Hydrophilic End Groups Research Articles

Mechanism of the formation of microphase separated water clusters in a water-mediated physical network of perfluoropolyether tetraol.

Perfluoropolyether tetraol (PFPE tetraol) possesses a hydrophobic perfluoropolyether chain in the backbone and two hydroxyl groups at each chain terminal, which facilitates the formation of hydrogen bonds with water molecules resulting in the formation an extended physical network. About 3 wt% water was required for the formation of the microphase separated physical network of PFPE tetraol. The mechanism responsible for the microphase separation of water clusters in the physical network was studied using a combination of techniques such as NMR spectroscopy, molecular dynamics (MD) simulations and DSC. MD simulation studies provided evidence for the formation of clusters in the PFPE tetraol physical network and the size of these clusters increased gradually with an increase in the extent of hydration. Both MD simulations and NMR spectroscopy studies revealed that these clusters position themselves away from the hydrophobic backbone or vice versa. The presence of intra- and inter-chain aggregation possibility among hydrophilic groups was evident. DSC results demonstrated the presence of tightly and loosely bound water molecules to the terminal hydroxyl groups of PFPE tetraol through hydrogen bonding. The data from all the three techniques established the formation of a physical network driven by hydrogen bonding between the hydrophilic end groups of PFPE tetraol and water molecules. The flexible nature of the PFPE tetraol backbone and its low solubility parameter favour clustering of water molecules at the terminal groups and result in the formation of a gel.

Retarding oxidation of copper nanoparticles without electrical isolation and the size dependence of work function

Copper nanoparticles (CuNPs) are attractive as a low-cost alternative to their gold and silver analogues for numerous applications, although their potential has hardly been explored due to their higher susceptibility to oxidation in air. Here we show the unexpected findings of an investigation into the correlation between the air-stability of CuNPs and the structure of the thiolate capping ligand; of the eight different ligands screened, those with the shortest alkyl chain, –(CH2)2–, and a hydrophilic carboxylic acid end group are found to be the most effective at retarding oxidation in air. We also show that CuNPs are not etched by thiol solutions as previously reported, and address the important fundamental question of how the work function of small supported metal particles scales with particle size. Together these findings set the stage for greater utility of CuNPs for emerging electronic applications.

An Environmental Friendly Fluorinated Oligoamide for Producing Nonwetting Coatings with High Performance on Porous Surfaces.

The changes in the surface wettability of many materials are receiving increased attention in recent years. It is not too hard to fabricate resistant hydrophobic surfaces through products bearing both hydrophobic and reactive hydrophilic end groups. More challenging is obtaining resistant nonwetting surfaces through noncovalent reversible bonds. In this work, a fluorinated oligo(ethylenesuccinamide), soluble in solvent benign for operators and environment, has been synthesized. It contains two opposite functional groups (perfluoropolyether segments and amidic groups) (SC2-PFPE) that provide water repellency while hydrophilicity is retained. Its performance has been tested on porous calcarenite and investigated by magnetic resonance imaging, water capillary absorption, and vapor diffusivity tests. The results demonstrate that SC2-PFPE modifies the wettability of porous substrates in a drastic and durable way and reduces the vapor condensation inside the pore space due to the perfluoropolyether segments that act at the air/surface interface.

Controlled Hydrolytic Degradation of Polyglycolide–Caprolactone-Based Bioabsorbable Copolymer

Polyglycolide–caprolactone (PGCL)-based copolymer was synthesized from glycolide and caprolactone by ring opening polymerization in the presence of stannous octoate catalyst and diethylene glycol initiator. The effects of prepolymerization time, monomer ratio, monomer-to-catalyst and monomer-to-initiator ratios on per cent weight conversion were optimized. The end-capped copolymer was synthesized to make absorbable sutures having controlled bioabsorbability at different pH levels. It was observed that endcapped absorbable copolymer was more stable at pH 10.0 compared to uncapped absorbable material. End-capped copolymer also retained higher tensile strength compared to uncapped copolymer after 21 days. This phenomenon of controlled hydrolytic degradation of PGCL-based bioabsorbable polymer having terminal group end-capping can be attributed to less availability of hydrophilic end groups facilitating hydrolytic degradation of polymers.

