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.     

Ethylene polymerization by 3‐oxa‐pentamethylene bridged asymmetric dinuclear titanocene/MAO system

An asymmetric 3‐oxa‐pentamethylene bridged dinuclear titanocenium complex (CpTiCl₂)₂(η⁵‐η⁵‐C₉H₆(CH₂CH₂OCH₂CH₂)C₅H₄) ( 1 ) has been prepared by treating two equivalents of CpTiCl₃ with the corresponding dilithium salts of the ligand C₉H₇(CH₂CH₂OCH₂ CH₂)C₅H₅. The complex 1 was characterized by ¹H‐, ¹³C‐NMR, and elemental analysis. Homogenous ethylene polymerization catalyzed using complex 1 has been conducted in the presence of methylaluminoxane (MAO). The influences ofreaction parameters, such as [MAO]/[Cat] molar ratio, catalyst concentration, ethylene pressure, temperature, and time have been studied in detail. The results show that the catalytic activity and the molecular weight (MW) of polyethylene produced by 1 /MAO decrease gradually with increasing the catalyst concentration or polymerization temperature. The most important feature of this catalytic system is the molecular weight distribution (MWD) of polyethylene reaching 12.4, which is higher than using common mononuclear metallocenes, as well as asymmetric dinuclear titanocene complexes like [(CpTiCl₂)₂(η⁵‐η⁵‐C₉H₆(CH₂)_nC₅H₄)] (n = 3, MWD = 7.31; n = 4, MWD = 6.91). The melting point of polyethylene is higher than 135°C, indicating highly linear and highly crystalline polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Structural characterization and thermal behaviour of block copolymers of polydimethylsiloxane and polyamide having trichlorogermyl pendant groups

Block copolymers having a pendant trichlorogermyl group as a part of polyamide segment? (CO? R′? CO? NH? Ar? NH? )_xCO? R′? CO? and polydimethylsiloxane of general formula [(? CO? R′? CO? HN? Ar? NH)_x? CO? R′? CO? NH(CH₂)₃SiO(CH₃)₂ ((CH₃)₂SiO)_ySi(CH₃)₂(CH₂)₃ NH? ]_n (where R′ = CH₂CH(GeCl₃), CH(CH₃)CH(GeCl₃), CH(GeCl₃)CH(CH₃); Ar = C₆H₄, (? C₆H₃? CH₃)₂, (? C₆H₃? OCH₃)₂, 2,5‐(CH₃)₂? C₆H₂, C₆H₄? O? C₆H₄) were prepared by a polycondensation reaction and characterized using CHN and Ge analysis, Fourier transform infrared (FTIR) and ¹H NMR spectroscopy, thermogravimetric analysis (TGA) and molecular weight determination. They have a lamellar structure with weight‐average molecular weight in the range 1.21 × 10⁵–4.79 × 10⁵ g mol^?1. These copolymers display two glass transition temperatures and have an average decomposition temperature of 489 °C. TGA, FTIR and gas chromatography/mass spectrometry studies indicate that degradation of these block copolymers results in carbon monoxide, oligomeric siloxanes and polyamide fragments. They are thermally stable due to the hydrogen bonded interlinked chains of polyamide, while they absorb water due to the presence of Ge? Cl bonding. Copyright © 2010 Society of Chemical Industry     

Synthesis and characterization of thermosetting polyacetylene-terminated silicone resins

A novel polyacetylene-terminated silicone (PTS) resins possessing low curing temperature and high heat resistance has been prepared by Grignard reaction using m-diacetylenylbenzene (DEB), 1,3,5-triacetylenylbenzene(TEB), and dichlorosilane as original materials. The reaction of the functional groups was characterized by in situ Fourier transform infrared spectrometer. The experimental results indicated that Si─H and C≡CH bonds are almost exclusively involved in the crosslinking reaction, while ─C≡C─ bonds only partially react. Further, Si─H and C≡CH bonds can participate in the curing reaction at relatively low temperatures, but ─C≡C─ bonds require higher temperature, indicating the higher activity of Si─H and C≡CH bonds than ─C≡C─ bonds. As determined by differential scanning calorimetry, PTS resins have low peak exothermic temperature at 184.5 °C, which is lower than MSP resin (~ 210 °C); in addition, rheological test showed that PTS resins have a very wide processing window from 40 to 163.3 °C, indicating that the PTS resins have excellent processability with a low curing temperature and wide processing window. What is more, TGA results of thermal-cured PTS resins revealed that T_d5 (5% weight loss temperature) of PTS-H10 reached the highest of 684.4 °C. Compared with PTS-H0 resin, there is an increase of 124.2 °C and the remarkably increased heat resistance correlated with a higher m-DEB input ratio. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48783.     

