The authors would like to acknowledge the University of Colorado Boulder for its support of this work.

CAUTION: Many of the chemicals used in this protocol are hazardous substances. Consult Material Safety Data Sheets (MSDS) and use appropriate personal protective equipment (PPE) when working with these substances.
1. Purification, Preparation, and Storage of Reagents
<ol>
	<li>Purify all solvents to be used using a solvent purification system according to manufacturer&#39;s protocol. If a solvent purification system is not available, use drying agents (e.g., molecular sieves, CaH2, etc.) and distillation. Once dried, store solvents under nitrogen atmosphere in the glovebox at room temperature.</li>
	<li>Purify all monomers by vacuum distillation according to manufacturer&#39;s protocol. Once distilled, store monomers in dark bottles under nitrogen atmosphere in a refrigerator.</li>
	<li>Purify initiators by vacuum distillation according to manufacturer&#39;s protocol. Once distilled, store initiators in dark bottles under nitrogen atmosphere in a refrigerator.</li>
	<li>Purify the perylene by sublimation according to manufacturer&#39;s protocol. Once sublimed, store the perylene on the benchtop at room temperature.</li>
	<li>Prepare a 250 ppm solution of butylated hydroxytoluene (BHT) in deuterated chloroform (CDCl3) by adding 25.0 mg BHT to a 100 g bottle of CDCl3. Prepare and store this solution on the benchtop.</li>
</ol>
2. Photopolymerization of Methyl Methacrylate Using Perylene as the Photocatalyst
<ol>
	<li>Allow all reagents to come to room temperature. Inspect all reagents prior to use to ensure there is no sign of contamination, such as discoloration or formation of solid particles.</li>
	<li>In a nitrogen atmosphere glovebox, place a small stir bar in a 20 ml scintillation vial. Add 2.36 mg (9.38 &#181;mol, 1.00 eq.) of perylene.</li>
	<li>Add 1.00 ml dimethylformamide (DMF).</li>
	<li>To this mixture, add 1.00 ml (9.38 mmol, 1,000 eq.) of methyl methacrylate (MMA).</li>
	<li>Place the vial on a stir plate set to 1,600 rpm and illuminated by strips of white light emitting diodes (LEDs). Limit any illumination from other light sources (e.g., overhead lights, nearby windows).</li>
	<li>To initiate the reaction, add 16.4 &#181;l (93.8 &#181;mol, 10.0 eq.) of &#945;-ethyl bromophenyl acetate (EBP) via pipette. 
	Note: To perform this reaction using natural sunlight, follow the above steps, ignoring step 2.5, then seal the vial, bring it out of the glovebox, and place the vial in an area illuminated by natural sunlight.</li>
	<li>Stir the reaction for 24 hr under constant illumination. Isolate and purify the product poly(MMA) by following the instructions in steps 4.1 - 4.4.</li>
</ol>
3. Kinetic Analysis of the Reaction
<ol>
	<li>On the benchtop, dispense 0.70 ml of the BHT in CDCl3 solution into a 2 ml vial and seal with septum cap. Bring this vial into the glovebox where the polymerization is being performed.</li>