Substrate chemistry regulates the surface phase separation of polyurethane films

The effect of substrate chemistry on surface phase separation of polyurethane films were investigated by using self-assembled monolayer (SAM) with chemically different modifications, i.e. hydroxy (–OH) and methyl (–CH3) end groups. Results showed that hydrophilic (–OH) and hydrophobic end groups (–CH[Formula: see text] could respectively promote the aggregation of hard and soft segments at polyurethane–substrate interface, which further regulates the phase separation of polyurethane surface that contacts the substrate. The aggregation of hard segments tended to enhance the surface smoothness of polyurethane films, especially on hydrophilic substrates with hydroxy modification. Further analysis of tensile testing revealed that the regulation of surface phase separation had no effect on the shape memory effect of polyurethane films. These findings suggest that the chemical properties of the substrates could regulate the phase separation and may provide some guidance on the design of specific polyurethane with desired morphology and properties.

Thermodynamic Parameters of Temperature-Induced Phase Transition for Brushes onto Nanoparticles: Hydrophilic versus Hydrophobic End-Groups Functionalization.

Quantification of the stimuli-responsive phase transition in polymers is topical and important for the understanding and development of novel stimuli-responsive materials. The temperature-induced phase transition of poly(N-isopropylacrylamide) (PNIPAm) with one thiol end group depends on the confinement-free polymer or polymer brush-on the molecular weight and on the nature of the second end. This paper describes the synthesis of heterotelechelic PNIPAm of different molecular weights with a thiol end group-that specifically binds to gold nanorods and a hydrophilic NIPAm end group by reversible addition-fragmentation chain-transfer polymerization. Proton high-resolution magic angle sample spinning NMR spectra are used as an indicator of the polymer chain conformations. The characteristics of phase transition given by the transition temperature, entropy, and width of transition are obtained by a two-state model. The dependence of thermodynamic parameters on molecular weight is compared for hydrophilic and hydrophobic end functional-free polymers and brushes.

Effective and Selective Trapping of Volatile Organic Sulfur Derivatives by Montmorillonite Intercalated with a μ-oxo Fe(III)-Phenanthroline Complex.

The μ-oxo Fe(III)-phenanthroline complex [(OH2)3(Phen)FeOFe(Phen) (OH2)3]+4 intercalated in montmorillonite provides a stable hybrid material. In this study, the ability and efficiency of this material to immobilize thiols in gas phase, acting as a trap at the solid-gas interface, were investigated. Aliphatic thiols containing both hydrophilic and hydrophobic end groups were chosen to test the selectivity of this gas trap. DR-UV-vis, IR, elemental analysis, thermal analysis and evolved gas mass spectrometry, X-ray powder diffraction, and X-ray absorption spectroscopy techniques were employed to characterize the hybrid material before and after thiol exposure and to provide information on the entrapping process. Thiol immobilization is very large, up to 21% w/w for heptanethiol. In addition, evidence was obtained that immobilization occurs through the formation of a covalent bond between the iron of the complex and the sulfur of the thiol. This provides an immobilization process characterized by a higher stability with respect to the methods based on physi-adsorption. Thiol immobilization resulted thermally reversible at least for 20 adsorption/desorption cycles. Unlike standard desulfurization processes like hydrotreating and catalytic oxidation which work at high temperatures and pressures, the present system is able to efficiently trap thiols at room temperature and pressure, thus saving energy. Furthermore, we found that the selectivity of thiol immobilization can be tuned acting on the amount of complex intercalated in montmorillonite. In particular, montmorillonite semisaturated with the complex captures both hydrophobic and hydrophilic thiols, while the saturated montmorillonite shows a strong selectivity toward the hydrophobic molecules.

Probing the Morphological Changes of in-Situ Degraded Membranes in Polymer Electrolyte Fuel Cells

