Investigations on some selected conducting polymers and polymer ...

polymerization, each growth step is a chemical reaction between two
molecules. In chain growth polymerization, a long chain molecule is
fonned by a series of consecutive steps that is completed in a very short
time. Unlike in the case of step growth polymerization, intermediate
size molecules cannot be isolated here and the products are final
polymers. In chain growth polymerization, each individual growth step
is a chemical reaction between a chain carrying species and a molecule.
In these reactions, the chain is carried by an ion or a free radical. Free
radical is a reactive substance with an unpaired electron formed by the
decomposition of an unstable molecule called initiator. The chain
growth is started by initiators, which initially undergo decomposition to
form radicals. Free radical polymerization is perhaps the most widely
studied reaction among chain growth polymerization mechanisms. Here
there are three steps-initiation, propogation and termination. Initiation
means the formation of initiator radical by the decomposition of the
initiator. The initiator radical then acts on the monomer forming
monomer radicals. The first monomer radical reacts with a monomer
molecule to form a dimmer radical. The dimmer radical then reacts
with a monomer molecule to produce a trimer radical and the process
propogates.
1.2 Glass transition temperature
Glass transition temperature is the temperature below which a
polymer is hard and above which it is soft[5]. The hard, brittle state is
known as the glassy state and the soft, flexible state as the rubbery or
viscoelastic state. On further heating, the polymer becomes a highly
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