	<li>Use a syringe to remove 0.20 ml of the reaction mixture. Inject the contents of the syringe into the 2 ml vial containing the 250 ppm solution of BHT in CDCl3. Draw back and push in the plunger several times to ensure thorough quenching of the polymerization.</li>
	<li>Transfer the contents of the 2 ml vial to an NMR (nuclear magnetic resonance) spectroscopy tube. Analyze this sample via 1H NMR spectroscopy for percent conversion.24</li>
	<li>For the specific example of polymerization of methyl methacrylate using perylene, calculate percent conversion from the 1H NMR spectrum of the sample by comparing the area under the peak corresponding to the methoxy hydrogens of the unreacted monomer (&#948; = 3.62) (M) and the area under the peak corresponding to the methoxy hydrogens of the polymer (&#948; = 3.50) (P) using the following formula: 
	<img alt="Equation 1" src="/files/ftp_upload/53571/53571eq1.jpg" /></li>
	<li>After analysis, pour the contents of the NMR spectroscopy tube into a clean 20 ml scintillation vial. Evaporate the solvent under reduced pressure. Re-dissolve the sample in 1.00 ml of tetrahydrofuran (THF).</li>
	<li>Send the sample through a syringe filter into a clean 2 ml vial. Analyze the sample via gel permeation chromatography (GPC) coupled with multi-angle light scattering to determine number-average molecular weight (Mn), weight-average molecular weight (Mw), and dispersity (&#272;).24</li>
</ol>
4. Isolation and Purification of the Product Polymer
<ol>
	<li>Quench the polymerization reaction by pouring the contents of the reaction mixture into a 50-fold excess of methanol and letting stir for at least 1 hr.</li>
	<li>Isolate the poly(methyl methacrylate) from the methanol by vacuum filtration according to manufacturer&#39;s protocol. 
	Note: The isolation method will vary depending on the polymer produced. For poly(methyl methacrylate) and polystyrene, vacuum filter the precipitated polymer from the methanol using a B&#252;chner funnel. For poly(butyl acrylate), decant the methanol from the viscous polymer.</li>
	<li>Rinse the polymer with an additional 100 ml methanol.</li>
	<li>Re-dissolve the polymer in dichloromethane and repeat steps 4.1 through 4.3 above twice.</li>
</ol>
5. Chain-extension of an MMA Macroinitiator with Styrene to Produce Poly(MMA)-b-poly(S)
<ol>
	<li>Allow all reagents to come to room temperature. Inspect all reagents prior to use to ensure there is no sign of contamination, such as discoloration or formation of solid particles.</li>
	<li>In a nitrogen atmosphere glovebox, place 136 mg (2.34 &#181;mol, 1.00 eq.) of poly(MMA) macroinitiator into a 20 ml scintillation vial fitted with a small stir bar.</li>
	<li>Add 0.59 mg perylene (2.34 &#181;mol, 1.00 eq.).</li>
	<li>Add 1.00 ml DMF.</li>
	<li>Place the vial on a stir plate set to 1,600 rpm and illuminated by strips of white LEDs. Limit any illumination from other light sources (e.g., overhead lights, nearby windows).</li>
	<li>To this mixture, add 1.24 ml (11.7 mmol, 5,000 eq.) of styrene (S) via pipette.</li>
	<li>Stir the reaction for 24 hr under constant illumination. Isolate and purify the product poly(MMA)-b-poly(S) by following the instructions in steps 4.1 - 4.4.</li>
</ol>

