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1.
Sequential living cationic polymerization of octadecyl vinyl ether (ODVE) and methyl vinyl ether (MVE) was used for the preparation of amphiphilic ABA‐type block copolymers. The polymerization of ODVE was initiated with the trimethyl silyl iodide/1,1,3,3‐tetramethoxy propane/ZnI2 system at 0°C in toluene. The living bifunctional polyODVE thus obtained was used as initiator for the polymerization of MVE. Below the LCST of polyMVE (37°C), the copolymers are amphiphiles. Above the LCST of polyMVE, the polyMVE‐blocks become hydrophobic and the amphiphilic nature of the block copolymer is lost. This was demonstrated by using the block copolymers as emulsifiers for water/decane mixtures. The emulsions were stable for several hours at room temperature, while the emulsion stability decreased to about 30 seconds at 40°C. PolyMVE‐α,ω‐bis‐methacrylates were obtained by end‐capping of living bifunctional polyMVE with 2‐hydroxyethyl methacrylate (HEMA). Copolymerization of these bis‐macromers with HEMA leads to segmented networks. The networks showed a reversible swelling/deswelling behavior in water as a function of temperature. This is caused by a change of the hydrophilicity of the polyMVE segments in the networks. Hexa(chloromethyl)melamine, combined with zinc chloride was found to be an efficient hexafunctional initiator for the living cationic polymerization of vinyl ethers. This simple initiating system opens new ways for the synthesis of endgroup‐functionalized star‐shaped poly(vinyl ethers).  相似文献   

2.
Novel rubbery wound closures containing various proportions and molecular weights of polyisobutylene (PIB) and poly(2‐octyl cyanoacrylate) [P(OctCA)] for potential clinical use were designed, synthesized, characterized, and tested. Homo‐networks were prepared by crosslinking 3‐arm star‐shaped PIBs fitted with terminal cyanoacrylate groups, [Ø(PIB‐CA)3], and co‐networks by copolymerizing Ø(PIB‐CA)3 with OctCA using N‐dimethyl‐p‐toluidine (DMT). Neat Ø(PIB‐CA)3, and Ø(PIB‐CA)3/OctCA blends, upon contact with initiator, polymerize within seconds to optically transparent strong rubbery co‐networks, Ø(PIB‐CA)3co‐P(OctCA). Homo‐ and co‐network formation was demonstrated by sol/gel studies, and structures and properties were characterized by a battery of techniques. The Tg of P(OctCA) is 58 °C by DSC, and 75 °C by DMTA. Co‐networks comprising 25% Ø(PIB‐CA)3 (Mn = 2400 g/mol) and 75% P(OctCA) are stronger and more extensible than skin. Short and long term creep studies show co‐networks exhibit high dimensional stability and <6% creep strain at high loading. When deposited on porcine skin co‐networks yield hermetically‐adhering clear rubbery coatings. Strips of porcine skin coated with co‐networks could be stretched and twisted without compromising membrane integrity. The co‐network is nontoxic to L‐929 mouse fibroblasts. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1640–1651  相似文献   

3.
Segmented polymer networks containing poly(methyl vinyl ether) (PMVE) segments were prepared by free‐radical‐initiated copolymerization of PMVE‐α,ω‐dimethacrylate with styrene or 2‐hydroxyethyl methacrylate (HEMA). These networks were evaluated as thermo‐responsive solid‐phase extraction materials. Suspension‐derived polymer networks consisting of 80% of PMVE and 20% of HEMA adsorb toluene from an aqueous solution at 40°C and release the adsorbed toluene quantitatively at 20°C.  相似文献   

4.
Poly(acrylic acid)‐l‐polytetrahydrofuran (PAA‐l‐PTHF) and poly(methacrylic acid)‐l‐polytetrahydrofuran (PMAA‐l‐PTHF) networks were synthesized by the free‐radical copolymerization of hydrophobic polytetrahydrofuran diacrylates with hydrophilic acrylic acid and methacrylic acid. Their swelling behavior was studied. Both PAA‐l‐PTHF and PMAA‐l‐PTHF networks had four solubility parameters, which indicated that they exhibited not only the properties of both hydrophobic and hydrophilic segments but also the combined properties of these two segments. The swell of these two series of networks was composition‐dependent in organic solvents and water. The relationship between the equilibrium swelling ratio (SRe) in nonpolar solvents and the composition of the networks [the weight fraction of the PTHF segment (PTHF%)] may be expressed with a linear equation: SRe = A × PTHF% + B. A and B are parameters that relate to the interaction of hydrophilic and hydrophobic segments with nonpolar solvents and to the properties of the networks, respectively. Because of the presence of a ? COOH group, these two network series were pH‐sensitive when the content of hydrophilic segments was higher. The pH sensitivity of networks could be controlled not only by the composition of the networks but also by the hydrophobic degree of the hydrophilic segments. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1784–1790, 2001  相似文献   

