Garnet particles effect on the cross-linking of PDMS and the network structures formed

Poly(dimethylsiloxane) (PDMS) cross-linked films with different concentrations of micrometer-sized garnet particles were prepared through hydrosilylation reaction between a di-vinyl-terminated PDMS and a four-functional silane cross-linker in the presence of a Platinum catalyst. The garnet particles, consisting of micrometer-sized Ce doped Y₃Al₅O₁₂ particles commonly used on light converters (for solid state light devices, e.g. Light emitting diodes LEDs), were homogeneously and individually dispersed through the bulk of the cross-linked films for a concentration up to 20% in volume.The effect of the garnet on the cross-linking of the composite films was investigated by in-situ ATR-FTIR Spectroscopy. When formulations with an excess of cross-linker were used the overall consumption of Si-H groups of the cross-linker is slowdown in the presence of the garnet. The same effect was observed for an increasing concentration of the garnet. This effect is attributed to a strong interaction of the catalyst with the garnet during the cross-linking process. The possible origins of this interaction are discussed.NMR Imaging was used to investigate the cross-linked networks formed in the composite films. All the networks are homogeneous through the depth of the cross-linked composite films (approx. 5 μm resolution). The films prepared in the presence of the garnet particles showed similar relaxation behavior, regardless of the cross-linker concentration used in the initial formulation, contrary to previous results with PDMS cross-linked films. This behaviour is explained based on the presence of different type of chemical cross-links, resulting from the occurrence of hydrosilylation and secondary reactions, which are influenced by the interaction between the garnet particles and the catalyst.     

聚二甲基硅氧烷对聚丙烯发泡成型的影响

以超临界CO2为发泡剂,以马来酸酐接枝聚丙烯(PP-g-MAH)为相容剂,在连续挤出发泡过程中研究了聚二甲基硅氧(烷PDMS)对无规共聚聚丙烯(R-PP)发泡性能的影响。结果表明:当CO2用量为5%时,少量PDMS和PP-g-MAH的加入能提高R-PP发泡样品的膨胀率;与纯R-PP相比,R-PP/PP-g-MAH/PDMS共混物在各个温度下发泡样品的泡孔密度要明显高于纯PP发泡样品的泡孔密度。     

Synthesis and properties of polymer brush consisting of poly(phenylacetylene) main chain and poly(dimethylsiloxane) side chains

A novel polymer brush consisting of poly(phenylacetylene) (PPA) main chain and poly(dimethylsiloxane) (PDMS) side chains was synthesized by the polymerization of phenylacetylene-terminated PDMS macromonomer (M-PDMS). The macromonomer was prepared by the esterfication of monohydroxy-ended PDMS (PDMS-OH, degree of polymerization (DP) = 42) with p-ethynylbenzoic acid. The polymerization of M-PDMS using [(nbd)RhCl]₂/Et₃N catalyst led to polymer brush, poly(M-PDMS), with M_n up to 349?000 (DP of main chain 104). Poly(M-PDMS) with narrow molecular weight distribution (M_n = 39?900, M_w/M_n = 1.11) was obtained with a vinyl-Rh catalyst, [Rh{C(Ph)CPh₂}(nbd){P(4-FC₆H₄)₃}]/(4-FC₆H₄)₃P. Poly(M-PDMS)s were brown to orange viscous liquids and soluble in organic solvents such as toluene and CHCl₃. The UV-vis absorptions of poly(M-PDMS) were observed in the range of 350-525 nm, which are attributable to the PPA main chain.     

A dielectric relaxometry study of segmental dynamics in PDMS/boron composite and hybrid elastomers

In this work, the motional dynamics and relaxation behavior of a series of model poly(dimethylsiloxane)-co-meta-carborane (PDMS-co-CB) hybrid elastomers have been studied in depth, using Broadband Dielectric Spectrometry over a temperature range of −130 to 100 °C and a frequency window of 10⁻¹ to 10⁷ Hz. The segmental α-relaxation of both the PDMS and carborane chain segments has been characterized at specific carborane backbone incorporation levels. A direct correlation between the ratio of PDMS to carborane segments and the motional constraint of the network as a whole was observed. In addition to the study of the α-motional modes associated with local intra-segmental motions and the onset of cooperative motion, we have also identified and studied a higher order cooperative (normal-mode) motion of extended segments of the carborane–siloxane co-polymer chains at elevated temperatures. These normal mode motions have been shown to follow an Arrhenius temperature dependence, are sensitive to the local chemical environment and have not been previously reported in this class of polysiloxane copolymer. The motional dynamics of the PDMS-co-CB networks have been compared and contrasted with those of a series of conventionally filled PDMS–Boron Nitride (PDMS–BN) composite systems. While the effects of the chemically bound carborane segment on the PDMS chain dynamics, local order and global network properties have been shown to be directly correlated, significant and predictable, the effects of the BN filler on the PDMS matrix are significantly less so and the results suggest that the filler material may in fact be disrupting the network order, with a consequently negative impact on the properties of the composite.     

