Facile synthesis of well-defined MDMO-PPV containing (tri)block-copolymers via controlled radical polymerization and CuAAC conjugation

A systematic investigation into the chain transfer polymerization of the so-called radical precursor polymerization of poly(p-phenylene vinylene) (PPV) materials is presented. Polymerizations are characterized by systematic variation of chain transfer agent (CTA) concentration and reaction temperature. For the chain transfer constant, a negative activation energy of −12.8 kJ·mol−1 was deduced. Good control over molecular weight is achieved for both the sulfinyl and the dithiocarbamate route (DTC). PPVs with molecular weights ranging from thousands to ten thousands g·mol−1 were obtained. To allow for a meaningful analysis of the CTA influence, Mark–Houwink–Kuhn–Sakurada (MHKS) parameters were determined for conjugated MDMO-PPV ([2-methoxy-5-(3',7'-dimethyloctyloxy)]-1,4-phenylenevinylene) to α = 0.809 and k = 0.00002 mL·g−1. Further, high-endgroup fidelity of the CBr4-derived PPVs was proven via chain extension experiments. MDMO-PPV-Br was successfully used as macroinitiator in atom transfer radical polymerization (ATRP) with acrylates and styrene. A more polar PPV counterpart was chain extended by an acrylate in single-electron transfer living radical polymerization (SET-LRP). In a last step, copper-catalyzed azide alkyne cycloaddition (CuAAC) was used to synthesize block copolymer structures. Direct azidation followed by macromolecular conjugation showed only partial success, while the successive chain extension via ATRP followed by CuAAC afforded triblock copolymers of the poly(p-phenylene vinylene)-block-poly(tert-butyl acrylate)-block-poly(ethylene glycol) (PPV-b-PtBuA-b-PEG)

Alpha and Omega: Importance of the Nonliving Chain End in RAFT Multiblock Copolymerization

Consecutive chain extensions via the RAFT process have been carried out, and polymers were investigated via ESI-MS to elucidate for the first time the chain end distributions in high detail. In this manner, the number of chains carrying living chain ends is assessed as well as the number of polymers carrying both RAFT typical R and Z groups. Polymerizations were carried out to practically full conversion, and two subsequent chain extensions have been carried out for each obtained material under systematic variation of the AIBN concentration between 1 and 10 mol % with regards to RAFT agent. Generally, very high percentages of living chains were observed the lower the AIBN concentration in the polymerization. With 1 mol %, up to 96% of chains (triblock structure) could be confirmed to be of living nature. In contrast, with 10 mol % of AIBN, only 85% of chains are living after addition of the third polymer block. When looking at the alpha–omega pure materials (carrying exclusively the RAFT-derived R group instead of an AIBN-derived end group), much lower values are deduced, yielding abundances of 90% for the low and 70% of the higher AIBN concentration. Loss of R groups indicates loss of the polymer block structure and must thus be seen as equally important as the information on livingness of the polymer. For multiblock copolymer synthesis it is thus strongly recommended to assess both the Z but also the R group integrity of the polymer

Synthesis of Macromonomers from High-Temperature Activation of Nitroxide Mediated Polymerization (NMP)-made Polyacrylates

Macromonomers are synthesized from thermal reactivation of three different precursors, Poly­(<i>n</i>-butyl acrylate) P­(<i>n</i>BuA), Poly­(<i>tert</i>-butyl acrylate) P­(<i>t</i>BuA), and Poly­(2-ethylhexyl acrylate) P­(EHA), synthesized via nitroxide mediated polymerization (NMP). Reactivation of the polymer chains is carried out at 140 °C, whereby the polyacrylate macroradicals undergo chain transfer reactions forming midchain radicals, MCR, followed by β-scission reactions leading to unsaturated macromonomers. Soft-ionization mass spectrometry of product samples reveals that in all cases predominantly macromonomers that carry a hydrogen end group on the other chain end are formed, which is also accompanied by small reductions in molecular weight (−200 g·mol^–1) and slight increases in polydispersity (+0.2). Furthermore, we demonstrate that macromonomers under these reaction conditions are not only formed through simple backbiting/β-scission via six-membered ring transition structures but also that complex addition–fragmentation equilibria must play a considerable role. As observed before for macromonomers made from activation of atom transfer radical polymerization (ATRP)-made precursors, a size-selective reaction pathway is observed that favors the generation of macromonomers with only odd numbers of monomer units on the backbone, supporting an MCR migration mechanism, which allows MCRs to move along the backbone

