Activity pubs.acs.org/jchemeduc
Modules for Introducing Macromolecular Chemistry in Foundation Courses Chris P. Schaller,* Kate J. Graham, Henry V. Jakubowski, and Brian J. Johnson Department of Chemistry, College of Saint Benedict/Saint John’s University, Saint Joseph, Minnesota 56374, United States S Supporting Information *
ABSTRACT: A series of guided inquiry modules that introduces students to aspects of polymer chemistry is described. The modules address topics such as biomacromolecules, molecular weight, structure−property relationships, and synthetic approaches, including step-growth and chain-growth polymerization as well as living polymerization. These materials are suitable for use in either a structure and reactivity sequence or a more traditional sequence in general chemistry, organic chemistry, and inorganic chemistry.
KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate, Polymer Chemistry, Curriculum, Interdisciplinary/Multidisciplinary, Inquiry-Based/Discovery Learning, Polymerization, Physical Properties
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the most frequently covered topics by Carraher and Deanin7 noted in addition the widespread inclusion of copolymerization, morphology, and rheology and indicated that the history of polymers had been displaced from the curriculum. In 1999, Jefferson and Phillips8 described a course for advanced undergraduates in the Australian curriculum that included weathering and degradation of polymers. A 2006 report by Stenzel and Barner-Kowollik9 on a two-semester sequence in polymer chemistry and physics highlighted one of the most significant developments in recent years: methods of living polymerization. Most schools do not have the flexibility for a full course on polymers, so they instead choose to deliver instruction on the topic as part of other courses. The approach is perhaps most accepted in organic chemistry, where some textbooks contain chapters on polymers.10 However, there are a number of concepts in general chemistry that can be illustrated using examples from polymer science;11 inorganic chemistry also offers a range of applications;12 biomacromolecules, of course, occupy a significant position in biochemistry. The laboratory is a popular venue to showcase polymer chemistry, and there is a rich literature in this area. Recent publications describe experiments on central topics, including molecular weight,13−15 crystallinity and morphology,16−19 elastomers,20 copolymers,21,22 and living polymerization,23,24 as well as subjects of
he importance of polymer chemistry has continued to grow1 since the field’s rise to industrial prominence following World War II.2 Modern chemistry students are expected to master fundamental concepts of polymer structure, synthesis, and properties. The American Chemical Society Committee on Professional Training (ACS CPT) Guidelines and Evaluation Procedures for Bachelor’s Degree Programs calls for coverage of macromolecular, supramolecular, and nanomaterials for certified graduates.3 In addition, the committee requires that undergraduate chemistry curricula must cover synthesis, characterization, and physical properties of at least two of these structural types: synthetic polymers, biological macromolecules, supramolecular aggregates, and nanomaterials. The ACS CPT has also published a supplement providing an outline for implementing key concepts of polymer education to be employed in foundation and in-depth courses across the curriculum.4 A 2001 review of the educational literature by Bigger and coworkers revealed that the number of publications regarding polymer chemistry had peaked in the 1980s.5 At that time, approximately 25% of publications had addressed synthetic aspects of polymer chemistry, with smaller numbers dealing with polymer properties (∼20%) and characterization (∼15%). The remainder discussed miscellaneous topics such as the history of the field or the use of specific teaching aids. Expected coverage in polymer chemistry has undergone moderate changes over the years. A 1959 paper by Butler6 described a one-semester course that emphasized the history of polymers, mechanisms of olefin and condensation polymerization, polymerization kinetics, structure−property relationships, and molecular weight determination. A 1980 survey of © XXXX American Chemical Society and Division of Chemical Education, Inc.
Special Issue: Polymer Concepts across the Curriculum Received: October 23, 2016 Revised: March 30, 2017
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DOI: 10.1021/acs.jchemed.6b00798 J. Chem. Educ. XXXX, XXX, XXX−XXX
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current interest such as conducting,25 sustainable,26 and selfhealing polymers.27 Because many schools lack faculty with training in polymer chemistry, it is useful to have readily available modules for use in the classroom.28 We describe here an approach in which topics of polymer chemistry are introduced as modules for courses in Structure & Properties and Reactivity.29 These courses are part of a structure, reactivity, and quantitation curriculum in chemistry at the College of Saint Benedict/Saint John’s University. In this novel curriculum, introductory courses develop concepts that cross traditional domains such as organic and inorganic chemistry. This approach reflects a growing trend toward collaborative research efforts that require researchers to bridge these domains in order solve problems. In addition, by deliberate blending of specific topics from different domains into one course, the development of storylines from fundamental concepts to ultimate applications can be illustrated. For example, students might learn about the principles of reactivity of organic carbonyl compounds, using these ideas to understand mechanisms in biological pathways and transition metal catalysis. The polymer modules described here could also be implemented in more traditional general, organic, and inorganic chemistry courses.
