Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.

Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.

(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)

The chiral induction of polycarbodiimides through diastereomer formation

David Scott Schlitzer, University of Massachusetts Amherst


The cooperativity of polycarbodiimides was probed at several length scales. Each experiment relies on formation of a predominance of a single-handed helix due to diastereomer formation. Polymerization of N-(R)-2,6-dimethylheptyl-$N\sp\prime$-hexyl carbodiimide, 1 ( ($\alpha$) $\sb{365}$ = +7.6, c = 1.67, 20$\sp\circ$C, chloroform), gives poly-1. Poly-1 adopts a kinetically controlled conformation during the polymerization ( ($\alpha$) $\sb{365}$ = 7.5, toluene, 20$\sp\circ$C); this polymer adopts a thermodynamic conformation upon annealing (65$\sp\circ$C, 24h ( ($\alpha$) $\sb{365}$ = $-$159, toluene, 20$\sp\circ$C)) or through the addition of benzoic acid (5 eq. acid per polymer repeat unit) at ambient temperature (ca. 1 h ( ($\alpha$) $\sb{365}$ = $-$144, chloroform, 20$\sp\circ$C)). The polymerization of 1 with its enantiomer (60% ee of 1) displays majority rules behavior; this polymer displays the same optical and conformational properties as a poly-1. The protonation of poly-1 with a chiral acid, camphorsulfonic acid (CSA), shows a diastereomeric interaction between the acid and the polymer. The (R)-CSA shows a more favorable interaction with poly-1 ( ($\alpha$) $\sb{365}$ = $-$300, chloroform, 20$\sp\circ$C) than the (S)-enantiomer ( ($\alpha$) $\sb{365}$ = 24, chloroform, 20$\sp\circ$C). Both acids protonate the polymer to the same extent as evidenced by similar pHs for the two samples (pH = $-$0.8 for both samples in THF). Polycarbodiimides are basic due to the presence of a guanidine-like repeat unit in the polymer backbone. Optically inactive poly(di-n-hexyl carbodiimide) was induced to adopt a predominance of one handedness through chiral protonation of the basic guanidine repeat units with (S)-CSA. At a ratio of 8:1 polymeric repeats:(S)-CSA a strong divergence from linearity occurred giving the polymer a specific rotation greater than 250$\sp\circ$ (365 nm, 20$\sp\circ$C, chloroform). Varying the amount of chiral anion present while holding the total acid concentration fixed demonstrates that the chiral anion concentration is independently responsible for the chiral induction.

Subject Area

Polymers|Organic chemistry

Recommended Citation

Schlitzer, David Scott, "The chiral induction of polycarbodiimides through diastereomer formation" (1998). Doctoral Dissertations Available from Proquest. AAI9841921.