We
present the synthesis and characterization of a new class of
high temperature thermoplastic elastomers composed of polybenzofulvene–polyisoprene–polybenzofulvene
(FIF) triblock copolymers. All copolymers were prepared by living
anionic polymerization in benzene at room temperature. Homopolymerization
and effects of additives on the glass transition temperature (T
g) of polybenzofulvene (PBF) were also investigated.
Among all triblock copolymers studied, FIF with 14 vol % of PBF exhibited
a maximum stress of 14.3 ± 1.3 MPa and strain at break of 1390
± 66% from tensile tests. The stress–strain curves of
FIF-10 and 14 were analyzed by a statistical molecular approach using
a nonaffine tube model to estimate the thermoplastic elastomer behavior.
Dynamic mechanical analysis showed that the softening temperature
of PBF in FIF was 145 °C, much higher than that of thermoplastic
elastomers with polystyrene hard blocks. Microphase separation of
FIF triblock copolymers was observed by small-angle X-ray scattering,
even though long-range order was not achieved under the annealing
conditions employed. In addition, the microphase separation of the
resulting triblock copolymers was examined by atomic force microscopy.
Anionic polymerization
is one of the most powerful techniques for
preparation of well-defined polymers. However, this well-known and
widely employed polymerization technique encounters major limitations
for the polymerization of functional monomers containing heteroatoms.
This work presents the anionic polymerization of 2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole
(VPyOzP), a heteroatom monomer that contains both oxadiazole and pyridine
substituents within the same pendant group, using various initiating
systems based on diphenylmethyl potassium (DPM-K) and triphenylmethyl
potassium (TPM-K). Remarkably, well-defined poly(2-phenyl-5-(6-vinylpyridin-3-yl)-1,3,4-oxadiazole)
(PVPyOzP) polymers having predicted molecular weights (MW) ranging
from 2200 to 21 100 g/mol and polydispersity indices (PDI)
ranging from 1.11 to 1.15 were prepared with TPM-K, without any additional
additives, at −78 °C. The effect of temperature on the
polymerization of PVPyOzP was also studied at −78, −45,
0, and 25 °C, and it was observed that increasing the polymerization
temperature produced materials with unpredictable MW’s and
broader molecular weight distributions. Furthermore, the nucleophilicity
of PVPyOzP was investigated through copolymerization with methyl methacrylate
and acrylonitrile, where only living poly(methyl methacrylate) (PMMA)
prepared by DPM-K/VPPy and in the absence of additives such as lithium
chloride (LiCl) and diethyl zinc (ZnEt2) could be used
to produce the well-defined block copolymer of PMMA-b-PVPyOzP. It was also demonstrated by sequential monomer addition
that the nucleophilicity of living PVPyOzP is located between that
of living PMMA and polyacrylonitrile (PAN). The pyridine moiety of
the pendant group also allowed for quaternization and produced PQVPyOzP
homopolymer using methyl iodide (CH3I) and bis(trifluoromethylsulfonyl)amide
[Tf2N–]. The resulting charged polymer
and counterion complexes were manipulated and investigated for potential
use as membranes for carbon dioxide (CO2) capture.
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