连锁聚合反应引发过程的分析讨论

在《聚合反应工程》课程中,引发反应过程是课程的一个核心内容,在教材中具有重要地位。不同连锁聚合反应机理所对应的引发反应过程不同,但它们具有很强的关联性。文中以自由基聚合、离子聚合、配位聚合机理为主线,对不同连锁聚合机理所对应的引发反应过程这一知识重点做分析讨论,包括链引发的引发体系、基元反应和反应速率等,指出了不同引发反应过程之间的相同之处和不同之处。旨在提高学生对连锁聚合的引发反应过程能有系统的认识和把握。     

不同聚合机理的聚合反应速率串讲

在《聚合反应工程》课程中,聚合反应速率直接影响聚合产物的平均聚合度,是课程的一个核心内容,在教材中占有重要地位。不同聚合反应机理所对应的聚合反应速率不同,但它们具有很强的关联性。文中以自由基聚合、离子聚合、配位聚合以及缩聚的聚合机理为主线,把不同聚合机理中的聚合反应速率这一重要知识点做了串讲;指出了不同聚合反应速率之间的相同之处和不同之处。旨在使学生对聚合反应速率能有一个系统的认识和把握。     

连锁聚合机理与单体结构和活性种匹配关系的讨论

在连锁聚合中,聚合机理与单体结构和活性种有关,明确选择单体的标准。分析乙烯基单体取代基吸电子、供电子诱导效应和共轭效应与单体阴离子聚合、阳离子聚合和自由基聚合相关性:氯乙烯只能自由基聚合,而异丁烯仅能阳离子聚合;单体具有吸电子效应的基团,容易进行阴离子聚合;单体具有供电子效应的基团易阳离子聚合;单体具有共轭效应的基团,可以进行三种聚合。归纳用Q值、σ值、pKa和聚合热半定量考察单体活性的知识体系,剖析影响选择单体各因素的交叉作用这一难点;理解单体与引发剂的匹配进行连锁聚合。     

接枝聚合中阻聚技术研究进展

论述了接枝聚合中阻聚技术的研究发展,包括3种接枝聚合过程中阻聚的研究,即高能辐射引发、紫外光辐射引发和过氧化物引发接枝聚合中的阻聚技术.讨论了各种阻聚剂和接枝工艺对接枝聚合的影响.探讨了各种阻聚技术的机理.归纳了对阻聚剂的特点,并对阻聚技术的发展趋势作了预测.     

RATRP/RAFT活性自由基聚合现象的考察

以α-二硫代萘甲酸异丁腈酯(CPDN)为链转移剂,偶氮二异丁腈(AIBN)为引发剂,CuCl2.2H2O为催化剂,2,2’-联二吡啶(bpy)为配体,对反向原子转移自由基聚合(RATRP)和可逆加成-断裂链转移自由基聚合(RAFT)的混合聚合体系进行了研究,得到了一系列末端带有双硫酯基团和-Cl的聚甲基丙烯酸甲酯均聚物。(1H-NMR)和(GPC)等测试结果表明,一锅法和两步法聚合体系均具有"活性"/可控聚合特征,其中两步法在反应初期分子量分布指数较一锅法宽,二者均存在短时间的诱导期。在混合聚合体系中,两种聚合机理共同起作用,使聚合体系具有"活性"聚合的特征。     

环硫化合物的开环聚合

详细论述了环硫化合物开环聚合的引发体系、聚合机理和动力学，并对环硫化合物的共聚和立体选择聚合，不对称立构选择聚合等作了概述。     

2,5-二苯甲酰氧基己二酸二乙酯的合成及引发甲基丙烯酸甲酯聚合

合成了"2,5-二苯甲酰氧基己二酸二乙酯"并将其用于引发甲基丙烯酸甲酯(MMA)聚合。利用核磁共振氢谱(1HNMR)、傅里叶变换红外光谱(FT-IR)和质谱(MS)对化合物结构进行表征;利用称量法确定了聚合物产率;利用凝胶渗透色谱(GPC)测定了聚合物的相对分子质量及相对分子质量分布。实验结果表明,2,5-二苯甲酰氧基己二酸二乙酯作为一种引发剂,能够引发甲基丙烯酸甲酯聚合,得到了较高的产率;聚合物产率随反应温度的上升和反应时间的延长而增大;当2,5-二苯甲酰氧基己二酸二乙酯使用量增加1倍时,聚合物的产率随之增加1倍左右,符合链式聚合特征;该引发剂的引发机理为碳自由基引发的自由基聚合。     

端烯丙基-聚谷氨酸苄酯的合成与表征

γ-苄基-L-谷氨酸-N-羧酸酐(Bz-L-Glu-NCA)在二烯丙基胺的引发作用下进行阴离子开环聚合得到端烯丙基-聚谷氨酸苄酯(A-PBLG).通过红外、氢谱、GPC等手段对A-PBLG进行了表征,结果表明Bz-L-Glu-NCA在二烯丙基胺的引发作用下主要按照"胺中间体"机理进行阴离子开环聚合得到A-PBLG.     

