Crosslinking of PVC and NBR blends

The purpose of our work is to control the interfacial bonds between PVC and NBR using the ammonium salts of triazine thiols and dithiodimorpholine (DTDM) and thereby reveal the relation between the interfacial bonds and the final mechanical properties of products. In the experimental work a two-stage process was used. At first, an NBR/PVC blend was mixed with a mono-tetra-n-butylammonium salt of triazine trithiol at a temperature of 100°C on a two-roll mill to give the branching structure of triazine thiols into PVC. In the second stage branched NBR/PVC reacted with DTDM to afford the branched PVC containing trithiomorphonyl groups. In the presence of ZnO at 160°C trithiomorphonyl groups react with NBR to form a crosslinking structure between NBR and PVC. The mechanical properties of cured NBR/PVC blends were markedly improved by the treatment process and after addition of tetramethylthiuram monosulphide also. The mechanical properties were not improved by increasing the concentration of TT-TBA (tetrabutylammonium salt of 1,3,5-triazine-2,4,6-trithiol) over 4.2 phr.     

Curing dynamics and network formation of cyanate ester resin/polyhedral oligomeric silsesquioxane nanocomposites

Curing dynamics and network formation of cyanate ester resin (PT-30)/TriSilanolPhenyl polyhedral oligomeric silsesquioxane (POSS) nanocomposites were studied by means of differential scanning calorimetry (DSC), modulated temperature differential scanning calorimetry MTDSC), Fourier transform infrared (FTIR) and Raman spectroscopies. The incorporation of the POSS showed a strong catalytic effect (decrease in curing temperature and activation energy) on the curing reaction of PT-30. The activation energy of the PT-30 decreased with increasing POSS content. The most effective catalytic effect was observed at 5 wt% of the POSS. Both FTIR and Raman spectra monitored the formation of triazine (i.e. cyanurate) ring in the PT-30 and its nanocomposites with the POSS. Raman spectra revealed that the PT-30 resin preferentially reacted with -OH group in the POSS firstly to form a -O-(CNH)-O- bond, rather than react with itself to form the triazine rings, during the network formation of the PT-30/POSS nanocomposites. The strong catalytic effect of the POSS on the curing process of the PT-30 appears to be due to the formation of this -O-(CNH)-O- bond.     

Aromatic disulfide polymers back to macrocyclic disulfide oligomers via cyclo-depolymerization reaction

A brand new and highly efficient method has been developed for the synthesis of aromatic macrocyclic disulfide oligomers. Cyclization was achieved by cyclo-depolymerization (CDP) of aromatic disulfide polymer in the presence of catalytic amount of thiols and weak base. The cyclic oligomers undergo a facile free-radical ring-opening polymerization to form high molecular weight polymer. Comparing with the conventional method for the preparation of macrocyclic aromatic oligomers by catalytic oxidation of dithiols, highly dilute condition was not necessary using the new method. The macrocyclics in high yield and with narrow molecular weight distribution were obtained. This method also provides a convenient technology for the recycle of aromatic disulfide polymers.     

A study of curative interactions in cis-1,4-polyisoprene. X. The cis-1,4-polyisoprene/sulfur/zinc dimethyldithiocarbamate and cis-1,4-polyisoprene/sulfur/zinc dimethyldithiocarbamate/ZnO systems

Aspects of the mechanism of zinc dimethyldithiocarbamate (ZDMC)-accelerated sulfur vulcanization were discussed. The trends in the efficiency parameter E, confirmed that crosslinking is preceded by the formation of pendent groups RS_xSX [R = polyisoprenyl, X = Me₂NC(S)] in ZDMC-based systems. The index x in RS_xX was calculated as 5.82 in the cis-1,4-polyisoprene (IR)/sulfur/ZDMC/ZnO compound at the initial stages of curing, compared to 3.23 in the absence of ZnO. The high value of x supports the postulation that elemental sulfur and ZDMC react at the early stages of vulcanization, to form the active sulphurating agent XS_xSZnSSX. Crosslinks form by either a disproportionation reaction between two α-methylic or α-methylenic pendent groups RS_xX, or a reaction between a pendent group RS_xX and the rubber chain—these routes are the same as that suggested for the IR/tetramethylthiuram disulfide (TMTD)/ZnO compound. The beneficial role of ZnO and zinc stearate is shown, as in the case of ZnO in the IR/TMTD/ZnO system, to be related to their ability to trap dimethyldithiocarbamic acid, which formed in the generation of pendent groups and crosslinks. ZnS is inactive in this regard. The formation of ZnS is characteristic of natural rubber/sulfur/ZDMC/ZnO systems, as opposed to IR/TMTD/ZnO mixtures where little ZnS forms.     

