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The high number of patients infected with the SARS-CoV-2 virus requiring care for ARDS puts sedation in the critical care unit (CCU) to the edge. Depth of sedation has evolved over the last 40 years (no-sedation, deep sedation, daily emergence, minimal sedation, etc.). Most guidelines now recommend determining the depth of sedation and minimizing the use of benzodiazepines and opioids. The broader use of alpha-2 adrenergic agonists (‘alpha-2 agonists’) led to sedation regimens beginning at admission to the CCU that contrast with hypnotics+opioids (“conventional“ sedation), with major consequences for cognition, ventilation and circulatory performance. The same doses of alpha-2 agonists used for ‘cooperative’ sedation (ataraxia, analgognosia) elicit no respiratory depression but modify the autonomic nervous system (cardiac parasympathetic activation, attenuation of excessive cardiac and vasomotor sympathetic activity). Alpha-2 agonists should be selected only in patients who benefit from their effects (‘personalized’ indications, as opposed to a ‘one size fits all’ approach). Then, titration to effect is required, especially in the setting of systemic hypotension and/or hypovolemia. Since no general guidelines exist for the use of alpha-2 agonists for CCU sedation, our clinical experience is summarized for the benefit of physicians in clinical situations in which a recommendation might never exist (refractory delirium tremens; unstable, hypovolemic, hypotensive patients, etc.). Because the physiology of alpha-2 receptors and the pharmacology of alpha-2 agonists lead to personalized indications, some details are offered. Since interactions between conventional sedatives and alpha-2 agonists have received little attention, these interactions are addressed. Within the existing guidelines for CCU sedation, this article could facilitate the use of alpha-2 agonists as effective and safe sedation while awaiting large, multicentre trials and more evidence-based medicine.

ABSTRACTDuring severe septic shock and/or severe acute respiratory distress syndrome (ARDS) patients present with a limited cardio-ventilatory reserve (low cardiac output and blood pressure, low mixed venous saturation, increased lactate, low PaO2/FiO2 ratio, etc.), especially when elderly patients or co-morbidities are considered. Rescue therapies (low dose steroids, adding vasopressin to noradrenaline, proning, almitrine, NO, extracorporeal membrane oxygenation, etc.) are complex. Fever, above 38.5–39.5°C, increases both the ventilatory (high respiratory drive: large tidal volume, high respiratory rate) and the metabolic (increased O2 consumption) demands, further limiting the cardio-ventilatory reserve. Some data (case reports, uncontrolled trial, small randomized prospective trials) suggest that control of elevated body temperature (“fever control”) leading to normothermia (35.5–37°C) will lower both the ventilatory and metabolic demands: fever control should simplify critical care management when limited cardio-ventilatory reserve is at stake. Usually fever control is generated by a combination of general anesthesia (“analgo-sedation”, light total intravenous anesthesia), antipyretics and cooling. However general anesthesia suppresses spontaneous ventilation, making the management more complex. At variance, alpha-2 agonists (clonidine, dexmedetomidine) administered immediately following tracheal intubation and controlled mandatory ventilation, with prior optimization of volemia and atrio-ventricular conduction, will reduce metabolic demand and facilitate normothermia. Furthermore, after a rigorous control of systemic acidosis, alpha-2 agonists will allow for accelerated emergence without delirium, early spontaneous ventilation, improved cardiac output and micro-circulation, lowered vasopressor requirements and inflammation. Rigorous prospective randomized trials are needed in subsets of patients with a high fever and spiraling toward refractory septic shock and/or presenting with severe ARDS.

The adsorption of lipids onto spherical polymer colloids led to original assemblies presenting structural characteristics adjustable with the lipid formulation. The model system selected for this work involved sulfate-charged poly(styrene) submicrometer particles and zwitterionic/cationic lipid mixtures composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP). According to the theoretical packing parameter calculations and whatever the DPPC/DPTAP ratio, the two lipids self-assembled in aqueous media to spontaneously form vesicles. A phase transition investigation of these DPPC/DPTAP vesicles using differential scanning calorimetry revealed particular thermotropic behaviors, especially for the equimolar formulation where very strong interactions occurred between DPPC and DPTAP. Furthermore, the coating of the lipids around particles was monitored versus DPPC/DPTAP ratio by means of numerous appropriate techniques. First, a thermogravimetric analysis, providing decomposition profiles of lipid/polymer particle assemblies with temperature, was atypically carried out for such nanostructures. Then, ¹H NMR spectroscopy enabled the exact DPPC/DPTAP molar ratios adsorbed on particles to be determined by differentiating both lipids. Subsequently, it also pointed out the major role of electrostatic interactions as driving forces in the assembly elaboration process. In addition to these findings, quantitative information has been collected and correlated with chemical lipid assays and permitted the statement of a lipid bilayer coverage for the assemblies prepared in water, in agreement with quasi-elastic light scattering data.

Abstract: Using the stepwise heterocoagulation concept, fluorescent and highly magnetic submicronic core-shell polymer particles were prepared. For this purpose a negatively charged oil-in-water magnetic emulsion was first modified by adsorbing the poly(ethyleneimine) (PEI). Secondly, low glass transition temperature (T g=10°C) anionic film-forming nanoparticles were adsorbed onto the cationic magnetic droplets. Finally the encapsulation was induced by heating the heterocoagulates above the T g of the film-forming nanoparticles. To produce labeled magnetic particles, fluorescent nanoparticles and film-forming nanoparticles were simultaneously adsorbed. PEI adsorption was investigated. Also investigated was the influence of the amount of film-forming nanoparticles and fluorescent nanoparticles on the encapsulation efficiency.

