The ablation characteristics of various polymers were studied at low and high fluences. The polymers can be divided into three groups, i.e., polymers containing triazene and ester groups, the same polymers without the triazene group, and polyimide as reference polymer. At high fluences, similar ablation parameters, i.e., etch rates and effective absorption coefficients, were obtained for all polymers. The main difference is the absence of carbon deposits for the designed polymers. At low fluences, very pronounced differences are detected. The polymers containing the photochemically most active group (triazene) exhibit the lowest threshold of ablation and the highest etch rates, followed by the designed polyesters and then polyimide. Neither the linear nor the effective absorption coefficients reveal a clear influence on the ablation characteristics. The thermal properties of the designed polymers also have only minor influence on the ablation activity. The amount of detected gaseous products follows the same trend as the ablation activity, suggesting a combined mechanism of photochemical decomposition and volume increase for the designed polymers. The different behavior of polyimide might be explained by a pronounced thermal part in the ablation mechanism.
ABSTRACT:The anionic polymerization of lauryllactam was initiated at 270°C using sodium hydride as an initiator and N,NЈ-ethylene-bisstearamide (EBS) as an activator (NaH:EBS molar ratio of 2). Polymerization occurred in less than 2 min and was successfully performed in an internal mixer and a twin-screw extruder with corotating intermeshing screws (Werner & Pfleiderer ZSK 25). The content of residual monomer, as determined by thermogravimetric analysis, was lower than 0.5 wt %. Molecular weight, as measured by size exclusion chromatography, was governed by the lauryllactam:NaH molar ratio calculated on a M n of 25 kg/mol at a constant NaH:EBS molar ratio of 2. Blends were prepared in situ by polymerization of lauryllactam solutions of various polymers. When poly(ethylene-co-butylacrylate) (Lotryl ; Atofina) was dissolved in lauryllactam, rubber-toughened polyamide 12 blends were obtained. Mechanical properties of the injection-molded polymers were examined by stress-strain as well as notched Charpy impact tests at different temperatures. Blend morphologies were imaged by scanning electron microscopy (SEM).
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