Cryogenic Mechanical Alloying of Poly(methyl methacrylate) with Polyisoprene and Poly(ethylene-alt-propylene)

Abstract

Mechanical alloying is performed at cryogenic temperatures to incorporate polyisoprene (PI) or its hydrogenated analogue poly(ethylene-alt-propylene) (PEP) into poly(methyl methacrylate) (PMMA) as an example of high-energy solid-state blending. Morphological characterization of the blends by X-ray and electron microscopies confirms that the degree of dispersion of the constituent polymers improves with increasing milling time. Such dispersion in the PEP/PMMA blends is, however, ultimately compromised by phase coarsening when the materials are postprocessed above the PMMA glass transition temperature in the melt. Milling-induced PI cross-linking serves to suppress phase coarsening in PI/ PMMA blends, which remain relatively well-dispersed even after postprocessing. These blends are generally less fracture-resistant than the as-received PMMA due mainly to the accompanying reduction in PMMA molecular weight. Their optical transparency is observed to decrease dramatically with increasing PEP or PI concentration until they appear opaque. An overall improvement in blend properties by mechanical alloying is, however, anticipated upon judicious selection of more degradation-resistant polymers.

Addition of a Block Copolymer to Polymer Blends Produced by Cryogenic Mechanical Alloying

“…As t m is increased, the size of the PMMA domains decreases substantially to less than 1 µm after 5 h (Figure 7d) and less than 200 nm after 10 h (Figure 7g). Similar results have been reported for PI/PMMA blends without added copolymer, 22 implying that this difference in morphology is due to t m and not to the incorporation of copolymer. When the pressing temperature is increased to 125°C, however, the role of the MI copolymer becomes more apparent.…”

“…These PI domains become as large as 4 µm in size and contain PMMA inclusions measuring as large as 0.5 µm across. The PMMA inclusions are attributed to the MI copolymer, since PMMA inclusions are not observed 22 for identical samples without the copolymer. As t m is increased, the PI phase again adopts a semicontinuous morphology in PMMA.…”

“…Chemically specific X-ray images of the PI/PMMA and PI/MI/PMMA blends, as well as near-edge X-ray absorption fine structure (NEXAFS) spectra of the neat (unblended) PMMA and PI homopolymers and MI copolymer, were acquired on the microscope located at the National Synchrotron Light Source (Brookhaven National Laboratory). Detailed descriptions of the microscope 25,26 and its use in this study 22 are presented elsewhere. Electron microscopy of blends in which isoprene units were stained with the vapor of 2% OsO4(aq) for 90 min was performed on a Zeiss EM902 electron spectroscopic microscope operated at 80 kV and energy loss settings of 40-120 eV.…”

“…We have previously demonstrated that nanostructured polymer blends composed of poly-(methyl methacrylate) (PMMA) and either poly(ethylenealt-propylene) (PEP) or polyisoprene (PI) can be produced by cryogenic mechanical alloying. 21,22 Another crucial consideration in the mechanical alloying of polymers is the possibility that the chains will undergo scission and generate free radicals that could combine to induce (i) chemical cross-linking of a single polymer species or (ii) chemical coupling of different species. In the latter case, compatibilizing agents would be formed in situ and serve to stabilize nanostructured blends.…”

On the similarity of macromolecular responses to high-energy processes: mechanical milling vs. irradiation

“…In several companion works, we have recently reported the effect of high-energy mechanical milling on the molecular characteristics of poly(methyl methacrylate) (PMMA), poly(ethylene-alt-propylene) (PEP) and polyisoprene (PI) [14], as well as the utility of high-energy cryogenic mechanical alloying to blend PMMA with either PEP or PI [15][16][17], poly(ethylene terephthalate) (PET) with poly(oxybenzoate-r-2-6-oxynaphthoate) (Vectra 1 ) [18], and PET with recycled tire [19]. An unexpected implication of our findings is that the molecular response of polymers subjected to high-energy ball milling appears mechanistically similar to that resulting from high-energy irradiation.…”