6,6′-Bisfunctionalized 2,2′-bipyridines as metallo-supramolecular initiators for the living polymerization of oxazolines

[Cu(I) {6,6′-bis(bromomethyl)-2,2′-bipyridine}₂](PF₆) complexes were used as metallo-supramolecular initiators for the polymerization of 2-oxazolines resulting in defined polymers with a central 6,6′-disubstituted 2,2′-bipyridine unit. The living character of the polymerization was demonstrated with the linear relationship between the weight-average molecular weight M̄_w and the [monomer]/[initiator] ratio as well as in the synthesis of block copolymers. The metal ions could be removed resulting in uncomplexed polymers with a free central metal binding unit.     

Synthesis and microwave assisted polymerization of fluorinated 2-phenyl-2-oxazolines: the fastest 2-oxazoline monomer to date

The living cationic ring-opening polymerization of 2-oxazolines with fluorinated aromatic substituents was found to be strongly accelerated by o-fluoro substituents.     

Block and graft copolymers of 2-oxazolines

The cationic ring-opening polymerization of 2-oxazolines is known to be initiated by alkyl halides, Lewis acids and esters of strong acids. The polymerization proceeds by a living mechanism. Numerous block and graft copolymers have already been described. Recently it was found that chloroformates (R-O-CO-CI) are also useful initiators. The mechanism of the initiation and propagation is discussed. This type of initiators allows the synthesis of different novel two-block and three-block copolymers, star-shape polymers, and a graft copolymer with a polyvinylacetate backbone.     

Synthesis and characterization of a series of diverse poly(2‐oxazoline)s

This article describes the synthesis and characterization of a variety of new poly(2‐oxazoline)s. With regard to functional polymers, 2‐oxazolines represent an interesting class of monomers because of the easy variation of the substituent in 2‐position. Starting from the corresponding nitriles, different 2‐oxazolines were obtained containing a diverse set of 2‐substituents, including thioether bonds ( M11 ), trifluoromethyl groups ( M8 , M10 ), and alkyl‐ or aryl groups ( M1 – M7 ). The subsequent polymerization of the majority of these monomers proceeded in a living manner, which was demonstrated by linear first‐order kinetics, a linear increase of molar mass with conversion, and relatively narrow molar mass distributions. In addition, selected thermal and surface properties of the polymers were studied utilizing DSC and contact‐angle measurements to determine the effects of different 2‐substituents on the macroscopic properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3829–3838, 2009     

Star Poly(2-alkyl-2-oxazolines) Based on Octa-(chlorosulfonyl)-calix[8]arene

Starlike thermosensitive polymers were synthesized by cationic polymerization of 2-alkyl-2-oxazolines using a new type of sulfonyl chloride macroinitiator. It was confirmed that the polymerization on the multisulfonyl chloride initiator proceeds in the absence of irreversible chain termination and makes it possible to obtain polymers with a narrow molecular weight distribution. The polymers demonstrate a lower critical solution temperature and an ability to form complexes with hydrophobic low-molecular-weight compounds.     

Molar Mass Dispersity Control by Iodine-mediated Reversible-deactivation Radical Polymerization

Dispersity(D)of polymers has a great effect on the properties of polymeric materials,and therefore how to control D is very important but still a huge challenge in polymer synthesis,especially for reversible-deactivation radical polymerization(RDRP)strategy.Herein,we successfully developed a novel strategy to adjust D of polymers by visible light-controlled reversible complexation mediated living radical polymerization(RCMP)and combination of single-electron transfer-degenerative chain transfer living radical polymerization(SET-DTLRP)at room temperature.In RCMP system,2-iodo-2-methylpropionitrile(CP-I)and ethyl 2-iodo-2-phenylacetate(EIPA)were used as alkyl iodide initiators,by using methyl methacrylate(MMA)as the model monomer and n-butylacrylate(BA)as the end-capping reagent to regulate D of polymers.Subsequently,we successfully prepared the block copolymer PMMA-b-PBA with adjustable D by reactivating the polymer end-chains via SET-DTLRP in the presence of copper wire,fully demonstrating that it is a promising strategy that can keep the"living"feature of polymers while regulating their molar mass dispersities easily.     

