Polymer hybrids of functionalized silsesquioxanes and organic polymers utilizing the sol-gel reaction of tetramethoxysilane

The ternary polymer hybrids were prepared by organic polymers such as poly(2-methyl-2-oxazoline) (POZO) or poly(N-vinylpyrrolidone) (PVP) and aminopropylsilsesquioxane (Cube-aminopropyl) utilizing the sol-gel reaction of tetramethoxysilane (TMOS). The prepared polymer hybrids were characterized by IR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), ¹H NMR, scanning electron microscopy (SEM), etc. In this hybrid system, hydrogen-bonding interactions played a critical role in the formation of the transparent polymer hybrids. Polymer hybrids using POZO showed high transparency and homogeneity in a wide range of the feed ratios of POZO to Cube-aminopropyl. On the other hand, in case of polymer hybrids using PVP, higher Cube-aminopropyl ratio brought about the phase separation, indicating the aggregation of the Cube-aminopropyl itself. The homogeneity of ternary polymer hybrids was found to be closely dependent on the difference between strength of hydrogen bonding interaction of polymer and residual silanol groups of silica gel and strength of that of polymer and Cube-aminopropyl. It is also observed that initial decomposition temperature of polymer hybrids was increased with increasing the Cube-aminopropyl ratio.     

Photochromic organic-inorganic polymer hybrids from spiropyran-modified poly(N,N-dimethylacrylamide)

Summary Photochromic organic-inorganic polymer hybrids were prepared by the sol-gel reaction of tetramethoxysilane (TMOS) in the presence of spiropyran-modified poly(N,N-dimethylacrylamide) 3. The obtained polymer hybrids were characterized by thermogravimetric analysis (TGA) and FT-IR, and photochromic behavior was followed by electronic absorption spectroscopy. Upon an irradiation of ultraviolet light, an absorption around 557 nm appeared in the visible region and the color of the hybrid turned to be violet. The effect of silica gel on the isomerization behavior seemed to be relatively small. Received: 8 November 1999/Revised version: 13 December 1999/Accepted: 15 December 1999     

Formation of IPN organic-inorganic polymer hybrids utilizing the photodimerization of thymine

Summary Formation of an interpenetrating polymer network (IPN) composed of organic polymer gel and silica gel in the form of polymer hybrids was conducted by utilizing the photodimerization of thymine bases. Thymine-modified poly(2-methyl-2-oxazoline) (POZO-T) was synthesized by the condensation reaction of partially hydrolyzed polyoxazoline and 1-(2-carboxyethyl)thymine. Organic-inorganic polymer hybrids were prepared from POZO-T and tetramethoxysilane (TMOS). Transparent and homogeneous polymer hybrids could be obtained. The photodimerization and the reverse reaction of thymine in the polymer hybrids were monitored by the UV absorption spectroscopy. Received: 27 March 2000/Revised version: 5 June 2000/Accepted: 15 June 2000     

Synthesis of cellulose/silica gel polymer hybrids via in-situ hydrolysis method

Homogeneous cellulose/silica gel polymer hybrids were prepared by hydrolysis of acetyl cellulose (AcCL) in a sol–gel reaction mixture of alkoxysilane such as tetramethoxysilane (TMOS). To a mixture of AcCL and TMOS in a mixed solvent of THF and methanol (v/v, 7/3), an HCl aqueous solution was added to initiate hydrolysis and condensation of the alkoxysilane. The resulting mixture was constantly stirred for 5 h and heated at 60 °C for two weeks to allow evaporation of the solvents. Consequently, corresponding transparent and homogeneous polymer hybrids could be obtained in a range of mass ratios (AcCL/TMOS = 1/5–1/2). In the FT-IR spectra, the absorption peaks corresponding to the acetyl group decreased as the amount of 0.1 M aqueous HCl solution increased, which indicates hydrolysis of acetyl groups of AcCL, whereas the intensity of the Si–O-Si stretching vibration peak increased. The thermal properties of the obtained polymer hybrids were evaluated by TG/DTA and DSC measurements.     

