Effect of porogenic solvent on the porous properties of polymer monoliths

Polymer monoliths with open pores and median pore size of about 15 nm–3 μm have been successfully synthesized by photoinitiated polymerization of butyl methacrylate and ethylene glycol dimethacrylate monomers. The solubility of the monomers in a porogenic solvent is determined by Hildebrand solubility parameter, and it is found that it has great effect on the pore size of the polymers synthesized. Polymers with larger pores are usually generated with poorer solvents for the monomers. However, polymers with different pore sizes and porosities have been obtained using porogenic solvents with similar Hildebrand solubility parameters. The evaporation rate of the porogenic solvents might be another critical factor affecting the properties of the polymer monoliths. Moreover, the effect of water as a cosolvent on the pore size and porosity of the polymers have also been investigated. Polymers with larger pore size have been prepared with the presence of water due to the occurrence of earlier phase separation in the polymerization. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and structure of polysiloxane liquid crystalline elastomers with a mesogenic crosslinking agent

A new mesogenic crosslinking agent M‐1 was synthesized to minimize the perturbations of a nonmesogenic crosslinking agent for liquid crystalline elastomers. The synthesis of new side‐chain liquid crystalline elastomers containing a rigid mesogenic crosslinking agent M‐1 and a nematic monomer M‐2 is described by a one‐step hydrosilylation reaction. The chemical structures of the obtained monomers and elastomers 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 measurements. The influence of the crosslinking units on the phase behavior is discussed. The elastomers containing less than 15 mol % of the crosslinking units showed elasticity, reversible phase transition, and nematic‐threaded texture. However, when the crosslinking density reached 21.6 mol %, the mesophase of polymer P‐8 disappears. The adoption of a mesogenic crosslinking agent diminishes the perturbation of a nonmesogenic crosslinking agent on mesophase of liquid crystalline elastomers, and isotropic temperature and a mesomorphic temperature range slightly decreased with increasing content of the crosslinking agent. In addition, X‐ray analysis shows nematic polydomain network polymers can transform into smectic monodomain by stress induction, leading to the orientation formation macroscopically. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1736–1742, 2004     

Synthesis of macroporous poly(styrene-divinyl benzene) microspheres by surfactant reverse micelles swelling method

Macroporous poly(styrene-divinyl benzene) microspheres with pore size of about 500 nm were prepared by a new method, surfactant reverse micelles swelling method. The macroporous microspheres were prepared by convenient suspension polymerization. The difference from conventional suspension polymerization was that a higher concentration of surfactant was added in the oil phase. The effects of the amount and type of surfactants on the morphology of microspheres were investigated, and the formation mechanism was also discussed. Macropores were formed when the concentration of surfactant was much higher than critical micelle concentration (cmc). It was proposed that a large amount of reverse micelles formed by adding a large amount of surfactant in the oil droplet phase, and the reverse micelles could absorb water from the external aqueous phase. The water in the oil phase formed macropores after polymerization. The method developed in this study was convenient to prepare microspheres with larger pore size than the conventional method such as agglomeration method of nanoparticles.     

Nonequilibrium morphology development in seeded emulsion polymerization. V. The effect of crosslinking agent

It is understood that a major controlling factor in the development of latex particle morphology is the extent to which second stage oligomeric radicals can diffuse into the particles after entry from the aqueous phase. This leads to the expectation that any factor which decreases the diffusion rate of second stage radicals should decrease radical penetration, and thus favor the formation of core–shell type morphologies. The occurrence of crosslinking reactions during the second stage may be one such factor, since the branched and crosslinked chains diffuse much more slowly (if at all) than their linear counterparts. This paper addresses the effect of the addition of crosslinking agent (a divinyl monomer) during the second stage polymerization on particle morphology. It is shown experimentally that, contrary to what one might expect, crosslinking during the second stage has very little, if any, effect on morphology. Modeling suggests that the reason is that the probability for radicals to develop a branch before penetrating a significant distance into the particles is very low (under conditions where full penetration is possible in the absence of crosslinking agent), especially for what is considered to be typical concentrations of crosslinking agent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2043–2054, 2006     

Silicone‐based cholesteric liquid crystalline polymers: Effect of crosslinking agent on phase transition behavior

Silicone‐based cholesteric liquid crystalline polymers (ChLCP) were fabricated with variable clearing temperatures as controlled by their chemical compositions. The chemical structures of the mesogenic monomers and ChLCP were confirmed by FTIR and ¹H‐NMR spectroscopy. The mesogenic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The experimental results demonstrated that the glass transition temperatures and the clearing points of the liquid crystalline polymers decreased with increasing proportion of mesogenic crosslinking agent up to 12.50 mol % (LCP‐3), and at higher proportion of crosslinking agent, the clearing points disappeared, indicating that the network chains have less chance to orient themselves. Thermogravimetric analysis showed that the LCP‐3 was the most stable up to 230°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Suspension thiol-ene photopolymerization: Effect of stabilizing agents on particle size and stability