Swellability of acrylate methacrylate-cellulose matrix systems and the effect on solute diffusion rates

During the vulcanization of cis-1,4-polyisoprene (IR) with thiruam-related curing systems, dimethyldithiocarbamic acid (DMDCA) is formed as a byproduct, in the formation of either pendent groups or crosslinks. DMDCA is unstable, and decomposes instantly to Me₂NH and CS₂ in the absence of ZnO. The facile reaction of Me₂NH and thiuram-related molecules such as tetramethylthiuram polysulfides, tetramethylthiuram disulfide (TMTD), tetramethylthiuram monosulfide and pendent groups caused (i) increased induction periods, (ii) lower maximum crosslink densities, and (iii) the excessive formation of tetramethylthiourea (TMTU). A most important function of ZnO was to trap the DMDCA via the formation of zinc dimethyldithiocarbamate and water, thereby preventing the detrimental reactions above. The IR/TMTD/ZnO and IR/sulfur/TMTD/ZnO systems were therefore characterized by (i) shorter induction periods, (ii) higher maximum crosslink densities, and (iii) the absence of TMTU.     

Surface treatment of fluorinated rubber with triazine thiols and their properties

Fluorinated (FKM) vulcanizates were treated by immersing in an aqueous solution of triazine thiols, NaOH, and onium salts for 15–60 min at 50–95°C (W-Method). Treated FKM vulcanizates further were postcured in an air oven for 20 h at 200°C to complete the reaction. The onium salt of triazine thiols were found to be formed by a reaction among the triazine thiols, NaOH, and onium salts and to act as cross-linking agents to the surface of FKM vulcanizates. In the acetone solution of onium salts of triazine thiols, FKM vulcanizates were also treated by immersing for a few minutes at 20°C and then by heating in an air oven for 20 min at 200°C (A-Method). Triazine thiols were introduced as crosslinks onto the FKM backbone. The degree of cross-linking in the surface increased by these treatments and the depth of cross-linking reached up to about 40 μm thickness by control of treating conditions. The coefficient of friction in FKM vulcanizates decreased as a result of the surface treatment up to about 0.5 from 2.6. FKM vulcanizates decreased the tensile strength by these surface treatments because of the generation of cracks on the surface at 50% or 100% elongation. The surface treatment of FKM vulcanizates suppressed markedly the fixing between FKM vulcanizates and stainless steel at 150°C. Especially, the A-Method was very effective treating for retarding the fixing between FKM vulcanizates and metals. © 1994 John Wiley & Sons, Inc.     

Synthesis and characterization of siloxane‐based cyanate ester elastomers from readily available materials: a top‐down approach

A number of siloxane‐based cyanate ester (SiCE) elastomers were prepared from commercially available starting reagents employing a hydrosilylation reaction. Each elastomer was designed to utilize 2,4,6‐tris(allyloxy)‐1,3,5‐triazine as a crosslinker and multifunctional vinyl component in the hydrosilylation reaction, ensuring that the triazine rings were completely formed, and thus the elastomers resemble fully cured cyanate ester networks. The hydride‐terminated siloxane components used were varied from small‐molecule siloxanes to pre‐polymers of different molecular weights. Attenuated total reflectance Fourier transform infrared analysis confirmed the successful hydrosilylation reaction and complete curing of the SiCE elastomers via functional group analysis. Thermal characterization by thermogravimetric analysis and differential scanning calorimetry demonstrated that thermal properties of the elastomers could be tailored depending on the type of siloxane component that was utilized. The gel content of the elastomers was also determined. Investigations into the effects of a platinum catalyst on the elastomers determined that the presence of the catalyst affected the thermochemical stability of the SiCE elastomers. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.     

