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Introducing small molecule-bridged hydrogen bonds (HBs) between polymer chains has been reported to effectively reduce the interchain cooperativity despite of strengthening the intermolecular interaction. Here, a systematic investigation on tuning the Johari-Goldstein β (βJG) relaxation by adding various low-molecular-weight phenols in poly(n-alkyl methacrylate)s is carried out to further clarify the anomalous dynamics. Given these small molecules capable of coupling the motion with pendent groups of host polymers due to forming at least two HBs per molecule, poly(n-alkyl methacrylate) mixtures exhibit rich dynamic changes in the βJG-properties and α, βJG separations. An increased loading of phenols with a small size and strong inter-HB strength (Δυi) clearly benefits for significant retardation and suppression of the βJG-relaxation, narrows the α, βJG separation and converges the βJG-peak with the α-peak, which demonstrates the alleviation of inter-chain topological constraints. However, small molecules with a relatively big size and weak Δυi are found to amplify the magnitude of the α, βJG separation of poly(butyl methacrylate), even though experimental results of changes in α-dispersion and dynamic fragility confirm a reduction of the coupling factor n in all of these hybrids. The counterintuitive phenomenon suggests that the crossover time tc in the Coupling Model is no longer a universal quantity if the inter-chain interaction of polymers is strengthened by HBs. These compelling findings shed vital insights into the HB-induced anomalous dynamics, and provide essential guidance for tailoring the βJG behavior and designing glassy polymeric materials.

This report studied changes in the dynamic fragility (m) of poly(butyl methacrylate) (PBMA) by introducing guest hindered phenols capable of forming two or three intermolecular hydrogen bonds (inter-HBs) per molecule with the host polymer. The small molecules effectively decrease the m value, even if they apparently increase the glass transition temperature (Tg) of mixtures. The reduction in m was confirmed by enthalpy relaxation in two aspects: adding the guest molecule leads to a stronger cooling rate dependence of the limiting fictive temperature together with an apparent increase in aging rate of PBMA hybrids at low concentrations. By varying the molecule size and steric hindrance of the hydroxyl group on the hindered phenols, we clarified that m is primarily governed by the strength of inter-HB interactions, while the Tg value of mixtures depends on a combined effect of additive bulkiness and HB interaction. The anomalous dynamics was further rationalized not only by the HB-induced flexibility balance between side groups and backbone, but also by the reduction of cooperative rearranging sizes and alleviation of long-chain connectivity in such HB-driven hybrids.

In this study, we report the effect of the number of formulated repeat units (n), the type of diamine and the cross-linker content on pore morphology, structure and mechanical properties of vacuum-dried polyimide aerogels. Morphology observations demonstrate that an excess of cross-linker is conducive to increase the pore size, strengthen and stiffen the network to avoid the collapse and suppress the irreversible shrinkage during the vacuum drying procedure. For 2,2'-dimethylbenzidine derived aerogels, the pore diameter increases with increasing cross-linker content or decreasing n. The shrinkage is higher in aerogels derived from 4,4'-oxidianiline due to the chain rigidity and mobility difference compared to rigid diamine-based aerogels, resulting in lower porosity and higher density. Compared with those previously reported aerogels with the same backbone chemistries, vacuum dried polyimide aerogels herein show higher compressive strength and Young’s modulus resulting from higher density and coarser skeleton networks. More importantly, isothermal aging results reveal very low increasement of shrinkage and density occurring over the aging period, which even can be ignored. The facile, low-cost vacuum drying procedure, dramatically improved mechanical properties, and superior thermal resistance will broaden the practical applications of polyimide aerogels.

Hindered phenols remarkably enhance the sound attenuation and vibration damping of acrylic polymers. However, this novel damping material suffers from gradual degradation during long-term use becau...

