Polyester-based Copolymers for Biomaterials Fabrication

Summary: Results on synthesis of poly(3-hydroxybutyrate)s possessing one or two hydroxyl groups at one terminus of the chain and carboxylic group at the other chain end are reported. These polymers were further functionalised via transesterification with dimethyl H-phosphonate thus incorporating a reactive/biodegradable center in the polyester backbone. Block/star-like copolymers composed of hydrophilic PEG and hydrophobic poly(3-hydroxybutyrate) segments linked by phosphoester moiety were also obtained. Chemical structure and composition of the reaction products were analysed applying different spectroscopic techniques (¹H, and ³¹P NMR, IR and ESI-MS) and size exclusion chromatography was applied to describe molecular weight averages and distribution.     

High Temperature Interaction Chromatography of Olefin Copolymers

Summary: The synthesis and characterization of polyolefins continues to be one of the most important areas for academic and industrial polymer research. One consequence of the development of new “tailor-made” polyolefins is the need for new and improved analytical techniques for the analysis of polyolefins with respect to molar mass and chemical composition distribution. The present article briefly reviews different new and relevant chromatographic techniques for polyolefin analysis. For the fast analysis of the chemical composition distribution of polyolefins a new high-temperature gradient high-performance liquid chromatography (HPLC) system has been introduced. The efficiency of this system for the separation of various olefin copolymers is demonstrated. The correlation between elution volume and chemical composition can be accessed by on-line coupling of high temperature HPLC with FTIR spectroscopy. For the elucidation of the chemical composition as a function of molar mass high-temperature size exclusion chromatography and ¹H-NMR spectroscopy can be coupled. It is shown that the on-line NMR analysis of chromatographic fractions yields information on microstructure and chemical composition in addition to molar mass distribution.     

New Curable Propylene Copolymers Containing Tert‐Butoxysilane Side Groups

In this work, new, crosslinkable copolymers from propylene and di‐tert‐butoxy(methyl)(oct‐7‐enyl)silane are presented. The silane‐functionalized monomer is obtained by hydrosilylation of 1,7‐octadiene with dichloromethylsilane, followed by the substitution of the chloro atoms by tert‐butoxy groups. Homopolymerization and copolymerization with propylene are performed using rac‐[ethylenebis(indenyl)]zirconium dichloride. The tert‐butoxysilane groups are easily cleaved by acid‐catalyzed processes. The resulting copolymer can be completely crosslinked via the tert‐butoxysilane functionality to obtain insoluble polymeric material and the gel content of the polymers with different silane content is determined. This method allows control of the copolymer composition and thus of the subsequent extent of crosslinking.     

Synthesis and Characterization of Ethylene/Propylene Copolymers in the Whole Composition Range

Summary: The incorporation of comonomer molecules in the backbone of a homopolymer can influence the final properties of the material, decreasing its crystallinity and the melting and glass transition temperatures, and increasing its impact resistance and transparency. In the present work, ten ethylene/propylene copolymers have been synthesized using a supported metallocene catalytic system covering the whole composition range. Any desired composition was obtained by controlling the feed composition during the reaction. These synthesized copolymers have been characterized by different techniques in order to study the effect of the comonomer incorporation onto their final properties. When the comonomer content is low, the behaviour of the copolymer is similar to that of the corresponding homopolymer. Nevertheless, if the comonomer content increases, the copolymer becomes more amorphous (low crystallization temperature and soft XRD signals) and easily deformable, reaching a behaviour close to that corresponding to an elastomeric material. In order to corroborate these results the samples have been characterized by TREF and GPC-MALS. TREF analysis showed that copolymers containing less than 10% and more than 80% of ethylene are semicrystalline, with elution temperatures typical of this kind of polymers. Molecular weights are higher for homopolymers and they decrease as the comonomer concentration increases, whereas the polydispersity index keeps almost constant at the expected value for this kind of samples.     

