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In this study, the influence of multiwalled carbon nanotubes (MWCNT) on β‐isotactic polypropylene (iPP) formation in preshear injection‐molded iPP/MWCNT nanocomposites is investigated layer by layer by wide angle X‐ray diffraction (WAXD). WAXD results suggest that in preshear injection‐molded pure iPP, β‐iPP exists in not only the shear region, but also the core region as a result of preshear‐induced nucleation. The addition of MWCNT can inhibit the β‐iPP formation. As the depth away from the specimen surface is decreased, the inhibiting effect is decreased. The reason responsible for that is given as follows: (1) with the addition of MWCNT, extra nuclei are induced during preshear. Both MWCNT and extra nuclei serve as α‐iPP nucleation point. Therefore, the formation of β‐iPP is restricted; (2) the cooling rate gradient is widely accepted to exist in the injection molded sample. A larger cooling rate at a smaller depth will give rise to a lower α‐iPP crystallization onset temperature and a lower nucleation efficiency of MWCNT. Since that β‐iPP grows only in the temperature range of 105°C‐140°C, the inhibiting effect of MWCNT on β‐iPP becomes weaker as the depth is decreased. POLYM. COMPOS., 39:E1149–E1158, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Abstract: Polyesters with 9,10‐dihydro‐9‐oxy‐10‐phosphaphenanthrene‐10‐oxide‐containing comonomers are synthesized aiming to improve the flame retardancy of aliphatic polyesters such as poly(butylene succinate) and poly(butylene sebacate). The influence of the chemical structure on the thermal decomposition and pyrolysis is examined using a combination of thermogravimetric analysis (TGA), TGA‐Fourier transform infrared (FTIR) spectroscopy, pyrolysis‐gas chromatography/mass spectrometry, and microscale combustion flow calorimetry. Thermal decomposition pathways are derived and used to select suitable candidates as flame retardants for PBS. The fire behavior of the selected polymers is evaluated by forced‐flaming combustion in a cone calorimeter. The materials show two modes of action for flame retardancy: strong flame inhibition due to the release of a variety of molecules combined with charring in the solid state. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) filled poly(vinylidene fluoride- co-hexafluoropropylene) (PVDF-HPF) copolymer nanocomposites as promising piezoelectric materials are developed, and their crystallization behavior and chain folding free energy are examined. Appropriate distribution of GO nanoparticles in the copolymer is confirmed by transmission electron microscopic analysis. The crystalline structure of nanocomposites is analyzed by wide-angle X-ray scattering and Fourier transform infrared spectroscopy. The results show an increase in the β-phase content of PVDF-HPF copolymer in the presence of GO. Non-isothermal crystallization kinetics of the neat polymer and corresponding nanocomposites are studied by a multiple heating rate differential scanning calorimetry using modified Avrami-Jeziorny and Liu models. Moreover, barrier energy of crystallization is calculated by Friedman and Kissinger models. It is found that addition of GO to the copolymer increases nucleation activity of the nanocomposites. Investigation on linear crystal growth via Hoffman's theorem indicates an enhanced nucleation activity upon increasing GO content. The surface folding free energy of the neat polymer is changed from 5.79 × 10−2 to 7.27 × 10−2 J m−2 upon addition of 5 wt% of GO. A bundle-like mechanism is proposed, which can explain the crystallite growth. Analysis based on Vyazovkin theorem reveals that the crystallization activation energy is independent of GO at elevated temperatures. [ABSTRACT FROM AUTHOR]

Diblock copolymers (BCP) with poly(methyl methacrylate) and poly(1H,1H,2H,2H-perfluorodecyl methacrylate) (PsfMA) blocks prepared by anionic polymerization in tetrahydrofuran at −78 °C and atom transfer radical polymerization (ATRP) at 60 °C, respectively, with stepwise varied composition over a wide range in the phase diagram are compared with respect to synthesis limits, phase separation behavior in bulk, and properties of thin films. Both methods yield BCPs with low dispersity (1.1-1.2) at molar masses below 100 kg mol−1. Higher semifluorinated contents can be achieved by ATRP in 1,3-bis(trifluoromethyl)benzene which ensured solubility of PsfMA. BCPs obtained by anionic polymerization show a more distinct phase separation, that is, more regular nanostructures. Additionally, self-organization of the semifluorinated side chains occurs generating smectic layers which alters in turn the BCP morphology especially in thin films as compared to non-semifluorinated BCP. All BCPs show amphiphilic behavior and form micelles in organic solvents which can be used to deposit nanoparticles. [ABSTRACT FROM AUTHOR]

