Dilute Tetrahydrofuran Solutions Research Articles

Study of Poly(methyl methacrylate) Stereocomplexes by Size Exclusion Chromatography and Dynamic Light Scattering

Poly(methyl methacrylate) stereocomplexes prepared in dilute tetrahydrofuran solutions were studied by size exclusion chromatography coupled with refractive index and light scattering detectors in ...

Crystallization of micelles and matrix in dilute diblock copolymer/homopolymer solutions

The crystallization, morphology, and crystalline structure of dilute solid solutions of tetrahydrofuran–methyl methacrylate diblock copolymer (PTHF-b-PMMA) in poly(ethylene oxide) (PEO) and PTHF have been studied with differential scanning calorimetry (DSC), X-ray, and optical microscopy. This study provides a new insight into the crystallization behavior of block copolymers. For the dilute PTHF-b-PMMA/PEO system containing only 2 to 7 wt % of PTHF content, crystallization of the PTHF micellar core was detected both on cooling and on heating. Compared the crystallization of the PTHF in the dilute solutions with that in the pure copolymer, it was found that the crystallizability of the PTHF micellar core in the solution is much greater than that of the dispersed PTHF microdomain in the pure copolymer. The stronger crystallizability in the solution was presumably due to a softened PMMA corona formed in the solution of the copolymer with PEO. However, the “soft” micelles formed in the solution (meaning that the glass transition temperatures (Tg) of the micelle is lower than the Tm of the matrix phase) showed almost no effects on the spherulitic morphology of the PEO component, compared with that of the pure PEO sample. In contrast, significant effects of the micelles with a “hard” PMMA core (meaning that the Tg of the core is higher than the Tm of the PTHF homopolymer) on the nucleation, crystalline structure, and spherulitic morphology were observed for the dilute PTHF-b-PMMA/PTHF system. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2961–2970, 1998

Solubility and Micellization Behavior of C60 Fullerenes with Two Well-Defined Polymer Arms

1,4-Disubstituted, low-polydispersity C60 derivatives of the types C60−(PS)2, C60−(PVP)2, and C60−(PS−PVP)2, where PS is polystyrene, PVP is poly(p-vinylphenol), and PS−PVP is a diblock copolymer of this sequence, were prepared by applying the nitroxide-controlled free radical polymerization technique and studied with their solubility behaviors in some organic solvents. The first clear experimental evidence was obtained for the formation of multimolecular micelles of C60-bearing polymers under certain conditions: for example, light-scattering measurements showed that the C60−(PVP)2, C60−(PS−PVP)2, and C60−(PS)2 samples with a number-average molecular weight of a polymer arm roughly about 10 000 formed stable micelles in dilute tetrahydrofuran (THF) solution with association numbers of about 20, 6, and 1 (no micellization), respectively. The solvent power of THF for the mother polymers increases in this order. The saturation solubilities SC60 of the C60 moiety in C60−(PS)2 and C60−(PVP)2 were determined as a function of the PS and PVP chain lengths, showing that, in THF, the SC60 in the PS adduct is exceptionally large, much larger than that in the PVP adduct of the same chain length, in accord with the mentioned micellization tendency in dilute solution. On the other hand, C60−(PVP)2 showed a reasonable solubility in a polar solvent (methanol), in which C60−(PS)2 was little soluble. The micellization was found to be accompanied by characteristic changes in the UV−vis spectra, depending on micelle size.

