Analytical scale supercritical fluid fractionation of a low molecular weight,high density polyethylene wax with carbon dioxide

This paper reports on the use of supercritical carbon dioxide to fractionate a low molecular weight, high density polyethylene into very narrow molecular weight distributions (MWDs). A simple extraction system was developed that allowed relatively trouble free extractions of the polyethylene samples. Fractions were collected at successively higher densities of CO₂ at constant temperature and then analyzed by capillary supercritical fluid chromatography (SFC), or high temperature gel permeation chromatography (GPC) and/or differential scanning calorimetry (DSC). Fractionations were performed at three different temperatures (60,80, and 100°C). Higher temperatures were found to yield greater recoveries and higher MWDs at any given density. Reducing the increment between successive extraction steps resulted in polydispersities being reduced to nearly “monodisperse” levels. Total recoveries ranged from 12 to 33% depending on the temperature, and the highest molecular weight fraction extracted by the CO₂ was centered around 1500.     

Initial steps of thermal degradation of PVC prepared at various temperatures

PVC samples were obtained by bulk polymerization initiated with AIBN and ultraviolet irradiation at 40, 25, 0, ?30, and ?50°C. They were characterized by ¹³C NMR measurements, infrared spectroscopy, GPC in hexamethylphosphoramide and B.E.T. surface area measurements. Their thermal degradation was studied between 110 and 185°C by using continuous titration of HCl evolved through a conductimetric cell. The ultraviolet spectra were recorded at various steps of the degradation. At high degradation temperatures, the more syndiotactic the polymer, the longer the polyene average sequences are. The amount of HCl evolved is minimum for a polymerization temperature of 0 or 25°C, depending on the degradation temperature and on the morphology of the polymer. The results are discussed in terms of chemical factors (tacticity distribution, molecular weight) as well as of physical factors (morphology, interval viscosity).     

Characterization of Branched Poly (vinyl Acetate) by GPC and Low Angle Laser Light Scattering Photometry

Abstract

Poly (vinyl acetate), PVAC, synthesized by bulk polymerization over a range of initiator concentrations ([AIBN] = 10^?5 to 4 × 10^?3 g-mole/1), temperatures (50°C, 60°C, 70°C, and 80°C) and conversion levels (3 to > 90%) were characterized using low angle laser light scattering (LALLS) photometry to measure M_w of the whole polymers. A number of these samples were characterized using GPC with a differential refractive index (DRI) and LALLS detector to measure the molecular weight distribution (weight fraction versus M_w). M_w for PVAC samples synthesized at suitably low initiator levels at various conversions were found to agree with classical light scattering measurements after Graessley.

An electronic device and a technique which optimizes the sensitivity and the signal-to-noise ratio of the LALLS photometer throughout the molecular weight distribution (MWD) of the GPC chromatogram were devised. These considerably simplify the operation of the LALLS for both offline and online operation with GPC.

Most importantly it was unambiguously shown that the commonly used universal calibration parameter (UCP) with GPC, [n]M_w, is incorrect for polymers with molecules having the same hydrodynamic volume but different molecular weights, i. e., those with only chain branching (LCB), copolymers with compositional drift, and polymer blends. The correct UCP was found to     

Synthesis of dihydroxy telechelic oligomers of β-butyrolactone catalyzed by titanium(IV)-alkoxides and their use as macrodiols in polyurethane chemistry

We report on a solvent-free approach for the synthesis of low molecular weight, α,ω-dihydroxy telechelic poly(β-butyrolactone). In the presence of Ti(IV) alkoxides, mixtures of β-butyrolactone and diols, like di- or triethylene glycol, were reacted in ratios between 4:1 and 10:1. The oligomerization proceeds at elevated temperatures (80–100°C). Different alkoxide substituents (R = Me, iPr, tBu) of the Ti(IV)(OR)₄ catalyst were investigated. The resulting oligomers were characterized by nuclear magnetic resonance (NMR), infra-red (IR), gel-permeation chromatography (GPC), titration, and matrix-assisted laser desorption-time-of-flight mass spectrometry (MALDI-ToF-MS) analysis. Aside from low molecular weight products, special effort was devoted to achieve high O-acyl cleavage selectivity and to circumvent the formation of unsaturated end-groups in order to form exclusively dihydroxy-telechelic oligomers. Optimized results in terms of selectivity and reaction rates were achieved at 100°C using catalyst loadings of 0.2 mol% with respect to the monomer. The molecular weights determined by GPC were in good accordance with the ratio of monomer to diol used, confirming successful oligomer formation. Polyurethanes prepared from crude macrodiols without any additional catalyst feature molecular weights up to 50,000 g/mol. The reported work serves as concept to utilize β-lactones for tailored polyol synthesis; the resulting products are suitable for polyurethane chemistry.     

