PolyNC: a natural and chemical language model for the prediction of unified polymer properties.

Language models exhibit a profound aptitude for addressing multimodal and multidomain challenges, a competency that eludes the majority of off-the-shelf machine learning models. Consequently, language models hold great potential for comprehending the intricate interplay between material compositions and diverse properties, thereby accelerating material design, particularly in the realm of polymers. While past limitations in polymer data hindered the use of data-intensive language models, the growing availability of standardized polymer data and effective data augmentation techniques now opens doors to previously uncharted territories. Here, we present a revolutionary model to enable rapid and precise prediction of Polymer properties via the power of Natural language and Chemical language (PolyNC). To showcase the efficacy of PolyNC, we have meticulously curated a labeled prompt-structure-property corpus encompassing 22 970 polymer data points on a series of essential polymer properties. Through the use of natural language prompts, PolyNC gains a comprehensive understanding of polymer properties, while employing chemical language (SMILES) to describe polymer structures. In a unified text-to-text manner, PolyNC consistently demonstrates exceptional performance on both regression tasks (such as property prediction) and the classification task (polymer classification). Simultaneous and interactive multitask learning enables PolyNC to holistically grasp the structure-property relationships of polymers. Through a combination of experiments and characterizations, the generalization ability of PolyNC has been demonstrated, with attention analysis further indicating that PolyNC effectively learns structural information about polymers from multimodal inputs. This work provides compelling evidence of the potential for deploying end-to-end language models in polymer research, representing a significant advancement in the AI community's dedicated pursuit of advancing polymer science.

Storage Stability of 6FDA-DMB Polyamic Acid Solution Detected by Gel Permeation Chromatography Coupled with Multiple Detectors.

Polyamic acid (PAA) is the precursor of polyimide (PI), and its solution's properties have a direct influence on the final performances of PI resins, films, or fibers. The viscosity loss of a PAA solution over time is notorious. A stability evaluation and revelation of the degradation mechanism of PAA in a solution based on variations of molecular parameters other than viscosity with storage time is necessary. In this study, a PAA solution was prepared through the polycondensation of 4,4'-(hexafluoroisopropene) diphthalic anhydride (6FDA) and 4,4'-diamino-2,2'-dimethylbiphenyl (DMB) in DMAc. The stability of a PAA solution stored at different temperatures (-18, -12, 4, and 25 °C) and different concentrations (12 wt% and 0.15 wt%) was systematically investigated by measuring the molecular parameters, including Mw, Mn, Mw/Mn, Rg, and [η], using gel permeation chromatography coupled with multiple detectors (GPC-RI-MALLS-VIS) in a mobile phase 0.02 M LiBr/0.20 M HAc/DMF. The stability of PAA in a concentrated solution decreased, as shown by the reduction ratio of Mw from 0%, 7.2%, and 34.7% to 83.8% and that of Mn from 0%, 4.7%, and 30.0% to 82.4% with an increase of temperature from -18, -12, and 4 to 25 °C, respectively, after storage for 139 days. The hydrolysis of PAA in a concentrated solution was accelerated at high temperatures. Notably, at 25 °C, the diluted solution was much less stable than the concentrated one and exhibited an almost linear degradation rate within 10 h. The Mw and Mn decreased rapidly by 52.8% and 48.7%, respectively, within 10 h. Such faster degradation was caused by a greater water ratio and less entanglement of chains in the diluted solution. The degradation of (6FDA-DMB) PAA in this study did not follow the chain length equilibration mechanism reported in literature, given that both Mw and Mn declined simultaneously during storage.

scAnnotate: an automated cell-type annotation tool for single-cell RNA-sequencing data.

