Morphology development of EPDM/PP uncross‐linked/dynamically cross‐linked blends

Ethylene‐propylene‐diene‐terpolymer (EPDM) and polypropylene (PP)‐based uncross‐linked and dynamically cross‐linked blends were prepared both in an internal mixer and in a corotating twin‐screw extruder. The effects of composition, plasticization and mixing equipment on the morphology development and the final viscoelastic properties were studied. In the uncross‐linked blends, the plasticization resulted in a coarser morphology. Furthermore, it was shown that the majority of the plasticizer resided in the EPDM phase, enabling its deformation in the flow direction. In addition, the intensive mixing conditions inside the twin‐screw extruder resulted in a finer morphology. In the dynamically cross‐linked blends, the twin‐screw extrusion process resulted in a higher level of gel content with larger EPDM domains. The plasticization showed again a coarsening effect, resulting in interconnected cross‐linked EPDM domains. An interesting interfacial phenomenon was observed especially in the plasticized vulcanized blends where nanometer size occluded PP domains were stripped off and eroded into the EPDM phase. With the exception of the nonplasticized uncross‐linked blends, the viscoelastic properties of all other blending systems were found to be directly affected by the morphology, gel content (in the case of cross‐linked blends), and the presence of the plasticizer. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Structures and properties of waste silicone cross‐linked polyethylene de‐cross‐linked selectively by solid‐state shear mechanochemical technology

Waste silicone cross‐linked polyethylene (Si‐XLPE) recycling effectively by using solid‐state shear mechanochemical (S³M) technology was investigated to make the better performance thermoplastic polyethylene. To make this thermoplastic material, the cross‐linked structures of waste Si‐XLPE that was consisted of the siloxane bonds must be de‐cross‐linked selectively instead of the destruction of the material main chains. The properties of recycled Si‐XLPE materials were investigated by gel fraction measurements, gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter, torque rheological measurements, scanning electron microscope (SEM) and thermogravimetric analyzer (TG). From the results, it could be seen that the cross‐linking bonds of the Si‐XLPE were destroyed selectively by S³M technology and the mechanochemical milling also played a significant role in improving the materials process‐ability and mechanical properties. Gel fraction measurements, GPC and FTIR showed that S³M technology could interrupt the cross‐linked structures of Si‐XLPE rather than the backbone chains by initiating the de‐cross‐linking reaction obviously; Torque rheological results further confirmed that the recycled Si‐XLPE materials gained better plastic characteristics and process‐ability after mechanochemical milling. Compared with the untreated Si‐XLPE, the tensile strength and elongation at break of Si‐XLPE samples after 10 cycles milling increased by 118.4% and 330.4%, respectively. J. VINYL ADDIT. TECHNOL., 25:149–158, 2019. © 2018 Society of Plastics Engineers     

Polyimides cross‐linked with amino group‐containing compounds

The commercially available linear polyimide Matrimid^® 9725 was crosslinked with amino groups containing both high‐molecular‐weight and low‐molecular‐weight compounds. The multi‐functional amine‐terminated hyperbranched polyimide precursor (hyperbranched polyamic acid), based on 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride and 4,4′,4″‐triaminotriphenylmethane, and its fully imidized form (amine‐terminated hyperbranched polyimide), bifunctional amine, 4,4′‐diaminodiphenylamine and trifunctional amine, 4,4′,4″‐triaminotriphenylamine, were used as the crosslinkers. Theoretically, 10% or 20% of the Matrimid imide groups was reacted with the amino groups of the crosslinking agent during the formation of the amide groups. The insoluble content (gel) in the final materials was very low at the crosslinking temperature of 80°C and was in the 55–90% range at the crosslinking temperature of 200°. The permeability coefficients of hydrogen, carbon dioxide and methane in the self‐standing, mechanically tough film (membrane) based on the combination of Matrimid and hyperbranched polyimide were approximately 30–45% higher compared with those in the membrane made of pure Matrimid at a comparable separating ability (selectivity). POLYM. ENG. SCI., 57:1367–1373, 2017. © 2017 Society of Plastics Engineers     

Cross‐linked and uncross‐linked biodegradable nanocomposites. I. Nonisothermal crystallization kinetics and gas permeability