SiO2溶胶在微滴乳液聚合中的原位纳米复合

本文提出将正硅酸乙酯(TEOS)的非水sol-gel反应与单体的微滴乳液聚合技术相结合,制备聚丙烯酸酯/二氧化硅纳米复合乳液。首先采用凝胶时间的测定与动态光散射等手段研究TEOS在甲酸催化下的非水sol-gel反应动力学,表明当甲酸/TEOS的摩尔比大于6,有利于形成颗粒状纳米二氧化硅溶胶。以硅烷偶联剂KH-570对非水溶胶原位改性,然后引入丙烯酸酯共聚单体中,研究硅溶胶的存在对单体微滴乳液聚合的影响。结果表明,聚合动力学与单体的微滴乳液聚合基本相似,但二氧化硅的引入改变了单体微滴的均一性和剪切分散的稳定性,导致乳胶粒径逐渐增大,粒径分布变宽。复合乳胶粒是若干无机粒子以微相区被包覆于有机聚合物中的纳米复合结构形态。     

In situ sol‐gel process of polystyrene/silica hybrid materials: Effect of silane‐coupling agents

The polystyrene–silica hybrid materials have been successfully prepared from styrene and tetraethoxysilane in the presence of silane‐coupling agents by an in situ sol‐gel process. Triethoxysilyl group can be incorporated into polystyrene as side chains by the free‐radical copolymerization of polystyrene with silane‐coupling agents, and simultaneously polystyrene–silica hybrid materials with covalent bonds between two phases were formed via the sol‐gel reaction. The 3‐(trimethoxysilyl)‐propyl‐methacrylate (MPS) systems were found to be more homogeneous than the corresponding allytrimethoxysilane hybrid system of equal molar content. In the MPS‐introduced system, the thermal properties of the materials were greatly affected by the presence of MPS. FTIR results indicate successful formation of the silica networks and covalent bonding formation of coupling agents with styrene. The homogeneity of polystyrene–silica systems was examined by scanning electron microscope and atomic force microscope. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2074–2083, 2002     

Synthesis of composite eccentric double-shelled hollow spheres

Eccentric double-shelled hollow polyethylacrylate (PEA)/polystyrene (PS) crosslinked composite spheres were synthesized by phase separation during swelling polymerization of their mother polymer hollow spheres. The group -NH₂ was introduced within the network by ammonization of PEA. Other materials for example silica could be favorably grown within the gel network by a sol-gel process. The polymer/silica hollow spheres gave the corresponding derivative hollow spheres with varied composition including SiO₂/carbon, carbon and β-SiC, with the eccentric double-shelled morphology retained.     

Organic–inorganic hybrid materials. II. Chain mobility and stability of polysiloxaneimide–silica hybrids

Polysiloxaneimide–silica hybrid materials (PSI‐SiO₂) were obtained using the sol–gel technique by polycondensation of tetramethoxysilane (TMOS) in a polyamic acid solution. IR, ²⁹Si‐ and ¹³C‐NMR spectroscopy, and thermogravimetric analysis were used to study hybrids containing various proportions of TMOS and hydrolysis ratios. The morphology, dynamics, and thermal stability of the hybrids were investigated. The chain mobility of the hybrids was investigated by spin–spin relaxation time (T₂) measurements. The apparent activation energy (E_a) for degradation of the hybrids in air was studied by the van Krevelen method. The T₂ value was independent of the silica content whereas that of the E_a decreased as silica content increased. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 965–973, 2001     

溶胶-凝胶法固定化Candida sp.99-125脂肪酶

利用正硅酸甲酯(TMOS)和丙基三甲氧基硅烷(PTMS)为复合硅源,以PEG(MW=20000)为稳定剂,以HCl为催化剂,经过溶胶-凝胶过程包埋假丝酵母99-125脂肪酶. 研究得到最适的固定化条件为：PTMS与TMOS的摩尔比4: 1, R值(水与硅源的摩尔比)20, 给酶量(酶占硅源的质量百分数)3.71%, PEG与酶的质量比(1~1.5):1, 硅源水解时间35 min. 在该条件下,固定化脂肪酶的最高酯化活力是游离酶最高酯化活力的2.02倍. 固定化脂肪酶在100℃保温2 h后酶活仍维持为59.1%,固定化酶催化特定酯化反应,经过8批连续反应96 h后酶活维持不变.     

