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In this contribution, we reported a new approach to crosslink linear polyurethane (PU) with dynamic boronic ester bonds. First, a linear PU was synthesized, which carries a plethora of 1,3-diol structural units. Second, two structurally similar diboronic acids were designed and synthesized, which contained amino and amido groups, respectively. Thereafter, the crosslinking between the linear PU and the diboronic acids was carried out via the generation of boronic ester bonds. Thanks to the crosslinking, the PU networks significantly displayed improved thermomechanical properties, contingent on types of crosslinkers. More importantly, the excellent reprocessing and shape memory properties were imparted to the PU networks, which were implemented by dynamic boronic ester bonds between 1,3-diol moieties of the linear PU and boronic acids of the crosslinkers. The dynamic exchange of boronic ester bonds is responsible for the reprocessing properties. For the shape memory properties, the PU networks featured the reprogramming behavior of original shapes via the dynamic exchange of boronic ester bonds. More importantly, the shape memory properties were also dependent on types of diphenylboronic acids, which was reflected with the difference in dynamicity of boronic ester bonds. For the PU networks with amino-containing crosslinker, the boronic ester bonds featured the B–N coordination. As a result, the boronic ester bonds had the increased dynamicity, which significantly affected the reprocessing properties. [Display omitted] • A linear polyurethane (PU) carrying a 1,3-diol structural units was synthesized. • The linear PU was crosslinked with two types of diphenylboronic acids. • It was demonstrated that B–N coordination was generated with diphenyl boronic acid bearing amino groups. • Generation of B–N coordination significantly affected the thermomechanical, shape memory and reprocessing properties of PU networks. [ABSTRACT FROM AUTHOR]

Stereocomplex crystal (SC) in poly(l -lactide) (PLLA)/poly(d -lactide) (PDLA) can significantly improve the heat resistance and mechanical performance of poly(lactic acid). In this work, a selective degradation method is developed to etch the PLLA/PDLA blend using proteinase K, and a two-phase co-continuous structure is observed directly using scanning electron microscope. Meanwhile, the evolution of the microphase morphology, inter-chain interaction, chains orientation, and crystallization of un-crosslinked and crosslinked blends during solid-state stretching, as well as the formation of SC during heating/annealing are comprehensively investigated. Results showed that the phase separation in the stretched blend could be drastically restricted by crosslinking; during stretching a blue-shift of 2995 cm−1 band shows up for both crosslinked and un-crosslinked blends as a result of the dipole-dipole coupling interaction between CH 3 and CH 3 , while the hydrogen bond interaction between CH 3 and C O is absent; only mesophase or homocrystal (HC) is formed in the stretching temperature range of 60∼105 °C; the critical strain for HC formation is advanced and the orientation of chains is enhanced by crosslinking under the same stretching condition. In the last, benefiting from the greatly reduced microphase size (namely enlarged interfacial area between PLLA and PDLA) and enhanced chains orientation, the crystallization rate of SC is accelerated during annealing, and the ultimate crystallinity of SC is elevated in the crosslinked blend. [Display omitted] • A method for direct observation of phase morphology in PLLA/PDLA is proposed by using proteinase K selective degradation. • Crosslinking could restrict the phase separation under both static condition and combined thermal/stretching field. • Crosslinking restricted phase separation and solid-state stretching induced orientation could promote the formation of SC. [ABSTRACT FROM AUTHOR]

The addition reaction of primary alcohols onto aromatic carbodiimides giving iso -ureas was studied in bulk at various temperatures. A side reaction at 60 °C was found to occur between carbodiimide and iso -urea yielding N,N′ -substituted polyguanidine oligomers. The occurrence of this side reaction coincides with a reduced conversion of the alcohol; the carbodiimide was always fully converted to either iso -urea or polyguanidine. The formation of the polyguanidine was reversible at higher temperatures to reform iso -urea and carbodiimide. The latter reaction was complete at about 130 °C. The thermo-reversibility of the guanidine bond was utilized to produce thermo-reversible self-healing polymer networks by reaction of polyether diol and a 1.5 to 2-fold molar excess of aromatic biscarbodiimide. The materials were soft and elastic and showed a glass transition at −60 °C. The guanidine linkages in the polymers started to unzip above 60 °C as was indicated by a drop in the E-modulus, at about 130 °C sufficient guanidine crosslinks had unzipped to provide the polymer liquid-like properties. The guanidine crosslinks were reformed after cooling to ambient temperature giving back the polymer network. [Display omitted] • The reaction of carbodiimide and hydroxyl gave stable isourea bonds. • Using excess carbodiimide yielded thermo-reversible guanidine linkages. • Reacting polyol with excess bis-carbodiimide provided crosslinked polymer. • The crosslinks were stable below 60 °C and unzipped above 130 °C. • The thermosetting polymers showed thermally self-healable properties. [ABSTRACT FROM AUTHOR]

Elastomers undergo thermo-oxidative aging when exposed to high temperatures and oxidation, leading to material degradation and potential failure. Understanding this process is crucial for preventing failure and improving elastomer design. This paper reviews the literature on thermo-oxidative aging effects on elastomers, detailing characterization techniques used and discussing impacts on microstructure and physical properties. It also identifies current limitations and future research directions, aiming to enhance understanding and mitigation of thermo-oxidative aging in elastomers. [Display omitted] [ABSTRACT FROM AUTHOR]

Since 2002, intensive research on glycerol polyester has been ongoing. Poly(glycerol sebacate) (PGS) is most often studied because of its high applicable potential in many medical uses. This polyester is commonly synthesised from glycerine and sebacic acid in a molar ratio G/SA = 1:1. Nowadays, synthesis and thermal crosslinking processes are very time-consuming. At least 24 h for each, sometimes even a few days. There is a lack of works comparing these processes with polymerisation theory, such as Carothers Equations or Flory-Stockmayer Theory. In this work, experiments were performed at characteristic points of molar ratio determined from mathematical modelling. Currently published syntheses and crosslinking processes are characterised by long times, probably due to the use of the wrong molar ratio of monomers. The most effective glycerine to sebacic acid ratio is 2:3, according to both theories. This parameter should be considered for further synthesis optimisation and scaling up. This is also important for industrial implementation due to economic and ecological aspects. Moreover, the study of the G/SA ratio outside the range of 0.5–1.0 has no theoretical and experimental justification. [Display omitted] • New perspective for effective synthesis for all glycerol an diacids polyesters. • Thermosets designed for short crosslinking time. • Fabrication process designed based on polymerisation theories. [ABSTRACT FROM AUTHOR]

