Partially dehydrochlorinated PVC. II. Reactions with dienophiles and hydroxylating agents

Samples of poly(vinylchloride) containing polyene sequences were made by partial dehydrochlorination by alkali in tetrahydrofuran solution, by alkali in dioxane, and thermally in dimethyl-formamide. The reactions of polyene PVC were followed by UV spectrophotometry. Dienophiles were found to have relative reactivities similar to those found in reactions with low molecular-weight dienes. The reaction with maleic anhydride yielded polymers which after hydrolysis contained carboxyl groups. Hydroxylation was made with osmium tetraoxide and performic acid. With the latter reagent the reaction proceeded to complete disappearance of the UV-absorption peaks from trienes and higher polyenes: Gel permeation chromatography analysis showed that hydroxylation could be made with only minor changes in molecular-weight distribution. The formation of gel upon thermal dehydrochlorination in DMF was shown to be due to physical cross linking probably arising by crystallization of polyene segments. The adhesion of the hydroxylated and carboxylated polymers to glass and stainless-steel surfaces was investigated. Films adhered stronger as the degree of dehydrochlorination of the polyene PVC used to make the derivative increased. Samples with long sequences adhered much stronger than those containing short sequences of corresponding degrees of total substitution.     

Chlorinated Long-Chain Fatty Acids — Their Properties and Reactions XI: Kinetics and Mechanisms of Base-Catalysed Dehydrochlorination of Sodium 9,10,12,13,15,16-Hexachlorooctadecanoate

The base-catalysed dechlorination reaction of sodium 9,10,12, 13,15,16-hexachlorooctadecanoate in aqueous ethylene glycol solutions has been studied. The kinetic and spectroscopic results obtained revealed that the dehydrochlorination reaction involves four successive steps. The first step includes almost simultaneous removal of three chlorine atoms as hydrogen chloride, one chlorine atom from each one of three vicinal dichloride groupings, after which the three remaining chlorines are released consecutively. The rate coefficients for the first and fourth (last) reaction steps were determined and the rate ratio at 363 K (90°C) was found to be about 500. The possible reaction pathways are discussed.     

On the thermal degradation of poly(vinyl chloride). II. The effect of atmosphere

The early stages of the thermal degradation of PVC were studied. Two commercial, suspension-polymerized resins were thermally treated at different temperatures and oxygen contents. Dehydrochlorination kinetics were followed by conductometric measurements and the formation of polyene sequences by ultraviolet-visible spectroscopy. Crosslinking and chain scission were followed by gel chromatography (GPC) and viscometry. No chain scission was observed in nitrogen atmosphere and no crosslinking in oxygen. Degradation in air proceeded by both reactions. The rate of dehydrochlorination for one of the investigated polymers increased linearly with the logarithm of the oxygen pressure. In nitrogen, an increasing degradation temperature was found to give both an increasing crosslinking and less discoloration. In oxygen, chain scission reactions showed a slight temperature dependence. The temperature effect on the discolorations was similar to that in nitrogen. The main difference between the investigated resins was the amount of internal doubled bonds in the original polymers, the ratio being 2:1. The higher amount resulted in a higher rate of dehydrochlorination, a larger extent of chain scission in oxygen, and a lower extent of crosslinking in nitrogen. Both in oxygen and nitrogen, the obtained results are consistent with allylic mechanisms. In nitrogen, the polyene formation supposedly proceeds by a unimolecular reaction and crosslinking by an intermolecular nonradical dehydrochlorination. In oxygen, radical reactions are superposed and may lead to chain rupture via β-scissions of alkoxy radicals.     

Partially dehydrochlorinated PVC. I. Structure

PVC made by suspension and anionic polymerization was partially dehydrochlorinated by three different methods. In the first one, a solution in THF and in the second one, particles swollen by dioxane were treated with alcoholic KOH at low temperatures. In the third method, a solution of PVC in DMF was heated to 130°C or refluxed (153°C). The reactions were followed by UV spectrophotometry and the products analyzed by GPC. Furthermore, the products were ozonolyzed and the molecular weights of the polymeric residues determined by GPC. Treatment with KOH in THF yielded products with randomly distributed polyene sequences. At higher degrees of dehydrochlorination a slight decrease in molecular weight was observed. The polymers were shown to be built up by PVC segments with an average degree of polymerization between 70 and 80, interspaced by polyene segments each with relatively few conjugated double bonds in sequence (fewer than 15). The reaction of KOH with particles swollen in dioxane was slower but yielded products with the same molecular structure. Thermal dehydrochlorination in DMF gave rise to long polyene sequences. They were fewer in number as evidenced by the higher molecular weights of the residues after ozonolysis.     

