Tailored Semiconducting Polymers: Living Radical Polymerization and NLO‐Functionalization of Triphenylamines

This paper describes the preparation of various polymers with triarylamine side groups. High molecular weight materials were obtained by free radical polymerization utilizing the gel effect. Polymers with a narrow polydispersity and a predetermined molecular weight could be prepared by living radical polymerization. The T_g could, thereby, be controlled between 50 and 140°C either by using different monomers or by varying the molecular weight. Living radical polymerization allowed in addition the preparation of block copolymers. The triarylamine side groups could be transformed into NLO‐chromophores by reaction with tetracyanoethylene. This leads to the incorporation of tricyanoethylene acceptor groups. As this reaction can be performed selectively on one block in block copolymers, microphase separated structures are accessible, which possess charge transport moieties in one phase and NLO‐chromophores in the other phase.     

Mesogen-jacketed liquid crystalline polymers via stable free radical polymerization

Stable free radical polymerization has been used in the controlled synthesis of poly(2,5-bis[(4-butylbenzoyl)oxy]styrene), PBBOS. This “mesogen-jacketed liquid crystalline polymer”, which has mesogenic units attached directly to the backbone in a side-on mode, has been found to exhibit thermotropic liquid crystallinity similar to more conventional main-chain architectures. Stable free radical polymerization of PBBOS consistently produced molecular weight distributions below the theoretical limiting polydispersity of 1.5 calculated for a conventional free radical polymerization process. Surprisingly, a comparison of the synthesis of polystyrene to the polymerization of PBBOS under nearly identical conditions showed that the PBBOS polymerized with a significantly higher reaction rate and monomer conversion efficiency. The nematic phase of these polymers was determined to be stable over the temperature range spanning the polymer glass transition temperature up to the temperature for thermal decomposition. The molecular arrangement of the PBBOS polymers was examined by wide-angle X-ray diffraction and is described here.     

From living to controlled aluminium alkoxide mediated ring-opening polymerization of (di)lactones,a powerful tool for the macromolecular engineering of aliphatic polyesters

The aluminium alkoxide mediated ring-opening polymerization of (di)lactones offers a great versatility to the point where the main situations covered by the definition of living and controlled polymerizations can be illustrated. Furthermore, substitution of a coordination-insertion mechanism for the traditional anionic polymerization of these monomers results in species of lower reactivity and in a kinetic control of the polyaddition reaction. This control, combined with the use of Al alkoxides of different structures and functionalities, has opened the way to the macromolecular design of a family of biocompatible and biodegradable polyesters, e. g., controlled synthesis of telechelic polymers, block and graft copolymers, and polymers of various molecular architectures. These polymers can be used as such, or as building parts of more sophisticated polymeric assemblies.     

Emerging Concepts in Iodine Transfer Polymerization

Controlled radical polymerization corresponds to variety of synthetic strategies that aim the generation of precise macromolecular architectures. Iodine transfer polymerization (ITP) is one of the oldest methods to conduct controlled radical polymerization; however, it seems to have lost visibility compared to other popular techniques. It relies on utilization of iodine species in reversible deactivation kinetics, and it has some significant advantages compared to other methods. Its simplicity, minimized toxicity, metal-free nature, no coloring on final product, and ease of purification provide widespread applicability, even in industry. In this perspective, the basics of ITP are re-introduced, and emerging technologies (heterophase polymerization, photoinitiation, and sustainability) in ITP are discussed.     

Fonctionalisation des polyalcadiènes: Étude sur molécules modèles des structures accessibles à partir des polymères de l'isoprène par utilisation de l'isocyanate de chlorosulfonyle

The reaction of chlorosulfonyl isocyanate ( 1 ) with alkenes permits to consider the preparation of lactames and N-chlorosulfonated amides as synthetic intermediates. With the goal to obtain functional macromolecular compounds the use of this reaction was considered for the chemical modification of polyisoprenes having a predominant 1,4- or 3,4-microstructure. With the intention to define the modifications of the microstructures caused by the action of 1 on these polymers, the reaction was studied with models. In this way it was possible to determine the percentages of the formation of lactame and N-chlorosulfonated microstructures for each type of chain arrangement in polyisoprene. On the other hand, the transformations of the N-chlorosulfonated lactames into free lactames, amino acid hydrochlorides, and unsaturated nitriles was studied. This work permits to define the spectral references of the microstructures which may be formed applying the reactions to the polymers. In addition it makes it possible to select the type of chain arrangement in polyisoprene which will lead to functional macromolecular compounds with the highest yields and the best selectivity for special applications.     