The exo-hydroxyl group (exo-OH) on isosorbide (ISB) has long been asserted as a highly reactive moiety compared with the endo-hydroxyl group (endo-OH). In this study, calculations based on density functional theory and experiments without adding catalysts reveal that endo-OH has strong nucleophilic ability, and in the case of transesterification with diphenyl carbonate, the nucleophilic attack surmounts steric hindrance in rendering endo-OH more reactive than exo-OH. The kinetics of transesterification with different catalysts is investigated to determine the catalytic reactivity and molecular structure evolution. The results show that preferential activation of exo-OH moieties can be achieved either by reducing the coordination ability of catalytic cations (lg β1) or by enhancing the alkalinity of catalytic anions. Despite the low reactivity of exo-OH on ISB monomers, terminal exo-OH on carbonate oligomers exhibits higher reactivity than terminal endo-OH, justifying the experimental fact that ISB-based polycarbonates (ISB-PCs) are mostly terminated by endo-OH. Balancing the reactivity between endo-OH and exo-OH can be promoted by increasing the reaction temperature, thus accelerating transesterification to a high equilibrium constant. These findings help to clarify the mechanism of ISB transesterification and provide new strategies for the synthesis of high-molecular-weight ISB-PCs.

How to control the spatial distribution of nanoparticles to meet different performance requirements is a constant challenge in the field of polymer nanocomposites. Current studies have been focused on the flexible polymer chain systems. In this study, the rigid polyimide (PI) chain grafted silica particles with different grafting chain lengths and grafting densities were prepared by “grafting to” method, and the influence of polymerization degree of grafted chains (N), matrix chains (P), and grafting density (σ) on the spatial distribution of nanoparticles in the PI matrix was explored. The glass transition temperature (Tg) of PI composites was systematically investigated as well. The results show that silica particles are well dispersed in polyamic acid composite systems, while aggregation and small clusters appear in PI nanocomposites after thermal imidization. Besides, the particle size has no impact on the spatial distribution of nanoparticles. When σ·N0.5 ≪ (N/P)2, the grafted and matrix chains interpenetrate, and the frictional resistance of the segment increases, resulting in restricted relaxation kinetics and Tg increase of the PI composite system. In addition, smaller particle size and longer grafted chains are beneficial to improving Tg of composites. These results are all propitious to complete the microstructure control theory of nanocomposites and make a theoretical foundation for the high performance and multi-function of PI nanocomposites.

We report the reaction of bio-renewable isosorbide-based polycarbonate (IcC-PC) with poly(bisphenol A carbonate) (BPA-PC) by melt-blending in the presence of dibutyltin dilaurate (DBTDL). The blends formed copolymers and transformed into transparent alloys with a single Tg after melt-blending. A remarkable reduction in molecular weight was observed in the reactively blended products. 1H NMR and 13C NMR results showed that the carbonate group of IcC-PC is less vulnerable to nucleophilic attack than that of BPA-PC and that transesterification is initiated by the exchange reaction between the laurate ligands of DBTDL and the carbonate groups of BPA-PC. Tin-containing BPA-PC chains were proposed to react with the carbonate group of IcC-PC via a coordination-insertion mechanism to produce the (IcC-PC)-(BPA-PC) copolymer. The hydroxyl end-groups of IcC-PC were also involved in transesterification under the catalysis of dibutyltin compounds and converted into low-reactive phenolic end-groups of BPA-PC. Degradation in the IcC-PC/BPA-PC blends after adding DBTDL was mainly caused by the exchange reaction between DBTDL and BPA-PC, hydrolysis, and phenolysis of IcC-PC and BPA-PC under the catalysis of dibutyltin compounds. Among these reactions, hydrolysis played the major role and occurred mostly at the BPA-PC chains.

