The pathway and degree of metallation of polymers were studied depending on the the conditions (temperature, concentration, nature, and component ratio) of metallation of poly(1-trimethylsilylprop-1-yne) (PTMSP) and poly(vinyltrimethylsilane) (PVTMS) by superbases, viz., BunLi and BusLi, in combination with potassium tert-pentyl oxide (PetOK). For the BunLi—PetOK system (1 : 3), the yield of modified PTMSP reached 90%. In the case of PTMSP, only the Me groups at the double bonds and at the Si atoms undergo metallation, whereas only the Me groups at the Si atoms are metallated in PVTMS. The kinetics of metallation with the BunLi—PetOK system was studied. 相似文献
Optical properties of poly-(1-trimethylsilyl-1-propyne) in solvents with different refractive indices and optical anisotropies have been studied by the dynamic birefringence method. An optical shape-effect has been detected in solvents characterized by refractive indices ns different from those of dry polymer nk. It was revealed that this effect is an effect of the macromolecule segment shape; this allowed us to estimate thermodynamic rigidity of the molecular chains under study (A = 82 × 10−8 cm). It has been found that the optical shear coefficient of the studied polymers solutions in anisotropic solvents exceeds considerably the same parameter in an isotropic solvent. It has been shown that this difference is caused by the solvent anisotropic molecules orientation by the axis of maximal polarizability along the macromolecule backbone. The assumption that the solvent molecules orientation order with respect to chain molecules does not depend on the chain molecule thermodynamic rigidity allowed us to obtain independent estimate of the sizes of static segments of the macromolecules under study (98 × 10−8 cm). 相似文献
In contrast to common glassy polymers, poly(1-trimethylsilyl-1-propyne) (PTMSP), a high free volume glassy polymer, shows a preferable permeation of large condensable organic vapors in comparison to permanent gases. In order to investigate this phenomenon, a systematic permeability study over a large activity range has been performed on PTMSP with three types of volatile organic compounds (VOCs) as diffusing probes: toluene, dimethylketone and dichloromethane. PTMSP was synthesized with different catalytic systems (Nb or Ta based) able to induce controlled sub-molecular cis–trans structures. Whereas dimethylketone and dichloromethane permeability can be correctly described by a classical dual-mode equation, a peculiar bell shaped pattern was obtained for toluene, with a minimum permeability located at an activity value around a=0.3–0.4. In that case, only a dual-mode expression taking into account a concentration dependent diffusion coefficient can account for the results.
On the other hand some apparent conflicting data recorded from PTMSP brand new films were related to the microstructure of the polymer main chain thanks to 13C NMR spectroscopy analysis showing importance of cis- and trans-forms of the main chain of PTMSP. cis-Structure is more flexible and can be responsible for the creation of a higher density physical network (HDN) in polymeric matrix; conversely, trans-structure is more rigid and can provide lower density physical network (LDN). The higher permeability recorded for several probes through PTMSP synthesized with TaCl5/Al(i-Bu)3 catalytic system compared to those of NbCl5 based polymer can be explained by the geometric difference of the macromolecule networks. 相似文献
The optical properties of poly(1-trimethylsilyl-1-propyne) solutions in solvents possessing optical anisotropy have been studied with dynamic birefringence measurements. In solvents characterized by refractive indexes different from the refractive index of a dry polymer, the optical form effect has been discovered. This effect is determined by the shape asymmetry of a macromolecular segment and its rigidity. Estimates showed that the length of the statistical segment, which characterizes the thermodynamic rigidity of the macromolecular chains under study, is 82 × 10?8 cm. The shear optical coefficient for solutions of the test polymer in an anisotropic solvent is markedly higher than the corresponding value in an isotropic solvent. This difference is related to the orientation of anisotropic solvent molecules along the main chain of a macromolecule by their highest polarizability axis. Under the assumption that the orientational order of solvent molecules relative to chain macromolecules is independent of the thermodynamic rigidity of chain molecules, the size of the statistical segment of the macromolecules in question has been independently estimated as 98 × 10?8 cm. 相似文献
The polymerization of 4-methyl-2-pentyne and 1-trimethylsilyl-1-propyne initiated by catalytic systems based on niobium pentachloride and Et3SiH, Bu4Sn, Ph4Sn, and Ph3SiH as cocatalysts has been investigated. Direct evidence for the living polymerization of 4-methyl-2-pentyne and 1-trimethylsilyl-1-propyne with the NbCl5-Ph4Sn catalytic system is derived. These are the linear molecular mass dependence on conversion and the continuation of chain propagation after introduction of a new monomer portion. 相似文献