Free-radical polymerization in inverse microemulsions

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 Proceduressupporting

confidence: 74%

On the Kinetics of Inverse Emulsion Polymerization of Acrylamide

Designed Monomers and Polymers

Fialová

Berek

2008

“…28 In this case, the released coemulsifier from polymer particles (pentanol is not compatible with PSt) Polym. J .…”

Section: Kinetic Parametersmentioning

confidence: 99%

Microemulsion Polymerization of Alkyl (Meth)acrylates Initiated by UV Light

1999

Polym J

ABSTRACT:Radical polymerizations of polar unsaturated monomers ethyl acrylate, methyl methacrylate and nonyl methacrylate in an o/w microemulsion photoinitiated by a UV light were investigated. Polymerizations were conducted at low temperature to follow the effects of a varied solubility of monomer (coemulsifier) and/or diffusional degradation of monomer droplets on the kinetic and colloidal parameters. The rate versus conversion curve showed four regions with two rate maxima ca. at 5% to 20% and 50 to 70% conversion. The first rate maximum results from abrupt decrease of the monomer concentration at microemulsion loci and the second one from the increased accumulation of radicals in the latex particles. The higher polymerization rate of ethyl acrylate compared to that for methyl methacrylate or nonyl methacrylate was attributed to higher monomer concentration at reaction loci and propagation rate constant and lower quenching rate. The rate of polymerization was found to increase with incident light intensity and was most pronounced with nonyl methacrylate. The reaction order (the dependence of the rate of polymerization or the number of particles on the incident light intensity) was taken as a measure of particle nucleation efficiency. Particle size distribution was observed to be very narrow at low conversion and increased with increasing conversion.KEY WORDS Microemulsion j Polymerization I Alkyl (Meth)acrylates I Kinetics I Particle I Nucleation/ Microemulsion and miniemulsion polymerizations offer convenient access to well-defined microlatex particles being typically one order of magnitude smaller than polymer particles obtained by conventional emulsion polymerization. The fine monomer emulsion exhibits a large interface between monomer droplets and the aqueous phase. Under such conditions, continuous nucleation up to (very) high conversion is operative. There is no apparent constant rate period in the o/w microemulsion or miniemulsion polymerization. 1 -3 Ugelstadt et a/. 4 clearly demonstrated that monomer droplets could effectively compete with monomer-swollen micelles for capture of free radicals generated in the aqueous phase when the total surface area of the droplets became large enough. In conventional emulsion polymerization, the principle locus of particle nucleation is the aqueous phase or the monomer swollen micelles depending on the degree of water solubility of the monomers, an initiator and amount of emulsifier. Monomer droplets are considered only as monomer reservoir supplying monomer to the growing polymer particles. However, the small size of the monomer droplets (micro-or minidroplets) enables them to become the principle locus of particle nucleation ..The principle behind the formation ofmicroemulsions (droplet size I 0-50 nm) is penetration of coemulsifier into the water/oil interface, thereby decreasing surface tension and increasing interface area. Coemulsifier also decreases the rigidity of interface film due to increasing the molecular disorder. Coemulsifier promotes the formatio...

“…The kinetics and mechanism of the inverse microemulsion polymerization are especially well understood [4]. This is not true for the inverse miniemulsion polymerization where few data on polymerization kinetics are available.…”

Section: Introductionmentioning

confidence: 99%

On the inverse miniemulsion copolymerization and terpolymerization of acrylamide, N, N′-methylenebis(acrylamide) and methacrylic acid

2003

Open Chemistry

The kinetics of free-radical copolymerization and terpolymerization of acrylamide (AAm), N; N 0 -methylenebis(acrylamide) (MBA) and methacrylic acid (MA) in the inverse water/monomer/cyclohexane/Tween 85 miniemulsion was investigated. Polymerizable sterically-stable miniemulsions were formulated in cyclohexane as a continuous medium. Polymerizations are very fast and reach the nal conversion within several minutes. The dependence of the polymerization rate vs. conversion is described by a curve with two nonstationary rate intervals. The maximum rate of polymerization slightly increases with increasing concentration of crosslinking monomer (MBA) and strongly decreases by the addition of MA. The rate of polymerization is inversely proportional to the 0.9 th and 1.8 th power of the particle concentration without and with MA, respectively. The number of polymer particles is inversely proportional to the 0.18 th and 0.13 th power of MBA concentration. The kinetic and colloidal parameters of the miniemulsion polymerization are discussed in terms of microemulsion polymerization model.