This work was supported by start-up funding from Virginia Polytechnic Institute and State University. Q.F. acknowledges support from National Natural Science Foundation of China (21504047), Natural Science Foundation of Jiangsu Province (BK20150834), Nanjing University of Posts and Telecommunications Scientific Foundation NUPTSF (NY214179).

Caution: Please consult all relevant materials safety data sheets (MSDS) before use. Many chemicals used in the synthesis are acutely toxic and carcinogenic. Please use all appropriate safety practices when performing reaction including the use of engineering controls (fume hood and glovebox) and personal protective equipment (safety glasses, gloves, lab coat, full-length pants, closed-toe shoes, blue-light blocking safety goggles). Following procedures involve standard air-free handling techniques in a glove box. All solutions are transferred using pipette.
1. Preparation of Catalyst and Initiator
NOTE: The whole process is conducted in a glove box with a cold trap. All chemicals are dried or purified before moving into the box.13 All vials and glassware are dried and heated in the oven before moving into the box.
<ol>
	<li>Preparation of (bpy)Ni(COD) solution 
	NOTE: (bpy)Ni(COD) should be freshly prepared in situ. It should be stored in the glove box freezer (-35 &#176;C) and used within one week. All other catalysts and initiator solutions can be stored in the glove box freezer over 1 month.
	<ol>
		<li>Weigh Ni(COD)2 (3.5 mg, 12.7 &#181;mol, 1.0 eq) into a 7-mL scintillation vial.</li>
		<li>Weigh 2,2&#8242;-bipyridine (5.9 mg, 37.8 &#181;mol) into a 7-mL scintillation vial.</li>
		<li>Dissolve the 2,2&#8242;-bipyridine in 1 mL of anhydrous tetrahydrofuran (THF).</li>
		<li>Add resulting 2,2&#8242;-bipyridine solution (337 &#181;L) into the vial containing Ni(COD)2.</li>
		<li>Dilute the mixture in 1 mL of anhydrous THF.</li>
		<li>Cap the vial and place the reaction mixture at room temperature for 2 h. 
		NOTE: Ni(COD)2 is not soluble in THF, whereas (bpy)Ni(COD) is soluble in THF. There should be no precipitation in the purple solution after 2 h.</li>
		<li>Store the (bpy)Ni(COD) in the -35 &#176;C freezer.</li>
	</ol>
	</li>
	<li>Preparation of Zn(HMDS)2 solution
	<ol>
		<li>Add Zn(HMDS)2 (3.3 mg, 4 &#181;L, 8.5 &#181;mol) to a 7-mL scintillation vial.</li>
		<li>Dissolve the Zn(HMDS)2 in 1 mL of anhydrous THF.</li>
		<li>Store Zn(HMDS)2 solution in the -35 &#176;C freezer.</li>
	</ol>
	</li>
	<li>Preparation of BnOH solution
	<ol>
		<li>Add BnOH (4.0 mg, 4 &#181;L, 37.0 &#181;mol) to a 7-mL scintillation vial.</li>
		<li>Dissolve the BnOH in 4 mL of anhydrous THF.</li>
		<li>Store the BnOH solution in the -35 &#176;C freezer.</li>
	</ol>
	</li>
	<li>Preparation of Ir-1 solution
	<ol>
		<li>Turn off the glove box light. 
		Caution: It is necessary to turn off the glove box light to avoid deactivation of Ir-1 before polymerization.</li>
		<li>Add Ir-1 (2.9 mg, 2.6 &#181;mol) to a 7-mL scintillation vial.</li>
		<li>Dissolve the Ir-1 in 3 mL of anhydrous THF.</li>
		<li>Store the Ir-1 solution in the -35 &#176;C freezer.</li>
	</ol>
	</li>
</ol>
2. Photoredox ring-opening polymerization of l-1
NOTE: The whole process is conducted in a glove box with a cold trap. All OCA monomers are recrystallized in the glove box before use.13 Here we give the example of the polymerization at DP=500 ([l -1]/[(bpy)Ni(COD)]/[Zn(HMDS)2]/[BnOH]/[Ir-1] = 500/1/1/1/0.1). Polymers at different DPs can also be prepared by adjusting the monomer mass accordingly.
<ol>
	<li>Preparation of l-1 solution for polymerization
	<ol>
		<li>Add l-1 (72.2 mg, 375.7 &#181;mol) to a 7-mL scintillation vial.</li>
		<li>Dissolve the l-1 in 722 &#181;L of anhydrous THF.</li>
		<li>Add 200 &#181;L of l-1 solution into another 7-mL scintillation vial equipped with a stir bar.</li>
		<li>Add 100 &#181;L of anhydrous THF into the 7-mL scintillation vial.</li>
		<li>Cap the vial and place the l-1 solution in the cold trap.</li>
		<li>Turn off the glove box light. 
		Caution: It is necessary to turn off the glove box light to avoid deactivation of Ir-1 before polymerization.</li>
	</ol>
	</li>
