HW4-Solutions from Canvas

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Homework # 4 (Canvas)- Solutions Name: Gower EMA 3066 Fall ’23 Question 1 5 / 5 pts Given the following polymers, predict whether they formed by a Step-Growth or Chain-Growth type of polymerization reaction: Fill in the blank with either SG or CG. A) Note, biochemists call these linkages, peptide bonds, but we know better, they are amide bonds. ;-) SG B) poly(vinyl alcohol): PVA CG C) Sulfonated Polyacrylic Acid Copolymer CG D) Polycaprolactone (PCL): a biodegradable polyester SG 92 pts

E) Polycaprolactone again, but now synthesized as shown below: CG Question 2 3 / 3 pts Given the 2 monomers shown below: A) What is the name of the –N=C=O functional group? isocyanate B) What type of linkage will be formed when they polymerize (ether, ester, amide, urethane, urea)? urethane C) What type of polymerization mechanism will it be, Step growth or Chain growth (Fill in blank with either SG or CG). SG Question 3 1 / 1 pts

Given the first step in a transesterification reaction shown below, what would be the leaving group that is removed from the end ‐ capped prepolymer to drive the reaction forward? A. CH 3 CH 2 OH B. HOCH 2 CH 2 OH C. CH 3 CH 2 CO 2 H D. HO 2 CCH 2 CH 2 CO 2 H E. HO(CH 2 ) 4 OH Question 4 2 / 2 pts For a chain addition polymerization, which would be better to use in the following circumstances, and inhibitor or retarder? A) Add to the monomer solution before transporting it by train to various labs. inhibitor B) Control the autocatalytic effect during the polymerization reaction. retarder Question 5 4 / 4 pts Answer true or false for the following statements regarding the kinetics of free radical polymerization : A) The rate of polymerization is considered approximately equal to the rate of propagation because most of the monomer is converted to polymer during this step of the reaction. true B) The rate equation assumes steady-state conditions, where the concentration of free radicals is assumed to be constant during this stage of the reaction, which occurs when r p = r t . false

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C) k d , the rate constant for disassociation of initiator, is much lower than k p , the rate constant for propagation. true D) Polyethylene must be synthesized under low pressure conditions, in order to slow the rate of propagation and avoid the Trommsdorff effect, enabling the formation of high M.W.. false Question 6 6 / 6 pts Fill in blanks with either increase or decrease: A) For free radical polymerization, an increase in initiator concentration will lead to a/an increase in the rate of polymerization and a/an decrease in the molecular weight. B) Because rate constants follow an Arrhenius relationship, an increase in temperature will cause a/an increase in all of the rate constants, but because the decomposition of initiator is rate limiting, the increase in initiator concentration will lead to a/an decrease in polymer M.W.. C) The typical polydispersity for a free radical polymerization is around 1.5, but chain transfer agents can cause a large decrease in the degree of polymerization, and a large increase in the PDI. Question 7 1 / 1 pts If measurements for a free radical polymerization determine that ξ is nearly equal to 2, that indicates that most of the chains were terminated by a ____ type of reaction. disproportiona Disproportionation Question 8 3 / 3 pts (Wikipedia) Polylactic acid, or polylactide (PLA), is a thermoplastic aliphatic polyester derived from renewable resources, such as corn starch (in the United States), tapioca roots, chips or starch (mostly in Asia), or sugarcane (in the rest of the world). In addition to its potential use as a biodegradable plastic, it is also a popular biomaterial due to the good biocompatibility of its degradation products (it degrades by hydrolysis back to lactic acid, a natural metabolic product

in the body). Some applications include biodegradable sutures, tissue engineering scaffolds, and drug delivery. Due to the chiral nature of lactic acid, several distinct stereoisomers of PLA exist: For example, poly-L-lactide (PLLA) and poly-D-lactide (PDLA) are the products resulting from polymerization of L-lactide and D-lactide monomers, respectively. The lactide monomer is an intermediate ring structure created as a dimer of two lactic acid mers. Polymerization of a racemic mixture of L- and D-lactides usually leads to the synthesis of poly- DL-lactide (PDLLA), although use of stereospecific catalysts can also lead to a heterotactic (alternating) PLA. As you might expect (analogous to the stereoisomers found in vinyl polymers), the degree of crystallinity, and hence degradation rate, is largely controlled by the ratio of D to L enantiomers used. This can be valuable for designing the time frame needed for the biomaterial to degrade (such as whether it is to be used as a suture or a tissue engineering scaffold, for example). A) What type of linkage is formed during polymerization of PLA? ester B) Predict which type of polymerization mechanism would produce a higher molecular weight PLA, condensation of polylactic acid monomers, or ring opening of lactide monomers? Fill in blank with underlined term(s). ring opening C) If PLA is polymerized to have all the same chirality (such as all D or all L), would it yield a polymer with the methyl side groups all on the same side of the chain, or on alternating sides of the chain? alternating sid alternating sides D) On an exam, I might ask you to sketch 5 repeats to illustrate your answer to part C).

