Synthesis of pH-responsive polysilane with polyelectrolyte side chains through γ-ray-induced graft polymerization

Polysilanes with polyelectrolyte side chains are synthesized by two methods utilizing γ-ray-induced grafting and the pH responsiveness for one of those polymers is revealed mainly by investigating interfacial behavior of its monolayer at the air/water interface. In the first synthetic method, poly(methyl acrylate) is grafted onto poly(methyl-n-propylsilane) (PMPrS) through γ-ray-induced grafting, and then the PMA chains are hydrolyzed to poly(acrylic acid) resulting in the yield of ca. 97%. Thus PMPrS with polyelectrolyte side chains is successfully synthesized by the graft chain hydrolysis. The other method is the direct grafting of electrolyte monomers. Poly(methacrylic acid)-grafted PMPrS (PMPrS-g-PMAA) can be obtained through γ-ray-induced grafting of methacrylic acid monomers onto PMPrS chains, which shows the effectiveness of radiation grafting for the synthesis of polyelectrolyte graft copolymers. PMPrS-g-PMAA exhibits pH responsive behavior. In addition to the pH-dependence of water solubility, interfacial behavior also depends on the pH. Langmuir monolayers of PMPrS-g-PMAA exhibit different surface pressure-area isotherms according to the grafting yield and the pH of the subphase water. This result suggests that radiation modification is useful for fabricating polysilane-based ordered materials responsive to outer stimuli.     

Effect of the graft chain length and density on the morphology of radiation-modified polysilane monolayers at the air/water interface

The variation in the morphology of monolayers at the air/water interface is investigated for two kinds of radiation-modified polysilanes with different structures: poly(diethyl fumarate)-grafted poly(methyl-n-propylsilane) (PMPrS-g-PDEF) and maleic anhydride-grafted PMPrS (PMPrS-g-MAH). PMPrS-g-PDEF has long but sparsely-attached PDEF graft chains, while PMPrS-g-MAH has short but densely-attached MAH graft units. Surface pressure-area measurements indicate that PMPrS-g-PDEF monolayers extensively spread at the air/water interface though PMPrS homopolymer hardly spreads. AFM observation reveals that PMPrS-g-PDEF monolayers have an inhomogeneous structure containing string-like microstructures. This result suggests that PMPrS main chains are detached from the water surface to aggregate together and only PDEF chains spread over the water surface. In contrast, PMPrS-g-MAH forms uniform monolayers with a smooth surface. PMPrS main chains of PMPrS-g-MAH are anchored to the water surface by densely grafted MAH units. It is also demonstrated that only the PMPrS-g-MAH monolayers are successfully deposited layer-by-layer on a solid substrate by the Y-type deposition.     

Formation and flocculation of graft copolymer micelles

Criteria for formation and flocculation of micelles from pure graft copolymers were investigated in single selective solvents by turbidimetry with the use of two series of graft copolymers from poly(vinyl acetate) (PVAC), i.e., PVAC–styrene graft copolymers with one branch and PVAC–methyl methacrylate graft copolymers with one and several branches. These graft copolymers could be completely coagulated through two processes in the selective solvents which had widely different ? temperatures. The first process is the formation of micelles. One sequence, i.e., either backbone or branch of the graft copolymers, becomes desolvated under conditions similar to those for the corresponding homopolymer. This results in formation of the core of the micelle, the other soluble sequence extending from the surface of the core into the solvent phase. As the soluble chains cover the micelle core, no macroscopic phase separation occurs, but a stable dispersion is formed. The second process is that the micelle becomes too unstable to exist as dispersed when the solvency of the medium for the soluble sequence decreases to a certain degree. As a result, flocculation of the micelle finally takes place.     

