Free Radical Polymerization Mechanism Research Articles

Sulphonated poly (Glycidyl Methacrylate-co-Styrene)-based adsorbents for the removal of Methylene Blue (MB) dye from aqueous solutions

In this work, sulphonated Poly(Glycidyl Methacrylate-co-Styrene) [SP(GMA-co-ST)] copolymers were developed as a novel adsorbent for water treatment applications through the removing methylene blue (MB) dye from its aqueous solution. The synthesized copolymers were obtained by the free radical polymerization mechanism using different ratios of (GMA) and (ST) monomers, which were then functionalized by sulfonation using sodium sulfite in alcoholic solution. FT-IR, Raman spectroscopy, SEM, XRD, and TGA were used to characterize the developed copolymers and their sulfonated forms. The influence of different parameters such as adsorbent dose, effect of temperature, contact time, dye concentration, and pH range on the adsorption of methylene blue have been studied. At 70 mg/100 ml of adsorbent, ambient temperature, and neutral medium, the highest dye clearance efficiency of 97.50 % was attained. It only took about 90 min to reach this maximum efficiency for the sulfonated copolymer [SP(GMA-co-ST) 2:1]. Studying the adsorption kinetics and adsorption showed that the adsorption process was well described by the pseudo-second-order and the Langmuir model (R2 = 0.9413), and the maximum adsorption capacity (qm) was 635.72 mg/g. Additionally, the reusability study revealed that the developed adsorbents could be used again for five consecutive cycles of adsorption and desorption.

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.

Influence of Oblique Angle Deposition on Porous Polymer Film Formation.

In this study, we applied oblique angle deposition to a modified initiated chemical vapor deposition (iCVD) process to synthesize porous poly(methacrylic acid) (PMAA) films. During the modified iCVD process, frozen monomer molecules are first captured on a cooled substrate, then polymerization occurs via a free radical polymerization mechanism, and finally, the excess monomer is sublimated, resulting in a porous polymer film. We found that delivering the monomer through an extension at an oblique angle resulted in porous films with three morphological regions. Region 1 is located nearest to the monomer extension outlet and consists of porous polymer pillars; region 2 consists of densified pillars, which occur due to the recapturing and polymerization of the sublimated monomer; and region 3 is located furthest from the monomer extension outlet and consists of dendritic structures, which occur due to low monomer concentration. We investigated the role of substrate temperature and monomer deposition time on the growth process. We found that changing the extension angle influenced the location of the regions and the film coverage across the substrate. Our results provide useful guidelines for tuning the structures within porous polymer films by varying the angle of monomer delivery.

Coupling of carboxymethyl starch with 2-carboxyethyl acrylate: A new sorbent for the wastewater remediation of methylene blue

Textile and printing industries play a vital role in the economy of any country. But the effluents of these industries, which contain toxic Methylene Blue (MB) dye when mixed with fresh water, make it unfit for human health and aquatic life. For the removal of MB, different adsorbents were used, but they were expensive, non-biodegradable or less effective. In this research, novel carboxymethyl starch grafted poly 2-carboxyethyl acrylate (CM-St-g-P2CEtA) was synthesized by reacting carboxymethyl starch with 2-carboxyethyl acrylate. The reaction followed a free radical polymerization mechanism. The structure and properties of CM-St-g-P2CEtA were investigated by advanced analytical techniques. The CM-St-g-P2CEtA was employed for the remediation of Methylene Blue (MB) dye from wastewater. The removal percentage (%R) of MB was checked under different parameters, like different pH levels, different initial concentrations of dye, different adsorbent doses, and different contact times. The results obtained during the experiment were subjected to different adsorption and kinetic models. In the kinetic investigation, the experimental results were best represented by the pseudo-second-order kinetic model due to its high R2 value of 0.999. Similarly, with a regression coefficient (R2) value of 0.947, the Langmuir adsorption isotherm was best represented by the experimental results. The Langmuir adsorption model showed that MB dye was adsorbed on the surface of CM-St-g-P2CEtA in a monolayer pattern. The pseudo 2nd order kinetic model suggested that the adsorption process favored chemisorption mechanism. The CM-St-g-P2CEtA showed maximum percentage removal efficiency (%R) of 99.3% for MB dye.