Accelerating effect of NaNO2 on the polymer plating of 6‐substituted‐1,3,5‐triazine‐2,4‐dithiol mono sodium salts

Organic polymer plating properties of 6‐substituted‐1,3,5‐triazine‐2,4‐dithiol mono sodium salts were investigated in the presence of various supporting electrolytes. Among these, the NaNO₂ supporting electrolyte greatly accelerated the film formation rate in polymer plating. The accelerating effect of NaNO₂ was further confirmed by comparing plating potentials in the presence of NaNO₂ and Na₂CO₃. The potentiostatic polymer plating of DAN in the presence of the NaNO₂ supporting electrolyte took place in the potential range of 1.65–1.8 V (compared against saturated calomel electrode reference). Film formation was influenced by such factors as the pH of solution and both the chemical structure and the concentration of triazine dithiol. In polymer platings, NO anions are thought to be electrochemically oxidized to yield NO radicals and these radicals react with DAN to yield new thiyl radicals. The thiyl radicals in the DAN molecules couple with each other by means of disulfide bonds, resulting in the growth of polymer film. Organic polymer plating films are shown to contain disulfide bonds, monosulfide bonds obtained by the reaction between allyl groups and thiyl radicals, and network chains. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2300–2309, 2001     

Curable polyester precursors from polylactic acid glycolyzed products

Curable precursors are prepared from chemical recycling of degradable polylactic acid (PLA) for development of aliphatic polyester thermoset materials. PLA resin (NatureWork 4042D) was de-polymerized via glycolysis under various conditions to produce PLA glycolysates (GlyPLAs), whose chain-ends mainly consist of hydroxyl groups with $\bar{M}_{n}$ M ¯ n ranging from 3,600 to 17,000 g/mol. Unsaturated double bonds (DB) were introduced into GlyPLA structures by end-capping with methacrylic anhydride to generate curable LA-precursors. The end-capping efficiency is strongly dependent on the molecular weight of GlyPLAs, where smaller-sized glycolysates produce LA-precursors with higher DB content. Curing behaviors of the precursors are thoroughly examined. DSC and FTIR results show that curing reactions at 140 °C are completed after 2 h for all samples. Results on gel fraction indicate that LA-precursor with $\bar{M}_{n}$ M ¯ n  ~ 3,600 g/mol is the most effective candidate for producing network products with high crosslink density.     

Polyurethane elastomers made from linear polybutadiene diols

Segmented polyurethane elastomers made from linear polybutadiene diols terminated with primary (Krasol LBH‐P) or secondary (Krasol LBH) hydroxy groups, alicyclic diisocyanate, and aliphatic chain extender were prepared and tested. The system was chemically crosslinked either through isocyanurate, that is, hexahydro‐1,3,5‐triazine‐2,4,6‐trione groups (formed by catalyzed cyclotrimerization of isocyanate groups), or by low molecular weight triols. The best balance of stress‐strain properties and reasonable thermal stability was obtained for systems in which only a small amount of chemical crosslinks was present in predominantly physically crosslinked networks. The influence of the type of polymer diol, chemical crosslinking, diisocyanate, and technique of preparation on mechanical, thermal, and swelling properties is discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 84–91, 2002     

Chemorheology of cyanate ester—organically layered silicate nanocomposites

The effect of nanoparticle addition on the flow and curing behavior of a phenolic triazine cyanate ester resin system has been studied using chemorheological, thermal and spectroscopic techniques. While the neat system exhibited Newtonian flow, the nanodispersed prepolymer exhibited pseudoplastic flow behavior, typical of polymeric fluids such as gels and pastes. Evolution of the morphology during curing has been found to be dependent on the rate of intergallery diffusion of the prepolymer and subsequent gelation and vitrification, as well as the intra and extragallery cure kinetics. Curing reactions of the cyanate ester nanocomposite system consisting of a di-functional phenol, a halogen cyanate and organically layered silicates were studied. Gel times were measured as a function of temperature by time sweeps on a controlled stress rheometer. Gelation and vitrification times and activation energies for the nanocomposite systems were lower than that of the neat resins, indicating a catalytic effect of the clays on the curing reaction. Curing kinetics experiments performed on DSC and FTIR confirmed this phenomenon. Based on above experiments, time-temperature-transformation diagrams for the different systems were constructed.     

