NIR‐Sensitized Cationic and Hybrid Radical/Cationic Polymerization and Crosslinking

Abstract

NIR‐sensitized cationic polymerization proceeded with good efficiency, as was demonstrated with epoxides, vinyl ether, and oxetane. A heptacyanine functioned as sensitizer while iodonium salt served as coinitiator. The anion adopts a special function in a series selected from fluorinated phosphates ( a : [PF 6 ] − , b : [PF 3 (C 2 F 5 ) 3 ] − , c : [PF 3 ( n ‐C 4 F 9 ) 3 ] − ), aluminates ( d : [Al(O‐ t ‐C 4 F 9 ) 4 ] − , e : [Al(O(C 3 F 6 )CH 3 ) 4 ] − ), and methide [C(O‐SO 2 CF 3 ) 3 ] − ( f ). Vinyl ether showed the best cationic polymerization efficiency followed by oxetanes and oxiranes. DFT calculations provided a rough pattern regarding the electrostatic potential of each anion where d showed a better reactivity than e and b . Formation of interpenetrating polymer networks (IPNs) using trimethylpropane triacrylate and epoxides proceeded in the case of NIR‐sensitized polymerization where anion d served as counter ion in the initiator system. No IPN was formed by UV‐LED initiation using the same monomers but thioxanthone/iodonium salt as photoinitiator. Exposure was carried out with new NIR‐LED devices emitting at either 805 or 870 nm.

Distinct Sustainable Carbon Nanodots Enable Free Radical Photopolymerization, Photo‐ATRP and Photo‐CuAAC Chemistry

“…However, results obtained indicate different activities to initiate FRP, CRP, and CuACC reaction. Internal activation barriers caused by individual shape of the potential curves between the substrates may explain these findings [22, 48] …”

“…Excitation results in formation of the excitated state, which transfers an electron to the acceptor that is a diaryl iodonium cation. This proceeds in the singlet state where the size of the anion [48] separates CD +. and the iodyl radical to diminish electron back transfer resulting in a higher yield of initiating radicals for polymerization.…”

“…Otherwise, the electron back transfer forms back CD. This also depends on the nature of the anion exhibiting the larges size in the case of c [54] . Electron back transfer plays a certain role in photoexcited CDs since the obtained in fluorescence measurements document that singlet state photochemistry possesses a major role in these systems vide supra.…”

Verschiedene nachhaltige Kohlenstoffnanopunkte für die freie radikalische Photopolymerisation, die Photo‐ATRP und die Photo‐CuACC Chemie

“…Eine Anregung führt zur Bildung des angeregten Zustands, welcher ein Elektron auf einen Akzeptor, ein Iodoniumkation, überträgt. Das erfolgt im Singulettzustand, in welchem die Größe des Anions [48] den Abstand zwischen CD +. und dem Iodylradikal separiert, um die Elektronenrückübertragung zu reduzieren, wodurch eine höhere Ausbeute an initiierenden Radikalen für die Polymerisation erreicht wird.…”

“…Die erhaltenen Ergebnisse zeigen jedoch unterschiedliche Reaktivitäten zur Initiierung der FRP‐, CRP‐ und CuACC‐Reaktion. Interne Aktivierungsbarrieren, welche durch die individuelle Form der Potentialkurven zwischen den reagierenden Komponenten verursacht werden, können diese Ergebnisse erklären [22, 48] …”