Membrane durability is one of the key criteria to be met to successfully commercialize polymer electrolyte fuel cell (PEFC) technology. Commonly used perfluorosulfonic acid (PFSA) ionomer membranes are prone to early degradation under the influence of common degradation stressors encountered in PEFCs. The important functional properties of PFSA membranes such as ionic conductivity and mechanical properties depend on its microstructure due to its unique hydrophobic backbone and side chains with hydrophilic end groups (1). Severe molecular changes to the PFSA membrane structure have been reported due to chemical and mechanical membrane degradation. Such changes in the molecular structure were found to affect thermal stability, water uptake, proton conductivity, and mechanical properties of the membrane; as well as the performance and durability of the fuel cell as previously published by our group (2-5). Although the effects of molecular changes on the degraded membrane characteristics have been explored, the impact on its internal morphology is generally not known. The present objective is therefore to understand the effect of degradation stressors on the morphological changes in order to improve membrane durability. In this work, standard PFSA membranes were subjected to a combined chemical and mechanical accelerated stress test (AST) used for rapid benchmarking of in-situ membrane stability. The chemical phase of the AST generates hydroxyl radicals that attack both the side chain and main chain of the polymer, while the mechanically generated stresses due to humidity cycling accelerate mechanical failures. Beginning-of-life (BOL) and end-of-life (EOL) membrane samples extracted after in-situ degradation were imaged using transmission electron microscopy (TEM). In order to enhance image contrast, the sulfonic acid end group sites in the membrane were selectively exchanged with Pb ions by soaking it in saturated lead acetate solution. The samples embedded in epoxy resin were sliced to thin films (~70-90 nm) using ultra microtome and collected on a Cu grid for imaging. The hydrophilic regions in the Pb exchanged membrane appear as dark spots in the TEM images due to enhanced electron scattering, while the hydrophobic backbone dominated regions appear bright. The BOL membrane micrograph is presented in figure 1(A), exhibiting a regular phase separated morphological layout typical for PFSA ionomer membranes. Since the chemical degradation operates at random locations through out the membrane and commences with ionomer side chain cleavage (2-3), the degraded regions at the nanoscopic level exhibited low concentration of dark spots and the image brightness becomes non-uniform. (figure 1(B)). The lower concentration and absence of dark spots in the degraded region is expected to resemble the absence of ion attractive sulfonic acid groups at that site due to side chain degradation. Also, the dark spots tend to align in a long range order as a result of combined chemical/mechanical degradation. Apart from the severely degraded regions, mildly degraded regions which exhibit BOL morphology were also seen while scanning the membrane at EOL. The images of cracks (not shown here) recorded at EOL reveal that cracks preferentially propagate along the region of lowest concentration of dark spots which represent depletion of SO3 -in the ion-rich hydrophilic domains. Elemental mapping of the degraded zone was carried out by selectively capturing the generated x-rays with characteristic energy due to electron interacting with the sample. The mapping of fluorine in the degraded zone revealed its absence at the most degraded sites (figure 1(C)). This can be correlated to the severe fluoride release from the membrane as a result of combined chemical/mechanical degradation. Overall, the observed effects of combined chemical/mechanical degradation on the membrane morphology contributes to the fundamental understanding of the complex membrane degradation mechanism occurring during PEFC operation. ACKNOWLEDGMENTS Research funding provided by Automotive Partnership Canada (APC), Natural Sciences and Engineering Research Council of Canada (NSERC) and Ballard Power Systems (BPS) is gratefully acknowledged. We also thank BPS for providing material samples and Chan Lim for carrying out AST experiments. REFERENCES [1] Y. Yang, A. Siu, T. J. Peckham, S. Holdcroft, in Advances in Polymer Sciences 215: Fuel cells 1, G. G. Scherer, Editor p. 55 Springer, Berlin Heidelberg 215(2008). [2] C. Lim, L. Ghassemzadeh, F. Van Hove, M. Lauritzen, J. Kolodziej, G.G. Wang, S. Holdcroft, E. Kjeang, J. Power Sources 257102 (2014). [3] L. Ghassemzadeh and S. Holdcroft, J. Am. Chem. Soc. 135 8181 (2013). [4] S. Venkatesan, C. Lim, E. Rogers, S. Holdcroft, and E. Kjeang, Phys. Chem. Chem. Phys. (2015), DOI: 10.1039/C5CP01641J. [5] S. Venkatesan and E. Kjeang, 11th International Fuel Cell Science, Engineering and Technology Conference, ASME, Minneapolis, MN (2013). Figure 1

Temperature-dependent in-plane structure formation of an X-shaped bolapolyphile within lipid bilayers.