Fluorene‐rich high performance polyesters: Synthesis and characterization of 9,9‐fluorenylidene and 2,7‐fluorenylene‐based polyesters with excellent optical property

Polyesters PEs containing high content of fluorene units in their backbones were synthesized from 9,9‐diarene‐substituted fluorene diols ( 1 ) and fluorene‐based diacid chlorides ( 2 ) by high temperature polycondensation at 185 °C in diphenyl ether. The molecular weights of the polyesters PE1‐PE5 were in a range of M_w 25,000–165,000. The polyesters displayed their high thermostability: the glass transition temperatures (T_g) by differential scanning calorimetry analysis ranged from 109 to 217 °C, while the 10% weight loss temperatures (T_d10) measured by thermogravimetric analysis were over 400 °C in nitrogen and 395 °C in air. The polyesters had good solubility in most common organic solvents such as chloroform and toluene and gave tough, transparent and flexible cast films. The transmittance of the films was over 80% in the wavelength range from 450 to 700 nm in any PEs . The PEs exhibited high refractive index values around 1.65, while they had very low degree of birefringence. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2549–2556, 2008     

A new high temperature gas chromatograph incorporating a temperature programmable direct injector

A high temperature gas chromatograph has been developed which is capable of operating at column oven temperatures up to 500°C. In addition, the detector can operate at temperatures up to 500°C, and the injector up to 450°C. The injector on this instrument is a temperature programmable direct injector, designed specifically to introduce labile or high molecular weight samples into the GC without molecular weight discrimination. The design of this GC and injector will be described, and high temperature applications will be discussed.     

Activity and stability spontaneously enhanced toward ethylene polymerization by employing 2‐(1‐(2,4‐dibenzhydrylnaphthylimino)ethyl)‐6‐(1‐(arylimino)ethyl) pyridyliron(II) dichlorides

A series of 2‐(1‐(2,4‐dibenzhydrylnaphthylimino)ethyl)‐6‐(1‐(arylimino)ethyl)pyridyliron(II) complexes ( Fe1 ? Fe5 ) was synthesized and characterized. The molecular structure of the representative Fe2 was determined by single‐crystal X‐ray diffraction, revealing a distorted pseudo‐square‐pyramidal geometry around the iron center. On activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all these iron complex precatalysts performed with high activities (up to 1.58 × 10⁷ g (PE) mol^?1 (Fe) h^?1) toward ethylene polymerization, producing highly linear polyethylenes with high molecular weight and bimodal distribution, which was in accordance with high temperature ¹³C NMR, high T _m values (T _m ～130 °C) and the GPC curves of the obtained polyethylenes. Meanwhile, DFT calculation results also showed the good correlation between net charges on iron and experimental activities. Compared with previous bis(imino)pyridyliron analogues, the current iron complexes containing the benzhydrylnaphthyl groups exhibited relatively higher activities and better thermal‐stability at elevated temperatures, especially at 80 °C as the industrial operating temperature, and still showed high activities toward ethylene polymerization up to 8.57 × 10⁶ g (PE) mol^?1 (Fe) h^?1 in the presence of co‐catalyst MMAO. In addition, these iron complex precatalysts all exhibited long lifetimes. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 988–996     

Synthesis and characterization of isomeric polyesters based on sebacic acid and hexanediols

Isomeric homopolymers and random copolyesters based on sebacic acid and isomeric hexanediols were synthesized by condensation techniques and characterized by NMR, GPC, intrinsic viscosity, and DSC. Among the homopolymers, only the polyester derived from the linear 1,6-hexanediol was found to be crystalline. Typical melting points were 65–70°C, depending on molecular weight, and a T_g of ?62°C was measured on a high molecular weight sample. Other isomeric homopolymers derived from the branched diols 2-methyl-2-ethyl-1,3-propanediol and 2,5-hexanediol were amorphous tacky fluids with glass temperatures of ?69 and ?66°C, respectively. In the case of the random copolymers, NMR analysis was particularly useful in determining the copolymer composition or the diol isomer ratio. DSC data indicated that all the random copolymers containing the linear 1,6-diol were crystallizable and their melting points depended on copolymer composition. The heat of fusion per repeat unit of poly(hexamethylene sebacate) was found to be 32 cal/g from measurements of the molecular weight dependence of the melting point.     

