Depurination of synthetic poly(inosinic acid) analogues

A poly(inosinic acid) analogue, poly{[1′-(β-hypoxanthine-9-yl)-5′-deoxy-D -erythro-pent-4′-enofuranose]-alt-[maleic acid]} (4), was synthesized by the alternating copolymerization of nucleoside derivative 1 with maleic anhydride and subsequent hydrolysis. N-Glycosidic bonds of the polymer were spontaneously hydrolyzed to liberate hypoxanthine from the polymer backbone in a buffer solution (pH 7.4) at room temperature. The depurination rate constant of the polymer at pH 7.4 and 37°C was measured to be 1.9 × 10⁻⁶ sec⁻¹, which was 10⁵-fold higher than that (3 × 10⁻¹¹ sec⁻¹) of the depurination of DNA that occurred in the biological systems. The increase in the depurination rate was attributable to the high potential energy of the polymer caused by the crowded environment around the bases, so that the polymer was more susceptible to the hydrolysis. Since natural nucleic acids often have compact structures with the crowded environment around the bases by the intricate chain folding, the depurination may also be accelerated in a similar manner in the biological system. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3361–3365, 1999     

Miscibility of poly(ϵ-caprolactone) and of poly(styrene-co-acrylonitrile) with poly(styrene-co-acrylic acid)

The miscibility of poly (?-caprolactone) (PCL) with poly (styrene-co-acrylic acid) (SAA) and of poly (styrene-co-acrylonitrile) (SAN) with SAA was examined as a function of the comonomer composition in the copolymers. For PCL/SAA blends it was found that PCL is miscible with SAA within a specific range of copolymer compositions. Segmental interaction energy densities were evaluated by analysis of the equilibrium melting point depression and application of a binary interaction model. The results suggest that the intramolecular repulsion in SAA copolymer plays an important role in inducing the miscibility. Additionally, the critical AA content in SAA for the blend to be homogeneous was predicted by correlating the segmental interaction energy densities with the binary interaction model. For SAN/SAA blends, it was also found that SAA is miscible with SAN within a specific range of copolymer compositions. From the binary interaction model, segmental interaction energy denisties between different monomer units were estimated from the miscibility map and were found to be positive for all pairs, indicating that the miscibility of the blends is due to the strong repulsion in the SAA copolymers.     

Highly efficient flame retardant poly(lactic acid) using imidazole phosphate poly(ionic liquid)

Because of good thermal stability, nonflammability and rich structural designability, ionic liquids (ILs) have been used as flame retardants for poly(lactic acid) (PLA). However, as a small molecule, IL has the disadvantages of poor thermal stability and water resistance, and so on. In this paper, an imidazole‐type poly(ionic liquid) (PIL) containing a phosphate anion was synthesized using 1‐vinylimidazole, triethyl phosphate, and 1,2‐divinylbenzene and marked as PDVE[DEP]. The PDVE[DEP] was used to improve the flame retardancy of PLA. The flame retardancy and thermal degradation behaviors of PLA/PDVE[DEP] composites were investigated by the limited oxygen index (LOI), UL‐94 vertical burning, cone calorimetry, and thermal gravity analysis, and so on. The results showed that only 1.0 wt% PDVE[DEP] allows PLA to achieve the UL‐94 V0 rating and obtain LOI value 25.6 vol%. The PDVE[DEP] improve the flame retardancy of PLA by melting‐away mode. In addition, it catalyzes the transesterification of PLA and changes the degradation products.     