强疏水性PDMS/PVDF微孔膜的制备及其性能研究

利用非溶剂相转化法（NIPS）,通过在聚偏氟乙烯(PVDF)铸膜液中加入聚二甲基硅氧烷(PDMS),制备了PDMS/PVDF共混疏水微孔膜,并研究了凝胶浴组成（水/乙醇）对铸膜液凝胶动力学、膜形貌、疏水性及力学性能的影响。结果表明,随着凝胶浴中乙醇百分含量由零增加至100 %时,PDMS/PVDF共混膜的断面上指状孔基本消失,海绵状孔结构贯穿断面;当凝胶浴中乙醇含量为100 %时,PDMS与PVDF发生分相;膜表面疏水性能增加,水接触角达到139.68 °;弹性模量、拉伸强度、断裂伸长率分别由（48.06±4.20）、（2.82±0.15） MPa、（92.90±2.53） %下降至（15.70±2.83）、（0.72±0.13） MPa、（15.47±1.63） %。     

Effect of filler amount on thermoelastic properties of poly(dimethylsiloxane) networks

End-linked poly(dimethylsiloxane) (PDMS) networks were prepared in the presence of fumed silica particles with hydroxyl groups at their surfaces. The silica particles were introduced into the polymer solution prior to end-linking. Hydroxyl ended PDMS chains were end-linked via the tetra functional crosslinker, tetraethoxysilane. The filler content varied in the range 0-5 wt%. Atomic Force Microscopy was used to image and characterize the silica particles. Swelling, stress-strain and thermoelasticity experiments were performed. The temperature coefficient and the energetic part of the force in uniaxial extension are found to increase with increasing silica amount. This observation is ascribed to effects contributed possibly by the adsorption layer around the silica particles.     

Synthesis and physicochemical characterization of a well-defined poly(butadiene 1,3)-block-poly(dimethylsiloxane) copolymer

For the first time, order-order and order-disorder transitions were detected and characterized in a model diblock copolymer of poly(butadiene-1,3) and poly(dimethylsiloxane) (PB-b-PDMS). This model PB-b-PDMS copolymer was synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene 1,3 (B) and hexamethylciclotrisiloxane (D₃), and subsequently characterized by nuclear magnetic resonance (¹H and ¹³C NMR), size exclusion chromatography (SEC), Fourier Transform infrared spectroscopy (FTIR), Small-Angle X-ray scattering (SAXS) and rheology. SAXS combined with rheological experiments shows that the order-order and order-disorder transitions are thermoreversible. This fact indicates that the copolymer has sufficient mobility at the timescale and at the temperatures of interest to reach their equilibrium morphologies.     

Crystalline morphology of poly(dimethylsiloxane)

The crystalline morphology of poly(dimethylsiloxane) was studied using a scanning electron microscope equipped with a cold stage. Samples of two different molecular weights were used. In both cases, spherulitic morphology is seen, from −70 °C, with spherulites of about 100 μ in size. Small single crystals of about a micron in size are also seen, and these are attributed to the presence of cyclics.     

Effect of crosslinking on the mobility of PDMS filled with polysilicate nanoparticles: Positron lifetime, rheology and NMR relaxation studies

We study the effect of adding trimethylsilyl-treated polysilicate nanoparticles (Rg ∼ 2.2 nm) to crosslinked poly(dimethylsiloxane) (PDMS) elastomers above the entanglement molecular weight. The results are compared to un-crosslinked PDMS of a similar molecular weight, reported in previous studies and filled with the same polysilicate nanoparticles.Three techniques are used and compared to assess the enhancement or reduction in mobility with addition of filler: positron annihilation lifetime spectroscopy (PALS), rheology and nuclear magnetic resonance (NMR) spin-spin relaxation (T₂) measurements. PALS measurements do not show any clear effect of the filler on the mobility of the chains, as assessed by the size of free volume holes, but reveal a net increase in free volume with temperature increase (from 30 °C to 60 °C). A reduction in the dynamic shear storage modulus (measured at 1 rad s⁻¹) is observed in the filled network relative to the unfilled polymer (from 63 kPa without filler to 44 kPa with 40 w/w% filler), attributed primarily to a partial inhibition of the chemical crosslinking reaction by the particles. The NMR relaxation measurements, instead, show a reinforcement of the polymer network with increasing addition of polysilicate particles, as revealed by the faster T₂ decays at higher filler loadings, caused by increasing polymer bridging and particle flocculation. Similar trends are observed at higher temperatures (up to 80 °C), with a higher overall mobility. The apparent disagreement between rheology and NMR stems from the fact that rheology reflects bulk mobility and is primarily sensitive to chemical crosslinks in the network, while NMR probes segmental dynamics, which are affected by the presence of particles.In un-crosslinked PDMS instead, both rheology and NMR show an initial increase in mobility at low filler content, followed by reinforcement with further particle addition. These results strongly suggest that entanglements and filler-induced packing disruption, rather than free volume, play a major role in polymer dynamics.     