Linear aliphatic copolyesters consisting of the biobased diols ethylene glycol, 1,3-propane diol, and 1,4-butane diol, the biobased dicarboxylic acids succinic acid, adipic acid, and sebacic acid, and a 9,10-dihydro-9-oxa-10-phospha-phenanthren-10-oxide (DOPO)-containing diol or dicarboxylic acid are presented. Structural characteristics of the new copolyesters are studied by 1H and 13C NMR spectroscopy. The influence of chemical composition on the property profile is examined evaluating glass transition temperature Tg, melting behavior, thermal degradation and combustion, mechanical and burning behavior. Incorporation of DOPO monomers suppresses crystallization and yields materials with reduced toughness except in case of sebacates. Tg rises with the content of DOPO monomer. Correlations between the number of methylene groups in the repeating unit and the thermogravimetric analysis degradation maximum, as well as the heat release capacity from pyrolysis combustion flow calorimeter reflect the systematic influence of chemical structure. Copolycondensation with DOPO monomers enhances the limiting oxygen index providing materials with improved overall value. [ABSTRACT FROM AUTHOR]

It has been reported in the technical literature that whiskers of rodlike single crystals can be used in order to generate shish-kebab structures or other different lamellae morphologies during isothermal or dynamic crystallization of sheared or presheared polymer melts. The expected advantage of the changed crystalline structure is a reinforcing effect of the composite. A lot of papers reported about the application of inorganic and organic whiskers such as cellulose and chitin whiskers. This study reports on an attempt to use acicular PCC as appropriate whisker for improving mechanical properties of polypropylene. In this article special attention is given to demonstrate the effect of flow induced crystallization under varying shear conditions in order to improve the mechanical properties. The effects were demonstrated using rheology, thermal analysis, tensile testing, and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

Comb-like copolymers based on a polyolefin backbone of poly(10-undecene-1-ol) (PUol) with poly(ε-caprolactone) (PCL) side chains are synthesized in two steps. After synthesis of PUol by metallocene-catalyzed polymerization, the side-chain hydroxyl functionalities of this polar polyolefin are used as an initiator for the ring-opening polymerization (ROP) of ε-caprolactone (CL). In this context, copolymers with different lengths of PCL grafts are prepared. The chemical structure and the composition of the synthesized copolymers are characterized by 1H and 13C NMR spectroscopy. It is shown that the hydroxyl end groups of PUol act effectively as initiating sites for the CL ROP. Size-exclusion chromatography (SEC) measurements confirm the absence of non-attached PCL and the expected increase in molar mass after grafting. The thermal and decomposition behaviors are investigated by DSC and thermogravimetric analysis (TGA). The effect of the length of the PCL grafts on the crystallization behavior of the comb-like copolymers is investigated by DSC and wide-angle X-ray scattering (WAXS). [ABSTRACT FROM AUTHOR]

New pH- and thermo-responsive hydrogels (HG) were synthesized by free radical polymerization of N-isopropylacrylamide and a macromonomer, which was a hydrolyzed random copolymer of 2-carboxyethyl- and 2-methyl-2-oxazoline, using a bisacrylamide as crosslinker. The polymerization was carried out in a mixture of water and ethanol at room temperature and was initiated by ammonium peroxodisulfate. The HG showed conformational transitions with variation of temperature and/or pH-value and as a function of hydrogel composition. This property was shown macroscopically as hydrogel contraction or expansion. The HG structures were characterized by high-resolution magic angle spinning (HRMAS) NMR spectroscopy. The thermal properties, in particular the lower critical solution temperatures, were determined by temperature-dependent HRMAS NMR measurements and differential scanning calorimetry. The pH responsibility was determined by swelling experiments in water at different pH values. [ABSTRACT FROM PUBLISHER]

