Copolymers In Water Research Articles

Formation of Hybrid Wormlike Micelles upon Mixing Cetyl Trimethylammonium Bromide with Poly(methyl methacrylate-co-sodium styrene sulfonate) Copolymers in Aqueous Solution

The association of cetyltrimethylammonium bromide, CTAB, with a series of P(MMAx-co-SSNa) random copolymers of sodium styrene sulfonate (SSNa) with methyl methacrylate (MMA) was explored in aqueous solution as a function of the MMA molar content, x, of the copolymers. The polyelectrolyte/surfactant complexation in aqueous solution was verified through pyrene fluorescence probing. In addition, turbidimetry studies in dilute or more concentrated aqueous solutions elucidated the phase separation behavior of the P(MMAx-co-SSNa)/CTAB systems as a function of the copolymer composition x and the surfactant to polyelectrolyte mixing charge ratio. It is found that practically phase separation is completely suppressed within the studied mixing range when the MMA content of the copolymers is ∼30-40 mol%. For lower MMA contents the polyelectrolyte/surfactant complex separates out from water, while for higher x values the solubility limits of the copolymers in water are attained. For the intermediate MMA contents, viscoelastic systems are obtained in more concentrated polymer/surfactant solutions provided that the polyelectrolyte is fully complexed with the cationic surfactant ((1)H NMR results). Moreover, the (1)H NMR studies indicate that hybrid P(MMAx-co-SSNa)/CTAB wormlike micelles are formed in water under these conditions. Finally, it is shown that addition of salt prevents syneresis problems and facilitates the rheological investigation.

Controlling Polymersome Surface Topology at the Nanoscale by Membrane Confined Polymer/Polymer Phase Separation

Nature has the exquisite ability to design specific surface patterns and topologies on both the macro- and nanolength scales that relate to precise functions. Following a biomimetic approach, we have engineered fully synthetic nanoparticles that are able to self-organize their surface into controlled domains. We focused on polymeric vesicles or "polymersomes"; enclosed membranes formed via self-assembly of amphiphilic block copolymers in water. Exploiting the intrinsic thermodynamic tendency of dissimilar polymers to undergo phase separation, we mixed different vesicle-forming block copolymers in various proportions in order to obtain a wide range of polymersomes with differing surface domains. Using a combination of confocal laser scanning microscopy studies of micrometer-sized polymersomes, and electron microscopy, atomic force microscopy, and fluorescence spectroscopy on nanometer-sized polymersomes, we find that the domains exhibit similar shapes on both the micro- and nanolength scales, with dimensions that are linearly proportional to the vesicle diameter. Finally, we demonstrate that such control over the surface "patchiness" of these polymersomes determines their cell internalization kinetics for live cells.

Controlling the micellar morphology of binary PEO–PCL block copolymers in water–THF through controlled blending

We study both experimentally and theoretically the self-assembly of binary polycaprolactone–polyethylene oxide (PCL–PEO) block copolymers in dilute solution, where self-assembly is triggered by changing the solvent from the common good solvent THF to the selective solvent water, and where the two species on their own in water form vesicles and spherical micelles respectively. We find that in water the inter-micellar exchange of these block copolymers is extremely slow so that the resultant self-assembled structures are in local but not in global equilibrium (i.e., they are non-ergodic). This opens up the possibility of controlling micelle morphology both thermodynamically and kinetically. Specifically, when the two species are first molecularly dissolved in THF before mixing and self-assembly (‘pre-mixing’) by dilution with water, the morphology of the formed structures is found to depend on the mixing ratio of the two species, going gradually on a route of decreasing surface curvature from vesiclesvia an intermediate regime of micelles in the shape of ‘bulbed’ rods, rings, Y-junctions and finally to spherical micelles as we increase the proportion of the “sphere formers”. On the other hand, if the two species are first partially self-assembled (by partial exchange of the solvent with water) before mixing and further self-assembly (‘intermediate mixing’), novel metastable structures, including nanoscopic ‘pouches’, emerge. These experimental results are corroborated by Self-Consistent Field Theory (SCFT) calculations which reproduce the sequence of morphologies seen in the pre-mixing experiments. SCFT also reveals a clear coupling between polymer composition and aggregate curvature, with regions of positive and negative curvature being stabilized by an enrichment and depletion of sphere formers respectively. Our study demonstrates that both thermodynamic and kinetic blending of block copolymers are effective design parameters to control the resulting structures and allow us to access a much richer range of nano-morphologies than is possible with monomodal block copolymer solutions.

