Unperturbed Chain Dimensions Research Articles

Physical properties of some organophosphazene copolymers. II. Thermoelasticity andin situ reinforcement of the cross-linked networks

Aryloxy phosphazene copolymers with phenoxy andp-ethyl phenoxy substituents were cross-linked into elastomeric networks and studied with regard to their stress-strain and thermoelastic (force-temperature) behavior. The thermoelastic results showed that the energetic contribution to the elastic force was negative, indicating that the unperturbed dimensions of the polymer chains decrease with increases in temperature.In situ precipitation of silica into the elastomers by hydrolysis of an absorbed alkoxysilane was found to give excellent network reinforcement.

Polystyrene in N-Methylpyrrolidone: Intrinsic Viscosity-Molar Weight Relations and Polystyrene Unperturbed Dimensions

Intrinsic viscosity-molar weight relations are reported for polystyrene in N-methylpyrrolidine (NMP) and NMP/LiBr solutions at 30, 45, 60, 75, 90 and 105 °C. Also, Mark-Houwink constants KΘ and the unperturbed dimensions of the polystyrene chains at these temperatures are calculated by applying Stockmayer-Fixman extrapolations of the viscosity/molar weight data. The use of in-line size exclusion chromatography and viscometry is shown to be a facile and accurate method for such studies.

Unperturbed chain dimensions of polysilane in the third-order interaction approximation

The configurational energies, the characteristic ratio and the temperature coefficient for a polysilane chain with the third-order interaction are calculated. The characteristic ratios (〈 R 2〉/ nl 2) ∞ and (〈 S 2〉 0/ nl 2) ∞ are 3.57 and 0.575, respectively, and the temperature coefficient is −3.0 × 10 −3 deg −1. These results are less than those in the second-order interaction approximation. The third-order interaction approximation are useful for calculating the dimensions of polymer chains.

Molecular dynamics simulations of poly(dialkylsiloxanes): conformational statistics and unperturbed chain dimensions

Molecular dynamics trajectories have been computed for isolated poly(dialkylsi1oxane) chains in which the alkyl groups are methyl, ethyl, propyl, butyl, isopropyl, isobutyl, or tert-butyl. The joint probability profiles for the pair of Si-0 bonds flanking a silicon atom are insensitive to the changes in the alkyl sub- stituents. In contrast, the joint probability profiles for the pair of bonds flanking an oxygen atom change systematically as the size of the alkyl group increases. There is a strong correlation in the dihedral angles at these two bonds when the alkyl groups are large. The features in these probability profiles are incorporated into a rotational isomeric state analysis that permits predictions of the characteristic ratio, C, in the limit as n - m. If the alkyl groups are not branched, the values of C, increase with the size of the alkyl group and reach a limit of about 8.3. Branching of the side chain reduces the characteristic ratio.

Conformational characteristics of some model polydienes and polyolefins

The unperturbed chain dimensions of monodisperse polymers based on 1,3-butadiene, 2,3-dimethylbutadiene, 2-ethyl-1,3-butadiene and 3-methylene-7-methyl-1,6-octadiene and their saturated polyolefinic analogues were evaluated under θ or near-θ conditions via intrinsic viscosity measurements. Information was obtained regarding the influence of side-chain length on chain dimensions as well as the influence of head-to-head structures in polypropylene.

Conformational characteristics of the polycarbonate of 4,4'-isopropylidenediphenol

Abstract : A classical force field has been developed to represent the conformational characteristics of the polycarbonate of 4,4'- isopropylidenediphenol ('bisphenol-A polycarbonate', PC) based upon recent experimental and quantum mechanical data reported for diphenylcarbonate and diphenylpropane. This force field is an improvement upon previously published molecular mechanics force fields because it allows for rotation about all the single bonds in the PC repeat unit. A rotational isomeric state model PC has been obtained using the force field results; the computer unperturbed chain dimensions agree well with reported experimental values.

Some Dilute Solution Properties of Highly Isotactic Polyacrylonitrile in Aq. Nitric Acid

An attempt was made to investigate the dilute solution properties of highly isotactic polyacrylonitrile (PAN) dissolved in aq. nitric acid and to estimate the molecular parameters, such as the unperturbed chain dimension A and the characteristic ratio C∞. For this purpose a highly isotactic polymer with isotactic triad content of 73.4% was synthesized by irradiating γ-ray on acrylontrile–urea canal complex at −78°C and was subjected to successive precipitation fractionation, using dimethyl sulfoxide as solvent and toluene as precipitant, into 7 fractions. Among them 2 fractions with isotactic triad of 71.0 and 77.9%, respectively were employed for further study. The weight-average molecular weight Mw and the second virial coefficient A2 of these fractions in 70 wt% aq. nitric acid soln. were measured by the light scattering method. The 70 wt% aq. nitric acid soln. was predicted to be able to dissolve perfectly-isotactic PAN with Mw of 1.5–2.6×105 at room temperature. The Mark–Houwink–Sakurada equations in aq. nitric acid solutions differ significantly depending on the stereoregularity of PAN employed, even if highly concentrated acids are used. A 57.5 wt% aq. nitric acid soln. is determined, by the dependence of A2 on the nitric acid concentration, to be a Flory’s theta solvent for PAN with isotactic triad of 71.0% at 25°C. A of PAN increases rapidly with isotactic triad content, especially in the range higher than 50%. C∞ of PAN is always far larger than the calculated value of non-polar Monte Calro chain for polypropyrene [P. J. Flory et al., J. Am. Chem. Soc., 88, 639 (1966)] over the whole range higher than 50% isotactic diad.

