Crosslinked poly(ethylene oxide) hydrogels

Poly(ethylene oxide) with a molecular weight of 2,000,000 was crosslinked by a difunctional peroxide in the molten state. We determined the molecular weight between crosslinks by swelling the samples with deionized water and by indentation and dynamic mechanical analysis. Results were compared with the calculated optimum molecular weight between crosslinks. Fair agreement was obtained between the experimental methods. However, the efficiency of peroxide‐induced crosslinking was very low. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1451–1455, 2003     

Synthesis of monomethoxy poly(ethylene glycol) without diol poly(ethylene glycol)

Since monomethoxy poly(ethylene glycol) (mPEG) inevitably contains diol PEG and is difficult to get high molecular weight through traditional synthesis at high temperature under high pressure, a novel synthetic technique via anionic solution polymerization was reported in this study. With a new initiating system, potassium naphthalene and methanol, was introduced, the polymerization proceeded at ambient temperature and side reactions were well restrained. Furthermore, a slight excess of potassium naphthalene can effectively remove the trace of water and oxygen in the reaction system. Under this condition, mPEG was nearly quantitatively obtained without containing diol PEG. Its Mn ranged from 1 to 30 kDa and the polydispersity was kept lower than 1.07. Characterization of the mPEG obtained was carried out using GPC to determine the content of diol PEG and ¹H‐NMR and MALDI‐ToF MS spectroscopic analysis to confirm the exact structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Photopolymerized hydrogel composites from poly(ethylene glycol) and hydroxyapatite for controlled protein delivery in vitro

The incorporation of hard particles into soft hydrogels can improve the mechanical properties and provide necessary bioactivity to the hydrogels for desired biomedical applications. Hydrogel composites containing hydroxyapatite (HA) are promising materials for orthopedic applications. In this study, injectable poly(ethylene glycol) (PEG) hydrogel precursor solutions containing HA particles and model protein bovine serum albumin (BSA) were synthesized in situ by photopolymerization. In vitro BSA release properties from the hydrogel composites containing various amounts of HA were investigated and discussed. Fourier transform infrared spectroscopy and scanning electron microscopy were employed to investigate the interaction between HA and the hydrogel network and the morphology of the hydrogel composites. It is found that PEG hydrogel composites containing HA sustained the release of BSA for at least 5 days and the presence of HA slowed down BSA release. Photopolymerized hydrogel composites containing HA may find potential use as a drug delivery matrix for orthopedic tissue engineering. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Molecular relaxation in cross-linked poly(ethylene glycol) and poly(propylene glycol) diacrylate networks by dielectric spectroscopy

The molecular relaxation characteristics of rubbery amorphous crosslinked networks based on poly(ethylene glycol) diacrylate [PEGDA] and poly(propylene glycol) diacrylate [PPGDA] have been investigated using broadband dielectric spectroscopy. Dielectric spectra measured across the sub-glass transition region indicate the emergence of an intermediate “fast” relaxation in the highly crosslinked networks that appears to correspond to a subset of segmental motions that are more local and less cooperative as compared to those associated with the glass transition. This process, which is similar to a distinct sub-T_g relaxation detected in poly(ethylene oxide) [PEO], may be a general feature in systems with a sufficient level of chemical or physical constraint, as it is observed in the crosslinked networks, crystalline PEO, and PEO-based nanocomposites.     

Biodegradability of poly(ethylene terephthalate) copolymers with poly(ethylene glycol)s and poly(tetramethylene glycol)

Poly(ethylene terephthalate) copolymers were prepared by melt polycondensation of dimethyl terephthalate and excess ethylene glycol with 10–40mol% (in feed) of poly(ethylene glycol) (E) and poly(tetramethylene glycol) (B), with molecular weight (MW) of E and B 200–7500 and 1000, respectively. The reduced specific viscosity of copolymers increased with increasing MW and content of polyglycol comonomer. The temperature of melting (T_m), cold crystallization and glass transition (T_g) decreased with the copolymerization. T_m depression of copolymers suggested that the E series copolymers are the block type at higher content of the comonomer. T_g was decreased below room temperature by the copolymerization, which affected the crystallinity and the density of copolymer films. Water absorption increased with increasing content of comonomer, and the increase was much higher for E1000 series films than B1000 series films. The biodegradability was estimated by weight loss of copolymer films in buffer solution with and without a lipase at 37°C. The weight loss was enhanced a little by the presence of a lipase, and increased abruptly at higher comonomer content, which was correlated to the water absorption and the concentration of ester linkages between PET and PEG segments. The weight loss of B series films was much lower than that of E series films. The abrupt increase of the weight loss by alkaline hydrolysis is almost consistent with that by biodegradation.     

