Metallocene ethylene-1-octene copolymers: Effect of extrusion conditions on thermal oxidation of polymers with different comonomer content

Metallocene ethylene-1-octene copolymers having different densities and comonomer content ranging from 11 to 36 wt% (m-LLDPE), and a Ziegler copolymer (z-LLDPE) containing the same level of short-chain branching (SCB) corresponding to one of the m-LLDPE polymers, were subjected to extrusion. The effects of temperature (210-285 °C) and multi-pass extrusions (up to five passes) on the rheological and structural characteristics of these polymers were investigated using melt index and capillary rheometry, along with spectroscopic characterisation of the evolution of various products by FTIR, ¹³C-NMR and colour measurements. The aim is to develop a better understanding of the effects of processing variables on the structure and thermal degradation of these polymers. Results from rheology show that both extrusion temperature and the amount of comonomer have a significant influence on the polymer melt thermo-oxidative behaviour. At low to intermediate processing temperatures, all m-LLDPE polymers exhibited similar behaviour with crosslinking reactions dominating their thermal oxidation. By contrast, at higher processing temperatures, the behaviour of the metallocene polymers changed depending on the level of comonomer content: higher SCB gave rise to predominantly chain scission reactions whereas polymers with lower level of SCB continued to be dominated by crosslinking. This temperature dependence was attributed to changes in the different evolution of carbonyl and unsaturated compounds including vinyl, vinylidene and trans-vinylene.     

Synthesis of novel crosslinked sulfonated poly(ether sulfone)s using bisazide and their properties for fuel cell application

Novel crosslinked sulfonated poly(ether sulfone)s (PESs) were prepared by thermal irradiation of the allyl-terminated telechelic sulfone polymers using a bisazide. The sulfonated polymers in different comonomer compositions were fully characterized by ¹H NMR, and the crosslinked structure was also verified by FT-IR spectroscopic analyses. Having both the uniform distribution of the hydrophilic conductive sites and controlled hydrophobic nature by minimized crosslinking over the rigid rod poly(ether sulfone) backbone, the crosslinked polymer membrane (PES-60) offered excellent proton conductivity of 0.79 S cm⁻¹ at 100 °C together with hydrolytic and oxidative stability. In addition, only 17% of methanol permeability of the Nafion^® was observed for the crosslinked PES-60.     

Solid sampling Fourier transform infrared determination of Mancozeb in pesticide formulations

A series of approaches have been assayed for FTIR determination of Mancozeb in several solid commercial fungicides using different calibration strategies. The simplest procedure was based on the use of the ratio between the absorbance of a characteristic band of Mancozeb and that of a KSCN internal standard measured in the FTIR spectra obtained from KBr pellets. It was employed the quotient between peak height absorbance values at 1525 cm⁻¹ for Mancozeb and 2070 cm⁻¹ for KSCN. In these conditions a precision as relative standard deviation (RSD) of 0.6% and a relative accuracy error of 0.8% (w/w) were found. For complex formulations, containing other compounds with characteristic absorption bands at different wavenumbers than Mancozeb, one of them was used as internal reference being employed the standard addition approach. In this case, the Mancozeb bands at 1525 cm⁻¹ or at 1289 cm⁻¹ were employed, being used the ferrocyanide band at 2075 cm⁻¹ as internal reference. RSD values between 0.7-1.4% and a relative accuracy error of 3% (w/w) were found. A third strategy was based on the use of partial least squares (PLS) calibration. A reference set was prepared mixing Mancozeb, Kaolin, Cymoxanil and KBr, being predicted the Mancozeb concentration in pesticide formulations by using the quotient between absorbance bands of Mancozeb and those of Cymoxanil. In these conditions a relative accuracy error of 0.6% (w/w) and a relative standard deviation of 1.3% were found.     

