24-07-2012, 04:44 PM
SYNTHETIC POLYMERS
[attachment=28768]
INTRODUCTION
A Polymer is a compound consisting of long-chain molecules, each molecule made up of repeating units connected together.
There may be thousands ,even millions of units in a single polymer molecule.
They are also known as macromolecules.
Normally most polymers are based on carbon and are therefore considered organic chemicals.
TYPES OF POLYMERS
Thermoplastic polymers – These are solid materials at room temperature, but they become viscous liquids when heated to temperature of only a few hundred degrees. This characteristic allows them to be easily and economically shaped into products. They can be subjected to this heating and cooling cycle repeatedly without significant degradation of the polymer.
1. Mechanical Properties :
(a) Much lower stiffness .
(b) Lower tensile strength , about 10% of the metals.
© Much lower hardness .
(d) Greater ductility .
2. Physical Properties :
(a) lower densities than metals or ceramics .
(b) Much higher coefficient of thermal expansion .
© Much lower melting temperatures .
(d) insulating electrical properties.
3. Important Commercial Thermoplastics :
(a) Polyoxymethylene :
e.g.- brass, zinc are used in automotive components such as door handles, pump housings etc.
Polymer Synthesis
The study of polymer science begins with understand-ing the methods in which these materials are synthesized. Polymer synthesis is a complex procedure & can take place in a variety of ways.
Normally we discuss about two methods of poly-
merization :
1. Addition Polymerization – it is also known as chain – polymerization. In this process a molecule with an unpaired electron. The tendency for this to gain an additional electron in order to form a pairs makes it highly reactive, so that these molecule by stealing an electron.It is after created by the division of a molecule.
2. Step Polymerization : The process in which two reacting monomers are brought together to form a new molecule of the desired compound . In most in this processes, a byproduct of the reaction is also produced .
[attachment=28768]
INTRODUCTION
A Polymer is a compound consisting of long-chain molecules, each molecule made up of repeating units connected together.
There may be thousands ,even millions of units in a single polymer molecule.
They are also known as macromolecules.
Normally most polymers are based on carbon and are therefore considered organic chemicals.
TYPES OF POLYMERS
Thermoplastic polymers – These are solid materials at room temperature, but they become viscous liquids when heated to temperature of only a few hundred degrees. This characteristic allows them to be easily and economically shaped into products. They can be subjected to this heating and cooling cycle repeatedly without significant degradation of the polymer.
1. Mechanical Properties :
(a) Much lower stiffness .
(b) Lower tensile strength , about 10% of the metals.
© Much lower hardness .
(d) Greater ductility .
2. Physical Properties :
(a) lower densities than metals or ceramics .
(b) Much higher coefficient of thermal expansion .
© Much lower melting temperatures .
(d) insulating electrical properties.
3. Important Commercial Thermoplastics :
(a) Polyoxymethylene :
e.g.- brass, zinc are used in automotive components such as door handles, pump housings etc.
Polymer Synthesis
The study of polymer science begins with understand-ing the methods in which these materials are synthesized. Polymer synthesis is a complex procedure & can take place in a variety of ways.
Normally we discuss about two methods of poly-
merization :
1. Addition Polymerization – it is also known as chain – polymerization. In this process a molecule with an unpaired electron. The tendency for this to gain an additional electron in order to form a pairs makes it highly reactive, so that these molecule by stealing an electron.It is after created by the division of a molecule.
2. Step Polymerization : The process in which two reacting monomers are brought together to form a new molecule of the desired compound . In most in this processes, a byproduct of the reaction is also produced .