Polymerization Of Vinyl Acetate Research Articles

Kinetics of MMA and VAc Miniemulsion Polymerizations Using Miglyol and Castor Oil as Hydrophobe and Liquid Core

AbstractMiniemulsion polymerization reactions of methyl methacrylate (MMA) and vinyl acetate (VAc) for the synthesis of biocompatible polymeric nanoparticles were comparatively studied. 2,2'‐Azo‐bis(isobutyronitrile) was used as initiator, lecithin as surfactant, and Miglyol 812 or castor oil as costabilizers. Despite the propagation coefficient of VAc being ten times higher than that of MMA, the reaction rates of the VAc polymerizations were much lower. In VAc polymerizations a higher amount of low‐molar‐mass polymer was formed which may be attributed to transfer reactions to low‐molar‐mass species. Polymerizations with a high Miglyol 812/VAc ratio were slower and resulted in the formation of a higher amount of low‐molar‐mass polymer compared to polymerizations with a low Miglyol 812/VAc ratio or VAc miniemulsion polymerizations with hexadecane as costabilizer. In reactions with high Miglyol 812/VAc ratios the peak area of the GPC trace corresponding to the polymer was substantially higher than the theoretical polymer content.

Preparation of miktoarm star-block copolymers PSn-b-PVAc4-n via combination of ATRP and RAFT polymerization

Three tetrafunctional bromoxanthate agents (Xanthate3-Br, Xanthate2-Br2, and Xanthate-Br3) were synthesized. Initiative atom transfer radical polymerizations (ATRP) of styrene (St) or reversible addition fragmentation chain transfer (RAFT) polymerizations of vinyl acetate (VAc) proceeded in a controlled manner in the presence of Xanthate3-Br, Xanthate2-Br2, or Xanthate-Br3, respectively. The miktoarm star-block copolymers containing polystyrene (PS) and poly(vinyl acetate) (PVAc) chains, PSn-b-PVAc4-n (n = 1, 2, and 3), with controlled structures were successfully prepared by successive RAFT and ATRP chain-extension experiments using VAc and St as the second monomers, respectively. The architecture of the miktoarm star-block copolymers PSn-b-PVAc4-n (n = 1, 2, and 3) were characterized by gel permeation chromatography and 1H NMR spectra. Furthermore, the results of the cleavage of PS3-b-PVAc and PVAc2-b-PS2 confirmed the structures of the obtained miktoarm star-block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Synthesis of diblock copolymers containing poly(N‐vinylcarbazole) by reversible addition‐fragmentation chain transfer polymerization

AbstractThe reversible addition‐fragmentation chain transfer (RAFT) polymerization of N‐vinylcarbazole (NVK) mediated by macromolecular xanthates was used to prepare three types of block copolymers containing poly(N‐vinylcarbazole) (PVK). Using a poly(ethylene glycol) monomethyl ether based xanthate (PEG‐X), the RAFT polymerization of NVK proceeded in a controlled way to afford a series of PEG‐b‐PVK with different PVK chain lengths. Successive RAFT polymerization of NVK and vinyl acetate (VAc) with a small molecule xanthate (X1) as the chain transfer agent was tested to prepare PVK‐b‐PVAc. Though both monomers can be homopolymerized in a controlled manner with this xanthate, only by polymerizing NVK first could give well‐defined block copolymers. The xanthate groups in the end of PVK could be removed by radical‐induced reduction using tributylstannane, and PVK‐b‐PVA was obtained by further hydrolysis of PVK‐b‐PVAc under basic conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Application of support vector regression for developing soft sensors for nonlinear processes

AbstractThe field of soft sensor development has gained significant importance in the recent past with the development of efficient and easily employable computational tools for this purpose. The basic idea is to convert the information contained in the input–output data collected from the process into a mathematical model. Such a mathematical model can be used as a cost efficient substitute for hardware sensors. The Support Vector Regression (SVR) tool is one such computational tool that has recently received much attention in the system identification literature, especially because of its successes in building nonlinear blackbox models. The main feature of the algorithm is the use of a nonlinear kernel transformation to map the input variables into a feature space so that their relationship with the output variable becomes linear in the transformed space. This method has excellent generalisation capabilities to high‐dimensional nonlinear problems due to the use of functions such as the radial basis functions which have good approximation capabilities as kernels. Another attractive feature of the method is its convex optimization formulation which eradicates the problem of local minima while identifying the nonlinear models. In this work, we demonstrate the application of SVR as an efficient and easy‐to‐use tool for developing soft sensors for nonlinear processes. In an industrial case study, we illustrate the development of a steady‐state Melt Index soft sensor for an industrial scale ethylene vinyl acetate (EVA) polymer extrusion process using SVR. The SVR‐based soft sensor, valid over a wide range of melt indices, outperformed the existing nonlinear least‐square‐based soft sensor in terms of lower prediction errors. In the remaining two other case studies, we demonstrate the application of SVR for developing soft sensors in the form of dynamic models for two nonlinear processes: a simulated pH neutralisation process and a laboratory scale twin screw polymer extrusion process. A heuristic procedure is proposed for developing a dynamic nonlinear‐ARX model‐based soft sensor using SVR, in which the optimal delay and orders are automatically arrived at using the input–output data.

