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Achieving long-persistent phosphorescence in polymers is a challenge even at low temperatures. In this work, long-persistent phosphorescence (>1 s) is observed in nonconjugated polyurethane derivatives at 77 K, which is among the longest reported phosphorescent lifetimes for an organic polymer. The mechanism for this unusual behavior has been shown by steady-state photophysical characterization and time-resolved emission spectra to arise from the formation of intra- and/or intermolecular carbonyl clusters at low temperature. The lifetime of long-persistent phosphorescence is increased by the introduction of an aromatic monomer into the nonconjugated polyurethane chains. This is attributed to intra- and/or intermolecular n-p* transitions from electron-rich carbonyl groups to the conjugated aromatic units, thereby enhancing the intersystem crossing rate. Coating an ultraviolet InGaAsN light-emitting diode with a polyurethane derivative as the emitter gives cryogenic afterglow with long-persistent phosphorescence that is observed for up to 7 s with the naked eye. [ABSTRACT FROM AUTHOR]

We demonstrate how to tune the surface chemistry and properties of copolymers obtained by the photopolymerization of polyoxyethylene (meth)acrylic monomers and a low polarity siloxane comonomer which spontaneously migrates to the free surface. By controlling the photopolymerization conditions, such as the light gradient through the thickness of the film and selecting the proper monomer functionality, it is possible to optimize and photoenforce the surface segregation of the siloxane comonomer. Photocured films containing the same amount of siloxane component (1 wt %) can exhibit a surface energy ranging from 42 to 22 mN m-1 depending on the process conditions. XPS and AFM analyses confirm that polymers with a compositional gradient are obtained and that the surface segregation can be finely photocontrolled. Photopolymerization is thus proven to be a facile, single step method for generating gradient films and for independently and simultaneously tune their surface and bulk properties. [ABSTRACT FROM AUTHOR]

We report the formation of oligomers with side-chain sequence control using ruthenium-catalyzed alternating ring-opening metathesis polymerization (AROMP). These oligomers are prepared through sequential, stoichiometric addition of bicyclo[4.2.0]oct-1(8)-ene-8-carboxamide (monomer A) at 85 °C and cyclohexene (monomer B) at 45 °C to generate sequences up to 24 monomeric units composed of (A-alt-B)n and (A'-alt-B)n microblocks, where n ranges from 1 to 6. Herein, monomer A has an alkyl side chain, and monomer A' has a glycine methyl ester side chain. Increasing microblock size from one to six results in an increasing water contact angle on spin-coated thin films, despite the constant ratio of hydrophilic and hydrophobic moieties. However, a disproportionately high contact angle was observed when n equals 2. Thus, the unique all-carbon backbone formed in the AROMP of bicyclo[4.2.0]oct-1(8)-ene-8-carboxamides and cyclohexene provides a platform for the nontemplated preparation of materials with specific sequences of side chains. [ABSTRACT FROM AUTHOR]

Block copolymers of polyisoprene and polystyrene are key materials for polymer nanostructures as well as for several commercially established thermoplastic elastomers. In a combined experimental and kinetic Monte Carlo simulation study, the direct (i.e., statistical) living anionic copolymerization of a mixture of isoprene (I) and 4-methylstyrene (4MS) in nonpolar media was investigated on a fundamental level. In situ ¹H NMR spectroscopy enabled to directly monitor gradient formation during the copolymerization and to determine the nature of the gradient. In addition, a precise comparison with the established copolymerization of isoprene and styrene (I/S) was possible. Statistical copolymerization in both systems leads to tapered block copolymers due to an extremely slow crossover from isoprene to the styrenic monomer. For the system I/4MS the determination of the reactivity ratios shows highly disparate values with rI = 25.4 and r4MS = 0.007, resulting in a steep gradient of the comonomer composition. The rate constants determined from online NMR studies were used for a kinetic Monte Carlo simulation, revealing structural details, such as the distribution of the homopolymer sequences for both blocks, which are a consequence of the peculiar kinetics of the diene/styrene systems. DFT calculations were used to compare the established copolymerization of isoprene and styrene with the isoprene/4-methylstyrene system. A variety of gradient copolymers differing in molecular weight and monomer feed composition were synthesized, confirming strong microphase segregation as a consequence of the blocklike structure. The one-pot synthesis of such tapered block copolymers, avoiding high vacuum or break-seal techniques, is a key advantage for the preparation of ultrahigh molecular weight block copolymers (Mn > 1.2 x 106 g/mol) in one synthetic step. These materials show microphase-segregated bulk structures like diblock copolymers prepared by sequential block copolymer synthesis. Because of the living nature of the tapered block copolymer structures, a vast variety of complex structures are accessible by the addition of further monomers or monomer mixtures in subsequent steps. [ABSTRACT FROM AUTHOR]

A novel synthetic route to polyquinolines with 6-substituted quinoline as the structural unit was developed based on the polymerization of alkyne-aldehyde monomers and aniline derivatives under the catalysis of Lewis acid B(C6F5)3. The polymerization was conducted in dichloroethane at 100 °C for 36 h under air atmosphere, affording polyquinolines with molecular weights up to 13 100 and good solubility in most organic solvents. The substituents in aniline exhibited significant effects on the molecular weight, yield, and solubility of the produced polyquinolines. The structures of prepared polymers were characterized and confirmed by GPC, NMR, and FT-IR. The thermogravimetry (TGA) and differential scanning calorimetry (DSC) analysis suggests that the polyquinolines are highly thermal stable. Further photoluminescence behaviors of the prepared polyquinolines were investigated. Based on the characterization results and small molecule reaction mechanism, the polymerization pathway of the polyquinolines was proposed. Our work has provided a novel simple strategy for the preparation of multifunctional polyquinolines with unique architectures by one-pot synthesis under metal-free catalysis. [ABSTRACT FROM AUTHOR]

Recent works demonstrated that the structure of self-assembled monomers can be engineered. Subsequently, performance in polymer-network assemblages of such monomers can be enhanced through microstructural design. This work presents a multiscale analysis of polymers comprising flexible V-shaped monomers. We show that two mechanisms enable the deformation of a chain: conformational entropy and elastic energy stemming from the monomers deformation. The mechanical behavior of a polymer network is obtained through an integration from the chain to the network level. We demonstrate that the shear modulus, the extensibility limit of the network, and the force-elongation response can be tuned by manipulation of the V-shaped monomer structure. As an example, the range of properties that can be achieved in an elastomer comprising 4-arm nanostar monomers subjected to uniaxial extension is examined. We find that appropriate manipulation of the monomer structure can lead to anywhere between an ~100% decrease to an ~40% increase in the shear modulus and the extensibility limit. [ABSTRACT FROM AUTHOR]

