Polystyrene/Sn–Pb alloy blends. I. Dynamic rheological behavior

The dynamic rheological behavior of polystyrene filled with low‐melting‐point (T_m) Sn–Pb was investigated at temperatures below and above the T_m of the alloy, 183°C. In the whole temperature range of interest, there existed a secondary plateau in the plot of the dynamic storage modulus versus frequency (ω) at low ωs, and the influences of alloy content and temperature on the plateau were related to the matter state (liquid or solid) of the alloy. We believe that the secondary plateau observed below the alloy T_m was due to the network‐type structure formed by the agglomeration of solid filler particles, whereas the plateau above T_m was due to the deformability and relaxation of the liquid alloy droplets. By analyzing the Cole–Cole diagrams, we suggest that the alloy fillers retarded the relaxation processes for polystyrene melt when the temperature was lower than the T_m. However, there existed two separated relaxation processes when the temperature was higher than the T_m, that is, the high‐ω relaxation of the phases and low‐ω relaxation of the droplets. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3166–3172, 2002     

Viscoelasticity and morphology of poly(ethylene‐co‐vinyl acetate)/polyisobutylene blends

Blends of an ethylene/vinyl acetate copolymer (EVA) and polyisobutylene of various compositions were prepared by mechanical mixing at a temperature above the melting point of EVA (T_m^EVA) but below the upper critical solution temperature of 170°C for given blends. The rheological properties of the components and blends were studied in the region of small‐amplitude oscillating deformation at temperatures above and below T_m^EVA in the frequency range of 0.01–100 rad/s. At temperatures lower than T_m^EVA, the rheological properties were determined by the existence of the yield stress. With diminishing frequency, the viscosity increased, and the plateau in the relaxation spectrum at low frequencies broadened. The morphology of the blends depended on the conditions of sample heating. The introduction of a finely dispersed filler into the blends led to an anomalous drop in the viscosity. The morphology of the systems that arose by mechanical blending of the molten components was the important factor in the rheological behavior. The observed effects were examined in the framework of the concept of structural networks formed in melts by nonmelted crystallites of EVA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2700–2707, 2006     

Dielectric properties of copolymers based on cyano monomers and methyl α‐acetoxyacrylate

With the aim of developing dielectric polymers containing CN groups with strong dipole moment, alternating and statistical copolymers of the cyano monomers vinylidene cyanide (VCN), acrylonitrile and methacrylonitrile with methyl α‐acetoxyacrylate (MAA) were synthesized and characterized. The copolymer's composition and microstructure were analysed by NMR spectroscopy, SEC and elemental analysis. The reactivity ratios calculated from the Q–e Alfrey–Price parameters for these copolymers indicated the alternating and statistical structures confirmed by NMR analysis. The copolymers have glass transition temperatures T_g in the range 83–146 °C and are stable up to 230 °C. The thermal stability of the copolymers depends on the nature of the cyano monomers. Their molecular dynamics were investigated by dielectric relaxation spectroscopy. We revealed a weak relaxation β at sub‐T_g temperature for poly(VCN‐co‐MAA) usually originating from molecular motions that are restricted to the scale of a few bond lengths. Strong α‐relaxation processes occurred above T_g for these copolymers. This primary relaxation was associated with cooperative movements of the polar groups (CN) at the time of mobility of the principal chains. The activation energy of the α‐relaxation process was also calculated. The values of the dielectric increment Δε for these copolymers were determined by Cole–Cole plots and indicated that the copolymers exhibit interesting dielectric properties compared with similar cyano materials. The polarity–permittivity relationship was also established. © 2012 Society of Chemical Industry     

Studies on the thermal properties of PVC : Polystyrene alloy

The effect of composition on the thermal properties of poly(vinyl chloride) (PVC)–polystyrene (PSt) alloy was investigated. Using the DSC, it was observed that the glass transition temperature (T_g) and melting point (T_m) as well as the enthalpic change at melting (ΔH) were altered with respect to their theoretical values. An attempt is made to explain these facts.     

