High-yield γ-ray-induced polymerization of bis-2-acetoacetoxyethyl methacrylate copper. II.

The copper (II) acrylic monomer Cu(aaem)₂ (aaem = 2-acetoacetoxyethyl methacrylate) undergoes high-yield γ-ray copolymerization with dimethylacrylamide, styrene, and hydroxoethyl methacrylate in the presence of methylene bisacrylamide as crosslinking agent in dimethylformamide. The metalloorganic copolymers are fully characterized. Polymer-protected Cu(II) results in being extremely stable toward a number of reducing agents in different media. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2201–2207, 1997     

γ-ray-induced degradation in ethylene–propylene copolymer

The stabilization of polypropylene-disposable medical syringes against the γ-ray-induced degradation has been the subject of active research during the last decade due to the large-scale use of γ-irradiation for sterilization purposes. Ethylene–propylene (EP) copolymers have been suggested as suitable alternatives to polypropylene for these purposes. In this article, we investigated the effect of irradiation dose and postirradiation time on the melt index and mechanical properties of an EP copolymer. We also determined the chemical changes occurring during irradiation and storage using IR spectroscopy and have made an attempt to co-relate the changes in chemical structure to the changes in mechanical properties and melt index measurements. © 1996 John Wiley & Sons, Inc.     

Structure and properties of polyethylene produced by γ-radiation polymerization in flow system

The radiation-induced polymerization of ethylene was carried out by use of a benchscale plant with a flow-type reactor of 1 liter capacity under the following conditions: pressure, 200–400 kg/cm²; temperature, 30–90°C; irradiation intensity, 3.8 × 10⁵ rad/hr; and ethylene flow rate, 300–3000 nl/hr. The molecular weight of polymer formed was shown to decrease with increasing reaction temperature and to increase with increasing pressure. When the ethylene flow rate increases, the molecular weight decreases in the polymerization at 30–60°C, but it does not change in the polymerization at 75–90°C. Methyl group content, which is a measure of short-chain branching of the polymer, increases with increasing reaction temperature, i.e., ca. 1 CH₃/1000 CH₂ at 30°C and ca. 9 CH₃/1000 CH₂ at 90°C. Methyl content is independent of the ethylene flow rate. The changes in the melt index of polymer with reaction conditions corresponds to the change of the molecular weight. The density, crystallinity, and melting point of polymer decrease with the reaction temperature as the short-chain branching increases, and they are almost independent of ethylene flow rate and pressure.     

Polymer precursor to diamondlike carbon prepared by the polymerization of α,α,α‐trichlorotoluene and acetonitrile

A novel liquid/solid two‐phase reaction of α,α,α‐trichlorotoluene (PhCCl₃) and acetonitrile (AN) has been discovered that produces a carbon‐based polymer with diamondlike structure at the atomic level. The solid phase is potassium hydroxide particles, and the liquid phase is a tetrahydrofuran solution of PhCCl₃ and AN containing a certain amount of tetrabutylammonium bromide as a phase‐transfer catalyst. The structure of the carbon‐based polymer has been characterized by elemental analysis, Fourier transform infrared spectroscopy, and ¹H‐ and ¹³C‐NMR spectroscopy. The pyrolysis of the carbon‐based polymer at 800°C under a nitrogen atmosphere leads to the formation of a diamondlike carbonaceous material according to the results of X‐ray photoelectron spectroscopy and Raman spectroscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 16–23, 2003     

TGA analysis of γ‐irradiated linear low‐density polyethylene

Linear low‐density polyethylene (LLDPE), based on butene‐1 or hexene‐1, was irradiated with γ‐rays under vacuum or in the presence of air. The study focused on the influence of the dose rate and the γ‐dose on the thermal properties of LLDPE. Differential scanning calorimetry, thermogravimetric analysis (TGA), and TGA/FTIR techniques were used to address the thermal behavior as a result of γ‐irradiation. During this irradiation, competition between crosslinking and scission reactions, subsequent to oxidation reactions, occurred in the polymeric material, which strongly depends on the experimental conditions. A decrease of the crystallinity for γ‐irradiated samples was observed in particular for samples irradiated under vacuum. This observation may be explained by increased hindrance of segment mobility due to crosslinking reactions that prevent crystal growth. TGA investigations revealed an enhancement of the thermal stability for samples irradiated under vacuum but not for those irradiated in air. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2790–2795, 2006     

