Sub-micrometer polyamide droplets dispersed in polyethylene: Dimensional stability above the melting point of polyethylene

Metallocene-catalyst polymerized ethylene-1-octene copolymers in which a polyamide 6 (PA6) is finely dispersed by means of a MA-grafted-polyethylene as compatibilizer show a non-conventional mechanical behavior at high temperatures. Once the ethylene-1-octene copolymer is melted the system still shows good mechanical properties and dimensional stability. Besides, due to the dispersed phase morphology of the system, so-called fractionated/homogeneous crystallization takes place (extra supercooling of around 50 °C compared to the bulk PA6 crystallization temperature) and the material can be processed in the same temperature range in which it later on will show good mechanical response. The explanation of this intriguing mechanical behavior is sought in the molecular architecture of the system and turns out to be related to the slower flow dynamics of the matrix chains in case of high enough molar mass. The slower dynamics is caused by an increase in entanglement density due to mixing/interactions between matrix chains and compatibilizer chains chemically attached to the droplets. The droplets thereby function as physical crosslinks.     

Mechanical behavior,microstructure and thermooxidation properties of sequentially crosslinked ultrahigh molecular weight polyethylenes

The aim of this study was to explore the impact of the sequential irradiation and annealing process on the microstructure, thermooxidation behavior and mechanical properties of GUR 1050 ultrahigh molecular weight polyethylene (UHMWPE) with respect to the postirradiation annealed material. For this purpose, the effects of a variety of irradiation and annealing conditions on microstructure and mechanical properties were investigated. Differential scanning calorimetry was performed to characterize melting temperature, crystalline content and crystal thickness, whereas transmission electron microscopy provided additional insights into crystal morphology. Thermogravimetric experiments in air served to assess thermooxidation resistance and changes associated to radiation‐induced crosslinking. Fatigue properties were studied from three different approaches, namely short‐term cyclic stress–strain tests, long‐term fatigue experiments and crack propagation behavior. Likewise, three experimental techniques (uniaxial tensile test, impact experiments, and load to fracture of compact tension specimens) allowed evaluation of the fracture resistance. The present findings confirm sequentially crosslinked UHMWPE exhibited improved thermooxidation resistance and thermal stability compared to post‐irradiation annealed UHMWPE. Also, the mechanical behavior, including the fatigue and fracture resistance, of these materials was generally comparable regardless of the annealing strategy. Therefore, the sequential irradiation and annealing process might provide higher oxidation resistance, but not a significant improvement in mechanical properties compared to the single radiation dose and subsequent annealing procedure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Study of crosslinked copolymer nanospheres with temperature resistance,salinity resistance,and deep profile control

Three crosslinked copolymer nanospheres were prepared by inverse microemulsion polymerization. Resistance temperature and resistance salinity of the copolymer CP(AM‐AA‐AMPS) [crosslinked poly(acrylamide‐acrylic acid‐2‐acrylamide‐2‐methylacrylic sulfonic acid)] nano‐spheres were superior to the CPAM (crosslinked polyacrylamide) nano‐spheres and CP(AM‐AA) [crosslinked poly(acrylamide‐acrylic acid)] nano‐spheres. The nanospheres had a tendency to plug the high‐permeability layer and drive crude oil from the low‐permeability layer. Meanwhile, these nanospheres displaced crude oil that existed in the pores or throats when they were conveyed in porous media. Consequently, deep profile control and oil displacement could be entirely actualized, and the ultimate goal of enhanced oil recovery could be achieved for high‐temperature and high‐salinity reservoirs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45131.     

Molecular design and synthesis of crosslinked polyimides using radical isomerization of vinylcyclopropane with thiols

Reactive polyimides bearing a vinylcyclopropane (VCP) moiety in the main chain were successfully synthesized from the corresponding diamine with the VCP moiety. Their radical crosslinking using a dithiol proceeded with the radical ring-opening reaction (RROR) of the VCP moiety to afford the corresponding crosslinked polyimides with the CC bonds in crosslinking moieties. Thermal properties of those crosslinked polyimides were evaluated by thermal gravimetry and differential scanning calorimetry. As a result, the increase of the crosslinking degree in the crosslinked polymer exhibited great residual weight at 600°C. In contrast, the tendency of the glass transition temperature was inverse because the increase in the amount of dithiol unit as a crosslinker would enhance the mitigation of the polymer packing structure and activates the mobility of polymer chains.     

