Introducing the Journal of Chemical Education's “Special Issue

Nov 14, 2017 - Recognizing the importance of synthetic polymers as well as biopolymers, supramolecular structures, and nanoscale materials, the Americ...
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Editorial Cite This: J. Chem. Educ. 2017, 94, 1595-1598

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Introducing the Journal of Chemical Education’s “Special Issue: Polymer Concepts across the Curriculum” Warren T. Ford* Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, United States Department of Chemistry, Portland State University, Portland, Oregon 97201, United States ABSTRACT: Synthetic polymers are all around us in the 21st century, ranging from commodity items made from poly(ethylene) and poly(vinyl chloride) to high-tech materials for aerospace, electronics, and medicine. Yet polymer chemistry is often neglected in formal chemical education. Once students recognize the many ways in which polymers are part of their everyday lives, they are motivated to learn about how polymers are made, their unique thermal, mechanical, and optical properties, and how plastics, fibers, elastomers, and adhesives all are possible because of long-chain molecules. Recognizing the importance of synthetic polymers as well as biopolymers, supramolecular structures, and nanoscale materials, the American Chemical Society (ACS) Committee on Professional Training now requires teaching of at least two of these topics in chemistry courses for ACS-certified undergraduate degrees. This special issue of the Journal is a contributed collection of papers describing how polymers are being taught in general, foundational, and advanced chemistry courses and also in high schools, workshops, and demonstrations for the public. The papers in general do not describe complete courses; instead, they describe modules and experiments that could be implemented at different educational levels and in different environments. The papers are sources of ideas of how instructors can incorporate polymer chemistry into their own courses. KEYWORDS: High School/Introductory Chemistry, First-Year Undergraduate/General, Second-Year Undergraduate, Upper-Division Undergraduate, Curriculum, Demonstrations, Interdisciplinary/Multidisciplinary, Laboratory Instruction, Polymer Chemistry, Materials Science

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INTRODUCTION Plastics, fibers, elastomers, and adhesives pervade our daily lives. Their properties are achieved only with high-molecularweight polymers. Some are natural biopolymers such as cellulose and wool, and most are products of synthetic chemistry. The reactions used for their syntheses are commonly covered in foundational organic and inorganic chemistry courses and appear in textbooks. However, the high-conversion conditions required to produce high-molecular-weight polyamides and polyesters and control the chain lengths by stepgrowth polymerization usually are not discussed. The mechanisms of initiation and propagation of radical, anionic, and cationic chain reaction polymerizations often appear in textbooks, yet the termination steps and the kinetics that control chain lengths are not discussed. The mechanical and thermal properties of plastics, fibers, and elastomers that make them so useful can be explained by chemical thermodynamics, although those properties are seldom discussed in foundational physical chemistry courses. Furthermore, the analyses of compositions, molecular weights, and properties of polymers seldom appear in foundational or advanced analytical chemistry courses. Recognizing deficiencies in the education of chemistry students about synthetic polymers, supramolecular materials, nanoscale materials, and biopolymers, the American Chemical Society (ACS) Committee on Professional Training (CPT) in 2015 added a requirement for inclusion of at least two of these topics as separate courses or as parts of foundational courses for ACS-certified B.S. degrees in chemistry.1 This Journal of Chemical Education special issue is the result of an open call for papers on polymer chemistry2 to provide © 2017 American Chemical Society and Division of Chemical Education, Inc.

