In-line dielectric monitoring of monomer conversion in a batch polymerization reactor

In-line monitoring of monomer conversion is studied using a low-frequency dielectric sensor during solution polymerization of methyl methacrylate in a laboratory-scale batch reactor. It has been found that the induction period due to the presence of an inhibitor can be determined by the dielectric sensor to detect the starting point of polymerization. The dielectric loss factor that changes with the progress of polymerization is empirically correlated with monomer conversion measured by the off-line gravimetric method at different temperatures and initiator concentrations. It is demonstrated that dielectrometry can be used as an in-line monitoring method in free-radical polymerization. © 1995 John Wiley & Sons, Inc.     

Theoretical and experimental investigations of the inverse emulsion polymerization of acrylamide

In this study, the inverse emulsion polymerization modeling of polyacrylamide with population balance equations (PBEs) was performed. The PBEs were derived on the basis of the zero–one kinetic model. The effects of the surfactant steric barrier and surfactant reaction with radicals, including monomeric radicals, on the radical entry rate into the particle were taken into account. In the modified model, the coagulation phenomenon was included through consideration of the effects of forces not included in the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory; these include hydration and steric forces in addition to DLVO forces. The effects of the surfactant and initiator concentrations on the conversion, particle size, and average molecular weight (MW) were investigated by simulation and experimental studies. Increasing the surfactant concentration initially increased the conversion and decreased MW. A further increase in the surfactant concentration resulted in a decrease in the conversion and an increase in MW. The average particle size decreased with an increase in the surfactant concentration. An increase in the initiator concentration led to an increase in the monomer conversion and a decrease in the average MW. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41916.     

ATR‐UV monitoring of methyl methacrylate miniemulsion polymerization for determination of monomer conversion

Attenuated Total Reflection (ATR) UV spectroscopy has been used to monitor monomer conversion in methyl methacrylate miniemulsion polymerization. It was found that the vinylic groups of methyl methacrylate strongly absorb the UV light with a maximum absorption at 225 nm. This absorption peak decreases as monomer is converted to polymer. The polymer has a strong absorption at a lower UV region. The results from this feasibility study indicate that ATR‐UV sensor technique has a great potential to be used for on‐line or in‐line process monitoring in emulsion and miniemulsion polymerization. With a partial least square (PLS) calibration model, very good prediction the monomer conversion was obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1471–1475, 2006     

Synthesis and polymerization of a new iodine‐containing monomer

A new iodine‐containing methacrylate monomer, 3,4,5‐triiodobenzoyloxyethyl methacrylate (TIBEM), was synthesized by coupling 2‐hydroxyethyl methacrylate (HEMA) with 3,4,5‐triiodobenzoic acid. The monomer was characterized by ¹H nuclear magnetic resonance, infrared (IR), and ultraviolet spectra. Homopolymerization and copolymerization of the monomer with methyl methacrylate (MMA) were carried out using 2,2′‐azobis isobutyronitrile as the initiator. A terpolymer of TIBEM, MMA, and HEMA was also synthesized. The copolymers were characterized by IR, gel permeation chromatography, differential thermal analysis, and thermogravimetric analysis (TGA). High molecular weight polymers were produced with MMA at different feed compositions of TIBEM. The polymers were found to be freely soluble in common solvents for acrylic polymers. TGA showed little decomposition of the copolymer below 280°C. Copolymers showed good radiopacity at 25 wt % of TIBEM in the feed. These copolymers could find applications in medical and dental areas where radiopacity is a desirable feature of the implants. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2580–2584, 2003     

Application of factorial experimental design to the study of the suspension polymerization of β‐cyclodextrin and epichlorohydrin

The suspension polymerization of β‐cyclodextrin (β‐CD) with epichlorohydrin (EP) has been studied using a fractionated factorial design with two levels and six variables (β‐CD:EP molar ratio, NaOH concentration, temperature, stirring speed, delay time before paraffin addition, and β‐CD concentration). Different variables, such as the amount of β‐CD in the product, particle size, degree of swelling, and sorption capacity, have been analyzed as the responses for the synthesized polymers. The experimental design approach permitted to select the optimal conditions of synthesis depending on the desired features of the product. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3393–3402, 2006     

Polymerization strategies to overcome limiting monomer conversion in silicone-acrylic miniemulsion polymerization

The limiting conversion phenomenon observed in high solid content silicone-modified acrylic miniemulsion polymerizations was investigated. It was found that the limiting conversion was mainly due to the formation of inactive radicals upon propagation of butyl acrylate radicals with the vinyl end groups of the polydimethylsiloxane. Polymerization strategies that allowed overcoming this problem and achieving high monomer conversion were implemented.     

