Synthesis and reactions of polytetrahydrofuran with thiolanium end groups

Living polytetrahydrofuran can be terminated with thiolane to form the corresponding thiolanium-terminated polymers. The thus obtained monotelechelic or ditelechelic polymers are unreactive towards water, but can selectively couple with charged nucleophiles by a nucleophilic ring-opening reaction of the terminal thiolanium ions. This process has been used to prepare well-defined homopolymers such as star polymers, segmented polymers or model networks.     

Pyrolysis Kinetics for the Conversion of a Polymer into an Amorphous Silicon Oxycarbide Ceramic

We present experimental and analytical results for the pyrolysis reactions underlying the conversion of a cross-linked polymer into an amorphous ceramic material. The activation energies, obtained from thermogravimetric data, and chemical analysis of the volatiles by mass spectroscopy are used to identify the reaction pathways. The reaction is determined to be first-order, which is consistent with its solid-state nature. The magnitude of the weight loss is analyzed to calculate the number of molecular sites in the polymer that participate in the reaction. The experiments were conducted on a polymer made from silsesquioxanes that convert into silicon oxycarbide ceramics on pyrolysis. The results show that <2.5% of the silicon atoms in the polymer are removed as volatile silanes, and less than one-half of the carbon atoms are lost as methane. These results are a first step in understanding the molecular basis for the ceramic yield, as well as the evolution of the nanostructure as the material changes from an organic into a ceramic state by reactions that can occur at <850°C.     

Photoinitiation of polymerization of styrene by oxotris(dimethyl dithiocarbamato) vanadium(V)

Oxotris(dimethyl dithiocarbamato) vanadium(V) [VO(S₂CN(CH₃)₂)₃] sensitizes the polymerization of styrene when irradiated by light of λ = 365 nm at 25°C. Under the experimental conditions employed, no retardation occurs, and the rate of initiation is independent of monomer concentration. The mean values of the quantum yield of iniiation (?_i) and polymerization (?_o) are 2.85 × 10^?3 and 6.72 respectively. Spectroscopic analysis shows that initiation occurs predominatly through scission of the N,N-dimethyl dithiocarbamate ligand (—SC(S)N(CH₃)₂) with reduction of vanadium(V) to (IV), and VO (S₂CN(CH₃)₂)₂ is the final photolytic product. A reaction mechanism is proposed based on an intramolecular photoredox reaction which leads to the primary formation of SC(S)N(CH₃)₂ radicals and a vanadium(IV) chelate complex. The rellevant kinetic parameters are evaluated. The polystyrene produced shows a photoactivity when irradiated with UV-light.     

Anionic synthesis and characterization of ω-formyl-functionalized polystyrenes

ω-Formyl-functionalized polystyrenes can be synthesized in quantitative yield by reacting poly(styryl)lithium (M _n = 2 × 10³?8 × 10³ g/mol) in benzene with a 0.1?0.4 molar excess of 4-morpholinecarboxaldehyde followed by methanol termination and precipitation into methanol. Narrow molecular weight distribution ω-formyl-functionalized polystyrenes were characterized by hydroxylamine end-group titration, thin layer chromatography and both ¹H and ¹³C NMR spectroscopy. The mechanism of the functionalization was studied by trapping the tetrahedral α-amino alkoxide intermediate with diphenylphosphinic chloride.     

Modeling emergency interregional electric power transfer

This paper describes a combined model of the U.S. power system that is the first to allow for emergency interregional transmission of electricity. The Interregional Transfer Model (INTRAN) is used with the Baughman-Joskow Regionalized Electricity Model (REM) to simulate the transshipment of emergency interregional electric power exchanges. REM-INTRAN is a tool to assist policy makers concerned with the reliability and adequacy of the U.S. bulk power system. It is the only model available that provides regional detail of the electricity sector and emergency interregional power transfer capabilities. REM-INTRAN considers generation plant mix and monthly load characteristics on a regional basis, and the limiting transfer capacities and costs of emergency interregional power transfers.     

丙烯酰胺中浓度水溶液的辐射聚合——EDTA二钠体系的研究

本文研究了用~(60)Coγ射线引发丙烯酰胺水溶液的聚合体系中,添加乙二胺四乙酸二钠盐(EDTA),对提高聚合物分子量,改善水溶性和掩蔽铜、铁等有害杂质的作用。同时也对剂量率、剂量、辐照温度等因素进行了探讨。制得了分子量高,水溶性好的聚丙烯酸胺(PAM)。本实验结果为中间试验和工业化生产提供了科学依据。     

聚合物合成反应的新进展

扼要阐述了传统聚合反应的进展,简要评述了环烯烃开环置换聚合、基团转移聚合、变换聚合反应以及端活性齐聚物的合成。     

Poly(1,5-hexadiyne) films prepared using rhodium(i) catalysts

Bis(1,5-cyclooctadiene)dirhodium(I)dichloride and bis(norbornadiene)-dirhodium(I)dichloride are effective catalysts for polymerization of 1,5-hexadiyne. The structure of the polymer obtained and its behaviour towards oxidation and oxidizing agents has been elucidated by means of infrared and ultraviolet spectroscopy. It is proposed that polymerization proceeds with formation of a polymer having a five-membered ring in each of its monomeric units. The polymer is highly conjugated and can be obtained directly during polymerization as film, which has a metallic lustre, is insoluble in common solvents, and shows good resistance to oxidation in air, if sufficiently thick.     

苯乙烯聚合动力学 （Ⅱ）热引发本体聚合动力学模型

在１２０～２００℃内研究了苯乙烯热引发本体聚合的动力学，建立了聚合速率及聚合度分布模型，所建立的模型能很好地描述在高转化范围内的转化率－时间关系及聚合度分布，上述研究结果可为苯乙烯热聚合反应器的设计、控制等提供可靠的依据。