ideas and tools that will be useful for chemistry instructors at all levels, not only the foundational undergraduate courses but also secondary school, general, and advanced chemistry courses. Some of the papers even describe outreach programs that entertain and spark interest in polymers in informal settings. For the most part, the papers do not provide fundamentals of polymer chemistry that can be taken directly into foundational chemistry courses or dedicated polymer chemistry courses. Kosbar and Wenzel list many of the fundamental concepts that belong in those courses and provide references to textbooks in which they are covered (DOI: 10.1021/acs.jchemed.6b00922). More details are available at the CPT Web site3 and at the ACS CPT Web page presenting ACS guidelines and supplements,4 including the supplements on Macromolecular, Supramolecular, and Nanoscale (MSN) Systems in the Curriculum5 and Polymers Across the Curriculum: Macromolecules as a Unifying Theme Across the Foundational Courses in Chemistry.6 Carraher and colleagues provide a history of the programs of PolyEd, the ACS committee on polymer education, with references to older fundamental papers and current Web sites (DOI: 10.1021/acs.jchemed.7b00614). This special issue will stimulate readers with ideas that they can adapt for their own purposes, which could be foundational courses, dedicated polymer chemistry courses, or outreach. When deciding what to teach, chemistry instructors should consider what fundamental knowledge will be of most value to Special Issue: Polymer Concepts across the Curriculum Published: November 14, 2017 1595

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both small-molecule compounds and polymers. Macroscopic physical properties of materials are vital for students to understand that organic chemistry is about real materials and not just memorization of hundreds of molecular structures and reactions in a textbook. Harrell and Bergbreiter report teaching of NMR principles via analysis of methoxy-terminated poly(ethylene glycol) and its acetate derivative (DOI: 10.1021/acs.jchemed.6b00801). They consider solvent peaks, peaks due to 13C−1H coupling in natural abundance in 1H NMR spectra, the reliability of integrated signal areas, and number-average degree of polymerization. Wackerly and Dunne report a laboratory exercise in which students prepare low-molecular-weight poly(styrene) and determine the number-average degree of polymerization by 1 H NMR end-group analysis (DOI: 10.1021/acs.jchemed.6b00814).

their students in future studies and in the workplace. More than half of chemistry graduates at some time in their careers work with polymers.7 Understanding of the fundamentals of polymers is vital to their education. However, there is not room in most chemistry department curricula to add another required course or to expand the amount of material covered in the foundational courses. Inclusion of polymer principles must come at the expense of deleting material currently in those courses and in the chemistry degree requirements. What to delete is a matter that chemistry faculties and instructors of individual courses must decide. I could relate what I have done in the second-year organic chemistry course, but all instructors will make their own decisions. No one solution fits all circumstances. Most importantly, we should give priority to what is best for the students rather than what is most interesting to the instructor.

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CONTENTS OF THE SPECIAL ISSUE Although the following brief descriptions of the papers are categorized by the class or audience for which the content was designed, the ideas in many of the papers could easily be adapted for a different audience.

Inorganic Chemistry

de Lill and Carraher describe the structures and uses of a wide range of inorganic polymers that could be included in descriptive and advanced inorganic chemistry courses (DOI: 10.1021/acs.jchemed.7b00028). Krumpfer and co-workers present three simple experiments to introduce siloxane polymers in courses for first-year, upperlevel, and non-science-major students (DOI: 10.1021/acs.jchemed.6b00769). Siloxane polymers could be included in polymer, materials, organic, or inorganic chemistry. Darensbourg reports the alternating copolymerization of epoxides and CO2 to afford poly(carbonates) for teaching principles of both polymer chemistry and catalysis (DOI: 10.1021/acs.jchemed.6b00505).

General Chemistry

Moore and Stanitski describe both a course and a textbook in which polymers and biopolymers are integrated into the general chemistry curriculum (DOI: 10.1021/acs.jchemed.6b00811). Schaller and co-workers report integration of modules on biomacromolecules, molecular weight, structure−property relationships, and synthetic principles, including step-growth, chain-growth, and living polymerization, into an unconventional structure and reactivity course sequence at a small college (DOI: 10.1021/acs.jchemed.6b00798). The modules could be adapted for a traditional sequence in general, organic, and inorganic chemistry. Bopegedera describes a stand-alone polymer chemistry unit that uses molecular modeling of β-D-glucose and cellulose, tiedying of cotton T-shirts, and a literature exercise in how dye molecules bind to cellulose as examples to teach basic principles of bonding and intermolecular interactions (DOI: 10.1021/ acs.jchemed.6b00796).

