Dynamics of entangled polymer chains with nanoparticle attachment under large amplitude oscillatory shear

This paper presents a nonlinear viscoelastic model for polymer nanocomposites and the computed model response to large amplitude oscillatory shear flow. The model predicts the stress in a mixture of entangled polymer chains, with different convective constraint release (CCR) rates for free chains and nanoparticle‐attached chains, through an averaging scheme which is consistent with double reptation in the Marrucci–Ianniruberto constitutive equation. The nonlinear response of the mixture is evaluated both numerically in terms of Q and by an asymptotic analysis in terms of four frequency dependent parameters of medium amplitude oscillatory shear (MAOS) as well as the intrinsic nonlinearity parameter Q₀ . In the case of free polymer chains alone, the MAOS signatures are comparable to those of the Giesekus model with the notable difference of a minimum in the elastic parameter [e₁] at De >1. The viscous nonlinear parameters of the mixture model depart significantly from those of the free chains, especially in mixtures where the CCR parameter for attached chains is larger than that for the free chains: [v₁] has a prominent minimum and [v₃] has a prominent maximum near De = 2/c, the low frequency plateau region, along with a higher Q₀ compared to the matrix at all Deborah numbers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 62–76     

Synthesis and characterization of poly(styrene‐maleic anhydride)‐montmorillonite nanocomposite

Poly(styrene‐maleic anhydride)‐montmorillonite nanocomposites were prepared by intercalation of layered montmorillonite with the polymer ions. Synthetic approaches including polymerization and phosphonium salt formation have been used for polymer intercalation and dispersion of the host layers in the polymer matrix. The ratio of the mineral in the composites ranged 30–50%. Wide‐angle X‐ray diffraction (WAXD) disclosed that the d₍₀₀₁₎ spacing between the internal lamellar surface were only expanding to about 13 and 15 Å according to the type of phosphonium salt suggesting packing of polymer molecules between the layers. Examination of these materials by scanning and transmission electron microscopy showed spherical nano size particles of average diameter, 350 nm. Copyright © 2002 John Wiley & Sons, Ltd.     

Interpenetrating polymer networks of poly(dimethyl siloxane–urethane) and poly(methyl methacrylate)

Simultaneous IPNs of poly(dimethyl siloxane-urethane) (PDMSU)/poly(methyl methacrylate) (PMMA) and related isomers have been prepared by using new oligomers of bis(β-hydroxyethoxymethyl)poly(dimethyl siloxane)s (PDMS diols) and new crosslinkers biuret triisocyanate (BTI) and tris(β-hydroxylethoxymethyl dimethylsiloxy) phenylsilane (Si-triol). Their phase morphology have been characterized by DSC and SEM. The SEM phase domain size is decreased by increasing crosslink density of the PDMSU network. A single phase IPN of PDMSU/PMMA can be made at an M_c = 1000 and 80 wt % of PDMSU. All of the pseudo- or semi-IPNs and blends of PDMSU and PMMA were phase separated with phase domain sizes ranging from 0.2 to several micrometers. The full IPNs of PDMSU/PMMA have better thermal resistance compared to the blends of linear PDMSU and linear PMMA. © 1993 John Wiley & Sons, Inc.     

Synthesis of silsesquioxane nanocomposites

In order to investigate the effect of presence of well defined nano-sized inorganic particles on the molecular mobility a conformation statistics of polymer chains, well defined polystyrene (PS) and poly(methyl methacrylate) (PMMA) macromolecules containing polyhedral oligomeric silsesquioxanes nanoparticles (POSS) were synthesized by copper-mediated atom transfer radical polymerization (ATRP). Two approaches were used for the synthesis — the first involves POSS as the initiator of ATRP; the second way considers an addition of POSS to the polymer (prepared by ATRP) with an appropriate functional group. Kinetics of polymerization was determined using common analytical methods and it was compared to the polymerizations initiated by low-molecular weight initiators, regarding the polymerization rate, initiation efficiency and polydispersity of the polymer. Efficiency of the initiation with POSS-containing initiators was low, causing remnants of inseparable free POSS in polymer. The second approach bypassed these disadvantages —POSS is connected to the polymer through a pending allyl group using the very efficient hydrosilylation reaction. Presented at the 1st Bratislava Young Polymer Scientists Workshop, Bratislava, 20–23 August 2007.     

