Kinetic study of the nitroxide‐mediated controlled free‐radical polymerization of n‐butyl acrylate in aqueous miniemulsions

The controlled free‐radical homopolymerization of n‐butyl acrylate was studied in aqueous miniemulsions at 112 and 125 °C with a low molar mass alkoxyamine unimolecular initiator and an acyclic β‐phosphonylated nitroxide mediator, N‐tert‐butyl‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl) nitroxide, also called SG1. The polymerizations led to stable latices with 20 wt % solids and were obtained with neither coagulation during synthesis nor destabilization over time. However, in contrast to latices obtained via classical free‐radical polymerization, the average particle size of the final latices was large, with broad particle size distributions. The initial [SG1]₀/[alkoxyamine]₀ molar ratio was shown to control the rate of polymerization. The fraction of SG1 released upon macroradical self‐termination was small with respect to the initial alkoxyamine concentration, indicating a very low fraction of dead chains. Average molar masses were controlled by the initial concentration of alkoxyamine and increased linearly with monomer conversion. The molar mass distribution was narrow, depending on the initial concentration of free nitroxide in the system. The initiator efficiency was lower than 1 at 112 °C but was very significantly improved when either a macroinitiator was used at 112 °C or the polymerization temperature was raised to 125 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4410–4420, 2002     

On the Nitroxide Quasi‐Equilibrium in the Alkoxyamine‐Mediated Radical Polymerization of Styrene

Summary: The range of validity of two popular versions of the nitroxide quasi‐equilibrium (NQE) approximation used in the theory of kinetics of alkoxyamine mediated styrene polymerization, are systematically tested by simulation comparing the approximate and exact solutions of the equations describing the system. The validity of the different versions of the NQE approximation is analyzed in terms of the relative magnitude of (dN/dt)/(dP/dt). The approximation with a rigorous NQE, k_c[P][N] = k_d[P N], where P, N and P N are living, nitroxide radicals and dormant species respectively, with kinetic constants k_c and k_d, is found valid only for small values of the equilibrium constant K (10⁻¹¹–10⁻¹² mol · L⁻¹) and its validity is found to depend strongly of the value of K. On the other hand, the relaxed NQE approximation of Fischer and Fukuda, k_c[P][N] = k_d[P N]₀ was found to be remarkably good up to values of K around 10⁻⁸ mol · L⁻¹. This upper bound is numerically found to be 2–3 orders of magnitude smaller than the theoretical one given by Fischer. The relaxed NQE is a better one due to the fact that it never completely neglects dN/dt. It is found that the difference between these approximations lies essentially in the number of significant figures taken for the approximation; still this subtle difference results in dramatic changes in the predicted course of the reaction. Some results confirm previous findings, but a deeper understanding of the physico‐chemical phenomena and their mathematical representation and another viewpoint of the theory is offered. Additionally, experiments and simulations indicate that polymerization rate data alone are not reliable to estimate the value of K, as recently suggested.

Validity of the rigorous nitroxide quasi‐equilibrium assumption as a function of the nitroxide equilibrium constant.     

端炔丙基化合物的聚合反应研究进展

端炔丙基化合物的聚合产物以其优异电导性,非线性光学特性等性能而引起人们的广泛兴趣,本文了近年来端炔丙基化合物的氧化聚合、易位聚合、自由基聚合、缩聚等聚合的研究进展。     

Ultrafast organocatalytic ring-opening polymerization of N-sulfonyl aziridine in the melt

An ultrafast approach for controlled synthesis of well-defined polysulfonamides is established through organocatalytic anionic ring-opening polymerization (ROP) of N-sulfonyl aziridine in the melt. Several different organobases are investigated, and it is found that N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) catalyzed ROP of 2-methyl-N-tosylaziridine (TsMAz) gives the desired polymer, while 1,4-diazabicyclo[2.2.2]octane (DABCO) and 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) initiate the polymerization along with initiator to produce uncontrolled polymers. Using PMDETA as the catalyst, poly(2-methyl-N-tosylaziridine) with molecular weight over 100 kg/mol can be synthesized in less than 90 s. Various initiators, including carboxylic acid, N-sulfonyl amide, unactivated amine, phenol, and thiol, are applicable for this protocol to give the molecular weight and end-group controlled polymers under the open-flask condition. Combining this ultrafast ROP with ring-opening metathesis polymerization (ROMP), a brush copolymer is facile synthesized. This approach allows the ultrafast metal-free synthesis of polysulfonamide and expands the scope of initiators for the ROP of N-sulfonyl aziridines.     

