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The membrane-less organelles (MLOs) with subcompartments are formed via liquid-liquid phase separation (LLPS) in the crowded cell interior whose background molecules are up to 400 mg/mL. It is still a puzzle how the background molecules regulate the formation, dynamics, and functions of MLOs. Using biphasic coacervate droplets formed by poly(l-lysine) (PLL), quaternized dextran (Q-dextran), and single-stranded oligonucleotides (ss-oligo) as a model of MLO, we online monitored the LLPS process in Bovine Serine Albumin (BSA) solution up to 200.0 mg/mL. Negatively charged BSA is able to form complex or coacervate with positively charged PLL and Q-dextran and thus participates in the LLPS via nonspecific interactions. Results show that BSA effectively regulates the LLPS by controlling the phase distribution, morphologies, and kinetics. With increasing BSA concentration, the spherical biphasic droplets evolve in sequence into phase-inverted flower-like structure, worm-like chains, network structures, and confined coacervates. Each kind of morphology is formed via its own specific growth and fusion pathway. Our work suggests that MLOs could be controlled solely by the crowded environment and provides a further step toward understanding the life process in cell.

The membraneless organelles (MLOs) play a key role in the cell, yet it is unclear what controls the morphology and dynamics of MLOs in crowded cell medium. Using a biphasic coacervate droplet as a model of MLO, we online monitored the liquid-liquid phase separation process in crowded medium provided by poly(ethylene oxide) (PEO) or dextran. In PEO solution, which has an affinity with the inner phase, the spherical droplets evolve into clusters, networks, and completely phase inverted spheres in sequence with increasing PEO concentration, while in dextran solution, which has an affinity with the outer phase, the coacervates maintain the morphology but vary in phase ratio. Flower-like and even Janus structures are formed in the mixed PEO/dextran medium. Our work demonstrates that MLOs could be controlled solely by the crowded cell medium.

We report a versatile method to tune the hydrolysis of the ortho ester-containing block copolymers by covalently incorporating oxidation-sensitive phenylboronic ester units. A series of block copolymers which contain a polyethylene glycol (PEG) block and a hydrophobic segment composed of different amounts of pendent ortho ester and phenylboronic ester groups were synthesized. These copolymers can self-assemble into narrowly dispersed micelle-like nanoparticles in phosphate buffer. The kinetics of phenylboronic ester oxidation and ortho ester hydrolysis in the nanoparticles were studied at different pH and H2O2 concentration. The results indicated that the phenylboronic ester oxidation rate was faster than the ortho ester hydrolysis rate at neutral pH, and both processes were accelerated with increasing H2O2 concentration. Nanoparticles which are extremely sensitive to the biorelevant concentration of H2O2 (50 μM) at pH 7.4 were obtained, suggesting great promise for inflammation-specific drug delivery.

The development of nanotechnology relies crucially on the ability to fabricate materials with desired nanostructures. Because of their precise side-chain structure and versatile ordered morphologies, side-chain liquid crystalline polymers can provide a novel material platform to obtain sub-10 nm structures via their self-assembly. Here we show that for a newly designed side-chain liquid crystalline (LC) polynorbornene (P1) with a slim hemiphasmid mesogen microphase separation between the main and side chains drives the spontaneous formation of hexagonal columnar phase (Φh) composed of cylinders with a uniform diameter of 8.3 nm. At every cross section of the cylinder there are more than a dozen P1 chains laterally bundled together. The cylinders can grow axially when more chains join in becoming extraordinarily long to over several micrometers. Simple shearing can produce P1 thin films with very good orientation of the Φh phase at the macroscopic scale. More interestingly, we show that directed self-assem...

Among numerous research studies focusing on macromolecular crowding and confinement, few are concerned with the medium at a broad range of concentrations, let alone the interplay between the crowdi...

The structure and kinetics of the complex formed by hyaluronic acid (HA) and poly(L-lysine) (PLL) were studied by time-resolved laser light scattering, TEM, and AFM. Because HA has a hydrophilic backbone, the complexes formed by HA and PLL are different from those formed by oppositely charged polyelectrolytes both having hydrophobic backbones. Instead of forming strong aggregates and even precipitates, the complex in the presence of excess HA is stable in the studied time period. More importantly, the complex spontaneously forms core-corona structure by the rearrangement of HA chains. The core is composed of complex rich of PLL and the corona is mainly HA. Further analysis shows that the hydrogen bond formed by HA creates a barrier hindering the further relaxation of HA chains. The automatic formation of core-corona structure by PLL/HA is helpful not only to understand the relaxation of polyelectrolyte in complex, but also to develop drug carriers with desirable properties.

The behavior of nano-carriers, even though they are well defined at equilibrium conditions, is unpredictable in living system. Using the complexes formed by plasmid DNA (pDNA) and K20 (K: Lysine), protamine, or polylysine (PLL) as models, we studied the dynamic behavior of gene carriers in the presence of fetal bovine serum (FBS) and under different shear rates, a condition mimicking the internal physical environment of blood vessels. Without shear, all the positively charged complexes bind to the negatively charged proteins in FBS, leading to the formation of large aggregates and even precipitates. The behaviors are quite different under shear. The shear generates two effects: a mechanical force to break down the complex into smaller size particles above a critical shear rate and a stirring effect leading to secondary aggregation of complexes below the critical shear rate. In the studied shear rate from 100 to 3000 s-1, the mechanical force plays a key role in K20/pDNA and protamine/pDNA, while the stirr...

