Introducing Polymer Chemistry into an Undergraduate Chemistry Curriculum Dr. Laura Kosbar IBM T.J. Watson Research Center ACS CPT Committee

Introductions  Why is this person talking to us about teaching polymers?  Three hats  Practicing (polymer) chemist with 30+ years experience in industry (IBM Research)  Worked in industry for 4 years after BS – convinced me to go into polymers  Perspective on how polymer chemistry is used by practicing chemists  Member of CPT for ~6 years  Participated in crafting new macro/supra/meso/nano (MSN) requirement  Teaching experience as a visiting and adjunct professor (Colorado School of Mines and State University of New York – New Paltz)  Recently developed/taught polymer course for undergraduates

ACS Guidelines  The MSN requirement: Principles that govern macromolecular, supramolecular, mesoscale and nanoscale systems must be part of the certified curriculum Preparation, characterization and physical properties Two of the following four: synthetic polymers, biological macromolecules, supramolecular, meso- or nanoscale Material (equivalent to approximately one-fourth of a standard semester course) can be taught As part of a required stand-alone course Distributed throughout required curriculum

My top 10 list of what chemists should know about polymers (suggestions): 1)Anatomy of a polymer (Any) 2)Polymer synthesis and kinetics (condensation, free radical, anionic/cationic polymerization, etc.) (O, I, P) - Reaction mechanisms (chain growth vs step growth) and extent of reaction -Implications on statistical size distribution -Influence of catalysts on stoichiometry 3)Molecular weight and molecular weight distribution (O, P, any) - Critical entanglement length – why length matters 4)Crosslinking and its implications (O, P) 5)Polymer “phases” and phase transitions (A, P) -“Crystalline” vs amorphous polymers -Glass transition temperature 6) Instrumental techniques used to evaluate polymer properties (GPC, light scattering, DSC, TMA, TGA, DMA, etc.) (A) 7)Rheology – non-Newtonian polymer properties (P) 8)Phase separation with polymers - like dissolves “exactly” like (P) - Thermodynamic influences when entropy is restricted 9)Interactions w/small molecules – dissolution, diffusion, swelling, and plasticizing - Polymers in solution 10) Bio-based polymers (B) – Not-exactly random coils - Structure vs function

My top 10 list of what chemists should know about polymers (suggestions): 1)Anatomy of a polymer (Any) 2)Polymer synthesis and kinetics (condensation, free radical, anionic/cationic polymerization, etc.) (O, I, P) - Reaction mechanisms (chain growth vs step growth) and extent of reaction -Implications on statistical size distribution -Influence of catalysts on stoichiometry 3)Molecular weight and molecular weight distribution (O, P, any) - Critical entanglement length – why length matters 4)Crosslinking and its implications (O, P) 5)Polymer “phases” and phase transitions (A, P) -“Crystalline” vs amorphous polymers -Glass transition temperature 6) Instrumental techniques used to evaluate polymer properties (GPC, light scattering, DSC, TMA, TGA, DMA, etc.) (A) 7)Rheology – non-Newtonian polymer properties (P) 8)Phase separation with polymers - like dissolves “exactly” like (P) - Thermodynamic influences when entropy is restricted 9)Interactions w/small molecules – dissolution, diffusion, swelling, and plasticizing - Polymers in solution 10) Bio-based polymers (B) – Not-exactly random coils - Structure vs function

2 - Polymer Synthesis and Kinetics (O, I, P)  Reactions to synthesize polymers similar/identical to small molecule analogs, but differences in conditions/considerations  Condensation reactions  Extent of reaction – at 90% extent or rxn, chains only ~10 monomers, at 99%, 100 monomers, at 99.9%, 1000 monomers  How do you push rxns to these limits?  Stoichiometry – will limit chain growth  Broad MW distribution  Addition reactions (radical, cationic, anionic)  Reaction conditions impact properties/use of polymer  Influence of catalysts on polymer linearity and stereochemistry  Same polymer (e.g. PE) can be synthesized by different methods – has different properties  “Living” polymerizations  High MW, low MW distribution

3 - Molecular weight (MW) and molecular weight distribution (MWD) (Any, O, P, A)  MW for polymers is ~2K - > 100 M (DNA)  Why does length matter?  Intra-molecular interactions and entanglements…  Affects material property and behavior  Strength (especially strength-to-weight)  Toughness  Viscosity (pure or in solution - even at low concentrations)  Solubility  Ways to define MW – M n vs M w  Techniques for determining M n and M w  MWD – not all polymers are created the same size  MWD (M w /M n ) varies dramatically depending on synthetic reaction and reaction conditions  Impacts the properties of the polymer  Short polymers don’t get entangled  Long polymers very viscous

5 - Polymer “phases” and phase transitions (A, P)  Amorphous, “glassy” phase  “Solid Liquid”  Glass transition temperature (T g )  Really a temperature range…  Energy for segmental motion, flow  Crystalline phase  Really “microcrystalline” regions – act as “crosslinks”  “Liquid Solid” – solid that is (well) above its T g  Degree of crystallinity often dependent on synthesis conditions  It’s all about stereochemistry and order  High vs low density polyethylene  External manifestations – opacity and toughness Intra-molecular chain folding Intra- or inter-molecular crystals

