Supercritical carbon dioxide crosslinking

Rinki K, Dutta PK (2008) Preparation of genipin crosslinked chitosan scaffolds using supercritical carbon dioxide (sc. CO2). Asian Chitin J 4 43 8... 

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 =... 

S. Kurosawa, A.S. Teja, J. Kowahk, and L. Tolbert, Supercritical carbon dioxide processing of conducting composites of polypyrrole and porous crosslinked polystyrene. Polymer, 47(9), 2997-3004 (2006). 

B. Wang, M. Wang, Z. Xing, H. Zeng, G. Wu, Preparation of radiation crosslinked foams from low-density polyethylene/ethylene vinyl acetate (LDPE/EVA) copolymer blend with a supercritical carbon dioxide approach. J. Appl. Polym. Sci. 127, 912-918 (2013)... 

A parallel study has reported the synthesis of crosslinked polymer microspheres in supercritical carbon dioxide [54]. Heterogeneous free-radical polymerization of divinyl benzene and ethyl benzene were carried out at 65 C and 310 bar using AIBN initiator to form the crosslinked polymer. It is shown that in the absence of surfactants as stabilizers, polymerization of the mixture containing 80 % divinyl benzene + 20 % ethyl benzene leads to poly(divinylbenzene) microspheres of about 2.4 micron diameter [Figure 14]. In the presence of a carbon dioxide-soluble diblock copolymer as a stabilizer, polymerization of the mixture with the same monomer ratio proceeds as an emulsion and lead to smaller crosslinked particles (ca. 0.3 micron). Thermal analysis shows that the crosslinked polymer that is formed from these polymerizations is stable up to 400 C. 

Figure 14. Polymer particles (ca. 2.4 micron) of crosslinked divinyl benzene can be produced via polymerization in supercritical carbon dioxide at 65 °C and 310 bar using AIBN as initiator. [Adapted from ref. 54].

Launch, J. C. (1988), The crosslinking polymerization of styrene and methylmethacrylate in supercritical carbon dixoide, Ph. D. Thesis, University of Akron, Akron, Ohio, USA. (Thesis Advisor H. M. Cheung), Cooper, A. I., Hams, W. P., and Holmes, A. B. (1998) Synthesis of cross-linked polymermicrospheres in supercritical carbon dioxide, Macromol. Rapid. Commun. 19, 353-357. 

Using of p-toluenesulfonic acid (p-TSA) or SiCiyC H OH mixture as catalysts for the reaction [16]. The reaction was performed in liquid and supercritical carbon dioxide in the presence of triethyl orthoformiate at presstrre of 20 MPa and temperature of 20 and 50°C with the polymer yield arotmd 20%. DTG-analysis revealed 5% weight loss of the polymer at 400°C with the weight of carbonized residue of 80% after heating at 750°C. When heated at 300°C, the process of crosslinking in the samples oc-... 

KOJ Kojima, M., Tosaka, M., Funami, E., Nitta, K., Ohshima, M., and Kohjiya, S., Phase behavior of crosslinked polyisoprene rabber and supercritical carbon dioxide, J. Supercrit. Fluids, 35, 175, 2005. 

The types of processes that are reviewed in this section are those that have an elevated temperature as a common denominator and, by the use of this, they target the thermally labile nature of the sulfur-sulfur bonds in the crosslinks. There are quite a few examples where chemical agents have also been used in the process to assist in the devulcanisation of the rubber. In these cases, the chemical agents that have been chosen have often been similar to those that are used in the mechanical-chemical processes (Section 4.5) and often their assimilation into the rubber matrix has been assisted by solvents that have a high affinity for both the rubber and the chemical agents. Other processes of this type have employed solvents (e.g., supercritical carbon dioxide (CO2), supercritical water, alcohols and so on) on their own, without any other chemicals, and sometimes they have reacted with the crosslinks and/or the polymer chains. 

Figure 7.2 Supercritical fluid chromatogram of polymer additives listed in Tables 7.1 and 7.2. Conditions 10 m x 50 pm id fused-silica capillary column, crosslinked methylpolysiloxane stationary phase (0.25 pm film thickness) carbon dioxide mobile phase at 140 "C 15 - 35 MPa at 0.3 MPa/min after an initial 12 minutes isobaric period ...

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