Ω-chain End Research Articles

Facile End-Functionalization of Poly(Quinolylene-2,3-Methylene) Using the Terminal Palladium Complex: Thiocarbonylation through Formation of an Acyl Palladium Complex at the Polymer Terminal.

The end-functionalization of poly(quinolylene-2,3-methylene)s (PQM) via thiocarbonylation is successfully achieved by forming an acyl palladium complex. The terminal palladium complex of the PQMs synthesized by living cyclocopolymerization of o-allenylaryl isocyanide is quantitatively converted to a tractable acyl palladium complex through the carbon monoxide insertion into a palladium-carbon bond. The resulting acyl palladium complex exhibits high reactivity toward thiols, thereby enabling the introduction of various substituents at the ω-chain end of PQM by selectively converting them to thioester groups. The one-pot procedure enables the arbitrary control of both terminal structures of PQMs, including the synthesis of multi-armed block copolymers and a triblock polymer. Additionally, the resulting thioester groups can serve as reactive sites and be converted into amide groups using amines. The new end-functionalization method has the potential to be applied not only to the synthesis of PQM but also to other polymerization reactions using transition-metal complexes, and can lead to a wide range of developments in polymer synthesis.

Utilization of Catechol End-Functionalized PMMA as a Macromolecular Coupling Agent for Ceramic/Fluoropolymer Piezoelectric Composites

An approach based on the use of a macromolecular coupling agent and the aim to improve the interfacial adhesion between piezoelectric ceramics and piezoelectric polymer matrix in piezoelectric composites is presented. Poly(methyl methacrylate) (PMMA) bearing a catechol moiety was used as a macromolecular coupling agent, as it is known to be miscible to piezoelectric fluoropolymers and catechol groups can strongly bind to a large variety of surfaces. Thus, entanglement between the PMMA chains and the amorphous segments of the fluoropolymer would ensure the desired interfacial adhesion. Well-defined PMMA was synthesized via RAFT polymerization using 2-cyano-2-propyl dodecyl trithiocarbonate as a chain-transfer agent. The PMMA ω-chain end was then functionalized with a catechol group via a one-pot aminolysis/thia-Michael addition procedure using a dopamine acrylamide (DA) derivative as a Michael acceptor. The presence of the catechol moiety at the chain end of PMMA was controlled by 1H NMR and cyclic voltammetry measurements. The resulting PMMA-DA was then grafted onto the surface of a lead-free piezoelectric ceramic film (i.e., a thin film of H2O2-activated (Bi0.5Na0.5)TiO3 (BNT) with a large contact area). The increase of the water contact angle confirmed the efficiency of the grafting. A commercial piezoelectric copolymer P(VDF-co-TrFE) was then spin-coated onto the modified BNT surface to form a bilayer composite. The composite cross section prepared by cryofracture was examined by scanning electron microscopy and revealed that the ceramic/polymer interface of the BNT-PMMA/P(VDF-co-TrFE) bilayer composite exhibits a much better cohesion than its counterpart composite prepared from nonmodified BNT. Moreover, the grazing incidence wide-angle X-ray scattering confirmed that the copolymer crystal structure was not impacted by the presence of the PMMA-DA coupling agent. A strong piezoelectric response was locally detected by piezoresponse force microscopy. This study highlights the potential of PMMA-DA as a macromolecular coupling agent to improve the ceramic/polymer interface in piezoelectric composite materials.