Polymers containing the s-triazine ring. II. Synthesis of poly(s-triazinylenehydrazones)

Poly(2-methyl- or 2-phenyl-s-triazinylenehydrazones) were prepared both by dehyhydration of dihydrazino-s-triazines with terephthalaldehyde and by dehydrochlorination of dichloro-s-triazines with terephthalaldehyde dihydrazone. The structure of the polymers was confirmed by infrared spectrometry and elemental analyses in comparison with those of a model compound. Dehydration yielded soluble polymers, while the dehydrochlorination yielded insoluble polymers. Most of the polymers degraded at about 350°C, and the polymers of higher molecular weight showed better thermal stability. The thermal behavior of the polymers indicated that the phenyl-substituted polymers obtained by dehydrochlorination and the methyl-substituted polymers obtained by dehydration had a degree of polymerization similar to that of the phenyl-substituted polymers obtained by dehydration. The soluble polymers could form chelate polymers, these took two accelerated decomposition phases. The lower phase suggested a decomposition accelerated by a metal. The higher phase, in which the chelate polymers decomposed more rapidly at a higher temperature (above 400°C) than their ligand polymer, was related to the atomic number and the electro-negativity of the metals. The formation of decomposition products, guanamines and nitrile compounds, in all cases indicate the preferential scission of nitrogen-nitrogen bonds.     

Graft copolymerization of poly(vinyl chloride) with styrene. II. Thermal behavior

Thermal behavior of graft copolymers of polyvinyl chloride with polystyrene prepared by using a cationic initiator (AlCl₃) was evaluated by measurement of rates of dehydrochlorination in nitrogen atmosphere. With increase in the extent of grafting the rates were found to decrease. Dynamic thermogravimetric analysis revealed an overall improvement in thermal stability of copolymers. Development of polyene sequences in degraded polymer samples was evaluated by measurement of electronic absorption spectra. In comparison to PVC, graft copolymer samples had fewer conjugated double bonds.     

聚 (β-烷氧基)对萘乙炔的超声合成

用β-萘酚、H(CH2)mBr(m=4、6、8、9)为原料，超声辐射合成出聚(β-烷氧基)对萘撑乙烯(PAONV)，研究了反应条件对中间体和聚合物产率的影响，用IR和1HNMR对中间体和聚合物的结构进行表征.实验结果表明：超声辐射合成PAONV的产率比回流搅拌合成的要高，PAONV总收率达74.4%，反应时间由35小时缩短到20小时；C2H5ONa作为碱性试剂比NaOH更有利于提高醚化反应的产率；强极性的二甲亚砜溶剂（DMSO）能提高脱氯化氢反应的产率；醚化、双氯甲基化和脱氯化氢反应的最佳反应时间分别是5h、5h、10h.     

Degradation of chlorinated polyethylene—III: Effect of additives on dehydrochlorination and oxygen absorption

Degradation of chlorinated polymers takes place via two simultaneous reactions; namely, dehydrochlorination and oxygen absorption. The dehydrochlorination and oxygen absorption of five grades of chlorinated polyenthylenes were studied at temperatures varying between 120 and 180°C. The chlorinated polyethylene grades varied in both molecular weight and chlorine content, the latter being in the range of 24.0 to 45.2 percent chlorine. Dehydrochlorination measurements on the pure polymers in both nitrogen and oxygen atmospheres showed that the rate of dehydrochlorination increases with an increase in the degree of chlorination of the polymer. The oxygen absorption rate, however, showed a decrease with higher chlorine content of the polymer. Dehydrochlorination and oxygen absorption studies were also carried out on chlorinated polyethylene containing dehydrochlorination stabilizers, antioxidants, antimony oxide, and other metal salts and metal oxides. Retardation of both oxygen absorption and dehydrochlorination was observed in the presence of antioxidants. More significant, however, was the observed action of some dehydrochlorination stabilizers as efficient antioxidants in the polymer.     