光引发淀粉-AM/AA反相乳液接枝聚合--光引发剂的影响

采用多种光引发剂引发淀粉-丙烯酰胺/丙烯酸反相乳液接枝聚合,IR光谱分析表明了淀粉接枝共聚物的生成,考察了光引发剂的种类和浓度对接枝聚合的影响并初步探讨了引发接枝的机理。     

关于自由基聚合几个值得关注的问题

总结了自由基聚合教学中的几个值得关注的问题,包括自由基聚合时不同引发剂类型的选择和确定、聚合温度及其区间选择及确定、聚合时间的确定、溶剂选择等。同时阐述了这些相关因素在自由基聚合研究方案设计时的相互关系。旨在使学生对自由基聚合的认识更为深刻和系统,培养学生独立进行自由基聚合研究方案设计的能力。     

828环氧树脂体系电子束固化反应机理的研究

对电子束（EB）辐射828环氧树脂的固化反应机理进行了研究，考察了不同引发剂，稀释剂对树脂体系辐射反应的影响。实验发现，阳离子型光引发剂可以引发环氧树脂的电子束辐射固化反应，传统的热固化体系并不适用于电子束固化，稀释剂的使用会降低反应体系的固化度，其中活性稀释剂的影响较小，供电子型溶剂会对环氧树脂的辐射固化反应起阻聚作用。以环氧丙烷作为单官能团环氧花合物，采用红外光谱，自由基捕捉技术与气相色谱－质谱相结合的方法，研究了电子束辐射环氧丙烷－碘Weng盐体系的辐射反应机理，推导出由碘Weng盐在电子束辐照下分解，随后产生质子酸，引发环氧丙烷阳离子开环聚合的反应过程。     

Synthesis of self-crosslinking sodium polyacrylate hydrogel and water-absorbing mechanism

In this paper, the super-absorbent, self-crosslinking sodium polyacrylate was synthesized by means of reversed-phase suspension polymerization under gamma-ray irradiation and the water-absorbing mechanism of the self-crosslinking hydrogel was revealed. Some physical parameters of such a network were estimated and investigated. The stable suspension polymerization of sodium acrylate was carried out in the presence of a surfactant complex consisting of anionic surfactant dodecylbenzen sulfonic sodium (DSS) and nonionic surfactant Span60 or Span20 with a certain ratio. The dual-electronic structure resulted from such a surfactant complex makes the dispersed monomer solution droplets a stable suspension in organic solvent. The water-sorbability was related to the radiation conditions such as dose, dose rate, and degree of monomer neutralization. Only under high dose and dose rate, some initiated branch side species on the main macromolecular chain can couple each other and cause a self-crosslinking network which may contain a lot of water. The gel dose was about 1.57 kGy (radiation dose unit), and G(X), or G value expressed as crosslinking probability at certain energy of 100 ev, was calculated and found to be 2.46 (1/100 ev). The water-sorbing procedure includes three stages, e.g., sorption on the pore surface, ionization of the fixed charges in the network, and swelling equilibrium. The crosslink chain length in the self-crosslinked sodium polycrylate network, expressed as Mc, can be calculated and related to gel dose.     

Autonomous Ex Novo Chemical Assembly with Blebbing and Division of Functional Polymer Vesicles from a “Homogeneous Mixture”

The chemical energy and radicals from an oscillating chemical reaction are used to synthesize a polymer vesicle from a homogeneous solution of monomeric units. Periodically formed radicals from the Belousov–Zhabotinsky (B–Z) reaction initiate radical polymerization between a polyethylene glycol based chain transfer agent (PEG‐CTA) and hydrophilic acrylonitrile monomers in water. The growth of a hydrophobic chain on the hydrophilic PEG chain induces self‐assembly of polymeric amphiphiles to form micrometer‐sized vesicles entrapping an active oscillating B–Z reaction. In our experimental conditions, the different chemical environments inside and outside the vesicles contribute to enlarge the area and diameter of the resulting self‐assembled vesicles and, in some cases, promote blebbing and division.     

超支化HPPVs共聚物的Gilch聚合机理研究

在以Gilch路线合成了一系列含烷氧基超支化聚对苯撑乙烯(HPPV)共聚物的基础上,对其聚合反应的过程及机理进行了初步研究。通常,PPV的聚合是按照自由基机理进行,即反应物单体在分子内脱去卤化氢(HX)后形成一种对醌二甲烷单体,再通过自由基链增长达到聚合的目的。通过DFT(B3LYP/6-311G(d))方法对反应单体1,3,5-三氯甲基-2,4,6-三甲氧基苯(TCMTMOB)在分子内脱去HCl后的结构进行了优化,发现此单体同样可以形成稳定的间二醌结构,易于与对醌二甲烷单体共聚生成超支化共聚物,这与实验结果相吻合。     

聚合温度对聚磷酸钙聚合度及结构的影响

聚合度作为一个重要影响因素对聚磷酸钙的性能必然产生影响. 采用磷酸二氢钙作为原料, 在不同聚合温度下制备了聚磷酸钙. 采用³¹P核磁共振波谱测定聚磷酸钙的聚合度, 评价聚合温度对聚合度及结构的影响, 结合磷酸二氢钙差示扫描量热-热失重分析结果, 提出了磷酸二氢钙缩聚反应的机理. 结果表明, 磷酸二氢钙缩聚产物以聚磷酸钙为主, 当聚合温度低于1000℃时, 升高聚合温度有利于聚合度的增大, 1000℃以上则反之; 此外, 升高聚合温度促进环状结构(偏磷酸钙)的生成, 其含量随聚合温度的升高而增大且1000℃以上增幅较大.     

