Photodegradation of polypropylene in the presence of ferric chloride

The effect of ferric chloride (FeCl₃) on photodegradation of isotactic polypropylene (PP) was investigated using mainly ESR spectrometry. PP powder, its oxidized samples, and FeCl₃-adsorbing PP samples were irradiated under a nitrogen atmosphere at 77°K with ultraviolet light from a high-pressure mercury lamp and a superhigh-pressure mercury lamp modified by various filters. Methyl, polymerci alkyl, and peroxy radicals were observed in the ESR spectra of the irradiated samples, and it was found that FeCl₃ depresses the formation of alkyl radicals and accelerates the formation of peroxy radicals catalyzing the reaction. From infrared study of UV-irradiated film samples, it was also inferred that FeCl₃ accelerates the photodegradation the hydroperoxide and carbonyl groups.     

The melt compatibility of blends of polypropylene and ethylene-propylene copolymers

Blends of polypropylene with ethylene-propylene copolymers of various compositions have been studied by small angle neutron scattering with regard to their compatibility at room temperature and in the melt. It has long been known that such blends separate into distinct phases at lower temperatures due to the crystallinity of the isotactic polypropylene, The work described herein has shown that these blends are also immiscible in the melt, even where the ethylene content of the copolymer is as low as 8 percent. Moreover, the separated phase domains grew rapidly at melt temperatures. Blends of atactic polypropylene with isotactic polypropylene did become miscible upon melting.     

E.s.r. studies of peroxy radicals in polyethylene: 1. Temperature dependence of spectra and molecular motion of radical sites

The temperature dependence of the e.s.r. spectrum of the peroxy radicals in polyethylene was successfully observed. Two kinds of radical site were found in the amorphous region of polyethylene, one bearing the radicals corresponding to the usual e.s.r. spectrum of the amorphous pattern as for the usual polymer peroxy radicals, and the other presenting the singlet-like pattern which has never actually been observed. Computer simulation of these spectra was carried out in order to determine the anisotropic g-values as well as the ratios of the amounts of the radicals located at respective radical sites. The temperature dependence of these values made it possible to discuss the difference of the radical sites and the molecular motion of these radical sites. The motion around the chain axis was found to be much more rapid than that around the CO bond axis in the peroxy raidcals.     

E.s.r. studies on free radicals generated in poly[p-(2-hydroxyethoxy) benzoic acid] fibres at low temperatures

Free radicals generated in stretched and ground poly [p-(2-hydroxyethoxy) benzoic acid] (PEOB) were studied by e.s.r. spectroscopy in an effort to isolate those formed by main chain scission. PEOB fibres stretched at ?86°C in a dry nitrogen atmosphere gave an asymmetric spectrum, which had patterns characteristic of both phenoxy and peroxy radicals in addition to some unknown peaks. The shape of the spectrum changed with increasing temperatures, finally becoming identical to that of phenoxy radicals at room temperature. The phenoxy radical was observed in all PEOB films ground or γ-irradiated in liquid nitrogen. In some cases a small peak of peroxy radical was observed. Theoretical spectra calculated for possible radical species or combinations of them were compared with those observed. No direct evidence was observed of the formation of alkyl type and radicals which were assumed to be formed with phenoxy radicals upon main chain rupture of PEOB. However, the relatively unstable peroxy radical observed in these experiments is thought to arise from them.     

ESR study of pressure dependence of the peroxy radical decay in irradiated isotactic polypropylene

By the use of gamma radiation the free radicals were generated in isotactic polypropylene. The polymer was exposed to the action of atmospheric oxygen and the peroxy radicals were formed. Then the decay of peroxy radicals was investigated at varying temperatures as a function of pressure. The rate constants of the free radical decay were determined, and the corresponding activation volumes were calculated. The kinetic characteristics imply that the peroxy radicals predominantly occured in amorphous region the polymer. The results suggest that useful information on molecular mechanism of radical reactions in the solid phase may be obtained from the determination of activation volumes.     

Contribution to the study of mechanism of stabilizing action of esters of phosphorous acid

The rate of the reaction of a series of phosphites with cyclohexene hydroperoxide and cyclohexene peroxy radicals was studied. The results of the measurements were compared with the stabilization efficiency of the same compounds in isotactic and in atactic polypropylene at 160°C and 120°C respectively and during the course of atmospheric ageing. It was found the reverse relation between the stabilization efficiency and the reaction constants of the reaction of phosphites with hydroperoxides. The main stabilization reaction of the phosphorous stabilizers seems to be the reaction of phosphites or of their decomposition products with radicals. The possibility of splitting off of free phenol from phosphites as a result of the reaction of the esters with hydroperoxide groups was checked.     