Freeze-Fracture TEM Imaging of Robust Order in Swollen Phases of Amphiphilic Diblock Copolymers

We report on the structures exhibited by two different diblock poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) copolymers in water, a selective solvent. Using a combination of X-ray scattering and freeze fracture-transmission electron microscopy (FF-TEM), we show that these structures can be widely swollen while retaining their initial morphology and a high degree of long-range order. The analysis of the FF-TEM pictures also evidences the presence of water crystallites of regular size and shape within the confined water domains. We relate the growth of these crystallites to the high local ionic strength of the water swelling the PAA brushes. Moreover, the confinement of the crystallites growth shows that the swollen phases have a very robust structure, potentially useful for confining colloidal particles.

Novel Photolabile Diblock Copolymers Bearing Truxillic Acid Derivative Junctions

Amphiphilic diblock copolymers, poly(ethylene glycol)-block-poly(acrylate), bearing truxillic acid derivatives at the junction point between the two blocks are described. The truxillic acid junction can be selectively cut by UV light, leading to a disassembly of the nano-objects made by self-assembly of the amphiphilic copolymers in water.

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

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

Hydrophilization of Magnetic Nanoparticles with Modified Alternating Copolymers. Part 1: The Influence of the Grafting.

Iron oxide nanoparticles (NPs) with a diameter 21.6 nm were coated with poly(maleic acid-alt-1-octadecene) (PMAcOD) modified with grafted 5,000 Da poly(ethyelene glycol) (PEG) or short ethylene glycol (EG) tails. The coating procedure utilizes hydrophobic interactions of octadecene and oleic acid tails, while the hydrolysis of maleic anhydride moieties as well as the presence of hydrophilic PEG (EG) tails allows the NP hydrophilicity. The success of the NP coating was found to be independent of the degree of grafting which was varied between 20 and 80% of the -MacOD-units, but depended on the length of the grafted tail. The NP coating and hydrophilization did not occur when the modified copolymer contained 750 Da PEG tails independently of the grafting degree. To explain this phenomenon the micellization of the modified PMAcOD copolymers in water was analyzed by small angle x-ray scattering (SAXS). The PMAcOD molecules with the grafted 750 Da PEG tails form compact non-interacting disk-like micelles, whose stability apparently allows for no interactions with the NP hydrophobic shells. The PMAcOD containing the 5,000 Da PEG and EG tails form much larger aggregates capable of an efficient coating of the NPs. The coated NPs were characterized using transmission electron microscopy, dynamic light scattering, ζ-potential measurements, and thermal gravimetry analysis. The latter method demonstrated that the presence of long PEG tails in modified PMAcOD allows the attachment of fewer macromolecules (by a factor of ~20) compared to the case of non-modified or EG modified PMAcOD, emphasizing the importance of PEG tails in NP hydrophilization. The NPs coated with PMAcOD modified with 60% (towards all -MAcOD- units) of the 5,000 PEG tails bear a significant negative charge and display good stability in buffers. Such NPs can be useful as magnetic cores for virus-like particle formation.

Well‐defined amphiphilic poly(p‐dioxanone)‐grafted poly(vinyl alcohol) copolymers: Synthesis and micellization

AbstractA series of amphiphilic biodegradable and biocompatible poly(p‐dioxanone)‐grafted poly(vinyl alcohol) (PVA) copolymers with well‐defined structure were obtained by a three‐step synthesis based on the “grafting from” concept. The first step (protection step), called the partial silylation of PVA hydroxyl groups, was accomplished by 1,1,1,3,3,3‐hexamethyldisilazane and catalyst chlorotrimethylsilane in dimethyl sulfoxide using THF as cosolvent. The second step was the ring‐opening polymerization of p‐dioxanone (PDO) initiated from the remaining OH groups of the partially silylated PVA. Finally, a deprotection step was followed: the silylether group was deprotected easily under very mild conditions. The synthetic conditions of the first two steps were investigated, and the structures of polymers formed in each step were characterized by various analytical methods. The results showed that the molecular structure of the PVA‐g‐PPDO could be controlled easily by the degree of silylation and the feed ratio. In addition, the micellization of amphiphilic PVA‐g‐PPDO copolymers in water was proved by fluorescence spectra and dynamic light scattering, and the relationship between structural parameters of copolymers and micellar properties was studied preliminarily. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Synthesis and self-assembly of tunable thermosensitive chitosan amphiphilic copolymers by click chemistry

