Crystallization of vulcanizates. I. Low‐temperature crystallization as a function of extent of cure for polyisoprene vulcanized with tetramethylthiuram disulfide/sulfur and 2‐bisbenzothiazole‐2,2′‐disulfide/sulfur

The crystallization of polyisoprene, vulcanized to various degrees of cure with tetramethylthiuram disulfide/sulfur and 2‐bisbenzothiazole‐2,2′‐disulfide (MBTS)/sulfur formulations, was studied in a density column at ?25°C. The densities of vulcanizates before crystallization decrease progressively with cure time, which is ascribed to an increase in free volume occasioned by the formation of accelerator‐terminated pendent groups on the polymer chain. The induction period before the onset of crystallization increases and both the rate of and the degree of crystallization decrease with extent of cure. This is attributed primarily to the presence of residual pendent groups on the polymer chain and secondly to crosslink formation. The changes are more marked with MBTS formulations where pendent groups are more bulky. MBTS compounds fail to crystallize once vulcanized to the point where a gel has formed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2565–2572, 2001     

Effect of carboxylic acids on 2‐bisbenzothiazole‐2,2′‐disulfide‐ and tetramethylthiuram disulfide‐accelerated sulfur vulcanization. II. Vulcanization of polyisoprene in the absence of ZnO

Polyisoprene was vulcanized by 2‐bisbenzothiazole‐2,2′‐disulfide (MBTS)/sulfur and tetramethylthiuram disulfide (TMTD)/sulfur in the absence and presence of benzoic and stearic acids. It was found that the crosslink density of MBTS vulcanizates is halved by the addition of carboxylic acids and this can be explained in terms of the attack of the acids on the accelerator polysulfides. TMTD polysulfides are more reactive toward polyisoprene than are MBTS polysulfides, and their addition to the polymer chain occurs before significant attack by the carboxylic acids can reduce the polysulfide concentration. Consequently, the acids have little effect on the crosslink density of TMTD vulcanizates. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1007–1012, 1999     

Polyisoprene,poly(styrene‐cobutadiene) and their blends. III. Tensile properties of tetramethylthiuram disulfide/sulfur and 2‐bisbenzothiazole‐2,2'‐ disulfide/sulfur compounds

Polyisoprene (IR), poly(styrene‐cobutadiene) (SBR) and IR/SBR blends were vulcanized with tetramethylthiuram disulfide (TMTD)/sulfur and 2‐bisbenzothiazole‐2,2′‐disulfide (MBTS)/sulfur formulations and their tensile properties were determined. MBTS vulcanized IR has inferior tensile properties to TMTD vulcanizates. This is attributed in part to main chain modification in MBTS vulcanizates decreasing the ability of chains to crystallize or to align as effective load‐bearing chains under stress. A similar discrepancy is not found in SBR compounds that cannot stress‐crystallize. Polybutadiene, which readily crystallizes on cooling, is used to demonstrate differences in the effect of MBTS and TMTD on the ability of chains in the vulcanizates to align. These differences are confirmed by X‐ray diffraction studies of stressed IR vulcanizates. The addition of zinc stearate reduces main chain modification, promotes crystallization, and improves tensile properties. Blends have inferior properties to IR, and tests involving the pulling apart of laminates and analysis of the tear surfaces are used to illustrate that failure does not occur in adhesion, but within the IR phase close to the interface. It is argued that diffusion of curatives from SBR to the faster curing IR phase, leads to the development of a layer of highly crosslinked material in IR close to the phase boundary. Failure occurs in this layer and may be attributed to a decrease in the number of effective load‐bearing chains in this region or to the shorter chains in this layer becoming taut. Less diffusion of the accelerator occurs with MBTS than with TMTD, leading to a less highly crosslinked IR zone close to the interface. Consequently, higher loads are required to initiate failure. Failure in blends is likewise considered to initiate in the highly crosslinked region in the IR phase close to the phase boundary with SBR. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2143–2149, 1999     

