Perspective and Summary

Randal W. Richards

INTERDISCIPLINARY RESEARCH CENTRE IN POLYMER SCIENCE AND TECHNOLOGY, UNIVERSITY OF DURHAM, DURHAM DH1 3LE, UK

In 1999 the Royal Society of Chemistry published a compendium booksetting out the contributions to society that have been made by chemistry. The title, 'The Age of the Molecule' neatly encapsulated the philosophy that a molecular understanding is the basis for optimum exploitation of new substances or materials provided by chemistry. Much of the material in the book was drawn from 20th Century developments but with evident foundations on the advances made in the latter half of the 19th Century. If the preceding 150 years is the 'Age of the Molecule' then the 20th Century has been 'The Century of the Macromolecule'.

It was not until the last century was some thirty years old that the concept of 'giant' molecules, polymers, was widely accepted. Evidently the science of polymers or macromolecules is relatively young compared to other aspects, e.g. quantum theory's beginnings pre-date polymer science by some twenty years. Of course mankind had been using polymers for many centuries before their macromolecular nature was recognised. These were mainly the naturally occurring polymers; cotton, wool, rubber, gums and leather. Driven by the blockade of raw materials during World War I, a process for the production of synthetic rubber was developed in Germany but the high cost of butadiene made the process commercially infeasible in peacetime. It was the rapid development and huge expansion of the petrochemicals industry catalysed by the strategic demands of World War I1 that led to the widespread use of synthetic polymeric materials by modern society. This use was just preceded by an understanding of the main facets of the molecular nature of polymers, quite unlike other materials, e.g. steel and alloys.

From the outset polymer science has involved physicists, chemists, engineers, materials scientists and design engineers. The multidisciplinary nature of polymer science from its earliest days is a feature that is not often exhibited by other fields of natural science until a certain 'maturity' has been reached. The synthetic polymer industry in the UK expanded greatly over the years from circa 1950 to circa 1995, as did the scope where polymeric materials are used. We rely on polymers to keep us warm and dry (fibres); to preserve and protect our food, housing and transport (packaging, protective coatings); to provide entertainment (recording media); contribute to defence systems and high speed travel (composites in military and civil aircraft); materials that are vital to the exploration of space (light weight antennae and ablative layers for re-entry) and developments over the last eight years presage their use as the next display medium and probably supplanting (eventually) the cathode ray tube. However, we still have much to learn in understanding and manipulating (for beneficial purposes) the macromolecules of life, proteins, polypeptides etc. The success of the Human Genome Project will undoubtedly accelerate that understanding.

During the last five years of the twentieth century it was evident that polymer science in the UK was changing both industrially and in academe. The industrial changes were caused by reduction in profit margins for the high volume polymers, polyolefins, polyesters, polyacrylics etc. as production plants with significantly lower operating costs elsewhere in the world came on stream. Increased need and use for speciality polymers, e.g. polyaromatic ketones, main chain liquid crystal polymers, needed a closer engagement with and understanding of the end-user market. These factors, and others, have led to a fragmentation of the industry with small units being more active in areas where the philosophy is production of smaller volumes of polymer but with more 'high tech' specifications. A rapidly developing area that exemplifies these aspects is electro-active and electroluminescent polymers. In the academic world, the 'bulge' of university expansion in the early to mid 1960s was passing through the system and recruitment of young academics was buoyant. This has resulted in the largest cohort for many years of academics with research interests in polymer science being recruited into British universities, such that at the end of 1999, some 35 academics all with less than 5 years appointment could be identified.

