Aggregation Behavior Of Poly Research Articles

Synthesis and aggregation behavior of poly(5‐alkyl‐2,3‐thiophene)‐based diblock copolymers

AbstractDespite impressive advances achieved in poly(3‐alkylthiophene)s (P3ATs) and P3AT‐based block copolymers (BCPs), the investigation into their ortho‐connected systems, poly(5‐alkylthiophene)s (P5ATs) and P5AT‐based BCPs is rather limited. Moreover, the aggregation behavior of P5ATs and their BCPs remains largely less understood. Herein, we report, for the first time, the judicious design and synthesis of a family of poly(5‐butylthiophene)‐block‐poly(5‐hexylthiophene) (P5BT‐b‐P5HT) BCPs with adjustable block ratios and reveal the effects of block ratios and thermal annealing process on their aggregated structures. Moreover, the optical properties of P5BT‐b‐P5HT BCPs have been investigated, which differs greatly from P3ATs. Overall, this work offers valuable insight into the aggregation and optical properties of P5AT‐based BCPs, strengthening our fundamental understanding of ortho‐connected P5AT systems.

Thermal phase transition of poly(N-vinyl caprolactam)-based copolymers: the distribution of hydrophilic units within polymeric chains

Here, cloud temperature and aggregation behaviors of poly(N-vinyl caprolactam)-based polymer were investigated with the addition of hydrophilic units. Copolymers composed of N-vinyl caprolactam and polyethyleneglycol methylacrylate (POEGMA) were firstly synthesized through a reversible addition fragmentation chain transfer technology with benzylsulfanylthiocarbonylsulfanyl propionic acid (BPA) as chain transfer agent and 4,4′-azobis(4-cyanovaleric acid) as initiator. The cloud points measurements indicated that comparing with pure poly(N-vinyl caprolactam), little amount of POEGMA would dramatically decrease copolymers’ cloud temperature while further addition of POEGMA would inversely increase the cloud temperature. The contribution of POEGMA within polymeric chains was modulated by adding POEGMA after 30 min of initiating polymerization. Both the DLS and TEM measurements showed that micelles instead of random structures were formed through a self-assembling process above the cloud temperature. These results emphasized the importance of the contribution of hydrophilic units in predicting the thermal phase transition behavior of poly(N-vinyl caprolactam)-based materials.

Synthesis and Aggregation Behavior of Poly(arylene alkenylene)s and Poly(arylene alkylene)s Having Dialkoxyphenylene and Aromatic Diimide Groups

Polycondensation reactions of 2,5-dialkoxy-1,4-diiodobenzene with N,N′-ω-dialkenylpyromellitic diimide and N,N′-ω-dialkenyl naphthalenetetracarboxylic diimide in the presence of a Pd(OAc)2–NaOAc catalyst produce six polymers containing the two aromatic groups connected alternatingly by alkenylene spacers. 1H NMR spectrum of a polymer prepared from 2,5-bis(dodecyloxy)-1,4-diiodobenzene and N,N′-(10-undecenyl)pyromellitic diimide (poly(1a-IA)) indicates that the polymerization involves 2,1- and 1,2-insertion of a vinyl group into the Pd–Ar bond in 70:30 selectivity. Matrix-assisted laser deportion/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) spectra of poly(1a-IA) and a polymer from 2,5-bis(dodecyloxy)-1,4-diiodobenzene with N,N′-dialkenyl naphthalenetetracarboxylic diimide (poly(1a-IIA)) contained a series of polymer fragments with Mn up to 4500. Measurement of electrospray ionization MS (ESI-MS) of the polymers revealed formation of cyclic molecules for 1:1 and 2:2 oligomers. Hydrogenations ...