A continuing challenge in polymer nanocomposites (PNCs) is to control nanoparticle (NP) dispersion and understand its role in property enhancements. Previous studies have been focused on the flexible polymer chain systems. In this study, we report the structure, glass transition behavior, segmental dynamics, and mechanical properties of polyimide (PI) nanocomposites that consisted of either bare or PI-grafted silica NPs to discriminate the role of grafted rigid chains in polymer–NP interactions and dynamic response of such hybrids. Silica NPs are well dispersed in the poly(amic acid) (the precursor of PI) nanocomposites. After thermal imidization, the aggregate structure and self-assembled small clusters of NPs are observed in ungrafted and grafted silica NP-filled PI composites, respectively. The glass transition temperature (Tg) shifts to high temperature by the addition of silica NPs resulting from strong polymer–NP interactions and steric hindrance, and Tg deviation is more visible with increasing the...

A great challenge of toner design is to improve the storage stability and energy saving. The reciprocal characteristics of endowing high glass transition temperature (Tg) while low fusing temperature (Tf) are essential. In this study, we investigate the influence of hydrogen bonding interactions on Tg and temperature-dependent viscoelastic of styrene/ethyl acrylate random copolymers [P(St-co-EA)] with different ratios of St/EA by the incorporation of small molecule 4,4′-thio-bis(6-tert-butyl-m-methyl phenol) (AO300). The results of FTIR spectra confirm the intermolecular hydrogen bonding between the carbonyl groups of acrylic copolymers and hydroxyl groups of AO300 small molecules. With increasing AO300 content, Tg of the hybrids increases due to the increased number of hydrogen bonding. The universal scaling law of temperature-dependent viscoelastic behavior is indeed valid for pure acrylic copolymers in both the Arrhenius and non-Arrhenius regions. However, the temperature-dependent viscoelastic behaviors of the hybrids are strongly influenced by the ratio of St/EA and AO300 content, showing positive or negative deviations from the universal plot for high and low ratio of St/EA copolymer based hybrids, respectively. The systematic deviations are greater with increasing small molecule content. Such irregular deviations can be attributed to either the disassociation of hydrogen bonding or plasticizing effect by the introduction of AO300. The P(St-co-EA)/AO300 hybrids possessing high Tg and low Tf provides a promising candidate of toner binder resin to realize the storage stability and energy efficient.

Isosorbide polycarbonate (ISB-PC) was prepared by melt transesterification and polycondensation reaction by employing ISB and diphenyl carbonate (DPC) as monomers. The effects of catalyst on the reactivity and the reactivity disparity of two hydroxyl groups (endo-OH and exo-OH) on ISB were investigated. The result shows that a metal chloride can form intermolecular hydrogen bonding with ISB hydroxyl groups, and the ISB intramolecular hydrogen bonding facilitates a stronger intermolecular hydrogen bonding between endo-OH and the catalyst. The intermolecular hydrogen bonding is capable of improving preferentially the endo-OH reactivity and thus increases the content of the endo–endo (a1) structure on the ISB-PC chain, resulting in a high Tg of the product. Further balancing of the reactivity disparity between endo-OH and exo-OH can be achieved by adjusting log β1 of the alkali metal chloride. It is found that the lithium chloride (LiCl) catalyst can significantly reduce the reactivity disparity, and the viscosity-average molecular weight of the synthesized ISB-PC reaches 51 000 g mol−1.

A dynamically adjustable ultra-wideband metamaterial perfect absorber (MPA) is proposed which consists of three resonance rings based on vanadium dioxide (VO2) and a metal ground layer separated by a dielectric spacer. The simulation results show that the terahertz (THz) absorption bandwidth of more than 90% absorptance reaches 3.30 THz, which covers from 2.34 to 5.64 THz, under different incident polarization angles. The range is better than that of previous VO2-based reports. Moreover, when the conductivity of VO2 changes from 200 S/m to 2×105 S/m, the absorption peak intensity can be adjusted continuously from 4% to 100%. The key is to optimize the geometric structure through interference cancellation and impedance matching theory, to achieve better absorption bandwidth and efficiency. Besides, the terahertz absorber has a wide-angle absorption effect both in TE and TM waves. Thus, the designed absorber may have many potential applications in modulating, sensing and imaging technology.