	<li>Cooling down the cold trap
	<ol>
		<li>Inside the box, put a thermometer into the cold trap.</li>
		<li>Outside of the box, add ca. 500 mL of ethanol into the dewar flask.</li>
		<li>Add liquid nitrogen into the dewar flask.</li>
		<li>Load the KGW dewar flask to the cold trap.</li>
		<li>Cool the cold trap to -50 &#176;C.</li>
		<li>Put a stir plate underneath the cold trap (see Figure 1).</li>
	</ol>
	</li>
	<li>Perform the photoredox ring-opening polymerization 
	NOTE: Before starting the polymerization, place safety goggles that block blue light within reach. All catalyst system solutions are immediately taken out from the freezer and added successively into the 7-mL scintillation vial containing 20 mg of l-1 without pause or disruption over 30 s.
	<ol>
		<li>Add (bpy)Ni(COD) solution (16.4 &#181;L, 0.208 &#181;mol) into the 7-mL scintillation vial containing l-1 (prepared in 2.1).</li>
		<li>Add Zn(HMDS)2 solution (24.4 &#181;L, 0.208 &#181;mol) into the vial.</li>
		<li>Add BnOH solution (22.5 &#181;L, 0.208 &#181;mol) into the vial.</li>
		<li>Add Ir-1 solution (24.2 &#181;L, 0.0208 &#181;mol) into the vial and cap the vial.</li>
		<li>Wear safety goggles blocking blue LED light. 
		Caution: As blue LED light with a relative high intensity is used, wear safety goggles during the whole process.</li>
		<li>Turn on the blue LED light (34 W) and the fan to dissipate the heat generated by the LED light. Direct the light towards the vial in the cold trap. (Figure 1)</li>
		<li>Turn on the stirrer.</li>
		<li>Cover the cold trap with aluminum foil.</li>
		<li>Keep the reaction temperature at -15 &#177; 5 &#176;C and add liquid nitrogen every 15-20 minutes. 
		NOTE: The maintenance of reaction temperature is important for polymerization and MW control.</li>
	</ol>
	</li>
</ol>
3. Monitor the monomer conversion by Fourier-transform infrared spectra
NOTE: Fourier-transform infrared spectra (FTIR) are recorded on an FT-IR spectrometer equipped with Diamond ATR and Transmission sampling accessory.
<ol>
	<li>At specific time points, add a small aliquot of polymer solution (20 &#181;L) into a 7-mL scintillation vial, and capped.</li>
	<li>Remove the vial out of the glove box.</li>
	<li>Immediately drop the solution (3 &#181;L) onto the FTIR-ATR diamond sampler. The solution forms a film within 10 s for the spectrum measurement.</li>
	<li>Measure the FTIR spectrum of the sample. 
	NOTE: The monomer conversion was determined by the intensity ratio between 1760 cm-1 and 1805s cm-1: conversion% = I1760/(I1760 + I1805) (Representative results in Figure 2). Generally, the polymerization takes about 1-8 h for DP ranging from 200 to 1000 (detailed kinetics are discussed in reference 13).</li>
</ol>
4. The measurement of polymer&#39;s molecular weight by gel-permeation chromatography
NOTE: Gel-permeation chromatography (GPC) experiments are performed on a system equipped with an isocratic pump with degasser, multiangle laser light scattering (MALS) detector (GaAs 30 mW laser at &#955; = 690 nm), and differential refractive index (DRI) detector with a 690-nm light source. Separations are performed using serially connected size exclusion columns (100 &#197;, 500 &#197;, 103 &#197;, and 104 &#197; columns, 5 &#181;m, 300 &#215; 4.6 mm) at 35 &#176;C using THF as the mobile phase at a flow rate of 0.35 mL/min. The polymer molecular weight (MW) and molecular weight distribution (&#208;) are determined using the Zimm model fit of MALS-DRI data. The presence of metal complex in the polymer does not affect the GPC measurement results.
<ol>
	<li>Remove a small aliquot of polymer solution (50 &#181;L) out of the glove box.</li>
	<li>Add 100 &#181;L of THF into the vial.</li>
	<li>Inject the sample into the GPC sampler.</li>
	<li>Analyze the result once the GPC run is completed. 
	NOTE: The polymer should be monodispersed with narrow &#272; (Representative results in Figure 3). The polymer (20 mg) can be dried and washed by 1 mL diethyl ether containing 1% HOAc and 1 mL methanol, which can remove 87% of Ni and 50% of Zn complexes, determined by inductively coupled plasma mass spectrometry (ICP-MS).</li>
</ol>

