Effects of organic groups on structure and viscoelastic properties of organic-inorganic polysiloxane hybrid system

The structure and viscoelastic properties of an organic-inorganic hybrid system composed of an organically modified polysiloxane network were examined, and the influence of organic groups on elastic-modulus variation by heat treatment was studied. The increase in the number of phenyl (Ph) groups per silicon decelerates the increase in elastic modulus; the substitution of the Ph group for a methyl (Me) group accelerates it. The system basically consists of R4-mSi[O-]m/2 units, where R is the organic group. The 29Si magic-angle spinning (MAS) NMR and gel permeation chromatography (GPC) measurements classified the structure related with the viscoelastic behavior into two factors: the number of bridging oxygens and the distribution of molecular weight. The elastic modulus was expressed by these structural factors through a simple empirical formula, irrespective of the type and number of the organic groups. The effects of the organic groups on the variation in elastic modulus by heat treatment were found to work mostly only through the molecular-weight change, and such effects can be controlled by the type or the number of organic groups.     

Ambient-curable polysiloxane coatings: structure and mechanical properties

Ambient-curable polysiloxane coatings were prepared by hydrolysis and condensation of 3-methacryloxypropylmethyldimethoxysilane (MPDS) and methyltriethoxysilane (MTES) and subsequently mixing with 3-aminopropyltriethoxysilane (APS). The structures of the as-obtained polysiloxane oligomers as well as the dried polysiloxane coatings on tinplate substrates were analyzed by FTIR and ²⁹Si NMR. The mechanical properties of the coatings were thoroughly examined at both macro-level and micro-level using a pendulum hardness rocker, an impact tester, and a nanoindentation/nanoscratch instrument. Effects of the molar ratio of MPDS/MTES, the dosage of aqueous ammonia solution, and the catalytic condition on the structure of polysiloxane oligomers as well as the structure and mechanical properties of the polysiloxane coatings were investigated. The dried coatings with thickness of 15–26 μm are highly elastic. The hardness (Koenig hardness and microhardness), impact resistance and scratch resistance are mainly dependent on the condensation degree of polysiloxane coatings rather than on the organic component of the coatings. A proper pre-hydrolysis process or more APS is benefit for enhancing the mechanical strength of the polysiloxane coatings. Polysiloxane coatings with high hardness and excellent scratch resistance can be prepared preferentially at low molar ratio of MPDS/MTES.     

Viscoelastic dynamic properties of heterogeneous polymer networks with domain structure

A dynamic model of a heterogeneous polymer network system is proposed. A polymer network is presented as an ensemble of cross‐linked regions (domains) of different sizes, the domains have similarly regular internal structures. To a first approximation, these domains are treated independently of each other. Relaxation modulus, storage modulus, and loss modulus of the heterogeneous polymer network are calculated. For the purpose of averaging over all network domains the exponential number distribution of chain segments in domains is used. This type of distribution has been previously proposed by one of the authors in the frame of the aggregation model. It is shown that a structure heterogeneity introduced into a network model according to the above domain approach leads, at long times, to the stretched exponential type of time dependence of relaxation modulus instead of the power‐law dependence predicted by the theories dealing with regular networks. The network heterogeneity also leads to a more rapid decrease in the storage modulus in the region of low frequencies, as compared with regular polymer networks. It is shown that the loss modulus in the region of its maximum is very slightly sensitive to the “long‐range” network heterogeneity considered.     

Heat capacities of a networked system of single-molecule magnet with three-dimensional structure

A magnetic-fields dependence of heat capacity of [Mn₅(hmp)₄(OH)₂{N(CN)₂}₆]2MeCN·2THF (hmp=hydroxymethylpyridinate) is investigated by the thermal relaxation calorimetry technique. This compound is a three-dimensional system consisting of Mn₄ single-molecule magnet (SMM) units and Mn²⁺ ions, which are linked by the dicyanamide ligands to form a coordination network structure. A sharp peak of C _p being associated with the formation of three-dimensional long-range order is observed around 1.96 K. The thermodynamic discussion based on the magnetic entropy suggests that both SMMs and Mn²⁺ ions are involved in the formation of the anitiferromagnetic spin ordering. However, this long-range ordering is very sensitive to the external magnetic fields which work to change the magnitude of the Zeeman splitting of the SMM levels. The behavior under magnetic fields is similar to that of the two-dimensional Mn₄-network system studied previously.     