These evident changes and the awareness that others, perhaps more momentous, were on the horizon prompted the Pure and Applied Macromolecular Chemistry Group (MacroGroup UK) of the Royal Society of Chemistry and the Society of Chemical Industry to attempt a 'survey of the landscape'. The subliminal questions to be addressed included 'What's going on now?' 'What aspects are likely to develop in the future?' 'What should we be aware of?' The meeting 'Emerging Themes in Polymer Science' was an attempt to do this survey; the brief was not to attempt to pick winners but to inform, foster debate and discussion, encourage boldness in future efforts. To foster these aspects the format of the meeting was highly structured in one aspect only; all papers were circulated well before the meeting, each invited contributor had ten minutes to 'hit the highlights' and express 'the bottom line' of their paper. Thereafter each paper had at least 20 minutes 'official' discussion time, this format was adopted from the model of the highly successful Faraday Discussions. The responsibility for organising the meeting and choosing the speakers was accepted by one of the newer centres of polymer science in the UK in the form of Professors Tony Ryan (Chemistry) and Richard Jones (Physics) at the University of Sheffield. It is the contributed papers, with some post meeting changes in a few cases, that forms the body of this volume. Their choice of speakers resulted in a meeting where there was true debate and discussion, participants were prepared to put forward radical opinions but at no point were the boundaries of good manners crossed. The themes aired may appear to be eclectic but they emphasise, to some extent, the multidisciplinarity and diversity that is modern polymer science.

The summary overview given here does not cover all aspects exhaustively; rather it is an attempt to capture the scope and contrasts that were expressed in the unscripted discussions. The subjects covered ranged from the philosophy of survival in rapidly changing companies driven by the need to generate revenue to stay viable, to speculations on the probability of producing 'machines' by molecular assembly processes at the nanometer scale, the moving parts being driven by fundamental physico-chemical processes. The common view expressed from industry was that change leads to clear decision-making and 'captures the essence of the evolutionary spirit'. What was not clear was whether this 'change' was in response to demand or a desire to lead the technology market. It is certainly accepted that during a person's working lifetime in industrial R&D, they may need to re-invent or change their expertise base as companies move into new market areas or shed more mature aspects for new, higher added value products generally produced in smaller quantities. Paradoxically, in one of the fastest developing areas already referred to, electroluminescent polymers, it was suggested that continual change might not be a good thing. Rather than wait for the 'next best polymer' to come along, more profitable results may come from optimisation of what is already available. For example, by developing the ability to control precisely the molecular packing in thin films and optimising interfacial area effects. The willingness and ability of synthetic chemists to meet the challenge of producing well defined complex molecular architecture in polymers needs to be balanced by the increased costs incurred and an awareness that sufficient architectural complexity is enough, any more is unnecessary and not cost-effective.

Polymer rheology and processing and colloidal dispersions of polymers (emulsions, latexes etc.) have been major components of the application and use of polymers over the past 50 years. The complexity of the systems or the apparent 'black arts' needed to make progress have daunted wide participation at the level of fundamental research. Challenging problems are indeed posed by both these areas and call for lateral thinking and ability to 'mine' apparently unrelated areas for ideas. Evidently the understanding and manipulation of polymer colloids requires a knowledge of surfactant behaviour, an appreciation of the concepts of particle stabilisation and some awareness of the rheology of the suspensions in addition to polymerisation kinetics and thermodynamics of multicomponent systems. This is an area that seems to require consolidation and proper evaluation rather than innovation before further advances are made in an optimised way. Elegant and sophisticated machinery is now commonplace in the polymer processing industry (extruders, moulders etc.) but these have been defined and designed by production engineers and the input of polymer scientist appears to be minimal. The question remains to be answered whether more optimal processing or products could be obtained by increased input from the latter group. Rheology is evidently a key aspect to understand in the processing of polymers and the recent availability of numerical flow solvers has greatly aided the 'visualisation' of melt flow during processing (and the use and further development of these solvers will undoubtedly grow). The link with molecular level theories and molecular level architecture is still rather tenuous despite rapid advances in the last few years. The molecular approach to discussing polymer rheology is well discussed herein as are other aspects of modelling polymers.

