Poly(N-vinyl-2-pyrrolidone) hydrogel production by ultraviolet radiation: new methodologies to accelerate crosslinking

Poly(N-vinyl-2-pyrrolidone) hydrogels produced by high-energy radiation relies on water radiolysis as a primary process leading to crosslinks. Conversely, ultraviolet direct irradiation into PVP leads to crosslinking trough pyrrolidinone moiety photolysis. However, this process showed to be rather inefficient. This work describes the crosslinking of poly(N-vinyl-2-pyrrolidone) based on hydrogen peroxide photolysis, therefore mimicking water radiolysis, using UV-C (e.g. low pressure Hg lamp) or UV-A radiation sources. The process efficiency and the properties of the hydrogel formed are discussed and compared with other methods of hydrogel production.     

Photoinitiated polymerization of bisphenol a epoxy diacrylates with bis[4(2-hydroxy-3- acryloyloxypropoxy)phenyl]sulfide

Photopolymerization of commercially available bisphenol A epoxy diacrylates with bis[4(2-hydroxy-3-acryloyloxypropoxy)phenyl]sulfide (BES-DA)—a monomer synthesized by our group in previous study was carried out. As this compound is solid at room temperature in its polymerization reactive diluent N-vinyl-2-pyrrolidone, which is also comonomer, has been applied. As a photoinitiator, 2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocur 1173) was used. Thermal and mechanical properties of the obtained compositions were studied. The results show that thermal properties of both epoxy diacrylates improve with the increasing concentration of BES-DA. The addition of N-vinyl-2-pyrrolidone causes decrease of their storage moduli and glass transition temperatures. Simultaneously, it allows to increase the conversion of double bonds. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Polymerization behavior and polymer properties of eosin-mediated surface modification reactions

Surface modification by surface-mediated polymerization necessitates control of the grafted polymer film thicknesses to achieve the desired property changes. Here, a microarray format is used to assess a range of reaction conditions and formulations rapidly in regards to the film thicknesses achieved and the polymerization behavior. Monomer formulations initiated by eosin conjugates with varying concentrations of poly(ethylene glycol) diacrylate (PEGDA), N-methyldiethanolamine (MDEA), and 1-vinyl-2-pyrrolidone (VP) were evaluated. Acrylamide with MDEA or ascorbic acid as a coinitiator was also investigated. The best formulation was found to be 40 wt% acrylamide with MDEA which yielded four to eightfold thicker films (maximum polymer thickness increased from 180 nm to 1420 nm) and generated visible films from fivefold lower eosin surface densities (2.8 versus 14 eosins/μm²) compared to a corresponding PEGDA formulation. Using a microarray format to assess multiple initiator surface densities enabled facile identification of a monomer formulation that yields the desired polymer properties and polymerization behavior across the requisite range of initiator surface densities.     

Triblock and star-block copolymers of N-(2-hydroxypropyl)methacrylamide or N-vinyl-2-pyrrolidone and D,L-lactide: synthesis and self-assembling properties in water

Novel A-B-A triblock and star-block amphiphilic copolymers, i.e. poly(N-(2-hydroxypropyl)methacrylamide)-block-poly(D,L-lactide)-block-poly(N-(2-hydroxypropyl)metha-crylamide), poly(N-vinyl-2-pyrrolidone)-block-poly(D,L-lactide)-block-poly(N-vinyl-2-pyrrolidone), star-poly(D,L-lactide)-block-poly(N-(2-hydroxypropyl)methacrylamide) and star-poly(D,L-lactide)-block-poly(N-vinylpyrrolidone), were synthesized and characterized. These polymers were prepared by free radical polymerization of N-(2-hydroxypropyl)methacrylamide and N-vinyl-2-pyrrolidone in the presence of either poly(D,L-lactide) dithiol or star-poly(D,L-lactide) tetrakis-thiol, both biodegradable macromolecular chain-transferring agents. All copolymers self-assembled in aqueous solution to form supramolecular aggregates of 20–180 nm in size. The critical aggregation concentration of the copolymers ranged from 5 to 24 mg/L, depending on their hydrophobicity. The partition equilibrium constant of pyrene in the hydrophobic core of micelles was between 0.71×10⁵ and 1.63×10⁵. The triblock copolymer micelles were loaded with two model poorly water-soluble drugs, namely, indomethacin (1.5–16.4% w/w) and paclitaxel (0.4–1.5% w/w), by a dialysis procedure. These triblock and star-block copolymers could prove useful as nanocarriers for the solubilization and delivery of hydrophobic drugs.     