97/01556 Ultrasound velocity in infinitely dilute tetrahydrofuran and pyridine solutions of coal and lignite extracts

97/01556 Ultrasound velocity in infinitely dilute tetrahydrofuran and pyridine solutions of coal and lignite extracts

Laser flash photolysis of poly(silylenes) in dilute solution. Generation of ionic species

Radical cations are generated via monophotonic processes upon irradiation of poly(methylphenyl silylene) (PMPSi), poly(biphenylmethyl silylene) (PBMSi), poly(dihexyl silylene) (PDHeSi), and poly(hexylmethyl silylene) (PHeMSi) in dilute tetrahydrofuran solution with 15- or 20-ns flashes of 266- or 347-nm light, respectively. This was inferred from electrical conductivity measurements. Typical quantum yields Φ(ion) are as follows: for PBMSi, 4×102 (λinc=266nm) and 3×103 (λinc=347nm); and for PDHeSi, 8×103 (λinc=266nm) and 9×104 (λinc=347nm). In all cases, a significant portion of the transient absorption spectrum recorded at the end of the flash is attributed to the spectrum of the radical cation. The latter strongly overlaps the spectra of other intermediates (presumably silyl radical and silylene).

Generation of ionic species by photolysis of polysilylenes in dilute solution

From flash photolysis studies (at λinc = 266 and 347 nm) involving the electrical conductivity and the optical absorption detection method it is inferred that poly(methylphenyl silylene), PMPSi, and poly(biphenylmethyl silylene), PBMSi, form ionic species in a monophotonic process in dilute tetrahydrofuran and dichloromethane solution at 295 K (ϕ(ion) ≈ 4×10−2, PBMSI and 1×10−2, PMPSi, in THF at λinc = 266 nm). The ionic species possess optical absorption bands between 350 and 500 nm with a maximum at about 380 nm. Both the photocurrent and the optical density at 380 nm decay with identical rates by a second order process (k2 ≈ 3 × 1011 dm3 mol−1 s−1, PBMSi in THF at 295 K).

Photophysical behavior of oligoethylene glycols labeled with naphthalene carboxylate and phosphate esters

The fluorescence spectra of tri- and tetraethylene glycol esterified with 2-(1-naphthyl)ethyl ethyl phosphate and 2-(1-naphthyl)ethyl 2-(ethoxy)ethyl phosphate were studied in dilute solutions of tetrahydrofuran (THF) and diethyl ether. They were compared with the fluorescence from tri- and tetraethylene glycol esterified with 1-naphthyl acetic acid. These compounds form intramolecular excimers. The extent of excimer formation is not extensive, but the relative amount of excimer emission from these compounds varies with the choice of solvent. Three synthetic intermediates to the phosphates, the 2-(1-naphthyl)ethyl N, N-diisopropylphosphoramidites of tri- and tetraethylene glycol and of 2-ethoxyethanol, were also examined. These compounds form intramolecular exciplexes. In THF, the relative amount of exciplex emission from the phosphoramidites follows the same trend as the carboxylate esters. In diethyl ether, the trend is different. Rates of fluorescence decay have been measured for these compounds. The results are discussed in terms of how information about the conformational and dynamic behavior of these molecules in solution can be obtained, and how the solvent can influence the relative amounts of excimer or exciplex fluorescence

(Liquid + liquid) equilibria of (water + tetrahydrofuran + 1-methylcyclohexanol) and of (water + tetrahydrofuran + 2-methylbutyl ethanoate) at the temperature (293.16±0.30) K and pressure (101.325±0.070) kPa

Solubility curve and tie-line measurements for (water + tetrahydrofuran + 1-methylcyclohexanol) and (water + tetrahydrofuran + 2-methylbutyl ethanoate) at the temperature (293.16±0.30)K and the pressure (101.325±0.070)kPa are reported. Tie-lines were correlated using a Hand equation. Consistency of our results was ascertained through an Othmer-Tobias correlation. Distribution coefficients of tetrahydrofuran and water from aqueous solutions to selected high-boiling solvents were determined and separation factors were evaluated. It is concluded that the high-boiling solvent, 2-methylbutyl ethanoate, may be considered a separating agent for dilute aqueous tetrahydrofuran solutions.

