibited a remarkably high separation efficiency for the separation of a synthetic mixture of five peptides in liquid capillary chromatography (in the pressure mode). The effect of monomer mixing ratio (styrene versus N-phenyl acrylamide) on the chromatographic separation efficiency has been studied. The column prepared with the optimum mixing ratio produced the number of theoretical plates (N) of 391,200 per column under the optimized elution pressure. The column to column repeatability estimated as relative standard deviation in plate count, retention factor, asymmetry factor, and resolution was found better than 3.0%.

Controlled Synthesis of Poly(vinyl ether)-Grafted Poly(phenylacetylene)s by a Combination of Living Coordination Polymerization and Living Cationic Polymerization.

We newly designed a functionalized monomer (PhAVE-AcOH) containing a phenylacetylene (PhA) group and a 1-(acetoxy)ethoxy group, the latter of which is expected to act as an initiator moiety in combination with Lewis acid-based activators under living cationic polymerization conditions. A polyPhA-based multifunctional initiator poly(PhAVE-AcOH) with a narrow molecular weight distribution (Mw/Mn = 1.02) was synthesized by Rh complex-mediated living coordination polymerization of PhAVE-AcOH. Then, living cationic graft polymerization of isobutyl vinyl ether (IBVE) was performed employing the pendant 1-(acetoxy) ethoxy initiating moiety of poly(PhAVE-AcOH) to form polyIBVE-grafted polyPhA(polyPhA-g-polyIBVE), where both the main chain and side chains possessed well-controlled structures (Mw/Mn = 1.05–1.10). We found that UV–vis absorption spectra of polyPhA-g-polyIBVE were progressively redshifted with increasing molecular weights of the graft chain.

Styrene-N-phenylacrylamide co-polymer modified silica monolith particles with an optimized mixing ratio of monomers as a new stationary phase for the separation of peptides in high performance liquid chromatography.

A stationary phase was prepared by chemical derivatization of the support particles with a layer of copolymer composed of styrene and N-phenyl acrylamide. Silica monolith particles of ca. 2.6µm (volume-based average) have been prepared as the support particles by sol-gel reaction followed by differential sedimentation. The particles were reacted with 3-chloropropyl trimethoxysilane followed by sodium diethyldithiocarbamate to introduce an initiator moiety. Then, the copolymer layer was immobilized via reversible addition-fragmentation transfer polymerization. The resultant phase was packed in glass-lined stainless-steel micro-columns (1 x 150mm) and evaluated for the separation of a mixture composed of five peptides (Trp-Gly, Thr-Tyr-Ser, angiotensin I, isotocin and bradykinin). The effect of monomer mixing ratio (styrene versus N-phenyl acrylamide) on the chromatographic separation efficiency of the stationary phase was examined. A number of theoretical plates (N) as high as 33600 plates/column (224000 plates/m, 4.46µm plate height) was achieved using the column packed with the optimized stationary phase. The column-to-column reproducibility based on three columns packed with three different batches of stationary phase was found satisfactory in separation efficiency, retention factor, and asymmetry factor.

Sub-surface initiated atom transfer radical polymerization for robust embedded polymer brushes

In this article, we demonstrate a new methodology—sub-surface initiated atom transfer radical polymerization (sSI-ATRP)–to construct thick and robust sub-surface polymer brushes layer. In this methodology, the haloid initiator moieties are covalently coupled with acrylic polymers, polyurethane, epoxy resin and other materials, and triggered atomic transfer radical polymerization in hydrophilic monomer solutions. In this process, surface-grafted hydrophilic polymer brushes make the surface of the materials hydrophilic and swell so that the monomer solution can contact the initiator embedded in the materails to trigger new ATRP reactions. This process is repeated and a thick polymer brush modified sub-surface layer can form on the substrate finally. In comparison to the conventional surface floated polymer brushes, the embedded polymer brushes give materails better mechanical property that can bear high load in frictional sliding and better chemical stability with longer duration antifouling activity in ocean field.