Electrical impedance spectroscopy of epoxy systems: The case of 1,4-butanediol diglycidyl ether/cis-1,2-cyclohexanedicarboxylic anhydride and triethylamine as initiator

A series of epoxy cured samples, with different molar composition of 1,4-butanediol diglycidyl ether (EP), cis-1,2-cyclohexanedicarboxylic anhydride (CH) and triethylamine (TEA) as initiator, was studied by Electrical Impedance Spectroscopy (EIS) in the frequency range 10⁻²-10⁵ Hz. The resistivity of the system was evaluated by using the complex impedance analysis method. Resistivity values in the range between 10⁷ and 10¹³ Ω cm were obtained and related to the composition (molar fraction x_EP or x_CH) of the epoxy system. The gel formation characteristics of the samples were obtained as theoretically described by Flory.     

Raman Structural Study of Copolymers of Propylene with Ethylene and High Olefins

Nascent form of random copolymers of propylene with ethylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene was studied by Raman spectroscopy. The most significant spectral alterations with a change in propylene content were observed in two lines at 809 and 841 cm⁻¹. The first line corresponds to vibrations of polypropylene helical chains in the crystalline phase, while the second one is associated with vibrations of polypropylene helical chains having isomeric defects. Raman data confirm that conformational composition and phase state of copolymer macromolecules strongly depend on the comonomer content as well as on the size of the comonomer units.     

The Stereochemistry of Styrene-Maleic Anhydride Copolymers: 13C-NMR Study and Pvcilo and Indo/1 Calculations

The stereochemistry of alternating copolymers of styrene (ST) with maleic anhydride (MA) was examined by ¹³C-NMR spectroscopy, and the stabilization energies and the most stable geometries of complexes and adducts between ST and MA were calculated by the PVCILO program and by INDO/1. The methine and carbonyl carbon atoms of the MA portion and the quaternary carbon atom of the ST portion reveal different stereochemistries due to various polymerization conditions, suggesting that the donor-acceptor complex may participate in the co-polymerization. The complex postulated according to the Diels-Alder geometry was more stable than that according to [2+2] cycloaddition geometry. It is believed that the stabilization energy is so great that the copolymerization occurs spontaneously via forming a donor-acceptor complex and adducts. The geometries of 1:1 adducts formed by endo and exo approaches in the Diels-Alder geometry mode were also calculated.     

Determination of Compositional,Configurational Sequences in High Conversion Methyl Methacrylate-Methacrylic Acid Emulsion Copolymers Using a Rapid and Selective Counting Procedure

High conversion methyl methacrylate (MMA)-methacrylic acid (MA) copolymers prepared by two different emulsion polymerization processes were characterized in terms of composition and sequence distribution by ¹H- and ¹³C-NMR, taking into account the conversion effect. A rapid and selective counting procedure for calculating the compositional configurational pentads (512 values) in these copolymers is described. From this counting procedure and using the Klesper's assignment of the 18 peaks observed in the ¹³C-NMR carbonyl resonance spectrum of the copolymers, a relatively good agreement was found between the calculated and experimental fractions of each peak intensity. Moreover, this study allows differences in compositional homogeneity to be characterized as a function of the nature of the emulsion polymerization process.     

Micellization and Adsorption Parameters of Poly(Propylene Oxide)/Poly(Ethylene Glycol) Block and Graft Copolymers in Aqueous Medium

This work aims to measure the adsorption and micellization parameters of new water soluble nonionic amphiphilic block and graft copolymers based on hydrophilic poly (ethylene glycol) (PEG) and hydrophobic poly (propylene oxide) (PPO) at ambient temperature and normal atmospheric pressure. The chemical composition and molecular weights of the prepared copolymers were determined from ¹H NMR analyses. The surface properties of the prepared surfactants were determined by measuring the surface tension at different temperatures. The surface tension, critical micelle concentration, and surface activities were determined at different temperatures. Surface parameters such as surface excess concentration, the area per molecule at interface and the effectiveness of surface tension reduction were determined from the adsorption isotherms of the prepared surfactants. Some thermodynamic data for the adsorption and micellization process were calculated and are discussed.     

