Spinodal of microphase separation in double comb copolymer melt

1
Spinodal of microphase separation in double comb
copolymer melt
Palyulin V.V., Potemkin I.I.
Division of Physics of Polymers and Crystals,
Department of Physics, Moscow State University
Block copolymer molecules are excellent systems
for studying phenomena related to molecular
self-assembly. Usually, researchers choose to
work with AB diblock architecture because it is
the simplest and best understood one. However,
if more than two different types of blocks are
involved there are a lot of new features
occurred. Monodisperse melts of ABC double comb
copolymer are examined using the weak segregation
theory (WST). The spinodal curves or curves of
order-disorder transition (transition from
homogeneous melt to microphase separated
structure) are obtained.
The architecture of double comb copolymer
Double Comb Copolymer
The number of side chains of each sort is n.
The length of side chain types A and B is fN
and (1-f)N respectively. The number of
segments between the branch points is m.
Interactions due to Flory-Huggins parameters
?AB, ?B?, ?AC
In general, system has 7 independent parameters
?AB, ?B?, ?AC, N, m, f, n. We studied all cases
when only one interaction parameter is left.
There are 5 such cases ?AB?, ?B????0 ?AB0,
?BC?AC? ?AB?BC0, ?AC? ?AB?BC?AC?
?AB?AC?, ?BC0. The fraction of the backbone
monomers fbb m(n-1)/(Nnn(m-1)) is additional
parameter very useful for plotting and physical
interpretations.
Case ?AB ? ? B? ?AC 0
Only the interactions between side chains are
exist. The molecule is number of connected
diblock-copolymers linked by non-selective chain.
Case ?AB ? B? ?AC ?
Spinodal curves for different values of n.
Increasing the number of segments between the
branch points
Spinodal curves for different values of n.
Changing the side chain composition.
If Flory-Huggins parameters are equal to each
other and f 0.5, we have found the two-scale
instability. With increasing of number of
segments between branch points we see the kink on
the spinodal curve and discontinues changing of
wavelength in the spinodal point. The structure
factor can have two minima. As in other cases
spinodal curves have different shapes in the
cases of small and large m.
Plot of a2q2N/6 versus backbone monomers
composition fbb
Spinodal curves for different values of f
depending of the backbone monomers composition fbb
Case ?AB0 ? B? ?AC ?
This is the case of double comb copolymer with
side chains, composed from the same monomers.
With the increasing of n and small m
Flory-Huggins parameter ? is raising, but if m is
large, ? is dropping with increasing n. ?(f) is
symmetric and has maximum in the point of
symmetric composition f 0.5 for all lengths of
backbone.
Spinodal curves for different values of n.
Changing the relative side chain length.
Plot of a2q2(Nm)/6 versus relative side chains
length
Spinodal curves for different values of n.
Changing the relative side chain length. Small m.
Spinodal curves for different values of n.
Changing the relative side chain length. Large m.
Double Comb Polymer synthesis (Lit.)
Synthesis and mechanical properties of double
comb copolymers are described for the case of
side chains, composed from the same monomers 2.
Series of polystyrene-polyisoprene copolymers
were synthesized using tetrafunctional branch
points.
Case ?AB ? ???, ??C 0
Spinodal curves for different values of n.
Changing the relative side chain length. Small m.
Spinodal curves for different values of f
depending of the backbone monomers composition fbb

Conclusions
1. Behavior of the system in most cases
significantly depends on m. 2. There are two
regimes case of small m and case of large m. 3.
The two-scale switching in the case ?AB?BC?AC?
is found. 4. The properties of the system have
weak dependence on the parameter n, if this
parameter exceeds 10.

• References
• Leibler L., Theory of Microphase Separation in
  Block copolymers, Macromolecules, 1980, 13,
  1602-1617
• Zhu Y., Weildisch R., Gido S.P., Velis G.,
  Hadjichristidis N., Morphologies and Mechanical
  Properties of a Series of Block-Double-Graft
  Copolymers and Terpolymers. Macromolecules, 2002,
  35, 5903-5909
• Werner A., Fredrickson G.H., Architectural
  Effects on the Stability Limits of ABC Block
  Copolymers,
• J. Polym. Sci. Part B Polym. Phys., 1997,
  35, 849-864

Case ?AB? B?0 ?AC ?
Spinodal curves are analogous ones in the case
?AB0 ? B? ?AC ? and large m.