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Solvent properties of surfactant solutions

Emulsion polymerization

The term "emulsion polymerization" is applied to a variety of processes which have in common that the main chemical reaction is a polymerization and that the end product is a latex, i. e. a suspension of polymer particles of colloidal dimensions in an aqueous medium. Such a process is called emulsion polymerization as the initial mixture of reagents usually consists of an aqueous emulsion of monomer and small amounts of other chemicals. Polymerizations in which the monomer is initially dissolved in water producing a suspension of small particles of polymer are sometimes named emulsion polymerizations as well, though rather inappropriately.

If the product of a polymerization consists of a suspension of relatively large particles (dimensions ~ 1), the process is termed a suspension polymerization. The difference between suspension and emulsion polymerization points to a process of formation of particles in the latter, whereas no such process occurs in suspension polymerization. In fact, suspension polymerizations

were found to show the characteristics of a polymerization reaction in bulk monomer, the aqueous phase playing only a minor role.

In 1926 German scientists succeeded in producing synthetic rubber latices by polymerizing monomer emulsions stabilized by various surfactive agents. The addition of surfactants profoundly influences the course of polymerization. In 1938 Fikentscher was the first to express the view that in emulsion polymerization the monomer, dissolved in the aqueous phase polymerizes rather than the monomer present as emulsified droplets.

A great deal of knowledge has been gained since emulsion polymers were first produced on a large scale. Smith and Ewart have developed a quantitative theory of particle formation and treated the growth of the particles during polymerization. One of the growth mechanisms considered has been found to hold true in many polymerizations with small particles.

The chemical reactions of emulsion polymerization take place in heterogenerous system in which polymer particles of colloidal dimensions are formed. Physical and chemical phenomena influence each other profoundly.

The extensive data obtained in emulsion polymerization of methyl methacrylate are in good agreement with the assumption that the rate of reaction at high conversion is governed only by the diffusion rate of the monomer and the radical end of the polymeric chains.

Exercises

I. Answer the following questions:

1. What is meant under " emulsion polymerization"?

2. What is meant under " suspension polymerization"?

3. What is the difference between emulsion and suspension polymerization?

4. Who treated the problem of the particle growth during polymerization?

5. What are the dimensions of the particles formed during emulsion polymerization?

II. Give a summary of the text.

III. Give Vietnamese equivalent to:

bulk layer

individual drops

initial mixture once emulsified liquid

radical end

IV. Translate the following sentences paying attention to the words in bold type:

1. A great deal of knowledge has been gained since emulsion polymers were first produced on a large scale.

2. The term "emulsion polymerization" is applied to processes which have in common that the main chemical reaction is a polymerization and that the and product is a latex.

3. Most often, particularly in the case of two pure liquids, the coalescence process is rapid.

4. Polymerizations in which the monomer is initially dissolved in water producing a suspension of small particles of polymer are sometimes named emulsion polymerizations as well.

5. Ultra-violet light is known to have a harmful influence on a rubber surface, as well as causing photochemical effects on antioxidants.

6. The chemical reactions of emulsion polymerization take place in heterogeneous system in which polymer particles of colloidal dimensions are formed.

7. One of the growth mechanisms considered has found to hold true in many polymerizations with small particles.

8. In 1926 German scientists succeeded in producing synthetic rubber latices by polymerizing monomer emulsions stabilized by various surfactive agents.

9. In 1938 Fikentscher was the first to express the view that in emulsion polymerization the monomer, dissolved in the aqueous phase polymerizes rather than the monomer present as emulsified droplets.

V. Form adjective from the following words:

action

addition

colloid

dilution

dispersion

heterogeneity

industry

line

minority

mixture

phase

polymer

quantity

relation

solute

stability

structure

synthesis

variety

viscosity

VI. Translate the following sentences paying attention to the Passive Voice:

1. The employment of latex is being aimed at reinforcing furs, particularly rabbit skins, which are very soft and weak.

2. When a solid is attacked by a liquid reagent the product might be either soluble or in soluble in the liquid.

3. Polyvinyl chloride was not thought of as a competitor of rubber until the war.

4. Branching may be referred to as changing mainly the shape of the molecule.

5. It was assumed that the rate of reaction at high conversion would be governed by the diffusion rate of the monomer.

6. Fundamental investigations concerning chemical catalysis were aimed at a quantitative expression of activity.

7. Polyethylene is not affected by aggressive mediums such as acids, alkalis and salt solutions.

8. Rubber is known to be unaffected by many neutral salts, organic acids, etc.

9. Soft vulcanized rubber in the presence of antioxidants was acted upon by the oxygen of the air.

10. If the substance being ground is a reactive one, the possibility of chemical alteration of the surface by chemisorption of oxygen or water vapour from the air must be reckoned with.

11. Since adhesion is greatly influenced by adsorption of gases and vapours, one would expect the bulk density to depend on the humidity of the air.

VII. Translate the following sentences paying attention to the Absolute Participle Construction:

1. The drops of rubber are suspended in water, when first obtained from the plant, the system resembling an emulsion.

2. Emulsion may " cream ", i. e., separate into layers of aqueous phase with a concentrated layer of oil droplets floating on the top, the rate depending primarily on the viscosity of the aqueous phase, the size of the droplets, etc.

3. The emulsifier being a solubilizing agent for the monomer, the rate of polymerization varies with the emulsifier content.

4. Most of the accelerators used today are derivatives of carbon disulfide, the commonest one being mercaptobenzothiazole.

5. The rate of polymerization varies with the emulsifier content, the emulsifier being a solubilizing agent for the monomer.

VIII. Translate into English

1. Nh­ ®• biÕt mñ (latex) lµ s¶n phÈm cuèi cïng cña sù polime ho¸ nhò t­¬ng.

2. Ph¶n øng ho¸ häc cña sù polime ho¸ nhò t­¬ng x¶y ra trong hÖ dÞ thÓ vµ ®­îc kÕt thóc bëi sù t¹o thµnh nh÷ng h¹t polime cã kÝch th­íc h¹t keo.

3. Khi nghiªn cøu sù polime ho¸ metyl metacrylat, c¸c nhµ khoa häc ®• thu ®­îc c¸c d÷ kiÖn ®¸ng chó ý.

4. Ng­êi ta ®• x¸c nhËn r»ng poly metyl metacrylat thu ®­îc b»ng c¸ch polime ho¸ nhò t­¬ng th× rÊt r¾n.

5. Latex tæng h¬p ®• ®­îc sö dông lµ nhò t­¬ng cña cao su tæng hîp vµ nhùa nh©n t¹o vµ chÝnh chóng ®­îc diÒu chÕ b»ng c¸ch polime ho¸ nh÷ng monome ban ®Çu trong cïng mét pha.