Synthesis and permeability properties of crosslinkable elastomeric poly(vinyl allyl dimethylsilane)s

This article presents the results of a systematic synthesis study of elastomeric crosslinkable polysilicon olefins, the related thermal crosslinking kinetics, and the main permeability parameters recorded for inorganic gases (He, N₂, O₂, and CO₂) and C₁–C₇ hydrocarbons. Poly(vinyl allyl dimethylsilane) (PVADMS; glass‐transition temperature < 273°K) was obtained by the anionic polymerization of bifunctional vinyl allyl dimethylsilane monomer. The polymers were amorphous, high molecular compounds with mixed carbo‐heterochain structures containing double bonds capable of intermolecular crosslinking under a thermal treatment. Thus, thermally crosslinked polymers exhibited a high resistance toward exposure to organic vapors, unlike noncrosslinked PVADMS. IR spectroscopy was used to investigate the polymer structural changes induced by the thermal treatment. An original technique based on a differential method was used to measure gas permeability during thermal crosslinking. PVADMS possessed higher permeability for C₁–C₇ hydrocarbons than for inorganic gases (excluding CO₂), even after crosslinking. Permeability coefficients ranging from 140 to 1780 Barrer for He and CH₄ were found before crosslinking; the thermal crosslinking induced a nonlinear permeability decrease that could be correlated with the disappearance of the double bonds in the polymer structures, that is, cis‐CH?CH? , trans‐CH?CH? , and CH₂?CH? in the side‐chain position. According to the found properties, PVADMS could be used as a prospective material for the preparation of highly permeable selective membranes suitable for lower hydrocarbon and volatile organic compound recovery from various chemical and petrochemical process streams. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 927–935, 2005     

Synthesis and characterization of poly(methyl methacrylate) nanoparticles by emulsifier‐free emulsion polymerization with a redox‐initiated system

In this study, the emulsifier‐free emulsion polymerization of methyl methacrylate (MMA) was initiated directly by a Cu²⁺/HSO redox system. Latex particles with negative charge due to the bonded anionic sulfite ion were successfully synthesized after 2 h of reaction at 40–60°C. Scanning electron microscopy pictures showed a uniform particle size distribution, and the average size decreased from 223 to 165 nm wit increasing reaction temperature from 40 to 60°C. The initiation step in the polymerization mechanism was proven to be a redox reaction, in which Cu²⁺ oxidized the bisulfite ion to produce an anionic sulfite radical and proton. The produced anionic sulfite radical then initiated the polymerization of MMA. Moreover, Cu²⁺ not only served as one component in the redox initiator system but also as a chain‐transfer agent that terminated growing polymer chains to produce chains with unsaturated end groups [poly(methyl methacrylate) (PMMA)? CH?CH₂]. For this system, about 17% PMMA? CH?CH₂ was produced. The tacticities of the PMMA latex prepared at 40–60°C were almost the same, about 62–64% syndiotactic, 33–35% heterotactic, and 3% isotactic. These PMMA latexes had almost the same glass‐transition temperature, 125–127°C, regardless of the reaction temperatures, and their weight‐average molecular weights were in the range between 254,000 and 315,000. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Comparison of thermal,thermomechanical, and rheological properties of blends of divinylbenzene-based hyperbranched and linear functionalized polymers

A range of polymer blends were prepared via a solvent-based film casting process using highly/hyperbranched (HB) polydivinylbenzenes (PDVB) polymers of two different molecular weights, linear functionalized (LF), hydrogenated hyperbranched (H-HB2) PDVB, and linear polystyrene (LP). The thermal, thermomechanical, and rheological properties of the pure polymers and blends were then investigated and the results related to the concentration of “branched” polymer in the blend and the level of branching/polymer end groups present in the “branched” polymers used. Differential scanning calorimetry (DSC) analysis revealed an increase of the glass transition temperature (T_g) for the blends containing the nonhydrogenated HBs (~108 °C compared to ~102 °C for LP), which was attributed to crosslinking via the unsaturated reactive chain end/pendant groups in the HB ( CHCH₂). In contrast at the blends, containing the hydrogenated polymers H-HB2, exhibited the same T_g as LP (~102°C) due to absence of crosslinking from the (H-HB2) polymer. As the unsaturated HBs were found to be thermally curable, curing temperature rheology measurements were carried out employing a temperature ramp. No specific T_gel (the temperature at which HB gets crosslinked) was identified for LP-HB1 and LP-HB2 blends, which might be suggested to be due to the fact that both chain entanglement from linear polystyrene. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48547.     