Well-Defined PIII-Terminated Polymers from Phosphorylated Carbodithioate RAFT Agents

Five S-alkyl di-tert-butylphosphorylated carbodithioates, Z–C(S)SR, were studied as chain transfer agents (CTAs) in the RAFT polymerization of vinyl monomers. These phosphorus-containing CTAs involve new PIII and PV moieties in the Z group (phosphine-borane or free phosphine). Two of them, with an S-bonded 1-methoxycarbonylethyl group as leaving group, have not previously been described. The CTAs with a PV Z group provide good control over the polymerization of styrene (St) and n-butyl acrylate (nBA). Molar masses are close to theoretical values, and dispersities are consistently low during polymerization. The monitoring of polymerization by 31P NMR spectroscopy supports the controlled character and the integrity of the polymer chain ends. Conversely, they inhibit the polymerization of the less-activated monomer vinyl acetate (VAc). The reactivity of the CTAs with a PIII Z group mainly depends on the reaction medium, and their performance for St, nBA, and VAc was surprising and unexpected. Theoretical calculations were carried out to rationalize their behavior. Finally, an innovative strategy was developed to obtain well-controlled polymers with free phosphine ω-chain ends.

Poly(N-vinylpyrrolidone) Antimalaria Conjugates of Membrane-Disruptive Peptides.

The concepts of polymer-peptide conjugation and self-assembly were applied to antimicrobial peptides (AMPs) in the development of a targeted antimalaria drug delivery construct. This study describes the synthesis of α-acetal, ω-xanthate heterotelechelic poly(N-vinylpyrrolidone) (PVP) via reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization, followed by postpolymerization deprotection to yield α-aldehyde, ω-thiol heterotelechelic PVP. A specific targeting peptide, GSRSKGT, for Plasmodium falciparum-infected erythrocytes was used to sparsely decorate the α-chain ends via reductive amination while cyclic decapeptides from the tyrocidine group were conjugated to the ω-chain end via thiol-ene Michael addition. The resultant constructs were self-assembled into micellar nanoaggregates whose sizes and morphologies were determined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The in vitro activity and selectivity of the conjugates were evaluated against intraerythrocytic P. falciparum parasites.

Copolymers and Hybrids Based on Carbazole Derivatives and Their Nanomorphology Investigation.

Oligomers of the low-band-gap PCDTBT polymer, based on either 3,6 or 2,7 carbazole units, were modified with vinyl ω-chain end functionalities. The vinyl-functionalized oligomers were used as comonomers in free radical polymerizations with quinoline-based monomers such as 6-vinylphenyl-(2-pyridinyl)-4-phenyl-quinoline (vinyl-QPy), and 6-vinylphenyl-(2-perfluorophenyl)-4-phenyl quinoline (vinyl-5FQ). The co-polymeric materials bearing the vinyl-QPy moiety were developed as potential compatibilizers in polymer electron donor–fullerene acceptor blends for non-covalent interactions with the fullerene part. The co-polymeric materials bearing the vinyl-5FQ moiety were developed for the covalent attachment of carbon nanostructures; specifically, PC61BM. Both copolymers and hybrids, after thorough purification, were characterized in terms of their spectroscopic and optical properties as well as their ability to form nanophased separated films as such, or as additives at various percentages into PCDTBT: PC71BM blends.

A new, simple, and efficient strategy for the preparation of active antifungal biodegradable materials via ring-opening polymerization of l-lactide with zinc aryloxides.

In this work, zinc aryloxides supported by monodentate hydroxybiphenyls [ArOH: ortho-phenylphenol (o-XenOH), meta-phenylphenol (m-XenOH), or para-phenylphenol (p-XenOH] and N,N,N',N'-tetramethylethylenediamine (TMEDA) were used to develop active polymeric materials for antifungal agents for agricultural use. The direct reaction of ligand precursor ArOH with ZnEt2 (1 : 2) in a toluene/TMEDA mixture (1 : 10) afforded a series of three isostructural monomeric compounds, namely [Zn(o-XenO)2(TMEDA)] (1), [Zn(m-XenO)2(TMEDA)] (2), and [Zn(p-XenO)2(TMEDA)] (3). These were characterized by single-crystal X-ray diffraction, and spectroscopic and other analytical methods. The results show that 1-3 are effective initiators for the ring-opening polymerization (ROP) of l-lactide (l-LA) via bifunctional activation of the monomer with Lewis pairs to give polymers terminated with TMEDA and Zn(OAr)2 as the α- and ω-chain ends, respectively. Combinations of ZnEt2 with two molar equivalents of ArOH proligands were used to synthesize polylactides containing fungicide molecules covalently bonded via ester linkers. The ROP of l-LA initiated by these zinc-based systems could be used for the preparation of polyesters with promising antifungal activities.