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The authors declare no competing financial interests. A provisional patent (U.S. Patent Application No: 62/414,016) has been filed pertaining to the results presented in this paper.

The critical step within the protocol is maintaining the reaction temperature at -15 &#177; 5 &#176;C. All catalysts solutions and OCA monomers have to be stored in a glove box freezer at -35 &#176;C before the polymerization. The reaction vials have to be pre-cooled in the cold trap. During the reaction, because the LED light dissipates heat, it is necessary to monitor the reaction every 15 - 20 minutes. Once the temperature is raised up to -10 &#176;C, liquid nitrogen should be added into the dewar to cool the trap. Th...

Poly(&#945;-hydroxy acid) (PAHA) is an important class of biodegradable and biocompatible polymers with applications ranging from biomedical devices to packaging materials.1,2 Although PAHAs can be prepared directly by polycondensation of &#945;-hydroxy acids, the molecular weights (MWs) of the resulting PAHAs are generally low.3 Ring-opening polymerization (ROP) of lactones (e.g., lactide and glycolide) is an alternative synthetic approach that provides the better control on MWs and molecular weight distribution (&#272;) than polycondensation. However, the lack of side-chain functionality in PAHAs and in lactones limit the diversity of physical and chemical properties and their applications.4,5 Since 2006, 1,3-dioxolane-2,4-diones, so-called O-carboxyanhydrides (OCAs), which can be prepared with a rich variety of side-chain functionalities,6,7,8,9,10,11,12,13 have emerged as an alternative class of highly active monomers for polyester polymerization.14,15
Catalytic systems for the ROP of OCAs can be categorized into organocatalysts,8,12,16,17 organometallic catalysts12,18,19,20,21 and biocatalysts.22 Generally, the ROP of OCAs promoted by organocatalyst proceeds in a more or less uncontrolled manner, such as epimerization (i.e., lack of stereoregularity) for OCAs bearing electron-withdrawing groups,8,17 unpredictable MWs, or slow polymerization kinetics.13 To address these problems, an active Zn-alkoxide complex was developed for the ROP of OCAs.12 Well-controlled ROPs were achieved at a low degree of polymerization (DP) without epimerization. However, this Zn-alkoxide catalyst cannot efficiently produce polymers with a high degree of polymerization (DP &#8805; 300).13
We have recently reported a promising approach that greatly improves customizability and efficiency of PAHA synthesis (Figure 1).13 We merge photoredox Ni/Ir catalysts that promote OCA decarboxylation with zinc alkoxide to mediate ring-opening polymerization of OCAs. The use of low temperature (-15 &#176;C) and photoredox Ni/Ir catalysis synergistically accelerates ring-opening and decarboxylation of OCA for chain propagation while avoiding undesired side reactions, e.g., the formation of Ni-carbonyl.23,24 Upon transmetalation with Ni complex the active Zn-alkoxide is located at chain terminus for chain propagation.13
In this protocol, we add fresh prepared (bpy)Ni(COD) (bpy = 2,2&#39;-bipyridyl, COD = 1,5-cyclooctadiene), Zn(HMDS)2 (HMDS = hexamethyldisilazane),25 benzyl alcohol (BnOH) and Ir[dF(CF3)ppy]2(dtbbpy)PF6 (Ir-1, dF(CF3)ppy = 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine, dtbbpy = 4,4&#39;-di-tert-butyl-2,2&#39;-bipyridine) into the monomer l-1 solution26 in a glove box with a cold trap, in the presence of a blue LED light (400-500 nm) and a fan to maintain temperature (Figure 1). The temperature is kept at -15 &#176;C &#177; 5 &#176;C during the polymerization. The conversion of OCA is monitored by Fourier-transform infrared spectroscopy. The resulting polymer MWs and &#272;s is characterized by a gel permeation chromatography (GPC). The homodecoupling 1H NMR study determines whether the obtained polymer is isotactic or not. As most chemicals are highly sensitive to moisture, the detailed video protocol is intended to help new practitioners avoid pitfalls associated with the photoredox ROP of OCAs.