5.
Group transfer polymerization was employed for the preparation of six amphiphilic terpolymer networks comprising the hydrophilic, pH‐responsive 2‐(dimethylamino)ethyl methacrylate (DMAEMA), the neutral hydrophilic methoxy hexa(ethylene glycol) methacrylate (HEGMA), and the hydrophobic n‐butyl methacrylate (BuMA). 1,4‐Bis(methoxytrimethylsiloxymethylene)cyclohexane was used as a bifunctional initiator, whereas ethylene glycol dimethacrylate served as the crosslinker to interconnect the linear terpolymer precursors to three‐dimensional terpolymer network structures. Five of the terpolymer networks were model, with linear chains between crosslinks of precise length. Four of the five model networks were based on ABCBA pentablock terpolymers with theoretical structure DMAEMA5b‐BuMAn/2b‐HEGMA10b‐BuMAn/2b‐DMAEMA5 with n values equal to 5, 10, 20, and 30. The model network based on the equimolar statistical terpolymer and the nonmodel randomly crosslinked terpolymer network were also prepared. The molecular weights and compositions of the linear pentablock terpolymer precursors to the networks were found to be close to the theoretically expected, while the network sol fractions were found to be relatively low. The degrees of swelling of the networks in water were found to decrease with increasing the hydrophobic content, whereas those in THF exhibited the opposite trend. Small‐angle neutron scattering in deuterium oxide indicated structural organization in the most hydrophobic pentablock terpolymer networks. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4420–4432, 2008  相似文献   

6.
Poly(N‐isopropylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N‐isopropylacrylamide) (PNIPAAm‐b‐PEO‐b‐PNIPAAm) triblock copolymer was synthesized via the reversible addition‐fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) process with xanthate‐terminated poly(ethylene oxide) (PEO) as the macromolecular chain transfer agent. The successful synthesis of the ABA triblock copolymer inspired the preparation of poly(N‐isopropylacrylamide)‐block‐poly(ethylene oxide) (PNIPAAm‐b‐PEO) copolymer networks with N,N′‐methylenebisacrylamide as the crosslinking agent with the similar approach. With the RAFT/MADIX process, PEO chains were successfully blocked into poly(N‐isopropylacrylamide) (PNIPAAm) networks. The unique architecture of PNIPAAm‐b‐PEO networks allows investigating the effect of the blocked PEO chains on the deswelling and reswelling behavior of PNIPAAm hydrogels. It was found that with the inclusion of PEO chains into the PNIPAAm networks as midblocks, the swelling ratios of the hydrogels were significantly enhanced. Furthermore, the PNIPAAm‐b‐PEO hydrogels displayed faster response to the external temperature changes than the control PNIPAAm hydrogel. The accelerated deswelling and reswelling behaviors have been interpreted based on the formation of PEO microdomains in the PNIPAAm networks, which could act as the hydrophilic tunnels to facilitate the diffusion of water molecules in the PNIPAAm networks. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012  相似文献   

7.
A series of supramolecular soft materials with hydrogen bonded transient networks was prepared by blending carboxy‐terminated telechelic poly(ethyl acrylate) (PEA‐(COOH)2) and polyethyleneimine (PEI). Effects of PEA‐(COOH)2 molecular weight (MPEA) and the blend ratio on the viscoelastic properties were investigated by rheological and small angle X‐ray scattering measurements. Rubbery plateau appeared by adding PEI due to network formation with ionic hydrogen bonded crosslinks between amines on PEI and carboxylic acids on PEA‐(COOH)2. The highest temperature of a storage modulus‐loss modulus crossover as well as the highest flow activation energy was attained at a certain mole ratio of amines to carboxylic acids, irrelevant to MPEA, indicating optimized supramolecular networks were achieved by stoichiometric balance of two functional groups. Since telechelic PEA‐(COOH)2 serves as a network strand, the plateau modulus was inversely proportional to MPEA, which was consistent with the correlation length between crosslinks estimated by X‐ray scattering measurements. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 755–764  相似文献   

