Styrene monomer Benzoyl peroxide - Sample Essay

Abstract The aim for this experiment is to find out how inhibitors or retarders can affect the process of polymerisation. As an initiator, a system of Benzoyl Peroxide was applied. Benzoquinone (inhibitor) and Nitrobenzene (retarder) were used in this experiment. This experiment contained three different samples all consisting Styrene and Benzoyl Peroxide. An inhibitor was added to the samples to conduct the experiment: Sample A was left as is; Sample B had Benzoquinone added; and Sample C had Nitrobenzene added. Each sample was then observed to measure its rate of polymerisation.

It was found that the initial rate of polymerisation was almost steady for all samples within the first 20 minutes. From then, the rate of polymerisation changed in each sample. In Sample A, where no inhibitor or a retarder was used, the rate of polymerisation was dramatically increased. Whereas in Sample B and C which contained an inhibitor and retarder, had a slower rate of polymerisation. However, it was found that Sample C containing Nitrobenzene (retarder) had a faster rate of polymerisation than Sample B which contained Benzoquinone.

The experiment concluded that the greater the content of the polymer and the higher the viscosity of the reaction system, the sooner the rise in the rate of polymerisation system. The experimental evidence of this study makes it possible to control the synthesis of Polystyrene from monomer to polymer. Objectives The following questions will be answered once this experiment has been carried out:  To find out the roles played by Benzoyl Peroxide, Benzoquinone and Nitrobenzene.  To find out how long the induction period lasts.

To find out how Benzoquinone and Nitrobenzene slow down the rate of polymerisation of styrene.  To work out the rate constant for decomposition of Benzoyl Peroxide. Introduction The synthesis of Polystyrene by free radical addition polymerisation involves three major kinetic steps: Initiation; Propagation; and Termination. Benzoyl Peroxide is a common initiator to start the reaction. General Equation 1- Initiation: On heating, Benzoyl Peroxide decomposes to give two free radicals. The initiation step usually includes the addition of the first monomer molecule:

In this reaction the free radical attacks the monomer and adds to it. The double bond is broke open and free radical reappears at the far end. 2- Propagation: After initiation reactions, many monomer molecules are added rapidly, perhaps in a fraction of a second. On the addition of each monomer, the free radical moves to the end of the chain. 3- Termination: In the termination reaction, two free radicals react with each other. Termination is either by combination where R represents a long chain of portions or by disproportionation where hydrogen is transferred from one chain to the other.

This latter result produces in a two final chains. While the normal mode of addition is a head-to-tail reaction, this termination step is normally head-to-head. Methodology Materials used: The following materials were used in order to conduct the experiment:  Styrene monomer  Benzoyl Peroxide (initiator) Benzoquinone (inhibitor)  Nitrobenzene (retarder) Equipments used: The following equipments were used in order to conduct the experiment:  Abbe refractometer  Sodium light  Separating funnel  Vacuum oven Procedure to be followed:

Note: Before starting the experiment, following measurements were taken to ensure safety:  Safety glasses were worn at all times while conducting the experiment When handling the hot screw-cap jars, gloves were always worn Stage 1: Firstly, a 110 cm3 of the styrene solution is shaken with an equal amount of dilute sodium hydroxide solution in a separating funnel. The mixture is then shaken twice with an equal volume of deionised water. Once this procedure has been carried out, the aqueous solution is disposed off. By carrying out this procedure, the inhibitor is removed from the styrene.