Installing a functional group into the inactive ω-chain end of PMMA and PS-b-PMMA by terminal-selective transesterification

Various functional groups were incorporated into the inherently inactive ω-chain end of polymethacrylate-based polymers by terminal-selective transesterification.

Synthesis of Highly Defined Graft Copolymers Using a Cyclic Acetal Moiety as a Two-Stage Latent Initiating Site for Successive Living Cationic Polymerization and Ring-Opening Anionic Polymerization

The synthesis of well-defined graft copolymers with designed intervals between branches was achieved using cyclic acetal moieties as two-stage latent initiating sites. A cyclic acetal was shown to initiate the living cationic polymerization of vinyl ethers (VEs), yielding a polymer with a hydroxy group at the α-end derived from the cyclic acetal. The newly generated hydroxy group was able to efficiently induce the subsequent ring-opening anionic polymerization of l-lactide (LLA), and a diblock copolymer with a narrow molecular weight distribution (MWD) was obtained. For the synthesis of a graft copolymer, a five-membered cyclic acetal moiety was introduced at the ω-chain ends of poly(VE)s, which was employed as the initiating site for the living cationic polymerization of VEs. Repeated polymerization and acetalization generated a macroinitiator with several hydroxy groups on the side chain of a poly(VE) backbone. Graft copolymers possessing branches with narrow MWDs and regular spaces between the branches...

One-Pot Synthesis of Thermoresponsive Amyloidogenic Peptide-Polymer Conjugates via Thio-Bromo "Click" Reaction of RAFT Polymers.

A synthetic strategy to efficiently prepare main-chain peptide-polymer conjugates probing their aggregation in solution is described. An in situ tandem reaction based on aminolysis/thio-bromo "click" reaction is performed to tether an amyloidogenic peptide fragment amyloid-β17-20 (Leu-Val-Phe-Phe (LVFF)) to the ω-chain end of poly(diethylene glycol methyl ether acrylate) (PDEGA), prepared via reversible addition fragmentation chain transfer polymerization. Structural confirmation of the constructed conjugates PDEGA-LVFF (Mn,SEC = 5600, Ð = 1.21), (Mn,SEC = 7600, Ð = 1.16), and (Mn,SEC = 8900, Ð = 1.15) is successfully made by combined studies of 1 H NMR, size-exclusion chromatography, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and electrospray ionization time-of-flight (ESI-TOF) mass spectrometry. The effect of the peptidic constituent on the thermoresponsive behavior of the polymer is examined by UV-vis spectroscopy, and the self-assembly behavior of the amphiphilic conjugate is further exploited, exhibiting micellar morphology in aqueous solution.

Iodosylbenzene-Pseudohalide-Based Initiators for Radical Polymerization.

Iodosylbenzene reacts with various (pseudo)halides (trimethylsilyl azide or isocyanate or potassium azide, cyanate, and bromide) to yield unstable hypervalent iodine(III) compounds, PhIX2 (X = (pseudo)halide), that undergo rapid homolysis of the hypervalent I-X bonds and generate (pseudo)halide radicals, which can initiate the polymerization of styrene, (meth)acrylates, and vinyl esters. Polymers are formed containing (pseudo)halide functionalities at the α-chain end but, depending on the termination mechanism and the occurrence of transfer of (pseudo)halide groups from the initiator to the propagating radicals, also at the ω-chain end. With slowly polymerizing monomers (styrene and methyl methacrylate) and initiators that were generated rapidly at high concentrations and were especially unstable, the reactions proceeded via a "dead-end" polymerization mechanism, and only low to moderate monomer conversions were attained. When the initiator was generated more slowly and continuously throughout the polymerization (using the combination of iodosylbenzene with the poorly soluble potassium (pseudo)halide salts), typically higher conversions and higher molecular weights were reached. The presence of (pseudo)halide functionalities in the polymers was proved by elemental analysis, IR, and NMR spectroscopy. The azide-containing polymers underwent click-type coupling reactions with dialkynes, while the (iso)cyanate-containing polymers reacted with diamines to afford high-molecular-weight polymers with triazole- and urea-type interchain links, respectively.