The tensile properties of strain‐crystallizing vulcanizates. III. The superiority of conventional over peroxide vulcanizates in terms of network microstructure

It is proposed that, when vulcanization is performed using peroxides, crosslinking leads to a simple network, whereas in conventional vulcanization crosslinking a partially interpenetrating polymer network (PIPN) is formed. Two unfilled polyisoprene networks of similar crosslink density, produced with dicumyl peroxide and 2‐bisbenzothiazole‐2,2′‐disulfide/sulfur formulations, were compared with respect to the effect of strain rate on their stress–strain and hysteresis curves at room and elevated temperatures. At high elongations, the stress–strain curves for peroxide vulcanizates show a steeper upturn than for conventional vulcanizates, but have lower tensile strength and elongation at break. On increasing the extension rate, stress–strain curves for peroxide vulcanizates rise less steeply, while conventional vulcanizates rise more steeply. For both vulcanizates the hysteresis ratio decreases on increasing the rate at which samples are extended and retracted. The effect on conventional vulcanizates is less than on peroxide vulcanizates. It is suggested that chains in peroxide networks disengage increasingly rapidly at higher strains, allowing increased strain‐induced crystallization. Rapid strain‐induced crystallization leads to low ultimate tensile strength (UTS). In more complex PIPNs, the disengagement and alignment of chains are retarded. The increased nonuniform extension of chains promotes early strain‐induced crystallization at low extensions, but overall it reduces the rate of crystallization, which occurs over a wider range of strains. This improves UTS and elongation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 876–884, 2006     

Effect of heterogeneities on the physical properties of elastomers derived from butadiene cured with dicumyl peroxide

The scope of this paper is to continue our earlier study of the peroxide curing of elastomers derived from butadiene. Experimental evidence indicates that abstraction of allylic hydrogen and addition to the double bonds can act as a mechanism for cross‐linking. The addition reaction may give rise to a polymerization reaction between adjacent double bonds, thus generating a heterogeneous network, with negative effects on the physical properties of the vulcanizates. Copyright © 2004 Society of Chemical Industry     

Synthesis and adsorption properties,toward some heavy metal ions,of a new polystyrene‐based terpyridine polymer

A novel polymeric ligand having 2,2′:6′,2″‐terpyridine as pendant group was prepared through a Williamson type etherification approach for the reaction between 4′‐hydroxy‐2,2′: 6′,2″‐terpyridine and the commercially available 4‐chloromethyl polystyrene. The chelating properties of the new polymer toward the divalent metal ions (Cu²⁺, Zn²⁺, Ni²⁺, and Pb²⁺) in aqueous solutions was studied by a batch equilibration technique as a function of contact time, pH, mass of resin, and concentration of metal ions. The amount of metal‐ion uptake of the polymer was determined by using atomic absorption spectrometry. Results of the study revealed that the resin exhibited higher capacities and a more pronounced adsorption toward Pb²⁺ and that the metal‐ion uptake follows the order: Pb²⁺ > Cu²⁺ > Zn²⁺ > Ni²⁺. The adsorption and binding capacity of the resin toward the various metal ions investigated are discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of waterborne polyurethane with outstanding fluorescence properties and programmable emission intensity

The hard segment content and hydrophilic group content of a fluorescent waterborne polyurethane (FWPU) were used to optimize the polymer structure which can influence the fluorescence properties. The synthesis of FWPU was based on 2,2′‐((4‐([3,3′:6′,2″‐terpyridine]‐4′‐yl)phenyl)azanediyl)diethanol (TPPDA) as fluorophore. The structure of FWPU was characterized using Fourier transform infrared and ¹H NMR spectroscopies, and the polymer molecular weight and polydispersity were measured using gel permeation chromatography. The relationship between fluorescence properties and FWPU structure was studied using luminescence spectrometry. Compared to TPPDA, the maximum emission wavelength of FWPU showed a hypsochromic shift, and the fluorescence emission intensity and quantum yield of FWPU were increased obviously. Moreover, increasing the hard segment content led to an enhancement of the fluorescence lifetime of FWPU, and to the fluorescence intensity increasing at first and then decreasing. The fluorescence emission intensity and quantum yield of FWPU were increased nearly 11 and 7 times, respectively, compared to TPPDA when the hard segment content was 65%. With an increase of hydrophilic group content, the fluorescence emission intensity of FWPU increased. The fluorescence emission intensity of FWPU exhibited a response to pH, which facilitated its employment as a fluorescence probe. FWPU with excellent solid fluorescence is very suitable for processing into optical devices, with increasing hard segment content and hydrophilic group content both enhancing the solid fluorescence emission intensity of FWPU. © 2016 Society of Chemical Industry     

