Polysiloxanes solid-state

Bridged polysilsesquioxanes having covalently bound acidic groups, introduced via modification of the disulfide linkages within the network, were studied as solid-state electrolytes for proton-exchange fuel cell applications.473 Also, short-chain polysiloxanes with oligoethylene glycol side chains, doped with lithium salts, were studied as polymer electrolytes for lithium batteries. 

Other crystalline inorganic polymers such as poly(dichlorophosphazene), poly(aryloxyphosphazenes), liquid crystalline polysiloxanes and poly(dichloro-silane) have also been studied by X-ray diffraction methods, enabling the conformations in the crystallites in the solid state to be established. 

Applications. Polymers with small alkyl substituents are ideal candidates for elastomer formulation because of quite low temperature flexibility, hydrolytic and chemical stability, and high temperature stability. In light of the biocompatibilily of polysiloxanes and P-O- and P-N-suhslituted ptilyphosphazenes. polytalkyl/arylphosphazenes) are also likely lo he hiocompatible polymers. A third potential application is in the area of solid-state batteries. 

Applications. Polymers with small alkyl substituents, particularly (13), are ideal candidates for elastomer formulation because of quite low temperature flexibility, hydrolytic and chemical stability, and high temperature stability. The ability to readily incorporate other substituents (in addition to methyl), particularly vinyl groups, should provide for conventional cure sites. In light of the biocompatibility of polysiloxanes and P—O- and P—N-substituted polyphosphazenes, poly(alkyl/arylphosphazenes) are also likely to be biocompatible polymers. Therefore, biomedical applications can also be envisaged for (3). A third potential application is in the area of solid-state batteries. The first steps toward ionic conductivity have been observed with polymers (13) and (15) using lithium and silver salts (78). 

In recent years the literature has furnished a wealth of information concerning chemical structures from solid-state 29Si NMR studies of crystalline and noncrystalline silicates and aluminosilicate, polysiloxanes, polysilanes and other organosilicon compounds. 

Figure 10 presents the kinetic trans-cis photoisomerization process, under UV irradiation in the solid state, hi this case, significant differences appear between samples behaviour, as a function of the nucleobase chemical structures. It is interesting to note that, in the case of azo-polysiloxane substituted with adeiune (sample 2 -Table 1), the behaviours in the solid state and in solution are similar. That means that the polysiloxane chain flexibility, combined with the amorphous polymer ordering assure enough free volume for the trans-cis isomerization process. 

A very interesting behaviour is obtained for the azo-polysiloxane modified with adenine (Sample 2 - Table 1). In spite of the fact that the trans-cis isomerization process, as a result of the UV irradiation, is very fast in the solid state (similar to the behaviour in solution), the relaxation takes place in two steps, the recuperation rate in the first step being only 15 %. This behaviour can be explained by some associations that can take place between the cA-azobenzenic groups and adenine. The same curve profile, but less evident, is obtained for the azo-polysiloxane modified with cytosine... 

Concerning the photochromic behaviour, the situation is different if we compare this polymer group with the azo-polysiloxanes modified with nucleobases, especially concerning the relaxation process. For the photochromic behaviour in solution and in the solid state, there are some differences concerning the maximum conversion degree of the azo-groups in the cA-form (about 15-20%). Figs. 14 and 15 present the photochromic response under UV irradiation of the Samples 6-8 in solution and in the solid state, respectively. 

One can observe that the response rate in solntion to the UV irradiation is faster for the systems containing naphthalene and anthracene nnits, comparatively with the p-nidophenol containing azo-polysiloxane. In the solid state, the differences concerning the response rate diminish, bnt the maximnm CM-gronp conversion degree is sitnated only at abont 52%. 

The polysiloxane-silica hybrids were characterized by elemental analysis, C NMR of the particle suspension, C and Si solid-state NMR spectra, FT IR spectroscopy and thermogravimetry. The examples of Si NMR solid-state and suspension C NMR spectra are shown in Fig. 1. 

The mesogenic structure of a benzoic acid dimer has been introduced as a noncovalent cross-linker for polysiloxanes [79]. Polymer 57 exhibits a smectic C phase due to the dynamics of H-bonding. In contrast, mesomorphic order is locked in the solid state of poly[(4-acryloyl)benzoic acid] by polymerization in its mesophase [128]. No liquid-crystalline state is observed for this material because of the lack of flexibility of the structures. Main-chain-type polymeric liquid-crystal associates are formed from carboxyl-bifunctionalized aromatic compounds [129]. 

G. E. Maciel, NMR Characterization of Functiona-hzed Polysiloxanes, in Solid State NMR of Polymers, I. Ando (ed.), Elsevier, Tokyo, Ch. 25 (1998). 

J. C. Pivin and M. Sendova-Vassileva, Visible photoluminescence of ion irradiated polysiloxane films. Solid State Commun. 1998, 106, 133-136. 

Solid state FT-IR characterization of sohd substantiated the presence of the aforementioned species. SEM analysis of this sohd manifested spherical morphology of polysiloxane-conjugated Pd nanoclusters in the 40-50 nm size regime. Based on the above results, it can be concluded that the solid is a partially condensed polysiloxane network conjugated with Pd nanoclusters. Furthermore, the possibility of reusability of precipitated solid as catalyst was explored by injecting the substrate into the Schlenk tube with precipitated sohd. After 30 min of stirring, the mixture became homogeneous. Multinuclear spectroscopy characterizations of the reaction mixture confirmed formation of polysilyl ester. 

Brus, J., Solid-State NMR Study of Phase Separation and Order of Water Molecules and Silanol Groups in Polysiloxane Networks. J. Sol-Gel Sci. Technol. 2002,25,17-28. 

Lindner, E Kemmler, M Mayer, H.A., and Wegner, P. (1994) Supported organo-metallic complexes. 5. Polysiloxane-bound ether-phosphines and ruthenium complexes. A characterization by solid-state NMR spectroscopy and catalysis. J. Am. Chem. Soc., 116, 348-361. 

---