Preparation of Glyptal

May 3 • General • 26121 Views • 2 Comments on Preparation of Glyptal

Polymer is a chemical compound or mixture of compounds which consist of repeating structural units.These are very large molecules which is made by adding many small molecules called monomers to form large chains.polymers may be natural or synthetic.Example of natural polymers are-protein, polysaccharide, starch, cellulose.Example of synthetic polymers are-nylons, polyesters, polyvinyls,glyptal, polystyrenes.

Cross-linked polymer is commonly known as “slime”. The polymerization of PVA with sodium borate decahydrate(Borax) in aqueous condition gives slime.The hydrogen bond between PVA and borate ion lead to a 3-D network with extensive cross-linking.These bonds are weak and can easily form and break.So,slime is often referred to as a reversible cross-linking gel.

An example of cross-linked polymer is Glyptal resin.If more than two hydroxyl groups are present on one of the monomers the chain can be linked to form large and strong 3-dimensional structure called thermosets. Thermosets are hard and insoluble even at room temperature and are often used for paints and coatings.Glyptal is formed using phthalic anhydride monomer and glycerol monomer.The addition of this hydroxyl group allows for extensive branching during polymerization.During polymerization reaction, the monomers are joined to form larger molecules and due to increase in attractive force between molecules,mixture become viscous.

Below figure shows the Glyptal formation reaction-:

Phthalic anhydride,an anhydride of phthalic acid,is the organic compound with formula C6H4(CO)2O and is colorless solid.The catalytic oxidation of ortho-xylene and naphthalene gives Phthalic anhydride.

C₆H₄(CH₃)₂ + 3 O₂ → C₆H₄(CO)₂O + 3 H₂O

C₁₀H₈ + 4.5 O₂ → C₆H₄(CO)₂O + 2 H₂O + 2 CO₂

Glycerol,a simple polyol compound,is a colorless,odorless, viscous liquid and is sweet-tasting.The soluble nature of glycerol is due to three hydroxyl groups that glycerol has.Glycerol is produced from fats and oils and from non-triglyceride sources.

Laboratory Preparation of Glyptal:

Glyptal is prepared using following steps-

• Construct strong aluminum foil cup  by pressing two layers of heavy-duty foil around the bottom of a 50ml beaker.Then place foil cup inside a 100ml beaker.
• Measure 10g of phthalic anhydride in a tin weighing pan and 0.50g of sodium acetate into another pan and mix them thoroughly in one pan.
• Transfer the mixture carefully into a test tube.Add 4ml of glycerol.
• Clamp the test tube near its top to a ring stand and adjust tube to an inclination angle of about 45 degree.
• Heat for 5-6 mins on low flame by continuously sweeping the flame over test tube surface.After the solid have dissolved to a clear liquid,then heat for another 3mins.The liquid may become dark.
• Turn off burner and pour the content carefully into the cup made of foil.
• Insert small object such as a coin into the mold with the help of tweezer and allow the glyptal polymer to cool to room temperature.
• Remove mold from beaker after 90 mins and peel away the foil gently.

                                                        RELATED QUESTIONS AND ANSWERS

Q1.List some of natural and synthetic polymers.

Ans.-Natural polymers are-protein,starch,cellulose, polysaccharide.

The example of synthetic polymers are-nylons,polyesters,polyvinyls,polystyrenes.

Q2.What is Polymerization?

Ans.In Polymerization the monomers are joined to form larger molecules and due to increase in attractive force between molecules,mixture become viscous.

Q3.Name monomers used to form glyptal.

Ans.-Monomers used to form glyptal are as follows-

i)Phthalic anhydride

ii)Glycerol

Q4.Why slime is referred to as reversible cross-linking gel?

Ans.-Slime is result of polymerization of PVA with Borax.the hydrogen bond between them leads to a 3-D network and these bonds can easily form and break,means they are weak.Hence,slime is referred to as reversible cross-linking gel.

Glyptal preparation

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