Polymers with macrocyclic architectures: Synthesis and properties

The preparation by living polymerization and the investigation of the properties of polymers with cyclic chain architectures have been recently undertaken. The cyclization involves a unimolecular end-to-end reaction of a heterodifunctional linear precursor. The elementary steps of the cyclization mechanism are examined in the light of matrix-assisted laser desorption/ ionization mass spectrometry (MALDI-MS) data obtained on linear polystyrene precursors and cyclized products. The synthetic procedures developed to prepare macrocyclic polymers of various structures, as well as macrocyclic random and block copolymers are then reviewed and discussed. The main characteristics of the cyclic (co)polymers are compared to the corresponding linear chains and some of the original properties that are induced by the cyclic chain architecture are presented.     

Synthesis and characterization of telechelic polymethacrylates via RAFT polymerization

The reversible addition–fragmentation chain transfer (RAFT) polymerization technique has been employed to synthesize linear α,ω ‐telechelic polymers with either hydroxyl or carboxyl end groups. Methyl methacrylate, butyl methacrylate, and butyl acrylate were polymerized with RAFT polymerization. The polymerizations exhibited the usual characteristics of living processes. Telechelic polymethacrylates were obtained from a hydroxyl monofunctional RAFT polymer with a two‐step chain‐end modification procedure of the dithioester end group. The procedure consisted of an aminolysis followed by a Michael addition on the resulting thiol. The different steps of the procedure were followed by detailed analysis. It was found that this route was always accompanied by side reactions, resulting in disulfides and hydrogen‐terminated polymer chains as side products next to the hydroxyl‐terminated telechelic polymers. Telechelic poly(butyl acrylates) with carboxyl end groups were produced in a single step procedure with difunctional trithiocarbonates as RAFT agents. The high yield in terms of end group functionality was confirmed by a new critical‐liquid‐chromatography method, in which the polymers were separated based on acid‐functionality and by mass spectrometry analysis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 959–973, 2005     

Free-radical synthesis of block copolymers on an industrial scale

Controlled free-radical polymerization has been monitored with great interest in recent years since it offers an opportunity to combine the advantages of conventional free-radical polymerization with those of living ionic polymerization. We present the 1,1-diphenylethene (DPE) method which enables us to produce block copolymers on an industrial scale by a free-radical mechanism. This DPE process enables industrially relevant monomers, such as styrene, methacrylates, acrylates, methacrylic acid, acrylic acid and N-vinyl compounds, to be converted into block copolymers. The synthesis can be carried out in organic solvents, without solvents or in water. We have been able to demonstrate, that the addition of 1,1-diphenylethylene to a normal free-radical polymerization results in polymers whose molar mass, after a short uncontrolled phase, increases in a linear manner with conversion. The amount of 1,1-diphenylethylene added also determines the order of magnitude of the final molar mass. It was also possible to employ the polymers isolated during this polymerization as initiators for the polymerization of a further monomer, resulting in the formation of block copolymers. With possibly somewhat reduced claims on the perfection of the structures, a wide variety of possibilities arise with the known advantages of free-radical polymerization. The one-pot synthesis is carried out by simple successive addition of the desired monomers and has already been used successfully on an industrially relevant scale.     

One-pot syntheses, coordination, and characterization of application-specific biodegradable ligand-polymers

Syntheses and chelation of tailored biodegradable polymers to rhenium for medicinal applications are described. A group of bifunctional ligand-initiators consisting of a chelating end for metal complexation and a hydroxyl end suitable to initiate polymerization was utilized in the ring-opening polymerization of l-lactide. The resulting biodegradable ligand-polymers were equipped with a tridentate donor set to coordinate specific metal ions. All synthesized compounds were characterized by IR spectroscopy, 1D/2D NMR spectroscopy and MALDI-TOF mass spectrometry, confirming successful polymerization and coordination to the [Re(CO)(3)](+) core. The pliability of designing application-specific polymers with respect to the nature of the metal ion facilitates extending the application of these biodegradable polymers to early detection of diseases (imaging) and radiotherapy of cancers.     

Polymerization of 1-aryl-2-trimethylsilylacetylenes by transition metal catalysts(II)

Polymerization of 1-aryl-2-trimethylsilylacetylene (aryl = thienyl, furyl, and pyridyl) was carried out by transition metal catalysts. The polymer yield was generally low due to the steric hindrance. R₄Sn (R = Me, n-Bu, Ph) exhibits some cocatalytic activities with respect to polymer yield and molecular weight. On the other hand, the polymerization was decelerated when organoaluminum compounds were used as cocatalysts. The polymer yield increased in the following order: phenyl > thienyl > furyl > pyridyl, according to the aryl substituents. The NMR (¹H- and ¹³C-), IR, and UV-visible spectra indicated that the resulting polymers have a linear conjugated polyene structure each containing the aromatic substituent and trimethylsilyl group. From ¹H-NMR integration, it was found that the resulting polymers are partially desilylated depending on the substituents of monomer and the polymerization conditions. The solubility behavior, stability and fluoride-ion induced desilylation reaction of the polymers were also studied.     

