Introduction to polymers About this free course This free course provides a sample of level 3 study in Science http://www.open.ac.uk/courses/find/science This version of the content may include video, images and interactive content that may not be optimised for your device. You can experience this free course as it was originally designed on OpenLearn, the home of free learning from The Open University: http://www.open.edu/openlearn/science-maths-technology/science/chemistry/introduction-polymers/ content-section-0. There you’ll also be able to track your progress via your activity record, which you can use to demonstrate your learning. The Open University Walton Hall Milton Keynes MK7 6AA United Kingdom Copyright © 2016 The Open University Intellectual property Unless otherwise stated, this resource is released under the terms of the Creative Commons Licence v4.0 http://creativecommons.org/licenses/by-nc-sa/4.0/deed.en_GB. 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All rights falling outside the terms of the Creative Commons licence are retained or controlled by The Open University. 2 of 122 http://www.open.edu/openlearn/history-the-arts/introduction-law-wales/content-section-0?utm_source=openlearnutm_campaign=olutm_medium=ebook Thursday 26 March 2020 Head of Intellectual Property, The Open University The Open University Hobbs the Printers Limited, Brunei Road, Totton, Hampshire, SO40 3YS Contents Introduction 5 Learning Outcomes 6 1 Polymer materials 7 1 1The growth of poymers 7 1.2 Polymer types 8 1.3 Product design and manufacture 17 2 Molecular engineering 26 2.1 Understanding the polymer state 26 2.2 Chain repeat units 28 2.3 Chain configuration 29 2.4 Chain conformations 39 2.5 Structure-property relationships 41 2.6 Molecular mass distribution 46 2.7 Commercial polymers 50 3 Manufacture of monomers 54 3.1 Primary sources of synthetic polymers 54 3.2 Petrochemical processing 54 3.3 Petrochemical intermediates and monomers 59 3.4 The petrochemical industry 62 4 Polymerization 64 4.1 Understanding the polymerization process 64 4.2 Chain and step growth 64 4.3 Chain growth polymerization 65 4.4 Step growth polymerization 73 4.5 Copolymerization 75 4.6 Polymer grades 80 5 Physical properties of polymers 85 5.1 The behaviour of polymers 85 5.2 Viscoelasticity of polymers 85 5.3 Viscoelasticity and master curves 88 5.4 Dynamic mechanical properties 93 5.5 Orientation in polymers 96 5.6 Crystallisation of polymers 99 6 Design in polymers 106 6.1 A fresh approach? 106 6.2 Manufacturing and process methods 106 6.3 Materials selection 108 3 of 122 http://www.open.edu/openlearn/history-the-arts/introduction-law-wales/content-section-0?utm_source=openlearnutm_campaign=olutm_medium=ebook Thursday 26 March 2020 6.4 Case history: the Topper boat 110 6.5 Market experience 119 Conclusion 121 Acknowledgements 121 4 of 122 http://www.open.edu/openlearn/history-the-arts/introduction-law-wales/content-section-0?utm_source=openlearnutm_campaign=olutm_medium=ebook Thursday 26 March 2020 Introduction Introduction Polymers are materials composed of long molecular chains that are well-accepted for a wide variety of applications. This unit explores these materials in terms of their chemical composition, associated properties and processes of manufacture from petrochemicals. The unit also shows a range of products in which polymers are used and explains why they are chosen in preference to many conventional materials. This OpenLearn course provides a sample of level 3 study in Science 5 of 122 http://www.open.edu/openlearn/history-the-arts/introduction-law-wales/content-section-0?utm_source=openlearnutm_campaign=olutm_medium=ebook Thursday 26 March 2020 Learning Outcomes After studying this course, you should be able to: ● isolate the key design features of a product which relate directly to the material(s) used in its construction ● indicate how the properties of polymeric materials can be exploited by a product designer ● describe the role of rubber-toughening in improving the mechanical properties of polymers ● identify the repeat units of particular polymers and specify the isomeric structures which can exist for those repeat units ● estimate the number- and weight-average molecular masses of polymer samples given the degree of polymerisation and mass fraction of chains present. 1 Polymer materials 1 Polymer materials 1 1The growth of poymers Polymers, or materials composed of long molecular chains, are now well-accepted for a wide variety of applications, both structural and non-structural, and for mass- manufactured as well as one-off speciality products. The growth in their use has continued in the last two decades or more, despite the effects of several recessions in industrial activity (Figure 1). In the same period the demand for traditional materials like metals, ceramics and glasses has remained static or even fallen. Steel usage in the UK, for example, has fallen from about 14 million tonnes in the 1970s to about 12 million tonnes in the 1990s, while that of aluminium has stayed at about 600 000 tonnes. The growth in use of polymers is forecast to continue into the next millennium, with consumption approaching 4 million tonnes in the UK. In one of the most active areas, that of thermoplastic polymers, consumption is divided between packaging, building, and a wide range of other applications (Figure 2). Figure 1 Growth in demand for polymers in the UK, 1980–2000. Source: data from British Plastics Federation 7 of 122 http://www.open.edu/openlearn/history-the-arts/introduction-law-wales/content-section-0?utm_source=openlearnutm_campaign=olutm_medium=ebook Thursday 26 March 2020 1 Polymer materials Figure 2 UK plastics applications 1995. Source: data from BPF Statistics, 1995 1.2 Polymer types Traditionally, the industry has produced two main types of synthetic polymer – plastics and rubbers (Figure 3). The distinction is that plastics are, by and large, rigid materials at service temperatures while rubbers are flexible, low modulus materials which exhibit long- range elasticity. Plastics are further subdivided into thermoplastics and thermosets, the latter type being materials where the long chains are linked together by crosslinks, a feature they share with conventional vulcanized rubbers. As Figure 3 shows, however, the distinction in terms of stiffness has become blurred by the development of thermoplastic elastomers (TPEs). Moreover, all polymers, irrespective of their nature, can be reinforced by a very wide range of fillers to produce composite materials. 8 of 122 http://www.open.edu/openlearn/history-the-arts/introduction-law-wales/content-section-0?utm_source=openlearnutm_campaign=olutm_medium=ebook Thursday 26 March 2020 1 Polymer materials Figure 3 Classification of polymers by property Another way of classifying polymers is in terms of their form or function, varying from additives to other bulk materials (e.g. viscosity modifiers in plaster), coatings to products (e.g. paints), film and membranes to fibres (e.g. textiles) and bulk products such as pipe, containers and mouldings (Figure 4). Some of these materials are of course used as products in their own right, or manipulated further into finished products. This does not always happen, however, some polymers being a disposable intermediary in certain industrial processes. Thus photoresists are used to create the circuit patterns on semiconductor chips through controlled degradation, and are entirely absent in the final product. Figure 4 Classification of polymers by design function 9 of 122 http://www.open.edu/openlearn/history-the-arts/introduction-law-wales/content-section-0?utm_source=openlearnutm_campaign=olutm_medium=ebook Thursday 26 March 2020 1 Polymer materials Exercise 1 Identify the products in a typical modern house associated with the supply and disposal of water (or prevention of entry) which may be of polymeric origin, giving details of their generic type (Figure 3) and form or function (Figure 4).