Kinetics and mechanisms of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane with cyanuric acid

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with cyanuric acid (CA) were investigated. Competitive free radical polymerization and aza-Michael addition reaction mechanisms involved in the BMI/CA reaction system were characterized by using DSC, 1H-NMR, electron spin resonance (ESR) and gel permeation chromatography (GPC). Free radical polymerization mechanism predominated in the BMI/CA reaction system. Both model-free and model-fitting methods were used to determine the isoconversional activation energy (Eα) and pre-exponential factor (Aα). The values of Eα and Aα for aza-Michael addition reaction evaluated at α = 0.1 were 86 kJ mol−1 and 2.42 × 1010 min−1, respectively, and the reaction model was f(α) = 1.73(1 - α)α0.11. By contrast, Eα gradually decreased with increasing α (decreased from 88 to 48 kJ mol−1) in the α range 0.15−0.9, which was attributed to the inherent multi-step kinetics in free radical polymerization.

Molecularly Imprinted Solid-Phase Extraction Sorbents for the Selective Extraction of Drugs from Human Urine.

Development of molecularly imprinted solid-phase extraction (MISPE) sorbents for the removal of drugs from human urine is described. MISPE sorbents are synthesized through free radical polymerization mechanism and non-covalent imprinting approach. After the completion of the polymerization, bulk polymer is ground using an analytical mill and then wet-sieved. Later on, MISPE sorbent has been dry-packed into solid-phase extraction cartridges after the extraction of template drug molecule. Eluates from the cartridges are analyzed using a spectrophotometer or spectrofluorimeter for the determination of target analyte by referring to the calibration curves.

Synthesis and characterization of hemicellulose-based polymeric gel film from tea leaf brewing waste

In this study, hemicellulose-based polymeric gel films were synthesized using the free radical polymerization mechanism. Hemicellulose was obtained from tea leaf brewing waste by using delignification process. Polymeric gel films were produced in accordance with solution-casting technique. The effects of synthesis parameters were investigated on the structure and properties of gel films. For this purpose, the hemicellulose-based synthesized gel films were characterized by analytical test. Experimental results indicated that hemicellulose- based gel films absorbed moisture at the rate of maximum 1% in 100% relative humidity environment. The lowest water vapor permeability (WVP) value was measured to be 5.88?10-10 g/(s Pa m), for the hemicellulose-based film including chitosan. The average solubility values of the produced polymeric films varied between approximately 0.4 and 1.8%. It was observed that the optical transparency of hemicellulose-based polymeric gel films changed from about 45 to 65% and the opacity/thickness values were from 0.0027 to 0.0011 ?m-1. As a result, it was found that the physicochemical and morphological properties of the synthesized films are greatly influenced by the composition of the films.

Photophysics and drug delivery behavior of methylene blue into Arabic-gum based hydrogel matrices

Methylene blue (MB) is an efficient photosensitizer for Photodynamic Therapy treatment. The photodynamic action is based on the interaction between light with a specific wavelength, a photosensitizer, and oxygen. Reactive oxygen species (ROS), including singlet oxygen (1O2), are created and support the photodynamic action. We verified that the MB presents a high 1O2 quantum yield in distilled water and simulated fluids (simulated gastric fluid (SGF, pH 1.2) and simulated intestinal fluid (SIF, pH 6.8)). Hydrogels are investigated for MB delivery to overcome undesirable effects and avoid the formation of non-effective leuco-methylene blue. The glycidyl methacrylate (GMA) was used to modify the Arabic gum structure. pH-responsive hydrogels composed of Arabic gum with different methacrylation degrees (82 and 94 % - MAG82 and MAG94, respectively) are created from the free-radical polymerization mechanism. The low methacrylation degree promotes high MB internalization in the hydrogel. The hydrogels' swelling degree depends on the MB incorporation, methacrylation degree, and pH of the simulated fluid. The MB release in the simulated fluids shows an unusual behavior due to the hydrogel erosion/degradation, attributed to the acid hydrolysis. The amount of released MB in SGF and SIF is similar for the hydrogel containing the high methacrylation degree. On the other hand, the MAG82 hydrogel releases more MB (twice) in SGF than in SIF. The erosion/degradation is more pronounced in the MAGH82 incorporated with the MB (hydrogel MAG82 + MB). Hydrogels matrices containing MB (which acts as photosensitizer) has showed great potential for the treatment of gastrointestinal cancer via Photodynamic Therapy.

