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Showing papers in "Macromolecules in 2012"


Journal ArticleDOI
TL;DR: The current status and future perspectives in atom transfer radical polymerization (ATRP) are presented in this paper, with a special emphasis on mechanistic understanding of ATRP, recent synthetic and process development, and new controlled polymer architectures enabled by ATRP.
Abstract: Current status and future perspectives in atom transfer radical polymerization (ATRP) are presented. Special emphasis is placed on mechanistic understanding of ATRP, recent synthetic and process development, and new controlled polymer architectures enabled by ATRP. New hybrid materials based on organic/inorganic systems and natural/synthetic polymers are presented. Some current and forthcoming applications are described.

2,188 citations


Journal ArticleDOI
TL;DR: The research community has made great progress in the field of bulk heterojunction (BHJ) polymer solar cells since its inception in 1995 as mentioned in this paper and the power conversion efficiency (PCE) has increased from 1% in the 1990s to over 8% just recently.
Abstract: The research on the polymer-based solar cells (PSCs) has attracted an increasing amount of attention in recent years because PSCs pose potential advantages over mainstream inorganic-based solar cells, such as significantly reduced material/fabrication costs, flexible substrates, and light weight of finished solar cells. The research community has made great progress in the field of bulk heterojunction (BHJ) polymer solar cells since its inception in 1995. The power conversion efficiency (PCE), a key parameter to assess the performance of solar cells, has increased from 1% in the 1990s to over 8% just recently. These great advances are mainly fueled by the development of conjugated polymers used as the electron-donating materials in BHJ solar cells. In this Perspective, we first briefly review the progress on the design of conjugated polymers for polymer solar cells in the past 16 years. Since a conjugated polymer can be arbitrarily divided into three constituting components—the conjugated backbone, the si...

1,403 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the recent developments of polymerization-induced self-assembly of amphiphilic block copolymers based on controlled/living free-radical polymerization (CRP) in water.
Abstract: This Perspective describes the recent developments of polymerization-induced self-assembly of amphiphilic block copolymers based on controlled/living free-radical polymerization (CRP) in water. This method relies on the use of a hydrophilic living polymer precursor prepared via CRP that is extended with a hydrophobic second block in an aqueous environment. The process thus leads to amphiphilic block copolymers that self-assemble in situ into self-stabilized nano-objects in the frame of an emulsion or dispersion polymerization process. Depending on the nature and the structure of the so-formed copolymer, not only spherical particles can be achieved but also all morphologies that can be found in the phase diagram of an amphiphilic block copolymer in a selective solvent. This paper focuses mainly on aqueous emulsion or dispersion polymerization and gives an overview of the CRP techniques used, the general conditions, and the morphologies obtained.

635 citations


Journal ArticleDOI
TL;DR: In this article, a conjugated polymer based on 5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione, named as PBDTBDD, was designed, synthesized and applied in polymer solar cells (PSCs).
Abstract: A new conjugated polymer based on 5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c′]dithiophene-4,8-dione, named as PBDTBDD, was designed, synthesized, and applied in polymer solar cells (PSCs). A power conversion efficiency (PCE) of 6.67% was obtained from the PBDTBDD/PC61BM-based PSC, which is a remarkable result for the PSCs using PC61BM as electron acceptor. The PBDTBDD/PC61BM-based device exhibits a narrow absorption band and excellent quantum efficiency in the range from 500 to 700 nm. Furthermore, PBDTBDD shows a strong aggregation effect in solution state, and the study indicates that although the temperature used in solution preparation has little influence on molecular orientation as well as crystallinity of the D/A blend, it plays an important role in forming proper domain size in the blend. This work provides a good example to reveal the correlation between the morphology of the blend films and the processing temperature of the solution preparation. Furthermore, the study in this work suggests an intere...

