Macromolecular Chemistry Volume 1 Edition. ed. Edition

A Review of the Literature Published during 1977 and 1978

By A. D. Jenkins, J. F. Kennedy

The Royal Society of Chemistry

Copyright © 1980 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85186-840-0

Contents

Chapter 1 Introduction By A. D. Jenkins and J. F. Kennedy, 1,
Chapter 2 Chain Reaction Polymerizations, 3,
Chapter 3 Step Growth Polymerization By R. H. Still, 81,
Chapter 4 Copolymerization and Multi-component Polymerization Reactions By A. F. Johnson and D. G. Catton, 105,
Chapter 5 Polysaccharides and Glycoproteins By R. J. Sturgeon, 126,
Chapter 6 Natural Polymers: Proteins and Enzymes By C. J. Gray, 152,
Chapter 7 Natural Polymers: Nucleic Acids By J. P. Goddard and J. T. Knowler, 190,
Chapter 8 Inorganic Polymers By K. M. Roch, 208,
Chapter 9 Configurations By S. B. Ross-Murphy, 222,
Chapter 10 Nuclear Magnetic Resonance Spectroscopy By F. Heatley, 234,
Chapter 11 Neutron Scattering Studies By D. G. H. Ballard, 250,
Chapter 12 Polymer Crystallization By J. N. Hay, 263,
Chapter 13 Characterization of Synthetic Polymers By N. C. Billingham, 282,
Chapter 14 Thermodynamics of Solutions and Mixtures By J. W. Kennedy, 296,
Chapter 15 Engineering and Technology By S. F. Bush, 331,
Chapter 16 Reactions of Polymers: Polymer Modification By G. G. Cameron, 350,
Chapter 17 Polymer Degradation, 370,
Chapter 18 Catalysis by Macromolecules By M. I. Page, 397,
Chapter 19 Biomedical Applications of Polymers By B. J. Tighe, 416,
Chapter 20 Computer Applications By A. H. Fawcett, 429,
Author Index, 451,

CHAPTER 1

Introduction

BY A. D. JENKINS AND J. F. KENNEDY

It is in the nature of macromolecules that it is hard to define any of their properties in precise terms, indeed it is no easy matter to define ‘macromolecule’ in a way that would be universally accepted even by those intimately concerned with such materials. Consequently, in setting out to delineate the areas to be covered in a report of recent research in the field of macromolecules, many demarkation issues have to be faced and resolved.

In aiming at a list of contents for this volume, the Senior Reporters have had to pay attention not only to the subject matter itself but also to the existence of other series of Specialist Periodicals Reports dealing with contiguous areas of chemistry. Without the least desire to poach on other people’s preserves, some small degree of overlap seems to be the only reasonable solution. This occurs in dealing with fields such as colloids, carbohydrates, proteins, and nucleic acids. It has seemed reasonable in the interests of providing a comprehensive treatment of the range of macromolecules to feel justified in including modest discussion in the context of ‘macromolecules’ rather than simply referring the reader to the individual volumes in which the information he requires may be buried within a large bulk of (to him) irrelevant material.

Another problem concerns the frequency with which individual topics should be examined. The more global subjects, like polymerization chemistry, will no doubt be treated in each issue but smaller topics, for example specific techniques for characterization, may adequately be dealt with if they are reviewed at intervals. Of course, much depends on whether a particular topic is advancing rapidly, in which case we recognize that there is an obligation to bring the reader as up-to-date as possible.

It will be apparent from the foregoing paragraph that the list of chapter headings will not be a constant factor although we shall, as a general principle, expect to maintain a watching brief over the following broad areas: Polymerization Chemistry; Particular Classes of Polymers; Natural Polymers; Degradation; Polymers as Catalysts and Reagents; Properties of Solid Polymers, Crystalline and Amorphous; Properties of Polymer Solutions; Characterization Techniques; Theoretical Treatment of Polymers; Applications of Polymers; Polymer Engineering.

Inclusion of the last two areas states our intention to embrace technology as well as pure science. Macromolecules, in the shape of synthetic plastics, fibres, films, paints, adhesives and the like, make an enormous contribution to everyday life; they occupy a large slice of the chemical industry in preparation and processing operations and the borderline between polymer science and plastics technology is very diffuse. It is fully in accordance with the attitude of many people in the field, and certainly of the Science Research Council, that one should as far as possible integrate the more academic and the more practical aspects of research on polymers, and that is the stand adopted here.

On balance the biennial frequency of publication has been chosen. For this reason the Literature Survey represented in this initial volume is principally concerned with the years 1977 and 1978, although earlier work is cited where it provides an important basis for current papers and for introduction of certain phenomena into the series.

