Cross-linking polymerization of acrylic acid in supercritical carbon dioxide

Cross-linking polymerization of acrylic acid in supercritical carbon dioxide (scCO₂) was studied in a batch reactor at 50 °C and 207 bar with either triallyl pentaerythritol ether or tetraallyl pentaerythritol ether as the cross-linker and with 2,2′-azobis(2,4-dimethyl-valeronitrile) as the free radical initiator. All polymers were white, dry, fine powders. Scanning electron microscopy showed that the morphology of the polymer particles was not affected by cross-linking. As the cross-linker concentration was increased, the polymer glass transition temperature first decreased, then increased. Water-soluble and water-insoluble polymers were synthesized by adjusting the cross-linker concentration. Viscosity measurements showed that the polymer thickening effect strongly depended on the degree of cross-linking. Finally, cross-linking polymerization of acrylic acid in scCO₂ was carried out in a continuous stirred tank reactor. The use of cross-linker decreased the monomer conversion in this system.     

Solventless UV crosslinkable acrylic pressure sensitive adhesives

The synthesis and characterization of solventless acrylic UV crosslinkable pressure sensitive adhesives are presented. Different prepolymers were synthesized using bulk polymerization procedure. The reaction mixture consisted of acrylic monomers (2-ethylhexyl acrylate, acrylic acid and t-butyl acrylate), azobisisobutyronitrile initiator, chain transfer agent n-dodecylmercaptan and unsaturated UV photoinitiator 4-acryloyloxybezophenone, which was copolymerized into polymer backbone. Different formulations were tested and the prepolymer was characterized by viscosity measurements and final monomer conversions. The prepolymers were coated onto PET foil and crosslinked by application of UV light source. Peel adhesion at 180° on glass plate was measured. Gel phase was determined using the Soxhlet extraction and copolymer glass transition temperatures (T_g) were analyzed by differential scanning calorimetry (DSC). Results showed that the final monomer conversions in highly exothermic bulk polymerization reached a level between 75% and 90%. Prepolymer viscosity was highly influenced by change in polymer molecular weight and by addition of acrylic acid as a comonomer. On the other hand, the viscosity remained at the low level when t-butyl acrylate was used. The amount of gel phase for all adhesives was above 60 wt.%. Peel strength measurements showed decrease in peel strength with decreasing polymer molecular weight and increase of peel, when acrylic acid was used as a comonomer. All adhesive coatings with t-butyl acrylate comonomer showed cohesive failure.     

Absolute online monitoring of acrylic acid polymerization and the effect of salt and pH on reaction kinetics

Using recently introduced Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP), the kinetics of acrylic acid polymerization was studied. ACOMP yields the absolute weight‐averaged mass (M_w), monomer conversion, and other quantities. As the initiator concentration increased, it was shown that the rate increased and the M_w decreased as in regular free‐radical polymerization. The effect of salt on acrylic acid polymerization in an aqueous solution was investigated. The polymerization rate and M_w both decreased with an increasing salt concentration. ACOMP molecular weights were also compared with size‐exclusion chromatography on aliquots periodically withdrawn during the reaction, and good agreement was found. The effect of the pH on the rate and the molecular weight was also investigated, and when the medium pH was changed from 2 to 5 with sodium hydroxide, the rate and M_w both decreased as the pH increased. Light‐scattering results of reaction end products in the reference solvent showed that molecules synthesized at higher pH were in a more expanded form. When equimolar sodium hydroxide was added to the acrylic acid (pH ? 5) and sodium acrylate formed, adding salt did not effect the reaction kinetics of the poly(sodium acrylate); its effect on the products was a relatively minor decrease of M_w. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1352–1359, 2004     

In‐depth characterization of granular starch‐graft‐polyester compositions as obtained by in situ polymerization of lactones from the starch surface