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The authors have nothing to disclose.

Although the protocol demonstrates a specific example of this polymerization technique, the options available to the researcher performing this reaction are quite broad. Modifications can be made at a number of points throughout the protocol to allow for the optimization of whatever particular photoredox ATRP is being performed. As new monomers, initiators, and catalysts for this reaction come under investigation, the stoichiometry and solvent used to perform the reaction can and should be modified as part of optimizatio...

The synthesis of technologically advanced polymers requires precise control over polymer molecular weight, dispersity (&#208;), composition, and architecture.1,2 Controlled radical polymerizations (CRPs)3-8 have revolutionized the synthesis of well-defined polymers, with atom transfer radical polymerization (ATRP) being the most used CRP, largely due to operational simplicity and synthetic versatility.9-14 The crux of ATRP is the ability to reversibly deactivate the polymerization, controlling the equilibrium between a propagating radical and a dormant species. Enforcing a low concentration of active radicals greatly minimizes bimolecular termination pathways and allows for the synthesis of well-defined polymers. 
Traditional ATRP relies on a transition metal catalyst to mediate this equilibrium.3 These metal catalysts contaminate the polymer product and impede implementation in biomedical or electronic applications while also raising environmental concerns. Although significant strides have been made to reduce the catalyst concentration to ppm levels, these methodologies require more demanding experimental conditions and metal contamination is still not entirely eliminated.15,16
Reversible addition-fragmentation transfer17,18 and nitroxide-mediated polymerizations19,20 are CRPs that do not require metal catalysts, although they have been used less often than ATRP.3 Recently, reversible chain-transfer21 and reversible complexation22,23 variants of ATRP that can use organic catalysts were reported. However, these methodologies require the use of alkyl iodide initiators and are not effective with the alkyl bromides commonly employed in ATRP. A highly desirable CRP would match the performance, feasibility, and robustness of traditional ATRP while being catalyzed by an organic catalyst under mild conditions.
Here, we describe a methodology for the radical polymerization of functionalized vinyl monomers using perylene as a visible-light photocatalyst. Through optimization of parameters such as stoichiometry, concentration, time, and light flux, the molecular weight of the polymers can be controlled.24, 25 Similar methodologies have been recently introduced using phenothiazine derivatives as photocatalysts for metal-free ATRP.26, 27 Because researchers in the field of polymerization catalysis are constantly developing new catalytic systems, the ability to compare catalyst performance across a number of metrics is vital. This ability to make comparisons relies heavily upon procedural consistency and clarity on the part of the researchers performing the experiments. As such, it is our goal that this video will be used to help precisely communicate the methods by which these polymers are synthesized and characterized.

<table><tbody><tr><td>perylene, min 98.0%</td><td>TCI America</td><td>TCP0078-025G</td><td>purify by sublimation</td></tr><tr><td>&lt;em&gt;N,N&lt;/em&gt;-dimethylformamide</td><td>VWR</td><td>EM-DX1726-1</td><td>Omnisolv</td></tr><tr><td>methyl methacrylate, 99%</td><td>VWR</td><td>200000-678</td><td>distilled prior to use, stored in refrigerator</td></tr><tr><td>ethyl &amp;alpha;-bromophenyl acetate&amp;nbsp;</td><td>Aldrich</td><td>554065</td><td>distilled prior to use stored in refrigerator</td></tr><tr><td>butylated hydroxytoluene&amp;nbsp;</td><td>Aldrich</td><td>W218405</td><td></td></tr><tr><td>Chloroform-D</td><td>Cambridge Isotope Labs</td><td>DLM-7-100</td><td></td></tr><tr><td>tetrahydrofuran</td><td>VWR</td><td>EM-TX0279-1</td><td>Omnisolv</td></tr><tr><td>methanol</td><td>VWR</td><td>BDH1135</td><td></td></tr><tr><td>dichloromethane</td><td>VWR</td><td>EM-DX0831-1</td><td>Omnisolv</td></tr><tr><td>styrene, 99%</td><td>VWR</td><td>AAAA18481-0F</td><td>distilled prior to use, stored in refrigerator</td></tr><tr><td>glass scintillation vial, 20&amp;nbsp;ml</td><td>VWR</td><td>66022-065</td><td></td></tr><tr><td>screw top vial, 2 ml</td><td>Agilent</td><td>5182-0715</td><td></td></tr><tr><td>septum cap for screw top vial</td><td>Agilent</td><td>5182-0717</td><td></td></tr><tr><td>heavy wall pressure vessel, 100 ml</td><td>Synthware</td><td>P160005&amp;nbsp;</td><td></td></tr><tr><td>syringe, 1 ml norm-ject</td><td>VWR</td><td>89174-491</td><td></td></tr><tr><td>NMR tube</td><td>New Era</td><td>NE-UL5-7&#039;</td><td></td></tr><tr><td>nylon syringe filter, 0.45&amp;nbsp;&amp;#956;m</td><td>VWR</td><td>28143-240</td><td></td></tr><tr><td>glovebox</td><td>Mbraun</td><td>LABstar</td><td></td></tr><tr><td>solvent purification system</td><td>Mbraun</td><td>MB-SPS-800</td><td></td></tr><tr><td>stirplate</td><td>IKA</td><td>3582401</td><td></td></tr><tr><td>light-emitting diodes</td><td>Creative Lighting Solutions</td><td>CL-FRS1210-5M-12V-WH</td><td>2x 12-inch strips of 5500 K white LEDs were used for illumination</td></tr><tr><td>12 V DC power supply for LEDs</td><td>Creative Lighting Solutions</td><td>CL-PS16001-40W</td><td></td></tr><tr><td>high performance liquid chromatograph&amp;nbsp;</td><td>Agilent</td><td>G1310B, G1322A, G1329B, G1316A</td><td></td></tr><tr><td>gel permeation size-exclusion columns</td><td>Agilent</td><td>PL1110-6500</td><td></td></tr><tr><td>multi-angle light scattering detector</td><td>Wyatt</td><td>WTREOS</td><td></td></tr><tr><td>differential refractometer</td><td>Wyatt</td><td>WTREX</td><td></td></tr></tbody></table>