The impact of several surfactant species employed in the suspension photopolymerization of water-borne thiol-ene polymer microspheres is reported. The focus of analysis was on how different surfactant species and the surfactant concentrations affected particle size and particle size distributions. Surfactants used included sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), and hexadecyltrimethylammonium bromide (HTAB), Tween 20, Tween 40, Tween 60, Tween 80, Lutensol XL 70, Lutensol XP 70, Pluronic PE 6400, and Pluronic F108 Pastille. Using stabilizing agents or surfactants is necessary to prevent extensive aggregation and agglomeration of crosslinked thiol-ene polymer. All surfactants used in this study for particle stabilization and development produced spherical thiol-ene polymer particles. The chemical structure and concentration of the surfactants influenced the final particle size and size distribution of particles obtained. In general, it was found that smaller particles are obtained with higher concentrations of stabilizing agent, especially for ionic surfactants.     

Comprehensive insight of crosslinking agent concentration influence on starch-based aerogels porous structure

In this work, we evaluated starch-based aerogels prepared using freeze-drying, and an eco-friendly crosslinking agent (trisodium citrate), in three different concentrations: 12.8, 19.3, and 25.7 mg ml⁻¹. Aerogels were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, relative density, porosity percentage, scanning electron microscopy (SEM), and water uptake. The results indicated a higher reticulation and crystallinity and lower water uptake, increasing crosslinking agent concentration (Aero 1:2). SEM images revealed the prominent presence of macroporous structure (more than 50 nm) within the aerogel, containing small and large pores within the aerogel structure. The small pores were statistically similar for Aero 1:1 and Aero 1:1.5, as observed by analysis of variance analysis, but they were statistically different from Aero 1:2. The large pores diameter increased with higher crosslinking concentration and induced them as closed pores, resulting in a less porous structure. This result is directly associated with a higher reticulation degree. Overall, the influence of crosslinking agent concentration was studied and indicated that Aero 1:1.5 presented valuable properties.     

Preparation of acrylic copolymers and crosslinking agents and properties as a film

Copolymers of butyl acrylate (BA)‐methyl methacrylate (MMA)‐acrylic acid (AA) and intraparticle crosslinking agents containing N‐methylol acrylamide (NMA) and ethylene glycol dimethacrylate (EGDMA) were prepared by emulsion copolymerization. After that, films were prepared from the mixture of copolymers and the interparticle crosslinking agents. The interparticle crosslinking agents were prepared from hexamethylene diisocyanate and aziridine ethanol. Mixtures of the copolymer and the interparticle crosslinking agent were cast to films and crosslinked in a convection oven. The effects of the contents of the intra/interparticle crosslinking agents were also evaluated. By increasing the contents of EGDMA, roughness of the films was increased because of the effects of EGDMA acting as an intraparticle crosslinking agent. By increasing the contents of the interparticle crosslinking agent, roughness was also increased by the reaction between the copolymers and interparticle crosslinking agent. Tensile strength and water and chemical resistance of the film were increased, whereas elongation of film was decreased by increasing the contents of interparticle crosslinking agents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of the degree of crosslinking on penetrant transport in polystyrene

The effect of the degree of crosslinking of glassy polymers on the transport mechanism of penetrants was investigated using a series of divinyl benzene (DVB)-crosslinked polystyrenes of nominal crosslinking ratio X from 0.001 38 to 0.060 mol DVB/mol styrene. The number average molecular weight between crosslinks, $\text{M}\text{?}{}_{\mathrm{<mtext>c</mtext>}}$, was determined from equilibrium swelling experiments in cyclohexane. Dynamic swelling experiments with cyclohexane at 30°C showed that the mechanism of penetrant transport was anomalous. An overshoot in the penetrant uptake was observed, characteristic of macromolecular relaxations and of changing solubility of the cyclohexane in the continuously swelling polystyrene. Photographs of various samples during the swelling process showed that solvent crazing occurred predominantly in loosely crosslinked samples.     

