Condensation Polymerization

Before understanding the types of polymerization one needs to understand what are polymers and what is polymerization? Polymers are long chain of two or more monomers. Polymerization is a chemical process which involves the reaction of two or more monomers to form a polymer. There are two types of polymerization:

• Addition Polymerization
• Condensation Polymerization

In addition polymerization, two or more molecules of monomers attach together to form a polymer. It is a chain reaction and no byproduct is release. Condensation polymerization on the other hand is a process in which the reaction takes place with a release of a byproduct like water, alcohol, etc. Let's study the latter polymerization in detail as it is a very important part of chemistry.

What is Condensation Polymerization?

It is a chemical reaction in which polymer is formed and a small molecule of byproduct with a lower molecular weight is released. The byproduct eliminated is known as condensate. The reaction can take place between two similar or different monomers. It is also called step-growth polymerization but there are some exceptions which react as condensation polymerization but follow the chain growth pattern. They can react with any number of molecules till they are big enough to be called polymers.

		O												O
		||												||
R	-	C	-	OH	+	H	-	N	-	R'	---->	R	-	C	-	N	-	R'	+	H2O
								|								|
								H								H

In the above reaction, carboxylic acid is reacting with an amine group. In the process, water molecule is released and an amide molecule is formed.

For Example:

			O				O																O				O
			||				||																||				||
	HO	-	C	-	(CH2)4	-	C	-	OH	+	H	-	N	-	(CH2)6	-	N	-	H	----->	HO	-	C	-	(CH2)4	-	C	-	N	-	(CH2)6	-	N	-	H	+	H2O
													|																|				|
													H																H				H

Here, in the above example, you can see reaction between carboxylic acid (adipic acid) monomer and an amine (1,6 diaminohexane) monomer to give a polyamide. This is further polymerized and is known as Nylon 66. In this process, a water molecule is eliminated.

Characteristics of Condensation Polymerization

• The molecules should have one or two functional groups and the reaction can take place between the same or different functional group.
• Hydrogen bonding gives them a crystalline structure with a tensile strength.
• They have a very high melting point.
• They are thermosets as once molded, they cannot be remolded.
• They have high Tg and Tm values that makes them rigid as glass and transparent.
• The reaction can take place between two monomers, one monomer and one dimer, or a dimer with an oligomer, or a chain with another chain of polymers.
• They possess mixed properties of both the molecules or functional group.

Given below are some of the examples with their components and uses.

Name	Components	Uses
Dacron	para HO2C-C6H4-CO2H HO-CH2CH2-OH	Used in making curtains, dress fabrics, woven sports wear, knetted wear, etc.
Nylon 66	HO2C-(CH2)4-CO2H H2N-(CH2)6-NH2	Used in making tires, ropes, carpet fibers, conveyor belts, air bags, etc.
Kevlar	para HO2C-C6H4-CO2H para H2N-C6H4-NH2	Used in making jackets, combat helmets, bicycle tires, loudspeaker cones, woven rope, etc.
Nomex	meta HO2C-C6H4-CO2H meta H2N-C6H4-NH2	Used in making nomex hood used by the firefighters, driving suits, flights suits, thermal blankets, etc.
Lexan	(HO-C6H4-)2C(CH3)2 (Bisphenol A) X2C=O (X = OCH3 or Cl)	Used as kitchen ware, alternative of glass, laparoscopic instruments, electric meters, cell phones, etc.

From the above given table you can easily make out the usefulness of this types of polymerization process. There are many disadvantages too. Everyone is aware about the dangerous effects of plastic and the threat it brought to life. But with plastic recycling methods, this can be taken care of. Hope this information has helped you to understand condensation type of polymerization better with the examples and its uses.