The electrolyte membrane plays a pivotal role in high temperature proton exchange membrane fuel cells (HT-PEMFCs). Herein, we develops a new triarylmethane-backboned polymer, poly (biphenyl dimethylamino benzene) (PBDAB), synthesized through a facile one-step Friedel-Crafts reaction using biphenyl and 4-(dimethylamino) benzaldehyde as monomers. The presence of tertiary amine groups in PBDAB facilitates strong interactions with phosphoric acid (PA) molecules. To enhance the membrane's dimensional and mechanical stabilities, covalent crosslinking is performed via the Menshutkin reaction between the tertiary amine groups in PBDAB and chloromethyl groups in various crosslinkers. In order to study the influence of crosslinker chemical structure on the properties of PBDAB-based membranes, five different crosslinkers are employed, including small-molecule types such as 1,2-bis(2-chloroethoxy) ethane (BCE) and 1,4-bis(chloromethyl) benzene (BCB), siloxane type 3-chloropropyl (trimethoxy) silane (CTS), polymer types such as poly (vinylbenzyl chloride) (PVBC) and polyepichlorohydrin (PECH). Results reveal that the flexible and ether containing polymer crosslinker of PECH crosslinked membrane, denoted as CL-y%PECH, exhibits superior overall performance. When doped in an 85 wt% PA solution, the CL-5%PECH membrane achieves a PA uptake of 201%, resulting in an anhydrous proton conductivity of 0.064 S cm−1 at 180 °C and a mechanical strength of 7.2 MPa at room temperature. Using H 2 and O 2 as fed gases without humidification and backpressure, a single cell with abovementioned membrane attains a peak power density of 302 mW cm−2 at 160 °C. This work offers a kind of promising PBDAB based membranes for HT-PEMFC applications. [Display omitted] • Crosslinked poly (biphenyl dimethylamino benzene) membranes are synthesized for HT-PEMFCs. • Macromolecular PECH crosslinked membranes exhibit superior overall performance. • CL-5%PECH/201%PA membrane exhibits a H 2 –O 2 fuel cell peak power density of 302 mW cm−2 at 160 °C without backpressure. [ABSTRACT FROM AUTHOR]

Utilizing biomass to create eco-friendly dielectric materials satisfies the criteria for sustainable development in terms of both environmental protection and economic growth, but the relatively low energy storage density is far below the application requirements. Here, regenerated cellulose/MXene (RC/M) composite films were manufactured, and a glutaraldehyde (GA)-assisted crosslinking was proposed to further tailor the microstructure and performances of the RC/M composite films. The results suggested that likened to the original RC/M composite films without crosslinking, the crosslinked composite films (CRC/M) exhibited more integrated structure and fewer defects, apparently reduced dielectric loss and largely enhanced breakdown strength. Consequently, at 288.61 MV/m with MXene concentration of 1 wt%, the energy storage density achieved to 2.41 J/cm3, which was around 6.34 and 1.13 times those of the neat RC film (0.38 J/cm3) and pure CRC film (2.12 J/cm3), respectively. Crosslinking reaction consumed the polar groups of MXene and cellulose matrix, leading to the great reduction of hydrophilicity of the composites, which reduced the water adsorption ability, facilitating the improvement of MXene stability. The effects of storage mode and time on evolution of dielectric performances were also studied. The good comprehensive properties endow the CRC/M composite films with potential applications in next generation dielectric capacitors. [Display omitted] • Crosslinked cellulose/MXene composite films were fabricated. • The crosslinked composite films display largely reduced dielectric loss. • Dramatically enhanced breakdown strength is achieved. • The crosslinked composite films exhibit reduced hydrophilicity. [ABSTRACT FROM AUTHOR]

Transcarbamoylation (or transurethanization) between carbamate (or urethane) and hydroxyl groups is the dynamic chemistry in polyhydroxyurethanes. However, its use in traditional polyurethanes (PUs) remained largely unexplored. In this contribution, we reported the introduction of transcarbamoylation into PUs. Toward this end, 2,2-dimethyl-5,5-bis(hydroxymethyl)-1,3-dioxane was synthesized and used as the chain extender to obtain a linear PU bearing ketal structural units; the deprotection of ketal moieties generated 1,3-diol structural units. The as-obtained linear PU carrying 1,3-diol moieties was post-crosslinked with a diisocyanate (i.e. , 1,6-diisocyanatohexane). It was found that the crosslinking resulted that the thermomechanical properties of PUs were significantly improved. Meanwhile, the shape memory properties were imparted to the PU networks. More importantly, the PU networks had the excellent reprocessing (or recycling) properties; the recovery of mechanical strength was as high as 90 %. It was demonstrated that the transcarbamoylation between carbamate (or urethane) moieties and hydroxyl groups was mainly responsible for the reprocessing behavior. The transcarbamoylation had the activation energy (E a) was much lower than those reported in literature based on polyhydroxyurethanes. For the shape memory PU networks, notably, the original shapes can be further reprogrammed by taking advantage of the reprocessing properties. [Display omitted] • A linear polyurethane (PU) was synthesized with a 1,3-diol carrying ketal group as the chain extender. • The linear PU was further derived into a linear PU carrying 1,3-diol structural units. • The linear PU carrying 1,3-diol structural units was readily crosslinked with diisocyanate. • The crosslinked PUs had shape memory and reprocessing properties. • Transcarbamoylation is responsible for the reprocessing behavior. [ABSTRACT FROM AUTHOR]

Poly(aspartic acid) (PASP) hydrogels have gained significant attention in recent years due to their excellent biocompatibility, biodegradability and tunable swelling behavior. This comprehensive review presents an overview of past and current research efforts focusing on PASP hydrogels, their functionalization strategies, processing methods and applications. The chemical functionalization of PASP is addressed, highlighting the ability to tailor the functionalities of PASP for customization. Precise control over functional groups for crosslinking enables the preparation of PASP hydrogels that can respond to environmental triggers, rendering them valuable for applications including, yet not limited to, controlled drug release, tissue engineering and self-healing concrete. Furthermore, the processing methods employed to produce PASP in different forms, such as films, nanoparticles and fibers are described. Finally, the applications of PASP hydrogels are overviewed, highlighting their potential to help improving human health and environmental sustainability by providing an alternative for fossil-based hydrogels. [Display omitted] [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations offer insights into high-performance polymer attributes and assist in creating novel materials. However, simulating cyanate resin systems remains a challenge due to the complexities of triazine ring formation. While earlier research efforts have been made, a consistent procedure for analyzing cyanate resins remains elusive. This research introduces a precise and replicable method for modeling cyanate resin systems, focusing on triazine ring formation processes. The technique combines a crosslinking method, a unique ring-formation algorithm, and a protocol for MD simulations. Using Bisphenol A dicyanate ester (BPACN) as the monomer, a polymer model is created. Predicted attributes like a glass transition temperature of 298.7 ± 3.7 °C and a Young's modulus of 2.95 ± 0.22 GPa align well with experimental data. This innovative method offers a blueprint for other triazine ring formations. [Display omitted] • Using the GRRM method, two cyanate resin crosslinking reaction mechanisms were identified. • Developed a novel algorithm incorporating reversible reactions to model crosslinking pathways. • Consideration of reversible reactions enhances accuracy in physical property predictions of cyanate crosslinking. • Crosslinking mechanisms directly affect key physical properties such as Young's modulus and glass transition temperature. [ABSTRACT FROM AUTHOR]