Online polymer molecular weight and conversion monitoring via calorimetric measurements in RAFT emulsion polymerization

BACKGROUND: Online measurements of key emulsion polymerization attributes, such as conversion and molar mass distribution, are unavailable. Costly offline measurements at low sampling frequencies with time delays usually lead to insurmountable challenges in real‐time product quality monitoring and process/product control. RESULTS: We developed an online calorimetric method monitoring the evolution of conversion and molecular weight in complex polymerization reactors. Our experiments were carried out in a 1 L reactor to produce polystyrene homopolymer. Monomer conversion was obtained in real time from polymerization rate, which was estimated from temperature measurements using platinum thermal transducers. The calorimetric model was validated offline for batch and semi‐batch emulsion polymerization of styrene with and without transfer agents. The conversion was validated using offline gravimetry. The molecular weights measured offline via size exclusion chromatography with multiple detectors compared well with those estimated online using the calorimetric method. CONCLUSION: We found that a semi‐batch emulsion polymerization process can be controlled online to approach living polymerization involving transfer agents. Thus our model is suitable as a ‘soft‐sensor’ for real‐time control applications. Copyright © 2009 Society of Chemical Industry     

MMA bulk polymerization and its influence on in situ resin viscosity comparing several chemorheological models

Earlier published rheological data of methyl methacrylate (MMA) heated and isothermally polymerized at temperatures between 50 and 80°C have been reanalyzed using three semiempirical models of viscosity advancement including a modified Boltzmann sigmoidal model, a microgel model for cure, and a first‐order isothermal kinetic model. These alternative models possessed few fitting parameters and could be used without requiring more experiments to be run. For each dataset as a function of temperature, the analysis resolved time constants associated with both the induction time for polymerization and the rate of viscosity rise, which were inversely related to the polymerization temperature. We found the sigmoidal model the most robust to accommodate nonlinearities in viscosity advancement with radical polymerization of MMA. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and properties of monomer casting nylon‐6/PEO blend prepared via in situ polymerization

A series of MC nylon‐6/ polyethylene oxide (PEO) blends were prepared via in situ polymerization. It was found that addition of PEO delayed the polymerization process of caprolactam. The apparent activation energy and pre‐exponential factor increased, indicating that the polymerization reaction became difficult with increasing PEO content. The stress–strain curves of the blends presented strain hardening behavior and increasing elastic deformation stress plateau at low PEO content. Nonisothermal DSC and XRD tests indicated that addition of PEO led to a decrease of the crystallization ability of the nylon‐6 matrix by reducing crystal grain size and crystallinity, whereas the crystallization ability of the PEO phase was improved. No co‐crystal formed between the two phases. PEO with low content only existed as amorphous state, while with increasing PEO content, PEO can crystallize gradually, forming interfibrillar segregation first, and then forming interspherilute segregation of the blend independently. By addition of PEO, the fracture surface of the blend became rough, displaying character of tough fracture. The interface between nylon‐6 phase and PEO phase was diffused, and the nylon‐6 matrix around the PEO particles presented fibrous structure, indicating the good compatibility between them. The toughening mechanism of the blend corresponded to the crazing‐shear banding mechanism. POLYM. ENG. SCI., 55:589–597, 2015. © 2014 Society of Plastics Engineers     

Preparation and properties of nanocomposite hydrogels containing silver nanoparticles by ex situ polymerization

A series of composite hydrogels containing silver nanoparticle used for bioadhesives were prepared from acrylic acid, poly(ethylene glycol) methyl ether acrylate, and silver nanoparticles through ex situ polymerization. Silver nanoparticles with a narrow size distribution were prepared by the reduction of a silver nitrate solution with ascorbic acid. The influence of the content of the silver nanoparticles in the hydrogels on the equilibrium swelling ratio, mechanical properties, electrical conductivity, and inactivation of Escherichia coli (E. coli) was investigated in this study. The results showed that the swelling ratios of the composite gels were reduced by silver nanoparticles in the gels but were not reduced with an increase in the content of silver nanoparticles. In addition, the crosslinking density and shear modulus of these hydrogels did not increase with an increase in the content of silver nanoparticles. The adhesive force of these hydrogels (the APECAg series) was not obviously changed. Finally, the initial rate of E. coli inactivation for the APECAg series hydrogels showed excellent antibacterial properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3653–3661, 2006     

Synthesis and gelation of novel fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide copolymers containing triol segments—Interaction of these fluorinated gels with various hydrophilic compounds

Fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide (DOBAA) copolymers containing triol segments were prepared by the reactions of fluoroalkanoyl peroxide with the corresponding monomer and N‐tris(hydroxymethyl)methylacrylamide (NAT). These obtained fluorinated copolymers [R_F‐(DOBAA)_x‐(NAT)_y‐R_F] were found to cause gelation in water, dimethyl sulfoxide, and N,N‐dimethylformamide under the non‐crosslinked conditions, although the corresponding nonfluorinated DOBAA–NAT copolymer [‐(DOBAA)_x‐(NAT)_y‐] could cause no gelation in these solvents. This gelation is governed by the synergistic interaction of strong aggregations of end‐capped fluoroalkyl segments and intermolecular hydrogen bonding between triol segments. We also studied the uptake and release of a variety of hydrophilic compounds such as methylene blue, methyl orange, 4‐hydroxyazobenzene‐4′‐sulfonic acid sodium salt, 2,4‐dihydroxyazobenzene‐4′‐sulfonic acid sodium salt, acriflavine hydrochloride, acridine hydrochloride, lucigenin, and fluorescein by this fluorinated copolymer gel and fluoroalkyl end‐capped NAT homopolymer gel [R_F‐(NAT)_n‐RF] for comparison. It was demonstrated that the uptake and release ratios of these hydrophilic compounds by R_F‐(DOBAA)_x‐(NAT)_y‐R_F gel become generally lower than those of R_F‐(NAT)_n‐R_F gel. Interestingly, R_F‐(DOBAA)_x‐(NAT)_y‐R_F gel has no releasing power toward methylene blue, acridine hydrochloride, lucigenin, and fluorescein, although R_F‐(NAT)_n‐R_F gel has a good releasing power toward these compounds. Additionally, R_F‐(DOBAA)_x‐(NAT)_y‐R_F gel was applied to the controlled release of anticancer drugs such as methotrexate (MTX), and the releasing ratios of MTX became higher with increasing pH values (from pH 4.3 to 9.1). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88:3212–3217, 2003     

Kinetics of styrene emulsion polymerization with a stable monomer radical

We have analyzed the electrical conductivity of a linear high charge density polyelectrolyte aqueous solution, finding that the counterion association order follows the same pattern as that described for a cyclic monomeric polyelectrolyte, i.e. NO > Br^? > Cl^? > F^?. However, these counterions interact in a very different manner with this polyion, making Eisenberg's relationship inapplicable in this system. Consequently, an alternative method is proposed for treating data.     

Diels–Alder reaction in water for the straightforward preparation of thermoresponsive hydrogels

Because the properties and applications of hydrogels are determined by the formation principle and conditions of the hydrogels, novel methods for preparing hydrogels have increasingly triggered scientists' interest. Here the Diels–Alder reaction was applied to the preparation of hydrogels. For the resultant polymeric diene and dienophile, the Diels–Alder reaction could be performed in water. The gelation time was found to be closely related to the temperature. The gelation time decreased with the temperature increasing. Moreover, the hydrogels were stable in water, and the retro‐Diels–Alder reaction could be performed in N,N‐dimethylformamide easily. A study of the swelling ratio indicated that the hydrogels were responsive to the temperature. The hydrogel formation method described here provides several advantages, such as mild reaction conditions, no initiator or catalyst, a tunable gelation rate, and thermal reversibility, and it has great potential for the preparation of biomaterials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Measurement and control of polymerization reactors

The measurement and control of polymerization reactors is very challenging due to the complexity of the physical mechanisms and polymerization kinetics. In these reactors many important variables, which are related to end-use polymer properties, cannot be measured on-line or can only be measured at low sampling frequencies. Furthermore, end-use polymer properties are related to the entire molecular weight, copolymer composition, sequence length, and branching distributions. This paper surveys the instrumentation technologies, which are of particular interest in polymerization reactors with emphasis on, for example, measurement of viscosity, composition, molecular weight, and particle size. This paper presents a hierarchical approach to the control system design and reviews traditional regulatory techniques as well as advanced control strategies for batch, semibatch, and continuous reactors. These approaches are illustrated by focusing on the control of a commercial multiproduct continuous emulsion polymerization reactor. Finally, the paper captures some of the trends in the polymer industry, which may impact future development in measurement and reactor control.     

Radiation synthesis and characterization of poly(N‐vinyl‐2‐pyrrolidone/acrylic acid) and poly(N‐vinyl‐2‐pyrrolidone/acrylamide) hydrogels for some metal‐ion separation

Two different hydrogels, prepared from N‐vinyl‐2‐pyrrolidone/acrylic acid (NVP/AAc) and N‐vinyl‐2‐pyrrolidone/acrylamide (NVP/AAm), were studied for the separation and extraction of some heavy‐metal ions from wastewater. The hydrogels were prepared by the γ‐radiation‐induced copolymerization of the aforementioned binary monomer mixtures. Further modification was carried out for the NVP/AAc copolymer through an alkaline treatment to improve the swelling behavior by the conversion of the carboxylic acid groups into its sodium salts. The thermal stability and swelling properties were also investigated as functions of the N‐vinyl‐2‐pyrrolidone content. The characterization and some selected properties of the prepared hydrogels were studied, and the possibility of their practical use in wastewater treatment for heavy metals such as Cu, Ni, Co, and Cr was investigated. The maximum uptake for a given metal was higher for a treated NVP/AAc hydrogel than for an untreated NVP/AAc hydrogel and was higher for an untreated NVP/AAc hydrogel than for an NVP/AAm hydrogel. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2642–2652, 2004     

