Trialkylsilyl-Protected Functional Initiators for Stereospecific Anionic Polymerization of Methacrylates

Anionic polymerizations of methyl methacrylate with trialkylsilyl-protected lithium benzylamides were conducted in the presence of aluminum compounds such as n-Bu₃Al. When the Me₃Si-protected amide was used, the carbonyl attack took place to some extent to form a methacrylamide derivative with slightly lower initiator efficiency (∼0.9). In the case of i-Pr₃Si-protected amide, the carbonyl addition was completely suppressed. The obtained polymers had narrow molecular weight distribution and carried benzylamino end-group, as revealed by NMR analysis, which is readily accessible for further chemical transformations such as acylation with acryloyl chloride and debenzylation with H₂/Pd-C. Difuntional initiators with protected groups were also examined.     

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.     

Controlling the Polymer Microstructure in Anionic Polymerization by Compartmentalization

An ideal random anionic copolymerization is forced to produce gradient structures by physical separation of two monomers in emulsion compartments. One monomer (M) is preferably soluble in the droplets, while the other one (D) prefers the continuous phase of a DMSO‐in‐cyclohexane emulsion. The living anionic copolymerization of two activated aziridines is thus confined to the DMSO compartments as polymerization occurs selectively in the droplets. Dilution of the continuous phase adjusts the local concentration of monomer D in the droplets and thus the gradient of the resulting copolymer. The copolymerizations in emulsion are monitored by real‐time ¹H NMR kinetics, proving a change of the reactivity ratios of the two monomers upon dilution of the continuous phase from ideal random to adjustable gradients by simple dilution.     

羟基硅油乳液合成中“漂油”现象的探索

研究了以DBSA为乳化剂与催化剂的阴离子乳液聚合D4过程中的乳液粒子形成及粒径的变化。分析实验现象发现,该体系中羟基硅油乳胶粒是通过胶束和单体珠滴两种方式形成的,由单体珠滴生成的体积较大的羟基硅油乳胶粒是形成羟基硅油乳液“漂油”的主要原因。     

Dual Reactivity of Magnesium Compounds as Initiators for Anionic and Cationic Polymerization

Organomagnesium compounds are well known initiators of anionic polymerization of polar monomers. However, we have found recently that in the presence of compounds with labile halogen atoms, e.g., benzyl chloride, they are also active initiators of cationic polymerization of isobutylene and styrene in hydrocarbon media. The tentative scheme of cationic initiation is suggested assuming the formation of benzyl cation connected with Mg₂Cl₅⁻ counter-ion. The scheme is confirmed by quantum-chemical calculations and ¹H NMR analysis of polyisobutylene. On addition of a polar monomer, N,N-dimethylacrylamide or 2-vinylpyridine, to Bu₂Mg-BzCl-isobutylene polymerizing mixture, the former readily polymerizes. The mixture of homopolymers rather than block copolymers is formed in this case, however, this fact proves the co-existence of anionic and cationic centers in the system.     

阻滞阴离子聚合的研究进展

介绍了阻滞阴离子聚合引发剂体系近十年的研究现状,详细讨论了几代阻滞引发体系各自的阻滞机理,以及在阴离子聚合制备苯乙烯共聚物树脂中的应用。简单介绍了BASF公司应用阻滞阴离子聚合制备高抗冲聚苯乙烯的应用现状,指出了阻滞阴离子聚合活性可控的优点使其具有更广泛的发展空间。     

苯氧铜/正丁基锂体系引发MMA负离子聚合及其活性特征的研究

采用苯氧铜/正丁基锂(PhOCu/n-BuLi)体系引发MMA聚合, 通过GPC, ¹H NMR对聚合物进行了表征. 实验结果表明, 该体系聚合反应速度较快, 温度、引发体系组成是影响聚合物分子量及其分布、单体转化率、引发剂引发效率、聚合物的立构规整性的主要因素; －40 ℃时分子量分布比较窄, 但引发效率也比较低(大约15%). 低引发效率、宽分子量分布与引发剂的聚集状态有关. 分子量与单体浓度、引发剂浓度的关系说明, 该体系具有一定程度的活性聚合特点.     

