Understanding About Emulsion Polymerization of Styrene

Introduction

Theoretically polymerization solution has two types. They are homogeneous and heterogeneous which homogeneous has single phase of solution and heterogeneous has multiple phase solution. In case emulsion polymerization is heterogeneous which the system of solution can’t be soluble. Comparing with the others heterogeneous solution, emulsion particles have size in the range 0.05 to 0.2 µm. Emulsion polymerization can be produced by dispersing monomer (in the experiment uses styrene as monomer) in the water with surfactant or emulsifier agent. Generally emulsion polymerization produce latex in the end of process.

Figure1. A schematic representation of the micelle formation

Micelle formation can be explained by figure1 which there are three steps. In the interval 1 which nucleation of monomers to swollen micelle by adding surfactant (radical surfactants) with dashed line (meaning there is no propagate formation) in order to polymerization increase by increase conversion rate of micelle formation.  Thus in interval 2 that growth latex particle by formatting propagation which in the steps polymerization rate drives constant that meaning micelle formation almost stop to growth.  In the last interval, micelle formation stops to grow in order to polymerization decreasing too. Illustration of those explanations will be shown in figure2 by graphic between polymerization and conversion rate.

14256944672033935876

Figure2. Interval area of micelle formation is shown by function of conversion rate

Producing emulsion polymerization which explained in previous paragraph, we need:

1.Water

2.Surfactants or emulsifier agent (there is three types of surfactants, they are anionic, cationic and nonionic surfactants) such as trimethylalkylammonium chlorides, and the chlorides or bromides of benzalkonium and alkylpyridinium ions (cationic surfactants), sodium lauryl sulfate, sodium stearate (anionic surfactants) and poly ethylene oxide, poly vinyl alcohol (nonionic surfactants).

3.Monomers such as styrene, butadiene

Emulsion polymerization has advantage and disadvantage in the process, they are:

The advantages

1.Easy to control the heat generation.

2.Having low viscosity in the end product.

3.The final product (latex product) can be used directly.

4.We have high Molecular weight at high rate with smaller molecular weight distribution.

5.The final product has small particle size.

The disadvantages

1.Surfactants, Emulsifier and Coagulants are difficult removed in the solution.

2.The polymers can be degraded by residuals.

Reaction Mechanism

14256944991198686263

Figure3. Decomposition of initiator

1425694514623197104

Figure4. Initiation of styrene

1425694528893333747

Figure5. Propagation process of styrene

14256945462096741265

Figure6. The Termination process by Disproportionation

1425694561214729010

Figure7. The Termination process by combination

Experiment

In the experiment we string up bottom flask, magnetic stir bar, coil condenser and oil bath together. We can see the structure of equipment in figure 8.  In this experiment we got milky appearance with keeping temperature at 50 oC.

In this experiment we used 7.1 gram of styrene, sodium dodecyl sulfate (SDS) 0.354 gram and Ammonium peroxodisulfate 2.1 gram. And in the end experiment we got polymers 4.48 gram. So normally produce micelle in emulsion polymerization at 70-80 %. In investigating that our product can’t reach up theoretic conversion. In my opinion that in this experiment, we drive it quickly. We should do experiment more than 2 hours for waiting emulsion process. Another reason is polymers dissolved in solvent. So we just got not many polymers in the end.

14256946151453426670

Figure8. Sequence of emulsion polymerization experiment

The characterized of surfactants usually have two parts. They are hydrophilic and hydrophobic. Detail characteristic of surfactants, we can see in the figure 9.

1425694636280404387

Figure9. Process of micelle formation and part of surfactants

Chemically surfactants can be characterized by their concentration that means surfactants concentration has effect to make micelle formation as well as explain in introduction step. Physically the concentration of surfactant influence in conductivity and surface tension.