Free Radical Bulk Polymerization Research Articles

Kinetically Limited Bulk Polymerization of Polymer Thin Films by Initiated Chemical Vapor Deposition.

An experimental study and kinetic model analysis of the initiated chemical vapor deposition (iCVD) of polymer thin films have been performed at saturated monomer vapor conditions. Previous iCVD kinetic studies have focused on subsaturated monomer conditions where polymer deposition kinetics is known to be limited by monomer adsorption. However, iCVD kinetics at saturated conditions have so far not been systematically investigated, and it remains unclear whether the adsorption-limited phenomenon would still apply at saturation, given the abundance of monomer for reaction. To probe this question, a series of depositions of poly(vinylpyrrolidone) (PVP) thin films as a model system were performed by iCVD at substrate temperatures from 10 to 25 °C at both fully saturated (100%) and subsaturated (50%) conditions. While the deposition rates at subsaturated conditions exhibit the expected adsorption-limited behavior, the deposition rates at saturated conditions unexpectedly show two distinct deposition regimes with reaction time: an initial adsorption-limited regime followed by a kinetically limited steady-state regime. In the steady-state regime, the deposition kinetics is found to be thermally activated by raising substrate temperature with an overall activation energy of +86 kJ/mol, which agrees reasonably well with the experimentally determined value of +89 kJ/mol in the literature for bulk PVP polymerization and a mechanistically derived value of +91 kJ/mol based on the bulk free radical polymerization mechanism of PVP. These findings open new operating windows for iCVD polymerization and thin-film growth in which fast polymer deposition can be achieved without substrate cooling that can greatly simplify the iCVD scale-up to roll-to-roll processing and enable iCVD polymerization of highly volatile monomers relevant for diverse applications in biomedicine, smart wearables, and renewable energy.

Altering Water Effect and Surface Properties of Heat Cured Poly Methyl Methacrylate by Adding Surface Treated Titanium Di Oxide Nano Particles

Titanium dioxide (TiO2) is extensively used part of our regular life. It can be observed in various commonly utilized goods & customer imports for instance drugs, plastics, cosmetics, food and paper. Universally, the quantity of titanium oxide manufactured in 2009 was 4.68 million tons for that reason the tenacity of the revision is controlling the amount of change on the denture base physical features such as the heat treatment in denture processing (PMMA)through the implementation of modified outer surface titanium di oxide Nano particles. Its properties are comprised of water solubility, surface roughness, water sorption and surface hardness. The contr olled TiO2 powder added to heat cured acrylic material according to the main weight of PMMA in concentration of 3% , 5% and 7%, and then it's mixed regularly by engine of probe ultra-sonication. Titanium oxide Nano fillers were m erged in denture based material with the help of more free radical polymerization in bulk. The nanoparticles were surface treated by a layer of trime thoxysilypropylmethacrylate (TMSPM). 120 specimens were created and separated into 3 sample sets affording to the examination (each sample sets consist of 40 samples) and each sample sets were sectioned in four subsets according to the TiO2 added ratio and ultimately containing 10 samples in each subset. The tests which conducted were indentation hardness (shore D), surface roughness properties as well as water sorption and solubility. For each test four of the sub groups (one control led and three with added Nano TiO2). Important to mention that extremely elevation in surface hardness score and roughness were detected at the ratio of 3%, 5%and7%. Thus escalation of added TiO2 nan-fillers considerably reduced the water solubility and sorption. The accumulation of the powder of TiO2 nanoparticles which have been surface treated to the PMMA acrylic resin thus changing the PMMA properties for example surface rigidity and surface coarseness. In which it’s increased in direct proportional relation with the raise of TiO2 concentration; at the same time addition of surface treated TiO2 Nano particles decrease water sorpt ion and solubility of (PMMA) also in direct proportional relation with the raise of TiO2 concentration.