Boehmite-based polyethylene nanocomposites prepared by in-situ polymerization

Polyethylene (PE)-boehmite nanocomposites were prepared by means of metallocene/MAO-catalyzed in-situ polymerization of ethylene in the presence of boehmites, which were rendered organophilic by modification with carboxylic acids such as stearic acid and undecylenic acid. Such organoboehmites are readily dispersed in the polymerization media such as toluene. Polymerization activity, filler dispersion and mechanical properties of the nanocomposites were investigated as a function of type and concentration of the organoboehmites. The catalyst activity of different metallocenes (Cp₂ZrCl₂ and rac-Me₂Si(2-Me-benz[e]-Ind)₂ZrCl₂) was increased up to 100% in the presence of organoboehmite fillers. The dispersion of nanoboehmites, as evidenced by TEM studies, was dependent upon the content of the carboxylate modifier. At 20 wt.% carboxylate content uniform dispersions of organoboehmite particles with average particle sizes smaller than 100 nm were obtained. According to stress-strain measurements, the Young's modulus increased with increasing boehmite content without sacrificing high elongation at break.     

Thermal,mechanical, and barrier properties of polyethylene terephthalate‐platelet nanocomposites prepared by in situ polymerization

This study used in situ polymerization to prepare polyethylene terephthalate (PET) nanocomposites incorporating Ethoquad‐modified montmorillonite (eMMT), unmodified hectorite (HCT), or phenyl hectorite (phHCT) particles to study the impact of platelet surface chemistry and loading on thermal, mechanical, and gas barrier properties. eMMT platelets reduced the PET crystallization rate without altering the ultimate degree of crystallinity. In contrast, HCT and phHCT platelets accelerated the polymer's crystallization rate and increased its crystallinity. DMA results for thermally‐quenched samples showed that as T increased past glass transition temperature (T_g), HCT and phHCT nanocomposites (and control PET) manifested precipitous drops in G′ followed by increasing G′ due to cold crystallization; in contrast, eMMT nanocomposites had much higher G′ values around T_g. This provides direct evidence of eMMT reinforcement in thermally‐quenched eMMT nanocomposites. These results suggest that eMMT has a strong, favorable interaction with PET, possibly through Ethoquad‐PET entanglement. HCT and phHCT have a fundamentally different interaction with PET that increases crystallization rate and T_g by 11 to 17°C. Water barrier improvement in eMMT nanocomposites agrees with previously published oxygen barrier results and can be rationalized in terms of a tortuous path gas barrier model. POLYM. ENG. SCI., 52:1888–1902, 2012. © 2012 Society of Plastics Engineers     

Microemulsion polymerization of butyl acrylate initiated by γ rays

Radiation polymerization of butyl acrylate was carried out in a microemulsion stabilized with sodium 12-butinoyloxy-9-octadecenate (SBOA). The stable and reddish latex with high polymer content and low emulsifier content was successfully produced in this way. It was found that, for most cases, the polymerization rate shows three intervals: the increasing period, the plateau period, and the decreasing period. The length of the nucleation period becomes longer at a higher dose rate (D) and lower emulsifier content (E). The plateau region of polymerization rate is lengthened with the increase of monomer and emulsifier content and shortened with the increase of dose rate. It was shown that monomer content, emulsifier content, and dose rate have great effects on R_p (the polymerization rate in the plateau region, or the maximum polymerization rate during polymerization) and M_n (the molecular weight of the polymer). R_p ∞ [M^0.93D^1.27[E]^−1.07; M_n ∞ [M]^0.65D^0.28[E]^−1.66. The polymerization mechanism is discussed based on these results. © 1996 John Wiley & Sons, Inc.     