Although the papers herein covering the theory and modelling of polymer systems are quite specific, the discussions were more philosophical and queried the basic approach. The tone of the discussion is perhaps judged by noting that one approach was described as 'epistemological anarchy'. Evidently, theoreticians are not particularly happy at the apparent evaporation of interest by experimentalists as soon as the theory fits the data! Perhaps theoreticians and experimentalists can agree that theory should entice cutting edge experiments and experiments should challenge theory, not in a combative manner but in the spirit of intellectual curiosity. Certainly, this seems to have been the dynamics of the process that produced the major development in polymer science in the late 1970s and early 1980s, the scaling law description of polymer configuration and dynamics. The major challenge to theoreticians in the field is little different to those in other areas of condensed matter theory; how to scale up detailed ideas at the quantum mechanical level to the length scales of bulk materials. Some advances have been made at meso scales but there is much, much more to do.

Evidently, from the birth of the macromolecular hypothesis in the 1920s, there has been significant development in the understanding, synthesis and application of synthetic polymers. For biopolymers the situation is much more 'patchy' and certainly the level of sophisticated understanding is not as great as for synthetic polymers. There are several aspects covered by the term biopolymers and not all were dealt with here. The use of polymers to generate new tissue and engineer its production at defined sites is evidently a very exciting area for synthetic chemists since new molecules with specific properties are needed. Some caution may be needed since enthusiasm to take on challenging syntheses may run ahead of the defined needs and indeed if there is a real need for the molecules. Furthermore, major influences in this area will be ethical issues, the need for regulation and public perception, Misunderstanding or manipulation of incorrect information to produce dramatic headlines (e.g. 'Frankenstein' molecules) may be a greater hindrance to developments than the actual scientific problems to be solved. The Royal Society of Chemistry has begun to define a strategy for the role of Chemistry in the life sciences. Perhaps more immediate benefits of polymers in the 'bio' area may result from more (apparently) mundane aspects. The increase in life span and more involvement in 'vigorous' leisure activities (e.g. skiing, climbing) has resulted in joint replacements at younger ages and the likelihood that the prosthetic joints will be replaced more than once during a lifetime. This is mainly due to wear of the polymeric components, consequently any improvement in the 'cushioning' of impact or wear of these components would improve the subsequent quality of life of the users. A major area for biopolymers is foodstuffs and polysaccharides. These are abundant; amenable to manipulation, have sufficient natural variants that a range of properties, morphologies and behaviours are accessible. They are generally accompanied by greater or smaller amounts of water and exhibit specific functionalities that may be a boon or a bane depending on what you wish to do with the polymer. Over the last few years, the application of well-developed techniques from other areas (mainly physics) and well-designed experiments has produced much new insight.

Whatever type of polymer is being dealt with, generally the first question to be dealt with concerns the provenance of the material. Is it what you believe it is? Does it have the desired properties, e.g. molecular weight, composition? Does it have the organisation that is required? All these questions come under characterisation. Mass spectrometry is being more and more applied to high molecular weight polymers and evidently is extremely useful and informative in the hands of the expert. Questions were asked about applicability to molecular weight ranges more typical of polymers and the observation that under different conditions, different data could be obtained. These questions notwithstanding, it is clear that recent developments in mass spectrometry will make it a key analytical tool for the more 'exotic' polymers that will be needed in, for example, tissue engineering applications. The desire to investigate and understand more complex systems or polymers under actual use conditions will lead to demands for more sophisticated, expensive instrumentation only available at nationally supported facilities. We are on the threshold of new neutron and synchrotron sources that will enable a greater range of experimental investigations, e.g. following reactions (of polymers) in real time, simultaneous investigation of molecular level dynamics and organisation when polymers are subjected to stimuli. I suspect we are only limited by our imaginations regarding the investigations that will be possible in the future. One area that has blossomed has been the qualitative and quantitative investigations of polymer surfaces and interfaces. The various probe microscopies are continually developing and are now approaching mesoscopic length scales, and amazing images will not be enough for discerning people when more fundamental information is extractable. Such probe microscopy techniques will be germane to the precise construction of 'molecular machines' either via simple reactions or self-assembly routes. However, these 'soft' processes must produce a strong assembly to be useful. The goal is to produce molecular shuttling, via local pH changes for example, that can be converted to mechanical work. The realisation of such devices is probably 10–15 years ahead but will rely on the ability to characterise them by some means.