Flexible clear coats—Effect of curing conditions

The effect of curing at different conditions was investigated for flexible model clear coat films for coil coating applications. Based on a commercial polyester binder two formulations with isocyanate based crosslinking agents (hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI)) were prepared. The clear coats were baked at laboratory (145 °C) and industrial processing (300 °C) conditions. While for high temperature curing the baking time was kept constant at 30 s, the curing time at 145 °C, which is above the deblocking temperature of the crosslinking agents, was varied from 10 to 90 min. The clear coat films were characterized as to their thermomechanical and mechanical properties by dynamic mechanical analysis (DMA) and by tensile testing. Regarding DMA loading in tensile and penetration mode was performed.     

Synthesis and characterization of binary copolymers of methyl methacrylate with glycidyl methacrylate and 2‐hydroxy ethyl methacrylate as carriers for cellulase

Cellulase was immobilized directly on methyl methacrylate‐glycidyl methacrylate copolymer (MMA‐co‐GMA) and methyl methacrylate‐2‐hydroxy ethyl methacrylate copolymer (MMA‐co‐HEMA) by covalent attachment and crosslinking methods. The properties of the immobilized cellulase were investigated and compared with those of the free one. For the assays carried out through crosslinking method at 25°C and pH 7, the retained activities were found to be 91.92% and 74.63%, respectively, for MMA‐co‐GMA and MMA‐co‐HEMA crosslinked with 0.1% of 1‐cyclohexyl‐3‐(2‐morpholino‐ethyl) carbodiimide metho‐p‐toluenesulfonate (CMCT), respectively. The immobilized cellulase had better stability and higher retained activities with respect to pH, temperature, and storage stability than the free one. In the repeated use experiments, the immobilized cellulase using (MMA‐co‐GMA)‐CMCT (0.1%) and (MMA‐co‐HEMA)‐CMCT (0.1%) did not change after 10 and eight times of repeated use and maintained 67% and 62% from their original activities after 25 times, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Crosslinking of the electrospun gelatin nanofibers

Gelatin (Gt) nanofibers have been prepared by using an electrospinning process in a previous study. In order to improve their water-resistant ability and thermomechnical performance for potential biomedical applications, in this article, the electrospun gelatin nanofibers were crosslinked with saturated glutaraldehyde (GTA) vapor at room temperature. An exposure of this nanofibrous material in the GTA vapor for 3 days generated a crosslinking extent sufficient to preserve the fibrous morphology tested by soaking in 37 °C warm water. On the other hand, the crosslinking also led to improved thermostability and substantial enhancement in mechanical properties. The denaturation temperature corresponding to the helix to coil transition of the air-dried samples increased by about 11 °C and the tensile strength and modulus were nearly 10 times higher than those of the as-electrospun gelatin fibers. Furthermore, cytotoxicity was evaluated based on a cell proliferation study by culturing human dermal fibroblasts (HDFs) on the crosslinked gelatin fibrous scaffolds for 1, 3, 5 and 7 days. It was found cell expansion took place and almost linearly increased during the course of whole period of the cell culture. The initial inhibition of cell expansion on the crosslinked gelatin fibrous substrate suggested some cytotoxic effect of the residual GTA on the cells.     

Synthesis and evaluation of a composite crosslinked copolymer as a particulate fluid diversion agent

To meet the needs for polymer particulates for the flooding of oil fields, a composite crosslinked copolymer of hydrophilic monomers [acrylamide (AM) and acrylic acid (AA)] and a hydrophobic monomer [methyl methacrylate (MMA)] was synthesized. In this study, we first added a rare‐earth thermal stabilizer and inorganic montmorillonite (MMT) clay to the copolymer; this showed that the composite crosslinked copolymer exhibited good water‐swelling performance at 200°C, with gel static grade of 5, a toughness index of 1.1170, and a salinity limit of 250,000 mg/L. It also had better injection abilities. The AM/AA/MMA ratio was 4 : 1 : 0.03 w/w, the crosslinker additive content was 0.03 wt %, the thermal stabilizer additive content was 5 wt %, and the clay (MMT) additive content was 13 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4429–4433, 2006     

Synthesis, mechanical properties and chemical/solvent resistance of crosslinked poly(aryl-ether-ether-ketones) at high temperatures

