Potentiometric titration behavior of poly(ethylene glycol methyl ether)-b-poly(ethylenimine)

Poly(ethylene glycol methyl ether)-b-poly(ethylenimine hydrochloride) was characterized using potentiometric and viscosimetric titration methods. The average chemical compositions of the polyamine hydrochloride salts estimated by the acid-base titration,¹H-NMR, and elemental analysis were compared. The apparent dissociation constant, pK, and the inherent viscosity of the polyamine hydrochloride were found to be highly dependent on the degree of neutralization. Very strong coulombic interactions among the charged sites were observed at low pH's for this polymer.     

Synthesis and characterization of poly(ethylene glycol) methyl ether endcapped poly(ethylene terephthalate)

Linear and branched poly(ethylene terephthalate) (PET) copolymers with polyethylene glycol) (PEG) methyl ether (700 or 2000 g/mol) end groups were synthesized using conventional melt polymerization. DSC analysis demonstrated that low levels of PEG end groups accelerated PET crystallization. The incorporated PEG end groups also decreased the crystallization temperature of PET dramatically, and copolymers with a high content of PEG (>17.6 wt%) were able to crystallize at room temperature. Rheological analysis demonstrated that the presence of PEG end groups effectively decreased the melt viscosities and facilitated melt processing. XPS and ATR-FTIR revealed that the PEG end groups tended to aggregate on the surface, and the surface of compression molded films containing 34.0 wt% PEG were PEG rich (85 wt% PEG). PEG end-capped PET (34.0 wt% PEG) and PET films were immersed into a fibrinogen solution (0.7 mg/mL BSA) for 72 h to investigate the propensity for protein adhesion. XPS demonstrated that the concentration of nitrogen (1.05%) on the surface of PEG endcapped PET film was statistically lower than PET (7.67%). SEM analysis was consistent with XPS results, and revealed the presence of adsorbed protein on the surface of PET films.     

Synthesis of linear poly(ethylenimine) containing nucleic acid pendants as polynucleotide analogs

Polynucleotide analogs with a linear poly(ethylenimine) (PEI) backbone and adenine, cytosine, and hypoxanthine pendants were synthesized. Linear PEI was synthesized by the cationic ring-opening polymerization of 2-H-2-oxazoline, followed by acid hydrolysis. 2-(Adenin-9-yl)- and 2-(N⁶-benzyladenin-9-yl)-, 2-(cytosin-1-yl)propanoic acids in addition to 2-(adenin-9-yl)-3-methyland 3-(cytosin-1-yl)butanoic acids were synthesized from their respective nucleic acid bases. 2-(Hypoxanthin-9-yl)propanoic acid and 3-(hypoxanthin-9-yl)butanoic acid were converted from the corresponding adenine derivatives by reaction with nitrous acid. Grafting reactions of pendant groups onto various molecular weight PEI backbones were carried out at room temperature, using the coupling agent norborn-5-ene-2,3-carboximido diphenyl phosphate (PPONB), generally resulting in percent graft values greater than 90%. PPONB showed selectivity against the amino group of adenine and cytosine rings. The appropriate model compounds were also prepared.     

Spectroscopic studies of poly(vinylamine) containing optically active thymine derivatives as grafted pendants

The optical properties of poly(vinylamine) containing optically active (+)- or (?)-2-(thymin-1-yl) propionyl groups as grafted pendants (PT) and the related monomer (MT) and dimer models (DT) were investigated by UV, circular dichroism (CD), and NMR spectroscopy. Highly syndiotactic PT has a smaller hypochromicity versus MT and a larger optical rotation than the less syndiotactic PT in various solutions. These results are attributed to an interaction between the configurational arrangement of thymines, the conformation of the polymers, and base stacking between thymines. The interactions of these polymers with poly(adenylic acid) (polyA) were also studied and the results compared with other vinyl-type nucleic acid model polymers. The isomers of the optically active dimer models [prepared from meso and (dl)-2,4-diaminopentane] were separated. The CD spectra of (+)-D(?)T in CHCl₃ and trifluoroethanol (TFE) displayed extremely solvent-dependent exciton coupling of the π–π^* (B_2u) transition of the base chromophore, which was not observed in the other models or polymers, except the meso-type dimer model (meso)-D-(?)T. This coupling decreased with increasing solvent dielectric constant, while UV hypochromicity increased. This behavior as well as the 360-MHz NMR spectra suggest that (+)-D(?)T exists in an extended form in solvents of low dielectric constant and gradually assumes a stacked conformation as the dielectric constant increases.     