Synthesis and characterisation of branched and partially crosslinked poly(ethylene terephthalate)

In the present study, a series of branched and partially crosslinked poly(ethylene terephthalate) (PET) samples were prepared by the two‐stage melt polycondensation method, using different amounts of trimethyl trimellitate (TMT) as polyfunctional monomer. The samples were characterised with respect to intrinsic viscosity, density and gel content as well as thermal and mechanical properties. The intrinsic viscosity of the polymers ranged between 0.7 and 1.6 dl g^?1 depending on the concentration of the TMT comonomer. When TMT was used at a concentration 0.625 wt% or higher, gel formation was observed. For the sample containing 1.25 wt% TMT, almost half of the polymer was insoluble in phenol–tetrachloroethane mixture, due to extensive crosslinking. The increase of TMT content resulted in a small decrease of crystallinity attributed to branching and crosslinking, both of which restrict the organisation of the polymer chains in the crystal structure. This was reflected directly in the thermal properties of the polymers prepared. Increasing the TMT content decreased the melting point and the heat of fusion. In contrast, cold crystallization and glass transition temperatures were shifted to higher temperatures. Mechanical properties like tensile strength and elongation at break increased with increasing the content in branching agent. However, crosslinking had a negative effect on elongation at break. Copyright © 2003 Society of Chemical Industry     

Thermal and wide angle X‐ray analysis of chemically and radiation‐crosslinked low and high density polyethylenes

Low and high density polyethylenes (PE) were crosslinked by two methods, namely, chemically by use of different amounts of tert‐butyl cumyl peroxide (BCUP) and by irradiation with different doses of electron beam. A comparison between the effects of these two types of crosslinking on crystalline structure, crystallinity, crystallization, and melting behaviors of PE was made by wide angle X‐ray diffraction and DSC techniques. Analysis of the DSC first heating cycle revealed that the chemically induced crosslinking, which took place at melt state, hindered the crystallization process and decreased the degree of crystallinity, as well as the size of crystals. Although the radiation‐induced crosslinking, which took place at solid state, had no significant influence on crystalline region, rather, it only increased the melting temperature to some extent. However, during DSC cooling cycle, the crystallization temperature showed a prominent decrease with increasing irradiation dose. The wide angle X‐ray scattering analysis supported these findings. The crystallinity and crystallite size of chemically crosslinked PE decreased with increasing peroxide content, whereas the irradiation‐crosslinked PE did not show any change in these parameters. As compared with HDPE, LDPE was more prone to crosslinking (more gel content) owing to the presence of tertiary carbon atoms and branching as well as owing to its being more amorphous in nature. HDPE, with its higher crystalline content, showed relatively less tendency toward crosslinking especially by way of irradiation at solid state. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3264–3271, 2006     

Acrylic copolymers crosslinked by click chemistry: Some aspects of synthesis,curing, and crosslinking

Acrylic polymers bearing pendant azide and propargyl groups were synthesized by chemical transformation of epoxy‐ and carboxylic functional acrylic precursor polymers and were characterized. These copolymers were crosslinked by reacting them in the presence of Cu(I) catalyst via the azide–alkyne click reaction leading to triazole networks. Influence of catalyst concentration on the crosslinking cure kinetics was investigated, and the activation parameters were evaluated. The activation energy decreased from 90 kJ mol^?1 to 25 kJ mol^?1 on catalyzing the cure reaction as estimated by Ozawa method. Differential scanning calorimetric analysis indicated thermal decomposition of the residual azide groups at around 200–220°C, which was catalyzed by Cu(I) with associated activation energy of 130–94 kJ mol^?1. Isothermal cure reaction and decomposition of the azide groups were predicted using these parameters. Estimation of crosslink density by solvent swelling and dynamic mechanical analyses showed a normal crosslinking behavior. While the solvent swelling rate and the equilibrium swelling decreased, the front factor and diffusion coefficient of swelling showed a transition from non‐Fickian to Fickian as the triazole concentration increased in the network. The click reaction offered an alternate means to crosslink acrylate polymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1289‐1300, 2013     

Triblock SEBS/DVB crosslinked and sulfonated membranes: Fuel cell performance and conductivity