Spontaneous S-Si bonding of alkanethiols to Si(111)-H: towards Si-molecule-Si circuits.

We report the synthesis of covalently linked self-assembled monolayers (SAMs) on silicon surfaces, using mild conditions, in a way that is compatible with silicon-electronics fabrication technologies. In molecular electronics, SAMs of functional molecules tethered to gold via sulfur linkages dominate, but these devices are not robust in design and not amenable to scalable manufacture. Whereas covalent bonding to silicon has long been recognized as an attractive alternative, only formation processes involving high temperature and/or pressure, strong chemicals, or irradiation are known. To make molecular devices on silicon under mild conditions with properties reminiscent of Au–S ones, we exploit the susceptibility of thiols to oxidation by dissolved O2, initiating free-radical polymerization mechanisms without causing oxidative damage to the surface. Without thiols present, dissolved O2 would normally oxidize the silicon and hence reaction conditions such as these have been strenuously avoided in the past. The surface coverage on Si(111)–H is measured to be very high, 75% of a full monolayer, with density-functional theory calculations used to profile spontaneous reaction mechanisms. The impact of the Si–S chemistry in single-molecule electronics is demonstrated using STM-junction approaches by forming Si–hexanedithiol–Si junctions. Si–S contacts result in single-molecule wires that are mechanically stable, with an average lifetime at room temperature of 2.7 s, which is five folds higher than that reported for conventional molecular junctions formed between gold electrodes. The enhanced “ON” lifetime of this single-molecule circuit enables previously inaccessible electrical measurements on single molecules.

Synthesis of nanoparticles based on pH-sensitive alginate-g-polyacrylonitrile copolymer and its application in drug loading

Different samples of sodium alginate grafted by polyacrylonitrile copolymer were synthesized via the grafting process through a free radical polymerization mechanism. Graft structures were characterized and confirmed using Fourier Transform Infrared (FT-IR) spectroscopy and X-Ray diffraction (XRD). Thermogravimetric analysis (TGA) showed that the graft copolymers acquired higher thermal stability compared to native alginate. Moreover, its solubility in several solvents was examined as compared to that of native alginate. The main outcome of this paper was that a grafted copolymer with hydrophobic enrichment (Wt% = 150 %) of polyacrylonitrile as a core was sufficient to form stabilize colloidal system within nanoparticles have Z-average diameter equal 55 nm and sodium alginate as a shell. The SA-g-PAN graft copolymer showed a higher degree of swellability in the basic medium than in acidic medium. The consequence of that was the SA-g-PAN graft copolymer exhibited pH-responsive properties. Moreover, the formed nanoparticles were loaded by a hydrophobic model and proofed by a transmission electron microscope (TEM).

Self-assembled heteromorphous raspberry-like colloidal particles from Pickering-like emulsion polymerization

Heteromorphous raspberry-like poly(vinylidene fluoride)/polystyrene (PVDF/PS) complex colloidal particles (CCPs) were prepared by a facile and high-efficiency approach with one pot Pickering-like emulsion polymerization following conventional free radical polymerization mechanism. Difference of hydrophobicity between PVDF and PS drove the initial generated snowman-like particles self-assembling into colloidal particle clusters and then a Pickering-like emulsion continued polymerization till formation of the heteromorphous raspberry-like PVDF/PS CCPs. In order to achieve heteromorphous raspberry-like PVDF/PS CCPs with homogeneous size and morphology, influences of St/PVDF feed ratio, polymerization time, and polymerization temperature were systematically investigated. When the feed ratio of St/PVDF was high for synthesis of the CCPs, double crystallization peaks for PVDF were observed with a strong peak at about 132 °C and a weak peak at near 70 °C, indicating that partial PVDF seed particles were covered completely by PS. Furthermore, the static water contact angle of latex nanocoating prepared with the heteromorphous raspberry-like PVDF/PS CCPs reached 153.9°, exhibiting a superhydrophobicity. As a result, an alternative way is provided for fabrication of hierarchical colloidal particles and even superhydrophobic smart coatings.