New Star‐Branched Poly(acrylonitrile) Architectures: ATRP Synthesis and Solution Properties

Summary: Atom transfer radical polymerization (ATRP) has been chosen as “living”/controlled free radical polymerization system to synthesize a number of novel poly(acrylonitrile) (PAN) architectures. The reaction conditions for the synthesis of linear samples with control over molar mass and molar mass distribution have been investigated together with the possibility of obtaining copolymers of acrylonitrile with small quantities of methyl acrylate (max. 5 mol‐%). Well‐defined star polymers with 3, 4 and 6 arms have been successfully synthesized together with linear chains initiated by a bifunctional initiator and star‐branched polymers with a hyperbranched poly(ester amide) as core. Molar masses were determined by NMR and GPC with the latter leading to a significant over estimation. Solution viscosity studies indicated that the stiff structure of the PAN chains is still maintained in the homopolymer star architectures and that the incorporation of small quantities of methyl acrylate as comonomer has a stronger effect on chain flexibility than the incorporation of star‐branch points.

     

Controlled Drug Release from Weakly Crosslinked Molecularly Imprinted Networks: The Benefit of Living Radical Polymerization

This work focuses on the complex relationship between molecularly imprinted polymer network formation, network structure, and composition, and template binding and transport. A comprehensive study of template binding and transport is performed using two different reaction schemes (living radical polymerization and conventional free radical polymerization) while altering template concentration, functional monomer concentration, solvent content, crosslinking monomer length, and extent of crosslinking. Imprinted poly(HEMA‐co‐DEAEM‐co‐PEG200DMA) networks prepared by living radical polymerization (LRP) exhibit enhanced molecular imprinting and have significantly higher template binding affinities (≈2×), higher binding capacities (≈2.3×), slower template release, and lower template diffusion coefficients (1/2×) compared with imprinted polymers prepared via free radical polymerization (FRP) with statistically similar parameters for non‐imprinted polymers. A synergistic effect between LRP and molecular imprinting is demonstrated. LRP has a profound structural effect on the network leading to reduced free volume and/or increased homogeneity in the mesh structure leading to enhanced macromolecular memory. In addition, by altering reaction parameters, like template and monomer concentrations, the template binding and release characteristics can be tuned. By using an LRP reaction scheme, improved control over release can be achieved enhancing the role the molecular imprinting technique can make in the design and engineering of novel drug delivery materials.

     

Synthesis, characterization, and in vitro cell culture viability of degradable poly(N-isopropylacrylamide-co-5,6-benzo-2-methylene-1,3-dioxepane)-based polymers and crosslinked gels

Poly(N-isopropylacrylamide-co-5,6-benzo-2-methylene-1,3-dioxepane) (poly(NIPAAm-co-BMDO)) was synthesized by atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. Using UV-vis spectroscopy, the lower critical solution temperature (LCST) of poly(NIPAAm) and poly(NIPAAm-co-BMDO) copolymers were measured, varying with respect to the amount of incorporated BMDO. This material is degradable and possesses a LCST above room temperature and below body temperature, making it a potential candidate for use as an injectable tissue engineering scaffold to enhance fracture repair. ATRP and RAFT enabled preparation of polymers with control over molecular weight up to M(n) = 50,000 g/mol and M(w)/M(n) < 1.2. Degradation studies were performed in basic solution and in complete Dulbecco's modified Eagle medium. The cytotoxicity of the material and its degradation products were analyzed by in vitro cell culture analyses, including cytotoxicity live/dead and CyQUANT cell proliferation assays. Crosslinked scaffolds with degradable units within the polymer backbone and at the crosslinking sites were prepared using an ester-containing diacrylate crosslinker. Furthermore, incorporation of a GRGDS peptide sequence improved cell attachment to the gels. Controlled/living radical polymerization techniques allow for precise control over macromolecular structure and are poised to become powerful tools for tissue engineering scaffold synthesis.     

“Living” free radical ring‐opening polymerization of 2‐methylene‐4‐phenyl‐1,3‐dioxolane by atom transfer radical polymerization

The “living” free radical ring‐opening polymerization of 2‐methylene‐4‐phenyl‐1,3‐dioxolane (MPDO) in the presence of ethyl α‐bromobutyrate/CuBr/2,2′‐bipyridine at various temperatures has been investigated. In comparison with the conventional ring‐opening polymerization of MPDO, a lower content of ring‐opened unit in the polymer was found. The results of ln[M]₀/[M]) against polymerization time, (M_n)_th and (M_n)_NMR vs conversion, and GPC of the polymers are strongly indicative of the “living” polymerization process. Initiator efficiency was measured. The mechanism of polymerization, and the effect of pyridine on the polymerization mechanism were discussed.     

