NMR observations of drawn polymers VI. Poly (ethylene oxide)

Wide line NMR spectra of cold drawn poly(ethylene oxide) (PEO) were recorded at temperatures between ?196°C. and 66°C. as a function of the alignment angle between the draw direction and the magnetic field. Line width, second moment, and mobile fraction were determined and are discussed in terms of segmental motion. In agreement with other authors two motional processes were found. (1) The β-process, commencing at temperatures around ?45°C., probably occurs in non-crystalline regions and causes the emergence of a narrow NMR line in addition to the broad one. (2) The β-process was observed between 0°C. and the melting point (66°C.) and led to a pronounced decrease of the width of the broad line and of the second moment. This decrease was anisotropic and was greatest at the alignment angle γ = 45°. As a consequence of this the dependence of the line width and of the second moment on γ is changed: whereas both these quantities show at low temperatures (<0°C.) a maximum at γ = 45° and an absolute minimum at γ = 0°, near the melting point, a minimum close to γ = 45° and an absolute maximum at γ = 0° were found. These changes are explained by oscillations of the helical molecules around their axes in crystalline regions.     

Glass transition temperatures of comb-like polymers. Poly(ethylene oxide)-polyacrylates and -polymethacrylates

A series of twelve poly(ethylene oxide) (PEO)-polyacrylates and -polymethacrylates with PEO side chains, ranging in molecular weight from 164 to 1000, was studied by differential scanning calorimetry in order to analyse the behaviour of the glass transition temperature. It is shown that the glass transition temperature T_g first decreases with increasing side-chain length to attain a constant value corresponding to the T_g of linear PEO. Contrary to the n-alkyl homologous polymers, the influence of the side-chain crystallization is weak and only appears for long side chains (number-average molecular weight M?_n > 450). The proposed reason is the higher content of amorphous side-chain units between the backbone and the crystallites in PEO as compared to alkyl chains. A relation predicting variations of T_g in comb-like polymers with the length of the side chains is proposed. This relation, based on variation of the T_g of the side chain with its length, fits the experimental results for n-alkyl and PEO side-chain polyacrylates and polymethacrylates using only one parameter characterizing the nature of the side chain.     

Poly(vinylsaccharide)s, 7 New surfactant polymers based on carbohydrates

New amphiphilic poly(vinylsaccharide)s (poly( 7 ) and poly( 8 )) were synthesized. Various alkylamino substituted mono- and disaccharides 3 and 5 were obtained by reductive amination of reducing mono- and disaccharides with alkylamines. The reaction of these monofunctionalized sugar derivates with 2-isocyanatoethyl methacrylate ( 2 ) leads to well-defined monomers ( 7 and 8 ) of the urea type. The monomers were polymerized in aqueous solution to high-molecular-weight polymers, using the redox initiator system (NH₄)₂S₂O₈/Na₂S₂O₅. The influence of structural variations by changing the hydrophilic sugar moiety or the lipophilic alkyl part was studied by viscometry, light scattering and measurements of the surface tension.     

Miscibility Enhancement on the Immiscible Binary Blend of Poly(vinyl phenol) and Poly(acetoxystyrene) with Poly(ethylene oxide)

Summary: The miscibility and hydrogen‐bonding behaviors of ternary polymer blends of poly(ethylene oxide) (PEO)/poly(vinyl phenol) (PVPh)/poly(acetoxystyrene) (PAS) were investigated by using DSC and Fourier transform infrared spectroscopy (FTIR). The PEO is miscible with both PVPh and PAS based on the observed single T_g over the entire composition range. FTIR was used to study the hydrogen‐bonding interactions between PEO with PAS and PVPh, respectively. Quantitative analyses show that the strength of hydrogen‐bonding strength is of the order of the hydroxyl‐ether inter‐association of PVPh/PEO blend > the hydroxyl‐hydroxyl self‐association of pure PVPh > the hydroxyl‐carbonyl inter‐association PVPh/PAS blend at room temperature. Furthermore, the addition of PEO is able to enhance the miscibility of immiscible PVPh/PAS binary blends at lower (20 wt.‐%) or higher (60 and 80 wt.‐%) PEO content. However, there exists a closed immiscibility loop in the phase diagram at 40 wt.‐% PEO content due to the “Δχ” and “ΔK” effects in this hydrogen‐bonded ternary polymer system. Therefore, an interesting and unusual sandwich phase diagram has been observed in this ternary polymer blend.