湿度对锦纶66帘线强伸性能的影响

进行了湿度对锦纶66帘线强伸性能影响的试验研究。通过统计分析断裂强力、断裂强力不匀率、定负荷伸长度、断裂伸长率、断裂伸长不匀率等旨标的试验数据并结合理论分析，得出随着相对湿度的增大，锦纶66帘线断裂强力下降，定负荷伸长率、断裂伸长率及断裂强力不匀率、断裂伸长不匀率增大的结论。     

Preparation and properties of novel fluorinated polyimides based on 2,2′,6,6′-tetrafluorobenzidine

Fluorinated polyimides were prepared from 2,2′,6,6′-tetrafluorobenzidine and four conventional dianhydride monomers by a solution polycondensation reaction followed by a chemical imidization. Polyimide based on 2,2′,6,6′-tetrafluorobenzidine and hexafluoroisopropylidene bis(3,4-phthalic anhydride) (6FDA) is soluble in organic solvents such as NMP, DMA, DMF, THF, chloroform, and acetone while those based on 2,2′,6,6′-tetrafluorobenzidine and pyromellitic dianhydride (PMDA), benzophenone-3,3′,4,4′-tetracarboxylic acid dianhydride (BTDA), diphenylether-3,3′,4,4′-tetracarboxylic acid dianhydride (ETDA) are not. Polyimide from 2,2′,6,6′-tetrafluorobenzidine and 6FDA possesses high optical transparency at 350–700 nm and has a in-plane refractive index of 1.558 at 632.8 nm. All polyimides exhibit glass transition temperatures above 350°C. They also possess very high thermal stability. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1605–1609, 1998     

Effects of addition orders on the properties of fluorine‐containing copolyimides

A series of fluorine‐containing copolyimides were synthesized by three different orders of addition of monomers. The fluorine‐containing copolyimides were prepared by the reaction of 4,4′‐diaminodiphenylmethane (DDM) with 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), and pyromellitic dianhydride (PMDA). The synthesis reactions of the copoly(amic acid)s (PA) were carried out by three different orders of addition of the monomers with different molar ratios of 6FDA to PMDA. The viscosity of the PA solution obtained by DDM–(6FDA+PMDA), that is, 6FDA and PMDA added simultaneously to DDM in N‐methyl‐2‐pyrrolidinone (NMP), was higher than the other two addition orders (i.e., DDM–6FDA–PMDA and DDM–PMDA–6FDA). The viscosity decreased as the relative amount of 6FDA to PMDA increased. The copolyimides formed by different addition orders but the same 6FDA‐to‐PMDA molar ratios contained different properties, such as dielectric constant, moisture absorption, contact angle, and optical transparency. All of these copolyimides were insoluble in common organic solvents, such as NMP and tetrahydrofuran. Thermogravimetric analysis showed that the onset temperature of 8% weight loss decreased slightly as [6FDA] : [PMDA] increased. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3252–3258, 2000     

Aerobic oxidative radical coupling catalyzed by TEMPO for the preparation of 2,2′‐dibenzothiazole disulfide