Aspects of the chemical- and the radiation-induced polymerization of biphenylyl acrylate (BPA)

Two chemical initiation routes have been used in the polymerization of biphenylyl acrylate. Radiation-induced polymerization was used in a comparable study. In each instance, dimethyl formamide was used as the solvent. The radiation-induced polymerizations were carried out over a range of dose rates and of monomer concentrations. The use of evacuated conditions provides a marked increase in chain length compared with products arising from polymerizations undertaken in air. Using evacuated systems as an example, for equivalent reaction times and conditions, the value of M_w increases in the order: AIBN initiated < BP initiated < radiation-induced initiation. High conversion levels were recorded. For the radiation-induced polymerization study, the initial rates of polymerization were calculated. The copolymerization of BPA with hydroxyethyl acrylate was also studied to give a guide to the relative reactivity status of the monomers. © 1992 John Wiley & Sons, Inc.     

Recent progress on the synthesis of cyclic polymers via ring-expansion strategies

Cyclic polymers are the simplest topological isomers of linear macromolecules, but exhibit properties that differ from linear chains in ways that remain imperfectly understood. The difficulty of synthesizing appropriately pure and high molecular weight cyclic samples has hindered experimental studies. Ring-closure methods, while versatile, are inherently limited in the range of molecular weights that can be achieved. Ring-expansion methods are a much more promising strategy toward obtaining high molecular weight cyclic polymers. The current review focuses on recent developments in ring-expansion polymerization strategies toward the synthesis of high molecular weight cyclic polymers. Significant progress in the last decade has made the synthesis of cyclic polymers possible by a variety of methods, such as ruthenium- and tungsten-catalyzed ring-expansion metathesis polymerization, organocatalytic and Lewis acid-catalyzed zwitterionic polymerization, RAFT and nitroxide-mediated radical polymerization, among many others. While the study of cyclic polymers has long been hampered by synthetic challenges, the recent resurgence of interest in this field presents an exciting opportunity for chemists. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2892–2902     

乙烯基阳离子聚合引发剂的新进展

本文围绕着乙烯基阳离子聚合这一核心，简要地介绍了近年来在阳离子聚合引发剂方面取得的新进展，包括活性阳离子聚合和普通阳离子聚合引发剂两个部分。     

高等规聚丁烯-1合成工艺研究进展

高等规聚丁烯-1以其优异的综合性能,得到了日益广泛的关注和研究。从催化剂体系出发,本文评述了合成高等规聚丁烯-1的Ziegler-Natta催化剂体系和茂金属催化剂体系的催化剂组成及其催化丁烯-1聚合的催化特征,综述了合成高等规聚丁烯-1的聚合工艺,包括淤浆法、液相本体法(均相和非均相)和气相法,详细介绍了三种聚合工艺的特点,并重点介绍了液相本体法合成高等规聚丁烯-1的工艺优缺点,指明了今后高等规聚丁烯-1合成工艺的发展趋势。     

Stimulation on the addition reactivity of fluorinated vinyl monomers—Facile carbon-carbon bond formation by the aid of fluorine substituents

The high addition reactivity of fluorinated vinyl compounds toward radical and anionic species was demonstrated to afford facile methods for the carbon-carbon bond formation by the aid of fluorinated substituents of vinyl groups. Some of the reactions are proved to be applicable to the preparation of polymers by radical or anionic polyaddition reaction mechanism. The investigation on the anionic reactivity order of fluorinated acrylates and methacrylates may contribute to the development in the field of the estimation by the computer chemistry to determine which effect of the fluorine-substitution would control the reactions.     

A study of the effects of thiols on the frontal polymerization and pot life of multifunctional acrylate systems with cumene hydroperoxide

In an effort to create frontal polymerization systems with a “fail‐safe” curing mechanism, we studied the effects of thiols on the thermal frontal polymerization velocity and pot life of a mixture of a multifunctional acrylate, kaolin clay (filler), and cumene hydroperoxide with either trimethylolpropane tris(3‐mercaptopropionate) or 1‐dodecanethiol (DDT). The acrylates were trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, 1,6‐hexanediol diacrylate, and di(ethylene glycol) diacrylate. Without a thiol, frontal polymerization did not occur. The front velocity increased with the concentration of either thiol, which has not been observed with peroxide initiators. The use of DDT yielded longer pot lives than the trithiol. The front velocities were inversely related to the pot lives. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3850–3855     

The effect of a trithiol and inorganic fillers on the photo‐induced thermal frontal polymerization of a triacrylate

Thermal frontal polymerization is a process in which a localized reaction propagates through an unstirred system by the coupling of the thermal diffusion and the Arrhenius kinetics of an exothermic polymerization. A trithiol was found to affect the front velocity and the time for inducing a front upon exposure to UV light for trimethylolpropane triacrylate polymerization fronts with either kaolin or calcium carbonate filler present. The addition of trithiol and filler both decreased the front velocity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8091–8096, 2008     

Kinetic aspects of styrene minisuspension polymerization using a mixture PVA-SDS as stabilizer: Effect of the time of addition of SDS

The styrene minisuspension polymerization at 70 °C using AIBN as initiator and Polyvinil alcohol (PVA) and mixture PVA-sodium dodecil sulfate (SDS) as stabilizers was studied focusing on the kinetic behavior of the process after the SDS was added (PVA is present from the beginning and SDS is added at a given time t_SDS). It was confirmed that the addition of SDS to the system initially stabilized with PVA highly enhances the colloidal stability of the polymer particles because of the association formed between SDS and PVA molecules. It was observed that when SDS is added the rate of polymerization, the average molecular weight and final latex viscosity increase. The earlier the addition of SDS the more marked these increments. This behavior is explained in terms of the colloidal stability of the particles formed via emulsion polymerization and its effect on kinetic aspects such as the evolution of molecular weight and particle size distributions during the minisuspension polymerization.     

