Influencing the phase transition temperature of poly(methoxy diethylene glycol acrylate) by molar mass,end groups,and polymer architecture

The easily accessible, but virtually overlooked monomer methoxy diethylene glycol acrylate was polymerized by the RAFT method using monofunctional, difunctional, and trifunctional trithiocarbonates to afford thermoresponsive polymers exhibiting lower critical solution temperature‐type phase transitions in aqueous solution. The use of the appropriate RAFT agent allowed for the preparation and systematic variation of polymers with defined molar mass, end‐groups, and architecture, including amphiphilic diblock, symmetrical triblock, and triarm star‐block copolymers, containing polystyrene as permanently hydrophobic constituent. The cloud points (CPs) of the various polymers proved to be sensitive to all varied parameters, namely molar mass, nature, and number of the end‐groups, and the architecture, up to relatively high molar masses. Thus, CPs of the polymers can be adjusted within the physiological interesting range of 20–40 °C. Remarkably, CPs increased with the molar mass, even when hydrophilic end groups were attached to the polymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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

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

Crystallization of poly(diethylene glycol terephthalate)

The crystallization of a low molecular weight fraction of poly(diethylene glycol terephthalate) (PDET) was studied from the melt and from benzene, ethyl acetate and chlorobenzene. From the melt, crystallization does not occur, irrespective of the crystallization temperature. When PDET is crystallized from solutions in the three solvents, by isothermal growth at temperatures from 10 to 30°, crystals are obtained in the concentration range examined. Crystals were investigated by X-ray diffraction and by differential scanning calorimetry in order to measure the crystallinity, the melting points, glass transition and melting depression of mixtures of the polymer with solvents. Prior to crystallization, at given undercoolings and sufficient concentrations, gelation occurs due to microstructural heterogeneity.     

Thermoresponsive amphiphilic symmetrical triblock copolymers with a hydrophilic middle block made of poly(N-isopropylacrylamide): synthesis, self-organization, and hydrogel formation

Several series of symmetrical triblock copolymers were synthesized by the reversible addition fragmentation chain transfer method. They consist of a long block of poly(N-isopropylacrylamide) as hydrophilic, thermoresponsive middle block, which is end-capped by two small strongly hydrophobic blocks made from five different vinyl polymers. The association of the amphiphilic polymers was studied in dilute and concentrated aqueous solution. The polymer micelles found at low concentrations form hydrogels at high concentrations, typically above 30–35 wt.%. Hydrogel formation and the thermosensitive rheological behavior were studied exemplarily for copolymers with hydrophobic blocks of polystyrene, poly(2-ethylhexyl acrylate), and poly(n-octadecyl acrylate). All systems exhibited a cloud point around 30 °C. Heating beyond the cloud point initially favors hydrogel formation but continued heating results in macroscopic phase separation. The rheological behavior suggests that the copolymers associate into flower-like micelles, with only a small share of polymers that bridge the micelles and act as physical cross-linkers, even at high concentrations.     

Surface modification of polyethersulfone membranes by blending triblock copolymers of methoxyl poly(ethylene glycol)-polyurethane-methoxyl poly(ethylene glycol)

The surface of polyethersulfone (PES) membrane was modified by blending triblock copolymers of methoxyl poly(ethylene glycol)-polyurethane-methoxyl poly(ethylene glycol) (mPEG-PU-mPEG), which were synthesized through solution polymerization with mPEG Mns of 500 and 2000, respectively. The PES and PES/mPEG-PU-mPEG blended membranes were prepared through spin coating coupled with liquid-liquid phase separation. FTIR and (1)H NMR analysis confirmed that the triblock copolymers were successfully synthesized. The functional groups and morphologies of the membranes were studied by ATR-FTIR and SEM, respectively. It was found that the triblock copolymers were blended into PES membranes successfully, and the morphologies of the blended membranes were somewhat different from PES membrane. The water contact angles and platelet adhesion were decreased after blending mPEG-PU-mPEG into PES membranes. Meanwhile, the activated partial thromboplastin time (APTT) for the blended membranes increased. The anti-protein-fouling property and permeation property of the blended membranes improved obviously. SEM observation and 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay proved the surfaces of the blended membranes promoted human hepatocytes adhesion and proliferation better than PES membrane.     