Osmotic deswelling of weakly charged poly(acrylic acid) solutions and gels

The osmotic pressure of weakly charged aqueous poly(acrylic acid) (PAA) solutions and the swelling pressure PAA gels were studied by osmotic deswelling at different degrees of ionization (α). In solution, the osmotic pressure was found to scale linearly with concentration, whereas the scaling power of the swelling pressure of gels was higher (1.66). The effect of the ionization degree on the osmotic coefficient in PAA solutions was in agreement with the theory of Borue and Erukhimovich [Macromolecules, 21 , 3240 (1988)]. Ionization increases the swelling capacity of the PAA gels until a plateau is reached at about 35% neutralization. The concentration at equilibrium swelling scales as C_e ～ α^?0.6. The contribution of the network to the gel swelling pressure is evaluated by subtracting the osmotic pressure of the polymer solution at the same concentration and degree of ionization. In swollen gels the extended network opposes swelling. As the gel is osmotically deswelled, a state of zero network pressure exists at a certain concentration, below which the network elasticity favors swelling. The crossover concentration shifts to lower values as the degrees of ionization increases. © 1995 John Wiley & Sons, Inc.     

Synthesis of poly(glycolic acid) in ionic liquids

The synthesis of poly(glycolic acid) (PGA) by polyesterification of glycolic acid was studied using ionic liquids, mainly 1,3‐dialkylimidazolium salts, as reaction media. The ¹H NMR spectra of PGA oligomers were assigned and end‐group signals were used to follow the reaction. Low PGA yields were obtained by the direct polyesterification of glycolic acid at 200–240 °C, because of monomer evaporation during the reaction. On the other hand, PGAs of DP _n up to 45 were obtained by the postpolycondensation of a preformed oligomer in 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIm⁺Tf₂N^?). The precipitation of PGA in reaction medium at long reaction times limited the achievable molar mass. Rate constants were determined for catalyzed and noncatalyzed reactions, assuming a second‐order reaction mechanism. The efficiency of esterification catalysts such as Zn(OAc)₂ was low in these media, as only about twofold increases in reaction rate were observed. This was assigned to the preferential interaction of Zn²⁺ with ionic liquid anion instead of the polymer carboxylic acid end‐groups. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3025–3035, 2006     

Ionic complexes of biosynthetic poly(malic acid) and poly(glutamic acid) as prospective drug-delivery systems

The hydrolytic degradability and erythromycin release from stoichiometric ionic complexes of biotechnological poly(beta,L-malic acid)s and poly(gamma,D-glutamic acid)s with alkyltrimethylammonium surfactants were investigated. The influence of pH, temperature and antibiotic load on hydrolysis rate was examined. It was found that poly(malic acid) complexes degraded by a surface erosion mechanism at a higher rate than poly(glutamic acid) complexes, which eroded in bulk. Erythromycin was lodged in the paraffinic subphase of the complexes and upon aging it was delivered according to a sigmoidal profile that appeared to be independent on the antibiotic load.     

The synthesis and characterization of monodisperse poly(acrylic acid) and poly(methacrylic acid)

A number of polyacrylic (PAA) and polymethacrylic (PMAA) acids have been synthesized by living anionic polymerization of the monomeric tert-butyl esters followed by subsequent hydrolysis of the corresponding polyesters. The necessary precautions were taken in order to assure good molecular weight control, as well as high yields in the polymerization reactions. The intermediate and final polymers were characterized by gel permeation chromatography and NMR-H¹ spectrometry.     

Swelling of hydrophobically modified poly(acrylamide) and poly(acrylamide)-co-(acrylic acid) gels in surfactant solutions

A series of hydrophobically modified polyacrylamide and polyacrylamide-co-poly(acrylic acid) gels with systematically varying hydrophobicity were prepared by free-radical polymerization of acrylamide, n-alkylacrylamides (n = 10, 12, and 14), and acrylic acid. The swelling of these gels was examined in water and in both anionic and cationic surfactant solutions. It was found that the gels which incorporated acrylic acid showed extremely high swelling in water. Maximum swelling was observed in gels which incorporated 10 mol% acrylic acid. The swelling of these gels was much less in solutions of both anionic and cationic surfactants than in water. The gels which did not incorporate acrylic acid demonstrated little swelling in water, but showed increased swelling in both anionic and cationic surfactant solutions with increased hydrophobicity of the gel. Received: 1 February 1999 Accepted in revised form: 5 March 1999     

MMTCA recognition by molecular imprinting in interpenetrating polymer network hydrogels based on poly(acrylic acid) and poly(vinyl alcohol)

