Development of novel plastic scintillators based on polyvinyltoluene for the hybrid j-pet/mr tomograph


Figure 24 Determination of intrinsic viscosity for a polystyrene solution in toluene


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Figure 24 Determination of intrinsic viscosity for a polystyrene solution in toluene. 


53 
Basing on the Kuhn-Mark-Houwink-Sakurada equation: 
(9) 
molecular weight of the polymer (M) was determined. 
Viscometry is an indirect method of 
molecular weight determination and requires knowledge of constant values: α and K. For 
polystyrene solution in toluene measured in 25 °C, these constants are equal to [87]: 
K= 10.5×10
-3
[ml/g] 
α = 0.73. 
Three samples of polystyrene obtained in different syntheses but the same 
conditions were tested using this method. Values of determined molecular weight are 
shown in Tab. 9. 
Table 9 Molecular weight of polystyrene. 
Sample number 
Molecular weight 

2.5×10
5


2.8×10
5


2.9×10
5

The exact values of polymers molecular weights are not very important in this 
case. The most significant is that determined values of molecular weights are higher
than
10
5
u. 
Since plastic scintillators are prepared in the same conditions, with identical 
temperature schedule, it is assumed that molecular masses of J-PET scintillators are equal 
to molecular weight of pure polystyrene. This means, that the light output of J-PET 
scintillators is maximized taking into account only polymer properties. Because 
polystyrene molecular weight is more than 2 times larger than 10
5
u, light output of the 
scintillators is not sensitive to small variations of this quantity. 
J-PET scintillators are based mainly on polyvinyltoluene, not polystyrene. However 
constant values: K and α are not determined for polyvinyltoluene solutions, so we took 


54 
into consideration only results for polystyrene. We assume that polyvinyltoluene as 
polystyrene homolog, differing only by an additional methyl group in the mer, polymerizes 
in the same way and its molecular weight is similar.

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