FT-RAMAN SPECTROSCOPIC STUDY OF THE FORMATION OF POLYENES DURING THERMAL DEGRADATION OF POLY(VINYL CHLORIDE) AND POLY (N-VINYL-2-PYRROLIDONE) BLENDS

In situ degradation of poly(vinyl chloride)/poly (N-vinyl-2- pyrrolidone) (PVC/PVP) blends has been studied by Fourier-transform Raman spectroscopy. PVP acts as a destabilizer in the thermal degradation of PVC as manifested by the reduction of temperature for the onset of degradation and the time the polymer is held at a particular temperature for this onset. Increasing the amount of PVP in the blends decreases the dehydrochlorination temperature and time. In blends containing high PVP concentrations, polyene bands dominate over nondegraded PVC bands. Maximum polyene lengths of around 35 were achieved. High PVP ratios and prolonged degradation at higher temperatures resulted in a decrease in mean polyene length due to crosslinking and oxidative scission.     

Color Stabilization of Polyvinyl Chloride) with Heat Treatment

Stabilization of polyvinyl chloride) (PVC) containing metal soaps was investigated by psychophysical colorimetry. A color difference observed among heated PVC films containing various metal salts depends on coloration of the π-complex of polyene with metal chloride converted from the metal salt added and that the stabilization effect of synergistic soaps should be based on an effect of complementary colors set up among a polyene color and metal chloride-polyene complex colors. These conclusions are well supported by colorimetry of heated PVC films containing various dyes. The color of heated PVC films containing Zn/Ca and Cd/Ba synergetic soaps markedly deviated from a polyene color with increased heat treatments, owing to greater degree of coloration of Zn complex and Cd complex, respectively. These color deviations usually decrease the thermal stability of PVC. The thermal stability of PVC was markedly improved by the use of synergetic soaps together with masking agent such as triethanolamine, urea, N,N′-dimethylol-urea, and vinylpyridine-methylmethacrylate copolymer, owing to the masking effect of these nitrogen-containing compounds. These masking agents did not slow down the dehydrochlorination of PVC.     

Degradation of PVCs obtained by controlled chemical dehydrochlorination

Thermal and thermo-oxidative degradation of poly(vinyl chloride)s (PVCs) containing increased concentrations of allylic chlorines, PVC(A)s, prepared by controlled chemical dehydrochlorination with potassium-t-butoxide (t-BuOK) have been studied. The introduction of small amounts of internal allylic chlorines into PVC significantly decreases the thermal and thermo-oxidative stability of the resin. A linear relationship exists between the initial rates (V_HCl)₀ of thermal and thermooxidative dehydrochlorination of solid PVC(A)s and the concentration S of internal allylic chlorines. Both the slope and the intercept of the thermo-oxidative (V_HCl)₀ vs. S plot are higher in oxygen than those obtained in nitrogen at the same temperature; this finding is attributed to fast oxidation of polyenes, and to peroxy radicals formed during polyene oxidation, which initiate subsequent HCl loss by attacking normal repeat units in PVC. The extent of HCl loss as a function of time during thermal degradation of PVC(A)s in intert solvent shows a rapid initial phase followed by a slower stationary phase. The first phase is due to dehydrochlorination involving the labile chlorines, while the stationary phase indicates random initiation of HCl loss at normal? CH₂? CHCl? repeat units. Initial rates of HCl loss increase with S, while the rates of HCl loss during the stationary phase are independent of S. The rate constant of initiation of HCl loss at internal allylic chlorines is almost four orders of magnitude higher than that of random initiation; however, the former is still orders of magnitude lower than that of chain propagation. Quantitative analysis of UV-visible spectra of PVC(A)s degraded in solution suggests geometric polyene distribution. The average length of polyenes decreases as the extent of HCl loss increases and reaches a constant value of ca. 3 at ca. 1% HCl loss for all the investigated PVC(A) samples.     

聚氯乙烯树脂的不饱和度和热稳定性的关系

用紫外 可见光谱法表征了不同来源的聚氯乙烯树脂（ＰＶＣ）的热稳定性，用一氯化碘加成法测量了ＰＶＣ的总的双键含量，用红外光谱法测量了ＰＶＣ的孤立双键和共轭双键的相对含量．结果表明，ＰＶＣ在加工期间的初期着色行为和长期热稳定性并不直接相关，前者取决于ＰＶＣ分子链中共轭双键的含量，而后者则和孤立双键的含量有关     

Mechanism of action of some stabilizers in the thermal degradation of poly(vinyl chloride)

The dehydrochlorination of PVC under vaccum has been studied at 170–200°C by a volumetric method. The accelerating effect of HCl is related to its interaction with the forming polyene units of macromolecules. A mechanism is proposed. The effects of various stabilizers, such as organic salts of Ca, Ba, Cd, trialkyl- and dialkyltin, trialkyl phosphites, and mixtures of phosphites with metal salts upon the rate of dehydrochlorination, polymer crosslinking, and electron absorption spectra of PVC during degradation in evacuated ampoules were investigated. The stabilizing activity of these compounds depends primarily on the effectivity of absorption of HCl and destruction of polyene units by these compounds.     

