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Polypropylene homopolymer samples were prepared with a Ziegler–Natta catalyst using two different external donors, namely diphenyldimethoxysilane (DPDMS), and methylphenyldimethoxysilane (MPDMS). Each donor was used in varying molar ratios to the catalyst in order to prepare samples for physical testing. The polymers were fully characterised and also fractionated by preparative TREF with characterisation of the fractions. In terms of the polymerisation reactions the DPDMS external donor exerts greater influence at the active sites than the MPDMS and produces polymer of higher molar mass and lower polydispersity. The physical properties of the polymers were investigated using microhardness measurements. It is revealed that the microhardness is strongly dependent on the stereoregularity of the samples.

The copolymerisations of the monomers 1 (1′,2,3,3′,4,4′,6-hepta-O-benzyl-6′-O-crotonyl-sucrose) and 2 (1′,2,3,3′,4,4′,6-hepta-O-benzyl-6′-O-methacryloyl-sucrose) with styrene/methyl methacrylate have been examined in the presence of Ziegler–Natta catalyst TiCl4/AlEt3. A study of the effect of the reaction conditions, the monomer structure and the initial quantity of the comonomers on the sugar incorporation and molecular mass of the final copolymers has been carried out. In this way, by the coordination mechanism of polymerisation we had obtained novel linear unbranched polymers and copolymers, potentially useful for biomedical applications.

Catalysts constituted by neodymium versatate, diisobutylaluminium hydride and t-butyl chloride were used in this work. After their synthesis, they were aged at 40 °C for 48 h. Afterwards, they were maintained at 10 °C for more 5, 15, 40, 80, 160 and 250 days and finally the aged catalysts were evaluated in butadiene polymerization. The polybutadienes were characterized by size exclusion chromatography (SEC) to determine the molecular weight characteristics and by infrared spectroscopy (FTIR) to determine the microstructure. The aim of this work is to evaluate the effect of ageing time on 1,4 polymerization of butadiene. The results showed that the stereoselectivity of the active sites was not affected by the ageing conditions. However, the catalyst activity increased for long times of ageing.

An analysis was carried out of some Ziegler–Natta catalysts precursors by small- and wide-angle X-ray scattering in order to get information on the crystallites dimensions, structural disorder and surface areas. The results were correlated with catalytic activities in polymerization of propylene. It was shown that the structural variations, which mainly influence the catalytic activity, are associated with the rotational disorder of the Cl–Mg–Cl triple layers and that the crystallites dimensions and surface areas play a determinant role in the same activity. Furthermore it was shown that the surface areas of the examined samples, determined by BET, are less meaningful than the data obtained by small-angle X-ray scattering, probably for the presence of intra-particle closed pores and/or microporosity.

Polymerizations of propylene were carried out by using the catalyst system MgCl 2 ·ID·TiCl 4 -AlEt 3 ·ED, where ID (internal donor) was an organic diester and ED (external donor) was a silane. The effect of preparation conditions on the chemical composition and morphology of the supports and catalysts are discussed with the aid of elemental analysis and microscopy. The ethanol content had a strong effect on the MgCl 2 · nEtOH adduct preparation, and its precipitation and dealcoholation are very important factors that must be considered for good morphology to be attained in the spherical catalysts and polymers. The rate profiles in propylene EC180 suspension polymerization changed with the type of external donor and Al/Ti molar ratio.

An i.r. study of MgCl 2 supported TiCl 4 Ziegler-Natta catalysts for propylene polymerization using Lewis base modifiers has been carried out. Two series of catalysts were prepared, differing mainly by the method used to prepare the MgCl 2 support. One was prepared by precipitation and the other by ball-milling. Four different Lewis bases, of which two are diesters (di-2-ethyl phthalate and diisobutyl phthalate) and two are monoesters (ethyl benzoate and 2-ethyl hexyl benzoate), were employed. The i.r. investigation of the catalyst was focused on the identification of complexes formed. It was found that the diester-containing catalysts contain significant amounts of TiCl 4 · diester complexes and phthaloyl mono- and di-chlorides complexed to MgCl 2 , whereas the monoester-containing catalysts are virtually free of these compounds. The chlorides are believed to be formed from the reaction of TiCl 4 and diester weakly bonded to MgCl 2 . The TiCl 4 · monoester complex is relatively weak so that the coordination of monoester with MgCl 2 is much more favorable. The effects of the complexes, particularly their relative amounts, on the catalyst activity was investigated by carrying out propylene polymerizations with catalysts prepared by precipitation and by ball-milling method at three different activation temperatures.

The effect of different cocatalysts in slurry phase polyethylene production using a high active Ziegler/Natta catalyst precursor was studied under different polymerization start-up methods. The study revealed that diffusion of cocatalyst molecules through produced polymer to reach potential active sites inside the catalyst precursor particles is an important factor as was already suggested in Ref. [1]. Increasing the molecular dimensions of the cocatalyst molecules thus results in a decrease in the rate of activation of the catalyst precursor. It was shown that polymer powder morphology is strongly effected by the time necessary to reach maximum polymerization activity which depends not only on the method of polymerization start-up [1], but also on the nature of the cocatalyst. Cocatalyst diffusion inside catalyst precursor particles can also be a possible explanation for the development of cobweb [2] structures in polymer particles.

