Ketocoumarin-based Photopolymerization, Holographic Recording And 3D Printing

Photopolymerization is a chemical process through which monomers can be converted to well-defined polymers efficiently and cost-effectively under light.It has been widely applied in the fields including surface grafting,controlled polymerization,micro-/nano-manufacturing,holographic recording and 3D printing.However,there are still many challenges for photopolymerizations,for example,the conflict of rapid manufacturing of polymer materials with precise control of microstructures.Therefore,new strategies are highly awaited to tune the photopolymerization.To address above challenges,it is rational to develop new photoinitiating systems since they play key roles to convert the light energy to chemical energy.It is well-accepted that photoinitiating systems are critical to fabricate polymer materials with complex but well-defined structures,due to that they can be used to precisely tune the photopolymerization kinetics and photorheological behaviors.To this end,photoinitiating systems based on ketocoumarins show unique advantages for tunning the photopolymerization due to that ketocoumarins exhibit good photostability,large intersystem crossing coefficients,high concentrations of triplet excited state,and can be photooxidized or photoreduced depending on coinitiators.Nevertheless,the reaction processes and product structures during the reaction of ketocoumarins with coinitiators have not been fully explored,which hinders their applications for dialing the photopolymerization and fabricating advanced photopolymer materials.This thesis aimed to formulate different photoinitiating systems based on one ketocoumarin named 3,3?-carbonylbis(7-diethylaminocoumarin)(KCD),and to investigate their effects on the photopolymerization kinetics,photorheological behaviors,and to control the behaviors of holographic recording and 3D printing.Details are given below:(1)The products and photoreaction processes of the KCD/2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine(TA)system,KCD/N-phenylglycine(NPG)system and KCD/NPG/TA system were disclosed by density functional theory calculations and characterization methods including electron paramagnetic resonance spectroscopy,laser flash photolysis transient absorption spectroscopy,gas chromatography-mass spectrometry,high performance liquid chromatography-high resolution mass spectrometry and gel permeation chromatography.Results show that KCD is oxidized by TA upon visible light irradiation,which produces a deethylated product,initiating radical and acetaldehyde in the KCD/TA system.By contrast,KCD is reduced by NPG to produce one initiating radical and another inhibiting radical in the KCD/NPG system,and it undergoes sequential photoreduction by NPG and photooxidation by TA in the KCD/NPG/TA ternary system,which generates two kinds of initiating radicals.Therefore,the KCD/NPG/TA system leads to the fastest photopolymerization,while the KCD/NPG system mediates the slowest one in the same condition.(2)Effects of KCD/NPG,KCD/TA and KCD/NPG/TA systems on the holographic recording of photopolymer/liquid-crystal composites were studied.Results indicate that the degree of phase separation,grating diffraction efficiency and electro-optical performance of holographic photopolymer/liquid-crystal composites(HPC-LCs)are greatly improved by the KCD/NPG system due to the generation of inhibiting ketyl radicals.In sharp contrast,no well-defined HPC-LCs are produced by KCD/TA and KCD/NPG/TA systems.Added control shows that the holographic recording performance is further decreased by adding xanthene as an inhibitor to the KCD/TA system,although xanthene does not participate in the photoreaction of KCD with TA.Thus,it can be concluded that the ketyl radical plays a unique role for boosting the holographic recording performance,which cannot be realized by added inhibitors.(3)Effects of KCD/NPG,KCD/TA and KCD/NPG/TA systems on the 3D print fidelity,print resolution and print speed were investigated.Results show that the high print fidelity(deviation of feature size:1.6%),high print resolution(20?m)and high print speed(5.1cm · h^-1)can be enabled by the KCD/TA system.This is because that the photooxidation product of KCD still holds a large molar extinction coefficient and its peak absorption only blue shifts for 10 nm,which benefits the decrease of light penetration depth of the printing resin.This breakthrough effectively resolves the conflict of fast print speed with high print resolution,and increases the light energy efficiency from 2%to 24%.In sharp contrast,the KCD/NPG system and KCD/NPG/TA system show poor 3D printing performance due to the large light penetration depth and uncontrolled diffusion of active species,respectively.