Heterogeneities at the Onset of Reaction Acceleration during Bulk Polymerization of Methyl Methacrylate Investigated by Small-Angle Neutron Scattering

During bulk free-radical polymerization of methyl methacrylate below the glass-transition temperature of poly(methyl methacrylate), the relative fraction of monomer and polymer changes as the reaction proceeds. The liquid monomer is eventually converted to a solid glassy polymer. In other words, polymerization-induced vitrification or glass transition occurs. This process was traced by small-angle neutron scattering (SANS). The scattering profile discontinuously changes at the vicinity of vitrification. This discontinuous change was correlated with a sudden reaction acceleration known as the Trommsdorff effect. Ornstein–Zernike analysis revealed that the intensity at q = 0 (I(0)) and the correlation length of concentration fluctuation (ξ) suddenly increase at the discontinuous change of the scattering profile. The obtained data implies that the increased heterogeneity (i.e., microscopic concentration fluctuation) is intimately related to the Trommsdorff effect.

Ni2+ ion sensitive sustainable sensors based on 4-vinyl pyridine-ethyl acrylate copolymer

Toxic metal ions present in environmental water samples and other samples need to be detected for their removal. The detection of trace metal ions using an ion selective electrode (ISE) holds great significance in analytical chemistry. A 4-vinyl pyridine-ethyl acrylate copolymer-polyvinyl chloride (VE-PVC) based polymeric matrix (electrode) has been fabricated by free radical bulk polymerization method which is an example of a green and sustainable method capable of detecting Ni2+ ions even in trace amounts. To fabricate the polymeric matrix (electrode) (PME), VE has been used as an ionophore. Further, the effectiveness of Ni2+ ion ISE has also been investigated in the presence of surfactants and detergents. Its performance has also been analyzed in the presence of plasticizers. The electrode is found to be very useful for the estimation of Ni2+ ions using ethylenediaminetetraacetic acid by potentiometric titration and also in the estimation of presence of Ni2+ ions in water. Compared to other metal ions, the fabricated membrane electrode developed in this work has been found to show efficient and better selectivity towards Ni2+ ions.

Preparation and Characterization of Poly(vinyl acetate-co-2-hydroxyethyl methacrylate) and In Vitro Application as Contact Lens for Acyclovir Delivery.

A series of poly(vinyl acetate-co-2-hydroxyethylmethacrylate)/acyclovir drug carrier systems (HEMAVAC) containing different acyclovir contents was prepared through bulk free radical polymerization of 2-hydroxyethyl methacrylate with vinyl acetate (VAc) in presence of acyclovir (ACVR) as the drug using a LED lamp in presence of camphorquinone as the photoinitiator. The structure of the drug carrier system was confirmed by FTIR and 1HNMR analysis, and the uniform dispersion of the drug particles in the carrier was proved by DSC and XRD analysis. The study of the physico-chemical properties of the prepared materials, such as the transparency, swelling capacity, wettability and optical refraction, was carried out by UV-visible analysis, a swelling test and measurement of the contact angle and the refractive index, respectively. The elastic modulus and the yield strength of the wet prepared materials were examined by dynamic mechanical analysis. The cytotoxicity of the prepared materials and cell adhesion on these systems were studied by LDH assay and the MTT test, respectively. The results obtained were comparable to those of standard lenses with a transparency of 76.90-89.51%, a swelling capacity of 42.23-81.80% by weight, a wettability of 75.95-89.04°, a refractive index of 1.4301-1.4526 and a modulus of elasticity of 0.67-1.50 MPa, depending on the ACVR content. It was also shown that these materials exhibit no significant cytotoxicity; on the other hand, they show significant cell adhesion. The in vitro dynamic release of ACVR in water revealed that the HEMAVAC drug carrier can consistently deliver uniformly adequate amounts of ACVR (5.04-36 wt%) over a long period (7 days) in two steps. It was also found that the solubility of ACVR obtained from the release process was improved by 1.4 times that obtained by direct solubility of the drug in powder form at the same temperature.

