Methacrylate Free Radical Polymerization Research Articles

Mechanism of light polymerization of composites

BACKGROUND: The article presents a review of the chemical aspects of the reaction of light polymerization of composites in dental practice. This reaction refers to free radical polymerization reactions, with photons as activators. In dentistry, composites are classified as chemically cured, light cured, doubly cured, and thermally cured. This depends on the origin of the activation energy of free radical polymerization of methacrylates. Chemically, dental composites are usually a mixture of four main components: an organic polymer matrix, an inorganic filler, an appret compound, a binder matrix and filler, and an initiatoraccelerator system. The radical polymerization process includes four main stages. The first stage is activation; in the case of light cured dental composites, it is photoactivation. In this case, a photoinitiator molecule is excited, for example, camphorquinone, which is widely used in the production of dental composite materials. If a free radical is formed, the polymerization process is similar for all composite materials based on a methacrylate organic matrix. The only difference is exactly how free radicals are formed and the rate of their formation. Under the influence of light quanta, the carbon atom of the ketone group of camphorquinone passes into an excited state, which allows the excited photoinitiator molecule to interact with two methacrylate molecules by a double bond. The double bond gives one electron to the excited camphorquinone molecule, and the second electron acts as a free radical agent; in other words, a macroradical is formeda monomer molecule that can attach other monomer molecules to itself.

Photo-Crosslinked Silk Fibroin for 3D Printing.

Silk fibroin in material formats provides robust mechanical properties, and thus is a promising protein for 3D printing inks for a range of applications, including tissue engineering, bioelectronics, and bio-optics. Among the various crosslinking mechanisms, photo-crosslinking is particularly useful for 3D printing with silk fibroin inks due to the rapid kinetics, tunable crosslinking dynamics, light-assisted shape control, and the option to use visible light as a biocompatible processing condition. Multiple photo-crosslinking approaches have been applied to native or chemically modified silk fibroin, including photo-oxidation and free radical methacrylate polymerization. The molecular characteristics of silk fibroin, i.e., conformational polymorphism, provide a unique method for crosslinking and microfabrication via light. The molecular design features of silk fibroin inks and the exploitation of photo-crosslinking mechanisms suggest the exciting potential for meeting many biomedical needs in the future.

Initiator Feeding Policies in Semi-Batch Free Radical Polymerization: A Monte Carlo Study

A Monte Carlo simulation algorithm is developed to visualize the impact of various initiator feeding policies on the kinetics of free radical polymerization. Three cases are studied: (1) general free radical polymerization using typical rate constants; (2) diffusion-controlled styrene free radical polymerization in a relatively small amount of solvent; and (3) methyl methacrylate free radical polymerization in solution. The number- and weight-average chain lengths, molecular weight distribution (MWD), and polymerization time were computed for each initiator feeding policy. The results show that a higher number of initiator shots throughout polymerization at a fixed amount of initiator significantly increases average molecular weight and broadens MWD. Similar results are also observed when most of the initiator is added at higher conversions. It is demonstrated that one can double the molecular weight of polystyrene and increase its dispersity by 50% through a four-shot instead of a single shot feeding policy. Similar behavior occurs in the case of methyl methacrylate, while the total time drops by about 5%. In addition, policies injecting initiator at high monomer conversions result in a higher unreacted initiator content in the final product. Lastly, simulation conversion-time profiles are in agreement with benchmark literature information for methyl methacrylate, which essentially validates the highly effective and flexible Monte Carlo algorithm developed in this work.

Design of New Amines of Low Toxicity for Efficient Free Radical Polymerization under Air

AbstractTwo new amines are proposed here as a new class of high performance coinitiators for camphorquinone (CQ)‐based systems for mild polymerizations of methacrylates under blue light irradiation (LED@477 nm). These new compounds are very interesting because they are much less toxic than commonly used amines such as ethyl 4‐(dimethylamino) benzoate or 4‐(dimethylamino) benzonitrile. The particularity of one of these two new amines is its dual role: it is a coinitiator and contains a copolymerizable group. Therefore, it is much less subject to migration or leaching, which is a major current issue of polymers. Excellent polymerization performances in the presence of CQ for the free radical polymerization of methacrylates under blue light irradiation and under air are observed. Remarkably, good bleaching properties are obtained after polymerization.

A New Phosphine for Efficient Free Radical Polymerization under Air.