This work investigated the elaboration of biocompatible nanoparticles from the pH-induced self-complexation of the amphoteric polysaccharide N-sulfated chitosan. The acidification of aqueous solutions of chitosan having a degree of acetylation of 24% and a degree of sulfation of 34% or 56% was followed stepwise by turbidimetry, dynamic light scattering, and electrophoresis. With the highest sulfated chitosan, no turbidity was recorded between pH = 7.8 and 2.0, traducing a high apparent solubility of the polymer chains in this domain of pH. With the lowest sulfated chitosan, a steady increase in turbidity was monitored from pH = 6.90 to 6.15 followed by the flocculation of the polymer at pH ~ 6.0. In this range of pH, the polymer phase separated to yield particles having hydrodynamic diameters decreasing from 350 to 260 nm and an almost constant negative charge. These particles were assembled by electrostatic interactions between the protonated amino residues and the sulfate functions and stabilized by an excess of surface sulfate groups. The particles could be separated from the reaction medium and concentrated by centrifugation−redispersion cycles without alteration of their structure.

An amphiphilic block copolymer poly(tert-butylacrylamide-b-(N-acryloylmorpholine-N-acryloxysuccinimide)) (poly(TBAm-b-(NAM/NAS)) and a random copolymer poly(NAM/NAS), synthesized by the reversible addition−fragmentation chain transfer (RAFT) polymerization process, have been used as support for oligonucleotide (ODN) synthesis, to elaborate polymer−oligonucleotide conjugates. In a first step, starters of ODN solid-phase synthesis were coupled to activated ester functions of polymers, and second, resulting functionalized polymers were covalently grafted onto hydroxylated controlled pore glass (CPG) support to further accomplish ODN synthesis. An efficient capping of residual hydroxyl functions of CPG was performed before synthesis, with both acetic anhydride and diethoxy-N,N-diisopropyl-phosphoramidite reagents, to suppress parasite-free ODN population present in conjugate crude material and resulting from syntheses directly initiated on silica beads. After purification, conjugates were evaluated in a DNA hybridization assay on a microarray, as macromolecules being able to favor capture of the target. Conjugate coating conditions were studied on the dT25/dA25 model. The role of the hydrophobic part (poly(TBAm)) of the conjugate synthesized with the block copolymer in the orientation of the conjugate after coating was revealed by spotting experiments achieved in a mixed solvent (DMF/H2O). The use of block copolymer−dT25 conjugate afforded a significant sensitivity improvement of the hybridization assay.

A model study was investigated to develop colloidal supramolecular assemblies consisting of particles coated with lipid layers. The interactions between monodisperse sulfate-charged poly(styrene) submicrometer particles and zwitterionic/cationic lipid vesicles composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dipalmitoyl-3-trimethylammonium propane were considered. The influence of relevant experimental parameters on the final associations was examined by quasi-elastic light scattering to point out some new phenomena occurring in these colloidal systems. The major role of electrostatic interactions as driving forces to control the organization between cationic lipids and oppositely charged poly(styrene) particles was clearly evident, whereas this influence was less pronounced when considering the zwitterionic lipids. The characterization of these original complex assemblies was completed by a thorough study of the surface modification. The combination of zeta potential measurements, X-ray photoelectron spectroscopy analyses, and microscopy observations proved that the envisioned model can really correspond to polymer particles surrounded by lipids.

The formation of colloids based on polyelectrolyte complexes (PECs) of biopolymers was investigated through the complexation between two charged polysaccharides, chitosan as polycation, and dextran sulfate as polyanion. The slow dropwise addition of components, generally used for the formation of PECs, allowed to elaborate both cationic or anionic particles with an excess of chitosan or dextran sulfate, respectively. The PEC particles featured a core/shell structure, the hydrophobic core resulting from the segregation of complexed segments whereas excess component in the outer shell ensured the colloidal stabilization against further coagulation. Considering the host/guest concept for the formation of PECs, the influence of the molecular weight of components on particles sizes could be well explained by the chain length ratios of the two polymers. As an irreversible flocculation occurred with a dropwise approach for both cationic and anionic PEC particles when the mixing ratio was close to unity, a more versatile, and simpler to setup, method was designed:  the one-shot addition of one solution to the other. Because process of addition is faster than the flocculation, cationic or anionic particles could be elaborated irrespective of the order of addition of the reactant. Characterization of these particles by quasielastic light scattering, electrophoresis, and scanning electron microscopy revealed very similar properties to those obtained by a slow dropwise approach. Critical coagulation concentrations of 0.12 and 0.09 M (with sodium chloride) for cationic and anionic particles evidenced a mostly electrostatic stabilization.

Formation of colloids based on polyelectrolyte complexes (PECs) was mainly studied with synthetic polyelectrolytes. In this study, we describe the elaboration of positively charged PEC particles at a submicrometer level obtained by the complexation between two charged polysaccharides, chitosan as polycation and dextran sulfate (DS) as polyanion. The complexes were elaborated by dropwise addition of default amounts of DS to excess chitosan. Quasi-elastic light scattering was used to investigate in detail the influence of the characteristics of components (chain length, degree of acetylation) and parameters linked to the reaction of complexation (molar mixing ratio, ionic strength, concentration in polymer) on the sizes and polydispersity of colloids. Chain length of chitosan is the major parameter affecting the dimensions of the complexes, high molar mass chitosans leading to the largest particles. Variations of hydrodynamic diameters of PECs with the molar mass of chitosan are consistent with a mechanism of particle formation through the segregation of the neutral and then hydrophobic blocks of the polyelectrolyte complexed segments. Resulting particles display probably a structure constituted by a neutral core surrounded by a chitosan shell ensuring the colloidal stabilization. Such a structure was evidenced by measurements of electrophoretic mobilities revealing that the positive charge of particles was decreasing with pH, in relation with the neutralization of excess glucosamine hydrochloride moieties.

