P849: Physical chemistry pedagogy via macromolecules: Polymer blend thermodynamics and ionic polymerization kinetics

Author: Sianna Bates, Northeastern State University, USA

Co-Author: Brittney Rogers and Carl Aronson, Northeastern State University, USA

Date: 8/6/14

Time: 2:05 PM2:25 PM

Room: MAN 123

Related Symposium: S56

Within an undergraduate physical chemistry course sequence, macromolecules are routinely isolated and treated as a group of materials with specialized structure, size, dynamics, and self-assembly properties. Nevertheless, polymeric materials can be incorporated into the natural flow of the course and utilized to illustrate both thermodynamic properties and chemical reaction kinetics in the laboratory and lecture. Polymer blends were synthesized within the laboratory course portion wherein the composition dependence of the resulting blend’s glass transition temperature was measured using differential scanning calorimetry. Varying the macromolecular architecture allowed students to gauge the overall accessibility of functional groups involving a thermodynamic competition between hydrogen bonding and steric hindrance. In a separate application, anionic polymerization has been used to extend the lecture course portion on the kinetics of complex reaction mechanisms. Living anionic polymerization provides a mechanistic pathway to vary macromolecular architecture. Although commonplace in research, anionic polymerization lab techniques remain challenging due to the inherent air and moisture sensitivity of the reaction. Student generated computational pedagogical kinetic modeling of living anionic homopolymerization has been used to investigate the effects of temperature and impurity concentration on molecular weight and polydispersity. Arrhenius energetics were included for each mechanistic step. Thermodynamics governing the dissociation equilibrium constant between propagating free ions and ion pair chain ends was modeled using the van’t Hoff equation. The kinetic model allowed for identity changes in monomer, solvent, initiator, and counter cation as well as impurity concentration. The initial model was extended to compute the kinetics of sequential addition anionic block copolymerization.

P702: Use of GOB content in the introduction of organic chemistry to medical laboratory science majors

Author: Carl Aronson, Northeastern State University, USA

Co-Author:

Date: 8/6/14

Time: 10:15 AM10:35 AM

Room: LOH 164

Related Symposium: S41

Registered medical laboratory scientists (MLS) are rigorously trained in the technology of clinical laboratory medicine. MLS professionals perform diagnostic tests to assist physicians and are conventionally employed in hospital settings. Grounding in the fundamentals of organic chemistry remains a prerequisite for MLS students studying clinical chemistry. Challenges to teaching selected organic chemistry elements to MLS students include centering on topics critical to the ultimate understanding of analytical biochemistry. The preponderance B.S. medical laboratory science majors at Northeastern State University begin as professional A.S. degreed medical laboratory technicians wherein laboratory practice is completed within their clinical employment setting and academic coursework is completed online. An online course in the essentials of organic chemistry encompassing bonding, acid-base equilibria, solubility, nomenclature, structure, elementary reactions, and stereochemistry of organic compounds was created for the primary purpose of teaching organic chemistry to MLS students. Within the online organic essentials course, additional introduction to organic structure/function is given using carbohydrates, lipids, proteins, nucleic acids, membrane osmosis, and energy metabolism using digital media as well as an instructional online homework/examination system. Due to the simultaneous employment-online MLS degree coursework combination, judicious choice of content and instruction level has led to full utilization of a GOB textbook for the essentials of organic chemistry course during the past four years. Students finishing the GOB based organic essentials course have shown efficient entree into the clinical chemistry course sequence of the MLS degree program in evidence-based laboratory medicine centered on symptomatic biochemical analytes and pathophysiology.

P553: Physical chemistry pedagogy via macromolecules: Solvent diffusion from polymer solutions with lyotropic liquid crystalline capability

Author: Sianna Bates, Northeastern State University, USA

Co-Author: Brittney Rogers and Carl Aronson, Northeastern State University, USA

Date: 8/5/14

Time: 3:40 PM4:00 PM

Room: ASH 2302

Related Symposium: S23

Within an undergraduate physical chemistry course sequence, polymers are routinely isolated and treated as a group of materials with specialized structure, size, dynamics, and self-assembly properties. Nevertheless, macromolecular chemistry can be incorporated into the natural flow of the course and utilized to illustrate thermodynamic principles in the laboratory such as chemical potential gradients in non-equilibrium dynamics involving diffusion. In focusing on pedagogy specific to phenomenological transport fluxes and forces, thin films of either functionalized cellulose or poly(n-alkyl isocyanate) solutions were juxtaposed against air in a diffusion couple geometry at room temperature. The solvent was allowed to diffuse away and evaporate from the solution in a controlled manner. The diffusion couple geometry produced a uniform film for optical assessment of liquid crystalline potential between crossed polarizers. After an induction period, a stable microstructure developed in which the interior of the sample remained isotropic followed by a liquid crystalline band, with characteristic disclination defects and texture, followed by a crystalline band nearest to the external surface. The width of the total characteristic birefringent band was measured over time and provided information concerning the dynamics and trajectory of solvent transport and evaporation from the cover slip edge. The apparent solvent diffusion coefficient for each system was measured at room temperature as a function of initial polymer concentration. Diffusion couple optical microscopy data from the physical chemistry teaching laboratory were compared to engineering literature data concerning rheological characteristics as well as finite difference calculations in order to validate the observed concentration dependence of diffusion.

P122: Case studies of historical research challenges in organic chemistry: Development of cationic polymerization

Author: Carl Aronson, Northeastern State University, USA

Co-Author: Rebecca McFarland, Northeastern State University, USA

Date: 8/4/14

Time: 11:30 AM11:50 AM

Room: LMH 176

Related Symposium: S3

The conventional series of lectures in undergraduate organic chemistry tend to follow a progression of archetypical textbook transformations described under optimized conditions. Hence, significant challenges encountered by a plethora of chemists while spearheading groundbreaking research may be vastly underestimated by many undergraduate students. Nevertheless, extending conventional lectures by studying the historical research sequence using case studies can allow the student to more deeply appreciate both total synthesis and methodology. The case of cationic polymerization is initially introduced during the addition reactions of alkenes. Although strong protonic acids appeared to be a viable option, significant hurdles to the efficient synthesis of high molecular weight materials included suppressing chain termination via covalent bond formation between the carbocation and nucleophilic conjugate base anion. Hence, strong protonic acid initiators with large conjugate bases of significantly diminished nucleophilicity were used initially in order to prevent termination. A pedagogical computational kinetics algorithm was generated by physical chemistry students using system dynamics software in order to model the cationic polymerization of styrene initiated by trifluoromethanesulfonic acid. Arrhenius energetics were included for initiation, propagation, transfer to monomer, spontaneous transfer, and termination mechanistic steps as well as the dissociation equilibrium constant between propagating ion pairs and free ions. Cationic propagation was monitored in order to compute molecular weight over time as a function of reaction temperature and compared to literature data. The model was expanded to potentially include a variety of monomers by considering the Mayr scale for nucleophilicity and electrophilicity in the calculation of rate constants.