A set of styrene-ethylene-butylene-styrene triblock copolymer (SEBS) membranes with 10 or 25 wt% divinyl-benzene (DVB) as a crosslinking agent were prepared and validated. Physicochemical characterization revealed suitable hydrolytic and thermal stability of photo-crosslinked membranes containing 25 wt% DVB and post-sulfonated. These compositions were evaluated in H₂/O₂ single cells, and electrical and proton conductivities were furtherly assessed. The membranes with the milder post-sulfonation showed greater proton conductivity than those with excessive sulfonation. In terms of electrical conductivity, a universal power law was applied, and the values obtained were low enough for being used as polyelectrolytes. At the analyzed temperatures, the charge transport process follows a long-range pathway or vehicular model. Finally, fuel cell performance revealed the best behavior for the membrane with 25 wt% DVB, photo-crosslinked during 30 min and mild sulfonated, with a promising power density of 526 mW·cm⁻². Overall, the results obtained highlight the promising fuel cell performance of these cost-effective triblock copolymer-based membranes and indicate that higher sulfonation does not necessarily imply better power density.     

pH and organic solvent‐sensitive properties of crosslinked polymeric spheres formed by a soap‐free emulsion polymerization

Narrowly distributed poly (styrene‐co‐(4‐vinylpyridine)) microspheres are facilely prepared by a soap‐free emulsion polymerization, and their structures and properties are investigated by TEM, FTIR spectra, DSC, and DLS, respectively. The sizes and glass transition temperatures of the polymeric spheres increase with an increase of 4‐vinylpyridine in the reactive system. In addition, these polymeric spheres show good stability in water and a series of organic solvents due to their crosslinked structures. When poly(styrene‐co‐(4‐vinylpyridine)) microspheres are obtained in the reactive system where the weight ratio of 4‐vinyl pyridine to styrene is less than 4/6, they can be well dispersed in water as well as in organic solvents such as ethanol, toluene and DMF, and show obvious pH sensitive and organic solvent‐sensitive characteristics. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermal and crystallization behavior of silane‐crosslinked polypropylene

Silane‐crosslinked polypropylene (PP) has been prepared first by the grafting of silane onto the backbone of PP in a melt process and then by crosslinking in warm water. The effects of type and concentration of silane and peroxide on the silane grafting on PP were investigated. The thermal behavior of the silane‐crosslinked PP was studied by thermogravimetric (TG) and differential scanning calorimetry (DSC) methods. TG results show that PP prepared via silane crosslinking increases its thermal stability greatly. It has been found from DSC measurements that the crystallization temperatures, ie the onset temperature and peak temperature of the exotherm of the silane‐crosslinked PP, increase compared with those of the pure PP. The silane crosslinking hardly changes the crystallinity degree of PP. The crystallization behavior of the silane‐crosslinked PP was also studied by wide‐angle X‐ray diffraction analysis. Copyright © 2004 Society of Chemical Industry     

交联聚乙烯的应用及技术进展

对交联聚乙烯(CLPE)的应用情况及生产技术的发展概况进行了综述，并从交联原理和生产工艺等方面对辐射交联、紫外光交联、过氧化物交联和硅烷交联等CLPE生产方法进行了对比介绍。由于硅烷交联和过氧化物交联比较容易实现且投资相对较少而被广泛应用，而辐射交联和紫外光交联对厚制品很难实现均匀交联，仅限于薄制品领域。建议国内相关单位加大专用料的研制开发力度，在提高塑料加工设备的精度和水平上多做工作。     

Antifouling and blood‐compatible poly(ether sulfone) membranes modified by zwitterionic copolymers via In situ crosslinked copolymerization

A novel and simple but practical method for the preparation of modified poly(ether sulfone) (PES) membranes was provided by the in situ crosslinked copolymerization of sulfobetaine methacrylate (SBMA) and sodium p‐styrene sulfonate (NaSS) in PES solution followed by a phase‐separation technique. Then, semi‐interpenetrating network membranes modified by the crosslinked copolymers of poly(sulfobetaine methacrylate‐co‐sodium p‐styrene sulfonate) [P(SBMA‐co‐NaSS)] were prepared. The SBMA‐containing copolymer‐modified membranes showed improved protein antifouling properties with flux recovery ratios above 90%. Furthermore, the anticoagulant properties of the NaSS‐containing copolymer‐modified membranes were obviously enhanced; their activated partial thromboplastin time could be prolonged to about 115 s. Thus, the P(SBMA‐co‐NaSS) zwitterionic copolymer‐modified membranes showed improved antifouling properties and blood compatibility and will provide wide choices for their specific applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41585.     

