Polymerization products of p-benzoquinone as thermal stabilizers for rigid poly(vinyl chloride). Part II—Evaluation of the stabilizing efficiency

Quinone-tin polymers prepared by the cationic polymerization of p-benzoquinone with tin(II)chloride in the absence of solvent have been investigated as thermal stabilizers for rigid PVC at 180°C in air by measuring the rate of dehydrochlorination. The results reveal the higher stabilizing efficiency of these products relative to dibutyltin maleate, basic lead carbonate and barium-cadmium stearate stabilizers commonly used in industry. The induction period in the early stages of the dehydrochlorination process increases as a function of the metal content in the stabilizer molecule. The evidence indicates that the quinone and the metal part (

) of the stabilizer participate in the stabilization process by trapping the radical intermediates, as well as blocking the odd electron sites formed on the PVC chains. The mechanism of stabilization suggested to account for the results obtained supports a radical mechanism for the dehydrochlorination reaction.     

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 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.     

p-Benzoquinone-tin polycondensates as stabilisers for polybutadiene rubber against photo-degradation

p-Benzoquinone-tin derivatives, obtained by polycondensation of the quinone and SnCl₄ in the absence of solvent, have been investigated as uv stabilisers for polybutadiene rubber. Intrinsic viscosity measurements have shown the greater efficiency of these products relative to phenyl salicylate which is commonly used in industry. The stabilising efficiency increases as the tin content of the stabiliser increases. A mechanism based on the involvement of both the quinone part of the stabiliser and the SnSn bonds in scavenging the radical species formed, as well as blocking the radical sites on the polymeric chains, has been developed. Moreover, it has been shown that prior oxidation of the stabilisers of higher tin content can afford complete protection of rubber from degradation by uv irradiation.     

Synergistic effect of maleimido phenyl urea derivatives mixed with some commercial stabilizers on the efficiency of thermal stabilization of PVC

Four novel antimicrobial maleimido phenyl urea stabilizers 1–4 were synthesized from N-[4-(chlorocarbonyl) phenyl] maleimide with phenyl urea and its derivatives (p-methyl, o-chloro and p-carboxy). The effect of mixing maleimido phenyl urea stabilizer 2 with each of the reference stabilizers, dibasic lead carbonate (DBLC), cadmium-barium-zinc stearate (Cd-Ba-Zn stearate) or n-octyltin mercaptide (n-OTM), on the stabilization efficiency in thermal degradation of rigid PVC at 180 °C in air, has been investigated. Mixing was effected in the range of 0–100 wt% of stabilizer 2 relative to each of the reference stabilizers. The stabilizing efficiency was evaluated by measuring the length of the thermal stability period (Ts), the period during which no detectable amount of hydrogen chloride gas could be observed, and also from the rate of dehydrochlorination as measured by continuous potentiometric determination, and by the extent of discoloration of the degraded polymer samples. The results show a true synergistic effect from the combination of stabilizer 2 with any of the reference stabilizers. Mixing of the stabilizers improves the Ts values, decreases the rate of dehydrochlorination and lowers the extent of discoloration of the polymer. The maximum synergism was attained when stabilizer 2 is mixed with either of the three reference stabilizers in equivalent weight ratio (50%/50%). The observed synergism may be attributed to the different mechanisms by which the investigated and the reference stabilizers work.     

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.     

N-(Substituted phenyl)itaconimide-phenyl salicylate blends as organic stabilizers for plasticized poly(vinyl chloride) against photo-degradation

The effect of blending some N-(substituted phenyl)itaconimide derivatives, N-(RPh)II, (R: -H, or -OMe) with phenyl salicylate UV absorber on the stabilizing efficiency in photo-degradation of PVC plasticized with dioctyl phthalate (DOP) has been investigated. Blending was effected in the range of 0-100 wt% of the itaconimide relative to reference stabilizer. The stabilizing efficiency was evaluated by measuring the length of the induction period (Ts), 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 determination on one hand, and the extent of discoloration of the degraded polymer on the other. The efficiencies are also evaluated by determining the amount of gel formation as well as the intrinsic viscosity of the insoluble and the soluble fractions of the degraded polymer. The results show a true synergistic effect from the blending of itaconimide derivative with phenyl salicylate UV absorber. Blending of the stabilizers improves the Ts values, decreases the rate of dehydrochlorination, and lowers the extent of discoloration and the gel content of the polymer. The synergism attains its maximum when both the itaconimide and the reference stabilizers are taken in equimolar ratios. The observed synergism may be attributed to the combination of mechanisms by which the itaconimide and the reference stabilizer work.     

