Limiting viscosity number—molecular weight relationships for phenol-formaldehyde resin in solution

The effect of molecular structure of phenol-formaldehyde resin on the Mark-Houwink-Sakurada equation for solutions in acetone is systematically studied. Random and high-orthophenol-formaldehyde resins are prepared by conventional, acid-catalyzed and Zn⁺⁺-catalyzed condensations, respectively. The relative contents of 2,2′-, 2,4′- and 4,4′-methylene linkages are determined by ¹³C NMR spectroscopy. From these the detailed distribution of structural isomers is calculated. Several fractions having number-average molecular weights (by vapor pressure osmometry) M?_n≥10⁴ are isolated by a successive solutional fractionation run from whole random polymers. For solutions of random polymer in acetone at 30°C, [η]=0,631 · M? (where [η] is limiting viscosity number) and for high-ortho polymer [η]=0,0813 · M? are established. The former equation can be interpreted in terms of the Zimm-Stockmayer theory of branched polymer solutions.     

Viscosities of dilute solutions of poly(tetrahydrofurfuryl methacrylate)

The intrinsic viscosities of seven fractions (from M?_n = 1,69.10⁵ to M?_n = 6,13.10⁵) of poly(tetrahydrofurfuryl methacrylate) in eleven solvents at temperatures between 30° and 50° show the following order: tetrachloroethane > dichloroethane > tetrahydrofuran > chloroform > benzene > bromobenzene > ethyl acetate > carbon tetrachloride > methyl pentyl ketone > acetone > 2-hydroxymethyltetrahydrofuran. Values of HUGGINS slope constants range between 0,34 to 0,48 for the unfractionated polymer and the magnitudes of a and k in the expression [η] = kM^a show little variations with temperature in case of good solvents whereas the opposite is observed in case of poor solvents. The theta temperature for 2-hydroxymethyltetrahydrofuran containing 20% methanol is 31,2 ± 0,3° and 3,49, 5,72, and 4,97 are the values for K₀.10⁴, (r /M)^1/2.10⁹ and (r /Z)^1/2.10⁸, respectively.     

Molecular size and configuration of poly(3-vinylpyrene)

Solution properties of poly(3-vinylpyrene) (PVπ) have been studied to determine the degree of hindrance to the flexibility of the vinyl chain by the pyrene pendant group. Fractionation of this polymer prepared by anionic polymerization, yielded nine narrow distribution fractions in the M_w range of 35 000–490 000 and the fractions were characterized by osmometry, light-scattering and viscometry. Intrinsic viscosities of the fractions were obtained in chloroform and tetrahydrofuran at 25°C and in o-dichlorobenzene at different temperatures from 25–80°C. From the KUHN-MARK-HOUWINK relationship, [η] = KM^a, K and a values were determined and the exponent varied in the order, chloroform (a = 0.500) < tetrahydrofuran (a = 0.547) < o-dichlorobenzene (a = 0.655) suggesting that chloroform at 25°C is a theta solvent for PVπ. Cloud point titration indicated that a mixture of THF/methanol in the ratio of 92:8 (V/V) is also a theta solvent for PVπ at 25°C. A K_Θ value of 5.2·10^?4 determined for PVπ at 25°C gave a value for the unperturbed dimension (R /M)^1/2 of 5.77·10^?9 cm. The conformational parameter, σ was computed as 2.84 for PVπ which suggests that the hindrance to rotation of the vinyl chain by the pyrene group is approximately the same as in the case of carbazole in poly(n-vinylcarbazole). Values of [η] in o-dichlorobenzene decreased with the increase of temperature yielding an average negative d log [η]/dT value of 1.1·10^?3. The expansion factor decreased in all cases with the rise of temperature. A decrease of unperturbed dimension with the increase of temperature was reflected in the d log K_Θ/dT value of ?2.0·10^?3 from which (R /M)^1/2 at 80°C was computed as 5.35·10^?9 cm.     

Solution properties and chain dimensions of poly(trimethylene sulfide)

Poly(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 cal^1/2 · 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, M?_n, and the intrinsic viscosity, [η], were measured in chloroform at 25°C. From these data the relation [η] = 3,10 · 10^?4 M? 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.     