Hydrogen Halide-Catalyzed Thermal Decomposition of Poly(vinyl Chloride)

The thermal decomposition of solid PVC was studied in the presence of added hydrogen chloride and hydrogen bromide over the temperature range 170–210°C. Under certain conditions the decomposition was shown to be dependent in a first-order manner on the hydrogen halide pressure. These gases acted as catalysts, increasing the rate of HCl evolution and the degree of discoloration but not producing longer polyene sequences. Activation energy for the HCl-catalyzed process was found to be similar to that of the uncatalyzed decomposition of PVC. A unified mechanism is presented for an overall process consisting of three steps: random generation of a single carbon-carbon double bond in the cis configuration; 1,4-elimination of HCl via a six-centered transition state yielding a polyene; HCl- or HBr-catalyzed isomerization of the polyene formed by HC1 elimination to regenerate the initial structure. Hydrogen chloride catalysis is seen as an integral part of the overall process.     

含氯聚合物和乙烯-醋酸乙烯酯共聚物共混体系的红外光谱研究

关于氯化聚乙烯(CPE)或聚氯乙烯(PVC)与乙烯—醋酸乙烯酯共聚物(EVA)共混体系相容性的研究,已有不少报道,其中Coleman等人运用FTIR方法研究了含VA45％的EVA与CPE、PVC的共混体系,测定了该体系的低临界共溶温度(LCST)。一般认为,如果VA含量更低,由于EVA本身的结晶,共混体系将变得难以     

Kinetics of the Alkaline Dehydrochlorination of Polyvinyl Chloride)

From previous investigations of the alkaline dehydrochlorination of PVC it is well known that polyene sequences are formed. In this paper the true overall kinetics of the dehydrochlorination reaction between PVC and alcoholic KOH in tetrahydrofuran solution was studied at 9.5°C by measuring the rate of disappearance of KOH. Titrations of the hydroxide ions consumed and the chloride ions evolved showed close agreement. IR spectra of the samples did not show any evidence of substitution by hydroxide ions. Small amounts of DMSO present in the solvent were found to increase the reaction rate markedly. The kinetic scheme was discussed and the first rate constant was determined. Preliminary results of reactions of the polyene sequences with various reagents are presented. These reactions were made in order to introduce new functional groups into the PVC chains.     

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。     

A fluorimetric study of the chemical,photochemical and thermal degradation of poly(vinylchloride)—I. Preliminary comparative studies

Fluorescence emission and excitation spectra of dilute tetrahydrofuran solutions of thermally degraded PVC, (TPVC), photochemically degraded PVC, (PPVC), chemically degraded PVC, (CPVC) and non-degraded PVC are compared. The spectra of CPVC and PPVC are similar and are composed of a mixture of polyene structures while those of TPVC are different. The reasons for these differences are discussed.     

强紫外光作用下PVC/增韧剂体系结构与性能的演变

通过UV, FTIR, DSC及力学性能和色差的测试分析, 实时追踪了在紫外光老化过程中, 聚氯乙烯/氯化聚乙烯(PVC/CPE), 聚氯乙烯/丙烯酸酯类共聚物(PVC/ACR)及聚氯乙烯/丙烯腈-丁二烯苯乙烯共聚物(PVC/ABS)体系的微观结构和宏观性能的演变过程. 结果表明, 在光老化过程中, ACR和CPE对PVC脱HCl生成共轭双键反应、氧化降解反应、交联反应及玻璃化转变温度(T_g)的变化等均有抑制作用, 而ABS则对这些反应起促进作用. 在宏观上表现为ACR和CPE的加入能提高体系的色泽稳定性, 体系的力学性能保持率较高. 而ABS的作用相反.     

