Commercially available hydrophobic porphyrins are investigated as an environmentally friendly catalytic system for iron‐mediated atom transfer radical polymerization (ATRP) of poly(ethylene glycol) monomethyl ether methacrylate (PEGMA). Polymerizations in organic solvent are optimized using activators generated by electron transfer (AGET ATRP), based on iron(III)–porphyrin complexes, and tin(II) 2‐ethyl hexanoate or ascorbic acid as a reducing agent. Copper‐free PPEGMA macromolecules are obtained with high conversion, controlled molecular weight, and polydispersity index compared with standard copper‐based ATRP. The facile preparation and availability of the catalyst, together with its expected low toxicity, represent clear advantages for the synthesis of PPEGMA‐based materials for biomedical use.
The accurate characterization of molar‐mass distributions of poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) by size‐exclusion chromatography (SEC) is addressed. Two methods are employed: direct aqueous‐phase SEC on P(M)AA and THF‐based SEC after esterification of P(M)AA to the associated methyl esters, P(M)MA. P(M)AA calibration standards, P(M)AA samples prepared by pulsed‐laser polymerization (PLP), and PAA samples prepared by reversible addition‐fragmentation chain transfer (RAFT) are characterized in a joint initiative of seven laboratories, with satisfactory agreement achieved between the institutions. Both SEC methods provide reliable results for PMAA. In the case of PAA, close agreement between the two SEC methods is only observed for samples prepared by RAFT polymerization with weight‐average molar mass between 80 000 and 145 000 g mol?1 and for standards with peak molar masses below 20 000 g mol?1. For standards with higher molar masses and for PLP‐prepared PAA, the values from THF‐based SEC are as much as 40% below the molar masses determined by aqueous‐phase SEC. This discrepancy may be due to branching or degradation of branched PAA during methylation. While both SEC methods can be recommended for PMAA, aqueous‐phase SEC should be used for molar‐mass analysis of PAA unless the sample is not branched.
Poly(ethylene glycol) (PEG) is partially furanylated with different feed ratios of furfuryl isocyanate and used as the macro initiator of ring‐opening polymerization of l ‐ and d ‐lactides to synthesize copolymer mixtures of furan‐terminated AB diblock and ABA triblock copolymers (poly(oxyethylene)–poly(l ‐lactide)/poly(l ‐lactide)–poly(oxyethylene)–poly(l ‐lactide) and poly(oxyethylene–poly(d ‐lactide)/poly(d ‐lactide)–poly(oxyethylene)–poly‐(d ‐lactide)) having different diblock/triblock ratios. The mixed micelle solutions of these enantiomeric copolymer mixtures undergo sol‐to‐gel or gel‐to‐sol transition depending on the diblock/triblock ratio of the copolymer mixtures. The rheological properties of the mixed micelle solutions could also be controlled by changing the diblock/triblock ratios or the initial furanylation ratio of PEG.
The synthesis of step‐growth polymers via a step‐growth click coupling reaction of diazides based on poly(ethylene glycol) (PEG) and dialkynes based on aromatics is reported. The polymers are characterized by proton nuclear magnetic resonance spectroscopy (1H‐NMR), carbon‐13 nuclear magnetic resonance spectroscopy (13C‐NMR), Fourier transform infrared spectroscopy (FT‐IR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Gas transport properties of one polymer are measured by the time lag (constant volume, variable pressure) method. Low gas permeabilities are a consequence of the rather high glass transition temperature. The rather high selectivities in separation of CO2/N2 and CO2/CH4 result from the CO2‐philic groups such as PEG, triazole, and benzoxazine. According to the gas permeation measurements, the membrane is stable in the temperature range from 30 to 90 °C.
Copolymerization of carbon dioxide (CO2) and propylene oxide (PO) is employed to generate amphiphilic polycarbonate block copolymers with a hydrophilic poly(ethylene glycol) (PEG) block and a nonpolar poly(propylene carbonate) (PPC) block. A series of poly(propylene carbonate) (PPC) di‐ and triblock copolymers, PPC‐b‐PEG and PPC‐b‐PEG‐b‐PPC, respectively, with narrow molecular weight distributions (PDIs in the range of 1.05–1.12) and tailored molecular weights (1500–4500 g mol?1) is synthesized via an alternating CO2/propylene oxide copolymerization, using PEG or mPEG as an initiator. Critical micelle concentrations (CMCs) are determined, ranging from 3 to 30 mg L?1. Non‐ionic poly(propylene carbonate)‐based surfactants represent an alternative to established surfactants based on polyether structures.