A new phosphine is proposed as efficient coinitiator for camphorquinone (CQ)-based photoinitiating systems for the free radical polymerization of (meth)acrylates. Remarkably, this new co-initiator can exhibit two functionalities: a phosphine moiety to overcome oxygen inhibition and an iodonium salt moiety as counter cation to initiate the polymerization process. Excellent polymerization performances in the presence of CQ for the free radical polymerization of methacrylates under blue light are observed, and amine-free systems can be easily developed from the proposed structure. The photopolymerization of composites is also investigated in the presence of the new phosphine (without iodonium counter cation) and very interesting depth of cure can be obtained from the new developed photoinitiating system after only 20 s of irradiation with a blue light-emitting diode.

2‐Oxo‐2(tert‐butyldimethylsilyl)Acetic Acid (DKSi‐COOH) as a New Water‐Soluble Visible Light Type I Photoinitiator for Free Radical Polymerization

Abstract2‐Oxo‐2‐(tert‐butyldimethylsilyl)acetic acid (DKSi‐COOH), is proposed here as a new high‐performance photoinitiator (PI) for the free radical polymerization of methacrylates under blue light irradiation. In the presence of DKSi‐COOH, very good polymerization performances are reached and outstanding bleaching properties are obtained compared to traditionally used camphorquinone‐based photoinitiating systems. Remarkably, this new developed PI exhibits good water solubility and excellent stability in acidic conditions and represents therefore a promising candidate for water‐based formulations.

A detailed description of methyl methacrylate free radical polymerization using different heating policies under isothermal and non-isothermal conditions: a kinetic Monte Carlo simulation

ABSTRACT A robust kinetic Monte Carlo (KMC) algorithm was precisely used to investigate and monitor the bulk free radical polymerization of methyl methacrylate (MMA) employing isothermal (ITPs) and non-isothermal (NTPs) heating policies. While temperature was fixed at 50°C (ITP50), 60°C (ITP60), and 70°C (ITP70) in isothermal policies, the non-isothermal policies are based on either a step increase in temperature profile from 50°C to 70°C at 120 or 60 min (NTP1 or NTP2, respectively), or a step decrease from 70°C to 50°C at 20 min (NTP3). The simulation data were in good agreement with the experimental data. It is revealed that the lower the average temperature is, the lower the rate of gel effect becomes. Furthermore, the initial gelation points, maximum gelation points, and glassy region interval are characterized. As a consequence of rising temperature, the initial glassy region shifts to a higher conversion. The maximum polymerization rate was achieved in a conversion range of 55-59%. It was found that temperature reduces average molecular weights and dispersity and narrowed molecular weight distribution (MWD); polymerization time was dropped by 85% too. Finally, NTP1 or NTP2 policies provide a narrower MWD at a higher average molecular weight.

3-Hydroxyflavone and N-Phenylglycine in High Performance Photoinitiating Systems for 3D Printing and Photocomposites Synthesis

We propose to use 3-hydroxyflavone as a versatile high performance visible light photoinitiator (PI) in combination with an amino acid (N-phenylglycine) for the free radical polymerization (FRP) of methacrylates in thick samples (e.g., 3D printing) or composites upon visible light exposure (light-emitting diode LED@405 nm or LED@477 nm). The high originality of this approach is the use of safer compounds in photoinitiating systems (combination flavone derivative/amino acid). 3-Hydroxyflavone can also be used in three-component systems with an iodonium salt and an amine for the cationic polymerization of epoxides upon exposure to near-UV light LED@385 nm. Also interestingly, a charge transfer complex (CTC) between N-phenylglycine NPG and iodonium salt gives also remarkable initiating performance for free radical polymerization of methacrylates upon mild light irradiation conditions (LED@405 nm). High polymerization initiating abilities are found, and high final reactive function conversions are obtained. T...

Effect of Azo and Peroxide Initiators on a Kinetic Study of Methyl Methacrylate Free Radical Polymerization by DSC

Free radical polymerization of methyl methacrylate was investigated in the presence of azo and organic peroxide initiator, such as 2,2′-azobisisobutyronitrile (AIBN), 1,1-bis(tert-butylperoxy)cyclohexane (BTBPC), tert-butyl peroxyneodecanoate (TBPND), and tert-butyl peroxy-2-ethylhexanoate (TBPEH) under isothermal condition (Tiso=60∼90 °C). The reaction heat generated in the bulk polymerization of methyl methacrylate was measured using a differential scanning calorimeter (DSC). The degree of polymerization and its reaction rate were expressed as a function of conversion (α) and its rate (dα/dt), respectively. We confirmed that autoacceleration proceeded predominantly during the autoacceleration regime (τauto) appearing after the onset of autoacceleration of MMA polymerization. In this work, kinetic models consisting of two contributions, such as n th order reaction and a kinetic equation representing autoacceleration, were suggested. The combined kinetic models were simulated and compared with the experimental data to evaluate the reliabilities.