The structure and stability of polyelectrolyte complex are controlled not only by electrostatic interaction but also by hydrogen bonding and hydrophobic interaction if they are present. The complexes formed by such multiple interactions should exhibit different responses to the environmental changes, such as ionic strength and pH. In this work, we designed a positively charged peptide S5R4, which can interact with poly(ethylene glycol)-block-poly(glutamate sodium) (PEG114-PGlu64) via electrostatic interaction, hydrogen bonding, and hydrophobic interaction. In deionized water at pH 7.1, the complexes formed by PEG114-PGlu64 and S5R4 assemble into wormlike micelles, spheres, and even hierarchical “wool balls”, depending on mixing ratio. However, a distinct dissociation–reassembly process is observed when 30 mM NaCl is added to screen the electrostatic interaction. The spheres transform into loose clusters after reassembly. This process is caused by the switch of driving force from electrostatic interaction ...

Oxidation stress has been becoming an important target for the development of smart nanomedicines, triggering research interest in oxidation responsive polymers. Herein, we report a new type of temperature/oxidation dual responsive copolymer. They were synthesized by the sequential atom transfer radical copolymerization (ATRP) of N-isopropylacrylamide (NIPAM, M1) and a phenylboronic pinacol ester-containing acrylate (M2) and dialysis against water to remove the pinacol protecting groups. The copolymers with a small amount of phenylboronic acid units (

The complexes formed by DNA or siRNA interacting with polycations showed great potential as nonviral vectors for gene delivery. The physicochemical properties of the DNA/siRNA complexes, which could be tuned by adjusting the characteristics of polycations, were directly related to their performance in gene delivery. Using 21 bp double-stranded oligonucleotide (ds-oligo) and two icosapeptides (with the repeating units being KKGG and KGKG, respectively) of the same charge density as model molecules, we investigated the effect of charge distribution on the kinetics of complexation and the structure of the final complexes. Even though the distribution of the charged groups in peptides was only adjusted by one position, the complexes formed by (KKGG)5 and ds-oligo were larger in size and easier to precipitate than those formed by (KGKG)5. Counterintuitively, it was not the charged groups but the hydrophilic neutral spacers that determined the kinetics and the structure of the complex. We attributed such an eff...

We demonstrate a new type of acid-sensitive amphiphilic polypseudorotaxanes (PPRs) formed via inclusion complexation between Pluronic F127 and the hydrophobic β-cyclodextrin (CD) derivative in alcoholic solvents. The 6-OH ortho ester-substituted hydrophobic β-CD derivative (EMD-CD) was prepared by “click” reaction of β-CD with 2-ethylidene-4-methyl-1,3-dioxalane under mild conditions. The water-insoluble EMD-CD (host) is capable of forming PPRs with F127 (guest) in ethanol or methanol but not in water, which is confirmed by 1H NMR, wide-angle X-ray diffraction, small-angle X-ray scattering, and the time-dependent threading kinetics. Depending on the host/guest ratio, the PPRs self-assembled into sheet-like structure or vesicular nanoparticles with different sizes in water. These PPR assemblies were stable at pH 8.4 but quickly dissociated into biocompatible products in neutral or in acidic buffers due to the hydrolysis of the ortho ester groups. Good biocompatibility, ease of fabrication, and extremely pH...

Using three designed peptides with precisely-controlled charge density and three types of DNAs with different length and flexibility, the effect of charge density on the formation of PEC was studied. Highly charged (KKKK)5 interacts strongly with 21 bp dsDNA to form large complex, followed by precipitation; while the medium charged (KGKG)5 only form complex with 21 bp dsDNA at proper +/− charge ratios; and no prominent complex between weakly charged (KGGG)5 and 21 bp dsDNA is observed at the same conditions. Similar trend is observed when the peptides form complex with 2000 bp DNA or 21nt ssDNA. It is also found that the complex formed by adding peptide to DNA is in random coil conformation, but the complex prepared by the inverse order is in molten globule state. Re-dissolution of the complex occurs only when DNA is added to peptides with similar or shorter length.

DNA complex has been widely used as non-viral vectors for the delivery of genes or siRNA. Owing to the strong and long-ranged electrostatic interaction, the structure and property of the DNA complex should evolve with time in a long-term. To test this hypothesis, we choose 2000 bp double-stranded DNA and 21 bp oligonucleotide as the model molecules, and comparatively studied their complexation with narrowly-distributed poly- l -lysine (PLL150) by time-resolved laser light scattering. In the time range of about one week, the complexation of both DNA samples underwent three stages: formation of preliminary complex, further aggregation, followed by precipitation. The aggregation and precipitation rate of the complex formed by oligonucleotide was much faster than that of the complex formed by 2000 bp dsDNA. After precipitation, the amount of the longer chain polyelectrolyte, as determined by UV and fluorescence, was about twice that of the short chain polyelectrolyte in the sediment. The precipitates were far from being fully neutralized. Moreover, the component ratio in the sediment was independent of the mixing charge molar ratio. A rational complex mechanism was proposed on the basis of these findings. During complexation, the relaxation of polyelectrolyte inside the complex and the exchange of polyelectrolyte between complex determined the aggregation and precipitation rate. The competition of the two kinetic processes governed the structure and property of the complex in the solution and in the sediment.

The effects of chain length and polydispersity on polyelectrolyte complexes (PEC) have not been fully clarified. In this work, we chose oligonucleotide and oligolysine, both of which have uniform length, and studied the chain length effect on their complex by time-resolved laser light scattering and atomic force microscopy. Results show that the chain length of oligolysine has to reach a critical value for the occurrence of complexation with 21 bp oligonucleotides, suggesting that PEC is an all-or-non process. However, the oligolysine with the chain length below critical value still plays a role if it is mixed with other oligolysine whose chain length is above the critical value. If oligonucleotide is in excess, the combination of oligolysines with chain lengths below and above critical value exhibits synergistic effect to enhance the PEC formation, while they exhibit antagonistic effect to deteriorate the PEC formation if oligolysine is in excess. Our study not only gains insight in the mechanism of PEC by polydispersed samples, but also helps to design and fabricate complexes with desirable structure and kinetics by combining polyelectrolytes with different chain lengths.