Calculation of polymer blend compositions from vibrational spectra: A simple method

In this work, the application of a new approach for quantitative analysis, originally developed for Raman spectroscopy, is extended to IR spectroscopy. The attractive features of this methodology are its simplicity and ease of use in comparison with traditional approaches. Unlike other methods, rich spectral information containing several overlapped peaks can be used in the calculations. A robust and well‐conditioned calculation scheme renders precise results, which are independent of the operator's decisions. The method was applied to study the chemical compositions of homogeneous polymer blends made of polystyrene and poly(vinyl methyl ether). Raman and IR blend spectra were acquired with confocal Raman microspectroscopy and attenuated total reflection/Fourier transform infrared, respectively. The blend compositions were calculated from the corresponding vibrational spectra with the proposed strategy, and excellent agreement between those values and the true ones was found for both techniques. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1144–1151, 2005     

Blends of a thermotropic liquid‐crystalline polymer and a poly(butylene terephthalate)/organoclay nanocomposite

Blends were synthesized via the melt blending of a thermotropic liquid‐crystalline polymer (TLCP) and a poly(butylene terephthalate) (PBT) hybrid containing 2 wt % organoclay. A TLCP was also synthesized with side groups based on a nematic liquid‐crystalline phase. The blends of TLCPs with PBT hybrids were melt‐spun with different concentrations of the liquid‐crystalline polymer and different draw ratios (DRs) to produce monofilaments. Regardless of the TLCP concentration in the hybrids, transmission electron microscopy photographs proved that the clay layers of the organoclay were intercalated and partially exfoliated in the PBT matrix. At DR = 1, the maximum enhancement in the ultimate tensile strength was observed for blends containing 8% TLCP, and the tensile strength decreased with further increases in the TLCP concentration. The initial modulus monotonically increased with increasing TLCP concentration. When DR increased from 1 to 44, the increased stretching caused the tensile property to decrease significantly, debonding to occur, and voids to form. These trends with increasing DR were observed in all the systems. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3667–3676, 2004     

DSC study of the miscibility of poly(methyl acrylate)-polystyrene sequential interpenetrating polymer networks

The phenomenon of forced compatibilization has been studied in poly(methyl acrylate)-polystyrene PMA-i-PS sequential interpenetrating polymer networks, IPNs, using differential scanning calorimetry. Both networks in the IPN were prepared using the same amount of ethylene glycol dimethacrylate, EGDMA, as crosslinking agent. The samples were subjected to thermal treatments which included annealing at different ageing temperatures T _a, for 300 min. From the DSC curves, recorded on heating the enthalpy loss during the isothermal annealing, Δh _a was calculated. The dependence of Dh _a with the annealing temperature was used to define the temperature interval in which the conformational mobility is significant. The comparison of the Δh _a(T _a) curves obtained in an IPN and the results obtained with the pure component homo-networks with the same crosslinking density reveal some details of the miscibility of the IPN. In the case of the IPN crosslinked with 10% EGDMA, two peaks are apparent in the Δh _a(T _a) curve, but the high-temperature peak is shifted towards lower temperatures compared to that of the polystyrene network while the low-temperature one is nearly at the same temperature than the one of the poly(methyl acrylate) homonetwork. This means that compatibilization is not complete and phase separation still exists even at this high crosslinking density. The different behaviour of the high and low temperature transitions can be explained by the dynamic heterogeneity of the sample, i.e. by the different length of cooperativity of the conformational rearrangements of PMA and PS domains at any temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

Deformation of styrene—divinylbenzene copolymers and hypercrosslinked polystyrenes during solvent adsorption and desorption