Supramolecular hydrogels composed of poly(ethylene glycol) (PEG) containing polymer and α‐cyclodextrins (α‐CDs) show great potential in drug delivery. Herein, PEGylated magnetic nanoparticles (MNPs) and gold nanoparticles (AuNPs) of ≈10 nm are synthesized in the presence of poly(poly(ethylene glycol) methyl ether acrylate) (PPEGMA) grafted poly(acrylic acid) copolymers (PPEGMA‐co‐PAA, P1) and PPEGMA grafted poly(2‐(dimethylamino)ethyl methacrylate) copolymers (PPEGMA‐co‐PDMAEMA, P2), respectively. The produced PEGylated NPs are hybridized into supramolecular hydrogels by mixing them with α‐CDs through inclusion complexation between PEG branches and α‐CDs. As a result, supramolecular hydrogels hybridized with inorganic MNPs and AuNPs are prepared and characterized by rheological measurements, X‐ray diffraction, and scanning electron microscopy. Both MNP and AuNP hybrid hydrogels show reversible sol–gel transition, which is stimulated by changes in temperature and pH. The nanoparticles hybridized in the hydrogels can be released gradually in the process of hydrogel disruption. These hydrogels may have potential applications in biomaterials and drug delivery.
Polymer electrolyte membranes (PEMs) are synthesized via in situ polymerization of vinylphosphonic acid (VPA) within a poly(2,5‐benzimidazole) (ABPBI) matrix. The characterization of the membranes is carried out by using Fourier transform infrared (FTIR) spectroscopy for the interpolymer interactions, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) for the thermal properties, and scanning electron microscopy (SEM) for the morphological properties. The physicochemical characterizations suggest the complexation between ABPBI and PVPA and the formation of homogeneous polymer blends. Proton conductivities in the anhydrous state (150 °C) measured by using impedance spectroscopy are considerable, at up to 0.001 and 0.002 S cm?1 for (1:1) and (1:2) molar ratios, respectively. These conductivities indicate significant improvements (>1000×) over the physically blended samples. The results shown here demonstrate the great potential of in situ preparation for the realization of new PEM materials in future high‐temperature and non‐humidified polymer electrolyte membrane fuel cell (PEMFC) applications.
Triple hydrophilic asymmetric poly(2‐hydroxyethyl acrylate)‐b‐poly(ethylene oxide)‐b‐poly(2‐hydroxyethyl acrylate) (PHEA‐b‐PEO‐b‐PHEA) triblock copolymers are obtained by copper(0) catalyzed reversible deactivation radical polymerization (RDRP). Copper wire catalyzed polymerization of HEA from large PEO (Mn = 35 000 g mol?1) macroinitiator in dimethylsulfoxide or in water fails to reach high monomer conversion in a controlled manner contrary to what is previously published with a shorter PEO macroinitiator. Catalysis by nascent Cu(0) particles generated by disproportionating CuBr in water allows rapid polymerization and high monomer conversion with a rather good control of both dispersity and HEA block length. Model disproportionation experiment shows that HEA influences the disproportionation/comproportionation equilibrium. Larger quantities of HEA lead to higher apparent rate constants and less disproportionation of CuBr which is in agreement with the supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) mechanism and not with the single electron transfer–living radical polymerization (SET‐LRP) mechanism.
Core–corona inversion of micelles of diblock copolymer poly(acrylic acid)‐block‐poly(N‐isopropylacrylamide) (PAA‐b‐PNIPAM), has been successfully realized by switching either pH or temperature. The strong interaction of doxorubicin with the PAA block and the pH‐sensitive drug release from the polymer make the system very useful as a controlled drug delivery system. The encapsulation of hydrophobic Nile Red molecules above the lower critical solution temperature of PNIPAM suggests that this polymer may be useful for removing hydrophobic pollutants.
A new thermosensitive poly(N‐propionyl‐aspartic acid/ethylene glycol) (PPAE) with no cytotoxicity and an upper critical solution temperature (UCST) is synthesized by polycondensation of l ‐aspartic acid and ethylene glycol. The chemical structures of the monomer and polymer are confirmed by FTIR and 1H NMR spectroscopy, and by elemental analysis measurements. Turbidimetric measurements indicate that PPAE shows a reversible UCST phase transition at 1.5–37.6 °C in pure water or an alcohol/water mixture. The UCST can be facilely tuned via changing the content of alcohol in water or the normal saline. Moreover, the survival rate of HeLa cells to PPAE is close to 100% within 48 h, demonstrating no cytotoxicity. Such aspartic acid‐based polymers with tunable thermosensitivity could be useful in the biomedical field.
