Chapter 4- Polymer Structures Chapter 4- Polymer Structures ISSUES TO ADDRESS... What are the basic • Classification? • Monomers and chemical groups? • Nomenclature? • Polymerization methods? • Molecular Weight and Degree of Polymerization? • Molecular Structures? • Crystallinity? • Microstructural features? TEM of spherulite structure in natural rubber(x30,000). • Chain-folded lamellar crystallites (white lines) ~10nm thick extend radially. MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 Polymer Microstructure Polymer Microstructure • Polymer = many mers • Covalent chain configurations and strength: More rigid Van der Waals, H Adapted from Fig. 14.2, Callister 6e. Polyethylene perspective of molecule Direction of increasing strength Adapted from Fig. 14.7, Callister 6e. A zig-zag backbone structure with covalent bonds MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 1 Common Examples Common Classification - Textile fibers: polyester, nylon… • Thermoplastics: polymers that flow more easily when squeezed, pushed, stretched, etc. by a load (usually at - IC packaging materials. elevated T). – Can be reheated to change shape. - Resists for photolithography/microfabrication. • Thermosets: polymers that flow and can be molded initially but their shape becomes set upon curing. - Plastic bottles (polyethylene plastics). – Reheating will result in irreversible change or decomposition. - Adhesives and epoxy. • Other ways to classify polymers. – By chemical functionality (e.g. polyacrylates, polyamides, - High-strength/light-weight fibers: polyamides, polyethers, polyeurethanes…). – Vinyl vs. non-vinyl polymers. polyurethanes, Kevlar… – By polymerization methods (radical, anionic, cationic…). – Etc… - Biopolymers: DNA, proteins, cellulose… MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 Common Chemical Functional Groups Common Hydrocarbon Monomers H H Alcohols Methyl alcohols Ethylene C C (ethene) H H H H Propylene C C = Ethers Dimethyl Ether H C H (propene) H H 1-butene Acids Acetic acid 2-butene trans cis Aldehydes Formaldehyde Acetylene H C C H (ethyne) Saturated hydrocarbons Unsaturated hydrocarbons Aromatic Phenol (loose H to add atoms) (double and triple bonds) hydrocarbons MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 2 Some Common Polymers Nomenclature Monomer-based naming: Common backbone with substitutions poly________ H H C C Monomer name goes here Polyacrylonitrile (PAN) H C e.g. ethylene -> polyethylene N Vinyl polymers (one or more H’s of ethylene can be substituted) if monomer name contains more than one word: H H H H poly(_____ ____) C C C C Monomer name in parentheses H X H X e.g. acrylic acid -> poly(acrylic acid) Note: this may lead to polymers with different names but same structure. H H H H H H H H … C C C C … … C C C C … H H H H H H H H polyethylene polymethylene MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 Polymerization Methods Polymerization Methods A. Free Radical Polymerization A. Free Radical Polymerization H H 2. Propagation C C H H 1. Initiation H H H H H H H H H Radical H H H H H H H H H R transferred R C C C C R C C C C R C C C C C C C C R C C H H H H H H H H H H H H H Free radical initiator H H H H H (unpaired electron) monomer H H R C C R H H R H H H C C 2 C C Both carbon atoms will sp carbons H change from sp2 to sp3. H H H H C C H H H σ bonds 3 sp carbon H π bond MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 3 Polymerization Methods Polymerization Methods Loses water B. Stepwise polymerization (condensation) A. Free Radical Polymerization 3. Termination O O O + H N C H N C R OH O H N C 2 2 + 2 R OH R OH R N C H H H H H H H O R C C + R R C C R H H H H Proteins (polypeptides have similar composition) O O H O H N C + (n-1) H H H H N H C R H H H H H H C Various R groups… n R C C + R C C R C C C C R R n H H H H H H H H C. Other methods Anionic polymerization, cationic Intentional or unintentional