Advanced Polymer Chemistry

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1 Advanced Polymer Chemistry 1) George Odian, Principles of Polymerization, 4 th Edition, Wiley- Interscience, ) 投影片講義 anced Polymer Chemistry 3) 成績計算 : 期末報告 : 50% 期末考 : 50% 2017 年 2 月 24 日 ~6 月 23 日上課時間 : 星期五 09:10~12:00 (93420 教室 ) 1 Chapter 1. Introduction Polymers ( 高分子 ) are macromolecules built up by the linking together of large numbers of much smaller molecules (monomers: 單體 ). * Scope of polymer science 1)Polymer synthesis: Organic chemistry 2)Polymer physics: Physical chemistry 3)Polymer processing: Fluid mechanics, Heat transfer, Mass transfer * Raw materials of polymers: Most synthetic polymers are derived from petrochemicals, such as ethylene, propylene and butadiene. May be derived from shale oil ( 頁岩油 )or shale gas ( 頁岩氣 ) in the future. * History of polymer science * Future trend of polymer science: 1) Functional polymers 2) High-performance polymers 2 1

2 Synthesis ( 合成 ) Process ( 製程 ) Processing ( 加工 ) Step Polymerization: Solution Injection molding Polycondensation Bulk Extrusion Polyaddition Interfacial Compression molding Addition-Condensation Emulsion Blow molding Radical Chain Polym. Suspension Calendaring Ionic Chain Polymerization: Dispersion Coating Anionic Polym. Precipitation Transfer molding Cationic Polym. RIM Ring-Opening Polymerization Coordination Polymerization Copolymerization (Chain) Polymer Reaction 3 平均分子量及其量測 The molecular weight of a polymer is of prime importance in its synthesis and application. The minimum useful MW, usually in the range of 5000~10000, differs for different polymers. Polymers are polydisperse ( 多分散 ) or heterogeneous in MW. Average MW and the exact distribution (MWD) are required to fully characterize them. 4 2

3 Number-average molecular weight (M n ) Simple average of molecular weight by counting the number of molecules. Absolute methods of determination: * End-group analysis, other colligative property measurements. * Colligative properties: Osmotic pressure. /c = RT[(1/M n ) + A 2 c + A 3 c 2 + ] 5 Relative Method: GPC or solution viscosity Molecular Weight and MWD by Gel Permeation Chromatography (GPC) [Size Exclusion Chromatography (SEC)] 6 3

4 The melt flow index (MFI, 熔融指數 ) is a measure of the ease of the melt of a thermoplastic polymer. It is defined as the mass of polymer, in grams, flowing in 10 minutes through a capillary of a specific diameter and length by a pressure applied via prescribed gravimetric weights for prescribed temperatures. Melt flow rate (MFR = MFI) is an indirect measure of molecular weight, with high melt flow rate corresponding to low molecular weight. At the same time, melt flow rate is a measure of the ability of the material s melt to flow under pressure ( 加工性 ). 7 Dependence of Polymer Properties on MW Many polymer properties of interest (T g, modulus, tensile strength, etc.) follow a peculiar pattern with increasing MW. Small molecules have small values, then there is a sharp rise in properties as the chains grow to intermediate size (oligomers: 寡聚物 ), and then the properties level off as the chains become long enough to be true polymers. However, a few properties important for polymer processing, like melt viscosity and solution viscosity, increase monotonically with MW. This means that the goal of polymer synthesis is not to make the largest possible molecules, but rather to make molecules large enough to get onto the plateau region. Increasing the MW beyond this does not improve the physical properties much, but makes processing more difficult. 8 4

5 CH 2 =CH 2 CH 3 (CH 2 ) 4 CH 3 CH 3 (CH 2 ) 28 CH 3 -(CH 2 CH 2 ) n - gas liquid wax crystalline solid Mechanical Property S = S (A/M) Oligomer UHMW Melt Viscosity S Polymer Low MW Molecular Weight 9 Physical State: Thermal Transitions of Polymers Polymers can be classified according to their thermophysical behavior. Those which soften and flow upon heating are termed thermoplastic ( 熱可塑性 ); those which do not are called thermosetting ( 熱固性 ) polymers. Glass transition temperature (T g ): polymer properties change from a glass to a rubbery material. Free volume of the polymer increases above T g. Melting temperature (T m ): change from solid to liquid. 10 5