Polymerization products of p-benzoquinone as thermal stabilizers for rigid poly(vinyl chloride): Part I—Preparation of the stabilizer

The solid phase cationic polymerization of p-benzoquinone using tin (II) chloride as catalyst has been investigated by isolation and identification of the reaction products. The polymerization reaction leads to formation of polymeric chains of hydroquinone nuclei linked together by SnOSn bonds and free from combined chlorine. The tin content of the polymer is increased by increasing the molar ratio of the catalyst and ranges from 4·7 to 55·6% tin. It is probable that the tin atoms are involved in the reaction products as a result of the interaction between polymeric chains having terminal catalyst residues. The resulting polymeric products are characterized by high thermal stability with a decomposition temperature in the region of 400°C. A mechanism which can account for the polymerization products has been developed. In view of the expected high potency of these products, together with their high thermal stability, they will be investigated as radical scavengers in the stabilization of polymeric material against radical degradation processes.     

热稳定剂对PVC紫外光老化过程中微观结构及宏观性能演变的影响

通过UV-Vis、FTIR、DSC、以及色差、力学性能的测试表征,实时追踪分析了在紫外光老化过程中,含Pb、Sn以及Ca-Zn热稳定剂的PVC体系微观结构和宏观性能的演变过程.结果表明,在相同光老化条件下,PVC/Pb、PVC/Sn和PVC/Ca-Zn体系的微观结构变化规律基本一致,过程中主要的化学反应是,大分子吸收光能后,发生脱HCl生成共轭双键的反应、生成羰基的氧化反应、交联反应和降解反应;不同热稳定剂的作用,主要表现在对于微观结构变化的幅度和动力学过程的影响不同.相应地,3种体系的外观色差和力学性能的变化规律也相似,但色差的变化程度和速度以及老化后力学性能的保持率因所含热稳定剂的不同而不同,其中含Sn体系的颜色稳定性最好,含Pb体系的力学性能保持率最高。     

Polymeric p-benzoquinone-tin derivatives as thermal stabilizers for rigid poly(vinyl chloride). I. Preparation of the stabilizers

The reaction of p-benzoquinone with tin tetrachloride in the absence of solvents was investigated by isolation and identification of the reaction products. This reaction leads to the formation of polymeric quinone-tin derivatives free from combined chlorine, chlorinated quinones, quinhydrone, and minute amounts of CI₂ and HCI gases. The tin content varies accroding to the molar ratios of the reactants and reaches its maximum (72%) at the smallest SnCI₄ ratio. The existence of the Sn-Sn bond in the polymeric derivatives was confirmed chemically and spectroscopically. A mechanism based on the formation of radical intermediates which can account for the reaction products was developed. In view of their quinonoid nature, high thermal stability, and the presence of Sn-Sn bonds, the polytin derivatives are to be investigated as radical traps in the stabilization of polymeric arcticles against radical degradation process.     

Influence of lanthanum stearate and calcium/zinc stabilizers on stabilization efficiency of dibutyltin dilaurate to polyvinyl chloride

<正>Influences of lanthanum stearate(LaSt_3) and calcium stearate/zinc stearate(Ca/Zn) stabilizers on stabilization efficiency of dibutyltin dilaurate(DBTDL) to polyvinyl chloride(PVC) in air were investigated.The results revealed that the stabilization effect of DBTDL could be achieved by the La/Sn stabilizers with a ratio of 8/2.Addition of DBTDL could enhance thermal property and reduce dynamic storage modulus(G′) at 180℃for PVC containing LaSt_3 or Ca/Zn stabilizers. On the other hand,incorporation of LaSt_3 did not influence the stabilization efficiency of DBTDL markedly;while addition of Ca/Zn stabilizers could significantly decrease thermal property for the DBTDL stabilized PVC.Furthermore,the effects of LaSt_3 and Ca/Zn stabilizers on the stabilization efficiency of DBTDL were explained in the framework of ionization potential.     

The discolouration of PVC—II : Kinetic studies

On the basis of previous results, a relation has been derived between the time of the dehydrochlorination and the grade of the discolouration of PVC. The correctness of this relation is experimentally proved by investigations with samples containing metal soap stabilizers and with non-stabilized samples. The relation permits direct calculation of the rate constants and other kinetic characteristics of the propagation and termination steps for the conjugated polyenic chains. The activation energies derived are in apparently good agreement with the measured values for model compounds having similar structure. From the rate constants, conclusions can be drawn on the influence of the stabilizers on the individual steps. The experimental results obtained with stabilizer pairs support the present ideas about the mechanism of synergism; they also elucidate further details of the mechanism of stabilizing action.     

