Low Levels Of Cross-linking Research Articles

Low crosslinking imprinted coatings based on liquid crystal for capillary electrochromatography

Low loading capacity is the main problem of molecularly imprinted stationary phase, which is attributed to the high level of crosslinking restricting distortion phenomena of polymer backbone in molecular imprinting. A new approach based on liquid crystal with recognition ability is demonstrated for synthesis of molecularly imprinted polymer coatings in a low level of crosslinking. The resulting low crosslinking (20%) open-tubular imprinted capillary was able to separate enantiomers by means of capillary electrochromatography. The resolution of enantiomer separation achieved on the (S)-amlodipine-imprinted capillary was up to 6.36 in less than 2.5min. The strong recognition ability with a selectivity factor of 1.81 and high column performance of template (up to 23,300plates/m) were obtained. Performance of imprinting comparable to that recorded in conventional MIP stationary phase was observed. The liquid crystal MIP coatings were also prepared using either (S)-naproxen or (S)-ofloxacin as template molecule. The resolutions of enantiomers separation were 1.41 and 1.55, respectively. The results illustrate that the synthesis of low crosslinking MIP coatings based on liquid crystal is not only an experimental-simplified process of high performance, but also an approach to produce chiral stationary phase comparable to other chiral stationary phases.

Crosslinked and stabilized in-kernel heat-moisture-treated and temperature-cycled normal maize starch and effects of reaction conditions on starch properties

Kernels of normal maize were subjected to a heat-moisture treatment (HMT) followed by a temperature cycling (TC) regime that was previously shown to produce slowly digesting starch (SDS) and resistant starch (RS) (Wongsagonsup, Varavinit, & BeMiller, 2008). This starch (in-kernel HMT-TC normal maize starch [NMS]) was then subjected to a low level of crosslinking with phosphoryl chloride, to hydroxypropylation, and to crosslinking followed by hydroxypropylation to determine if it could be converted into a slowly digesting modified food starch. Five controls were used. Digestibility after cooking, RVA parameters, and DSC parameters of gelatinization and retrogradation were determined. Crosslinked in-kernel HMT-TC NMS had the greatest amount of SDS, but only 3.1% (compared to 1.3% in the native starch). Hydroxypropylated and crosslinked and hydroxypropylated in-kernel HMT-TC NMS had the greatest amount of RS, but only 35% and 33%, respectively (compared to 16% in the native starch). Derivatization changed the physical properties of in-kernel HMT-TC NMS. It was also found that subjecting the starches used in this study to the time, temperature, pH, and salt concentration conditions used for derivatization made significant changes to the physical properties of the starch. In fact, subjecting in-kernel HMT-TC NMS and HMT-TC laboratory-isolated NMS to the conditions used for derivatization but without any added reagent made greater changes in the peak viscosity than did derivatization. The same was not true, however, for laboratory-isolated NMS. And for the most part, the starches subjected to the conditions of derivatization alone also produced different final viscosity values, indicating that whatever changes in granule structure and behavior occurred as a result of treatment with reaction conditions were carried through the RVA cooling cycle.

Preparation, Solid-State NMR, and Physicochemical Characterization of Surprisingly Tough Open Cell PolyHIPEs Derived from 1-Vinyl-1,2,4-triazole Oil-in-Water Emulsions

Interconnected microcellular polymeric monoliths have been prepared from oil-in-water concentrated emulsions of aqueous 1-vinyl-1,2,4-triazole using the high internal phase emulsion methodology. The polyHIPE materials thus obtained present a typical polyHIPE morphology having unexpectedly high mechanical strengths considering their low cross-linking level (3 mol % of N,N′-methylenebis(acrylamide)). 13C, 15N, and 1H solid-state NMR analyses confirm the expected polymer structure and evidenced the presence of polymer chain association by strong hydrogen bonding with water.

