Vinyl Sulfonate Esters: Efficient Chain Transfer Agents for the 3D Printing of Tough Photopolymers without Retardation

Abstract

The formation of networks through light-initiated radical polymerization allows little freedom for tailored network design. The resulting inhomogeneous network architectures and brittle material behavior of such glassy-type networks limit the commercial application of photopolymers in 3D printing, biomedicine, and microelectronics. An ester-activated vinyl sulfonate ester (EVS) is presented for the rapid formation of tailored methacrylate-based networks. The chain transfer step induced by EVS reduces the kinetic chain length of the photopolymer, thus shifting the gel point to higher conversion, which results in reduced shrinkage stress and higher overall conversion. The resulting, more homogeneous network is responsible for the high toughness of the material. The unique property of EVS to promote nearly retardation-free polymerization can be attributed to the fact that after the transfer step no polymerizable double bond is formed, as is usually seen in classical chain transfer agents. Laser flash photolysis, theoretical calculations, and photoreactor studies were used to elucidate the fast chain transfer reaction and exceptional regulating ability of EVS. Final photopolymer networks exhibit improved mechanical performance making EVS an outstanding candidate for the 3D printing of tough photopolymers.

Enhanced reduction of polymerization-induced shrinkage stress via combination of radical ring opening and addition fragmentation chain transfer

“…Recently, an ester-activated vinyl sulfonate ester (EVS) has been reported as powerful AFCT reagent showing no retardation during the radical polymerization process. 29 This improved curing behavior has enabled the 3D-structuring of such toughened photopolymers with low shrinkage stress.…”

Carbon Dots as a Promising Green Photocatalyst for Free Radical and ATRP‐Based Radical Photopolymerization with Blue LEDs

“…Photoinitiated polymerization with LEDs has received increased attention in many areas. [1] Owing to specific regulatory requirements,academia and industry are replacing existing mercury-based light sources with energy-saving and environmentally friendly light sources such as LEDs. [2] Interest has focused on UV LEDs and blue-emitting LEDs owing to their use in 2D and 3D printing, [3] coatings, [4] and dentistry.…”

“…[1a] Thel atter enables the synthesis of polymers with precise average molar masses,various compositions,a nd well-defined structures.N umerous examples of photomediated CRP techniques have been successfully developed, including photo-NMP, [6] photo-RAFT, [1a,c,e, 7] and photo-ATRP. [1,8] Regarding the latter,t he in situ photolytic generation of Cu I complexes from Cu II under irradiation as an initiator for controlled polymerization facilitates CRP with ac opper concentration in the ppm range. [9] This has been successfully demonstrated with systems requiring UV, [9d,e] visible, [9b,c] or NIR [9a] light.…”

Bicarbazole‐based oxalates as photoinitiating systems for photopolymerization under UV–Vis LEDs

“…For the most widely used FRP, two kinds of distinct PIs, namely, type I PIs with radical‐forming ability after α‐cleavage and type II PIs after H‐abstraction reaction, are used to produce free radicals . However, existing commercial PIs still have many shortcomings, such as requirement for a mercury lamp due to their short absorption wavelength range; thus, researchers are committed to the design and development of novel PIs to meet different applications . Light‐emitting diode (LED) light source has been recently developed, and it is rapidly replacing the traditional mercury lamp due to its environmental friendliness, low cost, long lifetime, and low energy consumption .…”