Improvement of Structural and Thermal Stabilities of PVC and Wood/PVC Composite by Zn and Pb Stearates,and Zeolite

Three different chemical stabilizers were introduced into neat PVC and a wood/PVC composite (containing 50 phr wood flour) to improve their thermal and structural stabilities. The changes in CIE yellowness index, polyene index, %wt loss, and decomposition temperature (T_d) were monitored. The effects of type and content of thermal stabilizers, thermal ageing time, and the presence of wood flour were our main interests. The experimental results suggested that the additions of Zn and Pb stearates into PVC and wood/PVC composite could improve the thermal stability of the PVC. At the test temperature of 177°C, the additions of Zn and Pb stearates could improve the thermal stabilities of PVC by retarding the upzipped reaction and by reducing the conjugated double bonds in PVC, Pb stearate being the most suitable for thermally stabilizing the PVC. Around the T_d range (～264°C), the addition of Zn stearate reduced the T_d value of PVC whereas that of Pb stearate had no effect on the change in T_d value. Zeolite loading could shift the T_d value of the PVC from 264 to 280°C. The addition of wood particles increased the polyene content and decreased the decomposition temperature of the PVC. The effect of wood flour on the thermal and structural changes of PVC overruled that of thermal stabilizer loading.     

The Effect of Hydrotalcite and Zinc Oxide on Smoke Suppression of Commercial Rigid PVC

To reduce the smoke release of poly(vinyl chloride) (PVC) during burning, layered double hydroxides (LDHs) and zinc oxide (ZnO) powders were used to modify the polymer. The results indicated that the addition of LDHs‐ZnO had a significant effect on smoke suppression. The limiting oxygen index (LOI) reached a maximum value and the smoke density rank (SDR) exhibited a minimum value when the weight percentages of LDHs and ZnO in PVC were 3% and 2%, respectively. Thermal stabilities of the modified PVC and degradation products were investigated by means of thermogravimetry and pyrolysis‐gas chromatography‐mass spectra (Py‐GC‐MS). The LDHs‐ZnO obviously accelerated the decomposition of PVC to release hydrogen chloride, and the decomposed PVC consequently produced the trans‐conjugated polyene sequences, which easily formed crosslinked structures. However, a cyclization reaction in PVC chain without the additives produced aromatic compounds such as benzene, toluene, and naphthalene at 350°C. Even though, an amount of aromatic compounds was released from the PVC modified with LDHs‐ZnO at the temperature of 600°C, the content of the decomposed products is relatively lower compared to unmodified PVC.     

Influence of the tacticity on thermal degradation of PVC. IV. Degradation in solution in comparison with degradation at solid state

Four fractions of PVC were obtained by successive extractions with appropriate solvents from PVC samples prepared in bulk at 60, 40, 0, and ?50°C. Then they were carefully characterized, especially as far as stereoregularity is concerned. The samples were submitted to thermal degradation both at solid state and as solutions in dioctyl phthalate. The type of the polyene sequence distribution in degraded samples was determined by both the UV-visible spectroscopy and the number of chain scissions resulting from the ozonization reaction. The degradation rate was proved to rise together with the syndiotactic sequence content in agreement with results in Parts I–III, obtained only with degradation at solid state. On the other hand, The content of the long polyenes relative to that of the short polyenes in the degraded polymers was found to be higher, and the number of chain scissions through ozonization reaction lower, when the syndiotactic sequence content is high. These results enable us to conclude that the actual mechanism of the PVC thermal degradation depends markedly on the tacticity distribution regardless of whether the degradation occurs either at solid state or in solution.     

Novel preparation of electrically conducting poly (vinyl chloride) by photo-dehydrochlorination from poly (vinyl chloride)/polypyrrole composite film

Polypyrrole (PPy) was deposited electrochemically on a platinum plate from a nitric acid solution of pyrrole. The PVC/PPy composite film was finally obtained by casting poly(vinyl chloride) (PVC) onto the PPy electrode from a tetrahydrofuran solution of PVC. The prepared composite film was irradiated at 90°C with a low-pressure mercury lamp in the stream of hydrogen gas saturated with steam, and the PVC film was dehydrochlorinated, leading to the formation of conjugated polyene. The electrical conductivity (σ) of the PVC film in the irradiated composite film was reveled: σ=2.51 × 10^?5S cm^?1. By iodine doping, σ was further enhanced up to 5.04 X 10^?3 S cm^?1. The tensile strength of the irradiated composite film became larger than that of the original PVC film; i.e., the stress at break was: 461 (composite film); 401 kg cm^?2 (PVC). These results were brought about by the doping of radical species to the conjugated polyene. The anion, NO^?₃, doped during the electrodeposition of PPy was photodecomposed to generate radical NO₂ and this species was doped to the polyene, resulting in the formation of electrically conductive PVC and mechanically improved composite film. © 1994 John Wiley & Sons, Inc.     

