Biologically Relevant Polymer PresentationPolyamides (Nylons) Commercial SynthesesNylon6,6Differences in Reactivity10.569 Synthesis of Polymers Prof. Paula Hammond Lecture 5: Interfacial Polymerizations, Application example: Polyamides Biologically Relevant Polymer Presentation Definitions of Biologically Relevant Polymers: • Enzymatically degradable – Polymer degrades through enzymatic breakdown in a biological (or ecological) environment (hydrolysis or oxidation catalyzed by enzyme). • Hydrolytically degradable – Polymer undergoes hydrolytic degradation without assistance from enzyme under biologic conditions – often accelerated by pH or pH/temperature. • Bioresobable or absorbable or resorbable – Polymer breaks down into remnants that are natural products readily absorbed into the body, resulting in complete loss of original mass. • Biocompatible – Polymer (degradable or not) does not cause a negative reaction or induce toxicity in the presence of or in contact with tissue, blood or organs Erdmann, L and K. E. Uhrich. “Synthesis and Degradation Characteristics of Salicylic Acid-derived Poly(anhydride-esters).” Biomaterials 21, no. 19 (2000): 1941-1946. Ikada, Y. and H. Tsuji. “Biodegradable Polyesters for Medical and Ecological Applications.” Macromolecular Rapid Communications 21, no. 3 (2000): 117-132. Poly α-hydroxyacids are hydrolytically degradable (PLLA, PDLA, PGA, PLGA) Poly(hydroxyalkanoates), poly(alkylene dicarboxylates) are enzymatically degradable Polycondensation of traditional monomer yields low molecular weight oligomer Polycondensation of cyclic monomer yields high molecular weight material Hydrophobic, hydrophilic nature determined by R groups For example, -CH2- groups affect hydrophobicity and make the polymer more difficult to degrade in water Stereochemistry affects crystallinity. Enzymatic breakdown dependent on ability of enzyme to adsorb to the PE macromolecule at appropriate sites. Aliphatic polyesters typically undergo enzymatic breakdown via esterases such as lipase (used in body to break down triacylglycerols to fatty acid and glycerol) Aromatic polyesters are too hydrophobic and too rigid to allow binding by enzyme. Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 course materials, MIT OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, DateLipases often ineffective on PEs with optically active center (PHB, PLLA, etc.) – PHA depolymerase effective in some cases, others require hydrolytic degradation or other enzymes. Factors in degradation rate: hydrophobicity, stereochemistry, bulkiness of side groups, and crystallinity. Manipulate with primary monomer structure, copolymerization. PGA, PLLA, PDLLA, and PCL have moderate glass transition temperature. Can create libraries of molecules: Anderson, D. G., D. M. Lynn, and R. Langer. “Semi-Automated Synthesis and Screening of a Large Library of Degradable Cationic Polymers for Gene Delivery.” Angew. Chem. Int. Ed. 42 (2003): 3153-3158. Polyamides (Nylons) Coin phrase by Dupont - Most common nylons: Nylon 6,6: 10.569, Synthesis of Polymers, Fall 2006 Lecture 5 Prof. Paula Hammond Page 2 of 4 Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 course materials, MIT OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date HNH2CH2CCOHNCO4n6 - aliphatic polyamides ⇒diamines + diacids NH2+HOCOKeq ∼ 10 – 100 (high rate of rxn) Commercial Syntheses 1) nH2NH2C NH36+HOCH2C COHO4conc'dH2OOCOH2C COO4H3NCH2NH36 pKa ∼ 9.0 pKa ∼ 5.0 “Nylon Salt” basic acidic Not nylon but precursorproton exchange salt - 50% wt concentration in H2O - Adjust pH of solution by titrating acid/base monomer ⇒ pH = 7.0 → stoichiometry r = 1.0 - If MW control desired, add monofunctional acid or amine 2) Salt solution concentration to a slurry - a concentrated solution containing particles (concentrated suspension) Raise T to ∼ 210oC, P = 250 psi (steam) Rxn proceeds at moderate rates (water → steam → …) 3) As np ↑, go to next stage: T ↑ to 275oC (above Tm of Nylons) P ↓ to 1 atm → reduces H2O ⇒ High MW with time/conversion ** One way to make a polyamide Nylon6,6 - 50% crystallinity - form flexible fibers: crystalline structures are strong good H-bonding - solvent resistance (Patagonia – clothing, carpets) Differences in Reactivity 1. HOOROOHROOOClOR ClOCl ClO diacids acid anhydride diacid chlorides phosgene (very reactive) (extremely reactive → poisonous) 2. Also very reactive 10.569, Synthesis of Polymers, Fall 2006 Lecture 5 Prof. Paula Hammond Page 3 of 4 Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 course materials, MIT OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, DateN C OisocyanategroupROHRNH2N COO RurethaneHNCOHNurethaneurea 3. HO R OH HO OHR NHRR'HN H2NR NH2 R = alkyl For highly reactive species: Ex: diacid chloride + diamine 10.569, Synthesis of Polymers, Fall 2006 Lecture 5 Prof. Paula Hammond Page 4 of 4 Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 course materials, MIT OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date + diol can treat these as irreversible Keq = 105 ∼ 108 → different reaction profiles and times - Kinetics can become diffusion controlled (stirring becomes more important) - Highly exothermic (high ΔH) - Need to consider heat transfer - Short reaction times (relative to diol + diacid) Most common: COCl+H2NCNHO+HClCOCl+OHCOO+HClN+OHC OHHNCOOno