A polymer that heals itself with unprecedented speed and efficacy when
cut—almost completely recovering its original strength within minutes—has
been developed by RIKEN researchers. It was produced using an advanced
catalytic method for combining multiple precursors into a single polymer in
a controlled fashion.
Increasing the structural complexity of polymers offers great promise for
developing new materials with novel or improved properties. The controlled
synthesis of complex polymers remains challenging, however.
Zhaomin Hou of the RIKEN Center for Sustainable Resource Science and his
colleagues recently developed a controlled catalytic method for combining
non-polar and polar olefin monomers into a single polymer. "We previously
discovered that we could synthesize multiblock copolymers that exhibited
excellent elasticity and self-healing by using the two-component
copolymerization of non-polar ethylene and polar methoxyaryl-substituted
propylenes by a half-sandwich scandium catalyst," says Hou.
The two-component polymers' properties depended strongly on the
methoxyarylpropylene used. "This raised the intriguing question of whether a
three-component 'terpolymer' of ethylene and two different
methoxyaryl-functionalized propylenes would show unique synergistic effects
on the mechanical and self-healing properties," adds Hou.
Now, Hou, four RIKEN colleagues and a collaborator have confirmed that
terpolymers can show unprecedented mechanical and self-healing performance.
Their elastomeric polymer could be stretched to almost 14 times its original
length before breaking. And when cut in two, the polymer healed itself
within five minutes to recover 99% of its toughness and 97% of its tensile
strength (Fig. 1).
The material's exceptional performance can be explained by its unique
molecular structure, Hou notes. The polymer consisted of three nanoscale
component subsections, or 'blocks," with quite different physical
properties, the team showed. Each methoxyarylpropylene formed relatively
long alternating ethylene-methoxyarylpropylene sequences. One
methoxyarylpropylene formed sequences that were soft and flexible, whereas
the other gave sequences that were hard. A third sequence type, consisting
of relatively short ethylene−ethylene blocks, was crystalline in nature.
"The polymer's excellent elastomeric and self-healing properties are due to
the formation of this nanoscale three-dimensional network," says Hou. The
long, soft sections form a highly flexible matrix, within which are hard and
crystalline sections that rapidly re-aggregate after the material is cut,
thereby self-healing any damage.
This polymerization method using a scandium catalyst offers many avenues for
further polymer development. "We anticipate our approach will enable
additional functions to be easily incorporated into this novel class of
self-healing polymer," says Hou. "And we expect our self-healing mechanism
will guide the design and creation of various new self-healing polymers
through microstructural control."
Reference:
Yang Yang et al, Terpolymerization of Ethylene and Two Different
Methoxyaryl‐Substituted Propylenes by Scandium Catalyst Makes Tough and Fast
Self‐Healing Elastomers, Angewandte Chemie International Edition (2021).
DOI: 10.1002/anie.202111161
Tags:
Chemistry