Characterization of the solvation environment provided by dilute aqueous solutions of novel siloxane polysoaps using the fluorescence probe pyrene

Solubilization environment afforded by several of the novel allyl glycidyl ether-modified methylhydrosiloxane polymers are investigated using a common polycyclic aromatic hydrocarbon fluorescence probe, pyrene. The backbone of the polymer has been modified by the addition of an alkyl chain of varying length (either C8, C12, or C18) and to differing degrees of substitution. The nomenclature adopted for the purposes of these studies is as follows: "AGENT" represents the backbone polymer with no alkyl substitution, and "OAGENT", "DAGENT", and "SAGENT" are substituted with n-octyl, n-dodecyl, and n-octadecyl, respectively. The percentage of alkyl substitution is designated as 10, 15, and 20%. The pyrene polarity scale (defined as the ratio of the intensity of peak I to peak III) was used to determine the relative dipolarity of the cybotactic region provided by approximately 1 w/w% aqueous polymer solutions compared to 10 mM sodium dodecylsulfate (SDS) micellar solution. Results indicate that 10-15% DAGENT afforded the most hydrophobic solubilization site, followed by 15% OAGENT and 15% SAGENT. In addition, as the degree of alkyl substitution of DAGENT increased from 10 to 20%, the cybotactic region appeared to become more hydrophobic. Furthermore, a deeper investigation into the relative size of the solubilization site revealed that all alkyl-substituted polymers promoted excimer formation at relatively low pyrene concentrations, indicating the possibility of localized concentration enhancement within the solvation pockets and/or compartmentalization of the solute molecules. The pyrene fluorescence excitation data strongly indicates ground-state heterogeneity that is most prominent in AGENT and decreases as the alkyl chain length is increased. This provides a relative sense of the size and shape of the solvation pockets afforded by each polymer solution. An overall analysis of the collected data indicated that these alkyl-substituted polymers may provide a more selective and efficient pseudostationary phase in electrokinetic chromatography with better solvation capacity for hydrophobic compounds compared to SDS.     

Synthesis and esterolytic reactions of linear and cross-linked asymmetric imidazole-containing polymers

Asymmetric linear and cross-linked imidazole-containing polymers were prepared from 1-[2(S)-methylbutyl]-4-vinylimidazole and 1-[2(S)-methylbutyl]-5-vinylimidazole. The esterolytic reactions of these linear and cross-linked asymmetric polymers with the enantiomeric substrates (R)- and (S)-4-(3-methylpentadecanoyl)-3-nitrobenzoic acid, (R)- and (S)-S, were studied by measuring the pseudo-first order kinetics of the solvolysis of these enantiomeric substrates in the presence of these asymmetric polymers. The linear homopolymers and copolymers of 1-[2(S)-methylbutyl]-4- and 5-vinylimidazole showed hydrophobic and electrostatic effects in the solvolysis of the enantiomeric substrates with these linear asymmetric polymers. Cross-links were introduced into these asymmetric polymers to increase the rigidity and reduce the number of conformations available to the polymer. The reduced conformational mobility was expected to enhance any enantioselectivity in the solvolysis of the enantiomeric substrates with these polymers. Using these cross-linked polymers, hydrophobic interactions were observed in the solvolysis of a series of substrates with increasing alkyl chain length. Also, on changing the polarity of the solvent, a bell-shaped rate profile was observed in the solvolysis of the long chain substrate S. This effect was attributed to a combination of the coiling of the cross-linked polymer chains and hydrophobic interactions with the substrate on changing solvent polarity. Even with the increased rigidity of these cross-linked polymers, no significant enantioselectivity in the solvolysis of the enantiomeric substrates was observed. So, neither the linear nor the cross-linked asymmetric polyvinylimidazoles showed enantioselectivity in the solvolysis of these enantiomeric substrates. In this case, the hydrophobic interactions and the reduced conformational mobility through crosslinking were not strong enough to bring about enantioselectivity in the solvolysis of these enantiomeric substrates.     