Mechanical behavior of highly filled natural CaCO3 composites: Effect of particle size distribution and interface interactions

The mechanical behavior of poly(di‐methyl siloxane) (PDMS) composites containing high volume fractions of natural CaCO₃ particles of various particle size distributions was studied under tensile and oscillatory bending stresses, emphasizing the unique behavior of high filler loaded compositions. Composites containing the maximal possible solid loading of raw CaCO₃ were investigated for the effect of fatty acids surface treatment. The elastic modulus increased with increasing filler loading, following Chantler's model for dental composites when correlated with the absolute filler volume fraction. Good fit to “traditional” models, e.g., Frankle‐Acrivos and Halpin‐Tsai, was obtained by correlating the modulus values with the volume fraction relative to the maximal possible filler loading. A master curve of different particle size distributions and filler levels composites was obtained by using the relative volume fraction values, illustrating the effect of particle packing characteristics on small deformation mechanical behavior. A minor increase in T_g was found in parallel to the appearance of a T_m relaxation peak at approximately −40°C. A peak temperature shift at T_m and a pronounced increase in this peak with increasing filler fraction was found as well. The changes in the melting transition are attributed to the constraints of the filler particles acting on the crosslinked melting polymer. Surface treatment with fatty acids significantly degraded the tensile properties. Interestingly, an increase of 4 vol% filler was enabled owing to the surface treatment, while restoring reasonable tensile properties. No significant effect was observed for excess of fatty acids resulting from physically adsorbed acids. Tan δ curves reveal low PDMS‐CaCO₃ particles interactions, and mobility of the PDMS chains in the increased filler fraction as in the treated 64 vol% composite, both higher than those in the raw composite. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Molding of syndiotactic polystyrene under its melting temperature

Syndiotactic polystyrene (SPS), a thermoplastic polymer that exhibits a high T_m in some crystalline forms, can be conveniently processed by a cold‐compaction technique. Processing temperatures in the range of 150–210°C, well below the T_m, gives rise to physicomechanical properties comparable and even better than those obtained by thermal compression or injection molding. The optimum treatment temperature seems to fall around 175°C. X‐ray diffraction analysis, thermal analysis, and density measurements suggest that such behavior is connected to phase transitions of SPS and favored by the presence of styrene included in the crystalline fraction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 377–383, 2001     

Investigation of the Tu(>Tg) relaxation in homopolymers and block copolymers of styrene by torsional braid analysis

Investigation of the T_u (>T_g) relaxation in amorphous polymers of styrene by the technique of torsional braid analysis is reviewed. For the most part the relaxation behaves like the glass transition (T_g) in its dependence on molecular weight, on average molecular weight in binary polystyrene blends, and on composition in a polystyrene homogeneously plasticized throughout the range of composition. Diblock and triblock copolymers also display a T > T_g relaxation above the T_g, of the polystyrene phase. Two results in particular suggest that the T_u relaxation is molecularly based. (1) The T_u temperature is determined by the number average molecular weight for binary blends of polystyrene when both components have molecular weights below M_c. (the critical molecular weight for chain entanglements). (2) Homopolymers, and diblock and triblock copolymers of styrene, have a T > T_g relaxation at approximately the same temperature when the molecular weight of the styrene block is equal to that of the homopolymer.     

Polystyrene composites of single‐walled carbon nanotubes‐graft‐polystyrene

Single‐walled carbon nanotubes (SWCNTs) dispersed in N‐methylpyrrolidone (NMP) were functionalized by addition of polystyryl radicals from 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐ended polystyrene (SWCNT‐g‐PS). The amount of polystyrene grafted to the nanotubes was in the range 20‐25 wt% irrespective of polystyrene number‐average molecular weight ranging from 2270 to 49 500 g mol^?1. In Raman spectra the ratios of D‐band to G‐band intensity were similar for all of the polystyrene‐grafted samples and for the starting SWCNTs. Numerous near‐infrared electronic transitions of the SWCNTs were retained after polymer grafting. Transmission electron microscopy images showed bundles of SWCNT‐g‐PS of various diameters with some of the polystyrene clumped on the bundle surfaces. Composites of SWCNT‐g‐PS in a commercial‐grade polystyrene were prepared by precipitation of mixtures of the components from NMP into water, i.e. the coagulation method of preparation. Electrical conductivities of the composites were about 10^?15 S cm^?1 and showed no percolation threshold with increasing SWCNT content. The glass transition temperature (T_g) of the composites increased at low filler loadings and remained constant with further nanotube addition irrespective of the length and number of grafted polystyrene chains. The change of heat capacity (ΔC_p) at T_g decreased with increasing amount of SWCNT‐g‐PS of 2850 g mol^?1, but ΔC_p changed very little with the amount of SWCNT‐g‐PS of higher molecular weight. The expected monotonic decrease in ΔC_p coupled with the plateau behavior of T_g suggests there is a limit to the amount that T_g of the matrix polymer can increase with increasing amount of nanotube filler. Copyright © 2012 Society of Chemical Industry     

