Showing papers in "Macromolecules in 2010"
TL;DR: Graphene has emerged as a subject of enormous scientific interest due to its exceptional electron transport, mechanical properties, and high surface area, and when incorporated appropriately, these atomically thin carbon sheets can significantly improve physical properties of host polymers at extremely small loading.
Abstract: Graphene has emerged as a subject of enormous scientific interest due to its exceptional electron transport, mechanical properties, and high surface area. When incorporated appropriately, these atomically thin carbon sheets can significantly improve physical properties of host polymers at extremely small loading. We first review production routes to exfoliated graphite with an emphasis on top-down strategies starting from graphite oxide, including advantages and disadvantages of each method. Then solvent- and melt-based strategies to disperse chemically or thermally reduced graphene oxide in polymers are discussed. Analytical techniques for characterizing particle dimensions, surface characteristics, and dispersion in matrix polymers are also introduced. We summarize electrical, thermal, mechanical, and gas barrier properties of the graphene/polymer nanocomposites. We conclude this review listing current challenges associated with processing and scalability of graphene composites and future perspectives f...
2,979 citations
TL;DR: In this article, a facial aqueous solution was used to extract fully exfoliated graphene nanosheets and polyvinyl alcohol (PVA) for the preparation of polymer nanocomposites.
Abstract: Graphene, flat carbon nanosheets, has generated huge activity in many areas of science and engineering due to its unprecedented physical and chemical properties. With the development of wide-scale applicability including facile synthesis and high yield, this exciting material is ready for its practical application in the preparation of polymer nanocomposites. Here we report that nanocomposites based on fully exfoliated graphene nanosheets and poly(vinyl alcohol) (PVA) are prepared via a facial aqueous solution. A significant enhancement of mechanical properties of the graphene/PVA composites is obtained at low graphene loading; that is, a 150% improvement of tensile strength and a nearly 10 times increase of Young’s modulus are achieved at a graphene loading of 1.8 vol %. The comparison between the experimental results and theoretical simulation for Young’s modulus indicates that the graphene nanosheets in polymer matrix are mostly dispersed randomly in the nanocomposite films.
1,308 citations
TL;DR: The use of photoinitiated polymerization is continuously growing in industry as reflected by the large number of applications in not only conventional areas such as coatings, inks, and adhesives but also high-tech domains, optoelectronics, laser imaging, stereolithography, and nanotechnology as mentioned in this paper.
Abstract: The use of photoinitiated polymerization is continuously growing in industry as reflected by the large number of applications in not only conventional areas such as coatings, inks, and adhesives but also high-tech domains, optoelectronics, laser imaging, stereolithography, and nanotechnology. In this Perspective, the latest developments in photoinitiating systems for free radical and cationic polymerizations are presented. The potential use of photochemical methods for step-growth polymerization is also highlighted. The goal is, furthermore, to show approaches to overcome problems associated with the efficiency, wavelength flexibility, and environmental and safety issues in all photoinitiating systems for different modes of activation. Much progress has been made in the past 10 years in the preparation of complex and nano-structured macromolecules by using photoinitiated polymerizations. Thus, the new and emerging applications of photoinitiated polymerizations in the field of biomaterials, surface modific...
1,082 citations
TL;DR: In this article, the ring-opening polymerization of cyclic monomers is used as a representative polymerization process to illustrate some of the features of organic catalysts and initiators and compare them to metal-based approaches.
Abstract: Organocatalysis offers a number of opportunities in polymer synthesis and was among the earliest methods of catalyzing the synthesis of polyesters. In the following Perspective we attempt to highlight the opportunities and challenges in the use of organic molecules as catalysts or initiators for polymerization reactions. The ring-opening polymerization of cyclic monomers is used as a representative polymerization process to illustrate some of the features of organic catalysts and initiators and to compare them to metal-based approaches. The convergence of convenience, functional group tolerance, fast rates, and selectivities will continue to drive innovations in polymerization catalysis, and it is our perspective that organocatalysis will continue to play an important role in these developments.
