AIBN Concentration Research Articles

Synthesis and properties of crosslinked waterborne polyurethane/acrylate copolymer latexes using AIBN initiator based on a solvent-/emulsifier-free method

In this study, a series of crosslinked waterborne polyurethane/acrylate copolymer latexes with different compositions were fabricated via emulsion polymerization using oil-soluble initiator (AIBN) based on a solvent-/emulsifiers-free method. Using the blend of styrene (St), butyl acrylate (BA) and crosslinkers (pentaerythritol triacrylate (PET3A) and pentaerythritol tetraacrylate (PET4A)) instead of acetone as a diluent and modifier, polyurethane prepolymers terminated with hydroxyethyl acrylate composite emulsions were prepared using polypropylene glycol (PPG), toluene diisocyanate (TDI), 2,2-dihydroxymethylpropionic acid (DMPA) and diethylene glycol (DEG) without other solvents. It was found that for all the emulsion polymerization of waterborne polyurethane and acrylates initiated by AIBN, the monomer conversions exceeded 96% when the concentration of AIBN was in the range of 0.5% to 0.9% (w/w) and the optimal reaction temperature was 75 °C. The introduction of St, BA and crosslinkers would form the polymer network, improving the tensile strength, water absorption of the copolymer latex films. Dynamic light scattering analyses showed that the copolymer latexes exhibited a unimodal distribution and showed no precipitates and unstable aggregates. The average particle size distribution was in the range of 131–154 nm. Transmission electron microscopy studies have confirmed the similar results and the latex particles possessed the core–shell morphology structure.

Precipitation copolymerization of methyl methacrylate/meth‐acrylate acid in supercritical carbon dioxide

AbstractUtilizing 2,2′‐azobis(isobutyronitrile) (AIBN) as the initiator, the copolymerization of methyl methacrylate/methacrylate acid is performed by precipitation copolymerization. The effects of pressure, initiation concentration, the methacrylic acid (MA) concentration, and small amount of water are investigated separately. The morphology and molecular weight are analyzed by scanning electron microscopy and gel permeation chromatography, respectively. The results indicates that the concentration of MA or AIBN affects the molecular weight greatly, and the maximum molecular weight reaches 213 kDa. The morphology of samples exhibits a certain degree of agglomeration. Most samples are obtained as free‐flowing powder with numerous spherical bulges under a proper polymerization condition.

A Comparative Study on Emulsion Polymerization Processes of Styrene Initiated by Water-soluble and Oil-soluble Initiators

The solubility of initiator determines its distribution and the roles played in emulsion polymerization as well as the final products, but this is still lack of systematic investigation. The present work focuses on this issue by comparing the kinetic behaviors and product properties of styrene emulsion polymerization initiated by 2,2-azoisobutyronitrile (AIBN) and potassium persulphate (KPS). Compared to KPS-initiated emulsion polymerization, the AIBN-initiated polymerization was found to be insensitive to the type of emulsifier, and have high polymerization rate as well as narrow molecular weight distribution and particle size distribution. This result indicates the effective free radicals are generated in micelles or colloids, which could decrease the proportion of homogeneous nucleation and make the process and product more controllable. As a consequence, there is a linear relationship between molecular weight of product and AIBN concentration in lg-lg coordinate. It provided a reference for the preparation of latexes with specified molecular weight and supported the possibility of the coexistence of multiple free radicals in one micelle or colloid when using oil-soluble initiator.

