Anionic polymerization of dienes using oligobutadienyl-lithium as initiator

The aim of this work is to combine the microstructure of a radical-polymerized diene (butadiene and isoprene) with the functionality of an anionically prepared one, which could be used for polyurethane preparation after functionalization. A two-step anionic procedure was used in order to obtain a hydrocarbon-soluble lithium-based initiator. When compared with the related anionic polymers obtained under classical conditions, the vinyl content of the polydienes was three times greater. These findings are discussed on a mechanistic basis. © 1998 Society of Chemical Industry     

Some light on the concept of unreactivity arising from active center association in anionic polymerizations

A long held assumption in hydrocarbon based anionic polymerization involving organolithiums is that the aggregated species are unreactive and thus serve only as reservoirs from which the active singlet species momentarily emerge to participate in the initiation or propagation events. This work demonstrates that contrary to the notion of aggregate dormancy such species can participate in monomer addition. The approach involved freeze-dried vitrified polystyryllithium which was found to be reactive toward butadiene and methanol vapors. The sub-glass transition state of the polystyryllithium eliminates the establishment of the aggregate: singlet equilibrium as a result of the inability of chains to undergo diffusion. Furthermore, it is shown that the lower bound gradient for the dependence of propagation rate on active center concentration, within experimental error, is about 1/5 for the majority of those diene systems where the active center concentration covers at least two decades. A computer evaluation of the propagation rate: active center data was done with the aim of testing and determining the equilibrium constants of these aggregated systems.     

Modelling studies of the controlled anionic copolymerization of butadiene and styrene

The anionic polymerization of isoprene with n-butyl lithium and polar modifier such as TMEDA and tripiperdinophosphine oxide were studied and kinetic and reactor models are proposed for these systems. Reactor conversion, molecular weight distribution and polymer glass transition temperature had been calculated from the model and compared favorably to the actual data for various combinations of reactor systems and operating conditions. Simulations of the model can be used to design reactor systems and predict polymer properties of large-scale operations from results of small scale batch reactor runs.     

氯乙烯悬浮聚合过程引发体系优化

在氯乙烯悬浮聚合过程机理模型的基础上,建立了复合引发体系的优化模型,并进行了二元引发体系的优化研究,得到了不同引发剂配比下的最大聚合速率等高线和临界转化率时的聚合时间等高线。结果可以用来指导复合引发剂的配方设计,有助于聚合热的均匀释放、聚合釜冷却能力的充分利用和聚合釜生产率的提高。     

Polymer reaction engineering: From reaction kinetics to polymer reactor control

Polymer reaction engineering is a relatively “young”, very broad, multidisciplinary, rapidly developing field. It is the combination of polymer science, chemistry and technology with process engineering principles. The outcome of this high degree of synergism has evolved over the last fifteen or so years towards an area that includes any or all of the following: polymerization and post-polymerization (chemical modification) reaction kinetics; mathematical modelling and process simulation; polymer reactor design and scale-up; sensor development and process monitoring; and polymer reactor optimization, state estimation and computer control. This article will attempt to give an overview of the results obtained in our laboratory over the last seven years from systematic studies of polymer reaction engineering and polymer production technology problems. These problems cover all aspects of polymer reaction engineering mentioned above. Going from fundamentals to practice, the basic premise of the article is that only by adopting a holistic approach can one devise effective strategies in order to achieve the final objective of more efficient polymer reactor design and control, and hence improved production systems of polymeric materials.     

Synthesis of well-defined block copolymers of n-hexyl isocyanate with isoprene by living anionic polymerization

n-Hexyl isocyanate (HIC) was polymerized at different reaction temperatures and times, using alkali metal naphthalenide, via anionic polymerization in THF. To prevent the formation of trimers, the polymerization of HIC was also performed utilizing sodium tetraphenylborate (NaBPh₄) as a common ion salt. As the reaction temperature decreases, yield of the polymer increases due to stabilization of the active amidate anion at low temperature. In the absence of the additive, a quantitative yield was obtained at −98 °C. However, after most of the monomer was polymerized, further reaction led to trimerization. This was prevented in the presence of NaBPh₄ effectively and the living polymerization was performed successfully at −98 °C. The reaction rate retarded with increasing concentration of NaBPh₄, the optimum concentration of NaBPh₄ was 10 times the concentration of the initiator for the living polymerization of HIC. The living system led to the polymers of molecular weight (MW) as high as 50,000 g/mol. The observed MW was well in agreement with the calculated one. At the higher reaction temperature, −78 °C, the quantitative yield was obtained at 2 min of the reaction time, however the living character was not observed at longer reaction time. The study indicated that the amidate anion was stabilized using NaBPh₄ having bulky contact ion pair. The block copolymer of HIC with isoprene, poly(HIC-b-isoprene-b-HIC), was synthesized with help of the living character of polyisoprene and NaBPh₄. The morphology and composition of the block copolymers were investigated using TEM and ¹H NMR, respectively.     

