Novel reactive thermosensitive polyethers – control of transition point

A new class of thermosensitive polymers based on polyethers is discussed. Using living anionic polymerisation techniques a series of homo- and block copolymers of 2,3-epoxypropanol-1 (the glycidol), ethoxy ethyl glycidol ether, its hydrophobic derivative, and ethylene oxide of different molar masses and topology (linear and comb-like) was obtained. By simple chemical modification of hydroxyl groups in polyglycidol segments hydrophobic elements were introduced into polymer chains, which allowed to control the transition point related to the lower critical solution temperature between 0 to 100°C. The relation between the transition temperature and the structure of obtained polymers is discussed.     

Synthesis of New Amphiphilic Comb-Like Copolymers Based on Maleic Anhydride and α-Olefins

Summary: Novel amphiphilic comb-like poly(α-olefin-co-maleic anhydride) with a controlled ratio of hydrophilic (polyoxyethylene) and hydrophobic (polymethylene) side chains have been synthesized and characterized. The comb-like copolymers are soluble in organic and aqueous media and form micelles whose behaviour could be correlated to the chemical structure of polymers. We foresee that amphiphilic properties of the novel comb-like polymers are obviously the basis of new architectures in solution which could be used in a broad range of applications. Using micelles from these copolymers, silver nanoparticles with a narrow particle size distribution have been obtained as stable dispersion in both polar and non-polar media.     

Molecular, conformational, and optical characteristics of poly(dodecylammonium-2-acrylamido-2-methylpropanesulfonate) in organic solvents

A number of samples of poly(dodecylammonium-2-acrylamido-2-methylpropanesulfonate)—a comb-like polymer with ionically bound side chains—are obtained by the polymerization of dodecylammonium-2-acrylamido-2-methylpropanesulfonate in an aqueous medium. The samples are obtained in a wide molecular-mass range. Molecular, hydrodynamic, and optical characteristics of the samples are determined by the methods of sedimentation-diffusion analysis, viscometry, and flow birefringence in dilute polymer solutions in chloroform and dimethyl sulfoxide containing small amounts of 0.1 M LiCl. It is shown that conformational and optical characteristics based on hydrodynamic and dynamo-optic investigations agree with the data available for acrylic and methacrylic polymers with the same lengths of side groups. In other words, the character of attachment (covalent or ionic) of long side chains to the backbone has no effect on the conformational and optical characteristics of macromolecules.     

Thermally responsive polymeric micellar nanoparticles self-assembled from cholesteryl end-capped random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide): synthesis, temperature-sensitivity, and morphologies

Cholesteryl end-capped thermally responsive amphiphilic polymers with two different hydrophobic/hydrophilic chain-length ratios were synthesized from the hydroxyl-terminated random poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) and cholesteryl chloroformate. The hydroxyl-terminated precursor polymers with narrow molecular weight distributions were synthesized by free-radical polymerization using 2-hydroxyethanethiol as a chain-transfer agent. The aqueous solutions of the cholesteryl end-capped copolymers exhibited reversible phase transitions at temperatures slightly above human body temperature, with the lower critical solution temperature values being 37.7 and 38.2 degrees C, respectively. The critical micelle concentration values of the two cholesteryl end-capped polymers were 9 and 25 mg/L, respectively. Polymeric micellar nanoparticles were prepared from the amphiphilic polymers using a dialysis method as well as a direct dissolution method. Transmission electron microscope studies showed that the micellar nanoparticles existed in different morphologies, including spherical, star-like, and cuboid shapes. Pyrene as a model hydrophobic compound could be readily encapsulated in these polymeric nanoparticles, at loading levels of 1.0 and 0.8 mg/g for the two cholesteryl end-capped polymers, respectively. The temperature sensitivity and unusual morphology of these novel polymeric nanoparticles would make an interesting drug delivery system.     