<table>
	<tbody>
		<tr>
			<td>Ni(COD)2</td>
			<td>Strem</td>
			<td>28-0010</td>
			<td>Stored in the glove box freezer.</td>
		</tr>
		<tr>
			<td>2,2&#8242;-bipyridine</td>
			<td>Strem</td>
			<td>07-0290</td>
			<td>Stored in the glove box freezer.</td>
		</tr>
		<tr>
			<td>Zn(HMDS)2</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Synthesized following reported procedures.25 Stored in the glove box freezer.</td>
		</tr>
		<tr>
			<td>Benzyl alcohol</td>
			<td>Sigma-Aldrich</td>
			<td>402834</td>
			<td>Stored with 4&#197; molecular sieve</td>
		</tr>
		<tr>
			<td>Ir[dF(CF3)ppy]2(dtbbpy)PF6</td>
			<td>Strem</td>
			<td>77-0425</td>
			<td>Stored in the glove box freezer.</td>
		</tr>
		<tr>
			<td>THF</td>
			<td>Sigma-Aldrich</td>
			<td>34865</td>
			<td>Dried by alumina columns and stored with 4&#197; molecular sieve in the dark bottle in the glove box.</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Sigma-Aldrich</td>
			<td>793175</td>
			<td></td>
		</tr>
		<tr>
			<td>GPC with an isocratic pump</td>
			<td>Agilent</td>
			<td>Agilent 1260 series</td>
			<td></td>
		</tr>
		<tr>
			<td>Dawn Heleos II Light Scatterer</td>
			<td>Wyatt</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Optilab rEX differential refractive index detector</td>
			<td>Wyatt</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Size exclusion columns</td>
			<td>Phenomenex</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glass Scintillation Vials - 7 ml</td>
			<td>VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>FTIR spectrometer</td>
			<td>Agilent</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Stir bars</td>
			<td>VWR</td>
			<td>58948-091</td>
			<td></td>
		</tr>
		<tr>
			<td>Balance</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Glove box</td>
			<td>Mbraun</td>
			<td>Labstar Pro</td>
			<td></td>
		</tr>
	</tbody>
</table>

controlled photoredox ring-opening polymerization of o-carboxyanhydrides mediated by ni/zn complexes

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, allowing for the synthesis of isotactic poly(&#945;-hydroxy acids) with expected molecular weights (&#62;140 kDa) and narrow molecular weight distributions (Mw/Mn &#60; 1.1). This ring-opening polymerization is mediated by Ni and Zn complexes in the presence of an alcohol initiator and a photoredox Ir catalyst, irradiated by a blue LED (400 - 500 nm). The polymerization is performed at a low temperature (-15 &#176;C) to avoid undesired side reactions. The complete monomer consumption can be achieved within 4 - 8 hours, providing a polymer close to the expected molecular weight with narrow molecular weight distribution. The resulted number-average molecular weight shows a linear correlation with the degree of polymerization up to 1000. The homodecoupling 1H NMR study confirms that the obtained polymer is isotactic without epimerization. This polymerization reported herein offers a strategy for achieving rapid, controlled O-carboxyanhydrides polymerization to prepare stereoregular poly(&#945;-hydroxy acids) and its copolymers bearing various functional side-chain groups.

