Tacticity of a linear polymer chain

trans conformation

Isotactic: -R groups on the same side of the C-C planeSyndiotactic: -R groups on alternating sideAtactic: -R groups on either side of the C-C plane

. . .breakage of covalent bonds required to change configuration/tacticity

States of polymers

“melt”& solutions “glasses” semi-crystalline

Gaseous Liquid Solid

decrease temperature or thermal motion

Polymer melt

polymer melt is like a bowl of spaghetti• entanglements limit motion• flows on long-timescales (reptation)• elastic on short-timescales

viscoelasticity

Melts ( pure polymer “liquid”) towards crystalline solids

. . towards crystalline state• motion frozen on scale of polymer• segmental motion persists

crystalline/amorphous lamellae• depends upon cooling rate• backbone/sidegroup structure• tacticity

100-200 Å, 40-80 PE monomers

spherulite

… to semi-crystalline melts

Some polymers do . . Some don’t (crystallise)

Inter-chain hydrogen bonding favors formation of semi-crystalline regions

Atactic polystyrene ?

Crystallisation is facilitated by• “regular” or ordered backbone structure,• favorable interchain interactions• lower molecular weight

nylon-6,6

“glasses” . . .intermediate between amorphous melts and possible semi-crystalline states

. . . “frozen” structure precedes crystallisation, if it happens;

melt conditions glass transition cyrstallisation

small scale molecular motions• limited backbone motion• rotations, “crankshaft”• vibrations• flips, wags of side groups

Tg Tm

Q4: Using complete sentences, and schematics if helpful, contrast the chain motion of a melt of atactic polypropylene under (a) slow temperature quench; (b) quick temperature quench

Q5: Complete Q4 again, starting from a melt of nylon6,6

Q6: Atactic-polyvinylchloride (PVC) is amorphous, whereassyndiotactic-PVC is partially cyrstalline. But atactic- polyvinylalcohol is partly crystalline. Why?

Q7: Do you predict the Tm of nylon-6,6 to be higher or lower than that of polyethylene? Why?

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