Tin Mercaptide Research Articles

Investigating the role of different stabilizers of PVCs by using a torque rheometer

Abstract Poly(vinyl chloride) (PVC) is one of the versatile thermoplastic materials that have tremendous applications almost everywhere but it is thermally unstable at high temperatures. Processing of PVC at elevated temperatures requires the use of thermal stabilizers that are considered crucial additives for the protection of PVC during both processing and useful life usage. Several thermal stabilizers are available commercially that mostly obstruct the dehydrochlorination reaction. Choosing appropriate stabilizer systems for a specific application is cumbersome. A Brabender torque rheometer at a constant temperature of 180°C and variable shear stress was used to evaluate the stabilizing efficiency of 12 different stabilizer systems combined with PVC. Fusion time, induction period, minimum torque, and rheological stability time were determined in order to evaluate the investigated stabilizer systems. It was found that dibutyl tin mercaptide was the best stabilizer, while the mixture of lead stabilizers was the worse one.

Pentaerythritol stearate ester-based tin (II) metal alkoxides: A tri-functional organotin as poly (vinyl chloride) thermal stabilizers

In this work, a non-volatile solid organotin thermal stabilizer, pentaerythritol stearate ester-based tin (II) metal alkoxides (PSE-Sn) was synthesized with a very simple process and its impact on the thermal stability and processing performance of PVC was evaluated by conductivity measurement, thermal aging, thermogravimetric analysis, and torque rheometer test. The results showed that the addition of PSE-Sn not only could significantly enhance the thermal stability of PVC, accelerate plasticization, but also improve lubrication performance during PVC processing. Thus, PSE-Sn played the role of tri-functional additives: thermal stabilizer, plasticizer, and lubricant. The joint effects of PSE-Sn with ZnSt2 and CaSt2 on the thermal stability of PVC were also evaluated. Results indicate that there is a good synergistic effect between PSE-Sn and ZnSt2 on the initial color and long-term thermal stability of PVC. However, such synergistic effect was not observed between PSE-Sn and CaSt2. In addition, the working mechanism of PVC stabilization by PSE-Sn was also explored. Furthermore, the thermal stability and processing performance of PSE-Sn and methyl tin mercaptide (MTM) on PVC were comparatively tested. PVC stabilized by MTM possessed the longest color stability. The addition of PSE-Sn could also improve the initial color stability and long-term thermal stability of PVC significantly. The results of tensile test showed that both PSE-Sn and MTM could reduce the average tensile strength of PVC but increase the average elongation at break of PVC.

Transesterification in the Solid State of Cyclic and Linear Poly(l‐lactide)s

Poly(l‐lactide)s are synthesized and annealed at 120 °C and changes of the molecular weight distribution (MWD) are monitored by matrix‐assited laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry. For example, benzyl alcohol+SnOct2 causes equilibration of odd‐ and even‐numbered chains and the final goal of the transesterification is the most probable distribution. The underlying intermolecular transesterification is even observed at 100 and 80 °C in the solid state. However, cyclic tin mercaptide catalysts transform the initial most probable distribution into a MWD with maxima, which display a conspicuous fine structure due to a preferential crystallization of certain ring sizes. The optimum ring sizes for the crystallization are provided by ring‐ring equilibration. The gradual formation of a special morphology shifts the melting temperature to values up to 187 °C. Annealing of commercial poly(l‐lactide) with a cyclic tin catalyst also yields a distribution of mass peaks with a maximum showing the characteristic fine structure. image

Thermal degradation of biocidal organic N-halamines and N-halamine polymers

Novel biocidal organic N-halamines (based on imidazoline dione rings) were used as a substituents for poly(p-methyl styrene). The biocidal polymers and substituents have been investigated using thermogravimetric analysis. The thermal resistance of investigated compounds was compared to those of non-halogenated precursors. The introduction of chlorine atoms to polymers decreases their thermal resistance comparing to precursors but efficient stabilization is possible by using octyl tin mercaptide. The complex mechanism of thermal decomposition of polymers has been discussed.