The conversion of OCA is monitored by Fourier-transform infrared spectroscopy, as shown in Figure 2. The peak at 1805 cm-1 is assigned as the anhydride bond stretch in OCA; the peak at 1760 cm-1 corresponds to the formation of the ester bond in the polymer. Once the monomer&#39;s peak at 1805 cm-1 completely disappears, the polymerization is finished.
The MW and ...

Watch this Scientific Journal Video about Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes at JoVE.com

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

A protocol for the controlled photoredox ring-opening polymerization of O-carboxyanhydrides mediated by Ni/Zn complexes is presented.

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, ...

controlled-photoredox-ring-opening-polymerization-o-carboxyanhydrides

Universidad de Cartagena UDEC

Research

JoVE Journal

Chemistry

8.0K Views.  Nanjing University of Posts and Telecommunications. A protocol for the controlled photoredox ring-opening polymerization of O-carboxyanhydrides mediated by Ni/Zn complexes is presented.

Video: Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies

Physical interactions among the lipid-embedded alpha-helical domains of membrane proteins play a crucial role in folding and assembly of membrane protein complexes and in dynamic processes such as transmembrane (TM) signaling and regulation of cell-surface protein levels. Understanding the structural features driving the association of particular sequences requires sophisticated biophysical and biochemical analyses of TM peptide complexes. However, the extreme hydrophobicity of TM domains makes them very difficult to manipulate using standard peptide chemistry techniques, and production of suitable study material often proves prohibitively challenging. Identifying conditions under which peptides can adopt stable helical conformations and form complexes spontaneously adds a further level of difficulty. Here we present a procedure for the production of homo- or hetero-dimeric TM peptide complexes from materials that are expressed in E. coli, thus allowing incorporation of stable isotope labels for nuclear magnetic resonance (NMR) or non-natural amino acids for other applications relatively inexpensively. The key innovation in this method is that TM complexes are produced and purified as covalently associated (disulfide-crosslinked) assemblies that can form stable, stoichiometric and homogeneous structures when reconstituted into detergent, lipid or other membrane-mimetic materials. We also present carefully optimized procedures for expression and purification that are equally applicable whether producing single TM domains or crosslinked complexes and provide advice for adapting these methods to new TM sequences.

Biophysical and biochemical studies of interactions among membrane-embedded protein domains face many technical challenges, the first of which is obtaining appropriate study material. This article describes a protocol for producing and purifying disulfide-stabilized transmembrane peptide complexes that are suitable for structural analysis by solution nuclear magnetic resonance (NMR) and other analytical applications.

Physical  interactions among the lipid-embedded alpha-helical domains of membrane  proteins play a crucial role in folding and assembly of membrane ...

Anticancer Metal Complexes: Synthesis and Cytotoxicity Evaluation by the MTT Assay

Titanium (IV) and vanadium (V) complexes are highly potent anticancer agents. A challenge in their synthesis refers to their hydrolytic instability; therefore their preparation should be conducted under an inert atmosphere. Evaluation of the anticancer activity of these complexes can be achieved by the MTT assay.
The MTT assay is a colorimetric viability assay based on enzymatic reduction of the MTT molecule to formazan when it is exposed to viable cells. The outcome of the reduction is a color change of the MTT molecule. Absorbance measurements relative to a control determine the percentage of remaining viable cancer cells following their treatment with varying concentrations of a tested compound, which is translated to the compound anticancer activity and its IC50 values. The MTT assay is widely common in cytotoxicity studies due to its accuracy, rapidity, and relative simplicity.
Herein we present a detailed protocol for the synthesis of air sensitive metal based drugs and cell viability measurements, including preparation of the cell plates, incubation of the compounds with the cells, viability measurements using the MTT assay, and determination of IC50 values.

A method for synthesis of air-sensitive titanium and vanadium anticancer agents is described, along with the evaluation of their cytotoxic activity towards human cancer cell line by the MTT Assay.

Titanium (IV) and vanadium (V) complexes are highly potent anticancer agents. A challenge in their synthesis refers to their hydrolytic instability; ...