The adsorption of a rhodamine X labeled oligonucleotide composed of 25-mers of thymine (dT25-ROX) onto the thermosensitive shell of PMMA/PNIPAM core−shell latex particles was studied at 22 and 40 °C, below and above the TVPT (volume phase transition temperature) of the PNIPAM shell, respectively. The experimental binding isotherms were well fitted with the cooperative Hill model. The Hill coefficient is lower than 1 at both temperatures showing that the adsorption is anticooperative. The polarity of the shell was probed by both the lifetimes and solvatochromic shifts of the zwitterionic form of rhodamine X. For temperatures below the shell TVPT has a polarity similar to that of water, while for temperatures above the transition the polarity is equivalent to that of a water/dioxane mixture with 30% (v/v) water.

A matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI−TOF MS) study of N-acryloylmorpholine (NAM) homopolymers, as obtained by reversible addition−fragmentation chain transfer (RAFT) polymerization technique, is reported. Polymerization of NAM was performed in dioxane using azobis(isobutyronitrile) (AIBN) as initiator and tert-butyl dithiobenzoate as RAFT chain transfer agent. Polymer samples of low molecular weights (<10 000 g mol^-1) and low polydispersity indices (PDI < 1.1) were obtained, which are essential requirements for such MALDI−TOF MS analysis. First, analysis of poly(NAM) samples in linear mode led to %@mt;sys@%%@ob@%%@ital@%M%@rsf@%%@sb@%n%@sbx@%%@obx@%%@mx@% values very close to both size exclusion chromatography/light scattering (SEC/LS) and ¹H NMR values as well as to the theoretical ones. Then, an accurate examination of chain end groups was performed using the reflectron mode. Two main chain populations were identified:  (i) dormant chains (i.e., initiated by a tert-butyl and terminated by a dithiobenzoate group) together with sulfine and thioester-ended chains probably resulting from oxidation of dithiobenzoate chain ends during storage; (ii) proton-terminated chains mainly produced by fragmentation of the former chains in the spectrometer. In addition, some chains which could correspond to termination reactions onto the intermediate radicals involved in the RAFT equilibrium were suspected. Finally, comparison of polymer samples before and after aminolysis indicated that dithioester-ended chains constituted the majority of chains initially present in these samples. This study confirms that it is indeed possible to use MALDI−TOF MS to investigate the structure of polymer chains synthesized by the RAFT technique.

The neutralization of a homogeneous series of chitosans with degrees of acetylation (DA) varying between 1% and 71% was followed stepwise by static light scattering. The determination of the gyration radii (RG,z) and the second virial coefficients (A2) allowed us a better understanding of the chitosan behavior during the neutralization in aqueous solutions. On increasing pH, a critical value was evidenced both by a drop of RG,z and a fall of A2. The values of the critical pH were also shown as highly dependent on the polymer concentration and the ionic strength of the media. On increasing DA, the range of pH where chitosan was apparently soluble enlarged although the second virial coefficient decreased with both the increase of DA and the degree of neutralization. Working at the critical pH, just before precipitation occurred, transmission electronic microscopy allowed us to evidence a sol/gel transition responsible for the formation of a stable colloidal dispersion. The average particle sizes increased with the degree of acetylation:  from 100 nm for DA = 1% to 300 nm for DA = 51%. These aggregates were probably assembled both by hydrophobic interactions and hydrogen bonding due to the neutralization of the ammonium groups into −NH2.

Nano size-ranged poly(d,l-lactic acid) (PLA) particles were obtained from 2 and 10 w% PLA solution in water-saturated ethyl acetate by the emulsification-diffusion method. An increase in the PLA solution concentration resulted in an increase of the particle mean size from ca 260 nm to 530 nm with a broadening of the distribution. After fractionation by centrifugation, the particle mean size was 980 nm. The Pluronic F68 used in the formulations at concentration ranging from 0.5 to 5% w/v, was shown to adsorb at the interface at 0.5 mg/m 2 for both particle sizes. The molecular occupied area of 24 nm 2/molecule suggested an expanded conformation of the surfactant at the interface, though an incomplete coverage could not be excluded. Coagulation kinetics measurements revealed a critical coagulation concentration (CCC) of 1.5 M sodium chloride, indicating a steric stabilization of the colloids by the adsorbed triblock copolymer. Nonetheless, variations in zeta potential with increasing salt concentration were observed, suggesting that the surface carboxylate groups were still accessible for further modifications.

Free-radical solution copolymerization of acrylamide (AAm) and of a disubstituted acrylamide derivative, N-acryloylmorpholine (NAM), with N-acryloxysuccinimide (NAS) was investigated with the aim to obtain a copolymer of at least 100,000 g mol⁻¹. Different polymerization conditions likely to increase the molecular weight were studied such as monomer and initiator concentrations, temperature, and nature of the solvent. The molecular weights were determined by SEC using a light-scattering detector. The grafting of end-functionalized polysaccharide chains onto such high molecular weight poly(NAM-co-NAS) was performed and a graft copolymer bearing a high number of saccharidic branches was obtained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1808–1816, 2003

Physicochemical properties of a homogeneous series of chitosans with different degrees of acetylation and almost the same degree of polymerization were investigated in an ammonium acetate buffer. Techniques such as interferometry, static light scattering (in batch or coupled on line with a chromatographic system), and viscometry were processed. All of the results agree with a unique law of behavior only depending on the degree of acetylation of the polymer. Indeed, values of the refractive index increment, radius of gyration, second virial coefficient, and intrinsic viscosity are decreasing in the same way as DA is increasing. Three distinct domains of DA were defined and correlated to the different behaviors of chitosans:  (i) a polyeletrolyte domain for DA below 20%; (ii) a transition domain between DA = 20% and 50% where chitosan loses its hydrophilicity; (iii) a hydrophobic domain for DAs over 50% where polymer associations can arise. Conformations of chitosan chains were studied by the calculations of the persistence lengths (Lp). The average value was found to be close to 5 nm, in agreement with the wormlike chain model, but no significant variation of Lp with the degree of acetylation was noticed.