Structural studies of polyesters. I. Crystal structure of polyglycolide

In the course of structural study of aliphatic polyesters, the crystal structure of polyglycolide, the simplest polyester of the type ? [? (CH₂)_z? CO? O? ]_n was determined by interpretation of the X-ray diffraction patterns of the fibers. The crystallographic data are: a = 5.22 Å, b = 6.19 Å, c (fiber axis) = 7.02 Å, the orthorhombic spacegroup, Pcmn-D. Two molecular chains pass through the unit cell. The crystal structure was determined by the help of two dimensional and three dimensional FOURIER syntheses. The planar zig-zag chain molecules form a sheet structure parallel to the ac plane and have not the polyethylene type arrangement. High density of the crystallite, 1.69 g/cm³, namely the tight molecular packing and the close approach of the ester groups might stabilize the crystal lattice and contribute to the high melting point of this polymer.     

Kinetics of the anionic polymerization of ϵ-caprolactone with K+ · (dibenzo-18-crown-6 ether) counterion. Propagation via macroions and macroion pairs

Following our earlier work on the polymerization of lactones involving crowned cations, kinetics of the anionic polymerization of ?-caprolactone (?CL) with K⁺ · (dibenzo-18-crown-6 ether) (K⁺DB18C6) counterion was studied calorimetrically in THF solution in the temperature range from 0 to 20°C. Dissociation constants of CH₃(CH₂)₅O^?K⁺DB18C6, modelling the active centers, were determined conductometrically: K_D (20°C) = 7,7 · 10^?5 mol · dm^?3, ΔH = 9,3 ± 0,2 kJ · mol^?1, ΔS = ?47 ± 2J · mol^?1 · K^?1. From kinetic measurements and from measurements of the dissociation constant of CH₃(CH₂)₅O^? K⁺DB18C6, rate constants of propagation via macroions and via macroion pairs were determined. Activation parameters for propagation via these species are equal to: ΔH = 39,2 ± 0,2 kJ · mol^?1, ΔS = ?63 ± 1 J · mol^?1 · K^?1, ΔH = 13,7 ± 0,1 kJ · mol^?1, ΔS = ?185 ± 2 J · mol^?1 · K^?1. At 20°C, k = 3,50 · 10² dm³ · mol^?1 · s^?1 and k = 5,2 dm³ · mol^?1 · s^?1. Due to the large difference of ΔH^≠ for propagation via macroions and macroion pairs (vide supra), the isokinetic point (k = k) would appear at ?65°C.     

Viscosity-molecular weight relationships for low molecular weight polymers. II. Poly(vinyl acetate) and poly(methyl methacrylate)

[η]/M?_n relationships at 25°C. have been found for low molecular weight fractions of poly(vinyl acetate) (PV Ac) in chlorobenzene and poly(methyl methacrylate) (PMMA) in toluene. The PMMA used contains about 75% of syndiotactic form. Due to the difficulties of PMMA fractionation, the constants in the equation [η] = K M? refer to an average degree of polydispersity equal to M?_w/M?_n = 1.2. For both PVAc and PMMA there is a range of molecular weight where a = 0.5; in these ranges [η] is practically indistinguishable from [η]Θ.     

Absolute determination of molar masses of standard polystyrenes by means of sedimentation-diffusion measurements in cyclohexane

Accurate measurements of the sedimentation coefficients at unit pressure and zero-concentration s, the diffusion coefficients at zero concentration D₀, and the intrinsic viscosities [η] were conducted at theta-conditions (cyclohexane, 34,5°C) on 11 polystryrene standard samples with narrow molar mass distribution. These samples with nominal mass-average molar masses (5 · 10⁴ < M_w < 2 · 10⁶ g · mol^?1), provided by three manufacturers for the use as calibration standards, were the same as in the previous paper of this series summarizing our measurements in toluene. Logarithmic correlations between s, D₀ and [η] are linear with deviations lower than ± 3% and indicate good consistency of all three independent sets of measured quantities. The molar masses M_sD as determined from s and D₀ by means of the Svedberg equation are in very good accordance with those previously determined in toluene, but for most samples the M_sD are lower than the nominal values M_w as given by the manufacturers. For some standards the deviations amount to 15?35% and cannot be explained by experimental errors or by the polydispersity of the samples. On the other hand, two pairs of standards exhibit the same values of s, D₀ and [η] in both solvents, although the nominal molar masses differ by 20%. These results lead to the conclusion that the experimentally determined M_sD values are more reliable characteristics of the standard samples than the nominal M_w values and that the sedimentation-diffusion technique is a powerful, though laborious, tool for an absolute determination of the molar mass.     