Litter decay rates are determined by lignin chemistry

Litter decay rates are often correlated with the initial lignin:N or lignin:cellulose content of litter, suggesting that interactions between lignin and more labile compounds are important controls over litter decomposition. The chemical composition of lignin may influence these interactions, if lignin physically or chemically protects labile components from microbial attack. We tested the effect of lignin chemical composition on litter decay in the field during a year-long litterbag study using the model system Arabidopsis thaliana. Three Arabidopsis plant types were used, including one with high amounts of guaiacyl-type lignin, one with high aldehyde- and p-hydroxyphenyl-type lignin, and a wild type control with high syringyl-type lignin. The high aldehyde litter lost significantly more mass than the other plant types, due to greater losses of cellulose, hemicellulose, and N. Aldehyde-rich lignins and p-hydroxyphenyl-type lignins have low levels of cross-linking between lignins and polysaccharides, supporting the hypothesis that chemical protection of labile polysaccharides and N is a mechanism by which lignin controls total litter decay rates. 2D NMR of litters showed that lignin losses were associated with the ratio of guaiacyl-to-p-hydroxyphenyl units in lignin, because these units polymerize to form different amounts of labile- and recalcitrant-linkages within the lignin polymer. Different controls over lignin decay and polysaccharide and N decay may explain why lignin:N and lignin:cellulose ratios can be better predictors of decay rates than lignin content alone.

Synthesis of beaded poly(vinyl ether) solid supports with unique solvent compatibility

Poly(vinyl ether) gels SLURPS (Superior Liquid Uptake Resin for Polymer-supported synthesis) with low cross-linking levels have been synthesized for the first time in beaded form using a non-aqueous inverse suspension polymerisation approach. The synthetic protocol was optimized with regards to several parameters including reactions conditions, type and concentration of suspension stabilizer and controlled low temperature addition of co-initiator. Particle size measurements confirm the production of beads with average diameters of 700–950 μm. Optimization of the monomer composition of the poly(vinyl ether) gels resulted in a novel beaded polymer support with considerably improved as well as unique swelling characteristics in solvents ranging from hexane to water. The synthetic utility of the new gel was confirmed by carrying out a set of transformations with complete conversion leading to a useful amino and hydroxy terminated solid-phase precursor resin. Reaction progress could be monitored easily by 1H and 13C gel-phase NMR.

Controlled Sparse and Percolating Cross-Linking in Waterborne Soft Adhesives

The effect of low levels of cross-linking on the adhesive and mechanical properties of waterborne pressure-sensitive adhesives was investigated. We have taken advantage of a core-shell latex particle morphology obtained by emulsion polymerization to create a heterogeneous structure of cross-links without major modification of the monomer composition. The latex particles comprise a shell containing cross-linkable diacetone acrylamide (DAAM) repeat units localized on the periphery of a slightly softer core copolymer of very similar composition. Adipic acid dihydrazide was added to the latex prior to film formation to react with DAAM repeat units and affect interfacial cross-linking between particles in the adhesive films. The honeycomb-like structure obtained after drying of the latex results in a good balance between the dissipative properties required for adhesion and the resistance to creep. The characterization of the mechanical properties of the films shows that the chosen cross-linking method creates a percolating lightly cross-linked network, swollen with a nearly un-cross-linked component. With this cross-linking method, the linear viscoelastic properties of the soft films are nearly unaffected by the cross-linking while the nonlinear tensile properties are greatly modified. As a result, the long-term shear resistance of the adhesive film improves very significantly while the peel force remains nearly the same. A simple rheological model is used to interpret qualitatively the changes in the material parameters induced by cross-linking.

Effects of structure and modification on sustained release properties of starches

Starches of different sources and compositions were investigated to determine the effect of structure and chemical modification on the sustained release properties of the resultant modified starches. Starches were cross-linked with epichlorohydrin and substituted with carboxymethyl or aminoethyl groups at different levels. Substitution efficiency was overall higher for waxy corn and potato starches than for Hylon VII, and was higher for starches at low cross-linking levels than those at high cross-linking ones. Waxy corn starch displayed better sustained release properties when cross-linked to a lower level, whereas Hylon VII showed better performances when cross-linked to a higher level. Matrices substituted with carboxymethyl and aminoethyl groups at the high level showed better sustained release properties than those substituted at the low level. The proportion and structure of amylose and amylopectin in starches from different botanical sources strongly influenced the level of modification required to produce a satisfactory sustained release matrix.