Amphiphilic chitosan- graft-P(2-(2-methoxyethoxy)ethyl methacrylate- co-oligo(ethylene glycol) methacrylate) (CS- g-P(MEO 2MA- co-OEGMA)) copolymers were synthesized by the “graft onto” method via click chemistry. The graft copolymers were characterized by 1H NMR and ATR FT-IR measurements. The self-assembly behavior and tunable thermosensitive properties of CS copolymers in water were investigated by TEM, DLS, and transmittance. The lower critical solution temperature (LCST) values of CS copolymer micelle solutions were tuned by altering the molar ratio of MEO 2MA and OEGMA in copolymers. Furthermore, the copolymer micelles can reversibly swell and shrink in response to external temperature. The obtained tunable thermosensitive amphiphilic CS copolymers have both the unique properties of P(MEO 2MA- co-OEGMA) and chitosan, and will have the potential applications in the biomedical field.

Hydrogen-Bonding-Induced Complexation of Polydimethylsiloxane-graft-poly(ethylene oxide) and Poly(acrylic acid)-block-polyacrylonitrile Micelles in Water

Polydimethylsiloxane-graft-poly(ethylene oxide) (PDMS-g-PEO) copolymers form micelles in water with PDMS as the core and PEO as the corona. The introduction of poly(acrylic acid)-block-polyacrylonitrile (PAA-b-PAN) block copolymers in water leads to the formation of micellar complexes due to the hydrogen bonding between carboxyl groups and ether oxygens among the PAA and PEO chains in the corona of the micelles. The effects of pH, molar ratios (r) of PAA/PEO, and the standing time on the directly mixing these two micelles in water have been investigated using laser light scattering (LLS) and transmission electron microscopy (TEM). Our results showed that the complexation between PAA and PEO in the corona was greatly enhanced at a pH below 3.5. For a fixed pH value, the interactions between these two micelles in water were governed by the value of r. At r < ∼0.6, mixing the two micelles in water resulted in a large floccule because the smaller PAA-b-PAN micelles act as physical cross-links, which are absorbed onto one PDMS-g-PEO micelle and simultaneously bonded to PEO chains on the other micelles, forming bridges and causing flocculation. At ∼0.6 < r < ∼1.2, the mixing led to stable micellar complexes with a layer of PAA-b-PAN micelles absorbed onto the initial PDMS-g-PEO micelles. At r > ∼1.2, the resultant micellar complexes first remained stable, but they precipitated from solution after a long time standing.

Hydrogen bonding-enhanced micelle assemblies for drug delivery

Ring-opening polymerization (ROP) of functionalized cyclic carbonates derived from 2,2-bis(methylol)propionic acid (bis-MPA) allows for incorporation of H-bonding urea-functional groups into block copolymers with a potential application of supramolecular drug-delivery systems. The strong H-bonding functionalities of poly(ethylene glycol)- block-poly(ethyl- random-urea carbonate) (PEG-P(E 1− x -U x )C) block copolymers not only lowered critical micelles concentration (cmc) of the block copolymer (to 1/4×) in aqueous environment compared to conventional PEG-poly(trimethylene carbonate) (PEG-PTMC) block copolymer without the non-covalent stabilization, but also improved kinetic stability of micelles and Dox-loaded micelles in the presence of a destabilizing agent. It was observed that the incorporation of anticancer drug doxorubicin affected the micellization process of block copolymers in water and caused a sudden increase in sizes of drug-loaded micelles above 200 nm. This phenomenon that can be a significant drawback in drug delivery applications was considerably mitigated in urea-bearing block copolymer/Dox micelles with simultaneously accompanying a significant improvement in drug loading. In vitro drug release profile showed that the increase in urea content led to a slight decrease in Dox release rate. Block copolymer did not have any significant cytotoxicity against HEK293 and HepG2 cells up to 400 mg/L. Importantly, Dox-loaded micelles exerted cytotoxic effect against HepG2 cells.