Characterization of copolymers of N-vinyl-2-pyrrolidone with 2-phenyl-1, 1-dicyanoethene

Copolymers of N-vinyl-2-pyrrolidone and 2-phenyl-1, 1-dicyanoethene were studied. Infrared, proton, and carbon-13 spectra of the copolymers are discussed by comparison with poly(N-vinyl-2-pyrrolidone), model compounds, and various copolymers. Thermal behavior of the copolymers was investigated by using DSC, TMA, and TGA methods. Thermal as well as thermooxidative stability of the copolymers was found to be lower than those of poly(N-vinyl-2-pyrrolidone).     

Preparation of potentially electroactive thallium polymers derived from the acidic copolymers of maleic anhydride

Maleic anhydride copolymers with vinyl ethyl ether and N-vinyl-2-pyrrolidone were prepared in tetrahydrofuran at 60°C, using AIBN as initiator. Copoly (MA-VEE) was hydrolysed to various degrees of hydrolysis and the extent of hydrolysis monitored by i.r. Various acidic derivatives of copoly (MA-VEE), copoly(MA-N-vinyl-2-pyrrolidone) and copoly(MA-ethylene) were prepared and characterized by elemental analysis and spectroscopy. The inter- and intramolecular crosslinking of carboxylic groups in copoly(succinic acid-VEE) were studied by g.p.c. Also thallium (III) derivatives of several acidic polymers were prepared and characterized.     

Molecular-hydrodynamic study of poly(<Emphasis Type="Italic">N</Emphasis>-methyl-<Emphasis Type="Italic">N</Emphasis>-vinylacetamide) macromolecules

High-velocity sedimentation, translational isothermal diffusion, and viscometry in H₂O and DMF are used to investigate the samples and fractions of poly(N-methyl-N-vinylacetamide) synthesized by free-radical polymerization and fractionated in a chloroform-diethyl ether system. Molecular masses M and the Mark-Kuhn-Houwink-Sakurada relations are obtained for the fractions in the molecular mass range M × 10⁻³ = 3.5−540.0. The negative temperature coefficient of intrinsic viscosity is revealed for both solvents. The length of the Kuhn statistical segment and the hydrodynamic diameter of poly(N-methyl-N-vinylacetamide) macromolecules are estimated; the hydrodynamic volumes occupied by water-soluble poly(N-methyl-N-vinylacetamide), poly(1-vinyl-2-pyrrolidone), poly(vinylformamide), and pullulan molecules are compared.     

Dispersion polymerization in supercritical carbon dioxide using comb-like fluorinated polymer surfactants having different backbone structures

Comb-like fluorinated polymers with different backbone structures, poly(heptadecafluorodecyl acrylate) (PA-R_f), poly[oxy[(2-perfluorooctylethylene)thiomethyl]ethylene] (PEO-R_f), and poly[p-[[(perfluorooctylethylene)thio]methyl]styrene] (PS-R_f), were used as surfactants in dispersion polymerization to examine the effect of backbone structure on the formation of polymer particles. Dispersion polymerization of monomers with different polarities using these comb-like fluorinated polymer surfactants in CO₂ showed that PEO-R_f containing a polar oxyethylene backbone was an effective surfactant for the dispersion polymerization of a polar monomer, such as N-vinyl-2-pyrrolidone, whereas PA-R_f was effective for less polar monomers, such as methyl methacrylate and N-vinyl caprolactam.     