8.
The morphological effect of polymeric networks (R) modified with terminal amino groups was studied on the adsorption of bovine serum albumin (BSA). Networks of ethylene glycol dimethacrylate and 2‐hydroxyethyl methacrylate [poly (EGDMA‐co‐HEMA)] were synthesized by suspension polymerization, using different EGDMA contents and agitation speeds. These matrices were characterized by FTIR, mercury intrusion porosimetry, SEM, and swelling degree. The increase of the EGDMA concentration led to the formation of networks with the highest crosslinking degree and porosity. An earlier phase separation yielded a higher aggregation of rigid microspheres, also forming stable pore systems. The increase in coalescence frequency, together with the impeller speed, and the decrease of the stabilizer molecules led to an increment in drop size. Large fused aggregates of microspheres were formed with additional loss of small pores as the stirring was increased, attaining also a higher pore volume (Vp) and a slight decrease of the surface area. Once characterized, networks were activated with butanediolglycidyl ether (BDGE), and then reacted with hexamethylenediamine (HMDA) through coupling reaction. Only the R‐BDGE‐HMDA networks synthesized with the highest EGDMA content and agitation speed showed BSA adsorption. Their base matrices exhibited a Vp higher than 1.4 mL/g, which allows easier protein diffusion into the support. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2557–2566, 2008  相似文献   

9.
Well‐defined alkoxysilane oligomers containing a cagelike carbosiloxane core were synthesized and used as novel building blocks for the formation of siloxane‐based hybrid networks. These oligomers were synthesized from the cagelike trimer derived from bis(triethoxysilyl)methane by silylation with mono‐, di‐, and triethoxychlorosilanes ((EtO)nMe3?nSiCl, n=1, 2, and 3). Hybrid xerogels were prepared by hydrolysis and polycondensation of these oligomers under acidic conditions. The structures of the products varied depending on the number of alkoxy groups (n). When n=2 and 3, microporous xerogels (BET surface areas of 820 and 510 m2 g?1, respectively) were obtained, whereas a nonporous xerogel was obtained when n=1. 29Si NMR spectroscopic analysis suggested that partial rearrangement of the siloxane networks, which accompanied the cleavage of the Si–O–Si linkages, occurred during the polycondensation processes. By using an amphiphilic triblock copolymer surfactant as a structure‐directing agent, hybrid thin films with a 2D hexagonal mesostructure were obtained when n=2 and 3. These results provide important insight into the rational synthesis of molecularly designed hybrid materials by sol–gel chemistry.  相似文献   

10.
Biodegradable poly(trimethylene carbonate) (PTMC) networks were prepared by photopolymerization of linear (L)‐ and star (S)‐shaped PTMC macromonomers for potential tissue engineering scaffold applications. The L‐ (Mn, 6400) and S‐shaped (Mn, 5880) PTMC macromonomers were synthesized using 1,4‐butane diol and 2‐ethyl‐ 2‐hydroxyl‐propane‐1,3‐diol co‐initiated ring‐opening polymerization of trimethylene carbonate (TMC) in the presence of stannous octoate and subsequent acrylation with acryloyl chloride. Chemical structures of the PTMC macromonomers and their corresponding networks were characterized by 1H NMR and 13C NMR spectroscopy. The human endothelial cell line, EA.hy926 was used to test the biocompatibility, cell adhesion, and proliferation behavior of both PTMC networks. The PTMC networks made from the S‐shaped macromonomers exhibited superior cell adhesion and proliferation behavior than those made of the linear macromonomers. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

11.
Bicontinuous structures with hyperbolic surfaces have been found in a variety of natural and synthetic systems. Herein, we present the synthesis and structural study of the shifted double‐primitive networks, which is known as the rare “plumber's nightmare”, and its interconversion into diamond networks. The scaffold was prepared by self‐assembly of an amphiphilic triblock terpolymer and silica precursors. Electron crystallography indicates that the structure consists of two sets of hollow primitive networks shifted along 0.75b and 0.25c axes ( 2pcu (38 63), space group Cmcm ). The “side‐by‐side” epitaxial relationship of the primitive and diamond networks with unit cell ratio of about 1.30 has been directly observed with the intermediate surface related to the rPD family. These results bring new insights to previous theoretical studies.  相似文献   

12.
Reaction of 3‐formylchromone ( 1 ) with 5‐amino‐1H‐pyrazoles ( 2 ) in ethanol, afforded 6‐(2‐hydroxy‐benzoyl)pyrazolo[1,5‐a]pyrimidines ( 3a‐g ) in good yields. The structures and the regiospecificity of the reaction were established by nmr measurements and X‐ray analysis, in which soft intermolecular hydrogen‐bonded networks were found.  相似文献   