Synthesis, structure and luminescent properties of yttrium benzene dicarboxylates with one- and three-dimensional structure

The synthesis and structure of two yttrium benzene dicarboxylates, 1 is proportional to [[Y2(C12N2H8)2(C8H4O4)3].H2O], I and 3 is proportional to [[Y2(C12N2H8)2(C8H4O4)3]], II with one- and three-dimensional structure has been accomplished employing hydrothermal methods in the presence of 1,10-phenanthroline. While I is formed with phthalic aid (1,2-BDC), II is formed using isophthalic acid (1,3-BDC). Both the structures appear to have comparable building units, an eight-membered ring and a paddle-wheel arrangement, connected through the carboxylic acid. The 1,10-phenanthroline, connected to Y as a secondary ligand, occupies the inter-chain spaces in I, and projects into the channels in II. The channels in II are inter-connected. Photoluminescence studies indicate that both I and II exhibit a bathochromic shift with respect to the acids (1,2-BDC and 1,3-BDC) and a hypsochromic shift with respect to 1,10-phenanthroline. Both the compounds exhibit reasonable pi...pi interactions.     

Synthesis and surface structural characteristics of new polysiloxane xerogel

Pyridylethylaminopropylpolysiloxane xerogel (PEAPPSX) was synthesized by sol-gel technology. The composition of the substance was determined via elemental analysis and 1H NMR spectroscopy. The surface structural characteristics of the xerogel were determined by electron microscopy and low-temperature nitrogen sorption; thermal analysis was also performed. It was established that the content of functional groups in PEAPPSX was 2.43 mmol/g, and that xerogel is a mesoporous substance with a developed surface (121.71 m²/g).     

侧链可降解聚硅氧烷的合成及其膜性能

以乳酸和聚乙二醇为原料,直接缩聚法制备出聚乳酸-聚乙二醇可降解嵌段共聚物,再将烯丙基缩水甘油醚和所得的嵌段共聚物在锌粉的作用下得到带有α烯基反应性官能团的大分子单体,然后在铂催化剂的作用下,合成了一种带有可降解侧链的亲水性聚硅氧烷(PDMS-g-PLA-PEG).对产物的结构、相对分子质量及其分布、热性能及成膜的表面性能等进行了研究.结果表明,由于分子链中硅氢键分布的不均匀性和聚乳酸-聚乙二醇共聚物分子量分布的不均一性,产物的分子量分布相对较宽,达到了1.87.由于聚乳酸-聚乙二醇共聚物侧链逐渐降解,所以PDMS-g-PLA-PEG所成的膜与水的接触角将随着时间的延长而逐渐增大,30天后从42°增至92°.     

Synthesis and physicochemical properties of polysiloxane functionalized with aminoacetic acid groups

Polysiloxane functionalized with aminoacetic acid groups was synthesized using sol–gel technology. Elemental analysis and FTIR spectroscopy were used to determine the composition of the polysiloxane show that it is a mesoporous material with a developed surface (109.4 m2/g). It was found that the selective properties of carboxymethylated polysiloxane towards transition metal ions simultaneously present in an ammonium acetate solution change in the order Zn < Cu > Ni > Co > Pb > Cd. It was shown that the sorption of copper(II) ions by carboxymethylated aminopropylpolysiloxane with particle sizes of 50–71 μm reaches its maximum level within 2 h; the rate-limiting step of the process is the chemical reaction between the ions and the polysiloxane functional groups; and the pseudo-second-order model is the best way of describing sorption.     