Metallocene ethylene-1-octene copolymers: Influence of comonomer content on thermo-mechanical, rheological, and thermo-oxidative behaviours before and after melt processing in an internal mixer

The influence of the comonomer content in a series of metallocene-based ethylene-1-octene copolymers (m-LLDPE) on thermo-mechanical, rheological, and thermo-oxidative behaviours during melt processing were examined using a range of characterisation techniques. The amount of branching was calculated from ¹³C NMR and studies using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were employed to determine the effect of short chain branching (SCB, comonomer content) on thermal and mechanical characteristics of the polymer. The effect of melt processing at different temperatures on the thermo-oxidative behaviour of the polymers was investigated by examining the changes in rheological properties, using both melt flow and capillary rheometry, and the evolution of oxidation products during processing using infrared spectroscopy.The results show that the comonomer content and catalyst type greatly affect thermal, mechanical and oxidative behaviour of the polymers. For the metallocene polymer series, it was shown from both DSC and DMA that (i) crystallinity and melting temperatures decreased linearly with comonomer content, (ii) the intensity of the β-transition increased, and (iii) the position of the tan δ_max peak corresponding to the α-transition shifted to lower temperatures, with higher comonomer content. In contrast, a corresponding Ziegler polymer containing the same level of SCB as in one of the m-LLDPE polymers, showed different characteristics due to its more heterogeneous nature: higher elongational viscosity, and a double melting peak with broader intensity that occurred at higher temperature (from DSC endotherm) indicating a much broader short chain branch distribution.The thermo-oxidative behaviour of the polymers after melt processing was similarly influenced by the comonomer content. Rheological characteristics and changes in concentrations of carbonyl and the different unsaturated groups, particularly vinyl, vinylidene and trans-vinylene, during processing of m-LLDPE polymers, showed that polymers with lower levels of SCB gave rise to predominantly crosslinking reactions at all processing temperatures. By contrast, chain scission reactions at higher processing temperatures became more favoured in the higher comonomer-containing polymers. Compared to its metallocene analogue, the Ziegler polymer showed a much higher degree of crosslinking at all temperatures because of the high levels of vinyl unsaturation initially present.     

Improving the aging resistance of styrene-butadiene-styrene tri-block copolymer modified asphalt by addition of antioxidants

The aging properties of base asphalt and styrene-butadiene-styrene tri-block copolymer (SBS) modified asphalts (PMA) are evaluated using Fourier Transform Infrared (FTIR) spectroscopy. An aging cell fitted to the FTIR microscope was used to continually and directly study the oxidation of the PMA. In particular, Attenuated Total Reflectance, ATR, with a zinc selenide prism was used to quantify the changes in the spectra of the PMA before and after thin film oven test (TFOT). The effect of a small amount (1 wt%) of some modifiers, zinc dialkyldithiophosphate (ZDDP), zinc dibutyl dithiocarbamate (ZDBC) or naphthenoid oil, on the chemical and physical properties of the PMA was studied. The modification extent of the modifiers increases in the order: oil, ZDBC, ZDDP. With the aging of the PMA, carbonyl groups formed and the intensity of the absorption peak at 965 cm⁻¹ (the characteristic peak of SBS) decreased. Antioxidants, ZDDP or ZDBC modified PMA are resistant to the formation of carbonyl to some extent, indicating the improvement of aging resistance of the PMA by the addition of the antioxidants. ZDDP and ZDBC as antioxidants can retard the oxidation of the PMA through the inhibition of peroxides and radical scavenging. Furthermore, ZDDP in a liquid state at room temperature acts as plasticiser, giving rise to a good aging resistance of PMA.     

Differential reactivity of aromatic diamines during polyimide formation in water

A series of mono and di-imide compounds were synthesized by the reaction of common aromatic diamines with 4,5-dichlorophthalic acid in aqueous solution (at temperature between 160 °C and 200 °C) as a precursor to determining the chemical reactivity changes in these diamines during copolyimide synthesis under the same conditions. The reactivities of the second amino group were shown to reduce dramatically, in number of examples, after substitution had occurred on the first amino group. The effect of these reactivity changes on polymer and copolymer properties was examined by the synthesis of a series of polymers containing two of the diamines with very different reactivity behaviours.The model compounds and polymers were characterized by FTIR, ¹H NMR and where possible by mass spectroscopy. The polymers were also characterized by GPC, Tg and some mechanical properties.     