Preparation and magnetic properties of Fe/Si/C/N ceramics derived from a polymeric precursor

Iron‐containing polysilazanes (PSZI) were prepared by the amine displacement reaction along with heat‐induced vinyl crosslinking reactions between Fe[N(SiMe₂Vi)₂]₃ (Vi = ? CH?CH₂) and polysilazane containing ? Si? Vi (PVSZ). The PSZIs were converted into magnetic ceramics by the pyrolysis in N₂. The ceramics produced were investigated by X‐ray diffraction, transmission electron microscope and vibrating sample magnetometer at room temperature. It was indicated that α‐Fe is the only magnetic crystalline embedded in the amorphous Si/C/N‐based matrix from 500 to 900°C. Moreover, the sample prepared at 500°C showed few hysteresis at room temperature, consistent with the behavior of superparamagnetic particles, which was confirmed by the zero‐field‐cooled and field‐cooled magnetization measurement. Additionally, the results indicated that the magnetic properties of the ceramics could be tuned by controlling the content of iron and the pyrolysis temperature. This flexibility may be advantageous for some particular magnetic materials applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Investigations on the curing of epoxides with phthalic anhydride

The anhydride curing of epoxides was studied by performing copolymerizations of epichlorohydrin, phenyl glycidyl ether (PGE), or bisphenol-A-diglycidyl ether (BADGE) with phthalic anhydride (PSA). As initiators, tertiary amines or ammonium salts were used. In the case of epichlorohydrin, linear polyesters were obtained at 100°C. At higher temperatures (140–160°C), a side reaction of the CH₂Cl group took place which caused branching and partial crosslinking of the polymer. The reaction of phenyl glycidyl ether with phthalic anhydride gave linear, strongly alternating copolymers at temperatures of 120–160°C. Molecular weights (M¯_n) were in the range of 4000–87,000, depending on the purity of the starting materials and the initiator used. The reaction of the diepoxide BADGE with phthalic anhydride yielded highly crosslinked products. Their crosslink densities (which correlate with the glass transition temperature T_g). however, did not show the same dependence on initiator and purity of the starting materials as the molecular weights of the linear polyesters obtained by the “model reaction” of PGE with PSA. Possible reasons for this effect are discussed.     

Thermomechanical behavior of poly(carborane–siloxane)s containing ?CB5H5C? cages

The thermomechanical spectra of two new carborane–siloxane polymers containing five-boron carborane cages in the backbones are reported and discussed. The polymers are the homopolymer, HO? [Si(CH₃)₂? CB₅H₅C? Si(CH₃)₂? O? ]_nH, and the random copolymer with 20 mole-% of the ten-boron meta-carborane analogue, ? [Si(CH₃)₂? CB₁₀H₁₀C? Si(CH₃)₂? O? ]. The mechanical spectra (～1 cps) were determined from ?180° → +625° → ?180°C (ΔT/Δl = 3.6°C/min for T > 25°C and 2°C/min for T < 25°C) using the semimicro thermomechanical technique, torsional braid analysis. In nitrogen, both polymers displayed secondary transitions at ?140°C. The glass transition (T_g) for the homopolymer was ?60°C and for the copolymer was ?52°C. The homopolymer had a melting point of +70°C. The copolymer was amorphous. The high-temperature stability in nitrogen of both polymers appeared to be identical; thermal stiffening commenced at 400°C, continued to 625°C, and resulted in materials that were typical of highly crosslinked resins. In air, the homopolymer began to stiffen catastrophically near 270°C, while the copolymer began to stiffen similarly nearly 50°C higher. The intrinsic elastomeric nature together with the thermomechanical results prompted further study of the copolymer. Thermomechanical cycling studies in nitrogen and air are reported for the copolymer. Some correlating TGA and DTA are also discussed.     