Thermal degradation of vinylidene chloride/vinyl chloride copolymers in the presence of N-substituted maleimides

As a consequence of their excellent barrier properties vinyl chloride/vinylidene chloride copolymers have long been prominent in the flexible packaging market. While these polymers possess a number of superior characteristics, they tend to undergo thermally- induced degradative dehydrochlorination at process temperatures. This degradation must be controlled to permit processing of the polymers. Three series of N-substituted maleimides (N-alkyl-, N-aralkyl, and N-aryl) have been synthesized, characterized spectroscopically, and evaluated as potential stabilizers for a standard vinyl chloride/vinylidene chloride (85 mass%) copolymer. As surface blends with the polymer, these compounds are ineffective as stabilizers. However, significant stabilization may be achieved by pretreatment of the polymer with N-substituted maleimides. The most effective stabilization of the polymer is afforded by N-aralkyl- or N-arylmaleimides, most notably, N-benzylmaleimide and N-p-methoxyphenylmaleimide.     

Stabilization of low density polyethylene with sterically hindered derivatives of 4-hydroxybenzoic acid

In comparison with other commercial light stabilizers, sterically hindered 4-hydroxybenzoates are found to possess only a weak power, if they are used for low density polyethylene (LDPE). It is known that these benzoates exhibit significant synergistic effects together with 2-hydroxybenzophenones and hindered amine light stabilizers in light stabilization of high-density and linear low-density polyethylene. The light stabilizing efficiencies of the above mentioned stabilizers and mixtures of them in different weight ratios are determined by weathering in a Xenotest 150 unit. Only small synergistic effects of about 15 −30% are found for light stabilizing LDPE. The effects can be explained by the stabilizing efficiency of sterically hindered 4-hydroxybenzoates during processing. Combining of light stabilizing structure components like 2-hydroxy-benzophenone resp. 2, 2, 6, 6-tetramethylpiperidine with sterically hindered 4-hydroxybenzoates in one stabilizer molecule only, from the first mentioned combination, results a powerful light stabilizer. Its efficiency is the sum of the powers of the single structure components.     

N-(Substituted phenyl) itaconimides as organic stabilizers for plasticized poly(vinyl chloride) against photo-degradation

Several N-(substituted phenyl)itaconimide derivatives, N-(RPh)II (R: -NO₂, -COOH, -H, -OH, -OMe, -Me, -Cl, or -Br), have been investigated as organic photo-stabilizers for poly(vinyl chloride) (PVC) plasticized with dioctyl phthalate (DOP). Their stabilizing efficiencies are evaluated by measuring the length of the induction period (Ts), 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 determination, and the extent of discolouration of the degraded polymer. The efficiencies are also evaluated by determining the amount of gel formation as well as the intrinsic viscosity of the insoluble and the soluble fractions of the degraded polymer, respectively. The results have proved the greater stabilizing efficiency of the N-(RPh)II derivatives relative to that of the phenyl salicylate UV absorber which is a commonly used industrial stabilizer. A radical mechanism is proposed to account for the stabilizing action of the investigated products.     

Anthraquinone derivatives as organic stabilizers for rigid poly(vinyl chloride) against photo-degradation

Anthraquinone derivatives have been prepared and investigated as photo-stabilizers for rigid PVC by measuring the extent of weight loss (%), the amount of gel formation as well as the intrinsic viscosity of the soluble fractions of the degraded polymer. The results indicated a reasonable stabilizing effect of these derivatives compared with UV-commercially used stabilizers. A synergistic effect is achieved when the anthraquinone derivatives are mixed with UV-absorbers in a weight ratio of 75% of investigated organic stabilizer and 25% of reference stabilizer.A probable radical mechanism is proposed to account for the stabilizing action of the organic investigated materials.     

Bulk polymerization of p‐dioxanone using a cyclic tin alkoxide as initiator

Poly(p‐dioxanone) with an inherent viscosity of over 1 dL/g has been synthesized using the cyclic tin alkoxide 1‐di‐n‐butyl‐1‐stanna‐2,5‐dioxacyclopentane as initiator. Poly(p‐dioxanone) was synthesized in bulk and the results have been compared with polymerizations using tin (II) 2‐ethylhexanoate (Sn(Oct)₂) as catalyst. Sn(Oct)₂ has often been reported to be an effective catalyst for the synthesis of poly(p‐dioxanone), but here it is compared with an initiator which is less prone to catalyze transesterification reactions. The results demonstrate that the cyclic tin initiator is a promising alternative for the synthesis of poly(p‐dioxanone) with a high inherent viscosity. Poly(p‐dioxanone) is a polymer with mechanical properties and a degradation rate suitable for tissue engineering applications. Both the cyclic tin initiator and Sn(Oct)₂ gave, under some reaction conditions, inherent viscosities around 1 dL/g. The best polymer synthesized using the cyclic tin initiator had a strain‐at‐break of 515% and a stress‐at‐break of 43 MPa. The inherent viscosity of this polymer was 1.16 dL/g, while Sn(Oct)₂ resulted in a polymer with an inherent viscosity less than 0.4 dL/g under the same reaction conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5552–5558, 2007     

