Polystyrene preparation

Zeinab Ahmed Elbhnsawi

193247

Submitted to: Dr. Mostafa Radwan

Polymer Chemistry

Year 2, Chemical Engineering

The British University in Egypt

Paper format: APA style with BUE guidelines

Abstract

The following lab report discusses the preparation of polystyrene using free radical initiator

which is a type of addition polymerization by following a certain procedure where at its end, a

solution is filtered on a filtering sheet where the precipitate of polystyrene is collected by this

sheet. Then solubility tests for polystyrene take place where it was tested in water, distilled water

and ethanol and found insoluble while in benzene, acetone and hexane it was found soluble.

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Table of contents

Abstract..........................................................................................................................................2

Table of contents............................................................................................................................3

Introduction....................................................................................................................................4

Experimental procedure and materials.......................................................................................8

Experimental materials.............................................................................................................8

Experimental procedure............................................................................................................9

Experimental results....................................................................................................................10

Discussion.....................................................................................................................................11

Conclusion....................................................................................................................................12

Sources of error............................................................................................................................13

References.....................................................................................................................................14

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Introduction

Polymerization is any process in which relatively small molecules named monomers combine

chemically to produce a very large chainlike or network molecule called a polymer. Usually at

least 100 monomer molecules must be combined to make a product that has certain unique

physical properties that differentiate polymers from substances composed of smaller molecules.

Two classes of polymerization usually are found. In condensation polymerization, each step of

the process is accompanied by the formation of a molecule of some simple compound, often

water. In addition polymerization, monomers react to form a polymer without the formation of

by-products. Addition polymerizations usually are carried out in the presence of catalysts, which

in certain cases exert control over structural details that have important effects on the properties

of the polymer (Britannica, 2020).

Figure 1. polymers

A polymerization mechanism is the order of chemical reactions by which polymerization

proceeds. The mechanism of polymerization used in the synthesis of polymers allows for the

classification of the polymerization into two types, addition and condensation polymers. The

addition kind is produced by the repeated and sequential addition of monomers without the loss

of a smaller molecule during the process. Therefore, no by-product is produced and the repeating

unit of additional polymers has the same formula as the alkene or functionally-substituted alkene

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monomers used to make them. These addition reactions follow a stepwise mechanism that

involves reactive intermediates such as radicals or ions that help in the conversion of a pi bond in

the monomer into a sigma bond in the polymer. The four different polymerization techniques

used in the synthesis of addition polymers are free radical polymerization, cationic

polymerization and anionic polymerization. The mechanism of free radical polymerization

follows three steps namely, initiation, propagation, and termination. During initiation, a molecule

called a radical initiator is broken down into free radicals either thermally or photolytically. A

radical then attacks the pi bond in the alkene monomer forming a covalent bond with one of the

carbon atoms and turning the other one into a reactive radical. The propagation stage then

follows with the latter continuously adding on more monomers and growing into a chain.

Termination of chain growth finally occurs when the radical chains either combine or participate

in disproportionation reactions involving pulling hydrogen from another radical chain. Cationic

and anionic polymerization follows an overall similar pathway with their initiators being strong

acids and Lewis acids, or strong bases, alkali metals, and organolithium compounds (Babooram,

2020).

Figure 2. free radical polymerization

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Polystyrene is one of the largest volume vinyl polymers, used in countless products from food-

packing and plastic cutlery to house insulation. The primary reasons for its great popularity are

its low cost, high transparency, good mechanical properties and ease of coloring, foaming, and

processing. Commercial polystyrene is mostly synthesized by bulk, suspension or solution

polymerization of styrene. The most common method is free radical polymerization, using

benzoyl peroxide as initiator. However, other initiators such as redox systems and azo

compounds can be used as well to start the polymerization. The reaction is exothermic, and thus

the monomer-polymer mixture must be cooled where the mechanism is illustrated in the

following figure. ( Polymer Properties Database, n.d.).

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Figure 3. mechanism of reaction of polystyrene

Polystyrene has huge number of uses. Polystyrene foam or expanded polystyrene as its more

often referred to, is mainly used within the packaging industry, used as a high impact packaging

solution to protect a large range of products from damage during transport or storage. As a hard,

solid plastic, it is often used in products that require clarity, such as food packaging and

laboratory ware. When combined with various colorants, additives or other plastics, polystyrene

is used to make appliances, electronics, automobile parts, toys, gardening pots and equipment

and more. Polystyrene in Appliances is used in refrigerators, air conditioners, ovens,

microwaves, vacuum cleaners, blenders – these and other appliances often are made with

polystyrene (solid and foam) because it is inert (doesn’t react with other materials), cost-effective

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and long-lasting. In Automotive, polystyrene (solid and foam) is used to make many car parts,

including knobs, instrument panels, trim, energy absorbing door panels and sound dampening

foam. Foam polystyrene also is widely used in child protective seats. In foodservice, polystyrene

foodservice packaging typically insulates better, keeps food fresher longer and costs less than

alternatives. In medical field, due to its clarity and ease of sterilization, polystyrene is used for a

wide range of medical applications, including tissue culture trays, test tubes, petri dishes,

diagnostic components, housings for test kits and medical devices (Polystyrene, n.d.).