Synthesis and characterization of dithienobenzothiadiazole-based donor–acceptor conjugated polymers for organic solar cell applications

New donor–acceptor conjugated polymers (P1 and P2) containing a fused-ring dithienobenzothiadiazole (DT-BTD building block) were synthesized by using the Stille copolymerization method. The synthesized polymers were characterized by ¹H NMR, GPC, and elemental analysis. The optical band gaps of the polymers were found to be 1.86 and 1.9 eV, respectively, as calculated from their film onset absorption edge. Upon annealing both produced a distinct shoulder peak in their film absorption spectra. The electrochemical studies of P1 and P2 revealed that the HOMO and LUMO energy levels of the polymer were −5.3, −5.1 eV, and −3.4, −3.2 eV, respectively. The polymers are thermally stable up to 250–350 °C.     

Cross‐linked poly(aryl ether sulfone) membranes for direct methanol fuel cell applications

Partially sulfonated poly(aryl ether sulfone) (PESS) was synthesized and methacrylated via reaction with glycidyl methacrylate (PESSGMA) and cross‐linked via radical polymerization with styrene and vinyl‐phosphonic acid (VPA). The chemical structures of the synthesized pre‐polymers were characterized via FTIR and ¹H NMR spectroscopic methods and molecular weight was determined via GPC. Membranes of these polymers were prepared via solution casting method. The crosslinking of the PESS polymer reduced IEC, proton conductivity, swelling in water, and methanol permeability of the membranes while increasing the modulus and the glass transition temperature. However, the introduction of the VPA comonomer increased the proton conductivity while maintaining excellent resistance to methanol cross‐over, which was significantly higher as compared with both PESS and the commercial Nafion membranes. Membranes of PESSGMA copolymers incorporating VPA, exhibited proton conductivity values at 60 °C in the range of 16–32 mS cm⁻¹ and methanol permeability values in the range of 6.52 × 10⁻⁹ – 1.92 × 10⁻⁸ cm² s⁻¹. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 558–575     

Conclusive chemical deciphering of the consistently occurring double‐peak carbonyl‐stretching FTIR absorbance in polyurethanes

Polyurethanes include an extremely vast and varied family of polymers, exhibiting a vast range of properties and applications. Although the urethane chemical structure consists of a single carbonyl group, the vast majority of polyurethane Fourier transform infrared spectroscopy (FTIR) spectra exhibit two distinct adjacent carbonyl‐stretching absorbances. It was the purpose of the present research to investigate and determine the reason of occurrence of this consistently observed phenomenon. A polyurethane, designed and synthesized here as linear and containing only urethane and methylene groups, strongly exhibited two very distinct carbonyl‐stretching FTIR absorbances. A new polyurethane, exhibiting an extremely high degree of trifunctional crosslinking, was hereby designed and synthesized to sterically inhibit diisocyanate access to already established urethanes and thus inhibit the allophanate and further tertiary oligo‐uret forming side‐reactions. The resulting polymer dramatically exhibited only a single, strong and sharp, carbonyl‐stretching FTIR absorbance belonging only to the urethane group. Synthesis of a polymer exhibiting a lower degree of crosslinking led to the reappearance of the split double carbonyl‐stretching FTIR absorbance. Solid‐state ¹³C NMR measurement results of the same polymers were highly consistent with the FTIR spectroscopy results. The experimental results of the present research conclusively prove and determine the exclusive side‐reaction‐related double carbonyl‐stretching absorbance in the FTIR analysis of polyurethanes. These research results conclusively reveal that, in fact, the so‐called linear polyurethanes synthesized from diisocyanates and diols are branched or even loosely crosslinked.     

Poly(ethylene-2,6-naphthalate) microfiber prepared by carbon dioxide laser-thinning method

Poly(ethylene-2,6-naphthalate) (PEN) microfiber was continuously obtained by using a carbon dioxide (CO₂) laser-thinning method. As a winding speed increased, the fiber diameter decreased, and its birefringence increased. When the PEN microfiber, obtained by irradiating the laser operated at a power density of 9.15 W cm⁻² to the original fiber supplied at 0.33 m min⁻¹, was wound up at 1594 m min⁻¹, the obtained microfiber had a diameter of 2.8 μm, a birefringence of 0.174, tensile modulus of 5.4 GPa, and a tensile strength of 0.36 GPa.     