A series of well-defined thermoresponsive diblock copolymers (PEO45-b-PtNEAn, n=22, 44, 63, 91, 172) were prepared by the atom transfer radical polymerization of trans-N-(2-ethoxy-1,3-dioxan-5-yl) acrylamide (tNEA) using a poly(ethylene oxide) (PEO45) macroinitiator. All copolymers are water-soluble at low temperature, but upon quickly heating to 37 °C, laser light scattering (LLS) and transmission electron microscopy (TEM) characterizations indicate that these copolymers self-assemble into aggregates with different morphologies depending on the chain length of PtNEA and the polymer concentration; the morphologies gradually evolved from spherical solid nanoparticles to a polymersome as the degree of polymerization ("n") of PtNEA block increased from 22 to 172, with the formation of clusters with rod-like structure at the intermediate PtNEA length. Both the spherical nanoparticle and the polymersome are stable at physiological pH but susceptible to the mildly acidic medium. Acid-triggered hydrolysis behaviors of the aggregates were investigated by LLS, Nile red fluorescence, TEM, and (1)H NMR spectroscopy. The results revealed that the spherical nanoparticles formed from PEO45-b-PtNEA44 dissociated faster than the polymersomes of PEO45-b-PtNEA172, and both aggregates showed an enhanced hydrolysis under acidic conditions. Both the spherical nanoparticle and polymersome are able to efficiently load the hydrophobic doxorubicin (DOX), and water-soluble fluorescein isothiocyanate-lysozyme (FITC-Lys) can be conveniently encapsulated into the polymersome without using any organic solvent. Moreover, FITC-Lys and DOX could be coloaded in the polymersome. The drugs loaded either in the polymersome or in the spherical nanoparticle could be released by acid triggering. Finally, the DOX-loaded assemblies display concentration-dependent cytotoxicity to HepG2 cells, while the copolymers themselves are nontoxic.

The polyelectrolyte complexes formed by DNA and polycations have been widely used as non-viral vectors for gene delivery. The DNA complex prepared in aqueous solutions is usually controlled by kinetics. In this work, we demonstrated, by using salmon testes DNA (2000 bp), poly-(L-lysine) (PLL35), and poly(ethylene oxide)-b-Poly-(L-lysine) (PEO45-b-PLL35), that the DNA complexes formed in dimethylformamide (DMF) was milder than those formed in aqueous solutions. In DMF, no precipitation of DNA complex is observed even at the stoichiometric charge ratio. Taking advantage of the weak complexation and better solubility of complex in DMF, we premixed DNA and PLL at higher concentration in DMF, followed by quenching the mixture into a large amount of aqueous solution. This method alleviates the kinetic control to a large extent, and the complex obtained is smaller in size and lower in molar mass than those prepared solely in aqueous solution. The morphology of the complex, as studied by AFM, is also different.

A series of photoresponsive dendronized polymers PGn-NB (n = 1, 2, 3) were synthesized by attaching o-nitrobenzyl alcohol-terminated amidoamine dendrons (G1–G3) to the alternating styrene and maleic anhydride copolymer (PSt-alt-PMAh). The structures and the molecular weights of the obtained polymers were characterized by 1H NMR and FTIR measurements. It is found that the coverage degrees of the dendrons are 74%, 42%, and 26%, respectively, indicating that the numbers of the appended dendrons decrease in the order of G1 > G2 > G3 due to the steric hindrance of higher generation dendrons with more branches. The photocleavable behavior of G1–G3 was detected by UV–vis and 1H NMR measurements. As a result, G2 showed a faster cleavage rate compared to G1 and G3. The critical aggregation concentration (CAC) of PGn-NB (n = 1, 2, 3), measured by using pyrene as a fluorescence probe, were 0.05 mg/mL (PG1-NB), 0.01 mg/mL (PG2-NB), and 0.03 mg/mL (PG3-NB), which displayed that the structure of PG2-NB was in favor of ...

We describe an efficient approach to modulate the hydrolysis of the ortho ester-containing polymers by incorporating different amount of tertiary amino (TA) groups. The block copolymers (NE0–NE3) contain a hydrophilic poly(ethylene glycol) (PEG) segment and hydrophobic chains constituted by random methacrylate copolymers with pendent acid-labile cyclic ortho ester and TA groups and were synthesized by a two-step approach. First, atom transfer radical copolymerization of 2-hydroxyethyl methacrylate and 2-(diethylamino)ethyl methacrylate using mPEG45-Br as a macroinitiator afforded the block copolymer precursors. Then, reaction of the precursors with 2-ethylidene-4-methyl-1,3-dioxolane transformed the pendent hydroxyl groups into cyclic ortho ester groups. The hydrophobic chains are similar in degree of polymerization, but the percent molar content of TA increases from 0% for NE0 to ∼15% for NE3. In phosphate buffer at pH 8.4, all the four amphiphilic block copolymers can self-assemble into stable nanoparti...