Surface structure and composition of narrowly-distributed functional polystyrene particles prepared by dispersion polymerization with poly(l-glutamic acid) macromonomer as stabilizer

A novel macromonomer composed of poly(α-l-glutamic acid) was used as a stabilizer for dispersion polymerization of styrene in DMF–water medium with AIBN initiator, giving narrowly-distributed functional polystyrene particles on which the poly(α-l-glutamic acid) was grafted. The resultant particles had 0.54–2.12 μm in size and 0.2–2.6 residue/nm2 in surface density and showed a pH-responsive colloidal behavior associated with a helix–coil transformation of the surface poly(α-l-glutamic acid). Not only the particle size but also the surface density were controlled with macromonomer concentration, macromonomer length, DMF composition, and styrene concentration, while no consistent trend for AIBN concentration was observed. A gel-permeation-chromatography curve of the particles was separated into three components. We tentatively identify the origin of each component and propose a possibility that unstable particles, which were generated even after the growing particles were stabilized, took an important role in particle growth and size distribution of the resultant particles.

Synthesis of a Fluorescence Labeled Spin Trap and Its ESR Study

Free radicals play a key role in physiological and pathological processes including aging and cancer development. To understand the biological role of free radicals,it is of critical importance to develop highly sensitive techniques for the detection and quantitation of free radicals being produced. Among the numbers of techniques used for the detection of free radicals,electron spin resonance( ESR)-spin trapping technique,owing to its relative higher specificity,is believed to be an indispensable method for the detection of free radicals in biological systems. However,the ESR-spin trapping technique was limited becauseit has the relative low sensitivity and it's hard to achieve real-time detection of free radicals in living cells. Considering that the fluorescence probes for labeling and tracking subcellular structures in living cells are easily available,a new spin trap conjugated with fluorescence moiety( DanPPN) was synthesized and characterized. The ESR study showed that the DanPPN could be used for the detection of superoxide anion,oxygen and carbon-centered radicals. Moreover,it was observed that the fluorescence intensity of DanPPN was decreased with the increase of the concentration of AIBN. The results suggested that the new spin trap may have a potential use for the detection of free radicals in biological systems.

Alpha and Omega: Importance of the Nonliving Chain End in RAFT Multiblock Copolymerization

Consecutive chain extensions via the RAFT process have been carried out, and polymers were investigated via ESI-MS to elucidate for the first time the chain end distributions in high detail. In this manner, the number of chains carrying living chain ends is assessed as well as the number of polymers carrying both RAFT typical R and Z groups. Polymerizations were carried out to practically full conversion, and two subsequent chain extensions have been carried out for each obtained material under systematic variation of the AIBN concentration between 1 and 10 mol % with regards to RAFT agent. Generally, very high percentages of living chains were observed the lower the AIBN concentration in the polymerization. With 1 mol %, up to 96% of chains (triblock structure) could be confirmed to be of living nature. In contrast, with 10 mol % of AIBN, only 85% of chains are living after addition of the third polymer block. When looking at the alpha–omega pure materials (carrying exclusively the RAFT-derived R group instead of an AIBN-derived end group), much lower values are deduced, yielding abundances of 90% for the low and 70% of the higher AIBN concentration. Loss of R groups indicates loss of the polymer block structure and must thus be seen as equally important as the information on livingness of the polymer. For multiblock copolymer synthesis it is thus strongly recommended to assess both the Z but also the R group integrity of the polymer.

Synthesis and Water Absorbency Property of Monodispersed Poly (acrylamide-co-itaconic acid) Spheres by Dispersion Polymerization

Monodispersed poly(acrylamide-co-itaconic acid) (P(AM-co-IA)) spheres were successfully prepared from acrylamide (AM) and itaconic acid (IA) monomers by batch dispersion polymerization and delayed addition dispersion polymerization, respectively. Effects of monomer ratios and concentrations of stabilizer (poly(N-vinylpyrrolidone), PVP), initiator (2,2’-azobisisobutyronitrile, AIBN) and cross-linker (N,N’-methylenebisacrylamide, Bis-A) on particle sizes and size distributions were systematically investigated. The particle size increased with the increase of IA content, whereas decreased with increase the concentration of PVP-K30, AIBN and Bis-A. After swollen in water, the particles prepared from batch method showed some dissociation. However, the particles from delayed addition method showed high swellability at 305.71%, due to the intense and homogenous network in the particles.