Effect of polymerization initiator on early colour of poly(vinyl chloride)

The development of early colour and the dehydrochlorination rate were compared for poly(vinyl chloride) samples obtained by suspension polymerization using two different initiators, dicetylperoxydicarbonate and butylperoxyneodecanoate. The degree of discolouration was measured on pressed plates and expressed as yellowness index (YI), the polyene sequence distribution was monitored by UV/Vis-spectroscopy, and the degradation rate was determined by measuring evolved HCI conductometrically. The PVC sample initiated by dicetylperoxydicarbonate exhibited more extensive early colour and a higher dehydrochlorination rate as compared to the sample obtained with butylperoxyneodecanoate as initiator. The UV/Vis-spectra showed that the early colour originates from polyene sequences. After extraction of the PVC resins with heptane: acetone (85 : 15) the early colour turned out to be almost the same for the two samples. From ¹³C-NMR measurements it was found that the extract of the sample polymerized with dicetylperoxydicarbonate contains unreacted initiator. We suggest that the radicals formed when the remaining initiator decomposes initiate dehydrochlorination. Our results also indicate that radicals from dicetylperoxydicarbonate may cause long-chain branches during polymerization. The radicals formed from butylperoxyneodecanoate, on the other hand, do not seem to react with the polymer molecules. © 1993 John Wiley & Sons, Inc.     

Thermal dehydrochlorination of poly(vinyl chloride) in the presence of Jatropha seed oil

Thermal degradation of poly(vinyl chloride) was studied in a nitrogen atmosphere in the presence of Jatropha seed oil, epoxidized Jatropha seed oil, and soaps (barium and cadmium) of Jatropha seed oil at various temperatures. The rate of dehydrochlorination measurement at 1% degradation, R_DH, and the time required for dehydrochlorination to attain 1% conversion were used to assess the effect of the additives on the susceptibility of the polymer to dehydrochlorination. It was found from the kinetic studies and the results from viscosity measurements on degraded polymer samples that the Jatropha seed oil derivatives suppressed the initial loss of HCl from the polymer and the extent of polymer chain scission accompanying the dehydrochlorination process. Thermal degradation studies of poly(vinyl chloride) in the presence of mixtures of barium and cadmium soaps of Jatropha seed oil were also carried out. It was found that soap mixtures containing less than 80 wt% cadmium soap exerted a deleterious (antagonistic) effect on the degradation of poly(vinyl chloride) while in the presence of soaps containing more than 80 wt% cadmium soap, considerably lower values of R_DH and higher values of t_DH were observed. The soap mixture containing 90 wt% cadmium soap was found to exhibit a remarkedly improved stabilizing effect on the dehydrochlorination of poly(vinyl chloride). © 1995 John Wiley & Sons, Inc.     

Zum Mechanismus der thermischen Abspaltung von Chlorwasserstoff aus Polyvinylchlorid. 8. mitt.: Copolymere aus Vinylchlorid und 2-Chlorpropen als polymere Modelle für tertiäre Chloratome in PVC

As polymer model compounds for branched poly (vinyl chloride) with tertiary chlorine atoms copolymers of vinylchloride and 2-chloropropene were prepared. The copolymerization was carried out in bulk at 25°C with acetylcyclohexane sulfonylperoxide. The rate of the thermal degradation of the copolymers in ethyl benzoate increases with growing content of 2-chloropropene monomer units in the polymers. In the same manner, the relative frequency distribution of polyene sequences shifts in favour of shorter sequences. The experimental results can be explained by an increased number of starting points for the dehydrochlorination due to the increasing content of tertiary chlorine atomes.     

