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 effect of six halogen-free flame retardant (FR) formulations was investigated on the thermal stability of two low-density polyethylenes (LDPE) and one linear low-density polyethylene (LLDPE), by means of thermogravimetric analysis (TGA) under nitrogen and air atmosphere. The relative data were combined with flammability properties and the overall performance of the FRs was correlated with the type of branching in the polyethylene grades and to their processing behavior. The thermal degradation kinetics was further determined based on the Kissinger and Coats-Redfern methods. In terms of flammability, the addition of a triazine derivative and ammonium polyphosphate at a loading of 35 wt. %. was found to be the most efficient, leading to UL 94 V0 ranking in the case of the LDPE grade produced in an autoclave reactor.

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.

Self‐healing systems are a next‐generation technology that can offer autonomous crack repair and increase the service lifetime of a protective coating. Polymeric microcapsules containing healing agents can be used in that perspective and exhibit significant potential. In the current study, poly(urea‐formaldehyde) microcapsules containing an epoxy healing agent as core material were successfully prepared using in situ polymerization. The effect of different process parameters was studied in respect to microcapsules' characteristics, that is, morphology, particle size, encapsulation efficiency and thermal properties. Spherical microcapsules with either smooth or rough surface were obtained with a size ranging from 90 to 165 μm, controlled by the stirring rate during the emulsification stage. The encapsulation efficiency varied between 65–77% with no significant dependence on the process conditions. Finally, the stability of the microcapsules during storage was investigated at different conditions.