Controlled tin catalyzed hydrolysis of 3-acryloxypropyltrimethoxysilane with mono- and multi-functional mercaptans

Mechanistic investigations were initiated to further our understanding of the reaction pathways for hydrolysis and condensation of organofunctional alkoxysilanes in organic media. Previous work has shown that addition of mercaptans to solutions that contain dibutyltin dilaurate (DBTDL), which functions as a catalyst, and 3-acryloxypropyltrimethoxysilane can greatly reduce the rate of silane hydrolysis and condensation. Gas chromatography/mass spectrometry (GC/MS) hydrolysis studies were carried out to understand how mercaptan structure and concentration affected the relative hydrolysis rate of the acrylate silane in solution. Detailed nuclear magnetic resonance spectroscopy (NMR) and electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry (MS) were carried out on simple mixtures of DBTDL and select mercaptans, and with varying mercaptan concentrations, to elucidate which significant tin complexes can form. These studies showed that mercaptans readily undergo ligand exchange reactions with the labile carboxylate groups of DBTDL and that an excess of mercaptans reduced the amount of proposed active catalyst species. It was found that an excess of mercaptan functional group was necessary to prevent significant and rapid hydrolysis of the organofunctional silane in organic media. A minimum of 1:4 DBTDL carboxylate group:mercaptan functional group was required for most mercaptans examined. A tetramercaptan, pentaerythritol tetrakis(3-mercaptopropionate), was shown to be effective in deactivating the DBTDL catalyst, even at relatively low concentrations of tetramercaptan. The findings in this work provide further support for the proposed mechanism for catalyzed hydrolysis and condensation. The tin metal was determined to be predominately 4-fold coordinated in the various tin mercaptide compounds studied. Evidence for transient tin hydroxide reactive intermediates was detected using mass spectrometry, as upon the addition of water, oligomeric condensation products were observed. However, the lifetime of these reactive intermediates precluded their direct observation by either mass spectrometry or NMR. Oligomeric and cyclic tin mercaptide species were shown to form when multifunctional mercaptans were combined with DBTDL in solution.

Structural and thermal stabilizations of PVC and wood/PVC composites by metal stearates and organotin

Structural and thermal stabilizations of poly(vinyl chloride) (PVC) and wood/PVC (WPVC) composites were studied using lead stearate (PbSt2), calcium/zinc complex (Ca/Zn) stabilizers, and methyl tin mercaptide (MT). Thermal and structural stabilities of PVC and WPVC composites were assessed using FTIR spectrometer, thermogravimetric analysis (TGA) and UV-Vis spectrophotometry. The results indicated that the additions of thermal stabilizers into PVC and WPVC composites could promote the thermal stabilities under both un-aged and thermally aged conditions. The presence of wood particles resulted in increases in polyene and carbonyl sequences during processing and decreases in the decomposition temperature (Td). The presence of wood was found to accelerate the thermal degradation in PVC, and suppressed the efficiencies of the thermal stabilizers used. By increasing the stabilizer dosage, the thermal degradations of PVC and WPVC were moderated. Under thermally aged condition at 177oC, the additions of thermal stabilizer could decrease the increase in yellowness index (YI) and discoloration at different ageing times. In this work, MT was found to be the most suitable and promising stabilizer for PVC and WPVC composites, considering the polyene and carbonyl contents, Td, the shift of derivative thermogravimetric (DTG) curves, and changes in YI value and visual color.

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XIII: Eugenol (4-allyl-2-methoxy-phenol)

Eugenol (4-allyl-2-methoxy-phenol) has been examined as a thermal stabilizer and co-stabilizer for rigid PVC in air, at 180 °C. Its high stabilizing efficiency is detected by its high thermal stability value (Ts) when compared with some of the common reference stabilizers used industrially such as dibasic lead carbonate, calcium–zinc soap and octyl tin mercaptide. Blending this organic stabilizer with some of the reference stabilizers in different ratios had synergistic effect on both the induction period and the dehydrochlorination rate together with the longer extent of discolouration of PVC stabilized by eugenol as compared with the blank and the samples stabilized with reference commercial stabilizers. A probable mechanism for the stabilizing action of eugenol has been proposed. The stabilizing efficiency is attributed partially to the stabilizer's ability to intervene in the radical chain degradation process of PVC and to the replacement of the labile chlorine atoms on PVC chains by a relatively more stable moiety of the organic stabilizer.

