Photoinduced Free Radical Polymerization Research Articles

Temperature-Sensitive Janus Particles PEG/SiO2/PNIPAM-PEA: Applications in Foam Stabilization and Defoaming.

The current study presents a scalable approach for the preparation of temperature-responsive PEG/SiO2/PNIPAM-PEA Janus particles and, for the first time, investigates their potential applications in stabilizing foam and defoaming by adjusting the temperature. The method utilizes a (W1 + O)/W2 emulsion system, which incorporates appropriate surfactants to stabilize the emulsion and prevent rapid dissolution of the hydrophilic triblock polymer PEG-b-PTEPM-b-PNIPAM in water. The PEG/SiO2/PNIPAM-PEA Janus particles with temperature-responsive characteristics were synthesized in a single step that combined the sol-gel reaction and photoinduced free radical polymerization. The contact angle of the hydrophilic PEG/SiO2/PNIPAM surface was measured to be 54.7 ± 0.1°, while the contact angle of the hydrophobic PEA surface was found to be 122.4 ± 0.1°. By incorporating PEG/SiO2/PNIPAM-PEA Janus particles at a temperature of 25 °C, the foam's half-life is significantly prolonged from 42 s to nearly 30 min. However, with an increase in temperature to 50 °C, the foam's half-life rapidly diminished to only 44 s. This innovative application effectively enhances foam stabilization at low temperatures and facilitates the rapid dissipation of foam at high temperatures.

Controlling Properties and Functions of Polymer Gels Using Photochemical Reactions.

Photoresponsive polymer gels have attracted increasing interest owing to their potential applications in healable materials, drug release systems, and extracellular matrices. Because polymer gels provide suitable environments for photochemical reactions, their properties and functions can be controlled with light with a high spatiotemporal resolution. Herein, the design of photoresponsive polymer gels based on different types of photochemical reactions is introduced. The mechanism and applications of irreversible photoreactions, such as photoinduced free-radical polymerization, photoinduced click reactions, and photolysis, as well as reversible photoreactions such as photoinduced reversible cycloadditions, reversible photosubstitution of metal complexes, and photoinduced metathesis are reviewed. The remaining challenges of photoresponsive polymer gels are also discussed.

Molecular Dynamics Simulations of Photo-Induced Free Radical Polymerization.

Curing kinetic models provide insight into how design parameters affect the kinetics of photopolymerization. However, they do not provide insight into how networks form or how they influence the process. This article describes a molecular dynamics simulation framework for simulating photoinitiated, chain growth, free radical polymerization. The framework was applied to simulate the photo-induced polymerization of bisphenol A (EO)10 diacrylate under varying conditions of curing light intensity and photoinitiator concentration. Results from the simulations agree very well with curing kinetic curves and gelation points derived from experiments. The simulations also reveal that: (1) gelation is highly correlated with the formation of giant molecules, (2) differences in the number of free radicals generated at the beginning of polymerization significantly affect polymer network formation at low to intermediate conversion, and thus affect the gelation point, and (3) increasing light intensity or photoinitiator concentration tends to delay the gelation point, but does not affect the ultimate polymer network structure near the latter stages of photopolymerization.

Efficient ion-enhanced adsorption of congo red on polyacrolein from aqueous solution: Experiments, characterization and mechanism studies

Polyacrolein (PA) was prepared by photoinduced free radical polymerization for adsorption of congo red (CR). The structural and physicochemical properties of PA were characterized using BET, zeta potential measurements, SEM, FT-IR and XPS. The adsorption process of CR accorded with the pseudo-second-order kinetics, while the adsorption isotherm conformed to be the Langmuir model and the adsorption was proved to be the spontaneous and endothermic process (ΔG0 < 0, ΔH0 > 0). Electrostatic attraction, hydrogen bond and chemical reaction (formation of imine) were the critical driving forces of adsorption. The good removal efficiency obtained during the five executed cycles suggested a good reusability of PA. It was noteworthy that salts in CR solution could promote the adsorption capacity of PA, in which Ca (II) could obviously improve the adsorption capacity and shorten the time to reach adsorption equilibrium. These results have provided very useful information for removing CR and enhanced our understanding of the adsorption mechanism of PA on CR.