A synthetic two-stage procedure was developed for the synthesis of moderately crosslinked polymers based on poly(aryl-ether-ether-ketone) (PEEK). Rigid crosslinks based on aromatic imines were synthetically introduced into PEEK polymer matrix resulting in PEEK materials with various degrees of crosslinking. Two specific crosslinked PEEK polymers (5% and 10% of ketone groups crosslinked) were characterized and studied in detail. Thermomechanical properties, as well as chemical/solvent resistance of these materials at high temperatures (175-280 °C) were investigated and compared to the original PEEK material (Victrex 151G). The introduction of rigid crosslinks was shown to disrupt crystallinity of PEEK very efficiently. Because tensile properties of PEEK depend on its crystallinity, we observed a decrease in properties such as Young's modulus and the ultimate elongation, the extent of which depended on the degree of crosslinking. We also observed an improvement in the elastomeric properties of the crosslinked materials, such as decrease in initial permanent set during high temperature cyclic tensile testing. Mechanical creep behavior at high temperature also improved for crosslinked polymers vs the original commercial Victrex 151G in terms of a reduced irreversible creep component. All crosslinked materials showed excellent resistance to hot oily, acidic and basic environments, as well as excellent thermal stability. Overall, we were able to synthesize “softer” materials that are more rubbery at high temperature than commercial thermoplastic Victrex 151G; these elastomer-like materials showed promising mechanical properties for high temperature applications in hot/corrosive environments.     

Modification of porous suspension‐PVC particles by stabilizer‐free aqueous dispersion polymerization of absorbed monomers

The modification of porous PVC particles by an in‐situ stabilizer‐free polymerization/crosslinking of a monomer/crosslinker/peroxide solution absorbed within the PVC particles is presented. The modifying crosslinked polymers are polystyrene (PS) crosslinked with DVB (divinyl benzene), polymethyl methacrylate (PMMA) crosslinked with ethylene glycol dimethacrylate (EGDMA), and styrene‐MMA copolymer crosslinked with DVB. The modified PVC particles characterization includes polymerization yield, non‐extractables, ¹³C solid‐state CPMAS NMR, porosity measurements and also morphology and dynamic mechanical behavior (DMTA). The levels of nonextractable fractions found and ¹³C solid‐state CPMAS NMR results are indicative of low chemical interaction in the semi‐IPN PVC particles. Particle porosity levels and SEM observations indicate that styrene and MMA mainly polymerize within the PVC particles' bulk and just small amounts in the pores. MMA polymerization in the PVC pores is as crusts covering the PVC pore surfaces, whereas styrene polymerization in the PVC pores is by filling the pores. Dynamic mechanical studies show that tanδ and the storage modulus curves are influenced by the incorporation of PS and XPS but not by the incorporation of PMMA and XPMMA.     

Crosslinking of poly(vinyl alcohol) and poly(vinyl acetate) using poly(maleic anhydride‐alt−2,4‐dimethyl‐1,3‐pentadiene) as polyfunctional crosslinker and decrosslinking by ozone degradation

Crosslinking and decrosslinking reactions of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc) using an alternating copolymer of maleic anhydride and 2,4‐dimethyl‐1,3‐pentadiene (PMAD) as the polyfunctional crosslinker and subsequent ozone degradation are reported. PVA and PVAc are heated at 200 °C for 0.5 to 3 h in the presence of 5 to 30 wt % of PMAD in the solid state to obtain the corresponding crosslinked polymers. The reactions of a hydroxy group of PVA and an acetate group of PVAc with an anhydride group of PMAD slowly proceed to give insoluble polymers with a loose crosslinking structure. Almost no change in the thermal decomposition temperatures and the IR spectra is observed during the crosslinking reactions. The crosslinked PVA produces hydrogels with a high swelling ratio of 500 to 1700%, which are readily degradable during a reaction with ozone in water at 0 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44229.     

Structure–property relationship in copolymers of methacrylic acid esters. I. Thermal behavior

This article describes the synthesis and thermal characterization of copolymers of methyl methacrylate (MMA) and alkyl methacrylates. The copolymerization was carried out using different mol fractions (0.05–0.25) of alkyl methacrylates, i.e., octyl methacrylate (OMA)/decyl methacrylate (DMA)/lauryl methacrylate (LMA)/stearyl methacrylate (SMA), in the initial feed at 80°C. The copolymer composition was determined from ¹H-NMR. The thermal stability of the copolymers was investigated by thermogravimetric analysis and pyrolysis gas chromatography. A two/three-step degradation was observed in the copolymer samples. The monomers were the major product of degradation in most of the copolymers except in SMA/MMA copolymers where the product of side-group elimination was also observed. An attempt was also made to determine the yield of the monomers during degradation and then to evaluate the copolymer composition. © 1994 John Wiley & Sons, Inc.     

