Pressure-Induced Crystallization and Topochemical Cross-Linking of
Polytriacetylene
Abstract
Topochemical reactions have been extensively studied in organic and
polymer chemistry, and are conventionally triggered by heat and/or
light. Pressure, as one of the fundamental thermodynamic parameters, has
recently been applied to study phase transitions of inorganic and hybrid
nanomaterials on both microscopic and macroscopic scales. Relatively
fewer studies have been focused on high-pressure behaviors, especially
pressure-induced reactions, on organic and polymer molecules and
assemblies. Polytriacetylenes (PTAs) are unique conjugated polymers with
all-carbon main-chains consisted of alternating double bonds and
diacetylene units. Although diacetylene units are prime examples capable
of light-induced topochemical polymerization into polydiacetylene, PTAs
are found to be very stable under light irradiation. Here we report our
observation that in a diamond anvil cell (DAC), applying low pressure
leads to crystallization and ordering of PTAs bearing linear alkyl
side-chains. Further increasing pressure leads to irreversible
cross-linking reactions, resulting in materials of graphyne-like
structures, appearances, optical properties, and solubilities. Findings
in this paper thus reveal the potential of using pressure to guide
conjugated polymer self-assembly and to induce chemical reactions toward
new materials discoveries.