Studies of cyclic and linear poly(dimethyl siloxanes). 4. Bulk viscosities

The bulk viscosities η of over fifty sharp fractions of cyclic and linear poly(dimethyl siloxanes) in the weight-average molecular weight range $\text{500 <}\text{M}\text{?}{}_2\text{< 25 000}$ have been measured at 298 K using a cone- and-plate microviscometer. In the Iow molecular weight region $\text{M}\text{?}{}_{\mathrm{W}}\text{< 1000}$) the η values for the cyclics were found to be at least three times as large as the values for the corresponding chain molecules. By contrast, in the highest molecular weight region ($\text{M}\text{?}{}_{\mathrm{W}}\text{> 16 000}$), the η values for the cyclics were approximately one-half those for the corresponding linears. Cyclics and linears containing about one hundred skeletal bonds were found to have similar bulk viscosities. The temperature dependence of the bulk viscosities of eighteen of the cyclic and linear fractions were investigated, and the relationship $\text{η = A}\text{exp}\text{(}\text{E}{}_{\mathrm{<mtext>visc</mtext>}}\text{RT}\text{)}$ was used to deduce values for the energies of activation for viscous flow E_visc and the constants A.     

Differences in the molecular weight and the temperature dependences of self-diffusion and zero shear viscosity in linear polyethylene and hydrogenated polybutadiene

Within the context of a generalized coupling model we can support the hypothesis that, while the mode of relaxation for self diffusion (D) and shear flow (η) are the same, the entanglement interactions are different. We assume that there are two distinct coupling parameters n_D and n_η for self diffusion and shear flow respectively. The model predicts the molecular weight and temperature dependences to be scaled by the relevant coupling parameters as:

for melts with Arrhenius temperature dependences. We have found that n_n=0.43 and 0.42 for polyethylene (PE) and hydrogenated polybutadiene (HPB) which scale η as M^3.5 and M^3.4. Also the apparent flow activation energies $\text{E1}{}_{\mathrm{a}}$ of 6.35 kcal mole^?1 for PE and 7.2 kcal mol^?1 for HPB scale to primitive activation energies E_a of 3.6 and 4.2 kcal mole^?1 for PE and HPB respectively. On the other hand the M^?2 dependence of D results in n_D=1/3. Then the reported activation energies for self-diffusion in PE and HPB of 5.49 and 6.2 kcal mole^?1 scale to primitive activation energies of 3.7 and 4.1 kcal mole^?1, respectively.     

Copoly(m,p-chloromethylstyrene-50% styrene): Copolymer molecular weights,fractionation and derivatization

Copolymerization of an equimolar mixture of m,p-chloromethylstyrene ($\text{M}$₁) and styrene ($\text{M}$₂) was carried out in chlorobenzene in the presence of AIBN at 80°C. Molecular weight analysis (by g.p.c.) of the resulting polymer samples was performed at various conversions. $\text{M}\text{?}{}_{\mathrm{<mtext>w</mtext>}}$, $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$, and ($\text{M}\text{?}{}_{\mathrm{<mtext>w</mtext>}}\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$) value of 21 300, 13 800 and 1.54 were obtained at 8.9% conversion. At higher conversions, the value of $\text{M}\text{?}{}_{\mathrm{<mtext>w</mtext>}}$ remained effectively constant while $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$ decreased to 9200 at ca. 80% conversion, and then increased to 12 000 at about 100% conversion (16 h), and to 13 700 if the polymer solutions were maintained at 80°C for an additional 44 h. These results suggest that, although the termination step initially involves the combination of polymer radicals, at high conversions a large number of very low molecular weight, and unsaturated, polymer molecules are formed possibly by disproportionation involving polymer radicals and primary radicals. The unsaturated polymer molecules are subsequently polymerized by growing polymer radicals towards the end of the polymerization. It was noticed that further reaction occurred after complete depletion of monomer, involving radical attack on the unsaturated polymer molecules. Other reactions including chain transfer to polymer will also be important at high polymer concentrations. A copolymer of $\text{M}$₁ and $\text{M}$₂ was separated into four fractions on a preparative scale, and molecular weight analysis of the resulting polymer samples provided more evidence of the above interpretation. G.p.c. analysis of several derivatives of a copolymer of $\text{M}$₁ and $\text{M}$₂ showed that most molecular weights were much lower than that of the starting polymer. These results in some cases may reflect the chemical or dimensional changes introduced into the polymer molecules during derivatization.     

