Types of Polymerisation
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11/8/2006
Techniques of Polymerisation: 1) Bulk or Mass Polymerisation: Method: Pre-polymerisation stage. Monomer is in liquid state and initiator dissolved in monomer is taken in a vessel and heated initially to poln temp. by a hot jacket to initiate the reaction. Monomer is added with constant agitation/ stirring for effective heat and mass transfer. Polymerisation reaction involves extensive bond formation in homogenous system and is exothermic. (25 – 30% poln) Post poln stage :- As the reaction proceeds, the reaction mixture becomes viscous and is then transferred to the main reactor and is placed in a thermostat maintained at a higher temperature. After a known period of time the content is poured into methanol when the polymer gets precipitated out. It can be extracted into rods or fabricated into sheets. The polymer product being free from any contaminations except the monomer can be used without further purification. BP is mainly used for the manufacture of condensation reaction where the reactions are mildly exothermic. Eg PS, PVC, PMMA. Advantages • Method is simple and needs simple equipment • Percentage of conversion is high – 100% • Easy work up procedure, no isolation or purification steps. Disadvantages: • As reaction proceeds agitation is difficult as the product becomes more and more viscous as concentration of mass increases. • Heat control is more difficult as poln progresses. The viscosity increases and local hot spats develop due to difficulty in agitation. Uncontrolled exothermic reactions lead to sudden temperature rise that may result in explosion. • The gel effect observed – As poln proceeds, viscosity increases, termination becomes difficult. Rate of poln increases rapidly. Auto acceleration of pol rate with decrease in termination rate is gel effect or auto acceleration. • The polymer molecules with wide range of molecular masses will be obtained • Removal of the last traces of monomers becomes extremely difficult 2) Solution
11/8/2006
Techniques of Polymerisation: 1) Bulk or Mass Polymerisation: Method: Pre-polymerisation stage. Monomer is in liquid state and initiator dissolved in monomer is taken in a vessel and heated initially to poln temp. by a hot jacket to initiate the reaction. Monomer is added with constant agitation/ stirring for effective heat and mass transfer. Polymerisation reaction involves extensive bond formation in homogenous system and is exothermic. (25 – 30% poln) Post poln stage :- As the reaction proceeds, the reaction mixture becomes viscous and is then transferred to the main reactor and is placed in a thermostat maintained at a higher temperature. After a known period of time the content is poured into methanol when the polymer gets precipitated out. It can be extracted into rods or fabricated into sheets. The polymer product being free from any contaminations except the monomer can be used without further purification. BP is mainly used for the manufacture of condensation reaction where the reactions are mildly exothermic. Eg PS, PVC, PMMA. Advantages • Method is simple and needs simple equipment • Percentage of conversion is high – 100% • Easy work up procedure, no isolation or purification steps. Disadvantages: • As reaction proceeds agitation is difficult as the product becomes more and more viscous as concentration of mass increases. • Heat control is more difficult as poln progresses. The viscosity increases and local hot spats develop due to difficulty in agitation. Uncontrolled exothermic reactions lead to sudden temperature rise that may result in explosion. • The gel effect observed – As poln proceeds, viscosity increases, termination becomes difficult. Rate of poln increases rapidly. Auto acceleration of pol rate with decrease in termination rate is gel effect or auto acceleration. • The polymer molecules with wide range of molecular masses will be obtained • Removal of the last traces of monomers becomes extremely difficult 2) Solution