Controlled radical polymerization of the bisubstituted acrylamide derivative N-acryloylmorpholine (NAM) has the potential to yield telechelic polymers, one end of which can subsequently be grafted to latex particles. Once grafted, the other chain end of the polymer can be used as an immobilization site for species with applications in molecular biology and biomedicine. The controlled polymerization of NAM using reversible addition−fragmentation chain transfer (RAFT) is performed using two new chain transfer agents S&dbd;C(Z)−SR bearing the same functional propanoic acid group (R) and two different Z groups, benzyl (CTA 1) and phenyl (CTA 2). RAFT polymerization of NAM mediated by CTA 1 is very fast (>80% conversion in less than half an hour at 65 °C). The linear evolution of &Mmacr;n and the low polydispersity indices (&Mmacr;w/&Mmacr;n < 1.2) are in accord with the expected characteristics of a living polymerization. CTA 2 leads to broader &Mmacr;w/&Mmacr;n's (<1.4). The resulting CTA-capped polymers were further used to yield an amphiphilic polyNAM-block-polystyrene. These α,ω-functionalized polyNAM chains were characterized by ¹H NMR and MALDI-ToF mass spectrometry.

The “living” cationic polymerization of a new saccharidic monomer, namely 1,2:3,4-di-O-isopropylidene-6-O-(2-vinyloxyethyl)-d-galactopyranose (GVE) has been investigated using acetaldehyde diethyl acetal/trimethylsilyl iodide as the initiating system in the presence of ZnCl2 as co-initiator. To determine if the process is living, the conversion was followed by dilatometry or by regularly withdrawing samples and analyzing them by ¹H NMR. Fast polymerization occurred together with a nonlinear ln([M]0/[M] t) = f (t) plot indicating an apparent loss of active centers. Nevertheless, the ¹H NMR- and SEC-determined molecular weights proved the absence of termination and transfer reactions during the polymerization process. MALDI−TOF mass spectrometry confirmed the absence of such side reactions and indicated a parallel initiation consecutive to the presence of water traces in the trimethylsilyl iodide solution. The nonlinear ln([M]0/[M] t) = f (t) plot was attributed to specific interactions between the saccharidic rings and ZnCl2 and/or the growing carbocations.

Homopolymers of N-acryloylmorpholine (NAM), a water-soluble bisubstituted acrylamide derivative, have been synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT). Several dithioesters were used as chain transfer agents:  carboxymethyl dithiobenzoate (CMDB), tert-butyl dithiobenzoate (tBDB), menthonyl dithiobenzoate (MDB), and a bifunctional dithiobenzoate, 1,3-bis(2-(thiobenzoylthio)prop-2-yl)benzene (TPB). Whereas CMDB is a commercial reagent, tBDB and MDB were synthesized by a novel biphasic process based on a thioacylation reaction and leading to very high yields. The performances of the four dithiobenzoates were compared in term of kinetics and molecular weight distribution control. Very good control of NAM polymerization was obtained with tBDB and MDB, with a linear increase of Mn vs conversion over the whole conversion range and with polydispersity indices (PDI) below 1.1, as determined by aqueous size exclusion chromatography with on-line light scattering detection. In addition, a degradation phenomenon of the dithioester functions was evidenced during the course of the polymerization, correlated with a Mn vs conversion curve leveling off and even sometimes decreasing above 80% conversion. Such observations were assumed to be the consequence of the formation of side products in the polymerization media, subsequently acting as nondegradative irreversible transfer agents.

Monodisperse, thermosensitive poly(N-ethyl methacrylamide) microgel particles were prepared by the batch precipitation/emulsion polymerization of water-soluble N-ethyl methacrylamide and the hydrophobic crosslinker ethylene glycol dimethacrylate initiated by potassium persulfate. Particular attention was paid to the effect of the crosslinker agent on the polymerization process (kinetics, conversion, and water-soluble oligomer content). Particles were characterized in terms of their size distribution and swelling capacity. A polymerization mechanism for the water-soluble monomer and non-water-soluble crosslinker is proposed and discussed on the basis of a combination of both emulsion and precipitation polymerization processes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1808–1817, 2002

Hydrophilic and stimuli-responsive submicronic latex particles based on polyalkyl(meth)acrylamide can be prepared owing to simple radical-initiated polymerizations in heterogeneous media using a water-soluble initiator and a crosslinker (methylenebisacrylamide). The paper aims at reviewing the synthesis and properties of functionalized polystyrene-polyN-isoprpylacrylamide core-shell particles or polyN-isopropylmethacrylamide microgel particles. Particle size of analysis showed that a short nucleation period afforded the synthesis of highly monodispersed latexes. The dramatic change of the colloidal properties (particle size, electrophoretic mobility) was found to reflect the thermal sensitivity of such particles. The hydrophilic nature of the particles below the volume phase transition temperature was found to drastically reduce the physical adsorption of proteins. Some examples of biomedical applications of these stimuli-responsive particles are briefly reported.