622 citations


Journal ArticleDOI
TL;DR: In this paper, orientational polarization in polar polymers can be utilized for high energy density and low loss dielectrics, which can be used for next-generation dielectric capacitors for pulsed power and power conditioning applications.
Abstract: The state-of-the-art polymer dielectrics have been limited to nonpolar polymers with relatively low energy density but ultralow dielectric losses for the past decades. With the fast development of power electronics in pulsed power and power conditioning applications, there is a need for next-generation dielectric capacitors in areas of high energy density/low loss and/or high temperature/low loss polymer dielectrics. Given limitations in further enhancing atomic and electronic polarizations for polymers, this Perspective focuses on a fundamental question: Can orientational polarization in polar polymers be utilized for high energy density and low loss dielectrics? Existing experimental and theoretical results have suggested the following perspectives. For amorphous polar polymers, high energy density and low loss can be achieved below their glass transition temperatures. For liquid crystalline side-chain polymers, dipole mobility is so high that they saturate at relatively low electric fields, and only li...

506 citations


Journal ArticleDOI
TL;DR: In this paper, the authors review the design and synthesis of RAFT agents and discuss the basic design features that should be considered when selecting a RAFT agent or macro-RAFT agent for a given polymerization and set of reaction conditions.
Abstract: This Perspective reviews the design and synthesis of RAFT agents. First, we briefly detail the basic design features that should be considered when selecting a RAFT agent or macro-RAFT agent for a given polymerization and set of reaction conditions. The RAFT agent should be chosen to have an optimal Ctr (in most circumstances higher is better) while at the same time it should exhibit minimal likelihood for retarding polymerization or undergoing side reactions. The RAFT agent should also have appropriate solubility in the reaction medium and possess the requisite end-group functionality for the intended application. In this light we critically evaluate the various methods that have been used for RAFT agent synthesis. These methods include reaction of a carbodithioate salt with an alkylating agent, various thioacylation procedures, thiation of a carboxylic acid or ester, the ketoform reaction, thiol exchange, radical substitution of a bis(thioacyl) disulfide, and radical-induced R-group exchange. We also co...

470 citations


Journal ArticleDOI
TL;DR: The different approaches of rational BCP design, making use of various photochromic moieties and photochemical reactions, and the underlying mechanisms leading to photoinduced disruption of BCP micelles are discussed.
Abstract: The association state of light-responsive block copolymer (BCP) micelles in aqueous solution can be altered, often reversibly, by light. Driven by the potential application in controlled drug delivery, this type of stimuli-responsive polymer micelles has received increasing attention. This Perspective highlights the progress achieved in recent years. On the one hand, we discuss the different approaches of rational BCP design, making use of various photochromic moieties and photochemical reactions, and the underlying mechanisms leading to photoinduced disruption of BCP micelles. On the other hand, we suggest possible future directions in this area, including exploration of new mechanisms and chemistry and solutions to the excitation wavelength problem crucial for biomedical applications.

462 citations


Journal ArticleDOI
TL;DR: The use of o-nitrobenzyl group (o-NB) in polymer chemistry has been extensively studied in this article, including the use of O-NB-based cross-linkers for photodegradable hydrogels, o-NB side chain functionalization in (block) copolymers, and oNB functionalization for thin film patterning for self-assembled monolayers.
Abstract: Polymers featuring photolabile groups are the subject of intense research because they allow the alteration of polymer properties simply by irradiation. In particular, the o-nitrobenzyl group (o-NB) is utilized frequently in polymer and materials science. This Perspective pays particular attention to the increasing utilization of this chemical group in polymer chemistry. It covers the use of (i) o-NB-based cross-linkers for photodegradable hydrogels, (ii) o-NB side chain functionalization in (block) copolymers, (iii) o-NB side chain functionalization for thin film patterning, (iv) o-NB for self-assembled monolayers, (v) photocleavable block copolymers, and (vi) photocleavable bioconjugates. We conclude with an outlook on new research directions in this rapidly expanding area.

