No abstract

In the current paper, a comparative study on the direct solid state polycondensation (DSSP) reaction of different terephthalate based semi‐aromatic salts (XT salts, X = 4–18) in the TGA micro‐reactor is reported. High purity XT salts were prepared in solution and were used as starting materials for DSSP. The reaction temperature (TDSSP) for each salt was suitably selected as 20 °C–30 °C below the melting point Tm of the respective salt. The PAXT products were characterized by TGA/DSC, liquid 1H‐NMR, and SEM. In the DSSP of XT salts, some diamine is always lost to the gas phase and as a consequence, the attainable molecular weight of the polymer formed gets limited by the unbalance of acid and amine end‐groups. The TGA curves show that as the diamine length increases and its volatility decreases, higher molecular weights are obtained. SEM pictures of the products reveal true solid character during the polymerization reaction up to and including PA10T, whereas PA5T, PA12T, and PA18T reveal stickiness and agglomeration during reaction. A possible mechanism explaining such behaviour is also provided. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2493–2506

The aim of this work was to develop and optimize a direct solid state polymerization (DSSP) process on a micro scale for alkyldiammonium-terephthalate salts. This was successfully demonstrated for the first time by the case of tetramethylenediammonium-terepththalate salt (4T salt). The derived polymer (PA4T) presents interesting properties, but the temperature-favored acid catalyzed cyclization of tetramethylenediamine (TMD) to mono-functional pyrrolidine and ammonia inhibits a high polymerization conversion. DSSP was performed in a thermogravimetrical analysis (TGA) chamber, and the continuously monitored weight loss was correlated to polymerization conversion via the release of water, excluding any mass and heat transfer limitations. It was found that the conditions under which the DSSP is performed and the morphology of the starting material affect both the reaction rate and the product quality. The effect of the critical process parameters, namely vent size, heating rate to reach SSP temperature, and reaction temperature were quantified by the observed mass loss and by 1 H NMR analysis. It was noticed that, besides the water formed by amidation, other volatile compounds were also released during the DSSP reaction, with main component, the TMD. In particular, it was observed that conditions favoring the evaporation of TMD also favored a higher reaction rate. The TMD loss was minimized by optimization of the aforementioned process conditions, leading to a more thermally stable and a higher molecular weight final product. The thermal stability of the PA4T was found to be inversely correlated to the concentration of carboxylic end groups present in the formed polymer.

A novel reactor configuration in which blocks of monoliths are arranged in a stirrer‐like configuration was studied. A substantial liquid flow rate can be realized through the monolith blades at relatively low power input, owing to the high permeability of the monolithic structure. The inside of the monolithic channels can be coated with a thin layer of either a conventional catalyst or a biocatalyst, thereby eliminating many of the problems associated with using a suspended catalyst. The basic relationship among stirrer speed, geometry, liquid viscosity, and the resulting torque and flow through the blades were studied. Furthermore, the fast decomposition of a dilute, aqueous hydrogen peroxide solution was used to characterize the rate of external mass transfer.

The direct solid state polycondensation (DSSP) reaction of tetramethylenediammonium and hexamethylenediammonium terephthalate (4 T and 6 T salts) in a laboratory scale autoclave reactor was investigated. The autoclave reactor is 3 orders of magnitude larger than the TGA micro‐reactor we used previously. The larger scale reactor allows more extensive analyses such as analysis of the formed condensate by titration and allows investigation of operating conditions that are important on industrial scale, such as batch (closed system) versus semibatch (open system) operation and flow of nitrogen used. Comparing the two scales has given important insight into the parameters that are important in scaling‐up direct solid‐state polycondensation. Furthermore, the effect of scaling up on the quality of the final semiaromatic polyamide products was determined, by comparing the obtained thermal properties, the solution viscosity and the end‐group concentrations obtained by 1H‐NMR spectroscopy. When operating the open reactor with a gentle nitrogen stream, the results show that products of similar properties were obtained from the micro and the laboratory scale reactors if critical parameters like temperature and pressure time profile were kept the same. The solid character of the reacting mass was retained only when maintaining the reactor at atmospheric pressure, allowing the condensation water to be removed. When keeping the autoclave reactor closed, both polyamide (PA) products (i.e., PA4T and PA6T) were agglomerated as a result of a solid melt transition during the direct solid state polycondensation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45080.