Diffusion of p-aminoazobenzene in SBS block copolymer

The temperature dependence of p-aminoazobenzene diffusion in a styrene–butadiene–styrene (SBS) triblock copolymer film, prepared from a toluene or ethyl acetate solution, was investigated in the temperature region from 40° to 110°C by using a sublimative desorption method. Parallel studies on the mechanical relaxations of this copolymer were carried out in the same temperature range to be compared with the diffusion data. The penetrant-diffusion characteristics were interpreted in terms of Fujita's free-volume theory with due consideration of the different SBS domain morphology. The value of B_d, defined as the diffusional volume ratio of a penetrant molecule to a segment, was then estimated as 0.45–0.55 above the T_g of the polystyrene phase or 0.7 below that temperature. Interestingly, sigmoidal desorption appeared in the range under the T_g of the polystyrene phase for film cast from ethyl acetate; the anomalous behavior was considered to reflect the slow relaxation process of the copolymer chain ascribable to the predominant exposure of the polystyrene phase on the film surface.     

Pulsed n.m.r. relaxation study of a polystyrene/poly(ethylene oxide) diblock copolymer: evidence for interaction at the phase boundary

Pulsed nuclear magnetic resonance relaxation measurements are presented for a hydrophobic-hydrophilic diblock copolymer of polystyrene and poly(ethylene oxide) along with results for the individual homopolymers. Although observation of the thermal transitions of the homopolymer components in the copolymer reveals a gross incompatibility, the n.m.r. data suggests strong interfacial effects. From the T₁ and T₂ data below the melting point of PEO (T_m = 335K), it was concluded that polystyrene creates localized defects which reduce PEO domain crystallinity to 75% from 93% in the homopolymer. Above T_m in the copolymer three motional domains can be distinguished, isolated rigid polystyrene, isolated molten PEO and an intermediate domain. The composition of the intermediate domain suggests that 23% of the polystyrene is plasticized whereas 80–90% of the molten PEO is motionally constrained. The results are interpreted in terms of a spatial segregation of the homopolymer components with a forced interaction at the phase boundary as a result of the covalent linkages tying the two components together.     

Study of the epoxy system BADGE (n = 0)/1,2‐DCH/CaCO3 filler by DMA and DSC

The influence of an inorganic filler, CaCO₃, on the curing kinetics of an epoxy system composed of diglycidyl ether of bisphenol A [BADGE (n = 0)], 1,2‐diaminecyclohexane (1,2‐DCH), and CaCO₃ filler was studied by DMA and DSC. Different contents of filler in the range from 10 to 30%, referred to the total weight of the mixture, were tried. It was found that maximum reproducibility of the results and better performance correspond to a filler content of 20%. As usual, the T_g's obtained by DMA and DSC are different at 10–20°C. The results obtained from this study were compared with those corresponding to the system BADGE (n = 0)/1,2‐DCH without filler; the T_g for this last system is higher than that for the system with filler incorporated, whereas E′ and M_c (molecular weight between repetition units) are lower for the system without filler. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 366–370, 2002     

Comparison of the enthalpic relaxation of poly(lactide–co‐glycolide) 50:50 nanospheres and raw polymer

The phenomenon of enthalpic relaxation was evaluated for poly(lactide‐co‐glycolide) (PLGA, 50:50), in terms of storage of nanospheres for use as a controlled drug delivery system. Samples were stored for different times and temperatures below the glass transition temperature (T_g). Relaxation occurred at a significant rate up to 15 degrees below the T_g of 39.2°C. The effect of polymer morphology was considered by comparing the relaxation kinetics of the raw polymer with that of nanospheres formed using a novel technique. The nanospheres were shown to have a larger change in heat capacity at the glass transition and a longer average relaxation time than that of the raw polymer, and the relationship between these two parameters was discussed. For both the raw polymer and the nanospheres, relaxation was found to occur at a significant rate at room temperature. The storage of this system at subambient temperatures was therefore deemed important for maintaining the physicochemical properties of the system. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1868–1872, 2002     

Dynamic mechanical analysis of polymers in the liquid state: Use of a perforated shim stock support

This report summarizes some initial results on the use of a perforated brass shim stock support to extend the useful range of dynamic mechanical testing well over 100 degrees above the traditional limiting polymer softening points of T_g or T_m. Weak secondary relaxations were observed above T_g in both polyisobutylene (PIB) and polystyrene (PS) homopolymer, copolymer, and blend systems and above T_m in gutta percha (trans-polyisoprene). The DuPont 981 Dynamic Mechanical Analyzer (DMA)–990 Thermal Analyzer system was used to characterize these weak liquid state processes. The DMA instrument deforms the specimen in flexure, thus minimizing the shear component present in some other techniques. Specimen-coating weights are typically in the range 20–40 mg. The perforations are particularly useful for polymers having low inherent adhesion to metals or systems which are very brittle in the glassy state, e.g., low MW PS's and many methacrylates.     