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.

Table 1 shows the range of polymerization results achievable through this method. These data show that perylene is capable of serving as a photocatalyst for the polymerization of a number of functionalized vinyl monomers. For a specific monomer, adjustment of any of a number of reaction parameters such as solvent, stoichiometry, initiator, and light source leads to polymers with varying molecular weights and dispersities ranging from very good to rather broad. Fig...

Watch this Scientific Journal Video about Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst at JoVE.com

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

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 ...

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11.6K Views.  University of Colorado Boulder. A method for the atom transfer radical polymerization of functionalized vinyl monomers using perylene as a visible-light photocatalyst is described.

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

Reductive Electropolymerization of a Vinyl-containing Poly-pyridyl Complex on Glassy Carbon and Fluorine-doped Tin Oxide Electrodes

Controllable electrode surface modification is important in a number of fields, especially those with solar fuels applications. Electropolymerization is one surface modification technique that electrodeposits a polymeric film at the surface of an electrode by utilizing an applied potential to initiate the polymerization of substrates in the Helmholtz layer. This useful technique was first established by a Murray-Meyer collaboration at the University of North Carolina at Chapel Hill in the early 1980s and utilized to study numerous physical phenomena of films containing inorganic complexes as the monomeric substrate. Here, we highlight a procedure for coating electrodes with an inorganic complex by performing reductive electropolymerization of the vinyl-containing poly-pyridyl complex onto glassy carbon and fluorine doped tin oxide coated electrodes. Recommendations on electrochemical cell configurations and troubleshooting procedures are included. Although not explicitly described here, oxidative electropolymerization of pyrrole-containing compounds follows similar procedures to vinyl-based reductive electropolymerization but are far less sensitive to oxygen and water.

A procedure for performing reductive electropolymerization of vinyl-containing compounds onto glassy carbon and fluorine doped tin-oxide coated electrodes is presented. Recommendations on electrochemical cell configurations and troubleshooting procedures are included. Although not explicitly described here, oxidative electropolymerization of pyrrole-containing compounds follows similar procedures to vinyl-based reductive electropolymerization.

Controllable electrode surface modification is important in a number of fields, especially those with solar fuels applications. Electropolymerization is ...

Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step process that finishes with Negishi coupling. Negishi coupling is a cross-coupling process in which a chemical precursor is first lithiated, followed by transmetallation with ZnCl2. The resultant organozinc compound can be coupled to a dibrominated aromatic precursor to give the conjugated monomer. Polymer films can be prepared via electropolymerization of the monomer and characterized using cyclic voltammetry and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. Nanoparticles (NPs) are prepared via emulsion polymerization of the monomer using a two-surfactant system to yield an aqueous dispersion of the polymer NPs. The NPs are characterized using dynamic light scattering, electron microscopy, and UV-Vis-NIR-spectroscopy. Cytocompatibility of NPs is investigated using the cell viability assay. Finally, the NP suspensions are irradiated with a NIR laser to determine their effectiveness as potential materials for photothermal therapy (PTT).