Polyethylmethacrylate in dilute solution

Polyethylmethacrylate (PEM) was prepared by bulk polymerization and fractionated using acetone/acetone-water (2:1 V/V) mixture. The solution properties of fractionated as well as unfractionated polymers were investigated in various solvents (ethylacetabte, toluene, ethylacetate-ethanol) by light scattering and viscosity at 35°C. Osmotic pressure measurements were also carried out on selected polymer samples for the evaluation of width of distribution. [η]–M _w and (r² )^1/2–M _w relationships for these systems were established. Ethylacetate was found to be a bad solvent compared to toluene and methylethyketone. In the case of unfractionated PEM, the parameters like [η]^2/3M ^1/3, M _w/[η], and Φ were corrected for molecular weight heterogeneity assuming SCHULZ-ZIMM distribution. For the evaluation of FLORY's constant K, and the unperturbed dimension (r )^1/2 of the polymer, FLORY-FOX, KURATA-STOCKMAYER, and STOCKMAYER-FIXMAN methods were employed. The K and (r )^1/2 values evaluated from the FLORY-FOX method were almost similar to those measured in a Θ solvent, while the other two methods yielded higher values. A comparison of the measured (r² ) and that calculated from KIRKWOOD-RISEMAN and DEBYE-BUECHE theories indicated the polymer coil as conforming to a statistical chain. The molecular weight dependence of A₂, the second virial coefficient, for PEM/ethylacetate was established and the value of A₂ compared well with that calculated from OROFINO-FLORY equation.     

Polymerization of 2-diethylamino-1,3,2-dioxaphosphorinane, 2. Kinetics

Kinetic studies of the anionic polymerization of 2-diethylamino-1,3,2-dioxaphosphorinane were performed in THF solution with (CH₃)₃SiO^?K⁺ as initiator at temperatures close to r.t. Initiation involves nucleophilic attack of the anion on P atom in the monomer molecule. Breaking of the P? O bond leads to an alcoholate anion as the growing species. Polymerization was shown to proceed via macroion-pairs and to be nearly living; e.g. at r.t. for every 250 propagations there is one termination. Rate constant of propagation k = 3,4 ± 0,31·mol^?1·s^?1 at 25°C, ΔH = 13,3 kcal·mol^?1 and ΔS = ?32,2 cal·mol^?1·K^?1. The ratio k/k was determined by solving a kinetic scheme involving propagation and termination. It was shown that termination consists in the alcoholate anion attack on P in either polymer or monomer molecule with expulsion of (C₂H₅)₂N^? anion and formation of a P? O bond. The dialkylamide anions cannot reinitiate polymerization. In solving the kinetic scheme it was assumed that termination involving both polymer and monomer proceeds with rate constants equal to each other.     

Static and dynamic light scattering studies of dextran from leuconostoc mesenteroides in the dilute region

Dextrans with mass-average molar masses 8.10⁴ g/mol ? M?_w ? 10⁸ g/mol have been studied in water by means of static and dynamic light scattering at different temperatures. Static light scattering (SLS) yields the z-average mean-square radius of gyration, 〈S²〉_z and the second virial coefficient A₂. It is found that the dependences of 〈S²〉 and A₂ on the mass-average molar mass, M?_w, can be well described by the power laws 〈S²〉 = K_S · M? and A₂ = K_A · M?. The exponent v_s is independent of the temperature T, while v_A decreases as T is raised. Dynamic light scattering (DLS) yields the apparent diffusion coefficient, D_app (q,c), and the hydrodynamic radius, R_h, where q is the wave vector and c the polymer concentration. For small q, a plot of D_app (q, c) versus q² · 〈S²〉_z gives a straight line. The intercept represents the centre-of-mass translational diffusion coefficient. Its dependence on the concentration, c, can be well simulated by the relation $ D_{\rm z} (c) = D_{{\rm z,}0} \left[ {1 + k_{{\rm D},2} \cdot c} \right] $. Here k_{D, 2} is the second hydrodynamic virial coefficient and D_z,0 the z-average of the translational diffusion coefficient at infinite dilution. The analysis of the k_D,2 -data shows that dextran molecules behave rather as interpenetrable than as non-interpenetrable spheres. The density p = (3 M?_w)/(N_A · 4 π R) proves to be a measure for the degree of penetration; p decreases with increasing M?_w, indicating that penetration becomes easier at higher molar masses.     

Enthalpy of polymerisation of 2-oxabicyclo[2.2.2]octan-3-one

The enthalpies of combustion of crystalline 2-oxabicyclo[2.2.2]octan-3-one ( 1 ), and five different crystalline poly(oxycarbonyl-1,4-cyclohexylene) samples formed from 1 were measured at 298, 15 K by high-precision bomb calorimetry. For 1 , the enthalpies of combustion and of formation were, ?ΔH(c) = 3717,5 ± 1,3 kJ·mol^?1 and ?ΔH(c) = ? 466,2 ± 1,6 kJ·mol^?1. After correction for the presence of n-butyl- or tert-butoxy-end groups in the polyester samples, a consistent enthalpy of polymerisation of 1 was obtained, ΔH(c → c) = ? 20,9 ± 2,3 kJ·mol^?1. The enthalpy of sublimation of 1 was measured, ΔH (1) = 69,6 ± 2,1 kJ·mol^?1; the value for the polyester unit was derived as 49 kJ·mol^?1.     