Nanocomposites have attracted more attention due to their extensive applications. However, it is still a huge technological challenge in fabrication of transparent hybrid materials because of nanoparticle aggregation resulting from their high specific surface energies. In this paper polymerizable molecule was controlled chemically grafted onto ZnS nanoparticles to obtain polymerizable-group-capped nanoparticles that can copolymerize with a mixture of acrylic monomers of N,N-dimethylacrylamide (DMA) and 2-hydroxyethyl methacrylate (HEMA) or glycidyl methacrylate (GMA) or methyl methacrylate (MMA) to prepare transparent high refractive index (RI) nanocomposite hydrogels. The dispersion homogeneity of the nanoparticles in the nanocomposites was studied by dynamic mechanical thermal analysis (DTMA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray mapping analysis (EDX). Moreover, the nanocomposites were characterized by transmittance, mechanical properties, and refractive index (RI). The results showed that grafted amount of polymerizable group on the nanoparticle surface influences the cross-link density and microphase structure of the resultant nanocomposites, leading to different transmittance and mechanical properties. The RI of hydrated and dry nanocomposites can be regulated to a peak value of 1.652 and 1.751, respectively, by a simple adjustment of ZnS content in the nanocomposites. Our approach was also proved to be effective in preparing DMA-free transparent nanocomposites with high RI of 1.824 by copolymerizing between polymerizable-group-capped ZnS and single monomer of HEMA or GMA or MMA. [ABSTRACT FROM AUTHOR]

Many natural materials such as intervertebral disk (IVD) are composed of regions with large mismatches in the mechanical properties, yet these regions are integrated through an extremely tough interface. To mimic the mechanical heterogeneity inherent in biological systems, we present here mechanically strong hydrogels consisting of hard and soft components joined together through a strong interface. Stratification of monomer solutions having different densities was used to create two layers of monomer solutions with an interlayer region of a few millimeters in thickness, at which the solutions mix completely. UV-initiated bulk copolymerization of stratified solutions of hydrophilic and hydrophobic monomers leads to the formation of supramolecular, semicrystalline hard/soft hydrogel hybrids with tunable mechanical and thermal properties. By adjusting the comonomer composition in the stratified layers, we were able to create gel/gel interfaces in hybrids that are stronger than their gel components so that they never rupture at the interface region. The hybrids exhibit a high modulus (0.46-74 MPa), tensile strength (0.19-3.9 MPa), and sustain 24-30 MPa stresses at 78-83% compressions, which are comparable to the natural IVD. They also exhibit thermally induced self-healing behavior as well as pseudo triple-shape-memory effect arising from different melting temperatures of crystalline domains belonging to the gel components of hybrids. [ABSTRACT FROM AUTHOR]

A furan-based synthetic biopolymer composed of a bifuran monomer and ethylene glycol was synthesized through melt polycondensation, and the resulting polyester was found to have promising thermal and mechanical properties. The bifuran monomer, dimethyl 2,2'-bifuran-5,5'-dicarboxylate, was prepared using a palladium-catalyzed, phosphine ligand-free direct coupling protocol. A titanium-catalyzed polycondensation procedure was found effective at polymerizing the bifuran monomer with ethylene glycol. The prepared bifuran polyester exhibited several intriguing properties including high tensile modulus. In addition, the bifuran monomer furnished the polyester with a relatively high glass transition temperature. Films prepared from the new polyester also had excellent oxygen and water barrier properties, which were found to be superior to those of poly(ethylene terephthalate). Moreover, the novel polyester also has good ultraviolet radiation blocking properties. [ABSTRACT FROM AUTHOR]

The ordering of semiflexible polymers with persistence length lp and contour length L confined in a sphere of radius R is studied by molecular dynamics simulations of a coarse-grained model. Monomer densities are chosen where the corresponding bulk lyotropic solution or melt is a well-ordered nematic, and purely repulsive walls of the rigid confining sphere are considered. It is found that polymers close to the walls are bent according to the curvature of the confining spheres with all their monomers in a few layers parallel to the sphere surface, whereas the remaining macromolecules closer to the sphere center have one chain end and their center of mass far from the surface. The latter chains are responsible for the average nematic order of the system for sufficiently stiff chains. If L exceeds R, a single transition from isotropic to nematic states is found when lp increases. However, if R is close to an even multiple of L, a second transition occurs where chain ends are enriched near the equatorial plane (and two further planes parallel to it, if R ≈ 2L); i.e., the system develops a distorted smectic structure. The order in the surface shell then is characterized by topological defects. [ABSTRACT FROM AUTHOR]

This work investigated the morphological behavior of an acrylate-based metallo-supramolecular polymer system. RAFT (reversible addition--fragmentation chain transfer) polymerization techniques were used to synthesize low molar mass, linear prepolymers of n-butyl acrylate and a 2,6-bis(1'-methylbenzimidazolyl)pyridine--acrylate monomer (MeBIP--Ac) of varying concentration (2-10%). This synthesis incorporated a systematic increase of cross-link points (MeBIP ligands) pendent to the polymer backbone. A zinc(II) salt (Zn(ClO4)2) complexed with the pendent MeBIP ligands in a 1:2 ratio to form cross-linked polymers as free-standing films. The morphology of the neat films as well as those with added unbound MeBIP--zinc--MeBIP metal--ligand (ML) complex were characterized using transmission electron microscopy (TEM), HAADF-STEM (high angle annular dark field scanning transmission electron microscopy), energy dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS), energy-filtered TEM (EFTEM), and small-angle X-ray scattering (SAXS) techniques. A vesicle morphology in the bulk material was found for films of the neat polymer containing 2% MeBIP, while films at all other compositions exhibited a disordered microphase-separated morphology. The vesicle morphology of the 2% MeBIP films was transformed into a morphology of cylinders with the addition of unbound MeBIP--zinc--MeBIP complex. [ABSTRACT FROM AUTHOR]

We have fabricated a series of supramolecular polymers with tailor-made structures and properties through supramolecular interfacial polymerization of miscible monomers. Compared with homogeneous solution polymerization, supramolecular interfacial polymerization is advantageous for fabricating supramolecular polymers with higher molecular weights. Their higher molecular weights are attributed to the higher effective concentration of monomers at the interface than in solutions and diffusion-limited characteristic of supramolecular interfacial polymerization. Moreover, the glass transition temperatures of supramolecular polymers are well tuned by tuning the monomer structures and supramolecular interfacial copolymerization. It is anticipated that this research will further enrich the methodology for fabricating supramolecular polymers with controlled structures and properties through supramolecular interfacial polymerization. [ABSTRACT FROM AUTHOR]

Here we report the room-temperature group transfer polymerization of conjugated polar alkenes, including linear methyl methacrylate (MMA) as well as biorenewable, cyclic γ-methyl-α-methylene-γ-butyrolactone (MMBL) and α-methylene-γ-butyrolactone (MBL), by the silyl ketene acetal (SKA)/Al(C6F5)3 ([Al]) system and the detailed study of its polymerization mechanism. The polymerization of MMA by SKA/[Al] was uncontrolled, while the MMBL polymerization by the bulky SKA (iBuSKA)/[Al] system is living and thus produces well-defined PMMBL with a predicted molecular weight (Mn up to 179 kg mol–1), a narrow molecular weight distribution (Đ as low as 1.02), and a high initiation efficiency (I* ≥ 97%). The living polymerization of MMBL was established through five lines of evidence, including predictable polymer Mn and low Đ values, a linear increase of polymer Mn vs monomer conversion, a linear increase of polymer Mn vs monomer-to-initiator ratio, chain extension experiments, and synthesis of well-defined random, diblock, and triblock copolymers. A combined mechanistic study through isolation and characterization of single-monomer-addition intermediates that simulate the active propagating species, polymerization kinetics, and characterization of polymer chain ends has led to a polymerization mechanism. The polymerization is initiated via intermolecular Michael addition of the SKA enolate group to the vinyl group of the [Al]-activated monomer, while the silyl group is transferred to the carbonyl group of the monomer and [Al] to the oxygen atom of SKA; the coordinated [Al] is released to the incoming monomer, followed by repeated intermolecular Michael additions in the subsequent propagation cycle. [ABSTRACT FROM AUTHOR]