Influence of chain microstructure on the conformational behavior of ethylene-1-olefin copolymers. Impact of the comonomeric mole content and the catalytic inversion ratio

The rotational isomeric state model was employed to provide a better understanding of the role of chain microstructure on the conformational behavior of homogeneous ethylene-1-olefin copolymers. The chain microstructure was assembled in accordance with the copolymerization theory using a set of conditional probabilities in direct relation to the reactivity ratios and the feed compositions of the comonomers. The catalytic inversion influence on the tacticity of the polymeric microstructure was also taken into account by considering the replication probability during the Monte Carlo simulation. Statistical weight factors of the rotational isomeric states were evaluated using molecular dynamics runs of the various homopolymers according to the earlier work of Mattice et al. Probability distribution surfaces constructed by the integration of the molecular dynamics trajectories of sufficient length to sample all of the conformational space indicated the increase of the probability of g^±t joint states at the expense of g^±g^± pairs with the increase in the side chain length of the 1-olefin comonomers. It was also indicated that this behavior had a maximum around poly(1-butene)/poly(1-hexene) with an apparent reversal in case of poly(1-octene) due to the side chain crowding, which forces the chain to favor more of the g^±g^± joint states. The characteristic ratios calculated for the copolymers on the basis of the rotational isomeric state model also indicated the increased extension of the polymer backbone with the increase in the side chain length. The lower characteristic ratio calculated for the octene polymers may, in fact, explain the experimental observation that poly(1-octene) has a lower melting point than those of other poly(1-olefin)s of shorter side chains. A complete account of the role of tacticity on the characteristic ratio and the radial distribution function is also given.     

Design and study of the potential of crosslinked cationic polymers as drug delivery systems for dermal application

Crosslinked carriers based on cationic monomer [2‐(acryloyloxy)ethyl]trimethylammonium chloride or 2‐(dimethylamino)ethyl methacrylate were developed and investigated as new platform for ibuprofen transdermal delivery. Series of networks of varied composition and structure were synthesized and characterized by FTIR spectroscopy and following swelling kinetics in different solvents. Dermal safety tests to examine the skin irritation and sensitization potential of the network films were performed in vivo. Chosen network compositions were loaded with ibuprofen by swelling in its ethanol solution. The structures of the drug carriers were investigated by scanning electron microscopy. Ibuprofen release from the developed drug delivery systems was followed in phosphate buffer solution at 37 °C. The investigation proved the feasibility of the developed cationic copolymer networks as effective platforms with modified ibuprofen release for potential dermal application. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46420.     

ENGAGE compatibilized HDPE/EPDM blends: Modification of some industrially pertinent properties and morphology upon incorporation of Mg(OH)2 filler and electron beam crosslinked network

To observe the effect of ENGAGE (a poly‐olefin elastomer) on compatibilization of industrially important incompatible blend, high‐density polyethylene (HDPE)/ethylene‐propylene diene elastomer (EPDM), 15 wt % ENGAGE is incorporated into the system and the latter is found satisfactorily efficient as compatibilizer for the above system. To improve some industrially pertinent properties another strategies are also followed in addition, incorporation of magnesium hydroxide [Mg(OH)₂] and electron beam (EB) crosslinking into the system. The gel content was found to increase with radiation dose, EPDM content and Mg(OH)₂ dispersion. ENGAGE interestingly increases the gel content that is, promotes crosslinking. It is unique that filler dispersion and crosslinked network formation maintain the compatibility of the ternary system, which is confirmed by X‐ray diffraction, differential scanning calorimetry, mechanical properties, and scanning electron microscope. The compatibilization, Mg(OH)₂ dispersion, and EB crosslinking improve the mechanical, thermo mechanical, flame retardant properties, and phase morphology considerably. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44922.     

