Basic HTML Version
227
[ ] .
[ ] .
.
.
η
η
=
=
01004
01493
0 5734
0 5734
M
M
w
n
(Note: exponent a differs from example 1
⇒
different polymer system)
In order to use these equations we must assume the unknown sample has the
same type of molecular weight distribution as the standards, in this case (and
generally in many other cases) the distribution of a randomly degraded
polymer. Applying the equations we obtain:
M
w
= 73.597 g/mol
M
n
= 36.841 g/mol
This assumption is often used in practical biopolymer chemistry. Both the
standards used to establish the MHS equation and the unknown samples are
obtained by random degradation, for example acid hydrolysis.
6.1.8. Using
the
intrinsic viscosity
to determine
the
shape of
biopolymers
in
solution
The simplest and possibly most common method is simply to determine the
MHS parameters, especially the exponent (a), to determine the basic shape of
the polymer (sphere-like, rod-like or randomly coiled) as explained in Section
6.1.6.
One may also determine stiffness parameters such as the characteristic ratio
(C
∞
) and the persistence length (q) on the basis of intrinsic viscosity
measurements. The method is quite analogous to that explained for the radius
of gyration (Section 2.3.3.), and is based an the same type of data as those
used to establish the MHS parameters, i.e. intrinsic viscosities and molecular
weights for a polymer system, covering a range of polymer sizes:
Sample/fraction
Molecular weight
Intrinsic viscosity
1
M
1
[
η
]
1
2
M
2
[
η
]
2
.
.
.
i
M
i
[
η
]
i