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Preparative Macromolecular Chemistry, Institut für Technische Chemie und Polymerchemie, Karlsruhe Institute of Technology (KIT), Engesserstr. 18, 76128 Karlsruhe, Germany.
Macromolecular Rapid Communications (Impact Factor: 4.61). 09/2010; 31(18):1616-21. DOI: 10.1002/marc.201000162
Source: PubMed

ABSTRACT In the current work we present results on the controlled/living radical copolymerization of acrylonitrile (AN) and 1,3-butadiene (BD) via reversible addition fragmentation chain transfer (RAFT) polymerization techniques. For the first time, a solution polymerization process for the synthesis of nitrile butadiene rubber (NBR) via the use of dithioacetate and trithiocarbonate RAFT agents is described. It is demonstrated that the number average molar mass, $\overline M _{\rm n}$, of the NBR can be varied between a few thousand and 60 000 g · mol(-1) with polydispersities between 1.2 and 2.0 (depending on the monomer to polymer conversion). Excellent agreement between the experimentally observed and the theoretically expected molar masses is found. Detailed information on the structure of the synthesized polymers is obtained by variable analytical techniques such as infrared spectroscopy (IR), nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry, and electrospray ionization-mass spectrometry (ESI-MS).

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• ##### Article: RAFT-based Polystyrene and Polyacrylate Melts under Thermal and Mechanical Stress
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ABSTRACT: Although controlled/living radical polymerization processes have significantly facilitated the synthesis of well-defined low polydispersity polymers with specific functionalities, a detailed and systematic knowledge of the thermal stability of the products–highly important for most industrial processes–is not available. Linear polystyrene (PS) carrying a trithiocarbonate mid-chain functionality (thus emulating the structure of the Z-group approach via reversible addition–fragmentation chain transfer (RAFT) based macromolecular architectures) with various chain lengths (20 kDa ≤ Mn,SEC ≤ 150 kDa, 1.27 ≤ Đ = Mw/Mn ≤ 1.72) and chain-end functionality were synthesized via RAFT polymerization. The thermal stability behavior of the polymers was studied at temperatures ranging from 100 to 200 °C for up to 504 h (3 weeks). The thermally treated polymers were analyzed via size exclusion chromatography (SEC) to obtain the dependence of the polymer molecular weight distribution on time at a specific temperature under air or inert atmospheres. Cleavage rate coefficients of the mid-chain functional polymers in inert atmosphere were deduced as a function of temperature, resulting in activation parameters for two disparate Mn starting materials (Ea = 115 ± 4 kJ·mol–1, A = 0.85 × 109 ± 1 × 109 s–1, Mn,SEC = 21 kDa and Ea = 116 ± 4 kJ·mol–1, A = 6.24 × 109 ± 1 × 109 s–1, Mn,SEC = 102 kDa). Interestingly, the degradation proceeds significantly faster with increasing chain length, an observation possibly associated with entropic effects. The degradation mechanism was explored in detail via SEC–ESI–MS for acrylate based polymers and theoretical calculations suggesting a Chugaev-type cleavage process. Processing of the RAFT polymers via small scale extrusion as well as a rheological assessment at variable temperatures allowed a correlation of the processing conditions with the thermal degradation properties of the polystyrenes and polyacrylates in the melt.
Macromolecules 10/2013; 46(20):8079–8091. · 5.93 Impact Factor
• ##### Article: Photo-Induced Ligation of Acrylonitrile-Butadiene Rubber: Selective Tetrazole–Ene Coupling of Chain-End-Functionalized Copolymers of 1,3-Butadiene
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ABSTRACT: A highly selective photo-induced nitrile imine mediated tetrazole–ene coupling (NITEC) of chain-end-functionalized nitrile–butadiene rubber (NBR) is reported, providing nitrile rubbers with molar masses of up to 48 000 g·mol–1. NBR was obtained via the reversible addition–fragmentation chain transfer (RAFT) mediated copolymerization of acrylonitrile and 1,3-butadiene employing a novel photoreactive tetrazole-functionalized trithiocarbonate. The herein reported tetrazole-functionalized trithiocarbonate represents—to the best of our knowledge—the first ever reported photoreactive RAFT agent capable of undergoing light-induced ligations with enes. Molar masses of the tetrazole-functionalized NBRs were in the range of 1000 to 38 000 g·mol–1 with dispersities between 1.1 to 1.6. By an appropriate choice of the tetrazole substituents, a reaction of the in situ formed enophile with the double bonds or the nitrile moieties of the incorporated monomer units within the polymer backbone—present in high excess relative to the dipolarophile linker molecule—was not observed. Underpinned by DFT calculations, the selectivity was identified to originate from a reduced LUMO energy level of the maleimide linker compared to the nonactivated backbone olefins when employing a nitrile–imine of moderate reactivity.
Macromolecules 08/2013; 46(15):5915-5923. · 5.93 Impact Factor
• ##### Article: RAFT-Mediated ab Initio Emulsion Copolymerization of 1,3-Butadiene with Acrylonitrile
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ABSTRACT: The successful RAFT-mediated ab initio emulsion copolymerization of acrylonitrile and 1,3-butadiene using 2-(((dodecylsulfanyl)carbonothioyl)sulfanyl)propanoic acid (DoPAT) is reported at 45–55 °C. The number-average molecular weight exhibits a linear evolution as a function of monomer conversion (5000 ≤ Mn (g mol–1) ≤ 41 000, 1.3 ≤ Đ (−) ≤ 3.3). Relatively good control (e.g., Đ ≈ 1.2 for selected conditions) over the polymerization up to moderate monomer conversion (50–60%) was attained when the employed initial molar ratio of RAFT agent to initiator was 2.5 or higher. Good ω-end-group functionality is evidenced by chain extension of NBR with a polystyrene block, with both 1H NMR and SEC showing the average fraction of the NBR block as ca. 75 mol%. A kinetic model implemented via the PREDICI software package confirms the experimental findings, including a semiempirical approach to account for branch formation. The onset of the loss in control over the copolymerization at conversions >40% was tentatively attributed to branch formation. The current study evidences that RAFT mediated ab initio emulsion polymerization of 1,3-butadiene and acrylonitrile is a viable polymerization protocol for the synthesis of well-defined next generation nitrile–butadiene rubbers including in industrial context.
Macromolecules 04/2014; 47(9):2820–2829. · 5.93 Impact Factor