H-complex formation and influence on the radical copolymerization of acrylic acid and 1-vinyl-2-pyrrolidone in tetrahydrofuran

The association constant of the H-complex formation between acrylic acid and 1-vinyl-2-pyrrolidone in tetrahydrofuran at 22°C (K₁ = 1350 mol 1^?1) was determined by means of ¹H NMR spectroscopy. A detailed equation for the copolymer composition, accounting for the participation in the chain propagation of the above complex and that between acid and solvent molecules, was derived. It was used for evalution of the relative reactivities of the complexes discussed and of the uncomplexed 1-vinyl-2-pyrrolidone molecules.     

Fabrication of a graphene oxide–gold nanorod hybrid material by electrostatic self-assembly for surface-enhanced Raman scattering

An electrostatic self-assembly procedure was used to fabricate graphene oxide (GO) and gold nanorod (AuNR) hybrids (GO–AuNR), in which poly (N-vinyl-2-pyrrolidone) was used as a stabilizing surfactant to prevent the aggregations of GO sheets. AuNRs were loaded onto the surface of GO, which was confirmed by zeta potential measurements, transmission electron microscopy, atomic force microscopy, UV–Vis–NIR and Raman spectroscopy. The GO–AuNR materials show a great increase of Raman signals for adsorbed aromatic dye molecules, which was demonstrated using cationic and anionic aromatic dyes as probe molecules.     

Observations on the homogeneity of crosslinked copolymers prepared by γ-irradiation

Bulk copolymerization in vacuo has been effected to 100% conversion via γ-irradiation. Visual assessment is made of the homogeneity of the products, which comprise n-butyl acrylate with N-vinyl-2-pyrrolidone over the whole composition range. Textural inhomogeneity (popcorn structure or spongy opacity), produced only below ≈5 × 10^?3 Mrad h^?1, is attributed to proliferous polymerization. At medium-high dose rates, the optical homogeneity, classified as opacity, translucency or transparency, is dictated only by the composition. Thus, transparency in a xerogel requires a minimum n-butyl acrylate content of 40 wt%, but the threshold composition is reduced by incorporating a hexa-functional crosslinking agent. There is a general trend towards decreased optical homogeneity on hydrating a xerogel to its hydrogel. The change in compositional distribution up to 100% conversion is analysed according to the procedure of Skeist and is shown to be consistent with the experimental observations on compatibility.     

Radiation synthesis,characterization and amidoximation of N-vinyl-2-pyrrolidone/acrylonitrile interpenetrating polymer networks

Interpenetrating polymer networks (IPNs) were synthesized by irradiating acrylonitrile solutions of poly(N-vinyl-2-pyrrolidone) with ⁶⁰Co-γ rays. The conversion to insoluble IPN structure was characterized using FT-IR and thermal analysis methods. The amidoximation of polyacrylonitrile moieties of IPN was carried out in aqueous solutions of NH₂OH·HCl–NaOH at 50°C. The conversion of amidoximation was followed by using FT-IR spectrophotometer and conversion of nitrile groups to amidoxime was determined as percentage. The structure of amidoximated IPN was characterized by FT-IR and thermal methods as well.     

Maghnite‐H+, a solid catalyst for the cationic polymerization of α‐methylstyrene

The polymerization of α‐methylstyrene (AMS) catalyzed by Maghnite‐H⁺ (Mag‐H) was investigated. Mag‐H is a montmorillonite sheet silicate clay, exchanged with protons. It was found that the cationic polymerization of AMS is initiated by Mag‐H at ambient temperature in bulk and in solution. The effect of the amount of Mag‐H, the temperature, and the solvent was studied. The polymerization rate increased with increase in the temperature and the proportion of catalyst, and it was larger in nonpolar solvents. These results indicated the cationic nature of the polymerization. It may be suggested that the polymerization is initiated by proton addition to monomer from Mag‐H. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and nitrosation of processible copolymers from pyrrole and ethylaniline