Photon correlation spectroscopy of dilute polymer solutions: Dynamic zimm plots and scaling of molar‐mass‐dependent properties

AbstractResults of photon correlation spectroscopy measurements on polystyrene (PS) standards in dilute tetrahydrofuran (THF) solutions are presented. The experiments were performed at 45°C on eight different samples covering the molar mass range between 5·105 and 1,6·107 g/mol. The first cumulant of the measured dynamic structure factor of the scattered light is discussed as a function of the scattering angle and of the solution concentration. The scaling constants of the centre‐of‐mass diffusion coefficient and of the Stokes effective hydrodynamic radius with molar mass are determined. The relationship between the concentration dependence of the centre‐of‐mass diffusion coefficient and the molar mass is derived. The values of the reduced first cumulants are presented by dynamic Zimm plots. The shape of the Zimm plots shows a deviation from the theoretically predicted form. This deviation is explained by applying the results of dynamic scaling considerations.

On the photolysis of poly-4-chloromethylstyrene and poly-4-chloromethylstyrene-co-styrene in solution

Poly-4-chloromethylstyrene (PCMSt) and copolymers (CP-CMSt-St) of 4-chloromethylstyrene (CMSt) and styrene (St) were irradiated in dilute tetrahydrofuran solution with UV light. Continuous irradiation of PCMSt at λ inc = 254 nm resulted in intermolecular crosslinking and formation of HCl. Flash photolysis at λ inc = 266 nm gave evidence of benzyl type radicals by the characteristic optical absorption spectrum ( φ(benzyl) = 0·3 ± 0·1). From light scattering and optical absorption measurements it was inferred that, apart from benzyl radicals, other unidentified radicals also contributed to crosslinking. In the presence of O 2, PCMSt predominantly underwent mainchain scission. Crosslinking was observed with CP-CMSt-St containing 28 mol% CMSt but no change in molecular size was detectable with a copolymer containing only 6 mol% CMSt. Excimers of styrene repeating units were very effectively quenched by CMSt repeating units. This reaction resulted in the formation of additional benzyl type radicals. Exciton migration along the chain in segments consisting of styrene units is assumed to promote quenching.

Stereoassociation of poly(methyl methacrylate): Study on the complexation stoichiometry and structural characteristics of the aggregates

AbstractA study of the composition of a poly(methyl methacrylate) (PMMA) stereocomplex and the structure of the stereocomplex particles is described. The study was conducted in dilute solutions of tetrahydrofuran (THF), using polymer pairs of an isotactic (ISO) and two syndiotactic (SYN) poly(methyl methacrylate)s of different tacticity. Gel permeation chromatography measurements of the stereocomplex obtained from mixing ISO and SYN‐1 give an optimum ratio of 1:1,5, while for the other polymer pair (ISO/SYN‐2) this relation ranges between 1:2,5 and 1:4. As the tacticity of the syndio‐PMMA samples decreases the optimum ratio increases. The study of the structure of the particles was performed by light scattering measurements of the stereocomplex fractions obtained at the outflow of the chromatographic system. The stereocomplex particles show an exponential relationship between the radius of gyration RG and the molecular weight M, viz. RG = K · Ma which is not very far from that of the linear unperturbed dimensions of PMMA. The numerical value of the exponent a being lower than 0,5 suggests a slight tendency towards the spherical shape of pseudobranched structures expected for these aggregates.

Enthalpic pair interaction coefficients of NaI–non-electrolyte in DMF solution at 25 °C. A comparison of electrolyte–non-electrolyte interactions in DMF and in aqueous solutions

Dissolution enthalpies of NaI in dilute solutions of N-methylformamide, dimethyl sulphoxide, tetrahydrofuran, acetonitrile, acetone and isobutanol in N,N-dimethylformamide have been measured. From these data, the enthalpic pair interaction coefficients hxy[(Na++ I–)–non-electrolyte] have been determined. The hxy values for all investigated systems containing NaI are positive, in contrast to aqueous solutions, where they are both positive and negative. A comparison of appropriate data concerning the hxy(electrolyte–non-electrolyte) values in water and in DMF solution indicates that in the former systems the unusual properties of water influence the analysed hxy values to a great extent, while in the latter, the hxy values mainly reflect the replacement of the solvent molecule by cosolvent molecules in the solvation region of the ions.