Conformation and Aggregation Behavior of Polyelectrolyte with Primary Amino Pendant Groups in Water or THF/Water Binary Solvent Mixture and Their Effect on the Morphology of AOT Vesicles in Aqueous Media

Cationic polyelectrolyte with primary amine pendant groups, poly (4-vinyl benzyl amine hydrochloride salt) (poly (4-VBAHS)), was characterized by static light scattering. Using light scattering measurement, the conformation transition of poly (4-VBAHS) chains in pure water, and THF/H₂O (v/v: 1/3) binary solvent mixture was discussed. Concentration-dependent multiple morphologies including interpenetrating networks, tubular micelles, branched micelles, hexagonal phases, vesicles, and needle crystals were observed by TEM. In addition, effect of poly (4-VBAHS) on the morphology, stability, and critical vesicle/micelle concentration of anionic surfactant sodium bis (2-ethylhexyl) sulfosucciante vesicles were detected using dynamic light scattering, zeta potential, surface tension, and transmission measurements.     

Cadmium sulphide quantum dots in morphologically tunable triblock copolymer aggregates

Cadmium sulfide (CdS) quantum dots (QDs) are formed within poly(ethylene oxide)-block-polystyrene-block-poly (acrylic acid) (PEO-b-PS-b-PAA) triblock copolymer aggregates of different architectures. These structures are obtained starting with the same ionically cross-linked primary micelles consisting of a cadmium acrylate core, a PS shell, and a PEO corona. One morphology is a worm-shaped micelle prepared in tetrahydrofuran (THF) in which the CdS QDs are surrounded by the PAA and aligned as a loose necklace in the PS matrix. The PEO serves as a corona around the PS rod. Another structure is a multicore spherical (ca. 50 nm) water soluble PS micelle, surrounded by PEO chains. The CdS particles within these two latter structures are formed by the reaction of cadmium ions present in the acrylate cores with hydrogen sulfide. In a third structure, the CdS QDs are located on the surface of PS micelles. A fourth spherical single-core micelle structure is postulated to exist in dilute THF solutions. The dimensions in all the aggregates can be controlled by the block length.     

聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质的研究

采用核磁共振 (NMR)、动态激光光散射 (DLS)、透射电子显微镜 (TEM )等方法研究了规整性聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质 ,研究表明两亲接枝共聚物在选择性溶剂中可形成球状胶束 ,溶液的浓度、温度和聚合物结构等因素影响其胶束的大小、形态     

Ionic strength and solvent control over the physical structure, electronic properties and superquenching of conjugated polyelectrolytes

In this paper, we investigate the photophysical properties of the conjugated poly electrolyte poly(2-methoxy-5-propyloxy sulfonate phenylene vinylene) (MPS-PPV), dissolved in both water and DMSO as a function of the solution ionic strength. Dynamic light scattering indicates that MPS-PPV chains exist in a highly agglomerated conformation in both solvents, and that the size of the agglomerates depends on both the ionic strength and the charge of the counter-ion. Even though the degree of agglomeration is similar in the two solvents, we find that the fluorescence quantum yield of MPS-PPV in DMSO is nearly 100-times greater than that in water. Moreover, intensity-dependent femtosecond pump-probe experiments show that there is a significant degree of exciton-exciton annihilation in water but not in DMSO, suggesting that the MPS-PPV chromophores interact to form interchain electronic species that quench the emission in water. Given that the emission quenching properties depend sensitively on the chain conformation and degree of chromophore contact, we also explore the superquenching may be either enhanced or diminished in either of the solvents via addition of simple salts, and we present a molecular picture to rationalize how the conformational properties of conjugated polyelectrolytes can be tuned to enhance their emissive behavior for sensing applications.     

Conformational transition of polyelectrolytes in mixed solvent by dielectric spectroscopy: Electrostatic and hydrophobic interactions