A new class of polymer electrolytes, consisting of poly(ethylene carbonate) (PEC) and metal salts, is expected to find application in all‐solid‐state batteries because of its excellent performance as an electrolyte. To study the ion‐conductive mechanism in PEC‐based electrolytes, broadband dielectric spectroscopy is used to analyze the correlation between dielectric relaxation and ionic conduction in PEC‐lithium bis‐(trifluoromethanesulfonyl) imide electrolytes over a broad range of salt concentration (0–150 mol%) at 40 °C. The PEC system has two relaxation modes, α and β, associated respectively with the segmental motion and the local motion of PEC chains. The conductivity increases exponentially with increasing salt concentration, while the α relaxation frequency (fα) decreases with increasing strength (Δεα) at low salt concentrations, whereas in contrast fα increases with Δεα being saturated at high salt concentrations above 10 mol%. It is believed that the mobility of PEC segment at high concentration is enhanced by two factors. The first is that intermolecular interactions decrease, given the existence of many ion pairs and aggregated ions around saturated PEC domains where the dissociated ions are highly concentrated. The second is that intramolecular interactions between C?O and CH2 are lowered by the ion–dipole interaction.
The preparation and structural organization of a new bioinspired nanomaterial are investigated. A hybrid conjugate is obtained by end‐linking a linear octapeptide with regular alternating enantiomeric sequence to poly(ethylene glycol). This conjugate is able to self‐assemble, forming well‐defined nanorods having core/shell morphology with an internal peptide single channel that has, for the first time, been clearly visualized by transmission electron microscopy (TEM) images. It is remarkable that well‐defined cylindrical nanoparticles can be formed starting from a linear oligopeptide, the synthesis of which is significantly easier than that of the homologous cycles. In addition, the synthetic strategy and the structure of the conjugate ensure a controlled and regular pegylation of the aggregates and high density PEG blocks in the corona, making the nanoparticles more resistant to phagocytosis and able to prevent biofouling. Such features, along with biocompatibility and stability, make these nanoparticles promising candidates for drug delivery.
The synthesis of telechelic poly(ether sulfone)s with methoxy end groups is reported. Molecular weights ranging from 1600 to 2800 g mol?1 and polydispersities of 1.1–1.2 are synthesized by chain‐growth condensation polymerization. The initiator is chosen by using semiempirical calculations and 19F NMR spectroscopy measurements. The polymers are characterized by NMR spectroscopy and matrix‐assisted laser desorption/ionization time of flight (MALDI‐TOF) mass spectrometry (MS), and are terminated by a methoxy group at one end and a fluorine at the other, and up to approximately 20% polymer of similar mass but slightly higher polydispersity, methoxy terminated at both ends, is present, along with less than 5% of polymer terminated at both ends by fluorine atoms. These do not need to be separated, and can be converted to methoxy‐ending telechelic blocks, yielding polyvalent, reactive rigid building blocks for copolymer synthesis.
Poly(ethylene 2,5‐furandicarboxylate) (PEF) is an emergent biobased polyester whose chemical structure is analogous to poly(ethylene terephthalate). Pilot‐scale PEF is synthesized through the direct esterification process from 2,5‐furandicarboxylic acid and bio‐ethylene glycol. Wide‐angle X‐ray diffraction (WAXD) measurements reveal similar crystallinities and unit cell structures for melt‐crystallized and glass‐crystallized samples. The non‐isothermal crystallization of PEF sample is investigated by means of DSC experiments both from the glass and the melt. The temperature dependence of the effective activation energy of the growth rate is obtained from these data, and the results show that the glass and early stage of the melt crystallization share common dynamics. Hoffman–Lauritzen parameters and the temperature at maximum crystallization rate are evaluated. It is found that the melt‐crystallization kinetics undergo a transition from regime I to II; however, the crystal growth rate from the melt shows an atypical depression at T < 171 °C compared with the predicted Hoffman–Lauritzen theory.
Improving fragility is important for the practical application of gels. In this study, the mechanical strength of gels composed of poly(N‐vinyl acetamide) (PNVA) and glycols is investigated focusing on the retained solvent in the gels. The solvent for the PNVA hydrogel is adequately replaced by various glycols. Using poly(ethylene glycol) (PEG) with molecular weights of 400 or 600 g mol?1, the compressive strength of the gel is dramatically enhanced to approximately 10 MPa while that of hydrogel is 0.2 MPa. This is because of solvent viscosity, interaction between PEG and PNVA, and the favorable aggregation of the PNVA. From FTIR spectroscopy investigations, the absorption bands of the carbonyl and amino groups of PNVA gels with PEG400 are shifted as compared with PNVA gels in water, suggesting hydrogen bond formation.