A series of copolymers were prepared by an oxidative polymerization of pyrrole (PY) and 2-ethylaniline (EA) in HCl. The polymerization process was followed by tracking open-circuit potential and temperature of the reaction solutions. The fine particles of the PY/EA copolymers obtained in situ were further N-nitrosated for the first time in order to improve their solubility. The size, structure, and properties of the fine particles and their N-nitroso products were systematically characterized by laser particle size analyzer, FTIR, UV-vis, GPC, solution casting, and TG techniques. It is found that both the open-circuit potential and temperature of the solutions exhibit a maximum during the copolymerization, while the particle size of the copolymers will decrease monotonically with prolongating polymerization time or doping. Both the polymerization yield and molecular weight of the copolymers exhibit a minimum with PY/EA ratio, indicating a mutual retarding effect between the PY and EA monomers. The top potential and top temperature of the copolymerization as well as the particle size and its distribution, solubility, film-forming ability, electroconductivity, and thermostability of the copolymers all depend significantly on the PY/EA ratio. The PY/EA copolymers have good solubility in the solvents with the solubility parameter from 23 to 27 J^1/2/cm^3/2, dielectric constant greater than 12 and polarity index from 6.4 to 7.4 and their solubility becomes further better with increasing EA content. The N-nitrosation of copolymers can also improve their solubility in polar solvents furthermore. The copolymers with PY content of less than 30 mol% in NMP and THF exhibit good thin-film formability. The copolymer films become smoother and tougher with increasing EA content and by N-nitrosation. With increasing PY content, the decomposition temperature, maximum decomposition rate, char yield at 500 °C, and activation energy all decrease but decomposition order increases. The temperature at the maximum weight-loss rate of the copolymers has a maximum at the PY/EA molar ratio of 30/70. These results suggest that the polymer obtained is a real copolymer containing two comonomer units.     

Increased enzyme activity in immobilised cell composites with a highly hydrophilic polymer matrix

Streptomyces phaeochromogenes cells were immobilised by radiation polymerisation of hydrophilic monomers; highest levels of glucose isomerase activity were found in immobilised cell composites with highly hydrophilic polymer matrices. The enzyme activity in the composites from the copolymerisation of hydroxyethyl acrylate (or methacrylate) and N-vinyl-2-pyrrolidone monomer increased markedly with increase in the content of the N-vinyl-2-pyrrolidone monomer, owing to the higher water absorption by the polymer matrix, and was close to that of the non-immobilised cells. The enzyme activity was affected by monomer concentration, the hydrophilicity, and chemical structure of the polymer matrix. The Michaelis constant of the composites from hydrophilic monomers was close to that of the intact cells.     

Non-classical free-radical polymerization: 5. The purification and polymerization of 1-vinyl-2-pyrrolidone

The impurities in 1-vinyl-2-pyrrolidone (NVP) have been investigated by g.c./m.s. and ¹³C n.m.r. The inadequacy of normal purification procedures is pointed out, and a simple technique for reducing the impurity-level to undetectable values is described. Sources of non-ideality in free-radical polymerization are classified and it is suggested that a plot of ωj^?0.5 vs. [M] could be particularly valuable in revealing the origins of non-ideal behaviour, including the presence of retarders. (ω, j are the rates of polymerization and initiation, respectively, and M represents monomer). Extensive data on NVP polymerization in ethanol solution at 60°C with azo-bis-isobutyronitrile as initiator have been obtained by dilatometric studies; for this purpose redetermination of the polymer density proved necessary. The data have been analysed as outlined above. The efficacy of the purification procedure in removing ‘active’ impurities has thus been demonstrated and it is concluded that, as already suggested by others, the polymerization under the prevailing conditions is subject to a medium effect operating principally on the propagation process. This is discussed briefly.     