Polyphilic compound B12 is an X-shaped molecule with a stiff aromatic core, flexible aliphatic side chains, and hydrophilic end groups. Forming a thermotropic triangular honeycomb phase in the bulk between 177 and 182 °C but no lyotropic phases, it is designed to fit into DPPC or DMPC lipid bilayers, in which it phase separates at room temperature, as observed in giant unilamellar vesicles (GUVs) by fluorescence microscopy. TEM investigations of bilayer aggregates support the incorporation of B12 into intact membranes. The temperature-dependent behavior of the mixed samples was followed by differential scanning calorimetry (DSC), FT-IR spectroscopy, fluorescence spectroscopy, and X-ray scattering. DSC results support in-membrane phase separation, where a reduced main transition and new B12-related transitions indicate the incorporation of lipids into the B12-rich phase. The phase separation was confirmed by X-ray scattering, where two different lamellar repeat distances are visible over a wide temperature range. Polarized ATR-FTIR and fluorescence anisotropy experiments support the transmembrane orientation of B12, and FT-IR spectra further prove a stepwise "melting" of the lipid chains. The data suggest that in the B12-rich domains the DPPC chains are still rigid and the B12 molecules interact with each other via π-π interactions. All results obtained at temperatures above 75 °C confirm the formation of a single, homogeneously mixed phase with freely mobile B12 molecules.

Synthesis, characterization and thermo-responsive behavior of end-functionalized poly(N-isopropylacrylamide)

N-Isopropylacrylamide was polymerized by atom transfer radical polymerization using 2-hydroxyethyl 2-chloropropionate and glycidyl 2-chloropropionate as initiators and CuCl/tris[2-(dimethylamino)ethyl]amine as the catalyst system in acetonitrile/water (10/1 v/v) at room temperature to afford an end-functionalized poly(N-isopropylacrylamide) with 2-hydroxyethyl and epoxy groups. Epoxy ring in glycidyl 2-chloropropionate was opened with tris(hydroxymethyl)aminomethane. The thermal phase transitions of aqueous solutions of synthesized polymers were studied; as expected hydrophilic end-group increased the lower critical solution temperature (LCST) while hydrophobic end-group decreased the LCST. All the polymers were characterized by means of FTIR and 1H NMR spectroscopy.

Effect of end-group modification, hydrophilic/hydrophobic block ratio and temperature on the surface, associative and thermodynamic behaviour of poly(ethylene oxide)-b-poly(butylene oxide) diblock copolymers in aqueous media

This study describes the surface, micellar, associative and thermodynamic properties of four diblock oxyethylene (E)/oxybutylene (B) copolymers with different hydrophilic block ends and various hydrophilic/hydrophobic ratios in aqueous media. The copolymers were denoted DE40B18, TE40B18, E56B19 and E56B7. The aqueous polymer solutions at various concentrations and temperatures were investigated by surface tensiometry and dynamic and static laser light scattering. Surface tension measurements were employed to detect the critical micelle concentration (CMC) as well as to calculate the surface-active and thermodynamic parameters of adsorption at the air/water interface. CMC values were also used to calculate the enthalpy of micellization (∆H0mic), free energy of micellization (∆G0mic) and entropy of micellization (∆S0mic). Similarly, various thermodynamic parameters for adsorption at the air/water interface were also deduced. Dynamic light scattering (DLS) was used to obtain the hydrodynamic radii (rh) and volumes (υh) of the micelle at different temperatures, and hence the hydrodynamic expansion parameter (δh) was also estimated. Likewise, static light-scattering measurements enabled us to determine various parameters of the copolymer micelles, such as the weight-average molar mass (Mw), association number (Nw), thermodynamic radius (rt), thermodynamic volume (υt), anhydrous volume (υa) and the thermodynamic expansion parameter (δt). Various thermodynamic and micellar parameters obtained from light scattering show that the micelles formed are spherical in shape and have rather soft interaction potentials at low temperature but become harder at higher temperature. Based on the different experimental results obtained, it can be said that various surface, micellar and thermodynamic parameters are dependent not only on the temperature and solution conditions but also on the hydrophobic/hydrophilic ratio and the end-group composition of the polymer. Modification of the hydrophilic end group of the polymer prominently affects various micellar properties. This effect can be assigned to the difference in polarity and the intermicellar charge effect.

