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Some recent results for the copolymerization of ethylene and α-olefins together with data relating to prepolymerization using propylene, butene-1, hexene-1 and 4-methylpentene-1 prior to ethylene homopolymerization are presented. Experimental data using the catalyst systems δ-TiCl 3 ‐ 0.33AlCl 3 and MgCl 2 /EB/TiCl 4 are reported and include kinetic data, active centre determinations and morphological studies. These results are discussed in the context of current models involving expanding multigrain microreactors.

Highly active MgC1 2 - supported TiCl 4 Ziegler-Natta catalysts were used for propylene polymerization and the effect of varying the triethylaluminium concentration was studied in relation to the polymerization rate and to the number of active centres. Active centre concentrations were carried out using 14 C -labelled carbon monoxide. An optimum AlE 3 :Ti molar ratio was found to be necessary in order to obtain the highest rates of polymerization and the highest active centre concentrations. The concentration of active centres, C * , remains more or less constant with polymerization time, but the average propagation rate coefficient, κ p decreases. For AlEt 3 :Ti molar ratios greater than 80:1 values of both C * and κ p decrease only slightly with increase in AlE 3 :Ti molar ratio. Only 4.4–6.6 mol% of the total titanium was active. The dependence of the maximum values of the rates of polymerization on the alkylaluminium concentrations were investigated using Langmuir-Hinshelwood isotherms.

The silylated cyclopentadiene derivative, (MeO) 3 Si(CH 2 ) 3 C 5 H 5 , synthesised from commerically-available (MeO) 3 Si(CH 2 ) 3 Cl, has been used to prepare the complexes [η 5 -(MeO) 3 Si(CH 2 ) 3 C 5 H 4 ]Rh(CO) 2 , [η 5 -(MeO) 3 Si(CH 2 ) 3 C 5 H 4 ]Rh(COD) (COD = cyclo-octa-1,5-diene), and [η 5 -(MeO) 3 Si(CH 2 ) 3 C 5 H 4 ] 2 TiCl 2 . The complex [η 5 -(MeO) 3 Si(CH 2 ) 3 C 5 H 4 ]TiCl 3 , prepared by reaction of NaC 5 H 4 (CH 2 ) 3 Si(OMe) 3 with TiCl 4 (1/1 molar ratio) and also by reaction of [η 5 -(MeO) 3 Si(CH 2 ) 3 C 5 H 4 ]Ti(OEt) 3 with CH 3 COCl, proved to be very unstable. Attempts to synthesise the complex [η 5 -(MeO) 3 Si(CH 2 ) 3 C 5 H 4 ](η 5 -C 5 H 5 )TiCl 2 , either by reaction of [η 5 -(MeO) 3 Si(CH 2 ) 3 C 5 H 4 ]TiCl 3 with NaC 5 H 4 or reaction of (η 5 -C 5 H 5 )TiCl 3 with NaC 5 H 4 (CH 2 ) 3 Si(OMe) 3 , gave none of the expected product and only (η 5 -C 5 H 5 ) 2 TiCl 2 could be isolated from these reactions. The cyclo-octadiene rhodium complex supported on silica has been shown to be an efficient cyclotrimerization catalyst, and the silica-supported titanium complex (SIL-(CH 2 ) 3 C 5 H 4 ) 2 TiCl 2 is, after reduction with butyllithium, an efficient and selective catalyst for the hydrogenation of alk-1-enes.

Factors affecting the duration of the settling period in the polymerization of 4-methylpentene-1 by the catalyst system VCl 2 AIR 3 in benzene have been systematically investigated. Plots of log10 (100 — %Rp) versus time show that the so-called settling period can be divided into two distinct regions; an initial region which is not time dependent and a steady state region in which the formation of Co follows a strictly first order time dependence. The initial region is believed to arise from the removal of adsorbed AlR2Cl species, while the steady state region can be interpreted as describing a rearrangement reaction involving the production of initiated chains.