The synthesis of poly(ε‐caprolactone) (PCL)‐grafted granular starch was carried out either in bulk (without solvent) or in toluene suspension by a two‐step procedure. First step relied upon the activation of the hydroxyl groups available at the starch surface by alkylaluminum derivatives like AlEt₃ and removal of non‐surface‐grafted organo‐aluminum active species. The latter species were made free in solution by reaction with the remaining water molecules still contaminating the polymerization medium despite intensive drying of the starch granules. In the second step, ε‐caprolactone was polymerized via a coordination‐insertion ring‐opening polymerization as initiated by the surface‐grafted aluminum alkoxide species. The present contribution aims at investigating various parameters such as nature of the alkyl aluminum activator and monomer (δ‐valerolactone was studied as well), temperature, concentration, and addition of a solvent (polymerization in toluene suspension), reaction time, and also the experimental procedure used to recover the polyester chains and measure the grafting efficiency. It turns out that, under the studied conditions, dialkylaluminum alkoxides surface‐grafted onto the starch granules were more likely generated and promote a fast polymerization reaction with the formation of grafted PCL chains with a molecular weight that can be as high as 225 000 (M_n value) for polymerization carried out in toluene suspension. Copyright © 2004 Society of Chemical Industry     

Surface graft polymerization of ionic monomers onto poly(ethylene terephthalate) by UV-irradiation without degassing

Graft polymerization of anionic and cationic monomers was performed onto the surface of poly(ethylene terephthalate) (PET) film with a simultaneous UV irradiation method, but using no photo-sensitizer. To effect graft polymerization, the PET film was immersed in an aqueous solution containing a monomer and periodate (NaIO₄) of appropriate concentrations, followed by UV irradiation without degassing. The monomers used were 2-acrylamide-2-methylpropane sulfonic acid and acrylic acid as anionic and N,N-dimethyl aminopropyl acrylamide and dimethyl aminoethyl methacrylate as cationic monomer. The role of NaIO₄ at the polymerization was to make the concentration of oxygen dissolved in solution zero by the photochemical reaction with the oxygen. The surface structure of grafted films was characterized by their contact angle, dyeing, X-ray photoelectron spectroscopy, and zeta potentials. Graft polymerization took place, not merely on the outermost surface, but also within the thin surface region of the PET film without any change in bulk properties. © 1993 John Wiley & Sons, Inc.     

H2O2-induced graft polymerization of acrylic acid/styrene mixtures on poly(ethylene terephthalate) fibers

Graft polymerization of acrylic acid/styrene mixtures on poly(ethylene terephthalate) fibers using H₂O₂ as initiator was investigated under different conditions including acrylic acid/styrene ratio, monomer mixtures concentration, initiator concentration, polymerization temperature, pH of polymerization medium, addition of metallic salts, and use of solvent/water mixture instead of aqueous medium. It was found that the rate and extent of grafting for acrylic acid/styrene mixtures were much higher than those of single monomers, indicating a synergestic effect. Maximum percent grafting occurred when acrylic acid/styrene mixture at a ratio of 30:70 was used. Increasing the monomer mixture concentration from 2% to 40% was accompanied by a significant enhancement in percent grafting. The latter increased also significantly as the H₂O₂ concentration increased from 10 to 150 meq/L; a further increase in H₂O₂ concentration decreased grafting. No grafting took place at 65°C even after 4 h. Raising the polymerization temperature to 75°C expedited grafting; the magnitude of the latter increased by increasing the temperature up to 95°C. Addition of copper sulphate and ferrous ammonium sulphate to the polymerization system offset grafting, the opposite holds true for lithium chloride provided that its concentration does not exceed 15 mmole/L. Methyl alchol/water mixture (20:80) constituted the optimal medium for polymerization. Grafting of acrylic acid/styrene mixtures to poly(ethylene terephtalate) fibers resulted in considerable improvement in moisture regain of the latter.     

Inverse suspension polymerization of sodium acrylate: Synthesis and characterization

Crosslinked Poly(acrylic acid) was synthesized by inverse suspension polymerization. This process was investigated to determine the influence of different parameters like temperature, stirring speed, solution pH, and crosslinker concentration and to obtain the best control of the kinetics. An aqueous phase containing partially neutralized acrylic acid, crosslinking agent, and initiator agent was dispersed in an organic phase and stabilized by a surfactant. The inverse suspension was carried out in heptane as the organic phase with a different ratio of neutralization of the monomer, different crosslinker concentrations, and several stirring speeds. The polymerization was initiated by potassium persulfate (K₂S₂O₈) with N‐N′‐methylenebisacrylamide (MBA_C) as the crosslinker and sorbitan monooleate as the surfactant. The influence of several parameters on the bead size and the swelling capacity was investigated. Particle diameters ranged from 10 to 130 μm. The kinetic results obtained by differential scanning calorimetry showed that conversion and polymerization rates are a function of the solution pH, and they fell when the concentration of the crosslinking agent was higher than 7.5% in the mass of MBA_C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2621–2630, 2000     

