Organometallic‐mediated radical polymerization (OMRP) has given access to well‐defined poly(vinyl acetate‐alt‐tert‐butyl‐2‐trifluoromethacrylate)‐b‐poly(vinyl acetate) and poly(VAc‐alt‐MAF‐TBE) copolymers composed of two electronically distinct monomers: vinyl acetate (VAc, donor, D) and tert‐butyl‐2‐trifluoromethacrylate (MAF‐TBE, acceptor, A), with low dispersity (≤1.24) and molar masses up to 57 000 g mol−1. These copolymers have a precise 1:1 alternating structure over a wide range of comonomer feed compositions. The reactivity ratios are determined as r VAc = 0.01 ± 0.01 and r MAF‐TBE = 0 at 40 °C. Remarkably, from a feed containing >50% molar VAc content, poly(VAc‐alt‐MAF‐TBE)‐b‐PVAc block copolymers are produced via a one‐pot synthesis. Such diblock copolymers exhibit two glass transition temperatures attributed to the alternating and homopolymer sequences. The OMRP of this fluorine‐containing alternating monomer system may provide access to a wide range of new polymer materials.
The controlled synthesis of poly(oligo(2‐ethyl‐2‐oxazoline)methacrylate) (P(OEtOxMA)) polymers by Cu(0)‐mediated polymerization in water/methanol mixtures is reported. Utilizing an acetal protected aldehyde initiator for the polymerization, well‐defined polymers are synthesized (>99% conversion, Ð < 1.25) with subsequent postpolymerization deprotection resulting in α‐aldehyde end group containing comb polymers. These P(OEtOxMA) are subsequently site‐specifically conjugated, via reductive amination, to a dipeptide (NH2‐Gly‐Tyr‐COOH) as a model peptide, prior to conjugation to the functional peptide oxytocin. The resulting oxytocin conjugates are evaluated in comparison to poly(oligo(ethylene glycol) methyl ether methacrylate) combs synthesized in the same manner for potential effects on thermal stability in comparison to the native peptide.
A novel bifunctional monomer, namely maleimide glycidyl ether (MalGE), prepared in a four‐step reaction sequence is introduced. This monomer allows for selective (co)polymerization of the epoxide group via cationic ring‐opening polymerization, preserving the maleimide functionality. On the other hand, the maleimide functionality can be copolymerized via radical techniques, preserving the epoxide moiety. Cationic ring‐opening multibranching copolymerization of MalGE with glycidol was performed, and a MalGE content of up to 24 mol% could be incorporated into the hyperbranched polymer backbone (Mn = 1000–3000 g mol−1). Preservation of the maleimide functionality during cationic copolymerization was verified via NMR spectroscopy. Subsequently, the maleimide moiety was radically crosslinked to generate hydrogels and additionally employed to perform Diels‐Alder (DA) “click” reactions with (functional) dienes after the polymerization process. Radical copolymerization of MalGE with styrene (Mn = 5000–9000 g mol−1) enabled the synthesis of a styrene copolymer with epoxide functionalities that are useful for versatile crosslinking and grafting reactions.
Self‐initiated photografting polymerization is used to couple the polymerizable initiator monomer 2‐(2‐chloropropanoyloxy)ethyl acrylate to a range of polymeric substrates. The technique requires only UV light to couple the initiator to surfaces. The initiator surface density can be varied by inclusion of a diluent monomer or via selection of initiator and irradiation parameters. The functionality of the initiator surface is demonstrated by subsequent surface‐initiated atom transfer radical polymerization. Surfaces are characterized by x‐ray photoelectron spectroscopy (XPS), ellipsometry, and atomic force microscopy (AFM), and UV‐induced changes to the initiator are assessed by 1H NMR and gel permeation chromatography (GPC). This is the first time this one‐reactant one‐step technique has been demonstrated for creating an initiator surface of variable density.