Crosslinked poly(vinyl alcohol) hydrogels as swollen elastic networks

Transparent crosslinked PVA hydrogels were prepared by electron beam irradiation of aqueous solutions under nitrogen. These weak hydrogels, upon swelling at 30°C in water, showed low elastic moduli (up to 50 psi), low ultimate tensile strength (up to 4 psi), and low extensibility to break (not higher than 85%). Values of the molecular weight between crosslinks M_c were calculated from swelling and from tensile experiments. In fact, two values of M_c were calculated for each swelling experiment, (a) allowing for observed variation in the polymer–solvent interaction parameter χ₁ with concentration, and (b) fixing χ₁ = 0.494 according to literature data. The correlation of the M_c obtained from tensile data with the M_c obtained from swelling data, by (a) or (b), was approximately linear and gave the same per cent agreement.     

Mixed micelles from methoxy poly(ethylene glycol)–polylactide and methoxy poly(ethylene glycol)–poly(sebacic anhydride) copolymers as drug carriers

mPEG–PLLA (poly l-lactic acid) is synthesized by ring-opening polymerization of lactide and conjugation with mPEG. Sebacic acid is modified with acetic anhydride and condensed with mPEG to form mPEG–PSA (poly sebacic anhydride). The micelles formed by mPEG–PLLA are characterized by slow degradation and low drug encapsulation efficiency; on the contrary, mPEG–PSA micelles are characterized by rapid degradation but high encapsulation efficiency. They can merge into spherical micelles (Φ = 140 nm) by self-assembly in water. The mixed micelles can successfully encapsulate a typical hydrophobic drug (curcumin), and significantly improve its solubility. Experimental results show that the mixed micelles have the features of high encapsulation efficiency and slow degradation.     

Structure-property relationships in novel poly(imide-amide)-poly(ethylene glycol) hybrid networks

Broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarisation currents (TSDC), differential scanning calorimetry (DSC) and to a lesser extent water uptake measurements, were employed to investigate molecular mobility, morphology and crystallization/melting events of PEG in poly(imide-amide)-polyethylene glycol hybrid networks (PIA-PEG) with short (M_n=1000 g/mol) and long (M_n=3400 g/mol) PEG crosslinks. The results obtained suggest long range connectivity of the PEG component in the hybrids with short PEG crosslinks at PEG content higher than 40 wt% and in these with long PEG crosslinks at PEG content higher than 20 wt%. Crystallization of the PEG component is observed by DSC in the hybrids with the longer crosslinks at sufficiently high content of PEG, only. The glass transition temperature, T_g, of PEG component in the hybrids with the shorter PEG crosslinks is shifted to higher temperatures compared to that of the hybrids with longer PEG crosslinks, while suppression of the glass transition of the PEG component is observed in the hybrids with the shorter PEG crosslinks at PEG content lower than 40 wt%. The results are discussed in terms of constraints to segmental motion of the PEG crosslinks, imposed by fixed PEG chain ends on the rigid PI chains.     

Miscibility of polystyrene with poly(ethylene oxide) and poly(ethylene glycol)

The intrinsic viscosity of polystyrene–poly(ethylene oxide) (PS–PEO) and PS–poly(ethylene glycol) (PEG) blends have been measured in benzene as a function of blend composition for various molecular weights of PEO and PEG at 303.15 K. The compatibility of polymer pairs in solution were determined on the basis of the interaction parameter term, Δb, and the difference between the experimental and theoretical weight-average intrinsic viscosities of the two polymers, Δ[η]. The theoretical weight-average intrinsic viscosities were calculated by interpolation of the individual intrinsic viscosities of the blend components. The compatibility data based on [η] determined by a single specific viscosity measurement, as a quick method for the determination of the intrinsic viscosity, were compared with that obtained from [η] determined via the Huggins equation. The effect of molecular weights of the blend components and the polymer structure on the extent of compatibility was studied. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1471–1482, 1998     

Complexation of pepsin poly(ethylene glycol)