Viscoelastic properties of polystyrene

An extension of the results of a previous to higher molecular weights is made. The viscoelastic parameters η_t, J_e, τ_m, and E_m are found experimentally through stress relaxation tests. The predictions of the Rouse-Bueche (RB) theory and its modified Ferry, Landel, Williams (FLW) form concerning the molecular weight dependencies of these perameters are compared with the data. It is found that the RB and FLW predictions are not rigorously obeyed.     

聚苯基硅氧烷/聚丙烯酸酯复合乳液的合成与性能

本文以二苯基二甲氧基硅烷(DPDMS)和γ-甲基丙烯酰氧基丙基三甲氧基硅烷(MAPTMS)合成了具有微交联结构的聚硅氧烷乳液,并以此为种子乳液再与丙烯酸酯类单体聚合,合成了稳定且性能优良的聚硅氧烷/聚丙烯酸酯复合乳液.用激光粒度分析仪、FTIR、DMA等进行了表征.结果表明,硅氧烷被有效的接枝到了聚丙烯酸酯分子链中;硅氧烷的加入,使聚合物的储能模量,损耗模量增大,玻璃化温度提高,加入量为10％时,Tg由50.5℃升高到57.2℃;加入20％的硅氧烷涂膜吸水率由13.8％降低到6.8％.     

Deactivation of silica surfaces with a silanol-terminated polysiloxane; structural sharacterization by inverse gas chromatography and solid-state NMR

Retention gape deactivated with Silicone OV-1701-OH show good chromatographic performance and remarkable stability against water induced stationary phase degradrdation. In an attempt to better understand the findamentals off the deactivation process using silanol terminated polysiloxanes, a fumed silica was deactivated with Silicon OV-1701-OH. In contrast to fused silic capillaries, fumed silica (Aerosil A-200) can be studied by ²⁹Si cross-polarization magic-angle-spinning (CPMAS) NMR, thus serving as a model substrate for fused silica. Retention data from inverse gas chromatography at infinite dilurion and ²⁹Si CP MAS NMR data of five Aerosil phases, differing in residual silanol surface concentration, are correlated with the aim of validating this approach for stationary phase characterization. A comparatively detailed model of the deactivating polymer layer that explains the observed absorption activities is deduced. Surface silanols are shown to play a key role in the polymer layer, the structure of which is of primary importance for the absorption behavior after deactivation. Contrary to common belief, the absolute silanol surface concentration after deativation is only of secondary importance for the overall absorption activity. High silanol surface concentrations enhance degradation of the polysiloxane chains into small cyclic fragments as well as subsequent absorption and immobolization to the silica substrate surface. The mobility of linear polysiloxane chains in the kHz regime (as determined bby NMR cross-polarization dynamics) appears to determine the extent which the residual silanols are accessible for analytes. It is therefore anticipated that there is an optimum silanol surface concentration of fused silica surfaces to be deactivated with silanol terminated polysiloxanes; it should be lazrge enough to adsord polymer fragments, but not large to avoid excessive residual silanol activity.     

Viscoelastic properties of microlatex dispersions

The viscoelastic properties of concentrated microlatex dispersions were investigated using oscillatory measurements. The latices were prepared by polymerisation of styrene-in-water microemulsions using UV and azobiisobutyronitrile initiator. The complex modulus, G*, storage modulus, G′ and loss modulus, G″ were measured as a function of strain amplitude (to obtain the linear viscoelastic region) and frequency at various latex volume fractions. Two latices with radii of 3.9 and 15.1 nm were investigated at 20°C. The results showed a change from predominantly viscous to a predominantly elastic response at a critical volume fraction, φ_c With the smaller latex, the concentration of the free surfactant in bulk solution was relatively low (2.6%) and the dispersions remained stable. φ_c was found to be 0.161. Assuming random packing of the particles (volume fraction=0.64), an estimate was obtained for the adsorbed layer thickness and this was found to be 1.4 nm, which is small for a surfactant chain with 15 ethylene oxide units. However, since the surfactant layer is a mixture of chains with 4 and 15 EO units, it is likely that the larger PEO chains will undergo interpenetration and/or compression on close approach of the particles. With the larger latex, on the other hand, there was high free surfactant concentration (9.1%) and this led to depletion flocculation. This results in a lower φ_c than would be the case in the absence of flocculation.     

