Catalytic Synthesis and Characterization of Biodegradable ...
Catalytic Synthesis and Characterization of Biodegradable ...
Catalytic Synthesis and Characterization of Biodegradable ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Chapter 1<br />
provide polycarbonates. (Figure 1.2.9). 28 They use (Salen)M III X as a catalyst for the<br />
copolymerization <strong>of</strong> CO2 <strong>and</strong> cyclohexene oxide in the presence <strong>of</strong> N-MeIm. At 80 <strong>and</strong><br />
58.5 bar CO2 pressure, (Salen)M III X alone copolymerized cyclohexene oxide <strong>and</strong> carbon<br />
dioxide to poly(cyclohexylenecarbonate), void <strong>of</strong> polyether linkages, with a TOF <strong>of</strong> 10.4 h-1.<br />
1.2.4 Lanthanide-Based Catalysts<br />
Figure 1.2.9. (Salen)M III X catalyst for epoxides ring opening.<br />
Yttrium, aluminum, rare-earth metals, <strong>and</strong> combinations <strong>of</strong> multiple metal reagents have<br />
shown activity for the copolymerization <strong>of</strong> epoxides <strong>and</strong> CO2. For example, PO–CO2<br />
copolymerization was effected by a rare-earth metal system comprised <strong>of</strong> yttrium<br />
tris[bis(2-ethylhexyl)phosphate], AliBu3, <strong>and</strong> glycerol. The PPC produced contained only<br />
10–30% carbonate linkages, although molecular weights <strong>of</strong> up to 476000 gmol -1 were<br />
achieved. 31 This system also exhibited activity for the alternating copolymerization <strong>of</strong> CO2<br />
with epichlorohydrin 32 <strong>and</strong> glycidyl ether monomers. 33 Other rare-earth metal systems<br />
consisted <strong>of</strong> yttrium carboxylates [Y(CO2CF3)3 or Y(CO2RC6H4)3 where R is H, OH, Me, or<br />
NO2], ZnEt2, <strong>and</strong> glycerine. 34-36 The alternating copolymerization <strong>of</strong> CO2 <strong>and</strong> PO yielded PPC<br />
with up to 98.5% carbonate linkages, turnover frequencies up to 2.5 h -1 , <strong>and</strong> molecular<br />
weights reaching 100 000 gmol -1 . CHO–CO2 copolymerization produced PCHC with 100%<br />
carbonate linkages, molecular weights <strong>of</strong> 19000–330000 gmol -1 , <strong>and</strong> Mw/Mn’s <strong>of</strong> 3.5–12.5. It<br />
must be noted that control experiments indicated that ZnEt2, but not Y(CO2CF3)3, was<br />
essential for polymerization. Finally, ternary catalysts composed <strong>of</strong> Nd(CO2CCl3)3, ZnEt2,<br />
<strong>and</strong> glycerol were also reported to copolymerize PO <strong>and</strong> CO2. 37<br />
‐ 10 ‐