Synthesis and aggregation properties of new biodegradable amphiphilic derivatives of p-tert-butylphenol for green separation of Gd(III) ions

The work introduces a synthesis of novel amphiphilic p-tert-butylphenol derivatives with the polyethyleneoxide and biodegradable ionogenic polyethylenecarbonate moieties. The dependence of their aggregation behaviour on the lengths of polyethyleneoxide and polyethylenecarbonate chains indicates the impact of the hydrophilic moieties and ionogenic end-groups in the aggregation behaviour of the amphiphiles. The micelles of the amphiphiles are negatively charged, although neither pH nor counter ions (exemplified by Gd(III) ions) affects the values of their critical micelle concentrations. The presence of the ionogenic end-groups is the main reason of the pH and concentration dependent extraction of Gd(III) ions from the neutral (pH 6.2-7.2) aqueous solutions of the amphiphiles through their phase separation at room temperatures. The extraction regularities point on the stoichiometric binding of the amphiphilic molecules with Gd(III) ions as the main reason of the phase separation in their aqueous solutions. Nevertheless the micellization of the amphiphiles is responsible for the peculiar concentration effect on the extraction of Gd(III) ions from the aqueous solutions.

Polystyrenes with Hydrophilic End Groups: Synthesis, Characterization, and Effects on the Self-Assembly of Breath Figure Arrays

We report the synthesis and characterization of a series of hydroxyl-end-functionalized polystyrenes (PS-OH) and the formation of patterned porous films. The polymers were synthesized by chain end reaction of polystyrene having a bromide end group (PS-Br) with hydramines including ethanolamine, diethanol amine, 2-amino-1,3-propanediol, and 2-(2-aminoethoxy) ethanol. The polymers were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), and differential scanning calorimetry (DSC). It was found that the end groups can influence the glass transition temperature (T(g)) of the polystyrenes. The polymers with different end groups were then used to prepare honeycomb-patterned porous films by the breath figure method. Results reveal that the subtle chain-end modification leads to a dramatic change in the morphology of the films. Honeycomb films with large area ordered structure can be easily prepared from PS-OH. Effects of the end groups as well as blending PS-OH with PS-Br on the surface pore diameter, pore center distance, and the hierarchical structure were studied in detail. As supported by the results of polymer hydrophilicity, in situ observation of the film formation process, as well as the chain mobility, the film structure is supposed to be mainly determined by the precipitation of polystyrene at the solution/water droplet interface and the interfacial activity enhanced by the end groups.

Specific functionalization and polymer grafting on multiwalled carbon nanotubes to fabricate advanced nylon 12 composites

This paper deals with polymer grafting of multi-walled carbon nanotubes (MWCNTs) via ultraviolet/ozone (UV/O3) assisted polymer grafting (UVOG) in order to improve the filler efficiency and thus giving a highly homogeneous dispersion, strong filler–matrix interactions and excellent distribution of individual nanotubes in the polymer matrix. Though several chemical procedures of grafting have been developed to obtain dispersible CNTs, grafting by a fast, low cost, non hazardous and controllable process is still under active research. 2-Acrylamido-2-methylpropane sulfonic acid (AMPS) monomers were employed for grafting onto MWCNTs due to their very hydrophilic and reactive sulfonic (SO3H) end groups. The structural and morphological changes in poly-AMPS grafted MWCNTs (PAG-MWCNTs) were characterized by FTIR spectroscopy, XPS, Raman spectroscopy, TEM and FESEM. When the PAG-MWCNTs were incorporated into nylon 12, the results showed excellent uniform dispersion of individual MWCNTs throughout the matrix and improved the mechanical properties of the composites. Addition of only 0.75 wt% PAG-MWCNTs showed an improvement of tensile strength and Young's modulus by ∼43% and 33%, respectively, compared with those of neat nylon 12. Moreover, the PAG-MWCNTs/nylon 12 composites exhibited a ∼12 °C improvement in the glass transition temperature (Tg) compared to the raw MWCNTs/nylon 12 composites. From a literature survey, these results are found to be quite promising. Therefore, we believe that the polymer grafting of MWCNTs presented herein will be a useful technique to produce novel filler materials for preparing various advanced nanocomposites. Moreover, this grafting technique may also be employed to introduce other functional polymers onto the surface of MWCNTs.

Thermoresponsive Dynamic Covalent Polymers with Tunable Properties

A bisaldehyde-containing trithiocarbonate chain transfer agent was prepared and mediated the synthesis of polymers with bisaldehyde-functionalized α-termini by reversible addition–fragmentation chain transfer (RAFT) radical polymerization. The α-termini of RAFT-derived thermoresponsive poly(N-isopropylacrylamide) was conjugated with hydrazides via reversible acylhydrazone bonds. Introduction of hydrophilic end-groups generated a dynamic covalent polymer with “isothermal” lower critical solution temperature (LCST) response to medium pH and dynamic chain exchange character. A biofunctional dynamic covalent polymer was prepared by conjugation with biotin hydrazide. Under appropriate reaction conditions, a dynamic covalent block copolymer with an aldehyde group at the junction point was constructed through a reversible arylhydrazone linkage by coupling with acylhydrazide-terminated poly(ethylene glycol). The dynamic covalent block copolymer exhibited pH-dependent LCST. The remaining aldehyde group was used to react with amino-containing molecules. Bioconjugated dynamic covalent block copolymers containing reversible imine and arylhydrazone linkages were constructed by conjugation of the block copolymer to glucosamine and protein.