Homopolymerization of octamethylcyclotetrasiloxane, D4, and two copolymerizations of this monomer with octaphenylcyclotetrasiloxane, D4Ph2, and hexaethylcyclotrisiloxane, D3Et2, were investigated by monitoring the courses of their occurrence using three different methods: size exclusion chromatography (SEC), thermal gravimetric analysis (TGA), and 29Si NMR spectroscopy. The results obtained showed that while homopolymerization of D4 and its copolymerization with D3Et2 occurred in a nearly identical manner, suggesting that reactivities of the two monomers toward the silanolate active species were practically identical, the copolymerization of D4 with D4Ph2 exhibited a distinct initial induction period resulting from two factors: (a) very low solubility of solid D4Ph2 in D4 and (b) significantly higher reactivity of D4Ph2 than D4 toward the dimethylsilanolate. On the basis of these results, we propose a new three-stage mechanism for the copolymerization of D4 with D4Ph2, which includes (a) initial formation of B-A-B triblocks of dimethylsiloxane (A) and diphenylsiloxane (B) segments, followed by (b) subsequent formation of A-B-A-B-A pentablock species, and (c) redistribution of the former multiblocks through a siloxane equilibration reaction into copolymers containing single diphenylsiloxy units separated by extended polydimethylsiloxane segments. [ABSTRACT FROM AUTHOR]

With Brookhart type a-diimine Ni(II) based catalysts, it is highly challenging to tune polymers branching level and branch-type distribution, which in turn strongly affects thermal and mechanical properties, through the aryl ortho-positions modification, while maintaining high turnover frequencies (TOFs). Herein, we are interested in performing a systematic investigation on the polymerization of 1-octene, 1-decene, and 1-octadecene catalyzed by a series of a-diimine nickel(II) complexes with methyl ligand backbone and different substituents in aryl positions (Ni1-Ni6). In addition to bulky isopropyl and tert-butyl substituents described in the original Brookhart's work, complexes with different aryl ortho- and para-substituted a-diimine ligands, including the less sterically demanding methyl and ethyl substituents, are investigated. The 13C NMR spectra of the polymers have been assigned in detail, and some unique features have been identified and related to the chain-walking coordination/insertion mechanism. Changes in the ligand structure and monomer size have important effects on the numerous combinations of insertion and chain-walking paths from which different branches are installed. We have also carried out a comprehensive investigation of the mechanical behavior of the polymers by means of uniaxial stretching until failure, step-cycle, and creep tensile tests. Overall, the resulting polymers exhibited a broad spectrum of tensile properties, depending on their microstructure and crystallinity which in turn are strongly affected by monomer length and type of a-diimine ligand. 1-Octene and 1-decene polymers behave as elastomers with excellent mechanical properties, i.e., high elongation at break (up to 2000%) and good strain recovery, while 1-octadecene polymers behave as plastomers. [ABSTRACT FROM AUTHOR]

Polymerization of monomers included by macrocyclic hosts has been found as an efficient way to synthesize sophisticated rotaxane-based nanostructures, whereas such a process triggered by photon has received little coverage so far. Herein, a new diphenyldiacetylene (DPDA) derivative (compound 1) comprising viologen as a binding site toward cucurbit[7]uril (CB[7]) macroring, and isophthalate as a bulky stopper, was rationally designed and prepared. After verifying the photo-cross-linking efficiency of compound 1 upon its regular self-assembly, we also achieved a straightforward construction of rotaxane-based nanoarchitecture 2 ⊂ CB[7] through an in situ photoirradiation on the corresponding pseudo[2]rotaxane 1 ⊂ CB[7]. Although the threading of CB[7] changed the self-assembly behavior of the DPDA derivative, the topochemical reaction could be definitely observed to afford the corresponding photo-cross-linked species. Such a process could be facilely indicated by distinctive photoluminescence enhancement on the basis of π-conjugated skeleton change of DPDA toward potential usage of rotaxane-based systems as smart optoelectronic materials. We anticipate this unique strategy will allow new visions for the synthesis and application of novel luminescent host-guest nanoarchitectures. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid nanoflowers, facilely made from bovine serum albumin and copper phosphate (BSA-Cu3(PO4)2·3H2O), have attracted considerable attention for the application of biocatalysts in recent years. The improved stability and activity of above-mentioned nanoflowers enhanced the efficiency of reversible addition-fragmentation chain transfer (RAFT) polymerization of functional methacrylate monomers with the assistance of acetylacetone (ACAC) and hydrogen peroxide (H2O2) in a mixed solvent of DMF and H2O. Such RAFT strategy can be employed for the polymerization of N,N-dimethylaminoethyl methacrylate (DMAEMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA500), in which both poly(DMAEMA) and poly(PEGMA500) could be synthesized in a controllable manner with typical RAFT features, e.g., precise control of molecular weight, specific molecular structure, and narrow polydispersity index (Mw/Mn). Significantly, the low-cost nanoflowers could be easily separated from reaction mixture after polymerization and will not adhere to resulting polymers as same as enzymes. Moreover, 1H NMR characterization of the retaining end groups of the resultant polymers and the chain extension experiments confirmed the mechanism of RAFT polymerization. The present biocatalytic system can serve as optimal alternatives of free enzymes in RAFT polymerization, which will hopefully enrich the methodology toward the construction of vinyl-based polymers with controlled radical polymerization (CRP). [ABSTRACT FROM AUTHOR]

Using coarse-grained molecular dynamics simulations, we investigate how ionomer behavior depends on ion and acid content. Our coarse-grained model builds on a prior model that was successful in capturing the low wavevector ionomer peak observed in X-ray scattering. As in prior work, we consider a linear backbone of neutral monomer beads with charged pendant beads and unbound counterions; we now also include "stickers" pendant to the backbone to represent unneutralized acid groups. These stickers are similar to backbone monomers but have higher cohesive interaction strength with each other and with the ionic groups, chosen to approximately match structural features of prior atomistic simulations. This allows us to simulate partially neutralized materials over longer time and length scales than is possible atomistically. We find that stickers can aid in ionic aggregate rearrangements such that samples containing sticker groups can show a lower viscosity than samples with the same ion content but without stickers; this agrees with experimental results of analogous materials. [ABSTRACT FROM AUTHOR]