As the first course to address synthetic polymer chemistry in the curriculum, Reactivity I also provides an introduction to concepts of average molecular weight. Students see the importance of entanglement and cross-linking in the viscosity and elasticity of polymers, and they are introduced to the glass transition temperature as a diagnostic feature of polymers. Students also see some common architectural motifs, such as linear versus branched polymers as well as block and statistical copolymers. These topics are subsequently reviewed in later courses.
POLYMER MODULES IN INTRODUCTORY AND FOUNDATIONAL COURSES Structure & Properties is an introductory course for firstsemester college students,30 whereas the Reactivity sequence is a foundation-level set of courses that blends concepts from organic, inorganic, and biochemistry.31−33 These courses lend themselves well to a number of aspects of polymer chemistry, including synthetic chemistry and general concepts of structure−property relationships. The modules based purely on structure−property relationships are easily adaptable to general chemistry, whereas the synthetic topics would work well in organic chemistry. In addition, a unit on main-group polymers could be used in a course in inorganic chemistry. All of these modules, briefly described below, are available in the Supporting Information.
Reactivity III
Reactivity II
This course includes a section on electrophilic addition to alkenes, so cationic chain polymerization is an obvious application of the material. Students are also introduced to characteristics of chain growth versus step growth in terms of changes in molecular weight with increasing percent conversion. The importance of molecular weight control is reviewed, and the concept of living cationic polymerization is developed. The topic is extended to include a unit on Ziegler− Natta polymerization, including the question of tacticity and stereocontrol. Finally, in a departure from purely organic polymers, students also complete an exercise involving silicone and phosphazene polymers.
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Reactivity III focuses primarily on single-electron chemistry, including redox chemistry, photochemistry, and radicals; radical chain polymerization provides an obvious application of the latter. Living polymerization, including atom transfer radical polymerization (ATRP) and radical addition−fragmentation transfer (RAFT) polymerization are covered. In addition, a short unit on pericyclic reactions and cycloadditions includes olefin metathesis as a loosely analogous reaction and also includes discussion of ring-opening metathesis polymerization (ROMP).
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IN-DEPTH ELECTIVES In addition to repeated exposure to concepts of polymer synthesis and properties in the Structure & Properties and Reactivity courses, students in our department have the opportunity to pursue more detailed coverage in half-semester elective courses, including Polymers, Nanomaterials, and Biomacromolecules. These courses are not novel and reflect a trend seen elsewhere toward devoting in-depth courses to more applied or interdisciplinary topics; for example, some in-depth inorganic chemistry courses focus on organometallic or bioinorganic chemistry.34 Nevertheless, the modules included here support a solid foundation in polymer chemistry for all students, even without in-depth instruction in the topic.
Structure & Properties
Polymer chemistry is first encountered in this introductory course in the form of biomacromolecules. This topic immediately follows a unit on intermolecular forces. Students see examples of carbohydrates and polysaccharides, proteins, and DNA and RNA. Hydrogen bonding is stressed as an important factor in the secondary structures of proteins as well as the structures of RNA and DNA. The idea of supramolecular assemblies is also introduced by looking at micelles and liposomes.
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ASSESSMENT Faculty who have used these modules report that students perform well on a range of polymer-related tasks (see the Supporting Information for learning goals and assessment). A range of tasks are routinely mastered by students after they work through the exercises described. In the area of biomacromolecules, students can identify structural features of proteins and can indicate intermolecular interactions with small molecules, such as inhibitors. Students can identify monomeric units in condensation polymers, propose mechanisms of polymer formation, identify sources of physical crosslinks between chains, and qualitatively predict entropy and enthalpy of polymerization. After learning about chain
Reactivity I
Reactivity I is an introduction to the themes of reactivity in organic, inorganic, and biochemistry. The organic portions of the course adopt a carbonyl-first perspective, presenting those reactions that are most central to major biochemical pathways such as glycolysis and fatty acid biosynthesis. Coverage of carboxylic substitution chemistry sets the stage for both protein polymerization in biochemistry and classic condensation polymers such as polyester and nylon. The reactions of difunctional monomers with complementary partners are explored, such as diamines with diacid chlorides. This chemistry is extended beyond step-growth polymers to include a chaingrowth process: ring-opening transesterification polymerization. B
DOI: 10.1021/acs.jchemed.6b00798 J. Chem. Educ. XXXX, XXX, XXX−XXX
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polymerization, students can demonstrate mechanisms for alkene polymerization via cationic and Ziegler−Natta methods, and they can use dispersity and molecular weight of products as criteria to choose the most effective method. Students also work through concepts of living polymerization and can subsequently demonstrate the equilibrium reactions responsible for maintaining a narrow molecular weight distribution. Final examinations in chemistry courses at CSB/SJU include a battery of questions chosen from different ACS exams and delivered online with the help of the ACS Examinations Institute. This practice provides the opportunity to compare the performance of CSB/SJU students on a specific question to nationally normed data. Two or three polymer-related questions appear on each of the exams used in Structure & Properties and the Reactivity courses, the results of which are summarized according to question category in Table 1. CSB/
The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.6b00798. Guided inquiry modules on polymer chemistry for use in the classroom; examples of learning goals; examples of assessment materials used in class; guide to suggested implementation in traditional courses (PDF, DOCX)
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*E-mail:
[email protected]. ORCID
Chris P. Schaller: 0000-0003-0763-0446 Kate J. Graham: 0000-0002-2301-0557 Notes
The authors declare no competing financial interest.
