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.