A novel IPN hydrogel designed to recognize MMTCA is prepared by applying the molecular-imprinting method. The IPN is characterized by FT-IR, DSC, and SEM. Langmuir analysis shows that an equal class of adsorption is formed in the hydrogel. The adsorption equilibrium constant and the maximum adsorption capacity are evaluated, and the effect of the pH on MMTCA adsorption is discussed. The selectivity of the imprinted polymer for MMTCA is studied in aqueous solutions of MMTCA/aspirin/riboflavin. The results suggest that the MMTCA-imprinted polymer shows superior selectivity for MMTCA as compared to riboflavin and aspirin. The reproducibility of the imprinted polymer to MMTCA is also studied.     

Molecular modeling of polymers. 10. Characterization of conformational transitions of poly(acrylic acid) and poly(methacrylic acid) using dyad structures

The conformational profiles of nearest side-chain neighbors, methylene-dyad structures, of poly(acrylic acid), PAA, and poly(methacrylic acid), PMA, were determined as a function of tacticity, extent of ionization, and presence of counterion. The dominant backbone conformer states are quite similar for both isotactic and syndiotactic diads in a common charge state. Thus, the overall dimensional properties of isotactic syndiotactic and atactic chains of PAA or PMA, based upon dyad interactions, are predicted to be alike for a given charge state. Significant deviations from precise t, g⁺, and g^? states are found for the dyad minimum energy conformations. The rod-to-coil and coil-to-rod transitions observed in PAA and PMA, respectively, as a function of increasing counterion concentration can be explained, to a large extent, by the conformational profiles of the corresponding dyad model structures. © 1994 John Wiley & Sons, Inc.     

Enhanced stereocomplex formation of poly(L-lactic acid) and poly(D-lactic acid) in the presence of stereoblock poly(lactic acid)

Stereoblock poly(lactic acid) (sb-PLA) is incorporated into a 1:1 polymer blend system of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) that has a high molecular weight to study its addition effect on the stereocomplex (sc) formation of PLLA and PDLA. The ternary polymer blend films are first prepared by casting polymer solutions of sb-PLA, PLLA, and PDLA with different compositions. Upon increasing the content of sb-PLA in the blend films the sc crystallization is driven to a higher degree, while the formation of homo-chiral (hc) crystals is decreased. Lowering the molecular weight of the incorporated sb-PLA effectively increases the sc formation. Consequently, it is revealed that sb-PLA can work as a compatibilizer to improve the poor sc formation in the polymer blend of PLLA and PDLA.     

Swelling kinetics of poly(aspartic acid)/poly(acrylic acid) semi‐interpenetrating polymer network hydrogels in urea solutions

Semi‐interpenetrating network (semi‐IPN) hydrogels, composed of poly(aspartic acid) (PAsp) and poly(acrylic acid) (PAAc) with various ratios of PAsp to AAc, were prepared. In this work, swelling kinetics was investigated through calculating some parameters. The swelling ratios were measured at room temperature, using urea solutions as liquids to be absorbed. Compared to in deionized water, the hydrogels showed larger swelling ratios in urea solutions, which might be attributed to the chemical composition of urea. The equilibrium swelling ratio could achieve 600 g/g, and the equilibrium urea/water contents were more than 0.99. The diffusion exponents were between 0.5 and 0.7, suggesting that the solvent transport into the hydrogel was dominated by both diffusion and relaxation controlled systems. Therefore, the PAsp/PAAc semi‐IPN hydrogels were appropriate to carry substances in a urea/water environment for pharmaceutical, agricultural, environmental, and biomedical applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 666–671, 2010     

Isothermal kinetics of dehydration of equilibrium swollen poly(acrylic acid) hydrogel

An isothermal dehydration of equilibrium swollen poly(acrylic acid) hydrogel in the temperature range from 306 to 361 K was investigated. The specific parameters connected with shape of the conversion curves were defined. The activation parameters (E, lnA) of the isothermal dehydration of equilibrium swollen poly(acrylic acid) hydrogel were calculated, using Johnson-Mehl-Avrami (JMA), ‘initial rate’ and ’stationary point’ methods. The reaction models for the investigated dehydration are determined using the ‘model-fitting’ method. It was established that both, the reaction model and activation parameters of the hydrogel dehydration were completely different for the isothermal process than for the non-isothermal one. It was found that the increase in dehydration temperature lead to the changes in isothermal kinetic model for the investigated hydrogel dehydration. It was established that the apparent activation energy (E) of hydrogel dehydration is similar to the value of the molar enthalpy of water evaporation.     