Effect of crosslinking on polyamide 11/butadiene-acrylonitrile copolymer blends

The effect of crosslinking of polyamide 11 and butadiene-acrylonitrile copolymer (nitrile rubber) was studied. The effect of static and dynamic crosslinking on blending are described. Static and dynamic crosslinking do not significantly improve impact strength of low-rubber-content PA11/NBR blends. For blends with dynamic crosslinking and high rubber contents, mechanical properties including impact strength improve. Thermal behavior of crosslinked PA11/NBR blends were studied by DSC and DMA. SEM was used for investigation of the effect of crosslinking on particle size and particle size distribution, phase morphology, and fracture surface morphology. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1605–1611, 1997     

Effects of dilution with PMMA and network formation on fluorescence from benzimidazolylphenylenes linked to PMMA network

N,N′‐5‐(2‐benzimidazolyl)‐1,3‐phenylenebis(methacrylamide) (BIPBMA) was synthesized and copolymerized with methyl methacrylate (MMA) by changing feed BIPBMA/MMA molar ratio. The swelling experiments suggest that these cross‐linked copolymers (c‐copolymers) have a polymer network structure. To compare with c‐copolymers, synthesized 3‐(2‐benzimidazolyl) phenylmethacrylamide (BIPMA) was copolymerized with MMA by changing feed BIPMA/MMA molar ratio. These linear copolymers (l‐copolymers) were dissolved in N,N‐dimethylacetamide (DMA). The fluorescence spectra of c‐copolymers were well fitted by trial‐and‐error contraction with sums of five or less of Lorentzian equations. The fluorescence spectra of l‐copolymers were so distributed that only the initial peak was fitted to a single Lorentzian equation. The fluorescence spectra of BIPBMA/DMA solutions with various concentrations were also fitted to sums of five or less of Lorentzian equations. The fitted coefficients were used to quantify dilution effect. The fluorescence intensity of c‐copolymers is higher than that of l‐copolymers in a same chromophore concentration. A relation between the intensity and the chromophore concentration shows a concentration quenching owing to chromophore aggregating for c‐copolymer, l‐copolymer, and the solution. A critical concentration point before which the intensity increases appeared in the plots of intensity against concentration for the c‐copolymer and the solution. The critical point of the c‐copolymer is higher than that of the solution and that of the l‐copolymer (if observed). This suggests that the network formation and the dilution break up the chromophore aggregates. The fluorescence spectra of c‐copolymers (1/200) adjusted by varying AIBN concentrations suggest that the fluorescence is independent of the extent of cross‐linking. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

叔胺型丙烯酸酯共聚物乳液室温可见光交联研究

本研究以甲基丙烯酸甲酯、丙烯酸丁酯、N -羟甲基丙烯酰胺、甲基丙烯酸二甲氨基乙酯为共聚单体进行乳液聚合制备叔胺基丙烯酸酯共聚物乳液 ,然后在该共聚物乳液中加入光敏性乙烯基不饱和单体和可见光下分解的光敏引发剂 ,共混物涂膜于自然光下室温固化交联。考察了光敏引发剂用量、交联单体种类和用量、交联时间对乳胶膜交联程度的影响。结果表明 ,以异丙基硫杂蒽酮为光引发剂 ,分别以甲基丙烯酸缩水甘油酯、三丙二醇二丙烯酸酯及三羟甲基丙烷三丙烯酸酯为交联单体时 ,乳胶膜交联度在 0 5～ 1h内 >70 % ,2h内 >80 %。     

Effect of crosslinking on the positive temperature coefficient stability of carbon black‐filled HDPE/ethylene‐ethylacrylate copolymer blend system

Carbon black‐filled high‐density polyethylene (HDPE)/ethylene ethylacrylate copolymer (EEA) blends were prepared and the effect of crosslinking of the blends on the positive temperature coefficient (PTC) stability was investigated. By irradiation and silane‐crosslinking methods, crosslinked composites with various degrees of crosslinking were obtained. Crosslinking of the matrix polymer led to the disappearance of the negative temperature coefficient (NTC) phenomenon. Also, the PTC intensity increased with an increasing degree of crosslinking. The PTC stability of silane‐crosslinked samples was notably improved at heat cycles of 140°C. This was sufficiently improved by both the silane‐ and radiation‐crosslinking methods when they were treated at 85°C. Therefore, the limiting temperature of self‐regulating heat is about 85°C. Both radiation‐ and silane‐crosslinked samples are thought to be of use to the industry.     