Effect of molecular weight on the refractive index increment of polystyrenes in solution

The variation of refractive index increment $\text{d}\text{n}\text{d}\text{c}$ with molecular weight has been studied using solutions of monodisperse polystyrenes (2000<M_w<4×10⁶) in benzene. The results are in good agreement with those obtained by several authors using other systems.We have shown that the linear relationship:

$\text{d}\text{n}\text{d}\text{c}\text{=}\text{d}\text{n}\text{d}\text{c}{}_{\mathrm{m}}\text{+}\text{K″}\text{Mn}$

where $\text{(}\text{d}\text{n}\text{d}\text{c)}{}_{\mathrm{m}}$ is the refractive index increment of the repeating unit and K″ a constant, holds only for low molecular weights. With the assumption of volume additivity, we have estimated quantitatively the linear portion of the curve, $\text{d}\text{n}\text{d}\text{c}\text{=f(}\text{1}\text{M}\text{)}$, observed for molecular weights below 20 000 as a function of polymer composition. Beyond this limit, the increase of $\text{d}\text{n}\text{d}\text{c}$ with molecular weight may be probably related to segment-segment interactions within the coil.     

Solid and liquid state relaxations in spin-labelled poly)ethylene glycol) at high temperatures (T>Tg)

Free and covalently bonded (esterified) nitroxyl radicals experienced in poly(ethylene glycols) (PEG; $\text{M}\text{?}{}_{\mathrm{n}}$ 200–22 000) at temperatures T >T_g several different isotropic rotational relaxation regions. As a first approximation it was assumed, that in the polyglycols $\text{M}\text{?}{}_{\mathrm{n}}\text{? 1000}$ there are at least three rotational relaxation regions: the liquid state (I), the melting state (II) and the solid state (III). The existence of the fourth region, the frozen solid state (IV), was also concluded. The existence of the relaxation region (II) indicated the close interaction between radicals and the crystalline phase. The order of rotational activation energies (E_a) was E^II_a >E^III_a >E^I_a >E^IV_a ($\text{M}\text{?}{}_{\mathrm{n}}\text{? 1000}$). In the polymer melts (I) E_a values of free and bonded radicals first diminished as a consequence of the decrease of the end group effect and they achieved constant high molecular weight values (～15 and 25 kJ respectively). E_a changed in the solid state as a function of $\text{M}\text{?}{}_{\mathrm{n}}$ principally in the same manner except of the higher numerical values (～40 kJ).E_a of free and covalently bonded radicals in the transition region (II) gained a maximum at $\text{M}\text{?}{}_{\mathrm{n}}$ 1550 (125 and 170 kJ) and another at $\text{M}\text{?}{}_{\mathrm{n}}\text{> 9500}$ (130 and 165 kJ) expressing the high degree of order in these polymers in the solid state.The results obtained correlated well with the proton magnetic resonance measurements but they did not correlate with the amorphous dielectric relaxation measurements.It was concluded that the following factors may affect the rotational relaxations of nitroxyl radicals in PEG: the free volume of the polymer, the crystallinity, the chain packing and the end-group effect. The segmental character of the relaxation process was clearly indicated.     

Characterization of poly(1,4-phenyleneterephthalamide) in concentrated sulphuric acid. 2: Determination of molecular weight distributions

By combining static and dynamic properties (M_w, A₂, k_dR_g and R_h) of poly(1,4-phenyleneterephthalamide), PPTA (commercially known as Kevlar), with a detailed analysis of measured time correlation functions at different scattering angles in dilute solution, we have been able to estimate the molecular weight dependence of the radius of gyration, R_g(M), the persistence length ? ($\text{≈ 290}\text{A}\text{?}$), and the molecular weight distribution (M_z:M_w:M_n ≈ 6.2:1.8:1) using an unfractionated PPTA sample (M_w = 4.3 × 10⁴ g/mole). Laplace inversion of the time correlation function was accomplished independently by means of two different algorithms: the singular value decomposition technique with discrete multi-exponentials to approximate the normalized characteristic linewidth distribution function G(г) and the method of regularization whereby a linearized smoothing operator was used. The non-intrusive laser light scattering technique permits us to characterize, for the first time, the molecular weight distribution of PPTA which has been difficult to perform by means of other more established methods, such as size exclusion chromatography, because of the corrosive nature of solvents used in preparing PPTA solutions.     