Question 9 1 / 1 pts The following series of questions was written to all be in one question, parts A thru Q, but because Canvas won't show you which answers are incorrect, I separated them into numerous questions to make it easier to identify your mistakes. For this set A - Q, indicate whether the description corresponds better to a Step Growth or Chain Growth (Addition) polymerization mechanism, by filling in the blank with either SG or CG: A) Usually involves a small molecule leaving group SG Question 10 1 / 1 pts B) The propagation steps are not reversible CG Question 11 1 / 1 pts C) Usually requires some type of initiator CG Question 12 1 / 1 pts D) All species in the reaction pot are reactive SG Question 13 1 / 1 pts E) Chain transfer is a common problem CG Question 14 1 / 1 pts F) Some very long chains are formed early in the reaction CG Question 15 1 / 1 pts G) As a chain is growing, only monomer is being added during each propagation step CG Question 16 1 / 1 pts H) One has to carefully control stoichiometry of monomer reactants to ensure high MW. SG Question 17 1 / 1 pts I) The free radical polymerization fits in this mechanistic category.

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CG Question 18 1 / 1 pts J) A high degree of conversion is necessary to achieve high MW chains. SG Question 19 1 / 1 pts K) The polymers tend to contain more polar groups due to the types of linkages formed. SG Question 20 1 / 1 pts L) There is a gradual increase in chain length throughout the polymerization. SG Question 21 1 / 1 pts M) There is a gradual increase in the number of chains throughout the polymerization. CG Question 22 1 / 1 pts N) The condensation polymerization fits in this mechanistic category. SG Question 23 1 / 1 pts O) The polymerization represented as a reaction between AA-BB monomers fits in this mechanistic category. SG Question 24 1 / 1 pts P) Olefins and vinyl compounds are polymerized by this mechanism. CG Question 25 1 / 1 pts Q) The polymer molecular weight follows a statistical most probable distribution. SG

Chain Addition and Polymerization Practice Question 26: 2 / 2 pts For some of the following questions, where you are to make a decision on which type of chain growth reaction can be used, it is assumed you will use the chart I provided on pg 8 in the T8 notes. If you wanted to make a polymer out of this monomer: CH 2 =C(CH 3 )(OCH 2 CH 3 ), which type(s) of reaction would work for this monomer? Note- there can be more than one answer, depending on whether it fits in the “only” categories, or combinations categories. condensation polymerization free radical polymerization anionic polymerization cationic polymerization Ziegler-Natta polymerization This fits with Cationic only category because the monomer has e ‐ donating groups (CH3 and ether) attached. It fits with the table that lists CH 2 =C(R)OR, where I just added in the specific R groups of ‐ CH 3 and ‐ CH 2 CH 3 Question 27 : 2 / 2 pts If you wanted to make a polymer out of this monomer: CH 2 =C(CH 3 )(CONH 2 ), which type(s) of reaction would work for this monomer? Note- there can be more than one answer, depending on whether it fits in the “only” categories, or the combinations categories. condensation polymerization free radical polymerization anionic polymerization cationic polymerization Ziegler-Natta polymerization This fits with combined category of Anionic or Free radical, because the monomer has e ‐ withdrawing groups CONH 2 attached. It fits with the table that lists CH 2 =C(R)CONH 2 , where I just added in a specific R group of CH 3 . Question 28 : 2 / 2 pts

If you wanted to make poly(N-vinylpyrrolildone), which is a popular hydrogel for biomaterials applications, which type(s) of reaction would work for this monomer? Note- there can be more than one answer, depending on whether it fits in the “only” categories, or the combinations categories. condensation polymerization free radical polymerization anionic polymerization cationic polymerization Ziegler-Natta polymerization This can be found in the combined category of Cationic or Free radical, because the monomer has e ‐ donating groups of –NCO, and alkyl groups ‐ CH 2 CH 2 CH 2 ‐ attached. Question 29 : 2 / 2 pts If you wanted to make isotactic polypropylene, which type(s) of reaction would work for this monomer? Note- there can be more than one answer, depending on whether it fits in the “only” categories, or the combinations categories. condensation polymerization free radical polymerization anionic polymerization cationic polymerization Ziegler-Natta polymerization This requires some type of coordination catalyst, like ZN. Although ionic polymerizations can provide some type of coordination for stereochemical control, propylene does not have sufficient polarity (e ‐ donating or withdrawing character) to be prepared ionically. Recall I listed the “non ‐ polar” for the monomers under category of “Coordination or Supported metal oxide catalysts”. More specifically, propylene is an  olefin, which are on the bottom of the chart. Question 30 : 2 / 2 pts If you wanted to make a predominantly cis -isomer of a polyisoprene, which type(s) of reaction would work best? Note- there can be more than one answer, depending on whether it fits in the “only” categories, or the combinations categories. condensation polymerization free radical polymerization