Novel Mesogenic Vinyl Ketone Monomers and Their Based Polymers

In the present research, we have synthesized new vinyl ketone monomers with mesogenic substituents, namely, 8-(3'-chloro-4'-pentyl-[1,1'-biphenyl-4-oxy)oct-1-en-3-one (BVK) and 8-[2'-chloro-4‴-octyl-[1,1':4',1″:4″,1‴-quaterphenyl-4-oxy]oct-1-en-3-one (QVK). The comparison of BVK, QVK, and previously synthesized 8-((4″-((1R,4S)-4-butylcyclohexyl)-2'-chloro-[1,1',4',1″-terphenyl]-4-yl)oxy)oct-1-en-3-one (TVK) has revealed that all of them are able to form crystals, while their ability to exhibit liquid crystalline behavior depends on the number of phenyl substituents attached to the para-position of the phenoxy group and is observed for TVK and QVK only. All of the monomers are able to achieve self-polymerization upon heating and free radical polymerization in bulk or in solution under the action of the common radical initiator AIBN. We have also succeeded in the RAFT polymerization of the synthesized vinyl ketones BVK and TVK using asymmetrical trithiocarbonates. The synthesized poly(vinyl ketones) exhibit LC behavior and are able to undergo photodegradation upon UV irradiation.

Development of Polymeric-Based Formulation as Potential Smart Colonic Drug Delivery System.

Conventional oral formulations are mainly absorbed in the small intestine. This limits their use in the treatment of some diseases associated with the colon, where the drug has to act topically at the inflammation site. This paved the way for the development of a smart colonic drug delivery system, thereby improving the therapeutic efficacy, reducing the dosing frequency and potential side effects, as well as improving patient acceptance, especially in cases where enemas or other topical preparations may not be effective alone in treating the inflammation. In healthy individuals, it takes an oral medication delivery system about 5 to 6 h to reach the colon. A colonic drug delivery system should delay or prohibit the medication release during these five to six hours while permitting its release afterward. The main aim of this study was to develop a smart drug delivery system based on pH-sensitive polymeric formulations, synthesized by a free-radical bulk polymerization method, using different monomer and crosslinker concentrations. The formulations were loaded with 5-amino salicylic acid as a model drug and Capmul MCM C8 as a bioavailability enhancer. The glass transition temperature (Tg), tensile strength, Young’s modulus, and tensile elongation at break were all measured as a part of the dried films’ characterization. In vitro swelling and release studies were performed to assess the behavior of the produced formulations. The in vitro swelling and release evaluation demonstrated the potential ability of the developed system to retard the drug release at conditions mimicking the stomach and small intestine while triggering its release at conditions mimicking the colon, which indicates its promising applicability as a potential smart colonic drug delivery system.

Contributing to a better comprehension of: the styrene bulk free-radical polymerization with n-pentane added as a blowing agent for producing expandable polystyrene

Contributing to a better comprehension of: the styrene bulk free-radical polymerization with n-pentane added as a blowing agent for producing expandable polystyrene

Nanosponge-Based Composite Gel Polymer Electrolyte for Safer Li-O2 Batteries.

Li-O2 batteries represent a promising rechargeable battery candidate to answer the energy challenges our world is facing, thanks to their ultrahigh theoretical energy density. However, the poor cycling stability of the Li-O2 system and, overall, important safety issues due to the formation of Li dendrites, combined with the use of organic liquid electrolytes and O2 cross-over, inhibit their practical applications. As a solution to these various issues, we propose a composite gel polymer electrolyte consisting of a highly cross-linked polymer matrix, containing a dextrin-based nanosponge and activated with a liquid electrolyte. The polymer matrix, easily obtained by thermally activated one pot free radical polymerization in bulk, allows to limit dendrite nucleation and growth thanks to its cross-linked structure. At the same time, the nanosponge limits the O2 cross-over and avoids the formation of crystalline domains in the polymer matrix, which, combined with the liquid electrolyte, allows a good ionic conductivity at room temperature. Such a composite gel polymer electrolyte, tested in a cell containing Li metal as anode and a simple commercial gas diffusion layer, without any catalyst, as cathode demonstrates a full capacity of 5.05 mAh cm−2 as well as improved reversibility upon cycling, compared to a cell containing liquid electrolyte.

