Phase Separated Blends

In the case of two diblocks with frs 0.8 forming spherical morphologies and a large molecular weight ratio d = 7.4 (case (ii)), the copolymers were found to be partly miscible (Koizumi et al. 1994c). The blend phase separated into large... 

PMMA is typical of many polymer pairs, for which the parameter is positive and of order 0.01, making only low molar mass polymers form miscible blends. PVME/PS, PS/PPO, and PS/TMPC have a strongly negative x parameter over a wide range of temperatures (of order — 0.01) but since >0 and Bblends phase separate on heating. PEO/ PMMA, PP/hhPP and PlB/hhPP, all represent blends with very weak interactions between components (x = 0). 

To achieve desirable macroscopic properties, one would like to control the degree of miscibility of a blend. Heat treatment/annealing is a simple technique to modify a phase structure of a blend. Morphological changes induced by heat treatment can also affect NMR observable (see Section 10.3.2.1). Furthermore, as shown in Section 10.2.1, several blends exhibit a lower critical solution temperature (LCST) phase diagram. Such a blend phase-separates at temperatures above its LCST temperature. The compositional fluctuation during the phase-separation process is examined in Section... 

While miscible blends have attracted considerable interest due to the thermodynamic implications and commercial relevance, phase separated blends have had a prominent role in polymer blend technology. While mechanical compatibility is assured in miscible blends, phase separated blends can often achieve property advantages not capable with single phase blends. (Mechanical... 

A variety of phase behaviors have been observed in binary homopolymer blends. Some blends phase separate on heating while others phase separate on cooling. This depends on whether x increases or decreases with temperature. Blends in which x changes nonmonotonically with temperature exhibit more complex phase diagrams. The... 

That figure shows that a melt processing window exists for blends that contain in excess of 75 % PBI. In this case, a processing window is defined as those temperatures between Tg and the blend phase separation temperature. For a 85/15 PBl/Ultem blend ratio, the glass transitiOTi temperature is about 400 °C and the processing window is 25 °C. 

Depending on MW, molten LDPE/HDPE blends phase separate, but on rapid cooling, they may crystallize into single-type crystals with single Tm- The structure is not at the thermodynamic equilibrium since slow cooling leads to separated peaks for LDPE and HDPE (sometimes with an intermediate residual peak). The phase separation in LDPE/HDPE blends mainly depends on the MW of the HDPE... 

Most polymer blends phase-separate with LCST thus the miscibility region stretches from the melting point or Tg up to the binodal while the phase-separated region exists above the spinodal temperature, Ts [1, 212]. Within the region between binodal and spinodal the system is metastable, characterized by strong interrelation between the rheology and thermodynamics [211, 213-215]. 

In the following sections a polymer-polymer-solvent blend phase separation is investigated, with the respect to self-assembly on a heterogeneously functionalized substrate. The evolutionary mechanisms were studied by measuring the characteristic length, and the influence of different compositions was examined. The effects of a heterogeneously functionalized substrate were studied, and a discrete cosine transform spectral method was employed to solve the nonlinear partial differential equation. A semi-implidt method was used in the time evolution this method was found to be efficient and unconditionally stable over large time steps [40] (see Section 15.1.4). 

PP COC COC = amorphous ethylene/norbornene copolymer Tg = 75 °C blend phase separated and fibrillation was observed 374... 

PVC PPC PPC = poly(propylene carbonate) PVC/PPC blends phase separated NBR-g-PPC provided compatibUization and improved mechanical properties 868... 

Until the mid-1970s, polymer chemists used to think that attempts at mixing two polymers would necessarily wind up in immiscible blends so that very few examples of homogeneous blends were known. The polystyrene/poly(2,6-dimethyl-1,4-oxyphenylene) blend (sold under the trademark Noryl ) was an exception. This field witnessed a real development only after it was realized that most homogeneous blends phase separate upon raising the temperature (LCST) (in general the researchers tend to increase the temperature in order to improve the miscibility of polymers). 

The miscibility limit between thermotropic liquid crystal polymers and flexible chain polymers can be predicted by calculations corresponding to the spinodal curve at constant temperature. This miscibility is increased with the increase of the degree of disorder (y/jc,) of the liquid crystal polymer and with the decrease of the degree of polymerization. Two quantitative parameters from the Hory s lattice theory can be used to estimate the phase behavior of this kind of blend at melt processing temperature the polymer-polymer interaction parameter and the degree of disorder (y/Xj). In binary polymer blends phase separation may occur for any value of degree of disorder (y/Xj)... 

For a symmetric polymer blend phase separation occurs already for x > Xait — 2/iV 1... 

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