Acrylonitrile graft copolymerization of casein proteins for enhanced solubility and thermal properties

Casein proteins are soluble in 5% aq. ethanolamine, triehtylamine, and triethanolamine, but insoluble in organic solvents. Graft copolymerization of casein (40 g/L) with acrylonitrile (AN) was carried out in 5% w/v aq. triethanolamine at 60°C using potassium persulfate K₂S₂O₈ as an initiator. Percent grafting and grafting efficiency increased with increasing initiator concentrations (up to 1.7 × 10⁻² mole L⁻¹) and reaction times, but decreasing [M]/[I] ratios. Fourier transform IR spectra confirmed the formation of the acrylonitrile‐grafted‐casein (AN‐g‐casein) copolymers. Under the reaction conditions studied, the grafted PAN side chains were characterized by gel permeation chromatography to have M_n between 1.58 and 5.88 × 10⁴ dalton and polydispersities between 2.6 and 4.5. The AN‐g‐casein copolymers behaved more like a PAN homopolymer in terms of their thermal properties and solubilities. The decomposition temperatures of AN‐g‐casein copolymers were between 255 and 273°C, closer to the T_d of the PAN homopolymer (275°C) and significantly higher than that of casein (180°C). The AN‐g‐casein copolymers are soluble in 50% aq. NaSCN and ZnCl₂, but are insoluble in 32:28:40 wt % CaCl₂/CH₃CH₂OH/H₂O like PAN and dimethylformamide‐like casein. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2543–2551, 2000     

Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. II. Structural changes occuring in low-density polyethylene at an oxygen content less than 0.0005%

Samples of low-density polyethylene, free from additives, were heated at temperatures between 284° and 355°C under high-purity nitrogen. Changes in molecular weight distribution (MWD), molecular weight averages, and degree of long-chain branching (LCB) were followed by gel chromatography (GPC) and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry (DSC). At 284° and 315°C, the MWD's were shifted toward higher molecular weights and the M?_w values increased. At 333° and 355°C, the MWD's shift toward lower molecular weight, but the high molecular weight, tail is largely retained. M?_w decreases slowly at 333°C. At 355°C, M?_w undergoes a rapid initial drop which levels off. M?_w/M?_n and the degree of LCB increase with heating time and temperature. Olefinic unsaturation increases. The vinyl groups show a larger relative increase than do the trans-vinylene and vinylidene groups. At 355°C, the peak of the unimodal DSC thermogram is shifted to ～3°C higher temperature. A lower melting peak then develops, and after 72 and 90 min the two peaks are about equal in size. The density increases from 0.922 g/cm³ to 0.930 g/cm³ for samples heated at 355°C, and the weight loss was 1.5% after 90 min. A reaction scheme for the thermal degradation of polyethylene is discussed. Initiation is suggested to be accomplished by scission of allylic C? C bonds. Propagation proceeds by both intra- and intermolecular hydrogen abstraction, followed by β-scission. Termination can occur by both combination and disproportionation. Combination reactions are suggested to account for the observed formation of LCB and high molecular weight material. Due to changes in the degree of LCB during the degradation, viscometry alone will not give a proper measure of the changes in molecular weight.     

High-temperature in situ FTIR spectroscopy study of LaOF and BaF2/LaOF catalysts for methane oxidative coupling

In situ FTIR spectroscopy was used to characterize the oxygen adspecies and its reactivity with CH₄ over LaOF and 15 mol% BaF₂/LaOF catalysts at OCM temperature (750-800°C). It was found that gas-phase oxygen was activated on the surface of LaOF and 15 mol% BaF₂/LaOF, which had been pretreated under vacuum at 750 or 800°C, forming O ₂ ^- species at high temperature (750-800°C). At 750°C, the adsorbed O ₂ ^- species can react with pure CH₄ accompanied by formation of gas-phase C₂H₄ and CO₂, and there is a good correlation between the rate of disappearance of surface O₂and the rate of formation of gas-phase C₂H₄. The O ₂ ^- species was also observed over the catalysts under working condition, and it reacted with CH₄ in a manner that was consistent with its role in a catalytic cycle. These results suggest that O ₂ ^- may be the active oxygen species for OCM reaction over these catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Helical and random coil conformations of N‐propargylamide polymer and copolymers