We report programmed self-assembly systems of amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic alkyl pendants into size-controlled and thermoresponsive micelles in water. This system affords simultaneous and precise control of the size, aggregation numbers, and cloud point (Cp) of micelles in water by primary structure (pendant alkyl groups, composition, and chain length) that is programmed in the copolymers. Typically, random copolymers bearing PEG and alkyl pendants (butyl, octyl, dodecyl, and octadecyl groups) universally induce intermolecular self-assembly in water to produce uniform size micelles (<10 nm). The size is just determined by the content and alkyl pendant length of the hydrophobic monomers, independent of main chain length (below critical length for self-folding): The size increased with increasing the content and the pendant length. Design of hydrophobic alkyl groups with tuning composition allow us to widely control the size (molecular weight: 20K-1350K) and cloud point (from 45 to 85 °C) of the polymer micelles. We can thus tailor-make various micelles with identical size yet different Cp or those with identical Cp yet different size. Thanks to such dual controllability, self-sorting and stepwise thermoresponsive micelle systems were also created with blends of different copolymers; binary copolymers induced orthogonal self-assembly in water to provide discrete micelles with different size and cloud point. [ABSTRACT FROM AUTHOR]

Vitrimers are cross-linked polymer networks containing linkages that undergo thermally activated, associative exchange reactions, such that the cross-link density and overall network connectivity are preserved. Polycarbonates are industrially relevant polymers that, to our knowledge, have not yet been explored as vitrimers. We developed hydroxyl-functionalized polycarbonate networks that undergo transcarbonation exchange reactions at elevated temperatures in the presence of catalytic Ti(IV) alkoxides. The rate of transcarbonation within the networks, estimated through stress relaxation experiments, was tuned by adjusting the catalyst loading or hydroxyl group concentration in the networks. The polymer networks exhibit recovery of their tensile strength and plateau storage modulus (71-133%) after reprocessing. In addition to being reprocessable, the networks were hydrolyzed and decarboxylated in aqueous acid to recover 80 wt % of the precursor to the bifunctional cyclic carbonate monomer. These observations demonstrate that PC vitrimers are a novel class of strong, repairable polymers with more facile end-of-life degradation compared to other vitrimers and conventional thermosets. These characteristics, along with the high likelihood of deriving their monomers from bio-based sources, make PC vitrimers outstanding candidates for sustainable manufacture and use. [ABSTRACT FROM AUTHOR]

Dynamic-covalent chemistry has enabled the facile synthesis of a new generation of degradable materials, but controlling the rate at which these materials degrade remains elusive. Using segmented hyperbranched polymers (SHPs) as model branched architectures, we demonstrate that SHPs containing imine cross-links degrade under acidic conditions into well-defined linear chains at rates controllable via modification of the imine N-substituent. Imine-cross-linked SHPs were synthesized in a one-pot protocol by reversible addition-fragmentation chain transfer (RAFT) copolymerization of novel divinyl compounds containing dynamic-covalent oxime, semicarbazone, and acyl hydrazone moieties. The extent of SHP branching could be controlled through the relative stoichiometric ratios of cross-linker and chain transfer agent (CTA), and studies of the polymerization kinetics confirmed the growth of polydisperse branched species at high monomer conversions. When subjected to aqueous acidic conditions, the polydisperse branched architecture degraded into well-defined polymers, a process that was accelerated under more strongly acidic conditions and by incorporating less hydrolytically stable imine cross-links. Finally, we found that the rate of SHP degradation could be tuned with an unprecedented level of control by cross-linking the polymers with different proportions of multiple imines. [ABSTRACT FROM AUTHOR]

We report a high-resolution electrospray ionization mass spectrometric (HR ESI-MS) access route leading to in-depth insights into the spontaneous zwitterionic copolymerization mechanism between cyclic imino ethers (i.e., 2-methyl-2-oxazoline (MeOx), 2-ethyl-2-oxazoline (EtOx), or 2-ethyl-2-oxazine (EtOz)) with acrylic acid (AA), exploiting the characteristic species accumulating during the copolymerization as well as tandem mass spectrometry (MS/MS). We demonstrate preferences in α,ω-end group formation by screening various feed ratios of cyclic imino ethers and acrylic acid (e.g., MeOx:AA = 1:1; MeOx:AA = 2:1; and MeOx:AA = 1:2). Critically, a calibration curve--based on AA-MeOx-AA dimer--was established allowing for the semiquantitative determination of the end-group ratios with different feed ratios of acrylic acid. The formation of previously suggested alternating copolymers was confirmed by MS/MS experiments. Deviations from an ideal alternating composition were found to decrease from MeOx to EtOx to EtOz. The results of (semiquantitative) HR ESI-MS and MS/MS measurements suggest, for the first time presented in such precision, a polymerization mechanism for the spontaneous zwitterionic (alternating) copolymerization indicating optimal monomer ratios and pairings. [ABSTRACT FROM AUTHOR]

A novel fused heterocycle-flanked diketopyrrolopyrrole (DPP) monomer, thieno[2,3-b]pyridine diketopyrrolopyrrole (TPDPP), was designed and synthesized. When copolymerized with 3,4-difluorothiophene using Stille coupling polymerization, the new polymer pTPDPP-TF possesses a highly planar conjugated polymer backbone due to the fused thieno[2,3-b]pyridine flanking unit that effectively alleviates the steric hindrance with both the central DPP core and the 3,4-difluorothiophene repeat unit. This new polymer exhibits a high electron affinity (EA) of -4.1 eV and was successfully utilized as an n-type polymer semiconductor for applications in organic field-effect transistors (OFETs) and all polymer solar cells. A promising n-type charge carrier mobility of 0.1 cm2 V-1 s-1 was obtained in bottom-contact, top-gate OFETs, and a power conversion efficiency (PCE) of 2.72% with a high open-circuit voltage (VOC) of 1.04 V was achieved for all polymer solar cells using PTB7-Th as the polymer donor. [ABSTRACT FROM AUTHOR]

A lattice model based on polymer self-consistent field theory is developed to predict the equilibrium statistics of arbitrary polymer networks. For a given network topology, our approach uses moment propagators on a lattice to self-consistently construct the ensemble of polymer conformations and cross-link spatial probability distributions. Remarkably, the calculation can be performed "in the dark", without any prior knowledge on preferred chain conformations or cross-link positions. Numerical results from the model for a test network exhibit close agreement with molecular dynamics simulations, including when the network is strongly sheared. Our model captures nonaffine deformation, mean-field monomer interactions, cross-link fluctuations, and finite extensibility of chains, yielding predictions that differ markedly from classical rubber elasticity theory for polymer networks. By examining polymer networks with different degrees of interconnectivity, we gain insight into cross-link entropy, an important quantity in the macroscopic behavior of gels and self-healing materials as they are deformed. [ABSTRACT FROM AUTHOR]

The significance of polymer topology to the size and morphology of polymeric assemblies was less studied. Herein we report the preparation of polymersomes with tunable sizes via topological engineering of the solvophobic block of the amphiphilic copolymer in polymerization-induced self-assembly (PISA). The topology of the solvophobic block could be facilely regulated by reversible addition-fragmentation chain transfer (RAFT) dispersion copolymerization of two kinds of monomers with distinctive molecular geometries at variable feed ratios. As a proof-of-concept study, RAFT dispersion copolymerization of benzyl methacrylate (BzMA) and stearyl methacrylate (SMA) produced polymersomes with size ranging from 200 to 1500 nm depending on the ratio of BzMA/SMA. Besides vesicles, assemblies with complex internal structures were obtained by varying the ratio of BzMA/SMA, suggesting the robustness of this strategy. The mechanism was revealed by a series of coarse-grained molecular simulations, which elucidated the dependence of the packing parameter on the composition of the solvophobic block. The generality and modularity for regulating vesicular size by topological engineering of solvophobic block were further established by RAFT dispersion copolymerization of BzMA and 2-(perfluorooctyl)ethyl methacrylate, which also generated polymersomes with tunable sizes. The topological engineering of copolymer by RAFT dispersion copolymerization thus serves as a versatile and modular approach to controlling the size and morphology of polymer assemblies. [ABSTRACT FROM AUTHOR]

