Cyclopolymerization of diallylcyanamide

A soluble polymer of cyclic structure has been obtained by radical polymerization of diallyleyanamide. A kinetic analysis of the polymerization indicated that the overall rate of the system is first-order with respect to concentration of initiator and either first- or second-order with respect to monomer concentration, depending on the solvent used. The molecular weight of the polymer is independent of the concentration of the initiator and the monomer. The intramolecular abstraction of hydrogen is proposed as a termination reaction.     

Anionic polymerization of 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane

In the first of a two-part series, a study has been made of the anionic polymerization of a five-membered cyclocarbosiloxane, 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane. The polymerization was initiated by lithium n-butyldiphenylsilanolate in the presence of tetrahydrofuran. The chemical shifts of the protons of the cyclic monomer and the polymer were found to be different, and therefore the rate of polymerization was obtained in an NMR spectrometer. The effects of varying the concentrations of THF, initiator, and water upon the rate of polymerization and upon the molecular weight and the molecular weight distribution were investigated. At a constant concentration of monomer and initiator, the rate of polymerization increased when the THF concentration was increased. At a constant concentration of monomer and THF the rate of polymerization reached a constant value when the initiator concentration was varied. The molecular weight and the molecular weight distribution were dependent upon the initiator to water ratio, whereas water concentration had little effect on the rate of polymerization. Essentially monodispersed polymers were obtained when the concentration of initiator was in large excess to that of water or vice versa. A bimodal distribution in molecular weight was obtained when the concentration of initiator was approximately equal to that of water. The apparent activation energy of polymerization was 12.7 kcal/mole.     

Use of Cryptates om Bulk Anionic Polymerization of Dienes

The bulk polymerization of isoprene and butadiene with organoalkati compounds in the presence of cryptants has been studied. The effects of monomer concentration, cryptant concentration and counterions on the inductioin period and molecular weight with these same monomers has also been studied. The microstructure of polymers has been determined by ¹H-NMR measurements. In the presence of complexed ion pairs the structure is independent of the temperature, of the initiator concentration, of the counterions, and of the organoalkali/cryptant molar ratio, but the vinyl structure increases with t he cryptant concentrtion.     

Polymerization of styrene with tetramethylthiuram disulfide as an initiator in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy

The bulk polymerization of styrene was investigated with tetramethylthiuram disulfide (TMTD) as an initiator in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) at 123 °C. The polymerization proceeded in a controlled/living way; that is, the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with conversion. The molecular weights of the polymers obtained were close to the theoretical values, and the molecular weight distributions were relatively low (weight‐average molecular weight/number‐average molecular weight = 1.1–1.3). The rate of polymerization with TMTD as an initiator was faster than that with benzoyl peroxide, and the rate was independent of the initial concentration of TMTD in the presence of TEMPO. The obtained polystyrene was functionalized with ultraviolet‐light‐sensitive ? SC(S)N(CH₃)₂ groups, which was characterized with ¹H NMR spectroscopy. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 543–551, 2005     

Simulation of styrene free radical polymerization over bi-functional initiators using Monte Carlo simulation method and comparison with mono-functional initiators

In the present study, based on a complete mechanism, a Monte Carlo simulation method is employed to investigate the kinetics of styrene free radical polymerization over bi-functional initiators in a bulk medium. The effects of the concentration of initiator and the monomer, of the temperature on monomer conversion, average molecular weights, polydispersity index, and molecular weight distribution are inspected and compared with mono-functional initiators. According to the simulation results, an increase in either the concentration of initiator or the temperature leads to the rise of the monomer conversion and to the reduction of the average molecular weights, while the increase of the monomer concentration results in the rise of both monomer conversion and molecular weights, which is in accord with predictions of the theory of free-radical polymerization. In addition, application of bi-functional initiators increases both monomer conversion and average molecular weight and results in narrower chain length distributions.     

Steady-state kinetics during initial stages of radical bulk polymerization of acrylonitrile

The bulk polymerization of acrylonitrile with azobisisobutyronitrile as initiator and FeCl₃ as terminator was studied at 60°C. It was found that the reaction proceeds like solution polymerization and does not exhibit the familiar autoacceleration found in bulk polymerizations. It was concluded that a steady-state condition of growing radical chains exists. Initial rates, to approximately 3% conversion, were measured dilatometrically and were found to be proportional to the ratio of the initiator to terminator concentration, where this ratio is smaller than 3 : 1 and are due to the predominance of the FeCl₃ monoradical termination mechanism. On increasing the ratio of initiator to FeCl₃, the usual biradical termination mechanism becomes important as well. Assuming that the ratio of propagation constant to termination constant in this work is similar to the knwon ratio in DMF solution, a monomer “effective” concentration in the bulk of about 20% of the nominal concentration of pure acrylonitrile (14.38 mole/l. at 60°C) can be calculated. This result is interpreted by a molecular mechanism for the bulk polymerization of acrylonitrile.     