An N‐propargylamide monomer, CH?CCH₂NHCOC(CH₃)₂CH₂CH₃ (monomer 9), was polymerized in the presence of (nbd)Rh⁺B^?(C₆H₅)₄ (nbd represents norbornadiene) in CH₂Cl₂, CHCl₃, tetrahydrofuran or dimethylformamide, to provide polymers with moderate number‐average molecular weights (M_n = 8700–12 100 g mol^?1) in high yields (≥92%). The resulting poly(N‐propargylamide) (polymer 9) dissolves almost completely in CHCl₃ (>95%). According to the UV‐visible spectra, measured at various temperatures, polymer 9 forms relatively stable helices over a wide temperature range (35–65 °C). Moreover, it exhibits reversible conformational transitions from an ordered helix to a random coil. On copolymerization of monomer 9 with CH?CCH₂NHCO(CH₂)₃CH₃ (monomer 4) or CH?CCH₂NHCO(CH₂)₇CH₃ (monomer 8), the solubility of polymer 9 improves noticeably. All the copolymers form helices under the experimental conditions. From the viewpoint of monomers 4 and 8, copolymerization with monomer 9 is favorable in terms of the copolymers forming helices. These findings reveal that the helical content and thermodynamic stability of the helices formed in the copolymers are likely to be controlled by selecting a suitable comonomer and by adjusting the composition of the copolymer. Copyright © 2007 Society of Chemical Industry     

Investigation of liquid crystalline and photocrosslinkable poly[4‐x‐phenyl‐4′‐(m‐methacryloyloxyalkyloxy)cinnamate]s

Three series of liquid‐crystalline‐cum‐photocrosslinkable polymers were synthesized from 4‐x‐phenyl‐4′‐(m‐methacryloyloxyalkyloxy)cinnamates (x = ? H, ? OCH₃ and ? CN; m = 6, 8 and 10) by free radical solution polymerization using azobisisobutyronitrile as an initiator in tetrahydrofuran at 60 °C. All the monomers and polymers were characterized using intrinsic viscosity, and FTIR, ¹H NMR and ¹³C NMR spectroscopy. The liquid crystalline behavior of these polymers was examined using a hot stage optical polarizing microscope. All the polymers exhibited liquid crystalline behavior. The hexamethylene spacer‐containing polymers exhibited grainy textures; in contrast, the octamethylene and decamethylene spacer‐containing polymers showed nematic textures. Differential scanning calorimetry data confirmed the liquid crystalline property of the polymers. Thermogravimetric analysis revealed that all the polymers were stable between 236 and 344 °C in nitrogen atmosphere and underwent degradation thereafter. As the methylene chain length increases in the polymer side‐chain, the thermal stability and char yield of the polymers decrease. The photocrosslinking property of the polymers was investigated using the technique of exposing the polymer solution to UV light and using UV spectroscopy. The crosslinking reaction proceeds via 2π–2π cycloaddition reactions of the ? CH?CH? of the pendant cinnamate ester. The polymers containing electron‐releasing substituents (? OCH₃) showed faster crosslinking than the unsubstituted polymers and those containing electron‐withdrawing substituents (? CN). Copyright © 2007 Society of Chemical Industry     

Kinetic study of the dehydrogenation reaction in polyacrylonitrile‐based carbon fiber precursors during thermal stabilization

The kinetics of dehydrogenation reaction and the structural evolution in polyacrylonitrile precursor fibers during thermal stabilization in air have been studied by Fourier transform infrared spectroscopy. The results indicate that, with the progress of dehydrogenation, the absorbance of methylene groups (? CH₂? ) gradually decreases, whereas that of methine groups (?CH? ) gradually increases. The dehydrogenation reaction in the fibers is basically completed after 20‐min stabilization above 255°C. According to the Beer–Lambert law, the values of the absorbance for both ? CH₂? groups and the resulting ?CH? groups have been calculated and converted into the concentration fractions of ? CH₂? groups via the Lorentzian multipeak fitting. According to the principles of chemical kinetics, the dehydrogenation reaction has been determined as a pseudo‐second‐order reaction with an activation energy of 107.6 kJ mol^?1. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Nonisothermal curing of a solid resole phenolic resin

A commercial solid resole phenolic resin was thoroughly characterized with Fourier transform infrared spectroscopy, NMR, and gel permeation chromatography, and its nonisothermal curing reaction was studied systematically with differential scanning calorimetry at a series of heating rates (βs) of 3, 4.5, 5.7, and 10°C/min. The results show that the solid resole had a higher molecular weight than conventional liquid resoles, and its reactive hydroxymethyl (CH₂ OH) and dibenzyl ether (CH₂ O CH₂) functionalities participated in the crosslinking reaction upon heating. The nonisothermal curing reaction of the solid resole exhibited a relatively constant reaction heat, whereas the onset, peak, and end curing temperatures increased gradually with increasing βs. In addition, the reaction kinetics of the solid resole was analyzed with an nth‐order reaction model, the global activation energy was determined with the Kissinger method, and the reaction order was derived from the Crane equation. The obtained rate equation was applied to simulate the reaction time, conversion, and reaction rate, with a good fit achieved between the experimental data and the model predications. In conclusion, this study provided us with new knowledge on solid resoles at a molecular level and was also a great help for the curing procedure design, property optimization, and practical application of this commercial solid resole. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of photocrosslinkable poly(organophosphazene)-bearing cinnamyloxide side groups