Stereoelective polymerization of β-butyrolactone

Racemic β-butyrolactone was polymerized using chiral initiators obtained from the reaction of organometallic derivatives (ZnEt₂, CdMe₂, AlEt₃) with R(−) 3,3 dimethyl-1,2 butanediol. With the zinc initiator, R(+) enantiomer is preferentially incorporated in the polymer chain with a stereoelectivity ratio r_R equal to 1.6. Crude polymer was fractionated into a crystalline, predominantly isotactic, part and an amorphous heterotactic part, both optically active. Sites of different stereospecificities, present in the initiator, are all active for the stereoelective polymerization. With the cadmium initiator, S(−) enantiomer is preferentially polymerized (r_s = 1.01), extending homosteric-antisteric rules previously established for thiiranes. Aluminium initiator leads to an homosteric process (r_R = 1.1). Chiroptical properties (o.r.d. and c.d.) of polymers prepared with zinc initiator show a predominance of R-configurational units, indicating that ring-opening occurs by O-acyl cleavage with retention of configuration.     

Study of solution properties of poly(α-methyl styrene) in various solvents by dilute-solution viscometry

The values of Mark–Houwink–Sakurada constants were determined for poly(α-methyl styrene) (PαMs) of high and low molecular weights in a variety of solvents by a new approach, which requires only polydisperse samples. The results are in accord with those reported in the literature. In addition, the present work reports the values of the Flory interaction parameter for PαMs in 13 solvents of distinct solvent power at various temperatures. Three refined methods pertaining to both polar and nonpolar solvents were applied to estimate the solubility parameter (δ₂) of PαMs resulting in δ₂ = 18.75 ± 0.15 (J/mL)^1/2 at 30°C. Finally, the scatter data of the Huggins coefficient over a range of expansion factors varying from 0.7 to 2.6 seem to conform better to a newly proposed empirical equation than to the contemporary model after Imai. © 1993 John Wiley & Sons, Inc.     

RAFT‐mediated graft polymerization of glycidyl methacrylate in emulsion from polyethylene/polypropylene initiated with γ‐radiation

The successful reversible addition‐fragmentation (RAFT)‐mediated graft polymerization of glycidyl methacrylate (GMA) in emulsion phase from polyethylene/polypropylene nonwoven fabric using 4‐cyano‐4‐[(phenylcarbonothioyl)thio]pentanoic acid under γ‐irradiation at ambient condition is reported. While conventional graft polymerization in emulsion phase yielded grafted materials with low of grafting (Dg) values [<7.5% at 10% (wt/wt) GMA], addition of RAFT agent to the graft polymerization system allowed the synthesis of polyethylene/polypropylene‐g‐poly(GMA) with more tunable Dg (8% ≤ Dg ≤ 94%) by controlling the grafting parameters. Relatively good control (PDI ～1.2 for selected grafting conditions) during polymerization was attained at 100:1 monomer‐to‐RAFT agent molar ratio. The number average molecular weight of free poly(glycidyl methacrylate) (PGMA) increased as a function of monomer conversion. NMR analyses of the free PGMA homopolymers indicate the presence of dithiobenzoate group from 4‐cyano‐4‐((phenylcarbonothioyl)thio) pentanoic acid on the polymer chain. The reactive pendant oxirane group of the grafted GMA can be modified for various environmental and industrial applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45270.     

Polymer/metal interpenetrating phase composites prepared via γ‐ray initiated in‐situ emulsion polymerization

The poly(methylmethacrylate)/metal and poly(butylacrylate‐co‐styrene)/metal interpenetrating phase composites (IPCs) were prepared via γ‐ray irradiation in‐situ bulk and emulsion polymerization, respectively. The monomers were first introduced into open‐cell aluminum foam and aluminum alloy foam and were in‐situ polymerized by γ‐ray irradiation at room temperature. The characterization and compressive test results showed that this method expands the variety of the polymer component resulting in a useful range of physical properties of the IPCs, such as density and porosity. The PMMA/metal IPC has a high polymer filling ratio, modulus and exhibits a similar compressive behavior to that of PMMA. On the other hand, the P(BA‐co‐St)/metal IPC has a relatively low polymer filling ratio and its compressive behavior is similar to that of metal foam matrix, but it has wider plastic plateau than the component metal foams, like the case of metal foam filled with rubber. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Dielectric γ relaxation in polyethylene at low temperature

