Viscoelastic properties of an organic hybrid of chlorinated polyethylene and a small molecule

The dynamic mechanical properties of an organic hybrid consisting of chlorinated polyethylene (CPE) and N,N‐dicyclohexyl‐2‐benzothiazolyl sulfenamide (DZ) were investigated. All the CPE/DZ hybrids showed a single loss tangent (tan δ) peak in the mechanical spectra. The peak area under the tan δ/temperature curves around the mechanical loss peak was examined to characterize the damping properties of the CPE/DZ hybrids. We found that there exists a bending point in the relation between the glass‐transition temperature (T_g) and DZ content and that the value of T_g is saturated in the higher DZ contents, suggesting that excess DZ molecules show self‐aggregation and are reorganized. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1341–1347, 2000     

Multicomponent latex IPN materials: 2. Damping and mechanical behavior

The integrals of the linear loss shear modulus vs. temperature (loss area, LA) and linear tan δ vs. temperature (tan δ area, TA) were characterized for various core/shell latex particles with synthetic rubber, poly(butadiene-stat-styrene) [P (Bd/S), 90/10], and interpenetrating polymer networks (IPN) as the cores. The IPN cores were composed of P(Bd/S) (T_g ≃ − 70°C) and an acrylate based copolymer (T_g around 10°C) for potential impact and damping improvement in thermoplastics. Poly(styrene-stat-acrylonitrile) (SAN, 72/28) was the shell polymer for all these polymers. Under the same loading, for both toughening and damping controls, among the IPN core/shell, blend of separate core/shell, and multilayered core/shell polymers, the IPN core/shell polymers were the best dampers. However, the other core/shell polymers also showed higher LA values than P(Bd/S)/SAN core/shell polymer. A comparison of LA values via a group contribution analysis method was made, the effect of particle morphology and phase continuity on damping being studied. Inverted core/shell latex particles (glassy polymer SAN was synthesized first) showed much higher LA and TA values than normal core/shell ones (rubbery polymer was synthesized first). Models for maximum LA and TA behavior are proposed. The damping property was essentially controlled by the phase miscibility and morphology of the core/shell latex particles. The LA values for each peak in these multiphase materials provided some indication of the several fractional phase volumes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1501–1514, 1997     

Electric,dielectric, and dynamic mechanical behavior of carbon black/styrene‐butadiene‐styrene composites

The conductivity of styrene‐butadiene‐styrene block copolymers containing different amounts of extraconductive carbon black (CB) was investigated as a function of the mold temperature. The composites exhibited reduced percolation thresholds (between 1.0 and 2.0 vol % CB). The dynamic mechanical analysis characterization revealed that the glass‐rubber‐transition temperatures of both segments were not affected by the CB addition, although the damping of the polybutadiene phase displayed a progressive drop with an increase in the CB concentration. The normalized curves of tan δ/tan δ_max (where tan δ represents the value of the loss tangent at any measurement temperature and tan δ_max represents the loss tangent peak value at the corresponding temperature T_max) versus T/T_max (where T is the temperature and T_max is the maximum temperature), corresponding to both polystyrene and polybutadiene phases as well as the activation energy related to the glass‐rubber‐transition process, did not present any significant change with the addition of CB. The dielectric analysis revealed the presence of two relaxation peaks in the composite containing 1.5 vol % CB, the magnitude of which was strongly influenced by the frequency, being attributed to interfacial Maxwell‐Wagner‐Sillars relaxations caused by the presence of different interfaces in the composite. The mechanical properties were not affected by the presence of CB at concentrations of up to 2.5 vol %. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2983–2997, 2003     

The effects of monophenol chain terminators on the structure–property relationships of controlled epoxy networks

