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Kaiser A.,Karlsruhe Institute of Technology | Brandau S.,Lanxess Emulsion Rubber | Klimpel M.,Lanxess Emulsion Rubber | Barner-Kowollik C.,Karlsruhe Institute of Technology
Macromolecular Rapid Communications | Year: 2010

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, M̄n, 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). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Hlalele L.,Karlsruhe Institute of Technology | D'Hooge D.R.,Ghent University | Durr C.J.,Karlsruhe Institute of Technology | Kaiser A.,Lanxess Emulsion Rubber | And 2 more authors.
Macromolecules | Year: 2014

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 ≤ D (-) ≤ 3.3). Relatively good control (e.g., D ≈ 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. © 2014 American Chemical Society.


Durr C.J.,Karlsruhe Institute of Technology | Lederhose P.,Karlsruhe Institute of Technology | Hlalele L.,Karlsruhe Institute of Technology | Abt D.,Karlsruhe Institute of Technology | And 3 more authors.
Macromolecules | Year: 2013

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. © 2013 American Chemical Society.


Durr C.J.,Karlsruhe Institute of Technology | Hlalele L.,Karlsruhe Institute of Technology | Kaiser A.,Lanxess Emulsion Rubber | Brandau S.,Lanxess Emulsion Rubber | Barner-Kowollik C.,Karlsruhe Institute of Technology
Macromolecules | Year: 2013

An efficient approach for the synthesis of block copolymers of poly(acrylonitrile-co-butadiene) (NBR) and poly(styrene-co-acrylonitrile) (SAN) is described. Conjugation of preformed polymer building blocks is achieved via a hetero-Diels-Alder (HDA) mechanism employing cyclopentadiene-capped NBRs with dienophile SAN copolymers, both synthesized via reversible addition- fragmentation chain transfer (RAFT) polymerization. The protocol is further extended toward the synthesis of 4-miktoarm star polymers, consisting of two NBR and two SAN arms. Molar masses of the obtained complex macromolecular architectures range from below 10 000 g·mol-1 up to 110 000 g·mol-1 with dispersities below 1.5. Molecular verification of the coupling moieties is provided via NMR spectroscopy as well as ESI mass spectrometry. Size exclusion chromatography (SEC) traces of the obtained block copolymers and miktoarm star polymers were analyzed via deconvolution techniques, revealing the presence of 9.9-12.6 wt % (block copolymers) and 20 wt % (stars) of polymer chains not participating in the HDA conjugation, respectively. The residual polymers were analyzed toward their origin from either the loss of functionality during RAFT polymerization or incomplete conversion during the conjugation process. The comprehensive analysis of the macromolecular material was underpinned by kinetic simulations to estimate the fractions of nonfunctional polymer chains generated during the NBR and SAN polymerizations. The simulations evidenced that NBR-b-SAN samples cannot contain more than 94.4 wt % (Mn 13 000 g·mol-1), 93.6 wt % (Mn 57 000 g·mol-1), or 93.9 wt % (Mn 110 000 g·mol-1) of polymer chains actually possessing the targeted block copolymer structures when assuming an ideal RAFT process. These results unambiguously reveal that nonfunctionalized polymer chains formed during RAFT polymerization cause the incomplete conjugation of polymer building blocks, evidencing the limitations of end-group control in controlled/living radical polymerizations. © 2012 American Chemical Society.


Hlalele L.,Karlsruhe Institute of Technology | Durr C.J.,Karlsruhe Institute of Technology | Lederhose P.,Karlsruhe Institute of Technology | Kaiser A.,Lanxess Emulsion Rubber | And 3 more authors.
Macromolecules | Year: 2013

An in-depth mechanistic study into the solution based initiator-free UV-induced radical copolymerization of 1,3-butadiene with acrylonitrile is reported. The light induced constant radical flux leads to moderate monomer conversions within 4 to 24 h. The number-average molecular weights of the prepared nitrile butadiene rubber (NBR) range from 2500 to 50 000 g mol -1 (1.7 ≤ PDI ≤ 2.4), while the achievable monomer conversion ranged from close to 7 up to 31% depending on the polymerization temperature, reaction time and UV light intensity. The rate coefficient for the generation of primary radicals, determined as the coupled parameter k1 *k3, showed a dependence on the UV light intensity with values between 6.0 s-2 and 34.6 s-2 deduced for the UV light intensity range of 280 to 700 W. The estimated values of the lower limit average termination rate coefficient displayed no dependence on the UV light intensity, with lower limit values between 2.6 × 108 L mol-1 s-1 and 6.3 × 108 L mol -1 s-1 for the UV light intensity range of 280 to 700 W. The deduced values for the average termination rate coefficient were above the expected values for comparable average termination rate coefficients. © 2013 American Chemical Society.

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