Configurational statistics of poly(dimethylsiloxane). 2. A new rotational isomeric state approach

A new RIS treatment, compatible with the molecular mechanics and dynamics considerations of a preceding paper, is introduced. The model yields satisfactory agreement with experiments on the mean-square unperturbed end-to-end separations, the mean-square dipole moment and its temperature dependence, and the molar cyclization equilibrium constants for dimethylsiloxane oligomers. It cannot account for the positive temperature coefficient of the unperturbed chain dimensions

Unperturbed chain dimensions of polyisobutylene in different solvents and at different temperatures

Intrinsic viscosity of polyisobutylene is determined in different solvents and at different temperatures. The intrinsic viscosity is found to increase with the increase in temperature. These variations are explained in terms of variation in thermodynamic quality of the solvent. From these data, the upertubed parameter (k0) is determined. It is observed that it firstly increases with temperature and then seems to level off and is found to be different for different solvents. k0 is also correlated with different thermodynamic parameters like ΔH, δA, ψ and χ.

Solvent effects on the unperturbed chain conformation of polysaccharides

A theoretical account of solvent effects on the unperturbed dimensions is given for two representative polysaccharides, amylose and cellulose. A solvation energy term is calculated for each conformational state by evaluating the contributions of cavity formation and of the interaction between solvent and solute. A significant change in the profiles of conformational surfaces is found in the three solvents considered (water, dioxane and dimethylsulphoxide). As a straightforward consequence, unperturbed chain dimensions are predicted to be solvent-dependent, as already found experimentally for the two polysaccharides considered, as well as for other polar polymers.

Solution properties and characteristic ratio of near-monodisperse poly(tert-butyl methacrylate)

The dilute solution properties of six near-monodisperse samples of poly(tert-butyl methacrylate) covering the molecular weight range \(3 \times 10^4 \leqslant \bar M_w \leqslant 1.1 \times 10^6 \) are reported. Unperturbed chain dimensions were derived from a combination of light scattering and intrinsic viscosity data. A characteristic ratio (C∞) of 12.0 was obtained in the theta solvent cyclohexane at 10°C. This C∞ value is considerably larger than the value of 8.8 reported previously for poly(n-butyl methacrylate) and reflects the greater bulkiness of the tert-butyl substituent and also, possibly, tacticity effects.

Solution and thermal properties of poly(1,3‐dioxocane)

AbstractPoly( 1,3‐dioxocane) was synthesized by cationic ring‐opening polymerization with triphenyl‐methane hexafluoroantimoniate as the initiator and was studied with regard to its solubility, unperturbed chain dimensions, and thermal transitions. The intrinsic viscosity and Flory‐Huggins interaction parameter were used to determine the solubility parameter, δp = 9.6 cal1/2cm−3/2, a value that agrees with that calculated empirically. Fractions were obtained from the solvent/non‐solvent system benzene/methanol at 25°C. The number‐average molecular weight Mn and intrinsic viscosity [η] were measured in toluene at 25°C. The relation [η] = 1.459. 10−4 Mn0.79 was found. A value of 5.3 was obtained for the characteristic ratio 〈r2〉0/nl2. Results are correlated with the main thermal transitions of this polyformal.

Characterization of p-t-butylstyrene-dimethylsiloxane triblock copolymers in solution

Anionically synthesized poly( p-t-butylstyrene)- b-poly(dimethylsiloxane)- b-poly(p-t-butylstyrene) block copolymers containing about 28% by weight p-t-butylstyrene were characterized by using differential refractometry, light scattering and viscosity methods in a good solvent, benzene, and in a selective solvent, methyl ethyl ketone. The unperturbed chain dimensions were estimated. Results were discussed with regard to the conformation of block copolymers in solution.