Comparative studies using gas chromatographic and vapour pressure techniques have been carried out on solutions of poly(vinyl chloride), polystyrene, and poly(methyl methacrylate) in the solvents toluene, methyl ethyl ketone, 1,4 dioxan, tetrahydrofuran and di-n-propyl ether. The values of the corresponding interaction energy parameters ( χ 1 ) are compared and analysed in terms of the Flory-Huggins theory of polymer solutions. The two techniques produced values of χ 1 for a wide range of solvents which were in good agreement with each other, thus substantiating the validity of both methods. Also, the vapour pressure results agreed with the Flory-Huggins theory over an extended range of solute composition. The gas chromatographic method yielded very self-consistent results and proved to be the more rapid technique. It also had the advantage that it could be used without much difficulty over a wider temperature range.

The activating effect of triethylamine in the VCl 3 AlR 3 system has been explained in terms of a previously proposed kinetic scheme. Activation is observed at low amine concentrations and is thought to occur by removal of adsorbed aluminium alkyl species from the catalyst surface. Deactivation occurs at higher donor concentrations and is believed to be due to competitive adsorption of donor with monomer. These proposals are consistent with the rate, molecular weight and polymer tacticity findings of other workers in Ziegler-Natta systems where the donor is capable of interaction with both the transition metal and metal alkyl components.

A kinetic scheme is postulated for Ziegler-Natta polymerization where propagation is considered to occur between adsorbed monomer and an active centre which has been formed by interaction of the metal alkyl with the transition metal halide. Chain transfer is considered to occur with adsorbed metal alkyl and also with adsorbed monomer. Rate, molecular weight and active centre dependencies are derived which are in qualitative agreement with the results of previous studies in Ziegler-Natta polymerization.

The catalyst system VOCl 3 /Al(iBu) 3 /THF has been examined and the role of the individual catalyst components investigated. Tetrahydrofuran is believed to undergo complex formation with the other catalyst components thus restricting reduction of the vanadium to V(IV). The complex VOCl 2 .2THF has been isolated and, when used with tri-isobutyl-aluminium in the presence of excess tetrahydrofuran, shown to produce polymerization systems of comparable activity to the VOCl 3 /Al(iBu) 3 /THF systems. The kinetic behaviour of the VOCl 3 /Al(iBu) 3 /THF system has been investigated and shown to be consistent with a simple Ziegler-Natta kinetic scheme involving a rapid bimolecular decomposition of either a transition metal alkyl compound, or of a complex formed on interaction of a transition metal alkyl with an aluminium alkyl.

The kinetics of the polymerization of 4-methylpentene-1 by the Ziegler-Natta system VCl 3 AlR 3 have been examined at 30°C and 40°C. The dependence of the overall rate of polymerization on the concentration of metal halide, aluminium alkyl concentration, monomer concentration, temperature, and nature of the aluminium alkyl has been established. The energy of activation of the overall polymerization process has been found to be 16·6kcal/mol in benzene and 13·7kcal/mol in heptane. The results have been examined in relation to a previously described kinetic scheme.

Chain transfer with adsorbed aluminium alkyl has been investigated for the system VCI3/AIR3/4-methylpentene-1, where adsorption of the metal alkyl onto the catalyst surface is described by a Langmuir type adsorption isotherm. Rate constants for chain transfer with metal alkyl and equilibrium constants for adsorption of a series of aluminium alkyls and 4-methylpentene-1 onto the transition metal halide surface have been determined. The activation energy for the chain transfer process with tri-isobutylaluminium has also been evaluated. The number of active centres is found to be reduced at low monomer concentrations probably because of slow initiation by monomer. Quantitative verification of a previously presented kinetic scheme has been effected.