亲核性调节剂在异丁烯阳离子聚合中的作用机理

亲核性调节剂在异丁烯活性阳离子聚合中发挥着极其重要的作用 ,其作用机理主要包括 :(1)碳阳离子稳定化作用 ,即亲核性试剂或它们与Lewis酸生成的络合物与增长链的末端结合 ,来降低活性中心阳离子的“阳离子性” ,抑制副反应 ,使聚合反应呈现活性聚合特征 ;(2 )质子捕获作用 ,即亲核性试剂捕获质子 ,抑制质子的不可控引发和链转移反应 ;(3)增长链表观稳定作用 ,即亲核试剂降低了增长速率与引发速率之比 ,提高引发效率 ,降低增长速率 ,降低分子量分布 ;(4)抑制自由离子增长作用 ,即亲核试剂与质子源和Lewis酸反应 ,生成同阴离子 ,产生同离子效应 ,抑制自由离子活性中心的引发增长作用。     

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.

     

油溶性减阻剂聚合方式的研究进展

综述了近年来油溶性减阻剂聚合方式的研究进展.聚合方式主要有溶液聚合、本体聚合.溶液聚合是研究较早的一种聚合方法,具有体系粘度低、反应温度易于控制的优点,但存在单体转化率低和分子量相对较低以及运输费用高的缺点.本体聚合在很大程度上可以提高单体转化率,改善减阻效果,利于分子量的提高,可以较好的控制分子量分布同时聚合产物纯净...     

Influence of sodium dodecyl sulfate on the kinetics and control of RAFT/MADIX polymerization of acrylamide

Aqueous radical polymerizations of acrylamide were conducted in the presence of varying concentrations of sodium dodecyl sulfate (SDS) and two xanthate reversible addition‐fragmentation chain transfer (RAFT) agents: the small, hydrophobic Rhodixan A1 and the oligomeric, amphiphilic PAm₇‐XA1. The presence of SDS led to significant retardation of the polymerization, while the apparent activity of both RAFT/MADIX agents decreased as the SDS concentration increased. PAm₇‐XA1 was affected to a lesser degree than Rhodixan A1, probably due to its lesser tendency to become sequestered in SDS micelles. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 760–765     

混杂聚合

混杂聚合是指同一体系内有两种或两种以上不同类型的聚合反应同时进行的过程,如自由基聚合与阳离子聚合,自由基聚合与缩聚等。混杂聚合能够在原位形成高分子合金,并有可能得到互穿网络结构（ＩＰＮ）,从而使聚合产物具备较好的综合性能。     

Influence of Metallocene Type on the Order of Ethylene Polymerization and Catalyst Deactivation Rate in a Solution Reactor

The solution polymerization of ethylene using rac-Et(Ind)₂ZrCl₂/MAO and (Dimethylsilyl(tert-butylamido)(tetramethyl- cyclopentadienyl)titanium Dichloride)(CGC-Ti)/MAO was studied in a semi-batch reactor at 120 °C under different monomer pressures and catalyst concentrations. The kinetics of ethylene polymerization with rac-Et(Ind)₂ZrCl₂/MAO can be described with first order reactions for polymerization and catalyst deactivation. When (CGC-Ti)/MAO is used, however, second order kinetics are observed for catalyst decay and the order of polymerization changes from 2 to 1 with increasing ethylene pressure.     

Thermal self‐initiation of styrene in the presence of TEMPO radicals: Bulk and miniemulsion

In TEMPO (2,2,6,6,‐tetramethyl‐1‐piperidinyloxy) controlled styrene radical polymerizations, the thermal self‐initiation reaction of styrene monomer is one of the main sources for the deviations from ideal living polymerization. However, it is also important because it continuously generates radicals to compensate for the loss of radicals caused by the termination reactions and thereby maintains a reasonable reaction rate. In this report, different initial TEMPO concentrations were used in styrene miniemulsion polymerizations without any added initiator. The consumption rate of TEMPO or radical generation rate was calculated from the length of the induction period and the increasing total number of polymer chains. It was found that there is little difference between the miniemulsions and the corresponding bulk systems in terms of the length of the induction period, which increases linearly with initial TEMPO concentration. After the induction period, the consumption rate of TEMPO or radical generation rate was reduced to a lower level, and a faster initial polymerization rate was found in the bulk system compared to the corresponding miniemulsion system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4921–4932, 2004