Transcript Diapositiva 1

BANDE CARATTERISTICHE DELL’ORDINE STRUTTURALE
• Picchi di regolarità (conformazionale): tipici dell’isomeria trans/gauche.
Esempi: 1450 cm-1 (trans) e 1435 cm-1 (gauche) nel trans-1,4-polibutadiene;
975, 1340 e 1470 cm-1 conformero trans del PET.
• Picchi associati a segmenti di catena stereoregolari. Esempio: picchi a 805,
972, 995 e 1100 cm-1 caratteristici della conformazione ad elica dell’i-PP.
La lunghezza critica di sequenza (CSL)
• Picchi di cristallinità, dovuti alle interazioni catena-catena che hanno luogo
nella struttura cristallina. Esempio tipico: doppietto 720-730 del PE (CH2 rocking )
I0
from source
I
T (%) 
I
100
I0
A  log
I0
I
to detector
IR beam
A  C
Beer-Lambert law
sample
Difference spectroscopy
At ( )  A1 ( )  A2 ( )
Additivity
At ( )   1 ( )C1   2 ( )C2
Beer-Lambert law
At ( )  K1 A1p ( )  K 2 A2p
K1 

 C1 ;
 1p
K

(1  X c )
'
K2 

 C2
 2p
Physical meaning of the K factors
For a two-phase semicrystalline polymer
POLIETILENE HD
POLISTIRENE SINDIOTATTICO
diff
a’
am
am
a’
diff
b
diff
diff
a’
am
INTENSITA’ DELLE BANDE RAMAN
 a ij 
( 0  ) 4
2 2 h



I ij 

c  [1  exp( hc / kT )]  Q 0
STOKES
 a ij 
( 0  ) 4
2 2 h



I ij 

c  [1  exp( hc / kT )]  Q 0
ANTI-STOKES
2
2
 0  absolute frequency of excitation radiation (cm -1 )
  frequency of band (Raman shift, cm -1 )
T  absolute temperatu re
h  Plank' s constant
c  speed of light (cm sec -1 )
k  Boltzmann constant (JK -1 )
 a ij 

  ij element of the polarizabi lity derivative tensor

Q
  0
I Raman  KVCI0
Selective surface modification of a polystyrene film
Bulk sulfonation of syndiotactic polystyrene (d-form):
SIDE VIEW
TOP VIEW
FT-Raman spectra in the 3700 – 200 cm-1 range of:
A) amorphous sPS film; B) parent sPS film (d-form).
Calibration curves I 636 / I 620
as a function of the sulfonation degree
FT-Raman spectra in the 1800 – 200 cm-1 range of:
A) the parent sPS film (d-form); B) sulfonated film
with SD = 14.2; C) sulfonated film with SD = 17.0.
Residual concentration of monomers located
into helical sequences with CSL  8 -12
(curve A) and CSL  2 – 5 (curve B) as a
function of the sulfonation degree.
The ratio
I1252 / I 2850
as a function of the crystallinity degree
Micrograph in the visible range of the
fracture surface of the sPS film (d form)
Depth profile of the sulfonation degree (SD)
of a d-form sPS film
Raman image of the fracture surface of the sPS film
Depth profile in terms of the Residual
Sequence concentration (m  8 – 12, left
Y-axis) and of crystallinity degree (right Yaxis) for the d-form sPS film