Dynamic evolution of gases in the γ‐ and helium‐ion radiolyses of solid polymers

The dynamic evolution of gaseous hydrogen, methane, and carbon dioxide in the γ‐ and ⁴He‐ion radiolyses of solid polymers was investigated. The polymers used include low‐density and high‐density polyethylene, polypropylene, polystyrene, poly(methyl methacrylate), Nylon 11, Nylon 6, and poly(dimer acid‐co‐alkyl polyamine). An inline quadrupole mass spectrometer was utilized to monitor the dynamic profiles of the gases produced in the radiolysis. One‐ and two‐dimensional numerical diffusion models were developed to simulate and extract optimum diffusion coefficients and gas yields from the experimental dynamic gas profiles. It was found that the dynamic evolution of molecular hydrogen from the bulk polymer is controlled by its diffusion in most cases, such as CO₂ in poly(methyl methacrylate). In the γ radiolysis of some polymers such as low‐density polyethylene and polypropylene, the dynamic evolution of methane is only partially controlled by the diffusion process, and some other postirradiation process is a factor. It is concluded that the simulation method developed in this article is helpful in understanding and predicting the mechanisms of gas evolution in the radiolysis of solid polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1449–1459, 2001     

Radiolytic Grafting of Styrene on Polymethylpentene Film

Gamma ray initiated grafting of styrene on three polymers gave rates in the order polyethylene > polypropylene > polymethylpentene, with saturation absorption of styrene in the order polymethylpentene > polypropylene > polyethylene, indicating that the plasticizing action of absorbed styrene possibly causes increased termination rate and reduced over-all grafting rate. The rate of styrene grafting on polymethylpentene was unaffected by temperature change in the range from 23 to 85°C. Above a certain critical film thickness, styrene grafting rate is proportional to film surface area rather than film weight.     

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.     

Catalytic activity of a ceria-lanthana system for 4-methylpentan-2-ol dehydration

A ceria-lanthana catalytic system prepared by the sol-gel technique proved to be active in 4-methylpentan-2-ol conversion, mainly leading to 4-methylpent-1-ene, a monomer for manufacturing polymers of high technological properties. The product distribution strongly depends on the acid-base features of the catalyst. The catalytic behavior of the samples was examined in the light of their acid-base properties. This revised version was published online in June 2006 with corrections to the Cover Date.     

Etude du phenomene pulsatoire periodique observe au cours de la rÉaction de certains polymeres fondus avec l'oxygene-III: Cas des copolymeres ethylene-propylene et autres polyolÉfines

The existence of the phenomenon of secondary cool flame (SCF) is considered for polymers other than polypropylene using two complementary techniques. A static reactor (self ignition reactor) and a semi-batch type reactor have been used. Polymers having structure similar to that of polypropylene, e.g. poly(1-butene) (PB1), poly(4-methyl-l-pentene) (PM4P1), exhibit the phenomenon as well as various elastomers (mainly ethylene-propylene copolymers). It was not observed for polyethylene. The theory of the secondary cool flames established previously allows calculation of an overall activation energy on the basis of frequency measurements. Further, for each of the studied materials, there is an oxygen molar fraction (No_2,m) in the oxidizing gas below which no oscillations can be observed. If No_2,m depends on the reactivity of the various polymers with oxygen around 300`, these reactivities can be arranged in the following decreasing order: polypropylene. PM4P1 and PB1. This order is confirmed by the overall activation energies. Vulcanization of the ethylene-propylene copolymers has a marked inhibiting effect on SCF. This vulcanization decreases the hydrogen located at tertiary carbon atoms: it is inferred that, at least in the studied cases, SCF is a manifestation of the reactivity of these tertiary carbon atoms.     