Synthesis and SFM Study of Comb‐Like Poly(4‐vinylpyridinium) Salts and Their Complexes with Surfactants

Summary: Poly(4‐vinylpyridinium) bromides containing octyl and dodecyl pendant groups were synthesized. Bromide anions in these polymer salts were substituted with dodecylsulfate and bis(2‐ethylhexylsuccinate) anions using ion‐exchange reactions. Initially, P4VP and its derivatives loaded with hydrophobic groups were deposited on a mica surface from diluted solutions in chloroform for visualization. Images of single adsorbed macromolecules were obtained using scanning force microscopy. Original P4VP chains form partially compacted self‐intersecting coils. Loading the polymer chains with large hydrophobic groups and especially the increase in the number of alkyl tails (see Figure) per monomer unit of the polymer chain leads to the stretching of the coils, and the comb‐like macromolecules adopt more and more extended self‐avoiding 2D conformations when deposited on the substrate.

Polymer chains with large hydrophobic groups and increasing number of alkyl tails per monomer unit of the polymer chain.     

Inclusion complexes of α‐cyclodextrin and (AB)n block copolymers

Cyclodextrins thread onto polymer chains to form inclusion complexes, especially when the polymer is hydrophobic relative to the solvent. Selective threading might occur when the polymer architecture contains both hydrophobic and hydrophilic segments. α‐Cyclodextrin formed crystalline inclusion complexes with (AB)_n microblock copolymers, where the A block was a linear alkyl segment containing a single double bond and the B block was an exact length segment of poly(ethylene oxide). The complexes were isolated and characterized by solution and solid‐state NMR, X‐ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. Each method confirmed complex formation and showed that the physical properties of the complexes were distinct from those of its individual components. The X‐ray data were consistent with known inclusion complexes having a channel or column crystal structure. The stoichiometry of the complex formation, 2.3 α‐cyclodextrin rings per polymer repeat unit, was determined by NMR analysis of the complexes and from an analysis of the inclusion complex yields. The data suggest that the inclusion complex stoichiometry is defined by the increasing insolubility of the polymer–cyclodextrin complex. Solid‐state NMR data were consistent with a preference for threading onto hydrophobic segments of the (AB)_n polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2731–2739, 2001     

Interaction of urea and urea derivatives with cyclohexamylose in aqueous solutions at 25°C

The interaction in water of urea, monomethylurea, monoethylurea, monopropylurea, and monobutylurea with -cyclodextrin(hexacycloamylose) was studied calorimetrically at 25°C. The results show that the last three substances form inclusion complexes with -cyclodextrin. The enthalpy and the association constants relative to the inclusion process were determined. The association constant values are low, indicating weak complexing that increases with increasing length of the alkyl chain. Urea and monomethylurea, on the other hand, do not form inclusion complexes. For these systems the calorimetric data were treated in terms of excess enthalpies, and the McMillan-Mayer approach was used to get an insight into the weak, non-bonding molecular interactions occurring in these solutions.Presented at the sixth Italian meeting on Calorimetry and Thermal Analysis (AICAT) held in Naples, December 4–7, 1984.     

Inclusion complexes of alcohols with α-cyclodextrin

Calorimetric studies of the inclusion complexes of straight and branched alcohols and of diols with alpha-cyclodextrin (-CD) have been carried out in water solvent. The data suggest that straight and branched chain alcohols enter the cavity of -CD alkyl end first. The hydroxyl group hydrogen bonds to the outer oxygen ring of the cyclodextrin. For branched chain alcohols the longer alkyl part of the molecule penetrates the -CD cavity up to the hydroxyl group. Diols form two hydrogen bonds to the outer oxygen ring of the cyclodextrin with some penetration into its interior.     