456 citations


Journal ArticleDOI
TL;DR: In this article, the authors report enhancements of 28-111% in mode I fracture toughness and up to 1580% in uniaxial tensile fatigue life through the addition of small amounts (≤1 wt %) of graphene oxide to an epoxy system.
Abstract: Epoxy systems have proven popular having important applications in aerospace and wind energy, but fracture and fatigue resistance of this polymer remain less than desired. Graphene oxide, a form of atomically thin carbon, possessing impressive multifunctional properties and an ideal interface for interacting with polymer matrices, has emerged as a viable reinforcement candidate. In this work, we report enhancements of 28–111% in mode I fracture toughness and up to 1580% in uniaxial tensile fatigue life through the addition of small amounts (≤1 wt %) of graphene oxide to an epoxy system. Graphene oxide was uniquely synthesized by unraveling and splaying open helical-ribbon carbon nanofibers. The resulting oxygenated basal planes and edges of the graphene oxide sheets were observed to promote onset of the cross-linking reaction and led to an increase in total heat of reaction effecting slightly higher glass transition temperatures of the cured composites. Measured improvements were also detected in quasi-st...

434 citations


Journal ArticleDOI
TL;DR: The present Perspective reviews recent achievements in strategies for the synthesis, self-assembly, and morphological control of multicompartment micelles and highlights future challenges and potential applications.
Abstract: Multicompartment micelles are an intriguing class of self-assembled aggregates with subdivided solvophobic cores. They have been subject to extensive research in part due to their unique morphological and sequestration properties as a result of multiple distinct chemical environments being in close proximity within one nanostructure. Multicompartment micelles hold potential for use in various applications that include the therapeutic delivery of multiple incompatible drug payloads. The present Perspective reviews recent achievements in strategies for the synthesis, self-assembly, and morphological control of multicompartment micelles and highlights future challenges and potential applications.

434 citations


Journal ArticleDOI
TL;DR: In this article, self-healing polymeric materials with branched architectures and reversible cross-linking functionalities at the periphery of branches were synthesized by atom transfer radical polymerization (ATRP).
Abstract: Self-healing polymeric materials with branched architectures and reversible cross-linking functionalities at the periphery of branches were synthesized by atom transfer radical polymerization (ATRP). Poly(n-butyl acrylate) grafted star polymers were prepared by chain extension ATRP from cross-linked cores comprised of poly(ethylene glycol diacrylate). These polymers were further used as macroinitiators for the consecutive chain extension ATRP of bis(2-methacryloyloxyethyl disulfide) (DSDMA), in which way disulfide reversible cross-links (SS) were introduced at the branch peripheries. The SS cross-linked polymers were then cleaved under reducing conditions to form thiol (SH)-functionalized soluble star polymers. The SH-functionalized star polymer solutions were deposited on silicon wafer substrates and converted to insoluble SS re-cross-linked films via oxidation. The self-healing of prepared polymer films was studied by continuous atomic force microscopy (AFM) imaging of cuts micromachined with the AFM ti...

Journal ArticleDOI
TL;DR: In this article, the authors calculated equilibrium phase diagrams for a selection of two-component block copolymer architectures using self-consistent field theory (SCFT) and found that the topology of the phase diagrams is relatively unaffected by differences in architecture, but phase boundaries shift significantly in composition.
Abstract: Equilibrium phase diagrams are calculated for a selection of two-component block copolymer architectures using self-consistent field theory (SCFT) The topology of the phase diagrams is relatively unaffected by differences in architecture, but the phase boundaries shift significantly in composition The shifts are consistent with the decomposition of architectures into constituent units as proposed by Gido and co-workers, but there are significant quantitative deviations from this principle in the intermediate-segregation regime Although the complex phase windows continue to be dominated by the gyroid (G) phase, the regions of the newly discovered Fddd (O70) phase become appreciable for certain architectures and the perforated-lamellar (PL) phase becomes stable when the complex phase windows shift toward high compositional asymmetry