Ternary phase diagram of the PEO/PAS/PVPh system.     

Sorption of Hydrophobic Compounds by Modified Poly(ethylene oxide) Networks

Various flocculates were prepared by irradiation and chemical modification of poly(ethylene oxide). It was found that the amphiphilic hydrogels are efficient for purification of waste waters and water‐organic systems contaminated with dyes and pigments, even at low concentrations (0.035–0.1 wt.‐%) of the polymeric PEO network flocculates. The affinity of the modified networks for ionic and nonionic species was studied as a function of the structure and crosslinking density of the networks, their degree of quaternization, and their hydrophilicity coefficients. It was established that hydrophobic organic compounds such as sodium picrate and bromophenol blue are bound predominantly to the lipophilic quaternary ammonium cations. The polyether chains remain inert (in the case of nonionic dyes) or form complexes with the alkali cations (in the case of sodium picrate). It was also found that the microenvironment of the active site (quaternary N⁺ ion or EO segment) affects the sorption ability of the modified networks.     

Melt rheology of compatible binary blends: Poly(ethylene oxide)-poly(methyl methacrylate) and poly(ethylene oxide)-poly(vinyl acetate)

A study of the rheological behaviour of poly(ethylene oxide)-poly(methyl methacrylate) and poly(ethylene oxide)-poly(vinyl acetate) compatible blends in the molten state is reported. Zero shear viscosity η₀ and the activation energy for the viscous flow ΔE* were obtained as function of both composition and molar mass of the components. Positive and negative deviations from the additivity rule were observed both in the case of log η₀ and ΔE*.     

Poly(ethylene glycol)-lysine dendrimers for targeted delivery of nitric oxide

We have synthesized dendrimers of the amino-acid lysine bound to a central poly(ethylene glycol) (PEG) core, and then formed multiple diazeniumdiolate nitric oxide (NO) donors on the lysine residues. NO release from these materials occurred for up to 60 days under physiological conditions. These materials display the ability to regulate vascular cell proliferation and inhibit platelet adhesion to thrombogenic surfaces. When modified with a targeting ligand specific for inflamed endothelium (Sialyl Lewis X), we were able to demonstrate binding of fluorescently-labeled dendrimers to endothelial cells activated by interleukin 1β (IL-1β).     

Poly(ethylene oxide)-b-poly(N-isopropylacrylamide) nanoparticles with cross-linked cores as drug carriers

Micelle-like nanoparticles that could be used as drug-delivery carriers were developed. The unique feature of these nanoparticles was that the core of poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PEO-b-PNIPAAm) micelle was lightly cross-linked with a biodegradable cross-linker, N, N-bis(acryloyl)cystamine (BAC). The nanoparticles were characterized by dynamic light scattering and fluorescence measurements. When the BAC content ranged from 0.75 wt% to 0.2 wt% of the mass of NIPAAm, the diameters of the nanoparticles were less than 150 nm. The anti-cancer drug doxorubicin (Dox) and 1,6-diphenyl-1,3,5-hexatriene (DPH) were used as fluorescent probes to study the hydrophobicity of the cores of the nanoparticles; the results showed that the cores of the nanoparticles were hydrophobic enough to sequester Dox and DPH. The nanoparticles with 0.5 wt% BAC stored at room temperature were stable up to 2 weeks, even at dilute concentrations. The degradation of BAC by reducing agent β-mercaptoethanol was investigated, and the nanoparticles were not detectable 14 days after adding β-mercaptoethanol.     