3-Ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVL), a substituent δ-lactone synthesized through telomerization of CO2 with 1,3-butadiene, is highly functionalized containing a six-membered ring and two vinyl groups. It can hardly be polymerized directly through common methods due to its poor polymerizability. In this paper, we report the controlled polymerization of a highly reactive trivinyl monomer derived from EVL, i.e. methyl-2-ethylidene-5-hydroxyhept-6-enoate methacrylate (MEDMA), which is synthesized through ring cleavage of EVL and subsequent esterification with methacryloyl chloride. Chemoselective RAFT polymerizations of MEDMA mediated by 2-cyanoprop-2-yl-dithiobenzoate (CPDB) are achieved and well-defined polymers with linear and hyperbranched topologies are obtained under optimized polymerization conditions. RAFT polymerizations show good control in producing linear PMEDMAs with predetermined molecular weights (4000 g/mol) and moderate polydispersity indices (below 1.22). The resultant hyperbranched PMEDMAs are fully characterized by ¹H NMR, 13C NMR, ¹H-13C HMQC, DEPT, DLS, and TEM. The incorporations of vinyl group in allylic ester into polymer chains lead to the hyperbranched topology. Both PMEDMAs are ready for the introduction of amino and carboxy groups through thiol-ene click chemistry, and the products self-assemble to the micelles with different morphologies. This protocol develops the utilization of EVL in synthetic polymers and is significant to the carbon dioxide transformation. [ABSTRACT FROM AUTHOR]

Two polymers with fully two-dimensional (2D) conjugated side chains, 2D-PTB-Th and 2D-PTB-TTh, were synthesized and characterized through simultaneously integrating the 2D-TT and the 2D-BDT monomers onto the polymer backbone. Resulting from the synergistic effect from the conjugated side chains on both monomers, the two polymers showed remarkably efficient absorption of the sunlight and improved π-π intermolecular interactions for efficient charge carrier transport. The optimized bulk heterojunction device based on 2D-PTB-Th and PC71BM shows a higher PCE of 9.13% compared to PTB7-Th with a PCE of 8.26%, which corresponds to an approximately 10% improvement in solar energy conversion. The fully 2D-conjugated side-chain concept reported here developed a new molecular design strategy for polymer materials with enhanced sunlight absorption and efficient solar energy conversion. [ABSTRACT FROM AUTHOR]

The dithioketal derivatives of industrially important, semicrystalline poly(arylene ether ketone)s undergo facile exchange with aliphatic diols in the presence of N-bromo-succinimide to give a range of novel poly(arylene ether ketal)s. These are amorphous and readily soluble in a wide range of organic solvents. Although generally stable under ambient conditions, they undergo rapid and quantitative hydrolysis in the presence of acids to regenerate the original polyketones. The poly(ether ketal)s reported here are not accessible from ketal-type monomers, nor can they be obtained by direct reaction of poly(ether ketone)s with aliphatic diols. The starting polyketones are essentially unchanged after sequential dithioketalization, dithioketal--ketal exchange, ketal hydrolysis, and redithioketalization. Poly(arylene ether ketal)s provide a new approach to the processing of poly(arylene ether ketone)s into carbon fiber composite materials. [ABSTRACT FROM AUTHOR]

Dynamic density functionals (DDFs) are popular tools for studying the dynamical evolution of inhomogeneous polymer systems. Here, we present a systematic evaluation of a set of diffusive DDF theories by comparing their predictions with data from particle-based Brownian dynamics (BD) simulations for two selected problems: interface broadening in compressible A/B homopolymer blends after a sudden change of the incompatibility parameter and microphase separation in compressible A:B diblock copolymer melts. Specifically, we examine (i) a local dynamics model, where monomers are taken to move independently from each other, (ii) a nonlocal "chain dynamics" model, where monomers move jointly with correlation matrix given by the local chain correlator, and (iii, iv) two popular approximations to (ii), namely (iii) the Debye dynamics model, where the chain correlator is approximated by its value in a homogeneous system, and (iv) the computationally efficient "external potential dynamics" (EPD) model. With the exception of EPD, the value of the compressibility parameter has little influence on the results. In the interface broadening problem, the chain dynamics model reproduces the BD data best. However, the closely related EPD model produces large spurious artifacts. These artifacts disappear when the blend system becomes incompressible. In the microphase separation problem, the predictions of the nonlocal models (ii-iv) agree with each other and significantly overestimate the ordering time, whereas the local model (i) underestimates it. We attribute this to the multiscale character of the ordering process, which involves both local and global chain rearrangements. To account for this, we propose a mixed local/nonlocal DDF scheme which quantitatively reproduces all BD simulation data considered here. [ABSTRACT FROM AUTHOR]

A series of monomers comprising units bearing both imidazolium bromide ionic liquid (IL) and zwitterionic imidazolium alkyl carboxylate moieties with different alkyl spacer groups are designed and synthesized. RAFT polymerization of these monomers produces a new class of ionic homopolymers, named poly(zwitterionic ionic liquid)s (PZILs), which behave like poly(ionic liquid)s as well as poly(zwitterion)s depending on the solution pH. Such PZILs exhibit an isoelectric point (pI) at pH 5.7, where they exist in their zwitterionic form, making them dual responsive to both pH and temperature. Above pH 5, the aqueous transparent solution of PZIL transforms into turbid suspension due to the formation of insoluble hierarchical nanoaggregates (NAs) of various morphologies such as small spheres, large spheres, flower-like, dendrite-shaped, and dendritic fibril-like depending upon the solution pH and PZILs' structures. The dissolution of aggregates upon heating and reaggregation upon cooling suggests existence of reversible upper critical solution temperature (UCST)-type phase transition above pH 5. Below pH 5, owing to the presence of cationic IL moieties, aqueous PZIL solution exhibits transparent-to-turbid transition due to the formation of anion-induced NAs of various dendritic morphologies upon addition of various chaotropic anions within the Hofmeister series. Upon heating, this colloidal turbid suspension becomes transparent, showing a distinct UCST-type phase transition, and the process is reversible. It is easily possible to fine-tune the cloud point and morphologies of the NAs by changing various parameters such as molecular weight, concentrations, structure of PZILs, nature and concentration of anions, and solution pH. [ABSTRACT FROM AUTHOR]

Probe diffusion in a gelation process provides unique information such as local viscosity and sol/gel fraction that general scattering and rheological measurements do not provide. In this study, we revisited a gelation process of radical copolymerization of monomers and cross-linkers by conducting a series of probe diffusion experiments with dynamic light scattering (DLS). By using an isorefractive solvent to the gel system, we exclusively monitored the dynamics of gold nanoparticles during its real-time gelation process at multiscattering angles. The obtained time-correlation functions (g²(τ) - 1) were analyzed by fitting with empirical stretched exponential functions. The ratio of mobile particles to the total particles, the relaxation time of mobile particles, and the heterogeneity of their dynamics were obtained as the fitting parameters. With those fitting parameters, the gel point, heterogeneity of local environment, and the local viscosity were evaluated. In addition, a unique up-and-down transition was found in the relaxation time, suggesting the local viscosity that the particles feel changes drastically around the gel point. This transition point in the relaxation time matches the gel point for homogeneous gels but showed a systematic deviation in heterogeneous gels by changing q-1 and the size of probe particles. [ABSTRACT FROM AUTHOR]

