Thermoresponsive poly(oligo ethylene glycol acrylates)

Thermoresponsive polymers have been the subject of numerous publications and research topics in the last few decades mostly driven by their easily controllable temperature stimulus and high potential for in vitro and in vivo applications. P(NIPAAm) is the most studied amongst these polymers, but recently other types of polymers are increasingly being investigated for their thermoresponsive behavior. In particular, polymers bearing a short oligo ethylene glycol (OEG) side chain have been shown to combine the biocompatibility of polyethylene glycol (PEG) with a versatile and controllable LCST behavior. These polymers can be synthesized via controlled radical polymerization techniques from various monomers consisting of an OEG chain and a polymerizable group like a (meth)acrylate, styrene or acrylamide. OEG acrylates offer significant advantages over, e.g., OEG methacrylates as the lower hydrophilicity of the backbone facilitates thermoresponsive behavior with smaller, more defined side chains. Furthermore, PEG acrylates can be polymerized using all major controlled radical polymerization techniques, unlike OEG methacrylates. This review will focus on OEG acrylate based (co)polymers and will provide a comprehensive overview of their reported thermoresponsive properties. The combination and comparison of this data will not only highlight the potential of these monomers, but will also serve as a starting point for future studies.     

Poly(styrene)s with oligo(ethylene oxide) side chains as ionic conducting matrices

Summary Solid phase ion conductors have been the object of studies during the last years for their potential use as conducting polymer matrices in electrochromic devices, sensors, photovoltaic and dry batteries. Comb polymers of poly(styrene) with oligo(ethylene oxide) side chains were investigated. They show reasonable conductivity of about 10^–7–10^–5 siemens/cm at ambient temperature and lithiumperchlorate as salt electrolyte. A dependence of the conductivity from the side chain length and the amount of added salt was found.     

Poly(styrene)s with oligo(ethylene oxide) side chains as catalysts for phase transfer reactions

Summary A very interesting part within the wide field of chemical reactions are-catalyzed reactions. To find an effective low cost catalyst for various applications is a primary goal of many workers. Polymer chemistry is able to provide systems with qualities not known for monomeric catalysts. Especially in heterogenic systems the use of polymeric catalysts has many advantages such as easy separation for reuse or low toxicity. A special type of heterogenic catalysis is the phase transfer catalysis. Comb polymers of poly(styrene) with oligo(ethylene oxide) side chains were investigated for their ability as phase transfer catalysts.     

Solid polymer electrolytes based on oligo(ethylene glycol)methacrylates

Summary Complexes of LiCF₃SO₃ and a polymer obtained by polymerization of triethylene glycol dimethacrylate (TRGDMA) and its copolymerization with acrylonitrile (AN) at molar ratios of 0.67, 2.0 and 4.0, both in the presence of poly(ethylene glycol) dimethylether as a plasticizer, provides a.c.conductivities in the range between 10^-5 and 10^-4 S/cm at ambient temperature. An increase of conductivities has been found at growing ratios of [AN]:[TRGDMA] from 0 to 2.0 and molar ratios of ethylene oxide (EO) units: LiCF₃SO₃ ranging from 12 to about 26. The conductivity is nearly independent on the content of AN at [EO]:[Li⁺]=52.The temperature-dependence of the conductivity shows an Arrhenius-type behaviour when the content of the salt and/or acrylonitrile in the network was high.     

Synthesis of polycarbonate urethanes with functional poly(ethylene glycol) side chains intended for bioconjugates