Synthesis and characterization of poly(ethylene glycol) derivatives

Five general routes for the preparation of polyoxyethylene [generally referred to as poly(ethylene glycol) or PEG] derivatives are described. These routes are (1) nucleophilic displacements with the alkoxide of PEG, (2) nucleophilic displacement on PEG–tosylate, –mesylate, or –bromide, (3) reductive amination of PEG–aldehyde, (4) reductive amination of PEG–amine, and (5) nucleophilic displacements on the s-triazine derivatives prepared from s-triazine trichloride (cyanuric chloride) and PEG. Eighteen derivatives are prepared and potential applications to catalysis, cell purifications, and other areas are discussed briefly.     

Spectroscopic examination of linear poly(ethylenimine) containing nucleic acid pendants as polynucleotide analogs

The NMR spectra and UV absorptions of polynucleotide analogs with a poly(ethylenimine) (PEI) backbone containing adenine, cytosine, and hypoxanthine pendants have been examined. As has been shown in single-stranded polynucleotides, these polymers also exhibited base stacking behavior in aqueous solution as well as in 2,2,2-trifluoroethanol. Such stacking resulted in significant UV hypochromicities and observed differences in the NMR spectra compared to the corresponding model compounds. From continuous variation mixing experiments, well-defined base pairing interactions were observed between complementary graft polymers in aqueous solutions. Enhanced UV hypochromicity due to such interactions was also observed.     

Synthesis of poly(vinylamine) containing asymmetric nucleic acid base derivatives as grafted pendants

The preparations of new model polymers of polynucleotides with stereoregular poly(vinylamine) (PVAm) backbones and an optically active nucleic acid base derivative as a pending side chain are described. The grafting of (±)-, (+)-, and (?)-2-(thymin-1-yl) propionic acid to linear PVAm prepared either by hydrolysis of poly(vinyl acetamide) or poly(vinyl-t-butyl carbamate) has proven to be more difficult than the case of polyethyleneimine. This may be due to a combination of the low solubility and steric factors of PVAm. PVAm formed a complex with oximes such as ethyl-2-hydroxyimino cyanoacetate (EHICA), which activates the amino group of PVAm; it became soluble in polar solvents and gave higher percent graft. These carboxylic acid derivatives were grafted onto PVAm through amide bonds by direct coupling with sulfonic acid esters of hydroxybenzotriazoles to give optically active graft polymers. These coupling agents were found to be much superior reagents than DEPC regarding racemization. The related monomer and dimer model compounds were also prepared by the same method from 3-aminopentane and (?)-, (+)-, and meso-2,4-diaminopentane, respectively. The dimer models were separated and purified by HPLC to give models for isotactic, heterotactic, and syndiotactic polymer models. The enantiomeric purity of the optically active monomer model was determined by 360-MHz NMR spectroscopy using optically active shift reagents.     

Thermoresponsive copolymers of methacrylic acid and poly(ethylene glycol) methyl ether methacrylate

Copolymers of methacrylic acid (MAA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were prepared and their cloud points in aqueous solution were studied as a function of comonomer ratio, solution pH, and presence of hydrophobic comonomers. Under acidic conditions, the cloud point falls below 0 °C for copolymers with between 25% to 60% ether content, because of the formation of hydrophobic H‐bonded ether–acid complexes. The cloud point also decreases with solution pH. For equivalent ether to acid ratios, the cloud point decreases with decreasing PEG chain length, because of the presence of a larger number of hydrophobic methyl and methacrylate groups. Similarly, the cloud point decreases upon incorporation of hydrophobic comonomers such as butyl, lauryl, or glycidyl methacrylates. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6095–6104, 2005     

Solubility of amino acids in aqueous poly (ethylene glycol) solutions

The solubilities of amino acids have been measured in water and aqueous poly(ethylene glycol) (PEG) solutions as a function of temperature and PEG concentration. The free energies of transfer from water to aqueous PEG solutions forl-alanine,l-valine,l-isoleucine andl-leucine were positive, while those forl-phenylalanine andl-tryptophan were negative. The corresponding enthalpies of transfer were almost zero for all amino acids. The equilibrium constants of the binding of amino acids to PEG chain were estimated from the solubility data. Amino acids with larger hydrophobicity are bound more strongly to the PEG chain due to the hydrophobic interaction between the methylene groups of PEG and the side chain of amino acid. The equilibrium constants showed a correlation with the dynamic hydration number (n _DHN) which expresses the hydration properties of amino acids in aqueous solution.     

Synthesis of poly(vinyl alcohol) containing asymmetric nucleic acid base derivatives as grafted pendants

The preparations of new model polymers of polynucleotides with linear poly(vinyl alcohol) (PVA) backbones and an optically active nucleic acid base derivative as a pending side chain are described. (±)-, (+)-, and (?)-2-(thymin-1-yl)propionic acid were grafted onto PVA through ester bonds by direct coupling with dicyclohexylcarbodiimide (DCC) in the presence of highly active catalyst 4-pyrrolidinopyridine (PPY) to give optically active graft polymers. The corresponding monomer and dimer models have been prepared.     

