Mechanical property tuning of semicrystalline network polymers by controlling rates of crystallization and crosslinking

Semicrystalline network polymers were obtained by the Diels–Alder (DA) reaction of furyl‐telechelic poly(ε‐caprolactone) and tris(2‐maleimide ethyl)amine. Controlling the rates of crystallization and crosslinking reaction gave materials with various properties. Curing at a temperature much below T_m of poly(ε‐caprolactone), at which crystallization proceeded first followed by DA reaction, gave a hard and stiff material, whereas curing above T_m gave a soft and stretchable one. When crystallization and crosslinking were promoted simultaneously, tough and ductile materials were obtained. Structural analysis of the network polymers showed that the variation in the properties was derived from the difference in the crystallinity, crystallite size, and network structure. Therefore, materials with various mechanical properties, from soft to hard, could be obtained by simple thermal treatment. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and crosslinking reaction of poly(hydroxyurethane) bearing a secondary amine structure in the main chain

This article describes the polyaddition of bifunctional five‐membered cyclic carbonates and diethylenetriamine. The polyaddition proceeded via the selective addition of the primary amino group to the cyclic carbonates to give poly(hydroxyurethane)s bearing a secondary amine structure in the main chain. The resulting poly (hydroxyurethane) having a secondary amine structure was crosslinked by a reaction with a bifunctional dithiocarbonate to give a networked poly(hydroxyurethane–mercaptothiourethane). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5899–5905, 2005     

Mechanism and kinetics of the crosslinking reaction between biopolymers containing primary amine groups and genipin

The reaction mechanism of chitosan, bovine serum albumin (BSA), and gelatin with genipin (a natural crosslinking reagent) was examined with infrared, ultraviolet–visible, and ¹³C NMR spectroscopies; protein‐transfer reaction mass spectrometry; photon correlation spectroscopy; and dynamic oscillatory rheometry. Two reactions that proceeded at different rates led to the formation of crosslinks between primary amine groups. The fastest reaction to occur was a nucleophilic attack on genipin by a primary amine group that led to the formation of a heterocyclic compound of genipin linked to the glucosamine residue in chitosan and the basic residues in BSA and gelatin. The second, slower, reaction was the nucleophilic substitution of the ester group possessed by genipin to form a secondary amide link with chitosan, BSA, or gelatin. A decreased crosslinking rate in the presence of deuterium oxide rather than water suggested that acid catalysis was necessary for one or both of the reactions to proceed. The behavior of the gel time with polymer concentration was consistent with second‐order gelation kinetics resulting from an irreversible crosslinking process, but was complicated by the oxygen radical‐induced polymerization of genipin that caused the gels to assume a blue color in the presence of air. The lower elastic modulus attained after a given time during crosslinking of the globular protein BSA as compared to the coiled protein gelatin, despite possessing more crosslinkable basic residues, demonstrated the importance of protein secondary and tertiary structures in determining the availability of sites for crosslinking with genipin in protein systems. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3941–3953, 2003     

Poling and crosslinking processes in NLO polymers

A series of photocrosslinkable polymers bearing hyperpolarizable side chain chromophores was synthesized, poled and evaluated on the basis of the thermal stability of Second Harmonic Generation (SHG). Photoinitiation allowed for control of the onset of curing. Crosslinking was monitored by infrared spectroscopy and optimal conversion was achieved by applying a slow temperature ramp during exposure. The ultimate stability of the poled polymers was directly related to the number of crosslinking substituents that were attached to the chromophore pendant group. With two reactive groups per chromophore significant SHG was retained at temperatures above the initial polymer glass transition temperature. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2769–2775     

Crosslinking of chlorine‐containing polymers by dicyclopentadiene dicarboxylic salts

Alkali‐ and alkali‐earth‐metal salts of dicyclopentadiene dicarboxylic acid (DCPDCA) were prepared and employed as crosslinkers for chlorine‐containing polymers such as polychloromethylstyrene (PCMS), chlorinated polypropylene (CPP), polyepichlorohydrin (PECH), and poly(vinyl chloride) (PVC). Thermally reversible covalent crosslinks (i.e.,  DCPD bridges) between polymer chains were generated through esterification between the chlorine–carbon bonds of the polymer and the carboxylic salt groups of the crosslinker. The crosslinking reactivity decreased in the following sequence: K > Na > LiDCPDCA > alkali‐earth‐metal salts of DCPDCA. In addition, PCMS and CPP had higher gelation rates than PECH and PVC. Good flowability at about 195 °C and solubility in maleimide‐containing dichlorobenzene on heating indicated that the crosslinked PCMS and CPP exhibited thermally reversible crosslinking because of dimer/monomer (cyclopentadiene) conversion of  DCPD moieties via reversible Diels–Alder cycloaddition. Samples of PECH and PVC crosslinked by the alkali salts of DCPDCA were insoluble even when heated in maleimide‐containing dichlorobenzene. However, these crosslinked polymers could be dissolved partially after the same treatment when the crosslinker was an alkali‐earth‐metal salt of DCPDCA. Thermal degradation such as dehydrochlorination of the PECH and PVC might have been responsible for uncontrolled crosslinking because these two polymers are known to be thermally unstable. The unreacted COOK, COONa, or COOLi of the crosslinkers might have initiated base‐induced dehydrochlorination when PECH and PVC were heated at high temperatures. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 818–825, 2000     