A novel non-planar coding metasurface optimized by discrete particle swarm algorithm (DPSO) is proposed in terms of the property of wideband radar cross-section (RCS) and diffuse scattering. The design consists of two unit cells, &ldquo, 0&rdquo, and &ldquo, 1&rdquo, which have a 180&deg, &plusmn, 37&deg, phase difference for phase interference cancellation. The 10 dB monostatic RCS reduction frequency range of the metasurface is from 6.4 to 29.6 GHz, and its bandwidth ratio is 4.62:1, under normal incidence of the two polarizations. Compared to the planar surface, the non-planar surface has a greater bandwidth with respect to the monostatic and bistatic RCS reduction. The results declare its properties of ultra-wideband, angle insensitivity, and polarization insensitivity. Finally, the theoretical analysis, simulation, and experimental results match perfectly, indicating that the metasurface can be used in the RCS reduction or other microwave applications with wider RCS reduction and diffuse scattering.

Hindered phenols have been reported effective to remarkably enhance the damping property of acrylic polymers. In this work, the long–term stability of these novel damping materials were investigated on the basis of thermodynamic phase diagrams. The Flory–Huggins interaction parameter χ between different small molecules and poly(butyl methacrylate) (PBMA) were determined through the melting point depression method proposed by Nishi and Wang. The calculated phase diagram curves agreed well with small-angle light scattering, wide-angle X-ray diffraction, and optical transparency measurements. χ gradually decreased to a negative value as temperature increased and the phase diagrams exhbited an upper critical solution temperature-type spinodal curve. The mixtures with the small-molecule loading of less than 28 vol% were found miscibile at temperatures near the glass-transition temperature. Increasing the intermolecular hydrogen bonding strength between the phenol and carbonyl groups of PBMA could effectively reduce the χ value. Meanwhile, increasing the steric hindrance of the phenolic hydroxyl groups and the sizes of small molecules may sufficiently weaken intramolecular hydrogen bonding interactions. These effects suppress the self-aggregation of small molecules and improve the long-term stability of the damping materials.

The effects of catalyst on the molecular weight, chemical structure, and yellowness of isosorbide-based polycarbonate (ISB-PC) in the melt-transesterification and polycondensation stages were investigated. Results showed that the high steric hindrance and intramolecular hydrogen bonding of the endohydroxyl group (endo–OH) of ISB enabled its reactivity to be lower than that of the exohydroxyl group (exo–OH). We also found that the reactivity of endo–OH with diphenyl carbonate can be preferentially activated by strong electrophilic catalysts, and that the configuration of the ISB-PC chain strongly depended on the reactivity balance between endo–OH and exo–OH. Various catalysts with different coordinate capacities, acidity coefficients, and radius of metal ion were further tested. Catalysts with a calcium or zinc ion showed a higher reactivity of endo–OH than exo–OH, resulting in a high glass-transition temperature of ISB-PCs. Results suggested as well that the thermal stability of ISB-PC may be correlated t...

This study aimed to improve polydimethylsiloxane (PDMS) conversion in the preparation of polycarbonate (PC)–polydimethylsiloxane (PDMS) copolymer through melt polycondensation. We examined the transesterification process of PDMS with diphenyl carbonate (DPC) and its copolymerization products with bisphenol-A (BPA) for different chain lengths of PDMS. The key factors affecting PDMS conversion were investigated. Results showed that long-chain PDMS required a higher critical transesterification level (38.6%) to improve miscibility with DPC. During polycondensation, side reactions were more prone to occur when the equilibrium transesterification level of long-chain PDMS was lower. PDMS conversion was also lower when more short-chain PDMS was fed. Increasing the chain length of PDMS also reduced PDMS conversion. Notably, increasing the amount of KOH can significantly improve PDMS conversion throughout the polycondensation stage by increasing the equilibrium transesterification level of long-chain PDMS, thereby inhibiting the occurrence of side reactions.