3-Hydroxyflavone and N-phenylglycine in High Performance Photoinitiating Systems for 3D Printing and Photocomposites Synthesis

In this work, we propose to use 3-hydroxyflavone as a versatile high performance visible light photoinitiator (PIs) in combination with an amino acid (N-phenylglycine) for the free radical polymerization (FRP) of methacrylates in thick samples or composites upon visible light exposure (Light-Emitting Diode LED@405 nm or LED@477 nm). The high originality of this approach is the use of safer compounds in photoinitiating systems (flavone derivative/amino acid). 3-Hydroxyflavone can also be used in three-component systems with an iodonium salt and an amine for the cationic polymerization of epoxides upon exposure to near UV light LED@385 nm. Also interestingly, a charge transfer complex CTC between N-phenylglycine NPG and iodonium salt gives also remarkable initiating performance for free radical polymerization of methacrylates upon mild light irradiation conditions (LED@405 nm). High polymerization initiating abilities are found and high final reactive function conversions are obtained. The use of the new proposed initiating systems as materials for laser write or 3D printing experiments was also especially carried out with the formation of printed green fluorescent photopolymers. This green fluorescence obtained with naturally occurring 3-hydroxyflavone compound can be ascribed to the excited state intramolecular proton transfer ESIPT character. A full picture of the included photochemical mechanisms is given. Remarkably, 3-hydroxyflavone is also very efficient for photocomposites synthesis with glass fibers (thick samples with good depth of cure) using UV or LED@395 nm conveyor.

Allylthioketone Mediated Free Radical Polymerization of Methacrylates.

By combination of high trapping free radical efficiency of the thioketone and resonance of the allylic radical, a new type of mediating agent, 1,3,3-triphenylprop-2-ene-1-thione (TPPT) has been successfully synthesized, and then is used to study controlled free radical polymerization of methacrylates. Very stable TPPT radicals at the end of poly(methyl methacrylate) (PMMA) are detected in the polymerization of MMA using TPPT and AIBN as the control agent and initiator. The MALDI-TOF MS spectra are used to identify terminal groups of the resultant poly(glycidyl methacrylate) (PGMA), and major component of the obtained polymer has the structure, (CH3)2(CN)C-PGMA-C7H9O3. Chain extension reaction tests ascertain formation of the dead polymers during the polymer storage and purification process of the polymers. Owing to very slow fragmentation reaction of the TPPT-terminated polymethacrylate radical and addition reaction of this radical with a primary radical, the growing chain radicals are difficult to be regenerated, leading to an unobvious change of the molecular weight with monomer conversion. The molecular weights of polymers can be controlled by the ratios of monomer/initiator and TPPT/initiator. However, the first order kinetics of the polymerization and the polymers with narrow polydispersity are obtained, and these phenomena are discussed. This study provides useful information on how to design a better controlling agent.

Ionic liquids in a poly ethylene oxide cross-linked gel polymer as an electrolyte for electrical double layer capacitor

Abstract In the present work, we developed a gel polymer electrolyte via the incorporation of a room temperature ionic liquid into a cross-linked polymer matrix. The cross-linked gel electrolyte was prepared using a free radical polymerization of methacrylate and dimethacrylate oligomers dissolved in 1-propyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide. Combining the advantages of the ionic liquids and of conventional polymers, the cross-linked gel polymer electrolyte was used both as a separator and as an electrolyte for a leakage-free and non-flammable EDLC supercapacitor. The quasi-all solid-state supercapacitors showed rather good capacitance, power and energy densities by comparison to a liquid electrolyte-based EDLC.

Mechanosynthesized copper(i) complex based initiating systems for redox polymerization: towards upgraded oxidizing and reducing agents

Significant improvements of the recently proposed Cu(i)/VitC + water/dibenzoyl peroxide (BPO) system for the redox free radical polymerization of methacrylates in air are presented here.

On-Demand Visible Light Activated Amine/Benzoyl Peroxide Redox Initiating Systems: A Unique Tool To Overcome the Shadow Areas in Photopolymerization Processes

A novel way to counterbalance the drawbacks and advantages of photopolymerization and redox polymerization is proposed. Photoinitiating systems based on charge transfer complexes (CTC) between a phosphine and an iodonium salt as well as an amine and iodonium salt are checked for the free radical polymerization of methacrylates. Polymer materials as thick as 8.5 cm can be produced under air upon exposure to a LED at 405 nm using an amine/phosphine/iodonium three-component photoinitiating system. When combined with benzoyl peroxide (BPO), these systems are active in photoinduced redox polymerization; i.e., the CTC is used to absorb the light and generates initiating radicals and the amine/BPO couple allows a redox polymerization. Therefore, a fast/slow time control of the radical reaction is feasible under air, and an excellent monomer conversion is obtained both at the top layer and in the core of the sample. The efficiency of this photoactivated redox system is assessed in terms of monomer conversion (fol...