Complexations of the hydrophilic and hydrophobic moieties of benzethonium chloride by cucurbit[7]uril in aqueous solution

The sequential complexations of the hydrophilic and hydrophobic end groups of benzethonium chloride by cucurbit[7]uril (CB[7]) in aqueous solution have been investigated using 1H NMR spectroscopy and electrospray ionization mass spectrometry. The initial binding is to the benzyldimethylammonium group, with a stability constant of (8.7 ± 3.1) × 107 (mol/L)–1. This binding constant and the complexation-induced upfield shifts of the benzyl guest protons are similar to those values observed with other cationic guests containing benzyl moieties. This equilibrium is followed by the binding of a second equivalent of the host to the hydrophobic 2-(2,4,4-trimethylpentyl) group, with a stability constant of (4.0 ± 1.9) × 103 (mol/L)–1. The relatively strong binding of this uncharged hydrophobic end of the guest molecule is consistent with the inclusion of eight heavy (nonhydrogen) atoms within the inner cavity of CB[7], with its low polarizability. The packing coefficient for the 2-(2,4,4-trimethylpentyl) group with the inner cavity is calculated to be 61%, close to Rebek’s ideal value of 55%.

Adsorption of Naphthalene and Ozone on Atmospheric Air/Ice Interfaces Coated with Surfactants: A Molecular Simulation Study

The adsorption of gas-phase naphthalene and ozone molecules onto air/ice interfaces coated with different surfactant species (1-octanol, 1-hexadecanol, or 1-octanal) was investigated using classical molecular dynamics (MD) simulations. Naphthalene and ozone exhibit a strong preference to be adsorbed at the surfactant-coated air/ice interfaces, as opposed to either being dissolved into the bulk of the quasi-liquid layer (QLL) or being incorporated into the ice crystals. The QLL becomes thinner when the air/ice interface is coated with surfactant molecules. The adsorption of both naphthalene and ozone onto surfactant-coated air/ice interfaces is enhanced when compared to bare air/ice interface. Both naphthalene and ozone tend to stay dissolved in the surfactant layer and close to the QLL, rather than adsorbing on top of the surfactant molecules and close to the air region of our systems. Surfactants prefer to orient at a tilted angle with respect to the air/ice interface; the angular distribution and the most preferred angle vary depending on the hydrophilic end group, the length of the hydrophobic tail, and the surfactant concentration at the air/ice interface. Naphthalene prefers to have a flat orientation on the surfactant coated air/ice interface, except at high concentrations of 1-hexadecanol at the air/ice interface; the angular distribution of naphthalene depends on the specific surfactant and its concentration at the air/ice interface. The dynamics of naphthalene molecules at the surfactant-coated air/ice interface slow down as compared to those observed at bare air/ice interfaces. The presence of surfactants does not seem to affect the self-association of naphthalene molecules at the air/ice interface, at least for the specific surfactants and the range of concentrations considered in this study.

Degradation Behavior of Porous Copolyester Microparticles in the Light of Dynamic Changes in Their Morphology

AbstractThe pore structures of microparticulate drug carriers are important diffusion pathways, which are not a static property but rather may be changing in the case of degradable matrix polymers such as poly[(rac‐lactide)‐co‐glycolide] (PLGA). In this study, the mutual impacts of dynamic changes in microparticle porosity and polymer degradation were analyzed for PLGA with different molecular weights and end groups as well as PLGA‐based triblock copolymers. In selected cases, particularly for PLGA with hydrophilic end groups and low initial number average molecular weight of 5 kDa, pore opening/pore closing phenomena were detected during incubation in phosphate buffer at 37 °C. Initially, pore closing was induced by water‐induced plasticization and the reduction of interfacial tension. The pattern of molecular weight decrease and mass loss suggested that pore closing did not result in undesired autocatalytic acceleration of degradation or delayed mass loss due to trapped acidic degradation products.

