Emusion polymerization of MMA

EMULSION POLYMERIZATION OF METHYLMETACRYLATE

In an emulsion polymerization, the soap, or surfactant, is dissolved in water until the critical micelle concentration (CMC) is reached. The interior of the micelle provides the site necessary for polymerization. A monomer (like styrene or methyl methacrylate) and a water soluble free radical initiator are added and the whole batch is shaken or stirred. Emulsion polymerizations are always performed free radically. Anionic and cationic chain ends would be rapidly quenched by the water. The product of an emulsion polymerization is called latex.

Effect Of Concentration Of Emulsifier:-

The emulsion polymerization of methyl methacrylate (MMA) in concentration of emulsifiers below their critical micelle concentrations (CMCs) initiated by K₂S₂O₈ (KPS) was studied. It was observed that the initiator concentration has little effect on both polymerization rate and particle size. However, the polymerization rate is faster and particle size is smaller obviously when decreasing the ratio of the water/monomer or increasing the temperature of polymerization or the amount of the emulsifier. In the range of a 200–400 rpm stirring speed, the polymerization rate is almost unchanged although the particle size become larger with increase in the stirring speed. The monodisperse particle (size about 100–200 nm) can be obtained using this process.

Functions Of Methanol:-

1.      Methanol is a traditional denaturant for ethanol, thus giving the term methylated spirit.

2.      Methanol is also used as a solvent, and as an antifreeze in pipelines and windshield washer fluid.

3.      In some wastewater treatment plants, a small amount of methanol is added to wastewater to provide a food source of carbon for the denitrifying bacteria, which convert nitrates to nitrogen to reduce the denitrification of sensitive aquifers.

4.      During World War II, methanol was used as a fuel in several German military rocket designs, under name M-Stoff, and in a mixture as C-Stoff.

5.      Methanol was used as an automobile coolant antifreeze in the early 1900s.

6.      Methanol is used as a denaturing agent in polyacrylamide gel electrophoresis.

7.      Direct-methanol fuel cells are unique in their low temperature, atmospheric pressure operation, allowing them to be miniaturized to an unprecedented degree. This, combined with the relatively easy and safe storage and handling of methanol may open the possibility of fuel cell-powered consumer electronics, such as for laptop computers and mobile phones.

8.      Methanol is also a widely used fuel in camping and boating stoves. Methanol burns well in an unpressurized burner, so alcohol stoves are often very simple, sometimes little more than a cup to hold fuel. This lack of complexity makes them a favorite of hikers who spend extended time in the wilderness.

9.      Methanol is mixed with water and injected into high performance diesel engines for an increase of power and a decrease in exhaust gas temperature. This is called water methanol injection.

emulsion polymerization of Styrene

Emulsion Polymerization Of Styrene

Emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water, monomer, and surfactant. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer (the oil) are emulsified (with surfactants) in a continuous phase of water. Water-soluble polymers, such as certain polyvinyl alcohols , can also be used to act as emulsifiers/stabilizers. The name "emulsion polymerization" is a misnomer that arises from a historical misconception. Rather than occurring in emulsion droplets, polymerization takes place in the latex particles that form spontaneously in the first few minutes of the process. These latex particles are typically 100 nm in size, and comprise many individual polymer chains. The particles are stopped from coagulating with each other because each particle is surrounded by the surfactant ('soap'). When water-soluble polymers are used as stabilizers instead of soap, the repulsion between particles arises because these water-soluble polymers form a 'hairy layer' around a particle that repels other particles, because pushing particles together would involve compressing these chains.

Polystyrene:-

Polystyrene is actually an aromatic polymer that is made from the monomer styrene. It is a long hydrocarbon chain that has a phenyl group attached to every carbon atom. Styrene is an aromatic monomer, commercially manufactured from petroleum. Polystyrene is a vinyl polymer, manufactured from the styrene monomer by free radical vinyl polymerization.

Polystyrene is a rigid, transparent thermoplastic, which is present in solid or glassy state at normal temperature. But, when heated above its glass transition temperature, it turns into a form that flows and can be easily used for molding and extrusion. It becomes solid again when it cools off. This property of polystyrene is used for casting it into molds with fine detail. Pure polystyrene polymer is colorless and hard with limited flexibility. 

Properties Of Polystyrene:-


The unique physical and chemical properties of polystyrene are responsible for its use in a wide range of applications. Let us have a look at some polystyrene properties.