Gas separation properties are reported for self-standing polymer of intrinsic microporosity (PIM) films after addition of palladium (II) acetate or iron (II) acetate by solid state or liquid state mixing. Membranes, with thicknesses in the range 35–55 μm, were prepared from three high molar mass PIMs, two different branched versions of the much-reported PIM-1 (PIM-1a and PIM-1b) and of PIM-Py. Addition of either Fe(OAc) 2 or Pd(OAc) 2 to all three PIMs led to a reduction in permeability and increase in selectivity, but the permeability reduction was much greater for Pd(OAc) 2 , which is able to interact with branch points in the PIM and crosslink the polymer. CO 2 /CH 4 selectivity of membranes containing Pd(OAc) 2 was poor upon aging, especially after solid state addition to the PIM-1 polymers, for which CO 2 permeabilities dropped to below 200 Barrer after 85 days. Hydrogen permeability and H 2 /N 2 selectivity of membranes containing Pd(OAc) 2 did more closely follow conventional permeability/selectivity trade off upon aging. This illustrates the profound differences that can arise in gas permeation properties and aging behaviour from variations in chemical structure and macromolecular characteristics, and from the addition of metal acetates that interact with the polymer in different ways. [Display omitted] • Branched PIM-1 crosslinked with Pd(OAc) 2 produced membranes with reduced permeability. • Loss in CO 2 permeability on aging not matched with increase in CO 2 /CH 4 selectivity. • Loss in H 2 permeability on aging matched with increase in H 2 /N 2 selectivity. • Crosslinks block smaller free volume elements that dominate CO 2 /CH 4 selectivity. • Fe(OAc) 2 mixed PIM-1 membranes maintain permeability/selectivity balance. [ABSTRACT FROM AUTHOR]

The ability of piperidine-based compounds to confer oxidative stability to polyolefin thermosets without compromising the yields of peroxide-initiated crosslinking and monomer grafting is demonstrated. Unlike phenolic, nitroxyl and phosphite antioxidants that lower the concentration of macroradical intermediates that support polyolefin modifications, additives based upon 2,2,6,6-tetramethylpiperidine (TEMPH) are shown to have little to no effect on the extent of LLDPE crosslinking or the conversion of vinyltriethoxysilane (VTEOS) to grafted hydrocarbon adducts. Notwithstanding this lack of interference in radical-mediated polymer modification, this class of hindered light stabilizer (HAS) compounds are shown to limit the extent of radical oxidation of linear low-density polyethylene (LLDPE) in an accelerated aging test. The origins of this paradox are discussed in terms of the current state of knowledge regarding HAS activation. The latent antioxidant concept is extended to an alternate approach, wherein 4-acryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl (AOTEMPO) is used as an alkyl radical scavenger bearing an oligomerizable functional group. When added at a fraction of the peroxide loading used to produce an LLDPE thermoset, ATEMPO is shown to provide a predictable induction delay without impacting ultimate crosslink density, and produces polymer-bound alkoxyamine functionality that stabilizes the product against oxidation. Image 10333879 [ABSTRACT FROM AUTHOR]

Natural rubber (NR) is one of Nature's most exceptional materials and is, therefore, widely used by industry, in particular by the tire industry. In spite of the interest in recycling vulcanized NR, there is no suitable way to do it and most of the tires are discarded in landfills. Here, we examine the use of a Diels-Alder reaction to obtain a NR fully and reversibly crosslinked and with self-repair capacity. NR was crosslinked via Diels-Alder (DA) reactions following a three-step procedure: i) NR was reacted with maleic anhydride; ii) furan moieties were then grafted to the maleated rubber; iii) pending furans were further crosslinked with a bismaleimide, resulting in a thermoreversible bridge which led to a crosslinked NR. The formation of the DA adduct was confirmed and the reversibility of the DA reaction was demonstrated through dynamic-mechanical analysis and rheological measurements. The self-healing capacity of the material was also evaluated; qualitatively, at different scales by scanning electron microscopy, optical profilometry and atomic force microscopy and; quantitatively, by tensile testing obtaining 80% of strength recovery at small deformations. We provide phenomenological explanations of the reversibility and healing performance of the DA reaction too. This research provides a framework to crosslink rubbers, yielding a straightforward strategy for both reusing and extending the lifetime of elastomeric goods. Image 1 • Natural rubber is crosslinked via Diels-Alder chemistry. • Molecular reversibility and healing capability are correlated. • Healing of macroscopic damage is studied at different scales of observation. • Repairing process starts from the lower planes until the damage surface is sealed. [ABSTRACT FROM AUTHOR]

Abstract Herein, we have developed pH-responsive shape-persistent polymersomes made of well-defined amphiphilic poly(ethylene oxide)- block -poly(diisopropylaminoethyl methacrylate- co -furfuryl methacrylate)s PEO- b -P(DPA- co -FMA) by exploiting Diels-Alder chemistry as a robust and simple crosslinking method. Using Photo-induced Copper Mediated Reversible Deactivation Radical Polymerization, we synthesized PEO- b -P(DPA- co -FMA) with optimal block ratios that favor the formation of polymersomes in aqueous media having pH-responsive P(DPA-co-FMA) membranes. Owing to the existence of furfuryl pendant groups within the polymersome membranes, the crosslinking of pH-responsive P(DPA- co -FMA) chains can be achieved via Diels-Alder chemistry. Interestingly, the resulting crosslinked polymersomes swell when the pH in the solution is decreased so that it lies in a biologically relevant range, as was demonstrated by cryogenic transmission electron microscopy. Here, the polymersomes' ability to swell can be controlled by adjusting the amount of crosslinker. A minimum threshold of crosslinking density is needed for the polymersomes to swell while an excess amount of crosslinker quenched their ability to swell. Furthermore, crosslinked polymersomes are capable of encapsulating hydrophilic model drug, such as Rhodamine B. At pH 7.20, due to the compact and hydrophobic membrane, the diffusion of the dye from the interior of the polymersomes to the media is minimized, while the pronation of PDPA at an acidic pH of 4.00, enables a permeable membrane, allowing the loaded cargo to leak much more quickly. The shape-persistent polymersomes that we developed herein, are a promising nano-platform for use in drug delivery applications. Graphical abstract Image 1 Highlights • PDPA-based polymer is synthesized by photo-induced living radical polymerization. • PEO- b -PDPA self-assembles in water to form either micelles or polymersomes. • The membranes of pH-responsive polymersomes are crosslinked by Diels-Alder Chemistry. • Crosslinked polymersomes reversibly swell upon the switching the pH of the media. • Crosslinked polymersomes show the pH-triggered release of pre-loaded hydrophilic dye. [ABSTRACT FROM AUTHOR]

Abstract Ductile functionalized polypropylene is of great interest in multi-layer composites development. A capped-end triblock polyether diamine (H 2 N-PO 2 -TMO 9 -PO 3 -NH 2) was used as a linker of two different maleated isotactic polypropylenes (iPP -g- MAH, at 1 and 3 wt%) by twin-screw reactive extrusion. The molecular architecture, the semi-crystalline microstructure and the mechanical properties of the resulting polymers were analysed as a function of the molar ratio of NH 2 :MAH (0:1, 0.33:1, 0.5:1, 0.66:1, 1:1, 1.5:1, 2:1). At the molecular scale, the chemically modified polymers were characterized by FTIR and by the determination of gel content following the ASTM D2765-84 standard method. Differential Scanning Calorimetry, Wide Angle X-rays Scattering and Self Successive Auto-nucleation techniques showed the impact of the crosslinking: a decrease of the melting temperature as compared with the unmodified iPP -g- MAH polymer, as well as a decrease of the crystallinity ratio for the iPP -g- MAH at 3 wt% of MAH. Interestingly, Dynamic Mechanical Analysis and video-controlled uniaxial tensile tests showed that the polymers obtained in stoichiometric NH 2 :MAH molar ratio exhibit the best mechanical properties enlightened by a switch from brittle to ductile mechanical behaviour with few differences between the two iPP -g- MAH. Graphical abstract A slight crosslinking enables maleated isotactic polypropylenes to switch from brittle to ductile mechanical behavior with higher resilience than the most conventional one. Image 1 Highlights • A capped-end triblock polyetherdiamine is used as a linker of different iPP- g -MAH by twin-screw reactive extrusion. • The three-dimensional networks are characterized by FTIR and by the determination of gel content. • The semi-crystalline microstructure is thermally described applying the Self-Successive Auto nucleation technique. • A switch from brittle to ductile mechanical properties is observed studying the intrinsic true mechanical behaviours. [ABSTRACT FROM AUTHOR]

