Page 31 - Engineering Plastics Handbook

Chemistry of Polymerization 5

limiting value of the specific viscosity/concentration η /c calculated to
sp
zero concentration [15]. To calculate intrinsic viscosity [9],

h =
[ ] lim h rel −1 = lim h sp
0
c →0 C c → C
where [η] = intrinsic viscosity
lim
c→0 = concentration of solution to zero
η rel = relative viscosity
c = concentration of solution
η = specific viscosity
sp
Since viscosity is a measure of the time of flow using a Ubbeholde vis-
1
cometer, viscosity is measured in its simplest form, in seconds.
η
η =
rel η
0
where η= viscosity of a dilute concentration
η = viscosity of pure solvent
0
and
−
ηη
η = η − = 0
1
η
rel
sp
0
A fourth molecular weight designation is Z average MW [9]. A different
value for MW is obtained for the different molecular weight designations.
The two principal types of polymerization for thermoplastics includ-
ing engineering thermoplastics are polycondensation polymerization
and chain-growth polymerization. Both types can usually produce linear,
branched, crosslinked; amorphous and semicrystalline; aromatic and
aliphatic polymers [14].
Factors affecting the rate of polymerization and yield include:
1. Molecular configurations: linear, branched, crosslinking; ring struc-
ture; amorphous or semicrystalline; aliphatic or aromatic
2. Type of polymerization: polycondensation (step-growth) or chain-growth
(addition); free-radical, ionic; solution including interfacial, emulsion,
suspension, bulk (mass); continuous or batch; graft, solid state
3. Monomers, comonomers, monomer ratio
4. Initiators, catalysts

1
Paul J. Flory, “Viscosity of Linear Polyesters. An Exact Relationship Between Viscosity
and Chain Length.”