7 Morphology: describes the arrangement/type of order assumed by polymer chains. 13 Glass Transition Temperature (T g ) T g : Temp of onset of segmental motion (segments ~5-20 atoms; heat capacity changes here). For an amorphous polymer, the T g reports the minimum processing temperature. The T g is strongly dependant on polymer structure (including stereochemistry), and ranges from far below 0 C for very flexible chains, and above 400 C for very stiff chains. The transition is detectable by a variety of methods, including Differential Scanning Calorimetry (DSC), Differential Thermal Analysis (DTA), and Thermal-Mechanical Analysis (TMA). Note that some authors report the T g as the onset temperature (i.e., the beginning of the range), while others report the midpoint of the range. 14 7

9 Structural Factors Effecting T g : * Increased chain backbone rigidity * Bulky R groups (pendant groups) * Increased interaction between chains * Molecular weight, up to a point then no effect Flory-Fox equation: Fox equation: 17 Melting Temperature (T m ) The temperature (actually a narrow range of temperatures) at which the ordered regions of a crystalline polymer melt, similar to a small molecule. Crystallization is essential for many high-performance polymers because it greatly increases the strength of the material. Like the T g, the T m is detectable by DSC, DTA, TMA, and other techniques. Factors Effecting T m : G m = H m T m S m = 0 Strength of intermolecular forces Structural rigidity, structural regularity Crystallinity Type/Structure T m = H m / S m Perfection of crystalline domains 18 9

10 Decomposition Temperature (T d ) The temperature above which chemical degradation occurs. This temperature is conveniently measured by Thermogravimetric Analysis (TGA), a technique in which one simply weights the sample continuously while heating it. Once decomposition begins, small molecular fragments are released which distill away, and the sample loses weight. 19 Solubility Parameter ( ): 溶解參數 * Hildebrand: E coh = H vap RT (Cohesive energy) CED = E coh /V (Cohesive Energy Density) = (CED) 1/2 (Solubility Parameter) * Solubility: G mix = H mix -T S mix < 0 S mix = -R[n 1 ln 1 + n 2 ln 2 ] > 0 No specific chemical interactions: H soln = V m 1 2 ( 1-2 ) 2 0 1, 2 : volume fractions of 1,

11 溶劑之溶解參數 ( ) (cal/ml) 1/2 n-hexane n-octane Cyclohexane Benzene Toluene Acetone Methylethylketone (MEK) Methyl acetate Ethyl acetate Butyl acetate Tetrahydrofuran (THF) Methanol Ethanol n-butanol Water 高分子之溶解參數 ( ) (cal/ml) 1/2 Plastics Diacetylcellulose PVAc PVC Polychloroprene Polystyrene Polyethylene Polyisobutylene Teflon 高分子之的實驗求法 22 11

12 Types of Polymers: There are many types of polymers including synthetic and natural polymers. Natural polymers include: * Proteins - silk, collagen, keratin. * Carbohydrates - cellulose, starch, glycogen * DNA RNA * Others: rubbers and silicones Classification of Polymers: Homopolymers ( 均聚合物 ): Copolymers ( 共聚合物 ): Addition Polymers ( 附加高分子 ): Condensation Polymers ( 縮合高分子 ): Thermoplastics: polyethylene (PE), polystyrene (PS), poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET), Thermosets: epoxy, natural rubber (NR), SBR, NBR, Plastics: PE, PS, PP, PVC, PET, Nylon Rubbers: NR, SBR, NBR Fibers: PET, Nylon, PP 23 Polymers are macromolecules built up by linking together of large numbers of smaller molecules (monomers). Types of Polymers and Polymerizations Composition & Structure: Carothers (1929) (Table 1-1 & 1-2) Condensation polymers ( 縮合高分子 ): (1) Its synthesis involves the elimination of small molecules, or (2) contains functional groups as part of the polymer chain, or (3) its repeating unit lacks certain atoms that are present in the (hypothetical) monomers to which it can be degraded. Addition polymers ( 附加高分子 ): n CH 2 =CHR -(CH 2 -CHR) n - vinyl monomer polymer Polymerization Mechanism: step (growth) polymerization Flory (1953) chain (growth) polymerization 24 12