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane with barbituric acid in dimethyl sulfoxide

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with barbituric acid (BTA) in dimethyl sulfoxide (DMSO) were investigated. The polymerization of BMI with BTA in DMSO was characterized by using differential scanning calorimeter (DSC), electron spin resonance (ESR) and 1H-NMR techniques. The polymerization was primarily governed by the Michael addition reaction and aza- Michael addition reaction mechanisms. By contrast, free radical polymerization mechanism of BMI/BTA could be ruled out in DMSO medium. Model-free (isoconversional) method in combination with model-fitting method were used to determine triplet kinetic parameters for the polymerization of BMI with BTA in DMSO. Average activation energy (Eα) and pre-exponential factor (Aα) were ca. 51 kJ mol−1 and 1.33 × 106 min−1 in the fractional conversion (α) range 0.1–0.9, respectively. The polymerization of BMI with BTA was primarily reaction-controlled [f(α) = (1 − α)].

Polymerization kinetics stability, volumetric changes, apatite precipitation, strontium release and fatigue of novel bone composites for vertebroplasty.

PurposeThe aim was to determine effects of diluent monomer and monocalcium phosphate monohydrate (MCPM) on polymerization kinetics and volumetric stability, apatite precipitation, strontium release and fatigue of novel dual-paste composites for vertebroplasty.Materials and methodsPolypropylene (PPGDMA) or triethylene (TEGDMA) glycol dimethacrylates (25 wt%) diluents were combined with urethane dimethacrylate (70 wt%) and hydroxyethyl methacrylate (5 wt%). 70 wt% filler containing glass particles, glass fibers (20 wt%) and polylysine (5 wt%) was added. Benzoyl peroxide and MCPM (10 or 20 wt%) or N-tolyglycine glycidyl methacrylate and tristrontium phosphate (15 wt%) were included to give initiator or activator pastes. Commercial PMMA (Simplex) and bone composite (Cortoss) were used for comparison. ATR-FTIR was used to determine thermal activated polymerization kinetics of initiator pastes at 50–80°C. Paste stability, following storage at 4–37°C, was assessed visually or through mixed paste polymerization kinetics at 25°C. Polymerization shrinkage and heat generation were calculated from final monomer conversions. Subsequent expansion and surface apatite precipitation in simulated body fluid (SBF) were assessed gravimetrically and via SEM. Strontium release into water was assessed using ICP-MS. Biaxial flexural strength (BFS) and fatigue properties were determined at 37°C after 4 weeks in SBF.ResultsPolymerization profiles all exhibited an inhibition time before polymerization as predicted by free radical polymerization mechanisms. Initiator paste inhibition times and maximum reaction rates were described well by Arrhenius plots. Plot extrapolation, however, underestimated lower temperature paste stability. Replacement of TEGDMA by PPGDMA, enhanced paste stability, final monomer conversion, water-sorption induced expansion and strontium release but reduced polymerization shrinkage and heat generation. Increasing MCPM level enhanced volume expansion, surface apatite precipitation and strontium release. Although the experimental composite flexural strengths were lower compared to those of commercially available Simplex, the extrapolated low load fatigue lives of all materials were comparable.ConclusionsIncreased inhibition times at high temperature give longer predicted shelf-life whilst stability of mixed paste inhibition times is important for consistent clinical application. Increased volumetric stability, strontium release and apatite formation should encourage bone integration. Replacing TEGDMA by PPGDMA and increasing MCPM could therefore increase suitability of the above novel bone composites for vertebroplasty. Long fatigue lives of the composites may also ensure long-term durability of the materials.