Characterization of ethylene/propylene copolymers by means of a GPC-4D technique

Copolymer composition and comonomer distribution are important magnitudes in polymer material that have a big effect on different kind of properties and consequently there are several ways to study.In this work several ethylene/propylene copolymers synthesized with two different metallocene catalysts and a Ziegler–Natta catalyst and covering a wide composition range were studied. Characterization was carried out by nuclear magnetic resonance (¹³C NMR) and by gel permeation chromatography with 4 detectors (GPC-4D): refractive index, viscosity, multi-angle light scattering and infrared detectors.Different behaviour in the comonomer distribution along the molecular weight was obtained for metallocene and for ZN copolymers as expected due to the differences between these catalytic systems. Nevertheless, Ziegler–Natta copolymers present more homogeneous comonomer distribution due to the synthesis method. Study of conformation of chains in solution was improved by defining the scaling law of R_g against the number of repeat units because it avoids the effect of the repetitive unit size. Both metallocene copolymer sets show similar dependence of q value with the copolymer composition, however Ziegler–Natta copolymers show different behaviour with q values independent on copolymer composition. This different behaviour has been related with the effects of the heterogeneity of the ethylene distribution and of the molecular weight of the samples.     

Strong covalent bonding modulated graphene oxide/epoxy interfacial enhancement and advanced corrosion resistance

Abstract

Chemically functionalized graphene oxide [multi-amino functionalized graphene oxide (MAGO)] was achieved by building covalent bonds between graphene oxide (GO) and a small molecule containing benzene structure and multi-amino groups. Fourier transform infrared, X-ray diffraction, X-ray photo electron spectroscopy and TEM-EDX results certified that the molecule was successfully grafted onto GO nanosheets. Subsequently, functionalized GO was incorporated into waterborne epoxy (EP) coating through ball-milling method. This molecular design can significantly improve the dispersion of MAGO in EP matrix, as well as the compatibility and interaction between MAGO and EP. Compared with GO/EP, the water absorption of MAGO/EP decreased from 4.38 to 2.59%, the adhesion strength of MAGO/EP increased from 4.72 to 6.32?MPa after immersion of 40?days in 3.5% NaCl solution. Incorporation of 1?wt% of MAGO into EP matrix prominently improved the long-term corrosion resistance. The impedance modulus of GO/EP coating decreased by four orders after 40 days immersion, while that of MAGO/EP coating only decreased by one order. The impedance modulus was still 1.47?×?10⁸ Ω cm², and two-time constant wasn’t detected for MAGO/EP coating. This research developed a novel green anticorrosion coating with enhanced durability for metal protection.     

Chemical Composition Distribution of Multicomponent Copolymers

The number and weight chemical composition distributions in random terpolymers were derived using a statistical approach. The solution was then generalized to comprise higher multicomponent copolymers. The analytical solution was verified with Monte Carlo simulations and by considering limiting cases. Chemical composition distributions for fractions of random terpolymers of various kinetic chain lengths were also investigated. In a similar way to the results for binary copolymers described by Stockmayer's distribution, broadening of the distribution is observed for low‐molecular‐weight chains.

Comparison of chemical composition distributions from Stockmayer (Equation ( 3 )) and statistical approach (Equation ( 4 )).     

High thermal conductivity EP adhesive based on the GO/EP interface optimized by TDI

Graphene oxide (GO) was used as the filler to modify the epoxy resin (EP) adhesive, and the GO/EP interface was optimized by toluene diisocyanate (TDI) in order to improve the thermal conductivity and T peel strength performance of the adhesive. Through the characterization of the GO product, which was modified by TDI, TDI was grafted onto the surface of GO, and there were NCO groups remaining; thus the chemical bonds were built onto the interface which was non‐wetting between GO and EP. The results of the properties characterization of the adhesive indicated that the bonding properties were significantly enhanced, especially the T peel strength, which was up to 9.62 N/mm, which was contributed by the optimized GO/EP interface. The thermal conductivity of the adhesive increased to 0.624 W m^?1 K^?1, as the interface thermal resistance was reduced after the interface between GO/EP was optimized by TDI. The insulation performance of the adhesive was also improved, since the well‐dispersed GO formed a micro‐capacitance model in EP, and the surface of GO was covered by the EP so that the electronic paths were blocked by the formed chemical bonds.     