13.
Supramolecular hidden chirality of hydrogen‐bonded (HB) networks of primary ammonium carboxylates was exposed by advanced graph set analysis from a symmetric viewpoint in topology. The ring‐type HB (R‐HB) networks are topologically regarded as faces, and therefore exhibit prochirality and positional isomerism due to substituents attached on the faces. To describe the symmetric properties of the faces, additional symbols, Re (right‐handed or clockwise), Si (left‐handed or anticlockwise), and m (mirror), were proposed. According to the symbols, various kinds of faces were classified based on the symmetry. This symmetry consideration of the faces enables us to precisely evaluate supramolecular chirality, especially its handedness, of 0D‐cubic, 1D‐ladder and 2D‐sheet HB networks that are composed of the faces. The 1D‐ladder and 2D‐sheet HB networks generate chirality by accumulating the chiral faces in 1D and 2D manners, respectively, whereas 0D‐cubic HB networks generate chirality based on combinations of eight kinds of faces, similar to the chirality of dice.  相似文献   

14.
Summary: Specific temperature‐responsive biodegradable hydrogels were synthesized and characterized in terms of their regulation of enzymatic accessibility based on the physical properties of the temperature‐responsive polymers. The hydrogels consist of glycidyl methacrylate‐modified dextran grafted with the poly(N‐isopropylacrylamide) (PNIPAAm) homopolymer, and cross‐linked by co‐polymerization with NIPAAm and N,N‐dimethylacrylamide (DMAAm). The coil‐globule change in the grafted poly(NIPAAm) chains and only a slight dehydration of the poly(NIPAAm‐co‐DMAAm) cross‐linkers are effective in controlling the enzymatic degradation over a specific temperature range.

The thermo‐responses of the graft chains (steric hindrance) and the crosslinkers (slight deswelling of the hydrogel networks) control the enzymatic degradation of the hydrogel.  相似文献   


15.
Semi‐interpenetrating polymer networks (semi‐IPNs) were prepared by reactions of 2,4‐tolylene diisocyanate (TDI) and hydroxy‐terminated 4‐arm star‐shaped l ‐lactide oligomers (H4LAOn's) with the degrees of polymerization of lactate unit per one arm, n = 3, 5, and 10 in the presence of poly(ε‐caprolactone) (PCL). Morphologies, thermal, and mechanical properties of the TDI‐bridged H4LAOn (TH4LAOn)/PCL semi‐IPNs were evaluated by comparing with those of poly(l ‐lactide) (PLA)/PCL blends. Compatibility between the two components of the TH4LAOn/PCL semi‐IPN with a PCL content not more than 50 wt % was much better than those of the PLA/PCL blends with the same PCL content. All the TH4LAOn networks were substantially amorphous and their tan δ peak or glass transition temperatures increased with decreasing n value. Most of the semi‐IPNs did not show clear glass transition temperature related to both the components. Tensile toughness and elongation at break for all the TH4LAOn/PCL semi‐IPNs were much higher than those for the PLA/PCL blends with the same PCL content. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1420–1428  相似文献   

16.
Thermal transitions in epoxy networks prepared by reaction of α, ω‐diamino terminated poly(propylene oxide)‐block‐poly(ethylene oxide)‐block‐poly(propylene oxide) and diglycidyl ether of brominated Bisphenol A, swollen in water, were studied by differential scanning calorimetry (DSC) in a broad temperature range (from ?100 °C to 20 °C). Networks of two different values of initial molar ratio of amino and epoxy groups were prepared, r (r = 1.00, 2.00), and swollen with different amounts of water up to equilibrium concentration values. The qualitatively different kinds of experimental thermograms have been obtained for two networks and classified according to the amount of water in the sample on the basis of the phase diagram of the system. Also, the concentration dependence of the curves in this diagram (glass transition, melting, and crystallization) as well as the fraction of noncrystallizable water supply some information about the morphology of the system. In this sense, the existence of a microphase separated structure of swollen networks is suggested. The structure consists of hydrophilic and hydrophobic domains and depends on the initial molar ratio of the reactive groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 699–708, 2005  相似文献   

17.
Poly(dimethylsiloxane) networks were prepared by tetrafunctionally end‐linking hydroxyl‐terminated chains with tetraethoxysilane (TEOS). Molecular composites were then prepared by in situ sol–gel reactions on additional TEOS swelled into the networks, resulting in the formation of reinforcing silica fillers within the host elastomers. The amount of filler generated generally increased linearly with an increase in the TEOS swelling ratio, as expected. The silica particles formed were examined by small‐angle X‐ray scattering. Of particular interest were the relationships between particle size and molecular weight Mc of the network chains (mesh sizes), amount of filler introduced, and catalyst concentration. Particle sizes were smallest for the smallest values of Mc, possibly demonstrating constraining effects from the very short network chains. At fixed Mc and filler concentrations, higher catalyst concentrations gave larger particles. Increase in filler concentration generally had little effect on particle size at low and high loadings, but markedly increased sizes at intermediate levels (10–20 wt %), presumably caused by coalescence of the scattering entities into considerably larger aggregates. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1421–1427, 1999  相似文献   