"Grafting to" of RAFTed Responsive Polymers to Glass Substrates by Thiol-Ene and Critical Comparison to Thiol-Gold Coupling.

Surface-grafted polymers have been widely applied to modulate biological interfaces and introduce additional functionality. Polymers derived from reversible addition–fragmentation transfer (RAFT) polymerization have a masked thiol at the ω-chain end providing an anchor point for conjugation and in particular displays high affinity for gold surfaces (both flat and particulate). In this work, we report the direct grafting of RAFTed polymers by a “thiol–ene click” (Michael addition) onto glass substrates rather than gold, which provides a more versatile surface for subsequent array-based applications but retains the simplicity. The immobilization of two thermoresponsive polymers are studied here, poly[oligo(ethylene glycol) methyl ether methacrylate] (pOEGMA) and poly(N-isopropylacrylamide) (pNIPAM). Using a range of surface analysis techniques the grafting efficiency was compared to thiol–gold and was quantitatively compared to the gold alternative using quartz crystal microbalance. It is shown that this method gives easy access to grafted polymer surfaces with pNIPAM resulting in significantly increased surface coverage compared to pOEGMA. The nonfouling (protein resistance) character of these surfaces is also demonstrated.

Controlled and selective placement of boron subphthalocyanines on either chain end of polymers synthesized by nitroxide mediated polymerization

In previous studies, we synthesized the first organic light emitting diode (OLED) using boron subphthalocyanines (BsubPcs) based polymers. When designing new polymer materials for organic electronic applications such as OLEDs or organic photovoltaic (OPV) devices it is important to consider not only the contribution of each monomer but also the polymer chain ends. In this paper we establish a post-polymerization strategy to couple BsubPcs onto either the α- or the ω-chain end using chemically selective BsubPc derivatives. We outline how the chain ends of two representative polymers, poly(styrene) (PS) and poly( n -butylacrylate) (BA), synthesized by nitroxide mediated polymerization (NMP), using BlocBuilder-MA as the initiating species, can be chemically modified by the incorporation of BsubPc chromophores. The addition of the BsubPc chromophore was confirmed through the use of a photodiode array detector (PDA) connected in-line with a gel permeation chromatography (GPC) setup. These findings represent the first reported method for the controlled and selective placement of a BsubPc chromophores on either end of a polymer produced by NMP. This strategy will therefore be utilized to make next generation BsubPc polymers for OLEDs and OPV devices. The extremely high molar extinction coefficient of BsubPc also make these polymers ideally suited for dye-labelling of polymers.

Stereoblock-like Brush Copolymers Consisting of Poly(l-lactide) and Poly(d-lactide) Side Chains along Poly(norbornene) Backbone: Synthesis, Stereocomplex Formation, and Structure–Property Relationship

Random and block copolymerizations of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) macromonomers having an exo-norbornene group at the α- or ω-chain end (D/L ratio = 1/1, Mn = ca. 5000 g mol–1) were performed via ring-opening metathesis polymerization to produce the brush random and block copolymers consisting of parallel or antiparallel aligned PLLA and PDLA side chains on a poly(norbornene) backbone. The molecular weight and polydispersity index of the brush copolymers were in the range of 40 300–458 000 g mol–1 and 1.03–1.14, respectively. Despite such high molecular weights, these brush copolymers formed a stereocomplex without homochiral crystallization. The melting temperature (Tm) and crystallinity (X) of the resulting stereocomplex varied depending on the backbone length, relative chain direction, and distribution of the PLLA/PDLA side chains. The parallel brush copolymers showed significantly higher Tm and X values than the antiparallel ones.

