Poly( p -phenylene-benzobisoxazole), PBO, is a member of a family of rigid-rod, lyotropic liquid crystal polymers which can be fabricated into fiber, film and composites. PBO exhibits exceptional ignition resistance, low heat release rate, and very low smoke emission. PBO's fire, smoke, and toxicity (FST) properties are one of the best thermally stable polymers. PBO begins to thermally decompose at 660 ° C and it has a char yield > 70% at 900 °C. It has LOI of > 56 and UL94 rating of VTM0 for 1 mil thick film. PBO generates almost no smoke, and very little toxic combustion products are generated during fire. PBO is more ignition resistant and has very low heat release (measured by the Cone Calorimeter) compared to other high temperature polymers. Carbon fabric/PBO composites do not ignite even after 15 minutes when exposed to a heat flux of 50 kW/m 2 . Preliminary results indicate that this carbon fabric/PBO composite meets the Navy's most critical fire, smoke, and toxicity requirements for applications inside submarines. PBO's unique combination of thermal, mechanical, and physical properties could provide enabling technology for the next generation of products for interior components of airplanes, ships, offshore structures, and other places where the fire, smoke, toxicity properties of the material and weight are critical.
Summary: The thermal polymerization of styrene is usually modeled by relying on a reaction scheme and a set of equations that were developed more than three decades ago by Hui and Hamielec. Many detailed models of styrene polymerization are available in the open literature and they are mostly based on the work of Hui and Hamielec, which nearly makes this the standard to follow in explaining the behavior of polystyrene reactors. The model of Hui and Hamielec does a very nice job of describing monomer conversion data but discrepancies are seen between observed and predicted values of number and weight average molecular weights, Mn and Mw. Discrepancies in number average molecular weight seem to be the result of random noise. Discrepancies in weight average molecular weight grow as the polymerization temperature decreases and some of the trends observed in the residuals over the entire temperature range cannot be attributed to random noise. Hui and Hamielec attributed the observed deficiencies to a standard deviation of ±10% in their GPC measurements. A new data set with an experimental error of 2% for average molecular weights is presented. The set contains measured values of Mn, Mw and Mz, so the polymerization scheme has been extended to include third order moments. The data set also includes the effect of ethylbenzene as a chain transfer agent. We present the results of comparing model predictions to our measurements and the adjustments made in the original set of kinetic parameters published by Hui and Hamielec.
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