Cross-linked degradable poly(beta-thioester) networks via amine-catalyzed thiol-ene click polymerization

A set of binary and ternary biodegradable cross-linked poly(β- thioester) networks have been synthesized via thiol-ene Michael additions, by reacting combinations of dithiols, diacrylates and multifunctional cross-linkers. Insoluble binary thermoset networks and soluble ternary branched polymers with broad molar mass distributions are obtained in a facile manner after polymerization at room temperature for only few minutes. The networks display excellent thermal stability up to 250 °C and exhibit low glass transition temperatures. The soluble branched polymers show degradation of the polyester backbone upon chemical degradation by acidic and basic solutions. Finally, the (bio)degradability of ternary PBT polymer films is examined via quartz crystal microbalance measurements. Weight loss is measured as a function of time upon exposure to phosphate buffers at different pH. PBTs carrying apolar chain segments display surface degradation, while PBTs with more polar ethylene glycol segments allow for swelling in aqueous solution, which is reflected in concomitant surface and bulk degradation of the materials. Because of their biodegradability, these easy to synthesize poly(β-thioesters) networks are considered to be suitable candidates to use in future biomedical or ecological applications. © 2014 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Cross-linked degradable poly(β-thioester) networks via amine-catalyzed thiol-ene click polymerization journaltitle: Polymer articlelink: http://dx.doi.org/10.1016/j.polymer.2014.05.043 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.status: publishe

Acid-Induced Room Temperature RAFT Polymerization: Synthesis and Mechanistic Insights

An acid-induced cyclohexanone/<i>tert</i>-butylhydroperoxide initiation system for ambient temperature reversible addition–fragmentation transfer (RAFT) polymerization of vinyl monomers is presented. The reaction system is optimized for the synthesis of poly­(<i>n</i>-butyl acrylate) of various chain length. The polymerization shows typical living characteristics and polymers with dispersities close to 1.1 are obtained. Analysis of the polymer end groups by means of soft ionization mass spectrometry reveals the typical distribution of polymer containing both <i>R</i> and <i>Z</i> RAFT end groups and a minor distribution of a RAFT polymer carrying a cyclohexanone end group in α position. This observation demonstrates that the polymerization is initiated solely by ketone radicals despite a relatively complex initiation mechanism that involves several intermediates. The room temperature-derived homopolymers are successfully chain extended with <i>tert</i>-butyl acrylate resulting in well-defined block copolymer structures. To demonstrate the versatility of the approach, the room temperature RAFT polymerization is also applied to synthesize styrene and <i>N</i>-isopropylacrylamide, yielding best results for polystyrene. Finally, also a bisperoxide structure is tested as an alternative for the ketone/peroxide mixture. Polymerization proceeds substantially faster in this case and successful controlled polymerization to full conversion is achieved even at 0 °C. In general the proposed room temperature RAFT technique is very easy to carry out, in principle easily up scalable, metal free and shows high potential toward the synthesis of well-defined temperature sensitive materials

Facile Synthesis of Well-Defined MDMO-PPV Containing (Tri)Block—Copolymers via Controlled Radical Polymerization and CuAAC Conjugation