Surface modification of glass beads with poly(acrylic acid)

Non‐porous P₂ glass beads were etched with sodium hydroxide to increase the number of silanol groups that could be used to modify the surface. The etched glass beads were then functionalized with 3‐aminopropyltriethoxysilane (APS) and/or glycidoxypropyltrimethoxysilane (GPS). The surface of the glass beads were further modified with poly(acrylic acid) (PAA) by reacting the carboxyl groups on PAA with the amino groups of the pregrafted APS. The chemical modifications were characterized by FT‐IR spectroscopy, particle size analyzer and tensiometry for contact angle and porosity measurements. Five different molecular weight PAA polymers ranging from 2000 to 3,000,000 were grafted with less than expected increase of grafted PAA with molecular weight. The amount of APS and PAA on the surface was determined from thermogravimetric analysis and elemental analysis data. The surface properties of the surface modified glass beads were determined by measuring water and hexane penetration rate and contact angle. The surface morphology was examined by scanning electron microscopy. Copyright © 2006 John Wiley & Sons, Ltd.     

Structures of poly(p-hydroxybenzoic acid) (PHBA) at ambient temperature

The molecular structure of poly (p-hydroxybenzoic acid) (C₆H₄COO)_x at ambient temperature was determined by x-ray powder diffraction analysis. The diffraction pattern is explained as a mixture of two orthorhombic phases having the same space group Pbc2₁ with four C₆H₄COO chemical repeats in the unit cell and the following cell parameters: a = 7.42 Å, b = 5.70 Å, and c = 12.45 Å for phase I (ρ_calc = 1.51 g cm^?3); and a = 3.83 Å, b = 11.16 Å, and c = 12.56 Å for phase II (ρ_calc = 1.48 g cm^?3). The chain conformation is the same in both phases, involving two benzoyl rings staggered by ca. 120° along the chain. Disorder has been considered in the packing of phase I by giving equal occupancy to the two molecules oriented up or down along the c chain axis. ©1995 John Wiley & Sons, Inc.     

Heat capacities of poly(amino acid)s and proteins

In an ongoing effort to understand the thermodynamic properties of proteins, solid-state heat capacities of poly(amino acid)s of all 20 naturally occurring amino acids and 4 copoly(amino acid)s have been previously reported on and were analyzed using our Advanced THermal Analysis System (ATHAS). We extend the heat capacities of poly(L-methionine) (PLMFT) and poly(L-phenylalanine) (PLPHEA) with new low temperature measurements from 10 to 340 K. In addition, analyses were performed on literature data of a first protein, zinc bovine insulin dimer C₅₀₈H₇₅₂O₁₅₀N₁₃₀S₁₂Zn, using both the ATHAS empirical addition scheme and computation with an approximate vibrational spectrum for the protein. For the solid state, agreement with the measurement could be accomplished to ±1.6% for PLMET, ±3.5% for PLPHEA, and ±3.2% for insulin, linking the macroscopic heat capacity to its microscopic cause, the group and skeletal vibrational motion. For each polymer, one set of parameters, Θ₁ and Θ₃, of the Tarasov function representing the skeletal vibrational contribution to the heat capacity are obtained from a new optimization procedure [PLMET: 542 K and 83 K (number of skeletal vibrations N_s = 15); PLPHEA: 396 K and 67 K (N_s = 11); and insulin monomer: 599 K and 79 K (N_s = 628), respectively]. Enthalpy, entropy, and Gibbs free energy have been derived for the solid state. © 1995 John Wiley & Sons, Inc.     