Structure–property relationships in photopolymerizable polymer networks: Effect of composition on the crosslinked structure and resulting thermomechanical properties of a (meth)acrylate‐based system

AbstractPhotoinitiated polymer networks were formed by copolymerization of tert‐butyl acrylate with di(ethylene glycol) dimethacrylate (DEGDMA) or poly(ethylene glycol) dimethacrylate (PEGDMA). The degree of crosslinking was systematically varied by modifying the weight fraction and molecular weight of the dimethacrylate crosslinking agent. An increase in effective crosslink density with increasing crosslinking agent concentrations was confirmed by decreasing equilibrium swelling ratios (q) and increasing rubbery moduli (ER). Glass transition temperatures (Tg) varied from −22 to 124°C, increasing with increasing DEGDMA content and decreasing with increasing PEGDMA content. Tensile deformation behavior (at Tg) ranged from an elastomeric‐like large‐strain response for lightly crosslinked materials to a small‐strain brittle response for highly crosslinked networks. At low crosslinking levels, the strain‐to‐failure of the network polymers decreased quickly with increasing crosslinking agent concentration. The stress at failure demonstrated a more complex relationship with crosslinking agent concentration. The effect of composition on network structure and resulting properties (q, ER, strain‐to‐failure) decreased as the crosslinking agent concentration increased. The results reveal trade‐offs in Tg, ER, strain‐to‐failure, and failure stress with composition and network structure, and are discussed in light of the wide range of potential applications suggested in the literature for (meth)acrylate‐based photopolymerizable polymer networks including biomaterials and shape‐memory polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effective oral delivery of insulin in animal models using vitamin B12-coated dextran nanoparticles

The potential utility of vitamin B12 carrier system for the oral delivery of conjugated peptides/proteins and enhancement of nanoparticles (NPs) transport has been demonstrated. The present study aims to optimize the effectiveness of VB12–NPs conjugates using different levels of cross-linking, linked with different VB12-coatings and evaluates in animal models to investigate an efficient insulin carrier. Amino alkyl VB12 derivatives suitable for oral delivery were synthesized at 5′hydoxy ribose and e-propionamide sites via carbamate and ester/amide linkages, and were coupled to succinic acid modified dextran NPs of varied cross-linking. VB12 binding was confirmed by XPS analysis, and was quantified by HPLC (4.0 to 5.7% w/w of NPs). These polydisperse NPs conjugates showed higher size, high insulin entrapment and faster insulin release with low levels of cross-linking. These VB12–NPs conjugates (150–300 nm) showed profound (70–75% blood glucose reductions) and prolonged (54 h) anti-diabetic effects with biphasic behaviour in STZ diabetic rats. NPs with the low levels of cross-linking were found to be superior carriers, and were more effective with VB12 derivatives of carbamate linkage. The pharmacological availability relative to SC insulin was found to be 29.4%, which was superior compared to NPs conjugate of ester linked VB12 (1.5 fold) and relatively higher cross-linked particles (1.1 fold). Further, the NPs carrier demonstrated a similar oral insulin efficacy in congenital diabetic mice (60% reduction at 20 h). Significant quantities of plasma insulin were found in both animal models (231 and 197 μIU/ml). At two investigated doses, the carrier system shows dose response. Pre-dosing with a large excess of free VB12 minimized the observed activity, indicating predominance of VB12 mediated uptake. It is concluded that VB12–dextran NPs conjugate is a viable carrier for peroral insulin delivery to treat diabetics.

Molecular architecture and rheological characterization of novel intramolecularly crosslinked polystyrene nanoparticles

AbstractNovel polystyrene nanoparticles were synthesized by the controlled intramolecular crosslinking of linear polymer chains to produce well‐defined single‐molecule nanoparticles of varying molecular mass, corresponding directly to the original linear precursor chain. These nanoparticles are ideal to study the relaxation dynamics/processes of high molecular mass polymer melts, as the high degree of intramolecular crosslinking potentially inhibits entanglements. Both the nanoparticles and their linear analogs were characterized by measuring their intrinsic viscosity, hydrodynamic radius (Rh), and radius of gyration (Rg). The ratio Rg/Rh was computed to characterize the molecular architecture of the nanoparticles in solution, revealing a shift toward the constant density sphere limit with increasing crosslink density and molecular mass. Further, confirming particulate behavior, Kratky plots obtained from neutron scattering data show a shift toward particle‐like nature. The rheological behavior of the particles was found to be strongly dependent on both the extent of intramolecular crosslinking and molecular mass, with a minimal viscosity change at low crosslinking levels and a gel‐like behavior evident for a large degree of crosslinking. These and other results suggest the presence of a secondary mode of polymer relaxation/movement besides reptation, which in this case, is influenced by the total number of crosslinked loops present in the nanoparticle. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1930–1947, 2006

Colloid Probe AFM Investigation of the Influence of Cross-Linking on the Interaction Behavior and Nano-Rheology of Colloidal Droplets