Degradation of poly(vinyl chloride). III. Kinetics of thermal dehydrochlorination catalyzed by slow-diffusing HCl

The dehydrochlorination reaction of poly(vinyl chloride) was investigated by subjecting molded polymer discs to thermal treatments at comparatively low temperatures and for low degradation extents, such as to maintain practically unchanged the sample's composition and physical state. The HCl evolution-versus-time curves exhibited accelerating behaviors to be ascribed to the catalytic action of HCl accumulating in the samples owing to a hindered diffusion. By assuming a catalyzed dehydrochlorination reaction occurring independently from the uncatalyzed one and being first order with respect to HCl, a kinetic equation describing satisfactorily the experimental evidence was deduced.     

On the influence of HCl on the thermal degradation of poly(vinyl chloride)

The thermal degradation of PVC was studied at 190°C in pure nitrogen and nitrogen containing 10, 20, and 40% HCl (by volume). The rate of dehydrochlorination was determined by gravimetry. Degradations in nitrogen were followed with conductometry in addition. Changes in molecular weight distribution and degree of long-chain branching (LCB) were determined by gel permeation chromatography–viscometry and polyene sequence distribution by UV spectroscopy. The rate of dehydrochlorination increases with the HCI content of the atmosphere. The rate of molecular enlargement also increases but only as a result of the increased dehydrochlorination rate. The increase in M _w and LCB are thus related to the extent of conversion only. Changes in the UV spectra indicate that the increase in rate of dehydrochlorination is mainly due to increased propagation rate in atmospheres containing less than 10% HCI. At higher HCI contents an increase in initiation rate is noted. It is suggested that this, at least in part, is due to the fact that HCI, by forming a cyclic transition state, catalyzes the random elimination of HCI. This process, in turn, is promoted by the presence of polyene sequences.     

Chemical modification of rigid poly(vinyl chloride) by the substitution with nucleophiles

The reaction of rigid poly(vinyl chloride) (PVC) with iodide, hydroxide, azide, and thiocyanate as nucleophiles (Nu) in ethylene glycol (EG) resulted in the substitution of Cl by Nu additional to the elimination of HCl, leading to the dehydrochlorination of the rigid PVC. High substitution rates were observed for hydroxide, azide and thiocyanate, while the addition of iodide accelerated predominately the elimination of HCl. The substitution by thiocyanate resulted at 150°C in both thiocyanate and isothiocyanate structures, whereas at 190°C, only isothiocyanate was observed in the polymer. The dehydrochlorination yield increased with an increasing molar SCN/Cl ratio, resulting in a maximum substitution at high molar SCN/Cl ratios. When EG was replaced by diethylene glycol (DEG) as solvent, the dehydrochlorination was found to be accelerated. It was assumed that DEG has a higher compatibility with PVC, making it easier to penetrate the rigid PVC particle. For triethylene glycol (TEG), the rapid dehydrochlorination resulted probably in the coverage of the surface of the PVC particle by methyl methacrylate/butadiene/styrene (MBS), preventing the penetration by the solution. The substitution/dehydrochlorination ratio decreased in the order of EG > DEG > TEG because of the declining polarity of the solvent, stabilizing the activated S_N2 complex. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

On the thermal degradation of poly(vinyl chloride). I. An apparatus for investigation of early stages of thermal degradation

A dehydrochlorination apparatus is described for studies of the early stages of the thermal degradation of poly(vinyl chloride) (PVC), combining good reproducibility, high accuracy, and a low detection limit. The evolved hydrogen chloride is absorbed in water and the electrical conductivity is continuously recorded. Measurements of the rate of dehydrochlorination repeated over an extended period of time showed a standard deviation of 2% of the mean value. The activation energies for the dehydrochlorination in nitrogen for two commercial suspension-polymerized samples were found to be 27.9 ± 1.5 and 26.2 ± 0.6 kcal/mole.     