Biodegradability and Biocompatibility of Thermoreversible Hydrogels Formed from Mixing a Sol and a Precipitate of Block Copolymers in Water

This study examines in vitro and in vivo biodegradation and biocompatibility of a thermogelling polymeric material, which we call a mixture hydrogel. The mixture contains two ABA-type triblock copolymers poly(d,l-lactic acid-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(d,l-lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) with different block ratios, and one polymer is soluble in water, but the other is not. The aqueous solutions of some mixtures with appropriate mix ratios form hydrogels at the body temperature. The degradation of mixture hydrogels proceeded by hydrolysis of ester bonds followed by the erosion of gel in phosphate saline buffer solution at 37 degrees C for nearly one month. The mass loss and reduction of molecular weight were detected. The mix ratio was found to significantly influence the degradation profiles. The rapid in vivo gel formation was confirmed after subcutaneous injection of the thermogelling copolymer mixtures into Sprague-Dawley rats. The in vivo degradation was a bit accelerated than in vitro hydrolysis, and the persistence time of injected hydrogels in vivo was found to be tuned by mix ratio. MTT assay and histological observations were used to examine the copolymer mixtures. Both in vitro and in vivo results illustrate acceptable biocompatibility of our materials. As such, the thermosensitive hydrogel of copolymer mixture is confirmed to be a promising candidate of an injectable biomaterial for drug delivery and tissue engineering.

Self-Aggregation of Gel Forming PEG-PLA Star Block Copolymers in Water

The aggregation behavior and dynamics of poly(ethylene glycol) (PEG) and poly(lactide) (PLA) chains in a homologous series of eight-armed PEG-PLA star block copolymers ((PEG(65)-NHCO-PLA(n))(8) with n = 11, 13, and 15) in water at different concentrations and temperatures were studied by means of (1)H and (13)C NMR spectroscopy and (1)H longitudinal relaxation time analysis. The state of water in these systems was also investigated through the combined use of (1)H and (2)H longitudinal relaxation time measurement. On the basis of the NMR experimental findings and of dynamic light scattering measurements, (PEG(65)-NHCO-PLA(n))(8) in water can be described as self-aggregated systems with quite rigid hydrophobic domains made of PLA chains and aqueous domains where both PEG chains and water molecules undergo fast dynamics. A smaller number of rigid domains was found for (PEG(65)-NHCO-PLA(11))(8) with respect to the homologous copolymers with longer PLA chains. At low concentrations, the PLA domains are mainly formed by chains belonging to the same molecule, thus giving rise to unimolecular micelles. At intermediate concentrations, that is, above the critical association concentration (CAC) but below the critical gel concentration (CGC), nanogels are formed by interconnection of several PLA domains through shared unimers. Above the CGC, the network is extended to the entire system, giving rise to macroscopic gels. In all cases, a fraction of PLA chains remains quite mobile and exposed to water due to topological constraints of the star architecture.

Microphase separation in copolymers of hydrophilic PEG blocks and hydrophobic tyrosine-derived segments using simultaneous SAXS/WAXS/DSC

Hydration- and temperature-induced microphase separations were investigated by simultaneous small- and wide-angle X-ray scattering (SAXS and WAXS) and differential scanning calorimetry (DSC) in a family of copolymers in which hydrophilic poly(ethylene glycol) (PEG) blocks are inserted randomly into a hydrophobic polymer made of either desaminotyrosyl-tyrosine ethyl ester (DTE) or iodinated I2DTE segments. Iodination of the tyrosine rings in I2DTE increased the X-ray contrast between the hydrophobic and hydrophilic segments in addition to facilitating the study of the effect of iodination on microphase separation. The formation of phase-separated, hydrated PEG domains is of considerable significance as it profoundly affects the polymer properties. The copolymers of DTE (or I2DTE) and PEG are a useful model system, and the findings presented here may be applicable to other PEG-containing random copolymers. In copolymers of PEG and DTE and I2DTE, the presence of PEG depressed the glass transition temperature (Tg) of the copolymer relative to the homopolymer, poly(DTE carbonate), and the DTE/I2DTE segments hindered the crystallization of the PEG segments. In the dry state, at large PEG fractions (>70 vol%), the PEG domains self-assembled into an ordered structure with 14–18 nm distance between the domains. These domains gave rise to a SAXS peak at all temperatures in the iodinated polymers, but only above the Tg in non-iodinated polymers, due to the unexpected contrast-match between the crystalline PEG domains and the glassy DTE segments. Irrespective of whether PEG was crystalline or not, immersion of these copolymers in water resulted in the formation of hydrated PEG domains that were 10–20 nm apart. Since both water and the polymer chains must be mobile for the phase separation to occur, the PEG domains disappeared when the water froze, and reappeared as the ice began to melt. This transformation was reversible, and showed hysteresis as did the melting of ice and freezing of the water incorporated into the polymer. PEG–water complexes and PEG–water eutectics were observed in WAXS and DSC scans, respectively.