Synthesis and characterization of new poly(azomethine ester)s having phenylthiourea units

New polyesters having azomethine and phenylthiourea groups in the polymer backbone were synthesized by interfacial polycondensation method. The dihydroxy monomer N-(4-hydroxy-3-methoxybenzal) N′-(4′-hydroxyphenyl)thiourea was condensed with six diacid chlorides: terephthaloyl, isophthaloyl, azeloyl, suberoyl, pimeloyl and adipolyl chlorides. The resulting polyesters were characterized by viscosity, IR, NMR and TGA analysis. The wholly aromatic poly(azomethine ester) derived from terephthaloyl chloride when blended with polyaniline/NH₄OH, polyaniline/HCl and pure polyaniline shows conductance in the range 3.2 × 10⁻³-0.91 × 10⁻¹ S cm⁻¹.     

Synthesis of novel soluble poly(imide-siloxane)s via hydrosilylation: Characterization and structure property behaviour

A series of novel poly(imide-siloxane)s (PIS) were synthesized by the grafting of amine terminated soluble imides to the siloxane backbone. The amine terminated imides were synthesized by choosing suitable anhydrides and amines to get the imides that are soluble in polar and non-polar solvents. The imides were grafted to the siloxane backbone by the epoxy group cleavage. All the polymers were obtained in quantitative yields with the inherent viscosities ranging from 0.22 to 1.2 dL g⁻¹. The polymers were characterized by FT-IR, ¹H and ¹³C NMR, and were examined for their thermal properties. The polymers were found to be stable up to a temperature 350 °C. The DSC results showed a single glass transition in the negative temperature, whereas the DTA revealed another glass transition in the positive end for some of the polymers showing phase separation. Polymer films were prepared employing the coupling reaction between PIS and the polydimethylsiloxane matrix by varying the amount of incorporation of PIS in the films. The polymer films had a tensile strength of 35-82 MPa with a percentage elongation of 86-271%. The contribution of polar and dispersion component towards the total surface energy was studied by the contact angle measurement and a reduction in surface tension of 14 mN m⁻¹ was achieved with the fluorine containing PIS membrane.     

Novel highly soluble 3,3′-bicarbazolyl based polymers for optoelectronics

Novel family of highly soluble polymers containing 3.3′-bicarbazolyl moieties is reported. Utilizing simple and efficient chemical oxidation of carbazole and its derivatives by iron trichloride exclusively and quantitatively yields the bicarbazolyl dimmers with reactive oxirane groups. The polymers were prepared in polyaddition reaction of bicarbazolyl-containing diepoxydes with 4,4′-thiobisbenzenethiol, 2,5-dimercapto-1,3,4-thiadiazole, or 1,3-benzenedithiol in the presence of catalyst triethylamine. Obtained compounds were characterized using GPC, DSC, IR, UV, fluorescence and ¹H NMR spectroscopy. The hole drift mobility reaches 10⁻⁴ cm²/Vs at high electric fields. Such processable polymers with conjugated-nonconjugated repeating units in the main chain and good charge carrier mobility are quite promising for fabrication of optoelectronic devices.     

Ionic transport in P(VDF-HFP)-PMMA-LiCF3SO3-(PC + DEC)-SiO2 composite gel polymer electrolyte

Composite gel polymer electrolytes composed of poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP) and polymethylmethacrylate PMMA polymers, PC + DEC as plasticizer and LiCF₃SO₃ as salt and fumed silica as filler have been synthesized by solvent casting technique with varying plasticizer-filler ratio systematically. Films of thickness in the range of 40-70 μm were characterized by a.c. impedance measurements in the temperature range 303 K to 373 K. Addition of filler to the polymer electrolyte was found to result in an enhancement of the ionic conductivity. A maximum electrical conductivity of ∼1 × 10⁻³ S/cm at 303 K and ∼2.1 × 10⁻³ S/cm at 373 K has been achieved with the dispersion of the SiO₂. FTIR spectral studies confirmed the polymer-salt interaction. XRD patterns exhibit the increased amorphicity in the blended composite gel polymer electrolytes. Scanning electron micrograph shows the dispersion of SiO₂ particle in the polymer electrolyte.     