We studied conformational transition of poly(acrylic acid)‐graft‐dodecyl (PAA‐g‐dodecyl), and PAA‐graft‐poly(ethylene oxide)‐graft‐dodecyl (PAA‐g‐PEO‐g‐dodecyl) molecules in DMF/H₂O solvent by dielectric analysis method utilizing a double‐layer polarization theory. In addition to the hydrophobic interaction which has been demonstrated to be vital for their conformational transition with water content, it is confirmed that the electrostatic interaction is crucial. For PAA‐g‐dodecyl molecules, at a critical value of water content, a peak value of correlation length is reached originating from the delicate balance between electrostatic and hydrophobic interactions. For PAA‐g‐PEO‐g‐dodecyl molecules, chains conformation is mainly determined by electrostatic interaction over the entire range of water content due to the low content of dodecyl groups. Meanwhile, H‐bond associative interaction prevents the dissociation of free carboxyl groups over the range of lower water content, thus their stretched transition moves to higher water content. Our results provide the underlying insights needed to understand solvent effect on the conformational transition for polyelectrolytes with hydrophobic groups. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1716–1724     

Synthesis of poly (ethylene oxide)-b-polysilane by anionic polymerization of masked disilenes using a macroinitiator method

Poly(ethylene oxide-)-poly(1, 1-dimethyl-2, 2-dihexyldisilene) block copolymers (PEO-b-PMHS) were synthesized by the anionic polymerization of masked disilenes initiated with the potassium alkoxide of poly(ethylene glycol). The block copolymer self-assembled into polymer micelles in water accompanied by a transition in the polysilane conformation.     

Blue-emitting PEGylated hyperbranched PAMAM: transformation of cross-linked micelles to hollow spheres controlled by the PEG grafting density

Here we reported the synthesis of polyethylene glycol 2000 monomethyl ether (PEG)ylated hyperbranched poly (amido amine) (h-PAMAM-g-PEG) and the study of an elaborate control over the structure transition by solvents. The double hydrophilic hyperbranched copolymers could form micelles with h-PAMAM core and solvophilic PEG shell in tetrahydrofuran (THF). It was found that the micellization stage was prolonged if more PEG chains were anchored onto h-PAMAM cores. After cross-linking the h-PAMAM cores, well-dispersed hollow spheres were obtained when the micelles were transferred into water from THF. More grafted PEG chains on h-PAMAM may prohibit the creation of a hollow cage upon the swelling of the hydrophilic h-PAMAM cores. Such engineered hollow spheres also retained the pH-sensitive fluorescence characteristic, identical with the luminescent behavior of the free h-PAMAM molecules. H-PAMAM-g-PEG hollow spheres with pH-sensitive fluorescence have a potential application as a drug delivery vehicle for chemotherapy.     

Synthesis and characterization of core–shell‐type polymeric micelles from diblock copolymers via reversible addition–fragmentation chain transfer

A method was developed to enable the formation of nanoparticles by reversible addition–fragmentation chain transfer polymerization. The thermoresponsive behavior of polymeric micelles was modified by means of micellar inner cores and an outer shell. Polymeric micelles comprising AB block copolymers of poly(N‐isopropylacrylamide) (PIPAAm) and poly(2‐hydroxyethylacrylate) (PHEA) or polystyrene (PSt) were prepared. PIPAAm‐b‐PHEA and PIPAAm‐b‐PSt block copolymers formed a core–shell micellar structure after the dialysis of the block copolymer solutions in organic solvents against water at 20 °C. Upon heating above the lower critical solution temperature (LCST), PIPAAm‐b‐PHEA micelles exhibited an abrupt increase in polarity and an abrupt decrease in rigidity sensed by pyrene. In contrast, PIPAAm‐b‐PSt micelles maintained constant values with lower polarity and higher rigidity than those of PIPAAm‐b‐PHEA micelles over the temperature range of 20–40 °C. Structural deformations produced by the change in the outer polymer shell with temperature cycles through the LCST were proposed for the PHEA core, which possessed a lower glass‐transition temperature (ca. 20 °C) than the LCST of the PIPAAm outer shell (ca. 32.5 °C), whereas the PSt core with a much higher glass‐transition temperature (ca. 100 °C) retained its structure. The nature of the hydrophobic segments composing the micelle inner core offered an important control point for thermoresponsive drug release and the drug activity of the thermoresponsive polymeric micelles. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3312–3320, 2006     

Detailed structure of hairy mixed micelles formed by phosphatidylcholine and PEGylated phospholipids in aqueous media

