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H. Svajdlenková, O. Sausa, G. Peer, C. Gorsche, R. Liska:
"Insight into microstructure of photopolymers by means of positron annihilation lifetime spectroscopy (PALS)";
Vortrag: European Polymer Congress 2019 (EPF 2019), Crete, Greece; 09.06.2019 - 14.06.2019; in: "European Polymer Congress 2019 (EPF 2019)", (2019), S. 405.

Photopolymerization has found widespread usage not only in classical coatings, but also in more advanced fields like biomedicine or 3D printing due to their appealing tuneable material properties. The polymerization of commonly used di(meth)acrylates gives inhomogeneous crosslinking with high shrinkage stress leading to the brittle character of such polymers. Here a promising approach is the change of the polymerization process by the use of chain transfer agents such as thiols [1] or addition fragmentation-based chain transfer reagents,[2,3] which form more homogeneous network architectures with reduced shrinkage stress and an significantly increased toughness.
Deeper view into the microstructure of cured materials but also the crosslinking process itself can contribute to the better understanding and tuning of the material properties.
The pilot free volume investigation of cured pure and regulated dimethacrylate-based resins revealed the microstructural arrangement at room temperature in terms of the free volume size and microstructural homogeneity. [3] A PALS study of both cured materials below and above glass transition and combined macro and micro expansion behaviour showed the others important key microstructural factors, i.e., free volume void size, the specific occupied volume V0, free volume number density per unit mass N′, and free volume fraction f, specifically for photopolymers with tailored network architectures.[4]
For the first time, the in situ investigation of microstructure during photopolymerization by the combination of PALS and NIR-photorheology were carried out.[5] Photopolymerization associated with the evolution of microstructural free-volume shrinkage was very well described by the Kohlrausch-Williams-Watts (KWW) function and evaluated via free volume distributions reflecting the homogeneity during network formation. PALS is a promising tool for better understanding of crosslinking process from the view of free volume aspects and dynamics.

Photopolymerization, classical coatings, biomedicine or 3D printing, tuneable material properties