A degradable atom transfer radical polymerization inimer: Synthesis, polymerization, and cleavage of the resulting polymer products

ABSTRACTA novel degradable inimer for atom transfer radical polymerization (ATRP), 2‐(6‐(2‐((2‐bromo‐2‐methylpropanoyl)oxy)ethyl)pyridin‐2‐yl)ethyl methacrylate (PyDEBrMΑ), was synthesized by the two‐step esterification of 2,6‐pyridinediethanol, first with α‐bromoisobutyryl bromide in order to introduce the initiator moiety, and then with methacryloyl chloride in order to introduce the monomer moiety. PyDEBrMA was subsequently used to initiate the self‐condensing ATRP of methyl methacrylate (MMA) to obtain a hyperbranched MMA homopolymer which could be cleaved at the PyDEBrMA residue either by treatment under mildly alkaline hydrolysis conditions (sodium deuteroxide in d6‐DMSO at room temperature) or thermolysis at 150 °C. The lability of the PyDEBrMA residue arises from the presence in its structure of two 2‐(pyridin‐2‐yl)ethyl ester moieties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2831–2839

Expanding vinyl ether monomer repertoire for ring‐expansion cationic polymerization: Various cyclic polymers with tailored pendant groups

ABSTRACTHerein, we clarified the ring‐expansion cationic polymerization with a cyclic hemiacetal ester (HAE)‐based initiator was versatile in terms of applicable vinyl ether monomers. Although there was a risk that higher reactive vinyl ethers may incur β‐H elimination of the HAE‐based cyclic dormant species to irreversibly give linear chains, the polymerizations were controlled to give corresponding cyclic polymers from various alkyl vinyl ethers of different reactivities. Functional vinyl ether monomers were also available, and for instance a vinyl ether monomer carrying an initiator moiety for metal‐catalyzed living radical polymerization in the pendant allowed construction of ring‐linear graft copolymers through the grafting‐from approach. Furthermore, ring‐based gel was prepared via the addition of divinyl ether at the end of the ring‐expansion polymerization, where multi HAE bonds cyclic polymers or fused rings were crosslinked with each other. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3082–3089

Modification of Silica Nanoparticles with Miktoarm Polymer Brushes via ATRP

Silica nanoparticles were successfully modified with miktoarm brushes via atom transfer radical polymerization (ATRP) using three different approaches. In the first approach: “graft onto and from”, a poly(tert-butyl acrylate) (PtBA) macroinitiator was grafted onto the surface of a monomer-modified silica nanoparticle. Then, polystyrene (PSt) brush was grafted from the surface-tethered reactive chain end. In the second approach: “two-step reverse ATRP”, the PtBA and poly(n-butyl acrylate) (PBA) brushes were consecutively grafted from initiator-modified silica particles via ATRP. The polymerization was initiated from the silica surface via a two-step controlled thermal decomposition of surface-tethered diazo initiator moieties. In the third method: “diblock first”, a diblock copolymer of poly(tert-butyl acrylate) and poly(glycidyl methacrylate) (PtBA-b-PGMA) was grafted onto amine-modified silica particles. The diblock copolymer was covalently attached to the silica surface via interaction between surface-tethered amine groups and the short reactive block containing glycidyl groups. Next, the polystyrene brushes were grafted from surface-tethered reactive chain end. The materials prepared by three different approaches were characterized using gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). The PtBA brushes were hydrolyzed under acidic conditions to form poly(acrylic acid) (PAA) brushes. The resulting materials were imaged using atomic force microscopy (AFM) and transmission electron microscopy (TEM).

Factors Affecting Grafting Density in Surface‐Initiated ATRP: A Simulation Study

In surface‐initiated atom transfer radical polymerization, knowledge of grafting density is of significant interest because it is one of the determining properties of grafted polymer. It is well known that not all of the immobilized initiators can grow into polymer chains. However, little is known about why this happens and what affects the grafting efficiency. The lack of information is partly due to the difficulty in experimental determination of grafting density on flat substrates. To circumvent the problem, Monte Carlo simulation with bond fluctuation model is used in this study to investigate the effects of various reaction conditions on the grafting density. The simulation results show lower grafting density when less deactivator is present. In systems with lower deactivator concentration, the number of monomer added per activation cycle is higher. Coupling this with close proximity of immobilized initiators results in chains initiated at earlier time to shield their neighboring initiator moieties from adding mono­mers, thus lowering the grafting density in such a system. These simulation results also provide an explanation to the seemingly conflicting trend reported in the literatures. image

Can Nonpolar Polyisobutylenes be Measured by Electrospray Ionization Mass Spectrometry? Anion-Attachment Proved to be an Appropriate Method.

