Influence of Block Copolymer Concentration and Resin Crosslink Density on the Properties of UV‐Curable Methacrylate Resin Systems

Abstract

Additive manufacturing is on the verge of replacing established processes in dentistry, as it offers the possibility of manufacturing individual parts simply and cost-effectively. Due to its suitability for a wide variety of materials and, above all, its high precision, the focus is currently on stereolithographic processes. Intrinsic brittleness of the used multifunctional acrylic monomers remains however one of the major challenges. One promising concept is the use of block copolymers (BCPs) guaranteeing minor effects on 3D-printing processing and UV-curing due to initially at least partial solubility, and hence low viscosity impact. A polycaprolactone-polysiloxane (PCL-PDMS-PCL) triblock copolymer is synthesized via ring-opening polymerization of caprolactone and used in radical UV-cured methacrylic resin systems. Small angle X-ray scattering measurements reveal the self-assembly of the BCPs to objects of around 20 nm prior to curing. Subsequently, thermo-mechanical characterization is carried out by dynamic mechanical analysis, flexural testing, and fracture toughness measurements (K IC ). Transmission electron microscopy and scanning electron microscopy micrographs show a homogenous distribution of the BCPs and effective toughening via cavitation and shear yielding. The influence of the crosslink density on the toughness and the high effectiveness of block copolymers for improving fracture toughness is clearly shown.

Evaluation of novel urethane dimethacrylates as crosslinkers for the development of fracture tough dental materials containing a poly(ε‐caprolactone)‐polydimethylsiloxane‐poly(ε‐caprolactone) triblock copolymer

“…For each of these mixtures, 0, 3, and 5 wt% of BCP1 were added. This triblock copolymer (PCL (1600 g mol −1 )–PDMS (3200 g mol −1 )–PCL (1600 g mol −1 )) was recently found to be a highly efficient toughening agent for low crosslink density methacrylate networks 44 . One weight percent TPO was systematically added as the photoinitiator.…”

“…Column chromatography was conducted on silica gel (FlashPure ID Silica, particle size: 35–45 μm) using Pure C‐815 Flash from BÜCHI Labortechnik AG (Switzerland). The compounds 2,2‐bis[4‐(2‐hydroxyethoxy)phenyl]propane (diol 2 ), 45 2,2‐bis‐[4‐(2‐(2‐hydroxyethoxy)ethoxy)phenyl]propane (diol 3 ) 46 and BCP1 44 were synthesized according to the literature.…”

“…(1600 g mol À1 )) was recently found to be a highly efficient toughening agent for low crosslink density methacrylate networks. 44 One weight percent TPO was systematically added as the photoinitiator. The viscosity of each monomer mixture was measured (Table 1).…”

“…Although BCPs were not able to significantly improve the fracture toughness of highly crosslinked dimethacrylatebased materials, 43 it was recently shown that such compounds are highly efficient for the toughening of methacrylate networks exhibiting a moderate crosslink density. 44 Such networks were obtained via the photopolymerization of a monomer mixture containing a urethane dimethacrylate as well as a monofunctional monomer (2-phenoxyethyl methacrylate) in the presence of a poly(ε-caprolactone)polydimethylsiloxane-poly(ε-caprolactone) (PCL-PDMS-PCL) triblock copolymer. Such resins are suitable for 3D printing applications.…”

From Unregulated Networks to Designed Microstructures: Introducing Heterogeneity at Different Length Scales in Photopolymers for Additive Manufacturing

“…A prime example is the comparison of impact testing or fracture mechanics values, the gold standards to measure a material’s toughness. Only a relatively small number of contributions apply sharp notches to their testing samples and assess their toughness by fracture mechanics testing methods. ,− Furthermore, an overwhelming majority of tests are done at room temperature, where a swift decline of the modulus due to a broad glass transition temperature range starting just above room temperature is not accounted for. A short overview of the applied testing conditions is given in Figure a, indicating that in the field of photopolymer development, tensile testing of un-notched specimens at low speeds is favored for toughness quantification.…”