Photo-chemically induced polycondensation of a pure phenolic resin for additive manufacturing

Bakelite© or phenoplasts are considered the first synthetic polymers in the world. These resins, produced by polycondensation, have always been known for their chemical resistance, excellent flame resistance and thermal stability. Originally, pressure and temperature are required for processing and limited the production of phenoplasts to compression and injection molding. However, with the invention of lithography and 3D printing, new desirable processing possibilities have emerged. Previous work in the area of additive manufacturing of phenoplasts has focused on thin-layer photoresists or parts that can only be printed using other polymers as a matrix. Here we report direct 3D printing of phenoplasts, without binders or matrix polymers, using Hot Lithography, a stereolithography-based 3D printing technology at elevated temperatures. In simultaneous thermal analysis and photo-DSC experiments we investigated suitable conditions for the UV-induced polycondensation of the phenolic resins. Based on these experiments, formulations are presented, which are stable under the selected printing conditions and yet reactive enough for the printing process. Direct 3D printing with Hot Lithography and post-curing gave bubble-free specimens, thus a simple production of complicated structures could be achieved without the conventional complex injection molding and more importantly the first bulk polycondensation process using this technique.