CO₂-Induced Stereocomplex Formation of Stereoregular Poly(methyl methacrylate) and Microcellular Foams

Abstract

Crystalline stereocomplex formation of isotactic poly(methyl methacrylate) (it-PMMA) and syndiotactic poly(methyl methacrylate) (st-PMMA) induced by high-pressure CO2 at pressures in the 5−35 MPa range and at temperatures in the 30−110 °C range was demonstrated by means of differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) investigations as a function of treatment pressure, temperature, and the it-PMMA/st-PMMA ratio. At a constant it-PMMA/st-PMMA ratio, the melting temperature of the stereocomplexes was shown to increase with increasing treatment pressure and temperature. The amount of the stereocomplex formed by high-pressure CO2 was found to be higher than that by thermal annealing in bulk. The heat of melting of the stereocomplex was the highest for the 1/2−1/1 it-PMMA/st-PMMA ratio. Compared with amorphous PMMA, the crystalline stereocomplex induced by high-pressure CO2 contributes to the superior morphology of the microcellular foams obtained. For the CO2-treated polymer, the average cell size decreases and the average cell density increases as the amount of the stereocomplex that was formed increases.

Solid State Foaming of Poly(lactic acid) Blown with Compressed CO2: Influences of Long Chain Branching and Induced Crystallization on Foam Expansion and Cell Morphology

“…23,25,28,36,37 Figure 1 shows the DSC thermograms of L-PLA and B-PLA at AP and various CO 2 pressures. At AP, both L-PLA and B-PLA had a broad cold crystallization peak at around 124°C and a melting peak at around 150°C.…”

Assisted heterogeneous multinucleation and bubble growth in semicrystalline ethylene-vinyl acetate copolymer/expanded graphite nanocomposite foams: Control of morphology and viscoelastic properties

“…In accordance with the classical nucleation theory, the cell density and the bubble shape are affected by the foaming pressure or pressure sharp drop during foaming process. In all related researches, it has been demonstrated that the number of cells per unit volume increases and the average cell size decreases by subjecting the matrix to a larger pressure decline [14,15,18,25]. Contrary to the foaming pressure, the effects of foaming temperature on the cell morphology have not been understood precisely.…”

“…Similarly, there are some reports about clay reinforced nanocomposite foams based on semicrystalline polymers [5][6][7][8]. Moreover, microcellular foaming process is one of the techniques that have been studied for this purpose [9][10][11][12][13][14][15][16]. By rapid pressure quenching [17], melt blending using polymers with high glass tran-sition temperature (T g ) [4] and incorporating nanoclay into polymers [7], micron or submicron size cellular structures have been successfully obtained.…”

Thermodynamics and Kinetic Processes of Polymer Blends and Block Copolymers in the Presence of Pressurized Carbon Dioxide

“…Smaller spherulites have been observed for poly(L-lactic acid)/PMMA blends exposed to CO 2 at 0°C and 10 MPa for 1 h. [126] The CO 2 -induced crystallization improves the mechanical properties and increases the heat distortion temperature relative to cold-crystallized blends without loss of transparency. Mizumoto and co-workers [127][128][129] have studied the formation of crystalline stereocomplexes composed of stereoregular isotactic PMMA (iPMMA, semicrystalline) and syndiotactic PMMA (sPMMA, amorphous) upon exposure to scCO 2 . The heat of fusion and T m of the stereocomplex both increase substantially with increasing CO 2 pressure up to 10 MPa.…”

“…However, in some systems, crystalline structures can assist foaming. For example, the dissolution of CO 2 into a blend of iPMMA/sPMMA leads to the formation of crystalline stereocomplex structures, [127] which aid foaming by i) providing surfaces on which heterogeneous nucleation can proceed and ii) increasing the melt strength of the amorphous matrix to limit cell growth. The resulting cells are smaller (1.76 to 0.26 lm in diameter) and more dense (9.5 × 10 10 to 2.1 × 10 13 cells cm À3 ) in the crystallized blend than in amorphous sPMMA, as depicted in Figure 12.…”