Dispersion polymerization of styrene in ethanol: Monomer partitioning behavior and locus of polymerization

A thermodynamic model has been proposed for the simulation of monomer partitioning behavior in the dispersion polymerization of styrene in ethanol. The monomer concentration in the polymer particles is very low (20 vol% at 5% conversion) and decreases further as the polymerization proceeds. It is independent of stabilizer concentration but is strongly dependent on initial monomer concentration. The partitio n coefficient ([M_p]/[M_c]) of styrene increases from 0.8 to 1.1 with incresing conversion. There are two polymerization loci in dispersion polymerization, namely the continuous and polymer phases. Competition between solution and heterogeneous polymerization has been observed in this system. The rate of dispersion polymerization is dependent on initial monomer concentration but is independent of initiator concentration at higher conversions. The molecular weight of the polymers produced by this process increases with increasing conversion and decreases with increasing initiator concentration.     

Unsymmetrical N-Heterocyclic Carbene: 1-Isopropyl-3-benzylimidazol-2-ylidene as Catalyst for Ring-Opening Polymerization of ϵ-Caprolactone

An unsymmetrical N-heterocyclic carbene, namely 1-isopropyl-3-benzylimidazol-2-ylidene, is a highly active catalyst for ring-opening polymerization of ?-caprolactone (CL) to give polycaprolactone (PCL) with number average molecular weight (Mn) as high as 2.66 × 10⁴ at 0°C in 100 min in tetrahydrofuran (THF). The effects of monomer/initiator molar ratio ([M]/[I]), catalyst/initiator molar ratio ([C]/[I]), monomer concentration, as well as polymerization temperature and time have been investigated. The kinetic studies of CL polymerization have indicated that the polymerization rate is first-order with respect to both monomer and catalyst concentrations. The apparent activation energy amounts to 56.04 kJ/mol. The proposed mechanism is a monomer-activated process.     

Use of germanium initiators in ring‐opening polymerization of L‐lactide

Three different, new germanium initiators were used for ring‐opening polymerization of L ‐lactide. Chlorobenzene and 120 °C was a usable polymerization system for solution polymerization, and the results from the polymerizations depended on the initiator structure and bulkiness around the insertion site. The average molecular weights as measured by size exclusion chromatography increased linearly with the monomer conversion, and the molecular weight dispersity was around 1.2 for initiators 1 and 2 , whereas it was around 1.4 for initiator 3 . The average molecular weight of poly(L ‐lactide) could be controlled with all three initiators by adding different ratios of monomer and initiator. The reaction rate for the solution polymerization was, however, overall extremely slow. With an initial monomer concentration of 1 M and a monomer‐to‐initiator ratio of 50, the conversion was 93% after 161 h for the fastest initiator. In bulk polymerization, 160 °C, the conversion was 90% after 10 h. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3074–3082, 2003     

Anionic heterogeneous polymerization of methacrylonitrile by n-butyllithium

The anionic heterogeneous polymerization of methacrylonitrile by butyllithium in petroleum ether was investigated. The polymerization was of the “living” type, as seen from the linear dependence of the molecular weights on [MAN]/[BuLi]. This behavior was further supported by block polymerization experiments in which the monomer was added in two portions and the molecular weights obtained were directly proportional to the total monomer concentration. The initiator efficiency was low, and initiator consumption was only about 2%. This fact, together with the results of the block polymerizations showed that there was preferential addition of monomer to the growing chain ends rather than to the initiator. The molecular weights were independent of the rate of monomer addition. This as well as the “living” behavior of the polymerization of methacrylonitrile on a wide range of monomer and catalyst concentrations and the absence of chain transfer to monomer was essentially different from that of the similar heterogeneous polymerization of acrylonitrile by butyllithium previously investigated. This is due to the absence of an α-acidic hydrogen in methacrylonitrile.     

Ring-opening polymerization of ε-caprolactone using rare earth tris(4-tert-butylphenolate)s as a single component initiator

Ring-opening polymerization of ε-caprolactone has been carried out by using single component rare earth tris(4-tert-butylphenolate)s initiators for the first time. The influences of rare earth element, solvent, monomer and initiator concentration as well as reaction time on the polymerization were investigated. The kinetics indicated that the polymerization rate is first-order with respect to monomer concentration and initiator concentration, respectively. The overall activation energy of the ring-opening polymerization amounts to 51.9 kJ/mol. Mechanism studies showed that monomer inserted into the growing chains with the acyl-oxygen bond scission rather than the break of alkyl-oxygen bond.     

