Modification of polymethylhydrosiloxane by dehydrocoupling reactions catalyzed by transition metal complexes: Evidence for the preservation of linear siloxane structures |
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| Authors: | Ruzhi Zhang Zhengcheng Zhang Khalil Amine Robert West |
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| Institution: | (1) Organosilicon Research Center, Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA;(2) Chemical Technology Division, Argonne National Laboratory, Argonne, IL 60439, USA;(3) Present address: National Starch and Chemical Company, 10 Finderne Avenue, Bridgewater, NJ 08807, USA |
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| Abstract: | Polysiloxanes with pendant poly(ethylene oxide) side chains (4 were prepared by the dehydrocoupling reaction of poly(methylhydrosiloxane) (PMHS, 3 with 2-(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethoxy)ethanol (1 and poly(ethylene glycol) methyl ether (2 using a metal catalyst. Catalysts investigated were tin(II) 2-ethylhexanoate, Rh(Ph3P)3Cl, and Pd2(dba)3. The reaction of a cyclic siloxane, D4H, with 1 catalyzed by Pd2(dba)3 was also carried out to synthesize siloxane 6. The polysiloxanes were characterized by 1H NMR, 29Si NMR, FT-IR, and GPC. 29Si NMR study of these comb-like polysiloxanes revealed that there is a significant difference in the structure of the siloxane polymers prepared depending upon the catalyst. M, D, and T units were observed when tin(II) was used as a catalyst, but only M and D units were detected when Rh(Ph3P)3Cl or Pd2(dba)3 was employed. Furthermore, M and T units are negligible for the cyclic siloxane 3 using Pd2(dba)3. A mechanism is proposed to account for these observations. |
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| Keywords: | dehydrocoupling polymethylhydrosiloxane siloxane backbone cleavage transition metal complex catalysts |
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