Supercritical carbon dioxide copolymerization

Thus far, the discussion of polymerizations conducted in carbon dixiode has centered on systems where CO2 acts only as a solvent for the polymerization. However, there are also examples of polymerization systems where CO2 acts as a comonomer. Most notable among these in the context of this chapter is the coploymerization of CO2 and epoxides. The copolymerization of propylene oxide and carbon dioxide was conducted in SCCO2 using a heterogeneous zinc catalyst [142]. Additionally, Beckman and co-workers have shown that a soluble, fluorinated ZnO-based catalyst can be effectively utilized to promote the copolymerization of CO2 and cyclohexene oxide [143]. These examples indicate that supercritical carbon dioxide can be viable as both a solvent comonomer in polymerization reactions. 

By proper selection of initial conditions or parameter values, the equations of Figures 12.2 and 12.3 can represent linear homopolymerization, linear copolymerization, or nonlinear copolymerization. Examples for the specific case of conventional (noncontrolled) copolymerization with crosslinking can be found in Vivaldo-Lima et al. [44-46]. As a matter of fact, the simulation profiles for homogeneous linear copolymerization of TFE and VAc in supercritical carbon dioxide (SC-CO2) shown in Chapter 15 (Fig. 15.6) were obtained with this model by setting k =... 

Case Study i Homogeneous Homo- and Copolymerizations IN scCOj The first case analyzed [42] was the homogeneous homopolymerization of dihydroperfluo-rooctyl acrylate (FOA) in supercritical carbon dioxide at the same conditions reported by DeSimone et al. [45]. Once the model was implemented, parameter sensitivity analyses were carried out. The first objective was to test the model implementation, namely, to verify that the expected trends were predicted by the model. The second objective of these... 

AHM Ahmed, T.S., DeSimone, J.M., and Roberts, G.W., Copolymerization of vinylidene fluoride with hexafluoropropylene in supercritical carbon dioxide. Macromolecules, 39, 15, 2006. 

I g Catalytic Polymerization of Ol ns in Supercritical Carbon Dioxide Table 8.11 Results of copolymerizations of ethylene and methyl acrylate in compressed carbon dioxide. 

Acrylamide monomer is a white crystal, available commercially as a 50 wt % aqueous solution. Acrylamide monomer can be polymerized to a very-high-molecular-weight (lO -lO g/mole) homopolymer, copolymer, or terpolymer. Polyacrylamide (PAM) is a nonionic polymer. The anionic polyacrylamide species can be obtained from the hydrolysis of the amide (—CONH ) functional group of the homopolymer, or from the copolymerization of acrylamide with an anionic monomer, such as acrylic acid (AA) or 2-acrylamino 2-methyl propane sulfonic acid (AMPS). Acrylamide can be copolymerized with a cationic monomer, such as dimethyl diallylammonium chloride (DMDAAC) or acryloyloxyethyl trimethyl ammonium chloride (AETAC), to form the cationic acrylamide polymer. Acrylamide can simultaneously react with anionic and cationic monomers to form a polyampholyte. The acrylamide homopolymer, copolymers, and terpolymers are synthesized (1-20) by free radicals via solution or emulsion or other polymerization methods. F. A. Adamsky and E. J. Beckman (21) reported the inverse emulsion polymerization of acrylamide in supercritical carbon dioxide. The product classes of acrylamide polymers include liquid, dry, and emulsion. 

IHA Ihata, 0., Kayaki, Y., and Ikariya, T., Aliphatic poly(methane-amine)s synthesized by copolymerization of aziridines and supercritical carbon dioxide. Macromolecules,... 

Giuronett and Mecking carried out copolymerizations of ethylene with 1-olefins in supercritical carbon dioxide by electron poor nickel complexes [385]. The catalyst can be illustrated as follows ... 

Dong, Q. and Liu, Y. 2003. Styrene-assisted free-radical graft copolymerization of maleic anhydride onto polypropylene in supercritical carbon dioxide. 

Supercritical carbon dioxide represents an inexpensive, environmentally benign alternative to conventional solvents for chemical synthesis. In this chapter, we delineate the range of reactions for which supercritical CO2 represents a potentially viable replacement solvent based on solubility considerations and describe the reactors and associated equipment used to explore catalytic and other synthetic reactions in this medium. Three examples of homogeneous catalytic reactions in supercritical CC are presented the copolymerization of CO2 with epoxides, ruthenium>mediated phase transfer oxidation of olefins in a supercritical COa/aqueous system, and the catalyic asymmetric hydrogenation of enamides. The first two classes of reactions proceed in supercritical CO2, but no improvement in reactivity over conventional solvents was observed. Hythogenation reactions, however, exhibit enantioselectivities superior to conventional solvents for several substrates. 

Darensbourg, D. J., Stafford, N. W. andKatsurao, T. (1995) Supercritical carbon dioxide as solvent for copolymerization of carbon dioxide and propylene oxide using a heterogeneous zinccarboxylate catalyst, J. Molecular Catalysis A Chemical 104, L1-L4. 

Hile DD, Pishko MV. Emulsion copolymerization of D,L-lactide and glycolide in supercritical carbon dioxide. J Polym Sci Part A Polym Chem 1999 39 562-70. 

PMMA is mostly homo- or copolymerized in aliphatic hydrocarbon dispersions, using different rubbers, polysiloxanes, long-chain polymethacrylates, or different block and graft copolymers as stabilizers. An interesting variant of the dispersion polymerization of acrylates is carried out in supercritical carbon dioxide [45,46]. Transition-metal-mediated living radical suspension polymerization is discussed in Ref. [47]. Common radical initiators are described in Refs. [48] and [49]. The entire field is reviewed extensively in Ref. [50]. 

TFE and monomer (I) were also copolymerized in supercritical carbon dioxide using a free radical initiator such as bis(perfluoro-2-propoxypropionyl)peroxide (III) at 35°C (the half-life time of the initiator is 40 minutes at 35°C) [9], The decomposition of the initiator proceeds through a single-bond homolysis mechanism [10], resulting in the formation of perfluorinated end group that yields thermally stable polymers [9] (Scheme 16.1). The reaction conditions and properties of the copolymers of (I) and TFE obtained in supercritical carbon dioxide are shown in Table 16.1. PTFE is crystalline, so that when the amount of TFE increases in copolymers, the polymer has some microcrystalline regions. The polymers obtained in carbon dioxide have similar properties with the commercial polymers. 

Table 5.64. Copolymerization of Tetrafluoroethylene and Perfluoropropylvinyl Ether in Supercritical Carbon Dioxide ...

Supercritical carbon dioxide (SCCO2) was employed for the first time to prepare polyesters via ROP of lactones. Lipase-catalyzed ROP of e-CL proceeded to give a polymer (PCL) with molecular weight higher than 10". Copolymerization of e-CL with DDL afforded a random copolyester. The enzymatic polycondensation between divinyl adipate and 1,4-butane diol also took place to produce the corresponding polyester [73]. Later, a similar study on ROP of e-CL in SCCO2 followed [74]. 

---