Photopolymerization kinetics of cycloaliphatic epoxide–acrylate hybrid monomer

An epoxide–acrylate hybrid monomer was synthesized by the controlled reaction of a cycloaliphatic epoxide and acrylic acid. The photopolymerization kinetics was investigated using a real‐time infrared spectroscopy technique. The influences of photoinitiator concentration, free radical initiator and polymerization atmosphere on the polymerization were studied. The hybrid monomer showed unique photopolymerization kinetics in the photopolymerization process and the final conversions of epoxy groups and acrylate double bonds were improved synchronously. Dynamic mechanical analysis results demonstrated that the hybrid monomer cured film formed a more uniform polymer network than the blend of epoxy acrylate and epoxide. Copyright © 2007 Society of Chemical Industry     

Effects of film thickness and inhibitor concentration on the sorption and thermal polymerization of acrylic acid in low-density polyethylene

We investigated the effects of hydroquinone monomethyl ether concentration and film thickness upon the thermal polymerization of acrylic acid on low-density polyethylene. The thermal polymerization of acrylic acid on low-density polyethylene depended on the concentration of hydroquinone monomethyl ether inhibitor. It was a free-radical reaction with initiation on the film surface and then proceeding to the bulk matrix. The process was not controlled by monomer diffusion for the range of film thickness of 90–200 μm. It became a diffusion-controlled process at higher film thicknesses ( > 200 μm). A film layer of up to 100 μm was proposed as the limiting thickness for a diffusion-free process. © 1993 John Wiley & Sons, Inc.     

Free radical polymerization kinetics of monomers functionalized with ?AsO(OH)2 in aqueous media

The free radical polymerization kinetics of the isomer sodium salts of o‐ and p‐methacryloylaminophenylarsonate in aqueous solution have been studied using a dilatometric method. The polymerizations, initiated with potassium persulfate, were carried out at a constant monomer initial concentration of 0.50 mol/L and the initiator initial concentration was fixed at one of the following: 1.00, 2.00, 5.00, 8.00, or 10.00 (× 10^?3 mol/L). Another set of polymerizations were carried out at a constant initiator initial concentration of 2 × 10^?3 mol/L and the monomer initial concentration was fixed at one of the following: 0.20, 0.30, 0.50, 0.70, or 1.00 (mol/L). The polymerization reactions were conducted isothermally at 70°C. The order with respect to initiator was consistent with the classical kinetic rate equation, while the order with respect to monomer was greater that unity. The effects of temperature on the polymerization rate were also investigated and the activation energy gave values of 20.66, 22.68, and 23.22 kcal mol^?1 K^?1 over a temperature range of 50–70°C. For the case of o‐methacryloylaminophenylarsonic acid monomer, its kinetic study was carried out in DMF as solvent and AIBN initiator. p‐Methacryloylaminophenylarsonic acid was too insoluble in DMF to be studied. The polymers obtained were characterized by H‐NMR, IR, and viscosity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1662–1669, 2004     

Surface modification of monodisperse‐crosslinked polymeric microspheres using a redox initiation system

The surface modification of monodisperse‐crosslinked polymeric microspheres was carried out by introducing hydroxyl groups on the surface and utilizing the redox initiation system. The emulsions of the second monomer mixture were swollen into the monodisperse PS seed particles. The hydroxyl groups were introduced by hydrolysis of the acetate groups on the surface of microspheres. Ceric ammonium sulfate in sulfuric acid solution was employed to graft the acrylic monomer onto the polymeric microspheres. The surface characteristics of the surface‐modified particles were confirmed by FTIR, SEM, and TGA measurements. From the FE‐TEM image, a uniform coating layer was confirmed on the surface of microsphere. In DSC analysis, only an exothermal peak appeared when high content of DVB was used in the seeded polymerization, while, T_gs emerged after hydrolysis and graft polymerization using the low content of DVB in the second monomer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1349–1356, 2006     

Modification of polyester fabric properties by surfactant‐aided surface polymerization