Journal ArticleDOI
TL;DR: Polymerization-induced self-assembly (PISA) of poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methACrylate) (PGMA-PHPMA) diblocks is conducted using a RAFT aqueous dispersion polymerization formulation at 70 °C as discussed by the authors.
Abstract: Polymerization-induced self-assembly (PISA) of poly(glycerol monomethacrylate)–poly(2-hydroxypropyl methacrylate) (PGMA–PHPMA) diblocks is conducted using a RAFT aqueous dispersion polymerization formulation at 70 °C. Several PGMA macromolecular chain transfer agents (macro-CTAs) are chain-extended using a water-miscible monomer (HPMA): the growing PHPMA block becomes increasingly hydrophobic and hence drives in situ self-assembly. The final copolymer morphology in such PISA syntheses depends on just three parameters: the mean degree of polymerization (DP) of the PGMA stabilizer block, the mean DP of the PHPMA core-forming block, and the total solids concentration. Transmission electron microscopy is used to construct detailed diblock copolymer phase diagrams for PGMA DPs of 47, 78, and 112. For the shortest stabilizer block, there is essentially no concentration dependence: spheres, worms, or vesicles can be obtained even at 10% w/w solids simply by selecting the DP of the PHPMA block that gives the appr...

Journal ArticleDOI
TL;DR: The nanometer-size crystallization of poly(3,4-ethylenedioxythiophene) (PEDOT) inside the hydrophobic core region of PEDOT:PSS (PSS: poly(4-styrenesulfonate)) in a solid film is found by small and wide-angle X-ray scatterings using a synchrotron radiation source as mentioned in this paper.
Abstract: The nanometer-size crystallization of poly(3,4-ethylenedioxythiophene) (PEDOT) inside the hydrophobic core region of PEDOT:PSS (PSS: poly(4-styrenesulfonate)) in a solid film is found by small and wide-angle X-ray scatterings using a synchrotron radiation source. The clarified PEDOT:PSS structure indicates that a nanocrystal of PEDOT surrounded by PSS is grown in the solid film from randomly oriented PEDOT in a micelle dispersed in water during the course of film fabrication. The addition of ethylene glycol (EG) to the PEDOT:PSS water dispersion and post-treatment of the pristine film with EG both provide similar improvements in PEDOT crystallinity. The crystallite size of PEDOT increases up to a comparable size (∼4.8 nm) to the hydrophobic PEDOT core region of the micelle. The electrical conductivity of the solid film is concurrently enhanced by 2 orders of magnitude with the growing nanocrystal of PEDOT. These findings clearly demonstrate the importance of the single crystalline PEDOT assisted by EG to ...

Journal ArticleDOI
TL;DR: In this paper, reduced graphene oxide (RG-O) was found to dramatically enhance the mechanical, electrical, and thermal properties of natural rubber (NR) by co-coagulating a stable RG-O suspension with NR latex, while two-roll mill processing broke down this structure, yielding a homogeneous and improved dispersion.
Abstract: Dispersion of reduced graphene oxide (RG-O) into natural rubber (NR) was found to dramatically enhance the mechanical, electrical, and thermal properties of NR. However, property improvements were strongly dependent upon the processing history and nanocomposite morphology. Co-coagulating a stable RG-O suspension with NR latex afforded a weblike morphology consisting of platelet networks between the latex particles, while two-roll mill processing broke down this structure, yielding a homogeneous and improved dispersion. The physical properties of RG-O/NR vulcanizates with both morphologies were compared over a range of loadings; it was found that the network morphology was highly beneficial for thermal and electrical conductivity properties and greatly increased stiffness but was detrimental to elongation. A detailed comparative analysis of composite models found the Guth equation gave excellent fit to modulus data of the milled samples when taking the shape factor as equal to the platelet aspect ratio qua...