Aqueous dispersions of mixed egg yolk phosphatidylcholine (PC) and poly(ethylene glycol) (PEG) modified distearoyl phosphatidylethanolamine (DSPE) were investigated with the purpose of determining shape, size, and conformation of the formed mixed micelles. The samples were prepared at a range of DSPEPEG to PC molar ratios ([DSPEPEG/PC] from 100:0 to 30:70) and with, respectively, DSPEPEG2000 and DSPEPEG5000, where 2000 and 5000 refer to the molar masses of the PEG chains. Particle shape and internal structure were studied using small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). The contrast of the micelles is different for X-rays and neutrons, and by combining SANS and SAXS, complementary information about the micelle structure was obtained. The detailed structure of the micelles was determined in a self-consistent way by fitting a model for the micelles to SANS and SAXS data simultaneously. In general, a model for the micelles with a hydrophobic core, surrounded by a dense hydrophilic layer that is again surrounded by a corona of PEG chains in the form of Gaussian random coils attached to the outer surface, is in good agreement with the scattering data. At high DSPEPEG contents, nearly spherical micelles are formed. As the PC content increases the micelles elongate, and at a DSPEPEG/PC ratio of 30:70, rodlike micelles longer than 1000 angstroms are formed. We demonstrate that by mixing DSPEPEG and PC a considerable latitude in controlling the particle shape is obtained. Our results indicate that the PEG chains in the corona are in a relatively unperturbed Gaussian random coil conformation even though the chains are far above the coil-coil overlap concentration and, therefore, interpenetrating. This observation in combination with the observed growth behavior questions that the "mushroom-brush"transition is the single dominating factor for determining the particle shape as assumed in previous theoretical work (Hristova, K.; Needham, D. Macromolecules 1995, 28, 991-1002).     

Novel amphiphilic graft copolymers bearing hydrophilic poly(acrylic acid) backbones and hydrophobic poly(butyl methacrylate) side chains

A novel amphiphilic graft copolymer consisting of hydrophilic poly(acrylic acid) backbones and hydrophobic poly(butyl methacrylate) side chains was synthesized by successive atom transfer radical polymerization followed by hydrolysis of poly‐(methoxymethyl acrylate) backbone. A grafting‐from strategy was employed for the synthesis of graft copolymers with narrow molecular weight distributions (polydispersity index < 1.40). Hydrophobic side chains were connected to the backbone through stable C? C bonds instead of ester connections. Poly(methoxymethyl acrylate) backbone was easily hydrolyzed to poly(acrylic acid) backbone with HCl without affecting the hydrophobic side chains. The amphiphilic graft copolymer could form stable micelles in water. The critical micelle concentration in water was determined by a fluorescence probe technique. The morphology of the micelles was preliminarily explored with transmission electron microscopy and was found to be spheres. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6857–6868, 2006     

Activity and Conformation of Yeast Alcohol Dehydrogenase (YADH) Entrapped in Reverse Micelles

Yeast alcohol dehydrogenase (YADH) solubilized in reverse micelles of aerosol OT (i.e., AOT or sodium bis (2-ethyl hexyl) sulfosuccinate) in isooctane has been shown to be catalytically more active than that in aqueous buffer under optimum conditions of pH, temperature, and water content in reverse micelles. Studies of the secondary structure conformational changes of the enzyme in reverse micelles have been made from circular dichroism spectroscopy. It has been seen that the conformation of YADH in reverse micelles is extremely sensitive to pH, temperature, and water content. A comparison has been made between the catalytic activity of the enzyme and the α-helix content in the conformation and it has been observed that the enzyme is most active at the maximum α-helix content. While the β-sheet content in the conformation of the entrapped enzyme was found to be dependent on the enzyme–micelle interface interaction, the α-helix and random coil conformations are governed by the degree of entrapment and the extent of rigidity provided by the micelle core to the enzyme structure.     