Highly crosslinked nanocomposites of aromatic dicyanates/SiO2 via the sol–gel method

Highly crosslinked nanocomposites of bisphenol A dicyanate (BADCy) containing silica clusters were successfully prepared via the sol–gel process. The silica clusters were generated from various metal alkoxide precursors, including methyltrimethoxysilane (TMOS), 3‐glycidoxypropyltrimethoxysilane (GPOS), and 2‐(3,4‐epoxycyclohexyl) ethyltrimethoxysilane (ECOS). The metal alkoxide precursors GPOS and ECOS were, in turn, used as coupling agents. Three kinds of systems involving BADCy/TMOS, BADCy/coupling agent, and BADCy/TMOS/coupling agent were individually prepared and thoroughly investigated using various methods. Each kind of system was of a particular characterization and morphology and had distinct physical and dielectric properties. Isolated silica clusters on a nanoscale were homogenously distributed in the highly crosslinked BADCy/TMOS hybrid system. The characterization of BADCy/TMOS nanocomposites showed improved physical properties, when compared with the neat BADCy network. The particle sizes can be controlled by adding different amounts of TMOS and are slightly increased (in the range of 50–105 nm) with increasing TMOS content. On the other hand, in the highly crosslinked BADCy/coupling agent hybrid system, the silica clusters were tethered to the BADCy matrix by the coupling agent. An oxazoline linkage was detected during the reaction of cyanate groups in BADCy with the epoxide groups in the coupling agent. These nanocomposites exhibited weakened mechanical properties but are of a smaller and more homogenous particle size in the range of 30–50 nm, irrespective of the silica content. Finally, the BADCy/TMOS/coupling agent system was successfully designed to combine the advantages of the two systems mentioned above. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1356–1366, 2007     

Direct synthesis of polymer-grafted inorganic hybrids via reversible chain transfer catalyzed polymerization

In this work, a new simple and robust method for preparation of polymer-grafted inorganic hybrids through “grafting to” reaction is presented. Polymer chains were synthesized by reversible chain transfer catalyzed polymerization (RTCP) are capped with iodine according to the RTCP mechanism. The obtained iodine-capped polymer chains can react irreversibly with the hydroxyl groups available on the surface of inorganic materials through a nucleophilic substitution (SN) reaction. In this method, there is no need to modify the surface of inorganic materials or to functionalize polymer chains prior to the “grafting to” reaction. RTCP produced polystyrenes with different molecular weights, e.g., 4,000, 6,000, and 8,000 g/mol, and silica nanoparticles were employed as the polymer and inorganic materials, respectively. The resulting hybrids were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, and transmission electron microscopy techniques. According to the results, graft density decreased by increasing the polystyrene molecular weight. Additionally, the rheological studies of prepared polystyrene nanocomposites containing 2 wt % of the produced hybrids confirmed the better dispersion of the modified hybrids in the polystyrene matrix. The glass transition temperature (T _g) of the polystyrene nanocomposites was driven by differential scanning calorimeter technique. Analysis of nanocomposites’ T _g results revealed that increment of the grafted polymer molecular weight of hybrids increased the glass transition temperature of the prepared nanocomposites due to improvement of the dispersion level.     

Synthesis and physicochemical characterization of silica aerogels by rapid seed growth method

Thanks to the high optical transparency and ultra-low thermal conductivity, silica aerogels are ideal materials for energy-saving windows. However, their preparation is commonly based on either one-step base-catalyzed method, or two-step acid-base catalyzed method, which is difficult to inhibit the aggregation of clusters while keeping the size of clusters as small as possible and thus degrading silica aerogel's properties. Here, a new idea for synthesizing silica aerogels is presented from the viewpoint of controlling the growth and aggregation of silica clusters. A certain amount of Tetramethoxysilane (TMOS) used as seed precursor is firstly added into the mixture of methanol and distilled water for hydrolysis. A certain time later, the additional TMOS and a defined amount of ammonia are added to the obtained sol for promoting the rapid formation of the gel in several minutes. The silica aerogels prepared by this method have higher optical transparency and lower thermal conductivity than those prepared by the other two methods. This approach may also shed substantial light on controlling the microstructure of other materials prepared by sol-gel process.     

Fine-tuning of phase behavior of oxazoline copolymer-based organic–inorganic hybrids as solid-supported sol–gel materials

Silica-supported organic–inorganic polymer hybrids were synthesized via in situ sol–gel condensation of silica monomer in the presence of oxazoline copolymer. A stable copolymer of 2-ethyl-2-oxaoline and 2-isopropyl-2-oxazoline was prepared using methyl p-tosylate as the living polymerization initiator with molecular mass of 4200 g mol⁻¹. Lower critical solution temperature (LCST) of this copolymer was thermally found to be at 77 °C. The copolymer was mixed with tetramethoxysilane (TMOS) in different amounts (0.039:1 to 0.158:1 weight ratios) via in situ sol–gel condensation to produce organic–inorganic hybrids including thermosensitive copolymer. Tuning of these solid-supported materials showed sharp phase transitions changes in a temperature range from 42 to 58 °C, which was confirmed using differential scanning calorimetry. Enthalpy of the phase transition was also calculated using the area above the endothermic peak. A typical concave curve was obtained for LCST-type phase diagram suggesting the dependence of phase transition temperature on the concentration of the copolymer in the hybrid. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48163.     