Complex formation between α-cyclodextrin and amines in water and DMF solvents

Complexation between -cyclodextrin (-CD) and aliphatic amines in water and DMF solvents was studied by calorimetry. Amines form complexes with -CD in both solvents but the nature of the complexes is quite different. In DMF the amines donate a hydrogen from the amine N–H group to the cyclodextrin forming a normal hydrogen bonded complex. In DMF solutions with large amine concentrations, complexes other than 11 are observed. In contrast, in aqueous environment the amines form inclusion complexes in which the amine alkyl group penetrates the -CD cavity and is stabilized by van der Waals interactions. The equilibrium constants for the complexes formed in water solvent increase with increasing alkyl chain length due to an entropy effect.     

Vine-twining polymerization: a new preparation method for well-defined supramolecules composed of amylose and synthetic polymers

In this article we describe a new method of polymerization called "vine-twining polymerization" for preparation of well-defined supramolecules, which are amylose-polymer inclusion complexes. The method was achieved by enzymatic polymerization of alpha-D-glucose-1-phosphate catalyzed by phosphorylase in the presence of various synthetic polymers such as polyethers, polyesters, poly(ester-ether), and amphiphilic block copolymer. Powder X-ray diffraction (XRD) and 1H-NMR measurements determined the structures of the products to be inclusion complexes. The XRD patterns were completely different from those of amylose and guest polymers. The 1H-NMR spectra of the products indicated that the structures were composed of amylose and guest polymers. The formation process of the inclusion complexes during the enzymatic polymerization was also evaluated. In addition, we revealed that the bulkiness of the end groups and the hydrophobicity of the guest polymers strongly affected the formation of the inclusion complexes. By means of this method of polymerization, a graft polymer having inclusion complexes as side chains was prepared. Furthermore, as an evolution of the "vine-twining polymerization," we attempted a system of parallel polymerization to form an inclusion complex of amylose with a strongly hydrophobic guest polymer.     

The use of naphthalene fluorescence probes to study the binding sites on cyclodextrin polymers formed from reaction of cyclodextrin monomers with epichlorohydrin

Three naphthalene-based fluorescence probes were used as guest molecules to study host/guest binding with cyclodextrin (CD) polymer hosts prepared by treating -,-, or -cyclodextrin monomers with epichlorohydrin. The fluorescence data indicate that the binding interaction is much stronger for the probes with the CD polymers than with the CD monomers. Moreover, the fluorophore binding site on the CD polymers is also more hydrophobic than that on the CD monomers. Fluorescence lifetime data from one of the bound probes (2-(N-methylanilino) naphthalene-6-sulfonic acid) suggest that more than one type of binding site may exist on the CD polymers with this probe. A comparison of fluorescence data using different molecular weight ranges of the CD polymers appear to rule out the possibility of a 12 host/guest complex, where the two CD units come from the same polymer chain.     

Amphiphilic block copolymers of vinyl ethers by living cationic polymerization. II. Synthesis and surface activity of macromolecular amphiphiles with pendant amino groups

Amphiphilic block polymers of vinyl ethers (VEs). $\rlap{--} [{\rm CH}_{\rm 2} {\rm CH}\left( {{\rm OCH}_{\rm 2} {\rm CH}_{\rm 2} {\rm NH}_{\rm 2} } \right)\rlap{--} ]_m \rlap{--} [{\rm CH}_{\rm 2} {\rm CH}\left( {{\rm OR}} \right)\rlap{--} ]_n \left( {{\rm R: }n{\rm - C}_{{\rm 16}} {\rm H}_{{\rm 33}} ,{\rm }n{\rm - C}_{\rm 4} {\rm H}_{\rm 9} ;m \simeq 40,{\rm n} = 1 - 10} \right)$ were prepared, each of which consists of a hydrophilic segment with pendant primary amino groups and a hydrophobic poly(alkyl VE) segment. Their precursors were obtained by the HI/I₂-initiated sequential living cationic polymerization of an alkyl VE and a VE with a phthalimide pendant (CH₂ = CHOCH₂CH₂Im; Im; phthalimide group), where the segment molecular weights and compositions (m/n ratio) could be controlled by regulating the feed ratio of two monomers and the concentration of hydrogen iodide. Hydrazinolysis of the imide functions gave the target polymers which were readily soluble in water under neutral conditions at room temperature. These amphiphilic block polymers lowered the surface tension of their aqueous solutions (0.1 wt%, 25°C) to a minimum ? 30 dyn/cm when the hydrophobic pendant R was n-C₄H₉ (n = 4–9). The polymers with n-C₄H₉ pendants in the hydrophobic segment exhibited a higher surface activity than those with n-C₁₆ H₃₃ pendants. The surface activity of the polymers also depended on the pH of the polymer solutions; the surface activity increased in more basic solutions where the ionization of the amino group (? NH₂)2? NH₃^⊕) is suppressed.     

