2023 The Complete Guide To Analysis of factors influencing the efficiency of photoinitiator polymerization

May 17, 2022 Longchang Chemical

2023 The Complete Guide To Analysis of factors influencing the efficiency of photoinitiator polymerization

 

In recent years, photoinitiated polymerization has been widely used in light-curing adhesives, light-curing inks, light-curing coatings, 3D printing and other fields. The photopolymerization process is often considered as a kind of “green chemistry”, using light as the driving force to induce polymerization reactions by absorbing photon energy and undergoing accompanying photochemical reactions to form suitable initiating active species, such as free radicals, cations and so on.
First of all, photoinitiator molecules are mostly dipole molecules with different charges at both ends of the molecule, which interact with the system such as dipole and thus gather in certain areas, so the solvent cage effect formed by the monomer will also affect the distribution of photoinitiator. For example, the mixed photoinitiator system in practice, the mixing process will affect the effect of the polymerization of the different order of addition, the fundamental reason is that the different order of addition of photoinitiator dipole interaction and solvent cage effect in the system is not the same state; secondly, the different compatibility will also lead to changes in initiation efficiency, such as containing fluorocarbon or silicone chain initiator molecules will float, etc.; and photoinitiator The inhomogeneity of the photoinitiator will also affect the photochemical process of the molecule in the photolysis process, for example, the absorption spectrum of the molecule in polar microenvironment is red-shifted and the quantum yield of the decomposition will be affected.
The polymerization process of photoinitiated polymerization occurs at the moment of receiving light, so the polymerization system may occur because of the different light absorption ability of the initiator, the surface layer may be cured first to produce surface morphology, the upper and lower layers can not be cured at the same time resulting in internal stresses that lead to coating flaking, or deep curing is not complete resulting in reduced adhesion; the addition of various additives or fillers, and the presence of oxygen during curing will also affect the final polymerization effect etc.
Therefore, in the formulation of curing, the selection of the appropriate photoinitiator is crucial. The internal factor is that the light-absorbing properties (mainly wavelength and molar extinction coefficient) and reactivity of the photoinitiator directly determine its initiation performance, and the external factor is that the absorption spectrum of the photoinitiator matches the emission spectrum of the light source, and the homogeneity and compatibility of the system also directly affects the efficiency of polymerization.
Therefore, in practical applications, the formulation should be adjusted according to the needs of.
Selecting photoinitiator systems with better overlap with light sources, using photoinitiators with low molar extinction coefficients for thick films, and selecting photoinitiators with high molar extinction coefficients for thin films.
adjusting the appropriate photoinitiator concentration, which can be increased or decreased based on the calculated theoretical dosage, including film thickness, light intensity of the light source, conveyor belt speed, etc.
Increasing the homogeneity of the system is beneficial to polymerization, but certain field applications require the pursuit of inhomogeneity, such as increased roughness, optical effects, water contact angle, etc.

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