Engineering Chemistry S Datta

POLYMERS 457
It can be reinforced with glass to form safety helmets, aeroplane parts, paratroop, wire
insulators, fighter parachute etc.
Terylene has several advantages over cotton in respect of
(i)Resistance to acids
(ii)Strength
(iii)Crease resistance and
(iv)Gives better finish and blendable with cotton or wool.
Silicones
Silicones have alternate silicon-oxygen bonds and organic radicals attached to the silicon
atoms.
The monomers are prepared as
Cu
(i) RCl + Si ⎯⎯→
(ii)From Grignard reagent
R 2
SiCl 2
SiCl 4
+ RMgCl ⎯⎯→ RSiCl 3
+ MgCl 2
The monomer is obtained by fractional distillation of the reaction products whereby
different organo-silicon chlorides are obtained.
In the next step the chlorides are polymerized by hydrolysis involving the following steps–
≡ SiCl + H 2
O ⎯⎯→ ≡ SiOH + HCl
≡ SiOH + HOSi ≡ ⎯⎯→ ≡ Si – O – Si ≡ + H 2
O
Thus, the OH groups of Si are involved in polymerization hence when there is one or
two —OH groups in Si, it leads to long chain polymers but when there are three OH groups,
crosslinked polymers are formed. Reactions:
Cu
(i) 2RCl + Si ⎯⎯→ R 2
SiCl 2
(ii)From Grignard reagent
SiCl 4
+ RMgCl ⎯⎯→ RSiCl 3
+ MgCl 2
HO 2
(iii)Me 2
SiCl 2
⎯⎯→ Me 2
Si(OH) 2
Structure of Silicone Polymers
HO.SiMe –[OSiMe ] OSiMe OH
2 2 –
n
2
Silicone
Di-alkyl-di-chlorosilicane and alkyl trichloro silicone undergo hydrolysis and condensation
polymerization to give a cross-linked silicone polymer.
R
R
R O
⏐
⏐
⏐
Cl⎯Si⎯ Cl + Cl⎯Si
⎯ Cl + Cl⎯Si⎯Cl
P
⏐
⏐
⏐
R
Cl
R
R
Cl
R
⏐
⏐
⏐
Cl⎯Si⎯ Cl + Cl⎯Si
⎯ Cl + Cl⎯Si
⎯Cl
⏐
⏐
⏐
R
R
Cl
QP
HO 2
⎯⎯→