Synthesis and surface properties of polyurethane modified by polysiloxane

A series of polyurethanes modified by polysiloxane (Si-PU) were synthesized based on 2,4-toluene diisocyanate (TDI), dihydroxybutyl-terminated polydimethylsiloxane (DHPDMS), polytetramethylene glycol (PTMG) and 1,4-butanediol (BDO). Fourier transform infrared spectroscopy analysis showed that DHPDMS had been incorporated into the polyurethane chains. With the increase of DHPDMS content, the water contact angle increased while the surface tension decreased. As the DHPDMS content increases above 5%, both the contact angle and the surface tension tend to approach a constant. The contact angle increases with increasing temperature, and it tends to approach a constant when the temperature is higher than 50°C. The result indicates that Si-PU exhibits good surface and mechanical properties when the DHPDMS content is 5%. __________ Translated from Polymer Materials Science and Engineering, 2007, 23(3): 47–50 [译自: 高分子科学与工程]     

Synthesis and properties of polysiloxane side chain cholesteric elastomers

The synthesis of new side chain cholesteric liquid crystalline elastomers containing the flexible non-mesomorphic crosslinking agent M-1 and the cholesteric monomer M-2 by a one-step hydrosilylation reaction is described. The chemical structures of the obtained monomers and network polymers were confirmed by ¹H NMR and FTIR spectroscopy. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. The glass transition temperatures and isotropic temperatures of the mesomorphic elastomers decreased as the concentration of crosslinking units increased; in the mesomorphic region the liquid crystalline elastomers showed elasticity, reversible phase transitions and Grandjean texture. The flexible crosslinking agent did not disturb the cholesteric structure; moreover, it was beneficial for adjusting the helix of the cholesteric liquid crystalline polymers, and cholesteric elastomers P-6, P-7, show reversible selective reflection of visible light.     

High hole mobility for a side-chain liquid-crystalline smectic polysiloxane exhibiting a nanosegregated structure with a terthiophene moiety

Side-chain liquid-crystalline siloxane polymers bearing terthiophene moieties as mesogenic pendant groups have been synthesized. An alkenylterthiophene derivative was treated with poly(hydrogenmethylsiloxane) and poly(dimethylsiloxane-co-hydrogenmethylsiloxane)s in Me(2)SiO/MeHSiO ratios of 1:1 and 7:3, respectively, in the presence of the Karstedt catalyst, to produce pale yellow polymers. The degrees of introduction of the mesogenic unit were 100, 50, and 30%, respectively. The polymers exhibit ordered smectic phases at room temperature. The copolymers with dimethylsiloxane units form smectic phases as a consequence of nanosegregation between the mesogenic units and siloxane backbones with the alkylene spacers. Time-of-flight measurement reveals that the hole mobility exceeds 1×10(-2) cm(2) V(-1) s(-1) in the ordered smectic phase of the copolymer with a degree introduction of the mesogenic units of 50%. This value is comparable to that of the highly ordered mesophases of low-molecular-weight derivatives of phenylnaphthalene and terthiophene. Because of the segregation behavior induced by the flexible backbone, a closer molecular packing structure favorable for fast carrier transport may be formed in the smectic phase of the copolymer in spite of the low density of the mesogenic groups.     

Synthesis of a hierarchical three-component nanocomposite structure system with enhanced electrocatalytic and photoelectrical properties

Effective control over the morphology and size of Pd/Pt nanoparticles is currently of immense interest because their electronic, optical, and catalytic properties are superior to pure platinum nanoparticles. However, control over the nanoparticle shape is still challenging. Therefore, a novel design and synthetic route needs to be developed to obtain a high-performance catalyst. Herein, a hierarchical three-component nanocomposite structure system (HTNSS) composed of graphene, TiO(2), and Pd@Pt core-shell nanoparticles was designed and synthesized by a sequential strategy that focuses on constructing the monolithic structure rather than limited single-component counterparts. The resulting composites were characterized by various techniques, which showed that the Pd@Pt core-shell nanoparticles were preferentially deposited on the peripheral interface of the graphene and TiO(2) nanoparticles. The photoelectrical and catalytic performances were obviously improved relative to the commercially available E-TEK Pt/C owing to their synergistic effect.     

