Chapter 24 Synthetic Polymer Contents Identifying the Repeating Units for Polymer Understanding the Mechanisms, Structures of Polymers and their Chemical, Physical Properties

Introdution : What is the Polymer ? Macromolecules Can be Classified according to Mechanisms Addition Polymers : Chain-growth Polymers (eg: Free radical mechanism) Condensation Polymers : Others: p. 1054

24.1 Radical Chain Polymerization Comment : p. 1054

Initiation Propagation Comment p. 1055

Termination h-t polymers More stable radical p. 1055

24.2 Structures of Polymers Linear Structure vs Branched Structure Chain transfer Mechanism Mechanism for the Formation of Long Branch Fig. 24-1, p. 1058

Mechanism for the Formation of Shorter Branch Irregularity  Polymer property change Irregularity: - from Branched Polymer - from Tacticity Thru 6-Member TS  Butyl Branch Fig. 24-2, p. 1059

Irregularity from Tacticity FR polymerization? ACTIVE FIGURE 24.2: MECHANISM OF THE FORMATION OF A BUTYL BRANCH DURING THE POLYMERIZATION OF ETHYLENE. p. 1059

24.3 Ionic Polymerization Cationic polymerization Vinyl monomers: - Anionic polymerization Oxirane: h-t polymers Needs stabilizing groups for carbocation p. 1060

Anionic polymerization Phenyl group stabilize carbanion Driving force: ring strain energy p. 1061

Focus On – Super Glue Two EWGs stabilize carbaion Any Nu can initiate Polymerizarion (Si-OH, Fe-OH, Skin-NH2,.. ) Anionic polymerization : acrylonitrile vs isobutylene (stabilization of cabanion vs carbocation) p. 1062

24.4 Coordination Polymerization Catalyst (TiCl4+AlEt3) Mechanism: Metal Coordination PP: Why not FR polymerization? Most important method - Linear, no branch - Gives Tacticity  better physical property Fig. 24-3, p. 1063

Syndiotactic polymer : Example. FIGURE 24.3: MECHANISM OF POLYMERIZATION INVOLVING A METAL COORDINATION CATALYST (SIMPLIFIED VERSION). Isotactic polymer : Syndiotactic polymer : p. 1064

24.5 Physical Properties of Polymers Two-Dimensional picture of a Crystallite Crystalline region: anti conformers, ~100nm in size, more polar structure, no branching  increase physical property; Tg, Tm Amorphous region: branching, irregularity, … p. 1064

24.6 Major Thermoplastic Addition Polymers Output of Thermoplastic Polymers (2002) PE> PVC> PP> PS PVC: polar C-Cl higher Tg PP: after 1957, stiff & hard PMMA: higher Tg, 110oC PVC is ridged, but can be flexible by adding Plasticizer (DOP) HDPE: by coordination catalyst, regular structure, high density, higher Tm LDPE: by radical polymerization, branching, used for films, low cost Table 24-1 p. 1066

24.7 Elastomers Amorphous, Tg below RT, random, coiled conformers, nonpolar structure Need cross-linkers to prevent from slipping: by vulcanization p. 1068

1, 4 addition makes trans conformer (higher Tg) vs 1, 2 addition vs 1,4 addition 1, 4 addition makes trans conformer (higher Tg) vs Natural rubber (cis conformer) SBR (25% St + 75% butadiene): Synthetic rubber, 2/3 of rubber w/w Random incorporation of St  rubber like structure p. 1069

24.8 Condensation Polymers Condensation polymerization : step growth polymerization Natural polymer : Proteins from AA, DNA form NA Synthetic polymers : Polyesters, Polyurethanes p. 1070

Poly(ethylene terephthalate); PET Water should be removed Highly crystalline due to linear & polar structure High MP(270oC) High tensile strength  good for fiber SMs should be very pure to get high MW via Trans esterification : MeOH can be easily distilled off p. 1071

Polycarbonate , Polyamide Interfacial polymerization (계면 중합) : MC/water with vigorous mixing High impact strength : helmets, CD, .. Acid chloride method  cheaper? Molten method : for industry Strong intermolecular force : HB  high mp (250oC) Fibers with food tensile strength eg) Nylon 6,10 : tooth brush p. 1072

Polyamide Highly crystalline, strong, stiff, high-strength fibers Nylon 6,6 : original from Dupont, USA Nylon 6 : EU, Jpn, Korea Highly crystalline, strong, stiff, high-strength fibers bulletproof cloth Need special condition for spinning  needs scale up research p. 1073

Polyurethane MW 1000~2000 Soft Segment –Hard Segment p. 1074

Polyurethane A lot of dialcohols can be used  different physical properties PU foams : via addition of water during molding process p. 1075

24.9 Thermoset Polymers Thermoplastic Polymers: linear, not crosslinked polymer Thermoset Polymer : crosslinked when heated not reversible, makes environmental problem Plastic : Mixture of polymer and others, solid after processing Polymer(major) + Plasticizer + Filller + Dye, Pigment + Lubricant + flame retardant + antioxidant + binder Phenolic resin : phenols + formaldehyde eg) Bakelite highly crosslinked  no melting : electrical insulator, PC board, Billard ball,.. Amino resin : urea (melamine) + formaldehyde Epoxy resin : bisphenol A + epichlorohydrin p. 1075

Partial mechanism of the polymerization of phenol and formaldehyde Fig 24-4 p. 1076

Epoxy Resin : mechanism of glue (by Mixing A and B) slightly in exess p. 1077

24.10 Chemical Properties of Polymers Same chemistry can be applied on the polymer Ion exchange resins : PS resin by suspension polymerization process p. 1078

Surface of the Beads Cation exchange resin Anion exchange resin Process for pure water p. 1078

Focus On – Recycling Plastics Collecting & Sorting : labor cost for collecting, automatic sorting machine (with IR sensor) Mixing to virgin polymer : Pyrolyze to Chemical Feedstock : Fuel : burning as a fuel, part of energy is recovered not safe in case of halogen containing plastics  Dioxin, HCl waste Reverse polymerization : In the case of condensation polymer Not applicable to Thermosetting Resin : - Have to change to Thermoplastic Resin - New process to reverse polymerization  New National Project p. 1080