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Chapter 4: Polymer Structures ISSUES TO ADDRESS... • What are the general _____________________ characteristics of polymer molecules? • What are some of the ____________________ materials, and how do theyindiffer _________? • How is the ________ state polymers different from that in metals and ceramics ? Chapter 4 - 1 What is a Polymer? Poly many mer repeat unit repeat unit repeat unit repeat unit H H H H H H C C C C C C H H H H H H H H H H H H C C C C C C H Cl H Cl H Cl Polyethylene (PE) Poly(vinyl chloride) (PVC) H C H H H C C CH3 H H H C C CH3 H H C CH3 Polypropylene (PP) Adapted from Fig. 4.2, Callister & Rethwisch 4e. Chapter 4 - 2 Ancient Polymers • Originally _______________ were used – Wood – ________ – Cotton – Wool – _________ – Silk • Oldest known uses – Rubber balls ____________ – Noah used _______ (a natural polymer) for the ark Chapter 4 - 3 Polymer Composition Most polymers are _________________ – i.e., made up of H and C • Saturated hydrocarbons – Each _______ singly bonded to four other atoms – Example: • Ethane, C2H6 H H C H H C H H Chapter 4 - 4 Chapter 4 - 5 Unsaturated Hydrocarbons • _______________ somewhat unstable – can form new bonds – _______ bond found in ethylene or ethene - C2H4 H H C C H H – ______ bond found in acetylene or ethyne - C2H2 H C C H Chapter 4 - 6 Isomerism • ______________ – two _________ with same _______________ can have quite different structures for example: C8H18 • normal-octane H H H H H H H H H C C C C C C C C H = H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3 H H H H H H H H H3C ( CH2 ) CH3 6 • 2,4-dimethylhexane CH3 H3C CH CH2 CH CH3 CH2 CH3 Chapter 4 - 7 Polymerization and Polymer Chemistry • ______________ polymerization R + H H H H H H C C R C C H H monomer (ethylene) free radical R C C H H + initiation H H H H H H H H C C R C C C C H H H H H H propagation dimer • ________: example - benzoyl peroxide H C O O C H H H H 2 C O =2R H Chapter 4 - 8 Chemistry and Structure of Polyethylene Adapted from Fig. 4.1, Callister & Rethwisch 4e. Note: ___________ is a long-chain hydrocarbon - paraffin wax for candles is short polyethylene Chapter 4 - 9 Bulk or Commodity Polymers Chapter 4 - 10 Bulk or Commodity Polymers (cont) Chapter 4 - 11 Bulk or Commodity Polymers (cont) Chapter 4 - 12 VMSE: Polymer Repeat Unit Structures Manipulate and rotate polymer structures in 3-dimensions Chapter 4 - 13 MOLECULAR WEIGHT • Molecular weight, M: __________________________. Low M high M Not all chains in a polymer are of the same length — i.e., there is a distribution of molecular weights Chapter 4 - 14 MOLECULAR WEIGHT DISTRIBUTION Adapted from Fig. 4.4, Callister & Rethwisch 4e. total wt of polymer Mn = total # of molecules M n = Sxi Mi M w = Swi Mi Mi = ___________ molecular weight of size range i xi = __________________ of chains in size range i wi = __________________ of chains in size range i Chapter 4 - 15 Molecular Weight Calculation Example: average mass of a class Student Weight mass (lb) 1 104 2 116 3 140 4 143 5 180 6 182 7 191 8 220 9 225 10 380 What is the average weight of the students in this class: a) Based on the number fraction of students in each mass range? b) Based on the weight fraction of students in each mass range? Chapter 4 - 16 Molecular Weight Calculation (cont.) Solution: The first step is to sort the students into weight ranges. Using 40 lb ranges gives the following table: weight range number of students mean weight Ni Wi mass (lb) 81-120 121-160 161-200 201-240 241-280 281-320 321-360 361-400 2 2 3 2 0 0 0 1 110 142 184 223 380 total number SNi 10 SNiWi 1881 mass (lb) number Calculateweight the number and weight fraction fraction fraction of students in each weight xrange wi as follows: i NiWi Ni wi = xi = 0.2 Ni å NiWi å0.117 0.2 0.150 0.3 0.294 For example: for the 81-120 lb range 0.2 0.237 2 0 x 0.000 = 0.2 81-120 = 0 0.000 10 0 0.0002 x 110 = = 0.117 0.1 w 81-120 0.202 1881 total weight Chapter 4 - 17 Molecular Weight Calculation (cont.) weight range mean weight mass (lb) Wi mass (lb) 81-120 121-160 161-200 201-240 241-280 281-320 321-360 361-400 110 142 184 223 380 number fraction