The focus of this work is on the nature of selfhealing of ionically modified rubbers obtained by reaction of brominated poly(isobutylene-co-isoprene) rubber (BIIR) with various alkylimidazoles such as 1-methylimidazole, 1-butylimidazole, 1-hexylimidazole, 1-nonylimidazole, and 1-(6chlorohexyl)-1H-imidazole. Based on stress−strain and temperature dependent DMA measurements, a structural influence of the introduced ionic imidazolium moieties on the formation of ionic clusters and, as a consequence, on the mechanical strength and self-healing behavior of the samples could be evidenced. These results are fully supported by a molecular-level assessment of the network structure (crosslink and constraint density) and the dynamics of the ionic clusters using an advanced proton low-field NMR technique. The results show distinct correlations between the macroscopic behavior and molecular chain dynamics of the modified rubbers. In particular, it is shown that the optimization of material properties with regard to mechanical and self-healing behavior is limited by opposing tendencies. Samples with reduced chain dynamics exhibit superior mechanical behavior but lack on self-healing behavior. In spite of these limitations, the overall performance of some of our samples including self-healing behavior exceeds distinctly that of other self-healing rubbers described in the literature so far.
In
this study we describe the synthesis of bis(pyrrolidone) based
dicarboxylic acids from itaconic acid and their application in 2-oxazoline
resins for fully renewable thermoset materials. The monomers are obtained
using a bulk aza-Michael addition of a diamine and two itaconic acid
molecules using a catalytic amount of water. The monomers can be isolated
in high purity after recrystallization, though their yield proved
to be highly dependent on the selected diamine spacer length: In general,
only the dicarboxylic acids containing diamines with an even number
of methylene spacers are isolated in high yields. Through NMR, GPC,
and FTIR analysis we demonstrate that these bis(pyrrolidone) based
dicarboxylic acids exhibit significantly enhanced curing rates in
2-oxazoline resins compared to resins containing aliphatic dicarboxylic
acids such as sebacic acid. Overall, we demonstrate that the rate
of 2-oxazoline ring-opening addition with carboxylic acid functionalities
is determined by the used dicarboxylic acid, whereas the ring-opening
addition of the 2-oxazoline functionality with amide groups is determined
by the used bis(2-oxazoline) compound. The thermosets obtained after
curing proved to be readily plasticized by water, opening up possibilities
for enzymatic degradation.
We
report on the role of temperature and shear on the melt behavior
of iPP in the presence of the organic compound N1,N1′-(propane-1,3-diyl)bis(N2-hexyloxalamide) (OXA3,6). It is demonstrated
that OXA3,6 facilitates a viscosity suppression when
it resides in the molten state. The viscosity suppression is attributed
to the interaction of iPP chains/subchains with molten OXA3,6 nanoclusters. The exact molecular mechanism has not
been identified; nevertheless, a tentative explanation is proposed.
The observed viscosity suppression appears similar to that encountered
in polymer melts filled with solid nanoparticles, with the difference
that the OXA3,6 compound reported in this study facilitates
the viscosity suppression in the molten state. Upon cooling, as crystal
growth of OXA3,6 progresses, the decrease in viscosity
is suppressed. Retrospectively, segmental absorption of iPP chains on the surface of micrometer-sized OXA3,6 crystallites
favors the formation of dangling arms, yielding OXA3,6 crystallites decorated with partially absorbed iPP chains. In other words, the resulting OXA3,6 particle
morphology resembles that of a hairy particle or a starlike polymer
chain. Such hairy particles effectively facilitate a viscosity enhancement,
similar to branched polymer chains. This hypothesis and its implications
for the shear behavior of iPP are discussed and supported
using plate–plate rheometry and slit-flow experiments combined
with small-angle X-ray scattering analysis.
This paper reports, for the first time, semi-crystalline polymers based on bis-pyrrolidone dicarboxylic acids (BPDA) obtained from the aza-Michael reaction between renewable itaconic acid and various diamines.
In this work, we report on a novel hydrogenb o n d i n g c o m p o u n d , N , N ′ -b i s ( 2 -h y d r ox y e t h y l )terephthalamide (BHET), and its potential as additive in poly-L-lactide (PLA). Although the hydroxyl groups of BHET can participate in transesterification with the PLA matrix, we demonstrate through gel permeation chromatography that extrusion at 200 °C does not result in a drastic decrease in molecular weight. When dissolved in the PLA matrix, BHET facilitates a plasticizing effect, indicated by a suppression in both melt viscosity and glass-transition temperature. Additionally, BHET can crystallize from the PLA melt during cooling, where the generated BHET crystals facilitate heterogeneous nucleation of the PLA matrix. In general, BHET crystallization is favored at high undercooling/superstaturation, as this yields BHET crystals with a high surface area-to-volume ratio. However, rapid cooling to temperatures below the glass-transition temperature prevents the crystallization of the BHET, effectively yielding samples where only the plasticizing effect of BHET is evident. A suppression in yield point is observed during mechanical analysis of samples with increasing BHET concentration, a characteristic feature for samples with decreasing glass-transition temperatures. In contrast, when allowed to crystallize during processing, BHET can be used to generate PLA crystals oriented along the flow direction, effectively enhancing the tensile modulus. Overall, the combined plasticizing and nucleating effect of BHET makes it a verstaile additive for controlled processing and performance of PLA.
The proximity (dJ between a diffusing species and its host crystal necessary for a successful diffusion for diffusion-controlled crystallization of barium tungstate from sodium tungstate melts in platinum crucibles was estimated. These distances increased with increased cooling rates ( RT) and crystallization temperatures (To). Energy ( R ) , enthalpy (AH,), entropy (AS,) and free-energy (AGra) of activation and the pre-exponential fe.ctor (k,) were evaluated using an ordinary Arrhenius equation k,, = k, e-EIRT, where k D , waa the diffusion rate-constant. These parameters were virtually unaffected by the changes in To and RT.
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