Analytical Chemistry

Dickson-Karn describes the identification of 18 polymer samples in an instrumental analysis laboratory course using attenuated total reflectance Fourier transform infrared spectroscopy (DOI: 10.1021/acs.jchemed.6b00438). Students then determine by differential scanning calorimetry whether poly(ethylene) samples are high density or low density and whether nylon samples are Nylon-6 or Nylon-6,6.

Organic Chemistry

Polymer Chemistry Courses

Howell categorizes many polymers by their applications, describes their syntheses, and shows how they can be incorporated into second-year organic chemistry courses (DOI: 10.1021/acs.jchemed.7b00033). Examples include polyethylene by coordination polymerization, common plastics and fibers from radical chain polymerization, synthetic rubber, polymers in the kitchen, and polymers to wear, to cushion, and to protect. The applications attract student attention to learn the fundamental chemistry that underlies the examples. Shulman describes synthesis by polycondensation and ringopening polymerization and degradation of poly(anhydrides), poly(esters), poly(amides), and poly(urethanes) with many examples that are not in standard organic chemistry textbooks (DOI: 10.1021/acs.jchemed.6b00673). Wnek relates the increase in melting point (Tm) with increasing chain length of unbranched alkanes up to poly(ethylene) and explains the effects of chain branching, molecular rigidity, and hydrogen bonding on melting points by fundamental thermodynamics, ΔHm = TmΔSm (DOI: 10.1021/acs.jchemed.6b00747). He then relates the glass transition temperature (Tg) to Tm and to the structures of

The Polymer Division of the International Union of Pure and Applied Chemistry (IUPAC) publishes standards for terminology and nomenclature that can be used in polymer chemistry instruction.8 Theato, Fellows, and co-workers list available materials and report examples of their use in teaching in countries with emerging economies (DOI: 10.1021/acs.jchemed.6b00800). Cheng and Howell provide a primer on polymer nomenclature that includes structure-based, source-based, and trade names (DOI: 10.1021/acs.jchemed.6b00979). The primer is important because structure-based names approved by IUPAC and the Chemical Abstracts Service are almost never used even in the primary chemical literature. Pilcher describes an upper-division hybrid polymer chemistry course that meets both face-to-face and online (DOI: 10.1021/ acs.jchemed.6b00809). He uses a textbook, specially prepared worksheets and quizzes, and the Macrogalleria9 for study assignments. Flores-Morales and colleagues report the development of the curriculum of the Department of Polymers, University of Concepción , Chile, over many years (DOI: 10.1021/ 1596

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acs.jchemed.7b00212). Complete polymer curricula can also be found at Web sites of polymer departments at universities in the United States and elsewhere. Shultz and co-workers report the process and outcome of teaching stress−strain behavior of amorphous and semicrystalline polymers as a write-to-learn exercise in a lower-level materials science engineering course (DOI: 10.1021/acs.jchemed.7b00363). Ardo and co-workers use saltwater desalination by electrodialysis to teach students the chemical physics of polymeric ionexchange membranes, which are also applied to desalination by reverse osmosis (DOI: 10.1021/acs.jchemed.7b00021).

