Thermoplastic-like mechanical performance of heterogeneous photopolymers for additive manufacturing with tailored hyperbranched rubbers

Abstract

Conventional photopolymers used in light-based additive manufacturing are typically brittle materials with thermoset characteristics. Here we introduce a one-step synthesis of hyperbranched polyethylene rubbers functionalized with pendant methacrylic groups and their application as tougheners of a model brittle photopolymer based on non-volatile styrene and maleimide derivatives. The rubber tougheners can be tailored to tune their compatibility with the matrix, influencing the morphology and the thermomechanical properties of the final printed resins. The resulting polymer structures were analysed by atomic force microscopy, revealing various degrees of phase separation related to the rubber molar mass and methacrylate functionalization. Further, the analysis of the prepared toughened materials revealed the ability of functionalized hyperbranched polyethylene rubbers to improve the mechanical properties significantly (doubled stress at break and improvement of strain at break by a factor of 10³ compared to the matrix), while glass transition temperatures around 100 °C could be maintained. Notably, even tensile behaviour mimicking typical thermoplastic yield strain comparable to ABS was observed in one of the prepared materials. This monomer/rubber system appeared to be the most promising and was therefore selected for in-depth analysis of the curing process using photo-rheology and photo-DSC. Finally, this material was used for hot lithography and several highly detailed objects were prepared, demonstrating the good printability of this toughened material.