Five families of new controlled epoxy thermosets (CENs) using three monophenol chain terminators were prepared to study systematic changes in the structure and amount of the monophenol and the initial molecular weight between crosslinks (M_c,i) on the properties of epoxy thermosets. Glass transition temperature (T_g) decreases with monophenol mole fraction (χ) in proportion to both the concentration and flexibility of the chain terminator. Distinct serial relations for T_g depression were observed for the three M_c,i families. Dynamic mechanical analysis (DMA) shows significant perturbations of the relaxation behavior with added terminator as evidenced by decrease in peak tan δ and in post T_g damping. The rubbery coefficients of thermal expansion (CTE) increases with monophenol concentration only at χ > 0.05 and shows distinct curvature versus temperature, but is largely invariant with monophenol flexibility. The thermal stability of terminated CENs decreases only slightly with χ and little difference was found with monophenol structure. Most surprisingly, fracture toughness decreases markedly and discontinuously with χ depending on M_c,i. The values of the critical monophenol concentration at which fracture toughness markedly decreases (χ_c) are inversely proportional to M_c,i but are independent of monophenol flexibility. No correlation of χ_c with any of the calculated network structure parameters was apparent. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1632–1640, 2008     

The glass transition temperature of nonstoichiometric epoxy–amine networks

Glass transition temperatures (T_g) of nonstoichiometric epoxy-amine networks based on the diglycidylether of bisphenol A (DGEBA), are analyzed in terms of the network structure. In most cases reasonable predictions of T_g can be made using an empirical equation reported by L. E. Nielsen together with the experimental T_g value of the stoichiometric network and statistical calculations of the concentration of elastic chains. It is stated that in these rigid networks the concentration of elastic chains is the main structural factor associated to the variations of T_g with stoichiometry. For flexible networks based on the diglycidylether of butanediol (DGEBD), the effect of elastic chains on the T_g value is much less significant.     

Glass transition of semi-crystalline PLLA with different morphologies as studied by dynamic mechanical analysis

Poly(l-lactic acid) was crystallized from the glassy state at different temperatures to produce fully transformed semi-crystalline specimens exhibiting different lamellar morphologies. The materials were tested by dynamic mechanical analysis, where a T _g decrease was found with an increasing crystallization temperature. Considering a three-phase model, this tendency was related to the corresponding increase in the thickness of the rigid amorphous phase. It is suggested that this phase could, in some extent, accommodate through local translational/rotational motions the cooperative motions taking place within the mobile amorphous phase. This could be due to the non-compact structure of the cooperatively rearranging regions, which can present a string-like or fractal structure in their edges. The width of the loss factor peak associated to the glass transition increases with increasing crystallization temperature, suggesting an increase in the broadness of the distribution of relaxation times. The drop in the storage modulus across T _g varies systematically with the crystallization temperature in the different materials and could be correlated with the crystalline content. Above T _g, the loss factor exhibits a plateau-like behaviour at significantly high values, which seems to be a rather general behaviour in semi-crystalline systems that could be related to the contribution of pure irreversible flow in the overall viscoelastic behaviour.     

Viscoelastic properties of nanostructured natural rubber/polystyrene interpenetrating polymer networks

The effects of the blend ratio and initiating system on the viscoelastic properties of nanostructured natural rubber/polystyrene‐based interpenetrating polymer networks (IPNs) were investigated in the temperature range of ?80 to 150 °C. The studies were carried out at different frequencies (100, 50, 10, 1, and 0.1 Hz), and their effects on the damping and storage and loss moduli were analyzed. In all cases, tan δ and the storage and loss moduli showed two distinct transitions corresponding to natural rubber and polystyrene phases, which indicated that the system was not miscible on the molecular level. However, a slight inward shift was observed in the IPNs, with respect to the glass‐transition temperatures (T_g's) of the virgin polymers, showing a certain degree of miscibility or intermixing between the two phases. When the frequency increased from 0.1 to 100 Hz, the T_g values showed a positive shift in all cases. In a comparison of the three initiating systems (dicumyl peroxide, benzoyl peroxide, and azobisisobutyronitrile), the dicumyl peroxide system showed the highest modulus. The morphology of the IPNs was analyzed with transmission electron microscopy. The micrographs indicated that the system was nanostructured. An attempt was made to relate the viscoelastic behavior to the morphology of the IPNs. Various models, such as the series, parallel, Halpin–Tsai, Kerner, Coran, Takayanagi, and Davies models, were used to model the viscoelastic data. The area under the linear loss modulus curve was larger than that obtained by group contribution analysis; this showed that the damping was influenced by the phase morphology, dual‐phase continuity, and crosslinking of the phases. Finally, the homogeneity of the system was further evaluated with Cole–Cole analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1680–1696, 2003     