Homopolymerization of 2-alkyl- and 2-aryl-2-oxazolines

2-Aryl- and 2-alkyl-2-oxazolines have been polymerized to poly-(N-aroyl)aziridines and poly(N-acyl)aziridines, respectively, in the presence of boron trifluoride. The polymers obtained were glassy, light yellow resins with molecular weights ranging from 3500 to 7500 (35–50 oxazoline units per chain). The polymerization rates have been determined for several of these monomers. A polymerization mechanism is proposed.     

Organosilicon hydrides in macromolecular design: Reactions of chain-transfer and hydrosilylation

The chain-transfer constants through silicon hydrides in bulk polymerization of styrene and methyl methacrylate (MMA) were measured with using 15 organosilicon compounds belonging to four classes: oligoorganohydrosilanes, oligoorganohydrosiloxanes, disilalkanes and alkylhydrosilanes. The linear dependences of the logarithm of chain-transfer constant on the sum of the Taft inductive constants of substituents at silicon atoms of a Si-H group were found. The negative values of reaction constants ρ indicate that an electrophilic attack of macroradical onto a hydrogen atom occurs at the limiting stage of the process. Oligoorganohydrosilanes proved to be the most effective chain-transfer agents that can be explained by high electron-donating properties of R₃Si substituents. The increase of the chain-transfer constant values takes place on the accumulation of both trimethylsilyl and silicon hydride groups in a molecule of hydrosilane. The high electrophilicity of PMMA macroradical as compared with a macroradical of polystyrene (PS) is responsible for a greater sensitivity of the polymerization reaction of MMA to the change of the electron density on a hydrogen atom of the organosilicon chain-transfer agent. In the radical polymerization of MMA and styrene in the presence of the chain-transfer agents till high conversion the polymers with a narrower molecular weight distribution (MWD) in comparison with those synthesized by usual polymerization in bulk are formed. The polymers prepared in the presence of multifunctional silanes can be functionalized by the reaction of hydrosilylation and further used in the synthesis of block copolymers.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and nuclear magnetic resonance analyses of end-functionalized saccharidic polymers: an example of a useful analytical technique combination

The living cationic polymerization of a saccharidic monomer (1,2:3,4-di-O-isopropylidene-6-O-(2-vinyloxyethyl)-D-galactopyranose, GVE) gives rise to aldehyde end-capped polymers (PGVE--CHO) of low molar masses (<10 000 Da) and low molar mass distribution (<1.2). These polymers were derivatized by selective introduction of either hexamethylenediamine (PGVE-NH2) or 9-fluorenylmethyl carbazate (PGVE-Fmoc) end groups. The resulting polymers were fully characterized by complementary use of nuclear magnetic resonance (1H NMR) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The expected structure according to the polymerization mechanism, the occurrence of side reactions and the success of the post-functionalization reactions were confirmed.     

Amphiphilic Polymers Based on Poly(2-oxazoline)s – From ABC-Triblock Copolymers to Micellar Catalysis

In this presentation we give an overview on our results in the field of poly(2-oxazolines). By means of living cationic polymerization in combination with the initiation and termination method, functionalized poly(2-oxazoline)s have been prepared, that were used as (i) macromonomers to form graft copolymers, (ii) lipopolymers to prepare stealth liposomes, (iii) ABC like polymers to form two compartment micellar networks and (iv) macroligand for micellar catalysis application. Within this report, we will discuss in detail the synthesis and characterization of various poly(2-oxazoline)s for the above mentioned research areas.     