Facile and Efficient Preparation of Tri-component Fluorescent Glycopolymers via RAFT-controlled Polymerization

Synthetic glycopolymers are instrumental and versatile tools used in various biochemical and biomedical research fields. An example of a facile and efficient synthesis of well-controlled fluorescent statistical glycopolymers using reversible addition-fragmentation chain-transfer (RAFT)-based polymerization is demonstrated. The synthesis starts with the preparation of &#946;-galactose-containing glycomonomer 2-lactobionamidoethyl methacrylamide obtained by reaction of lactobionolactone and N-(2-aminoethyl) methacrylamide (AEMA). 2-Gluconamidoethyl methacrylamide (GAEMA) is used as a structural analog lacking a terminal &#946;-galactoside. The following RAFT-mediated copolymerization reaction involves three different monomers: N-(2-hydroxyethyl) acrylamide as spacer, AEMA as target for further fluorescence labeling, and the glycomonomers. Tolerant of aqueous systems, the RAFT agent used in the reaction is (4-cyanopentanoic acid)-4-dithiobenzoate. Low dispersities (&#8804;1.32), predictable copolymer compositions, and high reproducibility of the polymerizations were observed among the products. Fluorescent polymers are obtained by modifying the glycopolymers with carboxyfluorescein succinimidyl ester targeting the primary amine functional groups on AEMA. Lectin-binding specificities of the resulting glycopolymers are verified by testing with corresponding agarose beads coated with specific glycoepitope recognizing lectins. Because of the ease of the synthesis, the tight control of the product compositions and the good reproducibility of the reaction, this protocol can be translated towards preparation of other RAFT-based glycopolymers with specific structures and compositions, as desired.

An efficient, three-step synthesis of RAFT-based fluorescent glycopolymers, consisting of glycomonomer preparation, copolymerization, and post-modification, is demonstrated. This protocol can be used to prepare RAFT-based statistical glycopolymers with desired structures.

Synthetic glycopolymers are instrumental and versatile tools used in various biochemical and biomedical research fields. An example of a facile and ...

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel &#945;-diimine ethylene polymerization catalyst. Initial polymerizations with the catalyst lead to optimized reaction conditions, including catalyst concentration, ethylene pressure and reaction time. Using gas-uptake data for these reactions, a procedure to calculate the initial rate of propagation (kp) is presented. Using the optimized conditions, the ability of the nickel &#945;-diimine polymerization catalyst to undergo chain transfer with diethylzinc (ZnEt2) during ethylene polymerization was investigated. A procedure to assess the ability of the catalyst to undergo chain transfer (from molecular weight and 13C NMR data), calculate the degree of chain transfer, and calculate chain transfer rates (ke) is presented.

A protocol for the high-throughput analysis of polymerization catalyst, chain transfer polymerizations, polyethylene characterization, and reaction kinetic analysis is presented.

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel ...

Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst

A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The procedure is performed under an inert atmosphere using air- and water-exclusion techniques. The outcome of the polymerization is affected by the ratios of monomer, initiator, and catalyst used as well as the reaction concentration, solvent, and nature of the light source. Temporal control over the polymerization can be exercised by turning the visible light source off and on. Low dispersities of the resultant polymers as well as the ability to chain-extend to form block copolymers suggest control over the polymerization, while chain end-group analysis provides evidence supporting an atom-transfer radical polymerization mechanism.

A method for the atom transfer radical polymerization of functionalized vinyl monomers using perylene as a visible-light photocatalyst is described.

A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The ...

Facile Synthesis of Worm-like Micelles by Visible Light Mediated Dispersion Polymerization Using Photoredox Catalyst

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins with the synthesis of a hydrophilic poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) homopolymer using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Under mild visible light irradiation (&#955; = 460 nm, 0.7 mW/cm2), this macro-chain transfer agent (macro-CTA) in the presence of a ruthenium based photoredox catalyst, Ru(bpy)3Cl2 can be chain extended with a second monomer to form a well-defined block copolymer in a process known as Photoinduced Electron Transfer RAFT (PET-RAFT). When PET-RAFT is used to chain extend POEGMA with benzyl methacrylate (BzMA) in ethanol (EtOH), polymeric nanoparticles with different morphologies are formed in situ according to a polymerization-induced self-assembly (PISA) mechanism. Self-assembly into nanoparticles presenting POEGMA chains at the corona and poly(benzyl methacrylate) (PBzMA) chains in the core occurs in situ due to the growing insolubility of the PBzMA block in ethanol. Interestingly, the formation of highly pure worm-like micelles can be readily monitored by observing the onset of a highly viscous gel in situ due to nanoparticle entanglements occurring during the polymerization. This process thereby allows for a more reproducible synthesis of worm-like micelles simply by monitoring the solution viscosity during the course of the polymerization. In addition, the light stimulus can be intermittently applied in an ON/OFF manner demonstrating temporal control over the nanoparticle morphology.

