Low volatile monofunctional reactive diluents for radiation curable formulations

Abstract

In the last decades the importance of UV curable formulations has increased continuously. Their fast curing speed, solvent‐free polymerization conditions, and the formation of hard and highly crosslinked photopolymer networks represent major benefits. Commercial UV resins generally consist of multi‐functional vinyl oligomers, photoinitiators, additives, and reactive diluents. Mono‐ and multi‐functional reactive diluents serve as thinners to lower the overall resin viscosity and to improve processability. However, many monofunctional reactive diluents like isobornyl (meth)acrylate or benzyl (meth)acrylate exhibit high volatility, often already at room temperature. This causes adverse effects such as unpleasant odor, potential health risks, and changing resin composition during processing. A new group of monomers that show high potential for replacing traditional highly volatile reactive diluents are salicylate (meth)acrylates. In this work, salicylate‐based thinners are synthesized, polymerized, and characterized with respect to their viscosity, volatility, thermal stability, photoreactivity, and thermomechanical properties of their homopolymers. Additionally, a first example of their diluting effect in a highly viscous difunctional polyester urethane methacrylate is demonstrated with 30 wt% of a cycloaliphatically and an aromatically substituted salicylate methacrylate. The polymers of the diluted resin exhibit similarly high glass transition temperatures of 110 and 126 °C, which are in the range of the polymers of the undiluted resin.

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

“…46 For example, triethylene glycol dimethacrylate (TEGDMA) may increase the filler capacity of the compound significantly, 84 and cyclopolymerizable monomers (CPMs) create bulky units in the backbone and thus effectively reduce volume shrinkage. 10,47,48 Furthermore, CPMs are, along with salicylatederived monofunctional (meth)acrylates, 49 a viable option to address the problem of volatility for photopolymerizations at elevated temperatures. 4,46,50,51 Ionically, induced ring-opening photopolymerizations are another highly efficient tool in this regard.…”

“…Hence, new monomers that contribute to dilution without sacrificing ultimate material properties, in particular shrinkage, are necessary to overcome the issue . For example, triethylene glycol dimethacrylate (TEGDMA) may increase the filler capacity of the compound significantly, and cyclopolymerizable monomers (CPMs) create bulky units in the backbone and thus effectively reduce volume shrinkage. ,, Furthermore, CPMs are, along with salicylate-derived monofunctional (meth)­acrylates, a viable option to address the problem of volatility for photopolymerizations at elevated temperatures. ,,, Ionically, induced ring-opening photopolymerizations are another highly efficient tool in this regard. While epoxides have been utilized to reduce shrinkage for a while already, cyclic oxazolines, esters , and carbonates , have only recently been introduced as versatile monomers for additive manufacturing.…”

Synthesis of UV-curable polyurethane-acrylate hybrids with tuneable hardness and viscoelastic properties on-demand

“…There are, however, concerns regarding this last component in the system. 8 Even though the reactive diluent reduces the system's intrinsic viscosity and thus eases its use into certain applications, issues of volatility and toxicity during its manipulation as well as during transport and storage must be managed. For all these reasons, the use of reactive diluents must be carefully studied in further developments of photocurable polymer systems.…”

UV-curable polyurethane-acrylate hybrids made by a prepolymer-free process and free-standing polymer–metal oxide films made in a wholly water-based UV curing process

“…For example, the reactive diluents used in the curing process pose issues of toxicity, volatility, and irritation to the eyes and skin. 15 The aqueous polyurethane dispersion process is complicated since it involves an inversion step of transferring the components from an organic solvent to the aqueous medium. This process not only introduces residual solvents but also requires volatile organic bases like triethyl amine or gaseous bases like ammonia to facilitate dispersion in water by neutralizing acidic functionalities present in the prepolymer.…”