Photo-degradation and photo-oxidation of polyolefins: Importance of oxygen-polymer charge transfer complexes

The effect of prior irradiation (λ's > 300 nm) in an inert atmosphere on the subsequent photo-oxidative stabilities of polypropylene and low density polyethylene films has been examined using luminescence, infra-red and ultraviolet absorption techniques. Prior prolonged irradiation in an inert atmosphere of nitrogen was found to have no significant effect on the subsequent rates of photo-oxidation of the polymer films. The importance of oxygen-polymer charge transfer complexes in initiating photo-oxidation of the polymers is discussed in relation to the behaviour of other major photo-initiators such as carbonyl/unsaturated carbonyl and hydroperoxide groups.     

Reaction of perfluoro-2-methylpent-2-ene with azoles

Perfluoro-2-methylpent-2-ene reacts with pyrazole, imidazole, 1,2,4-triazole, and benzotriazole to give products of the replacement of the vinylic fluorine atom. In the case of imidazole, the product of allylic fluorine substitution, 1,3-bisimidazolylperfluoro-2-methylpent-2-ene, is also formed. The structures of the products were confirmed by spectral data. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 835–837, April, 1997.     

ESCA study of the surface photo-oxidation of some non-aromatic polymers

Changes in the surface composition and structure of a number of non-aromatic polymers subjected to ultraviolet irradiation in oxygen (～ 1 atm., 20°C) have been studied. No changes in surface composition were detected after photo-oxidation of poly(vinylidene fluoride) (12 h of irradiation), low density polyethylene (7·5 h) or high density polyethylene (22·3 h). This reflects the absence in these polymers of an efficient ultraviolet absorber to initiate the photo-oxidation. The surfaces of poly(methyl methacrylate) and nylon 66 show an increase in oxygen content following irradiation. In these polymers this added oxygen is present principally as carboxyl groups and, in the case of poly(methyl methacrylate), as carbonyl groups. In nylon, there is no evidence for changes in the amide group and no oxidation of the nitrogen is detected.     

Photo-stabilising action of orthohydroxy aromatic compounds in low density polyethylene film: UV absorption versus radical scavenging

The importance of uv absorption versus radical scavenging in the photo-stabilisation of low density polyethylene by various concentrations of 4-methoxy and 4-n-octoxy substituted 2-hydroxybenzophenones and 2(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole is examined using infra-red and second-order derivative uv absorption spectroscopy and hydroperoxide analysis. Unlike our earlier study with polypropylene, the stabilisers were found to be just as effective when used as screens as when directly present in the polymer matrix. This effect was particularly prominent at concentrations >0·1 % w/w under both polychromatic light of λ's > 300 nm and monochromatic light of 365 nm wavelength. Under 254 nm wavelength exposure screening appeared to be dominant at all concentration levels examined > 0·01 % w/w. These data, coupled with rates of photo-decomposition, indicate that in low density polyethylene the additives migrate rapialy to the surface of the polymer whereupon they are capable of operating as both effective screens and radical scavengers; the effects observed are, as expected, wavelength dependent.     

Editorial

Hydrocarbon polymers are sensitive to thermo-oxidative degradation at all stages of their existence. Measurable oxygen consumption by unstabilized, powdered high density polyethylene was observed at as low a temperature as 40°C in this work. We also found relatively small degrees of oxidation and small degrees of chain scissioning of high density polyethylene resulted in drastic reduction of tensile elongation.Small amounts of antioxidants and other stabilizing additives are shown to be effective in protecting hydrocarbon polymers against thermooxidative degradation. Stabilizers protect polymers through the severe conditions of processing and fabrication and also in end use. Stabilized polypropylene samples which had been stored under ambient conditions for up to 20 years were found to retain high levels of original oven life. Hydrocarbon polymers usually can be stabilized through proper choice and concentration of stabilizing additives to meet most performance requirements.     