Aggregation Behavior of Poly(3‐hexylthiophene) in Solvent Mixtures: Linear Solvation Energy Relationship (LSER) Modeling and COSMO‐RS Calculations

AbstractThe solubility and self‐assembly behavior of poly(3‐hexylthiophene) (P3HT) in solvent mixtures, and the dominant intermolecular forces related to these attributes, have only been partially scrutinized. In this work, the extent of aggregation of amorphous P3HT and the structural order of P3HT aggregates (Mn ≈ 20 kDa and Mn ≈ 75 kDa) are investigated in 54 solvent mixtures of chloroform with acetone, acetonitrile, dichloromethane, ethyl acetate, ethanol, and n‐hexane. Correlations between the molecular mass, the extent of aggregation, the structural order of the aggregates, and the nature of the solvent‐P3HT interactions are studied using a (1) linear solvation energy relationship (LSER) modeling and (2) solubility parameter‐based Flory–Huggins interaction parameters, χ. In addition, COSMO‐RS calculations are used to assess correlations between the extent of aggregation and the activity coefficients, γ, of P3HT. The results reveal that the extent of aggregation and the structural order of the P3HT aggregates are governed by different solvent–P3HT interactions. LSER modeling shows that the nucleophilicity and polarity of the solvent blends are the principal determinant of the structural order of P3HT aggregates. This result, which is based on an independent experimental method, supports previous computational results using COSMO‐RS σ‐profiles to assess the nucleophilicity and polarity of the solvent.

Consequences of Chirality on the Aggregation Behavior of Poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV)

Poly[2-methoxy-5(2′-ethylhexoxy)-p-phenylenevinylene] (MEH-PPV) has been for the first time prepared and fully characterized in enantiopure (R) form. If the polymer molecular weight is sufficiently low, (R)-MEH-PPV assumes a helical supramolecular structure in the solution aggregates, with consequences on the tendency to aggregation and on the fluorescence quenching, both of which are reduced with respect to the racemic analogue.

Effects of Cu2+ on aggregation behavior of poly (l-Glutamic Acid)-functionalized gold nanoparticles

The effect of Cu2+ ions on aggregation behaviors of poly (l-glutamic acid) (PLGA)-functionalized Au nanoparticles was investigated. It was found that the concentration of Cu2+ ions had a significant influence on the folding and the formation of intermolecular hydrogen bonding of PLGA and thus the aggregation of the Au nanoparticles. In the absence of Cu2+ ions, the Au nanoparticles underwent reversible pH-dependent aggregation attributed to the folding/unfolding of PLGA and the formation/breakage of intermolecular hydrogen bonds between PLGA molecules. In the presence of low concentration of Cu2+ ions (i.e., 10 μM), folding of PLGA and aggregation of the Au nanoparticles were facilitated due to the charge screening effect of Cu2+ ions, while the reversibility was partly maintained. In the presence of high concentration of Cu2+ ions (i.e., 50 μM), aggregation of the Au nanoparticles was dominated by the coordination interaction between PLGA and Cu2+ ions and the aggregation became irreversible due to the blocking of the formation of intermolecular hydrogen bonds by Cu2+. These results suggested that Au nanoparticles may be used as a colorimetric probe to monitor the interactions between metal ions and peptides, which are essential for exploring the physiological effect of metals ions.

Conformational structure and aggregation behavior of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] in toluene/nonane solutions

We identified the conformational structure, aggregation behavior and photophysical properties of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) in various toluene/nonane solutions dependent on nonane content. In dilute solution region (e.g., below the overlap concentration, c*), static light scattering (SLS) revealed that the stiffness of MEH-PPV decreased as nonane content was increased, attributed to a stronger interaction force between MEH-PPV backbones. However, MEH-PPV chains presented a more extended-wormlike conformational structure in toluene. Therefore, a looser intermolecular micellelike aggregates occurred easily between the ether side chains of MEH-PPV at the concentration exceeded the overlapping concentration in toluene and toluene/nonane solutions. Nevertheless, at higher nonane content, the micellelike aggregates were became highly compacted by the π–π complex force between MEH-PPV backbones, dominating the dynamic behaviors and photophysical properties of MEH-PPV in toluene/nonane solution. These results proved that two types of segmental association with distinct stability were identified for the MEH-PPV/toluene/nonane solutions upon prolonged aging. The highly stable, which could not be disrupted by heating, was attributed to the interaction force between ether side chains of MEH-PPV in both solutions. Other type was a weaker affinity force through π–π complex, which could be disrupted thermally, making the micellelike aggregates more compact to form the network structure in MEH-PPV-enriched at higher nonane content.