无三苯CR/SBS/MMA/BA自交联鞋用胶粘剂的研制

采用复合引发剂 ,以N 羟甲基丙烯酰胺 (NAM )及丙烯酸 (AA)为功能单体 ,与CR、苯乙烯 丁二烯嵌段共聚物 (SBS)、甲基丙烯酸甲酯 (MMA)和丙烯酸丁酯 (BA)进行多元共混接枝共聚 ,再配以混合型增粘树脂 ,研制出不含苯、甲苯和二甲苯 (简称三苯 )自交联环保型鞋用胶粘剂。探讨了SBS用量、MMA/BA配比、功能单体NAM及AA用量对胶粘剂粘合性能的影响。结果表明 ,CR/SBS/MMA/BA/AA/NAM自交联型接枝胶粘剂对非极性鞋材的粘合性能明显优于CR/MMA/BA三元接枝胶和CR/SBS/MMA/BA四元接枝胶。     

Tacticity of methacrylic copolymers and their crosslinked polymers studied by pyrolysis–gas chromatography

Diad tacticity of methyl methacrylate (MMA) sequences in the copolymers of MMA and various acrylates and their crosslinked polymers was characterized by pyrolysis–gas chromatography (Py‐GC) based on the relative peak intensities of the diastereomeric MMA tetramers in the pyrograms. The diad tacticity in the copolymers synthesized at a given temperature proved to be almost consistent with that of corresponding MMA homopolymers (PMMA) prepared under the same conditions. Furthermore, the diad tacticity of PMMAs was also consistent with that of the corresponding crosslinked polymers. These results suggest that the tacticity of MMA sequences in the polymer chains would be dominated by polymerization temperature, independent of the copolymerization and crosslinking. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2140–2144, 2000     

Detection of the glass relaxation process of the PS-phase in block copolymers

The relaxation behavior of the glass process of the polystyrene (PS) phase in three different types of block copolymers has been investigated. Four triblock copolymers are used, namely, two styrene-butadiene-styrene (S-B-S), styrene-styrene butadiene-styrene (S-SB-S) and styrene-ethylene butylene-styrene (S-EB-S). The materials were crosslinked by means of dicumylperoxide (DCUP) with concentrations up to 10 phr, i.e. 10 g of DCUP per 100 g of the polymer. Dynamic mechanical measurements have been done for the complex shear compliance in wide temperature and frequency windows, 30-150 °C and 10⁻³-10 Hz, respectively. Complete master curves have been constructed for all samples and analyzed using Cole-Cole function. It is observed that crosslinking reduces the relaxation strength of the low frequency process much more than that of the high frequency process. Therefore, the glass relaxation process of the PS-phase can be easily detected in the crosslinked samples. The relaxation frequency of the maximum of the glass relaxation process of the PS-phase is found to be independent of the crosslinking concentration. The relaxation behavior of block copolymers with respect to crosslinking is compared to styrene butadiene rubber (SBR) statistical copolymer. A method to detect the glass transition temperature (T_g) of the investigated block copolymers is suggested.     

Carbon nanotubes prepared from three-layered copolymer microspheres of acrylonitrile and methylmethacrylate

Carbon nanotubes (CNTs) were synthesized from fine three-layered copolymer microspheres using the polymer blend technique. Diameter of PMMA core/Poly(AN-co-MMA) shell-1/PMMA shell-2 microspheres, prepared by a radical soap-free emulsion polymerization of methylmethacrylate (MMA) and acrylonitrile (AN), was between 400 nm and 500 nm. Microspheres were subjected to melt-spinning at 305 °C, stabilizing in oxygen at 220 °C for 4 h, and finally carbonizing at 1000 °C for 30 min. FE-SEM study of carbonized sample revealed the presence of CNTs arrays on carbon blocks. Similar arrays were observed in a comparative CNTs sample prepared from three-layered microspheres with the pure PAN shells-1 layers. HRTEM showed that the CNTs derived from copolymer microspheres had different structure when compared to the control sample, i.e. CNTs often adhered to each other and contained the internal compartments. The insufficient PMMA shell-2 coating of copolymer microspheres is believed to be a reason for CNTs adhesion. The possible mechanisms of the carbon block formation and the adhesion of CNTs are introduced.     

