Semi‐Crystalline Polyetherimide Microparticles via Liquid‐Liquid Phase Separation and Precipitation

Abstract

A novel approach for production of polyetherimide (PEI) microparticles by liquid–liquid phase separation (LLPS) and precipitation is demonstrated and the effect of the used solvents acetophenone and dimethyl phthalate on the obtained powders is outlined. Interestingly, the method allows one to produce semi‐crystalline particles, while PEI is known to be hard to crystallize and typically obtained in amorphous form. To get a deeper understanding of the phase behavior of the polymer‐solvent systems, cloud point curves in dependence on system composition are determined. The obtained particles are thoroughly characterized. They are highly semi‐crystalline, as proven by DSC and X‐ray diffraction and are an ideal novel feedstock for powder bed fusion of polymers with laser beam (PBF‐LB/P). Polymorphism and, thus, thermal characteristics like the melting point, can be tuned by the used solvent. After heating the precipitated powder samples above their melting temperature and subsequent cooling fully amorphous polymer is obtained, which is assessed to be advantageous with respect to mechanical properties (toughness) of the PBF‐LB/P‐produced component from this novel feedstock.

Control of Particle Properties in Thermally-Induced Precipitation of Polyetherimide

“…The structural formula of the repetition unit of the polyetherimide is given in Figure 2. The previously identified [21] acetophenone (ρ = 1.03 g cm −1 , 99%, VWR, Atlanta, GA, USA) was used as the moderate solvent.…”

“…The structural formula of the repetition unit of the polyetherimide is given in Figure 2. The previously identified [21] acetophenone (ρ = 1.03 g cm −1 , 99%, VWR, Atlanta, GA, USA) was used as the moderate solvent. For the post-processing steps, i.e., filtration and washing, denatured ethanol (96%, VWR, United States) was used.…”

“…Based on the solvent screening study [21], polymer concentrations of 10 and 15 wt.% were chosen because the obtained particles showed preferable properties. The complete two-level factorial plan is shown in Table 2, giving the total number of experiments investigated.…”

“…More recently, we were able to demonstrate that granule feedstock of amorphous polyetherimide (PEI), a high-performance thermoplast, can be transformed to semi-crystalline microparticles by thermal precipitation from acetophenone and dimethyl phthalate [21]. The aforementioned solvents were shown to impact the obtained thermal and structural product properties: a higher induced melting temperature and crystallinity were observed for the product precipitated from dimethyl phthalate.…”

“…Particles precipitated from acetophenone showed a somewhat superior shape and particle size distribution with respect to the desired application. The experimental setup used in [21] was based on small-scale autoclaves showing several restrictions regarding the variation of important process parameters for thermal precipitation, such as a well-defined stirring or the variation of the cooling rate. Consequently, the bulk solid properties of the powders obtained, in particular the particle morphology, may not yet be optimal with respect to, e.g., shape, surface texture or particle size distribution.…”