Microemulsion polymerization of butyl acrylate. 1. Effect of initiator type and concentration

Designed Monomers and Polymers

Fialová

Berek

2008

The inverse emulsion polymerization of acrylamide (AAm) initiated by a water-soluble initiator (ammonium peroxodisulfate, APS) was investigated. The rate of inverse emulsion polymerization increased with both increasing initiator and emulsifier concentrations. The molecular weight of polyacrylamide decreased with increasing the initiator concentration and slightly rose with increasing the emulsifier concentration. With increasing APS concentration the curves are broader. This indicates widening of molecular weight distribution. The decrease in M w with increasing APS concentration results from the increased termination of growing radicals mainly by primary or oligomeric radicals. The number of radicals per particle was inversely proportional to the APS concentration. The increased deactivation of primary and monomeric radicals decreased their desorption rate and re-entry rates as well. The desorption rate of radicals was interpreted using three models: the Nomura model (N model , k des,N ), the Gilbert model (G model , k des,G ) and the Ugelstadt model (T model , k des,T ). The desorption rate constant (k des ) for the different models differs by up to two orders of magnitude. The value of k des increases in the following order: N model < G model < T model . The radical entry rate decreases with rising emulsifier concentration and increases with rising initiator concentration.  Koninklijke Brill NV, Leiden, 2008

Section: Recipes and Proceduresmentioning

confidence: 99%

On the Kinetics of Inverse Emulsion Polymerization of Acrylamide

Designed Monomers and Polymers

Fialová

Berek

2008

“…The polymerization technique, conversion determination (dilatometric and gravimetric techniques) and the estimation of polymerization rate were the same as described earlier. 17,19,20 Polymer and Latex Characterization The measurements of average particle size (a static and dynamic light scattering-LS) and the estimation of particle number were the same as described earlier. 20,21 Limiting viscosity numbers [] were determined with Ubbelohde viscometer in acetone at 30 C and used to estimate the viscosity-average molecular weights.…”

Section: Polymerization Proceduresmentioning

confidence: 99%

Microemulsion Polymerization of Butyl Acrylate under Ultrasound Irradiation

Janíčková

Donescu

et al. 2006

Polym J

Self Cite

ABSTRACT:The microemulsion polymerization (MEP) of butyl acrylate (BA) stabilized by ionic emulsifier and initiated by oil-soluble dibenzoyl peroxide (DBP) or lauroyl peroxide (LPO) initiators have been studied under conventional (without ultrasound irradiation, CMEP) and ultrasonic (NMEP) conditions. The polymerization rate vs. conversion curve of the microemulsion polymerization of BA initiated by DBP was described by two nonstationary rate intervals. Four nonstationary rate intervals with two rate maxima appear in the microemulsion polymerization of BA initiated by LPO. The maximal rate of polymerization increases with temperature and the increase is much more pronounced under the conventional conditions. The overall activation energy is much larger under the conventional conditions (¼ 84 kJÁmol À1 ) than under the ultrasound (¼ 20 kJÁmol À1 ) conditions. The exit (desorption) rate constants The principle behind the formation of transparent or semitransparent microemulsions (fine emulsion with a droplet size 10-60 nm) is the very low interfacial tension caused by the penetration of coemulsifier into the droplet surface layer. Three-or four-component mixtures containing water, monomer, emulsifier and coemulsifier can form thermodynamically stable micellar solutions (microemulsions). The addition of coemulsifier increases the thermodynamic stability of micelles driving more emulsifier into micellar state, while on the other hand it can decrease the kinetic stability of micelles leading to faster formation and dissolution of micellar aggregates in solution. The thermodynamic stability of micelles is discussed in terms of how emulsifier distributes between the monomeric emulsifier and micellar state. The kinetic stability is discussed in terms of the average time of micellar aggregate. Cosolvents (coemulsifiers) are known to penetrate into micelles. The effect of such penetrating cosolvents can be discussed in terms of two aspects: an increase in distance between emulsifier groups and a decrease in the dielectric constant of micellar layer. This can explain the decrease of CMC as a result of dilution of micellar surface charge. 1 Furthermore, four-component mixtures (called miniemulsions with the droplet size 100-500 nm) containing water, monomer, emulsifier and hydrophobe form mostly kinetically stable emulsions. The principle behind the making of stable miniemulsions is the introduction of a hydrophobic compound into the monomer droplets to retard the diffusion of monomer out of the monomer droplets. In both microemulsion and miniemulsion, the principal locus of particle nucleation is the emulsified monomer droplet. In the former case the dependence of the rate vs. conversion is described by a curve with the maximum at ca. 20-40% conversion and the nucleation proceeds up to the final conversion. In the latter case, the particle nucleation is somewhat shortened up to ca. 30-50% and the dependence of the polymerization rate of styrene vs. conversion can be described by a curve with two maxima (four rate intervals...

“…The final monomer conversion was also controlled by the gravimetric method. The detailed polymerization technique was described earlier [16,17]. The measurements of average particle size (by dynamic light scattering (DLS)) and the estimation of particle number were the same as described earlier [18][19][20][21].…”

Section: Recipe and Proceduresmentioning

confidence: 99%

Micellar Aqueous Phase Polymerization of Acrylamide

Designed Monomers and Polymers

Kocsisová

2011

Self Cite

The kinetics of aqueous phase radical polymerization of acrylamide initiated by ammonium peroxodisulfate (APS) and 2,2 -azobisizobutyronitrile (AIBN) were studied in the presence of the non-ionic hydrophilic Tween-20 and hydrophobic Tween-85. The polymerization rate vs. conversion curve is described by a curve with two or three rate intervals and the maximal rate is located at medium conversion. This behavior strongly deviates from the kinetic model of the ideal solution polymerization with the steady-state kinetics at low and medium conversions. On the contrary, the present data indicate the kinetics typical for the transparent heterogeneous-micellar or microemulsion polymerization. The associates of polyacrylamide and acrylamide play the role of active particles. Indeed, the light scattering measurements confirmed the presence of polyacrylamide nanoparticles in both polymerization systems with and without emulsifier. The intra-and intermolecular association of polyacrylamide with its monomer is suggested to be the dominant process which induces the formation of particles responsible for the kinetics typical for the micellar or microemulsion polymerization. The experimental data show that the dependence of the maximal rate of polymerization (R p,max ) vs. conversion is the result of polymerization within the nanoscaled polymer aggregates and not by the gel effect. R p,max decreases with increasing emulsifier concentration and the decrease is much more pronounced with hydrophilic emulsifier. Polymerization is faster for the APS-initiated system than for the AIBN-initiated one. The radical polymerization of AAm polymerization with and without emulsifier was discussed in terms of the formation of polymer chain aggregation (nanoparticle) into polymer chains as a main reaction locus.