Various nanocomposites of poly(butylene succinates) (PBS) with different ratios of organically modified layered silicates (OMLS) were prepared. Moreover, such PBS nanocomposites cross‐linked by dicumyl peroxide (DCP) were also prepared in this work. Effects of cross‐linking and OMLS on nonisothermal crystallization kinetics and the gas permeability of PBS samples were investigated further. WAXD indicates that the layers of clay were intercalated by the modifiers, and that the interlayer distance of OMLS in the nanocomposites could be expanded to about 2.96 nm. The results of DSC analysis revealed that the crystallization temperatures of nanocomposites shifted to the lower temperature with the increase of OMLS content. With the addition of OMLS, crystallinity was decreased, whereas the half‐life of crystallization was increased. On the other hand, even the cross‐linked effects also increased the half‐life of crystallization of the materials, but did not necessarily decrease crystallinity in all cases. Moreover, the PBS/OMLS nanocomposites showed a 23.87–46.64% decrease in permeability of oxygen when compared with the pristine PBS sample. Yet, the cross‐linked nanocomposites exhibited decrements of 6.38–39.53%. This indicates that the gas permeability of PBS was more effectively depressed by the addition of OMLS than by the cross‐linking reaction. The cross‐linked structure of polymer seemed not to be very effective in decreasing the gas permeability of PBS. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Facile synthesis of 5,8‐linked quinoline‐based copolymers

Coupling quinoline at its 5,8‐positions provides a facile way to copolymerize quinoline with other conjugated moieties without breaking conjugation. Model compounds containing quinoline units, either at the periphery or in the core, were synthesized and one of them was characterized by X‐ray diffraction. Copolymers of quinoline and 9,9‐dialkylfluorene (R = n‐octyl or 2‐ethylhexyl) were synthesized in good yield by palladium‐catalysed Suzuki cross‐coupling. The copolymers are highly soluble in common organic solvents and gel permeation chromatography measurements against polystyrene standards showed the number‐average molecular weight to be in the range (1.02–2.06) × 10⁴ g mol^?1. Both copolymers emit in the blue region with an emission maximum centred at 435 nm. Copyright © 2012 Society of Chemical Industry     

Surfactant‐directed morphology of cross‐linked styrene‐ or vinylbenzyl chloride‐based materials

Polystyrene (PSt) or poly(vinylbenzyl chloride) (PVBC) crosslinked with divinylbenzyl (DVB) materials were synthesized through free radical polymerization into templates formed by the surfactant polyoxyethylene (4) lauryl ether (Brij‐30). The chemical composition of the final products was verified through attenuated total reflectance infrared spectroscopy (ATR‐IR) and the thermal behavior was investigated through thermogravimetric analysis (TGA). Depending on the organization of Brij‐30 in aqueous solution, three characteristic structures, namely spherical nanoparticles, platelet‐like objects and three‐dimensional networks, were identified through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The spherical nanoparticles and the platelet‐like objects form rather stable dispersions, especially in aqueous surfactant solutions, as exemplified by the evolution of the turbidity of the PSt‐based materials, using sodium dodecyl sulfate as surfactant. All materials retain their integrity even after thermal treatment at high temperature (～200–250°C). The benzyl chloride group of the PVBC‐based materials offers a significant potential for further elaboration and practical applications, since they can be further functionalized while retaining their integrity. This potential is demonstrated here through hydrolysis to obtain hydroxyl‐functionalized three‐dimensional networks. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43297.     

Genipin‐cross‐linked chitosan‐based hydrogels: Reaction kinetics and structure‐related characteristics

The main aim of this work is the synthesis and characterization of cross‐linked chitosan systems. Chitosan hydrogels can be prepared by physical or chemical cross‐linking of polymer chains. Chemical cross‐linking, leading to the creation of hydrogel networks possessing improved mechanical properties and chemical stability, can be achieved using either synthetic agents or natural‐based agents. In this work, the cross‐linker Genipin, a naturally derived compound, was selected because of the lower acute toxicity compared to many other commonly used synthetic cross‐linking reagents. In particular, the chemical stabilization of chitosan through genipin cross‐linking molecules was performed and characterized by calorimetric analyses (differential scanning calorimetry), swelling measurements in different pHs, and ionic strength. The reaction kinetics was carried out by means of rheological measurements, and both the activation energy (E_a) and the reaction order (m) were calculated. The hydrogel analyses were carried out at different concentrations of genipin (GN1 and GN2). The results were used to evaluate the possibility to use the chemical cross‐linked chitosan–genipin hydrogel for biomedical applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42256.     