Synthesis, structure and morphology of poly(dimethylsiloxane) networks filled with in situ generated silica particles

The morphology of silica particles generated in situ in PDMS networks in the presence of two types of catalysts is evaluated by using different techniques including solid-state ²⁹Si MAS NMR, near-infrared spectroscopies and small-angle X-ray scattering. The interactions with the poly(dimethylsiloxane) chains are examined through the swelling properties and thermal characteristics (in particular crystallization process) of the composites. In addition, ¹H NMR is used to investigate the adsorption layer of reduced mobility on the particle surface.     

Structure-property behavior of poly(dimethylsiloxane) based segmented polyurea copolymers modified with poly(propylene oxide)

Poly(propylene oxide) (PPO) was incorporated in a controlled manner between poly(dimethylsiloxane) (PDMS) and urea segments in segmented polyurea copolymers and their solid state structure-property behavior was investigated. The copolymers contained PDMS segments of MW 3200 or 7000 g/mol and an overall hard segment content of 10-35 wt%. PPO segments of MW 450 or 2000 g/mol were utilized. Equivalent polyurea copolymers based on only PDMS as the soft segment (SS) component were used as controls. The materials (with or without PPO) utilized in this study were able to develop microphase morphology as determined from dynamic mechanical analysis (DMA) and small angle X-ray scattering (SAXS). DMA and SAXS results suggested that the ability of the PPO segments to hydrogen bond with the urea segments results in a limited inter-segmental mixing which leads to the formation of a gradient interphase, especially in the PPO-2000 co-SS containing copolymers. DMA also demonstrated that the polyureas based on only PDMS as the SS possessed remarkably broad and nearly temperature insensitive rubbery plateaus that extended up to ca. 175 °C, the upper temperature limit depending upon the PDMS MW. However, the incorporation of PPO resulted in more temperature sensitive rubbery plateaus. A distinct improvement in the Young's modulus, tensile strength, and elongation at break in the PPO-2000 and PDMS-7000 containing copolymers was observed due to inter-segmental hydrogen bonding and the formation of a gradient interphase. However, when PPO was incorporated as the co-SS, the extent of stress relaxation and mechanical hysteresis of the copolymers increased relative to the segmented polyureas based on the utilization of only PDMS as the soft segment component.     

Tacticity effects on the miscibility behavior of poly(methyl methacrylate)/poly(ethylene oxide-b-dimethylsiloxane-b-ethylene oxide) blends

The miscibility of a triblock copolymer poly(ethylene oxide)-poly(dimethylsiloxane)-poly(ethylene oxide) with syndiotactic and isotactic poly(methylmethacrylate) wasstudied. Although isotactic poly(methyl methacrylate) (PMMA) was miscible with poly(ethylene oxide) (PEO) in the pure state, it was immiscible with the PEO end blocks in the copolymer. In comparison, the syndiotactic poly(methyl methacrylate) (sPMMA) was miscible with the PEO blocks as indicated by melting point depression, decrease in crystallinity, and slower rate of spherulite growth of PEO. When blends of the triblock copolymer were cooled to low temperatures, the poly(dimethylsiloxane) (PDMS) middle block which resided in the interlamellar region of PEO spherulites also crystallized; the development of PDMS crystals was clearly suppressed at high sPMMA contents.On leave from Union Chemical Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan     

