Polymers, organometallic

Organometallic species seem attractive candidates to enhance the etch resistance of a resist. Particularly, such materials can be used for maskmaking apphca-tions, where contamination by metallic impurities is not a problem. 

Previously, incorporation of organometallic functionalities into resist materials showed a great enhancement of the etch resistance of the resist. The incorporation can be accomplished either by direct covalent attachment or by blending the organometallic additives into the resist matrix. Blending may be limited by miscibility problems or inadequate solubility. 

To manufacture deep structures in a device, plasma etching requires the presence of a thick perpendicularly structured resist layer, unless the etch resistance of the resist is far greater then that of the substrate. Thick resist layers suffer from a variety of problems, especially when they are employed for high-resolution lithography. More specifically, high-aspect-ratio structures, specifically, tall and narrow features, suffer from collapse during the development steps due to capillary forces. 

To circumvent some of these problems, bilayer resist schemes have proved to be useful. hi such resist schemes, an etch resistant layer is combined with an image-able layer, thus obtaining the best of both worlds. Such bilayer resists are developed by a plasma. Therefore, the top layer of these resists requires a high resistance against removal by the developing plasma. It is for such applications that organometallic polymers may prove to be of interest. 

The difficulty of assembling metal-containing polymers has been and continues to be a synthetic challenge. The process of attempting to prepare these polymers has led to a number of novel preparative routes. 

The expectation that some members of this polymer family may have unusual electrical, magnetic or optical properties has also been a major motivation for stud dng these polymer systems [3-6]. 

Although many t) es of polymers are now known, in keeping with the objectives of this book, we will examine families of organometallic polymers that are now reasonably well developed and which already show 

this class is considered as a subclass of aU-Ceo polymers that should be considered as heteroatom-containing polymers, since their stractures contain metals or elements other than carbon. In 1994, Forro discovered that the fulleride 

On the other hand, much work has been devoted by Balch to the study of the electrochemical formation and properties of redox-active films formed from fuller-enes, or a fijUerene derivative, and selected hansition-metal complexes of Pd(ll), Pt(ll), Rh(ll) and lr(l) [29]. These organometallic films may find potential application as charge storage materials for batteries, photovoltaic devices and elecho-chemical sensors. 

Organometallic compounds containing polymerizable carbon-carbon double bonds have been synthesized and their polymerization studied [Archer, 2001 Pittman et al., 1987]. Among the organometallic monomers studied are vinylferrrocene and trialkyltin methacrylate. Much of the interest in these polymerizations has been to obtain polymers with 

A functional polymer is a polymer that contains a functional group, such as a carboxyl or hydroxyl group. Functional polymers are of interest because the functional group has a desired property or can be used to attach some moiety with the desired property [Patil et al., 1998], For example, a medication such as chloroamphenicol, a broad-spectrum antibiotic, 

Pendant-functionalized polymers are obtained by polymerization of a monomer containing the desired functional group. Conventional and living radical polymerization are both useful. ATRP, NMP, and RAFT have been studied, but RAFT much less than NMP, and NMP less than ATRP at this time [Coessens et al., 2001 Harth et al., 2001 Patil et al., 1998]. 

A telechelic polymer with one COOH and one Br end group is obtained in ATRP by using p-(l -bromoethyI)benzoic acid as the initiator. Similarly, NMP and RAFT can be used to 

Some functional groups can be introduced into polymers by conversion of one functional group to another. For example, pendant or end-group halogens can be displaced by nucleophilic substitution to yield hydroxyl or amino functional groups. 

The introduction of what are essentially diffused orbitals from the metal can allow the orbital overlap such as between two molecules in adjacent layers of crystal. Alternatively, d orbitals may enhance the intramolecular conduction paths by their conjugation with the orbitals of the polymer. Even if the polymer chain is not conjugated, enhanced conductivity may still be achieved, because with transition metals, a mixed valence system may be formed, allowing transport of electrons by redox behaviour between metal atoms in different oxidation states. An example of this type of behaviour occurs in the poly(ferrocenylene) polymers. The standard, unoxidized poly(ferrocenylene) is effectively an insulator, but oxidation of ferrocenium (Fe(II)) to ferricenium (Fe(III)) with I as counteranion results in a large increase in conductivity. If around 5% ferricenium is present, a 10-fold increase in conductivity occurs, while a maximum increase of 10-100 times has been reported with 35-65% ferrocenium [63]. The structure of the poly(ferrocenylene) polymer and two of its analogues are shown in Fig. 1.11. 

