Properties of poly[N-2-(methyacryloyloxy)ethyl-N,N-dimethyl-N-3-sulfopropylammonium betaine] in dilute solution

Poly[N-2-(methacryloyloxy)ethyl-N,N-dimethyl-N-3-sulfopropylammonium betaine] (1) which is an interesting polyzwitterion polymer by virtue of its “antipolyelectrolyte solution behaviour” has been prepared by free-radical initiated polymerization in aqueous solution. Isothermal fractionation was conducted at 294 K employing formamide as solvent and acetone as precipitant. Twelve fractions covering a wide range of weight-average molecular weight (215 000 ≤ M̄_w ≤ 2 070 000) were used to characterise the polymer by light scattering, membrane osmometry and viscosity measurements. The Mark-Houwink equations, established for 1 in two good solvents, 2,2,2-trifluoroethanol (TFE) and 1,0 M aqueous NaCl solution, show that the polymer has a random coil configuration and that TFE is a thermodynamically better solvent than 1,0 M aqueous NaCl solution. The random coil configuration of 1 in TFE was confirmed from the dependence of the polymer dimensions on molecular weight.     

The measurement of concentration and stability of weak acids and a study of the ionisation of polysaccharides using buffer capacity curves

A technique using buffer capacity has been developed for evaluating the approximate pK values of the stability constant K, of polyelectrolytes. The technique has been applied to hemicellulose extracted from woodpulp (pK ≈ 3,9 (0,1 M NaCl)) and dextran (pK = 13,55 ± 0,2 (2 M NaCl)). Verification of the method has been obtained by applying it to acetic acid (pK = 4,55 ± 0,02 (0,1 M NaCl), pK = 4,70 ± 0,02 (0,001 M NaCl)) and glucose (pK = 12,00 ± 0,05 (2 M NaCl)). Glucose was found to turn peppermint green in NaOH solutions. At least 50% of the surface charge of woodpulp was found to originate from its hemicellulose coating.     

Effect of the Density of ATRP Thiol Initiators in the Yield and Water Content of Grafted‐From PMETAC Brushes. A Study by Means of QCM‐D and Spectroscopic Ellipsometry Combined in a Single Device

Poly {[2‐(methacryloyloxy)ethyl] trimethylammonium chloride} (PMETAC) brushes are synthesized by atom transfer radical polymerization from mixed monolayers of ω‐mercaptoundecyl bromoisobutyrate thiol (initiator) and 1‐undecanethiol (blank). Initiator density is varied from 100% to 1% by the molar ratio of initiator to blank in solution. Brush growth is followed in situ by a single device combination of a quartz crystal microbalance with dissipation (QCM‐D) and spectroscopic ellipsometry. Acoustic mass (m_acous) and optical mass (m_opt) are simultaneously recorded. Brush hydration is calculated from the difference between m_acous and m_opt. The percentage of water lost during brush collapse in NaCl solution at concentration from 10^?3 M to 1 M is quantified for each initiator density.     

Characterization of molar mass and dilute solution properties of poly(ether sulfone) with high glass transition temperature

Characterization of high-temperature poly(ether sulfone) (HTPES) molar mass was performed using light scattering, viscometry and size-exclusion chromatography (SEC). In pure N-methyl-2-pyrrolidone (NMP), a large increase of the reduced viscosity at low concentration was observed. By addition of a salt such LiBr, this effect was suppressed. Using the viscosity laws of HTPES and poly(methyl methacrylate) (PMMA) in NMP + LiBr the SEC method was standardized via the universal calibration established with PMMA standards. The Mark-Houwink-Sakurada (MHK) relationship for HTPES in NMP containing 0,1 mol/L LiBr at 25°C with the intrinsic viscosity [η] and molecular weight M afforded the MHK constants K = 33,8 · 10^-5 dL · mol^a · g^1+a and a = 0,70. The weight-average molar masses obtained from SEC were very close to those obtained from light scattering. A comparison of number-average molar masses obtained from ¹H NMR, potentiometric titration of chain-ends, and from SEC has shown more discrepancy for high molar masses. The study of dilute solution properties of HTPES macromolecules has shown the marked decrease of anisotropy with the number of repeating units, the low values of the characteristic ratio and of the Kuhn segment. All these conformational properties are similar to those of freely rotating chains.     

