Polymer reactions. II. Thermal decomposition of polyethylene hydroperoxide

Polyethylene hydroperoxide (PEH) was prepared by low-temperature autoxidation initiated by AIBN. Over 85% of the total hydroperoxyl groups decompose by a rapid process, the remainder dissociate at about one-tenth of that rate. The results are the same whether PEH is decomposed in solution or in the solid state. Large amounts of scavenger have no effect on these decompositions; there is no radical-induced processes. The results suggest mechanisms of decomposition involving neighboring group assistance.     

Polymer reactions. VI. Inhibited autoxidation of polypropylene

The autoxidation of polypropylene inhibited by 2,6-di-tert-butyl-p-cresol (AH) and dilauryl thiodipropionate (S) was studied by the combined methods of electron spin resonance, oxygen absorption, and chemical analysis. With AH alone, there is a critical concentration of about 6 X 10^-3 mole/l. below which there is no inhibition. This critical concentration agrees with that determined for inhibited squalane autoxidation and that calculated from known rate constants. Above the critical concentration there is a well-defined induction period during which the ROO· concentration is estimated to be 10^-8 mole/l. [ROOH] decreased rapidly as did [A·] and [AH]; the latter are kinetically related. The rate constant for the reaction between A· and ROO· is estimated to be 7 X 10⁷ l./mole-sec. at 130°C. At the end of the induction period, [ROOH], [ROO·], and –d[O₂]/dt increased rapidly until steady-state values were attained for all of them. With S alone, there are only retarded oxidation but no well-defined induction periods. [ROOH] is greatly reduced by S. In all systems where the oxidation rates were appreciably suppressed there was formed a very stable paramagnetic species, S·, which was inert toward AH and I₂ but reactive toward triethyl phosphite. Because of its similarity with spin centers in carbon black, S· is postulated to be a delocalized polysulfide spin center. With both S and AH present, the combined effect of stabilization is synergistic. The observed time-dependent variations of [ROOH], [ROO·], and [A·] follow familiar mechanisms. Mathematical relationships describing each of these three systems are included.     

Polymer reactions. V. Kinetics of autoxidation of polypropylene

The rate constants for the autoxidation of polypropylene were determined by a combined ESR, volumetric, and chemical method. The values of k_i, k_p, and k_t at 110°C. are 3 × 10^?4 sec.^?1, 1.9 l./mole-sec., and 3 × 10⁶ l./mole-sec., respectively. The values of k_i and its activation energy are the same as those for the decomposition of polypropylene hydroperoxide, thus identifying the latter as the principal initiation process. The values of the temperature-independent k_t suggest that secondary peroxy radicals are the terminating species. The rate constants are compared with rate constant ratios for initiated autoxidations of squalane and other related systems.     

Polymer reactions. IV. Thermal decomposition of polypropylene hydroperoxides

The thermal decomposition of polypropylene hydroperoxide (PPH) consists of two consecutive reactions. The initial, faster reaction has rates up to 60 times that of the slower process. The former is largely suppressed by the addition of an excess of 2,6-di-tert-butyl-p-cresol. The course of reaction is the same in either solid state or in solution. The results are consistent with an intramolecular radical-induced mechanism for the initial reaction. This faster reaction consumes about 70–95% of the total hydroperoxides. The decomposition of PPH yields a maximum of about 1.8 radicals. Samples prepared from crystalline and amorphous polypropylenes have identical decomposition kinetics.     

Polymer reactions—Part VII: Thermal pyrolysis of polypropylene

Polypropylene has been pyrolysed in a carrier stream of helium from 388° to 900°C in both the programmed heating and flash pyrolysis modes. The products were on-line identified and quantitatively analysed by an interfaced GC peak identification system. The first order rate constants for pyrolysis are 3·7 × 10^?4 sec^?1 and 4·0 × 10^?4 sec^?1, respectively, for atactic and isotactic polypropylene at 388°C; the corresponding overall activation energies are 56 ± 6 and 51 ± 5 kcal mole^?1. The main products in decreasing yields are 2,4-dimethyl-1-heptene, 2-pentene, propylene, 2 methyl-1-pentene and 2,4,6-trimethyl-1-nonene. Also isolated, but in much smaller quantities, are: ethane, isobutylene, 4,6-dimethyl-2-nonene, 2,4,6-trimethyl-1-heptene, 3-methyl-3,5-hexadiene and methane. Propylene is the product of an unzipping reaction. Most of the other products can be accounted for by a mechanism involving first, random scission of carbon-carbon bonds to produce methyl, primary and secondary alkyl radicals, followed by intramolecular hydrogen transfer processes. Methane and ethane are formed from the methyl radicals. All the products found in high yields are derived from the secondary alkyl radicals.     