Journal ArticleDOI
TL;DR: In this paper, a well-controlled polymerization of oligo(ethylene oxide) methyl ether methacrylate (OEOMA) was conducted with 300 ppm or lower of a copper catalyst and tris(2-pyridylmethyl)amine (TPMA) ligand in the presence of an excess of halide salts.
Abstract: Activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) was successfully implemented in aqueous media for the first time. A well-controlled polymerization of oligo(ethylene oxide) methyl ether methacrylate (OEOMA) was conducted with 300 ppm or lower of a copper catalyst and tris(2-pyridylmethyl)amine (TPMA) ligand in the presence of an excess of halide salts. Ascorbic acid was continuously fed into the reaction mixture to regenerate the activator complex. The effects of the halide salt concentration, ligand concentration, feeding rate of the reducing agent, and copper concentration were systematically studied to identify conditions that provide both an acceptable rate of polymerization and good control over the polymer properties. The optimized polymerization conditions provided linear first-order kinetics, linear evolution of the molecular weight with conversion, and polymers with narrow molecular weight distributions (Mw/Mn < 1.3) at high monomer conversions (∼70%) ...

Journal ArticleDOI
TL;DR: In this paper, the authors presented a universal and versatile approach for the synthesis of polymers that show an upper critical solution temperature (UCST) in water, and established general requirements to obtain polymers with a UCST in water as well as electrolyte solution.
Abstract: We present a powerful universal and versatile approach for the synthesis of polymers that show a UCST in water. Up to now only a few polymers were known that show an upper critical solution temperature (UCST) in water. This study establishes general requirements to obtain polymers with a UCST in water as well as electrolyte solution. It is demonstrated that old homo- and copolymer systems like poly(methacrylamide) and poly(acrylamide-co-acrylonitrile) can exhibit a UCST in water and how polymers with a tunable UCST can be synthesized by copolymerization of acrylamide and acrylonitrile, monomers that are industrially produced on large scales. Controlled increase of the UCST by copolymerization of acryamide with varying amounts of acrylonitrile was shown, and it could be varied between 6 and 60 °C. The hysteresis between the cloud point upon cooling and heating was very small with only 1–2 °C in most cases. The cloud points in pure water were similar to the cloud points measured in phosphate buffered saline...

Journal ArticleDOI
TL;DR: In this article, the spinnability-solubility graph for poly(e-caprolactone) solutions was mapped for the first time to enable a comprehensive understanding of the processability of PCL solutions.
Abstract: Solvent–polymer interactions critically influence not only the viscoelasticity and the critical minimum solution concentration required for electrospinning but also the diameter, crystallinity, tensile strength, aspect ratio, and morphology of the electrospun fibers. Hence, a good understanding of the solvents and nonsolvents available and electrospinnable for a polymer of interest is important. The electrospinnability–solubility map uniquely presents the solubility and the electrospinnability of all solvents for a polymer in a single figure. Poly(e-caprolactone) (PCL), an important polymer in biomedical applications, has been electrospun in a few conventional solvent systems, but a comprehensive mapping of its solvents for electrospinning has not been performed. Based on 49 common solvents of diverse solubility parameters and functional groups, the spinnability–solubility graph for electrospinning PCL solutions was mapped for the first time to enable a comprehensive understanding of the processability of...

Journal ArticleDOI
TL;DR: In this article, a thermoresponsive block copolymer of poly(oligo(ethylene oxide) methyl ether methacrylate)-b-poly(oligosin-2-ylmethyl)amine-based catalyst was synthesized in aqueous media to prepare well-defined macromolecules.
Abstract: Initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) with ppm amount of Cu catalyst was successfully developed in water. For the first time, Cu catalyst concentrations of 100 ppm and lower were used in aqueous media to prepare well-defined macromolecules. Polymers of oligo(ethylene oxide) methyl ether acrylate were synthesized with low dispersity (Mw/Mn = 1.15–1.28) using 20–100 ppm of an active CuBr/tris(pyridin-2-ylmethyl)amine-based catalyst in the presence of excess bromide anions. This technique was used to synthesize a thermoresponsive block copolymer of poly(oligo(ethylene oxide) methyl ether methacrylate)-b-poly(oligo(ethylene oxide) methyl ether acrylate). The methacrylic block had a lower critical solution temperature (LCST = 77 ± 2 °C) below that of the acrylic block. The hydrodynamic diameter of ca. 10 nm at temperatures below the LCST is consistent with free polymer chains in solution, and the diameter of ca. 30 nm above the LCST is consistent with...