Self-organization of mesoscopic materials (≥10 μm) using capillary forces is an attractive strategy to assemble small objects into ordered structures. In this report, a small amount of epoxy resin (EP) is added as a “solder” in glass fibers (GFs)-reinforced silicone rubber (SR). The randomly dispersed GFs are found spontaneously self-welded into a three-dimensional GF-EP network under the driving force of capillarity. We center on investigating the effects of viscosity ratio of EP to SR (λ) and the matrix viscosity (ηm) on the size of EP domain, the encapsulation ratio (NEP) of EP on GF and the morphology evolution of self-welded GF scaffolds. NEP increases with decreasing ηm of the SR matrix. At a given matrix, enlarging the viscosity difference of EP from SR seems to maximize NEP. More interestingly, decreasing ηm can not only increase NEP, but also promote preferential segregation at the junction points of GFs. We confirm that NEP increases because of the viscosity-related enlargement of the EP domain size. The self-welded rigid GF-EP scaffolds mechanically support the SR matrix, thus providing a new strategy for the design of high-strength and pressure-resistant functional rubber composite materials.

In this study, polypropylene (PP) composites were fabricated by incorporating reduced graphene oxide (RGO) sheets and antioxidant pentaerythritol tetra [β-(3, 5-di-tert-butyl-4-hydroxyphenyl)-propionate] (AO1010) to comparatively investigate the effect of graphene and antioxidant on the radiation resistance. Morphological observation and X-ray diffraction reveal the uniform dispersion of RGO. The incorporation of antioxidant is beneficial to the improved dispersion and exfoliation of RGO nanosheets in the PP matrix. The melting temperature decreases significantly with increasing irradiation dose, whereas the crystallinity remains almost unchanged for all the samples before and after irradiation. Tensile strength analysis demonstrates that incorporating RGO sheets is more effective for radiation protection at low doses, and adding AO1010 is more applicable to radiation resistance at high doses. Furthermore, the mechanical performance and the decomposition temperature of PP/AO1010/RGO composites by simultaneously incorporating 0.5 wt% AO1010 and 1.0 wt% RGO sheets are higher than that of PP/AO1010 and PP/RGO composites upon gamma irradiation at various doses, indicating an additive effect between RGO and AO1010 in retarding the radiation-induced degradation of PP composites. The intrinsic mechanism of radiation resistance is attributed to the free radical scavenging and oxygen barrier effect. The additive effect between RGO and AO1010 can substantially reduce the number of peroxy radicals and oxygen concentration in the composites, resulting in the remarkable improvement in radiation resistance.

We present a facile, environmentally friendly approach to fabricate high-radiation-resistance poly(methyl methacrylate)/reduced graphene oxide (PMMA/RGO) composites through latex mixing of anionic PMMA latex particles and graphene oxide dispersion followed by coagulation and in situ hydrazine reduction. Morphological observation reveals the highly uniform dispersion of RGO nanosheets in the PMMA matrix. The dynamic mechanical properties demonstrate that the radiation-induced cross linking and chain scission of PMMA chains are significantly delayed in PMMA/RGO nanocomposites compared with that in pure PMMA irradiated at low and high doses, respectively. Additionally, the incorporation of RGO nanosheets delays the thermal oxidative degradation of the PMMA matrix. This delay is attributed to the fact that RGO can act as a radical scavenger, as confirmed by electron paramagnetic resonance spectroscopy analysis. The physical barrier effect of RGO provides a tortuous path for the diffusion of oxygen molecules and consequently leads to a decrease in peroxy radical concentrations. The synergistic effects keep the graphene-based materials mechanically and thermally stable in the irradiation environment. These findings provide a new strategy for the design of radiation-resistant nanocomposites, which can be considered promising candidates for protective materials in nuclear industrial and aerospace fields.