Amphiphilic and biocompatible properties of poly (EA‐MAA)

AbstractThe amphiphilic and biocompatible behaviors of Poly (acetate‐methylacrylic acid) Poly(EA‐MAA) were investigated in this study. The aggregation behavior of Poly(EA‐MAA) in aqueous media was investigated by steady‐state fluorescence spectroscopy and surface tensiometry. The critical aggregation concentration (cac) of Poly(EA‐MAA) was determined to be ∼0.03 mg/mL. Ultraviolet spectrum (UV) and fluorescence spectrum results indicated that there are interactions form between Poly(EA‐MAA) and bovine serum albumin (BSA). And β‐sheet can be changed into α‐helix of BSA in Poly(EA‐MAA) solution effectively revealed by Circular dichroism (CD), which is driven by the H‐bond and hydrophobic interactions. The good cell‐compatibility of Poly(EA‐MAA) makes it great potential in the biomedical fields. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Conformation and aggregation behavior of poly(ethylene glycol)‐b‐poly(lactic acid) amphiphilic copolymer chains in dilute/semidilute THF solutions

AbstractThe behavior of amphiphilic copolymer chains in a solvent is not the same as that of homopolymers. As an important synthetic biomaterial, poly(ethylene glycol)‐b‐poly(lactic acid) copolymers are often dissolved in tetrahydrofuran (THF) for study. Few studies have focused on the potential aggregation behavior and compact conformation of the amphiphilic macromolecules in a THF solution. In this study, a series of poly(ethylene glycol)‐b‐poly(lactic acid) diblock copolymers were synthesized and characterized using fourier‐transform infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis, and gel permeation chromatography methods. The aggregation behavior of amphiphilic molecular chains in a THF solution was studied using dynamic light scattering and transmission electron microscopy. The results showed that the aggregation size in solutions at a concentration of 2.0 mg/mL is within the range of 50–250 nm. It was further demonstrated that molecular chains exhibit a compact conformation in a dilute THF solution, which leads to a comparatively larger deviation in the characterization of molecular weights using GPC method. Here, a model is proposed to elucidate the dynamic evolution between compact amphiphilic single chains and aggregates. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Aggregation behavior of poly(methacrylic acid) with cucurbit[7]uril and the effect of ammonia ions on aggregation

The interaction between poly(methacrylic acid) (PMAA) and cucurbit[7]uril (CB[7]) in aqueous solution were investigated by dynamic light scattering (DLS), fluorescence techniques, UV-spectrophotometer, and resonance light scattering (RLS). The experimental results show that the aggregates were formed between CB[7] and H+ of PMAA by the hydrogen bonding interaction that increases with increasing the concentration of CB[7], which leads to the formation of the larger aggregates. Interestingly, PMAA has temperature sensitivity with the addition of CB[7] by UV-spectrophotometer and DLS. The pH of the solution of PMAA appears a inflection point with increasing the concentration of CB[7] comparing with the increase of the electrical conductivity all the time with the addition of CB[7]. In addition, in order to investigate the effect of cation on the size of the aggregates and avoid the effect of other anions at the same time, the dilute ammonia was added into the solution of PMAA. The experimental data show that the size of the aggregates increases with adding CB[7] because CB[7] could combine with both NH 4 + by the electrostatic and iondipole interactions and H+ by the hydrogen bonding interaction, and a possible model is proposed to explain the host-guest interactions between PMAA and CB[7].