Thermogravimetric Analysis of Vinyl Chloride/Acrylonitrile Copolymers

The dehydrohalogenation of several alternating and random vinyl chloride/acrylonitrile copolymers was characterized by thermogravimetry. The polymers were made in solution, and the conversions were kept below 5% to insure uniform sequence distributions. Hydrogen chloride was generated within a relatively narrow temperature range somewhere between 200 and 300°C depending on the sequence distribution, relative viscosity, and composition. The weight-loss during the dehydrohalogenation could be attributed completely to the hydrogen chloride available in the copolymer. Alternating copolymers were significantly more stable than random copolymers were significantly more stable than random copolymers at the same relative viscosity. For a given sequence distribution or composition, stability decreased with decreasing relative viscosity. The stability decreased as acrylonitrile content was increased from 23 to 57%.

The thermogravimetric analyzer was interfaced with a digital computer. The digitized data were smoothed and differentiated by convoluted integers. The differentiated data provided rates for a qualitative discussion of dehydrohalogenation kinetics.     

MCM/ZrO2 nanoparticles modified electrode for simultaneous and selective voltammetric determination of epinephrine and acetaminophen

A novel MCM/ZrO₂ nanoparticles modified carbon paste electrode (MZ-CPE) was fabricated and used to study the electro oxidation of epinephrine (EP) and acetaminophen (AC) and their mixtures by electrochemical methods. The modified electrode showed electrocatalytic activity toward EP and AC oxidation with a decrease of the overpotential by 173 mV to a less positive potential for EP at the surface of the MZ-CPE and an increase in peak current at pH 7.0. Differential pulse voltammetry peak currents of EP and AC increased linearly with their concentrations in the ranges of 1.0 × 10^?6–2.5 × 10^?3 and 1.0 × 10^?6–2.0 × 10^?3 M, respectively, and the detection limits for EP and AC were 5.0 × 10^?7 and 4.5 × 10^?7 M, respectively.     

Electrical impedance spectroscopy of epoxy systems II: Molar fraction variation, resistivity, capacitance and relaxation processes of 1,4-butanediol diglycidyl ether/succinic anhydride and triethylamine as initiator

The Electric Impedance Spectroscopy (EIS) was used to evaluate resistivity, capacitance and relaxation processes of a cured epoxy system with different molar composition of 1,4-butanediol diglycidyl ether (EP), succinic anhydride (SA) and triethylamine (TEA) as initiator. The measurements were done over range frequencies between 10⁻¹ and 10⁵ Hz. The systematic change of the molar fraction composition affected the resistivity and capacitance changes indicating gelation critical compositions according to the Flory’s aggregation theory. The complex electric functions, dielectric constant ε^•, electric modulus M^•, impedance Z^•, admittance Y^• and the loss factor tan δ were utilized in order to investigate the relaxation processes. Relaxation peaks were observed for different molar fraction composition only in the imaginary impedance, the electric modulus and the tan δ as frequency functions. The relaxation frequencies obtained by Z″, M″ and tan δ evaluation are distinct and have been discussed in terms of resin components molar fraction dependence.     

Synthesis of Propylene Diblock Copolymers via Metallocene and Borane Chemistry

An isotactic chain end unsaturated polypropylene was prepared by the homogeneous metallocene catalyst Et(Ind)₂ZrCl₂ with MAO. Herein, the chain end unsaturated polypropylene proceeded the hydroboration reaction to prepare borane‐containing polypropylene. The borane‐containing polypropylene could be transformed to hydroxyl‐terminated polypropylene, PPOH. And then the polypropylene‐nylon 6 diblock copolymer, PP‐b‐NY6, was synthesized from telechelic PPOH by converting this prepolymer with toluene diisocyanate and using the resulting materials as macroactivators for anionic caprolactam polymerization. Meanwhile, this investigation used borane‐containing polypropylene and oxygen to produce free radicals at the chain end on the polypropylene. Experimental results indicate that the free radical is an effective initiator for the polymerization of methyl methacrylate to produce diblock PP‐b‐PMMA. The block copolymers are characterized by IR, NMR, and DSC analyses. The diblock copolymer is a good compatibilizer for polymer blends.     

