Aspen Physical Property System - Physical Property Models

For a block copolymer, there is only one �� pair and the number of �� and
�� pairs depend on the length of each block; therefore:
For a random copolymer, the sequence is only known in a statistical sense. If
the sequence is completely random, then the number of �� adjacent pairs is
proportional to the product of the probabilities of finding a segment of type �
and a segment of type � in the copolymer. The probability of finding a
segment of type � is the fraction of segments z� in the copolymer:
The bonding fraction of each pair of types can be written as follows:
where C is a constant and can be determined by the normalization condition
set by Equation 2.70; the value for C is unity. Therefore:
A special case is the Sadowski’s model for random copolymer with two types
of segments only ( Gross et al., 2003; Becker et al., 2004). In this model, the
bonding fractions are calculated as follows:
When z� < z�
When z� < z�
The generalization of three common types of copolymers from two types of
different segments to multi types of different segments � within a copolymer
is straightforward.
For a generalized alternative copolymer, m� = m� = ... = mr = m/� ; there
are no adjacent sequences for the same type of segments. Therefore,
2 Thermodynamic Property Models 39