Anionic polymerization of n‐hexyl isocyanate with monofuctional initiators. Synthesis of well‐defined diblock copolymers with styrene and isoprene

Several monofunctional initiators, such as s‐BuLi, 1,1‐diphenyl‐4‐methylpentyl lithium (DPMPL), benzyl potassium (BzK), triphenylmethyl sodium (trityl sodium, TrNa) and benzyl sodium (BzNa) were tested and evaluated for the polymerization of n‐hexyl isocyanate (HIC) in THF at ?98 °C. The polymerizations were conducted either without or with additives, such as LiBPh₄, NaBPh₄, and crown ether 18C6. The products were characterized by size exclusion chromatography (SEC), membrane osmometry (MO), and ¹H NMR spectroscopy. The best results regarding polymerization yield, molecular weight distribution, and agreement between the stoichiometric and the experimentally observed molecular weight were obtained by the initiating system BzNa/NaBPh₄ in a molar ratio 1/10. By using BzNa/NaBPh₄ system, well‐defined block copolymers of HIC with styrene or isoprene were synthesized for the first time. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3533–3542, 2005     

Aziridine Termination of Living Anionic Polymerization

A switch from carbanions to aza‐anions is performed by the addition of N‐tosylaziridine (TAz) to living poly(styryl) (PS) chains. This is the first example of carbanionic aziridine ring‐opening which was previously activated by amidation with a tosyl group to enable nucleophilic ring‐opening by the living chain end. Poly(styrene)‐tosylaziridines (PS‐TAz) with narrow molecular weight distributions and variable molecular weights are synthesized. The removal of the tosyl group and subsequent functionalization is shown, evidencing quantitative transfer to azaanionic species. All polymers are characterized in detail by ¹H NMR spectroscopy, DOSY ¹H NMR spectroscopy, and size exclusion chromatography (SEC). This strategy allows the introduction of amine groups via anionic polymerization in analogy to the well‐established epoxide termination.

     

Structure of Charge Transfer Reaction Complexes Formed in Anionic Polymerization of Isoprene

A new mechanism is suggested for the anionic polymerization of isoprene. The key moment of this mechanism is thermal electron excitation of the complex of a living polymer with a monomer to the low lying S₁ (T₁) state involving a charge (electron) and (Li⁺) cation transfer from the terminal unit to the monomer molecule. It is stated that the probability of chemical bonding depends on the spin density on the radical centers of reactant molecules and on the geometry of the reaction complex. The semiempirical AM1 and ab initio 6-31G* quantum-chemical calculations revealed strong interaction for the ground electronic state of the complex (5-10 kcal/mole) and low energies of the excited triplet levels (<10 kcal/mole).     

活性阴离子聚合及其单体的研究进展

适用于活性阴离子聚合的单体拓展研究是有关活性阴离子聚合的一项重要的研究工作.本文重点介绍了近十年在活性阴离子聚合领域出现的新型单体的结构设计、合成及其聚合过程的研究进展.文中涉及到的新型单体主要包括非(弱)极性类单体、极性单体及其它单体.进一步细分,非(弱)极性类单体分为苯乙烯衍生物类单体和丁二烯衍生物类单体,极性单体中含有丙烯酸酯类单体、丙烯酰胺类单体、氯乙烯以及N-乙烯基咔唑,其它单体包括异氰酸酯类、烯酮类以及杂环类单体.最后本文对上述这些新型单体中的一些单体用于复杂大分子拓扑结构的设计合成情况也作了简要介绍.     

醇钾及酚钾在甲基丙烯酸甲酯阴离子聚合中的应用

以正丁基锂(n-BuLi)为引发剂,叔丁醇钾(t-BuOK)和苯酚钾(POK)为副反应抑制剂,实现了甲基丙烯酸甲酯(MMA)在四氢呋喃(THF)溶剂中的阴离子聚合。采用凝胶渗透色谱(GPC)、核磁共振氢谱(1 H-NMR)等研究了产物的数均分子量、分子量分布(MWD)和分子结构。结果表明:t-BuOK与n-BuLi之间发生反离子交换反应使活性中心的反离子Li~+被K~+替换,从而在一定程度上抑制了MMA聚合过程中的副反应,当n(t-BuOK)/n(n-BuLi)≥10时,可在0℃下实现MMA的可控阴离子聚合;PMMA分子量分布较窄(1.22),且数均分子量与设计值十分接近,MMA聚合的副反应得到了有效控制;进一步添加的POK能与活性中心的K~+配合,促进对MMA聚合副反应的抑制,使MMA的可控阴离子聚合能在较高温度(40℃)下得以实现,所合成的聚甲基丙烯酸甲酯(PMMA)数均分子量分布窄(1.24)且数均分子量符合设计值。     