基于环糊精包结络合作用的大分子自组装*

本文综述了基于环糊精包结络合作用的大分子自组装的研究进展,包括：（1) 线型、梳型、多臂星型或超支化聚合物与环糊精或其二聚体自组装形成多聚轮烷（分子项链）、多聚准轮烷、双多聚（准）轮烷、分子管、双分子管、超分子凝胶及其应用;（2）桥联环糊精与桥联客体分子自组装制备线型或超支化超分子聚合物;（3）温度、pH值、光及客体分子刺激响应智能体系; （4) 通过亲水性的环糊精线型均聚物与含金刚烷的疏水性聚合物之间的包结络合作用来制备高分子胶束及其空心球等。     

Acyloin condensation by polymer supported thiazolium salt: Relation between the catalytic activity and the degree of quarternization

Thiazolium salt polymers were synthesized by the quarternization of thiazole polymers by alkyl halides. It was found that these polymers had high catalytic activities for the acyloin condensation of furfural. The catalytic activities of thiazolium salt polymers increased as the degree of quarternization decreased. This tendency was observed both in the polar solvents such as MeOH and in the nonpolar solvents such as dioxane. From the results of the acyloin condensation catalyzed by more hydrophobic polymer catalyst PTS⁺–St (which had styrene unit instead of free thiazole unit) and CnPTS⁺ (which had a long alkyl chain around the active site), it became clear that the hydrophobicity and the steric hindrance around the active site greatly affected the catalytic activity.     

Substituent Effects on the Driving Force for Inclusion Complexation of α- and β-Cyclodextrin with Monosubstituted Benzene Derivatives

The association constant values, K_a, for the inclusion of - and -CD with monosubstituted benzene derivatives were determined by means of UV-vis and fluorescence spectroscopy. The stability of the complexes is influenced by the properties of the substituents of the guest compounds. Regression analysis was used to create a set of inclusion models with the experimental association constant ln K_a and the corresponding substituent molar refraction R_m, hydrophobic constant and Hammett constant of the benzene derivatives. The ln K_a value mainly correlated with R_m for -CD and with both R_m and for -CD complexes. The association constants predicted by the models are in good agreement with the experimentally determined data. This suggests that the inclusion complexation of benzene derivatives with -CD is predominantly driven by van der Waals force and with -CD mainly by van der Waals force and hydrophobic interactions.     

Temperature‐ and Redox‐Directed Multiple Self Assembly of Poly(N‐Isopropylacrylamide) Grafted Dextran Nanogels

