Synthesis, Characterization, and Expansion of Poly(tetrafluoroethylene-co-hexafluoropropylene)/Polystyrene Blends Processed in Supercritical Carbon Dioxide

Abstract

Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP)/polystyrene blends were prepared by the heterogeneous free-radical polymerization of styrene in supercritical (SC) CO2-swollen FEP substrates. Volume incorporations of up to 50% polystyrene were achieved, and the composition and phase morphology of the blends were controlled by varying the styrene monomer concentration and reaction time. The crystallinity and glass transition temperature of the FEP substrate are unaffected by the addition of the polystyrene component, indicating that polymerization occurs exclusively in the amorphous phase and that the polymers are immiscible. The molecular weight of the polystyrene formed within the FEP substrate is significantly higher than that which forms in the SC CO2 phase outside of the substrate. Attempts were made to prepare composite foams by saturation of the blends with SC CO2 and subsequent rapid depressurization. At lower temperatures (conditions under which polystyrene foams) the crystalline domains of FEP prevent expansion. At higher temperatures, in addition to expansion, large-scale phase segregation of the blends occurs.

CO2‐assisted polymer processing: A new alternative for intractable polymers

“…The crystallinity of the virgin polymer in this case is around 41.38%, using 92.94 J/g as the enthalpy of fusion for 100% crystalline FEP. 31 This value is very similar to that observed in the samples processed with and without CO 2 (40.37 and 37.0%, respectively), and it appears not to be affected in a significant way by the melting process. This general behavior is a consequence of the inherently larger processability of FEP that, despite the high molecular weight, does not restrict the recrystallization process, so that most of the crystallinity in the sample can be recovered after melting.…”

Quantifying Plasticization and Melting Behavior of Poly(vinylidene fluoride) in Supercritical CO2 Utilizing a Linear Variable Differential Transformer

“…18 In the solid state, supercritical CO 2 plasticization has been employed to enhance the solubility of styrene in poly(tetrafluoroethylene-cohexafluoropropene) followed by in situ polymerization of styrene to thereby produce polymer-polymer composites. 19 Compressed CO 2 was found to facilitate the crystallization of methyl-substituted poly(aryl ether ether ketone) and tert-butyl-substituted poly(ether ether ketone) (tBuPEEK), which normally do not undergo crystallization upon annealing. 20,21 Related to these applications are investigations of CO 2 polymer plasticization, with most studies focusing on amorphous polymers.…”

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

“…[210] Recall that blend compositions can be tuned by controlling parameters such as the exposure and reaction times, CO 2 pressure, temperature, and monomer/initiator concentrations. [203,207,[211][212][213] A decisive consideration here is that the blend composition is not limited by the solubility of the monomer in the fluid or matrix phase, since polymerization depletes the monomer reservoir and permits more than the equilibrium concentration of the monomer to penetrate into the polymer substrate. [201,202,207,214,215] The resulting blends can be further modified through additional chemical means such as chemical crosslinking and surface sulfonation; [201] alternatively, the polymerization can be restricted to the substrate surface, thereby yielding a grafted surface layer.…”

“…In one case, it has been observed that grafting poly(acrylic acid) (PAA) to iPP does not lead to any discernible changes in T m and the crystallinity of the iPP substrate (since the grafting reaction is limited to amorphous iPP regions). [212] Although the crystal structure of the substrate polymer remains largely unaffected by the incorporation of grafted chains, [202,211] accompanying reductions in T m have been reported. [216] Morphological analysis [202] of CO 2 -impregnated polymer blends reveal that polymerized PS resides in amorphous regions of HDPE, as well as throughout existing spherulites (Fig.…”