Column fractionation of partially stereoregular poly(propylene oxide)

A column packed with glass beads has been used to fractionate partially stereoregular poly(propylene oxide) (PPO). PPO was first crystallized onto the glass beads from isooctane solution by stepwise lowering the column temperature. Each layer of PPO, which was deposited at different temperature ranges, was extracted by washing the beads with several columns full of isooctane. Thus several fractions differing in both stereoregularity and molecular weight were obtained by progressively increasing the extraction temperature and the solvent residence time in the column. It is concluded that in the procedure described above PPO can be fractionated on the basis of structural and steric regularity. The observed steady increase in the molecular weight of fractions with extraction temperature was interpreted as being due to the fact that the stereoregularity of chains increases with their molecular weight.     

Efficiency of the Pruitt-Baggett Catalyst in the Stereoregular Polymerization of Propylene Oxide

Partially stereoregular poly(propylene oxide) (PPO), samples synthesized by the Pruitt-Baggett Catalyst (PBC) were fractionated at 25CEC and 50°C from acetone by adding small portions of water. At 25°C mainly solid-liquid phase separations took place. On the other hand, at 50°C, liquid-liquid phase separations were observed. Thus, it was possible to fractionate PPO on the basis of molecular weight. From the molecular weight measurements, it was concluded that 1 molecule of high PPO was formed for less than 10 Fe atoms.     

Nanoscale structure of SAN-PEO-SAN triblock copolymers synthesized by atom transfer radical polymerization

Low molecular weight triblock copolymers (TBCs) with poly(styrene-co-acrylonitrile) (SAN) end-blocks and poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO) or polycaprolactone (PCL) mid-blocks were synthesized using atom transfer radical polymerization (ATRP). The influence of molecular weight, composition (mid-block mole fraction), and interaction parameter on the crystallinity and on the formation of an ordered nanoscale phase-separated structure was investigated using thermal analysis, X-ray scattering, and electron microscopy. The TBCs with PEO mole fractions of over 0.5 exhibited PEO crystallinities of around 40% (compared to 72% for the PEO homopolymer) and lamellar nanoscale periodicities of around 176 Å (compared to 143 Å for the PEO homopolymer). The TBCs with PEO, PCL or PPO mole fractions of less than 0.5 exhibited relatively low crystallinities and did not exhibit ordered structures. These results emphasize the importance of the mid-block mole fraction in determining the ability to form an ordered nanoscale structure through mid-block crystallization. The ordered structure disappeared on heating the TBCs above the mid-block melting point, but below the SAN glass transition temperature. The crystallinity was reduced significantly in TBCs that were annealed or cast from a solvent.     

Application of infrared ATR spectroscopy to in situ reaction monitoring

The infrared horizontal ATR technique was adapted to be applied for in situ reaction monitoring even at high pressure and high temperature. Different types of reactors and flow cells were built which can be used for recording IR ATR spectra at pressures up to 200 bar and temperatures up to 300°C.

The use of the horizontal ATR technique is shown by the following application examples:

• addition reaction of n-butyl isocyanate with butyric alcohol;

• investigation of the equilibrium of isocyanate, HCl and carbamic acid chloride at elevated pressure and temperature;

• monitoring the polycondensation of bifunctional alcohols and carbonic acids;

• recording spectra of polymer melts at 280°C.

Synthesis of polyether-based block copolymers based on poly(propylene oxide) and terephthalates

Poly(propylene oxide) (PPO) is a low reactive telechelic polyether and the synthesis of high molecular weight poly(propylene oxide)-based block copolymers was studied. The poly(propylene oxide) used was end capped with 20 wt % ethylene oxide and had a molecular weight of 2300 g/mol (ultra-low monol PEO-b-PPO-b-PEO). The type of terephthalic acid based precursors was varied: terephthalic acid, dimethyl terephthalate, diphenyl terephthalate, di(trifluoro ethyl) terephthalate, di(p-nitrophenyl) terephthalate) and terephthalic acid chloride. High molecular weight poly(propylene oxide) based segmented block copolymers were obtained with diphenyl terephthalate (inherent viscosity: 1.6 dl/g).The synthesis of polyether(ester-amide)s comprising PPO and isophthalamide-based segments was also studied by varying the polymerization temperature and time. High molecular weight poly(propylene oxide) block copolymers could be obtained if the reaction was carried out for 2 h at 250 °C under vacuum. Higher temperatures (280 °C) and longer times result in lower inherent viscosities, probably due to degradation of the polyether.     