异戊二烯阴离子聚合机理的研究

研究了以环己烷为溶剂、正丁基锂为引发剂,异戊二烯阴离子聚合微观结构随ＴＨＦ极性调节剂用量的变化情况。结果表明：（１）异戊二烯在非极性溶剂中聚合时,所得产物的３,４－结构含量较低,仅为５％～８％;１,４－结构含量为９２％～９５％;（２）随ＴＨＦ用量的增加,３,４－结构含量逐渐增加,并且当Ｒ≥１２时,会出现１,２－结构,其变化趋势也是随ＴＨＦ用量增加而增加。根据以上结果,并以金关泰、李天虎的丁二烯阴离子聚合机理［１］为基础,提出了适用于异戊二烯阴离子聚合的σ－烯丙基型,π－烯丙基型活性中心的聚合机理;同时用公式ｌｇ（ａ－ｂａ－Ｉｖ－１）＝ｎｌｇ［ＴＨＦ］＋ｌｇＫ′对所得微观结构数据进行处理,结果线性关系很好,从而验证了机理的正确性。     

阴离子聚合尼龙6复合材料研究进展

摘要：综述了阴离子开环聚合尼龙6（APA6）及其复合材料在学术和工业上的研究成果。APA6复合材料包括短纤维增强APA6复合材料、连续纤维增强APA6复合材料、纤维织物增强APA6复合材料、自增强APA6复合材料和APA6纳米复合材料。详细介绍了相关APA6复合材料的成型工艺。APA6聚合过程中工艺参数、成型工艺、反应体系和界面结合性能是影响最终的制品性能的因素,自增强APA6复合材料解决了传统复合材料界面结合性能低的问题。自增强APA6复合材料、树脂流变学、聚合动力学、成型工艺和新的反应体系等是未来的研究方向。     

Simulation and optimization of cellulose and styrene graft copolymerization process

Graft polymerization of styrene into cellulose was investigated using Ceric ions redox systems as initiator. A mathematical model with the D-optimal design combined with the least squares method was applied to the system. The variables considered in the model are the reactant variables i.e. monomer and initiator concentrations and the processing variables i.e. reaction time, temperature and agitation rate. The optimal composition and processing conditions were determined using a three dimensional space analysis.     

Anionic telomerization of butadiene with toluene and diphenylmethane: microstructure and molecular weight

The frequency of chain transfer of polybutadienyllithium to toluene and diphenylmethane is increased in the presence of N, N, N′, N′-tetramethylethylenediamine. When the reactor is fed with monomer at a constant rate, the molecular weight of telomer falls steeply as the ratio [base]:[lithium] increases from zero to unity but much more slowly thereafter. Whenever an anionic chain end has a penultimate 1,2-placement, cyclization to form a vinylcyclopentane competes with propagation the more favourably the lower the monomer concentration. In consequence, telomers prepared in toluene have a far greater cyclic content than those prepared in diphenylmethane.     

玻纤增强尼龙6复合材料RTM工艺传热-反应过程的数值模拟

摘要：采用COMSOL有限元软件,对玻璃纤维(GF)增强阴离子聚合尼龙6 (APA6/GF)热塑性复合材料树脂传递模塑(RTM)成型中传热、反应过程进行了三维仿真模拟研究。建立了非线性瞬态传热和树脂反应动力学耦合模型,分析了模具温度和GF体积分数等工艺参数对复合板材内的温度场和反应转化率的影响。模拟结果表明,复合板材内部的温度分布与转化率均匀性较好;模具温度是影响温度变化和反应转化率变化的关键参数,当模具温度为150℃时,反应转化率为0.98,已满足复合材料制品的性能要求;GF体积分数的变化会对复合板材内温度峰值和反应前期的转化速率有所影响,但对最终反应转化率影响不大。     

高性能SSBR的制备及性能研究

采用阴离子聚合方法,分别以环己烷和环戊烷为溶剂,以十二烷基苯磺酸钠(SDBS)及四氢呋喃(THF)为复合结构调节剂,以n-BuLi为引发剂,SnCl4为偶联剂,合成了性能优异的SSBR。考察了不同溶剂对聚合过程的影响、复合结构调节剂用量对SSBR结构及偶联效率的影响,采用T型关联度分析法对门尼粘度的影响因素进行了研究。并采用国标方法对SSBR的物理机械性能进行了测定。结果表明,环戊烷可用于合成SSBR,且对SSBR性能影响不大;当复合结构调节剂SDBS/THF与正丁基锂的摩尔比为4∶0.7∶1时,SSBR的无规化程度较好;当SDBS与THF的用量较小时,偶联效率可达51.3%;对SSBR门尼粘度影响较大的因素为丁苯共聚物的组成(共聚物单体配比)、聚合物分子量及聚合物分子量分布。