Hydrophilic and stimuli‐responsive submicronic latex particles based on polyalkyl(meth)acrylamide can be prepared owing to simple radical‐initiated polymerizations in heterogeneous media using a water‐soluble initiator and a crosslinker (methylenebisacrylamide). The paper aims at reviewing the synthesis and properties of functionalized polystyrene‐polyN‐isoprpylacrylamide core‐shell particles or polyN‐isopropylmethacrylamide microgel particles. Particle size of analysis showed that a short nucleation period afforded the synthesis of highly monodispersed latexes. The dramatic change of the colloidal properties (particle size, electrophoretic mobility) was found to reflect the thermal sensitivity of such particles. The hydrophilic nature of the particles below the volume phase transition temperature was found to drastically reduce the physical adsorption of proteins. Some examples of biomedical applications of these stimuli‐responsive particles are briefly reported.

Abstract: Cationic nanoemulsions containing an oily core as potential carriers of nucleic acids were prepared by a solvent displacement method in the presence of a nonionic surfactant (Pluronic F68). With a view to functionalize such nanoemulsions for further incorporation of a fusogenic peptide, a poly(maleic anhydride-alt-methyl vinyl ether) (M n=67,000) grafted with variable amount of acetylspermine (or acetylspermidine) and decylamine was nanodeposited during the nanoemulsion formation step. Functionalized nanoemulsions were characterized in terms of particle size (by quasi-elastic light scattering and electron microscopy), electrophoretic mobility and long-term stability as a function of the amount of polymer used in the formulation. It was found that increases in the level of the copolymer led to a reduction in the particle size and a decrease in colloidal stability. In addition, the incorporation of the grafted copolymers at the interface of the nanoemulsions was clearly evidenced, a shift towards low pH at the point of zero charge being attributed to the formation of carboxylic groups induced by hydrolysis of the residual maleic anhydride groups of the copolymer.

Two negatively charged polystyrene latex dispersions with particles of similar diameter (around 100 nm) but different surface charge density (1.7 μC/cm² for CG18 and 2.3 μC/cm² for CG5) were compared in terms of their surface morphology. Since they were synthesized in the presence of a redox initiator (potassium persulfate/sodium metabisulfite), particles bore sulfate and sulfonate charged groups at the surface. Fluorescence decay measurements were performed in situ on these latex samples, using a pair of fluorescent cationic dyes adsorbed onto the surface:  Rhodamine 6G (R6G) as the energy transfer donor and malachite green carbinol hydrochloride (MG) as the acceptor. Since the kinetics of the direct nonradiative energy transfer process between the dyes is sensitive to the donor and acceptor distributions, fluorescence decay measurements provide information about the binding distribution of the cationic dyes, which reflects the distribution of the negative charges at the latex particle surface. For the highly charged sample (CG5), we found a dye distribution reflecting an interface thickness with an average value of δ = 2.9 ± 0.2 nm. For the CG18 sample, having a lower surface charge density, a thinner dye distribution was evidenced, with an interface thickness δ = 2.0 ± 0.1 nm. The broadening of the distribution with the increase of surface charge density was interpreted in terms of the steric hindrance and the electrostatic repulsion between the charged polymer chain ends extending into the aqueous medium.

Oligonucleotide−polymer conjugates have been described to improve the sensitivity of an enzyme-linked oligosorbent assay diagnostic test. To understand the influence of their structure and conformation in solution on the efficiency of the test during the capture step, two different ways of synthesizing these conjugates were compared. The first consisted of coupling 5‘ amino modified oligonucleotides to poly(maleic anhydride-alt-methylvinyl ether) and poly(maleic anhydride-alt-ethylene). The second resulted from direct synthesis of oligonucleotides from poly(maleic anhydride-alt-ethylene) previously grafted onto a controlled pore glass support. The different conjugates were analyzed by size-exclusion chromatography and viscometry. The former method for conjugate synthesis produced aggregates, which was not the case for the latter. These conjugates were then used in the capture phase of a hybridization assay using a HBV DNA target, on a bioMérieux VIDAS instrument. Different parameters were studied, such as the purity of the conjugate solution and the number of oligonucleotides per polymer chain. The amount of conjugate coated on the solid-phase receptacle surface at the time of the capture phase was evaluated by radioactive labeling. Finally, it was demonstrated that conjugates produced an amplification factor of 50 versus the capture oligonucleotide probe used as the reference. The detection limit reached 10⁸ copies/mL.

The adsorption of HIV-1 capsid p24 protein bearing six histidine residues (named RH24) onto well-characterized thermosensitive and cationic poly(styrene)−poly(N-isopropylacrylamide) core−shell particles was investigated as a function of temperature, pH, incubation time, and salinity. The maximum amount of adsorbed RH24 was observed when the temperature was above the lower critical solution temperature (LCST) of the hydrogel, whereas a negligible adsorbed amount occurred below the LCST. Adsorption isotherms were then determined above the LCST and exhibited well-defined plateaus, which were pH and ionic strength dependent. Isotherm data were tentatively discussed using the Freundlich power law, from which the standard free enthalpy of protein adsorption was estimated. The adsorption behavior of protein was mainly governed by hydrophobic interactions above the LCST; however, differences between the two latexes gave evidence that electrostatic forces also played a significant role.