We investigated the solution crystallization behavior of a high molecular weight (MW) poly(ethylene oxide) (PEO) (PEO400k, MW of 4 × 105 g/mol) in ethanol with the concentrations ranged from dilute to semi-dilute (i.e., from 0.02 to 2 wt %). We followed the dissolving process of PEO400k using differential scanning colorimetry, small-angle X-ray scattering and solution light scattering. The practical solution temperatures ( T s exp s ) of the solutions, where the PEO400k crystals were fully dissolved, were estimated. In comparison with that of the solution cooled from a dissolving temperature (Td) sufficiently higher than the T s exp , the crystallization kinetics of the solutions prepared at Tds in the vicinity of T s exp is much faster. The lower this Td is, the faster the crystallization takes place at a constant isothermal crystallization temperature. Moreover, for the solutions with Td > T s exp , prolonging the duration time of dissolving can significantly slow down the crystallization kinetics. The experimental results indicate that the solution crystallization of high MW PEO bears some memory effect, similar to that observed in bulk crystallization. As the PEO400k can be completely dissolved at Td > T s exp , we consider that the solution crystallization can also have a type of memory effect beyond the traditional self-seeding effect. This memory may be related to the relaxation of PEO chains after they are dissolved in solution. Probably, the topological structure of the freshly dissolved chains temporarily retains the less entangled segments, which can promote the subsequent crystallization. For the solution with 2 wt % PEO400k, the erasion time of this memory effect could be several hours long.

Charge transfer complex strongly affects the optical transparency of polyimide film. Here, solution behavior of a polyimide derived from 3,3′,4,4′ biphenyltetracarboxylic dianhydride and 1,4-bis(3-aminopropyl)piperazine in acetic acid, chloroform, and their mixed solvents is investigated in detail by light scattering. It is found that the polyimide existed as single chains in acetic acid owing to the acid-base interaction. However, association is observed in chloroform solution because of the charge transfer complex and enhanced by increasing the solution concentration. To break the charge transfer interaction and clear the association, only a small amount of acetic acid is required to add into the chloroform solution owing to the protonation of the diamine groups, confirmed by the zeta potential measurements. Simultaneously, the associates disappear quickly after addition of acetic acid. This study will provide a novel method for preparation of high optical transparent polyimide film by simply tuning the solvent. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A series of novel comb polymers, poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene}-g-polystyrene (PMPCS-g-PS), with mesogen-jacketed rigid side chains were synthesized by the “grafting onto” method from α-yne-terminated PMPCS (side chain) and poly(vinylbenzyl azide) (backbone) by Cu(I)-catalyzed 1,3-dipolar cycloaddition click reaction. The α-yne-terminated PMPCS was synthesized by Cu(I)-catalyzed atom transfer radical polymerization initiated by a yne-functional initiator. Poly(vinylbenzyl azide) was prepared by polymerizing vinylbenzyl chloride using nitroxide mediated radical polymerization to obtain poly(vinylbenzyl chloride) as the precursor which was then converted to the azide derivative. The chemical structure and architectures of PMPCS comb polymers were confirmed by 1H NMR, gel permeation chromatography, and multiangle laser light scattering. Both surface morphologies and solution behaviors were investigated. Surface morphologies of PMPCS combs on different surfaces were investigated by scanning probe microscopy. PMPCS combs showed different aggregation morphologies when depositing on silicon wafers with/without chemical modification. The PMPCS comb polymers transferred to polymer-modified silicon wafers using the Langmuir-Blodgett technique showed a worm-like chain conformation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

As a mimic of protein, a polyampholyte-based material should be able to duplicate the properties and functions of protein. A polyampholyte that is highly sensitive to both pH and temperature under physiological conditions is obtained when 80% butylamide-terminated poly(amidoamine) dentron is grafted to the backbone of styrene and maleic anhydride. The phase separation occurs at 33.7 °C at pH = 6.20, while the transition point increases to 43.9 °C at pH = 6.30. The superior performance is the consequence of the cooperative interactions among basic, acidic, and thermoresponsive groups. The polyampholyte with a suitable isoelectric point provides a platform for the development of multifunctional materials for biomedical applications.

Two mesogen-jacketed liquid crystalline polyelectrolytes, poly{sodium 2,5-bis[(4-sulfophenyl)aminocarbonyl]styrene} and poly{sodium 2.5-bis[(4-sulfophenyl)oxycarbonyl]styrene}, with rigid cores containing different linkages at the center and sulfonate groups on the two ends in the side chains were designed and successfully synthesized via conventional radical polymerization. X-ray scattering experiments revealed that the two polymers exhibited smectic A phases in bulk. Comb-shaped nonstoichiometric polymer–surfactant complexes were obtained by mixing the anionic sulfonated polyelectrolytes and cationic lipids of different lengths and shapes. The formation of ordered structures of the complexes depended on the length and shape of the lipids. Lamellar phases were observed when the two polyelectrolytes complexed with cetyltrimethylammonium bromide and fan-shaped 3,4,5-tris(dodecyloxy)benzenamine. Owing to the stronger bond strength of electrostatic interactions, the types of mesophases of the complexes based...

The solubility and chain conformation of different types of homopolymers in low viscosity ionic liquids (ILs), 1-allyl-3-methylimidazolium chloride ([AMIM][Cl]) at 50 °C and 1-butyl-3-methylimidazolium formate ([BMIM][COOH]) at 25 °C, were studied by laser light scattering (LLS). For neutral polymers, such as polyvinyl alcohol and polysulfonamide, aggregation occurred in all the cases except for polyvinyl alcohol in [BMIM][COOH]. For negative polyelectrolytes, such as DNA and polystyrene sulfonate, single chain conformation was observed. However, the hydrodynamic radius of both polymers was much smaller than that in good solvents, suggesting that the chains were condensed. Cellulose was soluble in [AMIM][Cl], and non-diffusive mode was observed by dynamic light scattering. Zeta potential analysis indicated that cellulose exhibited the feature of polyelectrolyte. The solubility of homopolymers could be qualitatively explained by treating polymer/IL as a ternary system: polymer, cation, and anion. It was the mutual interactions determined the solubility and conformation of polymers in ILs.