Nanoparticle surfaces grafted with polymers similar to the matrix have been widely used to eliminate interface incompatibility and control the spatial organization of nanoparticles. However, the absence of specific interactions between the matrix and the graft limits the intrinsic versatility of nanoparticles, such as high mechanical strength, heat resistance, and excellent thermal/electrical conductivity. In this study, the specific interaction between poly( d -lactide)-grafted graphene oxide (GO-g-PDLA) and the poly( l -lactide) (PLLA) matrix was investigated via differential scanning calorimetry, dynamic mechanical analysis, electrical measurement, microscopy observation and in situ Fourier transform infrared spectroscopy (FTIR). In situ FTIR results reveal the formation process of stereocomplex crystallites (Sc) on the surface of grafted GO. Remarkable improvement of the crystallinity of stereocomplex nanocomposites was detected because of the heterogeneous nucleating effect of grafted GO. The GO-guided stereocomplex networks endow polylactide-based nanocomposites with significantly improved mechanical strength and electrical conductivity at low GO concentrations.

Gd2O3/Al2O3 ceramic composites with different weight percent of Gd2O3 were prepared by adopting a pressureless sintering approach. The effect of Gd2O3 addition on the phase composition, sintering property, microstructure, bending strength, thermal conductivity and shielding property of the composites was investigated. The results show that the properties of ceramic can be improved greatly by introducing a small amount of Gd2O3, owing to the promotion of reaction between MgO, SiO2 and Al2O3 to produce spinel and forsterite. Compared with ordinary Al2O3 ceramic, the bending strength and thermal conductivity coefficient of Gd2O3/Al2O3 composite with 5 wt% Gd2O3 have increased by 38.03 MPa and 8.95 W/(m K), respectively. When the amount of Gd2O3 surpasses 15 wt%, however, the performances of the composite would become worse for excessive new phases formed in the composite hindering its densification. In addition, screening ratio of the composites for Co-60 gamma rays radiation increases with the addition of Gd2O3. And the Gd2O3/Al2O3 composites also exhibit good mechanical stability when exposed to continuous gamma rays irradiation.

We report a novel procedure to fabricate vacuum dried high-mechanical-strength polyimide (PI) aerogels cross-linked with dopamine-functionalized carbon nanotubes (mCNTs). Poly(amid acid) chains are in situ grafted onto the surface of mCNTs via “grafting from” method, thus providing the composite aerogels with superior mechanical properties due to covalently chemical cross-link networks and linear reinforcement. The addition of only 1.0 wt% of mCNT endows the composite aerogel with the specific modulus of 715.5 J/g, which is much higher than that of chemical agent cross-linked aerogels. The obtained composite aerogels also show high thermal stability and enhanced flame retardant performance, with only a slight increase in weight loss and shrinkage after firing test. Furthermore, mCNTs can serve as secondary reaction platform, thus superhydrophobic and oleophilic composite aerogels were fabricated by grafting octadecylamine onto the aerogel surface. The water contact angle is as high as 151°, and the maximum oil absorption capacity is 447%. Moreover, the composite aerogels exhibit stable hydrophobic and oleophilic properties after a long period of strong acid/base or high-temperature treatments, which is promising for practical oil-water separation applications under severe environments.

Early radar warning is a significant step to lessen the fine scanning range of a receiver. The small size two-dimension (2-D) angle-of-arrival (AOA) estimation part with moderate accuracy and sensitivity is important for an early radar warning receiver. In our method, we specially design an L-shaped antenna array (L-sAA) and connect it with dual-polarization binary phase shift keying modulator (DP-BPSKM). The dual-sideband (DSB) modulation is performed to transfer most of the optical power to electrical, so as to increase the sensitivity. It is also possible to map the AOA information of the incoming beam to photo-detected electrical power without a high extinction ratio modulator or optical filter. During the estimation, the 2-D AOA is firstly measured, whose measurement range is 18.22°∼90° and the measurement error is lower than 1°. Then, based on the 2-D AOA estimation results, the third one is mathematically calculated to construct 3-D location of the target. Noteworthy, the amplitude comparison function (ACF) is adopted in this method to make the system response irrelative to the received signal power, which endows the system with signal power fluctuation immunity. Experimental results show that this method is capable of measuring a single-tone signal and a bandwidth signal. This structure is very concise and meets the potential of on-chip integration.