Poly(N‐isopropylacrylamide) (PNIPAAm) grafted dextran nanogels with dodecyl and thiol end groups have been synthesized by RAFT process. Dodecyl‐terminated polymers (DexPNI) can be readily dissolved in water and further self assemble into ordered stable nanostructures through direct noncovalent interactions at room temperature. SEM, AFM and DLS measurements confirm the formation of spherical nanogels at hundred‐nanometer scales. The elevation of environment temperature will indirectly result in the formation of collapsed nanostructures due to the LCST phase transition of PNIPAAm side chains. Turbidimetry results show that the phase transition behaviors of DexPNI are greatly dependent on PNIPAAm chain length and polymer concentration: increasing PNIPAAm chain length and polymer concentration both lead to lower LCSTs and sharper phase transitions. Moreover, the dodecyl‐terminated polymers can transform into thiol‐terminated versions by aminolysis of trithiocarbonate groups, and further into chemical (disulfide) cross‐linked versions (SS‐DexPNI) by oxidation. SS‐DexPNI nanogels have “doubled” chain length of PNIPAAm, and hence sharper phase transitions. In situ DLS measurements of the evolution of hydrodynamic radius attest that the self assembly of SS‐DexPNI nanogels can be selectively directed by the change in either external temperature or redox potential. These nanogels thus are promising candidates for triggered intracellular delivery of encapsulated cargo. We can also expect that the polymer can be noncovalently (by dodecyl end groups) or covalently (by thiol end groups) coated on a series of nanomaterials (e.g., carbon nanotubes, graphene, gold nanomaterials) to build a variety of novel smart, and robust nanomaterials.

     

Manipulating interactions between functional colloidal particles and polyethylene surfaces using interfacial engineering

Polymer-hybridized liposomes (PHLs) of saturated lecithin were formed by association of poly(asparagines) grafted with alkyl chains (PAsn-g-Cn). The thermal, physical, and surface properties of the polymer-hybridized liposomes were examined with varying polymer concentration, alkyl chain length (C(8), C(12), C(18), C(22)), and degree of substitution (DS) in the polymer. The inclusion of the polymer raised the membrane fluidity of liposomes. By the incorporation of small amount of polymer, the membrane rigidity of liposomes dropped sharply and then increased close to the original level as the polymer concentrations increased in the cases of PAsn-g-C(18) and PAsn-g-C(22). Also, the membrane rigidity and stability of PHLs increased with alkyl chain length at the same polymer concentration. The surface charge of PHL associated with PAsn-g-C(22) was changed by DS of alkyl chains. The polymer bearing long alkyl chains (C(12), C(18), C(22)) formed PHLs well at low polymer concentration and the number of disk-shaped polymer-lipid mixed micelles increased with polymer concentration. The anchored polymers induced shifts in gel-to-liquid crystal transition temperature (Tc) of the vesicles and Tc varied with polymer concentration, alkyl chain length, and DS of the polymer.     

Excitation Frequency Dependence of the Surface Properties and Composition of Plasma Polymers from Aldehyde Monomers

The effect was investigated of varying the plasma excitation frequency in the range 125 to 375 kHz upon the air/water contact angles of plasma polymers prepared from the monomers ethylbutyraldehyde (EBA), acetaldehyde (AA), capronaldehyde (CA), and nonyl aldehyde (NA). The surfaces of EBA, CA, and AA plasma films were more hydrophilic when deposited at lower excitation frequencies whereas little frequency dependence was observed in the case of NA plasma polymers. Lower contact angles correlated with increased amounts of C=O and O–C=O groups measured by FTIR and XPS analyses. The effects of storage (aging) in air at room temperature upon the properties of the plasma polymers were also studied. Contact angles of EBA plasma polymers decreased during aging. The contact angles of NA plasma polymers were stable over a 3 months storage period. In the case of CA plasma polymers, the contact angles decreased on aging for films deposited at higher frequencies, whereas CA films deposited at lower frequencies showed increasing contact angles on storage. This aging behavior is interpreted as a result of competition between post-deposition oxidative reactions with atmospheric oxygen and reorientation of polar polymer segments away from the air interface.     