Two acrylate monomers with six-member cyclic ortho ester groups, i.e., 2-(1,3-dioxan-2-yloxy)ethyl acrylate (DEA) and 2-(5,5-dimethyl-1,3-dioxan-2-yloxy) ethyl acrylate (DMDEA), were synthesized. T...

Time-resolved laser light scattering, combined with transmission electron microscopy, was employed to study the kinetics of the sphere-to-rod transition. The brush−rod block copolymer based on poly[poly(ethylene glycol) monomethyl ether methacrylate] and poly{(+)-2,5-bis[4′-((S)-2-methylbutoxy)phenyl]styrene}, PEGMA37-b-MBPS141, formed spherical large compound micelles (LCM) in mixed solvent of THF and water. LCM underwent the transition to large compound rod (LCR) in the time scale of hours, and the transition was favored at higher polymer concentration and at intermediate water content. It was also found that a large amount of free polymer chains existed throughout the transition process. The depletion force generated by the free polymer chains was estimated to be in the order of 0.1kT. Therefore, besides the instability or defects of the LCM, the depletion effect also made a positive contribution to the sphere-to-rod transition.

The effects of heating rate on the aggregate behavior of poly(ethylene oxide)-b-poly(N-isopropylacrylamide) in aqueous solutions were investigated in detail by laser light scattering and TEM. By employing two separate heating protocols, step-by-step heating at < 5 K/step and one-step jump, to heat the sample from 15°C to the selected temperature, we found that the heating rate only showed significant effect on the aggregates above the cloud point. The aggregate formed by step-by-step heating exhibited a much larger size and a broader size distribution than those formed by one-step jump heating. Moreover, neither of the aggregates were ideal micellar structures as indicated by the size and the Rg/Rh values. On the contrary, at temperatures below the cloud point where the block copolymer formed core-shelled micelles, the heating rate showed negligible effect on the size and size distribution of the micelles. Since the system underwent a phase separation above the cloud point, the heating rate effect could be reasonably explained by the phase separation mechanisms: the nucleation-and-growth mechanism in the metastable region and the spinodal decomposition mechanism in the unstable region.

The first and second generation poly(amidoamine) dendronized poly(2-hydroxylethyl) methacrylate (PGn-macro (n = 1, 2)) were synthesized by the macromonomer approach. The structures and molecular weights of the obtained polymers were characterized by 1H NMR, FTIR, and GPC. UV−vis turbidity measurements revealed that all the resultant polymers were thermo-responsive, exhibiting the LCSTs in the range of 16−33 °C. The polymers also showed pH sensitive for the existence of the tertiary amino groups in the interior of the pendent dendrons. It was found that the generation of the dendrons, the molecular weights of the polymers, the concentrations, and the pHs showed great influence on the lower critical solution temperatures (LCSTs) of the polymer solutions. The higher LCST could be achieved either by increasing the generation of the dendrons or by decreasing the molecular weight. The dilute polymer solution with lower pH displayed the higher LCST. For example, the LCST of PG1-macro solution increased significa...

Using poly(acrylic acid) (PAA) and polyacrylamide (PAAm) as an example, we studied the mechanism of hydrogen-bonding complexation in dilute solution by both static and dynamic light scattering. In 20 mM phosphate buffer at pH = 3, the condition suitable for complexation of PAA and PAAm, neither PAA nor PAAm stayed as individual polymer chains at 8.0 mg/mL. Instead, most of PAA formed “multimacroion clusters” (or slow mode) due to the negative charges, and a small portion of PAAm formed associates mainly via hydrogen bonds. After PAA and PAAm solutions were mixed at stoichiometric ratio at room temperature, the slow mode, with PAA being dominant, persisted. The hydrogen-bonding complexation induced by cooling was evolved from the slow mode rather than from the single PAA or PAAm chains. Therefore, at the temperature where phase separation occurred, a fairly large amount of free PAAm chains still existed in the system. Our study demonstrated that the growth of the hydrogen-bonding complex, as well as the op...

A series of poly(meth)acrylamide derivatives with pendent six-member cyclic orthoester groups, i.e., poly(N-(2-alkyloxy-1,3-dioxan-5-yl)methacrylamide)s and poly(N-(2-alkyloxy-1,3-dioxan-5-yl)acrylamide)s, have been synthesized and characterized. The difference between these polymers lies in the type of alkyl substitutes (R3), the stereochemical structures of the pendent cyclic orthoester groups (trans vs cis), and the main chain structures (polymethacrylamide vs polyacrylamide). Aqueous solution properties and pH-dependent hydrolysis behaviors of these polymers were studied by various methods including turbidimetry, fluorescence probe, DSC, 1H NMR, microscopy, and light scattering. The results show that these polymers except PtNPM can be dissolved in water at low temperature, and all of the water-soluble polymers are thermosensitive with different lower critical solution temperatures (LCSTs) and susceptible to hydrolysis in mildly acidic conditions. Both thermosensitive properties and acid-triggered hydr...

The behavior of poly(ethylene oxide)-block-poly(N,N-dimethylacrylamide) (PEO-b-PDMA) in aqueous solution at dilute concentrations was studied by laser light scattering. Even though water was a nons...

The solvent-induced association and micellization processes of amphiphilic rod−coil diblock copolymers, poly(ethylene oxide)-b-poly{(+)-2,5-bis[4’-((S)-2-methylbutoxy)phenyl]styrene} (PEO104-b-PMBPSn, with n being 17, 30, 45, 53, and 106, respectively), were studied in situ by laser light scattering. In dioxane, a selective solvent for PMBPS block, the copolymer preserved the single-chain conformation. With the addition of water, a selective solvent for PEO block, the block copolymer underwent two difference processes: the association governed by PEO and the micellization governed by PMBPS. Because PMBPS would be dominant at elevated water content, three occurrences, the formation of associate, the formation of micelles, and the breakdown of associate, were observed in sequence with increasing water content. However, under the conditions where the rate of disassociation was much slower than that of micellization, the structure of the associate was “frozen” by the rod blocks, and mixed structures of associ...