Electrochemical synthesis, crystal structure, and photomagnetic properties of a three-dimensional cyano-bridged copper-molybdenum complex

A single crystal of Cs(I)2Cu(II)7[Mo(IV)CN8]4.6H2O was electrochemically prepared on a Pt wire electrode with a constant potential of +500 mV vs Ag/AgCl electrode. X-ray single-crystal structural analysis showed that this compound consists of a three-dimensional cyano-bridged Cu-Mo bimetallic assembly with a tetragonal structure of I4/mmm. The coordination geometry of Mo(IV) is bicapped trigonal prism, and that of Cu(II) is five-coordinate of square pyramidal or four-coordinate of square planar. This compound was also prepared as a 0.2-3.0 microm thick film on a SnO2-coated glass in the same electrochemical manner. When the sample, which shows paramagnetism due to Cu(II) (S = 1/2), was irradiated with 450-500 nm light at 5 K, spontaneous magnetization with a Curie temperature of 23 K was observed. This photoinduced change was recovered by a thermal treatment. In the infrared (IR) and electron spin resonance (ESR) spectra after light irradiation, variations in the stretching IR peak of CN bridged to Mo(IV) and the paramagnetic ESR peak of Cu(II) were observed, respectively. The data indicate that this photomagnetism is caused by the electron transfer from Mo(IV) to Cu(II) and the ferromagnetic ordering between Cu(II) (S = 1/2) and Mo(V) (S = 1/2).     

Viscoelastic properties of epoxy-diamine networks

Eight epoxy–diamine networks have been formed, diamines with 2 to 12 methylene groups being used as curing agents. Dynamic mechanical tests revealed four transition regions in the dynamic loss modulus/temperature relationship. Two possible explanations for the relaxation of the glycidyl portion of the structure are proposed. One of the relaxations could be due to the breakdown of hydrogen bonds through the hydroxyl and ether groups. The second could be ascribed to the relaxation of the unbonded glycidyl groups or a second relaxation of the glycidyl groups after the breakdown of the hydrogen bonds.     

Synthesis,structure, and magnetic properties of two new vanadocarboxylates with three-dimensional hybrid frameworks

(V(III)(OH))(2)[C(6)H(2)(CO(2))(4)].4H(2)O (labeled MIL-60) and V(III)(OH)[(2)(O(2)C)C(6)H(2)(COOH)(2)].H(2)O (labeled MIL-61) were hydrothermally synthesized from mixtures of VCl(3), 1,2,4,5-benzenetetracarboxylic acid, and water heated for 3 days at 473 K. The structure of MIL-60 was solved from single-crystal X-ray diffraction data in the triclinic centrosymmetric P1 (No. 2) space group with lattice parameters a = 6.3758(5) A, b = 6.8840(5) A, c = 9.0254(5) A, alpha = 69.010(2) degrees, beta = 85.197(2) degrees, gamma = 79.452(2) degrees, V = 363.53(5) A(3), and Z = 1. The structure of MIL-61 was ab initio determined from an X-ray powder diffraction pattern. MIL-61 crystallizes in the Pnma (No. 62) orthorhombic space group with lattice parameters a = 14.8860(1) A, b = 6.9164(1) A, c = 10.6669(2) A, V = 1098.23(3) A(3), and Z = 4. Both structures contain the same inorganic building block that consists of trans chains of V(III)O(4)(OH)(2) octahedra. The three-dimensional frameworks of MIL-60 and MIL-61 are constituted by the linkage of these chains via the organic molecules so delimiting the channels or cages where the water molecules are encapsulated. The magnetic behavior of these two phases is presented: MIL-60 is paramagnetic, and MIL-61 antiferromagnetically orders below T(N) = 55(5) K.