建筑用梳形共聚物分散剂溶液行为的光散射研究

采用激光光散射研究了一种主链为聚丙烯酸侧链为聚乙二醇的梳形共聚物分散剂的一些溶液行为.从静态光散射得出了较为合理的表观重均分子量、均方旋转半径等参数.动态光散射给出了流体力学半径分布及其角度和浓度依赖性.结合静态和动态光散射,上述梳形共聚物分散剂在溶液中的构象也得到初步的表征.通过与描述梳形聚合物的Gay-Raphae模型进行比较表明,这类梳形共聚物溶液在低盐离子和低pH值条件下存在聚集行为,形成以PAA主链为核PEG为壳层的类胶束聚集.     

含树枝体疏水缔合聚合物——聚醚树枝体改性聚丙烯酰胺的合成和性质

疏水缔合聚合物是一类含有少量疏水基团的水溶性功能高分子.在水溶液中,这类聚合物在疏水作用驱动下容易发生缔合,并伴随产生独特的缔合行为和溶液性质,因此研究这类聚合物具有重要的理论和应用意义.     

Preparation of polymer nanoparticles by self-assembling of amphiphilic poly-<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone derivatives in aqueous media

Amphiphilic N-vinylpyrrolidone polymers were prepared by a new one-step procedure consisting in radical polymerization of the monomer in the presence of long-chain monobasic saturated carboxylic acid chlorides as chain-transfer and chain-terminating agents. The behavior of the new amphiphilic polymers differing in the structure of the hydrophilic and hydrophobic moieties in aqueous media was studied. The synthesized polymers at definite concentrations undergo spontaneous aggregation with the formation of spherical nanosized micellar particles consisting of a hydrophobic core and a hydrophilic shell. The main characteristics of the polymer nanoparticles formed were determined, and the possibility of using them as promising carriers for the delivery of biologically active compounds and drugs was revealed.     

新型疏水缔合丙烯酰胺/2-苯氧乙基丙烯酸酯共聚物的合成与性质

采用胶束共聚方法合成了一种新型的疏水缔合共聚物 ,它由丙烯酰胺 (AM)和少量的 2 苯氧乙基丙烯酸酯 (POEA) (<1 0mol% )组成 ,具有良好的水溶性 .当溶液浓度超过一定值c 后 ,由于分子间的疏水缔合 ,产生很大的增粘作用 .研究了不同聚合条件下包括单体浓度、投料比和SMR值对聚合物的结构和性能的影响 .实验结果表明 ,聚合物的粘度性质和缔合行为取决于其分子量的大小、疏水单体含量及其嵌段的长度和分布 .     

结构明确的梳形支化聚合物的合成与表征

通过活性聚苯乙烯(PS)和聚异戊二烯(PI)负离子与含1,1-二苯基乙烯(DPE)侧基的聚苯乙烯(PSe)的偶联反应合成了结构明确的每个重复单元含一条侧链的梳形支化聚合物,其中,PSe是通过Sc单体的原子转移自由基聚合(ATRP)和Wittig反应制得的.用IR1、H-NMR、GPC和SLS等测试方法对所得梳形支化聚合物进行了详细表征,讨论了活性负离子链与PSe的DPE基团的配比对接枝率的影响.结果表明,活性负离子链与DPE基团的偶联反应是高效的,可以通过调节活性负离子链与DPE基团的加料比来控制接枝率.另外,还讨论了PSe和活性负离子链的分子量对接枝率的影响.结果表明,在实验范围内当活性负离子链过量时可获得几乎定量的接枝率.     

pH-controlled, polymer-mediated assembly of polymer micelle nanoparticles

We describe pH-controlled, polymer-mediated assembly of polymer micelles in aqueous media based on reversible complexation between the micelles of pyrene-labeled poly(epsilon-caprolactone)-b-poly(carboxylic acid) copolymers and proton-accepting water-soluble polymers such as poly(ethylene glycol) (PEG), poly(2-ethyl-2-oxazoline) (PEtOz), and poly(1-vinylpyrrolidone) (PVP). The key factor determining assembly phenomena was identified as the modulation of hydrogen-bonding interaction between ionizable anionic micellar shells and the proton-accepting polymers by the pH control. As pH decreased from 7.4 to 2.0, the mixture of the polymer micelles and polymers underwent assembly and formed solid hybrids at specific pH values. The micelles assembled in the hybrid could be reversibly dispersed as micelles above specific pH ranges. The assembly/disassembly behavior as well as phase transitions of the micelle/proton-accepting polymer could be precisely controlled by adjusting pH. This assembling behavior depended on the rationally designed parameters such as the chemical structure and length of micellar shell-forming poly(carboxylic acid)s and the class of proton-accepting polymers.     