手机按键PET披覆UV胶的研究

用聚酯丙烯酸树脂、单体、粘接促进剂、助剂等原料研制出用于手机按键PET披覆的紫外线固化胶,讨论了树脂、单体、硫醇、助剂等对粘附力、表面硬度及表干速度的影响。     

UV- and thermal-curing behaviors of dual-curable adhesives based on epoxy acrylate oligomers

Dual-curable adhesives were prepared using various epoxy acrylate oligomers, a reactive diluent, photoinitiators, a thermal-curing agent and a filler. The UV- and thermal-curing behaviors of the dual-curable adhesives were investigated using photo-differential scanning calorimetry (photo-DSC), Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy, and the determination of the gel fraction, pendulum hardness and adhesion strength.The reaction rate and extent of UV curing were found to be strongly dependent on the concentration of CC bonds in the epoxy acrylate oligomers. The FTIR-ATR absorption peak areas representing the relative concentration of CC bonds in the epoxy acrylate oligomers and trifunctional monomer decreased with increase in UV dose because of photopolymerization. When the dual-curable adhesives were irradiated with UV light, the gel fraction increased with increase in CC bond contents in the epoxy acrylate oligomers. Also, after thermal curing, the gel fraction was highly enhanced due to the cross-linking reaction of the unreacted glycidyl groups in epoxy acrylate oligomers induced by the thermal-curing agent. This cross-linked structure of the dual-curable adhesives affects the pendulum hardness and adhesion strength.     

Crosslinking of poly(arylene disulfide)s and poly(arylene sulfane)s derived from cyclic(arylene disulfide) oligomers

Cyclic(arylene disulfide) and polycyclic(arylene sulfide) oligomers were synthesized by catalytic oxidation of arylenedithiols or arylenetrithiols with oxygen in the presence of a copper‐amine catalyst. These cyclic(arylene sulfide) oligomers can undergo free radical ring‐opening polymerization at an elevated temperature in the melt or solution. Polycyclic(arylene sulfide) oligomers can be used to crosslink poly(arylene disulfide)s and poly(arylene sulfane)s derived from cyclic(arylene disulfide) oligomers and elemental sulfur. The crosslinking reactions were investigated by differential scanning calorimetry and by solubility of the cured products. The minimum concentrations of polycyclic(arylene sulfide) oligomers for producing a well crosslinked poly(arylene disulfide) and poly(arylene sulfane) are 7 wt % and 10 wt %, respectively. The crosslinking reactions between poly(arylene disulfide)s, poly(arylene sulfane)s, and triallyl‐1,3,5‐triazine‐2,4,6(1H,3H,5H)‐trione (TTT) were also investigated. TTT is more efficient for crosslinking than the synthesized polycyclic(arylene disulfide) oligomers. The crosslinkable poly(arylene disulfide)s and poly(arylene sulfane)s could be potentially used as high temperature coatings, sealants, adhesives, and as matrices for high performance thermoset composites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3069–3077, 1999     

Poly(2,4-perfluoroalkylene-6-Perfluoroalkyltriazine)s,new high temperature elastomers

Poly(perfluoroalkyleneimidoylperfluoroalkylenoamidine)s have been prepared by the reaction of perfluoroalkane dinitriles with ammonia or with the diamidines of the dinitriles. The imidoylamidine polymers were treated with anhydrides to give poly(perfluoroalkyIenetriazine)s. Treatment of the imidoylamidine polymer with perfluoroglutaric anhydride or 4-cyanoperfluorobutyryl chloride gave pendant carboxyl or nitrile groups, respectively, on the triazine polymer which served as crosslinking sites. The formation of triazine crosslinks from the nitrile-pendant groups by trimerization with catalysts such as tetraphenyltin has given crosslinked polymers with tensile strengths of 1500 p.s.i., 70% elongation, and with thermal stability aproaching that of the original gum. The milling of catalysts and fillers with the polymer decreased the thermal stability in comparison with the original gum.     

The Structural Elucidation of Oligomeric Blue Dyes Derived from 9-Alkylcarbazoles

Carbazoles react with a variety of one-carbon fragments at the 3- or 3,6-positions to give di- and trimeric products with CH₂: links. These precursors react by losing hydride ion to give blue oligomeric dyes. Carbazoles substituted in the 9-position by CH₂SPh, CH₂SOPh, and CH₂SO₂Ph rearrange to give carbazole oligomers linked at the 3,6-positions. Products are characterised spectrally, and their mechanism of formation is discussed.     