Effects of precipitate agents on temperature-responsive sol–gel transitions of PLGA–PEG–PLGA copolymers in water

This paper reports the effects of precipitate agents used in the collection of block copolymers composed of poly(lactic acid-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) on their thermogelling aqueous behaviors. We synthesized PLGA–PEG–PLGA triblock copolymers with a relatively wide distribution of molecular weight (MW) and then separated the crude polymers via three different precipitate agents (diethyl ether, hexane, or methanol). The obtained products exhibited, however, significantly different macroscopic states in water: some were sols, some were precipitates, and some underwent sol–gel transition upon heating. We found that by using different precipitate agents, ingredients of different MW were collected from the synthesized polymers, which accounted for the different states of the separated products in water. Our study strengthens the importance of an appropriate precipitate agent and reveals the subtle balance of hydrophobicity and hydrophilicity in this sort of amphiphilic block copolymers.

Sphere-to-Wormlike Network Transition of Block Copolymer Micelles Containing CdSe Quantum Dots in the Corona

Poly(styrene-b-4-vinylpyridine) (PS404-b-P4VP76, where the subscripts refer to the number-averaged degree of polymerization) forms spherical crew-cut micelles with a PS core and a P4VP corona when 2-propanol is added to a solution of the polymer in chloroform. When the CHCl3 solution also contains CdSe quantum dots, hybrid micelles form with the QDs bound to the corona. Here we report that vigorous magnetic stirring of a solution of these hybrid micelles in a solution containing 73 vol % 2-propanol leads to a morphology transformation to form three-dimensional wormlike networks that have structural features similar to that first reported by Jain and Bates [Science 2003, 300, 460−464] for a poly(butadiene-b-ethylene oxide) block copolymer in water. Under the influence of shear, PS404-b-P4VP76 micelles appear to aggregate and then rearrange to form colloidally stable networks consisting of wormlike micelles, uniform in width, that are present as loops and tails connected by T- and Y-junctions. The wormlike micelles are similar in width to the original hybrid micelles, whereas the tails of the micelles have thicker bulbous end-caps. This morphology transition is extremely sensitive to solvent composition and is also affected by the stirring rate.

Abstract 5489: The IVECT™ method, a versatile micelle for the delivery of chemotherapeutic drugs

Abstract The development of new therapeutic agents has dramatically improved the quality of life and survival rate of patients suffering from a variety of disorders. However, drug delivery innovations are required to further improve the success rate of these treatments because approximately 40% of the newly discovered, promising small molecule therapeutics have poor aqueous solubility and cannot be delivered systemically. Rationally-designed, nanoscopic drug carriers offer a promising approach to achieving these goals due to their inherent ability to overcome multiple biological barriers. Ideally, a drug delivery system will not only be stable to systemic administration, but also be versatile enough to encapsulate a diverse range of molecules leading to decreased developmental and regulatory hurdles. These goals were the driving force behind the development of Intezyne's IVECT™ Method, which is based on tri-block copolymer micelle technology; spherical nano-sized drug carriers formed by the assembly of amphiphilic block copolymers in water. This modular drug delivery platform can be tailored to accommodate a wide range of drugs, biologics or diagnostics, improve post-administration stability, vary the micelle size, control the release of the therapeutic, and target specific diseased cells based on active targeting strategies. The purpose of this study is to demonstrate encapsulation of a variety of chemotherapeutics utilizing one polymer system, and show that crosslinked micelles have improved pharmacokinetic and toxicology profiles compared to the free drugs in animal models. To this end, formulations of gemcitabine, paclitaxel, doxorubicin and SN-38 were prepared and characterized for nanoparticle size distribution by DLS and active drug weight loading by HPLC. All micelles were 30-80 nm in size with weight loadings of between 2 and 10 %. PK data from cannulated rats demonstrated significant improvement in the CMax and AUC for encapsulated crosslinked formulations, compared to the free drugs. Toxicity profiling in CD-1 mice demonstrated that the polymer alone was very safe, as an MTD was not reachable, and that the crosslinked encapsulated formulations were tolerated at significantly higher doses compared to the free drugs. In conclusion, we have demonstrated that Intezyne's IVECT™ Method is extremely versatile and results in significant improvements in the overall pharmacology of chemotherapeutics. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5489.