Heat capacities and volumes of some non-electrolytes in N,N-dimethylformamide at 298.15 K

Heat capacities and densities of dilute solutions of formamide, acetone, tetrahydrofuran, ethylene glycol, 2-methoxyethanol, and 2-ethoxyethanol in N,N-dimethylformamide were determined at 298.15 K. Apparent molal heat capacities and volumes for these solutes in DMF were calculated and compared with the analogous data for other substances in DMF solution as well as with the data concerning solutions in methanol and water. Heat capacities of cavity formation (ΔCcav) in DMF were calculated on the basis of the Scaled Particle Theory. ΔCcav appeared to be linearly correlated with the standard partial molal volume of corresponding solutes in DMF. Similar dependences were also found for aqueous and methanolic solutions of the non-electrolytes.

Chemical modification of polydienes, 3. Copolymers with polytetrahydrofuran by grafting‐from butadiene polymers

AbstractPolybutadienes of various microstructures and some butadiene copolymers were epoxidised to low levels (<1 mol‐%) with m‐chloroperbenzoic acid. The epoxide groups functioned as initiation sites for a “grafting‐from polymerization” of tetrahydrofuran (THF) catalysed by BF3. By conducting the reaction in dilute THF solution ([Monomeric unit] < 0,3 mol · 1−1) with a large excess of BF3 over epoxide groups, gel formation was avoided. The conversion of THF was less than 2% and the copolymers contained from 10 to 50% polytetrahydrofuran (PTHF) comprising graft chains of molar mass up to 43000 g · mol−1. The relative rate of grafting tended to decrease as the content of trans‐1,4 units in the backbone polymer increased, and, unusually, there was a small increase in volume during the graft copolymerization. The graft copolymers had a two‐phase morphology consisting of amorphous rubber and crystallites of PTHF. The latter function as physical crosslinks which break down above the melting point of PTHF, so that the materials behave as thermoplastic elastomers.

Photobehaviour of benzyl containing itaconate polymers

AbstractThe emission spectra of benzyl containing itaconate polymers were investigated in dilute tetrahydrofuran solutions. The polymers studied were poly(dibenzyl itaconate), poly(monobenzyl itaconate) and a (dibenzyl itaconate‐co‐dicyclohexylmethyl itaconate) copolymer. The photobehaviour of small compounds bearing the same chromophores was also investigated. The results obtained allow a discussion of the effect introduced by the polymer backbone upon the process of excimer formation.

Bestimmung des Aggregationsgrads lithiumorganischer Verbindungen durch Kryoskopie in Tetrahydrofuran

Degree of Aggregation of Organolithium Compounds by Means of Cryoscopy in TetrahydrofuranThe association behaviour of alkyl‐, aryl‐ and alkinyl‐lithium compounds as well as of lithium enolates and chiral lithium azaenolates is determined from freezing‐point depression values in dilute tetrahydrofuran solutions at −108°C. Compared toX‐ray‐crystallographic data (lithiated methyldithiane, phenyllithium, lithio derivatives of a ketone, carboxylic amide and ‐ester, and a diketopiperazine‐bislactim‐ether), desaggregation is found under these conditions. The structures determined by 13C‐NMR spectroscopy for BuLi, lithiophenylacetylene and (t‐butyl)lithioacetylene are confirmed. The dilithio salt of a carboxylic acid is polymeric, a chiral lithio‐hydrazone and a chiral lithio‐oxazolidine are monomeric and dimeric, respectively. Lithium diisopropylamide is a monomer‐dimer equilibrium mixture. The apparatus described permits both synthesis and measurement of the reactive species under inert atmosphere conditions in the same vessel.