An orthoester-containing monomer, trans-N-(2-ethoxy-1,3-dioxan-5-yl)acrylamide (tNEA), was synthesized. Atom transfer radical polymerization of tNEA using a poly(ethylene glycol) (PEG) macroinitiat...

An optically active poly(phenylacetylene), poly{2-(R)-methyl-2-[4 0 -(tetradecyloxy)biphenyl-4-yloxy]propyl 4-ethynylbenzoate} (P1) is synthesized in a high yield with a high molecular weight (1.3 � 10 6 g/ mol) by [Rh(nbd)Cl]2 catalyst. The chemical structure of the polymer is characterized by IR and NMR spectroscopies with satisfactory analysis data. The polymer is soluble in many common organic solvents. It shows circular dichroism (CD) band in the absorption region of the polyacetylene backbone, indicating that P1 is chiroptical owing to the formation of helical conformation with an excess screw sense. Combining the results of CD and light scattering experiments, we find that addition of poor solvent can induce the neighboring helical segments within a single polymer strand to become closer, resulting in exciton coupling prior to polymer precipitation. The exciton coupling can be kept in the solid state after solvent evaporation.

Two acid-labile, thermoresponsive poly(methacrylamide)s with the pendant cyclic orthoester moieties of trans and cis configurations, PtNEM and PcNEM, were synthesized via free radical polymerization of the corresponding trans and cis isomers of N-(2-ethoxy-1,3-dioxan-5-yl)methacrylamide (NEM). The thermally induced phase transition/separation behaviors of both polymers as well as the aqueous solution properties below and above their phase transition temperatures were investigated by means of turbidimetry, DSC, 1H NMR, microscopy, fluorescence probe, and dynamic light scattering. Both PtNEM and PcNEM showed aggregation behaviors below their respective LCSTs, and the former formed more hydrophobic microdomains which had greater capability to solvate pyrene molecules compared with PcNEM. These two polymers exhibited thermally induced sensitive and reversible phase transitions in aqueous solution. PtNEM showed a little lower cloud point but much greater phase transition enthalpy compared to PcNEM. The results...

A series of novel well-defined supramolecular ABA triblock copolymers of polyrotaxane are synthesized via atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methacrylate (DMA) initiated by a polypseudorotaxane initiator of α-cyclodextrins (α-CDs) and PEG. The molecular structure of the ABA triblock copolymer with a polyrotaxane as B block, poly(2-(dimethylamino)ethyl methacrylate)-b-PEG[included by α-CDs]-b-poly(2-(dimethylamino)ethyl methacrylate) (DMA-b-PEGCD-b-DMA), was confirmed by two-dimensional rotating frame Overhauser effect spectroscopy (2D ROESY) and X-ray diffraction (XRD) analyses. Self-assembly behaviors of the copolymers in water solution were studied by dynamic light scattering (DLS), static light scattering (SLS), and transmission electron microscopy (TEM). Different from the model triblock copolymer without α-CDs and the polypseudorotaxanes composed of homo-PEG and α-CDs, the supramolecular triblock copolymers in water self-assembled into spheres with an amorphous core...

The polymerization-induced micellization of poly(ethylene oxide)-b-poly(styrene-alt-maleic anhydride) (PEO-b-P(S-alt-MAn)) in CHCl3 was monitored in situ by laser light scattering. Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to grow the P(S-alt-MAn) block onto the PEO macromolecular chain transfer agents (macro-CTAs) at 55 °C. The whole process underwent three stages over time: the induction period, the formation of loose aggregates, and the formation of micelles. The polymerization process and the micellization process were affected mutually: the increase in the degree of polymerization induced the micellization of PEO-b-P(S-alt-MAn); meanwhile, the formation of core-shell micelles retarded the polymerization rate. At higher polymer concentrations, the mutual effect was even stronger, where smaller size micelles with higher density were obtained.

Synthesis of hyperbranched poly(1,2,3-triazole)s (hb-PTAs) has been a challenge: the AB2 monomers were inclined to self-oligomerize, and their Cu(I)-catalyzed click polymerizations failed to yield soluble polymers. We tackled the challenge in this work and succeeded in generating hb-PTAs with regioregularity, processability, and functionality. We took an A2 + B3 approach and used diazides 2 and triyne 3 as monomers, which are free of self-oligomerization concerns. Thermal polymerizations of 2 and 3 produced regiorandom polymers (hb-r-P1) with high molecular weights in high yields. Metal-mediated regioselective polymerizations afforded soluble 1,4- and 1,5-linked polymers (hb-1,4-P1 and hb-1,5-P1), presenting the first examples of regioregular hb-PTAs with macroscopic processability. The reactions were affected by substrate and catalyst: electron-rich alkyne generally slowed down the cycloaddition reaction, while ruthenium catalysts (Cp*Ru(PPh3)2Cl and [Cp*RuCl2]n) exhibited higher substrate tolerance than...

