The Fundamentals of Materials Science

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1 The Fundamentals of Materials Science An Introduction to Materials Science hapter 14: Polymer Structures Shengjuan Li

What are some of the common polymeric materials, and how do they differ chemically?

2 ISSUES TO ADDRESS... What are the general structural and chemical characteristics of polymer molecules? What are some of the common polymeric materials, and how do they differ chemically? ow is the crystalline state in polymers different from that in metals and ceramics? ermann Staudinger( ) 1953, Nobel prize. for his discoveries in the field of macromolecular chemistry 2

Most (poly)-(mer): polymeric materials (many)-(parts) are composed of

3 Most (poly)-(mer): polymeric materials (many)-(parts) are composed of very large molecular chains with Polysidegroups mer of various atoms (O, l, etc.) or organic groups many such repeat as unit methyl( 甲基 ), ethyl( 乙基 ), or phenyl( 苯基 ) groups. repeat unit Polyethylene (PE) 聚乙烯 l repeat unit l l Poly(vinyl chloride) (PV) 聚氯乙烯 Polypropylene (PP) 聚丙烯 3 repeat unit 3 3 Adapted from Fig. 14.2, allister & Rethwisch 8e. 3

4 Originally natural polymers were used - Wood Rubber - otton Wool - Leather Silk Oldest known uses Rubber balls used by Incas( 印加人 ) Noah( 诺亚 ) used pitch (rosin) (a natural polymer, waterproof) for the ark 4

5 Most polymers are hydrocarbons i.e., made up of and Saturated hydrocarbons Each carbon singly bonded to four other atoms Example: Ethane, 2 6 5

6 烷属化合物 6

7 Double & triple bonds somewhat unstable can form new bonds Double bond found in ethylene( 乙烯 ) or ethene Triple bond found in acetylene( 乙炔 ) or ethyne

8 Isomerism two compounds with same chemical formula can have quite different structures for example: 8 18 normal-octane( 正辛烷 ) A component of gasoline = ,4-dimethylhexane ( 二甲基己烷 ) 3 ( 2 ) Gas chromatographic analysis standard 8

9 Free radical polymerization R + R initiation free radical 自由基 monomer (ethylene) R + R propagation dimer 二聚体 Initiator: example - benzoyl peroxide ( 过氧化苯甲酰 ) O O 2 O = 2 R R and R ---represent organic groups such as 3, 2 5, and 6 5 (methyl 甲基, ethyl 乙基, and phenyl 苯基 ) 9

10 Adapted from Fig. 14.1, allister & Rethwisch 8e. Note: polyethylene is a long-chain hydrocarbon - paraffin wax for candles is short polyethylene 石蜡 10

11 聚乙烯聚氯乙烯聚四氟乙烯聚丙烯 11

12 聚苯乙烯聚甲基丙烯酸甲酯酚醛树脂 12

13 Bulk or ommodity Polymers (cont) 聚对苯二甲酸乙二醇酯聚碳酸酯 13

14 Molecular weight, M: Mass of a mole of chains. Molecular weights for high polymers may be in excess of a million. Low M high M Not all chains in a polymer are of the same length i.e., there is a distribution of molecular weights

15 M n totalwt. of polymer total#of molecules Mn x i M i Mw w i M i M i x i w i = mean (middle) molecular weight of size range i = number fraction of chains in size range i = weight fraction of chains in size range i 15

16 Example: average mass of a class(polymer) Student Weight (molecular) mass (lb,pound) What is the average weight of the students( molecules) in this class(polymer): a) Based on the number fraction of students in each mass range? b) Based on the weight fraction of students in each mass range? 16

17 Solution: The first step is to sort the students into weight ranges. Using 40 lb ranges gives the following table: weight number of mean number alculate weight the number and weight range students weight fraction fraction of fraction students in each weight N i W i x i range as follows: w i mass (lb) mass (lb) x i N i w i N iw i N i N i W i For example: 0.294for the lb range x x w total number N i N i W i total weight

18 weight mean number weight range weight fraction fraction Mn Mw x i M i mass (lb) mass (lb) (0.2 x x x x x 380) =188 lb w i M i (0.117 x x x x x 380) = 218 lb Mw w i M i 218 lb 18

19 DP = average number of repeat units per chain ( ) DP = 6 DP M n m where m average molecular weight of repeat unit. for copolymers this is calculated as follows : m f i m i hain fraction mol. wt of repeat unit i EXAMPLE PROBLEM

20 secondary bonding Linear Branched ross-linked Network Adapted from Fig. 14.7, allister & Rethwisch 8e. 20

21 Molecular Shape (or onformation) chain bending and twisting are possible by rotation of carbon atoms around their chain bonds note: not necessary to break chain bonds to alter molecular shape Adapted from Fig. 14.5, allister & Rethwisch 8e. 21

22 Bends, twists, and kinks. The end-to-end distance of the polymer chain r:this distance is much smaller than the total chain length. Some of the mechanical and thermal characteristics of polymers are a function of the ability of chain segments to experience rotation in response to applied stresses or thermal vibrations. Rotational flexibility is dependent on repeat unit structure and chemistry. 22