Summary Complexation of porcine pepsin (or pepsin A) (EC.3.4.23.1) with poly(ethylene glycol) (PEG) in an aqueous solution was studied as a function of pH and PEG concentration. The addition of PEG increased the reduced viscosity of the enzyme solution at pH 3 but not at pH 4.5. An increase in pH was observed by mixing both PEG and enzyme solutions which were previously adjusted to pH 3. Under conditions of pH 2.5–3 and 50°C, PEG contributed to an increase in the hydrolyzing activity of pepsin towardN-acetyl-l-phenylalanyl-3,5-diiodo-l-tyrosine. These results indicate that pepsin forms a water-soluble complex with PEG mainly through hydrogen bonds between the carboxyl groups in the enzyme and the ether groups in PEG.     

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.     

Pressure-volume-temperature properties for binary and ternary polymer solutions of poly(ethylene glycol), poly(propylene glycol), and poly(ethylene glycol methyl ether) with anisole

Pressure-volume-temperature properties were measured for polymer solutions of poly(propylene glycol) (PPG)+anisole, polymer blends of PPG+poly(ethylene glycol methyl ether) (PEGME), and the blends of PPG+PEGME and poly(ethylene glycol) (PEG)+PPG with anisole at temperatures from 298.15 to 348.15 K and pressures up to 50 MPa. The Tait equation represents accurately the pressure effect on the liquid densities over the entire pressure range. The excess volumes change from positive to negative as increasing the mole fraction of PPG in the binary systems of PPG+anisole and PPG+PEGME. The volumetric data of the related binary systems were correlated with the Flory-Orwoll-Vrij and the Schotte equations of state to determine the binary parameters. By using these determined binary parameters, both equations predicted the specific volumes of the polymer blends with anisole to average absolute deviations of better than 0.13%.     

End-group effect on chain conformation of poly(propylene glycol) and poly(ethylene glycol)

A comparison is made of the chain conformational distribution of hydroxy-terminated poly(propylene glycol) (PPG) and poly(ethylene glycol) (PEG) with their methoxy-terminated derivatives. The significant end-group dependence on the glass transition temperature in PPG was observed by differential scanning calorimetry. Raman active skeletal vibrations in the low-frequency region indicated a significant difference in chain conformation distribution between methoxy- and hydroxy-terminated PPGs, yet almost no difference between MPEG and HPEG. The increased chain stiffness in HPPG in comparison to MPPG has been attributed to the hydrogen-bonding interaction associated with the hydroxy end group in HPPG. Furthermore, the structural differences observed between PPG and PEG have been attributed to the differences in the interaction of the hydroxy end group to the ether oxygen in the two polymers. The interaction between the hydroxy end group and ether oxygen differs because the —CH₃ side group is present for one and not for the other. These structural differences are reflected in the glass transitions temperatures measured. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 197–202, 1997     

Methoxy poly(ethylene glycol)‐b‐poly(L‐lactic acid) copolymer nanoparticles as delivery vehicles for paclitaxel

Methoxy poly(ethylene glycol)‐b‐poly(L ‐lactic acid) (MPELLA) was prepared by the melt polycondensation of methoxy poly(ethylene glycol) and L ‐lactic acid. The structure and properties of MPELLA were characterized by IR, ¹H‐NMR, differential scanning calorimetry, and wide‐angle X‐ray diffraction. To estimate its feasibility as a vehicle for paclitaxel, MPELLA nanoparticles were prepared by a self‐emulsification/solvent evaporation method. The paclitaxel‐loaded nanoparticles (PMTs) showed a spherical morphology with an inner core and an outer shell. The size, size distribution, and loading capacity of PMTs were also measured. The release kinetics of paclitaxel from PMTs in vitro was studied. The results show that paclitaxel can be effectively incorporated into MPELLA nanoparticles, which provide a delivery system for paclitaxel and other hydrophobic or toxic compounds. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2116–2122, 2005     

Inhibition of bovine serum albumin adsorption by poly(ethylene glycol) soft segment in biodegradable poly(ethylene glycol)/poly(L-lactide) copolymers

