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Original scientific paper

Calorimetric Investigation of Grafting of Styrene and Methylmethacrylate onto Air-Preirradiated Polyethylene

M. Barić ; »Ruder Boskovic« Institute, 41001 Zagreb, Yugoslavia
F. Ranogajec ; »Ruder Boskovic« Institute, 41001 Zagreb, Yugoslavia
I. Dvornik ; »Ruder Boskovic« Institute, 41001 Zagreb, Yugoslavia

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page 223-231

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All existing and widely used methods for measuring reaction
rate of polymerization processes suffer from basic disadvantages
including indirect measurement, insufficient accuracy and limited
applicability. Their unsuitability is especially pronounced in the
investigation of graft copolymerization reactions in which the
accuracy of measurement could be affected even by the different
properties of individual polymer samples.
In this work a new method, calorimetry, free of mentioned
disadvantages is generally proposed for investigation of polymerization
processes and particularly its application to radiation induced
grafting of styrene and methylmethacrylate onto polyethylene
is demonstrated.
Experimental results showed the possibility of calorimetry
to measure the grafting rate continuously and directly in the whole
conversion range with the accuracy much better than with any
other method used so far.
It was concluded that styrene grafting is non-diffusion-controlled,
whereas methylmethacrylate grafting is not diffusion-
independent. With both monomers the reaction kinetics was
found to be dependent on the type of polyethylene a s a consequence
of different mechanisms, i. e. in the initiation step two different
species, peroxy radicals and peroxides, take part. Its concentration
is different in two types of polyethylene used. In the case of high
density polyethylene both active species participate in the initiation
process equally, according to their different nature. However, in
low density polyethylene the concentration of peroxy radicals is
negligible compared to that of peroxides and therefore peroxides
have dominating role in the initiation step of grafting reaction. The
change of the viscosity of reaction medium in the course of reaction
as well as the structure of polymer in the case of high density
polyethylene influence the kinetics of grafting reaction.


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