7 - Rheology – non-Newtonian polymer properties (P) How the world changes when you go from couscous to spaghetti…  Pseudoplastic behavior of polymers (shear thinning)  Polymer chain extends in direction of flow, reduces entanglements and viscosity  Dilatant behavior of polymers (shear thickening)  Polymers with transient “crosslinks” (crystallinity, non-covalent interactions)  Easily demonstrated non-Newtonian flow properties  Rod climbing – entanglements  Extrusion – deformation from random coil  Siphon effects – used for oil pipelines

9 - Interactions of polymers with small molecules (P, A)  It is not as easy as you might think, and it is all about entropy vs enthalpy…  Polymers in solution  What is an “ideal” solution for a polymer?  Redefine Raoult’s Law  Forming solutions – reduction in the influence of entropy….  “Good” and “bad” solvents – what does it mean for the polymer coil?  Diffusion and swelling  Crosslinked polymers can’t dissolve, but they can take up small molecule  Chemical “compatibility” of gloves  Plasticization  The difference between PVC plumbing pipes and ponchos

Making and working with Polymers – Examples of Laboratory Experiments  Polymer synthesis – relatively easy (and fun), many options  Condensation – ex. - nylon 6,6  Free radical – ex. - PMMA, PS  Cationic – ex. - PS  Oxidative – ex. - Polyaniline  Molecular weight determination (HPLC w/GPC columns and/or viscometry)  Use PS and PMMA samples from synthesis lab as well as commercial samples  Polymer properties (DSC, TGA)  Glass transition temperature (student synth nylon compared to commercial sample)  Degradation temperature(s) or commercial or student synth. polymers  Crosslink density of rubber by solvent swelling  Non-Newtonian properties of polymers  Siphoning, die swelling on extrusion, and rod climbing  Shear thickening

Examples from Industry: Soldermask degradation  Issue: discoloration of top coating (soldermask) on printed circuit boards during accelerated electrical testing 140 ° C 1A, 1 st discolor hrs 12.3 hr 7hr 3hr 2hr 1hr Standard cure Absorbance with aging at 200°C Arrhenius plot Absorbance vs time/temperature  Absorbance increased linearly with time, rate increased with temperature  Determined that unreacted crosslinking agent was continuing to degrade/react  Polymer T g increased with increased crosslinking, as did stiffness, likelihood of fracture Stress/strain at 120°C ambient Tan delta (related to T g ) vs temp

Examples from Industry: The Chemistry of Patterning Microelectronic Chips

Examples from Industry: Using Bio-based materials to replace common polymers Printed wiring boards (PWB)– epoxy/fiberglass composites

1 - Anatomy of a Polymer (Any, O, P)  Some key ideas:  How is a polymer different from a large non-polymeric molecule?  Monomers  Polymers  Length matters…  Polymer structures, and impacts on function  Linear, Branched, Crosslinked, Ladder  “Extra” states of matter  Glass, gel  Classes of polymers  Thermoplastic vs thermosetting  What’s in a name (and how many names can one molecule have)?  Why are these important?  Basic concepts needed to distinguish and discuss polymers  Introduces concepts of structural differences from small molecules as well as different solid states

4 - Crosslinking and its implications (O, P)  Monomers with at least 3 reactive sites can generate branched or crosslinked polymers  Can have huge MW – a rubber ball could be effectively ONE molecule  “Thermosetting” polymers – intractable once formed  Short/stiff links between crosslinks – resins  Hard, strong, inflexible, brittle – epoxys  Longer/flexible chains between crosslinks – rubbers or gels  Soft, flexible, tough, strong  Properties impacted by degree of crosslinking  Can determine chain length between crosslinks from polymer swelling

6 - Instrumental techniques used to evaluate polymer properties (A)  Molecular weight  Gel permeation chromatography (GPC)  Can be performed with HPLC with GPC columns  Determines both M n and M w  Light scattering (specialized, expensive equipment)  Viscometry  End group analysis  Physical properties of polymers  DSC – Differential Scanning Calorimetry  Glass and crystalline transition temperatures  TGA – Thermogravimetric Analysis  Chemical degradation temperatures  TMA – Thermomechanical Analysis  Glass transition temperatures, coefficient of thermal expansion, etc.  DMA – Dynamic Mechanical Analysis  Stress-strain, fracture toughness, etc.

8 - Phase separation with polymers - like dissolves “exactly” like (P)  Impacts of intramolecular interactions in an entropy limited system  Covalent bonding reduces number of possible configurations, reduces entropic states  Very difficult to form homogeneous mixtures of even chemically similar polymers  Often difficult to form homogeneous mixtures with small molecules that would be compatible with the polymers precursors (monomers)

10 - Biopolymers – formation, structure and function (B, O)  Types of biopolymers (DNA, RNA, proteins, carbohydrates, lignin, chitin, etc.)  Impacts of intra- and inter-molecular interactions in  Shape – modifications from “random” coils  Function – especially how shape influences function  Ordering in (most) biopolymers compared to disorder in (most) synthetic polymers  Synthetic pathways  Impacts of H bonding and other inter-molecular interactions