Each chapter opens with an introduction which is specialized with respect to the contents of the chapter and outlines the context of the chapter particularly for those not completely familiar with the subject treated.

Our Reporters have been asked to collate rather than to criticize but they have not been debarred from offering a personal opinion on points of particular interest. It is our hope that the reader will find this book a useful guide to the most important recent literature on the chemistry of macromolecules, and that future volumes will keep the major topics under perpetual review. The Senior Reporters will be glad to examine comments, suggestions, and offers of contributions to help the series to live up to their hopes.

CHAPTER 2

Chain Reaction Polymerization

BY P. J. T. TAIT, D. J. DUNN, J. M. ROONEY, R. N. YOUNG, J. C. BEVINGTON, C. H. BAMFORD, D. C. BLACKLEY, AND B. M. TIDSWELL

PART I Co-ordination Complex Polymerization

by P. J. T. Tait

1 Introduction

It is not often that a field of scientific discovery can re-live its original excitement. However this is happening to a large extent in the field of Ziegler–Natta polymerization. For, whilst the polymerization of olefins by means of Ziegler catalysts in 1954 was one of the more exciting chemical discoveries in the field of polymer science during the last twenty-five years, much of the original excitement and fire has been rekindled by discoveries of new ‘second-generation’ Ziegler–Natta catalysts, or catalysts of related types, which are characterized by very high activities. Progress in this area has been very rapid and there now exist industrial processes, based on the use of these new second-generation catalysts, for the production of both polyethylene and polypropylene. It is here that another similarity exists between the situation affecting first- and second-generation polymerization processes since the commercial exploitation of these second-generation catalyst systems has been achieved before the reasons for their higher activity have become fully understood.

Given these circumstances, it is not surprising that many of the more recent publications in this field have been concerned with either the development of new and more active catalyst systems or with the characterization of these systems so as to elucidate the reasons for their higher activities. Furthermore, since a higher catalyst activity may arise from either an increase in the number of active propagating centres or from an increase in the propagation rate constant, such investigations have usually involved a determination of the number of propagating centres.

This Report is primarily concerned with publications during the period 1977 — 79 and reference to earlier publications will only be made where this is considered necessary for a proper understanding of the material which is presented. For a wider, although still quite recent, coverage of the literature, the reviews by Boor, Pasquon and Porri, Billingham, Pino and Suter, Cooper, Vandenberg and Repka, Caunt, and Tait, as well as the books by Keii and Chienshould be consulted.

2 Catalyst Systems: Heterogeneous Ziegler–Natta Catalysts

Non-Supported Heterogeneous Catalysts. — Early attempts to increase the activity and stereospecificity of heterogeneous Ziegler–Natta catalysts included the use of dry milling, often in the presence of complexing agents such as ethers, ketones, amides, amines, phosphines, etc. Whilst improvements in stereospecificity and yield of polymer have been claimed for specific combinations, it was not until the discovery in 1972 by Solvay and Cie of ether-treated TiCl3-based catalysts, of significantly higher activity and stereospecificity, that the full potential of this type of approach became evident. Catalysts of the Solvay type are prepared in a three-stage process in such a way as to maximize their surface area. As a typical example, TiCl4 in an inert hydrocarbon diluent is reduced under mild conditions by AlEt2Cl at temperatures of 0 [+ or -] 2°C over a period of 3 h to give the product β-TiCl3. 0.33AlCl3 of surface area ~1 m2 g-1, which is isolated and treated with a complexing agent such as an ether (e.g di-isoamyl ether), thioether, alkyl sulphide, etc. The resulting solid is again isolated and reaction with TiCl4 for 2 h at 65 °C gives a violet product of composition, δ-TiCl3. Al(RnX3-n)x:Cy where C is the complexing agent and 0 ≤ n ≤ 2, x <0.3, and 0.11 >y > 0.009. The best results are obtained when n = 1. The objective in the overall reaction is to obtain a highly pure crystalline form of TiCl3 of high porosity and very high surface area (~200 m2 g-1), which can be used along with a cocatalyst, preferably AlEt2Cl, to polymerize propylene and other a-olefins (e.g. but-l-ene, pent-l-ene, 4-methylpent-l-ene, vinylcyclohexane, etc.) to give highly isotactic polymers. In the polymerization of propylene these catalysts show a five-fold increase in activity over conventional δ-TiCl3. 0.33AlCl3 type catalysts and produce only between 2 and 5% amorphous material. Solvay and Cie type catalysts may also be used for the polymerization of conjugated diolefins (e.g. butadiene and isoprene) and for the preparation of so-called block copolymers of α-olefins and ethylene and α-olefins and diolefins. Solvay and Cie catalysts are currently being used for the industrial preparation of polypropylene.

