Factors affecting the nascent structure and morphology of polyethylene obtained by heterogeneous Ziegler-Natta catalysts: 1. Polymerization kinetics

Kinetic measurements were carried out to study the influence of polymerization conditions on the morphology and macroconformation of nascent polyethylene obtained with a heterogeneous $\text{TiCl}{}_3\text{Al}\text{(}\text{C}{}_2\text{H}{}_5\text{)}{}_3$ Ziegler-Natta catalyst. The polymerization of ethylene in a n-paraffin viscous medium was studied for very different conditions, such as polymerization temperature from 0° to 120°C, pressures of 1 and 10 atm and stirring speed of 10 and 1000 r.p.m. It was established by electron microscopy that new polymer chains originate due to formation of new surfaces by break-up of catalyst aggregates and also through crystal scission. The average size of polymer globules growing on the catalyst surface was of the order of 10⁸cm^?2. The same kinetic relationships are approximately obeyed when the polymerization is controlled by mass transfer of the monomer. The overall activation energies for the maximum polymerization rate, decay period and the stationary polymerization rate were: 8.4, 3.4 and 5.0 kcal/mol, respectively. Molecular weight measurements combined with polymerization rate determinations lead to the conclusion that the number of growing polymer chains increases with the polymerization temperature, being of the order of 10¹²cm^?2 at low temperature. This corresponds to a concentration of active sites of about 10⁴ per polymerization locus.     

Molecular weight distribution and stereoregularity of polypropylenes obtained with Ti(OC4H9)4Al2(C2H5)3Cl3 catalyst system

The effects of temperature and catalyst homogeneity on the molecular weight distribution (MWD) and stereochemical regulation of polypropylenes produced by $\text{Ti(OC}{}_4\text{H}{}_9\text{)}{}_4\text{Al}{}_2\text{(}\text{C}{}_2\text{H}{}_5\text{)}{}_3\text{Cl}{}_3$ system have been investigated. The MWD of polymers obtained at temperatures below 21°C were unimodal and narrow ($\text{M}\text{?}{}_{\mathrm{w}}\text{M}\text{?}{}_{\mathrm{n}}\text{?2.0}$), whereas those obtained at temperatures higher than 31°C were bimodal with one narrow distribution and the other broad one ($\text{M}\text{?}{}_{\mathrm{w}}\text{M}\text{?}{}_{\mathrm{n}}\text{=18}$) at higher molecular weights. The existence of two different types of catalyst, one soluble with homogeneous catalytic centres and the other insoluble with heterogeneous catalytic centres was found in the polymerization at 41°C. At temperatures below 21°C only soluble catalyst was present and produced isotactic polypropylenes with [m]=0.65. The isospecific nature of soluble titanium-based catalyst is greatly contrasted to the syndiospecific nature of soluble vanadium-based catalyst.     

Studies on highly active coordination catalysts for polymerization of α-olefins: 3. Polymerization of propylene with MgCl2/TiCl4/AlEt3 or MgCl2/PhCOOC2H5/TiCl4/AlEt3 systems

Activity and stereospecificity of the $\text{MgCl}{}_2\text{TiCl}{}_4$ catalyst in the polymerization of propylene follow curves showing maxima with grinding time of the MgCl₂ support. Using MgCl₂/PhCOOC₂H₅/TiCl₄ catalysts, no decrease in activity and stereospecificity was observed presumably because of complex formation between MgCl₂ support and ethyl benzoate.     

Optically active poly[thio-1-(N,N-diethylaminomethyl) ethylene]

Poly[thio-1-(N,N-diethylaminomethyl) ethylene] [poly(TDAE)] of different optical purities were prepared by stereoelective polymerization of racemic N,N-diethyl-N-(thiirane-2-ylmethyl) amine (TDAE) using a (1:1) $\text{ZnEt}{}_2\text{R}$ (?) 3,3-dimethyl 1,2-butanediol (R(?)DMBD) chiral initiator system. Optically enriched TDAE samples were isolated as residual monomers. These monomers were thermally polymerized to give optically active poly(TDAE) with randomly distributed R and S repeat units in various proportions. The configuration of the enantiomer preferentially incorporated into growing chains during the stereoelective polymerization was determined as R on the basis of the presence of a positive Cotton effect at 260 nm in the c.d. spectrum of residual monomers. This configuration agrees well with the known homosteric character of the $\text{ZnEt}{}_2\text{(?)}\text{DMBD}$ initiator system. ¹³C n.m.r. spectra of the different optically active poly(TDAE) samples and those of more or less stereoregular racemic ones were compared. It was found that the carbon atom of the main chain methine group is the only one which is stereosensitive. Observed triad effects were used to determine the degree of isotacticity of optically active poly(TDAE)s prepared by thermal polymerization of partly enriched monomers. The stereoelectivity of the initiator system and the optical activity of optically pure TDAE and poly(TDAE) were deduced. Side-chain nitrogen atoms did not show any competitive effect with sulphur atoms in the coordination process to the chiral initiator system.     