Low-temperature methanol synthesis from carbon dioxide and hydrogen via formic ester

A new route of methanol synthesis, at 443 K and under pressurized conditions, from carbon dioxide and hydrogen through formic ester was investigated, by using Cu-based catalysts. This one-pot reaction consisted of three steps:

1. formic acid synthesis from CO₂ and H₂,

2. esterification of formic acid by ethanol to ethyl formate, and

3. hydrogenolysis of ethyl formate to methanol and ethanol.

Crystal Morphology of Mesoporous Silica Thin Films Synthesized by the Spin-Coating Method Using PEO–PPO–PEO Triblock Copolymer

Mesoporous thin films on Si substrates with thicknesses of about 460–610 nm have been synthesized by the spin-coating method using a Pluronic EO₇₇PO₂₉EO₇₇ (F68), EO₁₀₄PO₃₉EO₁₀₄ (F88), and EO₁₃₃PO₅₀EO₁₃₃ (F108) triblock copolymer system. The triblock copolymers were preserved within the synthesized mesoporous thin films. Transmission electron microscopy (TEM) characterization of these films clearly demonstrates that long-range mesostructural ordering strongly depends on the molecular weight of the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer, with lower molecular weight producing higher degrees of order. Plane and cross-sectional high-resolution TEM studies coupled with X-ray diffraction (XRD) analysis also show that highly ordered F68 mesoporous silica thin film forms a cubic structure with a lattice spacing a = 6.70 nm.     

Novel initiators for the synthesis of propylene oxide oligomers by anionic ring opening polymerization

A series of potassium alcoholates was obtained from the reaction between KOH and ethylene glycol, resorcinol, 4,4′-bisphenol A, 4,4′-(1,3 phenylenediisopropylidene)-bisphenol, 4,4′-sulfonyldiphenol. These salts were employed to initiate the anionic ring opening polymerization of propylene oxide (PO). The molecular weight distribution of the propylene oxide oligomers prepared by this method and the initiator structure were correlated. These oligomers were characterized through Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) spectroscopies and size exclusion chromatography (SEC). It was found that the molecular weight and polydispersity of the synthesized poly(propylene oxide) (PPO) is highly dependant on the initiator structure and solubility in the reactive medium. The oligomers obtained using di-potassium resorcinolate exhibited a molecular weight distribution more polydisperse than that of PO oligomers synthesized by means of di-potassium ethylene glycolate. In the case of the PO polymerizations started by the potassium salts of 4,4′-bisphenol A, 4,4′-(1,3 phenylenediisopropylidene)-bisphenol and 4,4′-sulfonyldiphenol, the oligomer chains showed very broad molecular weight distributions. In general, lower solubility and augmentation of the polymer polydispersity were observed when the number of aromatic rings in the initiator structure increased. The experimental results were contrasted with those obtained from quantum chemical semiempirical calculations at AM1 level. The peculiar behavior exhibited by the initiators with an aromatic structure could be explained in terms of different reactivities of the initiation sites. The theoretical studies revealed that the ring in the aromatic initiators promotes an unsymmetrical growing when the PPO chains are formed. In contrast, the identical reactivity of both initiation sites in the ethylene glycolate produces a symmetrical growing during the PO polymerization.     

Supercritical fluid chromatographic analysis of the propoxylated glycerol esters of oleic acid

Capillary supercritical fluid chromatographic methods were developed for the separation and quantitation of oligomers of propoxylated glycerols and fatty acid-esterified propoxylated glycerols. Samples containing mole ratios (propylene oxide to glycerol) of 5, 8 and 14 were chromatographed. Separations depended primarily upon the molecular weight or the number of the propylene oxide units. The oligomer distributions in the propoxylated glycerol and the oleic acid-esterified propoxylated glycerol samples were determined.     