Thermal-oxidative degradation of polyamide 6,6 containing metal salts

The thermal-oxidative stability of oven aged polyamide 6,6 (PA6,6) doped with Co, Cu, Ni and Zn chlorides combined with KI was examined. Aging caused a depression in melting temperature and an increase in enthalpy of fusion of PA6,6 films due to the formation of a strongly degraded crystalline fraction with a lower molecular weight. A build-up of carbonyl absorption in the range 1700-1780 cm⁻¹ due to primary and secondary photo-oxidation products was detected. The kinetics of carbonyl accumulation was affected by the morphology of the samples, and it was observed that at a later stage of aging the crystalline phase was also involved in the oxidation process. The above mentioned changes were greatest in the case of neat, Co and Ni doped polymer, suggesting that these metal salts acted as pro-oxidants. On the other hand, the use of Cu and Zn chlorides brought about a substantial increase in long-term polymer stabilization.Tensile tests revealed a large reduction in ductility as a result of aging for neat, Co and Ni doped polymer, whereas long-term retention of tensile properties was found for the polymer stabilized with Cu and Zn. The presence of the metal salts combined with KI led to increased stabilization for chlorides of Ni, and Co, owing to the participation of KI in non-radical decomposition of peroxides. No effect due to KI was observed for ZnCl₂.     

Evidence of a monoclinic-like amorphous phase in composites of LDPE with spherical, fibrous and laminar nanofillers as studied by infrared spectroscopy

Well-dispersed nanocomposites of LDPE with spherical silica and laminar and fibrous silicates have been prepared by melt compounding with nanofiller compositions ranging from 50 to 5 wt%. Spatial dispersion and size domains of the aggregates in the composites series have been evaluated by electron microscopies (SEM and TEM). The methylene rocking (700-740 cm⁻¹) and bending (1400-1480 cm⁻¹) modes of LDPE in these composites were studied by FTIR spectroscopy. When the nanofiller is present in a 40 or 50 wt%, the amorphous phase of polyethylene adopts a monoclinic arrangement. This arrangement is due to the confinement induced by the nanofillers on the polymer matrix. When the fibrous silicate or the spherical silica are used as nanofillers, a dilution of the concentrated composite or annealing bring about a relaxing of the amorphous structure of the polymer, and the monoclinic-like conformations disappear. When the nanofiller is a laminar silicate, dilution or annealing only partly eliminate the monoclinic-like structure, which remains in all cases an important fraction of the polymeric matrix.     

Polyaniline and polypyrrole: A comparative study of the preparation

Aniline and pyrrole have been oxidized with ammonium peroxydisulfate in aqueous solutions, in the presence of equimolar quantities of hydrochloric acid. The oxidation of pyrrole was faster; the induction period typical of aniline oxidation was absent in the case of pyrrole. As the proportion of oxidant-to-monomer molar concentration increased up to 1.5, the yield increased in both cases. Similarities between the two oxidations are illustrated and discussed. The oxidant-to-monomer molar ratio 1.25 is proposed to be the optimum stoichiometry, in the accordance with the data published in the literature. The conductivities of the polymers prepared were only slightly dependent on the oxidant-to-monomer ratio in the range 0.3-1.5, and were of the order of 10⁰ S cm⁻¹ for polyaniline and ∼10⁻²-10⁻¹ S cm⁻¹ for polypyrrole. Outside this interval, the conductivity of both polymers was reduced. Polyaniline having conductivity ∼10 S cm⁻¹ was produced in solutions of phosphoric acid of various concentrations. On the contrary, the conductivity of polypyrrole was reduced as the concentration of phosphoric acid became higher. The type of protonation is discussed with the help of FTIR spectra by analyzing the ammonium salts obtained after deprotonation. Sulfate or hydrogen sulfate anions produced from peroxydisulfate always constitute a part of the counter-ions.     