A protocol is presented for the synthesis and preparation of nanoparticles consisting of electroactive polymers.

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step ...

Engineering

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 ...

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 ...

Preparation of Polyoxometalate-based Photo-responsive Membranes for the Photo-activation of Manganese Oxide Catalysts

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic polymers, with the aim of photo-activating oxygen-evolving manganese oxide catalysts, which are important components in artificial photosynthesis. The cross-linking technique was applied to obtain a self-standing membrane with a high PW12O403- content. Incorporation and structure retention of PW12O403- within the polymer matrix were confirmed by FT-IR and micro-Raman spectroscopy, and optical characteristics were investigated by UV-Vis spectroscopy, which revealed successful construction of the metal-to-metal charge transfer (MMCT) unit. After deposition of MnOx oxygen evolving catalysts, photocurrent measurements under visible light irradiation verified the sequential charge transfer, Mn &#8594; MMCT unit &#8594; electrode, and&#160;the photocurrent intensity was consistent with the redox potential of the donor metal (Ce or Co). This method provides a new strategy for preparing integrated systems involving catalysts and photon-absorption parts for use with photo-functional materials.

Here, we present a protocol to prepare charge transfer chromophores based on a polyoxometalate/polymer composite membrane.

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic ...

[(DPEPhos)(bcp)Cu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst

Our group recently reported the use of [(DPEPhos)(bcp)Cu]PF6 as a general copper-based photoredox catalyst which proved efficient to promote the activation of a broad variety of organic halides, including unactivated ones. These can then participate in various radical transformations such as reduction and cyclization reactions, as well as in the direct arylation of several (hetero)arenes. These transformations provide a straightforward access to a range of small molecules of interest in synthetic chemistry, as well as to biologically active natural products. Altogether, [(DPEPhos)(bcp)Cu]PF6 acts as a convenient photoredox catalyst which appears to be an attractive, cheap and complementary alternative to the state-of-the-art iridium- and ruthenium-based photoredox catalysts. Here, we report a detailed protocol for the synthesis of [(DPEPhos)(bcp)Cu]PF6, as well as NMR and spectroscopic characterizations, and we illustrate its use in synthetic chemistry for the direct arylation of (hetero)arenes and radical cyclization of organic halides. In particular, the direct arylation of N-methylpyrrole with 4-iodobenzonitrile to afford&#160;4-(1-methyl-1H-pyrrol-2-yl)benzonitrile and the radical cyclization of N-benzoyl-N-[(2-iodoquinolin-3-yl)methyl]cyanamide to afford natural product luotonin A are detailed. The scope and limitations of this copper-based photoredox catalyst are also briefly discussed.

[DPEPhosbcpCu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst

Detailed and general protocols are presented for the synthesis of [(DPEPhos)(bcp)Cu]PF6, a general copper-based photoredox catalyst, and for its use in synthetic chemistry for the direct arylation of C-H bonds in (hetero)arenes and radical cyclization of organic halides.

Our group recently reported the use of [(DPEPhos)(bcp)Cu]PF6 as a general copper-based photoredox catalyst which proved efficient to promote the ...