Motivation: Single-cell RNA-sequencing (scRNA-seq) technology enables researchers to investigate a genome at the cellular level with unprecedented resolution. An organism consists of a heterogeneous collection of cell types, each of which plays a distinct role in various biological processes. Hence, the first step of scRNA-seq data analysis is often to distinguish cell types so they can be investigated separately. Researchers have recently developed several automated cell-type annotation tools, requiring neither biological knowledge nor subjective human decisions. Dropout is a crucial characteristic of scRNA-seq data widely used in differential expression analysis. However, no current cell annotation method explicitly utilizes dropout information. Fully utilizing dropout information motivated this work. Results: We present scAnnotate, a cell annotation tool that fully utilizes dropout information. We model every gene's marginal distribution using a mixture model, which describes both the dropout proportion and the distribution of the non-dropout expression levels. Then, using an ensemble machine learning approach, we combine the mixture models of all genes into a single model for cell-type annotation. This combining approach can avoid estimating numerous parameters in the high-dimensional joint distribution of all genes. Using 14 real scRNA-seq datasets, we demonstrate that scAnnotate is competitive against nine existing annotation methods. Furthermore, because of its distinct modelling strategy, scAnnotate's misclassified cells differ greatly from competitor methods. This suggests using scAnnotate together with other methods could further improve annotation accuracy. Availability and implementation: We implemented scAnnotate as an R package and made it publicly available from CRAN: https://cran.r-project.org/package=scAnnotate. Supplementary information: Supplementary data are available at Bioinformatics Advances online.

Effect of Annealing Process and Molecular Weight on the Polymorphic Transformation from Form II to Form I of Poly(1-butene).

Poly(1-butene) (PB-1) resin has excellent mechanical properties, outstanding creep resistance, environmental stress crack resistance and other excellent properties. However, PB-1 resin experiences a crystal transformation for a period, which seriously affects the production efficiency and directly restricts its large-scale commercial production and application. The factors affecting the crystal transformation of PB-1 are mainly divided into external and internal factors. External factors include crystallization temperature, thermal history, nucleating agent, pressure, solvent induction, etc., and internal factors include chain length, copolymerization composition, isotacticity, its distribution, etc. In this study, to avoid the interference of molecular weight distribution on crystallization behavior, five PB-1 samples with narrow molecular weight distribution (between 1.09 and 1.44) and different molecular weights (from 23 to 710 k) were chosen to research the influence of temperature and time in the step-by-step annealing process and molecular weight on the crystal transformation by differential scanning calorimetry (DSC). When the total annealing time was the same, the step-by-step annealing process can significantly accelerate the rate of transformation from crystal form II to I. PB-1 samples with different molecular weights have the same dependence on annealing temperature, and the optimal nucleation temperature (i.e., low annealing temperature, Tl) and growth temperature (i.e., high annealing temperature, Th) were -10 °C and 40 °C, respectively. At these two temperatures, the crystal form I obtained by step-by-step annealing had the highest content; other lower or higher annealing temperatures would reduce the rate of crystal transformation. When the annealing temperature was the same, crystal form I first increased with annealing time tl, then gradually reached a plateau, but the time to reach a plateau was different. The crystalline form I contents of the samples with lower molecular weight increased linearly with annealing time th. However, the crystalline form I contents of the samples with higher molecular weight increased rapidly with annealing time th at the beginning, and then transformation speed from form II to form I slowed down, which implied that controlling Tl/tl and Th/th can tune the different contents of form I and form II. At the same Tl/tl or Th/th, with increasing molecular weight, the transformation speed from form II to form I via the step-by-step annealing process firstly increased and then slowed down due to the competition of the number of linked molecules and molecular chain mobility during crystallization. This study definitely provides an effective method for accelerating the transformation of poly(1-butene) crystal form, which not only has important academic significance, but also has vital industrial application.

A Facile Approach to Produce Star Polymers Based on Coordination Polymerization.

Many efforts have been devoted to preparing star polymers. Research into coordination polymerization, the most powerful stereoselective process to endow polymers with superb properties, lags far behind those achieved by radical polymerization and ionic polymerization. Herein, we propose a facile strategy to prepare star polymers with regular arms based on coordination polymerization via an insertion reaction between the carbon-heteroatom unsaturated bond and the metal-alkyl species. Terminating a living cis-1,4-selective isoprene polymerization by using isocyanate as cross-linker (CL), a star polyisoprene with low polydispersity was obtained in high yield (91.8 %). A kinetic study showed the star polymer was formed via a step-growth procedure. The types of CL and the ratio of [CL]0 : [Cat.]0 are key factors to determine the arm number and the yield of star polymer. Finally, synthetic IR rubber with a green strength up to 1.99 MPa superior to natural rubber (1.43 MPa) was prepared for the first time.

