Polymer-Small Molecule Blends

Due to the easy processing, thin films of solution processable polymer-small molecule composites are more appealing for the realization of integrated circuits on large area by printing techniques. As for the coevaporated systems, the composition and microstructure of the film will affect the performances of the devices. For the polymer-small molecule blends, these characteristics can be tuned by the choice of solvents and spin coating parameters [52], until the optimal conditions are reached for balanced bipolar transport. 

Other examples of bipolar behavior have been reported for blends of poly(2-methoxy-5-(2c-ethylhexyloxy)-l,4- phenylenevinylene) (MEH-PPV) and Cfio [56], 

MEH-PPV and PCBM [57], CuPc and poly(benzobisimidazo-benzophenanthro-line) [58], and P3HTand PCBM [59]. 

---

The usefulness of inverse gas chromatography for determining polymer-small molecule interactions is well established (1,2). This method provides a fast and convenient way of obtaining thermodynamic data for concentrated polymer systems. However, this technique can also be used to measure polymer-polymer interaction parameters via a ternary solution approach Q). Measurements of specific retention volumes of two binary (volatile probe-polymer) and one ternary (volatile probe-polymer blend) system are sufficient to calculate xp3 > the Flory-Huggins interaction parameter, which is a measure of the thermodynamic... 

Molecular weight of a polymer and a certain concentration of the plasticizer determine the uniformity blend. If the molecular weight of PVC used in CPE-PVC-DOP blend is doubled, the concentration of DOP needed to obtain a homogeneous mixture is increased from 55 wt% to 70 wt% of DOP. A statistical thermodynamic approach was developed for mixing of polymers, small molecules (plasticizers), and holes which are different in sizes. Plasticizer efficiency is determined by polymer-plasticizer interaction and plasticizer segment size. 

Caneba, G. T, and Shi, L., 2002. Lower critical solution temperature of polymer-small molecule systems a review , in Phase Separation in Polymer Solutions and Blends, P. K. Chan (Ed.), Research Signpost, ISBN 81-7736-097-3, Chapter 4, pp. 63-104. 

All of the examples of PEMs discussed within Section 3.3 unhl now have been composed of only one polymer system without any other compounds present—be they small molecules, polymers, or solid-state materials. A wide variety of different polymer blend and composite PEMs has been made. However, in this section, only a brief overview highlighting some of the more interesting examples that have been reported in the literature will be presented. Eor discussion, these types of PEMs have been divided into three categories polymer blends, ionomer-filled porous substrates and reinforced PEMs, and composite PEMs for high-temperature operation and alternative proton conductors. 

As in the case of LCP/conventional polymer blending, little data exists on the blending of LCPs of different inherent chain architecture or mesophase symmetry. Publications from the laboratories of Ringsdorf [80] and Finkelmann [81] show phase separation in blends of sidechain nematics with other similar polymers or small molecule analogs. It is now established that, in contrast to the behavior of low molecular weight LCs, LCPs are often immiscible. 

Sax, J.E. "Transport of Small Molecules in Polymer Blends Transport-Morphology Relationships" University Microfilms Inter-national Ann Arbor, 1985. 

It is the purpose of this chapter to introduce photoinduced charge transfer phenomena in bulk heterojunction composites, i.e., blends of conjugated polymers and fullerenes. Phenomena found in other organic solar cells such as pristine fullerene cells [11,12], dye sensitised liquid electrolyte [13] or solid state polymer electrolyte cells [14], pure dye cells [15,16] or small molecule cells [17], mostly based on heterojunctions between phthalocyanines and perylenes [18] or other bilayer systems will not be discussed here, but in the corresponding chapters of this book. 

Thermal evaporation is one of the most efficient methods for the preparation of diketo-nate complexe layers. However, many of these compounds are thermally unstable at high temperatnre and reqnire an alternative method. Milder conditions are attained on incorporating snch componnds into polymer host materials, followed by thin film deposition by the spin coating method. In these cases, the luminance of OLED devices is comparable to those measnred for devices fabricated using small molecules and polymer blends. 

---