Abstract The influence of moisture supply on the crosslinking rate in room temperature vulcanizing poly(dimethyl siloxane) is investigated using spatially resolved 1H nuclear magnetic resonance relaxometry. Using this technique, we observe heterogeneous crosslinking manifested in a front moving into the material from the exposed surface, which separates the crosslinked and uncrosslinked parts of the material. The presence of a sharp boundary indicates that moisture transport towards the front is the limiting factor in the crosslinking process. As a result, the moisture supply controls the crosslinking front velocity, which we capture in a diffusion-reaction model. Reasonable agreement is found between the front diffusivity retrieved directly from nuclear magnetic resonance experiments and calculated values using independently measured properties of the crosslinked silicone rubber. This result demonstrates the direct relationship between exposure moisture content, moisture diffusion, and crosslink density on the crosslinking front dynamics in room temperature vulcanizing poly(dimethyl siloxane). Graphical abstract Image 1 Highlights • Transverse magnetization relaxation rate dependent on crosslinking. • Direct observation of a crosslinking front upon exposure to a moisture source. • Crosslinking front velocity directly related to moisture supply. • Reaction-diffusion model with material parameters reproduces front diffusivity. [ABSTRACT FROM AUTHOR]

Abstract The ε -caprolactam monomer having a triphenylimidazole moiety such as DL-3-[ α -4-(4,5-diphenyl-1 H -imidazole-2-yl)-phenylacryloyl-amine]- ε -caprolactam (1) was synthesized by the Heck reaction of 2-(4-bromophenyl)-1-(methoxymethyl)-4,5-diphenylimidazole and the ε -caprolactam derivative having an acryloyl group in a good yield. The copolymerization of 1 and ε -caprolactam was carried out at 250 °C by using H 2 O as an initiator to give copolymer (4) in a good yield. The crosslinking reaction of the obtained 2 proceeded with K 3 [Fe(CN) 6 ] and KOH in a mixed solvent of ethanol and phenol. The resulting crosslinked polymer (5) was de-crosslinked under irradiation with visible light. Consequently, the thiol-capped de-crosslinked polymer (6) was obtained in a good yield. Graphical abstract Image 1 Highlights • The ε -caprolactam monomer having a triphenylimidazole moiety was synthesized by Heck reaction. • The copolymer having a triphenylimidazole moiety was prepared at 250 °C by using H 2 O as an initiator. • The crosslinking reaction of the obtained copolymer proceeded with K 3 [Fe(CN) 6 ] and KOH. • The resulting crosslinked polymer was de-crosslinked under irradiation with visible light. [ABSTRACT FROM AUTHOR]

Freeze dried, highly porous materials made from cellulose nanofibrils (CNF) hydrogels are capable of absorbing and storing a significant quantity of liquid inside their 3D structure, with total absorption capacity increasing linearly with porosity. One of the challenges of freeze dried high porosity CNF gels is their propensity to break down rapidly in aqueous environments. Here we explore a method to overcome this deficiency by incorporating methacrylate functionalized carboxymethyl cellulose (MetCMC) into the CNF system followed by UV irradiation leading to crosslinking of the methacrylate groups of MetCMC. The resultant polymer composite matrix successfully maintains a robust 3D structure, without collapsing, even when rewetted and stored in water. When freeze dried, the CNF-MetCMC composite maintains its size and shape whereas air drying induces significant shrinkage. In contrast, air dried CNF-MetCMC hydrogels swell when rewetted. Swelling and shrinkage of CNF-MetCMC hydrogels were tuned by controlling the ratio between CNF and MetCMC in the composite. The crosslinking between the methacrylate groups of MetCMC also enhances the dry and wet modulus of CNF-MetCMC gels significantly. We invoke a simple model involving a balance between hydrogen bonding and crosslinking to explain these data. [ABSTRACT FROM AUTHOR]

This work addresses the impact of fabrication conditions (curing procedure, moisture) on the properties of a two-part polyurethane system. While Part I treats the chemical, dielectric and mechanical properties during cure and storage in dry conditions , this second part focuses on these properties, along with the caloric glass transition, in moist conditions , with moisture being introduced at different times during and right after cure. It is shown that the presence of water during fabrication severely affects final properties (increased polymer mobility, reduced mechanical stiffness) by reacting with isocyanate (forming primary amines and urea) and thereby lowering crosslink density, even for seemingly uncritical humidity conditions. Other chemical side reactions involving moisture are also identified. Water furthermore accelerates polymer dynamics substantially. Overall, moisture during cure and storage is clearly identified as a cause for property variations of PU. [ABSTRACT FROM AUTHOR]

The aromatic epoxy isomers triglycidyl p -aminophenol and triglycidyl m -aminophenol were cured with two aromatic diamine isomers 4,4′ diaminodiphenyl sulphone and 3,3′ diaminodiphenyl sulphone, creating four variations of epoxy resin. Dynamic and static mechanical analyses were used to understand the influence of chemical and network structure on the thermal, volumetric and mechanical properties of the epoxy resin. Fracture toughness increases are observed for networks containing meta substituted phenylene ring amines compared to the para equivalents, however no difference is noticed when the meta substituted phenylene ring epoxy is used. Use of meta substituted phenylene rings increases glassy modulus, yield stress, density and strain to failure. Correspondingly, decreases are seen in the glass transition temperature, intensity of the beta transition and the rubbery modulus. The results are entirely consistent with internal antiplasticisation caused by the presence of the meta substituted phenylene rings. [ABSTRACT FROM AUTHOR]

A new class of polyethylene-bonded antioxidants (PE-HP), containing several hindered phenol (HP) groups located along the polymer chain, has been prepared and investigated in this paper. The homogeneously distributed HP groups not only provide polymer stability but also form a completely polymer network under elevated temperatures. In a TGA comparative test, the PE-HP copolymer with 1.1 mol% HP concentration demonstrates no weight loss after heating at 190 °C in air for 1000 min, while the commercial HDPE exhibits weight loss within 100 min. A standard ASTM oxygen induction time (OIT) test also shows heat flow to commercial HDPE after 15 min at 190 °C in air, while the PE-HP copolymer with 1.1 mol% HP groups shows a complete flat OIT line up to 230 min, without any detectable onset heat flow into the sample. This new PE-HP copolymer shall expand HDPE application to high temperatures (>150 °C). [ABSTRACT FROM AUTHOR]

