Teaching Polymer Synthesis using Primary Literature: A User Guide to the CREATE Method
This page describes the content I used when applying the CREATE method of teaching to the CHEM 421: Polymer Synthesis course at UNC Chapel Hill in Fall 2020. The semester was 100% virtual due to the impacts of COVID-19.
CREATE (Consider, Read, Elucidate the hypothesis, Analyze and interpret and data, and Think of the next Experiment) is a pedagogical method that uses intensive analysis of primary literature to teach, demystify, and humanize scientific advances. In a CREATE course, students read and analyze a set of foundational papers published on the topic at hand. Content knowledge is acquired as an underlying principle to understand why and how the study was conducted, what hypotheses were presented, and the experimental evidence that was presented. More information can be found at https://teachcreate.org/.
For each class period, students were asked to read the introduction to a manuscript with the title, authors, abstract, and figures removed. Based on the introduction, students complete a pre-class assignment that asks them things like: identify the motivation behind the work and the hypothesis of the study or propose experiments and controls that would prove or disprove the working hypothesis. The in-class portion of the curriculum is focused on small group guided discussions and collective analysis. After completion of in class discussion, the complete paper is shared with the class. The student’s proposed experiments and their outcomes are compared to those included in the manuscript. A short summary of these comparisons, including strengths and weaknesses of the study, is discussed.
The following are a list of papers and resources that I used in the Fall 2020 course. There are many ways to conduct a CREATE course and many different papers that could be used. I found that some topics work far better in this format than a traditional lecture (i.e. RAFT polymerization), but some topics are better left to more traditional teaching methods. These CREATE classes were interspersed throughout the semester where they best fit in to complement and expand the topics we were discussing. In this course, approximately 20% of the content was delivered using CREATE. I hope to continue to expand that in the future.
I hope you find this helpful. I want to continue improving this approach, so please let me know if you have any comments, suggestions, or advice! –Frank
Paper #1: J. Am. Chem. Soc. 2016, 138, 1848-1851
Before Class
Provided students with the introduction to the paper: Link
Pre-class assignment (link) in Google Survey format with questions:
What is the problem in the field that the authors are proposing to solve?
What is the working hypothesis of this manuscript? Is this stated clearly in the introduction?
What is the author’s proposal for testing this hypothesis?
What experiment(s) would you run to test the working hypothesis?
What are some positive or negative control reactions you could run to further support your hypothesis?
In Class
We separated into groups (breakout rooms) and had each group compare their answers to the pre-class problems. Each group was assigned a note-taker to summarize the discussion
We came back together in class & discussed each question. The instructor led the discussion and provided the “correct” answer, which we compared/contrasted against each group’s answers
Note: After this 1st virtual CREATE assignment, I realized that I needed to have the in class questions build from the take home questions (not be identical). I found the discussion was a bit limited this 1st day because students had already thought through these questions.
Paper #2: Macromolecules 1995, 28, 1721-1723
Before Class
Provided students with the introduction to the paper (Link)
Pre-class assignment (Link) in Google Survey with questions:
The carbon–chlorine adduct of a vinyl ether did work to produce a controlled polymerization mechanism using cationic polymerization. Is it reasonable to think that a similar carbon–chlorine adduct could also work for radical polymerization?
In the process shown in Scheme 2, what happens to the oxidation state of the ruthenium catalyst during that atom transfer radical addition process?
To achieve polymerization, what must occur to adduct 3?
For a “living” polymerization to occur, what must be true of the reactivity of CCl4 compared to the reactivity of adduct 3?
In Class
Separated into group (breakout rooms) and collectively filled out a google doc (Link) that included the following questions (these are meant to be questions to test content knowledge):
In the process shown in Scheme 2, what happens to the oxidation state of the ruthenium catalyst during that atom transfer radical addition process? (i.e. Scheme 2 represents a reaction that goes through a distinct mechanism to achieve the stated transformation. What is the role of Ru in that mechanism?)
To achieve polymerization, what must occur to adduct 3? (Scheme 2 shows 1 reaction. If you want to transform this into a polymerization, what must occur?)
For a “living” polymerization to occur, what must be true of the reactivity of CCl4 compared to the reactivity of adduct 3? (What is adduct 3 serving as if this is a polymerization?)
After a discussion of those initial questions as a whole class, we again went into breakout rooms to discuss more practical aspects of the polymerization (these are meant to make student “think like a scientist”)
To determine livingness, you want to monitor the polymer growth over time. How would you practically (i.e. in a laboratory setting) conduct this experiment?
If the polymerization turned out not to be living, what are two things you could adjust in the reaction and check if it made the polymerization more living?
Why don’t the additional chlorines (CCl3) on the chain end (from the initiator) react to initiate further polymers?