Terpolymerization of methyl methacrylate, poly(ethylene glycol) methyl ether methacrylate or poly(ethylene glycol) ethyl ether methacrylate with methacrylic acid and sodium styrene sulfonate: determination of the reactivity ratios

Materials bearing ionic monomers were obtained through free radical terpolymerization of methyl methacrylate (MMA), poly(ethylene glycol) methyl ether methacrylate (PMEM) or poly(ethylene glycol) ethyl ether methacrylate (PEEM) with methacrylic acid (MA) and sodium styrene sulfonate (NaSS). The reactions were carried out in dimethyl sulfoxide using azobis(isobutyronitrile) as initiator. The reactivity ratios of the different couple of monomers were calculated according to the general copolymerization equation using the Finnemann-Ross, Kelen-Tüdos and Tidwell-Mortimer methods. The values of the reactivity ratios indicate that the different monomer units can be considered as randomly distributed along the chains for terpolymerizations of MMA, PMEM or PEEM with MA and NaSS. The average composition of the comonomers in the different terpolymers were calculated, showing a good agreement between the experimental and theoretical compositions. The instantaneous compositions are constant until about 70% of conversion. For higher conversions, the insertion of ionic monomers increases or decreases according to the system studied.     

Circular dichroism of polyethylenimine containing optically active thymine derivatives as grafted pendants

Optical properties of linear polyethylenimine containing optically active (+)- or (?)-2-(thymin-1-yl)propionyl group as grafted pendant were investigated by circular dichroism (CD) and compared with those of the related monomer and dimer model compounds. CD spectra of the polymer in neutral aqueous solution were different from those of related model compounds, which suggest that the polymer exists in some ordered conformation (at least locally) to allow exciton coupling of π–π^* (B_2u) transition in the base chromophores along the polymer chain. This ordered conformation tends to be randomized on heating. The effects of complementary base pairing on the CD spectra have also been studied by using a linear polyethylenimine containing (±)-2-(adenin-9-yl) propionyl grafts and its related monomer and dimer models.     

蠕虫状聚离子复合型胶束的合成、组装和胶体稳定性

采用开环聚合方法制备了嵌段共聚物聚乙二醇-聚乙烯亚胺(PEG-b-PEI), 通过静电组装方法使其与质粒DNA(pDNA)在溶液中自发构筑成蠕虫状聚离子复合型胶束(PICmicelle), 利用原子力显微镜、 动态光散射、 Zeta电势和凝胶电泳等方法研究了血液或细胞间质中各种因素对胶束稳定性的影响. 结果表明, 在蠕虫状聚离子复合型胶束中, PEI和pDNA通过静电吸引构成疏水性内核, 而亲水性的PEG分子作为保护型外壳包裹在内核的表面. 在保持PEG链段长度不变的前提下, 增加PEI链段长度可明显增强PEI与pDNA的静电结合力, 有效地防止了NaCl对胶体结构的破坏, 而且有助于抑制阴离子的取代. 但增加PEI链段长度会导致胶束表面PEG分子含量的降低, 不利于胶束抵抗蛋白质的吸附和DNA酶的降解. 因此合理地调整PEG-b-PEI分子的结构, 对于获得高效、 安全和稳定的蠕虫状聚离子胶束具有重要意义.     

Preparation and aggregation behavior of mannose-terminated poly(ethylene glycol)-b-poly(L-leucine) in water

Amphiphilic diblock copolymers composed of poly(ethylene glycol) (PEG) and poly(l-leucine) (PLeu) with mannose at the chain end of PEG were synthesized by a combination of ring-opening polymerization (ROP) and click chemistry. First, an α-azido, ω-amino PEG (N(3)-PEG-NH(2)) was synthesized and converted to the corresponding amine hydrochloride (N(3)-PEG-NH(2)·HCl), which was used as a macroinitiator to initiate the ROP of L-leucine-N-carboxyanhydride (Leu-NCA), yielding three amphiphilic block copolymers with different chain lengths of PLeu (N(3)-PEG-b-PLeu). Then, click chemistry of the alkynyl mannose with N(3)-PEG-b-PLeu anchored a mannose moiety to the PEG chain end of the copolymer. The self-assembly behavior of these copolymers in water was investigated using transmission electron microscopy (TEM), laser light scattering (LLS) and circular dichroism (CD). Depending on the copolymer composition and the initial concentration of the copolymer in organic solvent, different morphologies (e.g. spherical micelle, wormlike micelle) were observed. The aggregation behavior was demonstrated to be controlled by secondary structure formation and the hydrophobic interactions of the PLeu segments. With mannose moieties on the surface of the aggregates, these aggregates could bind reversibly the lectin Concanavalin A (Con A).     