Figure 4. polystyrene uses

Experimental procedure and materials

Experimental materials

1. 200 ml methanol.

2. 30 ml styrene.

3. 30 ml NaOH.

4. 2 g CaCO3.

5. 0.3 g benzoyl peroxide.

6. 20 ml toluene.

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7. Analytical balance.

8. Separating funnel.

9. Graduated cylinders.

10. Thermometer.

11. Filtering flask.

12. Glass stirring rod.

13. Test tubes.

14. Filtering papers.

15. Water bath.

16. Büchner funnel.

Experimental procedure

1. If the styrene contains an inhibitor, the inhibitor must first be removed. To do this,

measure 30 mL of inhibited styrene into a 250-mL separatory funnel and add 30 mL of

10% NaOH. Shake the contents several times while properly venting for 1 minute.

2. Separate the styrene from the separatory funnel and place into a beaker. Add

approximately 2 grams of calcium carbonate into the styrene and stir. This will dry your

styrene. Keep the inhibitor free styrene in a suitable brown glass bottle.

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3. Add 20 mL of toluene using 25 mL graduated cylinder and 5 mL of inhibitor free styrene

using 10 mL graduated cylinder to a 20- x 150-mm test tube and add 0.3 g of benzoyl

peroxide.

4. Place the test tube in a beaker half full of water on a hot plate or a water bath. Maintain

the temperature of the bath at 90 °C.

5. After 60 minutes remove the test tube, allow the contents to cool for 5 minutes, and note

the viscosity of the solution. Pour the solution into 200 mL of methanol contained in a

beaker. A white precipitate of polystyrene will form.

6. Collect the polystyrene by filtration using a Büchner funnel and wash the precipitate on

the funnel with 50 mL of methanol. Remove the precipitate from the funnel and spread it

out to dry on a large, clean sheet of filter paper.

7. Place 3 mL of acetone, water, distilled water, benzene, ethanol and hexane in clean test

tubes and add 0.2 g of dried polymer. Stir the mixtures then leave it to see if it is soluble.

Experimental results

After collecting polystyrene from the filtering papers, solubility tests where performed using

different solvents where results were as follows,

Solvent Solubility

Water Insoluble

Distilled water Insoluble

Benzene Soluble

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Ethanol Insoluble

Acetone Soluble

Hexane Soluble

Discussion

After polystyrene was filtrated and dried, test tubes were used to test its solubility in many

solvents. The first solvent was water where in lab, polystyrene didn’t dissolve in water. This is

true such that polystyrene doesn’t dissolve in water where it is resistant to water and moisture.

This means that it does not absorb them and that its insulating performance is not compromised

when in contact with these elements. Second one was distilled water which has the same exact

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behavior just like water. Third solvent was benzene, polystyrene dissolved in benzene

completely Since polystyrene only contains carbon hydrogen bonds, it is nonpolar and will only

dissolve in nonpolar solvents like benzene, because like dissolves like. Fourth one was ethanol

where in lab, polystyrene didn’t dissolve in ethanol. While theoretically polystyrene should

dissolve in ethanol but may be there were errors in the concentration of the used methanol or

may it need more time. Then comes acetone were polystyrene dissolved in it which is

theoretically true where like dissolves like, This is why the non-polar polystyrene dissolves in

acetone but not water and the polar starch molecules dissolve in water but not acetone. The last

one was hexane where it dissolved in hexane which isn’t theoretically true as it shouldn’t

dissolve in hexane due to low molecular weight where an error in test tubes labeling may have

occurred in lab causing these wrong results.

Conclusion

The aim of this experiment was to prepare polystyrene using free radical initiator which is

benzoyl peroxide where it was prepared in lab using addition polymerization and preparing the

polystyrene to be put in a water bath for an hour then using methanol to get all the precipitate by

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the usage of funnel and filtration sheets the solubility of polystyrene was tested using many

solvents where it was found soluble in some of them and insoluble in others.

Sources of error

The preparation of polystyrene is considered as a qualitative analysis where the slight difference

in concentrations doesn’t cause huge errors, but it should be somehow accurate. Errors may be

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found in the concentrations of the used substances such as inhibitors, methanol, NaOH or

benzoyl peroxide where any defect in their concentrations may cause errors. Human errors can

be found in not following the procedure or missing some of the steps like using the water bath

where this can be avoided by being very careful in following the procedure.

References

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1. Polymer Properties Database. (n.d.). Retrieved from

https://polymerdatabase.com/polymer%20chemistry/Polystyrene.html

2. Babooram, K. (2020). Polymer Science and Nanotechnology. Retrieved from science

direct: https://www.sciencedirect.com/topics/materials-science/mechanisms-of-

polymerization

3. Britannica, T. E. (2020, may 26). polymerization. Retrieved from Britannica:

https://www.britannica.com/science/polymerization

4. Polystyrene. (n.d.). Retrieved from https://www.chemicalsafetyfacts.org/polystyrene/

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