Supercritical carbon dioxide, polymerisation

Stassin F, Jerome R (2003) Effect of pressure and temperature upon tin aUcoxide-promoted ring-opening polymerisation of s-caprolactone in supercritical carbon dioxide. Chem Commun 232-233... 

Villarroya, S., Thurecht, K.J., and Howdle, S.M. 2008. HRP-mediated inverse emulsion polymerisation of acrylamide in supercritical carbon dioxide. Green Chemistry, 10 863-67. 

Polymerisation in supercritical carbon dioxide has generated great interest in recent years for a number of reasons, including its environmentally benign nature as a solvent and the ease of removing it from products at the end of a reaction, as well as more subtle issues such as the tuneability of its density and solvation... 

Villarroya, S., Thurecht, K.J., and Howdle, S.M. (2008) HRP-mediated inverse emulsion polymerisation of acrylamide in supercritical carbon dioxide. Green Chem., 10 (8), 863-867. Schomberg, D.S., Salzman, M., and Stephan, D. (1993) Enzyme Handbook vol. 7, Springer-Verlag, Berlin Heidelberg, pp. 1-6. 

Using supercritical carbon dioxide (scCOi), the polymerisation of L-lactide by immobilised CALB was achieved at 65 "C in a biphasic media system, where the supercritical phase coexists with a liquid organic phase (melted monomer), and the growing poly(L-lactide) (PLLA) chains are soluble. A semicrystalline polymer with MW up to 12,900 g/mol was obtained, with a monomer conversion rate dependent on enzyme concentration and its initial water activity [90]. 

A radical polymerisation can be carried out with a range of polymerisation techniques. Those with only a single phase present in the system are bulk and solution polymerisations, involving the monomer, a solvent if present and the initiator. By definition, the formed polymer in a bulk or solution polymerisation remains soluble (either in the monomer or the solvent). A precipitation polymerisation is one in which the system starts as a bulk or solution polymerisation, but the polymer precipitates from the continuous phase to form polymer particles which are not swollen with monomer. A precipitation polymerisation when the polymer particles swell with monomer is called dispersion polymerisation apart from polymerisation in the continuous phase, the polymer particles have an additional locus of polymerisation, and the particles in these systems are colloidally stabilised. Precipitation polymerisation is often performed in an aqueous medium (e.g. acrylonitrile polymerisation in water). Dispersion polymerisation is usually performed in organic solvents that are poor solvents for the formed polymer (supercritical or liquid carbon dioxide may also be used as a continuous medium for dispersion polymerisation). 

Supercritical carbon dioxide as a medium for the ring-opening polymerisation of lactones and lactides and a processing aid for aliphatic polyesters... 

Substitution of supercritical carbon dioxide for organic solvents in the macro-molecular engineering of aliphatic polyesters is also worth being considered for meeting the environmental concerns raised by industrial activities. Implementation of organic synthesis (Oakes, 2001) and polymerisation in its medium (Wells et al, 2001) has received increasing attention. Carbon dioxide is environmentally friendly, non-flammable, non-toxic and very cheap with easily accessible critical parameters (Tc = 31 °C Pc = 73.8 bar). 

Ring-opening polymerisation of lactones and lactides in supercritical carbon dioxide... 

Kinetic profile of extraction of tin residues after ring-opening polymerisation in supercritical carbon dioxide initiated by dibutyltin dimethoxide... 

Microparticles can be produced by a simple technique that consists of spraying a polymer, e.g., PLLA, solution in dichloromethane (or dimethylsulfoxide), through a nozzle into a reactor filled with supercritical carbon dioxide (Reverchon et al, 2000). This process is known as supercritical antisolvent precipitation (SAS). The experimental parameters have a limited influence on the particle size (1-4 /im). A modified version of the process, known as the SAS-EM process, allows nanoparticles of a controlled size (30-50 nm) to be produced (Chattopadhay et al., 2002). In order to restrict the use of an organic solvent. Pack and co-workers fed the SAS reactor with a solution of PLLA prepared by homogeneous ring-opening polymerisation in supercritical HCFC-22 (Pack et al, 2003a). 

Supercritical carbon dioxide turns out to be a very efficient solvent for the exfoliation of lamellar nanoelays, particularly in the case of in situ polymerisation (Jerome et al, 2001). JCTome et al initiated the eCL polymerisation in supereritieal earbon dioxide by dibutyltin dimethoxide in the presence of montmoriUonite organomodified by the exchange of the Na counterions by... 

In order to overcome the drawbacks related to metal contamination of polyesters prepared in the presence of tin and aluminium alkoxides, supercritical carbon dioxide is a promising polymerisation medium in order to prepare biomedical grade aliphatic polyesters, due to the possibiUty to extract the... 

Bratton D, Brown M, Howdle S M (2003), Suspension polymerisation of L-lactide in supercritical carbon dioxide in the presence of a triblock copol)mier stabilizer , Macromolecules, 36, 5908-5911. 

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