The action of concentrated sulphuric acid on polyethylene and polypropylene: Part 1—Evolution of sulphur dioxide and carbon dioxide

The evolution of sulphur dioxide and carbon dioxide during the reaction between concentrated sulphuric acid and low density polyethylene, isotactic polypropylene and atactic polypropylene at 100–125°C has been followed. Atactic polypropylene is the most susceptible, and isotactic the least susceptible, to acid attack, and this order of reactivity can be accounted for by both structural and morphological effects. It appears that acid attack is partially autocatalytic in nature.     

A permanganic etchant for polyolefines

A permanganic etchant has been developed which reveals lamellar and other fine detail in surfaces of at least three crystalline polyolefines, viz., polyethylene (of both high and low density), isotactic polypropylene, and isotactic poly(4-methylpentene-1). In typical treatments of high-density polyethylene ca. 2 μm of material is removed with defective regions suffering preferential attack. The etchant also discriminates between lamellar orientations, eating deeper where side surfaces of laminae are exposed than on fold surfaces, and between different polymers, attacking isotactic polypropylene more strongly than polyethylene. Comparison with other techniques authenticates the detail exposed and samples appear to be otherwise unaltered by their treatment. Besides normal imaging, it is also possible to use etched samples for transmission diffraction studies in the electron microscope. The method has very considerable application for revealing lamellar details in crystalline polyolefines (which can be chosen to be representative or selective according to the nature of the surface used). Examples are given of a wide variety of melt-crystallized morphologies for the three polymers cited and also of lamellae in a drawn polyethylene sample. It is pointed out that permanganic etching is complementary to the technique of chlorosulfonation used to stain polyethylene in a similar way as bright field microscopy is to dark field.     

Adsorption of Linear Polyethylene and Isotactic Polypropylene from 1,1,2,2-Tetrachloroethane and 1,2,3-Trichloropropane on to Polar Adsorbents

Linear polyethylene and isotactic polypropylene samples were dissolved in 1,1,2,2-tetrachloroethane or 1,2,3-trichloropropane and injected at 135 °C into columns packed with porous particles of hydroxyapatite, aluminium oxide, zirconium oxide, Florisil, or silica gel. Both polymers were retained, to different extents, within the columns. It is hypothesized that the polymers interact with the surfaces of the adsorbents and are adsorbed. Retention of isotactic polypropylene from 1,1,2,2-tetrachloroethane was in the order aluminium oxide > hydroxyapatite ≈ zirconium oxide ≈ Florisil ≈ silica gel. Recovery of polyethylene from 1,1,2,2-tetrachloroethane was almost the same on aluminium oxide, hydroxyapatite, zirconium oxide, and Florisil; it was more retained by silica gel. Polyethylene was usually more retained than polypropylene. Recovery of polyethylene from both chlorinated solvents was similar whereas recovery of polypropylene was better from 1,2,3-trichloropropane than from 1,1,2,2-tetrachloroethane. Both chlorinated solvents are toxic and may attack seals in a Waters 150C chromatograph. Moreover, the polymers may be chlorinated in these solvents. For these reasons they are not optimum solvents for routine analysis. This is the first time polyethylene and polypropylene have been found to be retained by adsorbents with pore diameters in the range 60–300 Å. Desorption of the retained polymers is possible with some polar solvents.     

Diffuse interphase layer in microheterogeneous polymer mixtures

The thickness of the interphase layer as a function of time at 160°C has been determined directly in a microheterogeneous polymer mixture, and the layer thickness between two bonded sheets has also been measured by phase-contrast microscopy. Two mixtures of polymers, isotatic polypropylene with polyethylene and poly(vinyl chloride) with polyethylene, were prepared by mixing size-sorted powders in suspension, followed by evaporating the suspension medium and compacting the powdered mixtures. The mutual penetration initially obeyed Fick's second law; then diffusion was retarded and stopped after 15–20 min. An equilibrium state was reached which did not correspond to the classical thermodynamic equilibrium, at which the so-called equilibrium thickness of the interphase layer for the pair isotactic polypropylene-polyethylene was about 28,000 Å and for the pair poly(vinyl chloride)-polyethylene was about 89,600 Å. The equilibrium values can be used as a quantitative criterion for the compatibility of the polymer pairs.     

