Post on 11-Jan-2016
melt conditions glass transition crystallisation Tg Tm
POLYMER Tg(oC)Polydimethylsiloxane -123Poly(vinyl acetate) 28Polystyrene 100Poly(methyl methacrylate) 105Polycarbonate 150Polysulfone 190Poly(2,6-dimethyl-1,4-phenylene oxide) 220
Polymers with more flexible backbones, and smaller substituent side groups have lower glass transition temperatures
melt conditions glass transition crystallisation Tg Tm
For semi-crystalline polymers Tg Tm (oC)Polyethylene (high density) -120 135Polycaprolactone -60 61Poly(vinylidene fluoride) -45 172Polyoxymethylene -85 195Poly(vinyl alcohol) 85 258Nylon-6,6 49 265Poly(ethylene terephthalate) 69 265
Both Tg and Tm increase with decreasing chain flexibility
From Fried, Joel R., “Polymer Science and Technology”, Prentice Hall PTR, Englewood Cliffs, NJ (1995)
From Fried, Joel R., “Polymer Science and Technology”, Prentice Hall PTR, Englewood Cliffs, NJ (1995)
From Fried, Joel R., “Polymer Science and Technology”, Prentice Hall PTR, Englewood Cliffs, NJ (1995)
Polymer solutions “dilute”, semi-dilute, through to concentrated
Rheology: a study of the flow of polymer melts and solutions (shear-thinning, die swell, energy requirements for mold filling, design of mixers, extruders
Block copolymer solutions and melts:
making patterned surfaces and ordered melt morphologies
Scientists, academics < 1930s Industrialists1830 Charles Goodyear,: vulcanised
rubber
Hevea brasiliensis + + S elastomeric material
1847 Christian Schonbern
Cellulose + nitric acid cellulose nitrate
1860 Leo Baekeland (Bakelite) phenol-formaldehyde resin
1930s DuPont (USA) nylon, teflon1938Dow (USA) polystyrene1939 ICI (UK) LDPE
WWII: shortage of natural rubber!
“A damned gooey mess”
Another failed synthesis
Scientists begin to look at complex systems . . . .
1920’s Hermann Staudinger, German Physical Chemist“long-chained molecules or macromolecules”
interacting, separate very long, alkane-like intermediate species but misunderstood .e.g., Tm, flow behaviour flexibility
Synthesis of polymers
• biosynthesis• step-growth polymerisation
All monomer/oligomers/polymers are equally reactive with one another so that there is a distribution of chain sizes
• chain-growth polymerisation
Monomers joined successively to a growing chainA few long chains in a sea of monomers
Step-growth polymerisation
An + Am -> An+m + by-product polydispersity
Chain-growth polymerisation
An + A -> An+1 Monodisperse, high-MW of chains
• Initiation of the active monomer
• Propagation of growth of the active (free radical ) chain by sequential addition of monomer
• Termination of the active chain to give final product
Q8: Contrast step-growth and chain-growth mechanisms in the synthesis of linear polymers and include statements comparing the final products of these two classes of synthetic mechanisms.