Poly(ethylene oxide)-b-poly(N-isopropylacrylamide) nanoparticles with cross-linked cores as drug carriers

Micelle-like nanoparticles that could be used as drug-delivery carriers were developed. The unique feature of these nanoparticles was that the core of poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PEO-b-PNIPAAm) micelle was lightly cross-linked with a biodegradable cross-linker, N,N-bis(acryloyl)cystamine (BAC). The nanoparticles were characterized by dynamic light scattering and fluorescence measurements. When the BAC content ranged from 0.75 wt% to 0.2 wt% of the mass of NIPAAm, the diameters of the nanoparticles were less than 150 nm. The anti-cancer drug doxorubicin (Dox) and 1,6-diphenyl-1,3,5-hexatriene (DPH) were used as fluorescent probes to study the hydrophobicity of the cores of the nanoparticles; the results showed that the cores of the nanoparticles were hydrophobic enough to sequester Dox and DPH. The nanoparticles with 0.5 wt% BAC stored at room temperature were stable up to 2 weeks, even at dilute concentrations. The degradation of BAC by reducing agent beta-mercaptoethanol was investigated, and the nanoparticles were not detectable 14 days after adding beta-mercaptoethanol.     

Poly(ethylene glycol)-poly(L-lactide) diblock copolymer prevents aggregation of poly(L-lactide) microspheres during ethylene oxide gas sterilization

Sterilization procedure is one of the most important obstacles in the clinical applications of biodegradable microspheres. The microspheres prepared with poly(alpha-hydroxy acid) were severely aggregated during ethylene oxide (EO) gas sterilization, and could not be used in clinical applications. In this study, the effects of EO gas sterilization on the poly(L-lactide) (PLLA) microspheres were analyzed by nuclear magnetic resonance spectroscopy (1H-NMR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), scanning electron microscope (SEM) and size fractionation. The aggregation between the microspheres might be stimulated by high mobility of amorphous regions of PLLA on the microsphere surfaces since both water vapor and gas mixture can reduce glass transition temperature (Tg) of PLLA below the sterilization temperature. During EO gas sterilization, there were no changes in the molecular structure and the molecular weight of PLLA in microspheres, but there were changes in the crystallinity of PLLA in microspheres. In this study, poly(L-lactide)-poly(ethylene glycol) diblock copolymers (PLE) were blended with PLLA homopolymers in various ratios to design the microsphere suitable for EO gas sterilization. Aggregation of PLLA microspheres was markedly prevented when more than 4wt% of PLE was blended in the microspheres. This inhibition effect on aggregation may be due to the increased initial crystallinity of the microspheres, which help to maintain the microsphere morphology during EO gas sterilization.     

Segmented Block Copolymers with Terephthalic‐Extended Poly(ethylene oxide) Segments

Segmented block copolymers comprised of flexible PEO segments and monodisperse crystallizable bisestertetraamide segments have been synthesized. The influence of the terephthalic units in the soft phase on the transitions and the thermal mechanical and elastic properties are studied. The presence of terephthalic units in the copolymer increases the glass transition temperature of the soft phase by ≈5 °C. The low‐temperature flexibility of the copolymers is improved because of the lower crystallinity and melting temperature of PEO. With the use of terephthalic‐extended PEO segments, segmented block copolymers with low moduli (G' < 15 MPa) and good elastic properties could be obtained.

     

Temperature-Sensitive Biodegradable Poly(ethylene glycol)

We report here that the incorporation of several disulfide bonds along poly(ethylene glycol) (PEG) gives temperature sensitivity, as well as biodegradability to PEG. To synthesize a PEG with temperature sensitivity in a physiologically important range (20–40°C), PEGs with molecular masses of 400 and 600 Da were randomly coupled by disulfide bonds. As the mol ratio of PEG (400 Da) disulfide to PEG (600 Da) disulfide increased from 40:60 to 60:40, the cloud point of the polymer aqueous solution decreased from 35°C to 27°C. The disulfide bonds between PEGs were degraded in the presence of a thiol-containing biomolecule of glutathione in a thiol-concentration-dependent manner.     

New monomers and polymers. II. Poly(pentamethylstyrene) and poly(pentamethylstyrene oxide)

Pentamethylstyrene was polymerized in high conversion to a high softening (>230°C.) solid using cationic initiators. Methanol insoluble polymer was not obtained under anionic, radical, or ZIEGLER-NATTA conditions. Attempts to radically copolymerize this monomer with styrene were unsuccessful. Blends of poly(pentamethylstyrene) and polystyrene were incompatible although enhanced thermal properties were observed. Pentamethylstyrene oxide was polymerized to a high melting, colorless solid.     

