Influence of Polymer Molecular Weight on the Chemical Modifications Induced by UV Laser Ablation

Abstract

This paper investigates the influence of polymer molecular weight (M(W)) on the chemical modifications of poly(methyl methacrylate), PMMA, and polystyrene, PS, films doped with iodonaphthalene (NapI) and iodophenanthrene (PhenI), following irradiation at 248 nm (KrF excimer laser, 20 ns fwhm and hybrid excimer-dye laser, 500 fs fwhm) and at 308 nm (XeCl excimer laser, 30 ns fwhm). The changes of intensity and position of the polymer Raman bands upon irradiation provide information on cleavage of the polymer bonds. Degradation of PMMA, which is a weak absorbing system at 248 nm, occurs to a higher extent in the case of a larger M(W), giving rise to the creation of unsaturation centers and to degradation products. For highly absorbing PS, no degradation is observed upon irradiation with a KrF laser. Consistently irradiating doped PS at 308 nm, where the absorption is low, induces degradation of the polymer. Results provide direct support for the bulk photothermal model, according to which ejection requires a critical number of broken bonds. In the case of irradiation of doped PMMA with pulses of 248 nm and 500 fs, neither degradation nor dependence with polymer M(W) are observed, indicating that mechanisms involved in the femtosecond laser ablation differ from those operating in the case of nanosecond laser ablation. Participation of multiphoton/avalanche processes is proposed.

Degradation of ultra-high molecular weight poly(methyl methacrylate-co-butyl acrylate-co-acrylic acid) under ultra violet irradiation

“…[1][2][3] This process is commonly observed in large molecules, particularly in polymers during their service lifetime. The long molecular chain of polymer makes the material susceptible to degradation and the level of deteriorations shows linear dependence to the polymers molecular weight, as reported by Rebollar et al 4 The strength of reacting ultra-violet (UV) photons (e.g. UVA, UVB, UVC etc.)…”

“…The degradation is more pronounced if cleavage happens at the main chain as compared to side chain scission as this may lead to photo-ablation. 4 In order to suppress the polymer sensitivity towards light, UV-inhibitors from the classes of benzotriazoles (e.g. 2-(2 0 -hydroxyphenyl) benzotriazoles), metallic complexes (e.g.…”

On the role of chemical reactions in initiating ultraviolet laser ablation in poly(methyl methacrylate)

“…This value of critical bond break fraction is specific to the MD-polymer model used here, which has relatively short polymer chains ͑19 MMA units͒. Recent experimental studies 57,58 have shown that shorter chains have lower levels of entanglement, requiring fewer bonds to be broken for an efficient removal of monomers and polymer fragments by ejection. Longer chains with higher molecular weight will require a higher degree of decompo- sition to achieve ablation.…”

Autofluorescence of Electrophoresis Chip Grooved by Excimer Laser

“…We can see the broad emission shoulder with a narrow peak at 630nm. It is feasible that the fluorescence was caused by some kind of functional group, such as a kind of cyclic compound, resulting from the UV laser ablation [13,14], but it cannot be identified from the narrow spectral area only.…”