Stereospecific polymerization of methacrylonitrile. VI. Effect of esters as a complexing agent with diethylmagnesium catalyst

The stereospecific polymerizations of methacrylonitrile with diethylmagnesium were carefully studied by using various ethers as complexing agents. The complexed ethers exhibit a beneficial effect on the stereoregularity of the resulting polymer, namely, the crystallinity increased by using ethers as a complexing agent. The polymerization rate and the molecular weight of the polymer also increased by using ether-complexed catalysts. The polymerization behavior was studied with the dioxane–diethylmagnesium complex as a typical complexed catalyst. The behavior was mostly similar to that of the diethymagnesium alone, that is, the rate of the polymerization increased in proportion to monomer concentration, and the solubility index increased with increasing monomer concentration. Interestingly, the viscosity of the acetone-insoluble fraction increased with increasing monomer concentration, while that of the acetone-soluble fraction was independent of monomer concentration. This is explained by considering that the catalyst has at least two kinds of catalytic species, one being the species that produces the crystalline polymer by a coordinated anionic polymerization, another being the one from which an amorphous polymer is obtained by a conventional anionic mechanism. The fact that the viscosity of the polymer decreased with increasing the initiator concentration is explained in terms of chain trasfer to the initiator. In case of diethylmagnesium alone, the viscosity of the polymer is independent of the initiator concentration.     

Atom Transfer Radical Polymerization of Styrene Using Multifunctional Iniferter Reagents as Initiators

Summary: Two multifunctional iniferters, 1,4-bis-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (BDCIB) and 1,3,5-tris-(α-N,N-diethyldithiocarbamyl-isobutyryloxy)-benzene (TDCIB), were successfully synthesized and used as initiators to initiate the polymerization of styrene in the presence of a CuBr/PMDETA complex. The polymerization results demonstrated that the kinetic plots in all cases were first-order to the monomer, the molecular weight of the polymers increased linearly with the monomer conversion; meanwhile, the molecular weight distribution of the polymer was kept to a very low value (M_w/M_n ≤ 1.35). Furthermore, the measured molecular weights were very close to the calculated values, which indicated the high efficiency of the initiator for the polymerization of styrene. The effect of catalyst concentration and initiator concentration was not obvious and the influence of polymerization temperature was apparent, and the polymerization rate increased with the polymerization temperature. The results of chain-extension and ¹H NMR analysis proved that the polymer obtained was capped with diethylthiocarbamoylthiy (DC) group.     

Synthesis and characterization of polyacrylonitrile nanoparticles by dispersion/emulsion polymerization process

Polyacrylonitrile nanoparticles in sizes ranging from approximately 35 to 270 nm were prepared by dispersion/emulsion polymerization of acrylonitrile in a continuous aqueous phase in the presence of potassium persulfate as initiator and various alkyl-sulfate and sulfonate surfactants. The influence of various polymerization parameters (e.g., concentration of monomer and initiator, type and concentration of surfactant, temperature and time of polymerization, ionic strength, pH and co-solvent concentration) on the properties (e.g., size and size distribution, yield, stability, etc.) of the particles has been investigated. The polymerization of acrylonitrile may occur in two major locations: in the aqueous continuous phase (dispersion polymerization) and/or within the surfactant micelles (emulsion polymerization). A discussion concerning the role of these two mechanisms under different conditions, including comparison with previous literature, is also presented. Surface and bulk characterizations of the particles were performed by methods such as transmission and scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, zeta potential, and gravimetric measurements.     

Photo-controlled/living radical polymerization of 2-(dimethylamino)ethyl methacrylate using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as a mediator

The photo-controlled/living radical polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) was attained using 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator and (2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) (r-AMDV) as the initiator. The bulk polymerization of DMAEMA produced a polymer with a comparatively narrow molecular weight distribution below 1.6. The first-order time conversion plots showed a linear increase. The molecular weight of the resulting polymer also increased with an increase in the monomer conversion. The molecular weights of the resulting polymers were in good agreement with the theoretical molecular weights. A linear correlation was also obtained for the plots of the molecular weight vs. the reciprocal of the initial concentration of r-AMDV. The GPC analysis demonstrated the living nature of the polymerization based on the fact that the curves were shifted to the higher molecular weight side without deactivation as the conversion increased.     

