Posts Tagged ‘MEPA’

Nexam Chemical Holding AB develops, manufactures and markets crosslinking chemicals for the polymer industry. The company is listed on NASDAQ OMX First North (ISIN SE0005101003, ticker symbol: NEXAM). 

CESI: A very interesting quote from the brand new Nexam patent application background section:

“PEPA, PETA and MEPA, the triple bonds will eventually react and cross-link to provide a cross-linked polymeric material, whereby improving the heat and chemical resistance, as well as the mechanical strength of the material. Using PEPA will require a heating to at least 350°C to cure the PETI (cf. US 5,567,800) and even somewhat higher, i.e. 380 to 420°C, to cure PEPA end-capped polyimides (cf. US 5,493,002).

However, for some applications such a high curing temperature profile may be considered a problem. For instance, the properties (such as the coefficient of thermal expansion) of flexible polyimide films, having a melting temperature below 350°C, may be improved via cross-linking. However, the high temperature (above 350 °C) needed to initiate cross-linking will make the processing impossible. Further, also for economic reasons the possibility to lower the curing temperature and/or increase the curing rate may be advantageous. Often such polymers are still to be processed above 300°C. PEPA may accordingly not always be replaced with an alternative cross-linker, e.g. MEPA, in applications requiring a lower curing temperature or a higher curing rate. Further, PEPA has the advantage of withstanding processing temperatures up to and even above 300°C without curing being initiated.

A process for modifying the curing temperature profile of PEPA-based system would thus be highly interesting, as it would allow for processing of “inert” acetylenical polymers, which subsequently may be activated and cured at temperatures tolerated by the molecular backbone.

As already described also acetylenical cross-linkers for thermoplastic polymers are available in the art. Thermoplastic polymers are processed in a wide temperature span above their softening point (Tg or melting point), but below their degradation temperature. It is often desired to affect the thermal curing behavior within this window to mirror/suit the process or parts manufacture. Especially, semi-aromatic polyamides end-capped by PEPA, as well as PA46 and PA66 end-capped by PEPA, represent types of acetylenical polymers, which would benefit from an altered thermal curing behavior.”


CESI: A very interesting quote from the brand new Nexam patent application Embodiments section:

“Upon continuously increasing the temperature of a composition comprising an acetylenical cross-linker, such as a polyimide end-capped with PEP A, the carbon-carbon triple bonds in the system will eventually start to react with each other. The cross-linking is believed to include a sequence of exothermic reaction steps, including chain-extension, probably due to ethynyl-to-ethynyl reactions, of the material and subsequent cross-linking, probably due to pericyclic reactions, e.g. Diels- Alder reactions and ene -reactions. Typically, the curing temperature profile may be studied by differential scanning calorimetry (DSC), as well as melt rheology measurements. DSC will provide information regarding the temperature required to initiate curing, while melt rheology will provide insight into the curing onset as well as into the degree of chain-extension and cross-linking, as such reactions will increase the viscosity of the material.

The melt viscosity of a polymer affects its processablity. A too high melt viscosity will make it difficult to process the composition, as the shear forces to generate sufficient flow will be extremely high. Thus, polymers are often processed at temperatures well above their softening point (glass transition temperature – Tg – or melting point – Tm). An increased processing temperature results in lowered viscosity, which may facilitate processing. However, the degradation temperature for the polymer of concern sets an upper limit for the processing temperature. Thus, polymers are processed at temperatures in between the softening point and the degradation temperature.

In processing and curing of compositions comprising an acetylenical cross-linker, not only the temperature required for initiating curing, but also the curing rate is of interest. Provided that the curing rate not is too high, some curing may be tolerated already during processing without rendering further processing, such as extrusion and injection molding, impossible.

As can be seen in FIG. 1, a peak corresponding to exothermic heat flow, i.e. curing, is seen upon continuously increasing the temperature of an oligomer end-capped with an acetylenical cross-linker. The exact shape of the peak, e.g. the temperature at which cross-linking is initiated and completed, as well as the temperature curing maximum, will depend on the temperature ramping profile applied. While the temperature at which cross-linking is initiated in principle is constant, the shape of the exotermic peak will, at least partly, be affected, by the temperature ramping profile applied.

The curing temperature profile of different acetylenical cross-linkers is different. In general, the chemical groups next to the carbon-carbon triple bond will through electronic and steric effects determine the curing temperature profile.

Furthermore, the mobility of the system of which the acetylenical cross-linkers is part, will affect the curing temperature profile, but to less extent. As can be seen from FIG. 2 the curing temperature profile of low molecular weight PEPA end-capped phenylene diamine, a model system for studying curing of PEPA, is similar to the one of oligoimide end-capped with PEPA (cf. FIG 1).

The present inventors have surprisingly found that combination of PEPA on one hand and MEPA on the other provides systems having another thermal curing behavior than the two individual cross-linkers if cured separately (cf. FIG 3). While the onset temperature for the curing is approximately the same, DSC-scans indicate that the curing mechanism is another. Especially, the curing of PEPA is completed at significantly lower temperatures and the curing of MEPA, from one perspective, seems to require higher temperatures to complete. The relative molar amount of the two cross-linkers will affect the thermal curing behavior.

Further, as can be seen from FIG 4b exchanging the cross-linker on the polymer does not affect the ultimate melt viscosity. However, the onset of the viscosity increase is shifted and the time required to attain the ultimate viscosity is prolonged. The somewhat higher initial viscosity for the PA-MEPA compared to the PA-PEP A indicates that some curing of MEPA has taken place already during compounding of PA-MEPA. FIG 4c shows that it is not as effective in this case to exchange the cross-linker of the oligomer/molecule as it retards the reaction too much for the specific example. The high initial viscosity for the PA-MEPA//HD-MEPA compound indicates that curing of MEPA has taken place already during compounding of the system.

As can be seen from Fig. 5, it was possible to affect the curing rate also in an acetylenical, semi-aromatic polyamide, i.e. PEPA end-capped PPA. Replacing HD-PEPA with HD-MEPA increased the curing rate (measured as pressure build up) of PPA-PEPA. Replacing also the end-capper, i.e. PEPA, with MEPA resulted in vary rapid build up of pressure, indicating that curing of PPA-MEPA//HD-MEPA at 340°C is rapid process.

Thus, it has been revealed that combined use of two distinct acetylenical cross-linkers, having different thermal curing behavior, provides a way of altering, and in some applications even tuning, the thermal curing behavior for a given polymer.

Accordingly, such combinations may be used to provide system with cross-linkers having thermal curing behavior adapted to suit that processing temperature and degradation temperature of concern.”

The full patent Source link is attached here


Best regards, CESI

The author, Cutting Edge Science Invest, is a Nexam Chemical share holder. Cutting Edge Science Invest can not guarantee, or take into accountability, the content of truth and accuracy of the information in this article/post. Thus, Cutting Edge Science Invest requires that a possible reader gather complimentary information if any type of investment in the company described above is considered. Cutting Edge Science Invest provides personally biased information and at best also “general information and opinions”. The article/post does not contain professional investment advice.