Controlling the self-assembly structure of magnetic nanoparticles and amphiphilic block-copolymers: from micelles to vesicles

We report how to control the self-assembly of magnetic nanoparticles and a prototypical amphiphilic block-copolymer composed of poly(acrylic acid) and polystyrene (PAA-b-PS). Three distinct structures were obtained by controlling the solvent-nanoparticle and polymer-nanoparticle interactions: (1) polymersomes densely packed with nanoparticles (magneto-polymersomes), (2) core-shell type polymer assemblies where nanoparticles are radially arranged at the interface between the polymer core and the shell (magneto-core shell), and (3) polymer micelles where nanoparticles are homogeneously incorporated (magneto-micelles). Importantly, we show that the incorporation of nanoparticles drastically affects the self-assembly structure of block-copolymers by modifying the relative volume ratio between the hydrophobic block and the hydrophilic block. As a consequence, the self-assembly of micelle-forming block-copolymers typically produces magneto-polymersomes instead of magneto-micelles. On the other hand, vesicle-forming polymers tend to form magneto-micelles due to the solubilization of nanoparticles in polymer assemblies. The nanoparticle-polymer interaction also controls the nanoparticle arrangement in the polymer matrix. In N,N-dimethylformamide (DMF) where PS is not well-solvated, nanoparticles segregate from PS and form unique radial assemblies. In tetrahydrofuran (THF), which is a good solvent for both nanoparticles and PS, nanoparticles are homogeneously distributed in the polymer matrix. Furthermore, we demonstrated that the morphology of nanoparticle-encapsulating polymer assemblies significantly affects their magnetic relaxation properties, emphasizing the importance of the self-assembly structure and nanoparticle arrangement as well as the size of the assemblies.     

New amphiphilic polyacrylamides: Synthesis and characterisation of pseudo-micellar organisation in aqueous media

In order to offer new tools for developing structure-property relationships for intramolecular associative polymers (polysoaps), the synthesis of three families of comb-like amphiphilic cationic polymers with great structure variability is described. These polymers with amphiphilic repeating units are polyacryl or methacrylamides laterally substituted by a group containing a quaternary ammonium site and a hydrophobic alkyl side chain with 10-16 carbon atoms. Two complementary synthesis methods were developed successfully. In the first method, the tertiary amine groups of neutral polymer precursors were quaternised with various n-alkyl bromides. Five polymers were obtained in this way. On the contrary, the second method consisted of synthesizing first amphiphilic cationic acryl or methacrylamide monomers. The 11 monomers thus obtained were then polymerised by conventional free radical polymerisation in solution. The polymers obtained by both methods only differed in their molecular weights, the second method leading to much higher molecular weights (up to 2 × 10⁶ g/mol). A preliminary investigation of the properties of a few of these polymers in solution showed interesting amphiphilic behaviour. The variation of the reduced viscosity of hydro-methanolic polymer solutions with polymer concentration revealed a strong intramolecular macromolecular folding. The microdomains corresponding to the intramolecular association of the hydrophobic alkyl side chains were eventually characterised by pyrene fluorescence spectroscopy. The local polarity of the pyrene probe was considerably lowered with respect to that of the surrounding aqueous phase and was dependent upon the macromolecular structure of the amphiphilic cationic polymers.     