749 citations
716 citations
TL;DR: In this paper, a review of microporous materials with a particular emphasis on amorphous polymers that possess intrinsic microporosity (IM), which is defined as microporeosity that arises directly from the shape and rigidity of component macromolecules.
Abstract: The past decade has seen the development of microporous materials (i.e., materials containing pores of dimensions <2 nm) derived wholly from organic components. Here we review this nascent area with a particular emphasis on amorphous polymers that possess intrinsic microporosity (IM), which is defined as microporosity that arises directly from the shape and rigidity of component macromolecules. Although IM can be readily identified within soluble non-network polymers and oligomers, for network polymers it is harder to differentiate IM from template effects that are responsible for the microporosity within hyper-cross-linked networks. The numerous examples of microporous polymers assembled from rigid monomers by the formation of rigid linking groups are surveyed and their IM assessed. The potential applications of these materials are highlighted.
704 citations
TL;DR: This Perspective provides context as to why these newly developed or recently reinvigorated reactions have been so readily embraced for the preparation of polymers with advanced macromolecular topologies, increased functionality, and unique properties.
Abstract: Precision synthesis of advanced polymeric materials requires efficient, robust, and facile chemical reactions. Paradoxically, the synthesis of increasingly intricate macromolecular structures generally benefits from exploitation of the simplest reactions available. This idea, combined with requirements of high efficiency, orthogonality, and simplified purification procedures, has led to the rapid adoption of “click chemistry” strategies in the field of macromolecular engineering. This Perspective provides context as to why these newly developed or recently reinvigorated reactions have been so readily embraced for the preparation of polymers with advanced macromolecular topologies, increased functionality, and unique properties. By highlighting important examples that rely on click chemistry techniques, including copper(I)-catalyzed and strain-promoted azide−alkyne cycloadditions, Diels−Alder cycloadditions, and thiol−ene reactions, among others, we hope to provide a succinct overview of the current state ...
640 citations
TL;DR: In this article, the authors reported an efficient method to prepare nylon-6− (PA6−) graphene composites by in situ polymerization of caprolactam in the presence of graphene oxide (GO).
Abstract: We reported an efficient method to prepare nylon-6− (PA6−) graphene (NG) composites by in situ polymerization of caprolactam in the presence of graphene oxide (GO). During the polycondensation, GO was thermally reduced to graphene simultaneously. By adjusting the feed ratio of caprolactam to GO, various composites with 0.01−10 wt % content of graphene were obtained. The highly grafting nylon-6 arms on graphene sheets was confirmed by XPS, FTIR, TGA and AFM measurements, showing the grafting content up to 78 wt % and homogeneous 2D brush-like morphology from AFM observations. The efficient polymer-chain grafting makes the graphene homogeneously dispersed in PA6 matrix and depresses the crystallization of PA6 chains. Furthermore, we prepared NG fibers by melt spinning process, and found that the tensile strength increased by 2.1 folds and Young’s modulus increased by 2.4 folds with the graphene loading of 0.1 wt % only, revealing an excellent reinforcement to composites by graphene. The in situ condensation...
628 citations
TL;DR: The unique attributes of CANs that must be considered when designing, fabricating, and characterizing these smart materials that respond to either thermal or photochemical stimuli are discussed.
Abstract: Polymer networks possessing reversible covalent cross-links constitute a novel material class with the capacity for adapting to an externally applied stimulus. These covalent adaptable networks (CANs) represent a trend in polymer network fabrication toward the rational design of structural materials possessing dynamic characteristics for specialty applications. Herein, we discuss the unique attributes of CANs that must be considered when designing, fabricating, and characterizing these smart materials that respond to either thermal or photochemical stimuli. While there are many reversible reactions which to consider as possible cross-link candidates in CANs, there are very few that are readily and repeatedly reversible. Furthermore, characterization of the mechanical properties of CANs requires special consideration owing to their unique attributes. Ultimately, these attributes are what lead to the advantageous properties displayed by CANs, such as recyclability, healability, tunability, shape changes, an...
