Question

36. What would be the composition of the product obtained by the cationic low-temperature polymerization of a solution of isobutylene in ethylene?

44. Below the glass transition temperature, a material should behave in what manner?

Answer 1

36. What would be the composition of the product obtained by the cationic low-temperature polymerization of a solution of isobutylene in ethylene?

Ans.

Since required activation energy for ionic polymerization is very small ( when we have stable intermediate ) , thus polymerization occurs at low temperature.

In Cationic polymerization , both initiation and propagation step dependent on stability of the carbocations. Since , only isobutylene as monomer can match these conditions , thus at low temperature reaction proceeds to give Polyisobutylene. ( Ethylene does not add to progressive polymer as its addition will lead to primary carbocation which is high energetic and very -unstable , thus at low temperature polymerization it doesn't form. )

44. Below the glass transition temperature, a material should behave in what manner?

The glass transition temperature , often called T_g, is the temperature range where the polymer substrate changes from a rigid glassy material to a soft (not melted) material, and is usually measured in terms of the stiffness, or modulus. Glass transition temperature is the macro-manifestation of polymer chain’s flexibility.With increasing rigidity of the polymer chain, the glass transition temperature of polymer will be increased too.

Glass transition temperature is the temperature, below which the physical properties of plastics/polymer change to those of a glassy or crystalline state. Above T_g they behave like rubbery materials. Below the T_g a plastic’s molecules have relatively little mobility. A plastic’s properties can be dramatically different above and below its T_g.

Thus, below the glass transition temperature, a material should behave as a solid/crystalline or glassy material.