Crosslinking Comonomer Research Articles

One-Pot Emulsion-Templated Synthesis of an Elastomer-Filled Hydrogel Framework

Sulfonated polymers are of interest as semipermeable ion-selective materials for membrane applications and as conductive materials for antistatic, electrode, and fuel cell applications. An innovative “one-pot” synthesis route was developed to produce relatively flexible systems containing a cross-linked polyacrylate elastomer within a continuous sulfonated hydrogel network. This synthesis route was based on the formation of a high internal phase emulsion (HIPE) containing an aqueous solution of styrenesulfonate and a cross-linking comonomer in the external phase and containing 2-ethylhexyl acrylate and a cross-linking comonomer in the internal phase. Both emulsifier-stabilized HIPEs and emulsifier-free polymer–nanoparticle-stabilized Pickering HIPEs were investigated using this route. A “three-step” route consisting of sulfonating a cross-linked polystyrene (xPS)-based polyHIPE in sulfuric acid and then polymerizing 2-ethylhexyl acrylate and a cross-linking comonomer within the polyHIPE was used for comparison. The chemical composition, two-phase morphology, water absorption, and mechanical properties of these materials were investigated. Unexpectedly, the walls of the materials based on cross-linked poly(styrenesulfonate) (xPSS) were found to contain cross-linked poly(2-ethylhexyl acrylate) nanodomains. Water absorption per mass sulfonated polymer was significantly greater in the xPSS-based material synthesized within a nanoparticle-stabilized HIPE.

PH-responsive microgels containing hydrophilic crosslinking co-monomers: shell-exploding microgels through design

pH-responsive microgels are crosslinked polymer colloids that swell when the pH approaches the pK a of the particles. They have potential application for injectable gels for tissue repair and drug delivery systems. This study focuses on the pH-triggered gelation behaviour of a series of poly (EA/MAA/X) microgels. EA and MAA are ethylacrylate and methacrylic acid. Here, we investigate the effect of crosslinking monomer type (X) on microgel properties. The crosslinking monomers used were poly (ethyleneglycol) dimethacrylate (PEGD), ethyleneglycol dimethacrylate (EGD) and butanediol diacrylate (BDD). The microgel containing PEGD (m-PEGD) is a new system. The microgel containing BDD (m-BDD) was used as a control system. The concentrated microgel dispersions formed physical gels when the pH was increased to 5.3–6.7, and the polymer volume fractions (ϕ p ) were above about 0.05. Evidence from photon correlation spectroscopy (PCS) and dynamic rheology was presented for abrupt pH-triggered increases, and then decreases of the hydrodynamic diameters for m-PEGD and the microgel prepared using EGD (m-EGD). This appears to be tuneable through crosslinker structure. An unexpected gelation behaviour, which may involve a new gel state for microgels, was found for m-PEGD dispersions. Uniquely, those dispersions formed gels at pH values less than the microgel's pK a . This behaviour was linked to an outer-shell electrostatic repulsive interaction. The data point to a phenomenon, whereby the m-PEGD shells appear to explode at pH values above 7.0. The control microgel prepared, using BDD (m-BDD), did not show any evidence of shell fragmentation at any pH. That microgel has potential as a model pH-responsive microgel system in that the properties measured by PCS and rheology agreed well. To probe that system in more detail, the rheological data for m-BDD was analysed using scaling theory. The variation of the storage modulus (G') with ϕ p gave a scaling exponent of 2.0.

Facile preparation of curved polymer composite nanosheets

A facile no-template approach for fabricating curved polystyrene (PS) nanosheets by miniemulsion polymerization technique was developed. Two essences of the high hydrophobicity of oil phase and the existence of cross-linking comonomer were found to ensure the stable curved sheet-like morphology. Here, when choosing tetradecane as the hydrophobic oil phase and divinylbenzene as cross-linker, the curved PS nanosheets with stable structure were obtained. Furthermore, after introducing functional groups by sulfonation reaction, these curved PS nanosheets can be used as a general template for preparing curved sheet-like inorganic/organic nanocomposites with broadly varied inorganic ingredients, such as metal Ag nanoparticles, inorganic titania, silica, etc. Otherwise, when calcining or carbonizing these inorganic/organic nanocomposites under air or nitrogen, novel mesoporous or microporous pure inorganic nanomaterials with curved sheet-like morphology were obtained conveniently further.

