Host polymers

The main advantage of PEO as a host is that it is chemically and electrochemically stable since it contains only strong unstrained C-O, C-C, and C-H bonds. The disadvantage is the inherent crystallinity, and considerable effort has gone into synthesizing all-amorphous polymer hosts. Unfortunately, with the bulk conductivity as the prime motivator, many amorphous polymer hosts incorporate organic functional groups which limit their practical application. Detailed accounts of many of the hosts synthesized have been reviewed [8, 32-36],... 

At present, intercalation compounds are used widely in various electrochemical devices (batteries, fuel cells, electrochromic devices, etc.). At the same time, many fundamental problems in this field do not yet have an explanation (e.g., the influence of ion solvation, the influence of defects in the host structure and/or in the host stoichiometry on the kinetic and thermodynamic properties of intercalation compounds). Optimization of the host stoichiometry of high-voltage intercalation compounds into oxide host materials is of prime importance for their practical application. Intercalation processes into organic polymer host materials are discussed in Chapter 26. 

Polymer gels and ionomers. Another class of polymer electrolytes are those in which the ion transport is conditioned by the presence of a low-molecular-weight solvent in the polymer. The most simple case is the so-called gel polymer electrolyte, in which the intrinsically insulating polymer (agar, poly(vinylchloride), poly(vinylidene fluoride), etc.) is swollen with an aqueous or aprotic liquid electrolyte solution. The polymer host acts here only as a passive support of the liquid electrolyte solution, i.e. ions are transported essentially in a liquid medium. Swelling of the polymer by the solvent is described by the volume fraction of the pure polymer in the gel (Fp). The diffusion coefficient of ions in the gel (Dp) is related to that in the pure solvent (D0) according to the equation ... 

This chapter provides an overview of the basic principles and designs of such sensors. A chemical sensor to detect trace explosives and a broadband fiber optic electric-field sensor are presented as practical examples. The polymers used for the trace explosive sensor are unpoled and have chromophores randomly orientated in the polymer hosts. The electric field sensor uses a poled polymer with chromophores preferentially aligned through electrical poling, and the microring resonator is directly coupled to the core of optical fiber. 

For the AJL8/APC polymer, saturation was not achieved until 250 h of exposure to the DNT vapor. However, the sensing polymer produces a detectable amount of refractive index change within a few minutes of exposure to DNT vapor of 100 ppb concentration. The response rate is thought to be limited by the diffusion of DNT molecules into the polymer. In the initial experiments reported here PMMA and polycarbonate were used as the host polymers. These polymers are relatively less permeable to DNT. The response rate is expected to improve if a more permeable polymer host is used. 

Typical host materials can be summarized as electron transport hosts, hole transport hosts, bipolar hosts, large band-gap hosts for blue or white emission, or polymer hosts. 

SCHEME 3.39 Chemical structures of some polymer hosts. 

Photophysical Parameters of Some Polymer Hosts and Phosphorescent Dopants... 

This investigation shows that it is indeed possible to study the flexibility of polymer chains in polymer matrices by means of excimer-forming probes and that the rotational mobility of these probes reflect the glass transition relaxation phenomena of the polymer host matrix, in agreement with the appropriate WLF equation. 

Miyamoto and Shibayama (1973) proposed a model which is essentially an extension to free volume theory, allowing explicitly for the energy requirements of ion motion relative to counter ions and polymer host. This has been elaborated (Cheradame and Le Nest, 1987) to describe ionic conductivity in cross-linked polyether based networks. The conductivity was expressed in the form... 

Since the kinetics of the doping processes is expected to depend upon the nature of the counterion, particularly its size (which may influence the mobility throughout the polymer host), it is possible to control the diffusion kinetics by selecting the nature of the supporting electrolyte employed in the electrodeposition process. 

More recently, Ingram et al. and Wright et al. independently tried to develop new polymer hosts with secondary structures similar to that of a liquid crystalline state, so that ion transport could occur with a higher degree of freedom in the highly oriented environments and become at least partially decoupled from the polymer segmental relaxations. Ion conductivities approaching liquidlike values have been obtained on the condition that the liquid crystalline state could be maintained. However, the incorporation of these novel polymer materials in electrochemical devices remains to be tested. 

Despite the wide variety of polymer hosts that have been synthesized and tested, the fundamental chemical structures adopted for SPEs remain strictly ether-based and are variations of the original oligo (ethylene oxide) structure, primarily due to the fact that no... 

The only commercial GPE cell that had been described in the open literature was perhaps the Bellcore/Telcordia technology based on a fluorinated polymer, PVdF, from which one could readily sense that the key factor controlling the success of certain polymer hosts in lithium ion cells is no longer material chemistry only, and that more often than not the processing and fabrication of the GPE plays the decisive role. ... 

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