Isothermal crystallization of poly(ethylene-terephthalate) of low molecular weight by differential scanning calorimetry: 1. Crystallization kinetics

The isothermal crystallization of poly(ethylene-terephthalate) (PETP) fractions, from the melt, was investigated using differential scanning calorimetry (d.s.c.). The molecular weight range of the fractions was from 5300–11750. Crystallization temperatures were from 498–513 K. The dependence of molecular weight and undercooling on several crystallization parameters has been observed. Either maxima or minima appear at a molecular weight of about 9000, depending on the crystallization temperature. The activation energy values point to the possibility of different mechanisms of crystallization according to the chain length. A folded chain process for the higher $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$ chains and an extended chain mechanism for the lower $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$ chains. The values of the Avrami equation exponent n vary from 2–4 depending on the crystallization temperature; non-integer values are indicative of heterogeneous nucleation. The rate constant K depends on T_c and $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$, showing maxima related to the T_c used. The plot of log K either vs. (ΔT)^?1 and (ΔT)^?2 or $\text{T}{}_{\mathrm{<mtext>m</mtext>}}\text{T(ΔT)}$ and $\text{T}{}^2{}_{\mathrm{<mtext>m</mtext>}}\text{T(ΔT)}{}^2$ is linear in every case.     

Crystallization kinetics and morphology of polymer blends of poly(tetramethyl-p-silphenylene siloxane) fractions

The crystallization behaviour of polymer blends or mixtures of the same system has been studied over a wide range of molecular weight and crystallization temperatures. Blends were made by mixing fractionated polymer samples. The spherulitic growth in these mixtures is dependent upon the number-average molecular weight of the system at the shorter chain lengths, but then becomes insensitive to molecular weight values when about 10⁵ to 10⁶ are reached. The growth rate kinetics of mixtures can be described by a kinetic model used for fractionated poly(tetramethyl-p-silphenylene siloxane) (TMPS) polymers. The crystal surface energies deduced from these rate data are molecular weight dependent as are the pre-exponential and transport factors in the rate equation. These parameters are explained in terms of the crystallite morphology. Mixtures (as well as fractions themselves) of all polymer fractions ranging from the monomer to the highest molecular weight (10⁶ approximately) have similar morphological features and form negatively birefringent spherulites. Although molecular weight segregation appears to play an important role in crystallization at comparatively small undercoolings, its influence seems to be minimal at large undercoolings (close to or below the growth rate maxima). Very low molecular weight additives significantly affect the overall crystallization kinetics. Compared to the undiluted sample, mixtures so formed have lower observed melting points and glass transition temperatures. Rates of crystallization are generally facilitated by the diluent with the peak in the growth rate being displaced to lower temperatures. The growth rates for diluted over the undiluted polymer at similar undercoolings are usually larger. At high molecular weights the log of the spherulitic growth rate varies as $\text{M}{}^{\mathrm{<mtext>?1</mtext><mtext>2</mtext>}}{}_{\mathrm{n}}$, over a considerable range, but at low molecular weight values the rate depends more strongly on M_n approaching a limit of M^?1.2_n as the monomeric state is approached.     

Water and solute transport through cellulose acetate reverse osmosis membranes

Reverse osmosis data on two different cellulose acetate membranes using seven organic solutes of varying molecular weight have been obtained.A combined viscous-flow and frictional model is presented and used to estimate the maximum retention, the friction between solute and membrane, the distribution coefficient for solute and the pore radius.The calculated values of the maximum retention and distribution coefficient have been compared with the Ferry-Faxen equation. For the more open membrane these are in good agreement. The tighter one, however, shows a greater interaction between solute and membrane than predicted by the Faxen equation.Some data on two-solute systems are presented and shown to give variation in the retention, which can be explained from the convection term.Furthermore, for experiments with dextran the permeate shows a significant reduction in both $\text{M}$_n and $\text{M}$_t     

Quasi-elastic light scattering from branched polymers: 1. Polyvinylacetate and polyvinylacetate—microgels prepared by emulsion polymerization