Effect of crosslinking on the properties of partially fluorinated anion exchange membranes

A series of crosslinked, ammonium‐functionalized, and partially fluorinated copolymers have been prepared and evaluated as anion exchange membranes. In order to investigate the effect of crosslinking on the membrane properties, precursor copolymers containing chloromethyl groups were crosslinked with various aliphatic diamines followed by quaternization with monoamines. Crosslinking was effective in lowering water absorbability at no expense of high hydroxide ion conductivity of the membranes. By tuning the degree of crosslinking (20 mol %) and crosslinker chain length (C6 and C8), the highest ion conductivity of 73 mS/cm (at 80°C in water) was achieved. Furthermore, alkaline stability of the membranes was also improved by the crosslinking; the remaining ion conductivity after the stability test (in 1 M potassium hydroxide at 80°C) was 8.2 mS/cm (after 1000 h) for the C6 crosslinked membrane and 1 mS/cm (after 500 h) for the uncrosslinked membrane, respectively. The ammonium groups attached with the crosslinkers seemed more alkaline stable than the uncrosslinked benzyltrimethylammonium groups, while the polymer main chain was intact under the harsh alkaline conditions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1059–1069     

Synthesis and application of hypercrosslinked polymers with weak cation-exchange character for the selective extraction of basic pharmaceuticals from complex environmental water samples

The synthesis of high specific surface area sorbents (HXLPP-WCX) in the form of hypercrosslinked polymer microspheres with narrow particle size distributions, average particle diameters around 6 μm, and weak cation-exchange (WCX) character, is described. The WCX character arises from carboxylic acid moieties in the polymers, derived from the comonomer methacrylic acid. A novel HXLPP-WCX sorbent with an attractive set of chemical and physical properties was then used in an off-line solid-phase extraction (SPE) protocol for the selective extraction of a group of basic compounds from complex environmental samples, a priority being the clean separation of the basic compounds of interest from acidic compounds and interferences. The separation power of the new sorbent for basic pharmaceuticals was compared to two commercially available, mixed-mode sorbents, namely Oasis WCX and Strata-X-CW. Under identical experimental conditions, HXLPP-WCX was found to deliver both higher capacity and better selectivity in SPE than either of the two commercially available materials. In an optimised SPE protocol, the HXLPP-WCX sorbent gave rise to quantitative and selective extractions of low μg l⁻¹ levels of basic pharmaceuticals present in 500 ml of river water and 250 ml of effluent waste water.     

Effect of crosslinking on the secondary relaxation in polyvinylethylene

The effect of network formation on the secondary (Johari–Goldstein) β‐relaxation was investigated for polyvinylethylene (PVE). Crosslinking affects the segmental (α‐) process in the usual fashion, the networks exhibiting slower and more temperature‐sensitive dynamics. However, the effect on the β‐process is the opposite. The secondary relaxation becomes faster and the activation energy slightly decreases with crosslinking. The strength of the intermolecular cooperativity governing the behavior of the α‐process was assessed using the coupling model, with consistent results obtained from analysis of both the timescale separating the α‐ and β‐relaxations and the activation energy for the latter. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 582–587, 2010     

傅克烷基化反应在超高交联聚合物中的应用

超高交联聚合物主要是通过傅克烷基化反应来制备的,具有合成简单、多孔、无毒、结构稳定、质轻等特点。本文介绍了傅克烷基化反应的条件和机理,展示了超高交联聚合物的合成方法及这些材料在气体储存/分离、水处理、催化、传感等领域中的应用,并对傅克烷基化反应与超高交联聚合物的进一步结合做出了展望。     

Dispersive solid-phase extraction of alkaloids and polyphenols using borate hypercrosslinked polymers