A study has been made of Ziegler-Natta polymerization of 2-vinylpyridine, using AlEt 3 -VCl 3 as catalyst system and natural nicotine as cocatalyst. Conversion was related to the formation time of the catalytic species, temperature and molar ratio of the components of the catalyst system. Relative crystallinites and average molecular weights for the polymers are given. The influence of natural nicotine as donor ligand has been examined and some asymmetric induction was observed.

The preparation and the crystal structure of the β (brown) form of TiCl3 have been re-examined. Accurate X-ray diffraction measurements on crystallographically pure samples, free from A1, allowed refinement of the structure originally proposed by the Natta school in 1958, and in particular to fix the x coordinate of the chlorine atoms in the unit cell. The X-ray characterization of products with composition (β-TiCl 3 + 1 3 AlCl 3 ) gave no indication of the existence (suggested in the literature) of solid solutions β-TiCl3 · (AlCl3)0.33 analogous to those known for the violet modifications.

The model previously proposed for the heterogeneous isospecific Ziegler-Natta polymerization, which agrees with a large number of experimental facts, has been examined in more detail. In particular a semiquantitative evaluation of the discriminating effects between the two faces of the co-ordinated prochiral l-propene molecule at the insertion step has been attempted. This study is presented together with a re-examination of the model at the co-ordination step, which considers in more detail the influence of the assumed values for the metal-carbon bond lengths on the stereospecificity. In agreement with previous suggestions, the analysis indicates the presence of enantioselectivity ( si olefin favoured on a Λ site independently of the configuration of the growing chain) at the insertion step also in the absence of enantioselectivity at the co-ordination step.

MgCl2 adducts with alcohols and ethers can be converted to more active supports through the elimination of the alcohol molecules from the adducts by thermal desolvation. Catalysts supported on the products of thermal desolvation of the MgCl2 adducts with methyl and ethyl alcohols have been prepared. The supports were characterized by elemental analysis, X-ray diffraction and N2-BET surface area. The supports were used in the synthesis of Ziegler-Natta catalysts through single and double treatments with TiCl4 and then evaluated in ethylene and propylene polymerizations.

A kinetic model involving two types of active sites of mixed stereospecifities is proposed for the polymerization of propylene over a supported TiCl 4 /MgCl 2 Ziegler-Natta catalyst. From a proposed reaction sequence, a set of mass balance expressions is derived and solved to evaluate continuous changes in polymerization rate and polymer properties with time. Discrepancies were observed between predicted and measured total polymer polydispersities, while lack of mechanistic information rendered the estimation of model parameters somewhat speculative. It is expected that, as further mechanistic knowledge is gained, models such as that presented here will prove useful in the study of supported Ziegler Natta catalysts.

Studies have been made of the effects of tributyl phosphate, ethyl benzoate (EB) and diisobutyl phthalate (DIBP) as second internal bases on the Ziegler-Natta catalysts prepared by the reduction of TiCl4 with AlClEt2 in the presence of n-butyl ether (DBE) as a first internal base. These catalysts were evaluated in propylene polymerization in the presence or absence of external bases (EB, DIBP and DBE). The effects of internal and external bases on the catalyst activity and stereospecificity are discussed.

The model proposed by Cossee for Ziegler-Natta polymerization of propene is re-examined by computing the non-bonded energies for all sets of possible internal coordinates of the atoms at the catalytic site. For catalytic sites in the bulk of (110) surfaces of TiCl 3 -α, it is possible to explain the regiospecificity of the reaction but, at variance with Cossee, we see no evidence that the surface conditions the methyl group of the olefin to protrude out of the crystal. The stereospecificity may arise however from the fixed, chiral orientation of the first carbon—carbon chain bond, due to interactions with the surface. Further computations seem to indicate that the polymerization could occur with much less steric hindrances on edges or reliefs of the surfaces, the relative positions of olefin and chain being exchanged in respect to the Cossee model.

A study was made of the effect of Et 3 N and 2,2,6,6-tetramethyl-piperidine (TMPip) as donor additives on the catalysts (a) MgCl 2 /TiCl 4 /AlEt 3 , (b) δ-TiCl 3 /AlEt 3 and (c) δ-TiCl 3 /ZnEt 2 for propylene polymerization. The productivity trends show a maximum, at low base concentration, in the presence of the AlEt 3 based catalysts (a) and (b), due (especially for TMPip) to a noticeable increase of the isotactic fraction. At the same base concentration, both amines cause a minimum of productivity in the presence of the ZnEt 2 based catalyst (c). These findings indicate that the amines may exert at least two different and concurrent effects: (i) poisoning of both isotactic and atactic sites; (ii) activation of the isotactic sites. Either the former or the latter effect prevails, depending on the equilibrium reactions in which the amines and the alkyl metal are involved.