The objective of this study was to investigate the effects of the incorporation of ether linkages into polylactide (PLLA) chains and the time of biodegradation on the behavior of protein adsorption. The content of poly(ethylene glycol) (PEG) in PLLA/PEG copolymers is from 4.4 to 18.3 wt %, and the length of the PEG soft segment is 1000, 2000, and 6000 daltons. The bovine serum albumin (BSA) adsorption onto the biodegradable PLLA/PEG copolymers was carried out using ultraviolet spectroscopy. The surface tension of PLLA and PLLA/PEG was measured using a contact angle. The data show that the incorporation of PEG segments makes the copolymer more polar and, therefore, leads to a reduction of protein adsorption. As the hydrolysis of polymers proceeds, both PLLA and PLLA/PEG turn out to be more polar. However, the initial compositions of degraded PLLA/PEG have a weak influence on the protein adsorption onto its hydrolyzed surface with a substantially long duration of hydrolysis. This phenomenon is attributed to the hydrophobic interaction between polar PLLA/PEG and BSA. © 1993 John Wiley & Sons, Inc.     

异端基遥爪聚乙二醇的合成

采用3种新式引发剂,即2-(苄氧基）乙醇钾、2-(四氢-2H-吡喃-2-氧基)乙醇钾、单丙烯基乙二醇钾引发环氧乙烷阴离子开环聚合,反应条件为25 ℃、48 h、醇与萘钾摩尔比例1∶1,得到3种异端基遥爪聚乙二醇。以2-(苄氧基）乙醇钾引发聚合所得产物为起始物,经一系列反应,得到两种两端均为活性基团的异端基遥爪聚乙二醇,这种方法具有普适性。通过1HNMR及GPC手段,表征了产物的结构、分子量及分子量分布。结果表明可以得到高产率、分子量可控且分布窄的异端基遥爪聚乙二醇。     

New active poly(ethylene glycol) derivative for amino coupling

The synthesis and characterization of an active poly(ethylene glycol) (PEG) derivative with new properties has been afforded starting from a side reaction of N-hydroxysuccinimide (NHS) in presence of N,N-dicyclohexylcarbodiimide (DCC). In particular, a ring opening of NHS in presence of DCC forms a β-alanine active derivative, through Lossen rearrangement, which then reacts with PEG–NH₂ yielding the active PEG derivative: PEG–NH–CO–βAla–NH–CO–NHS. The active group R–NH–CO–NHS showed lower reactivity towards amines and a higher stability in alkaline solution. This can be especially useful in polymer coupling to proteins, because it may lead to a better selectivity among all the amino groups present in a protein, thus yielding less heterogeneous PEG-protein conjugates mixture because only the most nucleophilic and solvent exposed amines can react. A comparison with one of the most used PEGylating agent, the PEG-succinimidyl carboxymethylate (PEG–O–CH₂–CO–NHS), displayed the usefulness of this new PEG derivative for obtaining PEG-protein conjugates. Furthermore, it is of interest that the obtained protein-conjugates are slowly hydrolyzed in water releasing the free protein, therefore they can be considered protein prodrugs.     

Unsaturated polyester based on poly(ethylene glycol)

Unsaturated polyesters were prepared by one-stage melt condensation of maleic anhydride, phthalic anhydride, propylene glycol, and poly(ethylene glycol)s with different molecular weight, and the properties of their castings from styrenated resins were investigated. Tensile and flexural properties decrease with the increase of molecular weight of poly(ethylene glycol), but impact strength, elongation, and water absorption have an inverse effect. This study improves the understanding of the effect of chain length of poly(ethylene glycol) in unsaturated polyester on the properties of its castings.     

Decomposition of poly(ethylene glycol) in nanocomposites

Poly(ethylene glycol) (PEG) has been widely used in studies of polymer–clay nanocomposites because it readily intercalates in smectite clays. Nanocomposites were formed from PEG with molecular weights (M_w) ranging from 300 to 20,000, as evidenced by expansion of the basal planar spacing of the clay (d₀₀₁) in X‐ray diffraction. However PEG with high molecular weight (≥ 10,000) readily underwent degradation during preparation of composites when heated at low temperature (60°C) due to oxidative attack. Molecular weight distribution determined by gel permeation chromatography showed that this degradation always happened with or without the presence of clay and it became more serious when the molecular weight was higher. The reduction in pH of aqueous PEG solutions after degradation increased with molecular weight. Since d₀₀₁ was independent of molecular weight over a wide range, such degradation cannot be detected by this method. Precautions against oxidative attack are therefore recommended to avoid decomposition when preparing PEG–clay nanocomposites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 548–552, 2004