In this study, a borate hyper-crosslinked polymer was synthesized by crosslinking 1-naphthalene boric acid and dimethoxymethane via the Friedel-Crafts reaction. The prepared polymer exhibits excellent adsorption performance toward alkaloids and polyphenols with maximum adsorption capacities ranging from 25.07 to 39.60 mg/g. Adsorption kinetics and isotherms model results indicated the adsorption was a monolayer and chemical process. Under the optimal extraction conditions, a sensitive method was established for the simultaneous quantification of alkaloids and polyphenols in green tea and Coptis chinensis by coupling with the proposed sorbent and ultra-high performance liquid chromatography detection. The proposed method exhibited a wide linear range of 5.0–5000.0 ng/ml with R² ≥ 0.99, a low limit of detection (0.66–11.25 ng/ml), and satisfactory recoveries (81.2%–117.4%). This work provides a simple and convenient candidate for the sensitive determination of alkaloids and polyphenols in green tea and complex herbal products.     

Thermally reversible crosslinking of polystyrene via the furan–maleimide Diels–Alder reaction

Mixtures of maleimidomethylated polystyrene with difurfuryl adipate or with furfuryl alcohol-esterified poly[styrene-co-(maleic anhydride)] underwent thermally reversible Diels–Alder crosslinking. Reversal of crosslinking occurred rapidly at 150°C. The instability of the furfuryl group, however, limits the practicability of the reaction. © 1992 John Wiley & Sons, Inc.     

Synthesis and thermal crosslinking of carbosiloxane and oligo(oxyethylene) polymers

Acyclic diene metathesis (ADMET) polymerization has been used in the synthesis of telechelic materials using alkoxy‐functionalized carbosiloxane or oligo(oxyethylene)‐based polymers, varying from internal to terminal cured materials or the combination of them. Previous investigations demonstrated that introduction of chain‐end crosslinking improves the stress–strain behavior of such materials. A series of saturated and unsaturated carbosiloxane and oligo(oxyethylene)‐based polymers were synthesized by ADMET polymerization using silacyclobutane as chain‐end, thermally induced crosslinker. The carbosiloxane derivatives presented pure amorphous behavior, whereas the oligo(oxyethylene) polymers were semicrystalline. The thermal curing process was monitored by differential scanning calorimetry via the exotherm between 160 and 210 °C. Mechanical properties on thermoset polymers were measured, where cured polymers showed moduli from 0.6 to 9.3 MPa, tensile strengths from 0.3 to 1.0 MPa, and elongations from 12 to 76%. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Comparison of hypercrosslinked polystyrene columns for the separation of nitrogen group-types in petroleum using High Performance Liquid Chromatography

High performance liquid chromatography in a quasi-normal phase mode (QNP) is used to separate the nitrogen group-types (pyrrole and pyridine) that are found in petroleum. A new type of stationary phase, hypercrosslinked polystyrene, is used to achieve this separation. Three different hypercrosslinked polystyrene stationary phases are compared under quasi-normal phase mode; a commercial 5-HGN packing, and two hypercrosslinked phases on silica particles. The utility of the columns for petroleum-based separations was explored with the use of 21 analytical standards. Partial elucidation of adsorption retention mechanisms for the columns are shown, as well as a comparison of retention characteristics for the three columns. The silica particle column derived with toluene (HC-Tol) was found to have the best selectivity for nitrogen group-types and polycyclic aromatic hydrocarbons (PAHs), attaining a separation under gradient conditions in less than 30 min.     

Maleation of poly(3,4‐epoxy‐1‐butene) for accelerated crosslinking in the presence of a redox catalyst

Accelerated crosslinking of novel poly(3,4‐epoxy‐1‐butene) (3,4‐PEPB) oligomers in the presence of a cobalt‐based redox catalyst was investigated. Previous studies using model compounds, 3,4‐dimethoxy‐1‐butene and 1,4‐dimethoxy‐2‐butene, suggested that maleation of hydroxyl‐terminated 3,4‐PEPB oligomers would result in more rapid crosslinking in thin films. Novel maleated oligomers offered a unique combination of both electron‐rich and electron‐poor olefinic sites, and quantitative maleation significantly increased the crosslinking rate of 3,4‐PEPB. Efficient copolymerization between terminal maleate groups and olefinic groups in the repeating unit was proposed to account for accelerated crosslinking rates. Furthermore, the addition of novel reactive diluents, such as maleic acid mono‐ethyl ester, also effectively improved the 3,4‐PEPB crosslinking rate. Sol fraction measurements as a function of coating thickness revealed that the crosslinking rate versus oxygen diffusion was less significant for the maleated oligomers because of the presence of reactive electron‐poor olefins. Sol fractions were constant for catalyst concentrations greater than 0.25–0.50 wt % (as compared with oligomer feed). This observation suggested that a redox process was not a dominant factor in determining crosslinking rates at various experimental conditions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2789–2798, 2002     