Traditional poly(ethylene glycol) (PEG)-modified polyurethanes usually exhibit high biocompatibility, but still lack reactivity with biological molecules to induce appropriate cell and tissue responses. In this study, PEG diglycidyl ether (M_n = 526 Da) and PEG bis(amine) (M_n = 1000 Da) were respectively grafted onto carboxyl-group-containing poly(carbonate urethane) backbones that chain-extended with lysine, to generate reactivity while maintaining biocompatibility. The PEG chains disordered and plasticized the hard segments where they attached, reducing H-bonded urea groups and lowering glass transition temperatures. The M_n ranged from 33,000 to 70,000 Da for the precursor polyurethanes, which largely decreased by 24–75% following PEG grafting. Hemocompatibility was enhanced due to the flexibility and hydrophilicity of the PEG chains. Solutions of the PEG-grafted polyurethanes were transformed into hydrocolloids when dropped into water. Reactivity was proved by immobilization of albumin onto the colloidal particles. These new functional PEG-grafted polyurethanes can potentially form multifunctional bioconjugates for applications as biomaterials and in pharmaceutics.     

Synthesis and characterization of amphiphilic graft copolymers with poly(ethylene glycol) and cholesterol side chains

Amphiphilic graft copolymers comprising monomeric units of methoxy poly(ethylene glycol) (mPEG)-acrylate, 2-hydroxyethyl methacrylate (HEMA)–cholesterol conjugates and HEMA were synthesized and their properties characterized. The value of the critical micelle concentration (CMC) for these copolymers is linearly proportional to the ratio of the number of mPEG–acrylates to that of the HEMA–cholesterol conjugates per macromolecule (N_PEG/N_c), which is the most important parameter which influences the formation of polymeric micelles. The latter show excellent colloidal stability and their sizes decrease with increasing CMC. Based on the quenching of pyrene fluorescence, the relatively high levels of the loading capacity of pyrene are attributed to the elevated hydrophobicity of the micelle core. The loading capacity of pyrene decreases with increasing CMC. The weight-average partition coefficient for pyrene in polymeric micelles increases with increasing polymer concentration because more micelles are available for accommodating pyrene. Copyright © 2004 Society of Chemical Industry     

Conformation of oligo(ethylene glycol) grafted polystyrene in dilute aqueous solutions

Temperature induced conformational changes of poly(p-oligo(ethylene glycol) styrene) (POEGS) in aqueous solutions were investigated by small angle neutron scattering (SANS), neutron transmission and dynamic light scattering (DLS). The molecular weight of the polymer studied was 9400 g/mol with a polydispersity index of 1.18 and each repeat unit of the polymer had four ethylene glycol monomer segments. The polymer was water soluble due to the hydrophilicity of the OEG side chains and these solutions showed lower critical solution temperature (LCST) depending on the concentration of the polymer. Measurements of solution behavior were made as a function of temperature in the range of 25-55 °C for three polymer concentrations (0.1 wt%, 0.3 wt%, and 1.8 wt%). Neutron transmission measurements were used to monitor the amount of polymer which precipitated or remained in solution above the cloud point temperature (T_CP). DLS revealed the presence of large clusters in all solutions both below and above T_CP while SANS provided information on the structure and interactions between individual chains. It was found that in the homogeneous region below T_CP the shape of individual polymers in solution was close to ellipsoidal with the dimensions R_a = 37 Å and R_b = 14 Å and was virtually independent of temperature. The SANS data taken for the most concentrated solution studied (1.8 wt%) were fit to the ellipsoidal model with attractive interactions which were approximated by the Ornstein-Zernike function with a temperature-dependent correlation length in the range of 24-49 Å. The collapse of individual polymers to spherical globules with the radius of 15 Å above T_CP was observed.     

New degradable polyesters from deoxycholic acid and oligo(ethylene glycol)s

A new class of polyesters was prepared by polycondensation of a bile acid, deoxycholic acid, and an oligo(ethylene glycol) (OEG) with molar mass ranging from 100 to 1500. The chemical structure and composition of the polyesters were confirmed by ¹H‐NMR, Fourier transform infrared spectroscopy and HPLC analysis. Polyester molar masses measured by gel permeation chromatography were between 5000 and 20 000. Thermal stability and glass transition temperature decreased with increasing length of OEG. Hydrolytic degradation was also enhanced by the presence of longer chain OEG. Polyesters obtained from OEG with molar mass ≥ 1000 were water soluble, semicrystalline and thermosensitive. As a function of the OEG length used for their preparation, the new polyesters can be useful for biomedical or industrial applications. © 2012 Society of Chemical Industry     