Photophysical investigations of interpolymer interactions in solutions of a pyrene substituted poly(acrylic acid), poly(vinyl amine), poly(1-aminoacrylic acid), and poly(1-acetylaminoacrylic acid)

Photophysical properties of the pyrene chromophore covalently bound to poly(acrylic acid) were used to investigate the interactions of a pyrene substituted poly(acrylic acid) (1) with poly(vinyl amine hydrochloride) (PVAm), poly(1-aminoacrylic acid) (PDA), and poly(1-acetylaminoacrylic acid) (PADA) in aqueous solutions. A number of photophysical parameters were obtained from fluorescence emission and excitation spectra, the deconvolution of decay curves for pyrene monomer, and excited state complex fluorescence and the quenching of pyrene monomer fluorescence by nitromethane in polymer solutions. These photophysical parameters were considered to reflect the inter- and intrapolymer interactions in solutions of 1 , PVAm, PDA, and PADA. The formation of interpolymer complexes between 1 and PVAm was noticed at low (< 4) as well as high (> 8) values, whereas PDA and 1 formed interpolymer complexes at low pH only. No interpolymer complex formation was detected in solutions of 1 and PADA under low or high pH conditions. The structures of interpolymer complexes formed between 1 and PVAm under low and high pH conditions were found to be determined by the conformation of 1 . There were significant differences in the interpolymer interactions of 1 and PDA in comparison to those of 1 and PVAm; in particular, the fluorescence from the excited state complex was enhanced in solutions of 1 and PVAm but quenched in solutions of 1 and PDA. The investigations of terpolymer solutions of 1 , PVAm, and PADA indicated that the nature of interpolymer complexes formed in terpolymer solutions was determined by Coulombic interactions of the amino and carboxylic group containing polymers.     

Reactions of polyolefins with strong lewis acids

Treatment of a cyclohexane solution of low density polyethylene and polystyrene with anhydrous aluminum chloride causes chemical reaction between the two polymers which results in the formation of a graft copolymer. The initial copolymer-forming reaction is very rapid, and prolonged contact of the polymers with aluminum chloride causes subsequent degradation in molecular weight. Treatment of separate solutions of polyethylene, isotactic polypropylene, and ethylene–propylene copolymers with aluminum chloride was studied as a function of time. The intrinsic viscosities of the polymers dropped from initial values of 2.4–6.5 to 0.55–0.85 in 5 min, followed by a slower decline over the next 2 hr. In the case of polypropylene, the low molecular weight fragments largely retained the isotactic structure, which demonstrates that stereochemical isomerization is not a major reaction.     

Mechanism of action of a fire retardant chloroparaffin

The mechanism by which a typical fire retardant chloroparaffin imparts fire retardant characteristics to high density polyethylene, polypropylene and polystyrene is studied by comparing the oxygen indices of these mixtures measured before and after dehydrochlorination. It is shown that flame poisoning by HCl evolved from the chloroparaffin is negligible in polystyrene and high density polyethylene, whereas it is noticeable in polypropylene. The results obtained are related to previous data on the thermal degradation of these mixtures. It is concluded that the chloroparaffin acts mainly by modifying the mechanism of pyrolysis of these polymers in the burning process. Only in the case of polypropylene is there an appreciable contribution by flame poisoning.     

Development of an analytical technique and stability evaluation of 143 C3-C12 volatile organic compounds in Summa canisters by gas chromatography-mass spectrometry