Journal ArticleDOI
TL;DR: An overview of existing theories of block polymer micelles is given in this article, where the authors focus on the equilibrium structure of nanoaggregates formed by solvophobic/solvophilic diblock copolymers in a dilute solution.
Abstract: We present an overview of existing theories of block polymer micelles. We focus here on the equilibrium structure of nanoaggregates formed by solvophobic/solvophilic diblock copolymers in a dilute solution and briefly address the association behavior of triblock terpolymer. We outline recent advances in the field and some challenging problems for theoretical developments.

Journal ArticleDOI
TL;DR: In this article, the authors systematically investigate at the density functional theory level how changes to the chemical structure of donor-acceptor copolymers used in a number of organic electronics applications influences the intrinsic geometric, electronic, and optical properties.
Abstract: We systematically investigate at the density functional theory level how changes to the chemical structure of donor–acceptor copolymers used in a number of organic electronics applications influences the intrinsic geometric, electronic, and optical properties. We consider the combination of two distinct donors, where a central five-membered ring is fused on both sides by either a thiophene or a benzene ring, with 12 different acceptors linked to the donor either directly or through thienyl linkages. The interplay between the electron richness/deficiency of the subunits as well as the evolution of the frontier electronic levels of the isolated donors/acceptors plays a significant role in determining the electronic and optical properties of the copolymers.

Journal ArticleDOI
TL;DR: In this paper, photochemically mediated atom transfer radical polymerization using a copper catalyst concentration as low as 50-100 ppm was achieved for methyl methacrylate at 35 °C.
Abstract: Well-controlled polymerization of methyl methacrylate at 35 °C was achieved by photochemically mediated atom transfer radical polymerization using a copper catalyst concentration as low as 50–100 ppm. Irradiation at λ > 350 nm provided both a reduction of initially added copper(II) catalyst complexed with either PMDETA or TPMA ligand to a copper(I) activator and a sufficient rate of polymerization. Poly(methyl methacrylate) with a narrow dispersity and predictable molar mass was obtained when an initiator, such as 2-bromopropionitrile, was used. Successful chain-extension polymerization confirmed the living character of the photopolymerization system.

Journal ArticleDOI
TL;DR: The gels containing SDS micelles exhibit, in addition to the fast mode, a slow relaxation mode in dynamic light scattering (DLS) and time-dependent elastic moduli, indicating the temporary nature of the hydrophobic associations having lifetimes of the order of seconds to milliseconds.
Abstract: Polyacrylamide hydrogels formed via hydrophobic interactions between stearyl groups in aqueous micellar solution of sodium dodecyl sulfate (SDS) present two faces depending on which state they are. The gels containing SDS micelles exhibit, in addition to the fast mode, a slow relaxation mode in dynamic light scattering (DLS) and time-dependent elastic moduli, indicating the temporary nature of the hydrophobic associations having lifetimes of the order of seconds to milliseconds. The gels where SDS had been removed after their preparation behave similar to chemically cross-linked ones with time-independent elastic moduli, a high degree of spatial inhomogeneity, and a single relaxation mode in DLS. Because of this drastic structural change, the physical gels are insoluble in water with a gel fraction close to unity. In surfactant containing gels, a large proportion of physical cross-links dissociate under force, but they do so reversibly, if the force is removed they reform again. The reversible disengageme...

Journal ArticleDOI
TL;DR: The single site catalyst character of metallocene and other transition metal complexes activated by MAO leads to a better understanding of the mechanism of the olefin polymerization as discussed by the authors.
Abstract: The discovery of methylaluminoxane (MAO) was the start for investigations and innovations of new classes of highly active olefin polymerization catalysts. Different transition metal complexes together with MAO as cocatalyst allow the synthesis of polymers with a highly defined microstructure, tacticity, and stereoregularity as well as new cycloolefin, long chain branched, or blocky copolymers with excellent properties. These new polyolefins could not be obtaind with such a purity before by Ziegler–Natta catalysts. The single site catalyst character of metallocene and other transition metal complexes activated by MAO leads to a better understanding of the mechanism of the olefin polymerization.