As diene rubber products are generally fabricated with complicated curing package involving toxic additives, the exploration of alternative green curing chemistry for diene rubber is of great importance. In this contribution, we demonstrate a curing chemistry based on oxa-Michael reaction for diene rubber to achieve the combination of simple curing system and tunable mechanical properties. Specifically, pendent hydroxyls are introduced onto the solution-polymerized styrene-butadiene rubber (SSBR) via thiol-ene click reaction and the modified SSBR is effectively cured by various acrylates without the use of any additional additives. The mechanical behaviors of vulcanizates can be widely regulated by manipulating the network structures, which is tuned by curing temperature, hydroxyl content of SSBR, content and functionality of acrylates. The correlation between mechanical properties and network structure is accordingly achieved, which provides essential basis for the future application of the diene rubbers cured by oxa-Michael reaction. [ABSTRACT FROM AUTHOR]

Hydrocarbon permselective membranes comprising of Poly (dimethylsiloxane) (PDMS) with Zeolitic Imidazole Framework (ZIF)-8 nanocrystals have been explored. ZIF-8—PDMS membranes of different ZIF-8 loadings were prepared in different solvents. The polymer chain conformations were observed by Ornstein-Zernike model fit to their small-angle neutron scattering profiles. The chain conformations were found to be varied for the membranes with different ZIF-8 loadings. The Debye-Anderson-Brumberger model showed larger scattering domains for the ZIF-8—PDMS membranes prepared in toluene than the membranes prepared in n -heptane. The membrane (toluene) of optimal ZIF-8 loading exhibited ∼60% increment of hydrocarbon permeability but ∼2% increment of N 2 permeability as against ∼300% increment of hydrocarbon permeability and >30% of N 2 permeability for the membrane ( n -heptane) of the similar ZIF-8 loading. This different phenomenon of hydrocarbon permeability enhancement for the membranes with the ZIF-8 loading can be attributed to their different membrane nanostructures. [ABSTRACT FROM AUTHOR]

Epoxy thermoset resins are widely used in industry due to their favorable thermomechanical properties. These properties depend strongly on the resin network topology formed during cure. In the past, there has been significant work to develop methodologies that simulate the cure process to predict the thermoset network topology and the properties of that network. However, very few of these simulations include anything more than a distance based criteria when determining which species in the simulation will bond. In this work, we show the importance of including additional bonding criteria based on the reaction kinetics for the system of interest. We simulate the cure of a model epoxy resin system, DGEBF and 44DDS, where the relative reaction rates, k 2 /k 1 , of epoxy-primary amine, and epoxy-secondary amine reactions are systematically varied to investigate the effect of competitive primary and secondary amine reactivity on the development of network structure and properties. [ABSTRACT FROM AUTHOR]

Liquid silicone rubber (LSR) is becoming increasingly popular due to its chemical, UV, and heat resistance as well as its excellent optical properties. However, there is currently a lack of research and understanding of the rheological properties of the material. During the processing of liquid silicone rubber, the material can assume different rheological states. In the present work, both the physical and the chemical gel behavior are investigated rheologically. For this purpose, measurements are carried out with a rotational rheometer and a high-pressure capillary rheometer. Depending on the temperature and pre-shear rate, times are given for the physical gel point, after which a significantly destroyed physical network is recovered. Investigations at higher temperatures, which lead to chemical crosslinking and, therefore, to a chemical gel point, resulted in a representation of the temperature-dependent chemical gel point. The presented results serve as a material database for reliable simulations. [Display omitted] • Uncured Liquid Silicone Rubber (LSR) has both a physical and a chemical gel point. • In the unstressed state, uncrosslinked LSR can also be present as a physical gel at room temperature. • The physical gel of hydrogen bonds, entanglements, Van-der-Waals forces and filler-matrix interaction can be destroyed by pre-shearing. • Depending on temperature and pre-shear rate, the reversible network rebuilds to a physical gel in a very short time. • A chemical gel replaces the physical gel at higher temperatures and is irreversible due to the formation of covalent bonds. [ABSTRACT FROM AUTHOR]

The selective distribution of silica nanoparticles(NPs) grafted with crosslinked poly(methyl methacrylate) (PMMA) in PMMA/poly(styrene- co -acrylonitrile) (SAN) blend is investigated by varying the crosslinking degree of grafted PMMA. NPs grafted with highly crosslinked PMMA chains mainly tend to be located in the PMMA-rich domains, while NPs grafted with linear PMMA chains mainly tend to be distributed at the interface of blend matrix. NPs grafted with slightly crosslinked chains are located partially at the interface and partially in the PMMA-rich domains. The deviation between the theoretical predication and actual location of modified NPs may be related with the heterogeneity of miniemulsion polymerization. Furthermore, different location of three modified NPs induced by different grafted chain structure may result in their various compatibilization effects on PMMA/SAN blend. NPs grafted with linear or slightly crosslinked PMMA aggregate at the interface of blend matrix to form the jamming structure and further inhibit completely the domain coarsening. [Display omitted] • Grafted chains structure for NPs determines their distribution in the blend matrix. • Different grafted NPs result in various compatibilization effects on blend matrix. • NPs at the interface forming jamming structure inhibit the domain coarsening. [ABSTRACT FROM AUTHOR]

With a diffusion-assisted post-crosslinking method, polymer microspheres containing epoxy groups are crosslinked with ethylenediamine (EDA), gradually diffusing and reacting in the particles via amine/epoxy ring-opening reactions as confirmed by FT-IR and DSC results. Using a microcompression test, we find that the mechanical property (deformability under different applied force, breaking points, and recoverability) of the crosslinked microspheres is varied when different amounts of EDA are used in the system, resulting from different crosslinking density of the particles. An additional feature of the EDA treatment is to generate amine groups on the surface of the microspheres, enabling us to produce hybrid microspheres. We exploit them as immobilization sites for gold nanoparticles, forming gold-coated crosslinked microspheres. We also introduce a sequential functionalization method to fabricate crosslinked microspheres with selective functional groups on the surface. This approach can be a facile method to produce functional microspheres with controlled mechanical and surface properties. [ABSTRACT FROM AUTHOR]

A highly robust and flame retardant borate-crosslinked poly (vinyl alcohol)/montmorillonite aerogel is fabricated through a novel melt-crosslink method. In this way, the PVA/MMT hydrogel was prepared by immersing the frozen PVA/MMT sol into a borax solution, inducing crosslinking between diols of PVA and borate exactly during the ice melt. As a result, rearrangement of the polymer chains and subsequent expansion result in finer and more compact network. The corresponding aerogel is obtained by freeze-drying. The optimal crosslinking conditions, including the borax concentration and crosslinking time, are determined by rheology of the hydrogels. This method provides a new idea for the preparation of crosslinked aerogels and improvement of mechanical and flame retardant properties simultaneously. The mechanical strength of the crosslinked aerogel is relatively high among the existing fire safety polymer/nanoclay composite aerogels with 30%–60% loading of inorganic matters at a low density level. The flame retardant properties are indicated by significant improvements of limiting oxygen index (LOI) to a value of 27.6% and achievement of UL-94 V-0 rating and remarkable decrease of the fire indexes in cone calorimetry (CC) test. The combustion behaviors are further studied by the results of SEM, energy dispersive X-ray spectrometer (EDX) and X-ray photoelectron spectroscopy (XPS). [ABSTRACT FROM AUTHOR]