An automated procedure was developed for monitoring fast changes in the size of spherical samples of polymers during their contact with a solvent or drying. The kinetics of bulk deformation in these processes was studied for a series of cross-linked polymers, viz., gel-type and porous styrene—divinylbenzene copolymers and poly(divinylbenzenes), and hypercrosslinked polystyrenes. Gel, macroporous, and hypercrosslinked polystyrenes are substantially different in the rate, mechanism, and degree of swelling, which is associated with the principal differences in their physical structures. An unusual effect of a sharp decrease followed by a temporary increase in the volume of porous polystyrene and poly(divinylbenzene) materials were observed during desorption (evaporation) of organic solvents. Water desorption is accompanied by an excessive bulk compression of porous granules giving rise to negative deformations, which gradually relax to the state equilibrium for the dry polymer. The results of dynamic desorption porometry (for water desorption) are indicative of a bimodal size distribution of micropores in hypercrosslinked polystyrene. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 467–476, March, 2007.     

Crystallization studies of isotactic polypropylene containing nanostructured polyhedral oligomeric silsesquioxane molecules under quiescent and shear conditions

Crystallization studies at quiescent and shear states in isotactic polypropylene (iPP) containing nanostructured polyhedral oligomeric silsesquioxane (POSS) molecules were performed with in situ small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC). DSC was used to characterize the quiescent crystallization behavior. It was observed that the addition of POSS molecules increased the crystallization rate of iPP under both isothermal and nonisothermal conditions, which suggests that POSS crystals act as nucleating agents. Furthermore, the crystallization rate was significantly reduced at a POSS concentration of 30 wt %, which suggests a retarded growth mechanism due to the molecular dispersion of POSS in the matrix. In situ SAXS was used to study the behavior of shear‐induced crystallization at temperatures of 140, 145, and 150 °C in samples with POSS concentrations of 10, 20, and 30 wt %. The SAXS patterns showed scattering maxima along the shear direction, which corresponded to a lamellar structure developed perpendicularly to the flow direction. The crystallization half‐time was calculated from the total scattered intensity of the SAXS image. The oriented fraction, defined as the fraction of scattered intensity from the oriented component to the total scattered intensity, was also calculated. The addition of POSS significantly increased the crystallization rate during shear compared with the rate for the neat polymer without POSS. We postulate that although POSS crystals have a limited role in shear‐induced crystallization, molecularly dispersed POSS molecules behave as weak crosslinkers in polymer melts and increase the relaxation time of iPP chains after shear. Therefore, the overall orientation of the polymer chains is improved and a faster crystallization rate is obtained with the addition of POSS. Moreover, higher POSS concentrations resulted in faster crystallization rates during shear. The addition of POSS decreased the average long‐period value of crystallized iPP after shear, which indicates that iPP nuclei are probably initiated in large numbers near molecularly dispersed POSS molecules. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2727–2739, 2001     

Layered silicate polymer nanocomposites: new approach or illusion for fire retardancy? Investigations of the potentials and the tasks using a model system

Polymeric nanocomposites are discussed as one of the most promising advanced materials whose nanoscale effects can be exploited for industry. Layered silicate polypropylene‐graft‐maleic anhydride nanocomposites are investigated as a model to clarify the potential of such materials in terms of fire retardancy. The nanostructure is characterized using transmission electron microscopy (TEM) and shear viscosity. The fire behavior is characterized using different external heat fluxes in cone calorimeter, limiting oxygen index and UL 94 classification. A comprehensive fire behavior characterization is presented which enables an assessment of the materials' potential with respect to different fire scenarios and fire tests. The influence of morphology and the active mechanisms are discussed, such as barrier formation and changed melt viscosity. To our knowledge, it is the first attempt to illuminate the concept's strengths, such as the reduction of flame spread, and weaknesses, such as the lack of influence on ignitability, in a clear, comprehensive and detailed manner. Copyright © 2004 John Wiley & Sons, Ltd.     