Studies of a CuY zeolite as a redox catalyst

The stability and behavior of CuY in the redox cycles with $\text{CO}\text{O}{}_2$, $\text{H}{}_2\text{O}{}_2$, and $\text{CO}\text{NO}$ have been studied using a microbalance operating in the flow mode and with a standard (BET) volumetric system. When CO was used as a reducing agent CO₂ was produced, thus removing oxygen from the zeolite lattice, but when H₂ was used only some of the H₂ consumed was evolved as H₂O. The rest was retained as lattice OH groups, but this was minimal when H₂ was used after treating the sample with CO. Oxidation with NO produced only N₂. At 500 °C the sample was stable and could be reversibly oxidized and reduced through many cycles using either $\text{CO}\text{O}{}_2$ or $\text{NO}\text{CO}$. In all cases the ratio $\text{O}\text{Cu}$ was close to 0.5, i.e., $\text{1e}\text{Cu}$. Treatment in CO at higher temperatures did not affect the reversible nature of the oxidation, but now the valence change was substantially larger; it approached $\text{2e}\text{Cu}$. The crystallinity of the exchanged zeolite was studied using X-ray diffraction and by measurement of the pore filling with liquid N₂. No significant changes could be detected after the different treatments, even those performed at 750 °C. Temperature-programmed reduction, temperature-programmed oxidation, and X-ray diffraction studies were made and the different maxima are reported. CuO and Cu ^o appeared in the oxidized and reduced samples, respectively, after treatment at 750 °C in CO but not at lower temperatures. Subsequent redox cycles at 500 °C did not appear to affect the size or amount of Cu ^o crystallites. CuY was active in the oxidation of CO with O₂ or NO. Its activity was lower than that of FeY zeolite when it exhibited an oxygen-carrying capacity of 0.5 $\text{O}\text{Cu}$. Treatment with CO at 750 °C, however, reversed the situation. Kinetic results showed that the fresh CuY catalyst was close to zero order in CO and fractional order in O₂ with an activation energy of 15 kcal/mole. After treatment at 750 °C in CO, the rate law became dependent upon the $\text{CO}\text{O}{}_2$ ratio. It was close to first order in CO and zero order in O₂ under oxidizing conditions ($\text{CO}\text{O}{}_2\text{≤ 2}$), but the orders were reversed under reducing conditions ($\text{CO}\text{O}{}_2\text{> 2}$). The activation energies were 12 and 15 kcal/mole, respectively. The data suggested that the Cu²⁺ with bound oxygen are the species active in the oxidation reaction.     

Effects of dextran molecular weight on graft copolymerization of dextran-methyl methacrylate

Effects of the molecular weight of dextran on its graft copolymerization with methyl methacrylate (MMA), initiated by ceric ammonium nitrate (CAN), have been investigated. The results indicate that grafting (%), graft polymerization (%) (ψ), the overall rate constant (k′) for consumption of Ce⁴⁺, and branch PMMA were influenced significantly by the molecular weight of the backbone polymer dextran. The number of branch PMMA chains per dextran molecule was 0.05 ～ 0.30 for $\text{M}\text{?}{}_{\mathrm{w}}$ 9000 dextran (D1), 0.35 ～ 0.55 for $\text{M}\text{?}{}_{\mathrm{w}}$ 61 000 (D2), and 0.8 ～ 1.6 for $\text{M}\text{?}{}_{\mathrm{w}}$ 196 000 (D3), respectively. The relationship between the rate of graft polymerization and $\text{M}\text{?}{}_{\mathrm{w}}$ (the weight-average molecular weight of dextran) was expressed by the equation: $\text{R}{}_{\mathrm{p}}\text{g = ?A}\text{log}\text{M}\text{?}{}_{\mathrm{w}}\text{+ B}$. Another linear relationship was obtained between In (100 ? ψ) and reaction time (t) for both D1 and D2 samples or In t for D3. Detailed kinetic analysis has been made on the basis of the latter relationship. Mechanical properties were also studied on the moulded sample plates of these copolymers.     