Interaction between polynucleotides in aqueous NaCl solution, 4. Poly(riboadenylic acid) — poly(2-riboinosinic acid) system

Solution properties of poly(A) and poly(I) solution at a mole ratio of poly(A) to poly(I) of 1/2 were studied by means of calorimetry and a modified differential scanning calorimetry (DSC) with the help of circular dichroism (CD) and ultraviolet (UV) spectral methods. It was found that the heat of mixing, ΔH^M, depends sharply on the ionic strength. At [NaCl] < 10^?2 mol · dm^?3 ΔH^M is nearly zero. At higher ionic strength ΔH^M decreases and reaches a minimum value at [NaCl] ≈? 2 · 10^?2 mol ? dm^?3. Above this ionic strength ΔH^M increases again. This behavior is explained on the basis of the formation of a triplex poly(A) · poly(2I) and the transition of poly(I) from a disordered to an ordered structure with increasing ionic strength. The heat of formation, ΔH, of the poly(A) · poly(21) triplex was estimated to be ca ?41 kJ per mole of base triplet. Above an NaCl concentration of 2 · 10^?1 mol · dm^?3 the triplex formation may be represented by the following scheme:      

The thermal behavior of cycloalkanes

The thermal behavior of cycloalkanes (CH₂)_n with 12 ≤ n ≤ 84 prepared by metathesis reaction of cyclododecene, GPC separation of the oligomers, and hydrogenation has been investigated. The molar enthalpies of fusion being lower by a certain amount than those of the corresponding n-alkanes are a linear function of the chain length n. The entropy of fusion per CH₂ increases with chain length in a not-linear mode (when plotted vs. 1/n). The melting points of the cycloalkanes are lower than those of the corresponding n-alkanes, the difference becoming smaller with increasing chain length.     

Solid Polymer Electrolytes Based on Copolymers of Cyclic Carbonate Acrylate and n‐Butylacrylate

Solid polymer electrolytes (SPEs) are prepared by mixing poly(2‐oxo‐1,3‐dioxolan‐4‐yl)methyl acrylate‐random‐n‐butylacrylate) [P(cyCA‐r‐nBA)] statistical copolymers with bis(trifluoromethane)sulfonimide lithium salt. The P(cyCA‐r‐nBA) copolymers are synthesized by reversible addition‐fragmentation chain transfer polymerization and different molar masses as well as copolymer composition are targeted in order to study the influence of the molecular parameters on the thermal, mechanical, and electrochemical properties of the SPEs obtained after mixing the copolymers with lithium salts. In the investigated experimental window, it is shown that the thermal and mechanical properties of the SPEs mainly depend on the composition of the copolymer and are poorly influenced by the molar mass. In sharp contrast, the ionic conductivities are more deeply influenced by the molar mass than by the composition of the copolymers. In this respect ionic conductivity values ranging from 4.2 × 10^?6 S cm^?1 for the lower molar mass sample to 8 × 10^?8 S cm^?1 for the higher molar mass one are measured at room temperature for the investigated SPEs.     

Star polymers and block copolymers of 2-oxazolines using chloroformates as initiators

Polyfunctional chloroformates were applied to the polymerization of 2-phenyl-2-oxazoline and 2-methyl-2-oxazoline. The use of a trifunctional initiator, viz. the chloroformate of 2,2-bis(hydroxymethyl)-1-butanol, led to three-arm star polymers of 2-oxazolines. Two macromolecular initiators, viz. poly(ethylene oxide) with two chloroformate end groups (α-chloroformyl-ω-chloroformyloxypoly(oxyethylene)) with number-average molar masses 350 g/mol ≤ M?_n ≤ 6000 g/mol and α-chloroformyl-ω-methoxypoly(oxyethylene) with M?_n = 350 and 750 g/mol were applied for the synthesis of poly(2-oxazoline)-block-poly(ethylene oxide)-block-poly(2-oxazoline) and poly(2-oxazoline)-block-poly(ethylene oxide) copolymers, respectively.     

Thermodynamics of hydrogen bonding polymer-solute interactions by inverse gas chromatography

The gaschromatographic retention behaviour of a series of solutes with potential hydrogen bonding activity has been studied, using polyethylene, poly(ethylene-vinyl acetate), poly(vinyl acetate), and poly(ethylene glycol) as stationary phases. Measurements were performed at various temperatures above the melting point and/or glass transition temperature of the polymers and the slopes of the ln V versus 1/T-functions (where V is the specific retention volume) were used to calculate partial molar heats of solution (ΔH_s). Correspondingly, the temperature dependence of the activity coefficient can be used to calculate partial molar heats of mixing (ΔH?₁^infin;) of the solute at infinite dilution in the polymer. Based on a “homomorph” concept with the inherent assumption of additive group contributions to the total interaction energy, hydrogen bonding energies of polymer-solute systems could be separated using polyethylene on one hand and appropriate model solutes on the other hand as reference materials.     