Triazolinyl radicals – new additives for controlled radical polymerization

The effect of the addition of the triazoline derivative 1 on the radical polymerization of styrene and some methacrylates is discussed. The polymerization of styrene in the presence of 1 exhibits the characteristics of a controlled radical polymerization such as a linear time-conversion development and increasing molecular weights versus conversion. Additionally, even monomers other than styrene, namely methacrylates, can be polymerized in a controlled fashion. Furthermore, the properties of the isolated PS and PMMA samples were studied. It will be shown, that polymers obtained by controlled radical polymerization in the presence of 1 possess triazolinyl end-groups and the degree of end-functionalisation will be estimated. To demonstrate the ability of the polymers to reinitiate, chain extension experiments were performed on our PS-samples.     

Free radical polymerization of a sugar residue-carrying styryl monomer with a lipophilic alkoxyamine initiator: synthesis of a well-defined novel glycolipid

Controlled free radical polymerization of N-p-vinylbenzyl-2,3,5,6-tetra-O-acetyl-4-O-(2,3,4,6-tetra-O-acetyl-β-D -galactopyranosyl)-D -gluconamide (Ac-VLA) was achieved by the nitroxide-mediated free radical polymerization with a lipophilic alkoxyamine “initiator” with a dioctadecyl group in 1,2-dichloroethane at 90°C. The polymerization proceeds in a “living” fashion, providing Ac-VLA polymers with low polydispersity. The hydrolysis of the polymers results in well-defined glycopolymer-carrying amphiphiles, viz., artificial “glycolipids”.     

Glycopolymers of Various Architectures—More than Mimicking Nature

Carbohydrates have a highly important role in biological functions. The increasing understanding of their biological interactions has also triggered a strongly increased interest in the preparation of synthetic glycopolymers of various architectures and well‐defined structure which can mimic biological functions in a less complex environment. In the last few years synthetic approaches in polymer science have been refined and newly developed in order to achieve complex carbohydrate architectures and to make use of them in various areas like glycomics, biotechnology, biosensors, and medicine. Besides the use of especially controlled radical polymerization techniques, highly efficient polymer analogous reactions that can be carried out in aqueous media have been developed and applied to linear and dendritic macromolecules. Self assembly aspects and their effectiveness in biological functions have been assessed.

     

Facile Synthesis of Helical Rod–Coil Block Polymers by the Combination of ATRP and Pd(II)‐Initiated Isocyanides Polymerizations

A bifunctional initiator containing propargyl bromoisobutyrate and alkyne‐Pd(II) (PBB‐Pd(II)) is designed and synthesized. The propargyl bromoisobutyrate unit of PBB‐Pd(II) can initiate the atom transfer radical polymerization (ATRP) of vinyl monomers, while the Pd(II) complex can initiate the polymerization of phenyl isocyanides. Both the ATRP and Pd(II)‐mediated isocyanide polymerization are proceeded in living/controlled manner. Thus, combining the two living polymerizations, a series of well‐defined block copolymers bearing rod poly(phenyl isocyanide)s and coil poly(acrylate) segments can be facilely prepared in high yield with tunable composition, controlled molar masses (M_ns), and narrow molar mass distributions (M_w/M_ns). What is more, benefiting from this synthetic strategy, well‐defined core cross‐linked star polymers are readily synthesized. Optically active block copolymers and star polymers can be facilely obtained by using chiral isocyanide monomers due to the formation of predominated one‐handed helix. The chiral star polymers show excellent enantioselective recognition ability in enantioselective crystallization of racemic compounds.     

Synthesis of Flower‐Like Polybutadiene

Synthesis of complex macromolecular architectures exhibiting no chain ends such as flower‐like polymers is still of interest in the aim of investigating their physicochemical properties. For this purpose, poly(3,4‐dimethyl maleic imidoethyl acrylate)‐block‐polybutadiene‐block‐poly(3,4‐dimethyl maleic imidoethyl acrylate) triblock copolymer is synthesized in a convergent manner using a combination of living polymerization (anionic polymerization), reversible deactivation radical polymerization, and click chemistry. This copolymer is self‐assembled in a selective solvent (heptane/THF mixture) of the polybutadiene block leading to the formation of flower‐like micelles in thermodynamic equilibrium in dilute solution. These resulting transient architectures are fixed by covalently crosslinking the micelles core by inducing [2+2] cyclodimerization of the 3,4‐dimethyl maleic imidoethyl groups borne by the short solvophobic blocks under UV irradiation. Single flowers are isolated from residual non‐crosslinked chains by semipreparative size exclusion chromatography (SEC) and characterized by ¹H NMR, SEC, dynamic light scattering (DLS), and transmission electron microscopy (TEM).