Studies on dielectric relaxation in ceramic multiferroic Gd1−xYxMnO3

Dielectric study over a broadband was carried out from 10 to 70 K on ceramic Gd_1?xY_xMnO₃ (x=0.2, 0.3 and 0.4). For all the compositions, a prominent sharp peak about ~18 K was observed in the temperature dependence of both ε′(T) and ε″(T) at all frequencies, indicating a long‐range ferroelectric (FE) transition. Using Cole‐Cole fit to the permittivity data, the relaxation time τ and the dielectric strength ?ε were estimated. Temperature variation of τ(T) in the Arrhenius representation is found to be nonlinear (non‐Debyean relaxation), with increasing barrier‐activation energy over successive temperature‐windows. Interestingly, for all the compositions, we witness a jump in τ(T) about the ferroelectric transition temperature, concurred by a broad‐maximum in ?ε(T),signifying the critical slow down of relaxations near long‐range FE‐correlations.     

Characterization of biodegradable polymers by inverse gas chromatography. II. Blends of amylopectin and poly(ε‐caprolactone)

Amylopectin (AP), a potato‐starch‐based polymer with a molecular weight of 6,000,000 g/mol, was blended with poly(ε‐caprolactone) (PCL) and characterized with inverse gas chromatography (IGC), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). Five different compositions of AP–PCL blends ranging from 0 to 100% AP were studied over a wide range of temperatures (80–260°C). Nineteen solutes (solvents) were injected onto five chromatographic columns containing the AP–PCL blends. These solutes probed the dispersive, dipole–dipole, and hydrogen‐bonding interactions, acid–base characteristics, wettability, and water uptake of the AP–PCL blends. Retention diagrams of these solutes in a temperature range of 80–260°C revealed two zones: crystalline and amorphous. The glass‐transition temperature (T_g) and melting temperature (T_m) of the blends were measured with these zones. The two zones were used to calculate the degree of crystallinity of pure AP and its blends below T_m, which ranged from 85% at 104°C to 0% at T_m. IGC complemented the DSC method for obtaining the T_g and T_m values of the pure AP and AP–PCL blends. These values were unexpectedly elevated for the blends over that of pure AP and ranged from 105 to 152°C for T_g and from 166 to 210°C for T_m. The T_m values agreed well with the XRD analysis data. This elevation in the T_g and T_m values may have been due to the change in the heat capacity at T_g and the dependence of T_g on various variables, including the molecular weight and the blend composition. Polymer blend/solvent interaction parameters were measured with a variety of solutes over a wide range of temperatures and determined the solubility of the blends in the solutes. We were also able to determine the blend compatibility over a wide range of temperatures and weight fractions. The polymer–polymer interaction coefficient and interaction energy parameter agreed well on the partial miscibility of the two polymers. The dispersive component of the surface energy of the AP–PCL blends was measured with alkanes and ranged from 16.09 mJ/m² for pure AP to 38.26 mJ/m² when AP was mixed with PCL in a 50/50% ratio. This revealed an increase in the surface energy of AP when PCL was added. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3076–3089, 2006     

Effect of hybrid nanoparticles on glass transition temperature of polymer nanocomposites

Changes in the glass transition temperatures of composites based on polystyrene and nanosized macromolecular nanostructures (molecular silicasols, dendrimers) are reported. Silicasols are nanosized particles consisting of a silica core and an ethyl phenyl shell; dendrimers are formed using a carbosilane core with ethyl phenyl end groups. It has been observed that the glass transition temperatures of the composites (T_gc) may be either above or below the glass transition temperature of polystyrene, depending on the size of the filler particles. A theoretical model based on the relation between the glass transition temperature and the configurational entropy of the composite, which satisfactorily describes the experimental dependence, was developed. It is found that the effect of the size of the hybrid nanoparticles on T_gc was determined using two factors. First, the presence of an organic layer on the surface of nanoparticles increases the number of degrees of freedom and the entropy of the system, thereby reducing T_gc. Second, the particles present in the polymer reduce the number of configuration states of macromolecules, which reduces the disorientation entropy. This effect leads to an increase T_gc. The competition between these two main factors determines the sign of the glass transition temperature deviation. The size of the particles and their organic surface layer play the key roles in the thermodynamic properties of the composites. POLYM. COMPOS., 37:1978–1990, 2016. © 2015 Society of Plastics Engineers     

Dynamic mechanical properties of highly loaded ferrite-filled thermoplastic elastomer

The dynamic mechanical properties in terms of the storage modulus E′, loss modulus E″, and the loss tangent δ has been studied for highly filled magnetic polymer composites. The effect of surface treatment on the relaxation spectra has been clearly elucidated and quantitative values indicating the extent of polymer–filler interactions have been given. Various models have been tested for describing the viscoelastic behavior of such highly filled systems. The Wiechert model using a single-arm with a Cole–Cole parameter has been shown to effectively fit the Argand diagram in the case of the present highly filled systems.     