Bioinspired Poly(2-oxazoline)s

Poly(2-oxazoline)s are regarded as pseudopeptides, thus bioinspired polymers, due to their structural relationship to polypeptides. Materials and solution properties can be tuned by varying the side-chain (hydrophilic-hydrophobic, chiral, bioorganic, etc.), opening the way to advanced stimulus-responsive materials and complex colloidal structures. The bioinspired “smart” solution and aggregation behavior of poly(2-oxazoline)s in aqueous environments are discussed in this review.

Aggregation Behavior of Poly(ethylene glycol)-block-poly (γ-benzyl L-glutamate)-graft-poly(ethylene glycol) Copolymer and its Blends with Poly(γ-benzyl L-glutamate) Homopolymer in Mixed Solvents

Poly(ethylene glycol)-block-poly(γ-benzyl L-glutamate)-graft-poly(ethylene glycol) (PEG-b-PBLG-g-PEG) copolymer was synthesized by the ester exchange reaction of PBLG-block-PEG copolymer with mPEG. The self-association behaviors of PEG-b-PBLG-g-PEG and its blends with PBLG homopolymer in the mixtures of ethanol and dimethylformamide (DMF) were investigated by transmission electron microscopy (TEM), dynamic light scattering (DLS), and viscometry. Effects of the introduction of PBLG homopolymer, the grafting ratio, and the DMF content on the self-association behaviors of PEG-b-PBLG-g-PEG copolymer in the mixtures of ethanol and DMF were mainly researched. It was revealed that PEG-b-PBLG-g-PEG copolymer could self-assemble to form polymeric micelles with a core-shell structure in various shapes from different preparation conditions. The critical micelle concentration (CMC) and the average particle diameter of the micelles formed by PEG-b-PBLG-g-PEG copolymer in the mixed solvents also changed with different preparation conditions.

Aggregation behavior of poly(γ‐benzyl‐L‐glutamate)‐b‐polyisoprene‐b‐poly(γ‐benzyl‐L‐glutamate) rod‐coil‐rod triblock copolymer in N,N‐dimethylformamide

AbstractSolution property of poly(γ‐benzyl‐L‐glutamate)‐b‐polyisoprene‐b‐poly(γ‐benzyl‐L‐glutamate) (GIG copolymer) was studied by using dynamic light scattering and static light scattering for N,N‐dimethylformamide (DMF) solution and DMF/toluene mixed solutions. GIG copolymer proved to aggregate in DMF and under DMF‐rich condition, that is, high‐polar region. The aggregate decreased in size, and completely disappeared under toluene‐rich condition, that is, low‐polar region. The correlation between solubility parameter and aggregate size of GIG copolymer in the DMF/toluene solution systems quantitatively demonstrated how strongly polarity caused by hydrogen bond made an impact on the aggregation behavior. Because the main driving force to the aggregation under DMF‐rich condition originates with polyisoprene (PIP) blocks, the aggregate in DMF is considered to be a core‐shell micelle consisting of flexible PIP core surrounded by rigid poly(γ‐benzyl‐L‐glutamate) (PBLG) shell. The values of dimensionless parameter ρ, defined as the ratio of radius of gyration 〈S2〉1/2 to hydrodynamic radius RH, revealed that a single chain of GIG copolymer had the form of rigid rod with flexibility, that is, once‐broken rod, caused by the incorporation of a flexible PIP chain between two rigid PBLG rods in the DMF/toluene solution system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1740–1748, 2010

Effects of the Type of Solvents on the Morphology of Styrene-Methacrylic Acid Random Copolymers Cast onto Silicon Wafer

The effects of the type of solvents on the aggregation behavior of poly(styrene-ran-methacrylic acid) (PSMAA) cast onto silicon wafer were studied using a SEM method. It was found that polystyrene prepared from DMF formed non-spherical aggregates but that PSMAA formed mixtures of ellipsoids and spheres. As the acid content increased, the spheres having a distinct boundary started contacting each other, and the average size of spherical particles decreased. Upon neutralization, the spherical particles became contacted spheres covered with much smaller spheres (ca. 20 nm in their sizes) and formed micro-gels. These results were compared to the data in the previous study of samples obtained from either water or THF. It was observed that the solubility parameters of the copolymers and ionomers, and polarity of solvents were some of key factors that determine the aggregation behavior of the polymers. The volatility of the solvent was also found to be an important factor for the aggregation behavior of polymers.