Preparation of an Al2O3—EVA Co-film and its Thermal Conductivity

To decrease the working temperature of the photovoltaic (PV) module in a solar PV system, an elastic co-film with excellent mechanical properties and adhesiveness, as well as high thermal conductivity, was fabricated based on the composition of a thermal-conductive alumina and ethylene vinyl acetate (EVA) polymer. The thermal conductivity of co-films with various particle sizes, dosage, surface properties, etc. of alumina was investigated by the laser scattering method. The scanning electron microscopic results showed that the co-film with 80 shares of submicron alumina in EVA polymer had a good interface binding. The thermal-conductive mechanism of the co-film was likewise discussed.

Heterocomplementary H-Bonding RAFT Agents as Tools for the Preparation of Supramolecular Miktoarm Star Copolymers

Supramolecular miktoarm stars (AB2 type) composed of poly (methyl methacrylate)-polystyrene2 (PMMA-PS2), poly(isoprene)-polystyrene2 (PI-PS2), and poly(vinyl acetate)-polystyrene2 (PVAc-PS2) were successfully synthesized by assembling reversible addition−fragmentation chain transfer (RAFT)-polymerized chains bearing hydrogen-bonding heterocomplementary associating units. To this end, thymine and diaminopyridine-functionalized chain transfer agents were designed to efficiently mediate the polymerization of vinyl acetate, methyl methacrylate, isoprene, and styrene. The selective associations of the resulting hydrogen-bonding macromolecular building blocks PVAc/PS, PI/PS, and PMMA/PS were demonstrated by 1H NMR in CDCl3 solutions. Miktoarm stars formation in the bulk was also confirmed by transmission electronic microscopy.

Controlled Radical Polymerization of Vinyl Acetate with Cyclopentadienyl Chromium β-Diketiminate Complexes: ATRP vs OMRP

The ability of compounds CpCrII(nacnacAr,Ar) (Ar = Dipp, 1; Xyl, 2) to catalyze the atom transfer radical polymerization (ATRP) of vinyl acetate has been explored using methyl 2-chloropropionate as initiator. Polymerizations were also carried out under reverse ATRP conditions with thermal initiation by 2,2′-azobis(4-methoxy2,4-dimethylvaleronitrile) (V-70) in the presence of compounds CpCrIII(nacnacAr,Ar)Cl (Ar = Dipp, 3; Xyl, 4). All data suggest that these processes are in fact proceeding by organometallic-mediated radical polymerization (OMRP). Stoichiometric reactions between complex 2 and the chlorinated compounds CH3CH(Cl)COOCH3, ClCH2COPh, CH3CHClOOCCH3, ClCH2OOCtBu, and ClCH2tBu in the absence of monomer aid in the interpretation of the polymerization results. The first two substrates show rapid one-electron oxidative additions to generate 4 and O-bonded CrIII products, whereas the third and fourth substrates add much more slowly to generate 4 and C-bonded CrIII products; ClCH2tBu does not react. ...

Synthesis of water-soluble poly(vinyl alcohol)-grafted multi-walled carbon nanotubes

A facile method for preparing waster-soluble poly(vinyl alcohol)-grafted multi-walled carbon nanotubes (PVA-grafted MWNTs) was developed. Well-defined poly(vinyl acetate) chains end-capped by a cobalt(II) acetylacetonate (Co(acac)2) complex [PVAc-Co(acac)2] were synthesized by the cobalt-mediated radical polymerization (CMRP) of vinyl acetate. PVAc macroradicals generated by the homolytic cleavage of the carbon-cobalt (C-Co) bonds of PVAc-Co(acac)2 chains were then grafted directly to the MWNTs via radical addition reactions in dimethyl sulfoxide (DMSO) at 50 °C. The amount of the PVAc grafted onto the surface of the MWNTs decreased with increasing molecular weight of PVAc-Co(acac)2. Hydrolysis of the grafted PVAc finally yielded PVA-grafted MWNTs, which showed good solubility in water. Surface functionalization of the MWNTs was confirmed by 1H NMR spectroscopy, FTIR spectroscopy and TEM.