Tandem mass spectrometry of poly(ethylene imine)s by electrospray ionization (ESI) and matrix‐assisted laser desorption/ionization (MALDI)

In this contribution, linear poly(ethylene imine) (PEI) polymers, which are of importance in gene delivery, are investigated in detail by using electrospray ionization‐quadrupole‐time of flight (ESI‐Q‐TOF) and matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF) mass spectrometry (MS). The analyzed PEIs with different end groups were synthesized using the polymerization of substituted 2‐oxazoline via a living cationic ring‐opening polymerization (CROP) and a subsequent hydrolysis under acidic conditions. The main goal of this study was to identify linear PEI polymers in a detailed way to gain information about their fragmentation pathways. For this purpose, a detailed characterization of three different linear PEIs was performed by using ESI‐Q‐TOF and MALDI‐TOF MS in combination with collision‐induced dissociation (CID) experiments. In ESI‐MS as well as MALDI‐MS analysis, the obtained spectra of PEIs resulted in fitting mass distributions for the investigated PEIs. In the tandem MS analysis, a 1,2‐hydride shift with a charge‐remote rearrangement via a four‐membered cyclic transition state, as well as charge‐induced fragmentation reactions, was proposed as the main fragmentation mechanisms according to the obtained fragmentation products from the protonated parent peaks. In addition, heterolytic and homolytic cleavages were proposed as alternative fragmentation pathways. Moreover, a 1,4‐hydrogen elimination was proposed to explain different fragmentation products obtained from the sodiated parent peaks. Copyright © 2012 John Wiley & Sons, Ltd.     

Oligomers Derived from 2-Oxazolines

This paper describes the synthesis and properties of oligomer chains derived from 2-oxazolines. First, poly(styrene-g-N-acetyl-ethylenimine) was prepared, and its hydrolysis gave poly(styrene-g-ethylenimine) which showed good chelating properties. Secondly, ABA type triblock copolymers were prepared in which an N-acylethylenimine chain is used as A block and ethylene oxide chain is employed as B block. These triblock copolymers showed good compatibility with Nylon 6, which were shown to posecess effective anti-electrostatic properties for Nylon 6. Thirdly, AB type block copolymers from 2-oxazolines have been prepared by using living polymerization technique. These block copolymers are soluble in water and showed good surfactant nature as reflected by surface tension (γ), when A block is consisted from N-acetyl- or N-propionylethylenimine chain (hydro-philic) and B block is made of N-tridecanoyl or N-aroylethylenimine chain (lipophilic). Finally, graft copolymers of cellulose diacetate having N-acetylethylenimine chain were prepared. It has been found by using a rheovibron that these graft copolymers are compatible with poly(vinyl chloride).     

Control of polymer topology through transition-metal catalysis: synthesis of hyperbranched polymers by cobalt-mediated free radical polymerization

A novel approach was demonstrated for the synthesis of hyperbranched polymers by direct free radical polymerization of divinyl monomers controlled by a cobalt chain transfer catalyst (1). By controlling the competition between propagation and chain transfer with 1, the free radical polymerization of ethylene glycol dimethacrylate (3) afforded soluble hyperbranched polymers in one pot. The structure of the hyperbranched polymers was confirmed by (1)H and (13)C NMR. The molecular weight and intrinsic viscosity of the hyperbranched polymers were measured by matrix-assisted laser desorption ionization (MALDI) mass spectrometry and size exclusion chromatography (SEC) equipped with triple detectors. The intrinsic viscosities of the hyperbranched polymers are much lower than those of their linear analogues and do not show molecular weight dependence. The unique structure and properties of these hyperbranched polymers combined with the commercial availability of many divinyl monomers and the robustness of free radical polymerization make this new approach attractive for the preparation of new functional materials.     

Selective functionalization of cyano-phenyl-2-oxazolines using TMPMgCl·LiCl

Metalated phenyl-2-oxazolines bearing cyano groups can be selectively obtained through the reaction of TMPMgCl·LiCl with the appropriate substrate. Subsequent reaction with different electrophiles furnished the functionalized derivatives in good yields. Density functional theory (DFT) calculations were performed to evaluate the influence of the ring substituents on the acidity of the aromatic hydrogens. Application to the synthesis of novel functionalized phthalides illustrates the great potential of the methodology to the synthesis of bioactive compounds.     

Terpyridine Based Metallo-Supramolecular Initiators: Towards Novel Self-Organizing Materials

[Fe(II){5,5- bis(bromomethyl)-terpyridin}₂](PF₂6)₂2 complexes were used as metallo-supramolecular initiators for the living polymerization of 2-ethyl-2-oxazolines yielding defined hydrophilic polymers with a central supramolecular building unit and star-like architectures. The living character of the polymerization allows an exact control of the molecular weight as well as the incorporation of additional (complexing) units at the polymer chain ends.