Styrene has been successfully copolymerized with various α-olefins, using Ziegler-Natta catalyst systems. The products of copolymerization were fractionated with respect to composition using a double-solvent elution technique. The copolymer obtained by the use of the VCl 3  Al (i Bu ) 3 catalyst was found to be much more heterogeneous than the polymer obtained with the more disperse system, i.e. VOCl 3  Al (i Bu ) 3 . This was considered to be good evidence for the presence of a higher degree of catalytic polyactivity in the more crystalline catalyst with the larger particle size. A series of structural investigations on the copolymer samples was undertaken using X-ray diffraction and infra-red spectroscopic techniques. It was shown that the copolymers of styrene and octadecene-1, and styrene and 4-methylpentene-1, prepared using VOCl 3  Al (i Bu ) 3 exhibited a high degree of crystallinity. Much evidence is presented for the existence of a stereoblock type of structure. The values of relative reactivity ratios were determined for each of the monomer pairs investigated. A reduction in reactivity ratio values was observed in all cases with the use of the more disperse catalyst system.

The stereospecific polymerization of styrene in n-heptane solution by α-TiCl 3 —alkylaluminium (or alkylaluminium halide) catalysts has been studied by means of a dilatometric procedure. After an initial settling period, the nature of which depends on the catalytic system, the overall rate of polymerization is proportional to the α-TiCl 3 concentration, but independent of the alkylaluminium (or alkylaluminium halide) to α-TiCl 3 ratio in the range 9·6–0·26. At styrene concentrations greater than 3·6 mole/l. the rate of polymerization is proportional to the styrene concentration but at lower concentrations the rate is more nearly second order. The overall energy of activation is approximately 9·4 kcal/mole for all catalysts. The catalytic system α-TiCl 3 -AlEt 3 is more active than the catalytic systems α-TiCl 3 -AlEt 2 Cl and α-TiCl 3 -AlEt 2 Br, and yields a higher percentage of isotactic polystyrene (over 90 per cent)

The number of active centres in the polymerization system VCl3/AIR3/4-MP-1 has been shown to lie in the range 2·3–6·1 × 10−4mol/mol VCl3 for a series of aluminium alkyls, and to vary with the nature of the aluminium alkyl used. Chain transfer with aluminium alkyl has been demonstrated. The propagation rate constant has been evaluated and found to be independent of the nature of the metal alkyl. The location of, and nature of, the active centre is discussed. The validity of the tritium labelling procedure is tested by comparison of calculated and experimentally determined molecular weights.

Molecular weight relationships in the polymerization of 4-methylpentene-1 by the Ziegler-Natta system VCl 3 AlR 3 have been examined at 30°C and 40°C. The dependence of the number-average degree of polymerization on the concentration of metal halide, aluminium alkyl concentration, monomer concentration, temperature, and nature of the aluminium alkyl has been established. The results have been examined in relation to a previously described kinetic scheme, and the rate constant for chain transfer with adsorbed monomer has been evaluated.

The polymerization of vinyl chloride by a number of modified Ziegler-Natta catalysts has been investigated. The most effective catalyst system is the soluble system prepared from vanadium oxytrichloride, tri-isobutylaluminium, and tetrahydrofuran. All three components are necessary for the formation of an active catalyst. The kinetics of the polymerization of vinyl chloride by this catalyst system has been examined at 30°C, and the dependence of the overall rate of polymerization on the transition halide concentration, aluminium alkyl concentration, monomer concentration and temperature established. Kinetic and copolymerization studies indicate that the polymerization process is not free radical in nature but is similar to that encountered in more conventional Ziegler-Natta systems.

The phenomenological behaviour shown by many Ziegler-Natta catalyst systems is outlined and the factors controlling the observed rate-time profiles are discussed in the light of existing kinetic models. Results for C* and derived values of kp are presented for the polymerization of propylene and 4-methylpentene-1 by MgCl2/EB/TiCl4-Al (i-Bu)3 catalysts. The concentrations and activities of polymerization centres giving rise to atactic and isotactic polymer in propylene polymerization are evaluated. The higher overall rates observed in both propylene and 4-methylpentene-1 polymerization are discussed in terms of C* and kp values. Increased values of C* obtained for higher α-olefin polymerization are also presented.