Polymerization-Induced Vitrification and Kinetic Heterogenization at the Onset of the Trommsdorff Effect

The reaction kinetics during bulk free radical polymerization is still not fully understood. As the reaction proceeds, many parameters, including monomer/polymer fraction, radical concentration, vi...

Epoxy-Based Structural Self-Adhesive Tapes Modified with Acrylic Syrups Prepared via a Free Radical Photopolymerization Process

New modifiers (i.e., acrylic syrups; ASs) of epoxy-resin-based thermally curable structural self-adhesive tapes (SATs) were prepared via a free radical bulk polymerization (FRBP) of n-butyl acrylate, butyl methacrylate, glycidyl methacrylate, and hydroxybutyl acrylate. In the process, two kinds of UV-photoinitiators (i.e., monoacylphosphine oxide/Omnirad TPO and bisacylphosphine oxide/Omnirad 819) and various mixing speed of the monomers mixture (200–1000 rpm) were applied. The TPO-based syrups exhibited a lower copolymers content (10–24 wt%), dynamic viscosity (<0.1 Pa·s), molecular weights (Mn and Mw, and polydispersity (1.9–2.5) than these with Omnirad 819. Additionally, the higher mixing speed significantly reduced monomers conversion and viscosity of ASs as well as molecular weights of the acrylate copolymers. These parameters influenced the properties of thermally uncured (e.g., adhesion) and thermally cured SATs (shear strength of aluminum/SAT/aluminum overlap joints). Better self-adhesive features were observed for SATs-TPO (based on ASs with lower monomers conversion, Mn and Mw); however, a slightly higher shear strength was noted for the thermally cured SAT-819 (ASs with higher monomers conversion, Mn and Mw). An impact of polydispersity of the acrylate copolymers as well as crosslinking degree of thermally cured SATs on the mechanical strength was also revealed.

Superabsorbent polymer: application in natural rubber for making rubber roofing sheets

PurposeThe purpose of this paper is to prepare superabsorbent polymers (SAPs) based on acrylic acid, which is considered hygroscopic material to incorporate in rubber formulation, which results in producing moisten rubber that is used as roofing sheets.Design/methodology/approachSAPs were synthesized via free radical bulk polymerization technique using different content of cross-linker N, N'-methylenebisacrylamide and potassium persulfate. Differential scanning calorimeter, thermal gravimetric analysis, Fourier transform infrared spectroscopy and transmission electron microscopy were used to characterize SAPs and confirmed the formation of cross-linked hydrogel structure. The water absorbency and the gel fraction for sodium polyacrylate (NaPA) were investigated. Then, the influence of obtained NaPA on the swelling behavior of the prepared natural rubber (NR) compound has been discussed.FindingsAbsorption characteristics and gel fraction of NaPA were found to depend on the content of the cross-linker in the system. SAPs are used to improve the absorbance behavior and performance of the NR to produce, roofing sheets using in hot weather. The morphology of the obtained rubber compound was well-explained by using a scanning electron microscope.Research limitations/implicationsThe research provides a simple way to produce moisten rubber that can be used as a roofing sheet to overcome warm weather.Originality/valueMoisten rubber roofing sheets provide a low-cost option in many developing countries with hot climates, and thus, help save the environment from global warming.

Processing maps based on polymerization modelling of thick methacrylic laminates

Control of the in-situ polymerization of thick methacrylic laminates is essential to minimize cavitation due to monomer boiling. To this end, a computationally efficient thermochemical model is developed to predict the temperature and degree of monomer conversion during polymerization of a methyl methacrylate (MMA)-based resin in a fibrous preform. The model couples the self-accelerating exothermic free-radical bulk polymerization of MMA (gel effect) with the heat transfer within the preform and to the environment. The predicted temperature profiles are in excellent agreement with experimental data measured during a series of in-situ polymerization tests with different heating conditions and preform thicknesses. Processing diagrams are constructed to reveal the regimes of interest for the production of thick fiber-reinforced methacrylic composites without voids induced by monomer boiling.