615 citations
554 citations
TL;DR: The field of responsive polymers has evolved well beyond the demonstration of novel and interesting properties, e.g., drug or gene carriers with triggered release properties, catalysis, detection and imaging, environmentally adaptive coatings, and self-healing materials.
Abstract: The past two decades have evidenced a tremendous growth in the field of responsive polymers, which can exhibit reversible or irreversible changes in physical properties and/or chemical structures to an external stimulus such as pH, temperature, ionic strength, light irradiation, mechanical forces, electric and magnetic fields, specific analytes, external additives (ions, bioactive molecules, etc.), or a combination of them. Responsive polymers can exist in the form of solutions, gels, self-assembled nanoparticles, (multilayer) films, and bulk solids. The field of responsive polymers has nowadays evolved well beyond the demonstration of novel and interesting properties. Currently, the exploitation of useful and advanced functions, e.g., drug or gene carriers with triggered release properties, catalysis, detection and imaging, environmentally adaptive coatings, and self-healing materials, has emerged to be a more relevant subject. In this Perspective, we focus on recent developments of responsive polymer-ba...
TL;DR: In this article, the authors highlight several recent advances in processing approaches that provide new levels of tailorability to the structures and encapsulated contents of block copolymer assemblies in solution.
Abstract: Block copolymers have the capacity to self-organize into a myriad of aggregate structures when placed in selective solvents, offering great promise for the construction of delivery vehicles and complex nanoscale assemblies. A key feature of these materials is their propensity to become kinetically trapped in nonequilibrium states, meaning that the structures they adopt depend sensitively on the processing route taken. While this makes it challenging to fully explore the landscape of possible morphologies, it also means that careful attention to the pathway of self-assembly can allow for remarkable control over the resulting nonequilibrium structures. In this Perspective, we highlight several recent advances in processing approaches that provide new levels of tailorability to the structures and encapsulated contents of block copolymer assemblies in solution.
TL;DR: This Perspective will emphasize polymers used in medicine and specifically those designed as scaffolds for use in tissue engineering and regenerative medicine.
Abstract: Biomaterials have been used extensively in medical, personal care, and food applications, with many similar polymers being used across disciplines. This Perspective will emphasize polymers used in medicine and specifically those designed as scaffolds for use in tissue engineering and regenerative medicine. The areas of active research in tissue engineering include: biomaterials design—incorporation of the appropriate chemical, physical, and mechanical/structural properties to guide cell and tissue organization; cell/scaffold integration—inclusion into the biomaterial scaffold of either cells for transplantation or biomolecules to attract cells, including stem cells, from the host to promote integration with the tissue after implantation; and biomolecule delivery—inclusion of growth factors and/or small molecules or peptides that promote cell survival and tissue regeneration. While a significant and growing area of regenerative medicine involves the stimulation of endogenous stem cells, this Perspective wi...
TL;DR: In this paper, the quaternized polymers PSGCl-x (where x represents the number of quaternary guanidinium groups/repeat units) were synthesized via chloromethylation of poly(arylene ether sulfone)s, followed by reactions with pentamethylguanidine.
Abstract: Poly(arylene ether sulfone)s were functionalized with quaternary guanidinium groups in order to investigate their properties as novel polymeric hydroxide exchange membrane materials. The quaternized polymers were synthesized via chloromethylation of poly(arylene ether sulfone)s, followed by reactions with pentamethylguanidine. The resulting quaternized polymers PSGCl-x (where x represents the number of the quaternary guanidinium groups/repeat units) presented an elevated molecular weight and exhibited an outstanding solubility in polar aprotic solvents. Consequently flexible and tough membranes of PSGCl-x with varying ionic content could be prepared by casting from the DMSO solution. Novel anion exchange membranes, PSGOH-x, were obtained by an anion exchange of PSGCl-x with 1 M NaOH at room temperature. The membranes displayed a high ionic conductivity and an excellent chemical stability. The obtained alkaline anion exchange membranes (AEMs) showed conductivities almost above 10−2 S cm−1 at room temperatu...
