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INHIBITION AND RETARDATION IN THE FREE REDICAL ADDITION POLYMERISATION OF STYRENE

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Introduction

INHIBITION AND RETARDATION IN THE FREE REDICAL ADDITION POLYMERISATION OF STYRENE 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. ...read more.

Middle

is added in to the second mixture of Styrene and Benzoyl Peroxide. Sample C: 0.5 wt % of Nitrobenzene (retarder) is added in to the third mixture of the Styrene and Benzoyl Peroxide solution. The three solutions are then placed separately in a small screw-cap jar and placed in an oven heated at 85? C. All three solutions were observed at ten-minute intervals: a few drops from each solution were withdrawn and its refractive index was measured with an Abbe-refractometer. Between every measurement, the prisms of the refractometer were cleaned with a tissue soaked in acetone. This cleared the surface of the refractometer so that the experiment remains fair. Result and Discussion Temperature = 85�C Refractive index of styrene = 1.5468 Refractive index of polystyrene = 1.59 - 1.60 S. No. Time (minutes) Sample A Sample B Sample C 1 0 1.5467 1.5467 1.5466 2 10 1.5466 1.5465 1.5465 3 20 1.5467 1.5466 1.5467 4 30 1.5490 1.5458 1.5489 5 40 1.5505 1.5462 1.5500 6 50 1.5516 1.5457 1.5510 7 60 1.5530 1.5467 1.5514 8 70 1.5537 1.5459 1.5522 Discussion As shown in the graphs above, it was found that the induction period 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 only initiator was used, the rate of polymerisation was spectacularly increased. ...read more.

Conclusion

The most direct method of finding the initiator efficiency depends upon finding the polymer for initiator fragments. As known previously, the refractive index of polystyrene is 1.59 to 1.60 (please refer to page 4). Through our observations, it has been found that the refractive index in Sample A increased progressively. This shows the decomposition rate of Benzoyl Peroxide takes place in polymerisation. Conclusion By performing this experiment it can be summarised that the amount of inhibitor and retarder added to the Styrene solution can affect the rate of polymerisation greatly. Therefore, the greater the content of the polymer, the higher the viscosity of the reaction system and the more rapid the rise in the rate of polymerisation system. The experimental evidence of this study suggests it is possible to control the synthesis of Polystyrene from monomer to polymer. In addition, it can be concluded that an important application of inhibitors is in the stabilising of monomer. It is dangerous to store polymerised monomers in its pure state on a large scale, since if oxidation producing peroxides or irradiation by ultra-violet light occurred, free radicals could be formed which would then result in polymerisation. This may accelerate to an explosive degree. This is prevented by the addition of a few parts of inhibitors such as the ones used in this experiment (Benzoquinone). Such inhibitors may be removed before the use of the monomer, by distillation, washing with alkali or passing down an ion exchange column. ...read more.

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