We demonstrate the reattachment of two chemically-crosslinked poly(ethylene oxide) (PEO) matrix samples prepared with the γ-ray irradiation method by a simple wetting process with a good solvent. The fractured polymer samples can be attached through chain diffusion, interpenetration into a crosslinked network, and intermixing/reentanglement. Reattached samples exhibit similar macro/microstructure and mechanical properties to those of pristine samples. This effective recovery process without any additional reactive chemicals or external stimuli highlights the importance of extending the use of simple, but fundamental, dynamic behaviors of polymer chains to obtain the desired properties as well as offering a unique and useful route toward effective healable materials. [ABSTRACT FROM AUTHOR]

An algorithm capable of incorporating multi-step reaction mechanisms into atomistic molecular dynamics simulations using traditional fixed valence force fields is proposed and implemented within the framework of LAMMPS (Large-scale Atomic Molecular Massively Parallel Simulator). This extension, referred to as fix bond/react , enables bonding topology modifications during a running MD simulation using pre- and post-reaction bonding templates to carry out a pre-specified reaction. Candidate reactants are first identified by interatomic separation, followed by the application of a generalized topology matching algorithm to confirm they match the pre-reaction template. This is followed by a topology conversion to match the post-reaction template and a dynamic relaxation to minimize high energy configurations. Two case studies, the condensation polymerization of nylon 6,6 and the formation of a highly-crosslinked epoxy, are simulated to demonstrate the robustness, stability, and speed of the algorithm. Improvements which could increase its utility are discussed. [ABSTRACT FROM AUTHOR]

Development of ionically crosslinked superabsorbent polyacrylic acid (PAA) self-healing hydrogels using trivalent aluminum ions was investigated. The PAA hydrogels exhibited excellent self-healing behavior depending on the amount of the aluminum within the matrix. The migration of these ions within the polymer matrix was responsible for the physical crosslinking of the hydrogel and the origin of self-healing ability. The PAA-Al hydrogels were insoluble in water and exhibited significantly high degree of swelling (∼4000%). Hydrogel also exhibited good mechanical properties with high level of elongation. Excellent self-healing efficiency was observed under dynamic as well as oscillatory rheological measurements. The presence of Al ions within PAA hydrogel facilitated the self-healing ability because of the ionic interaction in these gels which plays the key role of dynamic reversible sacrificial bonds which reforms upon reversal of the deformative force. [ABSTRACT FROM AUTHOR]

Cobalt based driers are the most commonly used primary catalysts in alkyd coatings as they promote fast drying and lead to hard coatings. However, several studies have suggested potential reclassification of cobalt-based alkyd driers. Therefore, cobalt based driers are being replaced by alternatives, e.g. based on iron or manganese. In practice primary driers (Co, Mn, or Fe) are used in combination with secondary driers (e.g. Ca, Zr) to enhance drying of the film. Coating formulators aim for a high drying speed and hardness development. However, each combination of primary and secondary driers leads to a different oxidative drying pattern resulting in variations in the crosslink density and hardness development. In this study we have systematically investigated the effect of two secondary driers, Calcium (Ca) and Zirconium (Zr), on curing behavior when added to different primary driers (Co, Mn, and Fe) using a high spatial resolution NMR set-up. As expected, we observed increased drying speed and higher crosslink densities when adding these secondary driers. While calcium showed to promote the front speed, zirconium showed to increase the measured crosslink density. The behavior seems to be generic as this was seen for all three the primary driers. [ABSTRACT FROM AUTHOR]

Due to their chemical and morphological versatility, polyurethanes may be susceptible to fabrication conditions (curing procedure, moisture). Industry reports ‘maturation’ phenomena, i.e. unstable mechanical properties of PU elastomers and PU based adhesive joints right after fabrication. This paper elucidates the impact of fabrication conditions and possible causes of maturation. Chemical and physical bulk properties of a crosslinking two-part PU are monitored during and after cure in dry atmosphere (at room temperature followed by a post-cure). The influence of curing procedure is revealed by processes characteristic of the post-cure, i.e. chemical side reactions (allophanate, carbodiimide) and a new dielectric relaxation. Tensile tests demonstrate the practical relevance of the findings (mechanical modulus). Properties of the fully crosslinked, dryly stored PU are stable during a three-week observation, indicating that maturation is preventable by complete cure and dry conditions. In contrast, chemical crosslinking after an insufficient cure likely causes maturation phenomena. [ABSTRACT FROM AUTHOR]

Commonly used crosslinking methods for polyethylenes result in the release of harmful by-products. Here, we demonstrate that an epoxy-bearing polyethylene copolymer, which contains 8 wt% glycidyl methacrylate, can be efficiently crosslinked without by-product formation. Click chemistry based on multifunctional amine curing agents, which carry at least two functional groups separated by a flexible spacer, was used to prepare thermosets. Compounding of the crosslinker and copolymer through extrusion at 120 °C could be carried out without onset of the curing reactions. Careful adjustment of the curing time and temperature, ranging from 20 to 120 min and 160–200 °C, resulted in a high network density of at least 2.8 crosslinks per 1000 carbons at a curing agent stoichiometry of as little as 0.5 wt%. [ABSTRACT FROM AUTHOR]

The organic-inorganic networks involving poly(propylene oxide) (PPO) and POSS were synthesized via the in situ crosslinking with disulfide bonds. First, a tri-armed PPO star with amino termini was reacted with 4-(phenoxymethyl)-1,3-dithiolane-2-thione, a cyclic five-membered thiocarbonate to obtain the tri-armed PPO star with mercapto thiourethane termini. In the meantime, 4-aminobutylhepta(3,3,3-trifloroproply) POSS was also reacted with 4-(phenoxymethyl)-1,3-dithiolane-2-thione to obtain a mercapto thiourethane -functionalized POSS macromer. Thereafter, both PPO star and POSS macromer which contained mercapto thiourethane moieties were co-crosslinked via the radical coupling reaction, in which the thiol groups were coupled into disulfide bonds. The POSS-containing PPO networks were microphase-separated. It was found that the POSS cages grafted onto PPO networks were self-organized into the spherical nanodomains. Compared to the control network, the nanocomposites displayed the improved thermomechanical properties and surface hydrophobicity. More importantly, the organic-inorganic networks were self-healable and can be repeatedly processed without sacrificing the mechanical strengths. The exchange reaction of dynamic disulfide bonds is attributable to the self-healing or/and reprocessing properties. In addition, the break and reform of the POSS microdomains are also contributable to the reprocessing behavior at elevated temperature. [Display omitted] • Networks of poly(propylene oxide) with POSS were crosslinked with disulfide bonds. • Disulfide bonds were in situ generated via the radical coupling reaction. • The networks displayed self-healing or/and reprocessing properties. [ABSTRACT FROM AUTHOR]

A uniform dispersion of reactants is necessary to achieve a complete reaction involving multiple components. Utilizing a combination of infrared spectroscopy, thermal analysis and low field NMR, we have elucidated the role of three types of reactive plasticizers on the crosslinking reaction between hexamethylenetetramine and phenol formaldehyde resin. These two seemingly dissimilar reactants are responsible for the exceptionally high mechanical strength in a number of organic-inorganic composites. The efficiencies of the curing reaction and the achieved crosslinked structures are strongly dependent on the type of plasticizer employed. Infrared active vibrations are used to characterize the changing molecular structures of the individual reactants as a function of temperature. The T 1 spin-lattice relaxation time measured using low field NMR is especially useful for the characterization of segmental dynamics of the chains in the formation of the extremely rigid crosslinked product. This study shows that the amount of crosslinking and the crosslinked structure can be very different for the three types of reactive plasticizers and also different in comparison to non-reactive plasticizers. We are also able to correlate the reactivity and functionality of the plasticizer to the crosslink density in the reacted product. [ABSTRACT FROM AUTHOR]

