PhD Thesis
Polarmodifikation von Butadienkautschuk mit Polyethylenglykol
Mabel Braun (01/2002-01/2002)
Summary
The
synthesis of polar modified polybutadiene rubbers by reaction of living
anions
of polybutadiene with chain-end functionalised polyethylene glycol
(PEG) was
investigated. The reaction system and the strategy of copolymer
synthesis were
determined by the copolymers potential use. Polybutadienes (PB) should
have a
high fraction of 1,4-units to serve as adhesion-increasing components
in
silica-filled rubber mixtures for tire applications. On the other hand,
modification reactions with functionalised PEG should be uncomplicated
and
cheap.
Two types of
functionalised PEG were
generated. First, PEG with a substitutable end group were reacted with
living
anions of polybutadiene. Those PEG were carrying chlorine or iodine
atoms or
sulfonic acid ester end groups. The latter were not suitable for
replacement by
PB anions under chosen conditions. Using halide-functionalised PEG,
chain
coupling efficiencies of up to 50 % of the theoretical value were
reached. Side
products were identified by liquid chromatography under critical
conditions
(LACCC) and two-dimensional chromatography (LACCC coupled with gel
permeation
chromatography). This reaction is uncomplicated in realisation and
hence
provides potential of industrial use - but it is not complete due to
its reaction
mechanism.
An
alternative way is to couple
living PB-anions with PEG carrying a non homopolymerisable double bond,
e. g.
polyethylene glycols with a diphenyl ethylene (DPE) or benzophenone end
group.
Numerous side products were found in the reaction of PEG-DPE with the
anions,
as was modification of PB with a benzophenone-functionalised PEG. The
latter
led to copolymers with PEG fractions of 67 % of the theoretical value.
Formation of side products was again clarified by two-dimensional
chromatography. By changing some parameters, better control of this
type of
reaction could be achieved. Thus it may be an interesting method in
synthesis
of block copolymers or branched polymers from dienes and polyethylene
glycol.
Within the
framework of an industry
cooperation several modified polybutadienes were synthesised in lots of
500 g,
using chlorine-functionalised PEG. The copolymers were utilised in
typical
rubber mixes for tire applications by the cooperation partner.
Mechanical
properties of the uncured mixes and of cured specimens were specified
by
typical methods. As a result of the very small polyethylene glycol
proportion
within the mixture no distinct influence of this fraction on the
determined
properties could be detected