Non-equilibrium molecular weight studies on the metathesis polymerization of cyclopentene initiated by WCl6AliBu3: Effect of catalyst ageing time

A study has been made of the molecular weight and distribution changes that take place during the polymerization of cyclopentene initiated by the non-living metathesis catalyst $\text{WCl}{}_6\text{AliBu}{}_3$. The system appears to be characterized by two distinct phases. In the first phase, the molecular weight distribution, which is bimodal, would appear to be kinetically controlled and the bimodal distribution to result from the presence of two kinetically independent metathesis species. The initial molecular weight distribution would, therefore, appear to be dependent upon the relative concentrations of these active species. The second phase of the polymerization is a slow conversion of the molecular weight distribution to that of an equilibrium distribution after a long reaction time.     

Characterization of styrene-ethylene oxide and methyl methacrylate-styrene block copolymers by light scattering

Several polystyrene-poly(ethylene oxide)-polystyrene (PS-PEO-PS) and poly(methyl methacrylate)-polystyrene-poly(methyl methacrylate) (PMMA-PS-PMMA) block copolymers, synthesized by free-radical polymerization, were studied in various solvents by using a light-scattering technique. The copolymers, which have different lengths of central blocks, had molecular weights within the range 3.0 × 10⁴ to 1.6 × 10⁶. It was found that almost all of them were confirmed as block copolymers from the variation of the product $\text{M}{}_{\mathrm{<mtext>app</mtext>}}\text{〈S}{}^2{}_{\mathrm{<mtext>app</mtext>}}\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ with $\text{W}{}_{\mathrm{<mtext>A</mtext><mtext>v</mtext><mtext>A</mtext>}}\text{v}$, although they were rather heterogeneous. The copolymer compositions determined either from the additivity of the refractive index increments of its constituent parts and the copolymer or from ultra-violet analysis were in excellent agreement with each other.     

Effects of metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H₂O₂ titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the $\text{Pd}\text{SiO}{}_2$ catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the $\text{Pd}\text{La}{}_2\text{O}{}_3$ catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

Properties of extremely high molecular weight polystyrene in solution

Extremely high molecular weight polystyrenes with a $\text{M}\text{?}{}_{\mathrm{w}}$ in the range 10.8 × 10⁶ to 2.2 × 10⁷ were prepared by emulsion polymerization initiated with a heterogeneous initiator at 30°C, which has a ‘living character’. Samples of polystyrene were characterized by light scattering and viscometry in toluene and benzene at 25°C, and in θ-solvent cyclohexane at 34.8°C. Also determined were the relationships of mean-square radius of gyration 〈s²〉 (m²) and the second virial coefficient A₂ (m³ mol kg^?2) on the molecular weight, which for toluene and benzene are described in equations: Toluene (25°C) $\text{〈s}{}^2\text{〉=1.59 × 10}{}^{\mathrm{?23}}\text{M}\text{?}{}_{\mathrm{w}}{}^{1.23}$; $\text{A}{}_2\text{=4.79 × 10}{}^{\mathrm{?3}}\text{M}\text{?}{}_{\mathrm{w}}{}^{\mathrm{?0.63}}$; Benzene (25°C) $\text{〈s}{}^2\text{〉=1.23 × 10}{}^{\mathrm{?22}}\text{M}\text{?}{}_{\mathrm{w}}{}^{1.20}$; $\text{A}{}_2\text{=2.59 × 10}{}^{\mathrm{?3}}\text{M}\text{?}{}_{\mathrm{w}}{}^{\mathrm{?0.59}}$. The parameters in the Mark-Houwink-Sakurada equation were established, for extremely high molecular weight polystyrene in toluene and in benzene, at 25°C into the form giving for $\text{[η] (}\text{m}{}^3\text{kg}{}^{\mathrm{?1}}\text{): [η] = 8.52 × 10}{}^{\mathrm{?5}}\text{M}\text{?}{}_{\mathrm{w}}{}^{0.61}$; $\text{[η] = 1.47 × 10}{}^{\mathrm{?4}}\text{M}\text{?}{}_{\mathrm{w}}{}^{0.56}$. The mentioned relations, as well as the obtained values of Flory parameter ?₀ and of ratio $\text{[η]}\text{M}\text{?}{}_{\mathrm{w}}{}^{0.5}$ were compared with solution properties of high molecular weight polystyrene with narrow molecular weight distribution prepared by anionic polymerization by Fukuda et al.     

Participation of lewis base on vinyl chloride polymerization with Al(C2H5)3CCl4 catalyst system

The polymerization of vinyl chloride has been investigated using an $\text{Al}\text{(}\text{C}{}_2\text{H}{}_5\text{)}{}_3\text{CCl}{}_4$ catalyst system in the presence of various Lewis bases. Effective Lewis bases are γ-butyrolactone, diglyme and diethylenetriamine which are multidentate. The rate of polymerization is dependent not only on the basicity of the Lewis base used but also on a coordination number of one. The latter is the predominant factor. For the effect of polymeric amines, a tentative hypothesis is discussed.     