Photocrosslinked hydrogels based on copolymers of poly(ethylene glycol) and lysine

A group of new, water-soluble poly(ether-urethane)s, derived from poly(ethylene glycol) and the amino acid L -lysine, provide pendent carboxylic acid groups along the polymer backbone at regular intervals. The carboxylic acid groups were utilized for the attachment of acrylate and methacrylate pendent chains (hydroxyethyl acrylate, hydroxyethyl methacrylate, aminoethyl methacrylate, and aminoethyl methacrylamide), leading to functionalized polymers. The pendent chains were attached via ester and/or amide bonds having different degrees of hydrolytic stability. The attachment reactions proceeded with high yields (up to 95%). The functionalized polymers were subsequently photopolymerized (UV irradiation) to obtain crosslinked hydrogels. Crosslinked membranes with the highest degree of mechanical strength were obtained when the crosslinking reaction was performed in dioxane with benzoin methyl ether (0.1 wt %) as the initiator. the crystallinity, thermomechanical properties, and hydrolytic stability of the crosslinked membranes were studied. All membranes were transparent and highly swellable (equilibrium water content: 64–88%). The tensile strength in the swollen state ranged from 0.15 to 1.09 MPa. Under physiological conditions (phosphate buffered water, 0.1M, pH 7.4, 37°C) the hydrolytic stability of the hydrogels varied depending on the bonds used in the attachment of the acrylate pendent chains: Hydrogels with hydroxyethyl acrylate pendent chains dissolved within 30 days, while hydrogels containing aminoethyl methacrylamide pendent chains remained unchanged throughout a 30 day period. Using high molecular weight FITC-dextrans as model compounds, complete release from the swollen hydrogels required between 60 and 150 h. Overall, the evaluation of poly(ethylene glycol)-lysine derived, photocrosslinked hydrogels indicated that these materials provide a range of potentially useful properties. © 1994 John Wiley & Sons, Inc.     

Thermoresponsive poly(N-isopropylacrylamide) nanogels/poly(acrylamide) nanostructured hydrogels

Here we report the preparation and characterization of nanostructured thermo-responsive poly(acrylamide) (PAM)-based hydrogels. The addition of slightly crosslinked poly(N-isopropylacrylamide) (PNIPA) nanogels to AM reactive aqueous solution produces nanostructured hydrogels that exhibit a volume phase transition temperature (T_VPT). Their swelling kinetics, T_VPT's and mechanical properties at the equilibrium-swollen state (H_eq) are investigated as a function of the concentration of PNIPA nanogels in the nanostructured hydrogels. Nanostructured hydrogels with PNIPA nanogels/AM mass ratios of 20/80 and above exhibit higher H_eq and longer time to reach the equilibrium swelling than those of the conventional PAM hydrogels. However, the PNIPA nanogels possess thermo-responsive character missing in conventional PAM hydrogels. The T_VPT of nanostructured hydrogels depends on PNIPA nanogel content but their elastic and Young moduli are larger than those of conventional hydrogels at similar swelling ratios. Swelling kinetics, T_VPT, and mechanical properties are explained in terms of the controlled in-homogeneities introduced by the PNIPA nanogels during the polymerization.     

Synthesis and characterization of a novel methoxy poly(ethylene glycol)-Tat peptide-chitosan copolymers

In this paper, a novel chitosan-g-(-O-methyl poly (ethylene glycol))-g-(-N-Tat peptide) (CS-mPEG-Tat) copolymer was synthesized. The synthesized intermediates and final products were characterized and confirmed by Fourier transform infrared spectrum, ¹H nuclear magnetic resonance spectrum, and X-ray diffraction, respectively. The particle sizes, size distributions, and zeta potentials can also be determined by dynamic light scattering. Agarose gel electrophoresis study showed effective DNA-binding ability of CS-mPEG-Tat. In vitro cytotoxicity assay indicated that CS-mPEG-Tat copolymers were low toxic and cell compatible as the polymer concentration was smaller than 5 mg/ml. This work provides a facile approach to prepare biocompatible PEG-peptide-chitosan copolymer nanoparticles with controllable performances. In conclusion, the obtained CS-mPEG-Tat copolymer might be attractive cationic polymers for nonviral gene therapy.     