Evolution of properties with increasing cure of a thermosetting epoxy/aromatic amine system: Physical ageing

Isothermal physical ageing below the glass‐transition temperature (T_g) of a high‐T_g thermosetting difunctional epoxy/tetrafunctional aromatic amine system was investigated at different ageing temperatures (T_a) and chemical conversions (monitored by the T_g) using the torsional braid analysis freely oscillating torsion pendulum technique. In the absence of chemical reaction during an isothermal ageing process, the rate of isothermal physical ageing passes through a minimum with increasing conversion. The minimum is related to the minimum in mechanical loss between the secondary relaxation in the glassy state (T_β) and the glass‐transition relaxation (T_g) (the temperatures of both of which increase with increasing conversion). If isothermal ageing rates for all conversions (beyond gelation) would have been measured directly from temperatures below T_β to above T_g, it is concluded that two maxima in isothermal ageing rate would have been observed corresponding to the two relaxation processes. There exists a superposition in isothermal ageing rate versus T_g ? T_a [by shifting horizontally (and vertically)], which implies that the ageing rate is independent of the details of the changing chemical structure attributed to cure. Controlling mechanisms during physical ageing are segmental mobility associated with the T_g region and more localized motion associated with the glassy‐state relaxation T_β. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2665–2675, 2003     

Hysteresis temperature dependence in filled rubbers. II. Mechanical mixing,filler microdispersion,and polymer–filler interactions

The effects of mechanical mixing and filler–filler (F–F) and polymer–filler (P–F) interactions on the normalized state of a filler microdispersion [d(x)] and the viscoelastic properties of silica‐filled rubbers were studied. The rubbers were prepared with or without the addition of n‐octyl‐triethoxysilane (OTES) to modify F–F interactions or coupling agents such as 3‐mercaptopropyl‐trimethoxysilane and 3‐mercaptopropyl‐triethoxysilane (MPTES) to increase P–F interactions. Increased mixing improved d(x) and enhanced the hysteresis temperature dependence (HTD) by giving a higher tan δ value near the compound glass‐transition temperature (T_g) but lowered tan δ at elevated temperatures for stocks containing a coupling agent. The changes in P–F and F–F interactions in rubbers with mixing and subsequent thermal treatment were shown to be responsible for the property differences observed among stocks containing different silanes. Attempts were made to quantify the efficiency for improving d(x) with various silanes. The increased P–F interactions in compounds containing MPTES showed better efficiency for improving d(x) and enhancing HTD in comparison with OTES. It was also demonstrated that the change in hysteresis near T_g was mainly governed by the degree of filler networking, whereas elevated‐temperature hysteresis was strongly influenced by the P–F interactions in compounds. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Film‐forming process from globular polytetrafluoroethylene latex particles

Film formation from an aqueous polytetrafluoroethylene (p‐TFE) latex dispersion on glass tissues was studied. The p‐TFE particles were of globular shape, had a diameter of 220 ± 20 nm, and were of high crystallinity (～ 100%). The melting point of the material was 332°C. For the study of the film formation, stripes of glass tissues were dipped in a concentrated p‐TFE latex dispersion and then removed. The samples were then dried in an oven at well‐defined temperatures below and above the melting temperature T_m of the p‐TFE latex. The film formation from the particles was then studied by taking SEM micrographs of the surface of the samples at various times and conditions. It was observed that the globular particles kept their globular shape and did not coalesce to a film as long as the temperature of the sample was kept below T_m. When the samples were tempered with T > T_m the film formation started. The neighboring globular particles coalesced into wormlike particles that grew in length with time. During the growth of the particles the thickness of the particles remained constant. In the first stages the film can be imagined as a porous network from short wormlike objects. It is concluded that the coalescence begins above T_m when the polymer chains become mobile along their axis. The chains of neighboring particles can therefore interdigitate into each other along their main axis and crosslink the particles. The proposed mechanism of film formation is confirmed by AFM micrographs on which the individual particles from the dispersion are still visible in the wormlike objects. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 733–742, 2004