Pd. Hong et Cm. Chou, Effects of phase separation on structural characteristics of poly(vinyl chloride) physical gels, MACROMOLEC, 33(26), 2000, pp. 9673-9681
The effects of phase separation on structural characteristics of poly(vinyl
chloride)/chlorobenzene (PVC/ClBz) physical gels were studied through the
time-resolved light scattering, pulsed NMR, and the gelation kinetic analys
es. The present study clarifies the characteristics of PVC solutions at var
ious concentration regions and their influence on the gel structure formed
from the spinodal decomposition of the solutions. According to the physical
meaning of the [eta ]C value capable of expressing the characteristics of
PVC solutions, one can divide the chain aggregation behaviors into four reg
ions with increasing PVC concentration. (1) At the concentration less than
the macroscopic percolation transition limit, the polymer-rich phase transf
orms into isolated droplets, and the gelation cannot occur. (2) When the co
ncentration is close to the critical gelation concentration C-gel* (ca. [et
a ]C similar to 1.5), the gelation behavior depends on the competition betw
een transitions of the sol-gel type and the dynamic percolation-to-cluster
type; moreover, the structure and properties of gels are mainly dominated b
y the evolution of the later-stage phase separation. (3) At the concentrati
on exists between the C-gel* and the chain overlapped concentration C* (ca.
[eta ]C similar to 4), the initial stage phase separation controls mainly
the structural formation of PVC gels. (4) As the concentration is further i
ncreased more than [eta ]C similar to 4, i.e., the overlapping between chai
ns coils is present in this region, the influence of phase separation on PV
C/ClBz gelation would be weakened. It should be noted that the C* value is
higher than the C-gel* value in this work, implying that the chain overlapp
ing is not a prerequisite for the gelation of PVC solutions to undergo liqu
id-liquid phase separation. Thus, the aggregation behavior of PVC solutions
in region 3 was focused in order to emphasize the effect of initial phase
separation on gelation. As a result, the gelation mechanism and the structu
ral characteristics of PVC gels can be interpreted well by our proposed mod
el.