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XII: N-phenyl-3-substituted-5-pyrazolone derivatives

N-phenyl-3-substituted-5-pyrazolone derivatives have been examined as thermal stabilizers or co-stabilizers for rigid PVC in air, at 180 °C. Their high stabilizing efficiency is detected by their high induction period values ( T s) when compared with some of the common reference stabilizers used industrially, such as dibasic lead carbonate, calcium–zinc soap and n-octyl tin mercaptide. Blending these derivatives with some of the reference stabilizers in different ratios had a synergistic effect on both the induction period and the dehydrochlorination rate. A probable mechanism for the stabilizing mode of N-phenyl-3-substituted-5-pyrazolone derivatives has been proposed. The stabilizing efficiency is attributed at least partially to the ability of the organic stabilizer to be incorporated in the polymeric chains, thus disrupting the chain degradation.

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XI: Anthraquinone derivatives

Anthraquinone and 1-aminoanthraquinone derivatives have been examined as thermal stabilizers or co-stabilizers for rigid PVC in air, at 180 °C. Their high stabilizing efficiency is detected by their high induction period values (Ts) when compared with some of the common reference stabilizers used industrially such as dibasic lead carbonate, calcium–zinc soap and octyl tin mercaptide. Blending these organic stabilizers with some of the reference stabilizers in different ratios had synergistic effect on both the induction period and the dehydrochlorination rate. A probable mechanism for the stabilizing mode of these derivatives has been proposed. The stabilizing efficiency is attributed partially to the stabilizers' ability to intervene in the radical chain degradation process of PVC and to the replacement of the labile chlorine atoms on PVC chains by a relatively more stable moiety of the organic stabilizer.

Organic thermal stabilizers for rigid poly(vinyl chloride) III. Crotonal and cinnamal thiobarbituric acids

Crotonal thiobarbituric acid (CTBA) and cinnamal thiobarbituric acid (CiTBA) have been investigated as thermal stabilizers for rigid poly (vinyl chloride) (PVC) at 180°C in air. Their stabilizing efficiency is evaluated by measuring the length of the induction period ( T s), the period during which no detectable amounts of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric titration on one hand and the extent of discoloration of the degraded polymer on the other. The results reveal the higher stabilizing efficiency of the investigated materials as compared with industrially used thermal stabilizers such as dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), n-octyl tin mercaptide ( n-OTM), dibutyl tin maleate (DBTM) and barium–cadmium–zinc stearate (Ba–Cd–Zn stearate). This is well illustrated by the longer T s values, and by the lower rates both of dehydrochlorination and discoloration of the polymer during degradation relative to those of the reference stabilizers. A radical mechanism for the stabilizing effect of the investigated materials is suggested. The results indicate the important role played by the extent of conjugation in thiobarbituric acid derivatives on the stabilizing efficiency of the stabilizers. The stabilizing potency of the stabilizer increases with the extent of conjugation. The effect of blending CiTBA with either of the reference stabilizers on the stabilizing efficiency of the thermally degraded rigid PVC has been also investigated. The results reveal that mixing of the stabilizers improve both the T s values, the rate of dehydrochlorination and the extent of discoloration. This improvement attains its maximum when both the investigated and the reference stabilizers are taken in equivalent weight ratios.

Organic thermal stabilizers for rigid poly(vinyl chloride) I. Barbituric and thiobarbituric acids

Barbituric acid (BA) and thiobarbituric acid (TBA) have been investigated as thermal stabilizers for rigid poly(vinyl chloride) (PVC) at 180°C, in air. The efficiency of these compounds as thermal stabilizers was evaluated by measuring the length of the induction period ( T s), during which no detectable amount of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric titration on one hand, and the extent of discoloration of the degraded polymer on the other. The stabilizing efficiencies were compared with that of dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), barium–cadmium–zinc stearate (Ba–Cd–Zn stearate), n-octyl tin mercaptide ( n-OTM) and dibutyl tin maleate (DBTM). With the exception of DBTM reference stabilizer which shows a comparable stabilizing efficiency with BA and TBA, the investigated organic stabilizers exhibit a greater efficiency than those of all other reference stabilizers. Moreover, they impart better color stability to the degraded samples. A radical mechanism for the stabilizing action is suggested. The stabilizing efficiency is attributed to the replacement of the labile chlorine atoms on the PVC chains by a relatively more stable moiety of the stabilizer. This disrupts the formation of conjugated double bonds, which are responsible for the discoloration.

