Chapter 17
Crystalline State
Crystal structure
Polymer single crystal and semicrystalline state Liquid crystalline state
Crystallization and melting
Crystallization of polymers
Regular chain polymers are crystallizable.
main chain polymers and
stereoregular [iso/syndio] polymers
amorphous upon quenching;
(semi)crystalline upon slow cooling
crystallization slow and incomplete
long chain
DGxtalliz’n
= DH – TDS
DH < 0 and DS < 0
Xtalliz’n upon (slow) cooling
from melt, or
upon annealing (at Tg < T < Tm)
from (amorphous) solid
Ch 16 sl 2
Specific volume
Temperature
amorphous semicrystalline
cooling
1st heating
(from quenched)
2nd heating cold
Xtalliz’n
melt Xtalliz’n
Tg Tcc Tmc Tm
exotherm
Semicrystalline state
models for semicrystalline structure
fringed micelle model
intuitive and historical view
A chain passes through crystallites.
non-crystalline region between crystals
explains structure from the melt better
folded chain model
modern view
A long chain folds back-and-forth.
suggested for single crystal lamella (grown from dilute solution)
found also in melt crystallized Xtals
Fold region is non-crystalline.
Ch 17 sl 3
Conformation in polymer crystal
Chains are of preferred conformation
lowest-energy conformation given by RIS
PE
t t t t ---
planar zigzag
PTFE
t t t t --- but with f = 17°
(13/6 or 15/7) helix
Ch 17 sl 4
Table 17.1 p 405 Don’t mind
planar zigzag
13/6 helix = 13 asym units in 6 turns
helix nomenclature A*u/t
A = # of skeletal atoms in the asymmetric unit [basic motif]
u = # of asym units in the helix repeat [pitch]
t = # of turns in the helix repeat
Ch 16 sl 5
PE ~ 1*2/1 PVA ~ 2*1/1
PTFE ~ 1*13/6
PP ~ 2*3/1
vinyl polymers, atactic
not crystallizable
crystallizable when subs small [OH, F]
PVA, PVF ~ t t t t --- ~ planar zigzag (2*1/1)
vinyl polymers, stereoregular
isotactic ~ t g+ t g+ -- or t g− t g− syndiotactic ~ t t g+ g+ -- or t t g− g−
(right or left-handed) helix
iPP, iPS ~ 31 helix
polyamides
amide plane and t t t t
planar zigzag
H-bonding between chains
Ch 17 sl 6
Fig 17.6
CH3 or Ph
Fig 17.5
Polymer crystal structure
crystal = regular repeating 3-D array of atoms
unit cell = smallest volume of repeating structure
crystal structure = shape of unit cell
In polymer crystal, chains are arranged to pack better.
PE
Ch 17 sl 7
Fig 17.4
unit cell
0.74 nm
0.49 nm
ab c
ab g
# of asym units
56/6.02/0.74/0.5/0.255
iPP
Ch 17 sl 8
crystal system
3 x 2 + (3/2) x 4 = 12 a b
c
b
orthogonal [orthorhombic] popular for polymers
Polymer crystals are anisotropic.
chain molecule
covalent bonding in c axis
E(c) >> E(a,b)
E(Spectra® ) = 150 GPa
birefringent (Dnc – Dna > 0)
polymorphic
depending on T and P
Ch 17 sl 9
Crystal structure anlysis: XRD
X-ray diffraction
Bragg’s law
powder pattern
semicrystalline, isotropic
fiber pattern
drawn, c-axis to fiber direction
Ch 17 sl 10
dhkl = spacing between crystal planes
Fig 17.2
Fig 17.3
powder pattern
fiber pattern
reciprocal space and diffraction pattern
Miller index for crystal planes
The plane passing
(a/h, b/k, c/l) is (hkl) plane.
Ch 17 sl 11
Polymer single crystal: lamella
Lamella
[
板晶] formed
as single crystal from (dilute) solution
as part of spherulite from the melt
in solution-grown polyethylene lamella
Chains are perpendicular to the surface.
by electron (not X-ray) diffraction exp’t
Chains are as long as 100 mm. [AR of 104]
Chains got to be folded.
Fold plane is {110}.
Ch 17 sl 12
Fig 17.7
10 nm
electron microscopy
fold plane fold surface
Shape of fold surface depends on crystal structure.
Ch 17 sl 13
PE
(orthorhombic)
polyoxymethylene (hexagonal) poly-4-methyl-1-pentene
(tetragonal) POM ~ -[CH2-O]- ~ g±g±g±g± preferred 21 helix hexagonal
truncated lamella
growth onto {100} at higher temperatures
multi-layer lamella
screw dislocation (defect)
Ch 17 sl 14
Fig 17.8
Fig 17.12 p 413 Fig 17.27 p 427
hollow pyramid
lattice mismatch upon folding
collapsed hollow pyramid
Ch 17 sl 15
Fig 17.9
Solid-state polymerized single crystal
polydiacetylene fibers
Ch 17 sl 16
Fig 17.11