A technique using Summa canisters with cryogenic preconcentration and gas chromatographic-mass spectrometric (GC-MS) detection was developed to determine 143 C3-C12 volatile organic compounds (VOCs) including alkanes, alkenes, aromatics and halohydrocarbons in ambient and indoor air. The method detection limits and practical quantification limits were sensitive at 0.02 and 0.10 ppbv, respectively, and the method precision and accuracy were also satisfactory. The stability of C3-C12 VOC standards at ppbv levels under elevated pressure in canisters was assessed over various time intervals (from 1 week to 4 months after preparation) and most of the compounds were found to be acceptably stable with a mean recovery of 85.6 +/- 9.9% during the course of a 4-month study. However, a small fraction (approximately 6%) of the compounds, including two halohydrocarbons (bromotrichloromethane and benzyl chloride) and six alkenes (2-methylbuta-1,3-diene (isoprene), cis-4-methylpent-2-ene, cis-3-methylpent-2-ene, hept-1-ene, oct-1-ene and styrene) displayed relatively low recoveries in the range 34.6-67.9%. The loss of these compounds is most probably caused by their physical adherence to the active sites of the canister surface, chemical decomposition and/or reactions with other species. The results indicated that one must be cautious in attempting to measure these compounds owing to their instability in canisters. Overall, this analytical technique, which has been used for the determination of the VOCs under study in the toxic air pollutant monitoring network administered by the HKSAR Government, was amenable to the measurement of airborne VOCs collected both outside and inside a semi-confined car park in the present study.     

Polymerization of hex-1-ene initiated by diimine complexes of nickel and palladium

The effect of monomer concentration, reaction temperature and initiator structure on the activity, molar mass, branching and thermal properties of poly(hex-1-ene)s was investigated for the polymerization of hex-1-ene initiated by four α-diimine complexes of nickel and palladium. Hex-1-ene polymerization exhibits an apparent negative kinetic order with respect to monomer concentration. Polymerization of hex-1-ene initiated by MAO activated 1,4-bis(2,6-diisopropylphenyl)acenaphtenediiminenickel(II) dibromide (1a/MAO) proceeds in living-like fashion not only at sub-zero temperatures but even at 20 °C. However, molar masses of the polymers are higher than predicted values in agreement with an initiator efficiency lower than one.     

Novel heterocyclic poly(pyridine‐imide)s with unsymmetric carbazole substituent and noncoplanar structure: High thermal,mechanical and optical transparency,electrochemical, and electrochromic properties

A diamine containing heterocyclic pyridine and unsymmetrical carbazole substituents, 4‐(9‐ethyl‐3‐carbazole)‐2,6‐bis(4‐aminophenyl)pyridine ( CBAPP ), was prepared for use in the synthesis of poly(pyridine‐imide)s PI‐1–8 by direct polycondensation with dianhydrides in N,N‐dimethylacetamide (DMAc). The poly(pyridine‐imide)s derived from the diamine are highly soluble in solvents such as N‐Methyl‐2‐pyrrolidone (NMP) and DMAc at room temperature. Noncoplanar polyimide (PI‐1) showed excellent solubility, high transparency, and high‐performance mechanical properties. These polymers had relatively high glass transition temperatures and exhibited good thermal stability in both nitrogen (T_d10 > 470 °C) and air (T_d10 > 450 °C). The PI‐3～5 cannot form flexible and tough films due to the unsymmetrical carbazole moiety, rigid structure, and polar–polar interaction. However, through copolymerization technique these polymers (PI‐6～8) could be enhanced through the solubility, mechanical, and thermal properties. The optical properties included a strong orange fluorescence (540 nm) after protonation with acid. When the HCl concentration was increased, a new absorption band at approximately 350 nm appeared, and the intensity of the fluorescent peak at 380 nm observed in the neutral polymer solution decreased, along with the appearance of the new fluorescent peak at 540 nm. The poly(pyridine‐imide)s presented here showed only slight fluorescence quenching in the presence of methanol. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 405–412     

Thermal conductivity and thermal expansivity of thermotropic liquid crystalline polymers