Aliphatic polycarbonate synthesis by copolymerization of carbon dioxide with epoxides over double metal cyanide catalysts prepared by using ZnX2 (X = F, Cl, Br, I)

As means of the chemical fixation of carbon dioxide and the synthesis polycarbonates, copolymerizations of carbon dioxide with various epoxides, such as cyclohexene oxide, cyclopentene oxide and propylene oxide were investigated in the presence of double metal cyanide (DMC) catalysts. The DMC catalysts were prepared by reacting K₃Co(CN)₆ with ZnX₂ (X = F, Cl, Br, I) together with tertiary butyl alcohol and poly(tetramethylene ether glycol) as complexing reagents and were characterized by various spectroscopic methods. The DMC catalysts showed high activity for epoxides and CO₂ copolymerization to yield aliphatic polycarbonates of narrow polydispersity and moderate molecular weight.     

Teaching and learning strategies and evaluation changes for the adaptation of the Chemical Engineering degree to EHES

An integrated learning methodology has been developed and implemented in order to adapt the Chemical Engineering degree in the University of Valladolid (Spain) to the European Higher Education Space (EHES) philosophy. It was necessary to modify the objectives and theoretical contents of the different subjects and also the learning methodology, considering the general chemical engineering skills and also the transferable skills reached by the students, according to the recommendations of the European Federation of Chemical Engineering (EFCE) for chemical engineering education in Bologna two-cycle degree system.

This methodology has been applied to the seventh semester of a 5 years Chemical Engineering degree. The main objectives of the proposed strategy were:

• To provide to the student with a holistic, integrated and applied vision of the different subjects involved in chemical engineering, coordinating all of them and planning common activities as a case study based on an industrial process.

• To help students to develop transferable skills by means of designing suitable teaching and learning strategies.

• To prepare the students for the long-life learning.

General and particular objectives were defined adapting the course to the EHES philosophy. In this sense, the programmes in terms of the learning outcomes and competences to be acquired were designed, the total student workload to get the objectives of the programme was estimated and the entire course was programmed and planned in a detailed schedule. A course guide was elaborated including all this information, resulting in a useful instrument for teachers and students.

This methodology was complemented with the evaluation of the global learning process. The evaluation made was based on the next two aspects:

• Student learning evaluation. Tutorial sessions, written reports, oral presentations, discussion sessions and partial and final written exams were considered.

• Learning methodology evaluation. External evaluation requires carrying out inquiries, both to students and teachers involved.

Zinc and tin xanthates in the coordination polymerization of propylene oxide

The polymerization of propylene oxide with zinc and tin xanthates was studied. Polymerization with both systems was found to be a zeroth‐order, nonterminating process, where the molecular weight was controlled by transfer reactions. It is discussed that these observations were consistent with a mechanism in which the rate‐determining step was the addition of monomer on the growing chain rather than the coordination of the monomer to active sites. These catalysts turned out to be quite stable, even under semiclosed conditions. With zinc isopropyl xanthate, high conversions in short polymerization times could be obtained. The product had a very broad molecular weight distribution and could be split into crystallizable and amorphous fractions. The crystallizable fractions consisted of stereoregular segments separated from each other by stereoirregularities or regioirregularities. The degrees of polymerization of stereoregular segments (S₁'s) were estimated from melting point measurements. It was found that the melting points and, hence, average S₁ values changed in different fractions. It was concluded that there was only one type of active center; however, the rates of wrong additions (e.g., head‐to‐head addition) of incoming monomer controlled the average S₁ value of the chain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Hydrotreating processes for catalytic abatement of water pollutants

Opportunities and problems in application of catalytic hydrotreating processes, which are presented a viable approach in the abatement of water pollutants, are discussed. Analysis of the hydrodechlorination (HDC) and hydrodenitrification (HDN) using Pd-based catalysts supported on various materials like granulated activated carbon (GAC), fibrous activated carbon cloths (ACCs) or glass fiber cloths (GFCs) studied recently in our laboratory suggests the following perspectives:

Exhaustive regeneration of Pd/GAC saturated with p-chlorophenol can be achieved in a two-step approach, incorporating gas-phase HDC by hydrogen followed by oxidation by air.