Side-chain crystallinity in comb-like polymers. Poly-(ethylene oxide)-polyacrylates and -polymethacrylates

Melting temperatures, heats of fusion and the derived enthalpies and entropies of fusion were obtained by differential scanning calorimetry for poly(ethylene oxide) (PEO)-acrylate and -methacrylate macromonomers and the corresponding polymers. The side-chain lengths varied from three to ninety-three ethylene oxide units. The thermodynamic data for macromonomers and polymers were calculated according to the theory of Flory and Vrij, which has been shown to describe well the melting behavior of linear PEO. It is shown that the melting parameters for macromonomers are identical to those of pure PEO in spite of the presence of the chain ends of different nature. With the PEO comb-like polyacrylates and polymethacrylates, the melting points are only a few degrees higher than those of the corresponding monomers. Their crystalline content calculated from the molar enthalpies are 83% and 78%, respectively. In contrast to linear PEO, the interfacial free energy is negative for both types of polymers due to a high value of the interfacial entropy. It is suggested that the tighter packing of the chain ends, including the backbone, is responsible for this high value, together with the possible presence between the lamellae of constructed amorphous side chains. The combined results lead to the conclusion that the crystalline organization is quite comparable to that of pure PEO of equal length with, however, one or two fewer crystallized EO units.     

The Aggregation Behavior of Poly(ethylene oxide)‐Poly(methyl methacrylate) Diblock Copolymers in Organic Solvents

Poly(ethylene oxide)‐poly(methyl methacrylate) and poly(ethylene oxide)‐poly(deuteromethyl methacrylate) block copolymers have been prepared by group transfer polymerization of methyl methacrylate (MMA) and deuteromethyl methacrylate (MMA‐d₈), respectively, using macroinitiators containing poly(ethylene oxide) (PEO). Static and dynamic light scattering and surface tension measurements were used to study the aggregation behavior of PEO‐PMMA diblock copolymers in the solvents tetrahydrofuran (THF), acetone, chloroform, N,N‐dimethylformamide (DMF), 1,4‐dioxane and 2,2,2‐trifluoroethanol. The polymer chains are monomolecularly dissolved in 1,4‐dioxane, but in the other solvents, they form large aggregates. Solutions of partially deuterated and undeuterated PEO‐PMMA block copolymers in THF have been studied by small‐angle neutron scattering (SANS). Generally, large structures were found, which cannot be considered as micelles, but rather fluctuating structures. However, ¹H NMR measurements have shown that the block copolymers form polymolecular micelles in THF solution, but only when large amounts of water are present. The micelles consist of a PMMA core and a PEO shell.     

Sorption of ethylene oxide by medical polymers

Conclusions 1. Sorption capacities have been measured for some polymer materials used in medical components in relation to E0 as sterilizing gas. 2. Effective sorption coefficients for E0 have been calculated for these materials. 3. The values of σ_ef lead to the recommendation that polyethylene and silicone rubbers should be used preferentially for components of apparatus that is to be gas sterilized. These rubbers have a fairly high sorption (close to that for natural rubber), but they differ from other rubbers in having very high diffusion coefficients [2], so they are degassed rapidly. 4. The effective sorption coefficients enable one to calculate the equilibrium E0 sorption by a polymer for various E0 concentrations and temperatures within the range examined. All-Union Disinfection and Sterilization Research Institute, Ministry of Health of the USSR, Moscow. Translated from Meditsinskaya Tekhnika, No. 6, pp. 46–48, November–December, 1982.     