Dielectric γ relaxation in polyethylene with various degrees of branching and/or with various heat treatment has been measured in the ranges of frequency 10–10⁴ Hz and temperature?90 to?130°C. The difference between the dispersion maps obtained from the frequency dependence of the dielectric loss and from the temperature dependence suggests that the temperature dependence of the relaxation intensity in polyethylene is not negligible. With an increase in crystallinity owing to the decrease in branching, the relaxation time shifts to longer time or higher temperature side and the activation energy increases steeply, whereas the quite opposite tendency was observed for the heat treated polyethylene with different crystallinity. The distribution of relaxation times becomes narrower with increasing temperature. At higher temperatures, the distribution in the specimens with various degrees of branching becomes narrower with the increase in the crystallinity, whereas in the specimens with various heat treatments, the dependence of the distribution on crystallinity tends to cease. Defects in the crystalline phase increase with an increase in branching and in crystallinity through heat treatments, and the dielectric γ relaxation in polyethylene differs depending on the branching and/or heat treatments.     

Emulsion polymerization of vinyl acetate initiated by intermittent γ radiation

The reaction kinetics of emulsion polymerization of vinyl acetate (VAc) monomer have been studied by using intermittent γ radiation. The purpose of this technique is to take advantage of the poly merization reaction which still continues after the radiation production has been stopped, as expected by the Smith–Ewart rate theory. Tween 20 (polyoxyethylene sorbitan monolaurate), was used as the emulsifier. The polymer conversion was determined by using the dilatometric method. The polymerization rate R_p decreased with increase in emulsifier content. The Smith–Ewart rate theory cannot explain the experimental evidence satisfactorily. The average polymerization rate R_p between 20% and 80% conversion is a function of irradiation dose rate and can be written where a₁ and a₂ is a constant in which the value depends on the emulsifier content in the emulsion and I is the irradiation dose rate.     

Microheterogeneous polymer systems prepared by suspension polymerization of methyl methacrylate in the presence of poly(ε‐caprolactone)

Poly(methyl methacrylate) – polycaprolactone (PMMA/PCL) microheterogeneous beads were synthesized by suspension polymerization starting from methyl methacrylate (MMA) monomer and PCL, which was synthesized by ring‐opening polymerization of ε‐caprolactone using ZnCl₂ as initiator. The resulting polymer was fully characterized by ¹H and ¹³C NMR, differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and dynamic mechanical thermal analysis (DMTA). The size distribution and morphology of the resulting beads were investigated by optical microscopy and scanning electron microscopy (SEM). Moreover, blends of PMMA beads and PCL in different proportions were prepared and the morphology of the films was examined by optical microscopy. The low compatibility between PMMA and PCL was clearly evidenced through these experiments.     

Enzyme-catalyzed polymerization and degradation of copolyesters of ε-caprolactone and γ-butyrolactone

Copolymers of γ-butyrolactone (γ-BL) and ε-caprolactone (ε-CL) were successfully synthesized by ring-opening polymerization using Novozyme-435 (immobilized lipase B from Candida antartica) as catalyst. Copolymers with different compositions were obtained and characterized by ¹H NMR, ¹³C NMR, GPC, DSC and X-ray diffraction. Increasing the [BL]/[CL] feed ratio resulted in decreases of molecular weight (M_n) of copolymers and reaction yield. Moreover, the BL contents in the copolymers varied according to the feed ratio. The T_m of the copolymers decreased from 58 to 49 °C with increase in BL content from 0 to 14%. The resulting copolymers were all semicrystalline with a PCL-type crystalline structure. Solution cast films were allowed to degrade in a pH 7.0 phosphate buffer solution containing Pseudomonas lipase. Weight loss data showed that the degradation rate of copolymers in the presence of Pseudomonas lipase decreased with the increase of BL contents.     

