摘要:

J. MATER. CHEM., 1994, 4( 1l), 1767-1768 BOOK REVIEWS Crystallization of Polymers. Edited by M. Dosiere. NATO AS/ Series C:Mathematical and Physical Sciences. VoL 405. Kluwer Academic Publishers, 1993. Pp. xvi +654. Price fl59.00.ISBN 0-7923-2350-5. The book is a collection of papers and posters presented at the NATO Advanced Research Workshop on Crystallization of Polymers in Mons, Belgium in September 1992, by dis- tinguished scientists covering an extensive range of topics. The four main workshop sub-divisions were Morphology and Structure of Polymer Crystals, Molecular and Sub-Molecular Organization in Polymer Crystals, Polymer Crystal Melting and Growth and Polymer Crystal Nucleation and Growth. The benefits in reading such a collection of papers include familiarization with current thinking on polymer crystalliz- ation processes, awareness of current techniques being applied to investigate polymer structures, and the acquisition of the current knowledge available on polymer structure.On the downside, it must be said that in seeking to develop new theories of crystallization processes most authors under-standably use as models well known materials. Many of the papers describe work based on the familiar polyethylene material, but there are also many other interesting papers on different polymeric materials. In addition to the papers and posters included in this book, there are sections of question and answer sessions from the workshop, which help in providing a more cohesive approach to the overall topic than would be obtained simply from presenting the collected papers.Synthetic macromolecules, unlike proteins, do not form, as a rule, large single crystals with structures that can be determined by routine X-ray diffraction procedures. Those that do can provide information on the crystalline regions of polymer systems, which often consist of crystalline and amorphous sections. In reality, the study of crystallinity in polymers is a study of the gross molecular structure of a crystalline amorphous mixture. The application of a variety of analytical techniques such as DSC, electron microscopy, X-ray electron and neutron diffraction, NMR and IR spec-troscopy, each provide a solution to part of the jigsaw.Use can also be made of molecular modelling using computer software packages to gain further insight into the actual structure of polymers and enable more precise theories of polymer crystallization to be evolved. As with most conferences, some papers contain kernels of wisdom for the reader eager to understand more fully the subject under consideration, and this conference was no exception. It would not be possible to refer to every paper in the book but the following points are some of those worthy of further consideration. The introductory lecture by Professor A. Keller linked the ‘main stream’ subject of chain-folded crystallization to the ‘speciality stream’ of extended chain crystallization. He pro- posed a scheme based on the recognition of thickening growth as a primary growth process of lamellae and on the existence and prominence of metastable phases.Under specific con- ditions, phase stabilities can invert with size, allowing crystals to appear and grow in a metastable phase. From this, a link can be established between general thermodynamic consider- ations and previously established kinetic criteria. Crystal growth can be considered as phase growth in its broadest generality, and thickening growth of the extended chain state needs to be differentiated from lamellar thickening due to rearrangement within lamellar stacks, in, for example, polyethylene. Professor Leo Mandelkern’s paper on the structure of polymers crystallized in bulk was given in the first section of the workshop on The Morphology and Structure of Polymer Crystals.In it, we are reminded that the most thermo-dynamically stable state of a collection of long-chain molecules is a large crystallite whose thickness is close to the extended molecular length. It is also useful to be reminded that the structures obtained are .based on nucleation and growth processes that are modulated by a variety of other factors. It is also important to bear in mind the difference between molecular morphology, which describes the structure of the crystalline state on a detailed molecular basis, arid gross morphology, which is observed when use is made of various microscopy techniques. The relationship between the two forms the basis for this Advanced Research Workshop.In order to define the crystalline state, use must be made of a set of independent structural variables, such as the degree of crystallinity, the structure of the amorphous (liquid-like) region, the crystallite thickness distribution, the ex tent and structure of the interfacial region, the overall habit and internal structure of the lamellar-like crystallites and the supermolecu- lar structure. The second workshop session dealt with Polymer- Crystal Growth, including the use of low molecular weight fractions of PEO as models for retardation of crystal growth with supercooling (Dr. G. Ungar). The accompanying change from faceted to round crystal habits with increasing retardation is consistent with growth surface roughening due to self-poison- ing. This is one manifestation of a productive reaction (erroneous chain folding depositions) that leads to thermo- dynamic stability being retarded by a competing low barrier reaction, which almost leads to a stable product.Session 3 considered the experimental aspects of Polymer Crystal Melting and Growth. Professor D. Basset describes an overview of the morphology of melt crystallized lamellae and their organization within the bulk polymer. The technique of permanganic etching for transmission electron microscopy enabled the interior morphologies of melt crystallized poly- mers to be elucidated. The use of this new technique prevented imaging electrons from destroying the polymer structure and led to the discovery that melt crystallized polymers are organized around an initial skeleton of individual dominant lamellae that establishes the framework of spherulites and other large scale organizations. Included in Session 4 of the workshop, Morphology and Structure of Polymer Crystals is a paper by Dr.I. G. Voigt-Martin on Polymer Liquid Crystals, an important area of polymer structural studies owing to the variety of properties that can be introduced by the addition of suitably func- tionalized groups to the polymer chains. The use of electron and X-ray diffraction studies are described to elucidate some of the structural characteristics of these materials. Further papers in this session describe other analytical techniques used to study structures such as DSC, neutron diffraction and small angle neutron scattering (Dr.J-M. Guenet). The thermal behaviour was investigated as a function of the annealing temperature and the temperature concentration phase dia- gram produced for isotactic