molecules/impurities can also terminate. polymerization, coordination polymerization… MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 Molecular Weights Number average molecular weight: N = # of polymer chains with length j ∑N jM j mo ∑N j j j Not only are there different structures (molecular arrangements) j j M = jm mass of polymer chain with length j Mn = j o …… but there can also be a distribution of molecular weights N = (m = monomer molecular weight). ∑ j ∑N j o (i.e. number of monomers per polymer molecule). j j N Note: ∑N jM j = Total weight ∑ j = Total # of polymer chains j j € Weight average€ molecular weight: 20 mers 16 mers 2 € ∑W jM j ∑N jM€j j j W N M Mw = = j = j j 10 mers ∑W j ∑N j M j j j 20 +16 +10 Average molecular weight = α€+1 M monomer =15.3M monomer ∑N jM j 3 In general: j M = If α = 0 then Mn If α = 1 then Mw € α This is what is called number average molecular weight. ∑N j M j j MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials € © D.D. Johnson 2004, 2006, 2007-08 € € 4 Molecular Weight: Different Notations Molecular Weights Why do we care about weight average MW? -some properties are dependent on MW (larger MW polymer chains can In Lecture Notes In Callister Textbook contribute to overall properties more than smaller ones). ∑N jM j Mn = ∑xiMi j i Mn = N Distribution of ∑ j polymer weights Ni NiMi j xi = wi = ∑N j ∑N j M j j j 2 € ∑N jM j € M j Examples – w = € Mw = ∑wiMi Light scattering: larger molecules scatter more light than smaller ones. ∑N j M j € i j Infrared absorption properties: larger molecules have more side groups and light absorption (due to vibrational modes of side groups) varies linearly with number of side groups. MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 € € Polydispersity and Degree of Polymerization Example 1 Mw Polydispersity: ≥ 1 Compute the number-average degree of polymerization for polypropylene, M given that the number-average molecular weight is 1,000,000 g/mol. n When polydispersity = 1, system is monodisperse. What is “mer” of PP? C3H6 € Degree of Polymerization: Mer molecular weight of PP is mo=3AC+6AH =3(12.01 g/mol)+6(1.008 g/mol) M n = 42.08 g/mol Number avg degree of polymerization nn = m o Number avg degree of polymerization Mw Weight avg degree of polymerization n 6 w = M n 10 g /mol m nn = = = 23,700 o m 42.08g /mol € o MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 € € 5 Example 2 (a, b, and c) Example 2 (cont.) A. Calculate the number and weight average degrees of polymerization and polydispersity for a polymer sample with the following distribution. B. If the polymer is PMMA, calculate number and weight average molecular weights. Avg # of monomers/chain Relative abundance 10 5 CH3 100 25 M if monomer is methylmethacrylate (5C, 2O, and 8H) | 500 50 w -CH2-C- 1000 30 So m = 5(12)+2(16)+8(1)= 100 g/mol 0 | 5000 10 50,000 5 CO2CH3 jN jN M m ∑ j j ∑ j j n = n = 0 = n m m N N M n = nnmo = 2860.4(100g /mol) = 286,040g /mol o 0 ∑ j j ∑ j j 5 *10 + 25 *100 + 50 * 500 + 30 *1000 + 10 * 5000 + 5 * 50000 M w = nwmo = 35,800(100g /mol) = 3,580,000g /mol = = 2860.4 5 + 25 + 50 + 30 + 10 + 5 M 3,580,000 Polydispersity: w = ~ 12.52 2 2 M n 286,040 ( jmo ) N j j N j M w 1 ∑ j ∑ j n = = = Note: m0 cancels in all these! w m m N ( jm ) jN € o o ∑ j j o ∑ j j 5 *102 + 25 *1002 + 50 * 5002 + 30 *10002 + 10 * 50002 + 5 * 500002 = = 35,800 5 *10 + 25 *100 + 50 * 500 + 30 *1000 + 10 * 5000 + 5 * 50000 € MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 MatSE 280: Introduction to Engineering Materials ©D.D. Johnson 2004, 2006, 2007-08 Example 2 (cont.) Sequence isomerism C. If we add polymer chains with avg # of monomers = 10 such that their relative abundance changes from 5 to 10, what are the new number For an asymmetric monomer and weight average degrees of polymerization and polydispersity? T H T H jN T H + T H T H H T M ∑ j j n = n = Add 5 more monomers of length 10 ….