TL;DR: High strength hydrogels were made by ionically cross-linking the polyelectrolyte midblock of a self-assembled, amphiphilic triblock copolymer network.
Abstract: High strength hydrogels were made by ionically cross-linking the polyelectrolyte midblock of a self-assembled, amphiphilic triblock copolymer network The polymer backbone consisted of glassy, sphe
TL;DR: In this article, an aqueous dispersion of graphene nanosheets (GNs) has been successfully prepared via chemical reduction of graphene oxide (GO) by hydrazine hydrate in the presence of poly[(2-ethyldimethylammonioethyl methacrylate ethyl sulfate)-co-(1-vinylpyrrolidone)] (PQ11), a cationic polyelectrolyte, for the first time.
Abstract: An aqueous dispersion of graphene nanosheets (GNs) has been successfully prepared via chemical reduction of graphene oxide (GO) by hydrazine hydrate in the presence of poly[(2-ethyldimethylammonioethyl methacrylate ethyl sulfate)-co-(1-vinylpyrrolidone)] (PQ11), a cationic polyelectrolyte, for the first time. The noncovalent functionalization of GN by PQ11 leads to a GN dispersion that can be very stable for several months without the observation of any floating or precipitated particles. Several analytical techniques including UV−vis spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) have been used to characterize the resulting GNs. Taking advantages of the fact that PQ11 is a positively charged polymer exhibiting reducing ability, we further demonstrated the subsequent decoration of GN with Ag nanoparticles (AgNPs) by two routes: (1) direct adsorption of preformed, negatively charged AgNPs; (2) in-situ chemical reduction of silver salts. It was found th...
TL;DR: In this paper, the properties of anion-conducting membranes synthesized by halomethylation and quaternization of benzylmethyl-containing poly(sulfone)s.
Abstract: This report details the properties of anion-conducting membranes synthesized by halomethylation and quaternization of benzylmethyl-containing poly(sulfone)s. The benzylmethyl moieties, which serve ...
TL;DR: It is shown that primary amines are more effective catalysts than either secondary or tertiary amines and certain tertiary phosphines are shown to be even more effective species even at concentrations 2 orders of magnitude lower than employed for hexylamine.
Abstract: A detailed evaluation of the kinetics of the thiol-Michael reaction between hexanethiol and hexyl acrylate is described. It is shown that primary amines are more effective catalysts than either secondary or tertiary amines with, for example, quantitative conversion being achieved within 500 s in the case of hexylamine with an apparent rate constant of 53.4 mol L−1 s−1 at a catalyst loading of 0.057 mol %. Certain tertiary phosphines, and especially tri-n-propylphosphine and dimethylphenylphosphine, are shown to be even more effective species even at concentrations 2 orders of magnitude lower than employed for hexylamine and performed in solution with quantitative conversions reached within ca. 100 s for both species and apparent rate constants of 1810 and 431 mol L−1 s−1, respectively. The nature of the thiol is also demonstrated to be an important consideration with mercaptoglycolate and mercaptopropionate esters being significantly more reactive than hexanethiol with reactivity mirroring the pKa of the ...
TL;DR: In this article, the authors used fluorescein-labeled poly(acrylic acid) (PAA) of four different chain lengths (N = 20, 50, 150, and 510) to determine the binodal compositions of polyelectrolyte complexes of PAA and poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) of similar chain lengths.