Interpolymer complexes of copolymers of vinyl ether of diethylene glycol with poly(acrylic acid)

 The complex formation reactions of poly(vinyl ether of diethylene glycol) as well as vinyl ether of diethylene glycol–vinyl butyl ether copolymers with poly(acrylic acid) have been studied in aqueous and alcohol solutions. The formation of interpolymer complexes which were stabilized by hydrogen bonds was shown. The effects of molecular weight of poly(acrylic acid) and the nature of the nonionic polymer on the composition and stability of interpolymer complexes were clarified. The critical pH values of complexation were determined for different systems with various molecular weights and hydrophobic–hydrophilic balances. The stability of the interpolymer complexes formed in aqueous and alcohol solutions with respect to dimethylformamide addition was evaluated. The role of hydrophobic interactions and the presence of active groups on stability of the interpolymer complexes is discussed. Received: 23 July 2001 Accepted: 27 September 2001     

Thermoresponsive star triblock copolymers by combination of ROP and ATRP: From micelles to hydrogels

Novel biocompatible, biodegradable, four‐arm star, triblock copolymers containing a hydrophobic poly(ε‐caprolactone) (PCL) segment, a hydrophilic poly(oligo(ethylene oxide)475 methacrylate) (POEOMA475) segment and a thermoresponsive poly(di(ethylene oxide) methyl ether methacrylate) (PMEO₂MA) segment were synthesized by a combination of controlled ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). First, a four‐arm PCL macroinitiator [(PCL‐Br)₄] for ATRP was synthesized by the ROP of ε‐caprolactone (CL) catalyzed by stannous octoate in the presence of pentaerythritol as the tetrafunctional initiator followed by esterification with 2‐bromoisobutyryl bromide. Then, sequential ATRP of oligo(ethylene oxide) methacrylate (OEOMA475, M_n = 475) and di(ethylene oxide) methyl ether methacrylate) (MEO₂MA) were carried out using the (PCL‐Br)₄ tetrafunctional macroinitiator, in different sequence, resulting in preparation of (PCL‐b‐POEOMA475‐b‐PMEO₂MA)₄ and (PCL‐b‐PMEO₂MA‐b‐POEOMA475)₄ star triblock copolymers. These amphiphilic copolymers can self‐assemble into spherical micelles in aqueous solution at room temperature. The thermal responses of the polymeric micelles were investigated by dynamic light scattering and ultraviolet spectrometer. The properties of the two series of copolymers are quite different and depend on the sequence distribution of each block along the arms of the star. The (PCL‐b‐POEOMA475‐b‐PMEO₂MA)₄ star copolymer, with the thermoresponsive PMEO₂MA segment on the periphery, can undergo reversible sol‐gel transitions between room temperature (22 °C) and human body temperature (37 °C). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Imparting antifouling properties of poly(2-hydroxyethyl methacrylate) hydrogels by grafting poly(oligoethylene glycol methyl ether acrylate)

The antifouling properties of poly(2-hydroxyethyl methacrylate- co-methyl methacrylate) hydrogels were improved by the surface grafting of a brush of poly(oligoethylene glycol methyl ether acrylate) [poly(OEGA)]. The atom-transfer radical polymerization (ATRP) of OEGA (degree of polymerization = 8) was initiated from the preactivated surface of the hydrogel under mild conditions, thus in water at 25 degrees C. The catalytic system was optimized on the basis of two ligands [1,1,4,7,10,10-hexamethyl-triethylenetetramine (HMTETA) or tris[2-(dimethylamino)ethyl]amine (Me6TREN)] and two copper salts (CuIBr or CuICl). Faster polymerization was observed for the Me 6TREN/CuIBr combination. The chemical composition and morphology of the coated surface were analyzed by X-ray photoelectron spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy, contact angle measurements by the water droplet and captive bubble methods, scanning electron microscopy, and environmental scanning electron microscopy. The hydrophilicity of the surface increased with the molar mass of the grafted poly(OEGA) chains, and the surface modifications were reported in parallel. The antifouling properties of the coatings were tested by in vitro protein adsorption and cell adhesion tests, with green fluorescent protein, beta-lactamase, and lens epithelial cells, as model proteins and model cells, respectively. The grafted poly(OEGA) brush decreased the nonspecific protein adsorption and imparted high cell repellency to the hydrogel surface.     

