Several organostibine chain‐transfer agents possessing polar functional groups have been prepared by the reactions of azo initiators and tetramethyldistibine ( 1 ). Carbon‐centered radicals thermally generated from the azo initiators were trapped by 1 to yield the corresponding organostibine chain‐transfer agents. The high yields observed in the synthesis of the chain‐transfer agents strongly suggest that distibines have excellent radicophilic reactivity. As the reactions proceeded under neutral conditions, functional groups that are incompatible with ionic conditions were incorporated into the chain‐transfer agents. The chain‐transfer agents were used in living radical polymerization to synthesize the corresponding α‐functionalized polymers. As the functional groups in the chain‐transfer agents did not interfere with the polymerization reaction, well‐controlled polymers possessing number‐average molecular weights (Mns) predetermined by the monomer/transfer agent ratios were synthesized with low polydispersity indices (PDIs). The organostibanyl ω‐polymer ends were transformed into a number of different functional groups by radical‐coupling, radical‐addition, and oxidation reactions. Therefore, it was possible to synthesize well‐controlled telechelic polymers with the same and also with different functional groups at their α‐ and ω‐polymer ends. Distibine 1 was also found to increase PDI control in the living radical polymerization of styrene and methyl methacrylate (MMA) using a purified organostibine chain‐transfer agent. Well‐controlled poly(methyl methacrylate)s with Mn values ranging from 10 000 to 120 000 with low PDIs (1.05–1.15) were synthesized by the addition of a catalytic amount of 1 . The results have been attributed to the high reactivity of distibine 1 towards polymer‐end radicals, which are spontaneously deactivated to yield organostibine dormant species. 相似文献
The development of chemically recyclable polymers promises a closed‐loop approach towards a circular plastic economy but still faces challenges in structure/property diversity and depolymerization selectivity. Here we report the first successful coordination ring‐opening polymerization of 4,5‐trans‐cyclohexyl‐fused γ‐butyrolactone ( M1 ) with lanthanide catalysts at room temperature, producing P( M1 ) with Mn up to 89 kg mol?1, high thermal stability, and a linear or cyclic topology. The same catalyst also catalyses selective depolymerization of P( M1 ) back to M1 exclusively at 120 °C. This coordination polymerization is also living, enabling the synthesis of well‐defined block copolymer. 相似文献
The catalyst (N,N‐bis(2,6‐dibenzhydryl‐4‐ethoxyphenyl)butane‐2,3‐diimine)nickel dibromide, a late transition metal catalyst, was prepared and used in ethylene polymerization. The effects of reaction parameters such as polymerization temperature, co‐catalyst to catalyst molar ratio and monomer pressure on the polymerization were investigated. The α‐diimine nickel‐based catalyst was demonstrated to be thermally robust at a temperature as high as 90 °C. The highest activity of the catalyst (494 kg polyethylene (mol cat)?1 h?1) was obtained at [Al]/[Ni] = 600:1, temperature of 90 °C and pressure of 5 bar. In addition, the performance of a binary catalyst using nickel‐ and palladium‐based complexes was compared with that of the corresponding individual catalytic systems in ethylene polymerization. In a study of the catalyst systems, the average molecular weight and molecular weight distribution for the binary polymerization were between those for the individual catalytic polymerizations; however, the binary catalyst activity was lower than that of the two individual ones. The obtained polyethylenes had high molecular weights in the region of 105 g mol?1. Gel permeation chromatography analysis showed a narrow molecular weight distribution of 1.44 for the nickel‐based catalyst and 1.61 for the binary catalyst system. The branching density of the polyethylenes generated using the binary catalytic system (30 branches/1000 C) was lower than that generated using the nickel‐based catalyst (51/1000 C). X‐ray diffraction study of the polymer chains showed higher crystallinity with lower branching of the polymer obtained. Also Fourier transform infrared spectra confirmed that all obtained polymers were low‐density polyethylene. 相似文献
Summary: The solvent‐free syndiospecific styrene polymerization as an example of a coordination polymerization has been investigated with a catalyst system consisting of η5‐octahydrofluorenyl titanium trimethoxide as a transition metal catalyst, MAO as a cocatalyst, and TIBA, in the presence of reaction products of sterically hindered phenolic compounds, usually applied as heat stabilizers of polymers. Unexpectedly, such reaction products led to a significant increase in polymerization activity of the catalyst system. Second, after deactivation of the catalyst system, such activators result in a significantly enhanced thermal stability of the syndiotactic polymers received.
Effect of the P8‐activator on polymerization activity in dependence on polymerization time (molar ratio–styrene:MAO:TIBA:P:Ti = 700 000:50:25:25:1; molar ratio–phenolic compound:TIBA = 1:3.2; polymerization temperature: 50 °C). 相似文献
The accomplishments in the copolymerization of ethylene with cyclic olefins such as norborn‐2‐ene or cis‐cyclooctene via tandem ring‐opening metathesis polymerization (ROMP) – vinyl insertion polymerization (VIP) are outlined. This approach provides polyolefins with high molecular weight (600,000 < Mn < 4,500,000 g mol−1) and substantial amounts of double bonds along the polymer main chain. Olefinic moieties in ROMP‐derived polymers can be converted into hydroxyl, amino, silyl, ester, or carboxylate groups by different means including controlled radical polymerization‐based grafting. The underlying concept for the switch in polymerization mechanism, the resulting pre‐catalyst requirements, limitations and challenges and the chemistry developed for functionalizing unsaturated polymers are outlined in detail.
Molecular Sieves (MS) were used as a recyclable support for atom transfer radical polymerization. The catalyst complex, CuBr2/ligand was supported on hydrated MS and used for the polymerization of benzyl methacrylate at room temperature in anisole. The polymerization using CuBr2/PMDETA (pentamethyl diethyltetraamine) catalyst that is physically held by the hydration of MS exhibited moderate control and produced catalyst free polymers (<0.1 ppm) with narrow molecular weight distribution (Mw/Mn ≤ 1.33). The polymerization occurred at the interface between the hydrated support and the solution containing initiator and monomer. The hydrated MS supported catalyst was recycled efficiently without a significant loss in activity. The polymerization proceeded in a “living”/controlled manner as was evident from first‐order time conversion plots. The split kinetics experiment affirmed that there was no propagation in the solution in the absence of the supported catalyst. The reaction order plot showed zero‐order dependence on the bulk initiator concentration in solution. The results of MS supported catalyst were compared to Na‐clay supported catalyst system and the improved results were attributed to high self‐diffusion coefficient and low diffusion activation energy of water on its surface. Published 2017.§ J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3875–3883 相似文献