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A series of chain-extended PET samples were obtained by the use of different amounts of a diepoxide as chain extender, which
was prepared for this purpose. These samples exhibited different intrinsic viscosities and degrees of branching or cross-linking.
The effects of this differentiation on the thermal properties were studied by differential scanning calorimetry. The thermal
parameters studied were the glass transition temperature (Tg), the cold-crystallization temperature (Tcc), the melting temperature (Tm), the enthalpy (ΔHm) and the degree of crystallinity. The data revealed that, the higher the quantity of chain extender or the chain extension
time, the higher Tgand Tcc, but the lower Tmand ΔHm, i.e. the more amorphous the chain-extended samples, as also shown by density measurements.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Maury Bramson 《Journal of statistical physics》1988,51(5-6):863-869
Recent results on two interacting particle systems on are summarized, the asymmetric simple exclusion process and the branching exclusion process. 相似文献
15.
In this paper, we establish the discrete approximation of continuous-state nonlinear branching processes in Lévy random environments by using tightness and convergence sequence in infinite dimensional product space via stochastic differential equations. Taking α-stable branching as an example, the conditions which are given to discretize continuous-state nonlinear branching processes in Lévy random environments are verified. © 2022 Chinese Academy of Sciences. All rights reserved. 相似文献
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The influence of the comonomer content in a series of metallocene-based ethylene-1-octene copolymers (m-LLDPE) on thermo-mechanical, rheological, and thermo-oxidative behaviours during melt processing were examined using a range of characterisation techniques. The amount of branching was calculated from 13C NMR and studies using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were employed to determine the effect of short chain branching (SCB, comonomer content) on thermal and mechanical characteristics of the polymer. The effect of melt processing at different temperatures on the thermo-oxidative behaviour of the polymers was investigated by examining the changes in rheological properties, using both melt flow and capillary rheometry, and the evolution of oxidation products during processing using infrared spectroscopy.The results show that the comonomer content and catalyst type greatly affect thermal, mechanical and oxidative behaviour of the polymers. For the metallocene polymer series, it was shown from both DSC and DMA that (i) crystallinity and melting temperatures decreased linearly with comonomer content, (ii) the intensity of the β-transition increased, and (iii) the position of the tan δmax peak corresponding to the α-transition shifted to lower temperatures, with higher comonomer content. In contrast, a corresponding Ziegler polymer containing the same level of SCB as in one of the m-LLDPE polymers, showed different characteristics due to its more heterogeneous nature: higher elongational viscosity, and a double melting peak with broader intensity that occurred at higher temperature (from DSC endotherm) indicating a much broader short chain branch distribution.The thermo-oxidative behaviour of the polymers after melt processing was similarly influenced by the comonomer content. Rheological characteristics and changes in concentrations of carbonyl and the different unsaturated groups, particularly vinyl, vinylidene and trans-vinylene, during processing of m-LLDPE polymers, showed that polymers with lower levels of SCB gave rise to predominantly crosslinking reactions at all processing temperatures. By contrast, chain scission reactions at higher processing temperatures became more favoured in the higher comonomer-containing polymers. Compared to its metallocene analogue, the Ziegler polymer showed a much higher degree of crosslinking at all temperatures because of the high levels of vinyl unsaturation initially present. 相似文献
18.
This study applies the theory of stochastic processes to the equilibrium statistical physics of polymers in solution. The topics treated include random copolymers and randomly branching polymers, with self-consistent mean field effects. A new and more natural way of dealing with Boltzmann weighting is discussed, which makes it possible from the beginning of a calculation to consider only the physical polymer conformations. We also show that in general the random copolymer problem can be reduced to the ordinary polymer problem, and treat the self-consistent field problem for a general branching polymer. 相似文献
19.
Yoshisuke Ueda 《Journal of statistical physics》1979,20(2):181-196
This paper deals with turbulent or chaotic phenomena which occur in the system governed by Duffing's equation, a special type of two-dimensional periodic system. By using analog and digital computers, experiments are carried out with special reference to the change of attractors and of average power spectra of the random processes under the variation of the system parameters. On the basis of the experimental results, an outline of the random process is made clear. The results obtained in this paper will be applied to various physical problems and will also serve as material for the development of a proper mathematics of this phenomenon. 相似文献
20.
Weiping Gan Xiaosong Cao Yi Shi Lei Zou Haifeng Gao 《Journal of polymer science. Part A, Polymer chemistry》2018,56(19):2238-2244
Copper-catalyzed azide-alkyne cycloaddition polymerization (CuAACP) of AB2 monomers demonstrated a chain-growth mechanism without any external ligand because of the complexation of in situ formed triazole groups with Cu catalysts. In this study, we explored the use of various ligands that affected the polymerization kinetics to tune the polymers’ molecular weights and the degree of branching (DB). Eight ligands were studied, including polyethylene glycol monomethyl ether (PEG350, Mn = 350), tris(benzyltriazolylmethyl)amine (TBTA), 2,6-bis(1-undecyl-1H-benzo[d]imidazol-2-yl)pyridine (Py(DBim)2), 2,2′-bipyridyl (bpy), 4,4′-di-n-nonyl-2,2′-bipyridine (dNbpy), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), N,N,N′,N″,N″-penta(n-butyl)diethylenetriamine (PBuDETA), and N,N,N′,N″,N″-pentabenzyldiethylenetriamine (PBnDETA). All ligands except PEG350 exhibited stronger coordination with Cu(I) than the polytriazole polymer, which freed the Cu catalyst from polymers and resulted in dominant step-growth polymerization with simultaneous chain-growth feature. Meanwhile, the use of PEG350 ligand retained the confined Cu in the polymer, demonstrating a chain-growth mechanism, but lower polymer molecular weights as compared with the no-external-ligand polymerization. Results indicated that aliphatic substituent groups on ligands had little effect on the molecular weights and DB of the polymers, but rigid aromatic substituent groups decreased both values. By varying the ligand species and amounts, hyperbranched polymers with DB value ranging from 0.53 ([TBTA]0/[Cu]0 = 5) to 0.98 ([PMDETA]0/[Cu]0 = 2) have been achieved. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2238–2244 相似文献