Phenol and formaldehyde undergo condensation to give a polymar (A) which on heating with formaldehyde gives a thermosetting polymer (B). Name the polymers. Write the reactions involved in the formation of (A). What is the structural difference between two polymers?
Phenol and formaldehyde undergo condensation to give a polymer novolac $(A)$ which on heating with formaldehyde gives bakelite $(B)$ as a thermosetting polymer.
Sequence of the reaction can be written as
Structural difference in between these two is that novolac is a linear polymer while bakelite is a cross linked polymer.
Low density polythene and high density polythene, both are polymers of ethene but there is marked difference in their properties. Explain.
Low density and high density polythenes are obtained under different conditions. These differ in their structural features. Low density polythenes are highly branched structures while high density polythene consists of closely packed linear molecules. Close packing increases the density.
Which of the following polymers soften on heating and harden on cooling? What are the polymers with this property collectively called? What are the structural similarities between such polymers? Bakelite, urea-formaldehyde resin, polythene, polyvinyls, polystyrene.
Polythene, polyvinyls and polystyrene soften on heating and harden on cooling. Such polymers are called thermoplastic polymers. These polymers are linear array of slightly branched long chain molecules.
These possess intermolecular forces whose strength lies between strength of intermolecular forces of elastomers and fibres while bakelite, urea formaldehyde resin are thermosetting polymers which on heating undergo extensive cross linking in moulds and again become infusible.