The internal properties of submicron poly(N-isopropylmethacrylamide) latex particles were investigated as a function of the methylene bisacrylamide (MBA) concentration used as a crosslinker. Two experimental approaches were performed. First, quasi-electric light scattering measurements provided the size variation of the particles as a function of temperature, from which the swelling capacity of the particles as a function of MBA were estimated. In addition, the broadening and lowering effects of the volume phase transition temperature were detected from the turbidity of the solutions versus the MBA concentration. Second, observations of the transverse relaxation of protons gave evidence for heterogeneous structures inside the particles; several structural parts were discriminated from one another from different proton mobilities detected through magnetic relaxation rates. Corresponding to the concentration gradients of the crosslinker, the internal particle structures were looser and looser from the core to the shell. The state of the gelation of the polymer particles was governed by the initial amount of the crosslinker introduced into the latex recipe. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 889–898, 2000

Adsorption and covalent binding of polythymidylic acid (dT35) on aminated polystyrene latex particles have been studied. Both the electrostatic interactions between negative charges of the dT35 and the positive charges of the cationic latex particles and hydrophobic interactions are the driving forces for the adsorption. Small-angle neutron scattering (SANS) has been used to determine the structure of the adsorbed or grafted dT35 layers. The thickness of the adsorbed oligonucleotide layer on the latex particles is small with respect to the extended length of dT35 molecules (~120 Å) indicating that the adsorbed molecules lay close in a flat conformation on the surface, irrespective of the pH and ionic strength. In contrast, the covalently grafted dT35 molecules at basic pH and high surface coverage extends more radially into the solvent, giving rise to a thicker layer in comparison to the case of adsorption.

Abstract: With a view to preparing monosized hydrophilic functional magnetic latex particles based on a two-step strategy using anionic iron oxide and cationic polymer latexes, the adsorption step was systematically investigated for a better control of the subsequent encapsulation step. The iron oxide nanoparticles were first obtained according to the classical precipitation method of ferric and ferrous chloride salt using a concentrated sodium hydroxide solution, whereas the polystyrene (PS), P(S/N-isopropylacrylamide (NIPAM)) core–shell and PNIPAM latexes were produced via emulsion and precipitation polymerizations, respectively. The polymer and inorganic colloids were then characterised. The adsorption of iron oxide nanoparticles onto the three types of polymer latexes via electrostatic interaction was studied as a function of iron oxide particle concentration, charge density and the cross-linking density of the hydrophilic layer. The maximum amounts of magnetic nanoparticles adsorbed onto the various latexes were found to increase in the following order: PS < P(S/NIPAM) < P(NIPAM). This significant difference is discussed by taking into account the charge distribution in the hydrogel layer and diffusion phenomena inside the cross-linked hydrophilic shell.

Monodisperse cationically charged core−shell poly[styrene/N-isopropylacrylamide] latexes, differing in their shell structure, were studied at temperatures around the lower critical solution temperature (LCST) of poly[N-isopropylacrylamide]. Near the LCST, a transition on the latex dimensions was observed by quasi-elastic light scattering measurements. The same transition could also be detected using the intensity ratio of the pyrene fluorescence vibronic bands, I1/I3, and the excimer to monomer fluorescence intensity ratio of 1,10-bis(1-pyrenyl)decane. The fluorescence spectra and decay curve measurements of 1,10-bis(1-pyrenyl)decane provided a better understanding of both the hydrophilic−hydrophobic variation and the conformational changes occurring in the poly[N-isopropylacrylamide] shell of the latex particles upon temperature variation.

Abstract:  This article reports the colloidal and physicochemical characterization of crosslinked poly (N-isopropylmethacrylamide) (poly[NIPMAM]) latexes. The latex particles were first characterized by determining the lowest critical solubility temperature by measuring the optical density variation as a function of temperature. In addition, the electrophoretic mobility behaviors of all latexes were examined as a function of pH and temperature. Finally, the colloidal stability was investigated by determining the critical coagulation concentration and the critical flocculation temperature, and the corresponding results were discussed by taking into account both the effect of salinity and temperature on the solvency of poly[NIPMAM].

Abstract:  In a previous paper [1], the synthesis of various polystyrene– poly[NIPAM] core–shell latexes bearing cationic amidino and/or amino charges has been described. Several colloidal properties of these cationic latexes have been charac-terized such as: particle size, surface charge density, electrophoretic mobility and finally colloidal stability. Due to the poly[NIPAM]-rich layer in the shell, it was found that temperature played a significant role on all these properties, a LCST around 33 C being exhibited. In addition, ionic strength was also found to affect the colloidal behavior of these latexes, the largest effect being observed with latexes having both amidino and amino surface charges. The critical coagulation concentra-tions (CCC) of the various latexes above and below the LCST were determined, highlighting the contribution of electrostatic and steric repulsive forces to the stability of these particles.

The core–shell particles considered were poly(butyl acrylate) core/epoxy groups functionalizing the poly(methyl methacrylate) shell. Physical and thermomechanical properties of benzyl dimethylamine (BDMA)-catalyzed diglycidyl ether of bisphenol A (DGEBA)/dicyandiamine epoxy networks toughened with core–shell particles were studied. The blends were prepared under well-defined processing conditions. The resulting properties were found to depend on the state of the dispersion of the particles in the prepolymer matrix before crosslinking. These particles were dispersed at different volume fractions in order to vary the interparticle distance. The relationships between the size of the core–shell particles and the level of toughening are reported. Static mechanical tests were performed in tension and compression modes on these core–shell polyepoxy blends. A slight decrease in the Young's modulus and an increase in the ability to plastic deformation were observed. Using linear fracture mechanics (LEFM), an improvement of the fracture properties (KIC) was measured. By varying the volume fraction of core–shell particles, an optimum toughness improvement was found for an interparticle distance equal to 400 nm (with an average particle size of 600 nm). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 849–858, 1999

