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.     

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.     

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 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     

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.     

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.     

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.     

Preparation and characterization of novel grafted polyethylene based azo-polymers bearing oligo(ethylene glycol) spacers

Novel grafted azo-polymers were prepared from commercial low density polyethylene plates (PE). First, precursor polymers were synthesized by reacting PE in the presence of acryloyl chloride using gamma radiation. Further esterification of the resulting grafted polymers with four new amino-nitro substituted azobenzene derivatives bearing oligo(ethylene glycol) segments: N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(5-hydroxy-3-oxapentas-1-yl)amine (RED-PEG-2), N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(8-hydroxy-3,6-dioxaoctas-1-yl)amine (RED-PEG-3), N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(11-hydroxy-3,6,9-trioxaundecas-1-yl)amine (RED-PEG-4) and N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(17-hydroxy-3,6,9,12,15-pentaoxaheptadecas-1-yl)amine (RED-PEG-6) led to the formation of branched azo-polymers. These polymers were characterized and their thermal and optical properties were studied. Besides, the influence of the irradiation dose, irradiation time and the structure of the dyes on the properties of the obtained polymers are discussed.     

Temperature and pH sensitive hydrogels composed of chitosan and poly(ethylene glycol)

Summary Chitosan based semi-interpenetrating polymer network (semi-IPN) hydrogels containing different amounts of poly(ethylene glycol) (PEG) were prepared. The crosslinking of the hydrogels was achieved by using a naturally occurring nontoxic cross-linking agent genipin. The swelling behaviour of these hydrogels was studied by immersing the films in deionized water at 25, 37 and 45 °C and in media of different pHs at 37 °C. Swelling was found to be dependent on temperature, pH of the medium and the amount of PEG in the gel. States of water in the hydrogels swollen in deionized water at 37 °C were determined using Differential Scanning Calorimetry (DSC). The equilibrium water content and the amount of freezing water in the swollen hydrogels increased with the increase in PEG concentration in the gels.     

Polymer gel electrolytes synthesized by photopolymerization in the presence of star-shaped oligo(ethylene glycol) ethers (OEGE)

The photoinitiated cross-linking polymerization of tri(ethylene glycol) dimethacrylate and its copolymerization with cyanomethyl methacrylate in the presence of LiCF₃SO₃ and of various oligo(ethylene glycol) methyl ethers as plasticizer was studied for potential use of the resulting polymer gel electrolytes in lithium batteries. Comparing linear and star-shaped (three and four arm molecules) oligo(ethylene glycol) methyl ethers, the influence of the architecture of the plasticizers on the polymerization course was investigated by means of differential scanning calorimetry. Linear and star-shaped plasticizers with molar masses < 1000 g/mol differ from each other concerning the dependence of their viscosity on their molar mass but not concerning the influence of the viscosity on the polymerization rate. Compared with linear plasticizers, the star-shaped ones have as an essential advantage a distinctly lower tendency to crystallize which is even completely suppressed in some cases. The gels were characterized with regard to the network density of their polymer matrix, to their thermal transitions, thermo-mechanical properties and ionic conductivity. The conductivity of solutions and gels with star-shaped plasticizers was slightly lower than that with linear ones at temperatures above room temperature.     

Concentration effects in the base-catalyzed hydrolysis of oligo(ethylene glycol)- and amine-containing methacrylic monomers

Concentration effects in the base-catalyzed hydrolysis of water-soluble methacrylates (3-(N,N-dimethylaminoethyl) methacrylate (DMAEMA), 2-hydroxyethyl methacrylate (HEMA) and oligo(ethylene glycol) methacrylates (OEGMAs)) have been studied. These monomers are rapidly hydrolyzed in the presence of bases at the room temperature in dilute aqueous solutions, but the reaction rate decreases sharply in highly concentrated solutions. A clear correlation was found between a form of the viscosity isotherm for DMAEMA solutions and the concentration dependence of the autocatalytic hydrolysis rate which indicates the connection of process kinetics with the structure of solutions. These data should be considered when carrying out homo- and copolymerization of the previously mentioned monomers in aqueous solutions.     

New thermogelling poly(organophosphazenes) with methoxypoly(ethylene glycol) and oligopeptide as side groups

A new class of thermogelling poly(organophosphazenes) bearing a hydrophilic methoxypoly(ethylene glycol) (MPEG) and a hydrophobic tri or tetrapeptide such as GlyPheLeuEt, GlyPheIleEt, GlyLeuPheEt, and GlyPheLeuGlyEt have been synthesized and characterized by means of multinuclear (¹H, ³¹P) NMR spectroscopy, gel permeation chromatography, viscometry, and elemental analysis. The gelation of the present polymers is presumed to be attributed to the intermolecular interaction between the hydrophobic oligopeptide side groups, which can form strong physical junction zones in the polymer aqueous solution. The gelation properties of the polymer were affected by the subtle change in the nature of the hydrophobic oligopeptide, composition of the hydrophilic to hydrophobic side groups, and the concentration of the polymer solutions. Among the present thermogels, the copolymer with equimolar MPEG and GlyPheIleEt as side groups showed the excellent gel phase persisting over 35-43 °C, which indicates that it is a new promising material for drug delivery and tissue engineering.     

Molecular packing of poly(azomethine)s having flexible (n-alkyloxy)methyl side chains in films

A new process for the sequential copolymerization of olefins has been devised (Multicatalysts Reactor Granule Technology); it allows the synthesis of thermoplastic polyolefin elastomers having polypropylene from Ti-based catalysts and ethylene-propylene rubbers from metallocenes. Such new materials have been cured with peroxides and the relevant mechanical properties measured in comparison with those of heterophasic copolymers synthesized with traditional catalysts. It resulted that the new materials present an improved balance between strength and elasticity, especially at high temperature. Received: 28 February 1997/Revised: 11 April 1997/Accepted: 14 April 1997