Macromolecular Chemistry Volume 3 Edition. ed. Edition

A Review of the Literature Published during 1981 and 1982

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

The Royal Society of Chemistry

Copyright © 1984 The Royal Society of Chemistry
All rights reserved.
ISBN: 978-0-85186-876-9

Contents

Chapter 1 Introduction By A. D. Jenkins and J. F. Kennedy, 1,
Chapter 2 Chain Reaction Polymerization,
Chapter 3 Step Growth Polymerization,
Chapter 4 Natural Polymers: Polysaccharides and Glycoproteins By R. J. Sturgeon, 98,
Chapter 5 Natural Polymers: Nucleic Acids By J. T. Knowler and J. P. Goddard, 133,
Chapter 6 Inorganic Polymers By K. M. Roch, 147,
Chapter 7 Configurations By S. B. Ross-Murphy, 159,
Chapter 8 The Chemical Microstructure of Synthetic Polymers Investigated by High Resolution Nuclear Magnetic Resonance By J. R. Ebdon, 175,
Chapter 9 Neutron Scattering Studies By J. S. Higgins, 189,
Chapter 10 Polymer Crystallization By J. N. Hay, 204,
Chapter 11 Characterization of Synthetic Polymers By J. M. G. Cowie, 224,
Chapter 12 Thermodynamics of Solutions and Mixtures By J. W. Kennedy, 248,
Chapter 13 Engineering and Technology,
Chapter 14 Reactions on Polymers By D. C. Sherrington, 303,
Chapter 15 Polymer Degradation,
Chapter 16 Reactions in Macromolecular Systems By M. I. Page and D. A. Crombie, 351,
Chapter 17 Biomedical Applications of Polymers By B. J. Tighe, 375,
Chapter 18 Computer Applications By A. H. Fawcett, 387,
Chapter 19 Selected Topics in the Photochemistry of Polymers By K. L. Petrak and M. D. Purbrick, 399,
Author Index, 414,

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 demarcation issues have again had 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 Periodical 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, particularly, 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 or her) 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. In the production of this volume and Series, the satisfactory resolutions of other factors have also to be superimposed, in particular, the trend of polymer chemistry, since this is now the third volume. In many instances, Reporters have had to sift through thousands of references in order to identify the major works of progress under the heading of any area of macromolecular chemistry.

It will be apparent from the foregoing paragraphs that the list of chapter headings cannot be a constant factor although, as a general principle, we 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 Polymers; 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 and Engineering 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. However, with increasing industrial interest in and application of polymer technology and biotechnology, the whole field of reporting on polymers, particularly biopolymers, becomes more and more open-ended.

In keeping with the original plan of biennial frequency of publication, the literature survey represented in this volume is principally concerned with the years 1981 and 1982. Work earlier than 1977, the initial year of coverage of the Series, was cited only in Volume 1 where it provided an important basis for current papers and an 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 others outline the context of the chapter particularly for those not completely familiar with the subject treated. Reference to the corresponding chapter in Volume 1 will also be helpful in this respect.

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.

CHAPTER 2

Chain Reaction Polymerization

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

PART I Co-ordination Complex Polymerization

by P. J. T. Tait

1 Introduction

The excitement associated with new discoveries has been fully justified in the field of co-ordination polymerization during recent years, and as a result the increase in the number of publications and patent citations forbids any attempt to present a comprehensive survey of the field. Nevertheless these last four or five years have been very important in the history of co-ordination polymerization, not only because of the discovery of new catalyst systems, but because of the valuable insights gained into some of the older problems associated with this field. In particular, many of the basic chemical and physical principles involved in catalyst preparation and chain initiation have become more apparent. The presence of a new type of polyethylene prepared by copolymerization of ethylene and a suitable higher α-olefin, and simulating some of the properties of low-density polyethylene, has become recognized, and has highlighted the importance of catalysis to a commercial world that is becoming increasingly aware of energy costs.

