Glass-forming miscible blends

Structural Relaxation and Fragility of Glass-Forming Miscible Blends Composed of Atactic Polystyrene and Poly(2,6-dimethyl-l,4-phenylene oxide)... 

Differential scanning calorimetry (DSC) experiments indicated that atactic polystyrene and polyvinyl methyl ether (PVME) form miscible blends [8,9]. Syndiotactic and isotactic polystyrene when blended with PVME, phase separate at aU temperatures above the glass transition temperature of PVME. Only weak van der Waals interactions between the phenyl rings in polystyrene with the methoxy group of PVME were detected using 2-dimensional nuclear magnetic resonance (NMR) spectroscopy. 

PPO forms miscible blends in all portions with polystyrene. The glass transition temperature, heat-deflection temperature, thermal stability and tensile property generally increase with polyether content leading to a wide range of properties needed in automotive, electronics and electrical industry. The major application fields are summarized in Table 2.3 (6). 

PEI forms miscible blends with polyesters such as polybutylene terephthalate (PBT) and polyethylene terephthalate (PET). These blends have a single glass transition temperature between that of the PEI... 

For immiscible polymers forming a blend, one observes just the two glass transition temperatures of the constituents. In the case of miscible polymers, however, one observes one monotonously changing glass transition temperature between the two r s of the pme components. We illustrate the situation again in the V-T plane, Figure 2. 

The miscibility of a polymer blend is usually ascertained by studying the optical, morphological, and glass transition behavior of the blend. When two amorphous polymers with different refractive indices mix intimately to form a miscible blend, the refractive index of the blend is uniform, and the blend appears transparent. On the other hand, when the two polymers do not mix intimately, the resulting blend is opaque. It must be cautioned that a two-phase immiscible blend may appear transparent if the refractive indices of the two polymers are closely matched or the domain size is smaller than the wavelength of the visible light. For a blend containing a crystallizable polymer, the blend may appear opaque even when the amorphous phases of the two polymers mix intimately. 

Erode and Koleske [134] demonstrated that PCL forms compatible (miscible) blends with phenoxy. They melt-mixed the components and prepared plaques by compression moulding. Samples with more than about 50 wt % PCL (M = 44,000) exhibited PCL crystallinity crystallisation took place over a few days at room temperature during which period samples became hazy and the modulus increased. Quenched samples were used to determine the glass-transition temperature behaviour of amorphous blends. Samples showed a single composition-dependent Tg, indicating miscibility in the amorphous material values of... 

Polycarbonate—polyester blends were introduced in 1980, and have steadily increased sales to a volume of about 70,000 t. This blend, which is used on exterior parts for the automotive industry, accounting for 85% of the volume, combines the toughness and impact strength of polycarbonate with the crystallinity and inherent solvent resistance of PBT, PET, and other polyesters. Although not quite miscible, polycarbonate and PBT form a fine-grained blend, which upon analysis shows the glass-transition temperature of the polycarbonate and the melting point of the polyester. 

The miscibilities of the components in polymer blends is often ascertained by the measurement of the material s glass transition temperature (Tg). The mixing of two polymers with no mutual interactions usually results in the mixture having two separate phases each with their own distinct glass transition temperature. However, when the two components do interact to form a single phase mixture, their glass transitions combine and there will be the emergence of only one transition temperature that is linearly dependent on composition [118]. 

The binary mixture of (two) polymers is considered a compatible blend, when a homogeneous solid system is formed, without phase separations. It means a complete mutual solubility of the two polymers in molten state as well. This compatibility is reflected in — among other physical and mechanical properties, — the fact that the system will have one single glass transition temperature (Tg). This miscibility of the most important thermoplastics in binary systems is seen on Fig. 1 [8],... 

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