IR Studies of Interfacial Interaction of the Succinic Surfactants with Different Head Groups in Highly Concentrated W/O Emulsions

The interfacial properties of three succinic surfactants (PIBSA) with different hydrophilic end groups and sorbitan monooleate (SMO) in water-in-oil emulsions of the liquid explosive type were studied. The aqueous phase contained 40% of ammonium nitrate (AN). The trend in equilibrium interfacial tension was found to be PIBSA-MEA > PIBSA-UREA > PIBSA-MEA/SMO mixture > PIBSA-IMIDE > SMO, where MEA, UREA, IMIDE are amid/amide, urethane and imide end groups, respectively. The same trend was observed for the interfacial elastic modulus. The FTIR study revealed interactions between surfactant head groups and an AN solution. The interactions depend on the polarity of head groups determined by their chemical structure. The packing efficiency of the surfactants under study is also influenced by the chemical structure of head groups. Attempts to model the conformation of the surfactants at the interface were made. The investigation of mixed interfacial cover (PIBSA-MEA/SMO) showed that SMO remained at the interface reducing the interfacial tension at the W/O interface. It was also demonstrated that variation of the nature of head groups influences the rheological properties of emulsions. Bulk elasticity and yielding correlate with interfacial interaction characteristics.

Efficient One‐Pot Synthesis of Water‐Compatible Molecularly Imprinted Polymer Microspheres by Facile RAFT Precipitation Polymerization

Molecular imprinting is a versatile and straightforward method for the preparation of polymer receptors with tailor-made recognition sites. Despite the tremendous progress made in this field, many challenges still remain to be addressed. In particular, it has been shown that the presently developed molecularly imprinted polymers (MIPs) are normally only organic solvent compatible and they mostly fail to show specific template bindings in pure aqueous solutions, thus significantly limiting their practical applications in the field of biotechnology. Although some approaches, which either use specifically designed functional monomers or apply the conventional imprinting protocol, have been developed for the preparation of MIPs with molecular recognition ability under aqueous conditions, versatile approaches for the preparation of MIPs that are applicable in pure aqueous environments are still rare. Herein, we report a new and efficient one-pot approach to obtain pure-water-compatible and narrowly dispersed MIP microspheres with surface-grafted hydrophilic polymer brushes by facile reversible addition/fragmentation chaintransfer (RAFT) precipitation polymerization (RAFTPP), mediated by hydrophilic macromolecular chain-transfer agents (Macro-CTAs; Scheme 1). The presence of hydrophilic polymer brushes on MIP microspheres significantly improved their surface hydrophilicity and dramatically reduced their hydrophobic interactions with template molecules in pure aqueous media, thus leading to their water compatibility. The easy availability of many different hydrophilic Macro-CTAs (by either RAFT polymerization of hydrophilic monomers or hydrophilic polymer end group modification), together with the versatility of RAFTPP for the controlled preparation of MIP microspheres, makes this strategy highly applicable for the design of hydrophilic and water-compatible MIPs. Two strategies have been developed for the synthesis of water-compatibleMIPs by improving their surface hydrophilicity; these strategies involve the use of a hydrophilic comonomer, functional monomer, or crosslinker in the molecular imprinting process, and the postmodification of the preformed MIPs. Although simple in principle, the former strategy either requires time-consuming optimization of MIP formulation components or can only be applied in some special systems. In comparison, the latter strategy, which involves the surface grafting of hydrophilic polymer layers, has proven highly attractive because it not only significantly improves the MIPs surface hydrophilicity, but also provides a protective layer to prevent protein molecules from blocking their imprinting sites in biological solutions. Very recently, we have successfully prepared pure-water-compatible MIP microspheres by the controlled grafting of hydrophilic polymer layers onto the preformed MIP particles. Compared with this two-step approach, the new strategy presented herein allows the more efficient controlled synthesis of pure-water-compatible MIP microspheres with surface-grafted hydrophilic polymer brushes by a one-pot RAFTPP method. To show proof-of-principle for our strategy, a model noncovalent molecular imprinting system was chosen because Scheme 1. Chemical structures of the utilized RAFT agents (including hydrophilic Macro-CTAs and CDB) and the schematic protocol for the one-pot preparation of water-compatible MIP microspheres by RAFT precipitation polymerization.