We report the preparation and features of environmentally friendly "Green Dynamers" (GDs), dynamic polymers presenting sequential double-degradation features, chemical and biological. They were obtained by connecting biodegradable oligomers (such as small units of polybutylene adipate, PBA, and polybutylene succinate, PBS) through chemically degradable reversible imine bonds. The GDs possess water disintegratability, mendability and biodegradability. Their degradation rate may be modulated through and increases with the number of imine groups in the polymeric chain. The GDs were thermodynamically stable and maintained their molecular weight and their mechanical strength in air. However, when they were contacted with water, the imine bonds easily hydrolyzed, breaking up the polymer chains into oligomers. After such water disintegration, the residual oligomers were biodegraded into CO 2 and water. In addition, the imine bonds were restored by evaporation of the water, leading to recovery of the molecular weight and of the mechanical properties of the GDs. The present GDs may be considered to represent a class of doubly-degradable polymers, combining chemical and biological degradability features, that operate in mild environmental conditions. This concept may contribute to solve the problem of waste elimination associated with the use of non-degradable polymeric materials.
Surface characteristics of nongraphitized carbon black (S-II) and
graphitized carbon black (S-III) were
investigated by analyzing the adsorption isotherms of Kr,
N2, and H2O. S-II was prepared by
heating
Spheron 6 (S-I) at 1273 K in vacuo, and S-III was prepared
by graphitizing Spheron 6 (S-I) at 2973 K in
an argon atmosphere. It was found from the Kr isotherms that the
surface of S-II was heterogeneous,
while that of S-III was homogeneous. The t-plot of the
N2 isotherm showed that S-II was nonporous.
However, the minute microporosity was detected in S-II from the
comparison plot of the water isotherm.
The size of the micropores present in S-11 may be larger than 0.22
nm (the water molecule size) and smaller
than 0.43 nm (the nitrogen molecule size). The adsorption
isotherms of water vapor on S-III were measured
at 283, 298, and 308 K in the range of Γ = 0.0004−0.6
H2O/nm2. The differential enthalpies
(ΔH̄
S) and
the differential entropies (ΔS̄
S =
S̄
S − S
L) of the
water molecules adsorbed on the S-III surface were
computed using the water isotherms. From the curves of
ΔH̄
S, ΔS̄
S,
vs coverage, it has been shown that
the adsorbed water molecules start to make the liquid-like clusters
from low coverage and that mobility
of the adsorbed water molecules is very large below Γ = 0.02
H2O/nm2.
The pyrolytic processes of polycarbosilane (PCS) to silicon carbide and of polycarbosilazane (PCSZ) to silicon carbonitride were studied by gas analysis, electron spin resonance (ESR), and X-ray diffraction. On the progress of conversion from organic polymers to ceramics above 800 K, decomposition gases like CH4 and H2 evolved, and free radicals as the intermediate active species in the chemical reactions were detected during the pyrolysis. The gas yield and the radical concentration profile against pyrolysis temperature indicated that there were several steps in the pyrolysis of PCS and PCSZ. At the last step in the pyrolysis of PCS, the microcrystals of β-SiC began to precipitate, while the microcrystals of β-SiC and Si3N4 precipitated in the pyrolysis of PCSZ.
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