     

Post‐Polymerization Thiol Substitutions Facilitated by Mechanochemistry

The use of mechanical force to facilitate post‐polymerization, solvent‐free thiol substitution reactions is described. These reactions are amenable to halogen‐containing materials prepared using ring opening metathesis polymerization and free radical polymerization reactions. Reactions of these polymers with various thiols can be carried out in a ball mill and are complete in a matter of minutes. Further, ¹H NMR and GPC analysis show no significant decomposition of the polymer chain.     

Synthesis of Hyperbranched Polymers via Metal‐Free ATRP in Solution and Microemulsion

Atom transfer radical polymerization (ATRP), as one of the most successful controlled radical polymerization techniques, has been broadly used by polymer chemists and nonspecialists for synthesis of various functional materials, although the use of copper as traditional catalyst often results in undesired color or properties. The first homopolymerization of an initiable monomer, that is, inimer, is reported via metal‐free ATRP using 10‐phenylphenothiazine (Ph‐PTH) as photocatalyst in both solution and microemulsion media. Although polymerizations of inimers in both media can be carried out, only the microemulsion polymerization of methacrylate‐based inimer 1 effectively confines the random bimolecular reaction within each segregated latex and produces hyperbranched polymers with high molecular weight and low polydispersity. Several experimental parameters in the microemulsion polymerization of inimer 1 are subsequently studied, including the Ph‐PTH amount, the solids content of microemulsion, and the light source of irradiation. The results not only provide an effective method to tune the structure and molecular weights of hyperbranched polymers in confined‐space polymerization, but also expand the toolbox of using metal‐free ATRP method for synthesizing highly branched polymers in controlled manner.     

Living radical polymerization of styrene and its block copolymerization with methyl methacrylate

The existence of living polymer radicals in emulsion polymerization with a macromolecular heterogeneous initiator has been ascertained by preparing block copolymers of styrene with methyl methacrylate. Polymerization of styrene initiated by oxidized polypropylene and triethylenetetramine (3,6-diaza-1,8-octanediamine) proceeds even after the removal of the initiator from the emulsion, reaches 100% conversion, and methyl methacrylate newly added to the system undergoes further polymerization. The molecular weight of polystyrene and of the block copolymer increases with the conversion. The yield of pure block copolymer is about 90% under optimal conditions. The turbidimetric titration curve of the block copolymer shows a characteristic plateau region and suggests monodispersity of the copolymer. Reasons for the absence of termination in this system are presented. This type of living radical polymerization offers some advantages for the preparation of block copolymers, as compared with the anionic living polymerization.     

Estimation of endgroups in acrylamide polymers by reverse dye partition technique

A new dye partition method, known as reverse dye partition(RDP)-technique for estimation of carboxyl and sulfoxy endgroups in water-soluble acrylamide polymers has been described. Detailed experimental conditions for the use of the RDP technique have been discussed and plausible theory underlying this technique has been proposed. The estimated numbers of endgroups in the polymers are in agreement with the existing free radical mechanism of initiation of polymerization. Particularly, the results support the existing idea that the termination of polymerization of acrylamide monomer occurs mainly by disproportionation.     

Synthèse par voie radicalaire de polymères à extrémités hydroxylées, 8. Synthèse de polybutadiènes: Etude de différents paramètres influençant la polymolécularité

It was shown that radical polymerization of butadiene in 1-butanol and 2-butanol, initiated by hydrogen peroxide cleaved into two hydroxyl radicals by heat, leads to three types of polymers according to their respective polydispersity. It was found that the formation of these products — oligomers, polymers, and high polymers — can be influenced by modifying the experimental conditions. Thus, it is possible to obtain selectively oligomers free of polymers and polymers free of low molecular weight oligomers.     

Polymere und Copolymere mit p-Vinyl-α.α-diphenyläthylen-Grundbausteinen

p-Vinyl-α.α-diphenylethylene (pNDPÄ) was polymerized radically in bulk at 80°C and copolymerized with styrene. The resulting polymers and copolymers had relatively low degrees of polymerization (ranging from 10 to 100). The polymerization took place primarily via the vinyl group and to a lower extend via the vinyliden group. The unsaturated side group enabled subsequent crosslinking reactions with these polymers. Copolymers with pVDPÄ-groups having higher molecular weights were obtained by GRIGNARD reaction of p-vinyl benzophenone/styrene copolymers with methyl magnesium iodide. These copolymers yielded the corresponding macromolecular polyanions upon treatment with naphthalene sodium in tetrahydrofuran; the latter were able to start graft-copolymerization of acrylonitrile, methylmethacrylate, and styrene; when using styrene, living side chains were formed. It was shown by dissolution experiments that no ungrafted backbone polymer and no free homopolymers were present in the graft-copolymers with acrylonitrile and methylmethacrylate.