The repulsive forces between a glass sphere and immobilized colloidal droplets of poly(dimethylsiloxane) (PDMS) (with various levels of internal cross-linking) have been determined in aqueous solution using colloid probe atomic force microscopy. On initial surface approach, droplet deformation is negligible and interaction forces resemble those expected for electrical double layer interaction of rigid spheres. Upon further approach, droplet flattening results in forces that deviate below rigid body electrical double layer interaction. The extent of droplet deformation has been determined in terms of the deviation from hard-sphere interaction. Droplet deformability is strongly dependent on the droplet cross-linking level and hence controlled by some combination of the bulk rheological and interfacial properties of the droplets. Droplet nano-rheology has been determined from the extent of force curve hysteresis. For liquidlike droplets, with low levels of cross-linking, no force curve hysteresis is observed and the elastic deformation may be described by a single spring constant, which is controlled by the interfacial properties. For highly cross-linked droplets, the extent of deformation is controlled by the droplet's bulk rheology rather than the interfacial properties. Upon retraction of the surfaces, force curve hysteresis is observed and is due to the viscoelastic response of the PDMS. The extent of hysteresis is dependent on the rate of approach/retraction and the loading force and has been theoretically analyzed to determine nano-rheological parameters that describe droplet relaxation processes. Elastic moduli and relaxation times of the PDMS droplets vary over several orders of magnitude as a function of cross-linking.

Phase behavior of liquid crystalline elastomers based on a tri-vinyl mesogenic cross-linker

A series of cross-linked liquid crystalline polymers are prepared by graft copolymerization, and their liquid crystalline properties are characterized by DSC and POM. The results show that low levels of cross-linking do not obviously affect the phase behavior of the network polymers; in contrast, high levels of cross-linking may have more drastic influences, and liquid crystalline phases may lose, and more marked variation in phase transition will occur in materials with more direct coupling through a shorter or stiffer coupling chain between mesogenic side units and polymer backbone. At the same time, the coupling between the polymer chain and sidegroups results in stress-induced orientation in LCEs.

Interaction forces, deformation and nano-rheology of emulsion droplets as determined by colloid probe AFM

Atomic force microscopy (AFM) has been used to determine the interaction forces between a spherical silica probe and immobilised colloidal droplets of polydimethylsiloxane (PDMS) in aqueous solution. Under mildly alkaline conditions where PDMS droplets and the silica probe are both negatively charged, a repulsive force is evident that increases less rapidly on surface approach than expected for electrical double layer interaction of rigid particles. The departure from hard-sphere behaviour enables the extent of droplet deformation to be determined and by varying the extent of internal cross-linking within the PDMS droplets, the influence of bulk rheology and interfacial tension on droplet deformation and nano-rheology has been isolated. For highly cross-linked droplets, the extent of deformation is controlled by the bulk rheology rather than the droplet's interfacial properties. Upon retraction of the surfaces, force curve hysteresis is observed and is due to the viscoelastic response of the PDMS. The extent of hysteresis is dependent on the rate of approach/retraction and the loading force, and has been theoretically fitted to obtain nano-rheological parameters, which describe the droplet relaxation processes. For liquid-like droplets, with a low level of cross-linking, no force curve hysteresis is observed and the elastic deformation may be described by a single spring constant. The spring constant is proportional to the surface tension (as controlled by surfactant adsorption) and the reciprocal of the droplet radius, i.e. the Laplace pressure exclusively controls droplet deformation. These colloid probe AFM studies offer due insight into the deformation and interaction of emulsion droplets and have implications when considering the stability, adhesion and processing of emulsions.

Interaction forces, deformation and nano-rheology of emulsion droplets as determined by colloid probe AFM

Atomic force microscopy (AFM) has been used to determine the interaction forces between a spherical silica probe and immobilised colloidal droplets of polydimethylsiloxane (PDMS) in aqueous solution. Under mildly alkaline conditions where PDMS droplets and the silica probe are both negatively charged, a repulsive force is evident that increases less rapidly on surface approach than expected for electrical double layer interaction of rigid particles. The departure from hard-sphere behaviour enables the extent of droplet deformation to be determined and by varying the extent of internal cross-linking within the PDMS droplets, the influence of bulk rheology and interfacial tension on droplet deformation and nano-rheology has been isolated. For highly cross-linked droplets, the extent of deformation is controlled by the bulk rheology rather than the droplet's interfacial properties. Upon retraction of the surfaces, force curve hysteresis is observed and is due to the viscoelastic response of the PDMS. The extent of hysteresis is dependent on the rate of approach/retraction and the loading force, and has been theoretically fitted to obtain nano-rheological parameters, which describe the droplet relaxation processes. For liquid-like droplets, with a low level of cross-linking, no force curve hysteresis is observed and the elastic deformation may be described by a single spring constant. The spring constant is proportional to the surface tension (as controlled by surfactant adsorption) and the reciprocal of the droplet radius, i.e. the Laplace pressure exclusively controls droplet deformation. These colloid probe AFM studies offer due insight into the deformation and interaction of emulsion droplets and have implications when considering the stability, adhesion and processing of emulsions.

