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Chemoselective polymerization control: from mixed-monomer feedstock to copolymers.

Romain DC, Williams CK - Angew. Chem. Int. Ed. Engl. (2014)

Bottom Line: A novel chemoselective polymerization control yields predictable (co)polymer compositions from a mixture of monomers.Using a dizinc catalyst and a mixture of caprolactone, cyclohexene oxide, and carbon dioxide enables the selective preparation of either polyesters or polycarbonates or copoly(ester-carbonates).The selectivity depends on the nature of the zinc-oxygen functionality at the growing polymer chain end, and can be controlled by the addition of exogeneous switch reagents.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Imperial College London, London SW7 2AZ (UK).

No MeSH data available.


Changes to the intensity of IR resonances during PCL-PCHC formation (Table 1, run 5). The plot shows the ROP of CL, the addition of CO2, and the ROCOP of CHO/CO2.
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fig05: Changes to the intensity of IR resonances during PCL-PCHC formation (Table 1, run 5). The plot shows the ROP of CL, the addition of CO2, and the ROCOP of CHO/CO2.

Mentions: A logical next step was to investigate 1 as a catalyst for sequential ROP and ROCOP (Table 1, runs 5–6) by exploiting this chemoselective polymerization control. First, the ROP of CL (100 equiv) was investigated, using 1 dissolved in excess cyclohexene oxide (900 equiv). This resulted in quantitative formation of PCL (Mn=4100 g mol−1, PDI=1.4) in less than 1 h. Figure 5 illustrates the in situ ATR-IR data and shows changes to the intensities of the resonances consistent with efficient CL ROP (1750 and 694 cm−1) and PCL formation (1420 cm−1). Next, carbon dioxide (1 bar total pressure) was added: ROCOP began immediately, leading to PCL-PCHC formation (evidenced by the increase in the intensity of the signal at 1237 cm−1). During the next 20 h, the resonances due to PCL and CL (1420 and 694 cm−1, respectively) did not change significantly. The intensities of the resonances at 1750 and 1237 cm−1 are affected by both CL/PCL and PCHC concentrations (Figure S5), but the dominant influences are apparent. Size-exclusion chromatography (SEC) analysis (53 % CHO conversion, Mn=4800, PDI=1.28) shows only a slight increase in Mn compared to the PCL formed after 1 h (Figure S6). The Mn determined by SEC is calibrated against polystyrene standards because the correction factors are unknown for the copolymers: this calibration issue is likely in part responsible for the smaller increase in Mn than might be expected from the monomer conversions. The 1H NMR spectrum (Figure S7) confirms the expected copolymer composition, with relative intensities of carbonate and ester signals in the expected ratios given the monomer conversions. The carbonyl region of the 13C{1H} NMR spectrum (Figure S8) indicated block copolymer formation, with signals due to PCL (174 ppm) and PCHC (154 ppm) only. There were no intermediate peaks, which is consistent with a lack of copolymer scrambling reactions, for example, transesterification/carbonation.


Chemoselective polymerization control: from mixed-monomer feedstock to copolymers.

Romain DC, Williams CK - Angew. Chem. Int. Ed. Engl. (2014)

Changes to the intensity of IR resonances during PCL-PCHC formation (Table 1, run 5). The plot shows the ROP of CL, the addition of CO2, and the ROCOP of CHO/CO2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4232277&req=5

fig05: Changes to the intensity of IR resonances during PCL-PCHC formation (Table 1, run 5). The plot shows the ROP of CL, the addition of CO2, and the ROCOP of CHO/CO2.
Mentions: A logical next step was to investigate 1 as a catalyst for sequential ROP and ROCOP (Table 1, runs 5–6) by exploiting this chemoselective polymerization control. First, the ROP of CL (100 equiv) was investigated, using 1 dissolved in excess cyclohexene oxide (900 equiv). This resulted in quantitative formation of PCL (Mn=4100 g mol−1, PDI=1.4) in less than 1 h. Figure 5 illustrates the in situ ATR-IR data and shows changes to the intensities of the resonances consistent with efficient CL ROP (1750 and 694 cm−1) and PCL formation (1420 cm−1). Next, carbon dioxide (1 bar total pressure) was added: ROCOP began immediately, leading to PCL-PCHC formation (evidenced by the increase in the intensity of the signal at 1237 cm−1). During the next 20 h, the resonances due to PCL and CL (1420 and 694 cm−1, respectively) did not change significantly. The intensities of the resonances at 1750 and 1237 cm−1 are affected by both CL/PCL and PCHC concentrations (Figure S5), but the dominant influences are apparent. Size-exclusion chromatography (SEC) analysis (53 % CHO conversion, Mn=4800, PDI=1.28) shows only a slight increase in Mn compared to the PCL formed after 1 h (Figure S6). The Mn determined by SEC is calibrated against polystyrene standards because the correction factors are unknown for the copolymers: this calibration issue is likely in part responsible for the smaller increase in Mn than might be expected from the monomer conversions. The 1H NMR spectrum (Figure S7) confirms the expected copolymer composition, with relative intensities of carbonate and ester signals in the expected ratios given the monomer conversions. The carbonyl region of the 13C{1H} NMR spectrum (Figure S8) indicated block copolymer formation, with signals due to PCL (174 ppm) and PCHC (154 ppm) only. There were no intermediate peaks, which is consistent with a lack of copolymer scrambling reactions, for example, transesterification/carbonation.

Bottom Line: A novel chemoselective polymerization control yields predictable (co)polymer compositions from a mixture of monomers.Using a dizinc catalyst and a mixture of caprolactone, cyclohexene oxide, and carbon dioxide enables the selective preparation of either polyesters or polycarbonates or copoly(ester-carbonates).The selectivity depends on the nature of the zinc-oxygen functionality at the growing polymer chain end, and can be controlled by the addition of exogeneous switch reagents.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Imperial College London, London SW7 2AZ (UK).

No MeSH data available.