Phase transition in swollen gels 29. Temperature dependences of swelling and mechanical behaviour of poly(N-vinylcaprolactam-co-1-vinyl-2-pyrrolidone) gels in water

Summary Ionized networks of statistical copolymers of N-vinylcaprolactam (VCL), 1-vinyl-2-pyrrolidone (VP) (mole ratios of VCL/VP = 1/0, 0.9/0.1, 0.8/0.2, 0.7/0.3 and 0.5/0.5), an ionic comonomer, N,N-diallyl-(N,N-dimethyl)ammonium chloride (mole fractions 0, 0.005, 0.01 and 0.02) and a crosslinker, 1,1'-divinyl-3,3'-(ethane-1,1-diyl)di(2-pyrrolidone) (mole fractions 0.016, 0.024, 0.032 and 0.048) were prepared by radiation polymerization in water/ethanol mixture (H₂O/EtOH = 0.5/0.5 by vol). Their swelling and mechanical behaviour was investigated in water at various temperatures. For all copolymers, a continuous transition was found from the expanded (at low temperatures) to collapsed (at high temperatures) state; the transition temperature T _tr increases with increasing contents of VP and the ammonium salt in gels. The shift of T _tr to higher temperatures is caused by hydrophilicity of network chains increasing with increasing VP contents. The decrease in swelling with increasing temperature is accompanied by an increase in equilibrium modulus, so that mechanical behaviour is predominantly determined by swelling. Received: 31 October 2000/Revised version: 18 December 2000/Accepted: 18 December 2000     

Crosslinked DADMAC polymers as cationic super absorbents

Loosely crosslinked cationic polyelectrolytes (polyquats) with super-water-sorption abilities are presented, for the first time. Hydrogels obtained by radically initiated copolymerization of N,N-diallyl, N,N-dimethyl ammonium chloride (DADMAC) with N-vinyl 2-pyrrolidone (NVP) in presence of N,N,N′,N′-tetraallyl piperazinium dichloride (TAP) as crosslinker showed reasonably high equilibrium swelling ratios, as high as those for poly(acrylic acid)-based super absorbents.The highest swelling ratios (up to 360) were attained by fully cationic hydrogels derived from DADMAC and 0.5% TAP. The hydrogels with 0.5–5% crosslinkers exhibited rapid expansion in neutral water, so that the equilibrium swelling values were attained within 2–3 min. The crosslinking densities of the gels were estimated by Flory-type swelling model using “phantom network elasticity” for the elastic contribution. This estimation revealed low crosslinking efficiencies of TAP (0.24–0.35) due to its double cationic charge.In the study “the salt effect” and effects of the comonomer ratios and crosslinker contents on the swellings were also investigated.     

Thiols as chain transfer agents in free radical polymerization in aqueous solution

The behavior of thiophenol and aliphatic thiols of different structure as chain transfer agents in the polymerization of acrylamide and 1-vinyl-2-pyrrolidone in aqueous solution at 25 °C was studied. Addition of millimolar concentrations of thiols to acrylamide polymerization reduced notably the polymer molecular weights, without change of the polymerization rate. Measurements at different pH showed that the reactive species towards the macroradicals is the protonated -SH group. Chain transfer constants, determined from Mayo plots, are only slightly dependent on the thiol structure. Aliphatic thiols and thiophenol react at similar rates. The selectivity is opposite for acrylamide (electron acceptor) and 1-vinyl-2-pyrrolidone (electron donor), pointing to significant charge transfer contributions. The reactions rates of these sulfur compounds with the electrophilic DPPH radical showed higher selectivity, and are not related with the chain transfer constants measured for the acrylamide macroradicals. These results are explained in terms of the different factors that control the reactivity of thiols with macroradicals.     

Direct UV photocrosslinking of poly(N-vinyl-2-pyrrolidone) (PVP) to produce hydrogels

Hydrogels for biomedical purposes, made from synthetic polymers as starting materials and free of co-adjuvant molecules, have been produced almost exclusively by high-energy radiative processes. On the other hand, UV photocrosslinking of such materials has been used in conjunction of monomers and/or photoinitiators. This work was addressed to the analysis of poly(N-vinyl-2-pyrrolidone) (PVP) submitted to direct photocrosslinking in aqueous solution, using low pressure Hg lamp (λ_em=254 nm). The process efficiency was evaluated, and the properties of the hydrogel formed were determined. The product thus formed has similar micro- and macroscopic properties, as compared to hydrogels produced by high-energy radiation and presents no cytotoxicity. These results demonstrated the viability of using this method as a versatile alternative to hydrogel production, broadening the possibility of its production where high-energy radiation facilities are not available.