The co-aggregation process of a diblock copolymer poly(ethylene oxide)- block -polybutadiene (PEO- b -PB) and a homopolymer poly(acrylic acid) (PAA) in solutions was studied. The number-average molecular weights of both the PEO and PB blocks are 5100 g/mol; the weight-average molecular weight of PAA is ∼2000 g/mol. The co-aggregation was induced by adding a PB selective solvent (i.e., alkane or cycloalkane) into the THF solution of the two polymers, with the processes characterized by turbidity, 1 H NMR, dynamic light scattering, and microscopy experiments. During the selective solvent titration, the solution underwent a macro-phase separation that was mainly related to PAA, followed by a micro-phase separation that corresponded to the formation of vesicles with the shell of PB block and the core of PAA/PEO complex. The experimental results indicated that the evolution of interpolymer hydrogen bonding complexation between the PAA and PEO blocks determined the co-aggregation process. The loose and soluble interpolymer complex could be formed at rather low selective solvent content ( f ). The complexation was enhanced with increasing f , resulting in “redissolving” the PAA-rich domains in the blend solutions. Afterwards, the more compact PAA/PEO complex chemically linked with a soluble PB block acted as the building blocks to form the vesicles at higher f .

Intelligent gene delivery systems based on physiologically triggered reversible shielding technology have evinced enormous interest due to their potential in vivo applications. In the present work, an acid-labile block copolymer consisting of poly(ethylene glycol) and poly(2-(dimethylamino)ethyl methacrylate) segments connected through a cyclic ortho ester linkage (PEG- a-PDMAEMA) was synthesized by atom transfer radical polymerization of DMAEMA using a PEG macroinitiator with an acid-cleavable end group. PEG- a-PDMAEMA condensed with plasmid DNA formed polyplex nanoparticles with an acid-triggered reversible PEG shield. The pH-dependent shielding/deshielding effect of PEG chains on the polyplex particles were evaluated by zeta potential and size measurements. At pH 7.4, polyplexes generated from PEG- a-PDMAEMA exhibited smaller particle size, lower surface charge, reduced interaction with erythrocytes, and less cytotoxicity compared to PDMAEMA-derived polyplexes. At pH 5.0, zeta potential of polyplexes formed from PEG- a-PDMAEMA increased, leveled up after 2 h of incubation and gradual aggregation occurred in the presence of bovine serum albumin (BSA). In contrast, the stably shielded polyplexes formed by DNA and an acid-stable block copolymer, PEG- b-PDMAEMA, did not change in size and zeta potential in 6 h. In vitro transfection efficiency of the acid-labile copolymer greatly increased after 6 h incubation at pH 5.0, approaching the same level of PDMAEMA, whereas there was only slight increase in efficiency for the stable copolymer, PEG- b-PDMAEMA.

Self-assembly behaviors of a series of hydrophobic side-chain liquid crystalline (LC) polyacetylenes, namely, poly(5-{((4'-alkoxy-4-biphenylyl)carbonyl)oxy}-1-pentyne)s (P-3,m (m ) 5, 7, 9)), were studied in dilute solutions. The assembly was induced by tuning the solvent property to be selective for the alkyl tails on the side chains, with the processes characterized by turbidity, dynamic light scattering, 1 H NMR, and excitation fluorescence anisotropy measurements. The morphology and structure of the P-3,m aggregates formed in the solutions were investigated using atomic force microscopy and wide-angle X-ray diffraction. The experimental results indicate that the P-3,m polymers can form monolayer lamellae in selective solvents. In the lamella, the P-3,m molecules are sheetlike and pack parallel to each other with their backbones located in the lamellar center and their alkyl tails covering the top and bottom lamellar surfaces. The lamellar thickness is largely determined by the width of the molecular sheet. When the solvent becomes selective for the tails, the P-3,m chains may undergo shape stiffening to become more sheetlike.

PDMA-g-PMMA (poly(N,N-dimethylacrylamide)-graft-poly(methyl methacrylate)) graft copolymers were synthesized by radical copolymerization of DMA (N,N-dimethylacrylamide) and vinyl-PMMA macromonomers with AIBN (2,2‘-azobis(isobutyronitrile)) as an initiator. The association behavior of high molecular weight graft copolymers of PDMA-g-PMMA with low graft density in methanol−TBE (tris(hydroxymethyl)aminomethane−boric acid−EDTA) buffer solvent mixtures has been investigated by laser light scattering. With changing solvent quality, the PMMA side chains could be associated. The association points acted as cross-linking points which effectively increased the molecular weight of the associated graft copolymers and also prevented the entangled backbone chains from sliding away against one another. This association behavior could be used to improve the quasi-network formation of such copolymers as better separation media in DNA capillary electrophoresis. pBR322/Hae III digest was successfully separated within 10 min...

Two high molecular weight copolymers of poly(N-isopropylacrylamide) (PNIPAM) densely grafted with short poly(ethylene oxide) (PEO) chains (PNIPAM-g-PEO) were studied by NMR and laser light scattering. The long PNIPAM chains with densely grafted PEO branches had a random coil conformation at very dilute concentrations and low temperatures (i.e., T ≤ 30 °C), When the temperature was increased above 31 °C, the copolymers could undergo a broad coil-to-globule transition. The collapsed copolymer chains had a / value of about 1.0 with PNIPAM chains inside the core and the hydrophilic PEO chains on the surface. This kind of PNIPAM-g-PEO copolymers was studied as a DNA separation medium in capillary electrophoresis. Several advantages of the copolymers as a separation medium for DNA fragments were achieved, such as an automatic coating ability for the capillary inner wall, an easier injection into the capillary channel due to the slightly adjustable viscosity with temperature (up to 31 °C), a high resolution (i.e., one base pair resolution), and fast separation time. In contrast, the homo-PNIPAM or PEO showed worse DNA separation efficiency under similar conditions. The high DNA separation efficiency of the PNIPAM-g-PEO copolymers is related to the polymer chain conformation. The long copolymer chains in a random coil conformation with densely grafted PEO branches could form a physical network with a relatively stable and uniform pore size at high concentrations (i.e., ≥10 wt %). The separation medium has a high sieving ability for DNA separation in terms of DNA migration mechanisms. The collapsed copolymer chains in the globule state could destroy the chain network and thus lose the DNA separation ability.

