Chemistry Reference
In-Depth Information
differences in resonance stabilizations due to differences in conjugation and hyperconjugation. Also,
due to steric strains that arise from bond angle deformation and bond stretching, as well as variations
in secondary bond forces, such as hydrogen bonding and dipole interactions.
3.15.2 Thermodynamics of the Constrains of the Free-Radical
Polymerization Reaction
Free-radical polymerization reactions are equilibrium reactions. The equilibrium between the mono-
mer and the growing polymer is subject to thermodynamic conditions. At equilibrium, therefore, the
change in free energy is zero:
DF ¼
0
The change in free energy for the reaction can, therefore, be written;
0
0
0
DF ¼ DF
þRT
ln
K ¼ DH
TDS
þRT
ln
K ¼
0
0
represent statistical variations in the changes in free
energy, enthalpy, and entropy, representing the transition that the monomer undergoes by being
placed into the polymeric chain.
The equilibrium constant can then be written as:
0
,
0
, and
In the above equation,
DF
DH
DS
PM
n
þ
1
=f½
PM
n
½
K ¼½
M
g
where, PM*
n+1
and PM*
n
are concentrations of species. Assuming that they are practically equal, one
can write:
K ¼
1
=
M
it would then mean that:
0
0
RT
lnM
¼ DH
TDS
0
0
RT
lnM
¼ðDH
=TÞDS
The ceiling temperature can then be written as
0
0
T
c
¼ DH
=f DS
þR
ln[M
equ
g
3.16 Polymer Preparation Techniques
Four general techniques are used for preparation of polymers by free-radical mechanism: polymeri-
zation in
bulk
,in
solution
,in
suspension
and in
emulsion
. The
bulk
or
mass
polymerization is
probably the simplest of the four methods. Only the monomer and the initiator are present in the
reaction mixture. It makes the reaction simple to carry out, though the exotherm of the reaction might