Two different poly(organophosphazene)s-bearing single-substituents (two cinnamyloxide side groups per repeating unit) and phenoxide-co-substituents (one phenoxide and one cinnamyloxide group per repeating unit) were prepared to study their photochemical reaction behavior. Structural formulas confirmed by the NMRs (¹H, ³¹P) and IR were ? [NP(OCH₂CH = CH ? C₆H₅)₂]_n ? ( I ) and ? [NP(OCH₂CH = CH ? C₆H₅)_0.8 (O ? C₆H₅)_1.2]_n ? ( II ). Molecular characterization yielded $ \overline {M_w {\rm s}} $ of the order of 10³ kg/mol for both the polymers. The onset temperature of decomposition found by TGA was about 250°C. DSC measurements gave T_gs as 1°C for I and 3°C for II . Their photolytic crosslinking behaviors were monitored by UV spectroscopy. The single-substituents polymer I showed a faster rate of photo reaction than the polymer II . The potential use for practical photosensitive application is considered to be greater for the polymer I .     

A glutamic acid-based polymer keeping intact the integrity of all the three original functionalities of the amino acid

Dimethyl glutamate, on treatment with allyl bromide, afforded dimethyl N,N-diallylglutamate which upon alkaline ester hydrolysis followed by acidification with aqueous HCl gave N,N-diallylglutamic acid hydrochloride [(CH₂=CH–CH₂)₂NH⁺CH(CO₂H)(CH₂)₂CO₂H Cl^?] I. Using Butler’s cyclopolymerization protocol, new monomer I underwent ammonium persulfate-initiated polymerization to give pyrrolidine ring-embedded linear cyclopolymer II i.e. ?[?CH₂(C₄H₆)NH⁺{CH(CO₂H)(CH₂)₂CO₂H Cl^?}CH₂?]?_n retaining the integrity of all the three functionalities of glutamic acid. Under the influence of pH, the repeating units of triprotic acid (+) in II were equilibrated to those of water-insoluble diprotic polyzwitterionic acid (±) III, water-soluble monoprotic poly(zwitterion-anion) (±?) IV, and its conjugate base polydianion (=) V. The critical salt concentration required to promote water solubility of (±) III has been determined to be 0.548 M NaCl, 0.271 M NaBr, 0.133 M NaI. The basicity constants of the carboxyl groups and trivalent nitrogen in (=) V have been determined. A 5 ppm and 20 ppm concentrations of III are effective in inhibiting the precipitation of CaSO₄ from its supersaturated solution with a ≈100% scale inhibition efficiency at 40 °C for a duration of over 3 and 16 h, respectively.     

Syndioselective propylene polymerization: Comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2

The kinetics and stereochemical control of propylene polymerization initiated by syndiospecific isopropylidene(1-η⁵-cyclopentadienyl)(1-η⁵-fluorenyl)-dimethylzirconium–methyl aluminoxane (1/MAO) and (1-fluorenyl-2-cyclopentadienylethane)-dimethylzirconium–MAO (2/MAO) were investigated. The influence of MAO concentration and polymerization temperature (T_p) on polymerization kinetics and polypropylene properties, such as molecular weight, molecular weight distribution (MWD), and stereoselectivity, have been studied in detail. The activity of both catalytic systems is very sensitive to the concentration of MAO. The 1/MAO and 2/MAO catalysts record maximum activity when [Al]/[Zr] ratio is around 1300 and 2500, respectively. The activity and the degree of stereochemical control are also sensitive to T_p. The 2/MAO catalyst is much more thermally stable than 1/MAO catalyst; the former shows maximum activity at 80°C, whereas the latter shows maximum activity at 20°C. The cationic active species generated by 2/MAO is not so stereorigid as those by 1/MAO so that 2/MAO catalyst produces sPP of broad MWD (4.43–6.38) and low syndiospecificity at high T_p. When T_p is above 50°C, 2/MAO catalyst produces completely atactic polypropylene. The results of fractionation of sPP samples produced by 1/MAO and 2/MAO demonstrate that 1/MAO catalyst is characterized by uniform active sites, but 2/MAO is characterized by multiple active sites. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 973–983, 1998