Direct Synthesis of Functional Thermoplastic Elastomer with Excellent Mechanical Properties by Scandium-Catalyzed Copolymerization of Ethylene and Fluorostyrenes.

Herein, we report copolymerizations of ethylene (E) and ortho-/meta-/para-fluorostyrenes (SF =oFS/mFS/pFS) by using quinolyl methylene fluorenyl scandium complex (Flu-CH2 -Qu)Sc(CH2 SiMe3 )2 . The copolymerizations proceed in a controlled fashion to afford copolymers composed of "soft" ethylene-fluorostyurene (E-SF ) random segments (Tg =-22.2-5.1 °C) and "hard" crystalline ethylene-ethylene (E-E) segments (Tm =42.3-130.2 °C). The copolymers behave like thermoplastic elastomers at room temperature by showing high stress values up to 39.5 MPa under elongation-at-break above 774 % with elastic recovery over 75 %. The excellent mechanical properties are mainly attributed to the microphase separation of the nanoscale crystalline E-E domain from the amorphous E-SF copolymer matrix proved by AFM, WAXD and SAXS. The mechanism investigation by the density functional theory (DFT) simulation reveals that the steric bulky and electron-withdrawing ligand of the catalytic precursor prefers E propagation to generate long E-E segments, while the incorporation of SF is thermodynamic control.

Conformation and persistence length of chitosan in aqueous solutions of different ionic strengths via asymmetric flow field-flow fractionation.

Conformation of chitosan in acidic aqueous solutions is strongly influenced by ionic strength, but the conventional employed size exclusion chromatography is limited to high ionic strength. Here we show that conformation of chitosan in acetate buffer down to millimolar ionic strength can be studied via asymmetric flow field-flow fractionation (AF4), where the separation is governed by the diffusion properties of the chitosan molecules and assisted by the electrostatic repulsion of the polyelectrolyte from the channel membrane. The size of chitosan decreases with ionic strength due to increasing screening of the polyelectrolyte effect. The persistence length of chitosan in the solutions, obtained by fitting the conformation plot by the wormlike chain model, decreases linearly with the Debye screening length from 44.5 nm at a salt concentration of 1.25 mM dominated by the electrostatic contribution to 8.6 nm in 800 mM acetate buffer close to its intrinsic persistence length of 7.7 nm.

Mesenchymal stem cell exosomes reverse acute lung injury through Nrf-2/ARE and NF-κB signaling pathways.

Acute lung injury (ALI) is associated with histopathological diffuse alveolar damage. The potential role of mesenchymal stem cells (MSCs) in the treatment of various clinical disorders have been widely documented, such as those for ALI. Recent evidence has demonstrated that exosomes from endothelial progenitor cells can improve outcomes of the lipopolysaccharide (LPS)-induced ALI. However, there has been no research on the potential role of MSC-exosomes in the treatment of sepsis-induced ALI, which is worth further exploration. Thus, the objective of our study was to identify whether the MSC-exosomes could reverse ALI. The ALI model induced by LPS was established in this study. MTT assay was performed to test cell proliferation. Expression of inflammatory factors (TNF-α, IL-6, and IL-10) in the LPS-treated type II alveolar epithelial cells (AECs) (MLE-12) was detected by ELISA. After co-culture of MSC-exosomes with LPS-treated MLE-12 cells, we found that the cell proliferation of MLE-12 cells gradually increased. Furthermore, we selected five of the Nrf-2/ARE- and NF-κB signaling pathway-related genes to explore if MSC-exosomes could reverse LPS-induced ALI through Nrf-2/ARE and NF-κB signaling pathways. QRT-PCR and western blot experiment results showed that the expression of these five genes were significantly regulated after stimulation with high-concentration LPS and exosome intervention. Taken together, these findings highlighted the fact that MSC-exosomes could reverse ALI through the Nrf-2/ARE and NF-κB signaling pathways. The MSC-exosome may be the potential future therapeutic strategy for the treatment of ALI.