Expanding the Scope of Controlled Radical Polymerization via Cobalt-Tellurium Radical Exchange Reaction.

Cobalt-mediated radical polymerization (CMRP) and tellurium-mediated radical polymerization (TERP) were combined for the first time, offering new perspectives in the precision design of macromolecular structures. In particular, the present work highlights the benefits of this strategy for the synthesis of novel poly(vinyl acetate)-based block copolymers. A range of well-defined poly(vinyl acetate)s (PVAc) were first produced via CMRP using the bis(acetylacetonato)cobalt(II) complex (Co(acac)2) as a regulating agent. Substitution of a methyltellanyl moiety for Co(acac)2 at the ω-chain end of the precursor was then achieved upon treatment with dimethylditelluride. In contrast to the PVAc prepared by TERP, the ones produced by sequential CMRP and Co/Te exchange reaction almost exclusively consist of regular head-to-tail-TeMe chain-end species that can be activated by TERP. Ultimately, a series of monomers problematic in Co(acac)2-mediated radical polymerization including N-isopropylacrylamide (NIPAM), 2-(dimethylamino)ethyl acrylate (ADAME), n-butyl acrylate (BA), isoprene (IP), and vinylimidazole (NVIm) were polymerized by TERP from the PVAc-TeMe macroinitiators leading to novel diblock copolymers that cannot be made by each technique used separately.

Straightforward RAFT Procedure for the Synthesis of Heterotelechelic Poly(acrylamide)s

Heterotelechelic, hydrophilic polymers with a primary amine and thiol group at the α- and ω-chain end, respectively, are synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization in a straightforward and versatile way and subsequently used for the design of dual-responsive polymer/gold nanohybrids. Therefore, a phthalimido-containing chain transfer agent (CTA) is synthesized and used for the polymerization of the hydrophilic monomers N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMA). After polymerization, the trithiocarbonate functionality at the ω-chain end, originating from the CTA, is converted into a thiol upon aminolysis. In the next step, the phthalimido α-chain end is hydrolyzed into a primary amine, resulting in heterotelechelic, hydrophilic polymers. End-group conversions are monitored by (1)H NMR spectroscopy, MALDI-TOF MS analysis, and UV-Vis spectroscopy, confirming that quantitative modifications are obtained during each stage. The amino groups of these heterotelechelic polymer chains are modified with citraconic anhydride, after which the obtained polymers are grafted with the thiol group onto citrate-stabilized gold nanoparticles resulting in the creation of dual-temperature- and pH-responsive gold particles.

Polymerization of long chain [meth]acrylates by Cu(0)-mediated and catalytic chain transfer polymerisation (CCTP): high fidelity end group incorporation and modification

The Cu(0)-mediated polymerization of lauryl (C12) and stearyl (C18) acrylate is reported under a range of reaction conditions. Good first order kinetics, a linear evolution of number average molecular weight (Mn) with conversion and dispersity (∼1.10) are observed. The polymerization of lauryl acrylate proceeds either homogenously or in a self-generated biphasic system, depending on the solvent employed, with little deviation in overall polymerization control. The near quantitative retention of ω-bromo end groups is exploited via nucleophilic thio-bromine substitution with thioglycerol to yield highly hydrophobic polymers with polar head groups. Modification is spectroscopically confirmed by both NMR and MALDI-TOF-MS. Highly ω-chain end functional methacrylic analogues have also been prepared by Co(II) mediated catalytic chain transfer polymerisation (CCTP). Reactive vinyl groups at the ω-chain end of poly(lauryl methacrylate) have been targeted with thioglycerol for nucleophilic thio-Michael addition with quantitative modification possible.

