浅谈自由基聚合动力学的教学与学习

自由基聚合动力学是高分子化学教学和学习中的重要内容。本文讨论了建立自由基聚合微观动力学模型的三个简化条件和三个基本假设,三个简化条件和三个基本假设是微观动力学研究聚合速率和聚合度的基础;同时也较为深入地探讨了动力学链长的物理意义、利用动力学链长概念建立起来的平均聚合度计算通用公式以及该公式的使用条件。     

氨基甲酸酯乙烯基醚类化合物光聚合性能研究

本文合成了一种双官能度的氨基甲酸酯乙烯基醚和一种三官能度的氨基甲酸酯乙烯基醚,并用实时傅立叶红外光谱分别监测了单官能度、双官能度和三官能度的乙烯基醚化合物在三芳基六氟锑酸锍鎓盐阳离子光引发剂(PAG-201)引发下的光聚合情况,对其光聚合动力学性能进行了比较,研究了引发剂PAG-201的浓度对双官能度单体光聚合的影响.结果表明,随着官能度的增加,乙烯基醚化合物的转化率和聚合速率降低.此外,对它们的聚合产物进行的热失重分析表明,随着官能度的增加,聚合产物的热稳定性增加.本文的结果对于研究开发基于氨基甲酸酯乙烯基醚单体的阳离子聚合体系具有较好的指导意义.     

红外光谱法研究苯乙烯原子转移自由基聚合反应动力学

利用红外光谱法测定反应转化率研究原子转移自由基聚合反应动力学。在环己酮溶液中,以卤代烃为引发剂,过渡金属卤化物与配位剂２,２‘－联吡啶为催化体系,进行了苯乙烯聚合。分别就反应温度,反应物浓度和引发体系对苯乙烯聚合速率的影响进行了动力学测定,证实了原子转移自由基聚合具有活性聚合的特征,同时计算并讨论了苯乙烯原子转移自由基聚合反应的动力学数据。     

苯乙烯的低温原子转移自由基聚合:扩散效应导致的加速现象

研究了以苯乙烯(St)和N-[4-(2-溴丙酰氧基)苯基]马来酰亚胺(BPPM)的交替共聚物P(St-alt-BPPM)为大分子多官能度引发剂,以CuBr/2,2′-联吡啶(bpy)为催化体系,环己酮为溶剂,在60或80℃下进行St的原子转移自由基聚合(ATRP).结果表明,反应呈现活性聚合的假一级反应动力学特征,聚合物分子量随着单体转化率上升而增加,降低反应温度将减低反应速率,但是所得聚合物[P(St-alt-BPPM)-g-PS]分子量分布更窄.水解实验证明该过程具有一定可控性.由于类似的单官能度引发剂无法在同等条件下顺利引发St的ATRP,因此采用大分子多官能度引发剂可以大幅度降低ATRP的反应温度.此加速现象被归因于CuBr/bpy从大分子引发剂线团外向线团内扩散,而CuBr2/bpy则从大分子引发剂线团内向线团外扩散,从而提高大分子引发剂线团中的自由基浓度和聚合反应速率.     

双官能度自由基引发剂应用研究的进展

双官能度引发剂在自由基聚合中的应用不断受到重视，本文介绍了常用的双官能度引发剂，并综述了其在制备嵌段共聚物及引发乙烯类单体（如苯乙烯、氯乙烯、丙烯酰胺等）聚合的研究进展。     

2,2′-二邻甲氧基苯基-4,4′,5,5′-四苯基-1,2′-二咪唑复合光引发体系的光聚合动力学研究

本文研究了对2,2′-二邻甲氧基苯基-4,4′,5,5′-四苯基-1,2′-二咪唑(BMOIM)复合光引发体系引发聚合动力学过程.采用紫外光谱仪对引发剂、供氢体、增感剂在紫外区的吸收谱图进行了表征.利用实时红外光谱仪对复合光引发体系引发聚合动力学过程进行实时监测,考察了不同光强、引发剂浓度以及不同官能度单体对反应速率及最终双键转化率的影响.结果表明,在引发剂浓度为0.6%(质量分数)时,20s内双键转换率达到96%,随着引发剂浓度的提高,聚合速率增大.聚合速率以及最终双键转化率随着光强增大而增大;双官能团单体的最终双键转化率比三官能团单体的最终双键转化率要高.     