The crosslinking copolymerization of styrene-divinylbenzene (DVB) with 6% (w/w) DVB was investigated quantitatively by liquid chromatography (LC), viscosity, GPC, and static and dynamic laser light. Through these experiments, reaction order, mechanism, and evolution of molecular weight, size, polydispersity, and branching of the copolymer chains during the gelation were measured. The critical exponents γ, β, δ, τ, and νp of the gelation were calculated. Furthermore, fractal behavior of the copolymer was evidenced firmly; the progression of fractal dimensions of these species following the gelation were also obtained using the dependence of intensity scattered on angles by synchrotron small angle X-ray scattering. A methodology for characterization of gelation forming network polymer is provided objectively. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:363–371, 1998

Linear reduction-degradable cationic polymers with different secondary amine densities (S2 and S3) and their nonreducible counterparts (C2 and C3) were synthesized by Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) step-growth polymerization of the dialkyne-oligoamine monomers and the diazide monomers. These polymers were studied with a goal of developing a set of new gene carriers. The buffering capacity and DNA binding ability of these polymers were evaluated by acid-base titration, gel retardation, and ethidium bromide (EB) exclusion assay. The polymers with lower amine density exhibit a weaker DNA-binding ability but a stronger buffering capacity in the range of pH 5.1 and 7.4. Particle size and zeta-potential measurements demonstrate that the polymers with higher amine density condense pDNA to form polyplexes with smaller sizes, while the disulfide bond in the backbone shows a negative effect on the condensing capability of the polymers, resulting in the formation of polyplexes with large size and nearly neutral surface. The reduction-sensitive polyplexes formed by polymer S2 or S3 can be disrupted by dithiothreitol (DTT) to release free DNA, which has been proven by the combination of gel retardation, EB exclusion assay, particles sizing, and zeta potential measurements. Cell viability measurements by MTT assay demonstrate that the reduction-degradable polymers (S2 and S3) have little cytotoxicity while the nonreducible polymers (C2 and C3) show obvious cytotoxicity, in particular, at high N/P ratios. In vitro transfection efficiencies of these polymers were evaluated using EGFP and luciferase plasmids as the reporter genes. Polymers S3 and S2 show much higher efficiencies than the nonreducible polymers C3 and C2 in the absence of 10% serum; unexpectedly, the lowest transfection efficiency has been observed for polymer S3 in the presence of serum.

Synchrotron small-angle X-ray scattering was used to study the nanostructures of the complexes formed by calf thymus DNA interacting with cationic lipids (or surfactants) of didodecyldimethylammonium bromide (DDAB), cetyltrimethylammonium bromide (CTAB), and their mixture with a zwitterionic lipid of 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (PHGPC). The effects of lipid/DNA ratios, DNA chain flexibility, lipid topology, and neutral lipid mixing on the nanostructures of DNA-lipid complexes were investigated. The complexes between double-stranded DNA (dsDNA) and double-tailed DDAB formed a bilayered lamellar structure, whereas the complexes between dsDNA and single-tailed CTAB preferred a structure of 2D hexagonal close packing of cylinders. With single stranded DNA (ssDNA) interacting with CTAB, the complexes showed a Pm3n cubic structure due to the different chain flexibility between dsDNA and ssDNA. The lipid molecules bound by rigid dsDNA like to form cylindrical micelles, whereas lipids bound to flexible ssDNA could form spherical or short cylindrical micelles. The addition of the neutral single-chained PHGPC lipids to the CTAB lipids could induce a structural transition of dsDNA-lipid complexes from a 2D hexagonal to a multi-bilayered lamellar structure. The parallel DNA strands were intercalated in the water layers of lamellar stacks of the mixed lipid bilayers. The DNA-DNA spacing depended on the ratios of charged lipid to neutral lipid, and charged lipid to DNA, respectively.

Ethyl carbamylated polyrotaxane (ECPR) and propyl carbamylated polyrotaxane (PCPR) were prepared based on the reactions between ethyl/propyl isocyanate and polyrotaxane (PR) in anhydrous DMSO under an argon atmosphere. By changing the alkyl type and substitution ratio, the PR derivative with good water-solubility was obtained and its solutions showed reversible sol–gel phase transition. During the heating process, transition temperature from sol to gel decreased from 32 °C to 18 °C with increasing the solution concentration from 2.44% to 13.5%, while in the cooling process, all the gels with various concentration did not turn into sols until the temperature decreased to 1 °C, exhibiting large hysteresis between heating and cooling.

The persistence length and the overlap concentration (c*) of poly(ethylene oxide) (PEO) and hydroxyethylcellulose (HEC) with similar molecular weight in 1 × TBE buffer were studied by laser light scattering and viscometry. Their effect on DNA separation was investigated by capillary electrophoresis. It was determined that the persistence length of HEC was at least 5 times higher than that of PEO. Therefore, the c* of HEC was smaller than that of PEO by a factor of ca. 2.5. It was also found that the c* values determined by laser light scattering were much lower than those by viscometry. We attributed it to the state of polymer chains in which c* was measured: laser light scattering determined the c* in ultradilute solution where the polymer chains were in the static state; while viscometry determined the c* in dilute or semidilute concentration region with polymer chains being in the hydrodynamic flowing state. When used in DNA separation, polymer chains were in different states due to the disturbance of DNA molecules, making c* region dependent. When the real concentration was normalized by c*, PEO and HEC showed almost equal performance in separating ΦX174/Hae III DNA digest in dilute solution, even though their persistence lengths were quite different.