Decomposition of polypropylene hydroperoxide by hindered amines

The hindered amine-induced decomposition of polypropylene hydroperoxide was studied in the solid state and in the presence of a liquid solvent and the polymer was compared with model hydroperoxides. The high reactivity of the macrohydroperoxides appears to be related to the adjacent, hydrogen-bonded hydroperoxide groups that occur in the polymer. The hindered amines are converted to nitroxides in the reaction via hydroxylamine intermediates. Amine-induced decomposition of polypropylene hydroperoxide is faster in the absence of a liquid solvent for the amine than in the presence of the solvent, probably because of the strong amine-hydroperoxide association that occurs in the solid state. The decomposition process in the solid state is sufficiently rapid for the reaction to contribute to the effectiveness of hindered amines in the light stabilization of polymers.     

Accumulation of radicals in the photodecomposition of polypropylene hydroperoxide

Summary According to EPR data, upon UV irradiation both in the near (<300m) and the far (>300m) region decomposition of polypropylene hydroperoxide take place, accompanied by the accumulation of radicals at rates of 1.5·10¹⁴ and 6·10¹⁴ particles per minute, respectively.In conclusion I must thank M. V. Alfimov and V. A. Smirnov for their help in obtaining the spectra.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12 p. 2212–2214, December, 1964     

Morphology of polypropylene crystals. III. Lamellar crystals of thermally decomposed polypropylene

Morphology and crystal structure of solution-grown and melt-grown crystals of thermally decomposed polypropylene have been studied by electron microscopy and x-ray diffraction. By crystallization from dilute α-chloronaphthalene or carbitol solutions well-defined lamellar crystals about 100–150 A. in thickness are obtained from fractions (number-average molecular weights 1600–2100) of thermally decomposed crystalline polypropylene. The structure is monoclinic as crystallized from very dilute α-chloronaphthalene or carbitol solutions (0.02–0.005 wt.-%). However crystals of the triclinic as well as of the monoclinic forms are precipitated from carbitol solutions of higher concentrations (0.05-1 wt.-%). On the other hand, the separated triclinic form has been obtained from the melt. Crystals of both modifications have similar morphology. In addition, the chain molecules cannot be expected to fold, within the thickness of lamellae in crystals of either modification prepared from the low molecular weight fractions used in this study.     

Direct synthesis of fluorinated peroxides. 9. Some reactions of perfluorotertiarybutyl hydroperoxide.

The reaction of (CF₃)₃COOH with perfluoroacyl fluorides in the pressure of NaF results in the formation of new peroxy esters of the type, (CF₃)₃COOC(O)R_f. Addition of the hydroperoxide to CF₃NCF₂ yields the unstable amine (CF₃)₃COOCF₂N(H)CF₃. These reactions of (CF₃)₃COOH are compared with analogous reactions of CF₃OOH and SF₅OOH.     

Nascent polypropylene morphology: Polymer fiber

A new morphological structure has been shown to be a general feature of polyolefin powders. This feature is a fiber approximately 0.5 μ in diameter and is common to a large number of samples of polyethylene, ethylene-propylene copolymer, polypropylene, polybutene-1, and poly-4-methylpentene-1 samples. Polymer particles prepared with different catalysts under different conditions are composed of these fibers. The fibers grow from globules formed during the initial phase of polymerization, and their formation at high catalyst efficiency suggests that not all primary catalyst particles have equivalent activities. The fiber structure is one of at least six levels of order prevailing in the polypropylene particle. While the catalyst particle is responsible for some of the distinctive morphological arrangements, polymer morphology is the primary cause for the other structures. The primary catalyst particle is thought to be the determinant for the fiber.     

Analysis of nonvolatile oxidation products of polypropylene. III. Photodegradation

The nonvolatile oxidation products of photodegraded polypropylene have been analyzed by infrared spectroscopy and chemical reactions. The major functional group is ester followed by vinyl alkene, then acid. In comparison, thermally oxidized polypropylene contains relatively more aldehyde, ketone, and γ-lactone and much less ester and vinyl alkene. Photodegraded polyethylene contains mostly vinyl alkene followed by carboxylic acid. Gel-permeation chromatography (GPC) determined the decrease in polypropylene molecular weights with exposure time. A calculation determined that there is one functional group formed per chain scission; in thermal oxidation there are two groups formed per scission.     

High-pressure reactions. III. Hydrolysis of polyacrylonitrile

Polyacrylonitrile prepared from γ-irradiated monomer was found to react readily with water over a pressure range of 5,130–34,200 atm. to yield polyacrylamide, while polymer prepared by conventional free-radical catalysts will not hydrolyze under the same conditions. Reaction rates at 85°C. were measured; hydrolysis was extremely rapid at higher temperatures. Results are presented to indicate the radical nature of the reaction. Addition of a free-radical source increases the amount of hydrolysis. Pressure has an effect on the properties of the resulting polyacrylamide.     