Synthesis of poly(propylene glycol)-block-polyethylenimine triblock copolymers for the delivery of nucleic acids

LPEIs, which are efficient DNA transfection agents, were found to be far less effective for the delivery of siRNAs. Here, two amphiphilic triblock copolymers LPEI(50) -b-PPG(36) -b-LPEI(50) (2) and LPEI(14) -b-PPG(68) -b-LPEI(14) (4) have been synthesized. The transfection assays showed that compound 2 was efficient for DNA transfection whilst it was almost inactive for siRNA delivery. In contrast, polymer 4 was inefficient for DNA transfection while it showed capabilities for siRNA delivery. Taken together, our results indicate that the properties required for DNA and siRNA delivery are different. Moreover, we show that introduction of a hydrophobic segment that allows self-assembly confers siRNA delivery capacities.     

Thermoresponsive behavior of poly(n-isopropylacrylamide) hydrogels containing gold nanostructures

We report the changes in the structure and thermoresponsive behavior of poly(N-isopropylacrylamide) (PNIPAm) hydrogels when gold nanostructures are synthesized in situ within the hydrogel matrix. Cross-linked PNIPAm hydrogels were synthesized using NIPAm and 0.00-3.50% (w/w versus NIPAm) of N,N'-methylenebisacrylamide (MBAm) and/or N,N'-cystaminebisacrylamide (CBAm) as cross-linking agents. The hydrogels were soaked in potassium tetrachloroaurate to introduce gold ions. The hydrogels containing Au3+ were then immersed in a sodium borohydride solution to reduce the gold ions. Infrared spectroscopy, UV-visible spectroscopy, and equilibrium swelling were used to examine the structural/physical differences between gels of different compositions; UV-visible spectroscopy and mass measurements were used to observe the kinetics and thermodynamics of the hydrogel volume phase transition. These studies revealed several differences in the physical characteristics and thermoresponsive behavior of hydrogels based on cross-linker identity and the presence or absence of gold nanostructures. Hydrogels with gold nanostructures and high CBAm and low MBAm content have equilibrium swelling masses 3-20 times their native analogues. In comparison, gold-containing hydrogels with high MBAm and low CBAm content have swelling masses that are equal to their native analogues. Additionally, the gold-containing PNIPAm hydrogels cross-linked with only CBAm have a deswelling temperature of approximately 40 degrees C, approximately 8 degrees C above the samples cross-linked with only MBAm. Varying the CBAm content and introducing gold enables tuning of the deswelling temperature.     

Synthesis and micellar characterization of short block length methoxy poly(ethylene glycol)-block-poly(caprolactone) diblock copolymers

A series of short block length methoxy poly(ethylene glycol)-block-poly(caprolactone) diblock copolymers was synthesized and characterized in order to assess the potential of these copolymers as a micellar drug-delivery system. Varying the caprolactone:MePEG weight ratio in the reaction mixture allowed the synthesis of diblock copolymers with a MePEG molecular weight of 750 g/mol and PCL block lengths of 2, 5 or 10 repeat units. Phase diagrams of aqueous solutions of the copolymers were constructed which displayed characteristic cloud points and Krafft points. As the degree of polymerization of PCL increased, critical micelle concentration (CMC) values decreased from 6.97 x 10(-1) to 3.38 x 10(-3) g/l, partition equilibrium coefficients (Kv) increased from 1.09 x 10(4) to 22.2 x 10(4),and hydrodynamic diameters increased from 12.2 to 19.5 nm. The micelle morphology was determined to be spherical by transmission electron microscopy.     

Thermoresponsive nanostructured poly(N-isopropylacrylamide) hydrogels made via inverse microemulsion polymerization

The synthesis of nanostructured poly(N-isopropylacrylamide) (polyNIPA) hydrogels by a two-stage polymerization process is reported here. The process involves the synthesis of slightly crosslinked polyNIPA nanoparticles by inverse (w/o) microemulsion polymerization; then, these particles are dried, cleaned and dispersed in an aqueous solution of NIPA and a crosslinking agent (N,N-methylene-bis-acrylamide or NMBA) and polymerized to produce the nanostructured hydrogels. Their swelling and de-swelling kinetics, volume phase transition temperatures (T _VPT) and mechanical properties at the equilibrium swollen state are investigated as a function of the weight ratio of polyNIPA particles to monomer (NIPA). The nanostructured gels exhibit larger equilibrium water uptake, faster swelling and de-swelling rates and similar T _VPT than those of the conventional ones; moreover, the elastic and Young moduli are larger than those of the conventional hydrogels at similar swelling ratios. The fast swelling and de-swelling kinetics are explained in terms of the controlled inhomogeneities introduced by the method of synthesis.     