This article describes a process for producing polymeric self-assembled nanoparticles using visible light mediated dispersion polymerization. Using low energy visible light to control the polymerization allows for the reproducible formation of self-assembled worm-like micelles at high solids content.

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins ...

Anionic Polymerization of an Amphiphilic Copolymer for Preparation of Block Copolymer Micelles Stabilized by &#960;-&#960; Stacking Interactions

In this study, an amphiphilic copolymer that includes a core-forming block with phenyl groups was synthesized by living anionic polymerization of phenyl glycidyl ether (PheGE) on methoxy-polyethylene glycol (mPEG-b-PPheGE). Characterization of the copolymer revealed a narrow molecular distribution (PDI &#60; 1.03) and confirmed the degree of polymerization of mPEG122-b-(PheGE)15. The critical micelle concentration of the copolymer was evaluated using an established fluorescence method with the aggregation behavior evaluated by dynamic light scattering and transmission electronic microscopy. The potential of the copolymer for use in drug delivery applications was evaluated in a preliminary manner including in vitro biocompatibility, loading and release of the hydrophobic anti-cancer drug doxorubicin (DOX). A stable micelle formulation of DOX was prepared with drug loading levels up to 14% (wt%), drug loading efficiencies &#62; 60% (w/w) and sustained release of drug over 4 days under physiologically relevant conditions (acidic and neutral pH, presence of albumin). The high drug loading level and sustained release is attributed to stabilizing &#960;-&#960; interactions between DOX and the core-forming block of the micelles.

The key steps of living anionic polymerization of phenyl glycidyl ether (PheGE) on methoxy-polyethylene glycol (mPEG-b-PPheGE) are described. The resulting block copolymer micelles (BCMs) were loaded with doxorubicin 14% (wt%) and sustained release of drug over 4 days under physiologically relevant conditions was obtained.

In this study, an amphiphilic copolymer that includes a core-forming block with phenyl groups was synthesized by living anionic polymerization of phenyl ...

A Simple and Efficient Protocol for the Catalytic Insertion Polymerization of Functional Norbornenes

Norbornene can be polymerized by a variety of mechanisms, including insertion polymerization whereby the double bond is polymerized and the bicyclic nature of the monomer is conserved. The resulting polymer, polynorbornene, has a very high glass transition temperature, Tg, and interesting optical and electrical properties. However, the polymerization of functional norbornenes by this mechanism is complicated by the fact that the endo substituted norbornene monomer has, in general, a very low reactivity. Furthermore, the separation of the endo substituted monomer from the exo monomer is a tedious task. Here, we present a simple protocol for the polymerization of substituted norbornenes (endo:exo ca. 80:20) bearing either a carboxylic acid or a pendant double bond. The process does not require that both isomers be separated, and proceeds with low catalyst loadings (0.01 to 0.02 mol%). The polymer bearing pendant double bonds can be further transformed in high yield, to afford a polymer bearing pendant epoxy groups. These simple procedures can be applied to prepare polynorbornenes with a variety of functional groups, such as esters, alcohols, imides, double bonds, carboxylic acids, bromo-alkyls, aldehydes and anhydrides.

We describe the catalytic insertion polymerization of 5-norbornene-2-carboxylic acid and 5-vinyl-2-norbornene to form functional polymers with a very high glass transition temperature.

Norbornene can be polymerized by a variety of mechanisms, including insertion polymerization whereby the double bond is polymerized and the bicyclic ...