Influence of Heating Rate on the Structure and Mechanical Properties of Aromatic BPDA-PDA Polyimide Fiber.

Aromatic polyimide fibers (PI) are usually produced in two steps. The precursor fibers of polyamic acid (PAA) are fabricated first, and then the fabricated fibers are converted into PI fibers through thermal treatment. In the second step (thermal treatment), the mechanical properties of the obtained PI fibers are remarkably affected. Here, the PAA fibers derived from 3,3',4,4'-biphenyltetra-carboxylic dianhydride and p-phenylenediamine are fabricated by a dry-jet wet-spinning method. Then, the PI fibers are prepared by heating PAA fibers from room temperature to 300, 350 and 400 °C under different heating rates, ranging from 1 °C/min to 80 °C/min. When the heating rate is low, the crystallization lags behind the imidization process, and begins only when the imidization degree reaches a high level. As the heating rate increases, the crystallization tends to occur simultaneously with the imidization process, and the degree of crystallinity of the PI fibers also greatly increases. Our findings suggest that a high heating rate causes the polymer chains to undergo high mobility during thermal treatment. The tensile modulus of the PI fiber further demonstrates a high dependence on the heating rate. Moreover, a short annealing process after treatment proves to be efficient in releasing residual stress and improving tensile strength.

Chromatographic mode transition from size exclusion to slalom chromatography as observed for chitosan.

Elution behavior of chitosan was studied using narrow-bore size exclusion chromatography (SEC) columns packed with 8 µm porous particles at different eluent flow rates. Delayed elution of the largest chitosan species from the columns was observed at high flow rates, which was attributable to strong chain deformation rather than chain degradation. In particular, a chromatographic mode transition from SEC to slalom chromatography (SC) was observed for high molar mass chitosan samples with abnormal elution behaviors, which originates from the coil-stretch transition of chitosan chains in elongational flow through the columns. By properly reducing the elongational rate in the columns via tuning the flow rate, particle size and column dimension, the chromatographic mode transition from SEC to SC for chitosan can be effectively suppressed.

Electrostatic Interaction Mediates the Formation of Vesicular Structures from Coassembly of PS-b-PAA with Quantum Dots.

Vesicular structures of block copolymers and inorganic nanoparticles with good stability have potential applications in therapeutic drug release and bioimaging. Herein, a block copolymer of polystyrene-b-poly(acrylic acid) (PS48-b-PAA67) and water-soluble AgInS2/ZnS core/shell quantum dots (QDs) capped with gelatin and thioglycolic acid were coassembled in tetrahydrofuran by adding water. The positively charged QDs bind to negatively charged PAA segments through electrostatic interaction. Numerous vesicular structures, such as uniform bilayer vesicles, flowerlike large compound vesicles, onionlike lamellar structures consisting of alternating PS and PAA&QD layers, and multilamellar vesicles with spaces between concentric vesicle layers were obtained from the coassembly of PS48-b-PAA67 with QDs. The binding of the positively charged QDs to the PAA block influenced both the intra-aggregate PAA corona conformation and the interaggregate interactions. The key parameters affecting the formation of these vesicular structures included the QD content, solution pH, and water addition rate. Thus, tunable vesicular structures can be prepared and regulated through this simple but effective coassembly method.

Associative behavior of polyimide/cyclohexanone solutions.

