苯乙烯阴离子高温本体聚合引发机理的新发现(一)

采用一种新的研究方法,进行了苯乙烯阴离子的高温本体聚合,突破了传统阴离子动力学研究中仅采用高真空、稀溶液、低转化率的局限.结果表明:当聚合转化率小于4%时,聚合反应机理完全符合经典阴离子活性聚合的理论;但继续聚合后将出现一个转化率停滞平台和聚合速率再次升高的现象,与传统理论不同.假设活性种引发聚合后形成的大分子链不再反...     

苯乙烯阴离子本体聚合引发剂缔合及其机理的研究

分别以正丁基锂和叔丁基锂为引发剂,采用自制管式流动反应装置,对较高温度下苯乙烯阴离子本体聚合动力学进行了研究.证实了正丁基锂主要以六元缔合结构形式引发聚合,并导致超分子团聚体的形成,从而使进一步的聚合因单体扩散受阻而受到限制,并伴随聚合转化率停滞平台（SCP）的产生.随后由于前期聚合累积的能量,使超分子结构完全解离.聚合温度越高,SCP持续时间越短.结果还表明,在正丁基锂引发剂中,存在一个以六元缔合结构为基础形成的更大的缔合体结构.原子力显微镜照片显示,超分子结构的直径分别为20～30nm和50～60nm.此外,在阴离子聚合过程中活性种的缔合结构只决定于初始引发剂的分子结构,而不同活性种缔合结构对阴离子聚合的链增长存在很大影响,从而解释了采用不同结构的锂系引发剂引发苯乙烯单体聚合时聚合速率存在巨大差异的原因.     

苯乙烯阴离子聚合仿真实验软件的研究

烯类单体的阴离子聚合是高分子化学课程中主要理论内容之一,为了使学生更好地掌握和运用理论知识,通常需要配合实验教学加以验证。而传统的烯类单体的阴离子聚合实验由于受各方面条件限制,实验效果欠佳。本文以苯乙烯阴离子聚合实验的开展为背景,介绍了聚合实验软件平台的设计、开发、硬件系统和实验的内容。经过验证,该实验软件平台功能完善,界面简洁,运行稳定,可以结合实际硬件设备以及具体需求进行实验教学。     

苯乙烯在炭黑表面的阴离子接枝聚合研究

利用正丁基锂（ｎ－ＢｕＬｉ）与炭黑（ＣＢ）表面含氧基团反应制得了表面含－ＯＬｉ基团的反应型炭黑，以该炭黑与聚氧乙烯－聚氧丙烯－聚苯乙烯（ＰＥＯ－ＰＰＯ－ＰＳ）多嵌段聚合物组成的阴离子引发体系作活性中心，研究了苯乙烯在炭黑表面的阴离子接枝聚合。ＦＴ－ＩＲ，ＴＥＭ和ＤＳＣ分析表明在接枝炭黑表面存在苯乙烯的聚合物。接枝炭黑在甲苯中有良好的分散稳定性。     

双金属引发体系苯乙烯活性聚合活性种的交互缔合动力学

自从发现烷氧基钾(ＲＯＫ)/烷基锂(ＲＬｉ)双金属引发体系对丁二烯苯乙烯阴离子共聚具有高效竟聚率调节作用以来[1],相关的机理研究一直十分活跃[2～6].在这类双金属引发体系中,由于含有Ｋ、Ｌｉ两种反离子,因此可能存在钾活性种(ＰＫ)和锂活性种(ＰＬｉ)的交互缔合体.但迄今有关不同反离子活性种形成交互缔合体的研究报道较少.本工作利用2甲基2己醇钾对苯乙烯均聚反应速度具有较大影响这一特性,对低Ｋ/Ｌｉ情况下可溶性醇钾/ｎＢｕＬｉ双金属引发体系苯乙烯均聚动力学进行了研究.建立了以交互缔合体为基础的反应动力学模型.求得了ＰＫ的增…     

激光作用产生离子引发的苯乙烯聚合

激光作用产生离子引发的苯乙烯聚合邹友思，林国良，黄荣彬，刘朝阳，郑兰荪（厦门大学化学系固体表面物理化学国家重点实验室，３６１００５）近年来，以高能量密度的脉冲激光束在高真空中溅射固体样品，已成为产生原子簇正负离子的一种有效手段。１９９３年，美国化学家...     

苯乙烯-甲基丙烯酸甲酯的高温阴离子溶液共聚

以正丁基锂(n-BuLi)为引发剂、四氢呋喃(THF)为极性调节剂,采用具有较大空间位阻和特定电荷环境的P配合物作为抑制剂,在80℃下实现了苯乙烯(St)与甲基丙烯酸甲酯(MMA)的阴离子嵌段共聚.采用GPC、FT-IR、1H-NMR等手段对共聚物的结构及分子量进行了分析.结果表明:共聚物中各链节的分子量与设计分子量接...     