Radical bulk polymerization of styrene in the presence of rubber particles from recycled tires: a kinetic study using DSC

The kinetic developments of the free-radical bulk polymerization of styrene in the presence of recycled rubber tire particles are studied by isothermal differential scanning calorimetry (DSC). Two different chemical initiators, namely benzoyl peroxide (BPO) and 2,2'-Azobis(2methylbutyronitrile) (AMBN), are tested in a series of variable-composition experiments, under three different polymerization temperatures, in order to selectively address the role of the different species on the evolution of the polymerization reaction. The variation of the overall effective kinetic rate constant and activation energy of the polymerization are also calculated to quantify the effect of the addition of the particulate filler. The results of the study demonstrate that the combination of the peroxide initiator agent with a composition of the reacting mixture in the order of 30 mass%, in terms of the rubber tire particles, results in a significant deviation of the evolution of the rate of polymerization and monomer conversion, with respect to that of the pure homopolymerization system in the absence of tire particles. The observed phenomena are consistent with previous studies reported in the literature and are mainly attributed to the chemical interactions taking place between the initiator agent and additives of the formulation of the tire particles.

Molecularly imprinted cryogel cartridges for the selective recognition of tyrosine.

Molecularly imprinted polymers are used for creating a specific cavity and selective recognition sites for the structure of a target molecule in a polymeric structure. In this study, specific molecularly imprinted cryogel cartridges were synthesized using two distinct functional monomers to compare imprinting efficiency for the selective recognition of Tyrosine (Tyr). Tyr-imprinted cryogel cartridge (MIP1) was prepared using metal-chelate coordination for the imprinting process by free-radical bulk polymerization under frozen conditions, and Tyr-imprinted cryogel cartridge (MIP2) was prepared in the same way using hydrophobic effects for imprinting. After the characterization of the cryogel cartridges was carried out, the optimum adsorption conditions of both were determined according to the different parameters such as flow rate (0.5-2.5 ml/min), pH of the medium (4.0-8.0), initial Tyr concentration (0.1-3.0 mg/ml), and temperature (4-45°C). Selectivity experiments of Tyr-imprinted and non-imprinted cryogel cartridges were carried out by using phenylalanine, tryptophan, and cysteine. Besides, the eluted Tyr from MIP1 and MIP2 cryogel cartridge were applied to FPLC system. Also, the reusability experiments of Tyr-imprinted cryogel cartridges was observed no significant decrease in the adsorption capacity.

Influence of radical photoinitiators on features of polyacrylate syrups and self-adhesives

Pressure-sensitive adhesives (PSAs) were prepared via UV-irradiaton of an acrylic syrups with reactive diluent (functional diacrylate) and photoinitiator. The acrylic syrups were received via free radical bulk polymerization process (FRBP) and influence of radical photoinitiator (α-hydroxyketones, acylphosphine oxides or mixtures thereof) was investigated. It was revealed that the mixture of bisacylphosphine oxide (Omnirad 819) and α-hydroxyketone (Omnirad 184) was the most effective in FRBP (the highest monomer conversion), but preferable features of acrylic syrups (viscosity and molecular weight of copolymers) and self-adhesive properties of PSAs (especially cohesion) was achieved due to α-hydroxyketones using.