Our previous work has demonstrated that soluble polyimide with relatively weak interaction can be transformed from neutral polymer to associative polymer by increasing molecular weight. Thus, it is necessary to find another way to vary the relatively weak interaction strength, i.e. variation of solvent quality. Herein, viscoelastic behaviors are examined for 2,2-bis(3,4-dicarboxy-phenyl) hexafluoropropane dianhydride (6FDA)-2,2'-bis(trifluoromethyl)-4,4'-diam (TFDB) polyimide (PI), with a relatively low molecular weight (M w) of 88 000 g mol-1, dissolved in cyclohexanone (CYC). The scaling relationship between viscosity (η 0-η s) and volume fraction is in good agreement with the associative polymer theory proposed by Rubinstein and Semenov. Oscillatory rheological results indicate that the PI solution tends to become a gel with increased volume fraction. The synchrotron radiation small-angle X-ray scattering results imply the existence of dense aggregates in the concentrated PI/CYC solutions. Shear thickening and thinning behaviors are observed in the solutions, and the shear thickening behavior of polyimide solution has not been reported in literature. Their mechanisms are studied by conducting dynamic and steady rheological experiments. Thus, enhancing the relatively weak interaction strength can also make the low M w polyimide show associative polymer behavior. This work can help us to gain deep insight into polyimide solution properties from dilute to semidilute entangled solutions, and will guide the preparation of polyimide solutions for different processing.

Adsorption of poly(vinyl alcohol) on gel permeation chromatography columns depends on the degree of hydrolysis.

Both fully (98%) and partially (88%) hydrolyzed poly(vinyl alcohol) (PVA) are characterized by aqueous gel permeation chromatography (GPC) coupled with multi-angle laser light scattering. Polymer adsorption on hydrophilic GPC columns is observed for partially hydrolyzed PVA but not for fully hydrolyzed PVA, which is driven by the hydrophobic interactions between the residual acetate groups on PVA and the stationary phase. Desorption of these partially hydrolyzed PVA chains from the packing materials is monitored by decay of the light scattering signal. It is found that the desorption of these polymer chains from porous particles is non-exponential and follows stretched exponential kinetics with index 0.36. It is also shown that asymmetric flow field flow fractionation can be successfully used for the molar mass characterization of PVA, irrespective of the degree of hydrolysis.

Strategy to improve the characterization of chitosan by size exclusion chromatography coupled with multi angle laser light scattering.

Here we present SEC-MALLS study for chitosan samples with weight average molar mass Mw between 33 and 427 kg/mol on columns packed with 8 µm porous particles. A low injection concentration on the order of 0.1-0.2 mg/mL must be used to avoid overloading of the SEC columns, due to the extended coil conformation of cationic chitosan in the dilute acid buffer as compared to neutral polymers. Additionally, SEC must be performed at an eluent flow rate no more than 0.5 mL/min for high molar mass chitosan samples. At flow rates of 1.0 and 1.5 mL/min, the elution of the largest chitosan species is delayed, which leads to a distortion of the molar mass distribution towards lower molar mass region. Such an abnormal behavior is due to a chromatographic mode transition from SEC to slalom chromatography, originated from the coil-stretch transition of chitosan chains in elongational flow through the packed columns.

Superfast and Reversible Thermoresponse of Poly( N-isopropylacrylamide) Hydrogels Grafted on Macroporous Poly(vinyl alcohol) Formaldehyde Sponges.

Poly( N-isopropylacrylamide) (PNIPAAm), a typical thermoresponsive polymer, exhibits potential application in smart materials. However, bulk PNIPAAm hydrogel monoliths undergo slow volume phase transition at least tens of minutes to hours as determined by the shape and size of polymers due to the formation of the skin layer. In this regard, novel macroporous sponges with rapid thermoresponse are prepared via grafting polymerization of N-isopropylacrylamide (NIPAAm) onto the macroporous poly(vinyl alcohol) formaldehyde (PVF) network as confirmed by attenuated total reflection-infrared (ATR IR) and 1H NMR spectra. As prepared PVF- g-PNIPAAm sponges display interconnected open-cell structures, and their average pore sizes and porosities are ∼90 µm and >85%, respectively. The equilibrium swelling ratio of PVF- g-PNIPAAm sponges varies from 11 to 50 with temperature. The volume phase transition temperature is at 30-34 °C, as detected in the DSC curves of swollen samples. These features indicate that the existence of the original PVF network exerts almost no influence on the PNIPAAm temperature responsibility. As prepared samples can reach the swelling equilibrium in less than 80 s, and their rapid swelling kinetics can be fitted using the pseudo-first-order rate kinetic equation. Notably, the samples also display rapid deswelling rate in less than 40 s at relative high temperature (48 °C), thereby indicating a superfast responsive behavior to temperature change. The PVF- g-PNIPAAm sponges exhibit rapid and reversible thermoresponse in repeatable swelling-deswelling cycles, which can satisfy the need of special smart materials. In particular, combined with iodine solution (i.e., PVF- g-PNIPAAm/I2), these sponges can serve as a novel temperature indicator and exhibit excellent antibacterial performances.