Poly(methyl methacrylate) (PMMA) was applied to polyester fabric using a surface analog of emulsion polymerization. The admicellar polymerization was carried out using 1.5 mM dodecylbenzenesulfonic acid (DBSA) at pH 4 with 0.15M NaCl, 1 : 8 DBSA:monomer, and 1 : 10 initiator:monomer molar ratio. The PMMA film, which was formed, was characterized by SEM and FTIR. Hydrolysis of the PMMA film on polyester fabric was carried out to introduce carboxylic acid groups to the polyester surface to increase its hydrophilicity. The results show that a PMMA thin film was successfully formed on the polyester fabric. The water contact angle of the PMMA‐coated polyester fabric after hydrolysis by 10M H₂SO₄ for 5 h was reduced from 117.3° to 0° and there was a significant increase in the moisture‐regain value of the treated fabric. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 4059–4064, 2007     

PVC片材表面的光接枝亲水化处理

采用光接枝聚合方法对商品化PVC片材进行了表面亲水化处理。以二苯甲酮作引发剂 ,丙烯酸为接枝单体研究了反应过程中单体浓度、引发剂浓度、反应时间对亲水化效果的影响。衰减全反射红外光谱 (ATR FTIR)分析发现 ,在 15 5 5cm-1处出现COO-的特征峰 ,证明丙烯酸已经接枝到材料表面。随着反应时间的延长 ,接触角持续下降 ,3 0s以后趋于恒定 ,最低可达 3 3°。较低单体浓度下 ,均聚反应较弱 ,材料的亲水性要好于高单体浓度时的情况。同样 ,较低引发剂浓度时 ,引发剂的自屏蔽效应弱 ,有利于接枝反应 ,接触角要比高引发剂浓度条件下小     

H2O2-induced graft polymerization of acrylic acid on poly(ethylene terephthalate) fibers

Graft polymerization of acrylic acid to poly(ethylene terephthalate) fibers using H₂O₂ as initiator was only possible in benzyl alcohol as reaction medium. The effect of initiator and monomer concentrations, reaction time, and temperature as well as addition of metallic salts to the polymerization medium was studied. Percent grafting was enhanced significantly by increasing H₂O₂ concentrations up to 100 mequiv/L and then decreased upon further increase in initiator concentration. The same held true for acrylic acid concentration of up to 10%, but above this concentration grafting leveled off. Raising the polymerization temperature from 85 to 115°C favored grafting at lower H₂O₂concentration. The reverse was the case at higher H₂O₂ concentration (more than 25 mequiv/L). Addition of copper sulfate to the polymerization medium decreased the rate of grafting, and no leveling off of grafting could be achieved even after 5 h. The ferrous ammonium sulfate functioned similarly but to lesser degree, and leveling off of grafting occurred after 4 h. This contrasted with grafting in the absence of metallic salts where grafting leveled off after 1 h. Action of initial graft formation as diffusion barrier is believed to account for this.     

UV‐radiation‐induced preirradiation graft copolymerization of methacrylic acid and acrylic acid onto jute fibre

UV‐radiation‐induced graft copolymerization of methacrylic acid and acrylic acid onto jute fibre was carried out using a preirradiation method with 1‐hydroxycyclohexyl‐phenylketone as a photoinitiator. 2‐methyl‐2‐propene 1‐sulfonic acid, sodium salt was incorporated into the grafting solution in suppressing the homopolymer/gel formation and facilitating graft copolymerization. In comparison, results showed that the type of monomer significantly influence on grafting. The results of the characterisation showed that the graft weight and the type of monomer have significant influence on the mechanical and water absorption properties in the case of grafted samples. Copyright © 2004 Society of Chemical Industry     

Kinetic studies of the chemical polymerization of substituted aniline in aqueous solutions and characterization of the polymer obtained Part 1. 3‐Chloroaniline

Aqueous polymerization of 3‐chloroaniline (mCA) was studied using sodium dichromate as oxidant in the presence of hydrochloric acid. The effect of hydrochloric acid, sodium dichromate and monomer concentration on the polymerization rate, specific viscosity of the obtained polymer and ac conductivity was investigated. The initial and overall reaction rates increase with increasing hydrochloric acid concentration or sodium dichromate concentration, but decrease with increasing monomer concentration. The specific viscosity values (η_sp) increase with increasing hydrochloric acid concentration or monomer concentration, which means that the molecular weight of the polymer samples increases accordingly. On the contrary, the molecular weight decreases with increasing sodium dichromate concentration. The highest ac conductivity value of the obtained polymer was found for 0.0255 mol l⁻¹ of Na₂Cr₂O₇, 0.8 mol l⁻¹ HCl and 0.0956 mol l⁻¹ monomer concentration in the reaction medium. The order of the polymerization reaction with respect to hydrochloric acid, Na₂Cr₂O₇ and monomer concentration was found to be 1.0, 0.9 and 0.75, respectively. The apparent activation energy (E_a) for this polymerization system was found to be 13.674 × 10⁴ mol⁻¹. The obtained poly(3‐chloroaniline) was characterized by UV–visible, IR and ¹H NMR spectroscopy. X‐ray diffraction analysis and electron microscopy studies were carried out. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) results were used to confirm the structure. © 2001 Society of Chemical Industry     