Kinetics of the polymerization of isoprene with isopropoxyneodymium dichloride/triethylaluminium binary lanthanide catalyst system

The kinetics of the polymerization of isoprene with the heterogeneous rare earth catalyst system isopropoxyneodymium dichloride/triethylaluminium (Nd(OPrⁱ)Cl₂-AlEt₃) was examined in a specially designed dilatometer. The rate of polymerization is expressed as R_p ≈ ?d[M]/dt = k[Nd]^1.40 [M]. The main kinetical parameters such as the concentration of active propagating chain, the efficiency of lanthanide catalyst used (ELCU), the absolute rate constant of propagation as well as the average life time of growing chains, were determined at 30°C, 40°C, 45°C and 50°C.     

Physicochemical studies of oligodextran. II. Intrinsic viscosity-molecular weight relationship

The viscosity behavior of dextran in two good solvents and four mixtures of a good and a bad solvent was studied over the molecular weight range of 410 < M _n < 32,000 at 25 and 50°C. In the molecular weight region larger than 2,000, the plot of log [η] versus log M _n gave the usual linear relationship for all solvents used. The constants K and a of the equation [η] = KM^a were determined and their dependence on the concentration of the nonsolvent in mixed solvents and on the temperature were discussed. Using the unperturbed dimensions of the dextran molecule estimated from the Stockmayer-Fixman plots, the value of {〈L〉/〈L〉}^1/2 was calculated to be 1.7–1.8. The viscosity behavior for dextran with M _n < 2,000 was qualitatively discussed as a deviation from the randomly coiled model.     

Cationic polymerization of N-vinylcarbazole by tropylium salts at low temperatures

Cationic polymerizations of N-vinylcarbazole (NVC) in methylene dichloride containing approximately 1% nitromethane were studied by adiabatic calorimetry at temperatures between ?40 and ?70°C. Tropylium salts containing AsF, SbF and SbCl counterions were used as initiators. Reaction halflives ranged from 2 to 80 seconds and first-order plots displayed induction periods. Evidence indicated that the majority of the initiator was consumed, permitting estimation of propagation rate constants. For polymerizations involving the SbF counterion, these rate constants were found to be relatively insensitive to the concentration of initiator or excess anion and the conclusion is drawn that paired and unpaired PNVC⁺ SbF ions have similar reactivities at low temperatures. Correlation of the present results with those from previous work at 20 and 0°C yielded an Arrhenius exponential factor for propagation by unpaired ions of 30±9 kJ mol^?1. The degree of polymerization approached the ratio [M]₀/[1]₀ at ?70°C. At higher temperatures, molecular weights appeared to be governed by transfer reactions. The absence of significant chlorine content in polymer samples precluded the possibility of chain transfer to solvent.     

Synthesis and cationic polymerization of a novel optically active vinyl ether with L-proline structure

Synthesis and cationic polymerization of a novel vinyl ether with an L -proline moiety, N-carbobenzoxy-L -proline 2-vinyloxyethyl ether (ZProVE), were carried out. ZProVE was prepared by the condensation of N-carbobenzoxy-L -proline and 2-hydroxyethyl vinyl ether. Cationic polymerization of ZProVE was carried out in dichloromethane at ?50, ?20°C, or room temperature. The number-average molecular weight (M _n) of the polymer obtained in the polymerization at ?50°C was 44900, and the [α] value of the polymer was ?36.1°, which was somewhat larger (more positive) than that of ZProVE (?46.4°). Cationic copolymerizations of ZProVE and isobutyl vinyl ether proceeded readily to afford the corresponding copolymers. Alkaline hydrolysis of poly(ZProVE) afforded poly(hydroxyethyl vinyl ether).     