Poly(dimethylsiloxane)-poly(ethylene oxide)-heparin block copolymers. I. Synthesis and characterization

Amphiphilic block copolymers containing poly(dimethylsiloxane), poly(ethylene oxide), and heparin (PDMS-PEO-Hep) have been prepared via a series of coupling reactions using functionalized prepolymers, diisocyanates, and derivatized heparins. All intermediate steps of the synthesis yield quantifiable products with reactive end-groups, while the final products demonstrate bioactive, covalently bound heparin moieties. Due to the solvent systems required, commercial sodium heparin was converted to its benzyltrimethyl ammonium salt to enhance its solubility. The same procedure was applied to heparin degraded by nitrous acid in order to covalently couple it in solutions with the semitelechelic copolymers. As might be expected, this derivatization reduces the apparent bioactivity of the heparin. However, preliminary findings suggest that the bioactivity can be restored by reforming the heparin sodium salt.     

Poly(ethylene oxide)-modified carboxylated polystyrene latices - immobilization chemistry and protein adsorption

α,ω-Diamino poly(ethylene oxides) (PEOs) with different molecular weights (148, 1000, and 3400) were covalently immobilized onto carboxylated polystyrene latices. The immobilization of PEO was carried out with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) in aqueous media. The reaction conditions were optimized to obtain a maximal coupling of PEO. The degree of coupling was determined by the surface concentration of amino groups. The maximal surface concentrations of amino groups were close to what is expected for a complete coverage of the surface with PEO. Adsorption of albumin from a buffer solution onto PEO-containing surfaces was about 85% less than the albumin uptake by unmodified polystyrene latices. Protein adsorption from plasma dilutions was lower on surfaces containing PEO molecules with a higher molecular weight. The reduction of the protein uptake from plasma by surfaces containing PEO-3400 molecules was only 40% compared to the adsorption to unmodified surfaces. These results indicate that plasma proteins have a low affinity for surfaces modified with PEO. However the PEO modified surfaces are by no means 'protein resistant' when exposed to plasma.     

Polyacrylate graft polymers prepared by grafting of monomethoxypoly(ethylene oxide) homopolymers onto acrylic acid: Self-gelling polymers

Polyacrylates of monomethoxypoly(ethylene oxide)

1 Systematic name for MePEO: α-hydro-ω-methoxypoly(oxyethylene).

(MePEO) were prepared by grafting MePEO on prepolymerized acryloyl chloride polymers of different molecular weights. Copolymers with carboxyl groups were also prepared by the addition of both water and MePEO. The polymers spontaneously form irreversible gels in water as soon as the degree of polymerization exceeds a certain limit. This gel formation confirms preceding results on similar polymers obtained by polymerization of MePEO acrylate and methacrylate macromonomers. It is concluded that the gelification phenomenon is not due to chemical cross-linking but rather to the presence of a high density of strongly interacting grafts of PEO on the polymer backbone. This new type of self-gelling system is considered to be of special interest.     

Synthesis and Liquid Crystalline Properties of Poly(ethylene oxide) Brushes with Amphiphilic Side Groups

Summary: Poly(ethylene oxide)s containing decylthiomethyl (DTP), decylsulfonylmethyl (DSP), methyl‐oligo(ethylene oxide) thiomethyl (MnOTP), methyl‐oligo(ethylene oxide) sulfonylmethyl (MnOSP), decyl‐oligo(ethylene oxide) thiomethyl (DnOTP), and decyl‐oligo(ethylene oxide) sulfonylmethyl (DnOSP) groups in the side‐chains, where n (the number of ethylene oxide units) = 1, 2, 3, or 4 for DnOTP and DnOSP, and n = 2, 3, or 7 for MnOTP and MnOSP, were synthesized to study the effect of the structure of the side‐chains on the ordered phases of the polymers. All of the MnOSPs, as well as M2OTP and M3OTP, were found to be amorphous polymers. DTP, M7OTP, D1OTP, D2OTP, and D3OTP showed crystalline phases below their isotropic temperatures. DSP, D1OSP, D2OSP, D3OSP, D4OSP, and D4OTP were found to be liquid crystalline. Therefore, the phase separation facilitated by the introduction of the sulfone group and/or by the addition of the longer ethylene oxide units between the ethylene oxide backbones and the hydrophobic decyl tails was found to be a key factor in the formation of the liquid crystalline phases. These ordered phases were characterized using differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction.

Schematic illustration of the structures of poly(ethylene oxide) brushes showing liquid crystalline phases.