Synthesis and characterization of azobenzene-functionalized poly(styrene)-b-poly(vinyl acetate) via the combination of RAFT and “click” chemistry

Here, we described a strategy for preparing well-defined block copolymers, poly(styrene)-b-poly(vinyl acetate) (PS-b-PVAc), containing middle azobenzene moiety via the combination of the reversible addition-fragmentation chain transfer (RAFT) polymerization and “click” chemistry. Firstly, a novel RAFT agent containing α-alkyne and azobenzene chromophore in R group, 2-(3-ethynylphenylazophenoxycarbonyl)prop-2-yl-9H-carbazole-9-carbodithioate (EACDT), was synthesized and used to mediate the RAFT polymerization of styrene (St). Well-defined α-alkyne end-functionalized poly(styrene) (PS) was obtained. Secondly, the RAFT polymerization of vinyl acetate (VAc) was conducted using functionalized RAFT reagent with ω-azide structure in Z group, O-(2-azidoethyl) S-benzyl dithiocarbonate (AEBDC). Well-defined ω-azide end-functionalized poly(vinyl acetate) (PVAc) was obtained. Afterwards, the resulting α-alkyne terminated PS was coupled by “click” chemistry with the azide terminated PVAc. The block copolymer, PS-b-PVAc, was obtained with tailored structures. The products from each step were characterized and confirmed by GPC, 1H NMR, IR and differential scanning calorimetry (DSC) examination. Kinetics of the trans-cis-trans isomerization from azobenzene chromophore in PS-b-PVAc and PS were investigated in CHCl3 solutions.

Free radical polymerization of vinyl acetate in the presence of liquid polysulfides

The free radical polymerization of vinyl acetate in the presence of a liquid polysulfide H(SCH2CH2OCH2OCH2CH2S)nH (thiocol) was investigated from the point of view of reaction mechanism and characterization of the resulting copolymers. It was shown that, besides the thiol end groups that were consumed very rapidly, the disulfide groups within the thiocol chain were also involved in chain transfer processes. The chain transfer constant of the thiocol S–S groups in the polymerization reaction was estimated from their rate of consumption versus the rate of monomer consumption (CT=0.89). The resulting copolymers, made up of randomly distributed thiocol sequences and PVAc blocks, were characterized by 1H NMR, GPC, DSC and TGA measurements. The copolymers displayed only one glass transition each, which decreased as the PVAc block length decreased, while their thermal stability was lower than that of both thiocol and PVAc. The molecular weight of the copolymers increased with VAc conversion as a consequence of the insertion of PVAc blocks within the thiocol chain.

Some comparative aspects of particle formation and rate of reaction in emulsion polymerization of vinyl acetate and butyl acrylate

AbstractThe comparative study of monomers, in terms of particle formation and rate of polymerization, facilitates the interpretation of the results from the corresponding copolymerization runs and can be considered as a preliminary step toward formulation of copolymerization reactions. Batch emulsion homopolymerization of vinyl acetate (VA) and butyl acrylate (BA), as model monomers with a wide water solubility disparity, were carried out to investigate the effects of variations in the monomer concentration, electrolyte concentration, reaction volume, and surfactant type on the kinetics of polymerization. With sodium lauryl sulfate as surfactant, VA emulsion polymerization produced more particles than BA at a lower monomer concentration, but fewer particles at a higher monomer concentration. At a lower VA concentration, a depressed growth for newly formed particles during interval III contributed to the formation of a large number of particles. The application of aerosol MA and OT surfactants improved the stability of polyvinyl acetate (PVA) particles so that a larger number of polymer particles was obtained for VA, in comparison with BA. BA emulsion polymerization showed little sensitivity to electrolyte concentrations and reaction volumes within the range studied. The colloidal stability of PVA particles was found to be quite sensitive toward the aforementioned variables. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Synthesis and application of new sizing and finishing additives based on carboxymethyl cellulose