Tissue engineering matrixes by emulsion templating

AbstractFoams containing poly(lactic acid) (PLA) have been prepared from the corresponding macromonomers using high internal phase emulsions (HIPEs) as templates to create the porous structure. The resulting PolyHIPE foams have been investigated by scanning electron microscopy and the influence of diluent type, either reactive (styrene or methyl methacrylate (MMA)) or unreactive (toluene), on foam morphology has been determined. The morphology was found to depend on the type of diluent: styrene resulted in cellular materials at low PLA levels but tended to give structures characteristic of phase separation at higher PLA content; MMA yielded porous cellular materials at all levels of PLA; toluene tended to give soft materials that collapsed on drying. The swelling of the foam materials in toluene, isopropyl alcohol (IPA) and water was also investigated. It was found that most of the foams swelled to a relatively low extent in all solvents, apart from that of low PLA content made with toluene. This was ascribed to a low crosslinking level and high porosity of this material. Cell and tissue growth studies on the resulting foams, as well as analogues prepared from poly(ε‐caprolactone) (PCL) macromonomers, using whole chicken embryo explants, rat skin explants or individual human skin cells, indicated excellent biocompatibility of all foams over the length of each experiment (maximum length 6 days). Comparative studies indicated that cells adhered to PCL‐based materials more rapidly than their PLA‐containing counterparts.© 2002 Society of Chemical Industry

Binding of Cross-Linked Glycosylphosphatidylinositol-Anchored Proteins to Discrete Actin-Associated Sites and Cholesterol-Dependent Domains

The mechanism by which cross-linked glycosylphosphatidylinositol (GPI)-anchored proteins are immobilized has been a mystery because both the binding to a transmembrane protein and attachment to a rigid cytoskeleton are needed. Using laser tweezers surface scanning resistance (SSR) technology, we obtained physical evidence for cross-linked GPI-anchored protein, Qa-2, binding to a transmembrane protein and for diffusion to discrete cytoskeleton attachment sites. At low levels of cross-linking of Qa-2 molecules, the resistance to lateral movement was that expected of monomeric lipid-anchored proteins, and no specific binding to cytoskeleton-attached structures was observed. When aggregates of the GPI-anchored protein, Qa-2, were scanned across plasma membranes, the background resistance was much higher than expected for a GPI-anchored protein alone and submicron domains of even higher resistance were observed (designated as elastic or non-elastic barriers) at a density of 82 (61 elastic and 21 small non-elastic barriers) per 100 μm 2. Elastic barriers involved weak but specific bonds to the actin cytoskeleton (broken by forces of 2 or 4 pN and were removed by cytochalasin D). Small non-elastic barriers (50–100 nm) depended upon membrane cholesterol and were closely correlated with caveolae density. Thus, cross-linked GPI-anchored proteins can diffuse through the membrane in complex with a transmembrane protein and bind weakly to discrete cytoskeleton attachment sites either associated with flexible actin networks or sphingolipid-cholesterol rich microdomains in live cell membranes. Our SSR measurements provide the first description of the physical characteristics of the interactions between rafts and stable membrane structures.