E.p.r. study of radicals produced mechanically in PGMA and their interaction with oxygen

The vibrational grinding of poly(ethyleneglycol methacrylate) (PGMA) in vacuo at the liquid nitrogen temperature gives rise to polymer radicals in high concentrations. Changes in the radical concentration as a function of temperature in the presence and absence of oxygen were followed by means of electron paramagnetic resonance. It was found that polymer radicals reacted at very low temperatures with oxygen with simultaneous formation of polymer peroxy radicals and of a non-paramagnetic polymer tetroxide. This polymer tetroxide, which has been proved indirectly, can decompose to yield polymer peroxy radicals and non-paramagnetic products; the observed anomalies on the curve of the thermal decomposition of radicals may be thus elucidated. The relative participation of polymer tetroxide depends on the oxygen concentration, on the temperature of the sample in contact with oxygen and on the concentration of polymer radicals arising by grinding predominantly on the surface of polymer particles.     

Electron spin resonance studies on graft copolymerization of gaseous styrene onto preirradiated polypropylene. III. Preirradiation under vacuum followed by exposure to oxygen at −78°C

Grafting of styrene vapor was carried out onto polypropylene γ-irradiated under vacuum followed by exposure to oxygen at ?78°C. A comparison with the results on polypropylene irradiated in an oxygen atmosphere leads to an interesting result. Two samples were irradiated at room temperature under vacuum and in an oxygen atmosphere, respectively, the former being followed by exposure to oxygen. Although irradiation was carried out at room temperature for either sample and nearly the same amounts of the peroxy radicals are trapped, the former showed more grafting than the latter. The origin of this difference was investigated by means of electron spin resonance. Significant differences were observed in ESR spectra as well as in isothermal decays of the trapped peroxy radicals. In the former sample, the trapped peroxy radicals had a higher mobility, and consequently a significant hydrogen abstraction by the peroxy radicals was observed during storage at 40°C. This result supports the conclusion of the previous paper that the radicals effective in the grafting reaction of polypropylene preirradiated in an oxygen atmosphere are the carbon radicals which are produced by hydrogen abstraction by the peroxy radicals.     

Polarized Raman spectra of doubly oriented poly(vinyl alcohol)

Polarized Raman spectra of doubly oriented samples of atactic poly(vinyl alcohol) have been measured. The great usefulness of such polarized spectra has been clarified for the vibrational analysis. The normal coordinate treatments of syndiotactic and isotactic poly(vinyl alcohol) chain models gave good agreement between the observed and calculated frequencies.     

Study of the molecular mobility in swollen poly(epichlorohydrin) 1. Nonpolar swelling agent

The broad line n.m.r. spectra of the amorphous fraction of poly(epichlorohydrin) have been analysed. Two motional transitions were observed and the T_g and a low temperature transition β assigned to the motion of the CH₂Cl groups. The study of the poly(epichlorohydrin) swollen by a low molecular weight liquid (deuterobenzene), has provided information about the influence of swelling on the molecular dynamics, and the participation of intermolecular interactions in the second moment of the resonance lines. The observed value of the second moment of the spectra is higher than that calculated for a planar chain conformation. This indicates that the chain conformation of the atactic, amorphous poly(epichlorohydrin) is different from the conformation observed in the crystalline, isotactic fraction of the polymer.     

Structural changes in glassy polymers

It has previously been shown that glassy poly(ethylene terephthalate) gives rise to endothermal peaks in DTA when annealed at temperatures near to the glass temperature. The present work describes results obtained from DTA and DSC on annealing a number of glassy polymers which have been rapidly cooled from above the glass temperature and on slowly cooled samples of the same polymers. The polymers which have been studied are: poly(ethylene terephthalate), poly(methyl methacrylate), atactic and isotactic polystyrene, bisphenol-A polycarbonate, poly(ethyl methacrylate) and poly(vinyl acetate). In every case, evidence of structural reorganization is observed, and the rate at which this takes place is reported. Separate studies on poly(ethylene terephthalate) reflect density changes which also take place upon annealing. These results are discussed in the context of the calorimetric observations.     

Aggregation behaviour of stereoregular poly(methyl methacrylates) in dilute solution: light scattering and proton n.m.r. study

The aggregation behaviour of syndiotactic and isotactic poly(methyl methacrylate) in methyl ethyl ketone, n-butyl acetate, and 2-ethoxyethanol was investigated by light scattering and ¹H n.m.r. spectroscopy. Syndiotactic poly(methyl methacrylate) remains in its molecular form in solution at temperatures above 60°–70°C; on cooling it undergoes aggregation followed by macroscopic separation (precipitation) of the polymer from solution. The rate of these processes depends on temperature, concentration of the polymer, and solvent. Molecular solutions of isotactic poly(methyl methacrylate) can be prepared only by long-term heating at temperatures above 100°–130°C. During cooling, isotactic macromolecules prior to separation form stable associates in the region limited by discrete temperatures, and below this region polymer precipitates. The individual stereo forms of poly(methyl methacrylate) are separated from solution at different temperatures which are above the θ-temperatures of the atactic polymer.     

Initiated oxidation of PE and PP in solution

Summary A study was made on the oxidation of a low density polyethylene and of an isotactic and an atactic polypropylene in solution. The solvent was 1,2, 4-trichlorobenzene and the process was investigated at different temperatures, with varying concentrations of the initiator and of the polymer. Under the experimental conditions, a non-accelerating chain reaction proceeds at the beginning of the process. The equation derived from the proposed simplified mechanism describes consistently the dependences of experimentally measured rates on the concentrations of the initiator and of the polymer.     