Rheology of isothermally crystallized poly(butylene terephthalate) nanocomposites with clay loadings under the percolation threshold

This article describes the structural evolution of clay in poly(butylene terephthalate) nanocomposites (PCNs) with clay loadings lower than the percolation threshold during the isothermal crystallization process. The study of the structure and rheological properties has revealed that the intercalation and detachment levels of clay are enhanced in samples crystallized at a high temperature (210 °C), in contrast to those of the original PCN, and this results in the formation of a rheological percolation network. However, for PCNs crystallized at a low temperature (190 °C), the further structural evolution of the tactoids is very small. All the experimental results indicate that the morphologies of clay can further evolve during the crystallization process, but the evolution level is strongly dependent on the crystallization temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 229–238, 2007     

Rheology and microstructures formation of immiscible model polymer blends under steady state and transient flows

Viscoelastic properties of model immiscible blend were studied here under steady state condition at different initial conditions and transient flow conditions. The flow‐induced microstructure has been studied on these model blends. For this system, the elastic properties of the blend are mainly governed by the interface. Measurement of the dynamic modulus and of the first normal stress difference, both reflecting this enhanced elasticity, have been used to prove the blend morphology. The dynamic moduli after cessation of shear flow, the mean diameter of the disperse phase as generated by the shear flow, have been calculated using the model of Palierne. A procedure based on a direct fitting of the dynamic moduli with the model is compared with the one that uses a weight relaxation spectrum. On the other hand, the steady state normal stress data have been related to the morphology of the blend by means of Doi and Ohta model. The specific interfacial area is found to be inversely proportional to the ratio of interfacial tension over shear stress for the blend. The flow behavior during transient shear flow was also discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3519–3533, 2005     

Semi-interpenetrating polymer networks toward sulfonated poly(ether ether ketone) membranes for high concentration direct methanol fuel cell

Semi-IPNs were constructed by forming the crosslinking networks via the reaction between BPPO and diamine cross-linkers to overcome the dimensional swelling and methanol-permeation issues of SPEEK.     

Ultrasonic treatment as recent and environmentally friendly route for the synthesis and characterization of polymer nanocomposite having PVA and biosafe BSA‐modified ZnO nanoparticles

The present study deals with the immobilization of ZnO nanoparticles (NPs) as nanofiller inside poly(vinyl alcohol) (PVA) by solution casting method which is a low‐cost, environmental‐friendly, and rapid method of sonochemistry. Firstly, the surface of ZnO NPs was treated by bovine serum albumin (BSA) in the phosphate‐buffered solution under ultrasonic cavitation. Three diverse polymeric nanocomposites (NCs) are formed by changing the percentage of ZnO@BSA NPs (3, 6, and 9 wt%) with same amount of PVA. The structure properties, morphology, and thermal stability of prepared NCs were determined through Fourier transform‐infrared spectroscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy (EDX) and optical UV‐Visible spectrum, transmission electron microscopy (TEM), and field emission scanning electron microscopy. The presence and the dispersal of the ZnO@BSA NPs in the PVA matrix were recognized by TEM. In the X‐ray diffraction analysis, the values of mean particle size using Debye‐Scherrer equation were estimated in the range 4 to 6 nm that is almost in agreement with TEM analysis. Increase of 14% in thermal stability and also increase of more than 2‐fold of the tensile strength of PVA/ZnO@BSA NC 9 wt% in respect to the pure PVA showed that the modified NPs well dispersed within PVA and attached to it.     

Synthesis and characterization of interpenetrating polymer networks with nonlinear optical properties

We report the synthesis and characterization of interpenetrating polymer networks (IPNs) exhibiting nonlinear optical (NLO) properties. The network consists of aliphatic polycarbonate urethane (PCU) and poly(methyl methacrylate-co-N,N-disubstituted urea), with a nonlinear optical (NLO) chromophore incorporated into N,N-disubstituted urea. The full IPNs have only one T_g, as determined by differential scanning calorimetry (DSC), together with scanning electron microscopy (SEM) observations, suggest a single phase morphology. The thin films of IPNs are transparent and the unpoled samples produced second harmonic generation (SHG) signals at room temperature. This result indicates that the NLO chromophore is oriented noncentrosymmetrically during the IPN formation process and is tightly held between the permanent entanglements of the two component networks of the IPN. © 1996 John Wiley & Sons, Inc.     