Small-angle neutron scattering study of poly(methyl methacrylate-block-sodium acrylate-block-methyl methacrylate) and poly(sodium acrylate-block-methyl methacrylate-block-sodium acrylate) triblock copolymers in aqueous solutions

 Small-angle neutron scattering experiments were made on poly(methyl methacrylate-block-sodium acrylate-block-methyl methacrylate) [p(MMA-b-NaA-b-MMA)] and p(NaA-b-MMA-b-NaA) solutions by varying the composition and the concentration of the polymer with and without 1 M NaCl added. Scattering curves could be evaluated by assuming that the polymers aggregate into polydisperse micelles. The experiments support the expectation that in the case of the p(MMA-b-NaA-b-MMA) block sequence the hydrophilic blocks form closed loops connected by both ends to the micellar cores; in the case of the p(NaA-b-MMA-b-NaA) block sequence they float freely in the solvent. The micellar cores exert considerable stability against dilution and added electrolyte. The interaction of charged micelles could be formally described in terms of volume exclusion and the Derjaguin–Landau–Verwey–Overbeek potential. Received: 20 December 2000 Accepted: 18 August 2001     

Modification of capillary electrophoresis capillaries by poly(hydroxyethyl methacrylate), poly(diethylene glycol monomethacrylate) and poly(triethylene glycol monomethacrylate)

Modification of capillary electrophoresis (CE) capillaries by poly(hydroxyethyl methacrylate) (poly(HEMA), poly(diethylene glycol monomethacrylate) (poly(DEGMA) and poly(triethylene glycol monomethacrylate) (poly(TEGMA), was studied. Methods based on physical adsorption of the modifier and on its chemical binding were compared on the basis of the electroosmotic flow (EOF) reproducibility, the EOF dependence on the pH, the symmetry of the peak of positively charged tyramine, the stability of the coating and the separation of standard and milk proteins in the modified capillaries. Reproducible coatings were obtained by chemical binding of the polymers to the capillary walls and by coating with a solution of a polymer, as also demonstrated by the atomic force microscopy.     

Thermoresponsive poly(poly(ethylene glycol) methylacrylate)s grafted cellulose nanocrystals through SI-ATRP polymerization

We report a series of thermoresponsive cellulose nanocrystals (CNCs) decorated with poly(poly(ethylene glycol) methylacrylate) copolymers (poly(PEGMA)-g-CNCs) synthesized by surface initiated-atom transfer radical polymerization (SI-ATRP). The chemical structures and surface morphologies were subsequently confirmed by FT-IR, XPS, and AFM measurements. With regard to thermally responsive behavior, poly(PEGMA)-g-CNCs show tunable lower critical solution temperature (LCST) values in the range of 34–66 °C by varying the feeding ratios of comonomers. The reversible morphological transformation from individual nano-rod structures to larger globule aggregates was further verified by AFM during the LCST transition. These functionalized CNCs have potential as smart film filters and biosensors.     

Methoxy poly(ethylene glycol)‐b‐poly(octadecanoic anhydride)‐b‐methoxy poly(ethylene glycol) amphiphilic triblock copolymer nanoparticles as delivery vehicles for paclitaxel

A series of amphiphilic triblock copolymers, methoxy poly(ethylene glycol)‐b‐poly(octadecanoic anhydride)‐b‐methoxy poly(ethylene glycol) (mPEG‐b‐POA‐b‐mPEG), were prepared via melt polycondensation of methoxy poly(ethylene glycol) (mPEG) and poly(octadecanoic anhydride) (POA). mPEG‐b‐POA‐b‐mPEG were characterized by FTIR, ¹H‐NMR, GPC, DSC, and XRD. Drug‐loaded mPEG‐b‐POA‐b‐mPEG nanoparticles (NPs) with spherical morphology and narrow size polydispersity index were prepared by nanoprecipitation technique with paclitaxel as the model drug. In vitro release behaviors of drug‐loaded NPs present that the biphasic process and the release mechanism of each phase are zero order drug releases. According to this study, mPEG‐b‐POA‐b‐mPEG NPs could serve as suitable delivery agents for paclitaxel and other hydrophobic drugs. Copyright © 2009 John Wiley & Sons, Ltd.