We report a general method to synthesize polymeric Janus nanosheets (PJS) by sequential RAFT grafting from a template particle surface. Layer number and composition of the PJS are tunable by feeding sequence and type of monomers. The cPNIPAM-PS PJS is flexible and thermal responsive, which can form a scrolled superstructure. A dually responsive cPAA-PNIPAM PJS is derived by hydrolysis of cPtBA-PNIPAM. Accordingly, stability of the emulsion with the cPAA-PNIPAM PJS is triggered by alternation of pH or/and temperature. [ABSTRACT FROM AUTHOR]

Polyampholytic copolymers have been synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization of protic ionic liquid monomers. The monomers were prepared by acid-base proton exchange between acid and basic precursor conjugates, each containing one or more vinyl pendant groups. The polymerization, which was carried out without additional solvents present, led to high molecular weight glassy polymers, which were stable in the form of bulk viscous liquid ionic complexes. Various polyampholytes belonging to both linear and cross-linked families were prepared by judiciously varying the molecular structure of the acid precursor. Furthermore, by using solid-state NMR, the molecular arrangement of the polymeric backbone was identified, highlighting the presence of copolymers with both random and alternating copolymer chains which in the latter case involves a regularly alternating acid monomer, whereas the base occurs as a random sequence with the average and most probable number of monomers dictated by the stoichiometry used. The structural and mechanical properties of the resulting copolyampholytes were characterized by atomic force microscopy, peak-force quantitative nanomechanical analysis, differential scanning calorimetry, and small-angle X-ray scattering. These showed that the final polymers were essentially glassy and amorphous, with weak compositional fluctuations of the order of a few monomers and Young moduli in the range 1-3 GPa. [ABSTRACT FROM AUTHOR]

Five para-substituted monoacyltrimethylgermane derivatives, i.e., p-fluorobenzoyltrimethylgermane (pFBG, λmax = 405 nm), p-methoxybenzoyltrimethylgermane (pMBG, λmax = 397 nm), benzoyltrimethylgermane (pHBG, λmax = 409 nm), p-cyanobenzoyltrimethylgermane (pCBG, λmax = 425 nm), and p-nitrobenzoyltrimethylgermane (pNBG, λmax = 429 nm) are investigated via a combination of pulsed laser polymerization with subsequent electrospray ionization and mass spectrometry (PLP-ESI-MS) as well as femtosecond transient absorption spectroscopy. The relative initiation efficiencies of the initiating benzoyl radical fragments of pFBG, pMBG, and pHBG are determined using PLP-ESI-MS. The para-substituted derivatives with the electron-donating groups, pFBG and pMBG, display a factor 1.5 and 1.3, respectively, superior overall initiation efficiency compared to the unsubstituted pHBG. In contrast, the derivatives pCBG and pNBG carrying electron-withdrawing groups display only weak initiation behavior at a factor 4 higher total energy of ∼112 J (∼28 J for typical PLP experiments with pMBG, pFBG, and pHBG at ∼320 J and 90 000 pulses). The differences in the initiation efficiencies are representative for two classes of monoacyltrimethylgermane initiators, i.e., efficient initiators and weak initiators, each distinct in their specific radical cleavage mechanism. The efficient initiators pMBG, pFBG, and pHBG show an ultrafast intersystem crossing within 2-4 ps after pulse irradiation and subsequent formation of benzoyl and trimethylgermyl radical fragments. In contrast, the weak initiators pCBG and pNBG relax to the ground state after photoexcitation via a dominating ultrafast internal conversion (IC) within 13 and 2 ps, respectively, disallowing effective initiation under typical PLP conditions (∼320 J/pulse with 90 000 pulses resulting in ∼28 J total energy per sample). pCBG features weak initiation behavior additionally forming methyl and p-cyanobenzoyldimethylgermyl radicals at a factor 4 higher total energy of ∼112 J. Consistent with a considerably faster IC relaxation, pNBG features a factor 10 weaker monomer conversion than pCBG. [ABSTRACT FROM AUTHOR]

Water is an abundant, natural, and sustainable resource. However, it has not been used as a monomer for the construction of polymers. In this paper, we take this challenge and develop a new polymerization of water and triple-bond based monomers of isocyanides and bromoalkynes, and polyamides with high molecular weights (up to 41 700) and stereoregularities (the fraction of Z-isomer generally higher than 80%) are obtained in excellent yields (up to 98.1%) under mild reaction conditions. The polymers possess good solubility and exhibit high thermal stability and refractive index. The tetraphenylethene-containing polymers show the unique aggregation-enhanced emission (AEE) characteristics. Moreover, thanks to their containing bromoacrylamide groups in the main chains, these polyamides could be easily postmodified through different reactions, providing a convenient platform for polymer functionalization. Thus, this work not only established a stereoselective polymerization of water and triple-bond based monomers but also provided a powerful strategy for the preparation of functional polyamides under mild reaction conditions. [ABSTRACT FROM AUTHOR]

We developed a novel wide-bandgap conjugated polymer PTzBI-O based on an alkoxylated electron-deficient monomer 4,8-di(thiophen-2-yl)-[1,2,3]triazolo[4,5-f]isoindole-5,7(2H,6H)-dione (TzBI-O). Regarding that of alkyl-substituted imide-functionalized benzotriazole (TzBI) unit, the incorporation of oxygen atom into the substitution of TzBI-O increased the electronegativity. The resulting polymer PTzBI-O exhibited an absorption onset of 708 nm, corresponding to a bandgap of 1.75 eV. The PTzBI-O:N2200 blend exhibited strong aggregation in toluene solution, resulting in the enhanced absorptivity in thin film compared to those of equivalent films processed with chlorinated solvents. The fabricated all-polymer solar cell based on PTzBI-O:N2200 blend film processed with toluene exhibited an impressive power conversion efficiency of 7.91%. The higher efficiency of the toluene-processed device than those based on films processed with chlorinated solvents can be attributed to more effective charge dissociation, trivial bimolecular recombination, greater charge transportation, and more favorable thin film morphology of the toluene-cast blend film. These findings indicated that the resulting copolymer has great potential for the construction of high-performance all-polymer solar cells. [ABSTRACT FROM AUTHOR]

3-D printing is a revolutionary manufacturing technique which makes it possible to fabricate objects of any shape and size that are hard to reproduce by traditional methods. We develop a coarse-grained molecular dynamics simulation approach to model the continuous liquid interface production (CLIP) 3-D printing technique. This technique utilizes a continuous polymerization and cross-linking of the liquid monomeric precursor by the UV light within a thin layer while pulling the cross-linked polymeric object out of a pool of monomers. Simulations show that the quality of the shape of the 3-D printed objects is determined by a fine interplay between elastic, capillary, and friction forces. Using simulation results, we identify the source of the object shape deformations and develop a set of rules for calibration of the parameters to meet the accuracy requirements. Comparison between different continuous 3-D printing setups shows that proposed modifications of the printing process could improve quality and accuracy of the printed parts. [ABSTRACT FROM AUTHOR]