Novel self-strengthening hybrid dentin adhesive via a facile visible-light irradiation triple polymerization

Event Abstract Back to Event Novel self-strengthening hybrid dentin adhesive via a facile visible-light irradiation triple polymerization Qiang Ye1, Linyong Song1, Xueping Ge1, Anil Misra1, 2 and Paulette Spencer1, 3 1 University of Kansas, Bioengineering Research Center, United States 2 University of Kansas, Department of Civil Engineering, United States 3 University of Kansas, Department of Mechanical Engineering, United States Introduction: In vivo biodegradation of the bond between the composite and tooth, i.e. the composite restoration’s adhesive bond layer, is considered a major contributor to premature failure of composite restorations[1]. The structure of methacrylate-based dentin adhesives suggests a general mechanism for their chemical and enzymatic degradation in oral fluids. In our previous study[2], the crosslink density of dentin adhesives can be improved with the addition of epoxide monomers. The objective of this work was to further develop a self-strengthening methacrylate-based dentin adhesive system by introducing an epoxy cyclohexyl trimethoxysilane (TS) containing both epoxy and methoxysilyl functional groups and cured by visible-light photopolymerization. Materials and Methods: Neat methacrylate monomer mixture (Scheme 1) of HEMA/BisGMA at 45/55 wt% was used as the control (C0). Experimental formulation with HEMA/BisGMA/TS (22.5/27.5/50, wt%) was used to investigate the free radical polymerization of methacrylate, ring-opening cationic polymerization of epoxy, and photoacid-induced sol-gel reaction. The polymerization behavior was monitored in-situ using real-time Fourier transform infrared spectroscopy (FTIR). The properties of copolymers at TS concentration from 5 to 35 wt% were determined using dynamic mechanical analysis (DMA). The leachables from polymer discs were determined by HPLC using a reverse phase C18 column and UV/diode array detectors. Results and Discussion: In this triple polymIn this triple polymerization system, free radical polymerization rate was the highest and the hydrolysis-condensation reaction was the slowest. In acidic environments, the fast hydrolysis reaction and the limited condensation gave rise to the self-strengthening process, which significantly improved the mechanical properties. When the TS concentration was 10-20 wt%, the copolymers became more homogeneous and the storage modulus at 70 0C reached maximum. The cumulative amounts of leached monomers were reduced significantly (Figure 1). Conclusion: With the introduction of both epoxy and trimethoxysilyl functional groups, a self-strengthening hybrid system has been developed for application as a dentin adhesive. During visible-light irradiation, a triple polymerization mechanism was involved (Figure 2). Supported by grant NIH/NIDCR R01 DE022054. Scheme 1. Chemical structures of monomers used in the formulations. Figure 1. Cumulative release of HEMA from the dentin adhesive copolymers as a function of incubation time in ethanol at 23±2 0C Figure 2. Proposed polymethacrylate-based matrix network structure and the autonomic self-strengthening process with different TS concentrations. (A1 and A2) Polymethacrylate-based network formed by free radical polymerization, cationic ring-opening polymerization, and limited photoacid-induced sol-gel reaction in dry conditions after 40 s irradiation; (B1 and B2) photoacid-induced ring-opening polymerization and sol-gel reaction after 24 h; (C1 and C2) self-strengthening process via sol-gel reaction and ring-opening polymerization in wet environment. Supported by grant R01DE022054 (PS, JSL), from the National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892.

Self-Strengthening Hybrid Dental Adhesive via Visible-light Irradiation Triple Polymerization.