Synthesis,characterization, and properties of polyurethanes containing 1,4:3,6‐dianhydro‐D‐sorbitol

Two‐ and three‐component polyurethanes containing 1,4:3,6‐dianhydro‐D ‐sorbitol (isosorbide) derived from glucose were synthesized using n‐BuSn(?O)OH·H₂O as a catalyst, and the thermal properties (T_g, T_d) of the polymers were investigated by differential scanning calorimetry and thermogravimetric analysis. We carried out molds for polyurethanes, the molds of polyurethanes were obtained. The dynamic mechanical analyzes showed that the storage modulus values of the three‐component polymers were constant to a higher temperature than those of the two‐component polymers. The storage moduli (E′), loss moduli (E″), and values of tan δ for the polymers were obtained. The rigidity of three‐component polymers was increased by the introduction of bisphenol A and diphenylmethane group to two‐component polymer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6025–6031, 2009     

Effect of AlN content on the performance of brominated epoxy resin for printed circuit board substrate

Polymer matrix composites, based on brominated epoxy, a type of material widely used in printed circuit boards (PCBs), as matrix and AlN particle as filler were prepared. The influences of AlN content on the mechanical, thermal, and electrical properties of the composites were investigated by uniaxial tensile test, TMA, thermal conductivity measurement, DMA, and dielectric properties measurement. It was found that the properties of composites monotonically varied with AlN content except that maximum tensile strength and strain of composites corresponded to a filler content of 10 wt %. The results of DMA also showed the AlN reinforcement was more pronounced above T_g, and the peak area of tan δ versus T curves decreased with AlN content, which implied the damping capacity of the composite gradually decreased. The increase in T_g and decrease in damping were probably due to strong interaction between the AlN and epoxy matrix inhibiting the mobility of the epoxy chain. In addition, different theoretical models reported in the literature were used to predict the E, CTE, k, and D_k, and compared with the experimental data. Finally, suitable models were recommended in the present materials system. For the significant improvement of performance of epoxy, we can conclude that these composite materials may be promising for PCB substrate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1662–1674, 2007     

Kinetic Studies of Bulk Ge22Se78−xBix (x=0, 4 and 8) Semiconducting Glasses

Results of phase transformations, enthalpy released and specific heat of Ge₂₂Se_78–xBi_x(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, T _g, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of T _g (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of T _g, at a heating rate of 5 K min^–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol^–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference T _c–T _g and the enthalpy released during the crystallization process. Below T _g, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal analysis of hydrolysis and degradation of biodegradable polymer and bio-composites

The purpose of this study was to conduct a thermal analysis of the hydrolysis and degradation behavior of biodegradable polymers and bio-composites at 50°C and 90% relative humidity (RH). With increasing hydrolysis time, the thermal stability and degradation temperature of polybutylene succinate (PBS) slightly decreased. The glass transition temperature (T _g) and melting temperature (T _m) of PBS and the anti-hydrolysis agent treated PBS did not vary significantly with increasing hydrolysis time, whereas those of the trimethylolpropane triacrylate (TMPTA)-treated PBS slightly increased. With increasing hydrolysis time, the storage modulus (E’) values of the bio-composites decreased, whereas those of the TMPTA treated bio-composites slightly increased. Also, the tan values of the anti-hydrolysis agent and TMPTA treated PBS-BF bio-composites were slightly lower than those of the non-treated bio-composites, due to the reduction in their degree of hydrolysis. The tanδ_max peak temperature (T _g) of the anti-hydrolysis agent treated bio-composites was not significantly changed, whereas that of the TMPTA treated bio-composites was increased.     