Poly[2-(methacryloyloxy)ethylphosphorylcholine] (pMPC) brushes provide extremely low friction coefficients up to high compressions, but their use as boundary lubricating layers is limited by the challenge of surface grafting of the chains. Coating by thin layers of cross-linked pMPC hydrogels may provide an attractive alternative. Here we use a surface force balance (SFB) and other techniques to examine the effect of light cross-linking (0.1% cross-linker) on the surface interactions and frictional behavior of grafted-from pMPC brushes on mica, up to physiologically high contact pressures. Atomic force microscopy, X-ray photoelectron spectroscopy, and interferometric surface-excess measurements show little difference between the non-cross-linked (linear) pMPC brushes and the cross-linked brushes prepared under otherwise identical conditions. Normal force-distance profiles between the polymer-bearing surfaces, however, reveal a marked compaction of the unperturbed thickness of the cross-linked brushes relative to linear ones, attributed to the cross-linking which limits chain swelling. The cross-linked pMPC layers exhibit very low friction (friction coefficients of order 10-3-10-4, depending on sliding velocities), similar to the corresponding linear brushes and due to hydration lubrication by the highly hydrated phosphocholine monomer structure. Within the range of our parameters, however, there is a marked qualitative difference in the dependence of friction on sliding velocity vs. While for the linear brushes friction is only very weakly vs-dependent (over 3 orders of magnitude in vs), due to a self-regulating brush interpenetration, for the cross-linked brushes friction increases markedly with vs (~vs1/2), an effect attributed to suppression of interpenetration by the cross-links. [ABSTRACT FROM AUTHOR]

Controlling self-assembled nanostructures in thin films allows the bottom-up fabrication of ordered nanoscale patterns. Here we report the unique thickness-dependent phase behavior in thin films of a bolaform-like giant surfactant, which consists of butyl- and hydroxyl-functionalized polyhedral oligomeric silsesquioxane (BPOSS and DPOSS) cages telechelically located at the chain ends of a polystyrene (PS) chain with 28 repeating monomers on average. In the bulk, BPOSS-PS28-DPOSS forms a double gyroid (DG) phase. Both grazing incidence small-angle X-ray scattering and transmission electron microscopy techniques are combined to elucidate the thin film structures. Interestingly, films with thicknesses thinner than 200 nm exhibit an irreversible phase transition from hexagonal perforated layer (HPL) to compressed hexagonally packed cylinders (c-HEX) at 130 °C, while films with thickness larger than 200 nm show an irreversible transition from HPL to DG at 200 °C. The thickness-controlled transition pathway suggests possibilities to obtain diverse patterns via thin film self-assembly. [ABSTRACT FROM AUTHOR]

Waterborne polymer-inorganic hybrids have the potential of both surpassing the performance and targeting applications that are out of reach of conventional polymer dispersions. The properties of these hybrids are determined by the particle morphology achieved during the synthesis. In this work, the evolution of the particle morphology during the polymerization of (meth)acrylate monomers in the presence of CeO2 was determined by cryo-TEM. Moreover, a mathematical model for the dynamics of the particle morphology during the synthesis of polymer-inorganic hybrids was developed, and its capabilities were checked against the experimental data. It is our hope that this study will help to further elucidate the mechanism involved in the process and to lay the foundations for a fine control of particle morphology of these materials. [ABSTRACT FROM AUTHOR]

Diketopyrrolopyrrole (DPP) derivatives are among the most efficient materials studied for both polymer solar cells (PSCs) and organic field-effect transistors (OFETs) applications. We report here the synthesis of new fluorinated dithienyldiketopyrrolopyrrole (fDT-DPP) monomers suitable for direct heteroarylation polymerization. fDT-DPP copolymers were then prepared to probe the effect of the fluorination. It was found that they feature deeper HOMO energy levels and smaller bandgaps than their non-fluorinated analogues. Moreover, some fDT-DPP copolymers show ambipolar behavior when tested in OFETs. For example, P2 shows hole mobility up to 0.8 cm2 V-1 s-1 and electron mobility up to 0.5 cm2 V-1 s-1. Inverted PSCs with power conversion efficiency (PCE) up to 7.5% were also obtained for P5. These results reported here (OFETs and PSCs) confirm that the fluorination of dithienyl-DPP moieties improves the performance of organic electronics devices. This study is also evidencing the strength of the direct heteroarylation polymerization and fDT-DPP as a new class of conjugated polymers. [ABSTRACT FROM AUTHOR]

Here we design and synthesize one novel fluorene side-chained benzodithiophene (BDT) monomer for polymer solar cells (PSCs) donor. By copolymerizing this monomer with 4,7-di(thiophen-2-yl)-2,1,3-benzothiadiazole (DTBT) or 4,7-di(4-(2-ethylhexyl)-2-thienyl)-5,6-difluoro-2,1,3-benzothiadiazole (DTffBT), two donor-acceptor (D-A) conjugated polymers PFBDT-DTBT and PFBDT-DTffBT are prepared. PSCs are prepared with these polymers as donor and PC71BM as acceptor. The maximum power conversion efficiency (PCE) of the two polymers PFBDT-DTBT and PFBDT-DTffBT based PSCs is 7.13% (VOC = 0.90 V, JSC = 13.26 mA cm-2, and FF = 0.598) and 7.33% (VOC = 0.96 V, JSC = 13.24 mA cm-2, and FF = 0.577). The UV-vis absorption and electrochemical cyclic voltammetry test results show that F atoms in DTffBT unit present an obvious influence on intermolecular effect and molecular energy levels of polymers. Furthermore, the energy loss of two PSCs devices in this work is confirmed to be 0.78 and 0.71 eV, lower than most results based on BDT PSCs devices, which is critical to obtain high PCE PSCs devices with a decent trade-off between JSC and VOC. [ABSTRACT FROM AUTHOR]

Electron-deficient borinic acid monomers and corresponding polymers were synthesized with different substituents via a one-pot reaction of Grignard reagents with trimethoxyborane and reversible addition-fragmentation chain transfer polymerization, respectively. Further investigations of substituent effects of borinic acid polymers (PBAs) were carried out, indicating that the thermoresponsive properties of PBAs benefit from the increase of steric hindrance of PBA substituent, while the binding affinity of PBAs with Alizarin Red S, 8-hydroxyquinoline (HQ), and fluoride ion decreases with the increase of steric hindrance of substituent. Attributed to the strong dative N → B bond and the strongly luminescent boron quinolate, the application of phenyl PBA for fluorescence detection of HQ is realized with high sensitivity at the ppm level. These results therefore confirm that borinic acid-containing polymer is a new type of stimuli-responsive polymer in the field of thermoresponsiveness over a wide temperature range and chemical sensor for diol and electron-rich compounds. [ABSTRACT FROM AUTHOR]