BACKGROUND: 2,2′‐disbenzothiazole disulfide is widely used as a vulcanization accelerator in rubber production and as an intermediate in the drug industry. Its current industrial process, the oxidation of 2‐mercaptobenzothiazole by sodium nitrite in acidic solution, produces large quantities of liquid waste water. A novel and green synthetic method was developed, which used dioxygen as the oxidant and 2,2,6,6‐tetramethylpiperidyl‐1‐oxyl (TEMPO) as the catalyst without any metallic compounds. RESULTS: The conditions, including temperature, solvents, amount of catalyst, dioxygen pressure and time, were optimized. Thus 94% yield of 2,2′‐disbenzothiazole disulfide was obtained at 60 °C in acetonitrile under 0.2 MPa oxygen pressure for 3 h. Theoretical calculations and UV spectra showed that hydrogen‐transfer reaction between 2‐mercaptobenzothiazole and TEMPO was the key step, and 2,2′‐disbenzothiazole disulfide was generated by the coupling of the formed thiyl radical of 2‐mercaptobenzothiazole. CONCLUSION: 2,2′‐disbenzothiazole disulfide was prepared efficiently by aerobic oxidative coupling of 2‐mercaptobenzothiazole with TEMPO as the catalyst. This ‘environmentally friendly’ approach with easy handling, mild reaction conditions and simple separation represents a viable means of producing 2,2′‐disbenzothiazole disulfide. Copyright © 2011 Society of Chemical Industry     

水在凝胶中的存在状态及其对凝胶力学性能的影响

以偶氮二异丁腈为引发剂,通过化学引发聚合合成甲基丙烯酸β-羟乙酯（HEMA）/N-乙烯基吡咯烷酮（NVP）二元共聚物和HEMA /NVP /甲基丙烯酸甲酯（或甲基丙烯酸丁酯）三元共聚物水凝胶,通过示差扫描量热法（DSC）结合热重法（TG）研究了不同单体配比的共聚物水凝胶中水的状态,证明了凝胶中存在3种不同状态的水：非冻结结合水、可冻结结合水和可冻结自由水.结果发现可冻结水的含量主要由NVP含量所决定,NVP单元基本不能键合水,而非冻结水的含量主要受HEMA含量和疏水性单体甲基丙烯酸酯含量影响.疏水性单体的引入使材料的力学强度提高,对凝胶体系具有增塑作用的是非冻结水而不是可冻结的结合水和自由水.     

Study on Terahertz Time‐Domain Spectroscopy of HNS by Sample Measure and Quantum Chemistry Calculation

The absorption spectra of 2,2′,4,4′,6,6′‐Hexanitrostilbene (HNS), in the frequency range between 0.2 and 4.0 THz, are calculated using quantum chemistry calculations and resulted in 1.9 THz and 3.3 THz. The experimental result offered by THz time‐domain spectroscopy and FTIR shows that the characteristic peaks are located at 1.7 THz and 3.1 THz. Compared with experimental results, all the evidences indicate that HNS has distinct characteristic peaks, which agree with the simulation results. It is believed that this method can detect this material quickly and accurately, which means a lot to the explosives detection.     

Influence of some additives on state‐of‐mix,rheological, tensile,and dynamic mechanical properties in SBR compounds

The influence of some additives (Flexon processing oil, Struktol WB 16 slipping agent, and Struktol NS 60 homogenizing resin) on state‐of‐mix, rheological, tensile, and dynamic mechanical properties were investigated. It was found that extrudate swell of the rubber compounds with either processing oil or NS 60 is governed mainly by the state‐of‐mix, but by wall slip in the case of compounds with WB 16. As for the dynamic mechanical properties, the plasticizing effect is the major factor controlling the properties in the case of processing oil, while the degree of crosslink and dilution effect are the main factors in the case of NS 60. Both degree of crosslink and state‐of‐mix are responsible for the dynamic mechanical properties in the case of WB 16. In addition, it was found that the tensile properties are controlled mainly by the plasticizing effect in the case of processing oil, but by the degree of crosslink in the cases of WB 16 and NS 60. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2474–2482, 2001     