Thermomechanical investigation of a thick film of aniline-formaldehyde copolymer and poly(methyl methacrylate)

A thick film of aniline-formaldehyde copolymer and PMMA is synthesized via dispersion of aniline-formaldehyde copolymer powder as filler particles in PMMA with two different concentrations. Variation of the complex elastic modulus and mechanical loss factor (tanδ) with temperature is studied. It is observed that the complex elastic modulus decreases with temperature owing to thermal expansion of films. On the other hand, tanδ increases up to a characteristic temperature beyond which it shows a decreasing trend toward melting. Transition temperature T _g of sample S₁ (pure PMMA) is found to be 80°C. In sample S₂ (1 wt % aniline formaldehyde copolymer), the peak of tanδ at a lower temperature (66°C) corresponds to glass transition temperature T _g of the PMMA matrix, while the peak of tanδ at a higher temperature (107.8°C) corresponds to T _g of a polymer chain restricted by filler particles of aniline-formaldehyde copolymer. A further increase (10 wt % aniline-formaldehyde copolymer) in the concentration of filler particles of aniline-formaldehyde copolymer results in a more compact structure and a shift of T _g to a higher temperature, 122.2°C. This shift in the glass transition temperature of thick films of aniline-formaldehyde copolymer and PMMA is dependent upon the concentration of filler particles in the sample.     

Isomer effects on transport properties of polyesters based on bisphenol-A

Pure gas sorption and transport properties of polyesters based on bisphenol-A and both pure isophthalic and pure terephthalic acid chloride were obtained for He, N₂, O₂, CH₄, and CO₂ at 35°C. The polymers were synthesized in our laboratory and amorphous films were prepared with a specialized solvent casting procedure. The polymer containing m-phenylene groups shows higher permselectivity for most of the gas pairs. The ideal selectivity of O₂/N₂ was increased by 33% when p-phenylene units were replaced by m-phenylene ones. On the other hand, the polyester containing only p-phenylene groups, shows higher permeability to all the gases studied. The polymer based on pure terephthalic acid chloride has a 75% higher oxygen permeability and a 1.1-fold higher carbon dioxide permeability than the isophthalic acid derivative. The polyester containing meta-phenylene units has lower T_g, higher permselectivity, lower permeability, lower fractional free volume (FFV), and lower d-spacing. The values of FFV, and lower d-spacing. The values of FFV and d-spacing were only slightly different between the two isomers. Moreover, for the sub-T_gγ transition the maximum in tan δ occured at essentially the same temperature (?55°C). The polymer with a higher concentration of p-phenylene units shows somewhat larger area under the γ-peak, indicating slightly more sub-T_g motion. The Distribution of FFV is considered to be the determining factor for the differences in transport properties observed. © 1993 John Wiley & Sons, Inc.     

Damping performance of Eucommia ulmoides gum

Eucommia ulmoides gum(EU gum),known as gutta percha in Southeast Asia,is a natural polymer with double characteristics of rubber and plastic.In present paper,tanδ-T curve and hysteresis loss(HL) were chosen to characterize its damping property.The results indicated that its tanδvalue would increase with rising of temperature when T>0℃and form another damping peak at 40-80℃besides T_g peak.This phenomenon resulted from meltage of crystals of EU gum could increase its damping property at ambient-high temperature.Its tanδvalue even exceeded those of conventional damping rubbers,such as nitrile-butadiene rubber(NBR) and chlorinated isobutene-isoprene rubber(CIIR).     