Emulsion polymerization of vinylacetate leads to branched polymers which at high monomer conversions form microgels of the shape and size of the latex particles. Quasielastic light scattering measurements from samples in the pre-gel state give at small q² a linear angular dependence of $\text{D}{}_{\mathrm{app}}\text{=}\text{Г}\text{q}{}^2$ which resembles that of randomly branched chain molecules, where Г is the decay constant of the time correlation function. Extrapolation of D_app towards zero scattering angle yields the translational diffusion constant D_z. The diffusion constant follows the molecular weight dependence D_z = 9.78 10^?5M_w^?0.478. The diffusion constant of the microgels, i.e. at molecular weights M_w > 14 10⁶, remains constant because of the finite and constant size of the latex particles. The coefficients k_f and k_D in the concentration dependence of the frictional and diffusion coefficients are related according to the equation $\text{k}{}_{\mathrm{D}}\text{= k}{}_{\mathrm{f}}\text{? 2A}{}_2\text{M}{}_{\mathrm{w}}\text{?}\text{v}\text{?}$ where A₂ is the second virial coefficient and v? the partial specific volume of the particle. The coefficient k_f is calculated from the experimentally determined quantities k_D, A₂ and M_w, and the result is compared with the theory by Pyun and Fixman. Accordingly the branched coils in the pre-gel state resemble soft spheres, but the microgels behave more like spheres of some rigidity.     

Burning of liquid fuels: effect of burner diameter on burning rate and measurements of quenching diameter

Laminar pool flames of four straight-chain alcohols were studied in uncooled glass and copper burners and water-cooled glass burners. The mass burning rate $\text{m}\text{?}$ increased with the burner diameter d decreasing as $\text{m}\text{?}$ ∝ d^?n, where n ≈ 1.2 for uncooled glass burners. The values of $\text{m}\text{?}$ in copper burners were lower by a factor of 1.5–2 than those in glass burners of the same diameter. Vigorous boiling of the subsurface layer of liquid occurred in sufficiently narrow uncooled glass burners, and numerous burning droplets were observed to traverse the flame. The quenching diameter d_c was measured. For uncooled copper burners d_c increased with increasing molecular weight M_r of the alcohol, from ≈ 2 mm for propanol to ≈ 20 mm for decanol. For uncooled glass burners d_c was much lower (1–2 mm) and less dependent on molecular weight. The product of d_c and the critical mass burning rate is assumed to have a characteristic value for the stability of diffusion burning, in accordance with the Zel'dovich criterion (Pe) = (Pe)_c = const. for flame stability in gas mixtures. However, the stability of diffusion burning increased with increasing heat losses from the burner wall. Two possible interpretations of this paradoxical effect are suggested.     

Studies of cyclic and linear poly(dimethylsiloxanes): 19. Glass transition temperatures and crystallization behaviour

Differential scanning calorimetry (d.s.c.) was used to investigate the thermal behaviour of cyclic and linear poly(dimethylsiloxanes) over the temperature range 103–298 K. Fractions of the polymers studied had number-average molar masses in the range 160 < M_n < 25 500 g mol^?1 and heterogeneity indices $\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{M}{}_{\mathrm{<mtext>n</mtext>}}\text{< 1.1}$ in most cases. D.s.c. was applied to measure the glass transition temperatures T_g cold crystallization temperatures T_c and polymer crystalline melting temperatures T_m of the oligomer and polymer fractions. Cyclic siloxanes [(CH₃)₂SiO]_x with number-average numbers of skeletal bonds n_n in the range 24 ≦ n_n ≦ 79 and linear siloxanes (CH₃)SiO[(CH₃)₂SiO]_ySi(CH₃)₃ with n_n in the range 10 ≦ n_n ≦ 40 were found not to crystallize. The T_g values of the linear siloxanes were found to be in agreement with values in the literature and they increased with increasing M_n. By contrast, the T_g values of the cyclics were found to decrease with increasing M_n.     

Small-angle neutron scattering studies of isotropic polypropylene

Small-angle neutron scattering studies have been made of molten and crystalline polypropylene using samples containing small amounts of deuterated polypropylene in a protonated polypropylene matrix. The specimens were characterized by small- and wide-angle X-ray scattering to determine the d-spacing and the degree of crystallinity χ and by gel permeation chromatography to determine molecular weight, M_w, and molecular weight distribution. The degree of crystallinity was varied from 0.5 to 0.7, the d-spacing from 120 to 250 Å and the molecular weight from 34 000 to 1 540 000. Clustering was not observed. The radius of gyration $\text{〈s}{}^2\text{〉}{}_{\mathrm{w}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of the tagged molecules was approximately proportional to $\text{M}{}_{\mathrm{w}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and almost independent of d and χ. In the melt similar values were obtained which are, within experimental uncertainties, the same as in a θ-solution. For 〈s²〉_wk²? 1 the scattering law approaches a k^?2 dependence. The results are discussed with reference to the chain-folded model but a fit cannot be obtained over all molecular weights. A simple random coil model fits the neutron scattering data partly but this does not explain the origin of the d-spacing.     