Poly(acrylates) via SET-LRP in a continuous tubular reactor

A simple, easy to construct, bench-top plug flow reactor consisting of PTFE tubing with a Cu(0) threaded core (wire) was used to perform SET-LRP of methyl acrylate. The reaction was optimized by changing the residence time within the flow reactor. Both changing the flow reactor length and changing the flow rate was seen to control the resultant polymer molecular weight. Using a 20 cm reactor length, 95% conversion of monomer was seen at a flow rate of 0.1 mL min−1. The polymers formed had narrow molecular weight distributions (PDI< 1.2), and very high ω-chain end fidelity, as seen by both 1H NMR and MALDI-TOF MS.

One-Pot Synthesis of α,ω-Chain End Functional, Stereoregular, Star-Shaped Poly(lactide)

The synthesis of stereoregular α,ω-chain end functional linear, telechelic, and star-shaped polymers and copolymers is reported using a one-pot chain end functionalization methodology. Aluminum methyl complexes are applied in combination with functional and multifunctional initiating species to synthesize stereoregular poly(lactide)s by the stereospecific ring-opening polymerization of rac-lactide. The quenching of the reactions with an excess of acid chloride functional molecules has enabled the in situ quantitative modification of the ω-chain ends of the polymers such that primary and secondary alkyl and aryl groups can be incorporated. This methodology has been extended to the synthesis of linear, telechelic, and star-shaped polymers with “click” functional handles for both copper-catalyzed Huisgen 1,3-dipolar cycloaddition and thiol−ene Michael additions and block copolymers through the application of a trithiocarbonate, suitable for mediating RAFT polymerization. This tolerant and mild method is used...

Synthesis of Poly(lactic acid) with Branched and Network Structures Containing Thermally Degradable Junctions

Polyperoxide, as a new kind of thermally degradable polymer, is synthesized by the radical alternating copolymerization of a 1,3-diene monomer with oxygen. The introduction of polyperoxide units into any other polymer is useful for the fragmentation of polymers and a change in the physical properties of polymeric materials. In the present study, we demonstrate the synthesis and fragmentation of poly(l-lactic acid) (PLLA) modified with thermally degradable branching and cross-linking points, which consist of a repeating polyperoxide structure as the degradable junctions. We prepared several PLLA with a dienyl group at the α- and/or ω-chain ends by the anionic and metal-catalyzed polymerizations of l-lactide. Radical alternating copolymerization of the mono- and difunctional PLLA with oxygen was carried out to obtain branched polymers and gels. These branched and cross-linked PLLA materials readily degraded upon heating to yield linear PLLA chains.

Precise Control of Lower Critical Solution Temperature of Thermosensitive Poly(2-isopropyl-2-oxazoline) via Gradient Copolymerization with 2-Ethyl-2-oxazoline as a Hydrophilic Comonomer

The lower critical solution temperature (LCST) of amphiphilic poly(2-isopropyl-2-oxazoline) (PiPrOx) was precisely tuned via the copolymerization with 2-ethyl-2-oxazoline (EtOx) as a hydrophilic comonomer. The copolymerization was cationically initiated by methyl p-tosylate at the optimum condition (42 °C in acetonitrile) for living polymerization, obtaining the copolymers with a narrow molecular weight distribution (Mw/Mn ≤ 1.02). The monomer reactivity ratios of 1.78 and 0.79 respectively were derived for EtOx and iPrOx from the cumulative and instantaneous compositions of the copolymers determined from the 1H NMR and MALDI-TOF mass spectrometry. This set of the reactivity ratios are sufficiently different enough to form the gradient copolymers, in which each polymer chain has a trend of a gradually decreasing EtOx and an increasing iPrOx composition along the backbone from the α-terminal to ω-chain end. These gradient copolymers followed a rather simple rule in their thermosensitive behaviors to show a...