Polycarbonate synthesis

ArOH Polycarbonate synthesis from bisphenol A and phosgene -... 

Polycarbonate synthesis by lipase-catalyzed polycondensation was demonstrated. Activated dicarbonate, 1,3-propanediol divinyl dicarbonate, was used as the monomer for enzymatic synthesis of polycarbonates.222 Lipase CA-catalyzed polymerization with a,co-alkylene glycols produced the polycarbonates with Mw up to 8.5 x 103. Aromatic polycarbonates with DP larger than 20 were enzymatically obtained from the activated dicarbonate and xylylene glycols in bulk.211... 

Gross, R.A. Kalra, B. Kumar, A. Polyester and polycarbonate synthesis by in vitro enzyme catalysis. Appl. Microbiol. Biotechnol. 2001, 55 (6), 655-660. 

Cyclic carbonate synthesis from epoxide and CO2 is one of the few industrial processes that use CO2 as a feedstock. The reaction proceeds in the presence of catalysts that are typically metal halides or tetraalkylammonium halides. The products (e.g. ethylene carbonate, which is an important intermediate of dimethyl carbonate) are utilized for polycarbonate synthesis via a non-phosgene, melt polymerization process. 

Following these results, Darensbourg et al. have continued the research and used other bifunctional Cr(salen) complexes as catalysts for polycarbonate synthesis. They observed that when a monofunctional Cr(salen) complex (5) was used to catalyze the reaction between epoxide and CO2, the product formed was cyclic carbonate. However, when a bifunctional Cr(salen) catalyst (6) was used, 79% selectivity towards the polycarbonate was obtained at 70 °C. The reason for this difference lies in the structure of the bifunctional catalyst, which provides steric hindrance in the epoxide ring-opening process to form the cyclic carbonate. Therefore, it can be inferred that spatial requirements in the active site of the metal catalyst determine the selectivity for the kinetic polymer product over the thermodynamically more stable cyclic carbonate product. 

Garcia-Martin M.G., Ruiz Perez R., Benito Hernandez E., Espartero J.L., Munoz-Guerra S., Galbis J.A., Carbohydrate-based polycarbonates. Synthesis, structure, and biodegradation studies. Macromolecules, 38, 2005, 8664-8670. 

However, acyl chlorides are too expensive for industrial processes. An exception is phosgene, COCI2, which is the basis of the polycarbonate synthesis. 

Early developments in aliphatic and aromatic polycarbonates. The first significant documentation of aromatic polycarbonates synthesis began with Einhom [24]. He reacted hydroquinone, resorcinol, and catechol with phosgene in a pyridine solution, obtaining linear polymers from hydroquinone (an insoluble crystalline powder that melted above 280°C) and resorcinol (an amorphous material that melted with decomposition at 190 to 200°C), and a cyclic carbonate from catechol. Subsequent research was focused on finding more efficient preparation methods and on improving material properties [25]. 

Melt polymerization of bisphenols (bisphenol A, bisphenol P, bisphenol AF, and bisphenol Z) with diphenyl carbonate in CO2 with several catalysts have been achieved (91,92). Polymers with number-average molecular weights ranging from 2.2 X 10 to 1.1 X 10 g/mol M = 4.5 x 10 to 2.7 x 10 ) were obtained over a range of reaction temperatures (180-250°C) and CO2 pressures [20.7-24.1 MPa (207-241 bar)]. Reaction conditions were chosen to ensure efficient removal of solubilized condensate (phenol) without extracting the reactants (diphenyl carbonate). Polycarbonate synthesis from bisphenol A and diphenyl carbonate catalyzed by tetraphenylphosphonium tetraphenyl borate were also performed in SCCO2 (93) (eq. (9)). 

SCHEME 2.2 CD-based polycarbonates synthesis from carbonates and polyols. (Aeiapted... 

Typical chemical systems are fast reactions between two difimctional monomers, AXA + BYB. The first monomer (diamine, bisphenolate) is dissolved in a water solution (in alkaline media in both cases), and the other monomer, with low water solubility (acid chloride, phosgene), is usually dissolved in an organic solvent. Either the neutral form of AXA is in an appreciable amount (in the case of amines), or a phase transfer catalyst is needed (as in polycarbonate synthesis), since ionized forms will not dissolve in the organic phase. A decrease in the pH is often used to quench interfacial polyamidation. 

Sugimoto, H. Ohshima, H. Inoue, S. Alternating Copolymerization of Carbon Dioxide and Epoxide by Manganese Porphyrin The First Example of Polycarbonate Synthesis from 1-atm Carbon Dioxide. J. Polym. Set, Part A Polym. Chem. 2003, 41,3549-3555. 

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