烷基-α-D-吡喃葡萄糖苷的合成与性能

以D-葡萄糖为原料,经全乙酰化、在SnCl_4催化下与脂肪醇糖苷化、脱保护3步反应合成了7种不同碳链长度的烷基-α-D-吡喃葡萄糖苷。利用核磁共振、表面张力仪和偏光显微镜等对其进行结构、表面张力和热致液晶等性能测试,结果表明,当烷基-α-D-吡喃葡萄糖苷烷基链长(n)为6~9时,均有发泡和乳化性能,其中正壬基-α-D-吡喃葡萄糖苷具有最佳的发泡和乳化性能;烷基糖苷(n=6~9)的表面张力(γ_(CMC))及临界胶束浓度(CMC)均比较低;饱和吸附量(Γ_(max))随烷基链的增长而减小,饱和吸附面积(A_(min))随烷基链增长而增大;形成胶束时的标准自由能(ΔG_(mic))和吸附自由能(ΔG_(ads))均为负值,其绝对值随烷基链增长而越来越大,其中正辛基-α-D-吡喃葡萄糖苷的表面活性最好;烷基糖苷(n=4~9)对皮肤均无急性刺激作用;所合成的烷基糖苷均具有热致液晶行为,随烷基链长的增加,液晶相的温度范围变宽,液晶相的稳定性越好。     

Novel thermotropic liquid crystalline‐cum‐photocrosslinkable polyvanillylidene alkyl/arylphosphate esters

A new class of linear unsaturated polyphosphate esters based on divanillylidene cyclohexanone possessing liquid crystalline‐cum‐photocrosslinkable properties have been synthesized from 2,6‐bis[n‐hydroxyalkyloxy(vanillylidene)]cyclohexanone [n = 6,8,10] with various alkyl/aryl phosphorodichloridates in chloroform at ambient temperature. The resultant polymers were characterized by intrinsic viscosity, FT‐IR, ¹H, ¹³C, and ³¹P‐NMR spectroscopy. All the polymers showed anisotropic behavior under hot stage optical polarized microscope (HOPM). The liquid crystalline textures of the polymers became more transparent with increasing spacer length. The thermal behavior of the polymers was studied by thermogravimetric analysis and differential scanning calorimetry. The T_g, T_m, and T_i of the polymers decreased with increasing flexible methylene chain. The photocrosslinking property of the polymer was investigated by UV light/UV spectroscopy; the crosslinking proceeds via 2π‐2π cycloaddition reactions of the divanillylidene exocyclic double bond of the polymer backbone. The pendant alkyloxy containing polymers show faster crosslinking than the pendant phenyloxy containing polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5215–5226, 2004     

Stabilization of dyes against hydrolytic decomposition by the formation of inclusion compounds

The decomposition reactions of the dyes phenol blue and murexide were measured spectroscopically in acidic solution at different temperatures. From these reaction rates and their temperature dependence in the absence and presence of various hosts, the stability constants and the reaction enthalpies of the dye complexes with noncyclic dextrins, cyclodextrins and cucurbituril were calculated.-Cyclodextrin enhances the stability of phenol blue in acidic solution. This effect is even more pronounced with cucurbituril. Due to the molecular structure of murexide this dye cannot form inclusion complexes with hosts containing hydrophobic cavities.     

Conformational behavior of polymers adsorbed on nanotubes

The importance of hydrophobic interactions in determining polymer adsorption and wrapping of carbon nanotubes is still under debate. In this work, we concentrate on the effect of short-ranged weakly attractive hydrophobic interactions between polymers and nanotubes (modeled as an infinitely long and smooth cylindrical surface), neglecting all other interactions apart for chain flexibility. Using coarse-grained Monte Carlo simulation of such simplified systems, we find that uniform adsorption and wrapping of the nanotube occur for all degrees of chain flexibility for tubes with sufficiently large outer radii. However, the adsorbed conformations depend on chain stiffness, ranging from randomly adsorbed conformations of the flexible chain to perfect helical or multihelical conformations (in the case of more concentrated solutions) of the rigid chains. Adsorption appears to occur in a sequential manner, wrapping the nanotube nearly one monomer at a time from the point of contact. Once adsorbed, the chains travel on the surface of the cylinder, retaining their helical conformations for the semiflexible and rigid chains. Our findings may provide additional insight to experimentally observed ordered polymer wrapping of carbon nanotubes.