Amphiphilic polysilane with poly(ethylene oxide) side chains

The synthesis of an amphiphilic polysilane with poly(ethylene oxide) grafted segments (PS-g-PEO) through the addition of an allyl-terminated poly(ethylene oxide) (AT-PEO) to poly[diphenylsilane-co-methyl(H) silane] (PSH) in a homogeneous system and using catalyst platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane is reported The process involves the activation of the polymer by microwave irradiation as a preliminary stage with the view to perform the subsequent addition stage at room temperature, when side reactions are prevented. The PS-g-PEO structure was characterized by NMR, FT-IR spectral analysis and GPC methods. The amphiphilic properties were estimated by comparison of the water sorption isotherms of the PS-g-PEO copolymer with those of the component segments. The core-shell micellization in water and the morphological aspects of the self-assembled structures were investigated by DLS and SEM. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Engineering oligo(ethylene glycol)-based thermosensitive microgels for drug delivery applications

Novel oligo(ethylene glycol)-based thermosensitive microgels with well engineered core-shell structures were developed for storage and delivery of chemotherapeutic agents. The core is consisted of hydrophobic poly[2-(2-methoxyethoxy)ethyl methacrylate], while the shell is consisted of hydrophilic copolymer of 2-(2-methoxyethoxy)ethyl methacrylate with oligo(ethylene glycol) methyl ether methacrylates. These core-shell microgels exhibit tunable volume phase transition temperature and excellent colloidal stability across the physiologically important temperature range. The thickness of the hydrophilic shell can control the collapsing degree (or mesh size) of the hydrophobic core network, which can be utilized to significantly increase the loading capacity of the model hydrophobic drugs dipyridamole by tailoring the shell thickness of microgels. While the microgels are nontoxic, the drug molecules released from the microgels remain active to kill the cancer cells. The presented results provide important guidelines for the rational design of core-shell structured polymeric microgels for drug uptake and release applications.     

Synthesis of amphiphilic (meth)acrylates with oligo(ethylene glycol) and (or) oligo(propylene glycol) blocks by the esterification of (meth)acrylic acid

Thermoresponsive PEG-based (PEG stands polyethylene glycol) polymers are unique for use in medicine because of their low toxicity, good biocompatibility and biodegradability, but usually more hydrophobic and more toxic comonomers are used to adjust lower critical solution temperature (LCST). A convenient way to overcome this problem and to finely tune LCST is to use alkoxy oligo(ethylene glycol)- or alkoxy oligo(propylene glycol) (meth)acrylates as starting comonomers. Here we report on the conditions for the simple and affordable synthesis of methoxy oligo(propylene glycol) (meth)acrylate- and methoxy oligo(propylene glycol)-block-oligo(ethylene glycol) (meth)acrylate-based macromonomers with high yields (80%–98.7%) by the acid-catalyzed esterification of (meth)acrylic acid with alkoxy oligo(alkylene glycols) containing oligo(ethylene glycol) (OEG) and/or oligo(propylene glycol) (OPG) blocks. p-Toluene sulphonic acid (pTSA), alkyl(C₁₂–C₁₄)benzene sulfonic acid (ABSA) and H₂SO₄ were used as catalysts. It has been shown that pTSA and ABSA are practically the same in catalytic activity and are superior to sulfuric acid. The reaction orders with respect to catalyst was found to be close to 1 in all cases. It has been shown that the reaction is actually insensitive to the lengths of OEG and OPG blocks, as well as to the structure of the terminal alkyl group, while the esterification of acrylic acid (AA) proceeds much faster compared to methacrylic acid (MAA) one under the same conditions. The influence of temperature on the equilibrium conversions of alcohols was determined, which were found to be 89%–93% for the esterification of AA and 61%–86% for MAA in the temperature range of 60–120°C. A further increase in conversion was achieved by introducing an azeotropic agent (toluene), its optimal concentration was found to be 10%–15%.     

