Step Growth or Condensation Polymerization

Polymer word is made up of two terms, “poly” which means many and “mer” which means entities or group. So polymers mean giant molecules which consist of a large number of small molecules. The molecular mass of these giant molecules is quite high as these are formed by repeating small entities which are called monomers. The structure of monomers are the same as polymers but these are smaller molecules having covalent bonding among them.

Polymers are formed from monomers and the process is called Polymerisation.

Properties of Polymers

• Polymers have a chain-like structure in which monomers are cross-linked to one another.
• Polymers are made from monomers so polymers have high molecular weights.
• Polymers are resistant to heat and can stand high temperatures.
• Polymers are highly flexible due to the dipole-dipole type of bonding across molecules.
• Crystalline polymers can change state to become semi-crystalline under suitable conditions.

Condensation Polymerization or step-growth polymerization

When two or more than two bi or tri functional monomers takes part in a condensation reaction again and again then such type of polymerization is called Condensation Polymerization or step-growth polymerization.

Molecules with low molecular mass get lost in the reaction and molecules with large molecular masses forms condensate polymers. Condensation Polymerization is also known as step-growth polymerization because a bifunctional unit is created at each step in these reactions which is independent in nature.

Characteristics of Condensation Polymerization

• Condensation polymerization is used in reacting small entities to form a big entity of heavy molecular mass.
• For condensation polymerization, two same or different functional groups are required.
• The reacting functional groups should be difunctional in nature so to initiate the condensation reaction.
• Condensate polymer formed from condensation polymerization reaction has the properties of reacting molecules.
• The final output polymer of condensation polymerization has a three-dimensional structure and is formed from cross-linking of reacting entities. Example: The reaction of Ethylene glycol and Terephthalic acid to create Dacron.

Reaction of Ethylene glycol and Terephthalic acid

Important Condensation Polymers 

Polyamides

Polyamides are those polymers that contain amides linking to the main branches. These polymers can be synthesized by the condensation reaction of dicarboxylic acids and diamines.

Examples: Nylon 6, Nylon 6, 6 etc.

Some Important Properties of Polyamides are-

• Polyamides are good temperature resistance means they can withstand high temperatures.
• Polyamides are abrasion-resistant means they do not wear or tear easily by mechanical action.
• These are not good chemical reactions and can get easily damaged by chemicals.
• The tensile strength of polyamides is high so these are used in making different types of fabrics.

Formation of Nylon 6, 6 polyamide

Formation of Nylon 6, 6 takes place when adipic acid polymerises with hexamethylenediamine at suitable pressure and temperature conditions. Reaction for preparing Nylon 6, 6 is

nHOOC(CH₂)₄COOH   +    nH₂N(CH₂)₆NH    →    [HN(CH₂)₆NHCO(CH₂)₄CO]_n  +  nH₂O

Adipic Acid        Hexamethylenediamine                  Nylon 6, 6                    

Polyesters

When diols and dicarboxylic acids react to form polymerise then polyester formation takes place. Polyesters are used in making special fabrics that are resistant to creases. Polyesters with other materials like glass are used to make different useful things like helmets.

Example: Terylene, etc.

Some Important Properties of Polyesters are-

• Polyesters are moisture-resistant and do not get damaged by the effect of moisture.
• Fibres of polyesters are strong in nature means they do not tear easily.
• Polyester fabrics are wrinkle resistance means they do not need to be ironed.
• Polyester does not decompose easily like other fibres.

Formation of Terylene

Terylene is prepared by the reaction of terephthalic acid with ethylene glycol at 145 to 185 degrees Celsius temperature and the catalyst used in this reaction is zinc acetate antimony trioxide.

Formation of Terylene

Bakelite

Bakelite is a synthetic plastic. It is also known as Polyoxybenzylmethylenglycolanhydride. Phenol and Formaldehyde is used as monomers to produce bakelite which is formed by the condensation reaction of these monomers. Its appearance is brownish and it is solid in nature. It is used for making electrical switches as it is resistant to heat, it is also used in making utensil’s handles and combs.

Some Important Properties of Bakelite are-

• Preparation: Bakelite is prepared by the condensation reaction of phenol and formaldehyde under suitable temperature conditions.
• Bakelite could be moulded easily means it takes less time in production.
• It has high heat resistant property and hence it is used in making string heat resistant materials like handles of utensils.
• It is resistant to chemicals and the polymer is lightweight.

Reaction of Bakelite Formation

Melamine formaldehyde polymer

Condensation polymerisation of formaldehyde and melamine is used to produce a melamine-formaldehyde polymer. It is used in making kitchen items that are tough and strong in nature.

Some Important Properties of Melamine formaldehyde polymer are-

• It is fire resistant and is able to withstand high heat.
• It is strong in nature so it does not break easily.
• Its appearance is white and it is also chemical resistant.

Sample Questions

Question 1: Show the formation process of melamine-formaldehyde polymer.

Answer: 

To make a melamine-formaldehyde polymer, formaldehyde and melamine react under suitable conditions and the formation of resin intermediate takes place after which repetition of condensation reaction occurs and Melamine polymer gets created.

Formation of melamine-formaldehyde polymer

Question 2: What is the process to form Nylon 6, 6?

Answer:

To form Nylon 6, 6 adipic acid and hexamethylenediamine polymerise using condensation reaction at high temperature and pressure.

Question 3: Mention some of the properties of Nylon 6.

Answer:

1. Nylon 6 fabrics are highly elastic in nature, they can be stretched easily.
2. Nylon 6 polymers are crease-resistant means they do not get wrinkles easily.
3. These polymers can absorb moisture but they dried up very fast.
4. Nylon 6 fibres are resistant to chemical effects.

Question 4: How can we make Bakelite from Novolac?

Answer:

Novolac is the intermediate product in the process of forming phenol-formaldehyde polymers, so when novolac is exposed to heat in the presence of formaldehyde reacts to make cross-links of solid material which is Bakelite.

Question 5: How can we prepare Nylon 6?

Answer:

Nylon 6 can be prepared easily from caprolactam by exposing it to high heat in presence of water.