Impact of radiation attenuation and temperature evolution on monomer conversion of dimethacrylate‐based resins with a photobleaching photoinitiator

Abstract

The photopolymerization process of a dimethacrylate copolymer system activated by the camphorquinone (CQ)/amine photoinitiator system (1 wt%), was experimentally studied under nonisothermal conditions in 1and 2-mm thick samples by measuring double bond conversion, temperature rise and radiation attenuation through the sample during polymerization. The peak temperature in 1-or 2-mm thick samples irradiated at 5 mW/cm 2 was 29 and 388C, respectively. The temperature evolution during polymerization was also predicted by solving the energy balance coupled with the kinetic expressions for the reaction rate. Radiation attenuation as a function of depth by the photobleachable CQ results in spatial and temporal variation in the local rates of the kinetic steps involved. General relationships for spatiotemporal variations in concentration of a photobleaching initiator, in systems where attenuation and initiator consumption are taken into account, were used to compute local polymerization rates. The effects of radiation attenuation, photobleaching of the photoinitiator and variation of cure temperature at different depths into the resin, all compete to determine the double bond consumption. The increased radiation attenuation in the 2-mm thick sample was accompanied by a higher cure temperature compared with the 1-mm thick sample, and as a result, the monomer conversion averaged over the sample thickness in the 1-and 2-mm thick samples was the same. Results obtained in this research highlight the inherent interlinking of thermal and radiation attenuation effects in bulk photopolymerizing systems.

Visible light polymerization of epoxy monomers using an iodonium salt with camphorquinone/ethyl-4-dimethyl aminobenzoate

“…This is attributed to different temperatures reached during polymerization in samples of different thicknesses. The polymerization reaction is highly exothermic, which results in an increase in the sample temperature during the process and this effect becomes more important as the sample thickness increases . A higher sample temperature induces an increase in the mobility of the reaction environment (i.e.…”

Encapsulants for light‐emitting diodes from visible light‐cured epoxy monomers

“…This effect occurs when the light fails to reach the deeper layers of a sample because the absorbing species near the irradiated surface absorb most of it. As a result of light attenuation in 2‐mm thick specimens of methacrylate monomer photoactivated with 1 wt % CQ/EDMAB, the values of conversion at the irradiated surface was about 18% higher than that at the non irradiated surfaces . On the other hand, the values of conversion of UVR and SIB at the irradiated and non‐irradiated surfaces in 2‐mm thick specimens were similar (Fig.…”

“…It is worth mentioning that the presence of light absorbing photoinitiators in a photocuring resin inevitably results in attenuation of the light intensity along the radiation path and often limits the cure depth in a sample to be polymerized . This effect occurs when the light fails to reach the deeper layers of a sample because the absorbing species near the irradiated surface absorb most of it.…”

“…The temperature during polymerization was monitored with fine K‐type thermocouples (Omega Engineering, Inc., USA) embedded in the monomer specimens in the upper half of the sample where the temperature is more uniform . This was verified after the experiment by visual examination of the sample with a magnifying lens.…”

Methacrylate and Epoxy Resins Photocured by Means of Visible Light-Emitting Diodes (LEDs)

“…26,27 Figure 15.7 shows the characteristic curing behavior of a 70 : 30 BisGMA/TEGDMA blend. 28 The data illustrates autoacceleration immediately after irradiation commences so that the reaction rate reaches a maximum value at a double-bond conversion of about 10%, 26,27 As the polymerization progresses, the polymer molecular weight increases and gelation occurs so that the mobility of the environment decreases resulting in a reduction in the termination rate constant and the initiation efficiency and an increase in reaction rate as shown in Figure 15.7. The photoinitiator in the present system is not totally consumed even at the end of the reaction.…”