Swelling behaviour of hydrogels from methacrylic acid and poly(ethylene glycol) side chains by magnetic resonance imaging

The swelling behaviour of hydrogels of methacrylic acid and poly(ethylene glycol) monomethyl ether monomethacrylate macromonomer, P[(MAA)‐co‐(PEGMEMA)], copolymers was investigated. Under pH 7, characteristic sigmoidal swelling appears depending on composition. This anomalous swelling phenomenon is related to the ability of moieties in the comonomeric units ? COOH and ? [? O? CH₂? CH₂? ]? to form complexes by hydrogen bonding, stabilized by hydrophobic interactions. The swelling was followed using magnetic resonance imaging (MRI) providing spatial and temporal resolution. Data from MRI are compared with gravimetric results and photographs during swelling. In the MRI images two processes were distinguished, corresponding to a swollen external region in contrast to a rigid core which starts to swell after a lag time depending on sample composition. Microscopic and macroscopic results are in good agreement. Copyright © 2007 Society of Chemical Industry     

Synthesis and performance of methacrylic ester based polycarboxylate superplasticizers possessing hydroxy terminated poly(ethylene glycol) side chains

The synthesis and performance of new methacrylate ester based polycarboxylate superplasticizers is shown. These new superplasticizers possess hydroxy termination of the poly(ethylene glycol) side chains instead of conventional methoxy termination. Properties of the new superplasticizers in cement paste were compared to those of conventional ones. For this comparison, methacrylic acid-poly(ethylene glycol) methacrylate ester copolymers having three different side chain lengths and either hydroxyl or methoxy terminated graft chains were synthesized. For characterization of the superplasticizers, gel permeation chromatography (GPC) as well as anionic charge density determination was carried out. The performance of the polymers in cement was tested by measuring paste flow, adsorption as well as zeta potential. Additionally, retardation of the copolymers possessing side chains of 45 ethylene oxide units was investigated by heat calorimetry. According to the data, macromonomers based on hydroxy terminated poly(ethylene glycol) methacrylate ester chemistry allow to produce superplasticizers of high quality.     

Phase behaviour of poly(benzophenoneimide)s having n-alkyloxymethyl side chains

A series of poly(benzophenoneimide)s (C_m-BP-PIs) having n-alkyloxymethyl side chains (−CH₂O-n-CmH_2m+1, m = 4, 6, 8) have been examined by X-ray diffraction, differential scanning calorimetry (DSC) and polarizing optical microscopy. The samples showed basically two phase transitions and both transition temperatures decreased with increasing side chain length. The first transitions were ascribed to glass transitions and the second ones were assigned to liquid crystal-to-isotropic transitions. Eicosane (n-C₂₀H₄₂) which is chemically very similar to the side chain was miscible with the side chains of C₈-BP-PI, which induced depression of the glass transition temperature. Received: 17 February 1997/Revised: 1 April 1997/Accepted: 4 April 1997     

Preparation and characterization of poly(ethylene glycol) crosslinked chitosan films

Poly(ethylene glycol) (PEG) crosslinked chitosan films with various PEG to chitosan ratio and PEG molecular weight were successfully prepared via the epoxy‐amine reaction between chitosan and PEG‐epoxy. The thermal and mechanical properties and swelling behavior were studied for the PEG crosslinked chitosan films. The mechanical strength of chitosan films were greatly enforced by the introduction of PEG‐epoxy, achieving an elongation of about 80%. It was found that the crosslinked chitosan films form hydrogel in water, achieving a swelling ratio higher than 20 times of original weight. The swelling behavior of chitosan films relied greatly on the molecular weight of the crosslinker PEG‐epoxy and the weight percent of PEG‐epoxy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Comparison of reaction kinetics and gelation behaviors in atom transfer, reversible addition-fragmentation chain transfer and conventional free radical copolymerization of oligo(ethylene glycol) methyl ether methacrylate and oligo(ethylene glycol) dimethacrylate