A novel photo‐induced homogeneous atom transfer radical polymerization (ATRP) system is constructed using an organic copper salt (Cu(SC(S)N(C2H5)2)2) as a photo‐induced catalyst at 30 °C. Herein, N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) is used as a ligand, ethyl 2‐bromophenylacetate (EBPA) as an ATRP initiator, and (2,4,6‐trimethylbenzoyl) diphenylphosphine oxide (TPO) as a photo‐induced radical initiator to establish an ICAR (initiators for continuous activator regeneration) ATRP using methyl methacrylate (MMA) as a modal monomer. The effect of the concentration of the organic copper on the polymerization is investigated in detail. It is found that well‐controlled polymerization can be obtained even with the amount of (Cu(SC(S)N(C2H5)2)2 decreasing to a 1.56 ppm level, with the molecular weight of the resultant polymers increasing linearly with monomer conversion while maintaining a narrow molecular weight distribution (/ < 1.3).
Atom transfer radical polymerization (ATRP) catalyzed by high oxidation state metal salts of FeX3 is developed for the first time in the absence of both external initiator and reducing agent. Methyl methacrylate (MMA) and styrene are polymerized successfully using FeX3/Phosphorous ligands with well‐controlled molecular weight distributions (=1.5). The molecular weight of the polymers increases with monomer consumption with the progress of time and the polymerization behaviors show a decent ATRP trend. Activators and initiators are suggested to generate in situ by the addition reaction of MMA and one equivalent of FeX3. The PMMA synthesized from without‐initiator system is characterized by 1H, 13C and DEPT (distortionless enhancement by polarization transfer nuclear magnetic resonance) nuclear magnetic resonance spectroscopy. Chain extension and copolymerization experiments prove the livingness of the obtained polymer.
In this work, the synthesis of various halogenated thiophenol derivatives is presented. These thiophenols are used as monomers in light‐initiated SRN1‐type radical polymerization reactions. The method provides easy access to industrially relevant poly(paraphenylene sulfide) and poly(metaphenylene sulfide). The influence of the halide leaving group and of other substituents in the thiophenol monomer on the polymerization process is investigated.
A switch from carbanions to aza‐anions is performed by the addition of N‐tosylaziridine (TAz) to living poly(styryl) (PS) chains. This is the first example of carbanionic aziridine ring‐opening which was previously activated by amidation with a tosyl group to enable nucleophilic ring‐opening by the living chain end. Poly(styrene)‐tosylaziridines (PS‐TAz) with narrow molecular weight distributions and variable molecular weights are synthesized. The removal of the tosyl group and subsequent functionalization is shown, evidencing quantitative transfer to azaanionic species. All polymers are characterized in detail by 1H NMR spectroscopy, DOSY 1H NMR spectroscopy, and size exclusion chromatography (SEC). This strategy allows the introduction of amine groups via anionic polymerization in analogy to the well‐established epoxide termination.
The accomplishments in the copolymerization of ethylene with cyclic olefins such as norborn‐2‐ene or cis‐cyclooctene via tandem ring‐opening metathesis polymerization (ROMP) – vinyl insertion polymerization (VIP) are outlined. This approach provides polyolefins with high molecular weight (600,000 < Mn < 4,500,000 g mol−1) and substantial amounts of double bonds along the polymer main chain. Olefinic moieties in ROMP‐derived polymers can be converted into hydroxyl, amino, silyl, ester, or carboxylate groups by different means including controlled radical polymerization‐based grafting. The underlying concept for the switch in polymerization mechanism, the resulting pre‐catalyst requirements, limitations and challenges and the chemistry developed for functionalizing unsaturated polymers are outlined in detail.
A direct and facile route toward semitelechelic polymers, end‐functionalized with palladated sulfur–carbon–sulfur pincer (PdII‐pincer) complexes is reported that avoids any post‐polymerization step. Key to our methodology is the combination of reversible addition‐fragmentation chain‐transfer (RAFT) polymerization with functionalized chain‐transfer agents. This strategy yields Pd end‐group‐functionalized materials with monomodal molar mass dispersities (Đ ) of 1.18–1.44. The RAFT polymerization is investigated using a PdII‐pincer chain‐transfer agent for three classes of monomers: styrene, tert‐butyl acrylate, and N‐isopropylacrylamide. The ensuing PdII‐pincer end‐functionalized polymers are analyzed using 1H NMR spectroscopy, gel‐permeation chromatography, and elemental analysis. The RAFT polymerization methodology provides a direct pathway for the fabrication of PdII‐pincer functionalized polymers with complete end‐group functionalization.