Synthesis of amphiphilic star-shaped block copolymers through photo-induced metal free atom transfer radical polymerization

Photo-induced metal free ATRP method was employed for the synthesis of star-shaped polymers. By using 21-Br-β-CD as the macroinitiator, 10-phenylphenothiazine as the photoredox catalyst, star-shaped PtBA homopolymers were synthesized. The photo-induced ATRP displayed all the characteristics of controlled/living polymerization systems and the good light control over the polymerization process. The successful chain extension with MMA demonstrated the high livingness of PtBA “arms” and good controllability of the Photo-induced metal free ATRP. Finally, the achieved PtBA-b-PMMA star-shaped copolymers were used as templates for the preparation of precisely size-tunable CdSe quantum dots after a simple hydrolyzing process.

Non-steady scaling model for the kinetics of the photo-induced free radical polymerization of crosslinking networks

A unified model expressed in closed-form is elaborated for the kinetics of free-radical polymerization and successfully compared to experimental data.

Optimizing grafting thickness of zwitterionic sulfobetaine polymer on cross-linked polyethylene surface to reduce friction coefficient

The purpose of this study involves reducing the friction coefficient of cross-linked polyethylene (CLPE) by optimizing the grafting thickness of zwitterionic poly(2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)ammonium hydroxide) (PMEDSAH) via a photo-induced free radical polymerization process. Cross-sectional TEM images and XPS spectra indicated that the PMEDSAH layers were successfully grafted on the CLPE. The grafting thickness increased when UV-irradiation time, UV-irradiation energy, and MEDSAH monomer concentration increased. The contact angle data indicated that the PMEDSAH layers successfully imparted hydrophilicity (below 20°) on the CLPE surface. The friction coefficient test and the resulting 3-D confocal images confirmed a significant decrease in the friction coefficient with increases in the grafting thickness. A minimum grafting thickness of 200 nm PMEDSAH was required to minimize the friction coefficient in an aqueous medium. However, a PMEDSAH-grafting thickness of approximately 40 nm was sufficient to reveal the minimized friction coefficient in simulated body fluids (ionic buffer solution) due to the salt-induced hydration effect. The results defined the minimum required thickness of PMEDSAH grafting to minimize the friction coefficient on CLPE surface that can potentially be applied for artificial hip joints.

Recent Advances in Photo-Induced Free-Radical Polymerization

Recent Advances in Photo-Induced Free-Radical Polymerization

Probing the first steps of photoinduced free radical polymerization at water–oil interfaces

Oil-soluble photoinitiators can initiate free radical polymerization in the aqueous phase of microemulsions with high efficiency.

Facile photo-flow synthesis of branched poly(butyl acrylate)s

We present the synthesis of branched poly(butyl acrylate)s using photo-induced free radical polymerization of (n/t)-butyl acrylate in the presence of tri(propylene glycol) diacrylate (TPGDA) as a crosslinker and varying amounts of dodecanethiol (DDT) as a chain transfer agent to prevent macroscopic gelation.

Synthesis, swelling, degradation and cytocompatibility of crosslinked PLLA-PEG-PLLA networks with short PLLA blocks

A series of triblock macromonomers with the general structure PLAa-PEGb-PLAa with acrylate end-groups and very short segments of PLA have been synthesized and characterized for potential use in the treatment of periodontitis. In the proposed application aqueous solutions of the triblock macromonomers would be injected into the pockets formed around the teeth and then crosslinked via photo-induced free radical polymerization to form drug-laden hydrogels. One of the macromonomers with the structure PLA4-PEG45-PLA4 showed optimum properties for the proposed application and was chosen for a more detailed study. In the study, the nature of the hydrogels formed by the macromonomer and by its copolymerization with PEG16 diacrylate has been investigated, along with its swelling and degradation in PBS at 37°C and pH 7.4. The hydrogels swell to equilibrium in water or PBS within approximately 5h, with swelling ratios in the range 4.5–3.5 and penetrant diffusion coefficients 1.5–2.4×106cm2s−1in PBS, depending on the PLA4-PEG45-PLA4 macromonomer content over the range 1.00–0.80wt fraction. The swollen hydrogels have an open pore structure, with the diameter of the largest pores in excess of 25μm. A detailed spectroscopic study confirmed that degradation in PBS proceeds as expected via hydrolysis of the lactide segments, and the polymer matrix completely dissolves after ≈22 days. The potential for control of degradation kinetics using the comacromonomer composition was also demonstrated. The cytotoxicity towards fibroblasts and osteoblasts, two important cell types involved in tissue repair and bone regeneration, has also been thoroughly evaluated. The hydrogels, and the products of hydrolytic degradation, were found to be non-cytotoxic towards these particular cells.