Role of Solvent Protic Character on the Aggregation Behavior of Polybenzimidazole in Solution

The aggregation behavior of poly(4,4'-diphenylether-5,5'-bibenzimidazole) (OPBI) in polar aprotic (dimethyl acetamide, DMAc) and protic (formic acid, FA) solvents is studied as a function of the polymer concentration and solution temperature. The effects of solvent protic character on the aggregation behavior of OPBI are elucidated. The photophysical studies suggest that the OPBI chains form aggregated structures in both DMAc and FA solutions when the OPBI concentration is increased. The dependences of the emission spectra on the polymer concentrations in two solvents are not similar in nature, indicating that in both of the solvents the aggregations are intermolecular processes, though their mechanisms are different owing to the polyelectrolytic nature of OPBI in FA medium. The triexponential decay profiles obtained from the time-resolved fluorescence study for the concentrated solutions (both in DMAc and FA) display a negative fractional coefficient and longer excited state lifetime, providing support for the aggregations at higher concentration. The temperature dependence emission spectra suggest that the aggregations in both of the solvents destabilize with increasing temperature. The higher activation energy of aggregation (E(A)) in DMAc (5.62 KJ/mol) compared with that in FA (3.07 kJ/mol) reveals that the aggregation formation pathways are different in two solvents and stronger aggregates are formed in the former solvent. The dilute solution viscometry (DSV) studies demonstrate that the OPBI chains adapt a bigger extended conformation in FA compared with DMAc owing to the stronger intramolecular chain repulsion in FA arising due to the polyelectrolyte nature of OPBI in this solvent. A conformation transition of OPBI chains from compact collapsed to extended conformer is observed in DMAc solvent with increasing concentration, whereas any such transition is absent in FA medium. Transmission electron microscope (TEM) images and circular dichroism (CD) spectra are also in agreement with the presence of a conformational transition in DMAc and the absence of it in FA. The temperature dependent DSV studies further support the disruption of aggregated structure with increasing temperature in both of the solvents. DSV studies exhibit that the deaggregation is driven by a conformation transition (extended to compact collapsed) in DMAc, whereas in FA the disruption happens without conformational transition.

Aggregation Behavior of Poly(N‐isopropylacrylamide) Semitelechelics with a Perfluoroalkyl Segment in Watera

AbstractTwo hydrophobically modified PNIPAM semitelechelics PxF9 were prepared by “clicking” PNIPAM containing an azide endgroup (PxN3) with nonadecafluoro‐1‐decyl hex‐5‐ynoate (F9). Micelles of PxF9 in water with a core of F9‐segments and a PNIPAM corona were detected by dynamic light scattering and by 1H and 19F NMR spectroscopy below the LCST. Just below the LCST, the PNIPAM chains start to collapse onto the F9 core followed by aggregation of several collapsed micelles to large particles in the range of ≈110 nm. The F9 segments shifted the LCST to lower temperatures when comparing PxN3 with PxF9. The existence of micelles in PxF9 solutions also improved the reversibility of the LCST behavior as measured by DSC.magnified image