Interaction of 1-pyrenebutyrate with poly(vinylbenzo-18-crown-6) and poly(vinylbenzoglyme) in water

Binding constants of 1-pyrenebutyrate (PB^?, 1-pyrenecarboxylate and 1-pyrenevaleriate to the polysoap-type macromolecule poly(vinylbenzo-18-crown-6) (P18C6) and the poly(vinylbenzoglyme) PVBG (a polystyrene with two CH₃O(CH₂CH₂O)₂-substituents at the 3 and 4 position of each benzene ring) were determined spectrophotometrically (λ_m 342 nm for free PB^?, 348 nm for polymer-bound PB^?). The binding appears to follow Langmuir adsorption behaviour. Interaction with P18C6 is enhanced on adding crown ether-complexable cations, which converts the neutral polymer into a polycation. The enhanced binding is chiefly caused by lower values of $\text{1}\text{n}$ (minimum number of crown monomer units per bound PB^? molecule). This decreases at 25°C from $\text{1}\text{n}\text{= 25}$, for neutral P18C6, to 6.2 and 2.7 in the presence of 0.01 M CsCl and 0.1 M KCl, respectively. It is argued that the COO^? substituent of bound PB^? is probably located in the aqueous layer at the polymer-water interphase. Its presence close to the crown ligands enhances the binding of K⁺ or Cs⁺ cations to these ligands by forming crown-complexed ion pairs PB^?, M⁺ … P18C6. The typical excimer fluorescence emission peak of PB^? is observed when P18C6 in 0.1 M KCl is saturated with PB^?. Some of the binding measurements were carried out in ethanol-water mixtures.     

Pressure dependence of upper critical solution temperatures in the polystyrene - cyclohexane system

The pressure dependence of the upper critical solution temperature $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ in the polystyrene-cyclohexane system has been measured over the pressure range of 1 to 50 atm. The value of $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ determined over the molecular weight (M_w) range of 3.7 × 10⁴ to ～145 × 10⁴ greatly depends on the molecular weight of polystyrene. The value of $\text{(}\text{d}\text{T}\text{d}\text{p}\text{)}{}_{\mathrm{c}}$ for a polystyrene solution of low molecular weight (M_w = 3.7 × 10⁴) is positive (3.14 × 10^?3 degree atm^?1), while the values are negative (?0.52 × 10^?3～?5.64 × 10^?3 degree atm^?) for solutions of polystyrene over the high molecular weight range of 11 × 10⁴ to ～145 × 10⁴. The Patterson-Delmas theory of the corresponding state and the newer Flory theory have been used to explain this behaviour.     

Cloud-point curves of the polystyrene-cyclohexane system near the critical point

Cloud-point curves for solutions of five polystyrene samples, including three well-fractionated polystyrenes, in cyclohexane have been examined near their critical points. Even for a solution of polystyrene characterized by $\text{M}{}_{\mathrm{w}}\text{M}{}_{\mathrm{n}}\text{<1.03}$, the critical point determined by the phase-volume method is generally situated on the right hand branch of the cloud-point curve. The precipitation threshold concentration is appreciably lower than the critical concentration, while the threshold temperature slightly deviates from the critical temperature. The agreement of the precipitation threshold point with the critical point has been found for a solution of polystyrene characterized by M_w=20×10⁴ and $\text{M}{}_{\mathrm{w}}\text{M}{}_{\mathrm{n}}\text{<1.02}$ in cyclohexane. The η(φ) function derived from critical miscibility data is expressed by $\text{χ(φ) = 0.2798+}\text{67.50}\text{T}\text{+0.3070φ+0.2589φ}{}^2$, which yields θ of 33.2°C and ψ₁ of 0.22.     

Comparison of the unperturbed dimension of polystyrene for endothermal and exothermal heats of dilution within the same system