苯乙烯—环氧乙烷嵌段共聚物的阴离子聚合与表征

用二苯甲烷钾为引发剂,阴离子聚合法合成了苯乙烯（Ｓｔ）－环氧乙烷（ＥＯ）嵌段共聚物,并用ＦＴＩＲ,＾１Ｈ－ＮＭＲ,ＳＥＣ,ＷＡＸＤ和动态粘弹谱对共聚物进行了表征。结果表明所得聚合物为分子量可控,窄分布的两嵌段共聚物。     

双官能度引发剂引发苯乙烯聚合微观动力学

采用 2 ,5 二甲基 2 ,5 二己酰基过氧化己烷 (DMDEHPH)为引发剂 ,在 5 5～ 80℃下引发苯乙烯聚合 .通过研究影响聚合速率的各种因素 ,得出了聚合速率对单体浓度和引发剂浓度的级数分别为 1 0和 0 5次、聚合活化能为 92 0kJ mol、引发效率为 0 5 5± 0 0 3.温度一定 ,引发效率随引发剂浓度的增加而减小 .求得 6 0和70℃下DMDEHPH向引发剂的链转移常数分别为 0 0 37和 0 0 4 8、向单体的链转移常数分别为 0 5 9× 10 - 4和0 75× 10 - 4.     

以二甲基硅二苯基硅共聚物引发苯乙烯光聚合的研究

本文研究了二甲基硅二苯基硅共聚物(P(DMS-co-DPS))作为光敏引发剂,引发苯乙烯进行光聚合的过程。结果表明,聚合为自由基引发的链式反应,聚合速率与P(DMS-co-DPS)浓度的0.37次方成正比;本体聚合活化能为30.6KJ/mol,氧气对聚合无明显影响。     

Sodium Hydride/Trialkylaluminum Complexes for the Controlled Anionic Polymerization of Styrene at High Temperature

Summary: A new generation of anionic initiators (butyllithium free), based on trialkylaluminum and a readily available alkali metal hydride, has been developed for the control of styrene polymerization at high temperature. Triisobutylaluminum and sodium hydride form heterocomplexes that are efficient for the initiation of styrene polymerization at 100 °C in toluene or in bulk. To be active under such conditions, these systems require the presence of an excess of metal hydride with respect to AlR₃ ([Al]/[Na] < 1). PS chains are specifically initiated by the hydrides coming from NaH, and molar masses are controlled in the range 0.8 < [Al]/[Na] < 1. Fast exchange between dormant 1:1 and active 1:2 complexes (Al:Na), and ligand rearrangements within the 1:2 complex, can explain the observed results.

Initiation of styrene with i‐Bu₃Al/NaH systems.     

Aluminate and Magnesiate Complexes as Propagating Species in the Anionic Polymerization of Styrene and Dienes

The influence of MgR₂ and AlR₃ additives on alkyllithium initiators in the anionic polymerization of butadiene has been investigated in non polar solvents. A strong decrease of the diene polymerization rate in the presence of the two Lewis acids was observed, similarly to that observed in the retarded anionic polymerisation of styrene. With n,s-Bu₂Mg, the percentage of 1,2 vinyl units increases with the [Mg]/[Li] ratio. This behavior is specific to magnesium derivatives bearing secondary alkyl groups and likely results from the additional complexation of lithium species by free dialkylmagnesium and/or a 1,4- to 1,2- chain end isomerization process during chain exchanges between polybutadienyl active chains and dormant ones attached to magnesium species. These reversible exchanges also lead to the formation of one supplementary chain by initial dialkyl magnesium which acts as reversible chain transfer agent. On the contrary with the R₃Al/RLi systems the number of chains is only determined by the concentration of initial alkyllithium and no modification of the polybutadiene microstructure compared to lithium initiators (1,4 units = 80%) is noticed. Dialkyl magnesiate complexes with alkali metal derivatives (i.e. alkoxide) are also able to influence the stereochemistry of the styrene insertion during the propagation reaction. Polystyrenes with different tacticities ranging from predominantly isotactic (85% triad iso) to syndiotactic (80% triad syndio) can be obtained with these initiators.     

New Perspectives in Living/Controlled Anionic Polymerization

Summary: Control of the reactivity and selectivity of active species remains a major challenge in the course of living/controlled polymerizations of vinyl and heterocyclic monomers. We have found that alkyl metal derivatives such as dialkylmagnesium or trialkylaluminum derivatives or the corresponding alkoxyakyl metal derivatives, when added to conventional anionic polymerization systems, are very effective mediators for the controlled anionic polymerization of both styrenic and oxirane monomers. When used as additives to alkali metal alkyl initiators (alkyl lithium, alkyl sodium) for the styrene anionic polymerizations, they strongly retard the reactivity of the propagating species and allow controlling the polymerization in very unusual conditions (bulk, very high temperature). On the contrary, when used in combination to the same alkali metal based initiators for the anionic polymerization of ethylene oxide or propylene oxide, these additives can drastically enhance the reactivity and the selectivity of the propagating species allowing a fast living-like polymerization to proceed already at low temperature in hydrocarbon media.     