A systematic investigation into the chain transfer polymerization of the so-called radical precursor polymerization of poly(p-phenylene vinylene) (PPV) materials is presented. Polymerizations are characterized by systematic variation of chain transfer agent (CTA) concentration and reaction temperature. For the chain transfer constant, a negative activation energy of −12.8 kJ·mol−1 was deduced. Good control over molecular weight is achieved for both the sulfinyl and the dithiocarbamate route (DTC). PPVs with molecular weights ranging from thousands to ten thousands g·mol−1 were obtained. To allow for a meaningful analysis of the CTA influence, Mark–Houwink–Kuhn–Sakurada (MHKS) parameters were determined for conjugated MDMO-PPV ([2-methoxy-5-(3\u27,7\u27-dimethyloctyloxy)]-1,4-phenylenevinylene) to α = 0.809 and k = 0.00002 mL·g−1. Further, high-endgroup fidelity of the CBr4-derived PPVs was proven via chain extension experiments. MDMO-PPV-Br was successfully used as macroinitiator in atom transfer radical polymerization (ATRP) with acrylates and styrene. A more polar PPV counterpart was chain extended by an acrylate in single-electron transfer living radical polymerization (SET-LRP). In a last step, copper-catalyzed azide alkyne cycloaddition (CuAAC) was used to synthesize block copolymer structures. Direct azidation followed by macromolecular conjugation showed only partial success, while the successive chain extension via ATRP followed by CuAAC afforded triblock copolymers of the poly(p-phenylene vinylene)-block-poly(tert-butyl acrylate)-block-poly(ethylene glycol) (PPV-b-PtBuA-b-PEG)

Kinetic Monte Carlo generation of complete electron spray ionization mass spectra for acrylate macromonomer synthesis

Absolute electron spray ionization mass spectrometry (ESI-MS) data are reported, for the first time, over the complete chain length range for the synthesis of welldefined macromonomers (MMs) obtained via activation of bromine-capped poly(n-butyl acrylate) (0.1 mass %; solvent: anisole; 140 °C) with CuBr2/Me6TREN (Me6TREN: tris(2 (dimethylamino)ethyl)amine) and tin ethylhexanoate. These data are generated based on bivariate kinetic Monte Carlo simulations, tracking the chain lengths and the positions of radicals/characteristic groups along the chains (>100 reactions, 12 radical/dormant species types, and 7 characteristic end/ mid-groups). Based on qualitative tuning to experimental data, migration is found to be 50 times slower than backbiting but 15 times faster than βC-scission, making it a dominant reaction. Benefiting from the absence of monomer, the chain transfer to polymer rate coefficient is assessed as 6 × 102 L mol−1 s −1 (140 °C). Model analysis shows that consecutive backbiting/migration/βC-scission leads to a favoring of MMs with even chain lengths and a hydrogen chain end over MMs with the nonreactive chain end originating from the initial dormant polymer. The obtained insights contribute to a better fundamental understanding of hydrogen abstractions in acrylate radical polymerization and open the path for a more detailed polymer product characterization in general

Anionic PPV polymerization from the sulfinyl precursor route:Block copolymer formation from sequential addition of monomers

<p>The sulfinyl precursor route for the synthesis of poly(p-phenylene vinylene) (PPV) materials via an anionic polymerization procedure employing dedicated initiators is evaluated in depth. Reaction kinetics are investigated to gain more control over the polymerization, since polymerization proceeds to full conversion already on the timescale of mixing of the reaction components. Even at -78 degrees C almost full conversion of the monomer is observed after few seconds. BEH-PPVs are obtained in the range of 3000 to 16,000 g mol(-1), whereby dispersity decreases with decreasing molecular weight, allowing for materials with a PDI of 1.1 for the smallest PPV chain. Block copolymerizations were performed via sequential addition of monomers to make use of the living PPV chain ends. Bimodal product mixtures are obtained, consisting of block copolymer as well as PPV homopolymer. The block copolymer PPV-b-poly(tert-butyl acrylate) could nevertheless be separated by selective precipitation as well as preparative chromatography techniques. (c) 2013 Elsevier Ltd. All rights reserved.</p>