Polyisobutylenes (PIBs) with different end-groups including chlorine, exo-olefin, hydroxyl, and methyl prepared from aliphatic and aromatic initiators were studied by electrospray ionization mass spectrometry (ESI-MS). Independently of the end-groups, presence or absence of aromatic initiator moiety, these PIB derivatives were capable of forming adduct ions with NO3 (-) and Cl(-) ions, thus allowing the direct characterization of these compounds in the negative ion mode of ESI-MS. To obtain [PIB + NO3](-) and [PIB + Cl](-) adduct ions with appreciable intensities, addition of polar solvents such as acetone, 2-propanol, or ethanol to the dichloromethane solution of PIBs was necessary. Furthermore, increasing both the polarity (by increasing the acetone content) and the ion-source temperature give rise to enhanced intensities for both [PIB + NO3](-) and [PIB + Cl](-) ions. Energy-dependent collision induced dissociation studies (CID) revealed that increasing the collision voltages resulted in the shift of the apparent molecular masses to higher ones. CID studies also showed that dissociation of the [PIB + Cl](-) ions requires higher collision energy than that of [PIB + NO3](-). In addition, Density Functional Theory calculations were performed to gain insights into the nature of the interactions between the highly non-polar PIB chains and anions NO3 (-) and Cl(-) as well as to determine the zero-point corrected electronic energies for the formation of [PIB + NO3](-) and [PIB + Cl](-) adduct ions.

Phosphazene-Promoted Metal-Free Ring-Opening Polymerization of 1,2-Epoxybutane Initiated by Secondary Amides

The in situ generation of an anionic initiator X– obtained by the deprotonation of various secondary amides with tBuP4 phosphazene base was tested as possible way to initiate the polymerization of 1,2-epoxybutane. The initiation efficiency of different amide-containing molecules was investigated. Particular attention was given to the detection of eventual transfer or side reactions, especially due to nucleophilic attacks on the initiator moiety at the α-chain end. In all cases, the initiation of the polymerization by the amidate anion was effective. And in most cases, the polymerization proceeded in a controlled manner to afford amide end-capped poly(butylene oxide) with narrow molar mass distribution and expected molar masses.

Non-Fouling Biodegradable Poly(ϵ-caprolactone) Nanofibers for Tissue Engineering.

Poly(ϵ-caprolactone) (PCL) nanofibers are very attractive materials for tissue engineering (TE) due to their degradability and structural similarity to the extracellular matrix (ECM). However, upon exposure to biological media, their surface is rapidly fouled by proteins and cells, which may lead to inflammation and foreign body reaction. In this study, an approach for the modification of PCL nanofibers to prevent protein fouling from biological fluids and subsequent cell adhesion is introduced. A biomimetic polydopamine (PDA) layer was deposited on the surface of the PCL nanofibers and four types of antifouling polymer brushes were grown by surface-initiated atom transfer radical polymerization (SI-ATRP) from initiator moieties covalently attached to the PDA layer. Cell adhesion was assessed with mouse embryonic fibroblasts (MEFs). MEFs rapidly adhered and formed cell-matrix adhesions (CMAs) with PCL and PCL-PDA nanofibers. Importantly, the nanofibers modified with antifouling polymer brushes were able to suppress non-specific protein adsorption and thereby cell adhesion.

Open tubular capillary column for the separation of cytochrome C tryptic digest in capillary electrochromatography.

A silica capillary of 50 μm internal diameter and 500 mm length (416 mm effective length) was chemically modified with 4-(trifluoromethoxy) phenyl isocyanate in the presence of dibutyl tin dichloride as catalyst. Sodium diethyl dithiocarbamate was reacted with the terminal halogen of the bound ligand to incorporate the initiator moiety, and in situ polymerization was performed using a monomer mixture of styrene, N-phenylacrylamide, and methacrylic acid. The resultant open tubular capillary column immobilized with the copolymer layer was used for the separation of tryptic digest of cytochrome C in capillary electrochromatography. The sample was well eluted and separated into many components. The elution patterns of tryptic digest of cytochrome C were studied with respect to pH and water content in the mobile phase. This preliminary study demonstrates that open tubular capillary electrochromatography columns with a modified copolymer layer composed of proper nonpolar and polar units fabricated by reversible addition-fragmentation transfer polymerization can be useful as separation media for proteomic analysis.