A comparative study on effects of two kinds of polymerization methods on grafting of polymer onto silica surface

In this article we present the result of a comparative study of two kinds of polymerization methods—solution polymerization (sol. poly.) and dispersion polymerization (dis. poly.) for grafting polymer onto silica. As a model for the grafting polymerization reaction, styrene was chosen as the monomer and azo diisobutyronitrile (AIBN) as the initiator. The study aims at supplying theoretical reference for better selecting polymerization method to graft polymer on the silica particle surface. First, monolayers of 3‐methacryloylpropyl trimethoxysilane were chemically bonded onto the surfaces of micrometer‐sized silica gel particles, and so double bonds were immobilized onto the silica surface. Second, the copolymerizations between the immobilized double bonds and the monomer styrene were carried out, homopolymerizations of styrene followed, and finally polystyrene was grafted to the silica surfaces. Two kinds of polymerization methods, sol. poly. and dis. poly., were adopted respectively, and the effects of polymerization methods on grafting process were examined mainly. At the same time, the effects of different polymerization conditions on the grafting degree were researched. It was found that in the dis. poly. system the grafting degree is obviously higher than that in the sol. poly. system under the same polymerization conditions, and the grafting degree can go up to 47%, i.e. 47g/100g. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5808–5817, 2006     

Reinforcing effect of silica on the properties of styrene butadiene rubber–reclaim rubber blend system

Incorporation of silica into styrene butadiene rubber (SBR)–reclaim rubber (RR) blend system was carried out by sol–gel technique and conventional method. A well known silica coupling agent bis(3‐triethoxysilyl propyl) tetrasulfide was found to affect the curing characteristics and mechanical properties of SBR/RR vulcanizate. Here, the effect of RR on silica reinforcement was studied for different SBR/RR blend system. Silica incorporation by conventional mechanical mixing in absence of TESPT showed a much higher tensile properties than that of silica incorporated by the in situ sol–gel reaction of tetraethoxy silane both in presence and absence of TESPT. Studies of equilibrium swelling in a hydrocarbon solvent were also carried out. ATR study indicates that RR forms bond with silica particles due to the presence of active functional site on RR. The amount of silica incorporated by sol–gel reaction was determined through thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) studies further indicate the coherency and homogeneity in the silica filled SBR/RR vulcanizate. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 957–968, 2006     

Corrosion behavior of aluminum/silica/polystyrene nanostructured hybrid flakes

The corrosion protection of aluminum flake pigments has been extended by means of an encapsulating inorganic/organic silica/polystyrene hybrid nanolayer. A silica nanolayer encapsulated the surface of aluminum flakes (Al) by hydrolysis and polycondensation of tetraethylorthosilicate via sol–gel process to yield Al/Si flakes. Then, 3-methacryloxypropyltrimethoxysilane (MPS) was used as surface modifier which has polymerizable groups to participate in polymerization reaction (Al/Si/MPS). A polystyrene (PS) coating layer was applied on Al/Si/MPS flakes by free radical polymerization of styrene initiating with Azobisisobutyronitrile at 60 °C and subsequent washing of free chains with solvent yielded Al/Si/PS flakes. Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy showed that silica and PS nanolayers were formed on the aluminum flakes. The attached PS chains on the surface were detached by hydrofluoric acid aqueous solution and analyzed by gel permeation chromatography (GPC). Also, a transmission electron microscopy image showed clearly that the encapsulating layers are in the scale of nano. Good results were obtained in terms of corrosion protection in acidic and alkaline solutions, indicating that the silica/polymer hybrid nanolayer coating acts as an efficient protective film. After encapsulating the flakes, the evolved hydrogen volume was dropped and hybrid nanolayer resulted in no evolved hydrogen volume.     