Toward HAZOP 4.0 Approach for Managing the Complexities of the Hazard and Operability of an Industrial Polymerization Reactor

Conventional HAZOP is a collaborative and multidisciplinary activity to identify the hazards associated to operability of the chemical processes. Then the consequences and required safeguards of each potential deviation or failure are assessed qualitatively one by one. It is performed with the assumption of "one failure at the time" for the process parameters. Furthermore, process complexities such as multiple failures, domino effects, time and amplitude dependent deviations etc. are avoided to keep the HAZOP brainstorming sessions systematic and effective. Therefore, the quality and outcomes of HAZOP study are relatively subjective and depend on the experience and competency of the HAZOP team. This simplified approach cannot fully cover the hazard identification and risk assessment of the complex processes such as polymerization. Furthermore, the incident investigations show that almost all major accidents have occurred due to multiple failures or domino effects. This paper aims at developing a practical methodology in the context of "Industry 4.0" and particularly illustrate how dynamic simulation liberates the HAZOP team from the simplification assumptions such as one failure at the time or neglecting the domino effects during the lifecycle of the complex processes. An industrial styrene bulk free radical polymerization process has been chosen as the case study to depict the applicability of the proposed method. In continuation of this research, the dynamic simulation integrated with Artificial Intelligence (AI) algorithms and Multivariable Process Monitoring (MPM) together with virtual collaboration tools will be invoked towards a more practical and effective HAZOP 4.0 platform. Such a platform can be the foundation of the further Process Safety Management (PSM) elements such as "Operating manuals", "Training and Competency management", "Condition monitoring and predictive maintenance", "Management of Change", "Pre-Start-up Safety Review", etc.

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.

The Trommsdorff effect under shear and bulk polymerization of methyl methacrylate via reactive extrusion

In this study, a concentric-cylinder and double-walled reactor accurately controlling shear rates was established to conduct the free radical bulk polymerization of methyl methacrylate, and the kinetics of Trommsdorff effect under constant shear was investigated. The results showed that increasing shear rate significantly enhanced the termination rate constant (kt), and thus effectively weakened and postponed the Trommsdorff effect. However, the polymerization rate during the “quasi-steady state” was almost not affected by shear rate. Differing from the classical theory, the chain initiation rate (Ri) also increased with shear rate, which was due to the improving initiation efficiency of polymerization reaction. On the other hand, it was found that the critical viscosity when Trommsdorff effect occurred was about 1000 ± 100 Pa·s, independent of shear rates, temperatures and initiator concentrations. Based on utilizing the Trommsdorff effect, polymethyl methacrylate (PMMA) was further synthesized via reactive extrusion, with superior performance comparing to commercial product.

Reduction in protein absorption on ophthalmic lenses by PEGDA bulk modification of silicone acrylate-based formulation

The absorption of protein and formation of biofilms on the surface of ophthalmic lenses is one of the factors that destroy their useful performance by causing severe visual impairment, inflammation, dryness and ultimate eye discomfort. Therefore, eye lenses need to be resilient to protein absorption, which is one of the opacity factors in minimizing protein absorption on the lenses. The purpose of this study was to investigate and reduce sediment biotransformation on the surface of the semi-hardened lens based on acrylate by bulk-free radical polymerization method. In this respect, the effect of poly(ethylene glycol) diacrylate (PEGDA) with two different molecular weights of 200 and 600 g/mol on the surface roughness, protein absorption, and hydrophilicity of the lenses were studied. The surface hardness of the lenses, on shore D scale, was measured using a durometer hardness test. The presence of higher molecular weight of PEGDA hydrophilic polymeric monomers reduced the hardness of the lenses. The effect of introducing PEGDA, with two molecular weights, into lens fabrication formulations was studied with respect to their water content parameters and hydrophilicity. The presence of a crosslinker such as poly(ethylene glycol) diacrylates, at two different molecular weights, increased the water content and hydrophilicity of the produced lenses. Surface roughness is associated with the formation of bio-film and accumulation of microorganisms on the surface. Due to the roughness of the lens surface developed in this research, the lenses containing PEGDA 600 exhibited less roughness compared to that of PEGDA 200, which could also affect the absorption of protein. Therefore, according to the results of protein absorption test, the PEGDA 600 lenses showed lower protein absorption, which could be due to their high degree of water absorption and hydrophilicity.