Photopolymerization-dual cure

Dual Photo/Thermal Initiation Studies. A series of studies were performed using reactive formulations containing both a photoinitiator and a thermal initiator dissolved in the Derakane resin. The objective of these studies was to investigate a dual cure strategy in which the heat liberated by the photo-induced polymerization leads to the production of additional active centers by the dissociation of a thermal initiator. In this way, the dual cure strategy could offer both the temporal control of the start of the reaction afforded by the photopolymerization, as well as enhanced reaction rate and completeness of cure provided by the thermal initiation. 

Dual Cure Photopolymerization The dual cure technique is a two-step process involving two different types of chemistry [ 1 i]. It usually consists in combining a UV irradiation and a thermal drying process and usually appears as a two-pack material, typically based on a polyisocyanate and an acrylate (10.87). The acrylate is... 

In this respect, it should be mentioned that dual-cure systems, combining UV irradiation and a thermal treatment, have been developed to address the issue of the lack of cure in shadow areas of 3D objects, as well as in thick pigmented samples." " A few centimeter thick nanocomposite materials can be produced by this two-step process which associates the photopolymerization of the acrylate resin and the thermally-induced polyaddition of isocyanate and alcohol groups ... 

In the second dual photo/thermal initiation strategy, the approach described above is augmented by the inclusion of a thermal initiator. Upon illumination, active centers produced by fragmentation of the photoinitiator start the polymerization reaction. The heat evolved from the exothermic photopolymerization elevates the temperature of the system and results in the production of additional active sites by the thermal initiator. This dual initiating strategy provides both the cure on demand (temporal control) afforded by photopolymerization, and the completeness of cure provided by the thermal initiator. 

At present most commercial fibers possess a dual coating, a soft buffer coating surrounded by a stiff external coating (Fig. 3). Typical diameters of fibers with their soft and hard coatings are 185 and 250 pm, respectively. Both can be cured in situ by means of photopolymerization. 

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