18.
Three series of semi‐interpenetrating polymer networks, based on crosslinked poly(N‐isopropyl acrylamide) (PNIPA) and 1 wt % nonionic or ionic (cationic and anionic) linear polyacrylamide (PAAm), were synthesized to improve the mechanical properties of PNIPA gels. The effect of the incorporation of linear polymers into responsive networks on the temperature‐induced transition, swelling behavior, and mechanical properties was studied. Polymer networks with four different crosslinking densities were prepared with various molar ratios (25:1 to 100:1) of the monomer (N‐isopropyl acrylamide) to the crosslinker (methylenebisacrylamide). The hydrogels were characterized by the determination of the equilibrium degree of swelling at 25 °C, the compression modulus, and the effective crosslinking density, as well as the ultimate hydrogel properties, such as the tensile strength and elongation at break. The introduction of cationic and anionic linear hydrophilic PAAm into PNIPA networks increased the rate of swelling, whereas the presence of nonionic PAAm diminished it. Transition temperatures were significantly affected by both the crosslinking density and the presence of linear PAAm in the hydrogel networks. Although anionic PAAm had the greatest influence on increasing the transition temperature, the presence of nonionic PAAm caused the highest dimensional change. Semi‐interpenetrating polymer networks reinforced with cationic and nonionic PAAm exhibited higher tensile strengths and elongations at break than PNIPA hydrogels, whereas the presence of anionic PAAm caused a reduction in the mechanical properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3987–3999, 2004  相似文献   

19.
Photocrosslinkable and biodegradable polymeric networks were formulated based on N‐vinyl pyrrolidone‐poly(ε‐caprolactone fumarate) (NVP/PCLF) compositions for hard tissue engineering applications using a new proton scavenger, propylene oxide (PO). The synthesized macromers were obtained as a white clear paste with no colorization. The obtained macromers were thoroughly characterized using spectroscopic (NMR and FT‐IR) and chromatographic (gel permeation chromatography (GPC)) techniques. Photocrosslinking of the PCLF/NVP compositions was achieved using camphorquinone and dimethyl toluidine (DMT) as a photoinitiator system. The cytocompatibility of the macromers and their corresponding networks were evaluated via MTT assay. Characterization of the networks indicated the importance of NVP content on the network properties. Sol fraction studies indicated that more than 90% of the PCLFs were crosslinked over the studied range of PCLF/NVP compositions; however most of the NVP above a stoichiometric ratio of one NVP to fumerate unit remained unreacted. It was also found that in the concentrations more than 10% NVP, the unreacted NVP monomer neither participated in the crosslinking reaction nor homopolymerized to poly(vinyl pyrrolidone) (PVP). The elastic modulus (G′) and estimated molecular weight between crosslinks also confirmed that at the higher NVP content the PCLF photocrosslinking was hindered. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

20.
A UPLC‐TOF/MS‐based metabolomics method was established to explore the therapeutic mechanisms of rattan stems of S. chinensis (SCS) in Alzheimer's disease (AD). Experimental AD model was induced by intra‐hippocampal Aβ1–42 injection in rats. Cognitive function and oxidative stress condition in brain of AD rats were assessed using Morris water maze tests and antioxidant assays [malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH‐Px)], respectively. UPLC‐TOF/MS combined with multivariate statistical analysis were conducted to study the changes in metabolic networks in serum of rats. The results indicated that the AD model was established successfully and the inducement of Aβ1–42 caused a decline in spatial learning and memory of rats. The injection of Aβ1–42 in rat brains significantly elevated the level of MDA, and reduced SOD and GSH‐Px activities. In addition, SCS showed significant anti‐AD effects on model rats. A total of 30 metabolites were finally identified as potential biomarkers of AD and 14 of them had a significant recovery compared with the AD model after SCS administration. Changes in AD metabolite profiling were restored to different levels through the regulation of 13 pathways. This is first report on the use of the UPLC‐TOF/MS‐based serum metabolomics method to investigate therapeutic effects of SCS on AD, and enrich potential biomarkers and metabolic networks of AD.  相似文献   

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