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anionic polymerization cationic polymerization Ziegler-Natta (with metallocene catalyst) polymerization Anionic since it can provide coordination, and ZN (and metallocene, which is actually a subcategory of ZN) catalysts are used to control geometric isomers of polydienes, Question 31 : 5 / 5 pts Which of the following is/are true for anionic polymerization? (there can be more than one answer) It is commonly applied as a “living” polymerization The active site is a carbocation If the n-butyllithium initiator is used, the gegen ion is Li^+ It can be terminated with water or other proton containing molecules It is limited to monomers with electron withdrawing substituents Question 32 : 2 / 2 pts Fill in the blanks with one of the choices provided: In anionic polymerization, a more polar solvent will cause a (smaller or larger) larger distance between the gegen ion and carbanion, which will cause a/an (increase or decrease) increase in the rate of polymerization. Question 33 : 5 / 5 pts Which of the following is/are true for cationic polymerization? (there can be more than one answer). It is commonly applied as a “living” polymerization The active site is a carbocation A common initiator used for this is [BF3OH]-, which leads to a BF 3 gegen ion Termination can be caused by the gegen ion itself, which can grab a proton, or transfer a hydroxl to the chain end. It is limited to monomers with electron accepting substituents Question 34 : 7 / 7 pts Fill in the blanks with one of the offered choices within each set of parentheses:

For a Ziegler-Natta polymerization, an important benefit is that it enables the polymerization of (low medium high ) [1] density polyethylene. Another major value is that it can lead to ( stereospecific atactic branched) [2] polyolefins. A primary example is polypropylene, which without control of its tacticity, would have (brittle sticky strong) [3] properties. The ZN polymerization is a (homogeneous heterogeneous misogynist) [4] system that leads to a (narrow broad ) [5] polydispersity distribution. It is referred to as a (cooperation coordination directional) [6] polymerization because the monomer is directionally attached at a vacant orbital of the organo-metallic complex during chain propagation. Alternatively, it is also referred to as an ( insertion extraction inset) [7] polymerization because the monomer is inserted into the growing chain at the metal-carbon bond. ZN consists of a suspension of microparticles, making it heterogeneous, and leads to a high PDI because the nucleation event occurs at a variety of times due to the variable surface sites, and there is not any particular control over when termination occurs either (in contrast to anionic, where initiation starts all at once (most rapid step), and termination occurs via quenching with acid, so it is also all at once, enabling chain lengths to be nearly monodisperse). Question 35 : 1 / 1 pts Which polyethylene is prepared at relatively low temperature and atmospheric pressure? LDPE HDPE The way polyethylene was prepared before the discovery of ZN catalysts was at high T and P, and it led to a lot of branching and therefore low density; but ZN catalyst do not require the high pressure and reduce branching from chain transfer. Question 36 : 2 / 2 pts Which of the following polymerization processes are multiphase systems? (there can be more than one answer) Bulk (Neet) polymerization Solution polymerization Suspension polymerization Emulsion polymerization Question 37 : 4 / 4 pts Which of the following polymerization processes is/are most prone to Trommsdorf effect? (there can be more than one answer)

Bulk (Neet) polymerization Solution polymerization Suspension polymerization Emulsion polymerization Question 38 : 5 / 5 pts Fill in the blank with true or false for the following descriptions relating to Solution polymerization? true The purpose of the solvent is to lower viscosity and aid in heat removal. true Solvents are expensive and flammable, and usually require some recovery system. false The polymer yield per reactor volume is high since no water is used. false It provides a higher monomer concentration (relative to bulk) to give a lower Rp. true Chain transfer to solvent can occur, decreasing the average chain length. Question 39 : 9 / 9 pts Fill in the blank with the indicated letter for Suspension (S) versus Emulsion (E), or Neither (N) or Both (B): (only put an S, E, N, or B in the blank) S The reaction volume, although small, follows the same kinetics equations as for bulk (as in the equations derived for free radical provided in LN6 on chain addition). E One can simultaneously increase both the Rp and the DP of the polymer B Low yield per reactor volume E The product is often directly used as a latex N The product is high purity since no additives are used B The polymerizing particles are dispersed in water to aid in heat removal

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S The microparticles are not stable and can coagulate and gunk up the reactor in stagnant areas if one isn’t careful E Polyvinyl alcohol (PVS) helps to stabilize the "latex" suspension in water based paints