In situ monitoring of mechanical properties during photopolymerization with particle tracking microrheology

Microrheology was employed to perform in situ monitoring of the liquid-to-gel transition during free-radical photopolymerization. Photosensitive acrylate resins were exposed to ultraviolet light, while the Brownian motion of micrometer sized, inert fluorescent tracer particles was tracked via optical videomicroscopy. Statistical analysis of particle motion yielded the rheological properties of the embedding medium as a function of time and location, thereby relating UV exposure to the progress of polymerization and gelation. Microscopy enabled a detailed study of three-dimensional gelation profiles; other experimental parameters that were varied include photoinitiator concentration, monomer composition, the presence of oxygen and light intensity. Significant changes in gelation time were observed with increasing distance from the illuminated surface into the sample under all conditions. The results were used to test the accuracy of the standard energy threshold model, which is often used to empirically predict the outcome of photopolymerization reactions.     

Development of calibration models for estimation of monomer concentration by Raman spectroscopy during emulsion polymerization: Facing the medium heterogeneity

This work compares different calibration models for the estimation of monomer concentrations by Raman spectroscopy during semicontinuous emulsion copolymerization reactions. The limitations of these models are discussed in terms of a complex reaction, namely the copolymerization of vinyl acetate and butyl acrylate, whose monomers present overlapping Raman spectra, especially the C=C stretching band. Additionally, the copolymerization was monitored in a spectroscopic setup arranged for fast spectral acquisition, which resulted in a low signal‐to‐noise ratio. These realistic conditions for in‐line monitoring of emulsion copolymerization, i.e., considerable noise level in the spectra and medium heterogeneity, are discussed in the context of different approaches for adjusting the calibration model and the ensuing model limitations. It was verified that combining data obtained during reactions with synthetic samples is interesting from the statistical point of view, since in this way it is possible to produce data sets with a wide range of variation, allowing the accurate estimation of statistical parameters. These parameters are of major importance for process variables and product property estimations, especially if they are to be used for process control and decision making purposes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1136–1150, 2004     

Polymer-clay nanocomposites prepared via in situ emulsion polymerization

A series of novel polystyrene and poly(butyl methacrylate) montmorillonites (MMT-Na) nanocomposite latexes have been successfully prepared by emulsion polymerization. First of all, chemical modification of MMT-Na with a reactive coupling agent (MMT-QS) has been employed for the synthesis of hybrids. Subsequently, in situ seeded emulsion polymerization of hydrophobic vinyl monomers, such as butyl methacrylate and styrene, using sodium dodecyl sulfate (SDS) and ammonium persulfate (APS) as surfactant and initiator, respectively, were used for nanocomposite preparation. This technique allowed preparing of stable nanocomposite latexes with high (30–45 wt.%) solids contents and with loading of inorganic particles up to 5 wt.%. The prepared wet dispersions were subsequently characterized by light scattering method. In order to characterize the microstructure of the clay layers, and that of the organoclay in polystyrene and poly(butyl methacrylate) nanocomposites, wide and small angle X-ray analyses (WAXS, SAXS) and transmission electron microscopy (TEM) techniques were used.     

Mechanical and crystalline properties of monomer casting Nylon‐6/Sio2 composites prepared via in situ polymerization

A series of monomer casting (MC) nylon‐6/SiO₂ composites were prepared via in situ polymerization. It was found that the tensile strength, storage modulus, and notched charpy impact strength of the composites were improved and reached maximum at 3–5 wt% loading of SiO₂. The α relaxation peak corresponding to the glass transition temperature (T_g) shifted to high temperature with increasing SiO₂ content. Addition of SiO₂ led to an increase of the melting and crystallization temperatures, and crystallinity. It also reduced the induction time of crystallization, advance the crystallization process of MC nylon‐6, and improve the crystal growth rate. The self‐nucleation crystallization analysis indicated that SiO₂ particles played the role of facilitating the crystallization of the matrix mainly via accelerating the generation of crystal nucleus. By addition of SiO₂ particles, the fracture surface of MC nylon‐6 changed to distant striations with many yield folds accompanied by a large number of stress whitening, displaying much obvious character of tough fracture. SiO₂ particles can be pulled‐out under stress by being covered with MC nylon‐6 resin due to strong interfacial interaction and presented a skin–core structure. © 2012 Society of Plastics Engineers.