Photo-induced atom transfer radical polymerization of MMA with chlorophll A as photoinitiator

In this work, photoinduced free radical polymerization of methyl methacrylate (MMA) was performed at ambient temperature in dimethyl sulfoxide with chlorophll A as a photosensitizer. Well controlled polymerization of MMA was achieved. The linear first order plot of ln([M]0/[M]) vs time was observed. Well-defined polymethyl methacrylates (PMMA) with narrow molecular weight distribution (Mw/Mn) were prepared. It indicated that the polymerization was controllable. The chain-end fidelity was demonstrated by 1H NMR spectra. Chain extension experiments demonstrated the living feature of polymerization. The initiation and moderation of polymerization were manipulated by the periodic light on-off experiments.

Improving permeability and chromatographic performance of poly(pentaerythritol diacrylate monostearate) monolithic column via photo-induced thiol-acrylate polymerization

A simple approach was developed for rapid preparation of polymeric monolithic columns in UV-transparent fused-silica capillaries via photoinitiated thiol-acrylate polymerization of pentaerythritol diacrylate monostearate (PEDAS) and trimethylolpropane tris(3-mercaptopropionate) (TPTM) within 10min, in which the acrylate homopolymerized and copolymerized with the thiol simultaneously. The morphology, permeability and chromatographic performance of the resulting poly(PEDAS-co-TPTM) monoliths were studied. It could be observed from SEM that the morphology of poly(PEDAS-co-TPTM) monolith was rather different from that of poly(PEDAS) monolith, which was fabricated via photo-induced free radical polymerization using PEDAS as the sole monomer. Compared with poly(PEDAS) monolith, poly(PEDAS-co-TPTM) monolith possessed better permeability when they were fabricated under the same preparation conditions. By adjusting the composition of porogenic solvents, poly(PEDAS-co-TPTM) monolith exhibited lower plate heights (15.7–17.7μm) than poly(PEDAS) monolith (19.1–37.9μm) in μLC. In addition, 66 unique peptides were positively identified on poly(PEDAS-co-TPTM) monolith when tryptic digest of four proteins was separated by μLC-MS/MS, demonstrating its potential in proteome analysis.

The active role of excited states of phenothiazines in photoinduced metal free atom transfer radical polymerization: singlet or triplet excited states?

The active role of phenothiazine excited states in photoinduced metal-free atom transfer radical polymerization (ATRP) was investigated by using laser flash photolysis, fluorescence, phosphorescence and electron spin resonance spectroscopy.

“Mono” and “bifunctional” aromatic esterificated benzophenone photoinitiators for free radical polymerization

Aromatic esterificated benzophenone derivatives, benzoic acid 4-benzoyl-phenyl ester (BPBz) and bis-benzoic acid 4-benzoyl-phenyl ester (BisBPBz) were simply synthesized and characterized. The triplet states of the photoinitiators were determined by laser flash photolysis and phosphorescence spectroscopy. The photodecomposition of the initiators was performed by UV light; the increase in the absorption spectra was attributed to the decreasing number of ester groups which led to an increase in ketone groups according to the Photo-Fries rearrangement of aromatic esters. The photoinitiation capabilities for methyl methacrylate (MMA) polymerizations were investigated under air and nitrogen atmospheres. Ester-functional benzophenone photoinitiators were found to be more effective than benzophenone (BP) in the presence of a co-initiator for photoinduced free radical polymerization of MMA. The kinetics of photopolymerization for different formulations which consist of multifunctional acrylates was also studied using the Real-Time Fourier Transform infrared spectroscopy (RT-FTIR) method. The film properties of these formulations were investigated after curing of films by Mini-UV-Cure equipment.