Mechanism and kinetics of polyethylene crosslinking by α,α′-bis(tert-butylperoxy)-p-diisopropylbenzene

The study of the mechanism of polyethylene crosslinking is realized by a kinetic analysis of the α,α-bis(tert-butylperoxy)-p-diisopropylbenzene decomposition, as well as by the determination of its decomposition products and crosslink formation in the polymer. The experiments were carried out in a temperature range of 118°–148°C in both polyethylene and its low-molecular model, n-octane. From the results obtained it follows that the peroxide decomposition in both hydrocarbon media is kinetically a unimolecular reaction with an activation energy of 36 ± 2 kcal/mole and with an equivalent participation of both peroxidic groups, whereby a biradical formation is improbable. Macroradicals arise by a dehydrogenization reaction in which mainly primary oxyradicals of various types take part and methyl radicals are also formed by a transformation process of the former. Both types of radicals decay exclusively in a substitution reaction with polymer chains. The whole process is terminated by macroradical recombination so leading to crosslink formation in polyethylene.     

Mechanistic studies of adhesion promotion by γ-aminopropyl triethoxy silane in α-Al2O3/polyethylene joint

In order to understand the mechanism of adhesion promotion by organo silane in joints where its chemical reaction with a polymer matrix may be negligible, we studied the role of γ-aminopropyl triethoxy silane (γ-APS) in α-Al₂O₃/ polyethylene joints. When adsorbed or deposited on α-A1₂O₃/ and moderately dried, γ-APS forms a multimolecular film that is not fully cured. Drying at elevated temperatures for an extended time leads to further curing, resulting in a glassy silane film with a T_g around 108°C, while prolonged dry may cause some degradation. Joint strength is markedly improved by the application of a γ-APS film with a maximum peel strength of 2.3 kg/cm when the silane is applied from a 2 percent aqueous solution. Drying the silane at an elevated temperature prior to joint formation reduces joint strength and also changes the failure mode from cohesive failure through the polyethylene to a mixed mode. Evidence of interdiffusion between γ-APS film and polyethylene at a temperature (149°C) that is above the melting point of polyethylene and the T_g of the silane film was obtained by measuring the Si concentration profile across the interface of the laminate of polyethylene/γ-APS/polyethylene. Diffusion constants in the order of 10^?12 cm²/s were obtained, with a teridency toward reduced diffusion as a consequence of extensive drying. DSC results indicate at least partial miscibility of the silane polymer in the amorphous region of polyethylene. It is proposed that the interdiffusion between γ-APS silane film and polyethylene is an important mechanism for adhesion promotion of the joints investigated in this study.     

Radical polymerization of acrylonitrile initiated by α-picolinium p-chlorophenacylid

The radical polymerization of acrylonitrile (AN) with α-picolinium p-chlorophenacylid (α-PCPY) as initiator using carbon tetrachloride as inert solvent was investigated at 50°C. The polymerization follows ideal kinetics: the exponent values calculated for the initiator and monomer were found to be 0.5 and unity, respectively. A free radical mechanism with bimolecular termination was confirmed by the inhibiting effect of hydroquinone, a radical quencher. The rate of polymerization was a direct function of initiator (α-PCPY) concentraction, monomer (AN) concentration and temperature. The overall activation energy calculated was 56 kJ/mol. The polymerization was favoured by polar solvents and retarded by non-polar solvents.     

Ring-opening polymerization of ε-caprolactone initiated by cyclopentadienyl sodium

Polymerization of ε-caprolactone had been investigated with cyclopentadienyl sodium as an initiator. The effects of reaction time, temperature, and concentration of the initiator on the yield and molecular weight of the polymer were discussed. It was shown that the high molecular weight of poly(ε-caprolactone) (13 × 10⁴) was obtained with cyclopentadienyl sodium initiator, and the mechanism of polymerization was also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1273–1276, 1998