Polymerization of oriented monomers. V. Radiation-induced polymerization of 3n-dodecyl-1-vinylimidazolium iodide in micellar aggregates

In the present study radiation-induced polymerization of 3n-dodecyl-1-vinylimidazolium iodide (I) in micellar aggregates was investigated. For comparison, the corresponding isotropic polymerization of I was also studied. Micellization was obtained in concentrated aqueous solutions; that is, above the monomer's critical micelle concentration (CMC) polymers obtained by both modes of polymerization were treated similarly and subsequently subjected to physical characterization. The main purpose of this study was to investigate whether the degree of organization of the monomer in micelles would affect polymer properties. Attempts to determine tacticity by ¹³C-NMR spectrometry failed because of the particular structure of the polymer. Crystallization of these polymers from ethyl alcohol or acetone was not possible as indicated by x-ray powder diffraction patterns that were characteristic of amorphous polymers. On the other hand, viscosity data of polymers do not depend on the mode of polymerization. It is therefore concluded that micellar aggregates are not sufficiently organized to affect polymer properties.     

Polymeric arylsulfonylmethyl isocyanide,a novel polymer reagent

p-Vinylphenylsulfonylmethyl isocyanide (1M) was synthesized starting with sodium p-styrenesulfinate via p-vinylphenylsulfonylmethylformamide (4M). Free-radical polymerization of 1M provided cross-linked insoluble polymers (1), whereas 4M provided soluble polymers, which could be converted to soluble polymer 1. Conversions of carbonyl compounds to nitriles and Schiff bases to 1,5-disubstituted imidazoles with both soluble and cross-linked polymers 1 as reagents proceeded almost as efficiently as with their low molecular weight analog. Reusability of polymer 1 was fairly good.     

A novel method to synthesize polystyrene nanospheres immobilized with silver nanoparticles by using compressed CO2

In this work, a novel route to synthesize polymer/metal composite nanospheres has been proposed. This method combines the advantages that the polymer chains collapse and entangle in the presence of compressed CO(2), which acts as antisolvent, and the metal nanoparticles and polymers can be precipitated simultaneously from micellar solutions by the easy control of CO(2) pressure. Ag/polystyrene (PS) nanocomposites have been successfully prepared using this method. The transmission electronic micrographs (TEM) of the obtained nanocomposites show that the smaller Ag nanoparticles are immobilized by PS nanospheres of about 50 nm; the phase structure was characterized by X-ray diffraction (XRD). The Ag/PS nanocomposites show absorption properties at a wavelength of approximately 417 nm. The results of X-ray photoelectron spectra (XPS) and FT-IR spectra indicate that there is no chemical linkage or strong interaction between PS and Ag nanoparticles in the resultant products. This method has many potential advantages for applications and may easily be applied to the preparation of a range of inorganic/ polymer composite nanoparticles.     

Fluorescent π‐Conjugated Polymer Dots versus Self‐Assembled Small‐Molecule Nanoparticles: What’s the Difference?

Fluorescent nanoparticles based on π‐conjugated small molecules and polymers are two different classes of π‐conjugated systems that have attracted much interest. To date, both emerging classes have only been studied separately and showed no clear differences in their properties. Herein these nanoparticles are compared on the basis of a fluorene co‐polymer and its corresponding small molecule. Both systems formed nanoparticles with the same diameter, whereas the fluorescence properties clearly differed. In case of the polymer the fluorescence diminished, whereas for the small molecules the fluorescence increased. In addition, the capability of encapsulation and release of a hydrophobic dye from the fluorescent nanoparticles was studied. For the polymer system, encapsulation was highly efficient and no release was observed, whereas for the small molecule system encapsulation was less efficient and release of the dye was observed. These studies show a clear difference between small molecules and polymers which has important implications for the design of fluorescent nanoparticles.     

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.     