Diffusion of stabilizers in polymers. II. 2-hydroxy-4-octoxybenzophenone in polyolefins

The migration of radioactively labeled 2-hydroxy-4-octoxybenzophenone in a number of polyolefins was investigated over the temperature range 36–75°C. The rates of diffusion in the polymers studied were found to decrease in the order low-density polyethylene > high-density polyethylene ～ isotactic polypropylene, the activation energies being approximately 17, 36, and 24 kcal/mole, respectively. The results of the present study were found to be in qualitative agreement with those previously determined for the same stabilizer/polymer systems, quantitative differences being attributed to the different methods of sample preparation and the resulting differences in the morphological structures of the test specimens. The calculated solubilities of the substituted 2-hydroxybenzophenone in the various polymers were substantially higher, at a particular temperature, than the corresponding values previously determined for 2,4-dihydroxybenzophenone, being 1.4, 0.4, and 0.8 wt-% for low-density polyethylene, high-density polyethylene, and polypropylene, respectively at 75°C. Studies to determine the rate of loss of the stabilizer from polymer samples immersed in water resulted in extremely low rates of extraction, in contrast to those found for 2,4-dihydroxybenzophenone, as a result of the octoxy substituent and the resulting increase in compatibility between the stabilizer and polymer.     

Continuous dosing of fast initiator during vinyl chloride suspension polymerization: Thermal stability of PVC resin

Thermal stability of poly(vinyl chloride) (PVC) produced using continuous dosages of a fast initiator method was investigated in terms of morphological and microstructural characteristics. The results were compared with the properties of the PVC prepared by conventional polymerization method. The Brabender^® Plastograph and DSC results showed a lower fusion time, higher stable time, and greater degree of fusion for PVC obtained by polymerization using initiator continuous dosage method. Also, chemical analysis indicated that the PVC produced under an initiator continuous dosage system have lower structural defects, that is, branch numbers, internal double bonds, labile chlorine, and tacticity index, thereby improving the thermal stability of PVC resin. The results obtained from dehydrochlorination and thermogravimetry analysis confirm the improvement of thermal stability of PVC chains synthesized with continuous dosages of a fast initiator. Moreover, it was found that the concentration of microstructural defects and the dehydrochlorination rates of the PVC samples prepared by both processes increase with monomer conversion, particularly after critical conversion. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44480.     

Effect of thermal decomposition on dielectric relaxation process of poly(vinyl chloride)

Dielectric absorption caused by the molecular relaxation of thermally decomposed poly(vinyl chloride) in air was studied on samples in the form of thin films. It was found that, with the progress of thermal decomposition, the magnitude of α dielectric absorption changes in three stages: (1) initial decrease in magnitude corresponding to the process of the formation of polyene sequences caused by dehydrochlorination; (2) ensuing increase corresponding to the deformation of polyene sequences attributed to oxidation; (3) final decrease corresponding to the formation of crosslinks.     

Studies of the solid-state thermal degradation of PVC. I. Autocatalysis by hydrogen chloride

The thermal degradation of virgin and HCI-treated PVC in powder form, as well as of PVC films of different thicknesses, has been studied as a function of time and temperature. The rate of dehydrochlorination was determined conductimetrically and from the polyene sequence distributions as obtained by UV spectroscopy. Increases in the rate of dehydrochlorination, ranging between 30 and 45%, were observed at all temperatures for the samples pretreated with HCI, while the corresponding activation energies were found to be lower by about 20%. For the PVC films, the rate increased with thickness, i.e., with longer residence time of evolved HCI within the sample. The results offer insight regarding the autocatalytic role of evolved HCI.     

Dehydrochlorination of poly(vinyl chloride) with Ca(OH)2 in ethylene glycol and the effect of ball milling

The dehydrochlorination behavior of pure and flexible PVC in ethylene glycol was studied in the presence of Ca(OH)₂ at temperatures between 170 °C and 190 °C. Although the dehydrochlorination proceeded slower in Ca(OH)₂ than in NaOH, similar dehydrochlorination yields were obtained. It was assumed that the slower reaction rate was a result of the low solubility of Ca(OH)₂ and the larger solvation shell of the Ca²⁺ ion. The dehydrochlorination rate and yield were improved by employing a ball mill. Additionally, diisononyl phthalate and CaCO₃ were quantitatively separated from flexible PVC during the ball-milling process. The maximum dehydrochlorination yield of pure PVC after 7 h at 190 °C was 74%. After 8 h at the same temperature, a comparable dehydrochlorination yield of 77% was achieved for flexible PVC, which could be increased by ball milling to 86%.