Preparation and pH‐sensitive swelling behavior of physically crosslinked polyampholyte gels

A novel polyampholyte hydrogels were prepared by free radical aqueous copolymerization of ionic complex consisting of acrylic acid (AAc), (N,N‐diethylamino) ethyl methacrylate (DEAEM), and acrylamide (designated as PADA). Without any chemical crosslinker, the formation of PADA network structures was mainly attributed to the electrostatic interaction of AAc (anionic monomer) and DEAEM (cationic monomer). The PADA gels exhibited a typical swelling behavior of polyampholyte gels in buffer solutions. The hysteresis of isoelectric point (pI) for PADA gels was observed after preswollen in alkaline solutions. The swelling behavior of PADA gels in response to change of pH was investigated. It was found that the equilibrium swelling ratio orderly decreased in buffer solutions with alternating pH between 2.2 and 5. An abrupt swelling was observed for the hydrogels at the pH near isoelectric point in the earlier stage of swelling process. The study of swelling kinetics of the hydrogels showed that the swelling process was in agreement with the second‐order swelling kinetics. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3857–3861, 2006     

Swelling and mechanical properties of crosslinked hydrogels containing N-vinylpyrrolidone

Copolymers of 2-hydroxyethyl methacrylate/N-vinyl-2-pyrrolidone (HEMA/NVP) and methyl methacrylate (MMA)/NVP were prepared in the presence of varying amounts of ethylene glycol dimethacrylate (EGDMA) and methylene diacrylamide (MDA) as crosslinkers by photopolymerisation. The resultant solid polymers were swollen to equilibrium in water at 293 K to produce hydrogels. These hydrogels were characterised by soluble fraction and equilibrium water content. The gels were also characterised by compression—strain measurements, which enabled the calculation of Young's modulus and effective crosslink density. The differences in these properties of HEMA/NVP and MMA/NVP polymer series and the effects of MDA versus EGDMA as a crosslinker were explained in terms of compositional drift of polymerisation, heterogeneous crosslinking and hydrophilicity/hydrophobicity of the components involved. In comparison with EGDMA, MDA was found to be more effective in reducing the soluble fraction of the polymers studied and to produce less rigid networks when swollen.     

Crystallization behavior and mechanical properties of crosslinked plasticized poly(L‐lactic acid)

Enhancing the stability of plasticized poly(L ‐lactic acid) (PLLA) with poly (ethylene glycol) (PEG) is necessary for its practical application. In this study, plasticized PLLA (PLLA/PEG 80/20 wt/wt) was crosslinked under γ‐ray (Co⁶⁰) in the presence of triallyl isocyanurate (TAIC) as crosslinking agent. FTIR analysis revealed that PLLA, PEG, and TAIC formed a cocrosslinking structure. Crystallization behavior and mechanical properties of the crosslinked plasticized PLLA were investigated by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), scanning electron microscopy (SEM), and tensile tests. Experimental results indicated that the crystallization behaviors of both PEG and PLLA in the blends were restrained after irradiation. The melting peak of PEG in the crystallized samples disappeared at a low irradiation doses about 10 kGy. Although PLLA still owned the behavior of crystallize, its cold crystallization temperature and glass transition temperature shifted to higher temperature. Mechanical properties of the plasticized PLLA were strengthened through crosslinking. Both yield strength and elastic modulus of the samples increased after crosslinking. Elongation at break of the crosslinked plasticized PLLA decreased with the increase of crosslinking density but remained a high value over 200%. SEM images of fracture surfaces confirmed that the ductile fracture behavior of plasticized PLLA was kept after suitable crosslinking. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and swelling behavior of crosslinked copolymers of neutralized maleic anhydride with other monomers

A series of novel copolymer superabsorbents based on maleic anhydride (MLN), acrylamide (AAM), hydroxyethyl methacrylate (HEMA), and N,N′‐methylenebisacrylamide (NMBA) were prepared by inverse‐suspension polymerization. The influence of the reaction parameters on the water absorption was investigated to improve the understanding and to identify the optimum reaction conditions. The water absorbences or swelling behaviors for these absorbents in various salt solutions and various alcohol solutions were studied. The tendency of the absorbency for these absorbents in salt and alcohol solutions is in the order Na⁺ > Ca²⁺ > Al³⁺ for NaCl, CaCl₂, and AlCl₃ aqueous solutions and a glycerol > glycol > methanol > ethanol solution, respectively. This article also explains the IR and SEM characterization of the water‐absorbing copolymers and their practical use in soil for water retention. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2725–2731, 2003