Investigations on poly(vinyl chloride). II. Pyrolysis of chlorinated polybutadienes as model compounds for poly(vinyl chloride)

The pyrolysis of chlorinated polybutadienes (CPB) was investigated by using a pyrolysis gas chromatograph. CPB corresponds to poly(vinyl chloride) (PVC) constructed with head–head and tail–tail linkages of the vinyl chloride unit. Benzene, toluene, ethyl-benzene, o-xylene, styrene, vinyltoluene, chlorobenzenes, naphthalene, and methylnaphthalenes were detected in the pyrolysis products from CPB above 300°C, and no hydrocarbons could be detected at 200°C. The pyrolysis products from CPB were similar to those from PVC and new products could not be detected. Lower aliphatics, toluene, ethylbenzene, o-xylene, chlorobenzenes, and methylnaphthalenes were released more easily from pyrolysis of CPB than from PVC; amounts of benzene, styrene, and naphthalene formed were small. These results support the conclusion that recombination of chlorine atoms with the double bonds in the polyene chain takes place and that scission of the main chain may depend on the location of methylene groups isolated along the polyene chain during the thermal decomposition of PVC.     

Photooxidation of PVC

Pure and peroxided PVC films were irradiated under monochromatic ultraviolet light between 300 and 400 nm. The degradation state of PVC is measured by means of carbonyl absorption in the infrared spectra and polyene content by UV spectroscopy. The initial rate of carbonyl formation depends on the wavelengths and oxidized impurities content. Peroxided PVC is oxidized faster than pure PVC with wavelengths above 320 nm. Two hazardous ranges of wavelengths have been detected: 300–320 and 350–370 nm. Good protection of PVC against UV radiation can be assured by the exclusion of wavelengths under 380 nm.     

界面粘结对聚氯乙烯/丁腈橡胶共混物脆韧转变的影响

应用丙烯腈（ＡＮ）含量不同的丁腈橡胶（ＮＢＲ）与聚氯乙烯（ＰＶＣ）共混，研究了界面粘结对ＰＶＣ／ＮＢＲ共混物脆韧转变的影响．结果表明：当基体层度Ｔ相等时，过强的界面粘结，使ＰＶＣ／ＮＢＲ共混物的冲击强度降低，并且其产生脆韧转变的临界基体层厚度Ｔｃ减小．界面粘结对于聚合物共混物的增韧行为具有直接的影响．损伤区分析给出：随着界面粘结强度增大，空洞化过程受阻，减弱能量的耗散，并且不利于诱导剪切屈服损伤的产生，因而不利于增韧；但是界面粘强度过小，意味着共混物的相容性太差，致使分散相粒径过大，也不利于增韧．所以对增韧来讲，共混物的界面粘结强度存在一个最佳范围．     

Heat Degradation of PVC Stabilized by Treatment with Alkylaluminum Compounds

Thermal degradation of PVC treated with alkylaluminum compounds has been studied. Four PVC samples of different molecular weights have been treated with Me₃Al, and Et₃A₁, and the dehydrochlorination rates of the polymers were determined at 190 and 220°C under a nitrogen atmosphere. The alkylaluminum-treated low molecular weight samples show marked increase in thermal stability, i. e., slower rate of dehydrochlorination right from the beginning of degradation, whereas with the higher molecular weight samples stabilization becomes pronounced only after a few percent of dehydrochlorination. The color of R₃Al-treated samples was much lighter (yellowish) than those of controls (dark brown) at 1% HCl loss. The average polyene sequence lengths formed during the early stages of dehydrochlorination are found to be much shorter with RsAl-treated PVC than with virgin samples. It appears as though polyene sequences which arose by zipping- initiation from allylic and/or tertiary chlorine sites are longer than those which form by random initiation along the chain. The autocatalytic (i. e., HC1-catalyzed) dehydrochlorination observed with virgin PVC disappears after treatment with R3A1. The HCl-catalyzed dehydrochlorination is minimized when thin films are used instead of powdery samples, which may be due to higher rates of HC1 diffusion through thin films. Autocatalysis of dehydrochlorination is affected by the concentrations of double bonds and HCl and the length of polyene sequences. Interaction between polyenes and HC1 by hydrogen transfer may lead to the re-initiation of unzipping, thus lengthening the polyene sequences.     

Reaction of poly(vinyl chloride) with superoxide anion

Reaction of poly(vinyl chloride) (PVC) with superoxide anion was carried out in tetrahydrofuran (THF) at 40°C in a nitrogen atmosphere. Remarkable changes in infrared (IR) spectra of the samples treated with superoxide anion were observed in the following regions: ca. 3300, 1680, 1620, and 765 cm^?1, which suggested the formation of hydroxyl groups, α,β-unsaturated ketone groups, and ethylenic structures. Ultraviolet–visible spectra also showed the formation of polyene structures. The content of chlorine in the polymer decreased and that of oxygen increased with reaction time. The reaction mechanism was discussed on the basis of these results.