2 Catalyst Systems

Heterogeneous Ziegler–Natta Catalysts. — Magnesium Chloride Supported Systems. In the field of propylene polymerization considerable activity has resulted from discoveries by Montecatini Edison Co. and Mitsui Petrochemicals Ind. that catalysts prepared from magnesium chloride, titanium tetrachloride, and electron donors, and activated by a mixture of trialkylaluminium and an electron donor, could polymerize propylene with a high yield (> 50 kg polypropylene per g Ti per h) and with a good stereospecificity (isotactic index >90%). The relevant patents describe two basic routes for the preparation of highly active catalysts. Typically, a 30-fold molar excess of dried anhydrous MgCl2 is ball-milled with a TiCl4–electron donor complex, such as TiCl4-ethyl benzoate, washed with n-heptane, and dried. The catalyst is then activated by a mixture of trialkylaluminium (TAA) and an electron donor such that TAA:EB:Ti ≈ 300:100:1. Alternatively, dried anhydrous MgCl2 is ball-milled for 20 h at 0 — 5 °C with ethyl benzoate (EB) (MgCl2:EB ≈ 1:0.15) and then treated with neat TiCl4 at 80 — 130 °C for 2h, washed with n-heptane, and then dried to yield a pale yellow solid catalyst containing typically 1 — 5% Ti and 5 — 20% EB. This catalyst is then activated by treatment with a mixture of trialkylaluminium and an electron donor (e.g., ethyl benzoate, p-ethyl anisate, p-methyl toluate, etc.).

(a) Effects of ball-milling magnesium chloride. ‘Activated’ magnesium chloride was first described by Bryce-Smith and later detailed by Kamienski. ‘Activated’ magnesium chloride may be prepared by (i) treating MgCl2 with activating agents such as electron donors, (ii) ball-milling anhydrous MgCl2, and (iii) reaction of Grignard reagents with chlorinating agents.

Crystalline MgCl2 exists in the form of agglomerates of small primary crystallites and when ball-milled in the presence of a donor such as ethyl benzoate these agglomerates are broken down. The small MgCl2 crystallites produced are believed to be stabilized by the ethyl benzoate which is adsorbed onto the freshly cleaved surfaces, thus largely preventing reaggregation of the primary crystallites (cf., protected colloids).

The structure of the usual crystalline form of MgCl2 is quite similar to that of γ-TiCl3 and may be represented in terms of a cubic close-packed structure of double chlorine layers with interstitial Mg2+ ions in 6-fold co-ordination. This layer structure is of the CdCl2 type and leads to a characteristic X-ray diffraction spectrum with a strong (104) reflection at d = 2.56 Å. Another less stable crystalline form of MgCl2 is also known, and has a hexagonal close-packed structure similar to that of α-TiCl3, and gives a strong (104) X-ray reflection at d = 2.78 Å.

Youchang et al., from their X-ray diffraction studies on samples of milled MgCl2, conclude that during milling the shear of the steel (or porcelain) balls causes the Cl–Mg–Cl double layers to slide over each other, leading to cleavage along the double layers, producing hexagonal MgCl2 microcrystallites of only a few layers in thickness. Figure 1 shows representations of both commercial and ball-milled MgCl2 crystallites.

During ball-milling there is a gradual disappearance of the (104) reflection with the appearance of a broad halo indicating stacking faults. Thus the stacking sequence no longer corresponds to that of a cubic close-packed structure. The spacing of the broadened halo (d = 2.65 Å) lies between those observed for the cubic and hexagonal structures. Galli et al have concluded that the model describing the structural disorder of activated MgCl2 (in the presence of TiCl4) is similar to that proposed by Allegra and Bassi for δ-TiCl3, although differing in mathematical details. They report that some features of the X-ray powder pattern of activated MgCl2 such as the shifting and broadening of the (104) peak, in comparison with that of the α-form, denotes the presence of rotational disorder in the stacking of the Cl–Mg–Cl triple layers, and have proposed an appropriate model. Giannini has pointed out that, unlike the atoms in the bulk phase, the cations located on the lateral surfaces and the crystal edges are co-ordinatively unsaturated, and can therefore form bonds with adsorbed molecules. Goodall has distinguished three different types of surface Mg ions:

(i) type 1 on the lateral faces; single vacancy Mg ions having an effective charge of 0 e;

(ii) type 2 on the comers: single vacancy Mg ions having an effective charge of – 2/3 e’

(iii) type 3 on the comers: double vacancy Mg ions having an effective charge of + 1/3 e.