Impact of molecular size of SMA-g-MPEG comb-like polymer on the dispersion of CaCO3 suspensions

Poly(styrene-co-maleic anhydride)-g-methoxypolyethylene glycols comb-like polymer was employed as the dispersant of CaCO₃ suspensions in this paper. The comb-like polymer had much better dispersability than traditional linear polyelectrolyte. By changing the length of side chains to alter the molecular size, the dispersion of CaCO₃ suspensions was greatly influenced. The absolute value of zeta potential and the adsorption density decreased with increasing the length of side chains, while the rheological and dispersion properties had a best value when using polymers with moderate length of side chain. Calculations were performed based on the scaling law and Flory theory. It was known from the calculations that by increasing the length of side chains, the molecular size and the steric repulsion were both increased. But due to the worse activity of adsorption, the comb-like polymers with longer side chains had lower adsorption amount. The dispersability was due to the cooperation of steric repulsion and adsorption, which resulted that comb-like polymers with moderate length of side chain presented the best dispersability in actual application.     

An Alternative Way towards Preparation of Hydrophobically Associating Polyacrylamide:Chemical Post-Modification

Hydrophobically associating polyacrylamides (HAPAMs) are derivatives from polyacrylamides by incorporating a small amount of hydrophobic moieties along the water-soluble mainchain. They are now becoming a class of promising candidates as thickeners or rheology modifiers in the formulations where rheology is necessary to be regulated, such as tertiary oil recovery, drilling fluids, hydraulic fracturing and coatings. Due to association of hydrophobes in nano-domains, their aqueous solutions exhibit very interesting rheological properties and better stability against salts than the unmodified precursor, polyacrylamide.Generally, there are two synthetic routes to introduce hydrophobic portion onto water-soluble polymer chains; i.e., direct copolymerization of hydrophobic and hydrophilic monomers, and post-polymerization functionalization[1]. In the case of HAPAM polymers, a commonly accepted method is micellar copolymerization in which an appropriate surfactant is employed to solubilize both monomers. However, it is widely reported[2] that the obtained polymers via micellar polymerization are characterized by: (i) blocky distribution of the hydrophobes; (ii) compositional inhomogeneity and (iii) strong dependence of solution properties on the block length.In this work, the alternative process, i.e., chemical post-modification, is employed to synthesize HAPAM polymers by direct N-alkylation of parent polyacrylamide (Figure 1) in dimethyl sulfoxide[3,4].PAM HAPAMFig. 1 Schematic route to prepare HAPAM by direct N-alkylation of PAMIt is found that the final incorporation of hydrophobic groups is in good agreement with the feed ratio[4], in contrast with that from micellar copolymerization which always brings about composition drift. Furthermore, unique rheological responses to shear rate, salt, temperature are also evidenced[5].     

Influence of side chains assembly on the structure and transport properties of comb-like polysiloxanes in hydrocarbon separation

We have synthesized a number of comb-like polysiloxanes with linear, branched, cyclic and silicon-containing substituents; most of them are new and previously not studied polymers. The physicochemical properties of comb-like polysiloxanes have been systematically investigated. Differential-scanning calorimetry and wide-angle X-ray scattering data revealed the side-chain microphase assembly for polymers with linear aliphatic substituents, while the polymers with bulky substituents did not form a microphase. It is shown that the ratio of microphase in the polymer is greater, the closer the values of the thickness of the microphase layer and the length of the cross-link. The effect of the side-chain substituent on the hydrocarbon transport properties of comb-like polysiloxanes was studied. All synthesized polymers are promising as membrane materials for a vital process of hydrocarbon separation. This is associated with an increase in the solubility selectivity of n-butane/methane because the solubility coefficient of methane sharply decreases when long side chains are introduced into the polysiloxane. It was shown for the first time that microphase forming polymers have a significantly higher butane/methane selectivity (23.2–27.5) than polysiloxanes not forming a microphase (selectivity 12.3–20.0). The effect is demonstrated on polysiloxanes with various types of side substituents. It was revealed that for the comb-like polysiloxanes, the diffusivity selectivity and permselectivity are proportional to the fraction of the side-chain microphase in the polymer. With the increase in the hydrocarbon microphase share, the diffusion coefficient of the permanent gas methane is decreasing more rapidly than n-butane, which dissolves well in hydrocarbons and plasticizes polymer. Consequently, the polymers forming the microphase have a higher selectivity C₃₊/CH₄ in the separation of a multicomponent hydrocarbons mixture.