[Back]

M. Kury, G. Peer, K. Seidler, C. Gorsche, P. Gauss, T. Koch, P. Dorfinger, J. Stampfl, R. Liska:
"Toughening photoploymers by means of addition-fragmentation chain transfer reagents for 3D printing";
Poster: European Polymer Congress 2019 (EPF 2019), Crete, Greece; 06-09-2019 - 06-14-2019; in: "European Polymer Congress 2019 (EPF 2019)", (2019), 762.

Today, photopolymers find broad application in everyday life. Especially, (meth)acrylates are photopolymerized in coating, semi-conductor, dental, and additive manufacturing industries. Their major advantages are fast curing, their solvent-free curing conditions, the formation of materials with beneficial mechanical properties e.g. high hardness, rigidity, and heat deflection temperature, as well as the possibility of 3D structuring.
However, the uncontrolled curing mechanism of photo-induced free radical polymerization yields materials with inhomogeneous network architectures resulting in brittle behavior when mechanically stressed.
A well-known strategy for regulating networks in photopolymerization is thiol-ene-chemistry1,2. In this case, thiols act as chain-transfer reagents (CTAs) that shorten the kinetic chain length leading to more homogeneous networks, and thus tougher materials. Another benefit is the reduction of shrinkage-induced stress in the final material. On the other hand, the utilization of thiols comes along with drawbacks like strong odor, short shelf life, and the formation of flexible thio-ether bridges that soften the material and lower its modulus.
Recently, addition-fragmentation chain transfer (AFCT) reagents were reported to represent an alternative method to regulate (meth)acrylates in photopolymerization. In particular, vinyl sulfonate esters [3,4] and β-allyl sulfones [4-7] demonstrated their high potential as AFCT reagents. Mechanistic studies with monofunctional (meth)acrylates (including photoreactor, GPC, and Maldi-TOF) revealed their efficient regulating abilities.
Applied to difunctional monomers, higher double bond conversions at gelation point and a reduction of shrinkage stress was observed by means of RT-NIR photorheology. The formation of more uniform network architectures was confirmed by DMTA. Moreover, impact resistance tests showed an increase in material toughness. Finally, the best performing AFCT reagents were used to successfully modify stereolithography printed model structures.

photopolymers, (meth)acrylates, 3D structuring, high hardness, rigidity, and heat deflection temperature