Adsorption Mechanism for 2‐Methylpyridine on Hypercross‐linked Fibers

Two types of novel hypercross‐linked fiber adsorbents, ZH‐01 and ZH‐02, were prepared by cross‐linking PP‐ST‐DVB fibers in solution with p‐xylylenedichloride and monochloromethylether according to the Friedel‐Crafts reaction. A series of static adsorption tests were performed. The results showed that the adsorbents have excellent adsorption capacities for 2‐methylpyridine and the adsorption equilibrium data can be fitted well by the Freundlich model. The thermodynamic studies supported the conclusion that the mechanism of adsorption for 2‐methylpyridine on the adsorbents is physical adsorption and a lower temperature is favorable to the exothermic physisorption process. In addition, kinetic studies were also carried out. The hypercross‐linked fiber adsorbents showed a faster adsorption rate than the base PP‐ST‐DVB fiber. The faster attainment of adsorption equilibrium for 2‐methylpyridine on the adsorbents (within 2 h), is advantageous for practical use. A first‐order reaction rate equation was assumed for the adsorption system and was suitable to describe the process. The equilibrium rate constants of the adsorbents correlated well with their adsorption capacities.     

Photo‐cross‐linked biodegradable thermo‐ and pH‐responsive hydrogels for controlled drug release

A new strategy was developed to prepare thermo‐ and pH‐sensitive hydrogels by the crosslinking of poly(N‐isopropylacrylamide) with a biodegradable crosslinker derived from poly(L ‐glutamic acid). Hydrogels were fabricated by exposing aqueous solutions of precursor containing photoinitiator to UV light irradiation. The swelling behaviors of hydrogels at different temperatures, pHs, and ionic strengths were examined. The hydrogels shrank under acidic condition or at temperature above their collapse temperature and would swell in neutral or basic media or at lower temperature. These processes were reversible as the pH or temperature changed. All hydrogels exhibited no weight loss in the simulated gastric fluid but degraded rapidly in the simulated intestinal condition. Bovine serum albumin were used as a model protein drug and loaded into the hydrogels. The in vitro drug release experiment was carried out at different pH values and temperatures. The pH and temperature dependent release behaviors indicated the promising application of these materials as stimuli‐responsive drug delivery vehicles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of cross‐linked polycarboxylate‐type superplasticizers on the properties in cementitious system

Fluidity and slump loss are main technical indicators for the quality of concrete. They are related to the dispersion of cement and hydration process, and are greatly affected by the structure of superplasticizers (SPs). For the purpose of obtaining SPs with excellent fluidity and slump retention, water‐soluble cross‐linked polycarboxylate ether copolymers (CLPCs) of acrylic acid and alkenyl alcohol type polyoxyethylene ether were synthesized. In order to gain full understanding of the effect of cross‐linked SPs on the properties in cementitious system, properties of the new SPs in cement paste were compared to those of traditional ones without cross‐linking agents. Mortar tests showed that CLPC performed obvious slow‐release function and kept about 10 mm higher than its initial paste flow after 150 min, while PC incurred loss of 15 mm after 150 min. Adsorption of CLPC on cement resulted in zeta potential being roughly the same as that in the case of PC, and enabled more effective slump retention to cement suspensions by rheological property tests. Ettringite peaks disappeared for CLPC on 1‐day curve and reappeared after 35 days, and the intensity of CH peaks for CLPC appeared weaker than Blank and PC after 1 day. The microstructure of CLPC after 1 day showed a very dense structure of smaller and thinner crystallites, which indicated that the early hydration was greatly delayed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40856.     