Although the discovery of these catalysts has caused considerable industrial interest, very few detailed studies have appeared in scientific journals apart from the patent literature. Burns, and Tait and co-workers’ have, however, recently carried out a detailed study, involving the use of both allene adsorption studies and 14CO radio-labelling in order to investigate whether the increased activity is due to an increase in the number of active centres, C*, or to an increase in the rate constant for propagation, kp. Some of their results are listed in Table 1.

The allene adsorption studies used by these workers thus show that the increased activity is entirely due to an increase in C*, kp remaining reasonably constant. However, 14CO radio-labelling indicated that, for the more highly active systems involving the use of AlEt3 as cocatalyst, both C* and kp increased. Hence clarification of this crucial question must await the publication of further investigations and perhaps also an evaluation of the validity of the methods used to determine C*.

Supported Heterogeneous Catalyst Systems. — Catalysts Based on the Products of some Reactions of Transition-metal Compounds, (a) With hydroxyl-containing compounds. There has been considerable activity in this field ever since the early developments during 1960 — 63. Whilst most of the work in this field has been described only in the patent literature, some detailed studies have now appeared. An earlier investigation which deserves attention is that by Soga et al. who studied the polymerization of propylene using catalysts derived from the interaction of TiCl4 and a variety of metal hydroxides and metal hydroxychlorides, notably Mg(OH)2 and Mg(OH)Cl, which were found to produce the most active systems. The catalyst-forming reaction was formulated as that shown in equation (1) and Soga et al. have postulated that the valence state of the titanium

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in the supported catalyst remains four. Triethylaluminium was used as the cocatalyst and, although the exact ratio of Al:Ti used was not reported, it would appear to be very high, probably > 100:1. These supported systems exhibit constant overall rates of polymerization for periods of several hours, consistent with the active centres being stabilized by the use of a support and thus preventing reactions such as (2). An important fact which was established is that the

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (2)

stereoregularity of the polypropylene is strongly influenced by the crystal structure of the support, indicating that the stereoregulation of the polymer formed arises mainly from the stereospecific co-ordination of the monomer on to the active centre.

A series of detailed studies have been carried out on catalysts derived from the interaction of TiCl4 and metal oxides. Chirkov et al. have described the use, in the polymerization of ethylene, of catalysts derived from TiCl4 and either MgO or aluminium silicate. For the catalyst system TiCl4–MgO(0.6% Ti)–AlEt3 it has been established that:

(i) Such catalysts have very high activities, producing yields of polymer per g of Ti from ten to forty times that produced by either the TiCl4–AlEt3 or the TiCl3–AlEt3 systems.

(ii) Some 20% of the titanium atoms are active as determined by tritium quenching (cf. values of ~1% for δ-TiCl3. 0.33 AlCl3–AlEt2Cl systems) and the propagation rate constant kp has the high value of 2380 dm3 mol-1 s-1 as compared to 76.5 for the γ-TiCl3–AlEt2Cl system. Hence the increased activity is reported as arising from an increase in both the number of active centres, C*, and in the value of kp. So far this is the only detailed study which has indicated this situation.

(iii) The activity of the catalyst system is affected by the type of support. Thus catalysts supported on MgO are more active than those supported on aluminium silicate, even though the surface area of the aluminium silicate is much higher. This increased activity arises mainly from an increased kp value and it is proposed that the nature of the ligands attached to the active centres can affect the reactivity of the centres.

(iv) High ratios of Al:Ti are used, viz., Al:Ti = 70:l. This is a typical feature of many of these supported catalyst systems.

Eley et al. have used infrared and microgravimetric techniques to study the interaction of TiCl4 and AlEt3 vapours with partially hydroxylated surfaces of MgO and TiO2. Treatment of both MgO and TiO2 with TiCl4 at 308 K followed by addition of AlEt3 produced low-activity catalysts for the polymerization from the vapour phase of ethylene and propylene at 293 K. No details of the effective Al:Ti ratios employed are given.

The interactions of TiCl4 and a MgO surface is represented by the now-accepted reactions (3) or (4) followed by (5), (6) and (7), (8). The catalyst-forming reactions are then formulated as (9) and (10) with further alkylation by AlEt3 and/or AlEt2Cl producing a TiIII — C bond, equation (11). The titanium in the active catalyst is regarded as TiIII in contradiction to the proposals of Soga et al.

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