Abstract: When oppositely charged polyelectrolytes are mixed below a critical salt concentration, their mixtures show macroscopic phase separation into a dilute and a dense, polyelectrolyte complex phase. Binodal compositions of the polyelectrolyte complexes have been measured experimentally using fluorescently labeled polyelectrolytes. We used fluorescein-labeled poly(acrylic acid) (PAA) of four different chain lengths (N = 20, 50, 150, and 510) to determine the binodal compositions of polyelectrolyte complexes of PAA and poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) of similar chain lengths. The water content of polyelectrolyte complexes obtained has a lower limit of about 65%, practically independent of chain length, and increases with increasing salt concentration. We interpret our results on binodal compositions, water content and critical salt concentration as a function of chain length using the mean-field model of Voorn and Overbeek and find good quantitative agreement with our experiments using only ...
TL;DR: In this paper, the effects of differently dimensional nanoparticles on the crystallization behavior of poly(l-lactide) matrices were investigated using time-resolved Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WAXD).
Abstract: Low-dimensional nanoparticles have a strong ability to induce the crystallization of polymer matrices. One-dimensional carbon nanotubes (CNTs) and two-dimensional graphene nanosheets (GNSs), both of which are both carbon-based nanoparticles, provide a good opportunity to investigate the effects of differently dimensional nanoparticles on the crystallization behavior of a polymer. For this purpose, respective nanocomposites of CNTs and GNSs with poly(l-lactide) (PLLA) as matrix were prepared by solution coagulation. Time-resolved Fourier-transform infrared spectroscopy (FTIR) and synchrotron wide-angle X-ray diffraction (WAXD) were performed to probe chain conformational changes and to determine the crystallization kinetics during the isothermal crystallization of the PLLA nanocomposites and neat PLLA, especially in the early stages. Both CNTs and GNSs could serve as nucleating agents in accelerating the crystallization kinetics of PLLA; however, the ability of CNTs to induce crystallization was stronger t...
TL;DR: The first bivalent-brush polymers are reported; these materials were prepared by graft-through ROMP of drug-loaded polyethylene-glycol (PEG) based macromonomers (MMs) and were at least 10-fold more toxic to human cancer cells after photoinitiated drug release.
Abstract: Graft-through ring-opening metathesis polymerization (ROMP) using ruthenium N-heterocyclic carbene catalysts has enabled the synthesis of bottle-brush polymers with unprecedented ease and control. Here we report the first bivalent-brush polymers; these materials were prepared by graft-through ROMP of drug-loaded polyethylene-glycol (PEG) based macromonomers (MMs). Anticancer drugs doxorubicin (DOX) and camptothecin (CT) were attached to a norbornene-alkyne-PEG MM via a photocleavable linker. ROMP of either or both drug-loaded MMs generated brush homo- and co-polymers with low polydispersities and defined molecular weights. Release of free DOX and CT from these materials was initiated by exposure to 365 nm light. All of the CT and DOX polymers were at least 10-fold more toxic to human cancer cells after photoinitiated drug release while a copolymer carrying both CT and DOX displayed 30-fold increased toxicity upon irradiation. Graft-through ROMP of drug-loaded macromonomers provides a general method for the systematic study of structure-function relationships for stimuli-responsive polymers in biological systems.
TL;DR: In this article, a simple and powerful method for developing nanostructured and CO2-philic polymer membranes for CO2 separation is described, where a poly(ethylene oxide)−poly(butylene terephthalate) multiblock copolymer is used as membrane material.
Abstract: Polymeric membranes are attractive for CO2 separation and concentration from different gas streams because of their versatility and energy efficiency; they can compete with, and they may even replace, traditional absorption processes. Here we describe a simple and powerful method for developing nanostructured and CO2-philic polymer membranes for CO2 separation. A poly(ethylene oxide)−poly(butylene terephthalate) multiblock copolymer is used as membrane material. Smart additives such as polyethylene glycol dibutyl ether are incorporated as spacers or fillers for producing nanostructured materials. The addition of these specific additives produces CO2-philic membranes and increases the CO2 permeability (750 barrer) up to five-fold without the loss of selectivity. The membranes present outstanding performance for CO2 separation, and the measured CO2 flux is extremely high (>2 m3 m−2 h−1 bar−1) with selectivity over H2 and N2 of 10 and 40, respectively, making them attractive for CO2 capture.