The thermal conductivity and thermal expansivity of a thermotropic liquid crystalline copolyesteramide with draw ratio λ from 1.3 to 15 have been measured parallel and perpendicular to the draw direction from 120 to 430 K. The sharp rise in the axial thermal conductivity K_par; and the drastic drop in the axial expansivity α_∥ at low λ, and the saturation of these two quantities at λ > 4 arise from the corresponding increase in the degree of chain orientation revealed by wide-angle x-ray diffraction. In the transverse direction, the thermal conductivity and expansivity exhibit the opposite trends but the changes are relatively small. The draw ratio dependences of the thermal conductivity and expansivity agree reasonably with the predictions of the aggregate model. At high orientation, K_par; of the copolyesteramide is slightly higher than that of polypropylene but one order of magnitude lower than that of polyethylene. In common with other highly oriented polymers such as the lyotropic liquid crystalline polymer, Kevlar 49, and flexible chain polymer, polyethylene, α_par; of the copolyesteramide is negative, with a room temperature value differing from those of Kevlar 49 and polyethylene by less than 50%. Both the axial and transverse expansivity show transitions at about 390 and 270 K, which are associated with large-scale segmental motions of the chains and local motions of the naphthalene units, respectively. ©1995 John Wiley & Sons, Inc.     

Structure of molten stereoregular polyolefins with different side‐chain sizes: Linear polyethylene,polypropylene, poly(1‐butene), and poly(4‐methyl‐1‐pentene)

The melt structures of linear polyethylene and the isotactic vinyl polymers polypropylene, poly(1‐butene), and poly(4‐methyl‐1‐pentene), along with the corresponding methyl, ethyl, and isobutyl side chains, were studied with wide‐angle X‐ray diffraction. As the size of the side branch increases from zero (polyethylene) to methyl, ethyl, and isobutyl, a prepeak appears below the main diffraction peak in the total structure factor. The prepeaks become stronger and shift to lower scattering vectors with increasing bulkiness of the side chain. There is a strong correlation between the position of the prepeaks in the melt and the average nearest‐neighbor helix–helix packing distance in the crystals, implying similar helical conformations in the melts. © 2000 John Wiley & Sons, Inc.* J Polym Sci B: Polym Phys 38: 2480–2485, 2000     

Addition of chlorofluorocarbene to poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene) and poly(1,1-dimethyl-1-sila-cis-pent-3-ene): Characterization of chlorofluorocyclopropanated polymer microstructures by 1H-, 13C-, 19F-, and 29Si-NMR spectroscopy

Chlorofluorocarbene, generated by the sodium iodide catalyzed decomposition of phenyl(dichlorofluoromethyl)mercury, adds to the carbon-carbon double bonds of poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene) (I) and poly(1,1-dimethyl-1-sila-cis-pent-3-ene) (II) to yield poly(3,4-chlorofluoromethylene-1-methyl-1-phenyl-1-sila-cis-pent-3-ene) (CIFC-I) and poly(3,4-chlorofluoromethylene-1,1-dimethyl-1-sila-cis-pent-3-ene) (CIFC-II). Similarly, two series of random partially chlorofluorocyclopropanated polymers have been prepared. The microstructures of these adduct polymers have been determined by ¹H-, ₁₃C-, ¹⁹F-, and ²⁹Si-NMR spectroscopy. The glass transition temperatures (T_g's) depend on the extent of chlorofluoropropanation of these polymers. These copolymers become less thermally stable as the extent of chlorofluorocyclopropanation increases. © 1993 John Wiley & Sons, Inc.     

Syntheses and antitumor and anti-aids activities of polymers containing pyrimidine derivative

The new monomer, 5'-O-methacryloyl-3'-azido-3'-deoxy-thymidine (MAZT), was synthesized from methacryloyl chloride (MAC) and 3'-azido-3'-deoxythymidine (AZT). Poly(MAZT), poly(MAZT-co-AA) and terpoly(MAZT-FUR-MAH) were synthesized by radical polymerizations. The average molecular weights of synthesized polymers were in the range of 8,800 ∼23,000 depending on polymers. The in vivo antitumor activities of polymers at 800mg/kg were increased in the following order: terpoly(MAZT-FUR-MAH) >x poly(MAZT-co-AA) > poly(MAZT) > AZT > 5-FU. The in vitro anti-HIV activities of synthesized polymers were less effective than those of AZT and D4T. But the cytotoxicities of the polymers on the MT-4 cell line were found to be much less toxic than AZT.