The synthesis of poly(styrene‐co‐sodium styrene‐p‐carboxylate)

AbstractThis article describes a technique for the homogeneous lithiation and subsequent carboxylation of high‐molecular‐weight polystyrenes containing up to 14 mol %p‐bromostyrene. Thus, poly(styrene‐co‐p‐bromostyrene)s were reacted in dilute tetrahydrofuran solution with large stoichiometric excesses ofn‐butyllithium with no precipitation of ionomer and subsequently carboxylated with anhydrous carbon dioxide or dry ice. By this technique polystyrenes in which up to 100% of the original bromine groups had been replaced by carboxyl functionalities were obtained.

Mechanical shear degradation of polymers in solution by turbulent flow, 3. The influence of chemical constitution and thermodynamic quality of the solvent on shear degradation

AbstractMechanical shear degradation of polyisobutylene, polystyrene, poly(vinyl chloride), poly(methyl methacrylate), poly(decyl methacrylate), poly(methyl acrylate), and 1,4‐polybutadiene in dilute solutions of tetrahydrofuran (THF) are studied under turbulent flow conditions through a capillary, in order to study the effect of the chemical constitution on shear degradation. In addition the influence of solvent quality on shear degradation is investigated. The changes of the molecular weight distribution curves were followed by gel permeation chromatography (GPC), in order to determine the degradation constants ki for the corresponding molecular weight distribution fractions M̄i. GPC calibration via the concept of universal calibration, Mark‐Houwink relations for polyisobutylene, poly(methyl methacrylate), poly(methyl acrylate), 1,4‐polybutadiene, and poly(dimethylsiloxane) in THF as solvent had to be established for this purpose. Substantial differences in the rate constants ki were observed as a function of M̄i, whereas a master curve resulted for all polymers except 1,4‐polybutadiene when ki was plotted against the number of main chain carbon atoms n̄i for each molecular weight M̄i. From this the shear degradation of CC single bond polymers can be represented by ki = C · n̄, C being independent of the chemical nature of the CC single bond polymer, and a varying from 1,7 to 2,6. This means that in addition to the shape of the deformed macromolecule to be degraded not only its hydrodynamic volume (in rest) but also its chain length plays an important role. As to the influence of solvent quality, the degradation constants were found to increase with decreasing solvating power of the solvent. Mechanical shear degradation of the type discussed here takes place in drag reduction by polymers.

Scaled-particle theory and salting constant of tetrahydrofuran in various aqueous electrolyte solutions at 298.15 K

The vapour pressure change upon addition of electrolytes to dilute aqueous tetrahydrofuran (THF) solutions has been determined at 298.15 K. From these data the salting constants ks(Setchenov constant) have been calculated for THF in aqueous electrolyte solutions with: NaCl, NaNO3, NaClO4, NaBr, CsBr, CsNO3, AgNO3, Ni(NO3)2, NiCl2, CaCl2, BaCl2, Na2SO4, CdSO4, CuSO4, LaCl3, Me4NBr, Et4NBr, Pr4NBr, Bu4NBr, NaPh4B and Ph4AsCl. Using classical extra-thermodynamic assumptions single-ion ks values are calculated. It is shown, using the scaled-particle theory (SPT) that a Lennard-Jones 6–12 potential can describe the interaction of the THF molecule with all the inorganic cations. This may be considered as evidence that collisions occur between the THF molecule and the inorganic cations studied, although the ions should be considered as preferentially hydrated. Comparison of the behaviour of dilute THF and benzene aqueous inorganic electrolyte solutions suggests that under these conditions, THF behaves as a non-polar molecule. In the case of the interaction with organic ions, the THF molecule induces, unlike benzene, an additional repulsion term.

A fluorimetric study of the chemical, photochemical and thermal degradation of poly(vinylchloride)—I. Preliminary comparative studies

Fluorescence emission and excitation spectra of dilute tetrahydrofuran solutions of thermally degraded PVC, (TPVC), photochemically degraded PVC, (PPVC), chemically degraded PVC, (CPVC) and non-degraded PVC are compared. The spectra of CPVC and PPVC are similar and are composed of a mixture of polyene structures while those of TPVC are different. The reasons for these differences are discussed.