Sili Putty

Sili PuttyCondensation Polymerisation

Silicone

Has anyone seen this before?

Does anyone know or has heard of silicone?

2Silicon putty is a compound that is made via condensation polymerisation.We are going to make it (and play with it) using two chemicals:dimethyldichlorosilane (CH3)2SiCl2WaterThis will form the silicon putty which looks like this chemically:

alternating silicon and oxygen atoms with organic groups (R) attached to the silicon atoms

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Condensation Reaction

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Experiment SummaryPreparation of silicone oilRemoving the hydrogen chloride (HCl) by-productRemoval of Ether (highly volatile)Conversion of silicone oil to bouncy/silly putty1. Preparation of Silicon OilYou have a conical flask containing dimethyldichlorosilane to this add 40cm3 of diethylether and swirl the flask gently to mix the two liquids.Slowly add 40cm3 of distilled water using a 100cm3 dropping funnel in a dropwise manner to start with. This is done slowly to ensure that hydrogen chloride gas is not evolved too quickly. After 10cm3 has been added dropwise the rate of addition can be increased2. Removing the HCl byproduct HCl is a product of this reaction and as we do not want it - we remove it. Pour the contents of the flask into a 250cm3 separating funnel and allow the two liquids to separate into layers. Run the bottom layer out into a beaker (label it 1) and keep this separate.Using a measuring cylinder take 100cm3 of 5% sodium bicarbonate solution and add it to the separating funnel. Put the stopper in firmly and turn the funnel upside down. Shake and periodically release the gas evolved using the tap. Repeat until no more gas is evolved indicating the HCl has been totally neutralised.

Removing the HCl (continued)Allow the layers to separate once again and run out the lower aqueous layer into a second beaker (label it 2).To the remaining top layer add 50cm3 of distilled water, stopper the funnel, invert and shake for 30 seconds. Release pressure as before and allow to separate drain the lower layer in beaker 2.Pour the top ether layer into a clean 100cm3 conical flask Add 3g of solid anhydrous magnesium sulphate and leave for about 10 minutes.

3. Removal of etherDecant the ether layer away from the MgSO4 by pouring it through a conical funnel into a 100cm3 round bottomed flask (use a cotton wool plug in the conical funnel).

Remove the ether using the rotary evaporator (ask a demonstrator to help you with this).

Conversion of silicon oil to 'putty'Take a clean dry boiling tube and place it in a 250cm3 beaker put onto a balance and zero it (press tare). Pour all of the silicone oil into the boiling tube and record its weight.Clamp the boiling tube vertically and heat carefully using a Bunsen burner until the temperature is around 160oC (monitor using a 200oC thermometer).Add an amount of boric acid equal to 8% of the weight of the silicone oil in small portions taking care to stir the oil after each addition to ensure the solid dissolves. Leave for 1 hour.Allow the mixture to cool and remove using a spatula. Thoroughly kneed the substance until it resembles putty.