13 25 CH 2 =CHR CH 2 =CR 1 R 2 Vinyl monomer ( 乙烯基單體 ) 26 13

15 Difference between chain and step Polymerization: Radical (chain) polymerization 1)Identities of species that can react with each other. 2)Variations of MW with conversion. Step polymerization: Stepwise reaction between functional groups of the reactants. Chain polymerization: Initiator is needed to produce an reactive center (R*). Polymerization occurs by the propagation of the reactive center by the successive additions of large number of monomer molecules in a chain reaction. Condensation (step) polymerization Living polymerization (Fast initiation, no termination) 29 Differences between step polymerization and chain polymerization Step polymerization Growth throughout matrix Rapid loss of monomer early in the reaction Similar steps repeated throughout reaction process Average molecular weight increases slowly at low conversion and high extents of reaction are required to obtain high chain length Ends remain active (no termination) No initiator necessary Chain polymerization Growth by addition of monomer only at one end of chain Some monomer remains even at long reaction times Different steps operate at different stages of mechanism (i.e. Initiation, propagation and termination) Molar mass of backbone chain increases rapidly at early stage and remains approximately the same throughout the polymerization Chains not active after termination Initiator required Yun Chen, NCKU 30 15

16 O H n H 3 C C H CH 2 CH 2 C O n CH 3 propylene oxide polypropylene glycol (PPG) n C O NH -caprolactam H O CH 2 CH 2 CH 2 CH 2 CH 2 N-C nylon 6 n O H 2 N CH 2 CH 2 CH 2 CH 2 CH 2 -C -amino-caproic acid OH Propylene oxide and -caprolactam usually proceed by chain polymerization mechanism to obtain condensation polymers. Polymers can be classified as Linear, Branched ( 分枝 ), and Crosslinked ( 架橋 or 交聯 ) polymers depending on their structure. 31 Nomenclature of Polymers (single-strand polymers) [NHCO(CH 2 ) 5 ] [NH(CH 2 ) 6 NHCO(CH 2 ) 4 CO] Nylon 6 Nylon 6,6 Based on Source: poly( -caprolactam) or poly( -aminocaproic acid) Based on Structure (Non-IUPAC): poly(hexamethylene adipamide) (Nylon 6,6) IUPAC Structure-Based: poly(imino(1-oxohexane-1,6-diyl)] Selection of a preferred Constitutional Repeating Unit (CRU) or structural repeating unit: the smallest possible repeating unit. Seniority: Heterocyclic rings > Heteroatoms or Acyclic subunits containing heteroatoms > Carbocyclic rings > Acyclic subunits containing only carbon. Trade Names or Nonnames: Nylon 6, Epoxy resin, Acrylics 32 16

http://iupac.org/polyedu/resources/iupac- Purple-Book.pdf The order of subunit seniority. The most senior is at the top center. Subunits of lower seniority are found by following the arrows.

33 Molecular Weight of Polymers 常用平均分子量定義 : Number-average molecular weight (colligative properties) M n = w/n = (N i M i )/ N i = N i M i Weight-average molecular weight (light scattering) M w

17 Purple-Book.pdf The order of subunit seniority. The most senior is at the top center. Subunits of lower seniority are found by following the arrows. The type of subunit, be it a heterocycle, a heteroatom chain, a carbocycle, or a carbon chain, determines the color arrow to follow. 33 Molecular Weight of Polymers 常用平均分子量定義 : Number-average molecular weight (colligative properties) M n = w/n = (N i M i )/ N i = N i M i Weight-average molecular weight (light scattering) M w = (N i M i2 )/ (N i M i ) = (w i M i )/ w i = w i M i Z-average molecular weight M z = (N i M i3 )/ (N i M i2 ) = (w i M i2 )/ (w i M i ) Viscosity-average molecular weight M v = [ (N i M 1+a i )/ (N i M i ) ] 1/a Polydispersity Index: PDI = M w /M n 34 17

18 M n < M v < M w < M z < M z+1 35 Molecular Weight and MWD by Gel Permeation Chromatography (GPC) [Size Exclusion Chromatography (SEC)] 36 18

19 Broken gel particle TEM of gel particle 37 Flow system of GPC 38 19

24 47 Application of Polymers: depending on mechanical properties Plastics Flexible plastics: modulus: 15,000-35,000 N/cm 2 tensile strength: 1,500-7,000 N/cm 2 ultimate elongation: % Rigid plastics: modulus: 75, ,000 N/cm 2 tensile strength: 3,000-8,500 N/cm 2 ultimate elongation: < 0.5-3% Elastomers (Rubbers) modulus: <100 N/cm 2 ultimate elongation: > % Fibers modulus: >35,000 N/cm 2 tensile strength: >35,000 N/cm 2 ultimate elongation: <10-50% 48 24

2. Amorphous or Crystalline Structurally, polymers in the solid state may be amorphous or crystalline. When polymers are cooled from the molten state

2. Amorphous or Crystalline Structurally, polymers in the solid state may be amorphous or crystalline. When polymers are cooled from the molten state or concentrated from the solution, molecules are often