Chemistry Reference
In-Depth Information
thermal stability in order to prepare new C
60
-based materials, as well as the nature
of the substituents (alkyl or aryl) which has a strong influence on the thermal
stability of the cycloadducts. In particular, this is a key issue in photovoltaic
cells, where long exposure to sunlight results in drastic temperature increases of
the photo- and electro-active materials [
65
].
3 Macromolecular Chemistry of Fullerenes
Soon after the first protocols for the chemical functionalization of fullerene were set
up, the rush for its incorporation in polymeric backbones started [
66
]. The main aim
was to combine the well established processability, ease of handling, and toughness
of polymers with the rather unique pool of properties of fullerenes in order to
achieve new materials with combined features or even with unprecedented
properties. Obviously, the final scope of the preparation of such hybrids is their
application in cutting edge technologies. Nevertheless, due to the incomplete
disclosure of the chemistry of fullerene, the firsts attempts to achieve fullerene-
polymers led to uncharacterisable or inutile materials often obtained by employing
empirical synthetic methods. Fortunately, these problematics were overcome with
the development of well established methodologies for the modification of
fullerenes, and nowadays the macromolecular-fullerene hybrids can be designed
and tailored at will and fully characterized. Thanks to the synthetic versatility of
polymers, several examples of polyfullerenes have been reported to the date, which
can be classified accordingly to their chemical structure or to their properties as well
as to their applications [
67
-
69
]. Herein we use a “classical” classification in which
each family is structurally homogeneous and few common protocols can be
followed to prepare their corresponding members.
3.1 Classification and Synthetic Strategies
An easy way to order polyfullerenes is accordingly to their increasing chemical
complexity and difficulty in preparing them (Fig.
6
). The synthesis of macromolec-
ular fullerenes may be as simple as the mixing of C
60
and a polymeryzing reactant,
or may require several carefully controlled reaction steps leading to unprecedented
superarchitectures.
Even simpler, in some ways, is the preparation of all-carbon fullerene polymers
[
70
,
71
], which are all those materials constituted exclusively by fullerene units
covalently linked to each other without any additional linking groups or side
groups. The members of this family are prepared by exposing pristine fullerene to
a strong external stimulus such as visible light [
72
], pressure [
73
], and plasma
irradiation [
74
], with no problems in getting the final structure. During the poly-
merization, [2+2] cycloaddition reactions between two double bonds of two neigh-
boring C
60
molecules take place generating new cyclobutane rings [
75
].