Polystyrene is hard and brittle and has a density of 1.050 g/cm³. It is represented by the chemical formula, C₈H₈. It is made up of three chemical elements, carbon, hydrogen and oxygen. Most of the polystyrene properties are as a result of the unique properties of carbon. It is highly flammable and burns with an orange yellow flame, giving off soot, as a characteristic of all aromatic hydrocarbons. Polystyrene, on oxidation, produces only carbon dioxide and water vapor. Have a look at the physical properties of polystyrene given below:

·        Density - 1.05 g/cc

·        Dielectric constant - 2.4 to 2.7

·        Thermal conductivity - 0.08 W/(m.K)

·        Young's modulus - 3000 to 3600 Mpa

·        Tensile strength - 46 to 60 Mpa

·        Melting point - 240 ºC

·        Water absorption - 0.03 to 0.1

Polystyrene is chemically nonreactive and hence, used to make containers for other chemicals, solvents and even food items. The transformation of carbon-carbon double bonds into less reactive single bonds in polystyrene is the main reason for its chemical stability. Polystyrene is flexible and can be made into moldable solid or thick viscous solids. This is mainly because of the Van der Waal's forces of attraction that exist between the long hydrocarbon chains. However, when heat is applied, the chains can slide over each other. This property of intermolecular weakness along with the intermolecular strength, due to the strong hydrocarbon backbone, allows polystyrene to be flexible and stretchable. Polystyrene is soluble in solvents that contain acetone, such as most aerosol paint sprays and cyanoacrylate glues.

Functions Of The Reactants

·        Monomers:-

Typical monomers are those that undergo radical polymerization, are liquid or gaseous at reaction conditions, and are poorly soluble in water. Solid monomers are difficult to disperse in water. If monomer solubility is too high, particle formation may not occur and the reaction kinetics reduces to that of solution polymerization.

·       Initiators:-

Both thermal and redox generation of free radicals have been used in emulsion polymerization. Persulfate salts are commonly used in both initiation modes. The persulfate ion readily breaks up into sulfate radical ions above about 50°C, providing a thermal source of initiation. Redox initiation takes place when an oxidant such as a persulfate salt, a reducing agent such as glucose, Rongalite, or sulfite, and a redox catalyst such as an iron compound are all included in the polymerization recipe. Redox recipes are not limited by temperature and are used for polymerizations that take place below 50°C.

Although organic peroxides and hydroperoxides are used in emulsion polymerization, initiators are usually water soluble and partition into the water phase. This enables the particle generation behavior described in the theory section. In redox initiation, either the oxidant or the reducing agent (or both) must be water soluble, but one component can be water-insoluble.

·       Surfactants:-

Selection of the correct surfactant is critical to the development of any emulsion polymerization process. The surfactant must enable a fast rate of polymerization, minimize coagulum or fouling in the reactor and other process equipment, prevent an unacceptably high viscosity during polymerization (which leads to poor heat transfer), and maintain or even improve properties in the final product such as tensile strength, gloss, and water absorption.

Anionic, nonionic, and cationic surfactants have been used, although anionic surfactants are by far most prevalent. Surfactants with a low critical micelle concentration (CMC) are favored; the polymerization rate shows a dramatic increase when the surfactant level is above the CMC, and minimization of the surfactant is preferred for economic reasons and the (usually) adverse effect of surfactant on the physical properties of the resulting polymer. Mixtures of surfactants are often used, including mixtures of anionic with nonionic surfactants. Mixtures of cationic and anionic surfactants form insoluble salts and are not useful.Examples of surfactants commonly used in emulsion polymerization include fatty acids, sodium lauryl sulfate, and alpha olefin sulfonate.

Initiation And Polymerization:-

Initiation takes place when an initiator fragment migrates into a micelle and reacts with a monomer molecule. Water soluble initiators, such as peroxides and persulfates, are commonly used (This also prevents polymerization in the big monomer droplets). Once polymerization starts, the micelle is referred to as a particle. Polymer particles can grow to extremely high molecular weights, especially if the initiator concentration is low. That makes the radical concentration and the rate of termination low as well. Sometimes a chain transfer agent is added to the mix to keep the molecular weight from getting too high.Decreasing the initiator concentration increases molecular weight and rate of polymerization.

Sodium Lauryl Sulphate:-

Soap a molecule in which one end is polar and water-soluble and the other end is non-polar and organic-soluble, such as sodium lauryl sulfate:

These form micelles in water, little balls in which the polar ends of the molecules point out into the water, and the non-polar ends point inward, away from the water. Water insoluble dirt can hide inside the micelle, so soapy water washes away dirt that plain water can't.

cross linking

Crosslinking

Crosslinking is when individual polymer chains are linked together by covalent bonds to form one giant molecule.