Interaction between polynucleotides in aqueous NaCl solution, 5. Temperature dependence of the heat of formation of poly(I) · poly(C) duplex

The heat of mixing of equimolar solutions of poly(I) and poly(C) containing various NaCl concentrations was measured at 288 and 308 K, and the heat of formation of Poly(I) · poly(C) duplex from the randomly coiled constituents, poly(I) and poly(C), was estimated from the heat of mixing with the aid of CD measurements. The temperature dependence of this heat of formation, ΔH, differs at lower and higher NaCl concentrations: In the region of NaCl concentration less than 0,5 mol · dm^-3, ΔH increases with temperature, while in the region of NaCl concentrations higher than 0,5 mol · dm^-3, ΔH decreases with temperature. The free energy change, ΔG, of the formation of poly(I) · poly(C) duplex decreases as the NaCl concentration increases, that is, the stability of poly(I) · poly(C) duplex increases with NaCl concentration. Moreover, the conformation of poly(I) · poly(C) duplex seems to differ at lower and higher NaCl concentration as derived from the CD spectra and the thermodynamic quantities.     

Synthesis of alkoxysilyl-terminated polyisoprenes by means of “living” anionic polymerization, 1. Modeling of the termination step by studying the reaction of butyllithium with various alkoxysilane reagents

In order to optimize the preparation of trimethoxysilyl- or triethoxysilyl-terminated 1,4-polyisoprene and to facilitate their characterization, the termination reaction of the anionic polymerization of isoprene was investigated by means of a model reaction. Butyllithium (n-Buli) was used as a model molecule of the “living” ω-carbanionic polymer chain, and its reaction with various alkoxysilyl reagents (3-chloropropyltrimethoxysilane, tetramethoxysilane and tetraethoxysilane) was investigated. Studies were carried out by varying the molar ratio r = [n-BuLi]/[alkoxysilane] (0.5 ≤ r ≤ 3). The corresponding rate of substitution depends on r and on the nature of the coupling reagent. It was shown that alkoxy groups at the silicon center are easily n-Bu-substituted. Whatever, r, higher n-Bu-substituted derivatives are always simultaneously formed with the n-Bu-monosubstituted compound. With tetraalkoxysilane reagents, the formation of butyltrialkoxysilane is always favoured, compared to that of the di- and trisubstituted homologs. This was interpreted in terms of reactivity differences existing between the reacting alkoxysilanes present in the mixture. Attempts realized with 3-chloropropyltrimethoxysilane in order to obtain selective formation of alkyltrimethoxysilane derivative showed that chlorine substitution was impossible because nucleophilic attack of butyl carbanion occurs exclusively on the silicon atom.     

Water-soluble polymers with styrenesulfonate and maleic acid units in the backbone

The radical copolymerization of maleic acid (MAc) with sodium p-styrenesulfonate (sodium 4-vinylbenzenesulfonate) (NaSS) in aqueous solution yielded copolymers containing both: carboxylic and sulfonic groups attached to the backbone. By changing initiator concentrations and temperatures, the weight-average molecular weights, M?_w, were tailored in the range between 83 · 10³ and 265 · 10³. The corresponding intrinsic viscosities extended from 0,270 to 810 cm³/g, giving rise to the Mark-Houwink equation: [η] = 7,65 · 10^?6 · M^0,924 solvent aqueous 0,1 M NaCl; (25°C). The highest degree of conversion at the conditions employed amounted to 83%. Based on the sulfur content found analytically, an equal share of both monomeric units was established. The structure of the copolymer poly[(maleic acid)-co-(sodium p-styrenesulfonate)] obtained was elucidated by means of ¹³C NMR, ¹H NMR and IR spectroscopy. After converting the sulfonate groups to their H⁺ -form through ion exchange, the copolymer was submitted to potentiometric 0,1 M NaOH titration yielding a dE/dV vs. α curve (with E electromotive force, V volume of titrant and α degree of neutralization), which deviates in shape from theoretical expectations. This deviation was attributed to high ionic strength within the polymeric coils.     

Kinetics of ϵ-caprolactone polymerization and formation of cyclic oligomers

The kinetics of the anionic polymerization of ?-caprolactone, including the kinetics of macrocyclization and the kinetics of macrocycles propagation in THF solution, initiated with (CH₃)₃SiONa, were investigated. Rate constants of propagation (k_p(n)) and of back-biting (k_d(n)) involving monomer and cyclic oligomers (macrocycles) with n = 2, 3, … monomeric units were determined for n ≤ 7. It was found that starting from the tetramer k_d(n) ～ n^?1,4±0,1 and k_p(n) ～ n^0,7±0,15 (in Jacobson-Stockmayer's theory k_p(n) ～ n). This discrepancy is explained in terms of “conformational hindrance”, increasing for small cycles with the increase of the ring size until a certain ring size is reached. This hindrance decreases the availability of some of the ester groups in the macrocyclics for attack of the growing species, lowering in this way the exponent in the dependence of k_p(n) on n from one to a lower value.     