A degradable, porous, emulsion‐templated polyacrylate

AbstractA polyHIPE is a highly porous, emulsion‐templated polymer synthesized by polymerizing a monomer and a crosslinking comonomer in the continuous phase of a high‐internal phase emulsion (HIPE). The synthesis of degradable polyHIPE could be of interest for biomedical applications such as tissue engineering scaffolds. In this research, a poly(ε‐caprolactone) (PCL) oligomer with terminal vinyl groups was used as the crosslinking comonomer for a polyHIPE based on t‐butyl acrylate (tBA). The porous structure, properties, water absorption, and hydrolytic degradation of the polyHIPE were investigated. The polyHIPE containing 50 wt % PCL exhibited very large voids, 1 to 3 mm in diameter that resulted from the destabilization of the HIPE on addition of PCL, making the polyHIPE more suitable for tissue engineering applications. The relatively flexible PCL enhanced segmental mobility, yielding two glass transition temperatures and a significant reduction in modulus. When exposed to a 3 M aqueous solution of NaOH, the t‐butyl groups underwent hydrolysis and the PCL underwent degradation, rapidly leading to the complete disintegration of the macromolecular structure. The tBA‐based polyHIPE containing 50 wt % PCL exhibited enhanced cell adhesion, penetration, and growth indicating that it is a suitable candidate for further research and development. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009

Photopolymerized Injectable RGD‐Modified Fumarated Poly(ethylene glycol) Diglycidyl Ether Hydrogels for Cell Growth

In this study, photopolymerized hydrogels of fumarated poly(ethylene glycol) diglycidyl-co- poly(ethylene glycol) diacrylate have been synthesized and modified with cell adhesion peptide, Arg-Gly-Asp (RGD). The structural and mechanical properties of the hydrogels are found to be poly(ethylene glycol) diacrylate (PEGDA) dependent. The percentage of gelation is increased from 72 to 89 wt.-% when the amount of the crosslinker co-monomer (PEGDA) in the hydrogel formulation is increased from 20 to 40 wt.-%. In the present case, the equilibrium mass swelling is decreased from 216 to 93%. The viscosities of the uncured formulations have also been measured and likewise, the results were influenced by the increasing amount of PEGDA that reduced the value from 83 to 36 cP. The compressive modulus of the prepared hydrogels was improved with the addition of the PEGDA. Cell growth experiments have been performed by comparing the properties of the hydrogels with and without RGD units. The results show that RGD units enhance the adhesion of cells to the surface of the hydrogels. SEM-EDS studies reveal that nitrogen and calcium are produced on the osteoblast-seeded surface of the scaffold within the culture time period. [Figure: see text].

Cross-linker flexibility in porous crystalline polymers synthesized from long side-chain monomers through emulsion templating.

A polyHIPE is a cross-linked, highly porous polymer from the polymerization of monomers and cross-linking comonomers in the external phase of a high internal phase emulsion (HIPE). Crystallizable polyHIPE were synthesized through the copolymerization of stearyl acrylate (A18) with ethylene glycol dimethacrylate (EGDMA). PolyHIPE synthesized with the more flexible EGDMA were compared to those synthesized with the more rigid divinylbenzene. The polyHIPE densities were around 0.11 g cm-3. EGDMA destabilized the HIPE yielding relatively large voids and a structure whose partial closed-cell nature increased with increasing EGDMA content. The EGDMA cross-linked polyHIPE exhibited higher melting peak temperatures and higher crystallinities than the divinylbenzene cross-linked polyHIPE. Organic phase initiation of the EGDMA cross-linked polyHIPE yielded lower melting temperatures, lower crystallinities, and a highly interconnected porous structure that resulted in a lower modulus.

Porous interpenetrating network hybrids synthesized within high internal phase emulsions

‘PolyHIPE’ are porous polymers from the polymerization of monomers and crosslinking co-monomers in the continuous phase of high internal phase emulsions (HIPE). Elastomeric polyHIPE have been reinforced through the synthesis of nanocomposites using several different routes including the addition of co-monomers such as vinyltrialkoxysilane, polyhedral oligomeric silsesquioxane (POSS) bearing vinyl groups, or vinyl silsesquioxane (VSQ). This paper describes the synthesis, structure, and properties of hybrid polyHIPE with interpenetrating polymer–inorganic networks synthesized by adding tetraethylorthosilicate (TEOS) to the monomers. The HIPE becomes unstable on addition of 14mol% TEOS and the resulting polyHIPE contains voids hundreds of micrometers in diameter. On addition of 25mol% TEOS the large voids become coated with a brittle Si–O shell as the TEOS migrates to the interface between the organic and aqueous phases. In general, the increases in tanδ peak temperature, tanδ peak breadth, and room temperature modulus with increasing TEOS content are similar to those observed with POSS and VSQ. Unlike the polyHIPE containing vinyltrialkoxysilane, POSS, or VSQ, pyrolysis of these hybrid polyHIPE did not yield porous inorganic monoliths.