Side-chain liquid crystalline polymers with silphenylene-siloxane main chains. I. Synthesis of silphenylene-siloxane polymers containing hydrosilane units

Siophenylene-siloxane polymers with repeating units containing hydrosilane, SiH, groups were synthesized for use as backbone polymers in side-chain liquid crystalline polymers. The polymerization of 1,4-bis (hydroxydimethylsilyl) benzene with a bis (Pyrrolidinyl) silane monomer formed a crosslinked polymer during the course of the reaction, while the use of a bis (ureido) silane monomer gave a polymer which crosslinked on storage after preparation. However, a soluble polymer could be prepared successfully by using a dichlorosilane as the comonomer. Polymers containing two and three Si? H groups in each unit were prepared by the last method. All Soluble polymers were characterized by gel permeation chromatography (GPC), infrared spectroscopy (IR) multinuclear NMR spectroscopy, and differential scanning calorimetry (DSC).     

Drug permeation modeling through the thermo-sensitive membranes of poly(N-isopropylacrylamide) brushes grafted onto micro-porous films

Temperature-sensitive N-isopropylacrylamide (NIPAAm) polymer brushes of known molecular weight (20k–25k) were grafted onto micro-porous polycarbonate (PC) films (pore size 0.4 μm) using argon plasma treatment. The resulting composite membranes were tested for controlled drug release at various grafted chain density, which was controlled using 1–3% polymer concentrations. The composites were also characterized in terms of graft yield, membrane thickness, Fourier transform infrared (FTIR) spectra and scanning electron micrography (SEM). The drug permeabilities of 4-acetamidophenol and ranitidine HCl in the resulting membranes were determined at temperatures between 30 and 40 °C. The drug permeability changed remarkably at 34 °C, near the lower critical solution temperature (LCST). The drug passage was regulated by swelling (which occurs at a temperature lower than the LCST) or shrinkage (occurring at an elevated temperature) of the PNIPAAm polymer brushes. These membranes demonstrated on–off ratios of drug permeabilities up to 11 and 14 for the model drugs, respectively. These values are higher than most literature data with similar-size model molecules. The excellent on–off valve mechanism was discussed in terms of the suitable molecular weight and grafted chain density in relation to the pore size and porosity of the PC support. A mathematical model was proposed to predict the drug permeation flux based on the gel conformation data, graft density, characteristics of the micro-porous support, and drug concentrations and diffusivities in water and in the PNIPAAm gel. The model can successfully estimate the drug permeation flux through the composite with higher (0.42 mg cm⁻²) graft density with a coefficient of determination of 0.95. The discrepancy between the predicted and experimental data at the lower graft density (0.12 mg cm⁻²) was ascribed to pore channel narrowing resulting from the uneven polymer chain distribution.     

Influence of binary/ternary complex of imprint ion on the preconcentration of uranium(VI) using ion imprinted polymer materials

Ion imprinted polymer (IIP) materials were prepared for uranyl ion (imprint ion) by forming binary (5,7-dichloroquinoline-8-ol (DCQ) or 4-vinylpyridine (VP)) or ternary (5,7-dichloroquinoline-8-ol and 4-vinylpyridine) complexes in 2-methoxy ethanol (porogen) and copolymerizing in the presence of styrene and divinyl benzene as functional and crosslinking monomers, respectively and 2,2′-azobisisobutyronitrile as initiator. IIP particles were obtained by leaching the imprint ion in these polymer materials with 50% (v/v) hydrochloric acid, filtering, drying in an oven at 50 °C and grinding. Control polymer particles were also prepared under identical conditions. The above synthesized polymer particles were characterized by IR, CHN, X-ray diffraction, and pore size analyses. These leached polymer particles can now pick up uranyl ions from dilute aqueous solutions. The IIP particles obtained with ternary complex of uranyl ion alone gave quantitative enrichment of traces of uranyl ions from dilute aqueous solutions. The optimal pH for quantitative enrichment is 4.5-7.5 and eluted completely with 10 ml of 1.0 M HCl. The retention capacity of uranyl IIP particles was found to be 34.05 mg of uranyl ion per gram of polymer. Further, the percent extraction, distribution ratio, and selectivity coefficients of uranium and other selected inorganic ions were also evaluated. Five replicate determinations of 25 μg of uranium present in 1.0 l of aqueous solution gave a mean absorbance of 0.036 with a relative standard deviation of 2.50%. The detection limit corresponding to three times the standard deviation of the blank was found to be 5 μg l⁻¹.