Effect of oxygen on the radical polymerization of acrylamide in ethanol and water

The polymerization of acrylamide has been studied in ethanol at 80°C with 2,2′-azobisisobutyronitrile (AIBN) as the initiator, and also in water at 60°C with 4,4′-azobis-4-cyanopentanoic acid (ACV) as the initiator. For the first system, it was found, approximately, that the well defined in duction period showed an inverse dependence on both the initial monomer and initiator concentrations, but was directly proportional to the square root of the initial oxygen concentration. For the second system, the rate of oxygen uptake was approximately directly proportional to the monomer and initiator concentration but independent of the oxygen concentration. The results obtained for these two systems are compared.     

Organometal-initiated polymerization of vinyl ketones. III. Polymerization of methyl isopropenyl ketone initiated by the triethylaluminum–methyl isopropenyl ketone complex

The kinetics and mechanism of the triethylaluminum–methyl isopropenyl ketone complex-initiated polymerization of methyl isopropenyl ketone (3-methyl-3-butene-2-one) in toluene have been studied over a range of temperature. Equimolar quantities of monomer and triethylaluminum were premixed to form the initiator species prior to the addition of the excess monomer for polymerization. Initial and overall reaction rates indicate a first-order dependence on monomer and initiator concentrations. The overall activation energy for the polymerization is 52 ± 3 kJ/mole. Molecular weight distributions were bimodal, with peaks corresponding to the trimer and high molecular weight material. The kinetic data are consistent with a coordinate polymerization mechanism.     

H_2O/TiCl_4/Py体系引发苯乙烯正离子聚合

研究了在少量吡啶(Py)存在下由水(H2O)四氯化钛(TiCl4)体系引发苯乙烯于二氯甲烷正己烷中进行碳正离子聚合,分别考察[Py]、[H2O]和[TiCl4]对聚合速率、产物分子量与分子量分布的影响.实验结果表明,少量亲核试剂吡啶(Py)对聚合反应起着重要作用,可有效地降低聚合速率和使分子量分布变窄;随着[H2O]和[Py]降低或[TiCl4]增加,聚合产物的分子量增加,而分子量分布指数(Mw Mn)基本维持在1.8左右;随着[Py]增加,聚合速率降低;随着[H2O]和[TiCl4]增加,聚合速率提高.聚合速率对单体浓度呈一级动力学关系,对Py、H2O和TiCl4的反应级数分别为-0.72、0.72和1.86.聚合速率对TiCl4浓度呈接近二级动力学关系,这可能与体系中TiCl4主要以二聚体形式存在有关.聚合转化率和产物分子量均随着反应时间延长而逐渐增大,PS的数均分子量与转化率呈线性增加关系.     

负离子引发丙烯腈沉淀聚合动力学研究

从负离子引发丙烯腈沉淀聚合的亚微观过程出发,建立了动力学模型,并通过初生态沉淀聚集体联结方法数的叠加,推导出了动力学方程.在不同条件下(单体浓度、引发剂浓度、时间)对丙烯腈沉淀聚合进行了研究,用推导的动力学方程处理数据后发现实验数据与理论相吻合.丙烯腈负离子沉淀聚合的聚合反应为对单体浓度的一级反应,对引发剂浓度的一级反应,反应速率方程为Rp=k0[M]1.0[I]1.0.     

First emulsion polymerization of styrene with sodium borohydride: evidence of the generation of radical intermediates by sodium borohydride in H2O

Emulsion polymerization of styrene with sodium borohydride (NaBH4) in an aqueous sodium dodecyl sulfate (SDS) solution was successfully accomplished for the first time. Polystyrene with a high molecular weight (M(w) > 2 000 000) and a broad molecular weight distribution (MWD approximately 3.5) was obtained in a conversion of less than 30%. Several pieces of evidence that the polymerization proceeded through radical intermediates were observed. Variations in the concentration of NaBH4 showed a critical range in said concentration, i.e., a borderline that determined whether the main reaction was directed to either a polymerization or a competed reaction with variations in the NaBH4 level. Kinetic studies on the emulsion polymerization of styrene with NaBH4 performed at 50, 55, and 60 degrees C showed that the initiator had an approximately 50-min induction period. A plot of -ln(1 - X), where X is the fractional conversion, as a function of time resulted in a linear relationship, showing that the present initiator system followed first-order kinetics with respect to monomer concentration. The Arrhenius plot between ln k vs 1/T gave a good linear relation, and the overall activation energy was observed to be about 37.5 kcal/mol. The employment of CH3I with NaBH4 significantly increased conversion (>95%) and provided polystyrene with a well-controlled Mw and MWD (<2.3).