Poly(sulphopropylbetaines): 1. Synthesis and characterization

The synthesis of aromatic and aliphatic poly(sulphopropylbetaines) is described within the series of vinylpyridines and tertiary amino-methacrylates. Two complementary strategies were used: (a) preparation and free radical polymerization in aqueous solution (60°C, 4,4'-azobiscyanovaleric acid) of the monomers; (b) heterogeneous quaternization of preformed poly(vinylpyridines) and poly(tertiary amino-methacrylates) by 1,3-propanesultone in propylene carbonate or tetramethylene sulphone solution (120°C). The high molecular weight poly (zwitterions) ($\text{10}{}^5\text{<}\text{M}\text{?}{}_{\mathrm{W}}\text{< 5 × 10}{}^6$) were characterized by ultra-violet and ¹H nuclear magnetic resonance spectroscopy, and their water affinity at 20°C was estimated by water vapour absorption measurements.     

Thermomechanical heat of deformation studies on cis-polybutadiene

Thermomechanical heat of torsional deformation measurements have been made on crosslinked cis-polybutadiene by means of a Calvet microcalorimeter operated at 30°C. When corrected for volume changes utilizing the Gaussian statistical theory of elasticity, the data gave a value for the relative energy contribution to the torsional couple, $\text{M}{}_{\mathrm{e}}\text{M}$, of 0.14 ± 0.02. Measurements were also made on a sample subjected to simple tensile deformations. The relative energy contribution to the tensile force ($\text{f}{}_{\mathrm{e}}\text{f}$) was found to agree within experimental error with the value obtained for $\text{M}{}_{\mathrm{e}}\text{M}$, and the two results gave an average value for din $\text{〈r}{}^2{}_0\text{〉}\text{d}\text{T}$ of 4.1 × 10^?4 K^?1.     

A calculation of the elastic constant c33 of a graphite crystal as a function of temperature

A calculation is presented of the elastic constant C₃₃ of a graphite crystal as a function of temperature up to 2500 K, taking into account the anharmonic contribution and the changes in interlayer interactions due to the large lattice thermal expansion. Parametric variations in the theory show that the anharmonic contribution to C₃₃ depends principally on the parameter ($\text{?}{}^2\text{C}{}_{33}\text{?e}{}^2{}_{\mathrm{zz}}$) Comparison of theoretical results with the experimental data, which is mainly from neutron scattering experiments, shows that the data can be accounted for if ($\text{?}{}^2\text{C}{}_{33}\text{?e}{}^2{}_{\mathrm{zz}}$) lies in the range 7–10 × 10¹³ dynes/cm². A theoretical estimate of ($\text{?}{}^2\text{C}{}_{33}\text{?e}{}^2{}_{\mathrm{zz}}$) based on Lennard-Jones potentials between atoms in adjacent basal planes gives a value of 9·07 × 10¹³ dynes/cm².     

The concentration dependence of the angular dissymmetry of light scattered by micellar solutions

A light scattering investigation was made of micelles formed from a polystyrene-poly(ethylene/propylene) two-block copolymer in n-nexane. n-Hexane is a selectively bad solvent for polystyrene and so polystyrene blocks formed the cores of the micelles. The light scattering measurements were made at 25°C for concentrations up to 0.015 g cm^?3. The dissymetry ratio ($\text{I}{}_{\mathrm{45°}}\text{I}{}_{\mathrm{135°}}$) was found to decrease with increase in concentration and it was below unity for measurements at c > 4.8 × 10^?3 g cm^?3. The effect of concentration on the dissymmetry ratio was predicted quite well by assuming the micelle packing could be described by radial distribution functions for hard spheres.     

Simultaneous heat and mass transfer in binary distillation—II: Experimental

A theoretical study of simultaneous heat and mass transfer in binary distillation has shown that heat and mass transfer coefficients can be appropriately evaluated if liquid phase temperatures and compositions are measured as functions of height in a column. In this study, the experiments were carried out in a wetted-wall column using a methanol-water binary system at one atmosphere.Special probes were designed to determine the state of the liquid phase. Temperatures were measured with microthermocouples and liquid samples were analyzed with a high precision refractometer. The liquid phase was found to be saturated which indicated, in accordance with the conclusions from a theoretical study, that all the resistance to mass transfer was in the vapor phase. Local transfer coefficients were calculated using the composition data as a function of column height. The results were correlated by an equation showing close agreement with the Chilton-Colburn equation. $\text{k}{}_{\mathrm{y}}\text{a}{}_{\mathrm{m}}\text{V}\text{= 0.039}\text{Sc}{}_{\mathrm{y}}$^{?$\text{2}\text{3}$}Re_y^?0.20 cm^?1.It is concluded that mass transfer in the vapor phase is the controlling resistance in distillation and that there is no additional evaporation within the liquid phase caused by heat transferred from the vapor phase as proposed by some previous investigators.     