Radiation-induced synthesis of poly(vinylpyrrolidone) nanogel

Studies of the radiation-induced synthesis of poly(vinylpyrrolidone) (PVP) nanogels, intended to provide a basis for obtaining intra-molecular cross-linked products, which are more useful in drug delivery, show that a sharp change in the controlling mechanism from inter-molecular to intra-molecular cross-linking occurs above a threshold temperature around 50 °C-55 °C, even though the rate of inter-molecular cross-linking is enhanced as the temperature is raised. When aqueous solutions of PVP are irradiated, the activation energy of the decay of the PVP· radical is observed to rise sharply above this threshold temperature. This can be attributed to the collapse of the polymer chains, which occurs at temperatures above approximately 55 °C and leads to a reduction of the R_h of the irradiated polymer molecules at 77 °C to (44 ± 3) % of that of PVP molecules that were not irradiated at 20 °C, as shown by the results of AFFFF measurements. The abrupt transition to a mechanism controlled by intra-molecular cross-linking is due to the thermal collapse of the polymer structure. This accounts for the observation that activation energy is higher within the temperature range above 55 °C. Higher pulse repetition rates during electron irradiation also promote intra-molecular cross-linking.     

Effect of molecular weight and content of PDMS on morphology and properties of silicone‐modified epoxy resin

To achieve a stable blend of a bisphenol A type epoxy resin and poly(dimethylsiloxane) (PDMS), reaction between hydroxyl (OH) groups of the epoxy and silanol groups of hydroxyl‐terminated(HT) PDMS has been investigated. The chemical structures of the HTPDMS‐modified epoxies were characterized by Fourier transform infrared (FTIR) and ¹H‐ and ¹³C‐NMR spectroscopy. To allow further understanding of the influence of viscosity and content of HTPDMS on the blend morphology, four different viscosities of HTPDMS were used in three content levels. The morphologies of modified epoxy resins were observed with optical microscopy. The modified epoxies were cured with a cycloaliphatic polyamine. The morphologies of modified epoxies were investigated by using scanning electron microscopy (SEM)/energy dispersive X‐ray (EDX) technique. The cured films showed droplet in matrix morphology with different mean droplets size which was influenced by the viscosity and the content of the incorporated HTPDMS. To illustrate the effect of the morphologies of the cured samples on mechanical properties, tensile strength tests were performed. The introduction of HTPDMS into the epoxy altered the tensile behavior according to its viscosity and content. Surface properties of the cured films were evaluated by sessile drop method. The results clearly indicate that the hydrophilic surface of the epoxy turns to a hydrophobic one due to the modification with HTPDMS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Enzymatic synthesis of silicone fluorinated aliphatic polyesteramides

The enzymatic synthesis of silicone fluorinated aliphatic polyesteramides (SFAPEAs) is reported. These materials were synthesized by incorporating both the fluorinated aliphatic segments and the dimethylsiloxane segments into the same linear chain backbone. Immobilized lipase B from Candida antarctica (Novozym-435) was used to catalyze the reactions to prepare fluorosilicones containing both amide and ester linkages. Simultaneous reactions of an amidation between α,ω-aminopropyl terminated poly(dimethylsiloxane) (APDMS) and diethyl adipate (DEA) and a transesterification between diethyl adipate and four different fluorinated alkanediols (FADs), respectively were conducted. The condensation reactions were carried out in the bulk, in the temperature range 70-90 °C and under reduced pressure (50 mmHg vacuum gauge). The molar masses of the synthesized fluorosilicones were determined by GPC analysis. The effect of the chain length of the FADs on the molar mass build up of the respective polymers was investigated. The highest molar mass fluorosilicones were obtained with the 3,3,4,4,5,5,6,6-octafluoro 1,8-octanediol (OFOD) monomer, which has an additional methylene (-CH₂-) spacer between the fluorocarbon chain (-CF₂-)_n and the hydroxyl end groups (-OH) when compared to the other three FAD monomers namely - 2,2,3,3-tetrafluoro 1,4-butanediol (TFBD), 2,2,3,3,4,4-hexafluoro 1,5-pentanediol (HFPD) and 2,2,3,3,4,4,5,5-octafluoro 1,6-hexanediol (OFHD). The formation of amide and ester linkages during the polymerization was confirmed by FTIR and ¹H NMR spectroscopy. A series of copolymers were synthesized by varying the feed ratios of FAD to APDMS. Fluorinated polyesters (FPEs) and silicone polyamides (SPAs) were also enzymatically synthesized under similar reaction conditions. The DSC analysis revealed that the fluorosilicones were semi-crystalline, principally due to the presence of the FPE segments. The FPEs were found to be white solids at room temperature. However, the SFAPEA’s were found to be viscous materials due to the presence of highly flexible silicone segments in the backbone chain. The crystallinity was seen to disappear completely for the SFAPEA’s with greater than 15 mol% of silicone content. The TGA analysis revealed that thermal degradation/depolymerization characteristics of the fluorosilicones improved with increased silicone content. We envisage that these new fluorosilicones have potential for a variety of low surface energy applications.     