Controlled radical copolymerization of vinyl acetate and dibutyl maleate by iodine transfer radical polymerization

Iodine transfer radical homo- and copolymerization of vinyl acetate (VAc) with dibutyl maleate (DBM) were carried out in the presence of ethyl iodoacetate (EtIAc) and 2,2′-azobis(isobutyronitrile) (AIBN) as chain transfer agent and initiator, respectively, at 60 °C. Molecular weight and its distribution and (co)polymer structure (i.e. copolymer composition and chain end groups) were analysed using gel permeation chromatography and 1H NMR spectroscopy, respectively. Homo- and copolymerization reactions proceed via a controlled characteristic with predetermined molecular weight and relatively narrow molecular weight distribution. The presence of DBM in the reaction mixture decreases the consumption rate of EtIAc as well as the polymerization rate. This is attributed to the effect of DBM on the transfer constant to the EtIAc and probably on the iodine exchange rate constant between the growing chains. The effect of the concentration of AIBN, EtIAc and overall monomers on the conversion, molecular weight and its distribution was studied. Simultaneously high conversion and molecular weight with a relatively narrow molecular weight distribution can be achieved only when equimolar and intermediate concentration of EtIAc and AIBN is used in the reaction mixture. End-group analysis by 1H NMR reveals that iodinated VAc end groups in the (co)polymer chains are unstable, resulting in aldehyde end groups. Thermogravimetric analysis shows that the thermal stability of the VAc-based polymer increases on incorporating DBM units into the copolymer chains. © 2013 Society of Chemical Industry

Preparation of Poly (dimethyl Diallyl Ammonium Chloride - Acrylamide) via Inverse Microemulsion Polymerization Process

The inverse microemulsion copolymerization of poly (dimethyl diallyl ammonium chloride-acrylamide) (PDMDAAC-AM) has been studied using a blend of two surfactants Span-80 and OP-10 as the composite emulsifier in kerosene-water media. The effects of various polymerization parameters (e.g., polymerization method, reaction time, addition of electrolyte, oil-soluble initiator concentration and aqueous-to-oil phase volume ratio (A/O)) on the conversion and copolymer characteristics have been investigated. The optimum operating conditions for preparing (PDMDAAC-AM) were determined as reaction time 1h, HCOONa concentration 0.05% (w), AIBN concentration 0.045% (w), A/O 2/3 and semi-continuous process. Stable latex with high conversion (97.42%) and 267cm3/g intrinsic viscosity was obtained. In the semi-continuous process, the size distribution peak narrows along with the reaction process and the average diameter of the final product is 15.2 nm, which is significantly less than that prepared by one-time process.

Dispersion polymerization of styrene using a polystyrene/poly(l-glutamic acid) block copolymer as a stabilizer

A block copolymer (PS-b-poly(l-Glu)) composed of polystyrene and poly(l-glutamic acid) was used as a stabilizer for dispersion polymerization of styrene. When dispersion polymerization of styrene was conducted at 70°C in 80% dimethylformamide–water with 0.5wt% PS-b-poly(l-Glu), spherical polystyrene particles with Dn=0.72μm and narrow size distribution were obtained. Whereas AIBN concentration did not have any effects on particle size, molecular weight of the polystyrene particles was strongly dependent on the initiator concentration. As concentration of the PS-b-poly(l-Glu) increased from 0.2 to 1.0wt%, particle size decreased from Dn=0.91 to 0.69μm with keeping surface area occupied by one poly(l-glutamic acid) chain about S=50nm2. On the other hand, an increase in initial concentration of styrene from 2 to 20wt% caused an increase in particle size from Dn=0.48 to 1.36μm and a decrease in surface area per poly(l-glutamic acid) block from S=91 to 45nm2. Colloidal stability of the polystyrene particles in aqueous solution was responsive to pH due to the surface-grafted poly(l-glutamic acid). For dispersion polymerization of styrene, the PS-b-poly(l-Glu) functions as both a stabilizer and a surface modifier.