Extraction properties of phthalic acid and aromatic polycarboxylic acids using various solvents

BACKGROUND: To explore the extraction properties of aromatic acids produced in the oxidation of coal, the extraction equilibrium of phthalic acid (as a typical product) was studied using three solvents, 1‐octanol, 50% tributylphosphate (TBP)/kerosene, and 10% trialkylphosphine oxide (TRPO)/kerosene, and the feasibility of separating phthalic, [1,1′‐biphenyl]‐2,2′‐dicarboxylic and trimellitic acids is discussed. RESULTS: Phthalic acid extraction followed the sequence: 10% TRPO > 50% TBP > 1‐octanol, with recoveries from the TRPO and TBP systems being much larger than that for 1‐octanol. The stoichiometry of formation of the complexes of TBP and TRPO with phthalic acid was 1:1. The apparent extraction equilibrium constant for TRPO is much larger than that for TBP. The distribution coefficient of [1,1′‐biphenyl]‐2,2′‐dicarboxylic acid is much larger than that of the other two acids using 1‐octanol as the extractant and this acid could be removed by 1‐octanol from a mixture of the three acids. The extraction equilibrium correlations obtained for the individual acid component systems can be used to predict that of the acid mixture. CONCLUSION: The extent of phthalic acid extraction by the three solvents investigated is as follows: 10% TRPO > 50% TBP > 1‐octanol. The stoichiometry of the complex formation of TBP or TRPO and phthalic acid is 1:1, and the apparent extraction equilibrium constant for TRPO is much larger than that for TBP. 1‐octanol shows a good extractive selectivity for [1,1′‐biphenyl]‐2,2′‐dicarboxylic acid as compared with phthalic and trimellitic acids. Copyright © 2011 Society of Chemical Industry     

Synthesis of novel polyurethanes containing dioxybenzylidenecyanoacetate,as non‐linear optical chromophores and their properties

Methyl 3,4‐di‐(2′‐hydroxyethoxy)benzylidenecyanoacetate (3) was prepared by hydrolysis of methyl 3,4‐di‐(2′‐vinyloxyethoxy)benzylidenecyanoacetate (2). Diol 3 was condensed with 2,4‐toluenediisocyanate, 3,3′‐dimethoxy‐4,4′‐biphenylenediisocyanate, and 1,6‐hexamethylenediisocyanate to yield polyurethanes 4, 5 and 6 containing the non‐linear optical (NLO) chromophore 3,4‐dioxybenzylidenecyanoacetate. The resulting polyurethanes 4–6 were soluble in common organic solvents such as acetone and DMF. T_g values of the polymers obtained from DSC thermograms were in the range 80–102 °C. Polymers 4–6 showed thermal stability up to 300 °C in TGA thermograms, and electro‐optic coefficients (r₃₃) of the poled polymer films were in the range 10–12 pm V^?1 at 633 nm, which are acceptable for NLO device applications. © 2002 Society of Chemical Industry     

Synthesis of novel poly(vinyl ether)s containing the oxybenzylidenemalononitrile group as a nonlinear optical chromophore,and their electro‐optic properties

2,4‐Di‐(2′,2′‐dicyanovinyl)‐1‐(2′‐vinyloxyethoxy)benzene and 2,4‐di‐(2′‐carbomethoxy‐2′‐cyanovinyl)‐1‐(2′‐vinyloxyethoxy)benzene were prepared by condensation of 4‐(2′‐vinyloxyethoxy)isophthaldehyde with malononitrile and methyl cyanoacetate, respectively. The two vinyl monomers were polymerized with boron trifluoride etherate as a cationic initiator to yield poly(vinyl ether)s containing two oxybenzylidenemalononitrile and oxybenzylidenecyanoacetate groups, which are effective chromophores for second‐order nonlinear optical applications. These polymers were soluble in common organic solvents such as acetone and dimethyl sulforide. They showed thermal stabilities up to 300 °C from thermogravimetric analysis (TGA), with differential scanning calorimeter (DSC) thermograms giving T_g values in the range 73–87 °C. The second harmonic generation (SHG) coefficients (d₃₃) of poled polymer films were around 1.8 × 10^?9 esu, and these polymers showed good long‐term thermal stability for 60 days at room temperature, which is acceptable for nonlinear optical (NLO) device applications. Copyright © 2004 Society of Chemical Industry     