Synergetic effect of multi-site phase transfer catalysis system mediated free radical polymerization of acrylonitrile – a kinetic study

In this work, the kinetics and mechanism of free radical polymerization of acrylonitrile (AN) using potassium peroxydisulphate (PDS-K2S2O8) as a water soluble initiator in the presence of synthesized 4,4'-dihexadecyl-1,1'-bipyridine diiumdichloride (DHBPDDC) as multi-site phase-transfer catalyst (MPTC) has been investigated. The polymerization reaction were carried out under nitrogen atmosphere and unstirred condition at constant temperature 60+1°C in ethyl acetate/water biphasic medium. The effects of variation of monomer(AN), initiator(PDS) and catalyst(MPTC) solvent polarity and temperature on the rate of polymerisation (Rp) were ascertained. The order with respect to monomer(acrylonitrile) was found to be unity. The order with respect to initiator and catalyst was found to be 0.51, 0.48 respectively. However, an increase in the polarity of the solvent has slightly increased the rate of polymerization value (Rp). Based on the results obtained, a suitable kinetic mechanism scheme has been proposed to account for the experimental observations and its significance was discussed. The other thermodynamic parameters such as entropy of activation ((∆S#), enthalpy of activation (∆H#) and free energy of activation (∆G#) have been calculated.

PHEMA Hydrogels Obtained by Infrared Radiation for Cartilage Tissue Engineering

Although the exposure of polymeric materials to radiation is a well-established process, little is known about the relationship between structure and property and the biological behavior of biomaterials obtained by thermal phenomena at 1070 nm wavelength. This study includes results concerning the use of a novel infrared radiation source (ytterbium laser fiber) for the synthesis of poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel in order to produce medical devices. The materials were obtained by means of free radical polymerization mechanism and evaluated regarding its cross-linking degree, polymer chain mobility, thermal, and mechanical properties. Their potential use as a biomaterial toward cartilage tissue was investigated through incubation with chondrocytes cells culture by dimethylmethylene blue (DMMB) dye and DNA quantification. Differential scanning calorimetry (DSC) results showed that glass transition temperature (Tg) was in the range 103°C–119°C, the maximum degree of swelling was 70.8%, and indentation fluency test presented a strain of 56%–85%. A significant increase of glycosaminoglycans (GAGs) concentration and DNA content in cells cultured with 40 wt% 2-hydroxyethyl methacrylate was observed. Our results showed the suitability of infrared laser fiber in the free radicals formation and in the rapid polymer chain growth, and further cross-linking. The porous material obtained showed improvements concerning cartilage tissue regeneration.

Hybrid copolymerization via mechanism interconversion between radical vinyl-addition and anion ring-opening polymerization

Here, we report a new hybrid copolymerization via an interconvertible living free radical and anion ring-opening polymerization mechanism, in which the copolymerization of cyclic monomers and vinyl-type monomers can be achieved.

Characterizations of hyaluronate-based terpolymeric hydrogel synthesized via free radical polymerization mechanism for biomedical applications.

In the present study, a novel terpolymeric hydrogel was developed using sodium hyaluronate (HA), 2-hydroxyethyl acrylate (2-HEA), and poly(ethylene glycol) diacrylate (PEGDA) via free radical polymerization for biomedical applications. To achieve elasticity, swelling ability, porous architecture and sufficient gel strength, hyaluronate was chemically modified by grafting and crosslinking methods using 2-HEA and PEGDA, respectively. The structure and compositions of the fabricated terpolymer (HA-g-p(2-HEA)-x-PEGDA) were verified by FTIR, 1H HR-MAS-NMR, and TGA analyses. The surface morphology and cross-section of the hydrogel was detected by SEM analysis. The gel nature of terpolymer in aqueous medium at 37 °C was confirmed from swelling study, and rheological experiment. Non-cytotoxicity and biocompatibility of the HA-g-p(2-HEA)-x-PEGDA hydrogel were ascertained by in vitro mouse osteoblastic cells (MC3T3) proliferation, and viability studies. Hematoxylin and eosin Y, and Masson's trichrome stainings were performed to show tissue regeneration ability on the prepared hydrogel. In vitro release results of proangiogenic drug-dimethyloxalylglycine (DMOG), and antibiotics-tetracycline (TCN) showed sustained release behaviour from the prepared hydrogel under different pHs at 37 °C. The mathematical models fitted data imply that both DMOG and TCN release follow first order kinetics, while, the release mechanism is primarily controlled by diffusion as well as erosion process. Finally, the novel biocompatible HA-g-p(2-HEA)-x-PEGDA gel, which showed sustained drugs release, and regeneration ability of extracellular matrix and collagen, could be employed in biomedical applications, especially, for the delivery of DMOG/TCN, and in tissue engineering.