Synthesis of geranyl acetate by esterification with lipase entrapped in hybrid sol-gel formed within nonwoven fabric

Candida cylindracea lipase was entrapped in organic-inorganic hybrid sol-gel polymers made from tetramethoxysilane (TMOS) and alkyltrimethoxysilanes. By forming the gels within the pores of a nonwoven polyester fabric, a novel immobilized biocatalyst in sheet configuration based on sol-gel en-trapment of the enzyme was obtained. Lipases immobilized in sol-gel matrices efficiently catalyzed the direct esterification reaction of geraniol and acetic acid in anhydrous hexane to produce geranyl acetate. The optimal formulation of the sol-gel solution for enzyme immobilization was at a 20∶1 molar ratio of water to total silane; a 4∶1 molar ratio of propyltrimethoxysilane to TMOS; hydrolysis time at 30 min; and enzyme loading of 200 mg lipase/g gel. Under these conditions, protein immobilization efficiency was 91%, and the specific activity of the immobilized enzyme was 2.6 times that of the free enzyme. Excellent thermal stability was found for the immobilized enzyme in dry form or in hexane solution in the presence of acetic acid, in which case severe inactivation of free enzyme was observed. The immobilized enzyme retained its activity after heating at 70°C for 2 h, whereas the free enzyme lost 80% of its activity.     

Synthesis of novel organoboron polymers by haloboration polymerization of bisallene compounds and their reactions

Summary. Novel organoboron polymers were prepared by haloboration polymerization of bisallene compounds. The polymers obtained have allylborane halide units in their main chain and can be expected as a novel type of reactive polymers. For example, the polymer prepared by haloboration polymerization between tribromoborane (1) and 1,2,10,11-dodecatetraene (2 b) was subjected to chain transformation reaction (dichloromethyl methyl ether rearrangement) to give the corresponding polyalcohol or polyketone. Haloboration-phenylboration polymerization of aliphatic bisallenes by using diphenylbromoborane also gave the corresponding polymers. Received: 8 July 1997/Revised: 23 July 1997/Accepted: 28 July 1997     

Enhancing the fraction of grafted polystyrene on silica hybrid nanoparticles

Polymer-grafted inorganic nanoparticles are being developed for a diverse array of applications, ranging from drug delivery to multifunctional composites. In many instances, performance of these core-shell hybrids is limited by relatively broad distributions of size and composition, as well as the presence of impurities, such as unattached polymer chains. Herein, further synthetic improvements, and associated characterization techniques, to enhance the fraction of the grafted polystyrene shell on silica hybrid nanoparticles are discussed. We found that during surface-initiated atom transfer radical polymerization (SI-ATRP) from the silica nanoparticles, thermal self-initiation of styrene produces unattached polymer chains. Size exclusion chromatography afforded a facile approach to quantify the mass of the unattached polymer, and provide a substantial refinement to estimates of chain graft density beyond traditionally-used approaches, such as thermogravimetry. This fraction of unattached polymer is still present even after post-polymerization work-up via precipitation and re-dissolution. Removal necessitates additional procedures, such as high speed centrifugation. Selection of a lower polymerization temperature, in concert with a more reactive Cu complex, significantly reduces the amount of unattached polystyrene impurity. The improved polymerization conditions and post-polymerization purification provide more refined polystyrene-grafted silica nanoparticles to clarify structure-property relationships of these core-shell hybrids.     

Cryostructuring of polymer systems. XXVI. Heterophase organic–inorganic cryogels prepared via freezing–thawing of aqueous solutions of poly(vinyl alcohol) with added tetramethoxysilane

Composite heterophase organic–inorganic hybrid cryogels of poly(vinyl alcohol) (PVA) containing silica constituents were prepared and studied. Such constituents were formed in the course of hydrolytic polycondensation (sol‐gel process) of tetramethoxysilane (TMOS) introduced in to the aqueous polymer solution prior to its freeze–thaw treatment. It was shown that moderate (over the range of ?15 to ?30°C) freezing, then frozen storage, and subsequent thawing of the water/PVA/TMOS systems resulted in the formation of macroporous composite cryogels filled with dispersed silica particles (discrete phase). The continuous phase of such gel materials represents the supramolecular PVA network, which is supposed to be additionally cured with the silicon‐containing oligomeric cross agents formed from TMOS in the course of hydrolytic polycondensation. The incorporated silica components influenced the morphology of cryogels. The effects of significant increase in gel strength and heat resistance with increasing TMOS concentration in the initial feed and with thawing rate decreasing have also been observed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007