Page 38 - Plastics News August 2020

A new polymer keeps its strength with added degradability

Thermosets are durable plastics that can hold their cross-links couldn't produce a degradable plastic, no
shape indefinitely—but that makes them notoriously matter how many cleavage sites they incorporated. This
difficult to recycle. A new, degradable thermoplastic suggests that having cleavable bonds is not enough—it
made by researchers at the Massachusetts Institute of also matters where researchers place them. By breaking
Technology breaks this mold, offering good performance the polymer network into soluble chunks of a controlled
and degrading on command.
Led by organic chemist
Jeremiah Johnson, the team
s t a r t e d w i t h
p o l y d i c y c l o p e n t a d i e n e
(pDCPD), a tough, lightweight
t h e r m o s e t u s e d f o r
automobile and aviation
components. They introduced
cleavable bonds in the
polymer strands using a
monomer that contains a silyl
ether group. This resulted in
materials that fully degrade when exposed to fluorine size, the researchers were able to directly interrogate
(Nature 2020, DOI: 10.1038/s41586-020-2495-2). The the molecular interactions that hold these polymer
new polymer is “virtually the same in all of its major networks together at higher resolution than ever before,
properties” as pure pDCPD, Johnson says, and the Johnson explains. Johnson hopes this strategy of
degraded fragments can be reincorporated into new carefully placing cleavable bonds will help make
polymerization reactions to make a partially recycled degradable versions of other thermoset materials, such
plastic. After their initial success, Johnson's team tried a as epoxies and vulcanized rubber. Moore agrees that the
second approach. pDCPD owes its strength not only to its proof of concept in pDCPD will likely spark interest in
long polymer strands, but also the dense junctions that other thermoset systems. This new thermoset shows
cross-link them together. So the researchers wondered if how a plastic's deconstruction can be conceived
placing cleavable bonds in these junctions would have alongside its synthesis.
the same effect. But installing silyl ether bonds in the

Sulfur-containing polymer generates high refractive index and transparency
Researchers reported a novel technology enhancing the
high transparency of refractive polymer film via a one-
step vapor deposition process. The sulfur-containing
polymer (SCP) film produced by Professor Sung Gap Im's
research team at KAIST's Department of Chemical and
Biomolecular Engineering has exhibited excellent
environmental stability and chemical resistance, which
is highly desirable for its application in long-term optical
device applications. The high refractive index exceeding
1.9 while being fully transparent in the entire visible produce a high refractive index polymer by polymerizing
range will help expand the applications of the vaporized sulfur with a variety of substances. This
optoelectronic devices. The research team successfully method suppresses the formation of overly long S-S
manufactured a whole new polymer thin film material chains while achieving outstanding thermal stability in
high sulfur concentrations and generating transparent
with a refractive index exceeding 1.9 and excellent
transparency, using just a one-step chemical reaction. non-crystalline polymers across the entire visible
The SCP film showed outstanding optical transparency spectrum. Due to the characteristics of the vapor phase
process, the high refractive index thin film can be coated
across the entire visible light region, presumably due to
the uniformly dispersed, short-segment polysulfide not just on silicon wafers or glass substrates, but on a
wide range of textured surfaces as well. We believe this
chains, which is a distinct feature unachievable in
polymerizations with molten sulfur. The team focused on thin film polymer is the first to have achieved an
the fact that elemental sulfur is easily sublimated to ultrahigh refractive index exceeding 1.9.

August 2020 36 Plastics News