ABSTRACT Linear low-density polyethylene (LLDPE) was melt-mixed with multiwalled carbon nanotubes (MWCNTs) and varying amounts of three different kinds of talc (phyllo silicate), each with a different particle size distribution, to examine the effect of these filler combinations with regards to the electrical percolation behavior. The state of the filler dispersion was assessed using transmission light microscopy and electron microscopy. The use of talc as a second filler during the melt mixing of LLDPE/MWCNT composites resulted in an improvement in the dispersion of the MWCNTs and a decrease of the electrical percolation threshold. Talc with lower particle sizes showed a more pronounced effect than talc with larger particle sizes. However, the improvement in dispersion was not reflected in the mechanical properties. Modulus and stress values increase with both, MWCNT and talc addition, but not in a synergistic manner. The crystallization behavior of the composites was studied by differential scanning calorimetry to determine its potential influence on the electrical percolation threshold. It was found that the crystallinity of the matrix increased slightly with the addition of talc but no further increments were observed with the incorporation of the MWCNTs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1680-1691 [ABSTRACT FROM AUTHOR]

Acicular precipitated calcium carbonate (PCC) was used as appropriate inorganic whisker for improving the mechanical properties of melt spun polypropylene fibers. Nucleation effects of the PCC in dependence to concentration, surface coating and pre-shearing were analyzed. Melt-spinning experiments were carried out in order to determine the reinforcing effect. [ABSTRACT FROM AUTHOR]

Poly(methyl methacrylate)/silica (PMMA/SiO x) nanocomposites were synthesized via sol-gel method and studied by various techniques. The dispersion of the silica particles (10-100 nm) in the matrix was probed by transmission electron microscopy (TEM), while solid-state NMR and Raman spectroscopy detected the formation of an inorganic network with high degree of crosslinking. To elucidate the impact of the filler on the molecular dynamics of the PMMA, different methods were used; namely differential scanning calorimetry, thermally stimulated depolarization current and broadband dielectric relaxation spectroscopy. All three methods observed a significant impact of the nanoparticles on the segmental dynamics of the matrix, which was expressed as an increase of the glass transition temperature ( Tg) in terms of calorimetry and as a shift of the α (segmental) relaxation to lower frequencies in terms of dielectric spectroscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Different amounts of multiwalled carbon tubes (MWCNTs) were incorporated into an epoxy resin based on diglycidyl ether of bisphenol A and both epoxy precursor and composite were cured with 4,4′-diamino diphenyl sulfone. Transmission and scanning electron microscopy demonstrated that the carbon nanotubes are dispersed well in the epoxy matrix. Differential scanning calorimetry measurements confirmed the decrease in overall cure by the addition of MWCNTs. A decrease in volume shrinkage of the epoxy matrix caused by the addition of MWCNTs was observed by pressure-volume-temperature measurements. Thermomechanical and dynamic mechanical analysis were performed for the MWCNT/epoxy composites, showing that the T g was slightly affected, whereas the dimensional stability and stiffness are improved by the addition of MWCNTs. Electrical conductivity measurements of the composite samples showed that an insulator to conductor transition takes place between 0.019 and 0.037 wt % MWCNTs. The addition of MWCNTs induces an increase in both impact strength (18%) and fracture toughness (38%) of the epoxy matrix with very low filler content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

A series of alternating polyester/polyamide block copolymers were prepared by sequential conversion of hydroxy-terminated polycaprolactone and amino-terminated polyamide-12 with a selectively reacting coupling agent. The thermal properties of the block copolymers were investigated using differential scanning calorimetry and dynamic mechanical analysis. Mechanical properties were determined using tensile and impact tests. All polymers were phase-separated, where the polyamide phase was semicrystalline in all compositions. Distinct crystallization of the polycaprolactone phase was observed only when the block length was greater than 2000 g mol−1. Mechanical testing showed that the polymers behave in a manner similar to that of thermoplastic elastomers. In particular, samples with a high content of polycaprolactone showed high strain and good impact behaviour. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Phosphorus polyesters provide sustainable flame retardancy to conventional polyesters like PET (poly(ethylene terephthalate)) and PBT (poly(butylene terephthalate)). Their use as a flame retardant additive results in the formation of a classical polymer blend. The morphology of such blends should determine the resulting fire behavior and has therefore to be examined in detail. This study investigates the state of miscibility in blends of standard polyesters (mainly PBT) with phosphorus (co)polyesters mainly using the behavior of the glass transition (Tg). The Tg values were determined by modulated DSC measurements and compared to the ones calculated assuming complete miscibility according to the Fox–Flory concept. The homopolyesters are completely immiscible with each other. Miscibility can be improved by transesterification reactions in the melt as well as by copolyester consisting of segments of PBT or PET and the phosphorus polymer. [ABSTRACT FROM PUBLISHER]