A Novel Efficient Ligand in Anionic Polymerization at Elevated Temperature

This work confirmed a novel ligand in the anionic polymerization, lithium phenoxide, which helped to improve the controllability of the polymerization. The stability of n‐BuLi against THF at 0°C was effectively improved by adding lithium phenoxide. More than 60% n‐BuLi in THF was alive with the presence of lithium phenoxide after stirring at 0°C for 20 min, compared to 2% under same conditions but without lithium phenoxide. The propagation of polymerization of styrene (St) and methyl methacrylate (MMA) were retarded after adding lithium phenoxide. And by adding more than 10 fold lithium phenoxide, completed conversion was achieved in the polymerization of MMA in THF at 0°C. The lithium phenoxide showed both promoting and inhibiting effects in the polymerization of isoprene (Ip): it promoted the formation of 3,4‐structure, while mitigated the formation of 1,2‐ and 1,4‐structures. In general, the polymerization rate of Ip was promoted by lithium phenoxide.     

A New View of the Anionic Diene Polymerization Mechanism

We investigated the anionic polymerization of butadiene in d-heptane solvent using tert-butyl lithium as initiator. Two complementary techniques were used to follow the polymerization processes: ¹H NMR and small angle neutron scattering (SANS). The time resolved ¹H NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The initiation event commences slowly and then progressively accelerates. This indicates an autocatalytic mechanism. The microstructure of the first monomer units attached is to a high extent 1,2. The disappearance of initiator --- at about 10% monomer conversion --- signals the onset of the normal ∼6% vinyl content of the chain. Small angle neutron scattering was used to study the aggregation behavior of the carbon lithium head groups. It is well known that the polar head groups aggregate and form micellar structures. For dienes in non-polar solvents the textbook mechanism assumes the formation of only tetramers during the propagation reaction. By combining ¹H NMR and SANS results we were able to determine quantitatively the aggregation number during all stages of the polymerization. Our measurements show the existence of large-scale structures during the initiation period. The initial degree of aggregation of more than 100 living polymer chains diminished as the polymerization progressed. In addition, even larger, giant structures with N_agg >>1000 and R_g ≈ 1000Å were found.     

高温水中多产物反应模型的构建及机理研究

建立了高温水中的反应模型并采用密度泛函理论(DFT)对香叶醇在高温水中的反应路径进行了研究. 通过前线轨道分析确定了反应的可能性. 高温水中香叶醇的反应路径与常温水中不同, 从常态下的酸催化反应路径转变为高温水状态下的酸碱共催化路径, 计算所得反应能垒为205.8 kJ/mol. 分别计算分析了高温水环境和周围水分子对反应能垒的影响, 结果表明, 高温水对反应物零点能的影响最大为0.966 kJ/mol, 水分子个数的影响最大可达94.7 kJ/mol. 官能团周围水分子个数变化对反应所产生的的影响大于高温水环境的影响.     

High Temperature Semibatch Free Radical Copolymerization of Styrene and Butyl Acrylate

Summary: High temperature semibatch free radical solution copolymerizations of n-butyl acrylate (BA) and styrene (ST) were carried out over a range of copolymer composition. The significant increase in experimental polymer weight-average molecular weight with time, as well as the shift in the entire polymer molecular weight distribution, is explained by assuming fast β-scission of BA midchain radicals with an adjacent styrene unit, followed by subsequent addition of the resultant macromonomer to growing radicals. A mechanistic model including backbiting and β-scission, macronomer incorporation, long-chain branching, and propagation and termination penultimate effects was constructed in Predici; the model provides a good representation of the experimental data using rate coefficients taken from literature.     

（Sr，Ba）_（1－x）Eu_xTiO_3的高温高压合成及XPS研究

用高温高压法合成了Ｓｒ１－ｘＥｕｘＴｉＯ３（ｘ＝０．０，０．１，０．２，０．３，０．４，０．５）及Ｂａ０．３Ｅｕ０．７ＴｉＯ３化合物．结果表明，所有样品均为立方结构，样品中存在Ｅｕ（Ⅱ）和Ｅｕ（Ⅲ）的混合价．Ｅｕ３＋的掺入直接影响了Ｓｒ离子与氧离子的结合，使Ｓｒ３ｐ３／２的结合能随ｘ的增加而增加．