Conformational energies and unperturbed chain dimensions of poly(phenylmethylsilylene) and poly(silastyrene)

Calcul a l'aide des techniques de mecanique moleculaire de la structure moleculaire et les energies conformationnelles de composes modeles des polymeres (SiPhMe) n et (SiPhH-SiH 2 ) n dans leur forme isotactique et syndiotactique. Calcul a partir de ces valeurs a l'aide de la theorie RIS des dimensions de chaine non perturbees et de leur coefficient de temperature

Temperature and solvent effects on the unperturbed chain dimensions of bisphenol-A polycarbonate

The temperature dependence (from 25 to 80°C) of the intrinsic viscosity of bisphenol-A polycarbonate fractions (0.6⩽ M × 10 −4⩽30) was determined in dioxan and tetrachloroethane. The temperature quotient of the unperturbed mean-square end-to-end distance, ( dln〈R 2〉 0 M ) ∞ d T, was estimated and found to be slightly negative. A weak solvent effect on the value of ( 〈R 2〉 0 M ) ∞ was established. The results are compared with theoretical predictions and with reported data.

Star branched polystyrenes: an evaluation of solvent and temperature influences on unperturbed chain dimensions

Temperature coefficients of unperturbed dimensions of three high molecular weight polystyrene stars have been evaluated from intrinsic viscosity measurements in six theta solvents and two solvent/nonsolvent mixtures over a temperature range of 10 to 70°C. Larger values of unperturbed dimensions were found in cyclic aliphatic solvents than in chloroalkanes at similar temperatures. Negative values of the temperature coefficient of unperturbed dimensions were found in both solvent series, values which were in essential agreement with those found for linear polystyrene. The values of the branching index, g′, were found to be independent of both temperature and solvent type.

Solution properties and chain dimensions of poly(trimethylene sulfide)

AbstractPoly(trimethylene sulfide) (PTS) synthesized by means of anionic polymerization was studied with regard to its solubility behaviour and unperturbed chain dimensions. The Flory‐Huggins interaction parameter was used to determine the solubility parameter of PTS, δ = 10,0 cal1/2 · cm−3/2, which agrees with the calculated one. PTS fractions were isolated by means of fractional precipitation from chloroform/hexane at 50°C. Their number‐average molecular weight, M̄n, and the intrinsic viscosity, [η], were measured in chloroform at 25°C. From these data the relation [η] = 3,10 · 10−4 M̄ was estimated. A value of the characteristic ratio, 〈r2〉0/(n l2) = 4,0, was determined from the Burchard‐Stockmayer‐Fixman plot, which shows that this chain molecule has high flexibility.

Temperature Dependence of Limiting Viscosity Number and Radius of Gyration for Cellulose Dissolved in Aqueous 8% Sodium Hydroxide Solution

A regenerated cellulose with a weight-average molecular weight Mw of 8.0×104 was dissolved in 8 wt% aq sodium hydroxide (NaOH) solution under adequately chosen conditions. The solution viscosity and light scattering measurements were carried out over a wide range of temperature T ranging 0.6 to 46°C and 3.5 to 45°C, respectively. The apparent Mw of the sample, determined by the light scattering in aq NaOH, remained practically constant (7.9×104) at 10≤T≤45°C, being in good agreement with the true Mw (8.0×104), evaluated by the light scattering method in cadoxen. This means that cellulose dissolves molecularly in 8 wt% aq NaOH. This solution was found to be a Flory theta solvent at about 40°C, at which the second virial coefficient A2 vanishes. The Flory viscosity parameter Φ was ca. 1/5 the theoretical value (2.87×1023) of the unperturbed undraining chain, indicating that cellulose is a partially free draining chain when dissolved in aq NaOH. The unperturbed chain dimension A decreased with T. The flexibility of the cellulose chain in aq NaOH lies between those in cadoxen and iron sodium tartarate and all of them are classified as semi-flexible. The negative temperature dependence of the limiting viscosity number [η] was explained as mainly due to a large negative ∂A/∂T.

Conformational energies and unperturbed chain dimensions of polysilane and poly(dimethylsilylene)

Calcul a l'aide de methodes de mecanique moleculaire. Comparaison avec les resultats de Damewood et West

Viscometric and Light Scattering Study in Dimethylacetamide of Linear Segment Polyurethane, Polymerized with Methylene Bis(4-phenyl isocyanate) Polytetramethylene Glycol and Ethylene Diamine

An attempt was made to determine the unperturbed chain dimension A of a segment polyurethane, prepared from polytetramethylene glycol (the number-average molecular weight 1500) methylene bis(4-phenyl isocyanate) and ethylenediamine. A whole polymer was fractionated by successive solution fractionation using dimethylacetamide (DMAc) as a solvent and methylalcohol as a precipitant into 23 fractions. Linearity of the segment polyurethane chain was confirmed by NMR and the solution viscosity change by addition of n-butylamine. The dilute solution properties of eight fractions in DMAc were investigated by the light scattering and viscometry at 25°C. The Mark–Houwink–Sakurada equation for the solution in DMAc at 25°C was [η]=0.101Mw0.59 (cm3 g−1) ([η]; limiting viscosity number, Mw; the weight-average molecular weight). A was found to be 1.02×108 cm for the solution. No significant solvation was observed by adiabatic compressibility measurement.