Why Crosslinking & Copolymerization? Interfacial Polycondensation. Why Copolymerization? Why Crosslinking? MSE 383, Unit 2-2

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1 Why Crosslinking & Copolymerization? MSE 8, Unit - Joshua U. taigbe Iowa State University Materials Science & Engineering Dept. Interfacial Polycondensation Why Copolymerization? >> Cost-Efficient route to new polymers >> Reduces development time for new polymers (Cf; 15 Yrs-Homopoly) >> Combines benefits of or more polymers in one material >> e.g. EVH, EMAC, SBR, SMA, etc. Why Crosslinking? >> Ease of application (polyfunctional fluids) >> Fast curing speeds with no VC s >> Thermal or radiation curing possible >> e.g. Epoxy, Phenolics, PET (unsaturated), Silicones, Urea & Melamine Formaldehyde, etc...1

2 Examples of Copolymers EVH (Evalca, EVAL Co.; NIPPN GSHEI) ETHYLENE + VINYL ALL (VAc) (processability & themal stab.) (excellent barrier properties) >> Excellent barrier properties for food packaging applications >> Coextruded multilayer to control moisture sensitivity >> Resistant to oils & many organic solvents >> Excellent optical clarity, antistatic, weatherability >> Reusable (enviromentally friendly) >> Coextruded multilayers, films, coatings (for various substrates)** >> Excellent adhesion to PA (tie resins needed for other polymers) >> Rigid & flexible packaging (ketchup, meat, cheese, chemicals, etc.) SBR (Stereosin, FIRESTNE; K-Resin, PHILLIPS 66) BUTADIENE + STYRENE (>50 Wt. %) (toughness & transparency) (plasticity, toughness, rigidity, high gloss) >> Bridges gap between brittle PS & PC, PET, acrylics, etc. >> Thermoplastic block copolymers (solution polymerized) >> Styrene allows compatibility with other styrenics** >> Excellent color fastness..

3 SBR (Stereosin, FIRESTNE; K-Resin, PHILLIPS 66), Cont d >> Injection molding & thermoformable grades available >> Polyblendable with PS, HIPS, PC, etc. >> Fast-food containers & cups, shrink & over wrap, medical, etc. S-MA (Dylark Resin, ARC Chemical Co.**)**sole producer STYRENE + MA (trace amounts) (raises useful temperature, crystal clear) >> Random incorporation of MA into PS backbone >> Rubber is optionally grafted to increase toughness >> ther variants include SAN, SMMA, etc. >> Fast injection molding cycle times; extrudable >> Excellent flow properties (melt stable at 550 F)!! >> Interior auto parts (instrument panels, floor & roof consoles, etc.) >> Domestic (microwave cooking trays, dishwasher tumblers) Crosslinking (or thermosetting) polymers Polyfunctional monomers to form a -D network polymer Recall practical motivation >> Ease of application (polyfunctional fluids) >> Fast curing speeds with no VC s** >> Thermal or radiation curing possible >> e.g. Epoxy**, Phenolics**, PET (unsaturated)**, Silicones, Urea & Melamine Formaldehyde, etc...

4 EPXY (Chemistry of:) Reaction between epoxy* and BPA >> Ambient temperature cure initiated by polyamines (-part component) >> High temperature cure initiated by anhydrides, phenol, acids (1-part) >> Stoichiometry controlled to eliminate byproducts formation >> Brominate to impart flame retardancy C C n + R NH NH H + H N H Uses of Epoxy Resins Protective and decorative coatings Bonding, adhesives, glues (automotive & aerospace) Molding, casting, and tooling for electrical & electronic Laminating & composites* used in circuit boards, sailboats Building & construction (epoxy terrazzo floors, rebars or reinforcing bars, repair of bridges & concrete) Non-recyclable* (pollution) PHENLICS (many suppliers) Chemistry of: >> Reaction product of phenol & formaldehyde at high temperature phenol + H acid pre-polymer solid heat HEXA* RESIN (*hexamethylene tetramine) >> NVLAC..4

5 PHENLICS (Chemistry of:) chemical types (novolac & resole) >> RESLE (i.e., phenol + excess H + base catalyst + heat) reaction is terminated prior to completion reactive soluble material Bakelite** [Baekeland (1907)] Uses of Phenolics High precision parts (tight dimensional tolerances) Heat resistant, creep resistant Resistant to methanol & gasoline mixtures Automobile, appliances, electrical components New grades are recyclable*!! PET (Unsaturated) Crosslinking of unsaturated* linear chains (free radical addition) >> Typically organic peroxide initiator & styrene curing agent >> ther curing agents are vinyl toluene, MMA, α-methyl styrene Properties depend on chemical ingredients used Numerous applications >> Boats, auto exterior parts, corrugated & flat paneling >> Corrosion-resistant tank, polymer concrete*, bowling balls, etc. Composites*, BMC, SMC (tbd)..5

6 Example of PET ethylene glycol + maleic anhydride + styrene ethylene glycol maleic anhydride prepolymer (unsaturated polyester) + styrene -dimensional network polymer End of Lecture Read class notes & Class text ptional reading Billmeyer (portions of:)..6