Antiferroelectric domains in liquid crystalline methacrylic polymers

The preparation of several liquid crystalline polymers obtained using different AIBN concentration and polymerization times are reported. The compounds were characterized by 1H NMR, differential thermal analysis (DTA), X-ray diffraction and pyroelectric measurements. For all polymers, a smectic C2 phase occurs over broad temperature range, where the molecules adopt an opposite tilt direction for alternate smectic layer. Crystalline polymers show an antiferroelectric behavior, developing an anticlinic phase responsible for the electric behavior. The arrangement of the side chain molecules within the partial crystalline network in these electrically active polymers is related with the kinetic of precipitation.

Preparation of polymer nanoparticles from renewable biobased furfuryl alcohol and maleic anhydride by stabilizer‐free dispersion polymerization

AbstractThe spherical polymer nanoparticles of biobased renewable monomers, furfuryl alcohol (FA) and maleic anhydride (MAn), with diameters (Dn) in the range of 120 to 500 nm have been prepared by stabilizer‐free dispersion copolymerization. In acetate or its mixture, the conversion of the monomers greatly depended on the concentration of AIBN. When the molar ratio of AIBN/monomers was 3.6% (wt), the monomer conversion could be as high as 80%. The aggregations of the solvated polymer chains formed the nuclei of the polymer particles. After the nucleation stage, both the monomer conversions and particle sizes increased steadily, while the coefficient of variation of the particle size decreased. The almost linear relationship between the Dn3 and the weight of polymer suggested that there is no significant secondary nucleation. The copolymer of FA and MAn could not dissolve in common organic solvents. Elemental analyses, FTIR and 13CP‐MAS spectra showed that the copolymer was close to the alternative copolymer of FA and MAn irrespective to the molar ratios of FA/MAn in monomer feed. Furthermore, the two 2,5‐ and 3,4‐dihydrofuran ring configurations exist in the copolymer and the later is the major one. The reaction of copolymer particles with triethylenetetramine confirmed the reactivity of the succinic anhydride groups at the surface of copolymer particles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Preparation of poly(methyl methacrylate) by ATRP using initiators for continuous activator regeneration (ICAR) in ionic liquid/microemulsions

In this study, we reported the synthesis of poly(methyl methacrylate) (PMMA) polymers via initiators for continuous activator regeneration atom transfer radical polymerization using CCl4 as initiator, FeCl3·6H2O/hexamethylene tetramine as catalyst complex, and 2,2′-azobis(isobutyronitrile) (AIBN) as reducing agent. The polymerization was conducted at 60 °C in the ionic liquid based microemulsion with hexadecyl trimethyl ammonium bromide (CTAB) as surfactant. Kinetics experimental results showed that the polymerization proceeded in a controlled/‘living’ process. The effects of the molar ratio of [CCl4]/[FeCl3·6H2O], the concentration of AIBN, temperature and the concentration of CTAB on the polymerization was investigated. The effect of CTAB concentration on the resulting PMMA particle size was also investigated. The obtained polymer was characterized by proton nuclear magnetic resonance and gel permeation chromatography. The living characteristics were demonstrated by chain extension experiment.

Iron-Mediated ICAR ATRP of Methyl Methacrylate

An iron(III) (FeCl3·6H2O) catalyst was found to be an active catalyst for initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) of methyl methacrylate (MMA), using triphenylphosphine (PPh3) as a ligand and azobis(isobutyronitrile) (AIBN) as a thermal radical initiator, and 1,4-(2-bromo-2-methylpropionato)benzene (BMPB2) as an ATRP initiator. Effects of reaction temperature, catalyst concentration and AIBN concentration on polymerization were investigated. These results showed that the catalyst was highly efficient for the ICAR ATRP of MMA. For example, even if the catalyst concentration decreased to 34 ppm, the polymerization with the molar ratio of [MMA]0/[BMPB2]0/[FeCl3·6H2O]0/[PPh3]0/[AIBN]0 = 500/1/0.03/1.5/0.1 could be carried out at 60 °C with a conversion 70.4% in 32 h. At the same time, the molecular weight of the obtained PMMA with a narrow molecular weight distribution (Mw/Mn = 1.37) was consistent with the theoretical one.