Nondestructive Covalent “Grafting-from” of Poly(lactide) Particles of Different Geometries

A nondestructive "grafting-from" method has been developed using poly(lactide) (PLA) particles of different shapes as substrates and three hydrophilic monomers as grafts. Irregularly shaped particles and spheres of PLA were covalently surface functionalized using a versatile method of photoinduced free radical polymerization. The preservation of the molecular weight of the PLA particle bulk and the retention of the original particle shape confirmed the negligible effect of the grafting method. The changes in surface composition were determined by FTIR for both spherical and irregular particles and by XPS for the irregular particles showing the versatility of the method. Changes in the surface morphology of the PLA spherical particles were observed using microscopy techniques showing a full surface coverage of one of the grafted monomers. The method is applicable to a wide set of grafting monomers and provides a permanent alteration of the surface chemistry of the PLA particles creating hydrophilic PLA surfaces in addition to creating sites for further modification and drug delivery in the biomedical fields.

Photopolymerization and photophysical properties of amine linked benzophenone photoinitiator for free radical polymerization

Synthesis of amine linked type II photoinitiator (BPDEA) was achieved in high yields and photopolymerization of mono and multiacrylate monomers was performed with this photoinitiator in the absence of a coinitiator. BPDEA is more effective than benzophenone (BP) with the coinitiator (MDEA) system under inert atmosphere in photoinduced free radical polymerization of acrylates.

Ease of Synthesis, Controllable Sizes, and In Vivo Large‐Animal‐Lymph Migration of Polymeric Nanoparticles

Polymeric nanoparticles were synthesized using both a photoinduced and base-catalyzed free radical polymerization method. These mild room temperature approaches allow sensitive molecules, such as dyes, to be encapsulated. Using this method, near infrared dye loaded nanoparticles for lymphatic migration and lymph nodes localization were synthesized. After injection into a large animal, we observed migration of the nanoparticles over 20 cm to the sentinel lymph. Nanoparticle migration was observed for nanoparticles of 50 nm but not 100 nm in diameter. These investigations further support the development of new materials and clinical approaches to treat cancer including identification of nodal disease, characterization of the extent of disease, and establishment of treatment regimes.

Photopolymerization of acrylamide with benzophenone/methylated-β-cyclodextrin inclusion complex in the presence of jeffamine based dendrimers as coinitiators in aqueous media

BP/Me-β-CD inclusion complex was synthesized and used in photoinduced free radical polymerization of acrylamide as a type II photoinitiator in the presence of a dendritic co-initiator. Characterization and photophysical studies of the inclusion complex were determined by 1H NMR, UV, laser flash photolysis and phosphorescence spectroscopy. According to acrylamide polymerization of the BP/Me-β-CD water soluble photoinitiator, BP/Me-β-CD initiates polymerization of acrylamide effectively with six and twelve armed dendritic co-initiators in aqueous media. The 24 armed dendritic co-initiator was not as efficient as the six and twelve armed dendritic co-initiators with the BP/Me-β-CD inclusion complex, due to the sterical hindrance of the amine groups in the co-initiator.

In Situ Synthesis of Oil-Based Polymer/Silver Nanocomposites by Photoinduced Electron Transfer and Free Radical Polymerization Processes

In this study, in situ synthesis of oil-based polymer–silver nanocomposites was achieved by using photoinduced free radical polymerization processes in which silver nanoparticles were formed by electron transfer reaction. An oil-based macromonomer was prepared and then copolymerized with styrene in the presence of AgNO3. Copolymerization was started with free radicals formed by photolysis of 2,2-dimethoxy-2-phenyl acetophenone and simultaneously silver nitrate was reduced to metallic silver in nanosize by electron transfer reaction. The amount of photoinitiator influenced the size of silver nanoparticles formed within the polymer films. Nanocomposite films were characterized by TEM and TGA analysis. The obtained polymer nanocomposite film was also examined in respect of surface coating material that would have an antibacterial effect against Gram-positive, Gram-negative and spore-forming bacteria. It was demonstrated that suitably coated nanocomposite samples exhibited an antibacterial effect against these bacteria.