Journal ArticleDOI
TL;DR: In this article, a diamine monomer, 3,3,3′, 3′-tetramethyl-1,1′-spirobisindane-5,5′-diamino-6,6′-Diol, was successfully used to synthesize two types of polyimides for membrane-based gas separation applications.
Abstract: A newly designed diamine monomer, 3,3,3′,3′-tetramethyl-1,1′-spirobisindane-5,5′-diamino-6,6′-diol, was successfully used to synthesize two types of polyimides for membrane-based gas separation applications. The novel polymers integrate significant microporosity and polar hydroxyl groups, showing the combined features of polymers of intrinsic microporosity (PIMs) and functional polyimides (PIs). They possess high thermal stability, good solubility, and easy processability for membrane fabrication; the resulting membranes exhibit good permeability owing to the intrinsic microporosity introduced by the highly contorted PIM segments as well as high CO2/CH4 selectivity that arises from the hydroxyl groups. The membranes show CO2/CH4 selectivities of >20 when tested with a 1:1 CO2/CH4 mixture for feed pressures up to 50 bar. In addition, the incorporation of hydroxyl groups and microporosity in the polymers enhances their affinity to water, leading to remarkable water sorption capacities of up to 22 wt % at 35...

Journal ArticleDOI
TL;DR: In this paper, a ring-opening copolymerization of a series of cyclic acid anhydrides with several epoxides using (salen)CrCl/onium salt catalysts has been shown to yield polyesters with high molecular weights and narrow molecular weight distributions.
Abstract: Copolymerization of a series of cyclic acid anhydrides with several epoxides using (salen)CrCl/onium salt catalysts has afforded polyesters with high molecular weights and narrow molecular weight distributions. The (salen)CrCl catalyst in the presence of the onium salts with formula PPNX (X = Cl–, N3–) for the copolymerization of the anhydrides, maleic (MA), succinic (SA), phthalic (PA), cyclohexene (CHE), and cyclohexane (CHA) with the epoxides, cyclohexene oxide (CHO), propylene oxide (PO), and styrene oxide (SO) resulted in completely alternating enchainment of monomers to provide pure polyesters. Temperature dependent studies of the ring-opening copolymerization of phthalic anhydride and cyclohexene oxide monomers in toluene solution have yielded activation parameters of ΔH‡ = 67.5 kJ mol–1 and ΔS‡ = −95.3 J mol–1, where the rate limiting step was ring-opening of the epoxide by the enchained anhydride. For the cyclic acid anhydride (CHA), the relative order of reactivity with epoxides decreased PO > C...

Journal ArticleDOI
TL;DR: In this article, the crystal forms of polylactide (PLA) have different band frequencies, correlation field splittings in FTIR spectra and different line shapes, and resonance splitting in solid-state NMR spectra, which become more distinct with cooling to the cryogenic conditions.
Abstract: Crystalline structure and molecular dynamics in alpha and alpha' crystals of poly(L-lactide) (PLLA) and PLLA/poly(Dlactide) (PDLA) stereocomplex (sc) crystals have been investigated by the temperature-variable FTIR and solid-state C-13 CP-MAS NMR spectroscopy. The crystal forms of polylactide (PLA) have different band frequencies, correlation field splittings in FTIR spectra and different line shapes, and resonance splittings in solid-state NMR spectra, which become more distinct with cooling to the cryogenic conditions. The well-resolved splittings in NMR resonances of alpha crystals, attributable to the crystallographically inequivalent sites within crystal unit cell, are considered to be due to the dipolar interactions related to the carbonyl, methyl, and methine groups. The splittings in FTIR bands and NMR resonances are absent in alpha' crystals, indicating the disordered conformation and loose molecular lateral packing within their crystal lattices. The significant FTIR frequency shifts of nu(C=O), nu(CH3), and nu(CH) modes during stereocomplex crystallization of PLLA/PDLA blend and the appearance of spectral splittings at cryogenic conditions suggest the coexistence of weak C-H center dot center dot O=C hydrogen bonds and dipolar interactions between PLLA and PDLA chains in the sc crystals of PLA Below the glass transition temperature (T-g), the spin lattice relaxation times of PLA with different crystalline structures increase in the order of amorphous approximate to alpha' < alpha < sc.