Paper #3: Macromolecules 1995, 28, 2093-2095
In Class
Before Class
Looking at the survey before class, many students struggled with this introduction. Therefore, the plan for class was modified.
First, we separated into group (breakout rooms) and talked about the questions provided before class.
Next, we came together and actively discussed each topic where I could better guide the discussion. The result was a presentation (Link) that provided students with a better understanding of the content and rationale included in the paper (and about chain transfer polymerization generally)
Provided students with the introduction to the paper (Link)
Pre-class assignment (Link) in Google Survey with questions:
Based on this reading, what is your definition of degenerative transfer?
Considering Scheme 1: Why are the reactions represented in the horizontal drawn an equilibrium while the reactions represented in the vertical drawn as irreversible steps?
What is the working hypothesis of this manuscript?
To achieve a polymerization with living characteristics, should the rate of propagation or degenerative transfer be faster?
Paper #4: Macromolecules 1998, 31, 5559-5562
In Class
Separated into group (breakout rooms) and collectively filled out a google doc (Link) that included the following questions:
Based on this reading, what is your definition of degenerative transfer?
To achieve a polymerization with living characteristics, should the rate of propagation or degenerative transfer be faster?
How do you think this polymerization is initiated?
In the last paper about degenerative chain transfer, the chain transfer agent (CTA) was a single atom (iodine). In this introduction, the CTA is changed to a thiocarbonyl group. What implications on the mechanism of polymerization might this have?
Before Class
Provided students with the introduction to the paper (Link)
Pre-class assignment (Link) in Google Survey with questions:
What does "X" refer to in Scheme 1?
Why do you think the authors chose thiocarbonyl compounds such as 1-9 as chain transfer agents?
In the last paper about degenerative chain transfer, the chain transfer agent (CTA) was a single atom (iodine). In this introduction, the CTA is changed to a thiocarbonyl group. What implications on the mechanism of polymerization might this have?
Paper #5: Nature Chem. 2019, 11, 488-494
In Class
Separated into group (breakout rooms) and collectively filled out a google doc (Link) that included the following questions:
Given the timeline below, how does that further inform your evaluation of the ethics of this study: 1) Initial paper published in 2015; 2) Manuscript retracted April 11th, 2018; 3) This new paper submitted April 16th, 2018.
A ruthenium alkylidene at the end of a growing polymer preferentially reacts with the endocyclic double bond of CTA2 due to steric reasons. Think about the products possible from that ring-opening metathesis product. Why (based on structure) is this molecule a successful CTA?
After Class
The students were provided the full paper & two follow up questions were asked:
In the full paper about the ROMP CTAs, what advantage was conferred by using the bridgehead-substituted monomer M2?
What advantages do you think this method has in terms of making block copolymers from ROMP?
These were discussed in the next period of class
What is one major disadvantage of ROMP that this study is attempting to solve?
The authors state that they reported a method based on degenerative chain transfer for ROMP, but that the data was not reproducible. They subsequently retracted that paper. In your opinion, what are the ethical considerations for publishing another report on that subject?
A key component of CTA1, CTA2, and CTA3 that allows them to work as ROMP CTAs is that they contain two non-aromatic doubled bonds. Why?
Which double bond in CTA2 do you think a ruthenium carbene is mostly likely to react with (the endo-cyclic or exo-cyclic olefin)? Why?
Paper #6: Macromolecules 2011, 44, 8537-8545
In Class
Separated into group (breakout rooms) and collectively filled out a google doc (Link) that included the following questions:
What is a key disadvantage to using amorphous poly(lactide) as the glassy block to provide physical crosslinks when compared to polystyrene? How does crystallinity affect the properties when using amorphous poly(lactide)?
The parameters dictating self-assembly include the molecular weight and dispersity of each block (mid-block & end-block), the Flory-Huggins interaction parameter, and the order-disorder transition temperature. What type of spectroscopic techniques could you use to determine these parameters (or what information would you require, even if you don’t know the exact characterization technique, to determine these parameters?
Before Class
Provided students with the introduction to the paper (Link)
Pre-class assignment (Link) in Google Survey with questions:
What is a key disadvantage to using amorphous poly(lactide) as the glassy block to provide physical crosslinks when compare to polystyrene?
When the authors state that the - "Parameters dictating self-assembly behavior and the microstructure of the triblock copolymers were established" - what "parameters" do you predict they are referring to?
CREATE Assessments: How do you test student’s content knowledge in a CREATE format
I gave two CREATE Quizzes. In these quizzes, the students were given an introduction and asked 3 to 4 questions on their understanding of the work from that document.
The students were then provided the full paper and 6 to 8 additional questions were asked based on the content of the full paper.
This actually worked quite well! The actual paper one chooses is very important. If you would like to discuss this assessment strategy more, please reach out to me individually. Happy to share and further brainstorm!