Kinetic Studies of the Initiation Step in Copper Catalyzed Atom Transfer Radical Addition (ATRA) in the Presence of Free Radical Diazo Initiators as Reducing Agents

Kinetic parameters for the reduction of copper(II) complexes in atom transfer radical addition (ATRA) in the presence of free-radical diazo initiator (AIBN) were determined using both experimental and kinetic modeling techniques. The rate constant of decomposition of AIBN (k(dc)) in various solvents was determined at 60 degrees C using UV-vis spectroscopy. Rate constants of deactivation (k(d,AIBN)) of [Cu(II)(TPMA)Cl][Cl] (TPMA = tris(2-pyridylmethyl)amine), [Cu(II)(Me(6)TREN)Cl][Cl] (Me(6)TREN = tris[2-(N,N-dimethylamino)ethyl]amine), [Cu(II)(PMDETA)Cl(2)] (PMDETA = N,N,N',N'',N''-pentamethyldiethylenetriamine), and [Cu(II)(bpy)(2)Cl][Cl] (bpy = 2,2'-bipyridine) complexes by radicals generated from the decomposition of AIBN were measured using the TEMPO-trapping method in a competitive clock reaction. Activation rate constants (k(a,AIBN)) were finally estimated from kinetic modeling utilizing the experimentally determined rate constants of decomposition of AIBN and deactivation. The effect of k(a,AIBN), k(d,AIBN), k(dc) and initial AIBN concentration on the overall copper(I) and copper(II) concentrations in the initiation step of the ATRA process was also evaluated through kinetic modeling.

Synthesis and Evaluation of New Dicarboxylic Acid Functional Trithiocarbonates: RAFT Synthesis of Telechelic Poly(n-butyl acrylate)s

We report herein the synthesis of three new diacid functional trithiocarbonates (TTCs) in which the substitution pattern about the TTC functionality is varied and compare their effectiveness alongside examples of previously reported trithiocarbonates as mediating agents in the RAFT polymerization of n-butyl acrylate. For direct comparative purposes we show that at an initial TTC concentration:initial AIBN concentration ([TTC]0:[AIBN]0) of 20 2-(2-carboxyethylsulfanylthiocarbonylsulfanyl)propionic acid (TTC5) and 2-(2-carboxyethylsulfanylthiocarbonylsulfanyl)-2-methylpropionic acid (TTC6) perform as well as 3-benzylsulfanylthiocarbonylsulfanylpropionic acid (TTC3) with respect to kinetics and molecular weight control. In contrast, 2-(1-carboxy-1-methylethylsulfanylthiocarbonylsulfanyl)-2-methylpropionic acid (TTC1)-mediated homopolymerization deviates from “ideal” behavior due, we speculate, to steric crowding of the central TTC core. Additionally, 3-(2-carboxyethylsulfanylthiocarbonylsulfanyl)propionic acid (TTC4) fails to confer any control on the homopolymerization of nBA with the polymerization exhibiting complex characteristics, as evidenced in the resulting molecular weight distribution, which may be indicative of hybrid behavior. Subsequently, we examine the effect of [TTC]0:[AIBN]0 for TTC5 and TTC6 and show that lower ratios result in faster polymerizations, consistent with previous reports. Finally, we demonstrate the ability to form block copolymers with high reinitiating efficiency. These new TTCs thus offer access to the direct synthesis of AB diblock dicarboxylic acid telechelic (co)polymers.