The covalent immobilization of bovin serum albumin (BSA) onto maleic anhydride-alt-methyl vinyl ether copolymers (MAMVE) was successfully achieved under aqueous conditions. The grafting reaction was shown to be controlled by attractive electrostatic interactions and so took place at a low salt concentration. Under these conditions, the covalent binding reaction was quite efficient, reproducible, and complete within 20 min. The maximum loading capacity of the polymer was of 20 BSA molecules per polymer chain. This preliminary study demonstrated that the immobilization of proteins in an aqueous medium could be an efficient process, despite the existing hydrolysis of the functional polymer by water molecules. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1565–1572, 1999

The covalent grafting of biological molecules to copolymers of maleic anhydride and methyl vinyl ether (MAMVE) has been used in various applications in diagnostics. To tentatively elucidate the phenomena involved in the control of the immobilization of oligodeoxynucleotides and proteins, the physico-chemical properties of MAMVE copolymers were investigated. Because the grafting mixture contains water, to allow dissolution of the biomolecules without loss of biological properties, the anhydride-based copolymer evolves from a neutral to a negatively charged macromolecule due to hydrolysis of the anhydride moities. The properties of both hydrolyzed and nonhydrolyzed polymers were investigated. As demonstrated by light-scattering measurements in batch, the copolymers showed some level of aggregation in DMF, DMSO, and aqueous DMSO. The presence of aggregates was confirmed by size-exclusion chromatography in DMF. However, partial deaggregation occurred for the lowest molecular weight sample, on adding 1% w/v of LiBr. The nonhydrolyzed copolymers exhibited a rigid conformation in a 5% water/DMSO mixture, as well as their hydrolyzed counterpart at a low ionization degree. The rate of the hydrolysis reaction was shown to be dependent on the pH of the reaction medium and on temperature. The activation energy of the hydrolysis reaction was 14 kJ/mol, and the rate constant in the order of 10⁻⁴ s⁻¹. On the basis of these data, the effect on the grafting reaction of biomolecules of different parameters such as ionic strength and the nature of the solvent, along with some other results were interpreted in terms of interactions between the synthetic and bioactive macromolecules. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 927–936, 1999

Abstract:  A series of P[N-isopropylacrylamide (NIPAM)] latexes with different contents of cyano groups were successfully prepared by either seeded or shot-growth polymerizations of an aqueous solution containing acrylonitrile (AN) onto a seed P[NIPAM] latex, respectively, and further characterized by FT-IR, 1H-NMR, elemental analysis, as well as by quasielastic light scattering (QELS) and scanning electron microscopy (SEM). All prepared surface-cyanofunctionalized P[NIPAM] latexes exhibited the same range of lower critical solution temperature (LCST) as a pure P[NIPAM] latex. The shot polymerization process proved more efficient at yielding cyano derivatized latexes than the seeded polymerization technique. The amount of incorporated cyano groups onto the particles was determined with a good correlation both by 1H-NMR and elemental analysis. The higher the amount of initially introduced AN monomer in the reaction mixture, the more cyano groups were incorporated onto the particles. The surface of the particles with high content of cyano groups appeared quite rough by SEM in comparison with that of the pure P[NIPAM] particles.

Latex particles bearing carbohydrate species were prepared by emulsion copolymerization of styrene or methyl methacrylate with polymerizable liposaccharide surfactants; 11-(N-p-vinylbenzyl) amido undecanoyl maltobionamide (LIMA), 6-(2-methylpropenoyloxy)hexyl β-d-cellobioside (CHMA) and 10-(2-methylpropenoyloxy)decyl β-d-cellobiouronoside (CDMA). Due to their amphiphilic structure, these three monomers exhibit surface active properties in dilute solutions and mesomorphic properties in concentrated solutions. Their incorporation onto latex particles was performed according to a batch process or a seed polymerization process. The presence of the carbohydrate residues at the particle surface was directly observed by NMR. The potential application of these functionalized latexes in the biomedical diagnostic field was evaluated by studying the adsorption of bovine serum albumin, and by performing covalent binding of antibodies and single-stranded DNA fragments on their surface.

Abstract: The encapsulation of seed polymer particles coated by anionic iron oxide nanoparticles has been investigated using N-isopropylacrylamide as a main monomer, N,N-methylene bisacrylamide as a crosslinking agent, itaconic acid as a functional monomer and potassium persulfate as an anionic initiator. The magnetic latexes obtained have been characterized with regard to particle size, iron oxide content and electrophoretic mobility. All these properties have been examined by varying several polymerization parameters: reaction medium, monomer(s) and crosslinking agent concentrations, nature of seed latexes and type of polymerization (batch versus shot process). The magnetic content in the polymer microspheres strongly depends on the polymerization procedure (i.e., encapsulation process) and varies between 6 and 23 wt%, and monodisperse magnetic polymer particles were obtained.

Emulsifier-free polystyrene latexes covered with disaccharide species have been prepared by a seed (co)polymerization method in the presence of a hexylmethacrylate-terminated oligosaccharide 6-(2-methylpropenoyloxy)hexyl ß-d-cellobioside (CHMA). First, the surface activity of this macromonomer was studied using ring and drop volume methods, respectively. Then, its polymerization onto polystyrene seed latexes was carried out upon varying experimental conditions: particle size, solid contents of the seed and type of comonomer. Analysis of the macromonomer distribution between aqueous and polymer phases suggested that an optimal surface yield can be reached upon increasing the overall surface area of particle and or using methylmethacrylate as comonomer. Finally, the presence of the disaccharide residues at the particle surface was shown, either directly using NMR and ESCA analysis, or indirectly through the comparison of the electrophoretic mobility behavior of the seed polystyrene and functionalized latexes.