Local mobility and structure of cationic amphiphilic diblock copolymer micelles in aqueous solutions

The local mobility and organization of micelles formed by the cationic diblock copolymer PS-poly(N-ethyl-4-vinylpyridinium bromide) in dilute aqueous solutions is studied by spin-probe ESR spectroscopy. Micelles composed of a hydrophobic PS core and a lyophilizing polyelectrolyte corona are prepared by two methods: dialysis from a nonselective solvent and direct dispersion of the diblock copolymer in water under long-term heating. Velocity-sedimentation studies and static and dynamic light-scattering measurements show that the micelles obtained by dialysis have smaller mean hydrodynamic sizes and weight-average molecular masses and are less polydisperse than micelles prepared by direct dispersion. The ESR spectra of spin probes localized in micelles of both types are found to be identical. This finding suggests that their local structure is independent of the dispersion procedure and molecular-mass characteristics. Probes are localized in the outer layer of the PS core near the core/shell boundary, and their local mobility is a factor of ∼2 higher than the local mobility of probes in the phase of the solid PS. It is inferred that the structure of the outer layer of the PS core in micelles is looser than the structure of PS in the solid phase. The localization sites of spin probes are partially penetrated by water.

Preparation of a Thermoresponsive Lignin-Based Biomaterial through Atom Transfer Radical Polymerization

Copolymerization of N-isopropylacrylamide (NIPAM) with technical hardwood kraft lignin (HWKL) was achieved by atom transfer radical polymerization (ATRP) using a selectively modified lignin-based macroinitiator. The degree of polymerization (DP) of polyNIPAM graft side chains was affected by varying the ratio of the DMF/water solvent system from 5:0 to 0:5, and an estimated DP(NIPAM) of >40 was obtained using a ratio of 1:4 (v/v). The thermal decomposition temperature of the lignin-g-polyNIPAM copolymers significantly increased with increasing DP(NIPAM). Likewise, the solubility of the lignin-g-polyNIPAM copolymers in water changed depending on copolymer structure. In both the water-soluble and suspended copolymers, at temperatures above 32 degrees C, the g-polyNIPAM component underwent the typical hydrophilic-to-hydrophobic transition, resulting in the precipitation of the copolymer.

Effect of Hydrophilic Block-A Length Tuning on the Aggregation Behavior of α,ω-Perfluoroalkyl End-Capped ABA Triblock Copolymers in Water

The tremendous influence of hydrophilic block length tuning on the aggregation behavior of novel water-soluble triphilic (i.e., hydrophilic, lipophilic, and fluorophilic) α,ω-perfluoroalkyl end-capped symmetric ABA triblock copolymers is demonstrated. The hydrophilic A and lipophilic B blocks are comprised of poly(glycerol monomethacrylate) (PGMA) and poly(propylene oxide) (PPO), respectively. The fluorophilic component consists of two “clicked” perfluoroalkyl segments (C9F19) at the ends of the block copolymers. Two of the different block copolymers synthesized, namely F9-PGMA24-PPO27-PGMA24-F9 (PB1) and F9-PGMA42-PPO27-PGMA42-F9 (PB2), differ only in the degree of polymerization of the hydrophilic PGMA blocks. Their critical micelle concentrations in water are determined from surface tension measurements. The aggregation behavior in aqueous medium studied by 19F NMR spectroscopy reveals that the fluorocarbon component forms part of the micelle corona of PB1, while in PB2 it aggregates to form part of the core. Furthermore, the aggregation behavior studied in aqueous medium by temperature-dependent 1H NMR spectroscopy and DLS measurements showed that PB1 forms only spherical micelles with hydrodynamic radius, Rh, of ∼18 nm in solution at all temperatures while PB2 forms mainly aggregate of micelles with Rh of 40 nm at 25 °C. The aggregates disintegrate into compact single “flowerlike” micelles with Rh of ∼17 nm at high temperatures. AFM and TEM investigations of the structures formed on solid supports after solvent evaporation also confirm the aggregation behavior of the two block copolymers. The marked difference in the aggregation behavior is a result of the inability of the shorter PGMA blocks of PB1 to loop during micellization and is explained based on random coil statistics.