Di(4-isopropenylphenoxy)alkanes as cross-linking comonomers in three-dimensional copolymerization with styrene

Di(4-isopropenylphenoxy)alkanes were synthesized by condensation of 4-isopropenylphenol with symmetrical dihaloalkanes in the presence of KI promoter. Three-dimensional polymeric structures were prepared by compolymerization of these monomers with styrene.

Porous poly(2-hydroxyethyl methacrylate) hydrogels synthesized within high internal phase emulsions.

Hydrogels, such as those based on poly(2-hydroxyethyl methacrylate) (PHEMA), are hydrophilic three dimensional network structures that undergo extensive swelling in water. PolyHIPEs are highly porous, crosslinked polymers typically synthesized within high internal phase emulsions (HIPEs). This research describes materials with enhanced water absorption that combine hydrogel water absorption with capillary action by synthesizing PHEMA-based polyHIPEs within oil-in-water HIPEs. The variation in the ,-methylenebisacrylamide (MBAM) crosslinking comonomer content yields a narrow synthesis window in which water-swollen micro-gel particles phase separate, agglomerate, and form a heterogeneous polyHIPE wall structure with nanoscale porosity. Surprisingly, a hydrogel polyHIPE with a relatively high MBAM content also had the highest surface area and the highest water absorption. Ultimately, it is the influence of the MBAM content on the polymer hydrophilicity and on the porous structure that determines its effects on the properties.

Preparation of Hollow Polystyrene Nanocapsules via a Miniemulsion Polymerization Process

Hollow polystyrene nanocapsules with sizes of ~100 nm have been prepared via a miniemulsion polymerization process by applying the encapsulation of a nonsolvent (i.e., isooctane). Divinylbenzene has been added to styrene as a cross-linking comonomer in order to improve a structural stability of the hollow polymer capsules. Morphology variation of nanocapsules with concentrations of divinylbenzene and also isooctane has been studied using transmission electron microscopy analysis. Kinetic study on the miniemulsion polymerization of styrene in the presence of divinylbenzene and isooctane has been carried out using fractional conversion data determined by the gravimetric analysis.

Surface analysis of the proton exchange membranes prepared by pre-irradiation induced grafting of styrene/divinylbenzene into crosslinked thin PTFE membranes

The proton exchange membranes were obtained by pre-irradiation induced grafting of styrene with or without divinylbenzene (DVB) into thin crosslinked polytetrafluoroethylene (RX-PTFE) membranes with the thickness around 10 μm and successive sulfonation. The surface chemical structure and morphology of the non-grafted, the grafted, and the grafted and sulfonated RX-PTFE membranes were studied by means of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis. From the F/C atom ratio result, it was known that there are mainly polystyrene grafts on the surfaces of the styrene grafted RX-PTFE membranes, while there are mainly PTFE chains on the surfaces of the RX-PTFE membranes grafted by styrene together with DVB. “Wave” shape morphology on the surfaces of the grafted RX-PTFE membranes was observed. The F/C atom ratios on the surfaces of the grafted and sulfonated membranes are little lower than the corresponding grafted membranes before sulfonation. On the surface of the sulfonated membranes, the “wave” shape morphology was also observed. The distributions of the polystyrene grafts in the RX-PTFE membranes matrixes were strongly affected by the concentration of the crosslinking co-monomer, DVB, used in the graft polymerization, and the sulfonation will not change the distribution of the grafts obviously.

Mechanistic studies on particle nucleation in the batch emulsion polymerisation of n-butyl acrylate containing multifunctional monomers

This paper reports the mechanistic details concerning the synthesis of crosslinked poly(n-butyl acrylate) dispersions intended to be used as seeds in the preparation of core-shell emulsions. The influence of crosslinking comonomers and the amount and type of surfactants on the kinetics, particle nucleation, particle size and particle size distribution in the batch emulsion polymerisation of n-butyl acrylate (BA) is explored. In the case of EGDA (ethylene glycol diacrylate) crosslinker the particle number decreased with increasing crosslink density, whereas the opposite trend was observed in the case of m-diisopropenylbenzene (m-DIPB) in the presence and absence of the surfactant sodium dodecyl sulfate (SDS). The observed behaviour is mainly attributed to the variation in the aqueous phase kinetics caused by the water solubility of the comonomer, which influences the formation rate of precursor particles during the nucleation stage. Only for the less water soluble crosslinker, DIPB, could the increase of particle number be explained within the Smith–Ewart theory by assuming prolonged nucleation due to reduced swelling of growing particles with monomer as a result of the crosslinking reaction.