Organic thermal stabilizers for rigid poly(vinyl chloride) II. Benzal thiobarbituric acid and some of its derivatives

Benzal thiobarbituric acid (BTBA) and two of its derivatives: para-methoxy benzal thiobarbituric acid ( p-MeO-BTBA) and para-chloro benzal thiobarbituric acid ( p-Cl-BTBA) have been investigated as thermal stabilizers for rigid PVC at 180°C, in air. Their stabilizing efficiency is based on measuring the rate of dehydrochlorination and the extent of discoloration of the degraded polymer. The results reveal the higher stabilizing efficiency of the investigated materials as thermal stabilizers for rigid PVC as compared with the industrially used thermal stabilizers: dibasic lead carbonate (DBLC), dibasic lead stearate (DBLS), n-octyl tin mercaptide ( n-OTM), dibulyl tin maleate (DBTM) and barium–cadmium–zinc stearate (Ba–Cd–Zn stearate). This is well illustrated by the longer induction period ( T s) values and by the lower rate of dehydrochlorination. The stabilization efficiency is affected by the nature of the substituent found in the phenyl ring of the BTBA derivatives. Moreover, it was found that these materials lower the extent of discoloration of the polymer during degradation as compared with the reference stabilizers. A radical mechanism for the stabilizing effect of BTBA and its derivatives is proposed. The effect of blending p-Cl-BTBA with either of the reference stabilizers on the stabilizing efficiency of the thermally degraded rigid PVC has been also investigated. The results reveal that mixing of the stabilizers improves both the T s values, the rate of dehydrochloration and the extent of discoloration. This improvement attains its maximum when both the investigated and the reference stabilizers are taken in equivalent weight ratio.

Poly(vinyl chloride) formulations: acute toxicity to cultured human cell lines.

Two quantitative cytotoxicity assay methods (cytoplasmic retention of carboxyfluorescein and mitochondrial cleavage of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT)) have been used to evaluate the response of two cultured human cell lines; HepG2 (hepatoma) and W138va13 (transformed lung fibroblasts) to extracts of a range of poly(vinyl chloride) (PVC) formulations. Two plasticizers; di(2-ethylhexyl)phthalate (DEHP) and di-isooctyl phthalate and a range of tin and non-tin stabilizers were incorporated in the study. Only those formulations containing both a plasticizer and a tin-based stabilizer produced extracts which were toxic. Extracts of those formulations which contained both plasticizer and dibutyl tin dimaleate stabilizer were toxic to both cell lines in both assay methods. Extracts of a formulation containing plasticizer and a dioctyl tin mercaptide were toxic to both cell lines in the carboxyfluorescein assay but were only toxic to the WI38va13 cells in the MTT assay. The WI38va13 cells were generally more sensitive to the extracts than the HepG2 cells. When serial dilutions of the extracts were evaluated, the carboxyfluorescein assay proved to be the more sensitive of the two. The acute toxicity of extracts of these PVC formulations cannot be directly attributed to the plasticizers or to the tin stabilizers. It is likely that a synergistic mechanism, such as plasticizer facilitated extraction of the tin stabilizer, exists.

Weatherable rigid PVC: The effect of light and thermal stabilizers

AbstractRigid PVC compositions used in outdoor applications such as siding, profiles, windows, and soffit predominantly contain a tin mercaptide thermal stabilizer. It is well known that tin mercaptides impart outstanding thermal stability to vinyl compounds, however, it is also well known that they provide only marginal light stability. Mercaptides can be used in these applications primarily because they are combined with high levels of titanium dioxide. They are not well suited for dark colored PVC and compositions without titanium dioxide. These require a more weatherable thermal stabilizer, such as a tin carboxylate. In this paper, principles for formulating rigid weatherable vinyl will be discussed. The influence of thermal stabilizers and the interdependence of light stabilizers and thermal stabilizers on PVC photostability will be emphasized. Data will be presented showing how one can formulate weatherable dark brown and pastel PVC through the use of tin carboxylate thermal stabilizers, the appropriate light stabilizers, and pigments. Traditional approaches to achieving weatherability will be compared to what can be attained by capitalizing on the latest advances in stabilization technology. Finally, methods for reducing TiO2 concentration will be shown.