Low flammability and smoke epoxy resins with a novel DOPO‐based imidazolone derivative

In this work, a DOPO‐based imidazolone derivative named DHI was synthesized using DOPO, 5‐amino‐2‐benzimidazolinone and 4‐hydroxybenzaldehyde as raw materials. The chemical structure of DHI was characterized by ¹H‐NMR, ³¹P‐NMR and Fourier transform infrared spectra (FTIR). Then, a series of different flame‐retardant epoxy resin (EP) thermosets were prepared by mixing flame retardant DHI. The thermal properties of the cured EPs was investigated by thermogravimetry analysis (TGA) and differential scanning calorimeter (DSC), and the results showed the thermal stability and glass transition temperature (T_g) of the cured EP modified with DHI declined slightly compared with that of neat EP. The limited oxygen index (LOI) and UL94 test results exhibited DHI imparted good flame retardancy to EP. The EP‐4 (phosphorus content of 1.25%) possessed a LOI value of 36.5% and achieved a V‐0 rating. Furthermore, the peak of heat release rate (PHRR) and total heat release rate (THR) of EP‐4 decreased by 38.7% and 24.5%, respectively. Excitedly, the total smoke production (TSP) of EP‐4 sample declined by 62.5%, which meant DHI also made EP obtain excellent smoke suppression property. Moreover, the flame‐retardant mechanism was studied by scanning electron microscopy (SEM) and pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS). It was reasonable inferred that DHI could not only promote EP to form dense char layer in condensed phase, but also restrain combustion in gaseous phase through catching the free radicals sourced from the degradation of EP.     

A Self-Assembled Capsule for Propylene/Propane Separation

The development of energy-saving technology for the efficient separation of olefin and paraffin is highly important for the chemical industry. Herein, we report a self-assembled Fe₄L₆ capsule containing a hydrophobic cavity, which can be used to encapsulate and separate propylene/propane. The successful encapsulation of propylene and propane by the Fe₄L₆ cage in a water solution was documented by NMR spectroscopy. The binding constants K for the Fe₄L₆ cage toward propylene and propane were determined to be (5.0±0.1)×10³ M⁻¹ and (2.1±0.7)×10⁴ M⁻¹ in D₂O at 25 °C, respectively. Experiments and theoretical studies revealed that the cage exhibited multiple weak interactions with propylene and propane. The polymer-grade propylene (>99.5 %) can be obtained from a mixture of propylene and propane by using the Fe₄L₆ cage as a separation material in a U-shaped glass tube. This work provides a new strategy for the separation of olefin/paraffin.     

Copolymers of conjugated dienes with maleic acid monoesters. IV. Reactivity ratios in copolymerization of isoprene with maleic acid monoesters

Research was carried out on copolymerization of isoprene with maleic acid monoesters in the presence of free radicals (AIBN). The aim of the study was to observe the effect of the different monoesters obtained with normal alcohols of the aliphatic series: monoethyl maleate, monopropyl maleate, monobutyl maleate, monoheptyl maleate, monolauryl maleate, and monocetyl maleate. On the basis of reactivity ratios determined by the Fineman-Ross method and compared with the Mayo-Lewis method, all the systems studied are typical cases of heterocopolymerization. The parameter r₁ is constant for this homologous series with the exception of the low terms. The experimental results agree with the ultimate model equation (with deviation at very high values of [M₁⁰]/[M₂⁰]), but not with the copolymer composition equation which considers the effect of the penultimate unity (penultimate model). Characterization of the sequential distribution is also presented (considering the effect of the terminal group only), and deviations of the experimental results are also discussed.