Star copolymers are known to phase separate on the nanoscale, providing useful self‐assembled morphologies. In this study, the authors investigate synthesis and assembly behavior of miktoarm star (μ‐star) copolymers. The authors employ a new strategy for the synthesis of unprecedented μ‐star copolymers presenting poly(N‐octyl benzamide) (PBA) and poly(ε‐caprolactone) (PCL) arms: a combination of chain‐growth condensation polymerization, styrenics‐assisted atom transfer radical coupling, and ring‐opening polymerization. Gel permeation chromatography, mass‐analyzed laser desorption/ionization mass spectrometry, and 1H NMR spectroscopy reveal the successful synthesis of a well‐defined (PBA11)2‐(PCL15)4 μ‐star copolymer (M n,NMR ≈ 12 620; Đ = 1.22). Preliminary examination of the PBA2PCL4 μ‐star copolymer reveals assembled nanofibers having a uniform diameter of ≈20 nm.
Polyethers—polymers with the structural element (R'‐O‐R)n in their backbone—are an old class of polymers which were already used at the time of the ancient Egyptians. However, still today these materials are highly important with applications in all areas of our life, reaching from the automotive and paper industry to cosmetics and biomedical applications. In this Review, different aliphatic polyethers like poly(epoxide)s, poly(oxetane)s, and poly(tetrahydrofuran) are discussed. Special emphasis is placed on the history, the polymerization techniques (industrially and in academia), the properties, the applications as well as recent developments of these materials.
Polyfluorene‐bearing bromohexyl side chains are quaternized by 1‐vinylimidazole in order to attach dialkylimidazolium bromide ionic liquid (IL) species along the conjugated backbone. Subsequently, polyfluorene polyelectrolyte nanoparticles (NPs) of 40 nm in average size are created via radical cross‐linking of the pendant vinylimidazolium groups. Anion exchange from Br− to BF4−, PF6−, and bis(trifluoromethylsulfonyl)imide anion (TFSI−) renders NPs adjustable dispersability in various organic solvents. The hydrophobic‐conjugated backbone and the hydrophilic dialkylimidazolium bromide IL moieties depict an amphiphilic profile, which allows the NPs to be deployed as conductive stabilizer in the emulsion polymerization of styrene. The resultant latexes are fluorescent, tunable in size and can be transferred to organic solvents without forfeiting their colloidal stability.
The successful chain‐growth copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) polymerization employing Cu(0)/pentamethyldiethylenetriamine (PMDETA) and alkyl halide as catalyst is first investigated by a combination of nuclear magnetic resonance, gel‐permeation chromatography, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. In addition, the electron transfer mediated “click‐radical” concurrent polymerization utilizing Cu(0)/PMDETA as catalyst is successfully employed to generate well‐defined copolymers, where controlled CuAAC polymerization of clickable ester monomer is progressed in the main chain acting as the polymer backbone, the controlled radical polymerization (CRP) of acrylic monomer is carried out in the side chain. Furthermore, it is found that there is strong collaborative effect and compatibility between CRP and CuAAC polymerization to improve the controllability.
Via electron paramagnetic resonance (EPR) spectroscopy, the type of radicals occurring during acrylamide (AAm) homopolymerization in aqueous solution is investigated between −5 and +100 °C. The radicals are produced photochemically under stationary conditions. Midchain AAm radicals (MCRs) are clearly identified by EPR which demonstrates that secondary propagating AAm radicals (SPRs) undergo backbiting reactions. Above 50 °C, the fraction of MCRs even exceeds the one of SPRs. The extent of backbiting is however well below the one in butyl acrylate polymerization at identical temperature.