Manganese‐based transition metal complexes as new catalysts for olefin polymerizations

Three manganese complexes, Mn(acac)₃ (acac = acetylacetonate), Cp₂Mn (Cp = cyclopentadienyl), and Mn(salen)Cl [salen = 1,2‐cyclohexanediamino‐N,N′‐bis(3,5‐dit‐butyl‐salicylidene)], were used for ethylene and propylene polymerizations. These complexes, in combination with an alkylaluminum cocatalyst such as methylaluminoxane (MAO) or diethyl aluminum chloride (AlEt₂Cl), could promote ethylene polymerizations that yielded extremely high molecular weight linear polymers, but were inactive for propylene polymerizations. The counterparts supported on MgCl₂ showed activities even for propylene polymerizations and had remarkably enhanced activities for ethylene polymerizations. In the presence of an electron donor such as ethylbenzoate, the MgCl₂‐supported manganese‐based catalysts yielded a highly isotactic polypropylene with a high molecular weight. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3733–3738, 2001     

Mechanism of inhibition by copper stearate of the photo-degradation of polyolefins

The effect of a series of transition metal (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) stearates in retarding the photo-degradation of isotactic polypropylene has been examined and it has been found that the results obtained are quite similar to those for high density polyethylene.Infra-red spectral analysis of the polyethylene and isotactic polypropylene films showed that, in the early stages of the photo-irradiation, photo-chemical reaction of the copper stearate took place in the films to change its structure and that rapid formation of terminal unsaturation occurred only in the films containing copper stearate. The results obtained suggest that the copper stearate provides a radical scavenging function, as well as an ultraviolet light absorbing function, to protect the polymers against photo-degradation.     

Chemiluminescence of hydrocarbon polymers

The thermal oxidation of some hydrecarbon polymers differing by their degree of branching was studied simultaneously by chemiluminescence and infrared spectrophotometry. In the case of isotactic polypropylene, measurements were made at various temperatures ranging from 140 to 180°C. The other polymers—ethylene–propylene copolymer, low and high density polyethylene—were studied only at 160°C. In all cases, the induction times of chemiluminescence coincide with those of carbonyl growth. The previously proposed mechanisms of light emission are not consistent with the kinetic data or with the structure effects on luminescence, which seems directly related with the presence of tertiary hydrogens. A hypothetical mechanism based on the β scission of tertiary alkoxyls is proposed.     

Ziegler polymerization of olefins. IX. Donor effects in metal alkyl-free and Ziegler-type stereospecific catalysts

Electron donors, especially trialkylamines and azulene, have been examined in aluminum alkyl-, CH₃TiCl₃- and hydrogen-activated TiCl₃ catalysts for the polymerization of propylene to isotactic polymer. A comparison and an evaluation were made with findings which were established earlier with zinc alkyl-based TiCl₃ catalysts. We find that the donor, when it is present in low concentrations in all of the above catalysts, can inactivate preferentially the less stereoregulating sites. In this way the isotactic content and the molecular weight of the polymer are increased, but only at the expense of a lower catalyst activity. The addition of hydrogen to the TiCl₃–donor catalyst at ?78°C produced a threefold effect: (1) the activity of the catalyst was increased about 5 to 15 times and higher, (2) the polypropylene formed with this more active catalyst was more isotactic (ca. 10–15%), and (3) the polymer had a lower molecular weight. It is proposed that the increase in catalyst activity was due to the generation of Ti-H bonds to which propylene molecules then added, the Ti-H bonds thus being transformed into active Ti-C centers.     

Hydrogen production in γ-ray and helium-ion radiolysis of polyethylene,polypropylene, poly(methyl-methacrylate), and polystyrene

The production of molecular hydrogen in the radiolysis of high-density polyethylene, isotactic polypropylene (PP), poly(methyl-methacrylate) (PMMA), and polystyrene (PS) by γ rays and 5–20-MeV helium ions was investigated. Molecular hydrogen is the dominant gaseous product from these polymers, and the yields with γ rays are 3.3, 2.6, 0.24, and 0.033 molecules per 100 eV of energy absorbed for polyethylene, PP, PMMA, and PS, respectively. The decrease in observed hydrogen is due to increased branching and the chemical nature of the groups on the side chains. There is an increase in hydrogen production with increasing linear energy transfer (LET) from γ rays to helium ions, but the relative increase depends on the polymer type. With incident 5-MeV helium ions, the respective yields of molecular hydrogen are 4.6, 3.2, 0.62, and 0.15 molecules per 100 eV. The increase in molecular hydrogen with increasing LET may be due to changes in the kinetics of hydrogen precursors in the particle tracks. The differences in the relative increases in molecular hydrogen with increasing LET for each of the polymers suggests that self-scavenging reactions may be important for low LET particles. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1656–1661, 2000     

Advances in propene polymerization using MgCl2‐supported catalysts. Fundamental aspects and the role of electron donors