3D Printing and In Situ Surface Modification via Type I Photoinitiated Reversible Addition-Fragmentation Chain Transfer Polymerization

3D printing provides facile access to geometrically complex materials. However, these materials have intrinsically linked bulk and interfacial properties dependent on the chemical composition of the resin. In the current work, 3D printed materials are post-functionalized using the 3D printer hardware via a secondary surface-initiated polymerization process, thus providing independent control over the bulk and interfacial material properties. This process begins with preparing liquid resins, which contain a monofunctional monomer, a crosslinking multifunctional monomer, a photochemically labile species that enables initiation of polymerization, and critically, a thiocarbonylthio compound which facilitates reversible addition-fragmentation chain transfer (RAFT) polymerization. The thiocarbonylthio compound, known commonly as a RAFT agent, mediates the chain growth polymerization process and provides polymeric materials with more homogeneous network structures. The liquid resin is cured in a layer-by-layer fashion using a commercially available digital light processing 3D printer to give three-dimensional materials having spatially controlled geometries. The initial resin is removed and replaced with a new mixture containing functional monomers and photoinitiating species. The 3D printed material is then exposed to light from the 3D printer in the presence of the new functional monomer mixture. This allows photoinduced surface-initiated polymerization to occur from the latent RAFT agent groups on the surface of the 3D printed material. Given the chemical flexibility of both resins, this process allows a wide range of 3D printed materials to be produced with tailorable bulk and interfacial properties.

3D Printing and In Situ Surface Modification via Type I Photoinitiated Reversible Addition-Fragmentation Chain Transfer Polymerization

The present protocol describes the digital light processing-based 3D printing of polymeric materials using type I photoinitiated reversible addition-fragmentation chain transfer polymerization and the subsequent in situ material post-functionalization via surface-mediated polymerization. Photoinduced 3D printing provides materials with independently tailored and spatially controlled bulk and interfacial properties.

3D printing provides facile access to geometrically complex materials. However, these materials have intrinsically linked bulk and interfacial properties ...

Photochemical Initiation Of Radical Polymerization Reactions

Source: David C. Powers, Tamara M. Powers, Texas A&#38;M
In this video, we will carry out the photochemically initiated polymerization of styrene to generate polystyrene, which is an important commodity plastic. We will learn the fundamentals of photochemistry and use simple photochemistry to initiate radical polymerization reactions. Specifically, in this module we will examine the photochemistry of benzoyl peroxide and its role as a photo-initiator of styrene polymerization reactions. In the described experiments, we will investigate the role of wavelength, photon absorption, and excited state structure on the efficiency (measured as quantum yield) of photochemical reactions.

Source: David C. Powers, Tamara M. Powers, Texas A&#38;M
In this video, we will carry out the photochemically initiated polymerization of styrene to ...