Electron self-exchange reaction of viologen and its derivatives in poly(ethylene glycol)

The electron self-exchange rates (k_ex) of viologen and its derivatives are estimated by using microelectrode voltammetry in poly(ethylene glycol) films. The dependences of supporting electrolyte concentration and sizes of viologen and its derivatives on k_ex and diffusion coefficients (D) are discussed. Results show that k_ex increases with the decrease of supporting electrolyte concentration and sizes of reactants.     

The behavior of poly(amino acids) containing l‐cysteine and their block copolymers with poly(ethylene glycol) on gold surfaces

Poly(ethylene glycol) (PEG) is often used to biocompatibilize surfaces of implantable biomedical devices. Here, block copolymers consisting of PEG and l ‐cysteine‐containing poly(amino acid)s (PAA's) were synthesized as polymeric multianchor systems for the covalent attachment to gold surfaces or surfaces decorated with gold nanoparticles. Amino‐terminated PEG was used as macroinitiator in the ring‐opening polymerization, (ROP), of respective amino acid N‐carboxyanhydrides (NCA's) of l ‐cysteine (l ‐Cys), l ‐glutamate (l ‐Glu), and l ‐lysine (l ‐Lys). The resulting block copolymers formed either diblock copolymers, PEG‐b‐p(l ‐Glu_x‐co‐l ‐Cys_y) or triblock copolymers, PEG‐b‐p(l ‐Glu)_x‐b‐p(l ‐Cys)_y. The monomer feed ratio matches the actual copolymer composition, which, together with high yields and a low polydispersity, indicates that the NCA ROP follows a living mechanism. The l ‐Cys repeat units act as anchors to the gold surface or the gold nanoparticles and the l ‐Glu repeat units act as spacers for the reactive l ‐Cys units. Surface analysis by atomic force microscopy revealed that all block copolymers formed homogenous and pin‐hole free surface coatings and the phase separation of mutually immiscible PEG and PAA blocks was observed. A different concept for the biocompatibilization of surfaces was followed when thiol‐terminated p(l ‐Lys) homopolymer was first grafted to the surface and then covalently decorated with HOOC‐CH₂‐PEG‐b‐p(Bz‐l ‐Glu) polymeric micelles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 248–257     

Synthesis and self-assembly behavior of thermoresponsive poly(oligo(ethylene glycol) methyl ether methacrylate)-POSS with tunable lower critical solution temperature

This article reports on the synthesis of a novel amphiphilic polyhedral oligomeric silsesquioxane (POSS) end-capped poly(2-(2-methoxyethoxy)ethyl methacrylate)-co-oligo(ethylene glycol) methacrylate) (POSS-P(MEO₂MA-co-OEGMA)). These thermoresponsive organic–inorganic hybrid polymers exhibit critical phase transition temperature in water, which can be finely tuned by changing the feed ratio of OEGMA and MEO₂MA. The lower critical solution temperature (LCST) of POSS-P(MEO₂MA-co-OEGMA) increases from 31 to 59 °C with the increasing of OEGMA content. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies show that these polymers can self-assemble into spherical micelles with the thermosensitive block into the corona and the POSS forming the core, and larger aggregates are formed when the temperature values are above their LCSTs. These thermoresponsive polymers POSS-P(MEO₂MA-co-OEGMA) with self-assembly behavior and tunable tempetature-responsive property have the potential applications in material science and biotechnology.     

Synthesis and characterization of amphiphilic diblock copolymers of methyl tri(ethylene glycol) vinyl ether and isobutyl vinyl ether

Water-soluble diblock copolymers of methyl tri(ethylene glycol) vinyl ether (hydrophilic block) and isobutyl vinyl ether (hydrophobic block) of different molecular weights and composition were synthesized by living cationic polymerization. The molecular weight and comonomer composition of these copolymers were determined by GPC and ¹H NMR spectroscopy, respectively. Aqueous solutions of the copolymers were characterized in terms of their micellar behavior using dynamic light scattering, aqueous GPC, and dye solubilization. All the copolymers formed aggregates with the exception of a diblock copolymer with only two hydrophobic monomer units. The micellar hydrodynamic size scaled with the 0.61 power of the number of hydrophobic units, in good agreement with a theoretical exponent of 0.73. An increase in the length of the hydrophobic block at constant hydrophilic block length or an increase in the overall polymer size at constant block length ratio both resulted in lower critical micelle concentrations (cmcs). The cloud points of 1% w/w aqueous solutions of the polymers were determined by turbidimetry. An increase in the length of the hydrophobic block at constant hydrophilic block length caused a decrease in the cloud points of the copolymers. However, an increase in the overall polymer size at constant block length ratio led to an increase in the cloud point. © 1996 John Wiley & Sons, Inc.