Pd/ACC catalysts are good candidates for the liquid-phase HDC showing activity higher than that of Pd/GAC or Pd/GFC; the high adsorption capacity of Pd/ACC lead suggesting its use in a technology with periodic adsorption and HDC, in similarity to adsorption with regeneration of GAC.

Pd/GFC and Pd–Cu/GFC are promising catalyst for removal of nitrites and nitrates, showing activity and selectivity that compares favorably with those of powdered catalysts.

Molecular motion in polyisobutylene and poly(propylene oxide) studied by 13C nuclear magnetic relaxation

The ¹³C spin-lattice relaxation times of low molecular weight (up to 2500) samples of polyisobutylene and poly(propylene oxide) have been measured as a function of molecular weight, temperature and concentration in chloroform solution. For both polymers there is little dependence on molecular weight indicating a flexible conformation in the liquid state, but the relaxation time increases with increasing dilution in CHCl₃. The motion of the polymer backbone therefore depends on the microviscosity of the solution, rather than the bulk viscosity. In polyisobutylene the methyl re-orientation rate increases in parallel with the backbone re-orientation rate, showing that the two motions are interlinked. In poly(propylene oxide) the methyl re-orientation rate is independent of the backbone motion.     

Chain structure and mechanical properties of polyethylene/polypropylene/poly(ethylene‐co‐propylene)in‐reactor alloys synthesized with a spherical Ziegler–Natta catalyst by gas‐phase polymerization

Two polyethylene/polypropylene/poly(ethylene‐co‐propylene) in‐reactor alloy samples with a good polymer particle morphology were synthesized by sequential multistage gas‐phase polymerization with a spherical Ziegler–Natta catalyst. The alloys showed excellent mechanical properties, including both toughness and stiffness. With temperature‐gradient extraction fractionation, both alloys were fractionated into five fractions. The chain structures of the fractions were studied with Fourier transform infrared, ¹³C‐NMR, and thermal analysis. The alloys were mainly composed of polyethylene, polyethylene‐b‐polypropylene block copolymer, and polypropylene. There also were minor amounts of an ethylene–propylene segmented copolymer with very low crystallinity and an ethylene–propylene random copolymer. The block copolymer fraction accounted for more than 44 wt % of the alloys. The coexistence of these components with different structures was apparently the key factor resulting in the excellent toughness–stiffness balance of the materials. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 640–647, 2005     

Cure and properties of unfoamed polyurethanes based on uretonimine modified methylene–diphenyl diisocyanate

The curing behaviour of a series of polyurethanes based on modified methylene–diphenyl diisocyanate (MDI) and poly(propylene oxide) polyols was studied using isothermal Fourier‐transform infrared spectroscopy (FTIR), temperature‐ramped differential scanning calorimetry (DSC) and adiabatic exotherm experiments. The effects of catalyst type and content, and of polyol molecular weight and functionality on the curing behaviour of the material were investigated. Increasing catalyst concentration or decreasing the polyol molecular weight raised the rate of reaction and shifted the DSC peak exotherm temperature to lower temperatures, but the heat of reaction was effectively constant. A marked increase in reaction rate was observed when a 1 °‐alcohol‐based polyol (from ethylene oxide end‐capping) was used in place of the standard poly(propylene oxide) end‐capped 2 °‐polyols. FTIR isocyanate conversion during polyurethane formation for a range of dibutyltin dilaurate (DBTDL) concentrations was satisfactorily fitted to second‐order kinetics. An approximately linear relationship between DBTDL catalyst concentration and reaction rate constant was found, but increasing the concentration of DBTDL was found to have no significant effect on the magnitude of the activation energy. The activation energy for polymerization was found to be independent of the molecular weight of the diol or triol systems. Dynamic mechanical thermal analysis revealed a linear increase of the glass transition temperature with decreasing triol weight fraction, and was in good agreement with a theoretical model based on copolymer and crosslinking effects. © 2000 Society of Chemical Industry     