直链型双官能度引发剂2,5-二甲基-2,5-二(2-乙基己酰基过氧)己烷(DMDEHPH)引发苯乙烯聚合实验与仿真研究

从基于聚合机理的基元反应和物料衡算出发, 考虑聚合过程中的体积收缩和热引发, 详细推导了直链型双官能度引发剂引发苯乙烯聚合的动力学模型, 考虑凝胶、玻璃化和笼蔽效应等对各速率常数和物性参数的影响, 利用基于自由体积理论的扩散控制速率参数和矩方法求解各物种浓度、聚合速率、分子量及多分散度的表达式. 利用模型计算了不同温度和引发剂[2,5-二甲基-2,5-二(2-乙基己酰基过氧)己烷(DMDEHPH)]浓度下的转化率、分子量和多分散度, 均与实验结果相符. 模型还可计算各自由基、含过氧键和双端终止聚合物浓度, 结果表明浓度对转化率曲线中均有一峰值, 双自由基浓度比单自由基浓度低几个数量级, 不同聚合物浓度则仅差几倍. 不同引发剂浓度下同物种浓度曲线无交点, 且引发剂浓度越大物种浓度越高; 不同温度下的曲线有交点, 凝胶效应阶段温度越低浓度越大, 凝胶效应之前和之后则温度越低浓度越小.     

乙烯基单体光聚合动力学与光固化流变行为

概述了光引发体系、光照强度、单体平均官能度、液晶含量、反应温度、助剂等对乙烯基单体/液晶混合物光聚合动力学及光固化流变行为的影响.在染料和胺组成的二元Ⅱ型(夺氢型)光引发体系中,引入适当的第三组分能显著提高反应速率和转化率;增加光照强度和升高温度也能显著提高反应速率和转化率.随着单体平均官能度的增加,体系的反应速率和转化率呈现先增加后降低的趋势.对于I型(裂解型)光引发剂,液晶含量增加,单体反应速率降低,但转化率基本不变;但对于Ⅱ型光引发剂,液晶含量增加能大幅提高单体反应速率和转化率.加入使体系黏度降低的助剂也能提高体系的反应速率和转化率.在体系相同、温度固定的条件下,反应速率越高,凝胶化时间越短;相同体系,温度升高,凝胶化时间提前;相同温度下,单体官能度愈高,体系凝胶时间亦愈短.     

双官能度单组分光引发剂的制备及其光引发活性研究

本文利用4-甲基二苯甲酮、哌嗪等原料合成了一种双官能度的单组分光引发剂（MBPPA）,其分子结构中具有两个二苯甲酮基团。通过紫外光谱研究了光引发剂的紫外吸收和光降解性能,并利用实时红外测试了光引发剂的光引发活性以及不同单体对光聚合动力学的影响。结果表明,在光照10 min后,MBPPA在257.2 nm处的吸光度降低了18.76%,光降解速度明显高于MBP。当光强为50 mW·cm^-2时,0.2%（摩尔分数）MBPPA单独引发乙氧基乙氧基丙烯酸乙酯（EOEOEA）聚合的转化率可达90%。在同等条件下,多官能度丙烯酸酯单体的聚合速率要明显高于单官能度丙烯酸酯单体,但其转化率有所降低。     

自由基聚合近20年的发展

自由基聚合是在上世纪50年代发展起来的,已成为工业生产高分子产品的重要技术。自由基聚合由通用自由基聚合而发展为今天的活性/控制自由基聚合,是近20多年的事情。通用自由基合的研究主要是高活性引发剂、氧化还原体系及多功能引发体系,ESR和激光技术在动力学和自由基精细结构测定的应用等。而活性自由基聚合由最初的引发转移终止剂活性自由基聚合(iniferter),演变为氮氧自由基调控聚合(NMP)或稳定自由基聚合(SFRP),原子转移自由基聚合(ATRP),茂钛金属/环氧化物自由基开环引发聚合,可逆加成断裂链转移(RAFT)聚合,碘转移自由基聚合和有机碲、有机锑调控聚合等活性/控制自由基聚合。本文就以上各方面的研究进展进行简要的综述。     

Kinetics of Nitroxide Mediated Radical Polymerization of Styrene with Unimolecular Initiators

Summary: This study examined the kinetics of nitroxide-mediated radical polymerization of styrene with unimolecular (alkoxyamine) initiators. Control of polymerization rate and polymer molecular weight in unimolecular nitroxide-mediated radical polymerization was studied by looking at the effects of the three main factors: initiator concentration, temperature, and initiator molecular weight on polymerization rate, molecular weight and polydispersity. In addition, the behavior of the unimolecular initiating systems was compared to that of the corresponding bimolecular system. The effective TEMPO concentration and degree of self-initiation of styrene were proved to be significant in dictating magnitudes of molecular weight averages and widths of molecular weight distribution.     

KINETICS AND MECHANISM OF PHASE TRANSFER CATALYZED FREE RADICAL POLYMERIZATION OF METHYL ACRYLATE

The kinetics of free radical polymerization of methylacrylate (MA) was investigated using benzyltributylammonium chloride (BTBAC) as phase transfer catalyst and potassium peroxydisulfate as initiator at aconstant temperature, 60°C, in an inert atmosphere under unstirred condition. The effect of concentrations of the monomer, initiator and the catalyst on polymerization was discussed and a mechanism of polymerization has been proposed. The order with respect to the monomer, initiator, and phase transfer catalyst was found to be 2, 0.5, and 0.5, respectively.     

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.     