The reaction kinetics and gelation behavior in atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT), and conventional free radical copolymerizations (FRP) of oligo(ethylene glycol) methyl ether methacrylate (OEGMEMA) and oligo(ethylene glycol) dimethacrylates (OEGDMAs) were investigated and compared with respect to the polymerization rate, gel point, and the evolution of network with vinyl conversion. All the three systems experienced autoacceleration in the reaction rate but occurred at different regions of vinyl conversion, caused by diffusion-controlled radical reactions: termination in the FRP, addition in the RAFT, and deactivation in the ATRP, respectively. In the FRP, significant amount of gel materials was collected by solvent extraction far before the onset of macro-gelation detected by an abrupt increase in complex viscosity. However, in the RAFT and ATRP, no gels were found until the systems approached their macro-gelation points. The observation suggests limited intramolecular crosslinking/cyclization reactions in the ATRP and RAFT systems. This is because the slow growth of primary chains (ATRP and RAFT in hours versus FRP in seconds) allowed adequate chain relaxation and diffusion of reacting species. The gel materials thus synthesized by ATRP and RAFT are expected to be more homogeneous in network structure than that by FRP.     

Phase behavior of poly (pyromellitimide)s having flexible (n-alkyloxy)methyl side chains

Summary Phase behavior of poly(pyromellitimide)s having (n-alkyloxy)methyl side chains (-CH₂OC_mH_2m+1, m=4, 6, 8) has been studied by wide angle X-ray scattering, differential scanning calorimetry and ¹³C solid-state NMR. While there are no observable transitions in the polymers bearing short side chain(m=4, 6), there is one transition in the polymer bearing the longest side chain(m=8), which is assigned to mesophase-mesophase transition. All the samples show layered mesophase at room temperature, in which the side chains are amorphous but the main chains form two-dimensional crystals in each layer. In the polymer bearing the longest side chain(m=8), it shows another layered mesophase at high temperature. In the high temperature mesophase, the main chains do not form two-dimensional crystals in each layer; only the lateral packing of the main chains remains undisrupted. Received: 7 July 2000/Accepted: 22 September 2000     

Synthesis and characterization of novel polythiophenes bearing oligo(ethylene glycol) segments and azobenzene units

New copolymers of thiophenes containing azobenzene moieties in the side chain, 3-((((((4-phenyl)azo)phenoxy)ethyl)triethoxy)oxy)-4-methylthiophene/3-methyltetra (oxyethylene)oxy-4-methylthiophene (CP1) and 3-((((((4-phenyl)azo)phenoxy)ethyl) triethoxy) oxy)-4-methylthiophene/3-dodecylthiophene (CP2), were synthesized from 3-bromo-4-methylthiophene. These copolymers were characterized by ¹H-NMR spectroscopy, and their thermal, optical, and electrochemical properties were determined by thermogravimetric analysis, differential scanning calorimetry, absorption spectroscopy, and cyclic voltammetry. CP1 possesses higher degree of conjugation and azobenzene content than CP2, and its structure is more regio-regular. Besides, CP1 exhibited a higher glass transition temperature (T _g = 35 °C, T ₅ = 225 °C) and a lower thermal stability than CP2 (T _g = 13 °C, T ₅ = 307 °C). Both copolymers showed a similar solvatochromic behavior when they were dissolved in chloroform and mixtures chloroform:methanol.     

Different ways for grafting ester derivatives of poly(ethylene glycol) onto chitosan: related characteristics and potential properties

The grafting of poly(ethylene glycol) functionalized by ester groups (MeO-PEG-ester) onto chitosan was studied and optimized using different reaction conditions. In a first procedure, the grafting was made from 6-O-triphenylmethyl-chitosan after protection of primary hydroxyl groups and in a second one, it was made directly onto chitosan. NMR spectroscopy was an important tool to study these reactions and the grafting is unequivocally showed up. Moreover, for each procedure, the solubility and surface properties of the obtained copolymers were evaluated and compared.