Folding of a single polymer chain and phase transition

Using an ultra-sensitive differential scanning calorimetry (US-DSC), we have investigated the folding and aggregation behaviors of poly(N-isopropylacrylamide) (PNIPAM) chains in dilute and semidilute solutions. In the heating process, the intrachain folding and interchain aggregation simultaneously occur in the dilute solutions, and the ratio of intrachain folding increases with decreasing concentration. In the semidilute solutions, PNIPAM chains show limited interchain aggregation with elevated temperature, because most of the PNIPAM chains have been collapsed at lower temperature. In an extremely dilute solution, PNIPAM chains undergo a single folding transition in the heating process. By extrapolating heating rate and concentration to zero, we have obtained the phase transition temperature (T S ) and enthalpy change (ΔH S ) of the single chain folding. ΔH S is higher than that for a phase transition involving intrachain collapse and interchain aggregation, indicating that a single chain folding can not be taken to be a macroscopic phase transition.

Morphological evolution of aggregates induced by the hydrophobic effect and hydrogen bonding interaction

The aggregation behavior of poly(ethylene oxide)- block-poly(methylmethacrylate) (PEO- b-PMMA) in toluene without and with the addition of polar small-molecules has been characterized using transmission electron microscopy (TEM). The preparation method involved copolymer dissolution in toluene which is a selective solvent for polymethylmethacrylate at room temperature, followed by the addition of polar small-molecules. By increasing polarity of the small-molecules at the same copolymer concentrations, these aggregates were found to undergo morphological transformations from spherical aggregates to multiple morphologies, including bean-pod liked structures (the morphologies are biomimetic), spheres and vesicles. A possible mechanism for the formation of this aggregate is proposed.

Poly(amidoamine) dendrimers with phenyl shells: fluorescence and aggregation behavior

The fluorescence and aggregation behavior of poly(amidoamine) (PAMAM) dendrimers modified with phenyl groups at the periphery (PAMAM-P) were investigated. For comparison, the third generation (G3) PAMAM dendrimer with a shell of positive charge (PAMAM-PA) was also synthesized. PAMAM-P G3, G4 and G5 show dual fluorescence emission due to the fluorescence emission of phenyl ring and its excimer. By increasing the generation number from G2 to G4, the fluorescence intensity of phenyl ring decreases, and the fluorescence of phenyl excimer appears and becomes obvious. The three-dimensional geometry arrangement or dendrimer architecture was found to have a strong effect on their fluorescence behavior. This result is further supported by the solvent effect and model compound studies. The lower generations (PAMAM-P G0 to G3) were self-organized into spherical aggregates. However, no aggregation behavior was observed for the higher generations (>G3). The critical aggregation concentration (CAC) values measured by fluorescence spectroscopy were found to decrease gradually with increasing generation number from G0 to G3.

Fluorescence and Aggregation Behavior of Poly(amidoamine) Dendrimers Peripherally Modified with Aromatic Chromophores: the Effect of Dendritic Architectures

PAMAM dendrimers of the zeroth to fifth generation (G0-5) have been peripherally modified with phenyl, naphthyl, pyrenyl, and dansyl chromophores. Their fluorescence behaviors are strongly affected by the dendritic architectures at different generations. These dendrimers modified with hydrophobic chromphores can self-organize into vesicular aggregates at the low generations G0-3 in water. The size and aggregation number of these vesicles decrease with increasing generation from G0 to G3. Critical aggregation concentration determined by fluorescence spectroscopy reveals that these aggregates can be favorably formed in the order of G3 > G2 > G1. In contrast to the vesicles made from traditional amphiphilic compounds, these dendrimer-based vesicles are very adhesive due to the H-bonding interaction and entanglement of dendritic branches located in the outer layer. A large number of multivesicle assemblies, i.e., "twins" and "quins" consisting of two and five vesicles, were clearly identifiable with transmission electron (TEM) and atomic force microscopy. For the dendrimers with peripheral pyrenyl chromophores, triangle-like vesicles were observed in water. The hydrophobic interphase thickness of the vesicular bilayer is ca. 2.0-3.2 nm determined by fluorescence resonance energy transfer methods, which agrees well with the thickness directly observed with TEM.