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane with 1,3-dimethylbarbituric acid

Mechanisms and kinetics of non-isothermal polymerization of N,N′-bismaleimide-4,4′-diphenylmethane (BMI) with 1,3-dimethylbarbituric acid (13BTA) were investigated. Competition between free radical polymerization and Michael addition reaction mechanisms for the BMI/13BTA reaction system was characterized by using DSC and 1H NMR technique. Model-free (isoconversional) method was used to determine triplet kinetic parameters for the polymerization of BMI with 13BTA. Average activation energy (Eα) and pre-exponential factor (Aα) are ca. 56kJmol−1 and 65.83×105min−1 in the fractional conversion (α) range 0.1–0.9, respectively. Particle nucleation involved in the polymerization process was satisfactorily predicted by the nucleation Avrami-Erofeev model {f(α)=n(1−α)[−ln(1−α)](n−1)/n} with n=1.46. The z-average particle size of microgel particles was measured by dynamic light scattering, which supported the particle nucleation and growth process.

Synthesis and evaluation of physicochemical properties of anionic polymeric surfactant derived from Jatropha oil for application in enhanced oil recovery

In this study an attention has been paid to synthesize polymer grafted anionic surfactant (PMES) derived from nonedible vegetable oil (Jatropha) for its application in enhanced oil recovery (EOR). The polymeric surfactant was prepared by reacting acrylamide monomer with methyl ester sulfonate (MES) synthesized from Jatropha oil by free radical polymerization mechanism. Polymeric surfactant with properties of both surfactant and polymer can control the mobility ratio and reduce interfacial tension (IFT), which are desirable for EOR. The synthesized polymeric surfactant was characterized through FTIR, 1H NMR, FESEM, EDX, TGA, DLS analysis. The effectiveness of PMES for chemically enhanced oil recovery process was investigated by measurement of physiochemical properties of its aqueous solution viz. reduction of IFT, wettability alteration and rheological behaviour. Rheological studies shows shear thinning behaviour with apparent viscosity comparable to conventional polymers. The IFT between crude oil and aqueous PMES solution at its critical micelle concentration (CMC) was observed as 2.74mN/m, which was further reduced to 0.37mN/m on addition of 2.5wt% NaCl. Core flooding experiments were conducted in sandpack system, to study the EOR efficiency using the synthesized polymeric surfactant and more than 26% additional recovery was observed after usual water flooding. Higher recoveries at higher temperature were observed because of swelling of crude oil and lowering of IFT.

Limits of Vinylidene Fluoride RAFT Polymerization

The investigations reported in this article probe the behavior of the RAFT polymerization of vinylidene fluoride (VDF) when degrees of polymerization higher than 50 are targeted: they demonstrate that higher molar mass PVDF (11 000 g mol–1) can indeed be prepared by RAFT polymerization, but only at rather low monomer conversions (<33%). This study more carefully examines the behavior of the reputedly nonreactive −CF2CH−XA chain ends (where XA designates the xanthate group) formed by inverse VDF addition and known to accumulate in the reaction medium during the polymerization. A combination of 1H and 19F NMR spectroscopic monitoring and comprehensive DFT calculations of the various exchange and propagation reactions at work explains the unexpected behavior of this polymerization. The present study disproves entirely the generally accepted belief that −CF2CH2–XA-terminated PVDF chains are “dead” and shows how these chains are reactivated, albeit slowly, throughout the polymerization. This activation occurs prevalently and counterintuitively through degenerative exchange by the minority PVDF–CF2CH2• radicals. The resulting kinetic scheme rationalizes the experimentally observed absence, after conversion of all the dormant chains into the less reactive −CF2CH2–XA end-group, of the longer polymer chains expected from a free radical polymerization mechanism.