Maynard, Craig, and co-workers describe a demonstration of a filled poly(dimethylsiloxane) elastomer that is covalently functionalized with a spiropyran (DOI: 10.1021/acs.jchemed.6b00806). The material changes reversibly from colorless to dark purple upon exposure to light from a blue laser pointer or to a mechanical stimulus, such as hitting the polymer with a hammer or dragging a blunt object across the surface, allowing children literally to “write without ink”. Rosu, Russo, and co-workers report the identification of volatile compounds from polymeric materials by solid-phase microextraction coupled to gas chromatography−mass spectrometry (DOI: 10.1021/acs.jchemed.6b00791). These compounds, originating from additives and fillers used to process weatherstripping, demonstrate the connection between detection using our olfactory sense and modern analytical instrumentation. Hurst reports a laboratory experiment on smart hydrogels for potential application in targeted drug delivery (DOI: 10.1021/ acs.jchemed.7b00235). Chitosan and poly(vinyl alcohol) are cross-linked to form a pH-sensitive hydrogel, and students observe the swelling behaviors, oscillatory functionality, and gelation, fluorescent, optical, and release properties of the system. Walter and co-workers describe a plastic electronics laboratory kit using polymer semiconductors to evaluate the conducting properties of poly(aniline), construct a lightemitting diode using poly(p-phenylenevinylene), and build a polymer solar cell (DOI: 10.1021/acs.jchemed.7b00332). Bode and co-workers teach economic and life cycle assessments in introductory chemistry and chemical engineering courses for ethylene, ethylene oxide, and terephthalic acid, major commodity chemicals that are precursors for plastics, synthetic fibers, and many other consumer products (DOI: 10.1021/acs.jchemed.6b00548).

Experiments and Demonstrations

Guedens and Reynders report a laboratory assignment for teams of chemistry and engineering students to identify seven different polymers by their physical properties, synthesize five different polymers, and present a “chemistry meets economics” poster for engineers to learn chemistry and chemists to learn industrial economics (DOI: 10.1021/acs.jchemed.7b00284). Lodge and co-workers describe a series of experiments carried out in one day with graduate student and postdoctoral supervision by high school students attending a week-long STEM summer camp (DOI: 10.1021/acs.jchemed.6b00767). The experiments include a ring-opening polymerization of δvalerolactone, happy/sad spheres (rubber elasticity as a function of temperature above and below Tg), light scattering by block copolymer micelles, swelling of a hydrogel, and nonNewtonian rheology of a poly(ethylene oxide) solution. All of the experiments could be adapted for different levels of instruction. Shen and Tonelli report demonstrations of four experiments for audiences from middle school to graduate students: comparison of the dilute-solution viscosities of a small molecule and a polymer, the properties of borate-cross-linked poly(vinyl alcohol) “slime”, the stretching of a rubber band, and paperand-pencil simulation of step-growth polymerization (DOI: 10.1021/acs.jchemed.7b00008). Scott and co-workers describe a program in which graduate students bring polymers to grade 1−9 classrooms (DOI: 10.1021/acs.jchemed.6b00805). The instructional modules on mechanical properties of polymers and other solid materials (grades 1−9), polymer recycling and remanufacturing (grades 5−9), and polymers in medicine (grades 5−8) are designed to meet many of the state Next Generation Science Standards. Enthaler reports teaching of concepts of polymerization and depolymerization with plastic building blocks (Legos) and the many ways end-of-life plastics may be reused rather than buried in a landfill (DOI: 10.1021/acs.jchemed.6b00888). Warren and co-workers report a laboratory experiment on the preparation and analysis of a clay nanoparticle composite hydrogel of poly(N-isopropylacrylamide) (DOI: 10.1021/ acs.jchemed.6b00389). The experiment has been carried out by high school students and could be adapted for an undergraduate course. Wissinger and co-workers describe a chemistry experiment for high school students that combines science and engineering principles while introducing polymer chemistry concepts (DOI: 10.1021/acs.jchemed.6b00835). Using medical sutures as a platform, students explore the physical and mechanical properties of threads drawn from poly(ε-caprolactone) samples with different molecular masses and of commercial absorbable and nonabsorbable medical sutures.