Facile Synthesis and Solid‐State Properties of Liquid‐Crystalline Polypeptides Bearing Biphenyl Mesogens and Alkyl Tails

A series of liquid‐crystalline 4‐alkyloxybiphenyl‐poly(γ‐propyl‐l ‐glutamate) conjugates (PPLG_n‐g‐BPC_m, n = 10, 54, 110, and 274, m = 4, 6, and 12) with end‐on biphenyl mesogens and variable alkyl tails is synthesized via a facile copper‐mediated alkyne–azide [2+3] 1,3‐dipolar cycloaddition. ¹H NMR and FTIR analyses reveal a quantitative conjugation efficiency for each sample. Variable‐temperature FTIR results indicate an irreversible α‐helical to β‐sheet transition of the PPLG₁₀‐g‐BPC₆ in the solid state, whereas PPLG_n‐g‐BPC_m samples with a longer main‐chain length (n ≥ 54) only adopt an α‐helical conformation in the temperature range between 25 and 200 °C. DSC, polarized optical microscopy (POM), and wide‐angle X‐ray scattering (WAXS) results collectively reveal that the PPLG_n‐g‐BPC_m samples undergo a reversible crystalline to liquid‐crystalline phase transition depending on the main‐/side‐chain lengths. The PPLG_n‐g‐BPC_m (n ≥ 54, m ≤ 6) samples form highly stable smectic (SmC or SmE) phases with a calculated tilt angle of 73–90°.

     

OH Radical-induced chemical reactions of polynucleotide complexes

Poly(A + U), the 1:1 complex of poly(riboadenylic acid), poly A, and poly(ribouridylic acid), poly U, at pH 8 and self-complexed poly A at pH 4 exist as double helices in dilute aqueous solution. These complexes exhibit a similar behavior as native calf thymus DNA upon irradiation with 16 MeV electron pulses. Thus time resolved Rayleight light scattering measurements showed that crosslinking and double strand breakage can be clearly separated, the former proceeding faster than the latter. The extent to which the two processes occur depends on the ionic strength of the solution. At ionic strenghts exceeding 10 ^?1 mol/l crosslinking is the dominant process indicating that h_crit, the critical length between two single strand breaks for the accomplishment of double strand breaks, is strongly reduced. The investigation of complexes of poly A and Mg²⁺ ions revealed that the destruction of salt bridges is the rate determining process for the decrease of the light scattering intensity due to mainchain scission. This implies that life-times of salt bridges can be determined.     

Evaluation of enzymatic proteoglycan loss and collagen degradation in human articular cartilage using ultrashort echo time-based biomarkers: A feasibility study

The objective of the current study was to investigate the feasibility of quantitative 3D ultrashort echo time (UTE)-based biomarkers in detecting proteoglycan (PG) loss and collagen degradation in human cartilage. A total of 104 cartilage samples were harvested for a trypsin digestion study (n = 44), and a sequential trypsin and collagenase digestion study (n = 60), respectively. Forty-four cartilage samples were randomly divided into a trypsin digestion group (tryp group) and a control group (phosphate-buffered saline [PBS] group) (n = 22 for each group) for the trypsin digestion experiment. The remaining 60 cartilage samples were divided equally into four groups (n = 15 for each group) for sequential trypsin and collagenase digestion, including PBS + Tris (incubated in PBS, then Tris buffer solution), PBS + 30 U col (incubated in PBS, then 30 U/ml collagenase [30 U col] with Tris buffer solution), tryp + 30 U col (incubated in trypsin solution, then 30 U/ml collagenase with Tris buffer solution), and tryp + Tris (incubated in trypsin solution, then Tris buffer solution). The 3D UTE-based MRI biomarkers included T₁, multiecho T₂*, adiabatic T_1ρ (AdiabT_1ρ), magnetization transfer ratio (MTR), and modeling of macromolecular proton fraction (MMF). For each cartilage sample, UTE-based biomarkers (T₁, T₂*, AdiabT_1ρ, MTR, and MMF) and sample weight were evaluated before and after treatment. PG and hydroxyproline assays were performed. Differences between groups and correlations were assessed. All the evaluated biomarkers were able to differentiate between healthy and degenerated cartilage in the trypsin digestion experiment, but only T₁ and AdiabT_1ρ were significantly correlated with the PG concentration in the digestion solution (p = 0.004 and p = 0.0001, respectively). In the sequential digestion experiment, no significant differences were found for T₁ and AdiabT_1ρ values between the PBS + Tris and PBS + 30 U col groups (p = 0.627 and p = 0.877, respectively), but T₁ and AdiabT_1ρ values increased significantly in the tryp + Tris (p = 0.031 and p = 0.024, respectively) and tryp + 30 U col groups (both p < 0.0001). Significant decreases in MMF and MTR were found in the tryp + 30 U col group compared with the PBS + Tris group (p = 0.002 and p = 0.001, respectively). It was concluded that AdiabT_1ρ and T₁ have the potential for detecting PG loss, while MMF and MTR are promising for the detection of collagen degradation in articular cartilage, which could facilitate earlier, noninvasive diagnosis of osteoarthritis.     

