Solid state polyamidation processes

Abstract

Low reaction rates and distinct transition phenomena from the solid to the melt state restrain solid state polymerisation (SSP) reactions of nylon salts for industrial application. To alleviate these problems, catalysts containing nylon salts are employed. In this study, hexamethylenediammonium adipate (HMA) particles were used containing a strictly controlled amount of catalyst, either phosphoric acid, sulphuric acid or boric acid. The results show considerable acceleration of the reaction rate, especially in the presence of boric acid, while the solid state character of the process is maintained throughout the total course of the reaction. Comparative polymerisation runs were monitored both by end‐group and quantitative water determinations of the reacting material to exclude any accumulation of the water of polycondensation within the reacting particles. The results obtained support further the mechanism proposed for the transition solid‐melt in SSP runs of nylon salts in the absence of catalysts. In the latter case extended water accumulation is the rule.

Direct solid state polycondensation of tetra‐ and hexa‐methylenediammonium terephthalate: Scaling up from the TGA micro‐reactor to a laboratory autoclave

“…The mechanism of DSSP is considered to follow a nucleation and growth model, in which defects inside the salt crystals react to polymer nuclei, gradually growing in size, according to well‐known principles of solid state chemistry . During the initial stages of DSSP of polyamide salts, some of the volatile diamine component, i.e., hexamethylenediamine (HMD), can escape, as has been observed for 66 and 610 salts and also for different aromatic polyamide salts .…”

Diffusion studies through fluorescence recovery after photobleaching in hydrated polyamides

“…The penalty for having such strong hydrogen bonds is a large decrease in T g upon hydration, as these strong interchain bonds are replaced by weaker bonding with water molecules [14]. This hydration was even found to play a fundamental role during the polymerization of nylon salts depending on the polar sites concentration, temperature conditions, and organization of polyamide structure [15–18]. This drawback of polyamides was used as a tool to study the diffusion behavior in different macromolecular mobility states of the polyamides, not due to temperature increase but due to hydration leading to different ( T − T g ) values for a given temperature.…”

New process for the production of dry hexamethylenediammonium adipate

“…This so‐called solid‐state finishing (SSF) can produce a substantial increase in the degree of polymerization of the polymer, while the material retains its solid shape 8, 9. However, a “direct” solid‐state polyamidation (SSP) of dry HMA salt has been also studied, using different techniques,10–22 and still attracts the interest of many polymer technologists, given that all the problems associated with the high temperature disadvantages of melt technology are completely absent 15. In fact, because of the much lower reaction temperatures at which SSP is performed, the danger of undesirable side reactions and gelling is reduced, resulting in polymers with improved properties, such as increased capability of spinning.…”