Modified suspension‐PVC particles as absorbents of ortho‐dichlorobenzene from water

AbstractModified porous PVC particles are studied as absorbents of o‐dichlorobenzene (DCB), from water. The modified particles were produced by an in‐situ stabilizer‐free polymerization/crosslinking of a monomer/crosslinker/peroxide solution absorbed within commercial porous suspension‐type PVC particles. The modifying monomers used include styrene with divinyl benzene (DVB) as a crosslinking comonomer, methyl methacrylate (MMA), butyl acrylate (BA), or ethylhexyl acrylate (EHA) with ethylene glycol dimethacrylate (EGDMA) as a crosslinking comonomer.The effect of the nature of the monomers, morphology, porosity, surface area and composition of the modified PVC particles on DCB absorption was studied. Batch experiments (absorption rate and isotherms) were used to screen the PVC absorbents on the basis of absorption rate and absorption capacity. Continuous absorption column experiments were conducted to study the parameters characterizing the absorption process.Both the unmodified and modified PVC particles absorb DCB from water. The PBA and PEHA‐modified PVC particles approach equilibrium capacity faster and have greater absorption capacity than neat PVC, PS‐modified PVC and PMMA‐modified PVC particles. The absorption characteristics are influenced by the modifying polymer's Tg. The rubbery nature of PBA and PEHA yields better absorption in spite of the significantly lower surface area and porosity obtained in the modified PVC particles. Thus, indicating that fast adsorption followed by bulk absorption of DCB is taking place. A clear influence of the crosslinking effect was not established. The continuous absorption experiments were found more efficient than the batch absorption experiments. Copyright © 2003 John Wiley & Sons, Ltd.

One-Pot Synthesis of Branched Poly(styrene−divinylbenzene) Suspension Polymerized Resins

Spherical particulate polymer resins have become ubiquitous support materials in both solid phase synthesis and in the heterogenizing of homogeneous catalysts. In the former case lightly cross-linked so-called gel-type species are favored whereas in the latter so-called macroporous species are finding increasing utility. Despite the success of these materials, mass transfer limitations can lead to poor performance, and in this context there is still a need for improvement in the morphology of these species. One potential advancement would be resins with a highly branched backbone architecture since such a molecular level structure would in principle generate a large proportion of functional groups near chain ends or at least on mobile chains anchored to the main matrix by a single linkage. In addition a high level of chain ends relative to that in conventional resins might lead to novel solvation characteristics. We now report a facile one-pot suspension polymerization which allows synthesis of both branched gel-type and branched macroporous resins. The procedure is an adaptation of our earlier reported methodology for producing soluble branched vinyl polymers and involves use of controlled levels of a free radical chain transfer agent which functions in effect to limit chain growth and in combination with a cross-linking comonomer leads essentially to branched backbone architectures. The system styrene/ divinylbenzene/dodecanethiol has been probed in detail, and a range of experimental conditions have been identified which lead to branched gel-type and branched macroporous resins. The structure of these has been evaluated from solvent swelling data, dry state surface area measurements, and inverse size exclusion chromatographic data.