Direct analysis in real time mass spectrometry (DART-MS) of highly non-polar low molecular weight polyisobutylenes.

Low molecular weight polyisobutylenes (PIB) with chlorine, olefin and succinic acid end-groups were studied using direct analysis in real time mass spectrometry (DART-MS). To facilitate the adduct ion formation under DART conditions, NH4 Cl as an auxiliary reagent was deposited onto the PIB surface. It was found that chlorinated adduct ions of olefin and chlorine telechelic PIBs, i.e. [M + Cl]- up to m/z 1100, and the deprotonated polyisobutylene succinic acid [MH]- were formed as observed in the negative ion mode. In the positive ion mode formation of [M + NH4 ]+ , adduct ions were detected. In the tandem mass (MS/MS) spectra of [M + Cl]- , product ions were absent, suggesting a simple dissociation of the precursor [M + Cl]- into a Cl- ion and a neutral M without fragmentation of the PIB backbones. However, structurally important product ions were produced from the corresponding [M + NH4 ]+ ions, allowing us to obtain valuable information on the arm-length distributions of the PIBs containing aromatic initiator moiety. In addition, a model was developed to interpret the oligomer distributions and the number average molecular weights observed in DART-MS for PIBs and other polymers of low molecular weight. Copyright © 2015 John Wiley & Sons, Ltd.

Electrospray ionization tandem mass spectrometry of the star-shaped propoxylated diethylenetriamine polyols.

The collision-induced dissociation of the protonated five-arm star propoxylated diethylenetriamine polyols was studied under electrospray conditions. Two product ion series were detected because of the cleavage of the C-N bonds in the initiator moiety. No backbone fragmentation of the polyether chains was observed, which allowed to explore the initiation and side-chain propagation process of the oligomers. On the basis of MS/MS spectra, it is probable that the rate of the initiation is larger than that of the chain propagation. The propylene oxide repeat units attach to the five arms with approximately the same probability. Furthermore, it was found that the collision energy necessary to obtain 50% fragmentation (CE50) was linearly dependent on the molecular weight of the polyols.

Robust preparation of core-shell type silica/polymer nanocomposites by using surface-initiated ARGET ATRP

A facile route for covalent functionalization of silica (SiO2) nanoparticles with poly(methyl methacrylate) (PMMA) has been investigated. The surfaces of the SiO2 nanoparticles were treated with 2-bromo-2-methyl-N-[3-(trimethoxysilyl)propyl] propanamide to introduce the initiator moieties on the surface. Subsequently, activators regenerated by using electron transfer atom transfer radical polymerization (ARGET ATRP) of methyl methacrylate were employed for the preparation of SiO2/PMMA nanocomposites with a CuBr2/ N,N,N′, N″,N″-pentamethyldiethylenetriamine catalyst system and a tin(II) 2-ethylhexanoate reducing agent. The modification of SiO2 was confirmed by surface analyses including Fourier transfer infrared spectroscopy and X-ray photoelectron spectroscopy. The morphology of the nanocomposites was investigated by using field-emission scanning electron microscopy and transmission electron microscopy. A thermogravimetric analysis was used to evaluate the thermal properties and the grafting density. The colloidal stability of silica nanoparticles in a common organic solvent was explicitly shown to have been remarkably improved by the grafting process.