Palladium-catalyzed domino protodecarboxylation/oxidative Heck reaction: regioselective arylation of coumarin-3-carboxylic acids

A protocol for straightforward and step-economical synthesis of neoflavones from coumarin-3-carboxylic acids is developed. This approach enables controlled protodecarboxylation/regioselective C–H arylation of coumain-3-carboxylic acids in one-pot using a monometallic catalytic system. A wide variety of electron-donating and -withdrawing substituents on both coumarins and arylboronic acid are tolerated under the reaction conditions and 4-aryl coumarins are constructed in high yields.     

Room-temperature oxidative Suzuki coupling reaction of 1,2,3-triazole N-oxides

This study develops a new efficient pathway for synthesis of 2,4-disubstituted 1,2,3-triazoles through regioselective direct arylation between 2-aryl-1,2,3-triazole N-oxides and Ar-B(OH)₂. The reaction proceeds smoothly at room temperature and exhibits good yield and high C5 position selectivity. The possible pathway of oxidative Suzuki coupling is also discussed. This simple methodology can be used to construct 2,4-disubstituted 1,2,3-triazole moiety.     

Thermally stable polymers containing 1,3,4-oxadiazole units obtained from Huisgen reaction

Thermally stable polymers containing 1,3,4-oxadiazole units have been synthesized through Huisgen reaction of the aromatic/aliphatic bis-tetrazole compounds with the aromatic/aliphatic bis-acid chlorides in pyridine as solvent.The obtained polymers are insoluble or slightly soluble even in polar aprotic solvents such as DMSO and DMF.Relatively high inherent viscosity values（0.61-1.33 dL/g,in 0.125%H₂SO₄ at 25℃） were observed for these compounds.Thermal analyses of the polymers using DSC and TGA techniques showed that the polymers have improved thermal stabilities.The glass transition temperature has not been observed in the fully aromatic polymers,but the polymers obtained from 5-[6-（1H-tetrazol -5-yl）hexyl]-lH-tetrazole（Ⅳ） showed very clear T_g.A model reaction was also investigated and the resulting bis-1,3,4-oxadiazole compound was characterized by conventional spectroscopy methods.     

Luminescent lanthanide-containing chiral liquid crystalline polymers in the side chain

Luminescent lanthanide-containing chiral liquid crystalline polymers are graft-copolymerised using poly(methylhydrogeno)siloxane (PMHS), crosslinking agent, liquid crystalline monomer and lanthanide complexes. The chemical structures of the monomers are characterised by FTIR, ^1?H NMR and elemental analyses. The mesomorphic properties and phase behaviour are investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy and X-ray diffraction. The polymers containing less than 9 mol% of the crosslinking units reveal reversible mesomorphic phase transition, wide mesophase temperature ranges and high thermal stability. With the introduction of lanthanide complex units, the polymers are enabled with the significant luminescent properties. The temperature dependence of fluorescence intensity was studied in the liquid crystalline phase. The IR imaging shows that the lanthanide complex units evenly distribute in polymers.     

Emulsion procedures for thermally reversible covalent crosslinking of polymers

Quaternization and dequaternization of tertiary amine compounds were employed to obtain thermally reversible ionene networks from aqueous colloidal polymer dispersions prepared via emulsion polymerization. Chlorine‐functionalized polymers prepared via the emulsion copolymerization of styrene (St), butylacrylate (BA), or both with chloromethylstyrene, and amino‐functionalized polymers prepared via the emulsion copolymerization of St, BA, or both with 2‐(dimethylamino)ethylacrylate or 4‐vinylpyridine, were reacted without polymer separation, with a ditertiaryamine crosslinker and a dihalide crosslinker, respectively, to obtain crosslinked polymers. Crosslinked polymers were also obtained via the reaction of a chlorine‐functionalized polymer dispersion with an amino‐functionalized polymer dispersion or via the drying of the polymer blend prepared from the two kinds of dispersions. Reactive solubility experiments, flowability investigations (by thermocompression at ca. 215 °C), IR, and ¹H NMR analyses of the obtained crosslinked polymers indicated that the generated ionene bridges dequaternized on heating and requaternized on cooling. In comparison with solution crosslinking, no organic solvent was employed, and simple procedures were required for the preparation of the thermally reversible covalent crosslinked polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4373–4384, 2000