Effect of Increasing Concentration of Each of Three Polar Solvents (1,4-Dioxane, Dimethyl Sulfoxide, N,N-Dimethylformamide) on Changes in the Shape of Polysorbate 20 Micelles

The effect of increasing concentration of each of three polar solvents [0–40 % (v/v) 1,4-dioxane, 0–40 % (v/v) dimethyl sulfoxide (DMSO), and 0–60 % (v/v) N,N-dimethylformamide (DMF)] on changes in the shape of the surfactant polysorbate 20 (Tween 20) micelles in the aqueous, polar solvent, sodium phosphate buffer solutions (pH = 7.2, ionic strength 2.44 mmol·L^?1) were investigated by using small-angle X-ray scattering. The effect of increasing concentration of 1,4-dioxane is that the micelle shape changed from core–shell cylindrical micelles to core–shell disc micelles between concentrations of 10 and 20 % (v/v) 1,4-dioxane, and then from core–shell disc micelles to core–shell elliptic disc micelles between concentrations of 30 and 40 % (v/v) 1,4-dioxane. The effect of increasing concentration of DMSO is that the micelles changed from core–shell cylindrical micelles to core–shell disc micelles between concentrations of 0 and 10 % (v/v) DMSO. The effect of increasing concentration of DMF is that it changed the core–shell cylindrical micelles to core–shell disc micelles between concentrations of 30 and 40 % (v/v) DMF. The common effect is that the solvents shortened the height of the micelle, that is, they squashed the micelle. Moreover, the specific effect of 1,4-dioxane is that this solvent squashed and squeezed the micelle.     

Amphiphilic Block‐Graft Copolymers Poly(ethylene glycol)‐b‐(polycarbonates‐g‐palmitate) Prepared via the Combination of Ring‐Opening Polymerization and Click Chemistry

Amphiphilic block‐graft copolymers mPEG‐b‐P(DTC‐ADTC‐g‐Pal) were synthesized by ring‐opening polymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and 2,2‐bis(azidomethyl)trimethylene carbonate (ADTC) with poly(ethylene glycol) monomethyl ether (mPEG) as an initiator, followed by the click reaction of propargyl palmitate and the pendant azido groups on the polymer chains. Stable micelle solutions of the amphiphilic block‐graft copolymers could be prepared by adding water to a THF solution of the polymer followed by the removal of the organic solvent by dialysis. Dynamic light scattering measurements showed that the micelles had a narrow size distribution. Transmission electron microscopy images displayed that the micelles were in spherical shape. The grafted structure could enhance the interaction of polymer chains with drug molecules and improve the drug‐loading capacity and entrapment efficiency. Further, the amphiphilic block‐graft copolymers mPEG‐b‐P(DTC‐ADTC‐g‐Pal) were low cytotoxic and had more sustained drug release behavior. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

pH-induced reversible conformational and morphological regulation of polyleucine grafted polyallylamine assembly in solution

One of the essential parts in the molecular mechanism of biological properties is the structural changes of proteins induced by stimuli. An amphiphilic copolymer, poly(L-leucine) grafted polyallylamine as a simple model of proteins, has been prepared by NCA polymerization with free amino groups of polyallylamine as an initiator. Here, we report the pH-induced reversible conformational and morphological regulation of the amphiphilic copolymer, whose hydrophobic peptide graft chains have no pH-sensitive groups, in an aqueous solution containing 50 vol % trifluoroethanol. The conformation of the poly(L-leucine) graft chain was found to be strongly pH dependent. Under acidic conditions, where electrostatic repulsion existed between the neighboring protonated amine moieties of the polyallylamine main chain, the rapid aggregation of the poly(l-leucine) graft chains was disturbed, and the peptide graft chains formed a beta-sheet structure owing to the intramolecular hydrogen bonding among the graft chains. Under this condition, the amphiphilic polymer formed amyloid-like fibrils, and then the fibrils grew into a planer plate composed of staked beta-sheets. On the other hand, under basic conditions, the poly(L-leucine) graft chains showed conformational transitions from a beta-sheet structure to an alpha-helical conformation owing to a distortion of the regular arrangement of the peptide graft chains by the conformational change of the polyallylamine main chain, whose amino groups were deprotonated. The conformational transition resulted in a disturbance of the regular sheet assembly of the amphiphilic copolymer and induced morphological changes to the amorphous globular aggregates. The pH-induced conformational and morphological changes of the poly(L-leucine) graft polyallylamine were reversible and synchronized with the protonation of the polyallylamine main chain.     