The profiles of X-ray diffraction patterns have been examined for several powder samples of δ-TiCl 3 , obtained by mechanical activation of γ-TiCl 3 and presenting different catalytic activities in the Ziegler-Natta stereospecific polymerization of propylene to isotactic polypropylene. Particular attention has been paid to the δ-TiCl 3 samples showing the best catalytic properties. On the basis of a previous investigation by Allegra, a mathematical treatment has been developed and a disorder function has been elaborated taking into account, in calculating the profiles of the X-ray diffraction intensities, not only the disorder effects but also the sizes of the δ-TiCl 3 crystallites. The selected experimental pattern (δ-TiCl 3 , highly activated) has been well reproduced in this way and fitted by overlapping the calculated spectra of two disordered forms, labelled ϵ 1 and ϵ 2 , which differ in the relative amounts cubic and hexagonal sequences of the Cl-Ti-Cl layers constituting the violet forms of TiCl 3 . The best fit was achieved by introducing into the calculations crystallite sizes of about 70 A. The results of the structural investigation are also discussed in terms of activity of the δ-TiCl 3 based catalyst for the stereospecific polymerization of propylene.

The computations performed in a previous paper for hypothetical structures of the site active in the polymerization of olefins at the (110) surfaces of TiCl 3 -α are extended to edges, steps and reliefs on (111) surfaces of all the layered modifications of TiCl 3 . Our computations suggest that edges, steps and reliefs of all the layered modifications of TiCl 3 should behave similarly in providing active sites; polymerization should occur on these more exposed sites because of the much lower activation energies than for plain surfaces. A unique general model emerges: lower steric repulsions appear to be implied for a coordination of the polymeric chain on the more hindered octahedral position at a titanium atom and this, in turn, causes a chiral orientation of the first carbon-carbon bond of the chain. This orientation may be the main factor in determining the stereospecificity.

A fractional poisoning method has shown that all groups of Ziegler catalyst centres, both stereospecific and non-stereospecific, have a similar distribution of propagation rate constants. The most regular and highly molecular isotactic fraction is quite uniform by stereoregularity. Most of the poison-resistable part of active centres in δTiCl 3 -AlEt 3 systems have properties similar to those of initial system TiCl 3 -AlEt 2 Cl, which may be caused by different adsorption abilities of co-catalysts AlEt 3 and AlEt 2 Cl at TiCl 3 surface. Values n p and k p have been estimated for δTiCl 3 (TAC)-AlEt 3 system.

A study was made of the effect of NEt 3 as a donor additive on the centres of different stereospecificities of the catalytic system δ-TiCl 3 (TAC)-AlEt 3 . It is shown that the addition of amine, both in a free form (D) and as part of the complex NEt 3 -AlEt 3 (C), produces a poisoning action on the catalytic centres. In the former case (D), the isospecific centres are also partially poisoned, leading to a drop in the system activity and a decrease in the M v value of the polypropylene iso-fraction. In the latter case (C), at C/TiCl 3 = 5, one can observe the effect of system modification which shows up in increasing the molecular weight and amount of the iso-fraction and also in improving its stereoregularity parameters with the general catalyst activity remaining unchanged. The effect of the modifying additive is explained by the increase of iso-addition propagation constant.

Polymerizations of styrene and 2-vinylpyridine were undertaken with AlEt 3 -VCl 4 as homogeneous catalyst, under several sets of conditions. Conversion was related to the formation time of the catalytic species. Relative crystallinity and average molecular weight for the polymers obtained at 25°, 50°, and 90° are given. Influences of donor ligands such as pyridine and 2- and 4-methylpyridine on the polymerizations have been considered.

Dilatometry was used to measure the rates of copolymerizations of styrene with hex-1-ene, hept-1-ene, 4-methylpent-1-ene and 4-methylhex-1-ene, in the catalyst system, AlEt3-αTiCl3 in toluene. The copolymerizations were found to be first order with respect to TiCl3 and independent of Al/Ti ratio. Increased temperature produced a rapid increase in rate; variation of monomer feed, over the whole range, resulted in a gradual change from one homopolymerization rate to the other. The nature of the α-TiCl3 sample was found to have considerable effect on the rate of copolymerization. The order of reactivity, both from rate measurements and reactivity ratios, implies that, for the polymerization of α-olefins by heterogeneous Ziegler-Natta catalysts, steric effects outweigh electronic consideration.

The rate at which 4-methyl-1-pentene polymerizes in the presence of the catalyst system γ-TiCl3/AlEt2Cl is greatly enhanced by hydrogen. In bulk experiments under nitrogen, the catalyst loses its activity via a first-order reaction; in a hydrogen atmosphere, a second-order decline is observed. A mechanism is proposed.