High pressure radical polymerization of ethylene with water dilution

The radical polymerization of ethylene has been performed in the presence of water. The structural characteristics of polymers prepared with 0-60% wt of water at 1400 atm and various temperatures (140–260°) were determined by the usual solution methods (viscometry, GPC), by density and by infrared spectroscopy. The experimental results show that, when water content increases, long chain branching (LCB) increases and molecular weight distribution broadens.     

Poly(methylene sebacate): Synthesis and characterization

The synthesis of poly(methylene sebacate) was carried out via the reaction of cesium sebacate with bromochloromethane in N-methylpyrrolidone over a range of temperatures (55–130°C). A number of polymers having limiting viscosity numbers in the range of 0.29–0.94 dL g^?1 (CHCl₃; 25°C) were characterized by elemental analyses, ¹H- and ¹³C-NMR, DSC, and GPC techniques. The polymerization was found to be very rapid at 100°C, being complete in ca. 15 min. and was relatively insensitive to the stoichiometric ratio of the monomers. As high molecular weight polymers were produced without the quantitative conversion of the reactants, the polymerization is considered to be occurring by an interfacial mechanism.     

Determination of molecular weight distribution of cellulose by conversion into tricarbanilate and fractionation

Two samples of cellulose (molecular weight 2.97 × 10⁵ and 1.25 × 10⁵) were transformed into carbanilates (CTC) which were then fractionated by the elution method at a constant composition of the acetone-water elution mixture with the column temperature gradually increasing from ?30°C to 30°C, and by the GPC method in acetone and tetrahydrofuran. Tetrahydrofuran appeared to be a more suitable solvent. The molecular weights of fractions obtained by the elution fractionation were determined by the light-scattering method in tetrahydrofuran. The width of fractions was determined by the GPC method (average M _w/M _n = 1.37); the [η] values and the Mark-Houwink constants (K = 5.3 × 10^-3, a = 0.84) for tetrahydrofuran at 25°C were determined. The calibration curve for the GP method was constructed by means of the fractions thus obtained; it was demonstrated that the universal calibration curve according to Benoit can also be used. It was demonstrated that the molecular weight distribution of cellulose can be conveniently determined by conversion into CTC followed either by the elution fractionation (for preparative purposes) or by fractionation by the GPC method (for analytical purposes).     

Anionic Polymerization of α-Methylstyrene. IX. Nature of the Propagating Species

Abstract

The nature of the initiating and propagating species involved in the anionic polymerization of α-methylstyrene has been explored. The earlier hypothesis that multimodal GPC molecular weight distributions in polymers arise solely out of different reaction steps or different ion-pair mechanisms being involved has been modified for poly-α-methylstyrene. Multimodal GPC molecular weight distributions in poly-α-methylstyrene initiated with potassium at 25°C and polymerized at 25°C or higher in THF, p-dioxane, or cyclohexane as solvents have been ascribed to the presence of two different types of tetramers which grow simultaneously but at different rates, each responding to its own well-defined thermodynamic equilibrium and yielding dormant and living polymers. Reaction schemes describing the initiation (at 25°C) and propagation reactions (between -25 and 60°C) in the polymerization (in solution of THF as well as in bulk) of α-methylstyrene initiated with potassium-naphthalene, butyl-lithium, and butyllithium-tetramethylethylenediamine (TMEDA) have been presented. The role of coordinating agents naphthalene and TMEDA in changing irreversible propagations into reversible ones has been emphasized.     

Solution properties of poly(dimethyl siloxane)

The solution properties of poly(dimethyl siloxane) (PDMS) were studied with light scattering (LS), gel permeation chromatography/light scattering (GPC/LS), and viscometry methods. PDMS samples were fractionated, and the weight‐average molecular weights, second virial coefficient, and the z‐average radius of gyration of each fraction were found according to the Zimm method with the LS technique. In this work, the molecular weight range studied was 7.5 × 10⁴ to 8.0 × 10⁵. Molecular weights and molecular weight distributions were determined by GPC/LS. The intrinsic viscosities of these fractions were studied in toluene at 30 °C, in methyl ethyl ketone (MEK) at 20 °C, and in bromocyclohexane (BCH) at 26 °C and 28 °C. The Mark–Houwink–Sakurada relationship showed that toluene was a good solvent, and MEK at 20 °C and BCH at 28 °C were θ solvents for PDMS. The unperturbed dimensions were calculated with LS and intrinsic viscosity data. The unperturbed dimensions, expressed in terms of the characteristic ratio, were found to be 6.66 with different extrapolation methods in toluene at 30 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2678–2686, 2000     

