Solid-State Polymerization of Polycarbonates Using Supercritical CO2
TL;DR: In this article, the authors report the extension of the crystallization process with supercritical CO 2 to granules or beads of low molecular weight polycarbonate in an effort to create a material that can undergo slid-state polymerization without using toxic organic solvents.
Abstract: We report the extension of the crystallization process with supercritical CO 2 to granules or beads of low molecular weight polycarbonate in an effort to create a material that can undergo slid-state polymerization without using toxic organic solvents
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TL;DR: Carbon dioxide is a clean and versatile solvent for the synthesis and processing of a range of materials as discussed by the authors, with particular attention being given to the formation of polymers with well defined morphologies.
Abstract: Carbon dioxide is a clean and versatile solvent for the synthesis and processing of a range of materials. This review focuses on recent advances in polymer synthesis and processing using liquid and supercritical CO2. The synthetic techniques discussed include homogeneous solution polymerisation, precipitation polymerisation, dispersion and emulsion polymerisation, and bulk polycondensation. The formation of porous polymers and polymer blends is also considered, and the specific advantages of CO2 in these processes are evaluated in each case. The use of CO2 as a solvent for polymer processing is reviewed from a materials perspective, with particular attention being given to the formation of polymers with well defined morphologies. The variable solvent strength associated with supercritical fluids has been utilised in areas such as polymer fractionation and polymer extraction. Plasticisation phenomena have been exploited for the impregnation and heterogeneous chemical modification of polymeric materials. The formation of microcellular polymer foams by pressure induced phase separation is considered, as is the use of CO2 for polymer particle formation, spray coating, and microlithography. The aim of the review is to highlight the wide range of opportunities available to the materials chemist through the use of carbon dioxide as an alternative solvent.
885 citations
TL;DR: In this paper, experimental and theoretical studies of solubility and viscosity of several polymer melts are discussed in detail, and detailed attention is also given to recently reported applications along with aspects related to polymer processing.
563 citations
TL;DR: Small changes in temperature and pressure cause dramatic changes in the density, viscosity, and dielectric properties of CO2, making it a tunable solvent that can be tailored for various applications.
Abstract: CO(2) is a good solvent for many substances when compressed into its liquid or supercritical fluid state. Above the critical temperature and critical pressure (T(c)=31 degrees C, P(c)=73.8 bar, see Figure 1 for the phase diagram for CO(2)), CO(2) has both gaslike viscosities and liquidlike densities. These moderate critical conditions allow CO(2) to be used within safe commercial and laboratory operating conditions. Small changes in temperature and pressure cause dramatic changes in the density, viscosity, and dielectric properties of CO(2), making it a tunable solvent that can be tailored for various applications. Combined, these unique properties make CO(2) a "solvent of choice" for the new millennium.
165 citations
TL;DR: The conventional solution to melt polymerization techniques stop at a low or medium molecular weight product, due to problems arising from severe increase of the melt viscosity and operating temperatures as discussed by the authors.
150 citations
TL;DR: In this paper, a poly(bisphenol A carbonate) was synthesized by solid-state polymerization (SSP) using supercritical CO2 to induce crystallinity in low molecular weight polycarbonate beads.
Abstract: Poly(bisphenol A carbonate) was synthesized by solid-state polymerization (SSP) using supercritical CO2 to induce crystallinity in low molecular weight polycarbonate beads. The CO2-induced crystallization was studied as a function of time, temperature, molecular weight, and pressure. There was an optimum temperature for crystallization which depended on the molecular weight of the polymer. The molecular weight and percent crystallinity of the polymer produced by SSP were determined as a function of time and radial position in the bead. The molecular weight and percent crystallinity were strong functions of the particle radius, probably because of the slow diffusion of phenol out of the polymer particles. Nitrogen and supercritical CO2 were used as sweep fluids for the SSP process. The polymerization rate was always higher in supercritical CO2 at otherwise comparable conditions. We hypothesize that supercritical CO2 plasticizes the amorphous regions of the polymer, thereby increasing chain mobility and the...
97 citations
References
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TL;DR: In this article, the mechanism of action of organic nucleating agents such as sodium benzoate and its derived salts completely differs from the generally accepted model, at least in the case of polyesters.
Abstract: Several attempts1–5 have been made to control the rate of crystallization and the morphology by the addition of very finely-divided substances which promote abundant nucleation. However, these studies have mostly been carried out on an empirical basis and, except in a few cases (self-seeding6, epitaxy2–5), the mechanism of action of these nucleating agents is poorly understood despite several attempts at modelling1,2. This is particularly so in the case of most technical nucleating agents such as mica, talc and organic salts. We report here that the mechanism of action of organic nucleating agents such as sodium benzoate and its derived salts completely differs from the generally accepted model, at least in the case of polyesters. The nucleating agent reacts as a true chemical reagent with the molten macromolecules and produces ionic end groups which constitute the true nucleating species.
122 citations
TL;DR: In this paper, supercritical carbon dioxide readily induces crystallization in bisphenol A polycarbonate and the degree of crystallinity increases sharply as the CO2 pressure is raised from 100 to 300 atm but levels off thereafter.
Abstract: Supercritical carbon dioxide readily induces crystallization in bisphenol A polycarbonate. Crystallization begins within one h of exposure to the CO2 at temperatures and pressures as low as 75°C and 100 atm. The degree of crystallinity increases sharply as the CO2 pressure is raised from 100 to 300 atm but levels off thereafter. This behavior is likely due to a minimum in the Tg of the polycarbonate/CO2 mixture owing to the opposite effects of the pressure on the Tg of the polymer and on the equilibrium weight fraction of CO2 absorbed. Percent crystallinities of over 20%, comparable to that achieved using acetone or other organic liquids, have been obtained after 2 h exposure to supercritical CO2. Since polycarbonate degasses quickly and quantitatively at ambient temperature and pressure, the high Tg of bisphenol A polycarbonate can be regained in the crystallized material without further vacuum treatment.
116 citations
TL;DR: In this article, a linear correlation was established between these two physical variables and from this an enthalpy of fusion for the polycarbonate crystal of 26 Kcal was deduced.
Abstract: Several measurements of the heat of fusion and of specific volume were carried out on bisphenol A-polycarbonate of varying degrees of crystallinity. A linear correlation was established between these two physical variables and from this an enthalpy of fusion for the polycarbonate crystal of 26 Kcal. was deduced.
39 citations
TL;DR: In this article, it was reported that poly(aryl carbonate) can undergo chain extension in the solid state to substantially high molecular weight polymers, and the increase in molecular weight was also accompanied by an increase in the polymer cryustallinity.
Abstract: It is reported that, under carefully controlled conditions, poly(aryl carbonate) can undergo chain extension in the solid state to substantially high molecular weight polymers. The increase in molecular weight was also accompanied by an increase in the polymer cryustallinity
30 citations
TL;DR: In this paper, solid state polycondensation (SSP) crystallizes polycarbonate in an orthorhombic configuration with a = 12.1 A, b = 10.5 A and c = 22.0 A.
19 citations