23 onfigurations to change must break bonds Stereoisomerism( 立体异构现象 ) R R R or Stereoisomers are mirror images can t superimpose without breaking a bond B A D E E D A B mirror plane 23

24 Tacticity stereoregularity or spatial arrangement of R units along chain 24 R R R R isotactic all R groups on same side of chain R R R R syndiotactic R groups alternate sides 全同立构间同立构

25 无规立构 atactic R groups randomly positioned R R R R 25

26 全同立构间同立构无规立构 Tacticities of vinyl polymers( 乙烯基聚合物 ) 26

27 cis cis-isoprene ( 异戊二烯 ) (natural rubber) atom and 3 group on same side of chain trans trans-isoprene (gutta percha 马来乳胶 ) atom and 3 group on opposite sides of chain 27

of A units alternate with large blocks of B units (homopolymer subunits) graft

28 two or more monomers polymerized together random A and B randomly positioned along chain alternating A and B alternate in polymer chain block large blocks of A units alternate with large blocks of B units (homopolymer subunits) graft chains of B units grafted onto A backbone A B random alternating block graft 28

29 Ordered atomic arrangements involving molecular chains rystal structures in terms of unit cells Example shown Polyethylene( 聚乙烯 ) unit cell Adapted from Fig , allister & Rethwisch 8e. 29

30 rystalline regions thin platelets with chain folds at faces hain folded structure 10 nm 30

Polymers rarely 100% crystalline Difficult for all regions of all chains to become aligned Degree of crystallinity expressed as % crystallinity. -- Some physical properties depend on % crystallinity.

31 Polymers rarely 100% crystalline Difficult for all regions of all chains to become aligned Degree of crystallinity expressed as % crystallinity. -- Some physical properties depend on % crystallinity. -- eat treating causes crystalline regions to grow and % crystallinity to increase. crystalline region amorphous region Adapted from Fig , allister 6e. (Fig is from.w. ayden, W.G. Moffatt, and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.) 31

32 Electron micrograph multilayered single crystals (chain-folded layers) of polyethylene Single crystals only for slow and carefully controlled growth rates Adapted from Fig , allister & Rethwisch 8e. 32

33 Spherulite surface 缚结分子 Some semicrystalline polymers form spherulite structures Alternating chain-folded crystallites and amorphous regions Spherulite structure for relatively rapid growth rates Adapted from Fig , allister & Rethwisch 8e. 33

34 聚乙烯 ross-polarized light ( 正交偏光 )microscope used -- a maltese cross appears in each spherulite 马尔他十字 Adapted from Fig , allister & Rethwisch 8e. 34

35 Transmission electron micrograph(tem) showing the spherulite structure in a natural rubber specimen. hain-folded lamellar crystallites approximately 10 nm thick extend in radial directions from the center; they appear as white lines in the micrograph. 30,000. Spherulite structure in a natural rubber 35

Thermoplastics polymers: soften when heated (and

are totally reversible and may be repeated.

poly(ethylene terephthalate) 聚对苯二甲酸二乙酯 (PET),poly(vinyl

temperature is raised, TPR secondary bonding forces are

36 Thermoplastics polymers: soften when heated (and eventually liquefy) and harden when cooled processes that are totally reversible and may be repeated. Examples :polyethylene 聚乙烯 (PE), polystyrene 聚苯乙烯 (PS), poly(ethylene terephthalate) 聚对苯二甲酸二乙酯 (PET),poly(vinyl chloride) 聚氯乙烯 (PV), polycarbonate 聚碳酸酯 (P),and,polyurethane 聚氨酯 (PU). Thermal Plastic Rubber On a molecular level, as the temperature is raised, TPR secondary bonding forces are diminished (by increased molecular motion) so that the relative movement of PET PU adjacent chains is facilitated when a stress is applied P PE 36

Thermosetting polymers are network polymers.

rubbers 硫化橡胶, epoxy 环氧树脂, and phenolics 酚醛塑料 and some polyester resins

Network polymers have covalent crosslinks between adjacent molecular chains.

37 Thermosetting polymers are network polymers. They become permanently hard during their formation, and do not soften upon heating. Most of the crosslinked and network polymers, which include vulcanized rubbers 硫化橡胶, epoxy 环氧树脂, and phenolics 酚醛塑料 and some polyester resins 聚酯树脂, are thermosetting. Network polymers have covalent crosslinks between adjacent molecular chains. During heat treatments, these bonds anchor the chains together to resist the vibrational and rotational chain motions at high temperatures. Thus, the materials do not soften when heated. polyester resins Epoxy coating phenolics 37

38 38

39 全同立构间同立构不规则立构 39

40 Final exam: Monday, the week after next (April 24 th ), 9:55-11:55 First School Building, Room? Exam way: lose-book with no notes allowed. Blanks Glossary rystallographic orientations and planes Answer questions alculations Phase diagrams... 40

41 Adhere to every day, there will be progress! Try everything!!!!

Chapter 5: Structures of Polymers

Chapter 5: Structures of Polymers hapter 5: Structures of Polymers ISSUES TO ADDRESS... What are the general structural and chemical characteristics of polymer molecules? What are some of the common polymeric materials, and how do they