Extension of the chain‐end,free‐volume theory for predicting glass temperature as a function of conversion in hyperbranched polymers obtained through one‐pot approaches

Compared with linear polymers, more factors may affect the glass‐transition temperature (T_g) of a hyperbranched structure, for instance, the contents of end groups, the chemical properties of end groups, branching junctions, and the compactness of a hyperbranched structure. T_g's decrease with increasing content of end‐group free volumes, whereas they increase with increasing polarity of end groups, junction density, or compactness of a hyperbranched structure. However, end‐group free volumes are often a prevailing factor according to the literature. In this work, chain‐end, free‐volume theory was extended for predicting the relations of T_g to conversion (X) and molecular weight (M) in hyperbranched polymers obtained through one‐pot approaches of either polycondensation or self‐condensing vinyl polymerization. The theoretical relations of polymerization degrees to monomer conversions in developing processes of hyperbranched structures reported in the literature were applied in the extended model, and some interesting results were obtained. T_g's of hyperbranched polymers showed a nonlinear relation to reciprocal molecular weight, which differed from the linear relation observed in linear polymers. T_g values decreased with increasing molecular weight in the low‐molecular‐weight range; however, they increased with increasing molecular weight in the high‐molecular‐weight range. T_g values decreased with increasing log M and then turned to a constant value in the high‐molecular‐weight range. The plot of T_g versus 1/M or log M for hyperbranched polymers may exhibit intersecting straight‐line behaviors. The intersection or transition does not result from entanglements that account for such intersections in linear polymers but from a nonlinear feature in hyperbranched polymers according to chain‐end, free‐volume theory. However, the conclusions obtained in this work cannot be extended to dendrimers because after the third generation, the end‐group extents of a dendrimer decrease with molecular weight. Thus, it is very possible for a dendrimer that T_g increases with 1/M before the third generation; however, it decreases with 1/M after the third generation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1235–1242, 2004     

Evidence of dynamic heterogeneity as obtained from dielectric and brillouin light-scattering studies of poly(n-hexylmethacrylate)

We report dielectric relaxation and Rayleigh-Brillouin spectroscopic measurements on the side chain polymer poly(n-hexylmethacrylate), PHMA (T_g = 268 K), exhibiting a broad glass transition region. The dielectric loss curves can be represented by single Havriliak-Negami functions in the temperature range of 260–450 K. The width of the distribution relaxation function is a decreasing function of temperature up to T = 333 K ≊ 1.24 × T_g and remains virtually constant above that temperature. This is interpreted as marking the merging of the α-process with a slow β-relaxation in agreement with the value of the cooperativity length associated with the α-mode. Hence above that temperature, the relaxation times confirm well to an Arrhenius temperature dependence. The hypersonic dispersion deduced from the Brillouin spectra (210–550 K) surprisingly peaks at temperatures near T_g which bears no relation to the main α-relaxation. This structural relaxation is rather associated with the side hexyl group motion showing striking resemblance with the hypersonic dispersion in molecular liquids. It is conceivable that the observed damping in PHMA is dynamically related to the internal plasticization effect of the hexyl group. © 1996 John Wiley & Sons, Inc.     

Dynamic mechanical and dielectric properties of epoxidized SBS triblock copolymer

The morphological and dynamic properties of epoxidized styrene–butadiene–styrene block copolymers were studied and compared with their parent styrene–butadiene–styrene block copolymer (SBS). Two peaks were observed in the mechanical loss (tan δ) curve which can be attributed to segmental motion of epoxidized polybutadiene (EPPB) and polystyrene. Analysis by DSC thermograms also showed the linear increase of glass transition temperature for EPPB domain with the epoxy group content. Phase separated structures of epoxidized SBS as observed by TEM suggests a considerable degree of mixing occurred between phases after 80 mol % of the double bonds in SBS were epoxidized. The interfacial region displays a third peak and causes much steeper drop in modulus at higher temperature than T_g of EPPB. Parallel dielectric relaxation measurements were also made in the frequency range of 30 Hz–1 KHz as a function of temperature. In each dielectric constant (?′) curve, there is a maximum near the T_g of EPPB determined from the dielectric loss tangent curve. The shift in T_g of EPPB versus epoxy group content was consistent with that measured by the thermal and dynamic mechanic analysis. These findings indicated an 8°C shift in glass transition temperature as the epoxy group content in EPPB increased 10%.     

