Page 418 - Carrahers_Polymer_Chemistry,_Eighth_Edition

11 Organometallic and

Inorganic–Organic Polymers

11.1 INTRODUCTION

Classical polymer chemistry emphasizes materials derived from about a dozen elements (including
C, H, O, N, S, P, Cl, and F). The following two chapters deal with polymers containing additional
elements. The present chapter focuses on inorganic and metal-containing polymers containing
organic units.
Elements such as silicon, sulfur, and phosphorus catenate similar to the way carbon does, but such
catenation generally does not lead to (homo) chains with high degrees of polymerization. Further,
such products might be expected to offer lower thermal stabilities and possibly lower strengths than
carbon-based polymers since their bond energies are generally lower (Table 11.1). The alternative
of using heteroatomed backbones is attractive since the resultant products can exhibit greater bond
energies (Table 11.1).
One common misconception concerns the type of bonding that can occur between inorganic
and organic atoms. With the exception of the clearly ionic bonding, many of the inorganic–organic
bonding is of the same general nature as that present in organic compounds. The percentage contri-
bution of the organic–inorganic bonding due to covalent contributions is typically well within that
found in organic acids, alcohols, and thio and nitro moieties (e.g., the usual limits are about 5% ionic
character for the B–C bond to 55% ionic for the Sn–O and both are clearly directional bonding in
character). Thus, the same spacial, geometrical rules apply to these polymers as to the more clas-
sical polymers such as PE, PS, nylons, polyesters, and PP. The exception is the ionomers where the
metals are bonded through ionic bonding to the oxygen atoms.
The number of potential inorganic–organic polymers is great. The inorganic portions can exist as
oxides, salts, in different oxidation states, different geometries, and so on. The importance of these
inorganic–organic polymers can be appreciated by considering the following. First, photosynthesis,
the conversion of carbon dioxide and water by sunlight to sugars is based on a metal-containing
polymer—chlorophyll. Also, a number of critical enzymes, such as hemoglobin, contain a metal
site as the key site for activity. Second, the inorganic–organic polymers produced thus far exhibit a
wide range of properties not common to most organic polymers, including electrical conductivity,

specific catalytic operations, wide operating temperatures, greater strengths, and greater thermal
stabilities (Table 11.2). Third, inorganic–organic polymers form the basis for many insulators and
building materials. Fourth, inorganic elements are present in high abundances in the Earth’s crust
(Table 11.3).
The topic of metal- and metalloid-containing polymers can be divided by many means. Here
the topic will be divided according to the type of reaction employed to incorporate the inorganic
atom into the polymer chain. While many other types of reactions have been employed to produce
metal- and metalloid-containing polymers, including redox, coupling, ring-opening polymeriza-
tions, the present will focus on addition, condensation, and coordination reactions. Emphasis is
given to unifying factors.

381

9/14/2010 3:41:28 PM
K10478.indb 381
K10478.indb 381 9/14/2010 3:41:28 PM