An Efficient and Selective Epoxidation of Olefins with Novel Methyltrioxorhenium/(Fluorous Ponytailed) 2,2′‐Bipyridine Catalysts

Novel complexes between methyltrioxorhenium (MTO) and bis(fluorous‐ponytailed) 2,2′‐bipyridines (bpy‐F_n) were synthesized and used for the oxidation of alkenes with hydrogen peroxide under fluorous catalysis. High conversions and yields of the corresponding epoxides were obtained.     

Synthesis of Substituted 2,2′‐Bipyridines and 2,2′:6′,2′′‐Terpyridines by Cobalt‐Catalyzed Cycloaddition Reactions of Nitriles and α,ω‐Diynes with Exclusive Regioselectivity

A variety of substituted 2,2′‐bipyridines were synthesized by a 1,2‐bis(diphenylphosphino)ethane (dppe)/cobalt chloride hexahydrate (CoCl₂⋅6 H₂O)/zinc‐catalyzed [2+2+2] cycloaddition reaction of diynes and nitriles, with all reactions exhibiting exclusive regioselectivity. Thus, symmetrical and unsymmetrical 1,6‐diynes and 2‐cyanopyridine reacted in the presence of 5 mol % of dppe, 5 mol % of CoCl₂⋅6 H₂O and 10 mol % of zinc powder to provide the corresponding 2,2′‐bipyridines. Under identical reaction conditions, 1‐(2‐pyridyl)‐1,6‐diynes and nitriles reacted smoothly with exclusive regioselectivity to produce 2,2′‐bipyridines in good yield. 2,2′‐Bipyridines were also obtained by the double [2+2+2] cycloaddition reaction of 1,6,8,13‐tetraynes with nitriles. Similarly, 2,2′:6′,2′′‐terpyridines were synthesized from 1‐(2‐pyridyl)‐1,6‐diyne and 2‐cyanopyridine. The regiochemistry observed can be explained by considering the electronic nature of cobaltacyclopentadiene intermediates and nitriles. A survey of the exclusive regiochemical trend gives reasonable credence to the synthetic potential of the present method.     

Study on syntheses and properties of 2,2′‐mercaptoethylsulfide dimethacrylate transparent homo‐ and copolymer resins having high refractive index

2,2′‐Mercaptoethylsulfide dimethacrylate (MESDMA) was synthesized from 2,2′‐mercaptoethylsulfide (MES) by a Phase‐Transfer Catalysis technique and, was characterized and corroborated by ¹H‐NMR and FTIR spectra. Except for the poor impact strength, the MESDMA homopolymer resin shows better comprehensive properties, such as a higher refractive index (1.625), lower dispersion (Abbe's number 36), and good heat‐resistance (T_g 150°C) and surface hardness (3H), etc. Copolymerizing with styrene (St) can modify most of the properties of the resin. The refractive index, Abbe's number, onset wavelength, density, water‐absorption ratio, and absorption intensity of peaks in NIR region, etc. all display a regular change along with the proportion of MESDMA/St. The main absorption peaks in NIR region are assigned as follows: 1680 (first overtone) and 1144 nm (second overtone) to the phenyl C—H vibration of polystyrene; 1694 nm (first overtone) to ν(CH₃); 1730 and 1750 nm (first overtone) to ν(CH₂) for ordinary CH₂ and for CH₂ connected with S or COS groups, respectively; and 1186 nm (second overtone) to aliphatic C—H vibration. The prominent advantage achieved by copolymerization is that the impact strength can be improved as much as 10‐fold at a proper composition of the monomers (75% St). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1474–1479, 2000