Nickel (salen) / methylaluminoxane catalyzed polymerization of norbornene

Summary Nickel (salen) in conjunction with methylaluminoxane (MAO) catalyzes the polymerization of norbornene to poly (2,3-bicyclo [2.2.1] hept-2-ene) [poly (norbornene)]. Methylaluminoxane (MAO) was used as cocatalyst as such (MAO-I) and after distilling off free trimethylaluminium (MAO-II). The catalyst system was very active in chlorobenzene at room temperature. It was also found that MAO-II gave higher activity as compared to MAO-I. The samples of polynorbornene were soluble in 1,2,4-trichlorobenzene. The poly (norbomene)s were characterized by intrinsic viscosity and thermal properties. Received: 4 November 1999/Revised version: 25 January 2000/Accepted: 31 January 2000     

Synthesis and characterization of linear asymmetrical poly(propylene oxide) diol

Linear asymmetrical poly(propylene oxide) was synthesized through four‐step reactions: selective benzylation, alcohol exchange reaction, propylene oxide anionic polymerization, debenzylation. One terminal of the asymmetrical polymer chains is alcohol hydroxyl and the other is phenol hydroxyl. It was characterized with infrared (IR) and ¹H Nuclear Magnetic Resonance (¹H‐NMR). Peaks at 1.11, 3.38, and 3.53 ppm were attributed to side groups (? OCH₂CH(CH₃)? ), backbone units (? OCH₂CH(CH₃)? ) and (? OCH₂CH(CH₃)? ) of poly(propylene oxide), respectively. Molecular weight and molecular weight distribution were measured with ¹H‐NMR and laser light scattering (LLS), which showed that the linear asymmetrical poly(propylene oxide) was mono‐disperse (PDI = 1.02–1.07). Then, its carbamate reaction with phenyl isocyanate was studied; the reaction rate constants for phenol hydroxyl and alcohol hydroxyl of poly(propylene oxide) were k₁ = 0.209 mol L^?1 min^?1 and k₂ = 0.051 mol L^?1 min^?1. There was a great reactivity difference for two types of hydroxyls in asymmetrical poly(propylene oxide), contrasting to the single carbamate reaction rate constant of symmetrical poly(propylene oxide) (k₃ = 0.049 mol L^?1 min^?1). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Safety assessment of polymeric additives for food packaging: Hydrolysis of polymeric plasticizers by digestive fluids

The in vitro hydrolysis of poly(1,2‐propylene adipate) by digestive fluid liquids was studied to assess the safety of polymeric plasticizers that could migrate into food. A high extent of hydrolysis was obtained with freshly prepared intestinal fluid solutions. High performance size exclusion chromatography analysis indicated that the bulk plasticizer completely disappeared and that low molecular weight oligomers were formed within 4 h. Hydrolysis did not result in a significant conversion to the free monomers, like adipic acid, as was shown by gas‐phase chromatography. Measurements by NMR indicated that the cleavage selectively occurred at primary ester linkages. Fractionation of the hydrolysis products on silica gel gave six oligomeric fractions, which were recovered and analyzed. The absolute molecular weight of the plasticizers and the average molecular weight of the hydrolysis products were evaluated using proton NMR. Hydrolysis did not take place (<2%) under simulated gastric and saliva conditions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 956–966, 2002     

Crystallization of poly(ethylene oxide) fractions: simultaneous dilatometry and calorimetry

The crystallization of two fractions of poly(ethylene oxide), with molecular weights of 6000 and 360 000, has been studied by simultaneous dilatometry and calorimetry. The crystallization isotherms obtained by the two techniques are identical for the low molecular weight fraction, but differ for the high molecular weight fraction.