Microwave preparation and adsorption properties of EDTA‐modified cross‐linked chitosan

A novel chitosan‐based adsorbent (CCTE) was synthesized by the reaction between epichlorohydrin O‐cross‐linked chitosan and EDTA dianhydride under microwave irradiation (MW). The chemical structure of this new polymer was characterized by infrared spectra analysis, thermogravimetric analysis, and X‐ray diffraction analysis. The results were in agreement with the expectations. The static adsorption properties of the polymer for Pb²⁺, Cu²⁺, Cd²⁺, Ni²⁺, and Co²⁺ were investigated. Experimental results demonstrated that the CCTE had higher adsorption capacity for the same metal ion than the parent chitosan and cross‐linked chitosan. In particular, the adsorption capacities for Pb²⁺ and Cd²⁺ were 1.28 mmol/g and 1.29 mmol/g, respectively, in contrast to only 0.372 mmol/g for Pb²⁺ and 0.503 mmol/g for Cd²⁺ on chitosan. Kinetic experiments indicated that the adsorption of CCTE for the above metal ions achieved the equilibrium within 4 h. The desorption efficiencies of the metal ions on CCTE were over 93%. Therefore, CCTE is an effective adsorbent for the removal and recovery of heavy metal ions from industrial waste solutions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dispersion polymerization of uniform cross‐linked polystyrene microspheres in butan‐1‐ol

Butan‐1‐ol can be used as the solvent in the synthesis of poly(styrene‐co‐divinylbenzene‐co‐acrylic acid) microspheres by dispersion polymerization of a mixture of styrene, divinylbenzene (DVB), and acrylic acid (AA). Varying the proportion of the crosslinker DVB affects the size distribution and particle morphology profoundly, with 0.5–1.0% w/w producing spherical particles, whereas 2.0% w/w DVB produces irregular, concave morphologies. Varying the amount of AA from 5–7% w/w increases the average diameter of the spherical particles, whereas 9% w/w AA results in ovoid particles with dimpled surface morphology. In an optimized synthesis using 1.0% w/w DVB and 5% AA, uniform polymer microspheres with an average diameter of 0.8 µm and a coefficient of variation (CV) of diameter of 8.2% are produced. The use of a medium‐polarity solvent, such as butan‐1‐ol, as the solvent for dispersion polymerization will facilitate the incorporation of non‐polar moieties, such as organically‐passivated quantum dots, into the polymer during synthesis. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43103.     

Acetamide‐modified hyper‐cross‐linked resin: Synthesis,characterization, and adsorption performance to phenol from aqueous solution

Acetamide‐modified hyper‐cross‐linked resin, HCP‐HMTA‐AA, was prepared and its adsorption performance was evaluated using phenol as the adsorbate. The prepared HCP–HMTA–AA owned predominant micro/mesopores and medium polarity, making it possess a superior adsorption to phenol as compared with polystyrene (PS), chloromethylated polystyrene (CMPS), hyper‐cross‐linked polymer (HCP) and amino‐modified hyper‐cross‐linked resin (HCP–HMTA). The adsorption enthalpy was ?99.56 kJ/mol at zero fractional loading, multiple hydrogen bonding contributed to such a great adsorption enthalpy and an approximately planar hexahydric ring was formed between acetamide of HCP–HMTA–AA and phenol. The dynamic capacity of phenol on HCP–HMTA–AA was 291.3 mg/g at a feed concentration of 946.2 mg/L and a flow rate of 48 mL/h and the resin column was almost regenerated by a mixed solvent including 50% of ethanol (v/v) and 0.01 mol/L of sodium hydroxide (w/v). HCP–HMTA–AA was repeatedly used for five times and the equilibrium adsorption capacity for the five time reached 94.2% of the equilibrium adsorption capacity for the first time. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41597.     

EWF method to study long term fracture properties of cross‐linked polyethylene

The influence of cross‐linking on fracture properties of polyethylene has been studied by the method of essential work of fracture (EWF). Three distinct values of the cross‐link density were obtained by β irradiation with three distinct radiation doses, and characterized by sol‐gel and solvent swelling measurements. EWF tests were performed at speeds of 0.045 to 100 mm min^–1 at 80 and 110°C. The fracture toughness, as defined from the EWF method, is analyzed through essential (w_e) and nonessential (βw_p) components. Both values were found to be decreasing functions of the cross‐link density. But cross‐linking also suppresses the toughness decrease observed in linear PE at low speeds/high temperatures. It is hypothesized that cross‐linking prevents the chain disentanglement that occurs during crack growth. In conclusion, EWF tests performed at low speeds appear as an interesting method to characterize the influence of structural factors on the fracture properties of polyethylene. POLYM. ENG. SCI., 45:424–431, 2005. © 2005 Society of Plastics Engineers     