The different types of surface Mg ions are shown in Figure 2.

X-Ray diffraction has also been used by Keszler, Bodor, and Simon to study the effects of ball-milling on particle size. Crystal sizes of unground MgCl2 in directions perpendicular to the (001) and (110) planes were found to be different, 111 and 65 nm, respectively. This difference was found to disappear after short grinding periods. There was also a marked reduction in the overall crystalline particle size. In a later paper, Keszler and Simon have reported on catalyst activity as a function of the time of grinding for both MgCl2/TiCl4 and MgCl2/EB/TiCl4 catalysts. In the absence of ethyl benzoate the optimum results were obtained for 20 h grinding, whereas for MgCl2/EB supports the activity of the catalyst increased continuously as a function of grinding time up to 100 h. Recently, Galli et al. have concluded that the activation process for grinding at 35 °C ends after milling for about 70 h and then decreases with further milling in contrast to reports by earlier workers. The effects of milling on the crystallite size were also investigated and are shown in Table 1. As can be seen, the lowering of the activity (referred to unit Ti) does not correspond to any significant variation in the residual Ti or to the crystallite size, but to a reduction in the surface area.

(b) Interaction of magnesium chloride with ethyl benzoate. The interaction between MgCl2 and ethyl benzoate has been extensively studied. Keszler et al. from their thermal studies have concluded that the interaction involves a two-step exothermic process. Initially there is rapid adsorption of ethyl benzoate onto the surface of the MgCl2. This adsorption is then followed by the much slower process of complex formation.

Infrared studies have also been used to study the interaction between MgCl2 and ethyl benzoate. Goodall has concluded that ethyl benzoate is co-ordinated to the MgCl2 crystalline surface via the C=O group. The C=O stretching frequency changes from 1721 cm-1 in the free ester to 1680 cm-1 in the adsorbed ester (cf., the corresponding values of 1720 cm-1 and 1650 cm-1 reported by Kashiwa), and is believed to arise from ester molecules bound to the basal edges and comers of the crystallites. The adsorption band observed at 1700 cm-1 is believed to arise from ethyl benzoate co-ordinated to lateral faces. Chien et al. have concluded that the complexes (1) and (2) were responsible for the shifts observed in the infrared spectrum for both the C=O and C — O stretching frequencies.

(c) Treatment of ball-milled MgCl2–ethyl benzoate with titanium tetrachloride. The second step of the catalyst preparation involves treatment of the solid products from ball-milling with hot neat TiCl4 at 80 — 130 °C, or by ball-milling the solid products with TiCl4. The resulting solid is then thoroughly washed and dried. During treatment with TiCl4, ethyl benzoate is extracted by the TiCl4 so that typical catalysts contain only 5 — 20% ethyl benzoate after treatment with TiCl4. At the same time TiCl4 is adsorbed onto free MgCl2 surface vacancies. Goodall has reported that the ethyl benzoate is lost not only from the weakly bonding sites on the lateral faces (1700 cm-1 adsorption) but also from the strongly co-ordinating comer sites (1650 cm-1 absorption). This would seem to indicate that the TiCl4 coordinates to these sites by replacement of the ethyl benzoate molecules.

The oxidation state of the adsorbed titanium has been studied by some workers. Baulin et al. have established that all the titanium is in the TiIV state. Chien et al. report 8% as TiII 38% as TiIII, and 54% as TiIV. It should be noted, however, that the catalyst studied by Chien et al. is more complex, having been treated with p-cresol and with AlEt3 prior to reaction with TiCl4.

(Continues…)Excerpted from Macromolecular Chemistry Volume 3 Edition. ed. Edition by A. D. Jenkins, J. F. Kennedy. Copyright © 1984 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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