Kinetics of copolymerization—II. Kinetic investigation of the polymerization of methyl acrylate in solution

The kinetics of methyl acrylate polymerization initiated by azobisisobutyronitrile were investigated in dimethylformamide at 40–60. The polymerization was 1/2 order with respect to initiator; the rate of initiation was independent of the initial concentration of monomer. The rate and the overall rate constant of polymerization strongly depend on the medium: the overall rate constant decreases with increase of solvent concentration. The solvent dependence of overall rate constant can adequately be described by the hot radical theory.     

Kinetics of copolymerization—I. Kinetic investigation of the polymerization of acrylonitrile in homogeneous phase

A detailed study was made of the kinetics of initiated homopolymerization of acrylonitrile in dimethylformamide and dimethylsulphoxide at 40–60°. The rate of polymerization was found to be proportional to the (initiator concentration)^1/2. The rate of initiation of polymerization was determined by the inhibition method, using three stable free radicals. Trends in the average rate of polymerization were also studied for various initial monomer and solvent concentrations. The overall rate constant (K) was strongly dependent on monomer concentration decreasing with decrease of monomer concentration. It has been shown that the hot radical theory describes accurately, without physical contradiction, the solvent dependence of rate constants of polymerization systems.     

A bidirectional ATRP‐NMRP initiator: The effect of nitroxide size on the rate of nitroxide‐mediated polymerization

An N‐alkoxyamine macroinitiator bearing a polymeric nitroxide cap was synthesized and used to investigate the effect of nitroxide size on the rate of nitroxide‐mediated radical polymerization (NMRP). This macroinitiator was prepared from asymmetric double‐headed initiator 9 , which contains both an α‐bromoester and an N‐alkoxyamine functionality. Poly(methyl methacrylate) was grown by atom transfer radical polymerization from the α‐bromoester end of this initiator, resulting in a macroinitiator (M_n = 31,000; PDI = 1.34) bearing a nitroxide cap permanently attached to a polymer chain. The polymerization kinetics of this macroinitiator in NMRP were compared with known N‐alkoxyamine initiator 1 . It was found that the rate of polymerization was unaffected by the size of the macromolecular nitroxide cap. It was confirmed that NMRP using this macroinitiator is a “living” process. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2015–2025, 2007     

异丙醇铝改进的原子转移自由基聚合催化体系

以α 溴代异丁酸乙酯［２ （ＥｉＢ） Ｂｒ］ 为引发剂,溴化亚铜（ＣｕＢｒ）／ 联二吡啶（ｂｐｙ）／ 异丙醇铝［Ａｌ（ＯｉＰｒ）３］ 为复合催化剂,在环己酮溶液中进行了甲基丙烯酸正丁酯（ＢＭＡ） 的原子转移自由基聚合（ＡＴＲＰ） ．研究了异丙醇铝对聚合速率及产物分子量分布的影响．异丙醇铝可与引发剂和聚合物中的羰基配位,使相邻的Ｃ—Ｂｒ 键活化,ＡＴＲＰ 反应可以在较低温度下进行．适量溴化铜的加入,可调节ＡＴＲＰ 活性,可得到分子量可控且分子量分布窄的ＰＢＭＡ（ ＭＷＤ＝ １－３ ～１－５） ．     

Living radical polymerization of acrylonitrile catalyzed by copper with a high concentration of radical initiator and its application in removal of Ag(I) after modification

In this study, we reported the synthesis of polyacrylonitrile (PAN) via living radical polymerization in N, N‐dimethylformamide using carbon tetrachloride as initiator, copper(II) chloride (CuCl₂)/hexamethylenetetramine as catalyst system, and 2,2‐azobisisobutyronitrile as a high concentration of thermal radical initiator. The polymerization proceeded in controlled/living manner as indicated by first‐order kinetics of the polymerization with respect to the monomer concentration, linear increase of the molecular weight with monomer conversion and narrow polydispersity. Higher polymerization rate and narrower molecular weight distributions were observed with CuCl₂ less than 50 ppm. The rate of polymerization showed a trend of increase along with temperature. The modified PAN containing amidoxime group was used for extraction of Ag(I) ions from aqueous solutions. The adsorption kinetics data indicated that the adsorption process followed pseudo‐second‐order rate model. The isotherm adsorption process could be described by the Freundlich isotherm model. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

RAFT聚合合成高分子量嵌段聚合物

以合成高分子量聚合物为目标,以苯基二硫代乙酸-1-苯基乙酯(PEPDTA)作为RAFT试剂,研究引发剂的种类(偶氮二异丁腈(AIBN)、1-1′-偶氮环己腈(ACC))、用量及聚合温度对苯乙烯/丙烯酸丁酯RAFT共聚合过程和聚合物结构的影响.结果发现,由于体系中RAFT浓度很低,相应的引发剂浓度要比传统自由基聚合低得多,只有采用较高的聚合温度和低分解速率常数的引发剂(ACC),才能制得无活性聚合物分率低(<0.1)、分子量高的聚合物,并进一步得到杂质含量少、分子量分布窄的嵌段聚合物.