Photopolymerization of acrylamide in the very low monomer concentration range

The polymerization kinetics of acrylamide (AAm) initiated by the photoinitiator DAROCUR₂₉₅₉ (DAR₂₉₅₉) under UV light irradiation were investigated. Variations of polymerization rate with AAm concentration and conversion were studied. Under the present low monomer concentrations the gel effect as well the difusion-controlled termination reactions are expected to be postponed or suppressed. The polymerization rate vs. conversion curve of the photoinduced polymerization of AAm was described by two non-stationary rate intervals and the initial rate maximum. In both intervals the polymerization rate decreased with conversion and the decrease was much more pronounced in the low conversion region. Furthermore, the polymerization rate was observed to decrease with increasing monomer concentration. The polymerization behavior was discussed in terms of the intra and intermolecular chain transfer processes (mainly to backbiting) and the decrease of propagation rate coefficient with the monomer concentration. Furthermore, the chain transfer reactions including backbiting step initiate the formation of less reactive radicals and/or the retardation of the polymerizaton.     

Synthesis and properties of acrylic‐based superabsorbent

Acrylic‐based superabsorbent polymers with partial‐neutralized acrylic acid were synthesized by inverse suspension polymerization. The effects of reaction parameters, including the concentration of crosslinking agent and initiator, the neutralization degree of monomer, the monomer concentration, and phase ratio of a system, on the water absorption have been investigated. Furthermore, to improve the properties of salt‐resistance and antielectrolyte for the polymer, acrylamide monomer containing nonionic and hydrophilic groups was introduced into the system, which can suppress the salt effect and homoion effect. The water absorption Q^5/3 is proportional to the reciprocal of ionic strength, 1/S, which follows Flory's elasticity gel theory. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 619–624, 2004     

Producing critical exponents from gelation for various photoinitiator concentrations; a photo differential scanning calorimetric study

Photoinitiated radical polymerization of an 80 wt% epoxy diacrylate (EA) and 20 wt% tripropyleneglycoldiacrylate (TPGDA) mixture with various 2-Mercaptothioxanthone (TX-SH) photoinitiator concentrations was studied by using photo-differential scanning calorimetric (Photo-DSC) technique. Photopolymerization reactions were carried out under the same conditions of temperature and light intensity. It was observed that all conversion curves during gelation at various photoinitiator concentration present nice sigmoidal behavior which suggests application of the percolation model. The critical time, where polymerization reaches the maximum rate (Rp_max) is called the glass transition point (t_g). The gel fraction exponents, β were produced from the conversion curves around t_g. The observed critical exponents were found to be around 0.55, predicting that the gel system obeys the percolation model. Rp_max and final conversion (C_s) values were found to be increased as the photoinitiator concentration was increased. On the other hand t_g values decreased as photoinitiator concentration was increased, indicating higher TX-SH concentration causes early glass transition during radical polymerization.     

Resistivity of conductive polymer–coated fabric

Preparation of conductive polymer–coated fabrics was carried out by admicellar polymerization. By this method, a thin layer of conductive polymers (polypyrrole, polyaniline, and polythiophene) was formed on cotton and polyester fabrics by a surfactant template. The effects of monomer concentration, oxidant to monomer ratio, and addition of salt on the resistivity of the resulting fabrics were studied. The results showed that the apparent surface and volume resistivity decreased with an increase in monomer concentration in the range 5–15 mM, but was not strongly dependent on the oxidant to monomer ratio over the range of 1 : 1 to 2 : 1. Addition of 0.5M salt was found to reduce the resistivity significantly. The lowest resistivity obtained was with polypyrrole‐coated fabric, with resistivity around 10⁶ ohm. SEM micrographs of the treated fabric surface showed a filmlike polymer coating, confirming that the fabrics were successfully coated by admicellar polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2629–2636, 2004