Fabrication of 3D Gradient of Polymer Brush Via Bipolar Electrochemical Method

Conducting substrates placed between driving electrodes are polarized by external electric field. When the external electric field is large enough, the substrate can behave as a bipolar electrode (BPE) possessing both anodic and chathodic surfaces with potential gradient. Bipolar electrochemical method is an ideal candidate for creating gradient materials by using its potential gradient. For example, we have reported the use of BPE for the gradient modification of conducting polymer surfaces [1]. In this study, we demonstrate the precise control of electrochemical introduction of small molecules onto BPE using bipolar electrochemistry, and following surface-initiated atom transfer radical polymerization (SI-ATRP) to give polymer-grafted surfaces with density gradient. Bipolar electrolysis and surface analysis; An aqueous solution of 1 mM of 4-(2-hydroxyethyl)phenyldiazonium tetrafluoroborate (for the attachment of phenethylalcohol moiety through cathodic reduction) and 1 mM of hydroquinone (as a sacrificial reagent at anodic oxdation) was used as electrolyte in a setup equipped with a pair of platinum electrodes (20 x 20 mm) as driving electrodes, and ITO electrode (20 x 5 mm) as BPE. After the bipolar electrolysis was conducted, the obtained phenethylalcohol-modified ITO plate were washed with solvents, and subjected into a solution of dichloromethane containing 0.5 M 2-bromoisobutyryl bromide and 0.05 M triethylamine for 3 h to achieve the surface with ATRP initiator. To estimate the contents of the ATRP-initiator on the substrate, the elemental ratio of C, O, N, and Br was calculated by X-ray photoelectron spectroscopy (XPS). The XPS analysis for each position of the initiator-modified substrate showed the gradual increase of bromine contents (derived from initiator moiety) with approaching to the cathodic surface. This result indicates that the electrochemical reactions successfully took place on the BPE, accompanying with the formation of density gradient of ATRP initiator. Moreover, by tuning the parameters such as voltage and reaction time, the steepness of the profile of bromine contents was successfully controlled. SI-ATRP; Surface-initiated polymerization of methyl methacrylate (MMA) was conducted under general conditions of ARGET-ATRP with the ITO substrate prepared above ([MMA]0/[free Initiator]0/[CuBr2]0/[bipyridine]0/[sodium ascorbate]0=1000/1/0.035/3.5/3.5), in the presence of the free initiator to estimate the degree of polymerization of PMMA. The density gradient of the grafted polymer was analyzed by infrared reflection absorption spectroscopy (IR-RAS). IR-RAS results measured at each position showed the gradual increase of absorption derived from PMMA from anodic surface to cathodic surface in a similar manner to the XPS results of the initiator-modified substrate. Thus the fabrication of polymer-grafted surface with density gradient was successfully demonstrated. Finally, the measurement of thickness of the polymer-grafted surface by stylus type surface roughness tester revealed that the thickness was dependent on the density of the initiator modified, showing 3D gradient of the polymer brush. Reference [1] N. Shida, Y. Ishiguro, M. Atobe, T. Fuchigami, S. Inagi, ACS Macro Lett., 2012, 1, 656-659.

Critical Salt Effects in the Swelling Behavior of a Weak Polybasic Brush

The swelling behavior of poly(2-(diethylamino)ethyl methacrylate) (PDEA) brushes in response to changes in solution pH and ionic strength has been investigated. The brushes were synthesized by ARGET ATRP methodology at the silica-aqueous solution interface via two different surface-bound initiator approaches: electrostatically adsorbed cationic macroinitiator and covalently anchored silane-based ATRP initiator moieties. The pH-response of these brushes is studied as a function of the solvated brush thickness in a constant flow regime that elucidates the intrinsic behavior of polymer brushes. In situ ellipsometry equilibrium measurements show the pH-induced brush swelling and collapse transitions are hysteretic in nature. Furthermore, high temporal resolution kinetic studies demonstrate that protonation and solvent ingress during swelling occur much faster than the brush charge neutralization and solvent expulsion during collapse. This hysteresis is attributed to the formation of a dense outer region or skin during collapse that retards solvent egress. Moreover, at a constant pH below its pKa, the PDEA brush exhibited a critical conformational change in the range 0.5-1 mM electrolyte, a range much narrower than predicted by the theory of the osmotic brush regime. This behavior is attributed to the hydrophobicity of the collapsed brush. The swelling and collapse kinetics for this salt-induced transition are nearly identical. This is in contrast to the asymmetry in the rate of the pH-induced response, suggesting an alternative mechanism for the two processes dependent on the nature of the environmental trigger.