Reactive processing of polyethylenes on a single screw extruder

AbstractThe modification of low density polyethylene, linear low density polyethylene, and their blend by dicumyl peroxide at the time of the extrusion on a single screw extruder is reported. The study shows that the optimum conditions of modification can be determined on a torque rheometer and these can then be applied for actual extrusion. A low level of crosslinking can be introduced by reactive extrusion for improving the heat stability without adversely affecting the processing behavior. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2545–2549, 2001

A Study on Gelatin Capsule Brittleness: Moisture Tranfer between the Capsule Shell and Its Content

□ Variation in moisture content of the capsule shells either due to the change of storage conditions or the moisture transfer between the capsule shell and its contents may lead to undesired physical properties, such as capsule brittleness and stickiness. DMP 504, a developmental bile-acid sequestrant, is a strongly basic anionexchange polymer which contains randomly distributed primary, secondary, tertiary, and quaternary amine groups in their hydrochoride salt form. The alkylammonium groups which comprise this polymer form a random network containing a high level of branching and a low level of cross-linking. DMP 504 is very hygroscopic and has a tendency to gain or lose moisture with ease. The transfer of moisture from the capsule shell to DMP 504 powder contained in a hard gelatin capsule can be expected, and if a low water content of the capsule shell is achieved, the capsules become brittle and fracture easily. The sorption isotherm for DMP 504 was generated by storing the drug substance under various relative humidity conditions. After equilibrium, the moisture contents for the samples of individual isotherm points were measured by thermogravimetric analyses. This report applies the sorption–desorption moisture transfer (SDMT) model to predict the equilibrium relative humidity in a system containing DMP 504 in hard gelatin capsules and to establish target loss on drying values for DMP 504 and the capsule shell. Application of this SDMT model resulted in finding a solution to the brittleness problem. The moisture levels of capsule shells and contents for two formulations in a 12-month stability program are also reported here. Results of this study further demonstrate that the SDMT model can be used as a tool to guide the formulator to select optimal initial moisture contents for the empty capsule shell and the formulation to avoid the incidence of brittle capsule problems.

Subunit Structure of Rod cGMP-Phosphodiesterase

The rod cGMP phosphodiesterase (PDE) is the G-protein-activated effector enzyme that regulates the level of cGMP in vertebrate photoreceptor cells. Rod cGMP PDE is generally viewed as a heterotrimeric protein composed of catalytic alpha and beta subunits ( approximately90 kDa each) and two copies of the inhibitory subunit gamma ( approximately 10 kDa). However, the possibility that rod PDE could exist as distinct isoforms, such as alphaalphagamma2 and betabetagamma2 has not been ruled out. We have studied this question using cross-linking of PDE subunits with maleimidobenzoyl-N-hydroxysuccinimide ester and para-phenyldimaleimide. The cross-linking resulted in major products with molecular mass of 100 and 150 kDa, a doublet at approximately 180-190 kDa, and a doublet at approximately 210-220 kDa. Cross-linked products were analyzed using polyclonal-specific anti-PDEalphabeta, anti-PDEalpha, anti-PDEbeta, or anti-PDEgamma antibodies. The anti-PDEalpha and anti-PDEalphabeta antibodies recognized all the cross-linked products, whereas anti-PDEbeta and anti-PDEgamma antibodies did not interact with the 150-kDa band, indicating that the composition of this band is most likely alphaalpha. Similar analysis of cross-linked products of trypsin-treated PDE preparations revealed bands that are likely formed by PDEbeta subunit. The molecular size of holo-PDE and trypsin-activated PDE were studied using analytical ultracentrifugation in order to determine if oligomerization of PDE could account for the cross-linking of identical PDE subunits. The sedimentation analysis of both holo-PDE and ta-PDE revealed homogeneous samples with molecular masses of approximately220 and approximately150 kDa, respectively. These results indicate that PDE is likely a mixture of the major species alphabetagamma2, minor species alphaalphagamma2, and possibly betabetagamma2. Our data are consistent with the detection of low PDE activity in the rd mouse, which lacks any functional PDEbeta subunit.

Effects of Cross-Linking on the Morphology of Structured Latex Particles. 1. Theoretical Considerations

Cross-linking of the seed latex polymer introduces elastic forces into the thermodynamic analysis of the morphology of composite particles. By determining the elastic storage energy necessary to maintain a deformation within the seed latex particle (as in an occlusion of second-stage polymer), it can be combined with the interfacial energies internal to the particle and at its aqueous phase boundary to compute the total free energy of a specific particle morphology. At low levels of cross-linking it is found that the elastic and interfacial energies are of the same order of magnitude, with the final morphology determined by the balance between them. Elastic energies are dependent upon the state of deformation within the particle, and this makes the thermodynamic equilibrium morphology analysis dependent upon cross-link level, seed latex particle size, stage ratio (second polymer/seed polymer), and the interfacial tensions at the polymer/polymer and polymer/water interfaces. Computational results are presented which show the effects of each of these variables on the predicted morphology.