The fundamental factors determining the performance of state‐of‐the‐art MgCl₂‐supported catalysts for polypropylene are becoming increasingly evident. Polymer yield, isotacticity, molecular weight and molecular weight distribution are dependent on the regio‐ and stereoselectivity of the active species. Chain transfer with hydrogen after the occasional regioirregular (2,1‐) insertion has a strong effect on molecular weight and is the main reason for the high hydrogen response shown by high‐activity catalysts containing diether donors. Hydrogen response is also dependent on stereoselectivity. The probability of a stereo‐ or regioirregular insertion can be related to the lability of donor coordination in the vicinity of the active species. Results with different catalyst systems can be interpreted on the basis of a propagation model involving interconverting active species, such that polypropylene produced using MgCl₂‐supported catalysts can be regarded as a stereoblock polymer comprising (highly) isotactic sequences, moderately isotactic (isotactoid) sequences and syndiotactoid sequences. Strongly coordinating donors will give stereoregular polymers in which highly isotactic sequences predominate.     

Universal calibration in GPC: A study of polystyrene,poly-α-methylstyrene,and polypropylene

The theoretical justification for using M[_η], or a similar quantity, as a universal calibration parameter in GPC is reviewed. The equation based on this parameter is applied to transform the primary calibration curve, obtained by means of polystyrene samples, into calibration curves for poly-α-methylstyrene, polypropylene, and linear polyethylene. The Mark–Houwink equations for these polymers, as they are used in the transformation, are discussed. The resulting GPC calibration curves are compared with molecular weights and peak elution volumes of fractionated poly-α-methylstyrene and polypropylene. The same comparison is made with samples of polypropylene and polyethylene having very broad molecular weight distributions. The agreement lies within experimental error.     

The action of concentrated sulphuric acid on polyethylene and polypropylene: Part 2—Effects on the polymer surface

The physical and chemical changes that occur on the polymer surfaces during the reaction between concentrated sulphuric acid and films of low density polyethylene, high density polyethylene and isotactic polypropylene at 75–125°C have been studied. Sulphonation-desulphonation reactions, leading to olefinic conjugation and, ultimately, carbonisation, are the most significant chemical changes. These, together with the disruption of the polymer surface, explain the autocatalytic evolution of SO₂ noted previously.     

Preparation of p-[(S)(—)-2-phthalimidopropionyl] polystyrene

Samples of atactic and isotactic polystyrene were acylated with N-phthaloyl-L -alanyl chloride under the conditions of Friedel-Crafts reaction. The degree of acylation was strongly dependent on molecular weight, but not on the tacticity of polystyrene. Similarly the specific rotation of acylated polymers was not influenced by the structure of the polymer chain.     

Spherulite boundary strengthening concept for toughening polypropylene

During spherulitic crystallization of polymers, there is a tendency for low molecular weight and other less crystallizable entities to be rejected from the body of the spherulites. This rejection process causes a segregation of these species to those areas where spherulites impinge. As a result of this segregation, lamellar and spherulite boundaries have a tendency to become weak, often resulting in premature mechanical failure. The objective of this work, anthropomorphically speaking, is to develop a melt miscible blend system in which a propylene copolymer “fools” a polypropylene homopolymer into rejecting the copolymer to the spherulite boundaries as an impurity. However, once the copolymer arrives at these boundaries, the copolymer subsequently connects adjacent spherulites through cocrystallization of the propylene copolymer segments. It was found that addition of either a random ethylene–propylene copolymer or an isotactic–atactic block copolymer was able to yield the desired effect. Cocrystallization was confirmed by calorimetry, and segregation of copolymer and subsequent reinforcement at the spherulite boundaries was directly observed microscopically. Using this approach, toughness was increased with little loss in stiffness. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2047–2056, 1998     

Neutron reflectivity studies of hot polymer melt interfaces

Neutron reflectivity data have been obtained using a specially designed cell that allows the investigation of the interfaces between polymers in the melt state. Systems which are semicrystalline at room temperature can be investigated for the first time. Example results from a polystyrene (PS)/ polyethylene (PE) interface (both with and without copolymer) and an isotactic polypropylene (PP)/ high density polyethylene interface are presented.     