Thermal decomposition reactions of 2-methyltetrahydrofuran hydroperoxide and peroxide

Conclusions A study was made of the thermal decomposition of the hydroperoxide and peroxide of 2-methyltetrahydrofuran in solution, the principal products were identified, and it was shown that the decomposition proceeds to a large degree with an opening of the tetrahydrofuran ring. A reaction mechanism was proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2281–2285, October, 1973.     

Lower limits of organic reactions. III

Summary Spectrofluorometry was used to confirm completeness of the reaction of carbonyls in 5.0 · 10^–4 to 5.0 · 10^–7 molar solutions. This procedure of estimation is 1000 times more sensitive than spectrophotometric methods.

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Zusammenfassung Die Vollständigkeit der Reaktion von Carbonylverbindungen in 5,0 · 10^–4-bis 5,0 · 10^–7-m Lösungen wurde durch Fluoreszenzmessung geprüft. Dieses Verfahren ist tausendmal empfindlicher als spektrophotometrische Methoden.

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Résumé On a utilisé la spectrofluorométrie pour confirmer la nature quantitative de la réaction des carbonyles en solutions de molarité 5,0 · 10^–4 à 5,0 · 10^–7. Ce procédé d'estimation présente une sensibilité 1000 fois supérieure à celle des méthodes spectrophotométriques.

     

Structure of pressure-crystallized polypropylene

The structure of polypropylene crystallized at pressures up to 5000 atm. has been studied. Upon slow cooling from the melt at 320 atm., the γ modification, previously found only in low molecular weight and stereoblock fractions, begins to appear in small amounts in addition to the normal α monoclinic form. As the pressure is increased further, a larger proportion of the sample crystallizes in the γ form until, at 5000 atm., only the γ modification is present. X-ray and DTA studies show that the γ form of polypropylene transforms to the normal α modification at a temperature only slightly below the γ melting point. Evidence is presented which favors the occurrence of a solid-state transition as a model of transformation to the α form. Results from isothermal crystallizations at low supercoolings and annealing experiments under high pressure show that the melting point of the γ modification of polypropylene is very sensitive to crystallite perfection.     

Destruction of carbonyl and hydroperoxide groups in oxidised polypropylene: Effect on photo-oxidation

The effect of destroying carbonyl and hydroperoxide groups in oxidised polypropylene on the subsequent rate of photo-oxidation has been examined using infra-red spectroscopy. The results show that carbonyl groups dominate the rate of photo-oxidation in severely oxidised polymer. In mildly oxidised polymer hydroperoxide groups control the rate, but to a much smaller extent. Destruction of the photo-active carbonyl and hydroperoxide groups in the unoxidised and oxidised polymers by prior photolysis in an inert atmosphere gave rise to some interesting and complex effects on subsequent photo-oxidation. The results indicate that although carbonyl and hydroperoxide groups may control the rates of photo-oxidation of thermally oxidised/processed polymer, their importance as primary photo-initiators is highly questionable. Oxygen-polymer charge transfer complexes appear to be the more likely photo-initiators.     

In-line rheometry of polypropylene based Wood Polymer Composites

A completely satisfactory off-line rheological investigation of Wood Polymer Composites (WPCs) is very challenging at processing temperatures: when using rotational rheometry in oscillatory mode, the linear viscoelastic region is often too small, while in capillary rheometry the sieving effect of the fibres may invalidate the results. Moreover, all off-line tests present the risk of wood degradation.To this aim, an in-line extrusion rheometer (slit die) has been developed. The major advantages are that the measurements are made in real processing conditions and degradation problems are less severe thanks to reduced oxygen level inside the extruder barrel.In order to verify the methodology, tests have been conducted on a commercial polypropylene based WPC with 30 wt.% white fir fibres and compared with off-line measurements performed at a lower temperature on the same material. For comparison, a temperature shift factor has been used, that has been estimated by characterizing the polypropylene matrix alone.     

Polymer additive analysis by pyrolysis-gas chromatography. III. Lubricants

Lubricants are widely used in thermoplastic polymers to increase the overall rate of processing or to improve surface release properties. Because of the low level of lubricants normally used in a polymer, it may not be possible to analyze the additive directly by common spectroscopic or thermal chemical techniques. However, lubricants as well as other additives in the polymer can be qualitatively analyzed by pyrolysis-gas chromatography (Py-GC) after extraction. In this work, several lubricants have been studied to demonstrate that Py-GC is a viable tool to investigate lubricants. The advantages of using Py-GC in the analysis of lubricant have also been discussed.