Streamlined ellipsometry procedure for characterizing physical aging rates of thin polymer films

Existing studies in the research literature showing conflicting changes in physical aging rates with decreasing film thickness in nanoconfined polymer films highlight the need for a single experimental technique to efficiently characterize physical aging rates in thin polymer films of varying chemical structure. To that end, we have developed a streamlined ellipsometry procedure to measure the structural relaxation of thin glassy polymer films. We evaluate different methods of calculating a physical aging rate β from the measured thickness h(t) and index of refraction n(t) data. We present extensive measurements of β as a function of aging temperature and aging time for polystyrene (PS) films supported on silicon, and determine that the physical aging rate β can be easily and reliably determined from β = −1/h₀ dh/d(log t), where h₀ is the initial measure of the film thickness at an aging time of 10 min. We have also carried out oxygen permeation studies on poly(methyl methacrylate) (PMMA) films from 800 μm down to 190 nm in thickness, and find no change in the permeability with film thickness or physical aging at room temperature for up to 65 days, which suggests that gas permeation may be insensitive to physical aging in such low free volume polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2509–2519, 2009     

Characterization of polyolefin melts using the polymer reference interaction site model integral equation theory with a single‐site united atom model

A general approach, based on the polymer reference interaction site model (PRISM) integral equation theory, suitable for characterizing arbitrarily complex polyolefin melts is described. We tested the method by calculating the melt structures of linear polyethylene (PE) and isotactic polypropylene (iPP) and the spinodal decomposition temperatures for PE/iPP blends. The computational expense of the PRISM calculation was reduced with a single‐site united atom model in which the polyolefin CH, CH₂, and CH₃ groups were approximated as chemically equivalent sites with spherically symmetric energetic interactions. The site–site interactions were defined by a potential function comprising a hard core with an attractive Lennard–Jones term. These energetic parameters were optimized with a central composite design strategy that enabled a simultaneous fit of experimental melt density and structure factor data. Values were obtained for PE and iPP individually and for common universal parameters that could potentially be used for all polyolefins. The rotational isomeric state–metropolis Monte Carlo (RMMC) technique was used to generate sets of conformers at specified temperatures covering the melt‐temperature range of the polymers. The characteristic ratio was used to assess the quality of the conformers and the RMMC method. Values of 9.68 for PE and 9.27 for iPP were obtained. The single‐chain structure factors calculated by the RMMC method were used to calculate the total structure factor for each melt. These were validated against published X‐ray diffraction results. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1803–1814, 2001     

Synthesis and characterization of poly(acrylic acid‐co‐acrylamide)/hydrotalcite nanocomposite hydrogels for carbonic anhydrase immobilization

To combine the advantages of a biopolymer with hydrotalcite in an enzyme immobilization system, the intercalation polymerization was used to prepare poly(acrylic acid‐co‐acrylamide)/hydrotalcite (PAA‐AAm/HT) nanocomposite hydrogels using sodium methyl allyl sulfonate as intercalation agent. Transmission electron microscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy results revealed that sodium methyl allyl sulfonate chains entered into the interlayer of HT, the interaction between them has taken place, and HT was dramatically exfoliated into nanoscale and homogeneously dispersed in the PAA‐AAm matrix. Transmission electron microscopy and cryo scanning electron microscope results showed that dried hydrogels were regular spherical particles, and swollen hydrogels revealed homogeneous porous network structures. Then, PAA‐AAm/HT nanocomposite hydrogels were used to immobilize carbonic anhydrase (CA), and the CO₂ hydration activities of free enzyme and immobilized enzyme were evaluated. Results showed that immobilized CA retained the majority of the enzyme activity. The reason may be the formation of a microenvironment almost all of which is composed of free water inside the porous network structures. Therefore, the immobilized CA is of great potential in the removal of trace CO₂ from the closed spaces. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3232–3240, 2009