Difficulty Index (National Norm) by Course
Protein structure Protein properties Polymer properties Polymer synthesis
Reactivity Ic
0.62 (0.34)
0.64 (0.72)
0.54 (0.54)
0.67 (0.70)
0.66 (0.46)
0.84 (0.45)
0.74 (0.55)
AUTHOR INFORMATION
Corresponding Author
a
Structure & Propertiesb
ASSOCIATED CONTENT
S Supporting Information *
Table 1. Comparative Performance on Polymer-Related Final Exam Questions
Topic
Activity
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ACKNOWLEDGMENTS This material is based upon work supported by the National Science Foundation under Grant 1043566. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. The authors thank Alicia A. Peterson and T. Nicholas Jones for discussions of these polymer modules.
Reactivity IId Reactivity IIIe
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a
Fraction of students with the correct response (national norm from ACS pool). bAcademic year (AY) 2012−AY 2016, n = 1926. cAY 2013−AY 2016, n = 874. dAY 2013−AY 2016, n = 339. eAY 2014−AY 2016, n = 138.
REFERENCES
(1) American Chemical Society. Polymer Chemistry. https://www. acs.org/content/acs/en/careers/college-to-career/areas-of-chemistry/ polymer-chemistry.html (accessed March 2017). (2) Stahl, G. A. A Short History of Polymer Science. In Polymer Science Overview; Stahl, G. A., Ed.; ACS Symposium Series, Vol. 175; American Chemical Society: Washington, DC, 1981; pp 25−44. (3) American Chemical Society Committee on Professional Training. Undergraduate Professional Education in Chemistry: ACS Guidelines and Evaluation Procedures for Bachelor’s Degree Programs, 2015. http://www.acs.org/content/dam/acsorg/about/governance/ committees/training/2015-acs-guidelines-for-bachelors-degreeprograms.pdf (accessed March 2017). (4) American Chemical Society Committee on Professional Training. Polymers Across the Curriculum: Macromolecules as a Unifying Theme Across the Foundational Courses in Chemistry. http://www. acs.org/content/dam/acsorg/about/governance/committees/ training/acsapproved/degreeprogram/polymers-across-thecurriculum-supplement.pdf (accessed March 2017). (5) Hodgson, S. C.; Bigger, S. W.; Billingham, N. C. Studying Synthetic Polymers in the Undergraduate Chemistry Curriculum. A Review of the Educational Literature. J. Chem. Educ. 2001, 78 (4), 555−556. (6) Butler, G. B. A Polymer Chemistry Course Based on Theoretical Principles. J. Chem. Educ. 1959, 36 (4), 171−174. (7) Carraher, C. R., Jr.; Deanin, R. D. Core Curriculum in Introductory Courses of Polymer Chemistry. J. Chem. Educ. 1980, 57 (6), 436. (8) Jefferson, A.; Phillips, D. N. Teaching Polymer Science to ThirdYear Undergraduate Chemistry Students. J. Chem. Educ. 1999, 76 (2), 232−235. (9) Stenzel, M. H.; Barner-Kowollik, C. Polymer Science in Undergraduate Chemical Engineering and Industrial Chemistry Curricula: A Modular Approach. J. Chem. Educ. 2006, 83 (10), 1521−1530.
SJU students performed comparably to or in some cases better than peers nationwide on a small number of polymer-related ACS exam questions. For example, on the topic of protein structure, Structure & Properties students appeared to outperform their peers at the national level; however, no such edge was seen when Reactivity I students faced a similar question. More convincingly, students in the Reactivity sequence seemed to consistently perform better than peers nationally on questions of polymer synthesis. In order to assess student retention of polymer concepts, a problem-solving assessment (PSA) was used on the first day of lecture in Polymers, an in-depth class populated by two secondyear, seven third-year, and five fourth-year students. The topic was living cationic polymerization, which students would have seen in Reactivity II during the autumn of their second year. The mean on this instrument was 80%, suggesting reasonable retention of this material. A copy of this PSA has been placed in the Supporting Information.
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CONCLUSION The steadily increasing importance of polymer chemistry in the economy has been accompanied by a mounting need for polymer chemistry instruction in the chemistry curriculum. A series of guided inquiry modules has been implemented in the classroom that guides students through several of the most basic aspects of polymer chemistry. C
DOI: 10.1021/acs.jchemed.6b00798 J. Chem. Educ. XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.jchemed.6b00798 J. Chem. Educ. XXXX, XXX, XXX−XXX