Relationship between the positive temperature coefficient of resistivity and dynamic rheological behavior for carbon black‐filled high‐density polyethylene

Studies on the relationship between resistivity and dynamic rheological properties of carbon black‐filled high‐density polyethylene (CB/HDPE) composites were carried out. Change of resistivity ρ is associated with the dynamic modulus before the positive temperature coefficient/negative temperature coefficient (PTC/NTC) transition temperature. When the temperature approaches the melting point of HDPE, ρ increases rapidly with a decreasing modulus, corresponding to PTC transition. The resistivity‐dynamic viscoelasticity relationship in the PTC region can be divided into two parts in which the changes of ρ with storage modulus G′ and loss modulus G″ can be described by the scaling laws given by the critical storage modulus and loss modulus G′_c and G″_c; adjustable parameters ρ′_1c, ρ′_2c, ρ″_1c and ρ″_2c; and nonlinear exponents n and m, respectively. The accordance between the experimental data and the scaling functions of the dimensionless quantities (G′/G′_c ? 1) and (G″/G″_c ? 1) in the PTC transition region suggests that the ρ jump may be the result of a modulus‐induced percolation. G′_c and G″_c increase, but the four scaling resistivitis, ρ′_1c, ρ′_2c, ρ″_1c, and ρ″_2c, decrease with increasing CB concentration, implying that the microstructure change of the composites is the determinant factor for the PTC behavior and the resistivity‐dynamic modulus relationship. However, ρ′_2c and ρ″_2c exhibit no scaling dependence. It is suggested that a threshold concentration exists for the modulus of the composites on the basis of examining the plot of both G′_c and G″_c against CB concentration. The scaling laws G′ ～ Φ^x and G″ ～ Φ^y hold for the concentration dependence of the critical modulus when Φ > Φ_c and the estimated values of x and y are 1.10 ± 0.10 and 0.89 ± 0.29, respectively. The resistivity‐dynamic modulus can shift to form a master curve. The horizontal factors a_G′ and a_G″ and the vertical factors a′ and a″ are relevant to the concentration dependence of the dynamic modulus or PTC behavior. It is believed that the former would be involved in changing the mechanical microstructure formed by the complicated interaction of CB particle and polymer segments, and the latter would be involved in the overall changes of conducting a network during the PTC transition region. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 983–992, 2003     

Effect of sample preparation on the glass‐transition of thin polystyrene films

We have investigated the effect of sample preparation on the glass‐transition temperature (T_g) of thin films of polystyrene (PS). By preparing and measuring the glass‐transition temperature T_g of multilayered polymer films, we are able to assess the contribution of the spincoating process to the reduced T_g values often reported for thin PS films. We find that it is possible to determine a T_g even on the first heating cycle, and that by the third heating cycle (a total annealing time of 15 min at T = 393 K) the T_g value has reached a steady state. By comparing multilayered versus single layered films we find that the whole T_g depends only on the total film thickness, and not on the thickness of the individual layers. These results strongly suggest that the spincasting process does not contribute significantly to T_g reductions in thin polymer films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4503–4507, 2004     

Effects of chemical structure on low-temperature modulus for UV-curable polybutadiene acrylates as an optical fiber coating material

The relationship between chemical structure and low-temperature modulus of ultraviolet(UV)-radiation-cured optical-fiber coating materials has been investigated. The coating materials are low-viscosity liquid compounds consisting of a 1,4-polybutadiene diacrylate oli-gomer, a monomer, and a photoinitiator. Dynamic mechanical test results show that low-temperature modulus and glass transition temperature (T_g) are affected by the monomer structure and monomer concentration in the coating material in cases where the same oligomer is used. With increasing alkyl group chain length of the alkylacrylate monomer, the T_g value is shifted to lower temperatures. Low-temperature modulus increases with increasing monomer concentration in the coating material. Low-temperature excess optical losses of coated fibers have been found to be closely related to low-temperature modulus of the coating.