Light scattering measurements for two samples of polystyrene (I, M_w = 2.15 × 10⁵; II, M_w = 2.5 × 10⁶) were performed in the iso-refractive mixed solvent dimethoxymethane-diethyl ether. For sample I the temperature dependence of the second osmotic virial coefficient A₂ was determined for three constant compositions of the mixed solvent. In the range ?30° to +25°C the three curves run practically parallel and exhibit a maximum at approximately ?10°C. For the volume fraction of 0.7 diethyl ether in the mixed solvent, an endothermal theta-temperature θ₊ was found at ?27.0° ± 1.5°C and θ_?, the exothermal theta-temperature, at ?5.0 ± 1°C. The investigation of sample II in the abovementioned solvent confirmed the observed θ_?-temperature and displayed a higher exothermicity compared with I. Similarly to the temperature variation of A₂, the chain dimensions of II, determined from the angular dependence of the scattered light, run through a maximum. The unperturbed dimensions in the mixed solvent are found to be: $\text{r}{}_{\mathrm{w}}\text{= 448 ± 5}\text{A}\text{?}$ at θ₊ = ?27°C and $\text{r}{}_{\mathrm{w}}\text{= 443 ± 5}\text{A}\text{?}$ at θ_? = ?5°C, as compared with $\text{r}{}_{\mathrm{w}}\text{= 420 ± 10}\text{A}\text{?}$ at θ₊ = +33°C in cyclohexene. The inter-relation of the chain expansion coefficient and A₂ is quantitatively described by the Zimm-Stockmayer-Fixman equation over the entire range of heats of dilution.     

The structure and elasticity of polyurethane networks: 1. Model networks of poly(oxypropylene) triols and diisocyanate

The equilibrium mechanical and optical behaviour of networks prepared from poly(oxypropylene) triols (PPT) and 4,4′-diphenylmethane diisocyanate (MDI) at various initial molar ratios of reactive groups, $\text{r}{}_{\mathrm{<mtext>H</mtext>}}\text{=}\text{[}\text{OH}\text{]}\text{[}\text{NCO}\text{]}$, in the range 0.6 < r_H < 1.75 have been investigated. The reaction proceeded at 80°C and in the presence of an organotin catalyst to a high conversion of minotirty groups (0.96–1.0). A comparison between experimental and theoretical (based on the theory of branching processes) dependences of the equilibrium modulus, G_e, on r_H or on the sol content, w_s, led to the following conclusions: (1) In the range r_H ? 1 the theory adequately describes experimental dependences, while in the range r_H < 1 excess crosslinking takes place, obviously due to the formation of allophanate groups. (2) In PPT networks with a higher molecular weight (M_n = 2630), G_e is about twice the theoretical value for the front factor A = 1, which is interpreted as a contribution due to permanent interchain interactions. (3) In networks of lower PPT (M_n = 708), experimental G_e values lie between the theoretical ones calculated for A = 1 (affine deformation crosslinks) and $\text{A =}\text{1}\text{3}$ (phantom network). (4) The difference between the eperimental and theoretical moduli for $\text{A =}\text{1}\text{3}$ may be adequately described by using Langley's concept of trapped entanglement contribution (for networks of the longer triol quite satisfactorily, for those of shorter PPT with some systematic deviation) with the same proportionality constant. (5) For correlations between the experiment and theory a generalized plot of the reduced modulus of the weight fraction of the gel proved to be useful.     

Electrochemical reduction of polymeric carbon

It was found that the electrochemical reduction of poly (tetrafluoroethylene) with lithium amalgam leading to the mixture of polymeric carbon and lithium fluoride as solid product is followed by a consecutive electrochemical reaction via a polymeric anion radical, [$\text{(}\text{?}$C_n$\text{)}\text{?}$^?]_m. The value of n was determined as 4.75 and was found to be independent of the reaction conditions. The charge of this radical is during the reaction neutralised with Li⁺ ions diffusing through the solid phase to form a chemical compound $\text{(}\text{?}$C_nLi$\text{)}\text{?}$_m whose CLi bonds have a localized character. Therefore, this compound does not evolve hydrogen in contact with water as the intercalation compounds C_nLi, but hydrolyses to a solid hydrocarbon $\text{(}\text{?}$C_nH$\text{)}\text{?}$_m.     

Polycondensation of benzyl chloride catalysed by ArCr(CO)3

Arene chromium tricarbonyls were found to function as effective homogeneous catalysts for the polycondensation of benzyl chloride when they are thermally activated. The catalytic activity and induction period depended upon the nature of the arene attached to the metal. Their activity decreased and induction time increased with respect to the nature of the arene in the order: anisole, toluene, p-xylene and benzene. The alkylation products of a model reaction, catalysed by ArCr(CO)₃, were only ortho- and para-substituted. The degree of polybenzyl branching, determined by ¹H n.m.r. and DP, was found to increase with increasing reaction temperature and $\text{M}\text{?}{}_{\mathrm{n}}$. Although there is experimental evidence that in the initiation step the arene ring remains loosely attached to the metal, a mechanism similar to that of polymerization by a Lewis acid catalyst is proposed.