英语翻译The effect of methanol on the grafting rate was clearly

英语翻译
The effect of methanol on the grafting rate was clearly demonstrated by grafting of PE
in a mixture of styrene and methanol (Fig 1).By dilution of styrene with methanol the
concentration of styrene inside PE decreases,the viscosity increases and due to the gel-effect
the grafting rate and yield increase until optimal concentration of monomer is reached.
The methanol being almost completely insoluble in PE has no direct effect on viscosity of the
amorphous region of the PE where grafting take place.Its sole function is to reduce the
concentration of the styrene in the PE (Machi et al.,1970).When less styrene is present to
swell the growing polystyrene radicals they are less mobile and the rate of their mutual
termination is lower.The decreased radical termination rate overcompensates for decrease in
the rates of initiation and propagation which also accompany the monomer dilution.Hence
the decrease in monomer concentration results in longer polystyrene chains and higher overall reaction rate.If the monomer will be diluted with the solvent which swells polymer equally or
better than monomer the decrease of grafting rate with solvent addition could be expected.
It is known that crosslinking of PE influences its swelling properties.Accordingly it could be
expected that pre-crosslinking of PE influences the rate and yield of grafting as well.We
demonstrated this by pre-crosslinking PE and by its subsequent grafting with styrene after the
trapped radicals had been annealed out.Grafting was induced by simultaneous irradiation
(Fig 2).
For pre-crosslinked PE the grafting rate is higher than for the uncrosslinked polymer.
We interpret the increase of grafting yield with crosslink density by hindered mobility of
polymer chains and in terms of the gel-effect,since the monomer concentration within the
film is reduced,viscosity increased and the rate of termination of growing grafted chains
descreases.
Two solvents different in chemical structure and radiation sensitivity were used for
swelling of PE during radiation crosslinking:benzene with aromatic structure and high
radiation resistivity and hexane similar in chemical structure and radiation sensitivity to PE.
If the PE was swollen with benzene and then crosslinked the subsequent increase in the
grafting yield was lower than in the case when dry polyethylene was crosslinked.
This result suggested that crosslinking could be less efficient in the presence of benzene.
When hexane was used as the swelling agent similar results were obtained as with benzene.
In order to obtain more direct information about the influence of swelling agent on PE
crosslinking we investigated the crosslinked polyethylene for its elastic modulus in the molten
state.