Dendrimer-influenced supramolecular structure formation of block copolymers

The water content-dependent supramolecular structure formation of polystyrene-block-poly(acrylic acid) (PS-b-PAA) copolymer in the presence of a fourth-generation amine-terminated poly(amido amine) dendrimer (PAMAM) is investigated by dynamic light scattering, turbidity measurements, and transmission electron microscopy. The solvent system for this study is a mixture of dioxane/THF and water. A very complex turbidity profile is observed with increasing water content in the system and is explained by the presence of various aggregated structures based on strong interactions between the amine-containing dendrimers and the poly(acrylic acid) blocks of the polymer. The onset of the self-assembly of single chains of PS-b-PAA (primary structure) into single and multiple dendrimer core inverse micelles (secondary structure) is detected as very low water contents of cw < 2% wt (cwc). These micelles consist of dendrimers coated with PAA blocks, which are connected to the corresponding PS chains that form the corona. Further addition of water leads to an association of these micelles into compound multiple dendrimer core inverse micelles (tertiary structure) in the range of cw = approximately 6 to approximately 10% wt. At still higher water content, some of the acrylic acid chains of the block copolymer move from the vicinity of the dendrimer to the outside of the aggregates, resulting in a decrease in the size of the formed structures and the acquisition of progressively increasing hydrophilic character of the aggregates. Multiple dendrimer core inverse onion micelles are formed, which agglomerate into compound multiple dendrimer core inverse onion micelles at cw = approximately 12 to approximately 18% wt. Above this water content, vesicular structures are formed. The complexity is unusual for block copolymer systems and illustrates the importance of strong interactions in structure formation.     

Interpolymer complexes based on the core/shell micelles. interaction of polystyrene-block-poly(methacrylic acid) micelles with linear poly(2-vinylpyridine) in 1,4-dioxane water mixtures and in aqueous media

The size and structural changes of nanoparticles formed after the addition of poly(2-vinylpyridine), PVP, to block copolymer micelles of polystyrene-block-poly(methacrylic acid), PS-PMA, were studied by light scattering and atomic force microscopy. Due to the strong hydrogen bonding between PVP and PMA segments, complex structures based on the core/shell micelles form in mixed selective solvents. As proven by a combination of light scattering and atomic force microscopy, individual PS-PMA micelles are "glued" together by PVP chains. The dialysis against solvents with a high content of water results in transient increase in polydispersity and turbidity of originally clear solutions. However, the precipitated polymer material dissolves in basic buffers and stable soluble nanoparticles reform in aqueous media. The behavior of their solutions was studied in a broad pH range by light scattering, atomic force microscopy and capillary zone electrophoresis.     

聚L-丙氨酸-聚乙二醇嵌段共聚物的胶束化行为研究

以氨基聚乙二醇单甲醚(MPEG-NH₂)为大分子引发剂, 采用开环聚合方法合成了聚L-丙氨酸-聚乙二醇嵌段共聚物(PAME), 并对其结构进行了表征; 用圆二色谱(CD)研究了嵌段共聚物在水溶液中的二级结构, 用芘荧光探针技术研究了共聚物胶束的形成及其临界胶束浓度(CMC), 利用动态光散射(DLS)和透射电镜(TEM)研究了胶束的粒径分布和形态. 结果表明, 在水溶液中共聚物链以α-螺旋构象形式存在, 在一定条件下嵌段共聚物能够形成球形的稳定胶束, PAME-1形成胶束的CMC为1.99×10^-5 mol/L, CMC值受共聚物中聚L-丙氨酸(PLA)链段含量的影响.