polystyrene/cis-decalin solutions. The existence of two phases that exist between the gel state and the crystalline state are described. Session 5, Structure and Polymorpism of Polymer Crystals, began with a paper by Professor Bernhard Wunderlich on unsolved problems of crystallization and melting of flexible macromolecules. He discussed the thermodynamic.;, kinetics and computer simulations of crystallization and melting and summarized by describing crystallization and melting as being well understood thermodynamically.Unfortunate1 Y, a large number of parameters are needed to describe the non-equilib- rium states. The kinetics can be measured experimentally but are more complicated than originally thought. Full computer simulation of the processes requires more computing power than is at present available. In this session, the paper by Professor Y. Chatani gives an interesting insight into the crystal structures of a variety of polymorphic syndiotactic polystyrene and poly( propylene) polymer chains. Session 6 was devoted to the computational and theoretical aspects of polymer crystal melting and growth and included a paper (Dr. V. Enkelmann et al.) on the crystallization of rod-like molecules with attached flexible side groups.The example chosen is a mixture of the diacetylene P-4-BCMU and CHC1, solution that yields lyotropic liquid crystals. Nematic lamellar structures are observed where the lamellar thickness is related to the number average molecular weight. Session 7 dealt with the Morphology and Structure of Polymer Crystals and contained an interesting paper by Dr. D. L. Dorset on the novel use of Direct Methods for determin- ing the phases in electron diffraction structure determinations. Although the technique yields valuable results for the centro- symmetric crystalline systems, it has yet to be shown to be applicable to the non-centrosymmetric case, although it works well for X-ray diffraction crystal analysis. Session 8 looked at further Experimental Aspects of crystal melting and growth and gives an insight into the experimental techniques that are currently in use.Professor H. G. Zachmann makes use of wide angle X-ray scattering, small angle X-ray scattering and light scattering to examine second- ary crystallization and was able to identify three processes, increase of crystal thickness, formation of new crystals within lamellar stacks and formation of new lamellar stacks. Dr. B. S. Hsiao describes the use of time-resolved synchro- tron X-ray techniques for studying rapid structural changes in polymers, and Professor Richard S. Stein describes the use of light, X-ray and neutron scattering to study the crystalliz- ation of polymers (PE) and blends, and, in addition, recent work on a blend of polycarbonate and poly(ecapro1actone) is described. The final oral session, Session 9, was based on Polymer Crystal Nucleation and Growth.Professor A. Ziabicki dis- cussed the basic function controlling crystallization tempera- ture and nucleation kinetics, i.e., the thermodynamic driving force for nucleation. By considering local and global configur- ational variables, predictions about the type of crystallization likely to be observed can be made. The final paper in this session (Dr. J. Van Ruiten) describes a Monte Carlo modelling method for deriving the three- dimensional morphology of crystallites in ethylene-propylene copolymers. He points out the need to define crystallinity carefully. It can be calculated from the drop in free energy due to crystallization divided by the maximum free energy drop of the whole sample crystallized into a single solid crystal. This energy-based crystallinity can be compared with a number-based crystallinity obtained by dividing the number of crystallized monomers by the total number of monomers present.There can be large discrepancies between both definitions. J. MATER. CHEM., 1994, VOL. 4 The above limited selection of extracts taken from the papers presented at this Workshop should give some idea of the diversity of the information contained in this NATO AS1 series book and the level at which it is presented, but can only represent a small part of the 653 pages of contents. In addition, the book contains a section devoted to the posters presented at the Workshop.The interested reader can learn much of current thinking, of practical methods that are used to elucidate polymer structures in the crystalline and amorph- ous state, and of the polymer systems that are currently of interest. Ample, up-to-date references are provided to enable the reader to extend his background reading. Whether all this is sufficient reason to spend El59 on the book is for the individual to decide. There are many spelling errors in the book, particularly in the discussion sections, but in most cases, these can be ignored. G. H. W. Milburn Received 2rid August, 1994 Essentials of Carbon-Carbon Composites. Edited by C. R. Thomas. Royal Society of Chemistry, 1993.Pp. x +234. Price f39.50.ISBN 0-851 86-804-5. Carbon-carbon composites (CCCs) were recognized nearly 50 years ago. They have good heat resistivity and strength and have high elasticity. In addition to these merits, their low density compared with other metals gives them a firm repu- tation for use as lightweight structural materials. It would not be possible for mankind to launch himself from the Earth without the use of CCCs. Nowadays we take carbon fibre for granted as a high-strength material, but it initially became familiar as a filament material. This Japanese reviewer learnt for the first time in this book that the first carbon filament for the lamp had not been from bamboo in Japan, but by Edison from cotton produced in the UK.This book covers the history of CCCs and their materials science, manufacturing conditions, mechanical properties and fracture mechanism. The authors are from academia and from industrial and government establishments and all have been specialists in their respective fields for a long time. The book consists of eight chapters: in Chapter 1 the general remarks give readers the basics of what is a CCC, and Chapters 2-8 are itemized discussions. Each of the chapters uses photographs and figures to allow the readers to gain an exact understanding and the list of more than 400 references give directions for further knowledge. It seems to be an unavoidable habit of multi-authored books that the subject matter overlaps between chapters, but this can sometimes be useful for readers’ understanding. CCCs have been widely utilized in military purposes, which connect with the space shuttle plans. However, it is regrettable that there are no specific examples in the book with researchers from the Ministry of Defence as authors. Although lacking in the most up-to-date topics, it is still an excellent book for those who want to start out in CCC studies. K. Kawasaki Received 12th July 1994

ISSN:0959-9428    

DOI:10.1039/JM9940401767

出版商:RSC    

年代:1994

数据来源: RSC