Synthesis and photovoltaic device studies of azo‐linked low‐bandgap polymers

We report the synthesis of a series of new polymers containing azo linkage as a part of the main chain. The monomer 1,2‐bis(7‐bromo‐9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazene was synthesized using a precursor approach which avoids non‐selective bromination and was copolymerized with various donor or acceptor units. The homopolymer poly[1,2‐bis(9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazene] ( P1 ) as well as the copolymers poly[1‐(9,9‐dioctyl‐9H ‐fluoren‐2‐yl)‐2‐(9,9,9′,9′‐tetraoctyl‐9H ,9′H ‐[2,2′‐bifluoren]‐7‐yl)diazene] ( P2 ), poly[1‐(9,9‐dioctyl‐7‐(4‐octylthiophen‐2‐yl)‐9H ‐fluoren‐2‐yl)‐2‐(9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazene] ( P3 ) and poly[4‐(7‐((9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazenyl)‐9,9‐dioctyl‐9H ‐fluoren‐2‐yl)benzo[c ][1,2,5]thiadiazole] ( P4 ) were synthesized by Suzuki polymerization. The copolymers poly[1‐(7‐(4,4‐dioctyl‐4H ‐cyclopenta[1,2‐b :5,4‐b ′]dithiophen‐2‐yl)‐9,9‐dioctyl‐9H ‐fluoren‐2‐yl)‐2‐(9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazene] ( P5 ) and poly[4‐(5‐(7‐((9,9‐dioctyl‐9H ‐fluoren‐2‐yl)diazenyl)‐9,9‐dioctyl‐9H ‐fluoren‐2‐yl)‐4‐octylthiophen‐2‐yl)‐7‐(4‐octylthiophen‐2‐yl)benzo[c ][1,2,5]thiadiazole] ( P6 ) were synthesized by direct arylation polymerization reaction. Polymers synthesized using the direct arylation method show good molecular weight, with absorption maxima in the range 500 to 532 nm. P5 and P6 possess low optical bandgaps of 1.81 and 1.86 eV, respectively. A power conversion efficiency of 0.53% with open circuit voltage of 0.53 V, short circuit current density of 3.1 mA cm^?2 and fill factor of 29% has been achieved with C71‐PCBM as acceptor in bulk heterojunction solar cells fabricated with P5 as donor. © 2016 Society of Chemical Industry     

Vitamin E can be used to hinder scissioning in radiation cross‐linked UHMWPE during high‐temperature melting

High‐temperature melting (HTM) of ultrahigh molecular weight polyethylene (UHMWPE) was shown to improve its elongation and toughness. This was believed to be due to increased scissioning and increased diffusion of polymer chains. It was hypothesized here that the toughness of previously radiation cross‐linked UHMWPEs could also be improved by HTM. To test this hypothesis, the wear resistance, tensile mechanical properties, and Izod impact strength of radiation cross‐linked virgin (no additive) and antioxidant‐blended (with vitamin E) UHMWPEs were tested. The results suggested that although the impact strength of cross‐linked UHMWPEs could be improved significantly by HTM, the wear resistance was decreased. Thus, this procedure can be optimized to be especially suited in high‐stress applications, such as total knee replacements with lessened wear concerns. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42735.     

Thermo‐Responsive Membranes with Cross‐linked Poly(N‐Isopropyl‐acrylamide) Hydrogels inside Porous Substrates

Thermo‐responsive membranes were prepared by fabricating cross‐linked poly(N‐isopropylacrylamide) (PNIPAM) hydrogels inside the pores of porous Nylon‐6 (N6) membranes by the free radical polymerization method. SEM micrographs of the prepared membranes showed that PNIPAM hydrogels were filled uniformly throughout the entire thickness of the porous N6 membranes. Both PNIPAM‐filled N6 membranes prepared at 60 °C and at 25 °C exhibited significant reversible and reproducible thermo‐responsive diffusional permeability. When the environmental temperature remained constant, the diffusional coefficient of vitamin B₁₂ (VB₁₂) across the PNIPAM‐filled N6 membrane prepared at 25 °C was ca. twice the value of that prepared at 60 °C due to different filling yields. The thermo‐response factor of the membrane prepared at 25 °C was higher than that prepared at 60 °C. The 3‐dimensional interpenetrating network structure of the cross‐linked PNIPAM hydrogels inside the N6 porous substrates could effectively ensure a repeatable thermo‐responsive permeation performance.