Curing Reaction of a Two-Component Methacrylate Sample by UV-DSC

Photopolymerization is nowadays a widely used process. Systems are used for medical applications, for example in dentistry, for adhesive applications, in coating technology, and quite recently for 3D printing [1]. This article describes how the curing behavior of a two-component UV-curing sample can be investigated.

Introduction

Photochemical polymerization is an alternative to thermal polymerization in which a sample is heated and then begins to polymerize or cure. In photochemical polymerization, a so-called photoinitiator is excited on exposure to radiation (UV and visible light). The initiator forms radicals or ions that then induce polymerization [2, 3].

This type of polymerization takes place at low temperatures and occurs rapidly. DMPA (2,2-dimethoxy-2-phenylacetophenone, Figure 1) is often used as photoinitiator for methacrylates.

This article describes the photopolymerization of a two-component sample (methacrylate) using DMPA. Figure 1 shows the structural formula of DMPA. The compound acts as a radical photoinitiator. As such, it decomposes under the action of light of a suitable wavelength into a methyl radical (·CH₃) that attacks the carbon-carbon double bonds in the material to be cured (in this example, the methacrylate molecule), and thereby starts the polymerization process. Polymerization is interrupted when two radicals react with each other. The process can also be interrupted or influenced if the radical chain starter is no longer formed, for example by switching off the UV lamp [3].

Conclusions

The curing behavior of a two-component sample was investigated using UV-DSC. DMPA was used as the photoinitiator. The results showed that the reproducibility of the determination of the curing enthalpy was very good and that a degree of cure of 85% was achieved after UV exposure for 3 minutes at 25 °C.

It is important to use freshly prepared samples and to make sure that the samples are not exposed to an oxygen atmosphere for too long before the measurement. Samples like this should be stored in a protective atmosphere in a refrigerator and always be freshly prepared for measurements.

_{Curing Reaction of a Two-Component Methacrylate Sample by UV-DSC | Thermal Analysis Application No. UC 444 | Application published in METTLER TOLEDO Thermal Analysis UserCom 44}