Transport properties of organic vapours in silicone/clay nanocomposites

Poly(dimethylsiloxane) (PDMS)/clay nanocomposites have been synthesized using a novel ω-ammonium functionalized oligo-PDMS surfactant (PDMS-N⁺(CH₃)₃) and processed in membrane form. In order to relate the clay morphological structure to the degree of dispersion and physical properties of the membrane, the clay ion-exchanged by PDMS-N⁺(CH₃)₃ has been compared to a non-exchanged sodium MMT and to two organoclays organo-modified by using either non-functional alkyl ammonium cations (C₃₈H₈₀N⁺) or hydroxyalkyl ammonium (C₂₂H₄₈ON⁺) cations. Morphological analysis and transport properties (sorption, diffusion and permeability) have been investigated using two penetrants: acetone and n-hexane. The mechanical and rheological properties of the PDMS nanocomposite membranes have also been studied. It has been found a significant effect of the clay organo-modifier on the morphology, physical and barrier properties of the systems.     

膜蒸馏用PDMS/PVDF/PTFE三元共混微孔膜制备

采用浸没沉淀相转化法制备了聚二甲基硅氧烷/聚偏氟乙烯/聚四氟乙烯（PDMS/PVDF/PTFE）三元共混微孔膜,并用于20 g/L NaCl水溶液的膜蒸馏脱盐实验。通过扫描电子显微镜观察以及接触角、膜孔隙率和膜平均孔径分析,研究了PTFE含量对膜结构与性能的影响。结果表明,随着PTFE含量的增加,共混微孔膜断面的指状孔逐渐被海绵状取代,平均孔半径由0.234 μm增加到0.354 μm,膜孔隙率由53.4 %增加到81.3 %;膜下表面与水接触角从118.52 °增加到131.11 °;膜蒸馏过程中通量逐渐增加,截留率先稳定后降低,PTFE含量为40 %（质量分数,下同） 时达最大,为99.99 %,此时膜蒸馏通量达16.60 kg/(m2·h)。     

Dependence of interaction parameter on molecular weight and concentration for solutions of poly(dimethylsiloxane) in methylethylketone

The polymer-solvent interaction parameter x for solutions of poly(dimethylsiloxane) (PDMS) of different molecular weights (4600–220000) in methylethylketone (MEK) at segment fractions of PDMS ø2 ranging from 0.3 to 0.7 was measured by means of the vapour pressure method at 30°C, (20°C higher than the θ temperature for the PDMS-MEK system). The x values obtained experimentally were found to be almost independent of the molecular weight of PDMS. The observed x values were reproduced by applying Flory's new theory with evaluated values of three quantities: (1) the ratio of the surface area per segment for the polymer to that for the solvent $\text{s}{}_2\text{s}{}_1$; (2) the enthalpy exchange parameter X₁₂ and (3) the entropy exchange parameter Q₁₂.     

Manufacturing and characterizations of flexible poly(dimethylsiloxane)/poly(vinyl acetate)/polythiophene ternary composite films

ABSTRACT

In this study, polythiophene and poly(dimethylsiloxane)/poly(vinyl acetate)/polythiophene ternary composites were synthesized. The new ternary composites obtained in powder and film forms were characterized using various techniques. Magnetic properties of all the materials were analyzed by Gouy balance measurements, and it was found that their conductivity mechanism is of polaron nature. The surface structure, surface roughness, and thermal properties of the prepared samples were identified by Scanning Electron Microscopy, Atomic Force Microscopy, and Thermogravimetric Analysis, respectively. The tensile-tension test studies were performed for mechanical properties. The PDMS/PVAc/PT (6%) composite demonstrated about 50% of the maximum strain value (%) of vulcanized natural rubber.     

Effects of curing temperature on poly(ethylene terephthalate)

The effect on poly(ethylene terephthalate) (PET) of thermal curing in a particular temperature range (T max =280-350C) in air have been studied. The changes in the structure were monitored using various characterization techniques such as differential scanning calorimetry, thermogravimetric analysis, optical microscopy equiped with hot-stage, and scanning electron microscopy. It was observed that when (PET) is cured at very high temperature above its original melting point, cross-linking of the (PET) samples occurs. The cross-linking takes place in the melt in this case. With increasing the curing temperature, the area of the higher melting peak temperature decreases due to the increase in cross-linking of (PET). In terms of spherulitic texture, it was found that with increasing the curing temperature more inter-lamellar intra-spherulitic inclusions are observed in the material.