New poly(arylene ether)s with pendant phosphonic acid groups

Soluble brominated poly(arylene ether)s containing mono‐ or dibromotetraphenylphenylene ether and octafluorobiphenylene units were synthesized. The polymers were high molecular weight (weight‐average molecular weight = 115,100–191,300; number‐average molecular weight = 32,300–34,000) and had high glass‐transition temperatures (>279 °C) and decomposition temperatures (>472 °C). The brominated polymers were phosphonated with diethylphosphite by a palladium‐catalyzed reaction. Quantitative phosphonation was possible when 50 mol % of a catalyst based on bromine was used. The diethylphosphonated polymers were dealkylated by a reaction with bromotrimethylsilane in carbon tetrachloride followed by hydrolysis with hydrochloric acid. The polymers with pendant phosphonic acid groups were soluble in polar solvents such as dimethyl sulfoxide and gave flexible and tough films via casting from solution. The polymers were hygroscopic and swelled in water. They did not decompose at temperatures of up to 260 °C under a nitrogen atmosphere. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3770–3779, 2001     

Alkyl-substituted poly(2,5-benzophenone)s synthesized via Ni(0)-catalyzed coupling of aromatic dichlorides and their miscible blends

High molecular weight poly(2,5-benzophenone) derivatives were prepared by Ni(0)-catalyzed coupling of 4′-substituted 2,5-dichlorobenzophenones. Monomers were synthesized by the Friedel–Crafts reaction of 2,5-dichlorobenzoyl chloride and alkyl-substituted benzenes in the presence of aluminum chloride. The resulting polymers are soluble and show no evidence of crystallinity by DSC. Number average molecular weights are in the range of 9.2 × 10³–11.7 × 10³ g/mol by multiple angle laser light scattering (MALLS). Molecular weights obtained by MALLS are only slightly lower (∼90%) than those obtained by GPC (polystyrene standards). These polymers exhibit high thermal stability with glass transition temperatures ranging from 173 to 225°C and weight loss occurring above 450°C in nitrogen and 430°C in air. Additionally, the polymers were blended and the resulting polymer films appear to be miscible by DSC results. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2611–2618, 1998     

Poly(arylene sulfide)s by nucleophilic aromatic substitution polymerization of 2,7‐difluorothianthrene

Poly(thianthrene phenylene sulfide) and poly(thianthrene sulfide) have been prepared by nucleophilic aromatic substitution polymerization of the activated monomer 2,7‐difluorothianthrene with bis thiophenoxide and sulfide nucleophiles, respectively. The resulting polymers are thermally stable, amorphous materials that have been characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), matrix‐assisted laser desorption/ionization‐time‐of‐flight (MALDI‐TOF) mass spectrometry, UV‐Vis spectroscopy, refractometry, and intrinsic viscosity (IV) measurements. The polymers produced exhibit 5% weight loss values approaching 500 °C in inert and air atmospheres and glass transition temperatures that range from 149 to 210 °C. Poly(thianthrene phenylene sulfide) with a number average molecular weight of 22,100 g/mol has been synthesized with an IV in DMPU of 0.62 dL/g at 30 °C. Creasable films of this polymer have been prepared by solvent casting and melt pressing at 250 °C. Films of poly(thianthrene phenylene sulfide) exhibit transparencies greater than 50% at wavelengths exceeding 400 nm and a high refractive index value of 1.692 at a wavelength of 633 nm, making the polymer interesting for optical applications. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2453–2461, 2009     

Benzylated pulps from sugar cane bagasse

An optimized ethanol/water process has been employed for the pulping of fibres from sugar cane bagasse. After pretreatment with aqueous NaOH, unbleached pulps were subjected to benzylation at 110 °C for different periods of time. The resulting purified products were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and infrared spectroscopy (IR). The results showed that benzylation proceeded to various extents depending on the reaction time, as assessed by weight gain. During the first 3 h, a loss of mass was observed due to the occurrence of benzylation of low molecular weight polyoses, which were eliminated in the purification step. After that period of time a drastic weight increase was observed probably because crystalline regions had developed. The samples with low degrees of benzylation were insoluble, whereas the more benzylated counterparts showed limited solubility in THF. Partially soluble samples and a completely soluble one showed very different GPC elution profiles. This may be attributed to the efficiency of the pre treatment which, in the latter case, employed more concentrated alkali. Thermogravimetric analyses showed that all samples were degraded above 310 °C. Glass transition temperatures ranged between 42 °C and 65 °C, increasing as the extent of benzylation increased This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. VII. Effect of pretreatment temperature of silica gel on styrene–silica gel system