Fabrication of Thermosensitive Cyclic Brush Copolymer with Enhanced Therapeutic Efficacy for Anticancer Drug Delivery.

Adaptation of cyclic brush polymer for drug delivery applications remains largely unexplored. Herein, cyclic brush copolymer of poly(2-hydroxyethyl methacrylate-g-poly(N-isopropylacrylamide-st-N-hydroxyethylacrylamide)) (cb-P(HEMA-g-P(NIPAAm-st-HEAAm))), comprising a cyclic core of PHEMA and thermosensitive brushes of statistical copolymer of P(NIPAAm-st-HEAAm), is designed and synthesized successfully via a graft-from approach using atom transfer free radical polymerization from a cyclic multimacroinitiator. The composition of the brush is optimized to endow the resulting cyclic brush copolymer with a lower critical solution temperature (LCST) slightly above the physiological temperature, but lower than the localized temperature of tumor tissue, which is suitable for the hyperthermia-triggered anticancer drug delivery. Critical aggregation concentration determination reveals better stability for the unimolecular nanoparticle formed by the cyclic brush copolymer than that formed by the bottlebrush analogue. The dramatically increased size with elevated temperatures from below to above the LCST confirms hyperthermia-induced aggregation for both formulations. Such structural destabilization promotes significantly the drug release at 40 °C. Most importantly, the drug-loaded cyclic brush copolymer shows enhanced in vitro cytotoxicity against HeLa cells than the bottlebrush counterpart. The better stability and higher therapeutic efficacy demonstrates that the thermosensitive cyclic brush copolymer is a better formulation than bottle brush copolymer for controlled drug release applications.

Fabrication of Hyperbranched Block-Statistical Copolymer-Based Prodrug with Dual Sensitivities for Controlled Release.

Dendrimer with hyperbranched structure and multivalent surface is regarded as one of the most promising candidates close to the ideal drug delivery systems, but the clinical translation and scale-up production of dendrimer has been hampered significantly by the synthetic difficulties. Therefore, there is considerable scope for the development of novel hyperbranched polymer that can not only address the drawbacks of dendrimer but maintain its advantages. The reversible addition-fragmentation chain transfer self-condensing vinyl polymerization (RAFT-SCVP) technique has enabled facile preparation of segmented hyperbranched polymer (SHP) by using chain transfer monomer (CTM)-based double-head agent during the past decade. Meanwhile, the design and development of block-statistical copolymers has been proven in our recent studies to be a simple yet effective way to address the extracellular stability vs intracellular high delivery efficacy dilemma. To integrate the advantages of both hyperbranched and block-statistical structures, we herein reported the fabrication of hyperbranched block-statistical copolymer-based prodrug with pH and reduction dual sensitivities using RAFT-SCVP and post-polymerization click coupling. The external homo oligo(ethylene glycol methyl ether methacrylate) (OEGMA) block provides sufficient extracellularly colloidal stability for the nanocarriers by steric hindrance, and the interior OEGMA units incorporated by the statistical copolymerization promote intracellular drug release by facilitating the permeation of GSH and H+ for the cleavage of the reduction-responsive disulfide bond and pH-liable carbonate link as well as weakening the hydrophobic encapsulation of drug molecules. The delivery efficacy of the target hyperbranched block-statistical copolymer-based prodrug was evaluated in terms of in vitro drug release and cytotoxicity studies, which confirms both acidic pH and reduction-triggered drug release for inhibiting proliferation of HeLa cells. Interestingly, the simultaneous application of both acidic pH and GSH triggers promoted significantly the cleavage and release of CPT compared to the exertion of single trigger. This study thus developed a facile approach toward hyperbranched polymer-based prodrugs with high therapeutic efficacy for anticancer drug delivery.