TL;DR: In this article, a poly(lactic acid) (PLA) ternary blend system consisting of PLA, an epoxy-containing elastomer, and a zinc ionomer was introduced and studied in detail.
Abstract: In this study, a poly(lactic acid) (PLA) ternary blend system consisting of PLA, an epoxy-containing elastomer, and a zinc ionomer was introduced and studied in detail. Transmission electron microscopy revealed that the “salami”-like phase structure was formed in the ternary blends. While increase in blending temperature had little effects on the tensile properties of the resulting blends, it greatly changed the impact strength. For the blends prepared at 240 °C by extrusion blending, the resulting PLA ternary blends displayed supertoughness with moderate levels of strength and modulus. It was found that the zinc ions catalyzed the cross-linking of epoxy-containing elastomer and also promoted the reactive compatibilization at the interface of PLA and the elastomer. Both blending temperature and elastomer/ionomer ratio were found to play important roles in achieving supertoughness of the blends. The significant increase in notched impact strength was attributed to the effective interfacial compatibilizatio...
TL;DR: In this paper, the role played by strong physical interactions between silica nanoparticles and the PDMA polymer on the properties of chemically cross-linked highly swollen PDMA networks is investigated.
Abstract: The synthesis and mechanical characterization of novel, tough poly(N,N-dimethylacrylamide) (PDMA)−silica hydrogel hybrids are presented to understand the role played by strong physical interactions between silica nanoparticles and the PDMA polymer on the properties of chemically cross-linked highly swollen PDMA networks. A detailed comparison of the hybrids with unmodified PDMA gels indicates that the incorporation of silica nanoparticles in the hydrogel increases the compression strength and the fracture toughness of notched samples up to an order of magnitude while increasing its modulus by a factor of 6 with a volume fraction of particles of the order of only 7%. The hybrid gels present a strain-dependent hysteresis but no permanent damage or residual strain upon unloading even after repeated cycling, a very unique property for such tough hydrogels. The reason for this exceptional increase in toughness is attributed mainly to the combined effect of breakable silica/polymer bonds and of a wide distribut...
TL;DR: In this article, the authors reported the synthesis and properties of network polymers of intrinsic microporosity derived from triptycene monomers that possess alkyl groups attached to their bridgehead positions.
Abstract: We report the synthesis and properties of network polymers of intrinsic microporosity (network−PIMs) derived from triptycene monomers that possess alkyl groups attached to their bridgehead positions. Gas adsorption can be controlled by the length and branching of the alkyl chains so that the apparent BET surface area of the materials can be tuned within the range 618−1760 m2 g−1. Shorter (e.g., methyl) or branched (e.g., isopropyl) alkyl chains provide the materials of greatest microporosity, whereas longer alkyl chains appear to block the microporosity created by the rigid organic framework. The enhanced microporosity, in comparison to other PIMs, originates from the macromolecular shape of the framework, as dictated by the triptycene units, which helps to reduce intermolecular contact between the extended planar struts of the rigid framework and thus reduces the efficiency of packing within the solid. The hydrogen adsorption capacities of the triptycene-based PIMs with either methyl or isopropyl substit...
TL;DR: In this article, it was shown that for small enough particles the layer of polymer affected by the particles (bound” polymer layer) must be much smaller than that for large particles: the favorable effect of increasing particle surface area can thus be overcome and lead to the small solvent limit with unfavorable mechanical properties.
Abstract: Polymer properties, such as their mechanical strength, barrier properties, and dielectric response, can be dramatically improved by the addition of nanoparticles. This improvement is thought to be because the surface area per unit mass of particles increases with decreasing particle size, R, as 1/R. This favorable effect has to be reconciled with the expectation that at small enough R the nanoparticles must behave akin to a solvent and cause a deterioration of properties. How does this transition in behavior from large solutes to the solvent limit occur? We conjecture that for small enough particles the layer of polymer affected by the particles (“bound” polymer layer) must be much smaller than that for large particles: the favorable effect of increasing particle surface area can thus be overcome and lead to the small solvent limit with unfavorable mechanical properties, for example. To substantiate this picture requires that we measure and compare the “bound polymer layer” formed on nanoparticles with th...