Catalytic activities of metal laurates with different coordination capabilities and sodium salts with different ligand alkalinities toward the transesterification between isosorbide (ISB)-based polycarbonate (IcC-PC) and bisphenol-A polycarbonate (BPA-PC) are investigated to accelerate asymmetric chain exchange without aggravating chain degradation. Only catalysts capable of direct reaction with PC chains to form metal alkoxide containing active species (PC–O-M) can initiate and thus accelerate chain transesterification. Sodium salts exhibit the highest catalytic activity and can be further improved by complex formation of 15-crown-5, demonstrating the key role played by alkalinity of reactive ligands. Different from weak catalytic selectivity and serious chain scissions by tin-based catalysts, it is found that, for sodium-catalyzed systems, BPA-PC chains prefer to bond to ISB segments in endo position and the high reactivity of sodium-based catalysts not only significantly reduces essential loading but also suppresses chain degradation. We confirm that these differences must arise from whether active PC-O-M acts as a direct nucleophilic attacker or works with coordination process.

Grafting a nanoparticle surface using a polymer similar to the matrix has been widely applied to control the spatial organization of nanoparticles. However, the fabrication of target materials with well-defined nanoparticle arrangement remains fundamentally difficult because of the absence of specific interactions between the matrix and the graft. In this study, the self-networking structure of poly( d -lactide)-grafted carbon nanotubes (CNT-g-PDLA) in poly( l -lactide) (PLLA) matrix was investigated. Specific interactions between enantiomeric pairs not only promoted CNT dispersion, but also contributed to the regular phase-separation-like CNT self-networking. Furthermore, the grafted PDLA chains preferably formed stable stereocomplex crystallites with the PLLA matrix, and the CNT self-networking resulted in the self-assembly of 3D continuous stereocomplex scaffold. It was demonstrated that the CNT-guided stereocomplex network endows polylactide-based nanocomposites with significantly improved mechanical strength, heat-resistance, and electrical conductivity at low CNT concentrations.

Due to the strong hydrogen bonding interactions, hindered phenol 3,9-bis[1,1-dimethyl-2{ I² -(3-tert-butyl-4-hydroxy-5- methylphenyl)propionyloxy}ethyl]- 2,4,8,10-tetraoxaspiro[5,5]-undecane (AO-80) demonstrated a remarkable damping effect when it was hybridized with acrylic rubber (ACM). The loss factor of ACM could be largely increased and the position of loss peak could be regulated by controlling the content of the hindered phenol. This kind of high damping hybrids can be used as the laminated layer of sandwich beam for vibration control. Instead of the traditional method ASTM E756-98, a new method based on dynamic mechanical analyzer (DMA) was developed to characterize the damping behaviors of ACM/AO-80 laminated beam. Testing results demonstrated that DMA can reflect the variation of damping behaviors of sandwich beams with various factors effectively, and a theoretical model established here was used to explain the damping behaviors. Based on this model, by means of adjusting the content of AO-80, a high damping ability for the sandwich beam could be obtained at appointed temperature during a wide frequency range.

The effects of heterogeneous distribution of organoclay and silica nanoparticles on the co-continuity and thermal expansion of the injection-molded ethylene–propylene–diene terpolymer (EPDM)/isotactic polypropylene (PP) blends were investigated. The organoclay was selectively located in the EPDM domains regardless of the blending sequences, which significantly induced a fine but co-continuous microlayer structure. The silica nanoparticles were preferentially dispersed in the PP domains, and the addition of silica showed negative effects on the formation of the co-continuous structure. The coefficient of linear thermal expansion of the injection-molded EPDM/PP composites exhibited a sharp decrease with the addition of organoclay, whereas the silica-filled composites decreased linearly with the increasing amount of silica. This discrepancy in the thermal expansion behavior was further discussed based on considerations of various factors including PP crystallinity, the ratio of Young's modulus between EPDM and PP, aspect ratio of the PP microlayers, as well as their co-continuities. The co-continuity of the microlayer structure was shown to play a vital role in reducing the thermal expansion coefficient.