We present the results of applying a computationally efficient Monte Carlo (MC) method to simulate the reaction kinetics and molecular architecture development during free-radical, bulk copolymerizations of a homologous series of methacrylate monomers with ethylene glycol dimethacrylate. The overall objective of the work was to determine the extent to which the ester side chains of the methacrylate monomers hinder chain-end radical propagation reactions through the pendent vinyl groups of the crosslinking monomer. We have determined that this steric hindrance is quite significant and increases with ester side chain length. This is expressed by a reduced reactivity parameter, Ψ C , X , that is different for each monomer–crosslinker pair. With this single kinetic parameter adjustment, the MC model was able to effectively predict the reaction kinetics, gel points, and sol−gel fractions throughout the entire reactions, including, to a limited extent, the solvent swelling ratio of the gel for two different levels of crosslinker. [ABSTRACT FROM AUTHOR]

Polymer dielectrics with outstanding temperature resistance and mechanical properties are expected to be used in 5G communication systems. Here, self-reinforced cross-linked polyarylene ether nitrile (CPEN) films were rationally designed and fabricated by introducing polyarylene ether nitrile terminated with hydroxyl (PEN-OH) into phthalonitrile end-capped polyarylene ether nitrile (PEN-Ph) and applying post-solid phase chemical reaction. For the catalytic effect on cross-linking reaction and crystallization enhancement of PEN-OH, the comprehensive performance of composite had been greatly improved, which showed a synergistic effect of crosslinking-crystallization. Intriguingly, properties of CPEN films can be finely tuned with the increase of PEN-OH crystallinity. The results show that CPEN films have excellent overall performance with a T g of 390 °C, a long service life at 300 °C (4.05 × 102 min, 95 wt% residual weight), and low dielectric constant of 2.9. More commendably, CPEN film possessed a higher tensile modulus (3.6 GPa) of over 194% compared to the untreated film due to the crystals immobilized by chemical crosslinking reaction. Tuning the properties of composites by modulating the crosslinking-crystallization behavior opens up a new way to design high-performance polymeric dielectric materials. [Display omitted] • PEN-OH is firstly applied as a novel catalyst and plasticizer to reinforce PEN-Ph. • The mechanical of composites is sharply improved through crystals anchor. • The thermal property of composite shows significant improvement after crosslinking. • The crosslinking density of composites was adjusted by the PEN-OH molecular-weight. [ABSTRACT FROM AUTHOR]

Seven ethylene-octene copolymers (EOC) with a wide range of octene content (17–45 wt. %) were crosslinked by e-beam radiation (in range 30–120 kGy). Testing methods included differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), high-temperature creep test, analysis of the gel content and rheology. It has been found that copolymers with higher initial molecular weight (or lower MFI) and higher branching density (or higher octene content) attain a higher level of crosslinking density. Increasing octene content brings about lower melting point (T m ), crystallization temperature (T c ), crystallinity (X), glass transition temperature (T g ) and storage modulus. Crosslinking influenced the properties below T m only marginally. However, the properties above T m were extremely influenced (high temperature creep). Above T m (without the presence of crystals) only the chemical bonds hold the amorphous chains together which was manifested by creep gradually decreasing at 150 °C with an increasing irradiation level. Loss factor (tanδ at 0.1 Hz), which is a very important parameter in evaluation of molecular structure, was measured by rheology at 150 °C, and it revealed a decreasing trend (or increasing crosslinking level) with the increasing octene content, surprisingly regardless of the initial molecular weight (or MFI) at 120 kGy. [ABSTRACT FROM AUTHOR]

The generation of graphene nanocomposites by curing of a new resin material via the Cu(I) catalyzed azide-alkyne click reaction (CuAAC) has been investigated by using graphene supported copper nanoparticles (TRGO-Cu 2 O) as catalyst directly embedded into the curing resin. Low molecular weight trivalent azide and alkyne were used as resin-components for “click” crosslinking by graphene supported copper nanoparticles (TRGO-Cu 2 O) in comparison to different commercially available homo- and heterogeneous copper catalysts. The kinetics of the crosslinking process were investigated by differential scanning calorimetry (DSC) and melt rheology, proving the superior performance of the (TRGO-Cu 2 O). Additionally the physical and mechanical properties of the finally cured resins were studied via melt-rheology, broadband dielectric spectroscopy (BDS) and thermogravimetric analysis (TGA), proving the outstanding catalytic activity of the TRGO-Cu 2 O catalyst performing “click” crosslinking without addition of base or oxidizing/reducing agents. Along with its catalytic performance, TRGO-Cu 2 O acts as reinforcing filler, significantly improving the mechanical and physical properties, as well as the conductivity and the thermal stability of the final resin material. [ABSTRACT FROM AUTHOR]

In the present work, a synthetic strategy based on oxazine-thiol ring-opening reaction for the synthesis of organogels is reported for the first time. For this purpose, main-chain polybenzoxazine (PBZ) was synthesized by the reaction of bisphenol A, 1,6-diaminohexane and paraformaldehyde in toluene:methanol mixture (2:1, v:v). The obtained reactive PBZ was then reacted at room temperature with dithiol compounds in CHCl 3 :CH 3 OH (1:1, v:v), namely 1,2-ethanedithiol and 1,6-hexanedithiol. The obtained PBZ based gels was characterized by spectral, thermal analysis and uniaxial compression measurements. The influences of the gel preparation conditions on the swelling behavior and the mechanical properties of the resulting gels were investigated. Swelling ratios (J) up to 8.4 in CHCl 3 :CH 3 OH solution was obtained. Moreover, the curing of the gels was performed over remaining oxazine moieties in the gels and the thermally activated curing was found to be at lower temperatures than that corresponding PBZ. [ABSTRACT FROM AUTHOR]

The reactions of methylenediphenyl 4,4’-diisocyanate (MDI) with hydroxy-terminated 4-armed star-shaped l -lactide oligomer (H4LAO n ) and 4-armed star-shaped ε-caprolactone oligomer (H4CLO n ) with the degree of polymerization per one arm, n = 3, 5 or 10 produced conetworks [MH4(LA/CL)O n s] with the feed H4LAO n /H4CLO n weight ratios of 75/25, 50/50 and 25/75. The formation of conetwork structures with different crosslinking densities was confirmed by the swelling test and FT-IR spectral analysis. Scanning electron microscopic analysis revealed that the oligolactate (LAO) and oligocaprolactone (CLO) segments are compatibilized for all the conetworks except for MH4(LA/CL)O 10 25/75. Differential scanning calorimetry and dynamic mechanical analyses revealed that all the conetworks are substantially amorphous, and that only one glass transition temperature ( T g ) was observed for each of the conetworks except for MH4(LA/CL)O 10 25/75. Tensile properties of MH4(LA/CL)O n s were largely affected by the influence of the T g value which changes according to the LAO/CLO ratio. MH4(LA/CL)O 5 50/50 ( T g : 33.3 °C) exhibited the highest tensile toughness among all the conetworks. [ABSTRACT FROM AUTHOR]