The preparation of stimuli‐responsive aminomethyl functionalized poly(p‐xylylene) coatings by chemical vapor deposition polymerization is reported. Modification of the paracyclophane precursor with ionizable aminomethyl groups leads to polymer coatings with pH‐responsive swelling properties. The swelling behavior is monitored in situ using spectroscopic ellipsometry and additional streaming potential measurements are performed. With decreasing pH‐value, the coating becomes increasingly charged and reversibly swells to several times its dry thickness. The swelling ratio is sensitive to the ionic strength of the solution. By using a mixture of unfunctionalized and functionalized precursors in the chemical vapor deposition process, the number of charges in the polymer layer can be tuned and with it the swelling ratio of the coating. As a proof‐of‐concept for possible applications, a commercial paper filter is coated. This results in a pH‐dependent wetting behavior and pH‐dependent transport through the capillaries of the paper.
Cyclic imino ethers (CIEs), such as 2‐oxazolines and 2‐oxazines are a unique class of monomers, which because of their manifold reactivities can be polymerized via multiple techniques. Most prominent, the living cationic ring‐opening polymerization (CROP) of CIEs enables the synthesis of well‐defined tailor‐made poly(CIEs), which have tremendous importance as functional and biocompatible polymers. On the other hand, CIEs are also powerful monomers in polyadditions resulting in the formation of a variety of biodegradable polyamide‐based systems. In this contribution, the enormous potential of CIEs as functional building blocks is discussed, which goes well beyond the CROP. Besides trends in the CROP of CIEs, recent developments in step‐growth polymerizations of CIEs are highlighted, including the spontaneous zwitterionic copolymerization (SZWIP) which provides access to functional alternating N‐acylated poly(amino ester)s (NPAEs) and polyadditions of multifunctional CIEs which give main‐chain poly(ester amide)s (PEAs).
An amphiphilic penta‐telechelic polyhedral oligomeric silsesquioxane (POSS)‐containing inorganic/organic hybrid poly(acrylic acid), (Glu‐PAA‐POSS5), is prepared by hydrolysis of penta‐telechelic poly(tert‐butyl acrylate) (Glu‐PtBA‐POSS5), synthesized by the combination of atom transfer radical polymerization (ATRP) and a “click” reaction. The self‐assembly behavior of Glu‐PAA‐POSS5 in aqueous solution at pH 8.5 is investigated by using transmission electron microscopy (TEM), scanning electronic microscopy (SEM), atomic force microscopy (AFM), and dynamic light scattering (DLS). The results show that Glu‐PAA‐POSS5, with a long poly(acrylic acid) (PAA) chain, can self‐assemble in water into giant capsules, which provides an optional approach in the construction of capsules.
In this paper, covalently linked graphene oxide–poly(ethylene glycol) methyl ether methacrylate–reversible addition‐fragmentation chain transfer (GO–PEGMEMA–RAFT) and physically mixed GO–PEGMEMA hydrogel nanocomposites are synthesized. Spectroscopic and imaging techniques such as UV–vis, Fourier transform infrared, Raman spectroscopy, and transmission electron microscopy show that the PEGMEMA is successfully grafted on GO sheets. The rheology of the nanocomposites is studied by small angle oscillatory shear, which shows a competition between reinforcement and lubrication behavior of GO. In the case where lubrication effect dominates reinforcement, the covalently linked GO–PEGMEMA–RAFT has higher G′ compared to the physically mixed GO‐PEGMEMA. Hence, in the covalently linked system, the grafted polymer chains appear to minimize the lubrication effect.
With fac‐Ir(ppy)3 as photoredox catalyst and ethyl 2‐bromoisobutyrate (EBiB) as initiator, the homopolymerization of methyl methacrylate (MMA) in different solvents, such as N,N‐dimethylformamide (DMF), acetonitrile, and anisole are run under irradiation of an LED lamp. The results show that anisole is a better solvent for the polymerization with regard to the polydispersity index (PDI). A well‐controlled polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) is demonstrated and the clean block copolymer of PMMA‐b‐PPEGMA is prepared with PDI less than 1.3; however, the 2‐(dimethylamino) ethyl methacrylate (DMAEMA) polymerization is poorly controlled. With the PMMA as macromolecular initiator, the block copolymer PMMA‐b‐PDMAEMA can be prepared with PDI around 2.0.
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