A self-strengthening methacrylate-based dental adhesive system was developed by introducing an epoxy cyclohexyl trimethoxysilane (TS) which contains both epoxy and methoxysilyl functional groups. The experimental formulation, HEMA/BisGMA/TS (22.5/27.5/50, wt%), was polymerized by visible-light. Real-time Fourier transform infrared spectroscopy (FTIR) was used to investigate in situ the free radical polymerization of methacrylate, ring-opening cationic polymerization of epoxy, and photoacid-induced sol-gel reactions. Among the three simultaneous reactions, the reaction rate of the free radical polymerization was the highest and the hydrolysis/condensation rate was the lowest. With 40s-irradiation, the degrees of conversion of the double bond and epoxy groups at 600 s were 73.2±1.2%, 87.9±2.4%, respectively. Hydrolysis of the methoxysilyl group was initially <5%, and increased gradually to about 50% after 48 h dark storage. Photoacids generated through the visible-light-induced reaction were effective in catalyzing both epoxy ring-opening polymerization and methoxysilyl sol-gel reaction. The mechanical properties of copolymers made with TS concentrations from 5 to 35 wt% were obtained using dynamic mechanical analysis (DMA). In wet conditions, the storage moduli at 70 °C and glass transition temperature were significantly higher than that of the control (p<0.05); these properties increased with TS concentration and storage time. The post reaction of hydrolysis/condensation of alkoxysilane could provide persistent strengthening whether in a neutral or acidic environment and these characteristics could lead to enhanced mechanical properties in the oral environment. The cumulative amount of leached species decreased significantly in the TS-containing copolymers. These results provide valuable information for the development of dental adhesives with reduced leaching of methacrylate monomers and enhanced mechanical properties under the wet, oral environment.

Light‐induced controlled free radical polymerization of methacrylates using iron‐based photocatalyst in visible light

ABSTRACTA novel visible light mediated catalytic system based on low cost iron complex, that is, Fe(bpy)3(PF)6 photocatalyst that initiates and control the free radical polymerization of methacrylates using ethyl α‐bromoisobutyrate (EBriB) as an initiator and 20 watt LED as light source is developed. The polymerization is initiated with turning the light on and immediately terminated by turning the light off. In addition, the molecular weight of polymer can be varied by changing the ratio of monomer and initiator. The merits of the present methodology lie in the use of low cost less precious, highly abundant iron‐based photocatalyst, avoidance of sacrificial donor and need of lower catalyst amount under visible light. The optimum amount of catalyst and initiator were established and successful polymerization of various methacrylates was achieved under the optimized polymerization conditions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2739–2746

Modeling methyl methacrylate free radical polymerization: Reaction in hydrophilic nanopores

In previous work, we developed a simplified model for the diffusion controlled bulk polymerization of methyl methacrylate and extended the model to capture the reaction under nanoconfinement. The calorimetric conversion versus time data in bulk and in silanized hydrophobic nanopores was well captured by the model. Here we further extend the model to capture the reaction in native hydrophilic controlled pore glass (CPG) nanopores accounting for catalysis by surface silanol groups. The ability of the model to describe experimental data is tested. In order to fit the data, the parameters describing monomer and active chain diffusion differ from that in hydrophobic pores.

Modeling methyl methacrylate free radical polymerization: Reaction in hydrophobic nanopores

Free radical polymerization of methyl methacrylate in nanopores has been shown to result in a decrease in the time for the onset of autoacceleration. In this work, we simplify our previous kinetic model of nanoconfined methyl methacrylate polymerization, which was based on the work of Verros and coworkers, and incorporate diffusion effects into the model using the Doolittle free volume theory. The simplified model well describes the experimental calorimetric conversion versus time data for isothermal bulk methyl methacrylate polymerization, capturing autoacceleration and the dependence of the limiting conversion on temperature. In order to model the reaction in nanopores, we assume that the diffusion coefficient scales with molecular size to the −3 power and with nanopore diameter to the 1.3 power. Experimental calorimetric conversion versus time data for polymerization in hydrophobic nanopores are well captured by the model, including the decrease in the time to reach autoacceleration with decreasing pore size. The scaling assumed is consistent with that predicted using molecular simulations for good solvent conditions by Avramova and Milchev and by Cui, Ding, and Chen. According to the fit of the experimental data, chain diffusivity is 20–50% of the bulk value in 13 nm-diameter pores.

Investigating the effect of pristine and modified silica nanoparticles on the kinetics of methyl methacrylate polymerization

To study the effect of silica nanoparticles on the kinetics of methyl methacrylate free radical polymerization, a number of batch polymerizations were performed using pristine and methacrylate-modified silica nanoparticles at 75 °C. In addition, effect of temperature was investigated on the kinetics of polymerization with 1 wt% loading of pristine nanoparticles. Monomer conversion, reaction rate, molecular weight and polydispersity index (PDI) of each polymerization were monitored during polymerization. According to results, no considerable change was obtained on the polymerization kinetics by introduction of any type of nanoparticles, while there is an optimum loading value in which the polymerization rate reaches its maximum level. A similar trend is observed for molecular weight of free chains; however, increasing silica content results in increased PDI values. Also, polymerizations rate is slower for batches containing modified nanoparticles. For chains which are grafted on the surface of modified nanoparticles, molecular weight and PDI values increase by increasing nanoparticle content.