Anionic polymerization of butyl cyanoacrylate by tetrabutylammonium salts, 2. Propagation rate constants

Anionic polymerizations of butyl cyanoacrylate were initiated in tetrahydrofuran (plus a few experiments in 1,2-dimethoxyethane) by the salts tetrabutylammonium hydroxide, bromide, acetate and three substituted acetates. The hydroxide gives near-ideal ‘living polymerization’ kinetics, with k_p close to 10⁶l·mol^?1. s^?1 at 20°C. The kinetics of the reactions initiated by the acetates and bromide are analysed by the slow-initiation-no-termination theory, using values of the initiation rate constants evaluated in Part 1. The k_p values derived are in the same range as those from the OH-initiated reactions and those of the zwitterionic polymerizations initiated with covalent bases, i.e., tertiary phosphines and amines. A ca. 4-fold variation of k_p with concentration of active species is given a speculative analysis in terms of dissociation from paired to free ions, yielding tentative estimates for k ≈ 10⁵ and k ≈ 10⁷l·mol^?1·s^?1 in THF at 20°C. Molecular weights were all high M _n ≈ 10⁶, with M _w/M _n ≈ 2.     

Ion pairs,cations and anions in ternary solutions of bis(polystyryl)magnesium and magnesium bromide in tetrahydrofuran

A conductometric method is developed for the study of the ternary solutions in tetrahydrofuran of bis(polystyryl)magnesium (PStMgPSt) containing various proportions r of magnesium bromide. The concentration of bis(polystyryl)magnesium varies from 10^?4 to 2.10^?3 mol.dm^?3, the ratio r from O to 17,4 and the temperature from +20°C down to ?60°C. The addition of MgBr₂ provokes the replacement of the ion pairs PStMgPSt by PStMgBr, the dismutation constant being at 20°C K_dism = 42 ± 2 with a molar enthalpy of ? 5 ± 2 kJ.mol^?1. The dismutation is chiefly ruled by a conjugated steric effect that lowers the stability of PStMgPSt. In this concentration range, aggregation of styryl ion pairs is negligible. Moreover for a given r the degree of dissociation of the polymer is independent of its concentration. This is due to the complete predominance in this concentration range of the triple anions Mg(PSt), MgBr(PSt) and MgBr₂PSt^?, approximately in the proportions of the ion pairs f_pp, f_bp and f_bb as calculated from the dismutation constant. The triple anions MgBr are still completely negligible, as are also the triple cations. The single cations MgPSt⁺ and MgBr⁺ are approximately in the proportion f_pp. K_dism/f_bp, the latter are ones becoming predominant above r = 3.     

Intramolecular phase transitions of block copolymers in solution from viscosity — temperature studies

Intrinsic viscosity against temperature plots for two sequence block copolymers of isoprene and styrene in decalin and methyl cyclohexane confirm the general behaviour of these polymers in preferential solvents. The operative parameters are the mol. wt., composition and ? temperature of the less soluble polymer in the particular solvent. The STOCKMAYER -FIXMAN relation [η]M = Φ₀(A + 0.51 B_ηM )is obeyed, for a particular composition, at all temperatures, but the unperturbed dimensions in the block appear to drop significantly at temperatures below the transition temperature. Since the constant Φ₀ is influenced by the segmental distribution, the drop in unperturbed dimensions may be considered to reflect the conformation change from the phase-mixed to phase-separated form. The characteristic ratio, C_∞ = 〈r²〉₀/nl², which is calcd. from K in the KUHN-MARK-HOUWINK Eq. determined directly from [η]₀ (? = 44°C in methyl ethyl ketone) is identical with that obtained by extrapolation using the STOCKMAYER-FIXMAN relation at 46°C. Moreover, C_∞ may be calcd. directly from C_∞Block = xC_∞PS + (1 ? x) C_∞PI after taking account of the isomeric composition of the polyisoprene.     

Excluded volume effects in dilute solutions of linear polystyrene

The second virial coefficient A₂ and the limiting viscosity number [η] were obtained for polystyrene solutions in toluene, in 1.2-dichloroethane and in methylethyl ketone over a molecular weight interval of 0.33 < M_w · 10^?5 < 65 at 35°C from light scattering and viscosity measurements. The relations in the form of α ? αⁿ = k₁z for the viscosity expansion factor α_η and α^p ? α^q = k₂z for the expansion factor α deduced from A₂ were studied, where m, n, k₁, p, q, and k₂ are constants independent of the interaction parameter z = (4π)^?3/2BA^?3M^1/2. The constants m, n, and p, q were determined from the molecular weight dependence of [η] and A₂. The value of the polymer-solvent interaction parameter B, with which the constants k₁ and k₂ were obtained, was determined so that the calculated value of 2A₂/N₀B goes to unity as z goes to zero. Here, N₀ is the AVOGADRO number. The viscosity data at high molecular weight was explained by the relation α ? α = 0.85z. The expansion factor deduced from A₂ in the good solvent was described by the relation α⁵ ? α² = 1.05z. A₂M^1/2A^?3α^?3 was practically constant over a wide range of z.