Preparation of liquid crystalline networks doped with azobenzene molecules and their photochemical grating formation behavior

Liquid crystalline (LC) networks with macroscopically uniaxial molecular orientation were prepared by photopolymerization of mixtures of LC mono‐ and diacrylates and a donor–acceptor azobenzene compound in a homogeneous glass cell at the nematic phase, and their photoresponsive properties were investigated. The transparency of the LC networks decreased with a decrease in the crosslinking density with LC diacrylate. The LC networks crosslinked with a few mol percent of LC diacrylate showed an enantiotropic phase transition from an anisotropic phase to an isotropic phase as well as high transparency. Formation and removal of the grating were investigated by irradiating two writing beams with an argon ion laser. Grating less than 1.0 μm could be achieved, and the response time of formation and removal of the grating were in a range of a few tens of microseconds. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 943–951, 2003     

Effect of ion-binding on the formation of temporary viscoelastic networks of proanthocyanidin biopolymers

The gel formation of the alkali salts of proanthocyanidin polymers from Pinus radiata bark with calcium(II) and aluminum(III) has been investigated. The calcium- and aluminum-induced gelation of the hot water extract (HWE) has been studied by UV spectroscopy as well as through conductivity and rheological measurements. The ability of an HWE to complex was observed to increase significantly as the solution's pH became more alkaline, and the conductivity data are consistent with UV spectra with respect to structural change as metal binding occurs. The addition of the cationic species Ca²⁺ and Al³⁺ markedly increased the elasticity of the extracts, even at low extract concentration. Rheological measurements of metal binding in the HWE paralleled the UV spectral and conductivity behavior, thus indicating that the HWE binds more readily with calcium than with aluminum. In the concentrated HWE system, maximum association of the HWE with metal ions was found to appear at the same molar ratio of 3.6. The addition of such cationic species to the extracts is thought to reduce their fluidity primarily by increasing the number of physical electrostatic crosslinks. Such an increase results, in turn, in an increase in the apparent molecular weight of extract polymers and a decrease in fluidity. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1795–1805, 1997     

Synthesis and mesomorphic properties of cholesteric elastomers based on chiral mesogenic crosslinking agent

Six chiral monomers ( M ₁? M ₆), and their corresponding polymers ( P ₁, P ₄) and elastomers ( P ₂, P ₃, P ₅, P ₆) derived from chiral mesogenic crosslinking agent were synthesized. The chemical structures of M ₁? M ₆ were confirmed by FTIR and ¹H NMR spectroscopy. The structure‐property relationships of M ₁? M ₆ and P ₁? P ₆ were discussed. Their mesomorphic properties and phase behavior were investigated by differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), polarizing optical microscopy (POM), and X‐ray diffractometer (XRD) measurements. All monomers obtained, except M ₂ and M ₅, showed typical oily streaks texture and focal conic texture of cholesteric phase on heating and cooling cycles. The selective reflection of cholesteric monomers and elastomers shifted to the short wavelength region with increasing temperature. The elastomers P ₂ and P ₅ did not reveal the mesomorphic properties, and P ₃ and P ₆ showed cholesteric phase. TGA showed that P ₁? P ₆ had a high thermal stability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

交联剂对合成高吸油性树脂的影响

采用水分散相悬浮聚合法，以甲基丙烯酸长链烷基酯为单体，二甲基丙烯酸乙二醇酯为交联剂合成高吸油性树脂；并且探讨了交联剂对聚合过程和树脂吸油性能的影响。实验证明，交联剂用量越大，体系凝胶化现象到来得越早，转化率随反应时间增长得较快，但是最终转化率相差不大。交联剂用量越大，树脂对各种油品的吸油倍率越小；交联剂的用量大于0.4mL时，吸油倍率变化不明显。     

Influence of crosslinking on the characteristics of thermally expandable microspheres expanding at high temperature

Free‐radical suspension polymerization was used to synthesize thermally expandable microspheres (TEMS); in this process, a poly(acrylonitrile‐co‐methacrylonitrile) shell encapsulated isooctane. Different amounts of dimethacrylate, diacrylate, or divinyl ether functional crosslinker were added to investigate the effects on the crosslinking density of the polymer and the expansion properties of the TEMS. The optimum amount of crosslinker was found to be approximately 0.05–0.1 mol %. However, a significantly better expansion could be obtained with 1,4‐butanediol dimethacrylate as a crosslinker, compared to 1,4‐butanediol divinyl ether or 1,4‐butanediol diacrylate. From monitoring the conversion of monofunctional analogues by gas chromatography, we suggest that the differences in expansion obtained with different crosslinkers, originated from the difference in the reactivity of the radicals in the system toward the vinyl functionalities of the crosslinkers. This regulated the incorporation of the crosslinker into the polymer and, thereby, the mechanical properties of the microsphere shell. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Statistical treatment of allophanate crosslinking in the formation of polyurethane networks

Summary Crosslinking of polyurethanes by a reaction of isocyanate groups with urethane groups leading to trifunctional allophanate branch points is treated statistically using the theory of branching processes. The occurrence of gelation in the diol — diisocyanate system and its dependence on the excess of isocyanate groups and the intensity of allophanate formation is discussed.     