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CONCLUSION Materials made from synthetic polymers are one of the most practical achievements of chemistry and are an essential part of life in the 21st century. Despite their importance, polymers are often neglected in chemistry education. The synthesis and properties of polymeric materials should be included in chemistry instruction at all levels to inspire student interest in chemistry and to provide students with fundamental knowledge for their future careers. The many ideas in this issue should stimulate instructors to incorporate more polymers and polymer concepts into their courses. This issue is not a stand-alone guide to teaching polymer chemistry. For the fundamental chemistry and physics, instructors will need to consult more fundamental sources of information.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

Views expressed in this editorial are those of the author and not necessarily the views of the ACS. Warren T. Ford is Regents Professor of Chemistry Emeritus at Oklahoma State University and Adjunct Professor of Chemistry at Portland State University. At Oklahoma State he taught organic chemistry every year at all levels and polymer chemistry biannually. He has published more than 200 refereed scientific papers on polymeric catalysts and reagents, polymer colloids, 1597

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modified dendritic polymers, and functionalization of C60 and single-walled carbon nanotubes by radical polymerization. He was the faculty coordinator of the Oklahoma Network for Nanostructured Materials, 2001−2009. He has served for many years on PolyEd, the education committee sponsored by the ACS Divisions of Polymer Chemistry (POLY) and Polymeric Materials: Science and Engineering (PMSE). He was Program Chair for POLY, 1998−2000, and has organized more than 30 technical symposia at ACS national meetings. He is a Fellow of the American Association for the Advancement of Science, ACS, and POLY.

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ACKNOWLEDGMENTS I thank the editors and staff of this Journal and all of the authors of contributed papers for making this issue possible. Members of ACS PolyEd have contributed greatly to my thinking about teaching polymer chemistry, and Frank Blum (Oklahoma State University) and Bob Howell (Central Michigan University) provided vital editorial advice and assistance.

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REFERENCES

(1) American Chemical Society Committee on Professional Training. Undergraduate Professional Education in Chemistry: ACS Guidelines and Evaluation Procedures for Bachelor’s Degree Programs. https:// www.acs.org/content/dam/acsorg/about/governance/committees/ training/2015-acs-guidelines-for-bachelors-degree-programs.pdf (accessed October 2017). (2) Pienta, N. J. Journal of Chemical Education Special Issue on Polymer Concepts across the Curriculum. J. Chem. Educ. 2016, 93 (5), 806−807. (3) Committee on Professional Training homepage. https://www. acs.org/content/acs/en/about/governance/committees/training.html (accessed October 2017). (4) ACS Committee on Professional Training. ACS Guidelines & Supplements. https://www.acs.org/content/acs/en/about/ governance/committees/training/acs-guidelines-supplements.html (accessed October 2017). (5) ACS Committee on Professional Training. Macromolecular, Supramolecular, and Nanoscale (MSN) Systems in the Curriculum. https://www.acs.org/content/dam/acsorg/about/governance/ committees/training/acsapproved/degreeprogram/macromolecularsupramolecular-nanoscale-supplement.pdf (accessed October 2017). (6) ACS Committee on Professional Training. Polymers Across the Curriculum: Macromolecules as a Unifying Theme Across the Foundational Courses in Chemistry. https://www.acs.org/content/ dam/acsorg/about/governance/committees/training/acsapproved/ degreeprogram/polymers-across-the-curriculum-supplement.pdf (accessed October 2017). (7) United States Department of Labor, Bureau of Labor Statistics. Occupational Employment Statistics: Occupational Employment and Wages, May 2016: 19-2031 Chemists. https://www.bls.gov/oes/ current/oes192031.htm (accessed October 2017). (8) International Union of Pure and Applied Chemistry. Compendium of Polymer Terminology and Nomenclature (The Purple Book), 2nd ed.; RSC Publishing: Cambridge, U.K., 2008; https://iupac.org/ projects/project-details/?project_nr=2002-048-1-400 (accessed October 2017). (9) Polymer Science Learning Center. The Macrogalleria: A Cyberwonderland of Polymer Fun! http://pslc.ws/macrog/maindir. htm (accessed October 2017).

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DOI: 10.1021/acs.jchemed.7b00760 J. Chem. Educ. 2017, 94, 1595−1598