Ammonium persulfate (NH 4) 2S 2O 8 was used to initiate the polymerization of vinyl acetate (VAc) monomer in presence of carboxymethyl cellulose (CMC) to produce (CMC-g-PVAc) adduct under different conditions including, initiator concentration, temperature and time of polymerization, as well as VAc to CMC ratio. The produced adduct was further saponified to produce the adduct CMC-g-poly vinyl alcohol (CMC-g-PVA). Saponification was conducted in ethanol using 40% aqueous sodium hydroxide solution. IR spectra of CMC, CMC-g-PVAc adduct and CMC-g-PVA adduct were investigated. CMC and CMC-g-PVA adduct in comparison with a physical mixture of CMC and PVA (Vinarol STH) were utilized as a sizing or finishing agent for 100% cotton and 50/50% cotton/polyester blend. It was found that samples finished using the produced CMC-g-PVA adduct acquired better mechanical properties such as wrinkle recovery angle, tensile strength, dyeability and oily stain release than CMC alone or physical mixture with PVA. On the other hand, it appears that (CMC-g-PVA) adduct is a promising easily removals sizing agents.

Mark–Houwink Parameters for the Universal Calibration of Acrylate, Methacrylate and Vinyl Acetate Polymers Determined by Online Size‐Exclusion Chromatography—Mass Spectrometry

AbstractSize exclusion chromatography coupled online to electrospray ionization mass spectrometry (SEC/ESI‐MS) is employed to establish universal calibration (UC) relationships for a number of linear poly(alkyl acrylates) and poly(alkyl methacrylates) as well as poly(vinyl acetate) synthesized via radical chain transfer polymerization. It is demonstrated that in the analyzed molecular weight range, Mark–Houwink–Kuhn–Sakurada (MHKS) coefficients can be successfully determined in relation to values of pMMA. The agreement between the UC model using mass spectrometry‐derived MHKS coefficients and the measured data was generally better than 10%. The MHKS values reported herein are expected to remain valid up to 20 kDa. A comparison with the outcome of UC using literature reported MHKS coefficients determined by intrinsic viscosity—molecular weight (IV‐MW) measurements is provided. Errors of more than 30% can result when these literature values are employed in the low molecular weight range ( < 20 kDa). Use of MHKS coefficients derived from IV‐MW measurements in UC is, therefore, strongly discouraged at molecular weights below 20 kDa.magnified image

Effects of agitation in emulsion polymerization of vinyl acetate, ethylene, and N-methylol acrylamide

The emulsion polymerization of vinyl acetate monomer (VAM), ethylene and N-methylol acrylamide (NMA) was carried out in a high pressure stirred reactor using an Rushton flat blade impeller at a rotational speed of 300 rpm under a semi-batch polymerization process, which was subsequently grown by the continuous addition of monomers (VAM, ethylene, and NMA). The particle diameters of the samples withdrawn during polymerization were determined by using capillary hydrodynamic fractionation (CHDF). Also, the number of particles was calculated from the data obtained by CHDF. Coagulum formation was studied. It was found that coagulum formation increased with increasing conversion and auto-accelerated from ca. 20% conversion. The definition of coagulum in this research was presented. The coagulum formation pattern on the impeller was shown. Also, the flow pattern in the reactor under the same geometrical configuration and operating conditions was simulated.

Modeling of diffusion‐controlled reactions in free radical solution and bulk polymerization: Model validation by DSC experiments

AbstractIn this work, a detailed experimental study of diffusion‐controlled reactions in free radical polymerization by using differential scanning calorimetry (DSC) was carried out. The systems studied include the methyl methacrylate bulk polymerization as well as the solution and the bulk polymerization of vinyl acetate at a wide range of experimental conditions including initial initiator concentration, reaction temperature, and type and amount of solvent. The conversion data obtained by DSC was successfully simulated by using a mathematical model based on sound principles such as the free volume theory. The estimated parameters, by fitting predictions of this model to conversion data obtained by DSC were found to be in close agreement with the reported parameters in the literature, thus validating both the experimental and theoretical methods used in this work. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Controlled radical polymerization of vinyl acetate mediated by a vanadium complex

Initiation of the polymerization of vinyl acetate with azobis(isobutyronitrile) in the presence of a vanadium bis(iminopyridine) complex generates vanadium-capped dormant polymer chains with excellent correlation between molecular weight and conversion and good molecular weight distributions.