In the case of poly(3-vinylbisfulvalene di-iron), when 71% of its iron is in the ferricenium iron form, conductivities of 9 x 10 S m have been achieved. 

More recently, a highly conductive class of organometallic polymers known as the poly(metal-tetrathio oxalates) has been synthesized. These 

These complexes are generally produced as amorphous powders that are insoluble and air-stable. When pressed into pellets, they have conductivities in the range (1-50) x 10 S m depending upon the metal. 

Another example of conducting organometallic polymers comprises the tetrathiofulvalene-metal bis-dithiolene class of compounds [64]. These insoluble powders have the general structure indicated in Fig. 1.13, with conductivities as high as 3 x lO S m when the metal atom is nickel. 

This means the coordination of the copper d-orbital with the loss of the orbitals of at least two acetylenic groups. Photoelectron X-ray spectroscopy confirms this structure [268]. The same results were confirmed by the external photoemission method [269]. The photoelectrical work functions for copper acetylenides with different substituents are in the range 5-5.4 eV. This means that the upper filled state is conditioned by the CuGsC structure motif. 

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Harrod JF (1988) In Inorganic and organometallic polymers, Zeldin M, Wynn KJ, Alcock HR (eds) ACS Symposium Series 360, Washington DC... 

In summary, for metal surfaces in boundary lubrication, complex tribochemical reactions occur along with the physical/chemical adsorptions, which lead to the formation of surface hlms, consisting of reaction products, oxide layer, the mixture of particles and organometallic polymer, and perhaps a viscous layer. The surface hlms operate as a sacri-... 

There are, however, other classes of inorganic and organometallic polymers that deserve consideration due to their considerable scientific and applicative relevance, such as polysilanes [28-31], polycarbosilanes [32,33],polysilazanes [33],polyborazines [34,35],polythiazenes [36], and, as an example,polymetal-locenylsilanes [37]. 

Carraher CE,Sheats JE, Pittman CU (eds) (1978) Organometallic polymers. Academic, New York... 

Archer RD (2001) Inorganic and organometallic polymers. Wiley-VCH, New York... 

NeUson RH, Hani R, Scheide GM.Wettermark UG,Wisian-NeUson P.Ford RR.RoyAK (1988) In Zeldin M, Wynne KJ, AUcock HR (eds) Inorganic and organometallic polymers. ACS Symposium Series, Washington, chap 22,360 283... 

Gleria M, Bortolus P, Flamigni L, Minto F (1992) In Laine RM (ed) Inorganic and organometallic polymers with special properties. Nato ASI Series E Applied Sciences 206 375... 

Singler, R. E., Sennett, M. S., and Willingham, R. A., Phos-phazene polymers Synthesis, structure, and properties, in Inorganic and Organometallic Polymers (M. Zeldin, K. J. Wynne,... 

Metal-acetylide complexes have been used as a unit of organometallic polymers that have metallic species in the main chain [20]. Representative examples are metal-poly(yne) polymers (19) of group 10 metals depicted in Scheme 5. These polymers are easily prepared from M(PR3)2Cl2 (M=Pt, Pd) and dialkynyl compounds catalyzed by Cu(I) salts in amine. Recently, this synthetic method was successfully applied to the construction of metal-acetylide dendrimers. 

Finally, one additional comment concerning the nature of progress from interdisciplinary research is evident from the results reported in this Symposium Volume. Once again it is seen that most rapid progress is made when synthetic chemists collaborate with their colleagues in materials science or physics to determine properties of new inorganic and organometallic polymers. 

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