Rigid PVC: New developments for improving weatherability

AbstractPolyvinyl chloride is rapidly becoming recognized as a versatile polymer. It has a unique ability to accept additives, and the properties of the finished article often depend more on formulation than the resin itself.A wide variety of chemical may function similary in PVC, yet processors often have to compromise in selecting one additive over another. For example, both tin mercaptides and metal carboxylates function as thermal stabilizers. The mercaptide is superior as a thermal stabilizer while the carboxylate offers better weathering stability. Today's market tends to compromise at the expense of weathering. To compensate, high levels of reflective pigments (TiO2) are used.Recently, we initiated a research program and discovered a class of compounds which provide excellent weatherability with processability comparable to the highly‐efficient tin mercaptide. This cost‐effective development allows reduction of TiO2 levels by 25–50%. In addition, dark pigmented profiles remain relatively undeveloped because of serious weathering problems. Accelerated weathering and outdoor exposure tests demonstrate this technology is quite effective for UV stabilization of dark brown systems.

ChemInform Abstract: A Novel Method for the Stereoselective Synthesis of β‐Aminoacid Derivatives via Tin(II) Carboxylic Thioester Enolates.

AbstractThe ketene (I) reacts with the tin mercaptide (II) to yield the thiolester enolate (III), which couples with the imines (IV) in the presence of tin triflate (V), giving the isomeric adducts (VI) and (VII).

Effect of stabilizer type on artificial weathering of rigid PVC. II

The determination of the effectiveness of lead (Pb) and mercaptotin (MT) stabilizers on the useful service life of poly(vinyl chloride) PVC in outdoor applications, necessitates testing the mechanical properties of the polymer before and after weathering, to learn its behavior in the outdoor environment. Artificial weathering was used, and four mechanical tests were carried out, namely tensile, flexure, impact, and fracture toughness tests. The Pb stabilizer system used gave better fracture toughness and impact strength after exposure. The tensile strength and modulus of elasticity of MT-stabilized specimens increased significantly after exposure, unlike Pb-stabilized specimens. Brittleness in unplastisized PVC can be attributed to a number of factors, such as unsaturation, carbonyl group concentration, stabilized concentration, crystallinity, and extent of dehydrochlorination. The tensile strength and modulus of elasticity increase in tin mercaptide stabilizers significantly with increased UV exposure, while the increase in Pb specimens is less significant. There is a continuous diminution of the percent of elongation at break in both types of Pb or MT specimens, with increased exposure. The ductility of Pb may be accounted for by PbO and Pb stearate (C17H35COO)2Pb. One of the possible causes for the brittleness of tin mercaptide stabilized specimens is antiplasticization.

Effect of stabilizer type on the physicochemical properties of rigid PVC. III

AbstractThe crystallinity of rigid PVC specimens, stabilized by a tin mercaptide or a lead stabilizer, has been studied. It is found that the crystallinity of rigid PVC is greatly influenced by the type of stabilizer added, and that the response of the PVC toward subsequent UV exposure was also different. The effects of unstable structures and crystallinity, after UV irradiation, on the mechanical properties of rigid PVC have been investigated.

Effect of stabilizer type on the mechanical properties of rigid poly(vinyl chloride). I

AbstractThe effect of stabilizers on the mechanical properties of UPVC and how these are affected by different formulations has been studied. Three stabilizers, tin mercaptide MT, lead system Pb, and Ba/Cd/Zn complex BCZ, were used. A high ‐intensity blender was used for dry blend compounding, and the blend was injection ‐molded on a Kuasy single Screw injection molding machine. A two ‐cavity mold was made for forming the specimens. The specimens were tested for their impact strength, fracture toughness, tensile strength, and flexural strength. Increasing MT stabilizer was shown to increase the tensile strength and to decrease fracture toughness, impact strength, and ductility; this was attributed to antiplasticization. Increasing the Pb stabilizer conferred ductility and improved fracture toughness and impact strength. It is concluded that stabilizers have a marked effect on the mechanical behavior of rigid PVC.

Vinyl Polymerization. 375. Radical Polymerization of Vinyl Monomer in Water Initiated with Tin Mercaptides and Iron(III) Ion

Abstract The polymerization of the vinyl monomer was carried out in water, using either dimethylbis(ethylthio)tin or triethyl(p-tolylthio)tin as an initiator. The polymerization required the coexistence of the iron(III) ion. The initiating species was concluded to be a thiyl radical. Macromolecular tin mercaptide was much more effective than monomeric tin mercaptide.