Novel terpolymers with furan and maleimide units as functional moieties for the reversible crosslinking by the Diels–Alder (DA) reaction with different polar and nonpolar co-monomers and linkers have been prepared for potential applications as self-healing coatings. The synthesized linear one-component systems are able to crosslink via the functional units in the side chain ( i.e. furan and maleimide) resulting in a highly crosslinked network. The terpolymers contain different maleimide methacrylates with three different linkers (MIMA 1, MIMA 2, MIMA 3), which vary in the length and the composition of the spacer unit as well as furfuryl methacrylate (FMA) as active units. Moreover, as polar co-monomers hydroxyethyl methacrylate (HEMA), dimethylaminoethyl methacrylate (DMAEMA) as well as 2-(hydroxyethoxy)ethyl methacrylate (DEGMA) and as nonpolar co-monomer butyl methacrylate (BMA) were used. The terpolymers were characterized using 1 H NMR spectroscopy and SEC measurements; the thermal properties were studied by TGA and DSC investigations as well as the self-healing properties by real-time analyses using a microscope equipped with a camera. [ABSTRACT FROM AUTHOR]

Functionalized hybrid monomers with crosslinking ability can provide advantages over the other monomers due to the flexibility of using it with any vinylic family of monomers. Azide alkyne click reaction is a convenient way of introducing triazole moieties into a molecule and opens up the possibility to add more functionality by suitable design of azide and alkyne compounds. In the present study, we report synthesis and use of new azide click linker containing allyl ether functionality, (3-(2-azidoethoxy) prop-1-ene) as a first example in the click reaction with a siloxane functionalized dialkyne to make a novel triazole, siloxane functionalized diallyl ether (TSDE) monomer. Chemical structure of the as synthesized TSDE, azide click linker and other compounds were characterized by FT-IR, 1 H NMR, 13 C NMR, and ESI-MS techniques. Hybrid coatings of TSDE with methyl methacrylate (MMA) were evaluated for chemical structure, morphology, wettability, tensile and thermal properties by FTIR, XRD, SEM, UTM, WCA, DSC & TGA. Experimental results from EPS and fog tests indicate significant enhancements in the anticorrosion and antibacterial performance of the as synthesized new Poly (MMA-co-TSDE) hybrid coatings in comparison to PMMA. [ABSTRACT FROM AUTHOR]

A series of cross-linkable membrane materials based on the 6FDA-DAM:DABA (3:2) polyimide with enhanced transport plasticization resistance were synthesized to separate CO 2 from CH 4 . Glycidol was used as a cross-linking agent to modify 6FDA-DAM:DABA (3:2) efficiently and form a transesterification reaction-based cross-linking. The conversion was calculated by solution 1 H NMR. These materials were also characterized via density, glass transition temperature, permeation, and sorption measurements. Pure (CO 2 , CH 4 ) and mixed gas (CO 2 /CH 4 ) permeation was studied on dense films of these materials up to 700 psia (1000 psia) for pure CO 2 (50%:50% CO 2 :CH 4 mixed gas) feed. Compared to the 6FDA-DAM:DABA (3:2) membrane, CO 2 -induced plasticization resistance for cross-linked membranes was enhanced in aggressive feed streams. Under CO 2 feed conditions at 35 °C, plasticization for the 41% glycidol-modified cross-linked membrane was not observed up to approximately 450 psia. Glycidol-induced cross-linking offers an excellent balance of selectivity, permeability, and plasticization resistance. The glycidol-modified 6FDA-DAM:DABA (3:2) is competitive with the earlier reported 1,3-propanediol modified materials. Possible issues such as resistance to contaminants may be final determinants in choice of approach; however, this topic was beyond the scope of the current study. [ABSTRACT FROM AUTHOR]

Three polyurethanes ( PRX1500Me-PU , PRX4000Me-PU , and PRX6000Me-PU ) crosslinked by polyrotaxanes (PRXs), which consist of half-methylated α-cyclodextrins (CyDs) and poly(oxyethylene)glycols with different chain lengths (PEG1500, PEG4000, and PEG6000), were synthesized. The filling ratios of CyD in PRX1500, PRX4000 and PRX6000 are 75, 63 and 37%, respectively. A polyurethane crosslinked by half-methylated CyD ( CDMe-PU ) was also prepared for comparison of their structure and properties. ATR-FT-IR spectra of the PUs showed that the formation ratio of hydrogen bond between the PU chains around PRXs increased with increase in the filling ratio. DSC and dynamic viscoelastic measurements and tensile tests for the PUs revealed that (i) reorganized-crystallization of the soft segment chains of PRX1500Me-PU easily occurred because of formation of a pure phase for them; (ii) the thermal and physical behaviors of PRX6000Me-PU are similar to those of CDMe-PU because CyDs as the crosslink points disperse in a similar fashion in the PUs; (iii) the PRX4000 with the moderate filling ratio of CyD in PRX4000Me-PU makes slow reorganized-crystallization of the soft segment chains in the PU as well as improves the tensile performance among the PUs. [ABSTRACT FROM AUTHOR]

High-performance polymer plays critical roles in 5G communication and electronic applications. Hence, special engineering plastic polyarylene ether nitrile (PEN) suitable for use in a harsh environment (T g ＞ 400 °C,T 5% ＞ 500 °C, and tensile strength 100 MPa) has been developed. Bisphthalonitrile (BPh) units form a flexible bridge between the nitrile of PEN. In the preparation, DDS acts as a catalyst and ZnCl 2 functions as both a catalyst and a reinforcing phase, to enhance the degree of crosslinking and mechanical properties of the resulting compositions. Therefore, the structure of a linear polymer is converted into a 3D network, resulting in greatly enhanced performance. The mode of action for DDS/ZnCl 2 and the transformation of nitrile groups has been described. These insights provide an understanding of the impact of crosslinking factors in structure formation and supply a feasible design strategy for the preparation of high-performance polymer films. [Display omitted] • BPh acts as a flexible bridge between the nitriles side groups of the PEN-CN. • ZnCl 2 uses as both a catalyst and reinforcing-phase to enhance PEN-CN. • The thermal property of PEN-CN/BPh/ZnCl 2 show significant improvement after modification. • The crosslinking structure plays a high-temperature-resistance role in polymers. [ABSTRACT FROM AUTHOR]

Crosslinking polymerization has been studied by means of a four-dimensional population balance model accounting for chain length, free pending double bonds, crosslinks, and multiradicals as dimensions. The model, for the first time and to a full extent resolves the crosslinking problem as formulated by Zhu et al. [1] and covers both pre-gel and gel regimes, in a straightforward manner. Approximations on radial basis functions have been employed to reduce the size of the system with minimal information loss. The model has been validated with data from an experimental crosslinking polymerization, Methyl Methacrylate with Ethylene Glycol Dimethacrylate. Non-trivial patterns in the time evolution of average quantities like crosslink densities, partly observed in prior studies [2-4], are naturally emerging from the model by computing marginals of the four-dimensional distribution possessing an interesting multimodal structure. [ABSTRACT FROM AUTHOR]