Development of radical initiator based on o-imino-isourea capable of photo/thermal polymerization

Using o-imino isourea, three photo- and thermal dual-responsive radical initiators dicyheDCC, CyheDCC, and BnDCC were systematically developed and synthesized. By adding an aromatic ring to the free radical initiators, the ultraviolet-visible absorption was redshifted, and the absorption coefficient was increased. Compared with other initiators, BnphDCC exhibited an exceptional photoinitiation rate under photo-differential scanning calorimetry (DSC) and a high absorption coefficient (ε = 15 420 M-1 cm-1). Therefore, it is an appropriate potential photoinitiator. DicyheDCC, which was composed of a cyclic hydrocarbon, exhibited rapid thermal initiation (Tpeak = 82 °C) during thermal DSC, making it a valuable thermal radical initiator. Because of the low stiffness of the N-O link in radical initiators, density functional theory predicts that the aliphatic ring has a significantly lower enthalpy than the aromatic ring. Moreover, in this study, CyhephDCC and BnphDCC, as dual-responsive radical initiators, indicated the potential for a photo- and heat dual-curing system through the universal free-radical polymerization of acrylates. These significant discoveries may be useful for developing efficient and diversified polymer network systems that require synergistic photo- and thermal effects.

Modeling the Enhanced Efficacy and Curing Depth of Photo-Thermal Dual Polymerization in Metal (Fe) Polymer Composites for 3D Printing

This article presents, for the first time, the efficacy and curing depth analysis of photo-thermal dual polymerization in metal (Fe) polymer composites for 3D printing of a three-component (A/B/M) system based on the proposed mechanism of our group, in which the co initiators A and B are Irgacure-369 and charge-transfer complexes (CTC), respectively, and the monomer M is filled by Fe. Our formulas show the depth of curing (Zc) is an increasing function of the light intensity, but a decreasing function of the Fe and photoinitiator concentrations. Zc is enhanced by the additive [B], which produces extra thermal radical for polymerization under high temperature. The heat (or temperature) increase in the system has two components: (i) due to the light absorption of Fe filler and (ii) heat released from the exothermic photopolymerization of the monomer. The heat is transported to the additive (or co-initiator) [B] to produce extra radicals and enhance the monomer conversion function (CF). The Fe filler leads to a temperature increase but also limits the light penetration, leading to lower CF and Zc, which could be overcome by the additive initiator [B] in thick polymers. Optimal Fe for maximal CF and Zc are explored theoretically. Measured data are analyzed based on our derived formulas.