Role of a chelating agent in the formation of polyaniline films on aluminum

A chelating agent, alizarin, was used to pretreat an aluminum surface before the electrochemical synthesis of polyaniline. Alizarin had two main effects on the process: (1) it suppressed the hydrogen evolution reaction and increased the current efficiency and (2) it stabilized the open‐circuit potential in a corroding environment, such as in 0.1M NaCl. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 819–823, 2003     

Water absorption in epoxy resins: The effects of the crosslinking agent and curing temperature

Epoxy systems were prepared with the same epoxide (diglycidyl ether of bisphenol A) with five different hardeners: 4,4′‐diaminodiphenylmethane (H1), diethylenetriamine (H2), a cycloaliphatic amine based on isophorone diamine (H3), a polyaminoimidazoline‐based hardener (H4), and a polyamidoamine‐based adduct hardener (H5). Samples were subjected to four different postcure treatment temperatures (23, 55, 75, and 150°C). Water absorption kinetics were obtained for each material and for each postcure treatment. The water absorption behaviors for the materials with H1, H2, and H3 were similar, whereas those for H4 and H5 were quite different. This is discussed in terms of the molecular structures of the hardeners. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2544–2549, 2005     

反相微乳液聚合制备丙烯酰胺类聚合物微球的研究进展

反相微乳液聚合技术具有稳定性好、固含量高、聚合速率快等优点而成为研究热点。本文系统地综述了近年来国内外应用反相微乳液聚合制备丙烯酰胺类聚合物微球的研究进展,概述了微乳液的基本理论及其特征,对稳定微乳液的制备进行了讨论;着重归纳了丙烯酰胺类的反相微乳液聚合,详述了聚合体系各组分的选择,同时探讨了影响聚合反应的因素,认为应研究新型表面活性剂以实现高单体浓度的聚合;介绍了聚合物微球在油田应用中提高采收率方面的应用现状。最后指出了其在深部调剖堵水领域存在的问题,以离子液体代替传统聚合体系组分制备集智能性、复合性、多功能性等综合性能于一体的聚合物微球是其未来发展方向之一。     

Dithioester functionalization of poly(cyclohexene oxide) and its application to obtain block copolymers

A new method of introducing dithioester groups into the polymer chain of poly(cyclohexene oxide) is reported. It includes the use of diaryliodonium salt and an aromatic dithioacid as a redox couple to initiate the cationic polymerization of cyclohexene oxide. It was found that the dithioacid by itself cannot start the polymerization of cationic polymerizable monomers; however, in combination with a diaryliodonium salt, an exothermic reaction was produced, yielding a thiocarbonylthio‐functionalized polyether. Thermal profiles of the redox polymerizations were determined by means of optical pyrometry. A preliminary study showed that when the poly(cyclohexene oxide) functionalized with dithioester groups was introduced into the radical polymerization of styrene, the polystyryl growing radicals reacted with the dithioester‐functionalized polyether to form a block polymer. The amount of polyether actually incorporated into the block copolymer was calculated to be 70% of the initial amount of poly(cyclohexene oxide)/dithiobenzoic acid charged into the reactor. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of chemical structure and crosslinking density on the thermo-mechanical properties and toughness of (meth)acrylate shape memory polymer networks

The objective of this work is to characterize and understand structure-mechanical property relationships in (meth)acrylate networks. The networks are synthesized from mono-functional (meth)acrylates with systematically varying sidegroup structure and multi-functional crosslinkers with varying mole fraction and functionality. Fundamental trends are established between the network chemical structure, crosslink density, glass transition temperature, rubbery modulus, failure strain, and toughness. The glass transition temperature of the networks ranged from −29 to 112 °C, and the rubbery modulus (E_r) ranged from 2.8 to 129.5 MPa. At low crosslink density (E_r < 10 MPa) network chemistry has a profound effect on network toughness. At high crosslink densities (E_r > 10 MPa), network chemistry has little influence on material toughness. The characteristic ratio of the mono-functional (meth)acrylates' components is unable to predict trends in network toughness as a function of chemical structure, as has been demonstrated in thermoplastics. The cohesive energy density is a better tool for relative prediction of network mechanical properties. Due to superior mechanical properties, networks with phenyl sidegroups are further investigated to understand the effect of phenyl sidegroup structure on toughness.