Cytoplasmic distribution of poly(A)-containing RNA in developing Necturus maculosus oocytes with reference to annulate lamellae

The cytoplasmic distribution of poly(A)⁺ mRNA and its relationship to annulate lamellae were examined in developing Necturus maculosus oocytes by in situ hybridization with [³H]poly(U). The specificity of [³H]poly(U) binding was tested by incubating control ovarian sections with either KOH or RNase A before in situ hybridization. In both experiments, the silver grain densities were markedly reduced. Poly(A)⁺ RNA is uniformly distributed in the cytoplasm until the mid-growth phase and then later in vitellogenesis becomes localized in the subcortical ooplasm. The silver grain density in the cytoplasm varied during oogenesis and was greatest in previtellogenic oocytes. Annulate lamellae commonly are observed with the light microscope in oocytes prior to vitellogenesis. In such oocytes, the labeled mRNA probe is observed over cytoplasmic regions of annulate lamellae. The results suggests that a differential localization of messenger RNA occurs during oogenesis in Necturus maculosus. Furthermore, poly(A)⁺ RNA is present in cytoplasmic regions of annulate lamellae.     

Small angle neutron scattering (SANS) of cyclic and linear polystyrene in toluene

Samples of ring and open chain polystyrene in dilute perdeuterated toluene solution were measured by small angle neutron scattering up to a value of the scattering vector Q = 2 nm^?1. The molar masses 12000 ≤ M/(g/mol) ≤ 22000, the mean square radii of gyration 〈R²〉 and the second virial coefficients A₂ of the samples were determined. The results are compared to theories which describe the dependencies 〈R²〉 = f(M) and A₂ = f(M) for both cyclic and linear chain molecules. A qualitative agreement between theory and experiment is obtained.     

Preparation of ordered and crosslinked films from liquid crystalline p-vinylphenoxy-based monomers

The synthesis of the following monofunctional and bifunctional liquid crystalline p-vinylphenoxy-based monomers is described: 4-methoxyphenyl 4-[11-(4-vinylphenoxy)-undecyloxy]benzoate ( 1 ), 4-cyanophenyl 4-[11-(4-vinylphenoxy)undecyloxy]benzoate ( 2 ) and 3-(4-vinylphenoxy)propyl 4-{4-[11-(4-vinylphenoxy)undecyloxy]benzoyloxy}benzoate ( 3 ). Both free radical and cationic polymerization of the monofunctional monomers 1 and 2 yielded side-chain liquid crystalline polymers exhibiting smectic A mesomorphism. The polymers exhibited high molar masses (M _n = 40000 – 100000 g/mol) and relatively narrow molar mass distributions (M _w/M _n between 1.5 and 3). Ordered thin films were prepared by in-situ photopolymerization of monomers 1 , 2 and 3 oriented in their nematic mesophases. Thin films of a thermally stabilized ordered side-chain liquid crystalline polymer were prepared by copolymerization of the monofunctional monomer 1 and the bifunctional monomer 3 , the latter present in low concentration. The films regained orientation when cooled down from temperatures above the isotropization point (137°C) as evidenced by polarized FT-Raman measurements.     

Die Wärmekapazität von vollständig kristallinen Copolymeren des Polyoxymethylens

The molar heat capacity of fully crystalline copolymers of trioxane and 1,3-dioxolane can be discribed by the equation C_p(x₂, T) = 36,75 + 0,1425 (t₂ ? 25) + 80 x₂ in the temperature range 25°C < t < 140°C and at mole fraction of oxyethylene units x₂ < 0,16. For x₂ < 0,1 the molar heat capacity depends linearly on the reduced temperature T/T_m(x₂), but is independent from counit content.