Novel benzoxazine monomer containing diacetylene linkage: An approach to benzoxazine thermosets with low polymerization temperature without added initiators or catalysts

A novel benzoxazine monomer containing diacetylene linkage has been synthesized by applying an oxidative coupling approach. The structure is confirmed by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. Differential scanning calorimetry (DSC) is used to study crosslinking behavior of synthesized material. The benzoxazine monomer exhibits unexpectedly low exothermic peak with the onset around 140 °C, which is significantly lower than conventional benzoxazines or benzoxazines containing additional crosslinking sites. Benzoxazine polymerization at this low temperature is also confirmed by FTIR. The initial model studies are made in order to understand this phenomenon and preliminary explanation is given. High thermal stability of the crosslinked thermoset was confirmed by thermogravimetric analysis (TGA).     

Crosslinking of PET through solid state functionalization with alkoxysilane derivatives

A new way for crosslinking poly(ethylene terephthalate) (PET) films and fibers is described using solid state functionalization of the PET end groups (alcohol and acid) with two reagents, respectively, 3-isocyanatopropyltriethoxysilane (IPTESI) or/and 3-glycidoxypropyltrimethoxysilane (GOPTMSI). This functionalization is then followed by hydrolysis-condensation reactions of PET-alkoxysilane end groups leading to the PET crosslinking.First of all, the functionalization reactions were investigated on model compounds by ¹H NMR spectroscopy in a range of temperature 80-160 °C. Furthermore, the diffusion of reagents in solid PET, depending on the initial degree of PET crystallinity, was characterized in the same temperature range through the variation of sample mass. On the other hand, this method allowed us to determine the diffusion coefficients and the solubility of the reagents in solid PET at different temperatures and initial crystallinity degrees.End groups functionalized PET films and fibers by alkoxysilane were then crosslinked by immersion of the samples in hot water. The crosslinking density was characterized by measuring the insoluble fraction of PET in good solvent constituted by a mixture of trifluoroacetic acid and dichloromethane (50/50 vol.). An insoluble fraction close to 70% was obtained by the functionalization treatment of amorphous PET film (8% crystallinity) by a mixture of GOPTMSI + IPTESI (50/50 M) at 155 °C for 1 h followed by hydrolysis-condensation reactions at 80 °C for 72 h. Thermomechanical and thermal properties of films and fibers were observed and found to be considerably enhanced in comparison to the untreated samples. The tensile properties of these partially crosslinked samples were maintained up to 320 °C.     

Thermal crosslinking of ethene copolymers containing 1,2-cyclopropane units

The possibility to obtain crosslinked polyethene (XLPE) from new ethene copolymers containing cyclopropane rings (C3), synthesized by ethene/1,3-butadiene copolymerizations with a hindered metallocene catalyst, has been explored. In particular, the thermal crosslinking of these copolymers, for C3 molar content in the range 0.3-2.7%, has been studied for annealing temperatures up to 200 °C and compared with the thermal behavior of other ethene-butadiene copolymers. Only for the ethene-C3 copolymers, the annealing procedures in the temperature range 160-200 °C lead to high gel fractions. These crosslinking processes occur in reasonable times and leave nearly unaltered the polymer crystallinity. Moreover, annealing procedures up to 140 °C do not produce appreciable crosslinking. All these features suggest that these new copolymers could be suitable for possible industrial fabrication processes of XLPE.     

Copolymerisation of 1,9-decadiene and propylene with binary and isolated metallocene systems

1,9-Decadiene/propylene copolymers were obtained with isolated metallocenes and with a binary metallocene catalyst system activated by methylaluminoxane. The metallocenes under investigation were syndiospecific diphenylmethyl(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (1) and isospecific rac-dimethylsilylbis(4-tert-butyl-2-methyl-cyclopentadienyl)zirconium dichloride (2). A copolymer structure, in which 1,9-decadiene linked isotactic and syndiotactic polymer chains, was obtained when copolymerisation was started with catalyst 2 at 80 °C followed by injection of catalyst 1 and instantaneous lowering of polymerisation temperature to 40 °C after 15 min of polymerisation. The copolymer was also shown to work as a compatibiliser in a blend of syndiotactic and isotactic polypropylene. We propose that catalyst 2 incorporates 1,9-decadiene into the isotactic main chain without any significant crosslinking within the first 15 min of polymerisation at 80 °C and the produced isotactic macromonomers are further incorporated at 40 °C into the syndiotactic main chain in polymerisation with catalyst 1.