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101.
An-Long Li 《Polymer》2004,45(19):6533-6537
The first example of living cationic random copolymerization of β-pinene and isobutylene was achieved with 1-phenylethyl chloride/TiCl4/Ti(OiPr)4/nBu4NCl (TiCl4/Ti(OiPr)4 mole ratio: 3/1) initiating system in CH2Cl2 at −40 °C. β-Pinene and isobutylene was consumed at almost the same rate, suggesting that the two monomers exhibit almost equal reactivity. At any monomer feed ratio, the number-average molecular weight (Mn) of the copolymers increased in direct proportion to the total monomer conversion, and the molecular weight distribution was relatively narrow (Mw/Mn=1.1-1.2) throughout the reaction. The reactivity ratios determined by the Kelen-Tüdõs method were rβ-pinene=1.1 and risobutylene=0.89, which indicated that the composition of copolymer is approximately identical to the monomer feed ratio. The analysis of the structure and sequence distribution of the copolymers by 1H NMR spectroscopy further confirmed that perfectly random copolymers were obtained by this living cationic polymerization system. The glass transition temperatures of the copolymers obtained with varying monomer compositions were also determined by DSC method. 相似文献
102.
Radical polymerization of butyl acrylate (BA) and random copolymerizations of styrene (St) and BA and St and methyl methacrylate (MMA) in the presence of 7-aza-15-hydroxydispiro[5.1.5.3]hexadecane-7-yloxyl (1) and 1-aza-2,2-dimethyl-4-hydroxyspiro[5.6]dodecane-1-yloxyl (2) were carried out. Radical polymerization of BA at 120 °C in the presence of 1 gave poly(BA) with Mn=20200 and Mw/Mn=1.30 at 23% conversion. The termination of polymerization observed around ∼20% conversion was solved to a certain extent by an addition of small amounts of dicumyl peroxide, and poly(BA) with Mn=37400 and Mw/Mn=1.33 was obtained in 46% yield. Random copolymerizations of St and BA and St and MMA in the presence of 1 and 2 at 80 °C gave the corresponding random copolymers with narrow polydispersities of 1.12-1.38 at the molar fraction above 0.30 of St in feed. The kinetic study for the NO-C bond homolysis of the corresponding alkoxyamines prepared from 1 and 2 were carried out, and evaluation of the preexponential factors (Aact) and the activation parameters (Eact) showed that the steric factors of the nitroxides are reflected mainly on Eact. 相似文献
103.
Alexander Theis 《Polymer》2006,47(4):999-1010
Living free radical polymerization technology (macromolecular design via the interchange of xanthates (MADIX)) was applied to give accesses to chain length and conversion dependent termination rate coefficients of vinyl acetate (VAc) at 80 °C using the MADIX agent 2-ethoxythiocarbonylsulfanyl-propionic acid methyl ester (EPAME). The kinetic data were verified and probed by simulations using the PREDICI® modelling package. The reversible addition-fragmentation transfer (RAFT) chain length dependent termination (CLD-T) methodology can be applied using a monomer reaction order of unity, since VAc displays significantly lower monomer reaction orders than those observed in acrylate systems (ω(VAc, 80 °C)=1.17±0.05). The observed monomer reaction order for VAc is assigned to chain length dependent termination and a low presence of transfer reactions. The α value for the chain length regime of log(i)=1.25−3.25 (in the often employed expression ) reads 0.09±0.05 at low monomer to polymer conversion (10%) and increases significantly towards larger conversions (α=0.55±0.05 at 80%). Concomitantly with a lesser amount of midchain radicals, the chain length dependence of kt is significantly less pronounced in the VAc system than in the corresponding acrylate systems under identical reaction conditions. The RAFT(MADIX)-CLD-T technique also allows for mapping of kt as a function of conversion at constant chain lengths. Similar to observations made earlier with methyl acrylate, the decrease of kt with conversion is more pronounced at increased chain lengths, with a strong decrease in kt exceeding two logarithmic units from 10 to 80% conversion at chain lengths exceeding 1800. 相似文献
104.
A star polymer was synthesized by addition of 1,4-diethynyl-2,5-dimethylbenzene as linking agent (30 °C, 24 h) after living polymerization of [(o-trifluoromethyl)phenyl]acetylene (o-CF3PA) with MoOCl4-n-Bu4Sn-EtOH catalyst (in anisole, 30 °C, 20 min; [Mo]=10 mM, [P∗]/[Mo]=40%, [o-CF3PA]0=200 mM). The Mn values of the living and star polymers were 8.1×103 and 5.3×104, respectively, according to gel permeation chromatography, while these values determined by multi-angle laser light scattering (MALLS) were 7.8×103 and 2.5×105. The Mw/Mn and arm number of the star polymer were 1.04 and 29, respectively, according to MALLS. The molecular weight and arm number of star polymer increased with increasing linking agent concentration and polymerization temperature. 相似文献
105.
106.
广告英语有别于普通英语,它的词汇简洁别致又富于创新。力图用最简洁、最准确的文字,为商品提供丰富的信息,使读者一目了然、过目不忘。由于商品市场竞争特别激烈,为了保证商品的广告可以最大限度的吸引人的眼球,广告撰写者总是选择新颖别致的词汇、简洁的语句和生动的修辞,以赢得消费者的喜爱。 相似文献
107.
陈克云 A.L.Epstein F.M.Chen D.C.P.Chen K.H.Lee G.L.Hung J.Y.Hong K.Y.Hong S.Ballard D.Payne M.E.Siegel J.Halls 《核技术》1989,(4)
不同浓度的~(131)I-Lym-2 MoAb与ARH-77和CEM细胞进行结合试验,结果表明:随浓度增大,结合值均升高;实验组裸鼠模型9只获得动力学数据。实验组和对照组注射~(131)I-Lym-2 MoAb后144h解剖,进行生物学分布(%D/g)测定,实验组肿瘤为16.88±12.64,肌肉为0.72±0.56。结果表明,~(131)I-131-Lym-2MoAb对临床B细胞淋巴瘤的放射免疫分析、显像有良好的效果。 相似文献
108.
When considering the full range of Web service-related activities, it becomes clear that dealing with context is a major challenge, requiring greater expressiveness, reasoning capabilities, and architectural components than are provided by the current widely accepted building blocks of the Web services stack. This paper presents an informal overview of concepts, requirements and challenges for handling contextual knowledge in connection with Web services, and briefly discusses several interesting projects in this area of research. 相似文献
109.
生活污水用于园林绿化的实验 总被引:1,自引:0,他引:1
通过对11种在天津石化公司有代表性的绿化植物10年来应用生活污水的跟踪调查及进行的相关实验证明,直接应用生活污水浇灌绿化植物,对绿化植物生长及对环境造成的负面影响不大.根据实验结果认为,生活污水可以有条件地用于园林绿化,并应注意密切跟踪调查. 相似文献
110.
This paper presents an approach to assist authors during the authoring of multimedia presentations. We extend the existing authoring support by integrating processes of topic identification, content collection and discourse structure building in a single environment. This integration allows identification of the context of the authoring process. Our approach combines this process context awareness with explicit domain and discourse knowledge to steer system suggestions. We evaluate our approach with an experimental system prototype. 相似文献