In-situ polymerization behaviour of bone cements

The polymerization behaviour of bone cements during total hipreplacements is characterized by a fast and highly non-isothermal bulk reaction.In the first part of this paper the reaction kinetics are analysed bycalorimetric analysis in order to determine the rates of polymerization inisothermal and non-isothermal conditions. A phenomenological kinetic model,accounting for the effects of autoacceleration and vitrification, is presented.This model, integrated with an energy balance, is capable of predicting thetemperature across the prosthesis, the cement and the bone and the degree ofreaction in the cement, during in situ polymerization. The temperatureand the degree of reaction profiles are calculated, as a function of the settingtime, taking into account the system geometry, the thermal diffusivity of bone,prosthesis and cement, and the heat rate generated by the reaction according tothe kinetic model. Material properties, boundary and initial cond!itions are the input data of the heat transfer model. Kinetic and heat transfermodels are coupled and a numerical solution method is used. The model is appliedin order to study the effects of different application procedures on temperatureand degree of reaction profiles across the bone–cement–prosthesissystem.     

Preparation of an ion-exchange chromatographic support by a "grafting from" strategy based on atom transfer radical polymerization

A new "grafting from" strategy based on surface-initiated atom transfer radical polymerization (ATRP) was first used for the preparation of a polymer-based ion-exchange support for HPLC. The most important property of the proposed method is to be applicable for the synthesis of any type of ion exchanger in both the strong and the weak forms. Monodisperse, porous poly(glycidyl methacrylate-co-ethylene dimethacrylate), poly(GMA-co-EDM) particles 5.8 mum in size were synthesized by "modified seeded polymerization". Poly(dihydroxypropyl methacrylate-co-ethylene dimethacrylate), poly(DHPM-co-EDM) particles were then obtained by the acidic hydrolysis of poly(GMA-co-EDM) particles. The ATRP initiator, 3-(2-bromoisobutyramido)propyl(triethoxy)silane was covalently attached onto poly(DHPM-co-EDM) particles via the reaction between triethoxysilane and diol groups. In the next stage, the selected monomer carrying strong cation exchanger groups, 3-sulfopropyl methacrylate (SPM), was polymerized on the initiator-immobilized particles via surface-initiated ATRP. The degree of polymerization of SPM (i.e., length of polyionic ligand) on the particles was precisely controlled by adjusting ATRP conditions. Poly(SPM)-grafted poly(DHPM-co-EDM) particles obtained with different ATRP formulations were tried as chromatographic packing in the separation of proteins by ion-exchange chromatography. The proteins were successfully separated with higher column yields with respect to the previously proposed materials. The plate heights between 100 and 150 mum were achieved with the column packed with the particles carrying the shortest poly(SPM) chains. The plate height showed no significant increase with increasing flow rate in the range of 0.5-16 cm/min.     

高分子化学教学中难点的选析

缩聚和自由基聚合是《高分子化学》教学的重要内容,笔者在该部分内容教授的过程中发现了一些疑难问题。针对缩聚和自由基聚合教学中的疑难问题,如缩聚反应中摩尔系数表达式中的系数、自由基聚合引发和终止反应动力学方程中的系数、动力学链长的表达式等,介绍了笔者的理解和相关推导。     

过渡金属催化烯烃聚合

论述了烯烃聚合催化剂的发展更新过程,催化聚合的过程。涉及配位聚合的链增长机理、单体几种可能的插入模式及聚合的立构控制方式、链转移或链终止机理以及可能存在的催化活性中心的失活过程。对于过渡金属催化烯烃聚合的理解有助于催化剂设计的理性化。     

Evaluation of Photopolymerization Kinetics by Means of Transmittance Measurements

Polymeric resins are widely used for dental reconstruction, and most resins use camphorquinone as activator of the polymerization reaction, through the absorption of light at a defined wavelength range (from 400 nm to 460 nm). During the photopolymerization curing, transparency of these resins changes and transmittance variation can be detected by photodiode and bolometer measurements. This change can be used as an index of the reaction rate, and the kinetic parameter k (reaction rate) can be evaluated from transmittance data by means of nonlinear regression. The relation between k and the light intensity impinging on the resin sample can thus be obtained. In the present work, tests were carried out using the resin Enamel Plus HFO GE2. Results reveal the presence of two different polymerization reactions at two different intensity ranges. The obtained k values were used to predict the most suited curing times for different light intensities. The proposed methodology can be applied to different dental reconstruction materials, provided that the material is partially transparent and that its transparency changes during the polymerization reaction.