Effect of Alkyl Group Substituents, Temperature, and Solvents on the Ultrasonic Degradation of Poly(n-alkyl acrylates)

The effect of alkyl group substituents on the degradation rate of poly(n-alkyl acrylate) was investigated by studying the ultrasonic degradation of poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA), and poly(n-butyl acrylate) (PBA) in o-dichlorobenzene at 30 °C. A continuous-distribution kinetic model with midpoint scission was used to determine the rate coefficients. The rate coefficient increased with a decrease in the number of carbon atoms in the alkyl group substituent; thus, the degradation rate followed the order PMA > PEA > PBA. This was explained based on the delocalization of charge on the carbon atoms joining two monomer units. The effect of temperature and solvents on the ultrasonic degradation of PBA was also investigated. The degradation rate coefficient decreased with an increase in the vapor pressure of the solvent and with an increase in the temperature. The effect of an initiator, 2,2‘-azobis(isobutyronitrile) (AIBN), on the degradation of PBA was also investigated. The degradation rate decreased with an increase in the AIBN concentration, and the experimental results were simulated by the model.

Dispersion copolymerization of styrene with vinylbenzyl-terminated polyoxyethylene macromonomer

Macromonomer with styrenic polymerizable group was synthetized by anionic polymerization of ethylene oxide initiated by potassium vinylbenzyl alcoholate, p-Vinylbenzyl-terminated polyoxyethylene macromonomer (PEO-VB) was then copolymerised with styrene in water/alcohol continuous phase. The resulting polymer is chiefly non soluble in that medium, and the final state is polymer particles in the range 500-1000 nm in diameter stabilized by a macromonomer-rich copolymer. The conversion time curve consists of three regions. The length of nucleation period was inversely proportional to the volume ratio ethanol/water (E/W). The dependence of the polymerization rate (Rp) vs. conversion is described by a curve with two-rate intervals. The rate of polymerization increased with increasing PEO-VB and initiator AIBN concentration but was nearly independent of the volume ratio E/W. The particle number slightly increased with increasing PEO-VB and AIBN concentration. The molecular weight of graft copolymer increased with increasing the volume fraction of water, PEO-VB and AIBN concentration.

Low molar mass polybutadiene made crosslinkable by silane moities introduced via addition of thiol to double bond: 3. Synthesis and kinetic study

Low molar mass polybutadiene was made crosslinkable under moisture by the addition of mercapto propyl triethoxy silane to double bonds. The reaction was carried out at 75°C in the presence of AIBN as initiator. AIBN concentration and time showed that triethoxy silane groups were introduced quantitatively in the range of 1.05 to 7.9 per chain. A 1H n.m.r. study showed clearly that only vinylic units reacted at low modification rates. Volumetric titration of the remaining thiol was used to follow the reaction. A new mechanism is proposed here to lead to a kinetic relation, similar to the one already used by several authors, but kinetically provable. Moreover, it has been pointed out that there is probably an evolution of kinetic constants with the progress of the reaction due to, among other reasons, a local steric hindrance at the level of vinyl sequences and/or a variation in chain conformation.

Controlled Radical Copolymerization of Styrene and the Macromonomer of PEO with a Methacryloyl End Group

The amphiphilic copolymer with uniform poly(ethylene oxide) as side chains was prepared by initiating of AIBN polymerization of methacryloyl-terminated PEO macromonomer (PEOM) and styrene (St) in the presence of 4-hydroxyl-2,2,6,6-tetramethylpiperidine-1-oxy (HTEMPO). The copolymerization is controllable, the molecular weight of the copolymer and the conversion of the monomer increase with the polymerization time, and the distribution is rather narrow and is in the range 1.23−1.33. It was confirmed that the relative reactivity of PEOM macromonomer decreases with an increase in its molecular weight, and the variation of concentration of HTEMPO and AIBN can affect the copolymerization greatly.