JoVE Science Education

Inorganic Chemistry

Free-Radical Chain Reaction and Polymerization of Alkenes

The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a repeating unit, while the terminal groups are considered insignificant. The average degree of polymerization represents the number of repeating units in the polymer molecule and is denoted by the subscript n.
<img alt="Polymer chain structure diagram; hydrocarbon backbone with side groups, chemistry, material science." src="/files/ftp_upload/11773/11773_PT_Figure_1.svg" style="text-align: center; height: 60px;" data-altupdatedat="1747908711000" data-alt="Figure1">
Alkenes undergo polymerization via a free-radical mechanism involving three steps: initiation, propagation, and termination. 
Radicals are generated in the initiation step by heating a small quantity of free-radical initiators such as benzoyl peroxide. The benzoyloxy radical loses CO2 and forms a phenyl radical (Ph·), which adds to the double bond of the alkene to initiate the polymerization process. One of the electrons of the alkene π bond pairs with one electron from the phenyl radical to form a new C–C bond.
<img alt="Radical reaction mechanism diagram, benzoyl peroxide decomposition into radicals, chemical process." src="/files/ftp_upload/11773/11773_PT_Figure_2.svg" style="text-align: center; height: 60px;" data-altupdatedat="1747908711000" data-alt="Figure2">
<img alt="Chemical reaction diagram of phenyl cation formation via decarboxylation process with equations." src="/files/ftp_upload/11773/11773_PT_Figure_3.svg" style="text-align: center; height: 60px;" data-altupdatedat="1747908711000" data-alt="Figure3">
<img alt="Chemical reaction diagram showing radical polymerization steps with benzene and propylene." src="/files/ftp_upload/11773/11773_PT_Figure_4.svg" style="text-align: center; height: 80px;" data-altupdatedat="1747908711000" data-alt="Figure4">
In the propagation step, the carbon radical generated in the initiation step adds to another molecule of alkene to generate a new radical. The continuous addition of alkene monomers at the radical site yields the polymer.
<img alt="Allylic polymerization process, chemical reaction equation, polymer chain formation." src="/files/ftp_upload/11773/11773_PT_Figure_5.svg" style="text-align: center; height: 80px;" data-altupdatedat="1747908711000" data-alt="Figure5">
The termination step of the free-radical mechanism occurs via recombination or disproportionation. In a recombination step, two growing chains form a bond at their radical sites.
<img alt="Polymerization process diagram with structural formulas and reaction arrows." src="/files/ftp_upload/11773/11773_PT_Figure_6.svg" style="text-align: center; height: 60px;" data-altupdatedat="1747908711000" data-alt="Figure6">
In termination by disproportionation, a β-hydrogen atom is transferred from one radical to another radical center, resulting in two non-radical products.
<img alt="Free radical reaction diagram; benzyl radical formation; organic chemistry mechanism." src="/files/ftp_upload/11773/11773_PT_Figure_7.svg" style="text-align: center; height: 300px;" data-altupdatedat="1747908711000" data-alt="Figure7">
The free-radical polymerization of ethylene yields low-density polyethylene (LDPE), where the low density is a consequence of significant branching in the polymer chains. Articles made from polymers surround us in various forms, such as food packaging materials, plastic bags, bottles, stationery, and automotive parts.

Free-radical Polymerization Reaction of Alkenes

The conversion of alkenes to macromolecules called polymers is a reaction of high commercial importance. The structure of the polymer is defined by a ...

KEY TERMS AND CONCEPTS

Radical Chain-Growth Polymerization: Overview

Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is used to minimize radical coupling.
<img alt="Figure1" src="/files/ftp_upload/12920/12920_PT_Figure_1.svg" style="text-align: center; height: 75px;" />
Figure 1: The homolytic fission reaction of radical initiator dibenzoyl peroxide to generate benzoyloxy radicals and the subsequent decomposition to phenyl radicals
This free radical initiates polymerization by reacting with a monomer molecule. Unsaturated monomers are suitable for radical chain-growth polymerization; a substituent group across the unsaturated bond that stabilizes the free radical increases the reaction feasibility. Ethylene, propylene, vinyl chloride, and styrene are examples of monomers that can be polymerized via free-radical chain-growth polymerization.
The reaction between a monomer and a free radical generates a new free radical. This new radical reacts with another monomer and creates yet another free radical. The polymer chain grows as the reaction between free-radical intermediates and monomers repeats sequentially. Typically, the propagation step repeats one thousand to ten thousand times before the termination of polymerization.
Often, chain transfer reagents, such as thiol, are used to control the molecular weight (Figure 2). A chain transfer agent must be sufficiently reactive to transfer a hydrogen atom to the growing chain to terminate the polymer growth. The resultant radical must add to a double bond in the monomer to initiate polymerization.
<img alt="Figure2" src="/files/ftp_upload/12920/12920_PT_Figure_2_.svg" style="text-align: center; height: 150px;" />
Figure 2: (Top): The termination reaction of chain transfer agent thiol and a growing polymer chain; (Bottom): Subsequent reaction of thiol radical and monomer molecule to initiate polymer growth
Inhibitors are the reagents used to reduce the reactivity of radicals in the growing polymer chain. Figure 3 depicts the reaction of benzoquinone as an inhibitor.
<img alt="Figure3" src="/files/ftp_upload/12920/12920_PT_Figure_3.svg" style="text-align: center; height: 200px;" />
Figure 3: The reaction between chain inhibitor benzoquinone and a growing polymer chain to generate a less reactive free radical

Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the ...

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

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