A modified polymer gel for radiotherapy dosimetry: assessment by MRIand MRS

The characteristics of a new formulation of polymer gel are assessed forMRI-based radiotherapy dosimetry. The gel, based on the firstBANG® gel formulation, replaces acrylamide with the less toxicmonomer sodium methacrylate. The relationship between MR T2 relaxation timeand radiation dose for the gel formulation was studied using spin-echoimaging. Proton magnetic resonance spectroscopy was also used to assess thegel composition as a function of dose. The effect of gel pH on thedose-response and baseline R2 was then investigated. A calibrationperformed on gel without pH modulation (pH = 6.6) revealed adose-response of 0.14 s-1 Gy-1 within the range 0-8 Gy.The baseline R2 increases with pH above neutrality, rising from1.2 s-1 at pH = 5.1 to 5.0 s-1 at pH = 10.1. The dose-response is also pH dependent, having a minimum valueof 0.09 s-1 Gy-1 at pH = 10.1 and peaking at0.21 s-1 Gy-1 at pH = 7.7. Undertaking protonspectroscopy on the gels enabled resonances associated with the monomer andco-monomer to be studied. By integrating the peaks from the respectivemonomers and normalizing to the signal at 0 Gy it was shown that only 50%of the methacrylate monomer was used at 10 Gy, whereas 80% of theco-monomer was used at this dose.The data indicate that this gel has a reduced toxicity and a comparabledose response to the previously reported BANG® gel. In addition, theperformance of the gel can be optimized by controlling the pH. MRspectroscopy revealed that the crosslinking co-monomer is consumed morereadily than the monomer, which is in agreement with previous compositionalstudies.

Facile, versatile and cost effective route to branched vinyl polymers

Free radical one-step polymerisation of methyl methacrylate in the presence of a crosslinking comonomer and balancing levels of a chain transfer agent allow facile high conversion synthesis of polymers with a branched architecture. Broad GPC curves have been obtained for these materials and branching has been demonstrated using GPC coupled with a triple detection system allowing evaluation of g′, the Zimm branching factor. In addition the bridging residues in branched polymers arising from use of an unsaturated crosslinking comonomer have been chemically cleaved to yield the linear oligomers of much narrower molecular weight distribution that comprise the branched structure. The methodology promises to be generic, utilises only readily available starting materials and holds out good prospects for providing branched vinyl polymers on a technically useful scale at low cost.

Acrylovinylic macromolecular compounds with adhesive properties

The effect of some crosslinking comonomers on the function of an acrylovinylic copolymer with pressure-sensitive adhesive properties is examined. It is concluded that there is dependence of the adhesion/cohesion balance on the existence of a threshold domain of concentration for each crosslinking component that is introduced in the copolymer composition. Evidence is obtained of the influence of temperature, UV irradiation and humidity on the adhesive properties.

Beaded reactive polymers. 3. Effect of triacrylates as crosslinkers on the physical properties of glycidyl methacrylate copolymers and immobilization of penicillin G acylase.

Various glycidyl methacrylate (GMA) copolymers were synthesized by suspension polymerization, using pentaerythritol triacrylate (PETA), trimethylolpropane triacrylate (TMPTA), and trimethylolpropane trimethacrylate (TRIM) as crosslinking comonomers. These copolymers were evaluated for the immobilization of penicillin G acylase. Broad pore-size distribution that was observed was in the range 5-300 nm. Both surface area and pore volume increased with increase in the mole fraction of crosslinking comonomer (increasing crosslink density). The pore volume of the copolymers was more than doubled by including lauryl alcohol as porogen. Binding of penicillin G acylase (PGA) was quantitative on highly crosslinked copolymers. The expression of bound PGA was better on the relatively more hydrophilic GMA-TMPTA and GMA-PETA copolymer supports compared to the GMA-TRIM copolymers. Among the different copolymers studied, GMA-TMPTA copolymer 7411 exhibited highest activity of immobilized penicillin G acylase (167.4 IU/g) with 35.1% expression.

Kinetics of a drug release from a delayed release device

Reaction of sodium salt of benzoic acid with methacryloyl chloride provides an anhydride which is polymerized by the radical method or copolymerized with various percentages of ethylene glycol dimethacrylate to obtain crosslinked products. Hydrolysis reactions of the resulting polymers were carried out in various aqueous solutions and the rate of release of benzoic acid (simulator of drug) seems to depend both on the percentages of crosslinking comonomer and on the pH of the solution. A model of this delayed release of benzoic acid is also proposed.

Synthesis, characterization and polymerization of waxy monomers

AbstractWaxy monomers and crosslinkers, respectively, were synthesized from commercially available waxes by esterification with 2‐hydroxyethyl methacrylate, glycerol dimethacrylate, or glycidyl methacrylate or by functionalization with 2‐isocyanatoethyl methacrylate. The resulting opaque methacrylates with melting points between 45 and 80°C were polymerized in bulk and in toluene solution in presence of free radical initiators. The obtained polymers were characterized by a broad molecular weight distribution. Opposite to the bulk polymerization, the double bond conversion in solution polymerization is nearly quantitative. The observed volume shrinkage during polymerization is very low due to the high molecular weight of the monomers. Polymerizates containing crosslinking comonomers exhibit improved mechanical stability.