A study of curative interactions in cis-1,4-polyisoprene. VIII. Network maturing reactions in the cis-1,4-polyisoprene/tetramethylthiuram disulfide/ZnO system

Several aspects concerning the network maturing reactions of the cis-1,4-polyisoprene (IR)/tetramethylthiuram disulfide (TMTD)/ZnO curing system, were evaluated with reference to previously published literature. The crosslink density increased progressively from 1.42 × 10^?5 mol cm^?3 rubber at 140.0°C, to 8.30 × 10^?5 mol cm^?3 at the higher temperature of 190.0°C, which tied in with the fact that natural rubber (NR) or IR/TMTD/ZnO systems show negligible reversion provided sufficient ZnO is present. The increase in the crosslink density value was accompanied by a systematic buildup of monosulfidic crosslinks, and a substantial decrease in the concentration of tetramethylthiuram monosulfide (TMTM). Calculations showed, in addition, that the increase in the concentration of zinc dimethyldithiocarbamate (ZDMC) and the decrease in the TMTM concentration, were interdependent. It is shown that TMTM, rather than ZDMC, was involved in the crosslink shortening reactions.     

Organosiloxane-Cross-Linked Poly(2,6-Dimethyl-1,4-Phenylene Oxide) Network Structures

The use of two types of siloxane bridges as chemical cross-links in poly(phenylene oxide) (PPO) network structures was investigated. The PPO was initially functionalized through a bromination process and then cross-linked using two systems. The first used -aminopropyltriethoxysilane to produce relatively few siloxane bonds between cross-links, while the second utilized the same silane in combination with a higher molar mass, , -functionally terminated poly( dimethyl siloxane) (PDMS) to provide longer chains between crosslinks. The resulting networks showed notable differences in tensile properties which depended on the type of crosslinks present. In addition, both elastomers showed good strength and elongation characteristics and reduced craze formation when compared to the PPO homopolymer.     

Viscoelastic properties and heat generation in urethane elastomers

Static and dynamic properties were studied in a series of polyurethane elastomers as a function of selected compositional variables such as curative system, curative level, catalyst level, and curing temperature. A number of physical properties including swelling ratio, density, glass transition temperature, stress–strain behavior, and thermal conductivity were also measured on these elastomers. The selected variables affect dynamic mechanical properties as well as heat buildup. A good correlation was noted between the loss modulus and the heat generation. The loss modulus and the heat generation decrease with decreasing curative level. The elastomers cured with a mixture of triol and diamine give lower loss modulus and heat buildup than those cured with diamine alone. These responses are believed due to the increase in covalent crosslinks. The observed low heat generation of the elastomer cured with 0.2 phr azelaic acid as a catalyst level was also attributed to the high crosslink density. The curing temperature, in the range investigated, appears to have very little effect on the properties. Thus, the choice of formulation variables, especially the use of diamine–triol blends, provides an effective means of minimizing heat generation in dynamic applications of polyurethane elastomers.     

Beiträge zum Vernetzungs- und Abbauverhalten von Acrylelastomeren

The aim of this investigation was to obtain additional knowledge of the curing mechanism and the aging properties of acrylic polymers containing active chlorine. These were cured with amine or metal-soap/sulphur combinations. For this purpose, we used sulphur, chlorine, and nitrogen analyses, together with measurements of crosslink density and stress-relaxation. These investigations were partly made with vulcanisates based on technical acrylic polymers, and partly with crosslinked products of homo- and copolymers containing chlorine. Using the amine curing system, the diamine, after vulcanisation, is completely incorporated. Curing with metal-soap/sulphur combinations sulphur crosslinks are formed. The crosslink density is proportional to the concentration of amine or potassium-stearate in the compound. Comparing polyethylacrylate polymers containing vinyl-chlorecetate and 2chloroethyl-vinylether comonomers one always h d s the higher crosslink densities in polyethylacrylat/vinylchloracetat copolymers. We proved by stress relaxation measurements that scission of the network occurs at the crosslinks during air aging. Using amine as the curing agent oxidativedegradation exceeds the thermal one. In case of metal-soap/sulphur curing system thermal degradation exceeds the oxidative portion. Remarkable differences in aging properties between the two types of polymers could not be found. These results fit with our conception of the types of networks built up duringvulcanimtion, based on the other examinations.