Journal ArticleDOI
TL;DR: A series of conjugated donor (D)-π-acceptor (A) copolymers, P(BDT-F-BT), P( BDT-T-BT, and P(BDT-TT-BT) based on benzodithiophene (BDT) donor unit and benzothiadiazole (BT) acceptor unit with different π-bridges, were designed and synthesized via a Pd-catalyzed Stille-coupling method as discussed by the authors.
Abstract: A series of conjugated donor (D)-π-acceptor (A) copolymers, P(BDT-F-BT), P(BDT-T-BT), and P(BDT-TT-BT), based on benzodithiophene (BDT) donor unit and benzothiadiazole (BT) acceptor unit with different π-bridges, were designed and synthesized via a Pd-catalyzed Stille-coupling method. The π-bridges between the BDT donor unit and BT acceptor unit are furan (F) in P(BDT-F-BT), thiophene (T) in P(BDT-T-BT) and thieno[3,2-b]thiophene (TT) in P(BDT-TT-BT). It was found that the π-bridges significantly affect the molecular architecture and optoelectronic properties of the copolymers. With the π-bridge varied from furan to thiophene, then to thieno[3,2-b]thiophene, the shape of the molecular chains changed from z-shaped to almost straight line gradually. Band gaps of P(BDT-F-BT), P(BDT-T-BT) and P(BDT-TT-BT) were tuned from 1.96 to 1.82 to 1.78 eV with HOMO levels up-shifted from −5.44 to −5.35 to −5.21 eV, respectively. Bulk heterojunction solar cells with the polymers as donor and PC71BM as acceptor demonstrat...

Journal ArticleDOI
TL;DR: This Perspective summarizes and discusses recent progress in this nascent area of research, including synthesis of different types of SIPs, design and evaluation of triggering moieties, depolymerization mechanisms and kinetics, applications of Sips, and the outlook and challenges facing the field.
Abstract: Self-immolative polymers (SIPs) are unique macromolecules that are able to react to multiple types of environmental influences by giving amplified response outputs. When triggering moieties installed at SIP chain ends are activated by their corresponding stimuli, a spontaneous head-to-tail depolymerization ensues, often involving multitopic release of small molecules. SIP designs have evolved a high degree of modularity in each of their functional components, enabling a broad range of utility and applications-driven tuning. In this Perspective, we summarize and discuss recent progress in this nascent area of research, including (i) synthesis of different types of SIPs, (ii) design and evaluation of triggering moieties, (iii) depolymerization mechanisms and kinetics, (iv) applications of SIPs, and (v) outlook and challenges facing the field.

Journal ArticleDOI
TL;DR: In this article, a kind of bio-based polyester (BE) is synthesized by polycondensation between plant-derived diols and diacids, and it is then grafted onto graphene oxide (GO) via the easterification between hydroxyls of BE and carboxyls.
Abstract: Many reported polymer/graphene composites, even some with excellent graphene dispersion, do not possess impressive conductivity, which may be due to the failure in forming interconnected conductive paths. In this work, a kind of bio-based polyester (BE) is synthesized by polycondensation between plant-derived diols and diacids. It is then grafted onto graphene oxide (GO) via the easterification between hydroxyls of BE and carboxyls of GO. Subsequently, the grafted GO is subjected to reduce by vitamin C. Because of the presence of terminal hydroxyl group in both ends of the BE chains and multiple carboxyl groups on GO, the grafts form specific spatial interconnection structure in BE matrix. The resulting BE/graphene composites possess impressive low threshold percolation of electrical conductivity, in combination of high thermal conductivity.