Analysis of polyolefin stabilizers and their degradation products

Polymeric materials are complex samples, as they contain various groups of additives, compounding ingredients, and fillers. An important group of additives are stabilizers. Efficient stabilization is essential especially for polypropylene, as it is sensitive to oxidation and radical attack due to the numerous tertiary carbon atoms in its structure. How long a polymer will be sufficiently stabilized can be deduced from the contained amount of intact stabilizer. Different approaches for the analysis of stabilizers in polyolefins are available, which include sample preparation with subsequent chromatographic separation as well as direct analysis techniques. In round-robin tests, stabilizer concentrations obtained varied strongly. This shows the demand for reliable and robust methods. Stabilizers get consumed while protecting the polymer and are then present as degradation products. They were observed while quantifying intact stabilizers, in migration studies, and - if volatile - in emission studies of polymers. Furthermore, e.g. interactions with other polymer ingredients or irradiation degraded stabilizers. The identification of degradation products provides a better insight into the reactions associated with stabilization. Their quantitation makes it possible to deduce the original level of stabilization. Furthermore, polymer ingredients degrading stabilizers can be identified. Knowledge on these interactions contributes significantly to improved polymer stabilization.     

Degradation of vinylidene chloride/methyl acrylate copolymers in the presence of metal formates

Vinylidene chloride copolymers have a number of superior properties, most notably, a high barrier to the transport of oxygen and other small molecules. As a consequence, these materials have assumed a position of prominence in the packaging industry. At processing temperatures these copolymers tend to undergo degradative dehydrochlorination. The dehydrochlorination reaction is a typical chain process with distinct initiation, propagation, and termination phases. It has been demonstrated that initiation of degradation is strongly facilitated by the presence of unsaturation along the backbone. Such unsaturation may be introduced via interaction of the polymer with a variety of agents which might commonly be encountered during polymerization or processing. The presence of an unsaturated unit within the polymer generates an allylic dichloromethylene which may function as a major defect (labile) site for the initiation of degradation. The conversion of these dichloromethylene units into non-reactive groups would interrupt propagation of the dehydrochlorination reaction and lead to the stabilization of the copolymer. Potential stabilization in the presence of metal formates has been examined using a vinylidene chloride/methyl acrylate (five mole percent) copolymer and thermogravimetric techniques. The effect of the metal formate on the stability of the polymer reflects the relative halogenophilicity of the metal cation present. Metal formates (sodium, calcium, nickel(II) and to a lesser extent lead(II), cadmium, manganese(II) and magnesium) may be expected to be ineffective as stabilizers for vinylidene chloride copolymers. At the other extreme, metal formates which contain cations sufficiently acidic to actively strip chlorine from the polymer backbone, e.g., zinc formate, will function to enhance the degradation process. An effective carboxylate stabilizer must contain a metal cation sufficiently acidic to interact with allylic chlorine and to facilitate its displacement by the carboxylate anion. Copper(II) formate may possess the balance of cation acidity and carboxylate activity to function as an effective stabilizer for vinylidene chloride copolymers.     

Thermal stability of poly(vinyl chloride) with epoxidised soybean oil as primary plasticizer

Epoxidised soybean oil (ESBO) has been tested as a primary plasticizer in suspension PVC. The stabilization of the material with different traditional stabilizers has been evaluated and compared to a compound with PVC-ESBO only. Surprisingly, the addition of stabilizers seems to decrease the stability of PVC-ESBO. Traditional stabilizers, for instance Ca/Zn-stearate have been evaluated as well as metal carboxylates regarding yellowness index and UV-Vis absorption. Among the metal carboxylates, a decrease in initial discolouration, i.e. yellowness was observed with addition of Zn-stearate whereas the addition of Al-stearate improved the colour after ageing compared to PVC-ESBO without stabilizer.The stabilizing mechanism of ESBO itself, without the addition of stabilizers, has also been investigated. Analyses with ion chromatography of ESBO extracted from PVC samples without stabilizer revealed that the chlorine content of ESBO had increased when ageing the sample. MALDI analysis revealed that hydrochloric acid likely had attached to the ESBO. Reactions between ESBO and PVC were found through NMR analysis.