Modeling of Anionic Polymerization of Isoprene in an Industrial Reactor

One of the most important reasons for modeling polymerization processes is to provide a tool for estimating the risks of runaway reactions in polymer industry. This is especially important for batch processes, such as anionic polymerization of isoprene or butadiene. This work presents a theoretical and experimental research of the anionic polymerization of isoprene using cyclohexane as solvent and n‐butyllithium as initiator. In the first part, a phenomenological kinetic expression is obtained that describes the anionic polymerization of isoprene initiated by n‐butyllithium in cyclohexane. In the second, the mass and energy balance equations are solved to model the anionic polymerization of isoprene in a quasi‐adiabatic batch reactor. Adjustment of reactor parameters is made using the data obtained from a laboratory reactor. The proposed model predicts adequately the obtained temperature, pressure, and conversion profiles from this set of experiments. Finally, a mathematical model is developed to predict the behavior for the anionic polymerization of isoprene in an industrial reactor.     

Organosilicon‐Assisted Transformation of Living Anionic into Living Cationic Polymerization

A novel method is described for transforming an anionic polymerization process into a cationic polymerization process assisted by organosilyl groups. The reaction of the p‐tolyldimethylsilyl end group of polystyrene and trifluoromethanesulfonic acid produced a silyl triflate end group that served as a macroinitiator for the living cationic polymerization of isobutyl vinyl ether. The Si O linkage in the block copolymers underwent specific cleavage by reaction with tetrabutylammonium fluoride.

     

基于高真空实验技术活性阴离子聚合方法学研究进展

活性阴离子聚合能够得到分子量及分布可控的模板聚合物,是环状、树枝状以及多臂星形等复杂拓扑结构聚合物的重要合成方法。高真空实验技术能够使反应环境彻底封闭、杜绝杂质影响从而得到更加精确的实验数据,因此成为活性阴离子聚合理论研究的重要手段。本文对基于高真空实验技术的活性阴离子聚合方法学研究进行了总结,通过多官能引发剂、“大单...     

Metal‐Free Activation in the Anionic Ring‐Opening Polymerization of Cyclopropane Derivatives

The successful activation observed when using Bu^tP₄ phosphazene base and thiophenol or bisthiols for the anionic ring opening polymerization (ROP) of di‐n‐propyl cyclopropane‐1,1‐dicarboxylate is described. Well‐defined monofunctional or difunctional polymers with a very narrow molecular weight distribution were obtained through a living process. Quantitative end‐capping of the propagating malonate carbanion was accessible by using either an electrophilic reagent such as allyl bromide or a strong acid such as HCl. Kinetics studies demonstrated a much higher reactivity compared to the conventional route using alkali metal thiophenolates.

     

Living Anionic Polymerization of N-Methacryloyl-2-methylaziridine

Anionic polymerization of N-methacryloyl-2-methylaziridine ( 1 ) proceeded with 1,1-diphenyl-3-methylpentyllithium (DMPLi) in the presence of LiCl or Et₂Zn to give the polymers possessing predicted molecular weights and narrow molecular weight distributions (M_w/M_n < 1.1) at −78 ∼ −40 °C in THF. In each polymerization initiated with DMPLi/LiCl at the various temperatures ranging from −40 to −60 °C, the linear relationship between polymerization time and conversion of monomer was obtained from the GLC analysis. The rate constant and the activation energy of the anionic polymerization for 1 were determined as follows: ln k = −5.85 × 10³/T + 23.3 L mol⁻¹ s⁻¹ and 49 ± 4 kJ mol⁻¹, respectively. Poly( 1 ) showed the glass transition temperature at 98 °C, and gave the insoluble product at higher temperature around 150 °C through the thermal cross-linking of highly strained N-acyl-aziridine moiety.