Polystyrene(1)/poly(n-butyl acrylate-methacrylic acid)(2) structured latex particles were prepared through a two-stage emulsion polymerization procedure, using a polystyrene (PS) latex seed (118 nm), and differentn-butyl acrylate (BA)/methacrylic acid (MAA) ratios. Polymerization kinetics, particle morphology, and MAA location have already been discussed in the first part of this series. In this second part the thermomechanical behavior of films cast from these latexes was studied. Differential Thermal Analysis and Dynamic Mechanical Analysis (DMA) were employed as characterization techniques for the films. Two polymer phases corresponding to polystyrene and a poly(BA-MAA) copolymer were distinguished. Comparison was made to analogous unfunctionalized PS/PBA systems, as a result of which an effect of MAA upon the phase arrangement in the film was found. Scanning Electron Microscopy of film samples and DMA showed that the evolution of the phase arrangement as a result of annealing was strongly dependent on the type of mechanical and heat treatments being applied to functionalized systems. Finally, the thermomechanical behavior of films was related to the structural features of the corresponding latexes, and computer simulation techniques wer eemployed to establish a mechanistic support for these relationships.

Polystyrene (PS) (1)/Poly(n-butyl acrylate (BA)-methacrylic acid (MAA)) (2) structured particle latexes were prepared by emulsion polymerization using monodisperse polystyrene latex seed (118 nm) and different BA/MAA ratios. Three main aspects have been investigated: i) the polymerization kinetics; ii) the particle morphology as a function of reaction time; iii) the distribution of MAA units between the water phase and the polymer particles.

Polycationic polymers have been obtained through a two-step procedure. First, poly-vinylbenzylchloride [P(VBC)] latexes were prepared under emulsifier-free conditions using a cationic initiator: 2,2'-azobis(2-amidinopropane) hydrochloride; then the resulting latexes were reacted with trimethylamine. Particular attention was paid to side reactions occurring during the hydrolysis of the chloromethyl groups and the crosslinking reaction due to a transfer reaction onto polymer. The influence of various parameters on the particle size and structure of latexes as well as secondary reactions were investigated through a careful characterization.

The emulsion polymerization process allows production of polymer particles with different structural morphologies. Films obtained after coalescence keep some memory of this morphology, but large modifications can occur during coalescence. In the present case, one of the polymers, polystyrene (PS), exhibits a glass temperature (Tg) much higher than the filmification temperature (close to room temperature), while the other one, poly(butyl acrylate) (PBA), has a much lowerTg. Furthermore, it is well known that dynamic mechanical measurements can be very helpful in providing information on the morphology of polymer materials, i.e., on geometrical and topological arrangement of homopolymer domains. At first, this method was used for comparison of two types of films: i) the first one obtained from structured-core (PS)-shell (PBA) particles, ii) the second one obtained from a blend of homopolymer particles (PS and PBA). It appears that the expected core-shell particles lost their geometric structure in the second film. Second, comparison of the predicted dynamic modulus and experimental data shows that i) strong interactions exist between PS nodules unless their coalescence has occured, leading to an abnormally high modulus at room temperature, ii) after achieving their coalescence, PS forms a more or less continuous phase. Both phenomena strongly depend on the particle size and their respective volume fractions.

The measurement of the complex dielectric constant (e*=e'-je?) in the dipolar absorption domain of the “free” water molecule (microwave region) permits us to follow quasi-specifically and precisely the water circulation during the coalescence process of a latex. Weight losses and dielectric constants variations have been simultaneously recorded upon latex drying, in a resonant cavity at 5 and 9 GHz and under controlled atmosphere and temperature. Two different latexes were studied (polybutylacrylate (PBuA) and polystyrene (PS)) from which the glass transition temperature effect was investigated. It is found that the harder the polymer particles, the more clearly evidenced the flocculation and packing points are. This method appears to be quite reliable for discriminating the various steps in the film formation process of latexes.

The dielectric behavior (e', e?) of three well-cleaned monodisperse polystyrene latexes having the same particle size and the same number of chemically-bound surface groups has been studied at a fixed microwave frequency (9.4 GHz), as a function of temperature and surface group (SO4-, COO-, OH).

The technique of spin trapping of polymer radicals by 2-methyl-2-nitrosopropane has been applied to the study of acrylonitrile copolymerization. Provided the concentration of the spin trapping agent is kept low, and the samples are kept at low temperature during storage before obtaining the ESR spectra, quantitative studies of styrene-acrylonitrile copolymerization are possible. However, the spin-trapping reaction is a competitive one, and the trapping efficiency is dependent on the reactivity of the radicals present. In the case of acrylonitrile copolymerization with either vinyl chloride or vinyl acetate, these two last radicals are trapped preferentially. Furthermore, the cyclization reaction observed with many acrylonitrile copolymerization is nearly eliminated in the presence of the spin-trapping agent.

Penultimate effects detected on the vinylidene chloride-ended radical in the vinylidene chloride-vinyl chloride copolymers prepared in thtrahydrofuran had previously been interpreted in terms of head-to-head addition. But new 1H-NMR analysis of the homopolymers and copolymers synthesized in proton-donor and inert solvents suggest these effects, giving abnormal structures, might be due to the proton-transfer reactions, particularly in strong proton-donor solvents. Chain transfer reactions have been found degradative, so the overall polymerization rate is drastically decreased.