Comparative study of crystallization rates by d.s.c. and depolarization microscopy

Markedly slower crystallization half times for poly(butylene terephthalate) and poly(ethylene terephthalate) are found by d.s.c. than by depolarization microscopy although similar values are obtained for isotactic polypropylene. In both the microscopic and calorimetric experiments an Avrami analysis of data on each polymer gives n ～ 3 (predetermined nucleation, spherulitic growth), over the range of crystallization temperatures investigated. Possible reasons for the observed discrepancies are discussed.     

Deformation-Induced Structural Changes in Crystalline Polyolefins

The crystal structures and the hierarchy of structural order in melt crystallized polyolefins are well known. Structural changes that occur at various levels during solid-state deformations of polyolefins have received significant attention only in polyethylene. Studies for other polyolefins have been more limited. This article is divided into separate sections on polyethylene, polyethylene-co-olefin copolymers, isotactic polypropylene, isotactic poly(butene-1), and isotactic poly(4-methylpentene-1). We first discuss in each case the crystal structure of melt crystallized polymers. We then discuss structural changes during solid-state deformations. The differences in the structural changes occurring in the various polyolefins are compared.     

E.s.r. study of u.v.-irradiated polypropylene: effect of the stereoregularity on the behaviour of free radicals produced by u.v. irradiation

The effect of stereoregularity on the behaviour of free radicals produced in polypropylene by ultra-violet light at low temperature was investigated by an electron spin resonance method. Ultra-violet (u.v.) light is absorbed mainly by carbonyl groups produced in polypropylene by oxidation. The radicals produced at low temperature are identified as ---CH₂---CH(ĊH₂)---CH₂--- and methyl. A large yield of radicals is obtained in samples of poor tacticity. Some of the ---CH₂---CH(ĊH₂)---CH₂--- radicals convert to acyl and some to ---CH₂---Ċ(CH₃)---CH₂--- on warming the sample. The conversion to acyl is remarkable in atactic and stereoblock polypropylene, and that to ---CH₂---C(CH₃)---CH₂--- in isotactic polypropylene. These acyl and ---CH₂---Ċ(CH₃)---CH₂--- radicals return to ---CH₂---CH(ĊH₂)---CH₂--- by illumination, respectively, by visible and u.v. light at 77K. The decay of radicals is attributed to the local motion or microbrownian motion of molecules.     

Kinetics of autoxidation of atactic polypropylene by infrared spectroscopy

The autoxidation of a film of atactic polypropylene was studied by means of infrared spectroscopy. Reaction temperatures varied from 110°C to 135°C and oxygen concentrations, from 5% to 100% by volume. A general reaction scheme previously reported for the autoxidation of polyolefins was utilized for atactic polypropylene. Various results obtained for this polymer were compared with those previously reported for isotactic polypropylene.     

Thermomechanical analysis of binary polymer blends

Thermomechanical analysis by penetration and extension modes, was performed on polyolefin/polystyrene blends (high density polyethylene, low density polyethylene or isotactic polypropylene with atactic polystyrene) and polyolefin/polyolefin mixtures (high density polyethylene or low density polyethylene with isotactic polypropylene). All the measurements were performed on cylindrical specimens obtained directly by extrusion on which extensive mechanical and morphological studies were previously made. It was found that the addition of small quantities of a polymer to a different polymeric matrix tend to modify the thermomechanical behaviour of the whole system. Furthermore the results showed that such an analysis seems to be a suitable tool to get useful information on the thermal and morphological transitions as well as on the interactions between the components in the blends.     

Chemical modification of polypropylenes by maleic anhydride: Influence of stereospecificity and process conditions

An investigation about the possibilities of atactic polypropylene in order to be chemically modified either in solution or in molten state processes, and further predictions about the reaction conditions' influence in the process, have been carried out. For those purposes the Box–Wilson experimental design method has been used. Besides, in order to check the experimental design polynomials forecasting of the models, additional experiments were performed at different working temperatures, kind of solvent, and stereospecificity of the polymer by comparison of processes carried out on atactic and isotactic polypropylenes. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 483–495, 1998     

Cryogenic relaxations of polystyrene and poly(fluorinated styrenes)

The effect of structural and morphologic modifications of styrene and fluorinated styrene polymers on their internal friction was studied by means of a free-oscillating torsional pendulum at temperatures from 300° to 4.2°K and frequencies of 1 to 2 Hz. Atactic and isotactic polystyrene gave the previously observed δ and β′ loss peaks at 38° and 100°K, respectively. These losses decrease in intensity with crystallinity in isotactic polystyrene but remain relatively unchanged in uniaxially drawn atactic polymer. Atactic polypentafluorostyrene showed an intense δ loss peak at 52°K and a broad shoulder around 100°K, which extends toward the β′ relaxation. In poly-α,β,β-trifluorostyrene, the δ loss peak is largely suppressed, the logarithmic decrement showing only broad maxima at 22° and 100°K. Plasticization of atactic polystyrene with 2% mineral oil gives rise to a sharp loss maximum at 100°K, which does not occur in the pure atactic polymer.