Analysis of Factors Affecting the Polymerization Efficiency of Photoinitiators

　　In recent years, photoinitiated polymerization has found widespread application in areas such as photocurable adhesives, photocurable inks, photocurable coatings, and 3D printing. The photopolymerization process is generally regarded as a form of “green chemistry,” in which light serves as the driving force: by absorbing photon energy and undergoing associated photochemical reactions, it generates appropriate initiating species—such as free radicals or cations—thereby triggering the polymerization reaction.

　　First, photoinitiator molecules are predominantly dipolar, with opposite charges at their two ends. They engage in dipole–dipole interactions with the surrounding medium, leading to local clustering. Consequently, the solvent cage effect formed by monomers also influences the distribution of photoinitiators. For instance, in mixed photoinitiator systems, the order of addition during blending can significantly affect polymerization outcomes; this stems from the distinct intermolecular dipole–dipole interactions and the varying states of the photoinitiators within the solvent cage depending on the addition sequence. Second, differences in compatibility can likewise modulate initiation efficiency—for example, initiator molecules bearing fluorocarbon or siloxane chains may exhibit phase‑separation tendencies. Moreover, the nonuniformity of photoinitiators and other components during photolysis can alter molecular photochemical processes: in polar microenvironments, for instance, the absorption spectra of molecules undergo a red shift, and the quantum yield of decomposition is correspondingly affected.

　　The photopolymerization process occurs instantaneously upon exposure to light; consequently, depending on the photoinitiator’s light‑absorption characteristics, the system may exhibit surface curing that induces surface morphology, internal stresses arising from non‑simultaneous curing of the top and bottom layers that lead to coating delamination, or incomplete deep‑layer curing that compromises adhesion. Moreover, the addition of various additives or fillers, as well as the presence of oxygen during curing, can also influence the final polymerization outcome.

　　Therefore, in cured formulations, selecting an appropriate photoinitiator is of paramount importance. Internally, the photoinitiator’s light‑absorption characteristics—primarily its absorption wavelength and molar extinction coefficient—and its reactivity directly determine its initiation efficiency. Externally, factors such as the match between the photoinitiator’s absorption spectrum and the light source’s emission spectrum, as well as the system’s homogeneity and compatibility, also have a direct impact on polymerization efficiency.

　　Therefore, in practical applications, the formulation should be adjusted according to specific requirements:

　　Select a photoinitiator system with better overlap with the light source; for thick films, use photoinitiators with low molar extinction coefficients, while for thin films, choose photoinitiators with high molar extinction coefficients.

　　By adjusting the appropriate photoinitiator concentration—either increasing or decreasing it from the calculated theoretical dosage—you can account for factors such as film thickness, light source intensity, and conveyor belt speed.

　　Enhancing the uniformity of a system promotes polymerization; however, certain applications require deliberately engineered non-uniformity, such as increasing surface roughness, optical effects, or the water contact angle.