1. Volume 2, Issue 1, Pages 93-101 (January 2017)
Ultra-High Molecular Weights via Aqueous Reversible-Deactivation Radical Polymerization 
R. Nicholas Carmean, Troy E. Becker, Michael B. Sims, Brent S. Sumerlin 
Chem 
Volume 2, Issue 1, Pages (January 2017)
DOI: /j.chempr
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2. Chem 2017 2, DOI: ( /j.chempr )
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3. Figure 1 Synthesis of UHMW Polymers via Trithiocarbonate Iniferter
(A) DMA was irradiated with long-wave UV light (λ = 365 nm, 7.0 mW/cm2) in the presence of a trithiocarbonate iniferter to produce UHMW poly(DMA). Size-exclusion chromatography (SEC) curves are shown as a function of the targeted degree of polymerization; each trace represents a different polymerization. The void volume of this SEC system was 10 mL.
(B) The polymerization of DMA to UHMW (Mn,SEC 1.03 × 106 g/mol) displays near-linear pseudo-first-order kinetics, indicating a constant radical concentration up to >95% monomer conversion.
(C) On/off kinetic plot demonstrates temporal control of the polymerization rate and suggests rapid reversible termination between carbon- and sulfur-centered radicals and that a similar polymerization rate is maintained through activation cycles.
(D) During on/off polymerization, measured molecular weights closely matched theoretical values, and MWDs remained narrow, indicating rapid reinitiation and high end-group retention.
Chem 2017 2, DOI: ( /j.chempr )
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4. Figure 2 Synthesis of UHMW Block Copolymers
UHMW block copolymer poly(DMA)-b-poly(DMA) was prepared upon full monomer conversion of the homopolymer poly(DMA) in a one-pot process. The near-linear pseudo-first-order kinetic plot indicates a constant radical concentration during chain extension to produce poly(DMA)-b-poly(DMA) in 8 hr. SEC of the chain-extended diblock copolymer shows a shift to shorter elution times and higher molecular weights, demonstrating good blocking efficiency and high end-group retention.
Chem 2017 2, DOI: ( /j.chempr )
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5. Figure 3 Alternative Avenue for Photolytic Cleavage
(A) UV-Vis spectroscopy of the two iniferters reveals that xanthate has a blue-shifted absorbance spectrum in comparison with that of trithiocarbonate. This shift yields an alternative activation route under mild long-wave UV irradiation (λ = 365 nm).
(B) A low-molecular-weight model polymer, prepared with either a xanthate or trithiocarbonate iniferter, was irradiated in the presence of a large excess (20 molar equiv) of a persistent radical, 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO). By monitoring conversion of the iniferter-terminated polymer to the unreactive TEMPO-terminated product, photolytic trapping revealed that the xanthate-terminated polymer was consumed considerably faster than the trithiocarbonate-terminated analog. (i) Irradiation with long-wave UV light (λ = 365 nm, 7.0 mW/cm2) in DMSO at 35°C.
Chem 2017 2, DOI: ( /j.chempr )
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6. Figure 4
Rapid UHMW Synthesis in Minutes via Xanthate-Mediated Polymerization
(A) DMA was irradiated with long-wave UV light (λ = 365 nm, 7.0 mW/cm2) in the presence of a trithiocarbonate iniferter to produce UHMW poly(DMA). SEC curves are shown as a function of the targeted degree of polymerization; each trace represents a different polymerization. The void volume of this SEC system was 10 mL.
(B) The polymerization of DMA to UHMW (Mn,SEC 1.30 × 106 g/mol) displays near-linear pseudo-first-order kinetics, reaching 93% monomer conversion in 30 min.
Chem 2017 2, DOI: ( /j.chempr )
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7. Scheme 1
Comparison of Traditional Polymerization Approaches to the Photoiniferter Polymerization Technique for Synthesis of UHMW Polymers
(A) RAFT relies on the decomposition of an external initiator to begin chain growth mediated through degenerative chain transfer.
(B) The current work relies on photolysis of a thiocarbonylthio mediating agent to begin polymerization that is mediated through a combination of reversible termination and degenerative chain transfer.
Chem 2017 2, DOI: ( /j.chempr )
Copyright © 2017 Elsevier Inc. Terms and Conditions