TL;DR: In this article, the authors examined the structure of densely grafted polymer layers grown from the surfaces of spherical nanoparticles over a broad range of graft densities and chain lengths, and showed that the hydrodynamic thickness of the polymer layer scales as h √ N4/5 for short chains and high grafting densities, that is, in the concentrated polymer brush (CPB) regime, whereas h ∆ ∆ N3 /5 for long enough chains (semidilute polymer brush, SDPB).
Abstract: We examine the structure of densely grafted polymer layers grown from the surfaces of spherical nanoparticles over a broad range of graft densities and chain lengths. Dynamic light scattering (DLS) experiments show that the hydrodynamic thickness of the polymer layer, h, scales as h ∝ N4/5 for short chains and high grafting densities, that is, in the concentrated polymer brush (CPB) regime, whereas h ∝ N3/5 for long enough chains (semidilute polymer brush, SDPB). The mean field theory of Wijmans and Zhulina is able to collapse approximately all of our data and those in the existing literature (even on other polymers) into an apparently universal form. From these findings, we conclude that the result h ∝ N4/5 for the CPB is an intermediate crossover scaling, relevant to particles of finite curvature, analogous to the h ∝ N observed for concentrated flat brushes. Second, the scaling h ∝ N3/5 uniquely reflects the increased space available to the chain segments as one proceeds away from a curved grafting sur...
TL;DR: A brief account of the research efforts devoted to the development of click reaction into a new polymerization process is given in this article, where the existing limitations and challenges as well as the promising opportunities and directions in fostering the click polymerization into a versatile tool for the construction of new macromolecules with well-defined structures and multifaceted functionalities.
Abstract: Chemical transformations of small molecules have served as a rich source of reactions for the development of new polymerization processes, and “click” reaction has the potential to become a powerful polymerization technique. We herein give a brief account of the research efforts devoted to the development of click reaction into a new polymerization process. Remarkable progresses have been made in recent years in the exploration of metal-mediated and metal-free click polymerization systems and in the syntheses of linear and hyperbranched polytriazoles with regioregular molecular structures and advanced functional properties. We also discuss the existing limitations and challenges as well as the promising opportunities and directions in fostering the click polymerization into a versatile tool for the construction of new macromolecules with well-defined structures and multifaceted functionalities.
TL;DR: In this paper, the effect of several imidization methods on the properties of thermally rearranged (TR) polymer membranes was investigated, and the synthesis of ortho-functional polyimides from 4,4′-hexafluoroisopropylidene diphthalic anhydrides and 2,2′-bis(3-amino-4-hydroxyphenyl)hexafeluoropropane by three different imidizatio...
Abstract: Conversion of hydroxyl-containing polyimides into polybenzoxazole can be achieved by thermal rearrangement of the aromatic polymer chain with decarboxylation at elevated temperature. Synthetic methods to prepare polyimide precursors are important for the resulting thermally rearranged (TR) polymer membranes. Here, we report on the effect of several imidization methods on the properties of TR polymer membranes. Thermal and chemical imidizations are the most common routes to prepare polyimides, and solution thermal imidization using an azeotrope is also widely used, especially to obtain soluble polyimide-containing functional groups. We report here on the syntheses of ortho-functional polyimides from 4,4′-hexafluoroisopropylidene diphthalic anhydrides and 2,2′-bis(3-amino-4-hydroxyphenyl)hexafluoropropane by three different imidization methods. Acetate-containing polyimides by chemical imidization and further silylation treatment as well as hydroxyl-containing polyimides by thermal and azeotropic imidizatio...