Graft Polymerization of Vinyl Acetate onto Potato Starch Dissolved in an Alkaline Solution

AbstractGraft polymerization of vinyl acetate (VAc) onto gelatinized and dissolved granular potato starch has been carried out using an initiation system of ceric ammonium nitrate (CAN)/nitric acid (HNO3) at 50°C. The granular starch was dissolved in an aqueous alkaline solution (0.25 M NaOH) for 24 h before graft reaction. The effects of reaction variables, such as the concentrations of acid, monomer, and initiator, on the grafting parameters of prepared starch/VAc copolymers have been investigated in both grafting methods for comparison. Although the scanning electron microscopy (SEM) images showed a rather similar homogeneous structure for dissolved and gelatinized starch, a higher grafting level, especially at lower monomer concentrations, was obtained for the copolymers prepared using the dissolved starch. A larger number of reactive sites uniformly created on the starch molecules led to greater accessibility of the monomer and improved considerably the grafting efficiency in the grafting conditions using the dissolved starch. The effects of the grafting methods on the microstructure, morphology, and thermal stability of the resulting copolymers have been studied by Fourier‐transform infrared (FTIR) spectroscopy, scanning electron microscopy, and thermogravimetric analysis (TGA), respectively. The TGA results showed that the grafting of VAc onto dissolved starch led to the formation of more thermally stable graft copolymers.

Characteristics of Continuous Emulsion Polymerization of Vinyl Acetate with a Compartment Reactor

Emulsion polymerization of vinyl acetate with a compartment reactor consisting of 3 well-mixing compartments has been investigated. A step response method revealed that the mixing of this reactor is characterized by a 4 CSTRs-in-series model. Higher conversion of the vinyl acetate monomer is obtained by the compartment reactor than by a single CSTR since the restricted axial dispersion suppresses the effluent of unreacted monomer. The oscillation of the mean particle size induced by the co-presence of small and large particles is inhibited due to narrow residence time distribution of particles, and stable particle size distributions are obtained under steady state operation. Back-mixing causes polymerization with short mean residence time in the first compartment. Since there is little back-mixing, polymerization occurs in the first vessel even when the mean residence time of feed is so low that the polymerization did not occur in a single CSTR. The compartment reactor can be a possible method to convert the batch process into a continuous process.

Organometallic‐Mediated Radical Polymerization: Developing Well‐Defined Complexes for Reversible Transition Metal‐Alkyl Bond Homolysis

AbstractOrganometallic‐mediated radical polymerization (OMRP) has emerged as a powerful new class of living controlled radical polymerization. In order to fulfill its potential in the polymerization of vinyl acetate (VOAc) and other challenging monomers, the effects of ancillary ligands on the metal‐alkyl bond dissociation energy in OMRP reagents must be thoroughly explored. Recent results investigating structure‐activity relationships in well‐defined cobalt, iron and chromium complexes will be discussed. The involvement of radical intermediates in oxidative addition of secondary alkyls for catalytic cross‐coupling reactions catalyzed by first row transition metals will also be examined for relevant design concepts.magnified image

Cyclopentadienyl Chromium β-Diketiminate Complexes: Initiators, Ligand Steric Effects, and Deactivation Processes in the Controlled Radical Polymerization of Vinyl Acetate

The new compounds CpCr(nacnacAr,Ar′) with nacnacAr,Ar′ = Ar−N---C(Me)---CHC(Me)---N−Ar′ (Ar = Ar′ = C6H2Me3-2,4,6 or mes, 2; C6H3Et2-2,6 or dep, 3; Ar = C6H3Me2-2,6 or xyl and Ar′ = C6H3iPr2-2,6 or dipp, 4) have been synthesized and used in polymerization experiments in addition to the previously known analogues with Ar = Ar′ = xyl, 1, or dipp, 5. The compounds were used as moderators for the polymerization of vinyl acetate (VAc) initiated by V-70, according to an OMRP mechanism. The alkylchromium(III) thermal initiator CpCr(nacnacxyl,xyl)(CH2CMe3) (8) was synthesized from CpCr(nacnacxyl,xyl)(OTs) (7) and Mg(CH2CMe3)2(dioxane), while 7 was obtained from CpCr(nacnacxyl,xyl)Cl (6) and AgOTs. The polymerizations carried out with (1−5)/V-70/VAc at elevated temperatures yielded rapid deactivation, suggestive of irreversible radical trapping. On the other hand, room-temperature polymerizations carried out with 6/VAc proceeded, albeit slowly, to greater conversions. A labilizing effect of the Ar/Ar′ steric bulk is suggested by QM/MM calculations of CrIII−C BDE for models of the OMRP dormant species with 1, 5, and the parent system where Ar = Ar′ = Ph. Thermal deactivation of the nacnacxyl,xyl system has been evidenced, with formation of the acetate complex CpCr(nacnacxyl,xyl)(OAc), 9, as confirmed by an UV−vis study and by independent synthesis. This product is proposed to form by β-acetate transfer from the growing radical chain, triggered by a head−head monomer insertion. Compounds 2, 3, 6, 7, 8, and 9 have been structurally characterized by X-ray diffraction methods.