To investigate the reaction mechanism of radiation-induced polymerization of styrene adsorbed on silica gel, the effect of pretreatment temperature of silica gel was studied. Preheating of silica gel was carried out at 200, 500, and 800°C. The number of silanol groups of silica gel surface decreased as preheating temperature increased. The rate of polymerization on the silica gel preheated at 500°C was faster than that at 200°C, but the polymerization rate on the silica gel preheated at 800°C was the lowest. These results suggest that rate of polymerization on the silica gel is affected by the conditions of silica gel surface such as the number of silanol groups and the pore size. At the same monomer conversion, percent grafting decreased as preheating temperature of silica gel increased. The GPC spectra of both graft polymers and homopolymers have two peaks at all preheating temperatures. The monomer conversion of low molecular weight peaks of graft polymers decreased as preheating temperature of silica gel increased. This result suggests that there is a probability that the grafting sites of low molecular weight peaks of graft polymers somehow interact with silanol groups.     

Synthesis and properties of new aromatic polyisophthalamides with adamantylamide pendent groups

A new diacid monomer containing a pendent adamantyl ring was reacted with various aromatic diamines to prepare novel aromatic polyisophthalamides (PIPAs). The polymers were obtained in high yield and high molecular weight by the Yamazaki‐Higashi phosphorylation method of polycondensation. Inherent viscosities ranged from 0.40 to 0.82 dL/g, which corresponds to weight‐average and number‐average molecular weights (GPC) in the range 21,000–63,000 g/mol and 9000–31,000 g/mol, respectively. The polymers were essentially amorphous and soluble in a variety of polar aprotic solvents, and they afforded transparent, creasable films by the solution‐casting method. The great size of the polyhedral adamantyl moiety brought about a significant restriction of segmental mobility, which translated into a strong increase of T_g, so that very high glass transition temperatures were observed, in the range 335–370 °C (DSC), which are 70–90 °C above the glass transition temperatures of homologous PIPAs without pendent groups. Thus, it can be stated that these adamantyl containing polyamides are among the soluble aromatic PIPAs with highest T_g ever described. Conversely, the initial decomposition temperature, as measured by thermogravimetric analysis, was about 400 °C, which is lower by 40–70° than that of unsubstituted counterparts. Polymer films exhibited good mechanical properties, with tensile strengths over 65 MPa and tensile moduli between 2.0 and 2.6 GPa. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1743–1751, 2010     

Poly(2,6-diphenyl-1,4-phenyl oxide): Characterization by gel-permeation chromatography,light scattering,and solution viscosity

Ten unfractionated poly(2,6-diphenyl-1,4-phenylene oxide) samples were examined by gel permeation chromatography (GPC) and intrinsic viscosity [η] at 50°C in benzene, by intrinsic viscosity at 25°C in chloroform, and by light scattering at 30°C in chloroform. The GPC column was calibrated with ten narrow-distribution polystyrenes and styrene monomer to yield a “universal” relation of log ([η]M) versus elution volume. GPC-average molecular weights, defined as M?gpc = \documentclass{article}\pagestyle{empty}\begin{document}$\Sigma w_i [\eta ]_i M_i /\Sigma w_i [\eta ]_i$\end{document}, w_i denoting the weight fraction of polymer of molecular weight M_i, were computed from the GPC and [η] data on the polyethers. The M?GPC were then compared with the weight-average M?_w from light scattering. The intrinsic viscosity (dl/g) versus molecular weight relations for the unfractionated poly(2,6-diphenyl-1,4-phenylene oxides) determined over the molecular weight range 14,000 ≤ M?_w ≤ 1,145,000 are log [η] = ?3.494 + 0.609 log M?_w (chloroform, 25°C) and log [η] = ?3.705 + 0.638 log M?_w (benzene, 50°C). The M?_w(GPC)/M?_n(GPC) ratios for the polymers in the molecular weight range 14,000 ≤ M?_w ≤ 123,000 approximate 1.5 according to computer integrations of the GPC curves with the use of the “universal” calibration and the measured log [η] versus log M?_w relation. The higher molecular weight polymers (326,000 ≤ M?_w ≤ 1,145,000) show slightly broadened distributions.