xi weight fraction wi 0.2 0.2 0.3 0.2 0 0 0 0.1 0.117 0.150 0.294 0.237 0.000 0.000 0.000 0.202 Mn = å xi Mi = (0.2 x 110 + 0.2 x 142 + 0.3 x 184 + 0.2 x 223 + 0.1 x 380) = 188 lb Mw = å wi Mi = (0.117 x 110 + 0.150 x 142 + 0.294 x 184 Mw = å wi Mi = 218 lb + 0.237 x 223 + 0.202 x 380) = 218 lb Chapter 4 - 18 Degree of Polymerization, DP DP = average number of ___________ per chain H H H H H H H H H H H H H C C (C C ) C C C C C C C C H DP = 6 H H H H H H H H H H H H Mn DP = m where m = average molecular weight of repeat unit for copolymers this is calculated as follows: m = Sfi mi Chain fraction mol. wt of repeat unit i Chapter 4 - 19 Molecular Structures for Polymers secondary bonding Linear Branched Cross-Linked Network Adapted from Fig. 4.7, Callister & Rethwisch 4e. Chapter 4 - 20 Polymers – Molecular Shape Molecular Shape (or ______________) – chain bending and twisting are possible by rotation of carbon atoms _____________________ – note: not necessary to _______________ to alter molecular shape Adapted from Fig. 4.5, Callister & Rethwisch 4e. Chapter 4 - 21 Chain End-to-End Distance, r Adapted from Fig. 4.6, Callister & Rethwisch 4e. Chapter 4 - 22 Molecular Configurations for Polymers _____________– to change must break bonds • _________________ H H C C H H H H R or C C R Stereoisomers are mirror images – can’t superimpose without breaking a bond C C H R B H H A A C C E E D D B mirror plane Chapter 4 - 23 Tacticity ________ – ____________ or spatial arrangement of R units along chain ________ – all R groups on same side of chain __________ – R groups alternate sides H H H H H H H H H H H R H H H R C C C C C C C C C C C C C C C C H R H R H R H R H R H H H R H H Chapter 4 - 24 Tacticity (cont.) _____ – R groups randomly positioned H H H H H R H H C C C C C C C C H R H R H H H R Chapter 4 - 25 cis/trans Isomerism CH3 H CH3 C C CH2 CH2 C C CH2 CH2 H cis trans cis-isoprene (natural rubber) trans-isoprene (gutta percha) H atom and CH3 group on ______ side of chain H atom and CH3 group on ________ sides of chain Chapter 4 - 26 VMSE: Stereo and Geometrical Isomers Manipulate and rotate polymer structures in 3-dimensions Chapter 74--19 27 Copolymers two or more monomers polymerized together • ______ – A and B randomly positioned along chain • __________ – A and B alternate in polymer chain • ________ – large blocks of A units alternate with large blocks of B units • _______ – chains of B units grafted onto A backbone A– B– Adapted from Fig. 4.9, Callister & Rethwisch 4e. random alternating block graft Chapter 4 - 28 Crystallinity in Polymers Adapted from Fig. 4.10, Callister & Rethwisch 4e. • Ordered atomic arrangements involving __________________ • Crystal structures in terms of ___________ • Example shown – ___________ unit cell Chapter 4 - 29 Polymer Crystallinity • Crystalline regions – thin _______ with chain folds at faces – ____________ structure Adapted from Fig. 4.12, Callister & Rethwisch 4e. 10 nm Chapter 4 - 30 Polymer Crystallinity (cont.) Polymers rarely _________________ • Difficult for all regions of all chains to become aligned crystalline region • Degree of crystallinity expressed as ___________. -- Some physical properties depend on % crystallinity. -- _________________ causes crystalline regions to grow and % crystallinity to increase. amorphous region Adapted from Fig. 14.11, Callister 6e. (Fig. 14.11 is from H.W. Hayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.) Chapter 4 - 31 Polymer Single Crystals • ___________________ – multilayered single crystals (chain-folded layers) of polyethylene • _____________ – only for slow and carefully controlled growth rates Adapted from Fig. 4.11, Callister & Rethwisch 4e. Chapter 4 - 32 Semicrystalline Polymers Spherulite surface • Some semicrystalline polymers form __________ structures • ________ chain-folded crystallites and amorphous regions • ________ structure for relatively rapid growth rates Adapted from Fig. 4.13, Callister & Rethwisch 4e. Chapter 4 - 33 Photomicrograph – Spherulites in Polyethylene ______________ light used -- a maltese cross appears in each ____________ Adapted from Fig. 4.14, Callister & Rethwisch 4e. Chapter 4 - 34