CW-CO2 Laser photoinitiated polymerization of Methyl Methacrylate

Photoinitiated polymerization of methyl methacrylate has been observed using cw-CO2 laser radiation of (10.6 μm). Both of DSC and CW-CO2 Laser photoinitiated polymerization of Methyl Methacrylate. 25 TGA thermal analysis techniques were used for identification of the thermal characteristics (Tg, Tc, and Tm) as well as the thermal stability of the laser photoinitiated PMMA and they compared with that corresponding to classical, conventionally initiated PMMA. In cw-CO2 laser radiation, each of powers (10, 15, and 20W) was used. Although a definite increase in Tg value and thermal stability were observed while power are (10W,15W and 20W), the polymerization pattern remained basically the same in all these cases. Multi-Photon absorption reaction phenomenon was attributed to elucidate the mechanism of interaction between the CO2 laser light and MMA monomer molecule. Introduction: Methyl Methacrylate (MMA) [H2C=C (CH3) CO2CH3] is considered nowadays as the most important methacrylic acid ester commercially available, it is in particular used as a monomer for the fabrication of poly methyl methacrylate (PMMA). This polymer is in its turn widely used as a contact lens material and as a resist in microelectronics, among other applications [1]. The mechanism of CO2 laser photoinitated polymerization can be performed via free radical polymerization process which is chain reaction process and it consists of three main steps: initiation, propagation, and termination. Laser photo-initiated polymerization has demonstrated distinctive features such as it is free-initiator as well as free-solvent process. Other interesting attributes were observed for laser-initiated polymers like high crosslinking and high thermal stability than the conventional initiated polymers [2]. Infra-red laser-induced process studied most extensively is multiphoton excitation of molecules to high vibrational states from which reaction, usually dissociation, may occur. First reason is especially connected with (CW) lasers, that the high intensities associated with laser radiation can, by increasing the transient concentration of radical intermediates, substantially increase the extent to which sequential absorption processes enter into the reaction. A second reason is more directly connected with pulsed nature of the radiation. The radical chain propagation responsible for linking successive monomer units proceeds between pulses; subject the normal radical decay kinetics, only until the onset of a succeeding pulse [3]. Then, the sudden increase in initiator radical concentration leads to radical–radical termination process that prevents further chain lengthen. Laser–produced polymer has a high molecular weight and it is tougher and it displays better tensile and D. Hussain A. Jawad & D. Awatif S. Jassim & M. Youisf B. Yousif 26 thermal properties than the polymer that produced using conventional photo-initiation [4]. Multi-photon absorption process involving interaction of two or more photons with a molecular entity; The multi-photon absorption processes which can be induced by intense radiation become particularly efficient if one or more resonance condition can be satisfied by the molecular energy levels. Where a single frequency of uv/visible radiation is involved, the unequal spacing of most electronic levels means that it is rare to obtain even one intermediate state resonance. Vibrational energy levels are more or less equally spaced, at least for the lowest levels of excitation. Hence, with infra-red radiation of the appropriate wavelength, multi-photon absorption can become highly significant [5].