Extraction of Ramie Fiber in Alkali Hydrogen Peroxide System Supported by Controlled-release Alkali Source

This protocol demonstrates a method for ramie fiber extraction by scouring raw ramie in an alkali hydrogen peroxide system supported by a controlled-release alkali source. The fiber extracted from ramie is a type of textile material of great importance. In previous studies, ramie fiber was extracted in an alkali hydrogen peroxide system supported only by sodium hydroxide.However, due to the strong alkalinity of sodium hydroxide, the oxidation reaction speed of hydrogen peroxide was difficult to control and thus resulted in great damage to the treated fiber. In this protocol, a controlled-release alkali source, which is composed of sodium hydroxide and magnesium hydroxide, is used to provide an alkali condition and buffer the pH value of the alkali hydrogen peroxidesystem. The substitution rate of magnesium hydroxide can adjust the pH value of the hydrogen peroxide system and has great influence on the fiber properties. The pH value and oxidation-reduction potential (ORP) value, which represents the oxidation ability of alkali hydrogen peroxide system, were monitored using a pH meter and ORP meter, respectively. The residual hydrogen peroxide content in the alkali hydrogen peroxide system during the extraction process and the chemical oxygen demand (COD) value of wastewater after fiber extraction are tested by KMnO4 titration method. The yield of fiber is measured using a precision electronic balance, and residual gums of fiber are tested by a chemical analysis method. The polymerization degree (PD value) of fiber is tested by an intrinsic viscosity method using the Ubbelohde viscometer. The tensile property of fiber, including tenacity, elongation, and rupture, is measured using a fiber strength instrument. Fourier transform infrared spectroscopy and X-ray diffraction are used to characterize the functional groups and crystal property of fiber. This protocol proves that the controlled-release alkali source can improve the properties of the fiber extracted in an alkali hydrogen peroxide system.

Presented here is a protocol for extraction of ramie fiber in alkali hydrogen peroxide system supported by controlled-release alkali source.

This protocol demonstrates a method for ramie fiber extraction by scouring raw ramie in an alkali hydrogen peroxide system supported by a ...

Preparation of Hollow Polystyrene Particles and Microcapsules by Radical Polymerization of Janus Droplets Consisting of Hydrocarbon and Fluorocarbon Oils

In this article, we have demonstrated a method for producing hollow particles and microcapsules using oil droplets consisting of hydrocarbon oil (styrene) and fluorocarbon oil (perfluoro-n-octane, PFO) in aqueous surfactant (sodium dodecylsulfate, SDS) solutions. Since fluorocarbon oils are immiscible with hydrocarbon oils, the two oils are separated. Emulsions are prepared by stirring styrene/PFO/aqueous SDS solution mixtures at 80 &#176;C. The type of emulsions and the morphology of droplets in the emulsions are observed by light microscope and scanning confocal fluorescence microscope. It is found that oil droplets with Janus-type morphologies consisting of mutually immiscible styrene and PFO are formed in aqueous SDS solutions. Polystyrene particles are fabricated by radical polymerization of the ternary mixtures of styrene/PFO/aqueous SDS solution at 80 &#176;C. The morphologies of the polystyrene are confirmed by scanning electron microscopy and scanning transmission electron microscopy observations. These observations show the preparation of hollow polystyrene particles with a single hole on the surface. To our knowledge, this method is a novel strategy using the immiscibility of hydrocarbon and fluorocarbon oils. The hollow particles can also be applied to the preparation of microcapsules.

A protocol for the fabrication of hollow polymer particles and microcapsules by radical polymerization using emulsions consisting of styrene, perfluoro-n-octane, and aqueous SDS (sodium dodecylsulfate) solution is presented.

In this article, we have demonstrated a method for producing hollow particles and microcapsules using oil droplets consisting of hydrocarbon oil (styrene) ...

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Summary

Explore More Videos

Chapters in this video

Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies

Anticancer Metal Complexes: Synthesis and Cytotoxicity Evaluation by the MTT Assay

Facile and Efficient Preparation of Tri-component Fluorescent Glycopolymers via RAFT-controlled Polymerization

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst

Facile Synthesis of Worm-like Micelles by Visible Light Mediated Dispersion Polymerization Using Photoredox Catalyst

Anionic Polymerization of an Amphiphilic Copolymer for Preparation of Block Copolymer Micelles Stabilized by π-π Stacking Interactions

A Simple and Efficient Protocol for the Catalytic Insertion Polymerization of Functional Norbornenes

Extraction of Ramie Fiber in Alkali Hydrogen Peroxide System Supported by Controlled-release Alkali Source

Preparation of Hollow Polystyrene Particles and Microcapsules by Radical Polymerization of Janus Droplets Consisting of Hydrocarbon and Fluorocarbon Oils