Control over the orientation of cylindrical and lamellar domains is required for pattern transfer in block copolymer lithography. Previous work mainly focuses on the use of random copolymer brushes to control the wetting behaviors of block copolymers (BCPs), but random copolymerization is only limited to a few monomer pairs. Here we demonstrate the use of homopolymer brushes/mats to modify the substrate to form a chemically homogeneous surface. The surface affinity is tuned by changing the monomer substituent, and a variety of wetting behaviors are obtained in BCP films on homopolymer brushes/mats. Three series of hydroxy-terminated or cross-linkable homopolymers, including polymethacrylate, polyacrylate, and polystyrene derivatives, are prepared for controlling the BCP-substrate interaction. Both preferential and nonpreferential wetting behaviors of poly(styrene-b-methyl methacrylate), poly(styrene-b-rac-lactide), and poly(styrene-b-propylene carbonate) films are obtained as the homopolymer structures change in terms of the carbon contents, indicating that this homopolymer approach may be applicable to any BCPs. Moreover, homopolymer brushes can also substitute random copolymer brushes in directed self-assembly of BCP films with density multiplication on the chemical pattern. The use of homopolymer brushes/mats may have advantages over random copolymer brushes or blend brushes in terms of reproducibility and uniformity of brush formation, reduction of defect density, and increase of assembly kinetics. [ABSTRACT FROM AUTHOR]

Ultrathin films of covalent molecular networks were deposited onto substrate surfaces by carrying out layer-by-layer cross-linking polymerization (LBLCP), which enabled the thickness of the resulting polyurea network film to be precisely controlled on the molecular length scale. The LBLCP was performed by alternatingly dipping the substrate into solutions of a tetrafunctional tetrahedral network former and a bifunctional counter-monomer. We investigated how the chemical and geometrical structure of the bi- or tetrafunctional amine or isocyanate monomers used in the LBLCP affected the growth behavior of the network films. Structural characteristics of these monomers such as meta/para phenylene substitution, rigid/flexible linkages, and aliphatic/aromatic nature determined whether molecular networks of these monomers could grow and how the thickness of the network increased from one deposition cycle to the next. The results showed the LBLCP method to be an efficient way of synthesizing ultrathin network films as they can be prepared by combining diverse monomer systems through multiple-cycle deposition processes. [ABSTRACT FROM AUTHOR]

Conventional anionic ring-opening of polymerization (AROP) of cyclic esters suffers from the nonselective and concomitant attack of the monomer and of the polymer chains by the growing active species, which results in polyester samples with uncontrolled molar masses and broad polydispersity due to the competition between propagation and transesterification reactions. In this report, we describe a new AROP system mediated by a controlled amount of CO2 which prevents transesterification reactions from occurring. Using lithium monomethyl diethylene glycoxide (MEEOLi) as initiator and 1.5 equiv of CO2, ε-caprolactone could be polymerized under truly "living" conditions in dichloromethane (DCM) at 70 °C, as evidenced by the control of molar masses, the narrow polydispersity indexes (Mn up to ~40 kg/mol, Đ < 1.16), and also successful chain extension experiments. Lithium carbonate used as initiator in the presence of 0.5 equiv of CO2 afforded similar polymerization results. Experiments carried out with other alkoxide salts and solvents demonstrate that CO2 is indispensable as well as lithium and noncoordinating solvents for the suppression of transesterifications. A similar strategy was applied for the AROP of l-lactide (LLA). At -20 °C, LLA could be polymerized under living conditions with undetectable level of transesterification as demonstrated by MALDI-ToF analysis. To account for the polymerization mechanism occurring in the presence of a slight excess of CO2, we resorted to computational studies. It appears that a fast equilibrium takes place between two tetrameric aggregates, one dormant comprising four carbonates (RCO3Li)4, and an active one involving three carbonates and one alkoxide (RCO3Li)3(ROLi). The latter is shown to selectively ring-open cyclic ester without indulging in transesterifications like (ROLi)4 precursors. [ABSTRACT FROM AUTHOR]

A novel difunctional benzoxazine with o-trifluoroacetamide functionality has been synthesized via Mannich condensation. The chemical structure of synthesized monomer has also been confirmed by ¹H, 13C, and 19F nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The ring-opening polymerization of the resin and the subsequent conversion of the freshly generated polybenzoxazine into polybenzoxazole are studied by FT-IR and differential scanning calorimetry (DSC). In addition to the advantage of low polymerization temperature as other reported o-amide benzoxazines, the o-trifluoroacetamide benzoxazine also exhibits an unexpected lower benzoxazole formation temperature. Furthermore, the resulting fluorinated polybenzoxazole derived from the benzoxazine monomer possesses the combined excellent properties of facile synthesis, easy processability, low dielectric constant, high thermal stability, and long shelf life, evidencing its potential applications in microelectronic industries, aerospace, and other high-performance areas. [ABSTRACT FROM AUTHOR]

A series of allyl ansa-lanthanidocenes, [{Me2C(C5H4)(Flu)}Nd(1,3-C3H3(SiMe3)2)2]K (Flu = 9-fluorenyl; 1-Nd-K(allyl)) and {R2C(C5H4)(R'R'Flu)}Ln(1,3-C3H3(SiMe3)2)(THF)x (R = Me, R' = 2,7-tBu2, Ln = Y (2-Y), Sc (2-Sc), x = 0; Ln = La (2-La), Pr (2-Pr), Nd (2-Nd), Sm (2-Sm), x = 1; R = Me, R' = oct = octamethyloctahydrodibenzo, Ln = Nd, x = 1 (3-Nd); R = Ph, R' = H, Ln = Nd, x = 1 (4-Nd); R = Me, R' = 3,6-tBu2, Ln = Nd, x = 1 (5-Nd)), were prepared in good yields and characterized by NMR spectroscopy (for diamagnetic complexes 2-Sc, 2-Y, and 2-La) and by single-crystal X-ray diffraction (1-Nd-K(allyl), 2-La, 2-Pr, 2-Nd, 2-Sm, and 4-Nd). Those complexes, especially 1-Nd-K(allyl), 2-Nd, 4-Nd, 2-La, and 2-Sm, act as single-component catalyst precursors for polymerization of styrene (in bulk or in aliphatic hydrocarbon solutions, (nBu)2Mg as scavenger, Tpolym = 60-140 °C), affording highly syndiotactic polystyrene (sPS) ([r]5 = 63-88%; Tm up to 260 °C). High productivities (up to 4560 kg(sPS) mol(Ln)-1 h-1) were achieved at 120-140 °C, at low catalyst loadings ([St]/[Nd] = 20 000-76 000 equiv), with 2-Nd and 2-Pr. On the other hand, precursors having bulky substituents on the fluorenyl moieties in 3,6-positions (3-Nd, 5-Nd) or based on small ionic radius metals (2-Y, 2-Sc) were poorly or not active under standard polymerization conditions. These results have been rationalized by DFT computations, which included the solvent, carried out on the putative 1-Nd, and the isolated 2-Nd and 5-Nd complexes. Three consecutive styrene insertions were studied, and it was revealed that (i) the formation of sPS is thermodynamically controlled by two effects--minimization of repulsions between fluorenyl/styrene phenyl ring and (in the initiation phase) fluorenyl/SiMe3 substituents of the allyl ligand--and (ii) the presence of bulky substituents on the fluorenyl moiety does not influence the activation barrier of monomer insertion, but it may destabilize thermodynamically the insertion product. [ABSTRACT FROM AUTHOR]