Emulsion Polymerization:-

A mixture in which two immiscible substances, like oil and water, stay mixed together thanks to a third substance called an emulsifier. The emulsifier is usually something like a soap, whose molecules have a water-soluble end and an organic-soluble end. The soap molecules form little balls called micelles, in which the water-soluble ends point out into the water, and the organic-soluble ends point into the inside of the ball. The oil is stabilized in the water by hiding in the center of the micelle. Thus the water and oil stay mixed.

Function Of The Reactants

·        Sodium Lauryl Sulphate:-

Soap a molecule in which one end is polar and water-soluble and the other end is non-polar and organic-soluble, such as sodium lauryl sulfate:

These form micelles in water, little balls in which the polar ends of the molecules point out into the water, and the non-polar ends point inward, away from the water. Water insoluble dirt can hide inside the micelle, so soapy water washes away dirt that plain water can't.

·        Hydroxyethyl Acrylate:-

Hydroxyethyl Acrylate gives hydroxyl functional groups to an acrylic polymer backbone. The hydroxyl groups act as crosslinking sites for hydrophilicity, improving adhesion and resistance against corrosion, fogging and abrasion. End applications include adhesives, coatings, sealants and thermosetting paints. It is also used in additives for personal care products.

·        Potassium Persulphate:-

Both thermal and redox generation of free radicals have been used in emulsion polymerization. Persulfate salts are commonly used in both initiation modes. The persulfate ion readily breaks up into sulfate radical ions above about 50°C, providing a thermal source of initiation. Redox initiation takes place when an oxidant such as a persulfate salt, a reducing agent such as glucose, Rongalite, or sulfite, and a redox catalyst such as an iron compound are all included in the polymerization recipe. Redox recipes are not limited by temperature and are used for polymerizations that take place below 50°C.

Although organic peroxides and hydro peroxides are used in emulsion polymerization, initiators are usually water soluble and partition into the water phase. This enables the particle generation behavior described in the theory section. In redox initiation, either the oxidant or the reducing agent (or both) must be water soluble, but one component can be water-insoluble.

·        Sodium Metabisulfite:-

It has been found that the system diazonium salt/sodium Metabisulfite (Na₂S₂O₅) is an effective one for the initiation of polymerization of an aqueous solution.

·        Sequestrene:-

A series of complexing agents and metal complexes consisting of ethylenediaminetetraacetic acid and salts. It is acting as an anti-coagulating agent.

Bulk Polymerization

Bulk Polymerization

Dilatometery:-

Dilatometery is used to determine the rate of polymerization and the effects of initiator concentration and chain transfer agent on the rate. In this experiment the rate of polymerization will be measured by the use of dilatometer. Dilatometery utilizes the volume change that occurs upon polymerization to follow conversion versus time. The conversion is conveniently followed in a dilatometer whose volume includes a capillary region. The dilatometer is placed in a constant temperature bath and the volume change of the polymerizing system, is followed with time. Dilatometery is not useful for most step polymerizations where there is a small molecule by-product that results in no appreciable volume change upon polymerization.

                        As the dilatometer is placed into the constant temperature bath, initial meniscus movement is due to two factors:

1. Thermal expansion of the monomer

2. Contraction due to polymerization.

                        The reaction mass is heated for initiating the polymerization. As the polymerization proceeds, the viscosity of medium increases. The disadvantage of bulk polymerization is that as the medium gets viscous, the diffusibility of the growing polymer chains becomes restricted, the probability of chain collision becomes less, termination becomes difficult, and the rate of polymerization increases. This whole phenomenon is called auto acceleration, the gel effect or the trommosdorff effect. Trommosdorff effects complicate the kinetic study of polymer formation.

                        This involves an increase in viscosity which leads to a decrease in the rate of termination, since the bulky growing polymer radical cannot diffuse easily through the medium. Thus, the possibility for two polymer radicals to approach each other and participate in a termination process becomes lessened. The rate of termination reaction is limited by the rate at which the reactants can diffuse together to react. Thus lower the effective rate constant Kt, the net effect is to increase the rate of polymerization.

Bulk Polymerization:-

 The polymerization of a monomer in the absence of any medium other than a catalyst or accelerator. The monomers are usually liquids, but the term also applies to the polymerization of gases and solids in the absence of solvents, Also known as Mass Polymerization.

Polymerization of the undiluted monomer. Viscosity increases dramatically during conversion.

Advantages	Disadvantages
Pure products	heat control
Simple equipment	Dangerous
No organic solvents	Molecular weights very disperse

Rate of polymerization:-

The rate of polymerization is defined as the rate at which monomer is consumed.

The rate of polymerization is the same as the rate of disappearance of monomer. Monomer disappears faster when there are more particles. Now suppose the concentration of initiator is left the same. This will give us more particles and fewer radicals. In other words, the rate of termination will be low since there are fewer radicals.