Polyimide/carbon black (PI/CB) nanocomposite films were fabricated via the direct ball-milling method with poly(amic acid) (PAA), the precursor of PI, as an in situ formed impurity-free dispersant. FTIR and Raman spectral results reveal that, besides physical adsorption, chemical grafting of PAA chains onto the CB surface occurs during the ball-milling process. Comparative studies show that introduction of various commercial dispersants improves the dispersion of CB. However, the mixtures exhibit poor reproducibility, unstable electrical properties, and decreased tensile strength; these issues may be attributed to interfacial pollution brought about by differences in the chemical structures of the dispersant and the matrix. The impurity-free dispersant is effective not only in ensuring the uniform dispersion of CB particles but also in enhancing filler-matrix interfacial adhesion. High-molecular weight PAA chains are effective reagents for impurity-free modification and can therefore be used to improve the electrical and mechanical properties of the resultant composite.

Enhancing the intermolecular interaction generally leads to an increased topological constraint, thus resulting in a decreased non-exponential parameter βKWW of segmental cooperative rearrangement during glass transition. In this report, we illustrate a counterintuitive case when the inter-chain interaction is strengthened by small molecule-bridged hydrogen bonds. It was found that hindered phenols capable of forming double hydrogen bonds per molecule can effectively narrow the dielectric loss peak of poly(ethyl acrylate) and the βKWW increases monotonically with the intermolecular hydrogen-bonding strength even if the small molecule (AO300) has a glass transition temperature Tg much higher than the host polymer. Further experiments revealed an increased Tg but a decreased dynamic fragility m, accompanied by gradual merging of the suppressed secondary relaxation toward the primary peak, demonstrating that introduction of AO300-bridged hydrogen bonds appears to enhance the intermolecular interaction, but actually reduces the inter-chain cooperativity. This anomalous dynamics stemming from hydrogen bonding was rationalized in terms of small molecule-alleviated chain connectivity, flexibility of bulky pendant groups and changes in enthalpic contributions to segmental cooperative rearrangement.

The effects of morphological changes on the thermal expansion, toughness and heat resistance of polyamide-6 (PA)/styrene–ethylene–butylene–styrene (SEBS)/polyphenylene ether (PPE) blends were investigated. Compared with the typical ‘sea (PA matrix)–island (PPE domain)–lake (SEBS in PPE domain)’ morphology, an injection-molded ternary blend with a preferential distribution of SEBS component at the interface between PA and PPE exhibited a low coefficient of linear thermal expansion (CLTE) in the flow direction. This low CLTE was ascribed to the deformation of SEBS and PA into a co-continuous microlayer network structure during injection molding. Consequently, the expansion preferentially occurred towards the thickness direction. Further CLTE reduction either by a change in PA viscosity or by the selective location of an inorganic filler was examined, and its influences on impact strength and heat resistance are discussed based on transmission electron microscopy observations. © 2015 Society of Chemical Industry

High-Tg polymers exhibit high fragilities in general. Here, we report for the first time that small molecules with double phenolic end groups are effective to independently mediate the dynamic fragility (m) and glass transition temperature (Tg) of acrylic polymers. Broad band dielectric spectrometer (BDS), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimeter (DSC) measurements showed that the addition of small molecules with a concentration lower than 30 wt % leads to a narrower relaxation time distribution of the intermolecular cooperative rearrangement motion because of the formation of hydrogen bonding networks. These acrylic polymers exhibited a significant decrease in m while showing a linear increase in Tg by changing the loading of the small molecules. Further experimental results demonstrated that m decreases monotonically with intermolecular hydrogen bonding strength for a given host polymer matrix. The m/Tg value diminishes with increasing small molecule content,...