Vinyl acetate is polymerized in the living way under the irradiation of blue light‐emitting diodes (LEDs) or sunlight without photocatalyst at ambient temperature. 2‐(Ethoxycarbonothioyl)sulfanyl propanoate is exclusively added and acts as initiator and chain transfer agent simultaneously in the current system. Poly(vinyl acetate) with well‐regulated molecular weight and narrow molecular weight distribution (Đ < 1.30) is synthesized. Near quantitative end group fidelity of polymer is demonstrated by nuclear magnetic resonance (NMR) and matrix‐assisteed laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS).
Ring‐opening metathesis polymerization of 4‐phenylcyclopentene is investigated for the first time under various conditions. Thermodynamic analysis reveals a polymerization enthalpy and entropy sufficient for high molar mass and conversions at lower temperatures. In one example, neat polymerization using Hoveyda–Grubbs second generation catalyst at −15 °C yields 81% conversion to poly(4‐phenylcyclopentene) (P4PCP) with a number average molar mass of 151 kg mol−1 and dispersity of 1.77. Quantitative homogeneous hydrogenation of P4PCP results in a precision ethylene‐styrene copolymer (H2‐P4PCP) with a phenyl branch at every fifth carbon along the backbone. This equates to a perfectly alternating trimethylene‐styrene sequence with 71.2% w/w styrene content that is inaccessible through molecular catalyst copolymerization strategies. Differential scanning calorimetry confirms P4PCP and H2‐P4PCP are amorphous materials with similar glass transition temperatures (Tg) of 17 ± 2 °C. Both materials present well‐defined styrenic analogs for application in specialty materials or composites where lower softening temperatures may be desired.
For the first time, the successful Gilch synthesis of poly(ortho‐phenylene vinylenes) (ortho‐PPVs) is reported. The molar mass of the constitutionally homogeneous ortho‐PPVs reaches values as high as Mw ≈ 300 000 Da. The ortho‐connectivity of the repeating units forces the chains to assume closely packed conformations even in good solvents. Significant perturbation of the π–electron systems and considerable shortening of the conjugation lengths are the consequences. UV–vis absorption and photoluminescence maxima consequently are shifted clearly toward shorter wavelengths compared to, e.g., classic para‐PPVs.
Iron‐mediated atom transfer radical polymerization (ATRP) has gained extensive attention because of the superiority of iron catalysts, such as low toxicity, abundant reserves, and good biocompatibility. Herein, a practical iron catalyst recycling system, photoinduced iron‐based water‐induced phase separable catalysis ATRP with initiators for continuous activator regeneration, at room temperature is developed for the first time. In this polymerization system, the polymerization is conducted in homogenous solvents consisting of p‐xylene and ethanol, using commercially available 5,10,15,20‐tetraphenyl‐21H,23H‐porphine iron(III) chloride as the iron catalyst, ethyl 2‐bromophenylacetate as the ATRP initiator, 2,4,6‐trimethylbenzoyl diphenylphosphine oxide as the photoinitiator, and poly(ethylene glycol) methyl ether methacrylate as the model hydrophilic monomer. After polymerization, a certain amount of water is added to induce the phase separation so that the catalyst can be separated and recycled in p‐xylene phase with very low residual metal complexes (<12 ppm) in the resultant polymers even after six times recycle experiments.
A commercially available palladium N‐heterocyclic carbene (Pd‐NHC) precatalyst is used to initiate chain‐growth polymerization of 2‐bromo‐3‐hexyl‐5‐trimethylstannylthiophene. The molecular weight of the resultant poly(3‐hexylthiophene) can be modulated (7 to 73 kDa, Đ = 1.14 to 1.53) by varying the catalyst concentration. Mass spectrometry data confirm control over the polymer end groups and 1H NMR spectroscopy reveals that the palladium catalyst is capable of “ring‐walking”. A linear relationship between Mn and monomer conversion is observed. Atomic force microscopy and X‐ray scattering verify the regioregular nature of the resultant polythiophene.