Polymers from a levopimaric acid–acrylonitrile Diels–Alder adduct: Synthesis and characterization

The Diels–Alder adduct of levopimaric acid with acrylonitrile was efficiently prepared from resin acids. Excellent addition reaction yields (ca. 95%) were obtained. The adduct was converted into polyamides by polycondensation with diamines. When the same adduct was subjected to a dehydrodecarboxylation reaction, a novel ketone dinitrile derivative was obtained. This trifunctional product was also converted into polyamides by polycondensation with diamines. When the ketone dinitrile was hydrolyzed in the presence of alkalies and the reaction product was chlorinated, a ketone diacid chloride was obtained. A polyester was synthesized by the polycondensation of the diacid chloride with a diol. The structures of the Diels–Alder adduct, ketone dinitrile derivative, ketone diacid chloride, and polymers were established by means of elemental analysis, IR and NMR spectroscopy, and molecular weight determinations. Both the polyamides and the polyester were low‐molecular‐weight polymers soluble in polar solvents. The thermal behavior of the monomers and polymers was evaluated by thermogravimetric analysis. The thermal studies showed that the polymers were fairly thermostable substances, except the polyester, which appeared to be a substance with good thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6308–6322, 2005     

Autoxidation of polypropylene catalyzed by cobalt salt in the liquid phase

The autoxidation of isotactic polypropylene suspended in the organic solvent was found to proceed very rapidly in the presence of cobalt salts. The rate of oxidation increases and the induction period decreases as the concentration of the cobalt is increased. The rate of oxidation depends on solvent and is quite fast in fatty acids. Polypropylene has shown a rapid decrease in molecular weight at the initial stage of oxidation, and the volatile products were mainly composed of carbon dioxide and small amount of carbon monoxide. Other oxidation products were acetic acid-soluble resinous materials, having molecular weights of 250–730, with a molar ratio of carbon to oxygen of 3.0–5.4. Atactic polypropylene, relatively stable against oxidation, was oxidized easily in the presence of cobalt and bromide ion. The difference in the rate of oxidation depending on the tacticity of polypropylene is attributed primarily to steric hindrance to the intramolecular hydrogen abstraction step.     

Diffusion of Cu2+ catalysts from Cu-metal polymer or Cu-oxide/polymer interfaces into isotactic polypropylene

Diffusion coefficients of Cu²⁺ in the form of its carboxylate have been measured in isotactic polypropylene as a function of temperature (90–128°C) and extent of preoxidation. Diffusion take place from the metal catalyst/polymer interface into the bulk polymer. The diffusion is dependent on the extent of preoxidation and temperature but not on the type of catalyst (Cu, CuO, CuO_0.67). Analysis of polymer sections for Cu²⁺ ions was carried out with a selective Cu²⁺ electrode. Diffusion in isotactic polypropylene is about 1000 times faster than in lowdensity polyethylene. The carboxylate anion appears to have about 7 C-atoms for diffusion in isotactic polypropylene compared with 29 C-atoms for low-density polyethylene.     

Selective removal of polyethylene or polypropylene from their blends based on difference in their adsorption behaviour

The adsorption of polyethylene and polypropylene on zeolites depends on the nature of zeolite, the solvent as well as the molar mass of the polymer sample. For example, linear polyethylene is strongly retained on zeolite SH-300 from decalin, while isotactic, syndiotactic or atactic polypropylene is fully eluted in this system. On the other hand, polypropylene is retained on zeolite CBV-780 from diphenylether, while linear polyethylene is eluted. These differences in the elution behaviour have been utilised for selective removal of either linear polyethylene or polypropylene from blends of both polymers. The desorption of the retained polymer is difficult, or at times impossible. However, the selected adsorption systems have complimentary character, i.e. either one or second component is eluted or fully retained. Thus these sorbent/solvent systems, identified herein, are the first isocratic chromatographic systems, which enable selectively to remove polyethylene or polypropylene from their mixture. Moreover, decalin/SH-300 enables the removal of both linear and branched polyethylene from mixtures with random ethylene/propylene copolymers (polyethylene fully retained, ethylene/propylene copolymers eluted).     

Viscoelastic behavior of semicrystalline polymers at elevated temperatures on the basis of a two‐process model for stress relaxation

Viscoelastic behavior at elevated temperatures of high‐density polyethylene and isotactic polypropylene was investigated by using the stress relaxation method. The results are interpreted from the view of an established two‐process model for stress relaxation in semicrystalline polymers. This model is based on the assumption that the stress relaxation can be represented as a superposition of two thermally activated processes acting in parallel. Each process is associated either with the crystal or amorphous phase of a polymer sample. It was found that the temperature dependence of viscosity coefficients and elastic moduli of these two fractions are similar in the two materials. The experimental data was correlated with literature data of α and β processes in polyethylene and polypropylene obtained from dynamic mechanical thermal analysis. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3239–3246, 2000