Viscoelastic behaviour and relaxation modes of one polyamic acid organogel studied by rheometers and dynamic light scattering.

A novel polyamic acid (PAA from BAPMPO-BPDA) organogel was synthesized and characterized via dynamic light scattering (DLS), a classical rheometer, and diffusion wave spectroscopy (DWS). In situ monitoring was performed using a classical rheometer to observe the formation of the PAA organogel. The rheological curves confirm the formation of the PAA gel network and the origin of hydrogen bonding from the -NH- group (donor) and P[double bond, length as m-dash]O group (acceptor). The autocorrelation functions of PAA under different conditions (pure gel, gel with NaNO3, gel with formamide) are measured via DLS, and different characteristic times are obtained via the CONTIN method. Three different relaxation modes of the PAA gel, i.e., fast, intermediate and slow modes, are observed. The fast and intermediate modes show a diffusive behaviour (τ ∼ q-2), whereas the slow mode did not. When enough formamide is added into the PAA gel, the fast mode disappears; addition of enough salt (NaNO3) leads to disappearance of the slow mode. The relationship between characteristic time and diffusion vector demonstrates that the different decorrelation modes consisted of two homodyne and two heterodyne components. Two single-exponential functions and two stretched exponential functions were used, and the different decorrelation modes of the PAA gel are expressed with a non-linear function, which fits the autocorrelation function very well. And the different decorrelation modes are also discussed. DWS results in the high-frequency region not only demonstrate the formation of a PAA gel network but also indicate that the semiflexible chains of PAA are due to electrostatic interaction. The DWS results at different time scales are analyzed by applying the de Gennes' reptation model.

Nanoparticle Loading Induced Morphological Transitions and Size Fractionation of Coassemblies from PS-b-PAA with Quantum Dots.

Inorganic nanoparticles play a very important role in the fabrication and regulation of desirable hybrid structures with block copolymers. In this study, polystyrene-b-poly(acrylic acid) (PS48-b-PAA67) and oleic acid-capped CdSe/CdS core/shell quantum dots (QDs) are coassembled in tetrahydrofuran (THF) through gradual water addition. QDs are incorporated into the hydrophilic PAA blocks because of the strong coordination between PAA blocks and the surface of QDs. Increasing the weight fraction of QDs (ω = 0-0.44) leads to morphological transitions from hybrid spherical micelles to large compound micelles (LCMs) and then to bowl-shaped structures. The coassembly process is monitored using transmission electron microscopy (TEM). Formation mechanism of different morphologies is further proposed in which the PAA blocks bridging QDs manipulates the polymer chain mobility and the resulting morphology. Furthermore, the size and size distribution of assemblies serving as drug carriers will influence the circulation time, organ distribution and cell entry pathway of assemblies. Therefore, it is important to prepare or isolate assemblies with monodisperse or narrow size distribution for biomedical applications. Here, the centrifugation and membrane filtration techniques are applied to fractionate polydisperse coassemblies, and the results indicate that both techniques provide effective size fractionation.

Molar mass fractionation in aqueous two-phase polymer solutions of dextran and poly(ethylene glycol).

Dextran and poly(ethylene glycol) (PEG) in phase separated aqueous two-phase systems (ATPSs) of these two polymers, with a broad molar mass distribution for dextran and a narrow molar mass distribution for PEG, were separated and quantified by gel permeation chromatography (GPC). Tie lines constructed by GPC method are in excellent agreement with those established by the previously reported approach based on density measurements of the phases. The fractionation of dextran during phase separation of ATPS leads to the redistribution of dextran of different chain lengths between the two phases. The degree of fractionation for dextran decays exponentially as a function of chain length. The average separation parameters, for both dextran and PEG, show a crossover from mean field behavior to Ising model behavior, as the critical point is approached.