The time dependent strain potential function for a polymeric glass

Torsion and normal force measurements were made during single step stress relaxation experiments on a polymeric glass (PMMA). Isochronal data were analysed using an approach adapted from that developed by Penn and Kearsley¹ (for incompressible elastic materials) to determine the derivatives $\text{?W}\text{?I}{}_1$, and $\text{?W}\text{?I}{}_2$ of the time dependent strain potential function. $\text{?W}\text{?I}{}_1$ and $\text{?W}\text{?I}{}_2$ are determined from existing solution to the torsion of an incompressible cylinder. A special solution to the torsion of a compressible cylinder is presented and it is shown that the values of $\text{?W}\text{?I}{}_1$ and $\text{?W}\text{?I}{}_2$ obtained using this solution to analyse the data do not differ greatly from those obtained using the incompressible solution. It is found from both solutions that $\text{?W}\text{?I}{}_1$ is negative and increases towards zero with increasing time and deformation while $\text{?W}\text{?I}{}_2$ is positive, greater in magnitude than $\text{?W}\text{?I}{}_1$ and decreases towards zero with increasing time and deformation. These results were unexpected and a full understanding of their meaning has yet to be reached.     

Non-classical free-radical polymerization: 3. Diffusion-control in degradative addition

The different kinetic features associated with polymerizations in which retardation arises through degradative transfer and degradative addition processes are considered. Reasons are given for believing that in reactions retarded by degradative transfer neglect of the interaction between ‘inactive’ radicals is justifiable, while with degradative addition this is not so. A kinetic treatment of the latter is developed in which all three termination reactions between propagating and inactive radicals are assumed to be diffusion-controlled with a single rate coefficient and equations are derived which permit from experimental data on rates of polymerization estimation of the definitive kinetic parameters $\text{k}{}_{\mathrm{p}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$, $\text{k}{}_{\mathrm{pm}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$ and $\text{k}{}_{\mathrm{fm}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$ (k_p, k′_t, k_pm, k_fm are the rate coefficients of propagation, termination, reinitiation and degradative additions, respectively). The kinetic equations are satisfactorily consistent with ew experimental data on the polymerization of 1-vinylimidazole in ethanol solution at 70°C, for which there is strong evidence for the occurrence of degradative addition. A modified procedure for processing data for polymerizations with degradative transfer is put forward which is convenient for estimating the kinetic parameters and reveals in a simple manner the importance of re-initiation. It is suggested that this treatment could be generally useful in the early stages of the study of a retarded polymerization.     

Studies of cyclic and linear poly(dimethyl siloxanes): 10. Calculations of radii of gyration

A Monte Carlo method has been devised for calculating the conformation-dependent properties of cyclic poly(dimethyl siloxanes) (PDMS), using Flory, Crescenzi and Mark's rotational isomeric state model. Calculated values of the mean-square radii of gyration 〈s²_r〉 of ring molecules unperturbed by excluded volume effects and containing 8–100 skeletal atoms are compared with the 〈s²_l〉 values for the corresponding unperturbed chain molecules. Exact enumeration methods were also employed for rings $\text{[(}\text{CH}{}_3\text{)}{}_2\text{SiO}\text{]}{}_{\mathrm{<mtext>w</mtext><mtext>2</mtext>}}$ with w ? 24 and the results found to be in close agreement with those obtained by the Monte Carlo method. The ratio $\text{〈s}{}^2{}_{\mathrm{l}}\text{〉}\text{〈s}{}^2{}_{\mathrm{r}}\text{〉}$ was found to attain limiting values close to 2.0 for w > 30, in agreement with theoretical predictions.     

Twenty-five years of Brown and Ladner's parameters

Brown and Ladner's parameters have been compared with those of Williams for the same conditions. The combination of experimental data from ¹H n.m.r. and ¹³C n.m.r. spectra gives the value of the Brown and Ladner's parameter $\text{H}{}_{\mathrm{aru}}\text{C}{}_{\mathrm{ar}}$. A comparison of the $\text{H}{}_{\mathrm{aru}}\text{C}{}_{\mathrm{ar}}$ values was performed on a group of different coal oil samples.