Thermal analysis of the double-melting behavior of poly(L-lactic acid)

The melting and crystallization behavior of poly(L -lactic acid) (PLLA; weight-average molecular weight = 3 × 10⁵) was studied with differential scanning calorimetry (DSC). DSC curves for PLLA samples were obtained at various cooling rates (CRs) from the melt (210 °C). The peak crystallization temperature and the exothermic heat of crystallization determined from the DSC curve decreased almost linearly with increasing log(CR). DSC melting curves for the melt-crystallized samples were obtained at various heating rates (HRs). The double-melting behavior was confirmed by the double endothermic peaks, a high-temperature peak (H) and a low-temperature peak (L), that appeared in the DSC curves at slow HRs for the samples prepared with a slow CR. Peak L increased with increasing HR, whereas peak H decreased. The peak melting temperatures of L and H [T_m(L) and T_m(H)] decreased linearly with log(HR). The appearance region of the double-melting peaks (L and H) was illustrated in a CR–HR map. Peak L decreased with increasing CR, whereas peak H increased. T_m(L) and T_m(H) decreased almost linearly with log(CR). The characteristics of the crystallization and double-melting behavior were explained by the slow rates of crystallization and recrystallization, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 25–32, 2004     

Synthesis and characterization of poly(succinimide-co-6-aminocaproic acid) by acid-catalyzed polycondensation of L-aspartic acid and 6-aminocaproic acid

The polycondensation of L -aspartic acid ( ASP ) with 6-aminocaproic acid ( ACA ) using o-phosphoric acid produced poly(succinimide-co-6-aminocaproic acid). The yield of the MeOH-insoluble copolymer decreased from 99 to 52% and that of the MeOH-soluble one increased from 9 to 47%, with increasing molar ratio of ACA in the monomer feed. The compositions of the succinimide ( SCI ) unit in the MeOH -insoluble and -soluble copolymers tended to be higher than those of ASP in the monomer feed. The copolymers with the 35 mol % SCI units or above were soluble in DMSO , DMF , and conc- H₂SO₄ , but those with the 20 and 21 mol % SCI units were soluble only in conc-H₂SO₄. The melting temperature appeared for the copolymers with less than 76 mol % SCI units. Poly(succinimide-co-6-aminocaproic acid) was easily hydrolyzed to yield poly(aspartic acid-co-6-aminocaproic acid), and it exhibited biodegradability toward activated sludge. © 1997 John Wiley & Sons, Inc.     

Preparation, characterization and application of pyrene-loaded methoxy poly(ethylene glycol)–poly(lactic acid) copolymer nanoparticles

Pyrene-loaded biodegradable polymer nanoparticles were prepared by incorporating pyrene into the polymer nanoparticles formulated from amphiphilic diblock copolymer, methoxy poly(ethylene glycol)–poly(lactic acid) (MePEG–PLA). Their morphological structure and physical properties were characterized by nuclear magnetic resonance (NMR), dynamic light scattering, fluorescence spectroscopy, transmission electronic microscopy and zeta potential measurements. Further, MePEG–PLA nanoparticles containing pyrene as fluorescent marker were administered intranasally to rats, and the distribution of nanoparticles in the nasal mucosa and the olfactory bulb were visualized by fluorescence microscopy. NMR results confirmed that MePEG–PLA copolymer can form nanoparticles in water, and hydrophilic PEG chains were located on the surface of the nanoparticles. The particle size, zeta potential and pyrene loading efficiency of MePEG–PLA nanoparticles were dependent on the PLA block content in the copolymer. Following nasal administration, the absorption of nanoparticles across the epithelium was rapid, with fluorescence observed in the olfactory bulb at 5 min, and a higher level of fluorescence persisted in the olfactory mucosa than that in the respiratory mucosa. These results show that pyrene could serve as a useful fluorescence probe for incorporation into polymer nanoparticles to study tissue distribution and MePEG–PLA nanoparticles might have a great potential as carriers of hydrophobic drugs.