Page 68 - Plastics News July 2018

teChnoLogy

Tailored polymers from a printer

new approach for the tailored production of then attack the monomer, such as the C=C double bond
A methacrylate-based photopolymers without inhibiting in a vinyl group, which forms a new radical that becomes
the curing process has been developed by a team led starting point of a growing polymer network by attacking
by Robert Liska at the Technical University of Vienna more monomers and binding to them.Newer methods
(Austria). Their success relies on the addition of an to better control radical photopolymerization and the
ester-activated vinyl sulfonate ester (EVS), which acts material properties of the products tend to slow the
as a chain transfer agent. It is activated because it curing process, which is not ideal for 3D printing. A short
easily splits off one portion of itself.An ever-growing irradiation phase is critical for high spatial resolution
and economical production times.A new approach
for the tailored production of methacrylate-based
photopolymers without inhibiting the curing process
has been developed by a team led by Robert Liska
at the Technical University of Vienna (Austria). Their
success relies on the addition of an ester-activated
vinyl sulfonate ester (EVS), which acts as a chain
transfer agent. It is activated because it easily splits
off one portion of itself.
If the growing polymer network attacks EVS instead
of the next monomer, an intermediate forms and
quickly splits apart to form a terminated polymer
chain in the network and a highly reactive radical
(tosyl radical), which starts a new chain reaction.
The more EVS is added, the shorter the average
chain length in the polymer network. Because shorter
polymer chains remain mobile longer, the danger
of shrinkage cracks during curing is significantly
reduced. In contrast to conventional chain transfer
agents, the polymerization is not inhibited, because there
number of coatings, including varnishes and printing are no stable intermediates or reversible reaction steps
inks, as well as tooth fillings, are cured with light. Yet, involved. The splitting off of the tosyl radical is favored.
homogenous, tailored, polymer networks cannot be The researchers prepared a scaffold-like sample structure
produced, and the materials tend to be brittle, which using a methacrylate copolymer. Individual layers with
limits the use of photopolymers in applications like 3D a thickness of 50 ?m were spatially well resolved. The
printing, biomedicine, and microelectronics. In the journal material is very homogenous, solid but elastic and impact
Angewandte Chemie, researchers present a method by resistant with high tensile strength. These properties
which methacrylate-based, homogenously crosslinked, can be adjusted by changing the amount of EVS added.
tailored, tough polymers can be made -- even at high Without EVS, the material was very brittle. This new
resolution for 3D printing.
approach prepares the way for tough, photopolymers
Light-curing is usually a radical chain polymerization. for applications in biomedicine, such as shape-memory
An initiator is split into radicals by light energy. These polymers for tissue growth and as fillings for teeth.

Plastics News July 2018 68