Isoprene Polymerization by Butyllithium in Cyclohexane. II. Propagation Reaction

The kinetics of the propagation reaction in the polymerization of isoprene initiated by n-, sec-, or t-butyllithium, in the absence or in the presence of the three corresponding lithium butoxides, are studied in the two possible major cases. In the first case, the propagation takes place without simultaneous initiation; the reaction is then first-order versus the monomer concentration and one-sixth-order versus the polyisoprenyllithium concentration. The lithium butoxides decrease the propagation rate, but the effect is not very dependent on the nature of the butoxide. In the second case, the presence of the initiator decreases the propagation rate in a manner which depends on the concentrations of the reactants and on the nature of the initiator. The effect of the lithium butoxide is not simply additive. Depending on the relative concentrations, a synergistic effect may be observed. It is suggested that the active species are chiefly ion pairs of unassociated polyisoprenyllithium. Ion pairs from associated molecules may have limited activity.     

Aziridine Termination of Living Anionic Polymerization

A switch from carbanions to aza‐anions is performed by the addition of N‐tosylaziridine (TAz) to living poly(styryl) (PS) chains. This is the first example of carbanionic aziridine ring‐opening which was previously activated by amidation with a tosyl group to enable nucleophilic ring‐opening by the living chain end. Poly(styrene)‐tosylaziridines (PS‐TAz) with narrow molecular weight distributions and variable molecular weights are synthesized. The removal of the tosyl group and subsequent functionalization is shown, evidencing quantitative transfer to azaanionic species. All polymers are characterized in detail by ¹H NMR spectroscopy, DOSY ¹H NMR spectroscopy, and size exclusion chromatography (SEC). This strategy allows the introduction of amine groups via anionic polymerization in analogy to the well‐established epoxide termination.

     

Living Polymerization via Anionic Initiation for the Synthesis of Well‐Defined PPV Materials

The anionic polymerization of PPV via the sulfinyl precursor route is further investigated. When LHMDS is employed as the base to form the actively propagating quinodimethane system and THF as the solvent, anionic polymerizations can be observed. With the use of tert‐ butyl‐substituted anionic initiators, specific functional groups can be built in the polymer chain and the chain length can be efficiently controlled, which is demonstrated here for the first time. With introduction of branched side chains on the aromatic core, soluble conjugated PPV material can be obtained with molecular weights in the range of 5000–16 000 g mol⁻¹.     

Synthesis of Poly(methyl acrylate) Grafted onto Silica Particles by Z-supported RAFT Polymerization

RAFT polymerization of methyl acrylate (MA) mediated by silica-supported 3-(methoxycarbonyl-phenyl-methylsulfanylthiocarbonylsulfanyl) propionic acid (Si- MPPA) and 3-(benzylsulfanylthiocarbonylsulfanyl) propionic acid (Si-BSPA) was investigated. The molecular weight and polydispersity of grafted polymeric chains and the grafted chain transfer agent (CTA) efficiency (G_e) were strongly dependent on the types and loading of Si-CTAs and free CTA used in solution. Under similar reaction conditions, the graft polymerization mediated by Si-MPPA was better controlled than that using Si-BSPA. The introduction of a free CTA in solution during Si-MPPA mediated polymerization could significantly decrease the polydispersity of free and grafted polymeric chains and enhance the grafted CTA efficiency, and longer polymeric chains could be grafted onto silica support when Si-MPPA with a higher CTA loading was used to mediate the polymerization. In all cases, the RAFT polymerization using 2-(2-cyanopropyl) dithiobenzoate (CPDB) as a free CTA could afford well-defined grafted PMA and significantly increased G_e value, while the polymerization rate was also decreased.     

Electrochemical Polymerization of Methylene Green

The electrochemical polymerization of methylene green has been carried out using cyclic voltammetry. The electrolytic solution consisted of 4° 10^?3 mol/L methylene green, 0.1 mol/L NaNO₃ and 1 × 10^?2 mol/L sodium tetraborate with pH 11.0. The temperature for polymerization is controlled at 60°C. The scan potential is set between ?0.2 and 1.2 V (vs. Ag/AgCl with saturated KCl solution). There are an anodic peak and a cathodic peak on the cyclic voltammogram of poly (methylene green) at pH≤3.8. Both peak potentials shift towards negative potentials with increasing pH value, and their peak currents decrease with increasing pH value. Poly (methylene green) has a good electrochemical activity and stability in aqueous solutions with pH≤3.8. The UV‐Visible spectrum and FTIR spectrum of poly (methylene green) are different from those of methylene green.     

Polymerization of vinyl monomers in the presence of silica having surface functional groups

The surface of silica was modified by mercaptopropyl, chloropropyl, aminopropyl, and methacryloxypropyl groups by the treatment of silica with the corresponding silane coupling agents, and the effects of functional groups on the surface on the polymerization of vinyl monomers initiated by benzoyl peroxide or 2,2-azobisisobutyronitrile were investigated. Although the rate of the polymerization of vinyl monomers in the presence of silica was almost equal to that in the absence of silica, a part of polymer formed was grafted onto silica surface. The polymerization was considerably retarded in the presence of these functionalized silicas and the corresponding polymers were effectively grafted onto the surface. The molecular weight of ungrafted polymer formed in the presence of the functionalized silica was lower than that formed in the presence of unmodified silica. This indicates that the chain transfer reaction of growing polymer radical to functionalized silica surface forms radicals on the surface, which then couples with growing polymer radical and/or reinitiates the polymerization to give rise to the grafting of polymers onto the surface. In the case of silica having methacryloxypropyl groups, the grafting based on the copolymerization of vinyl monomer with the surface methacryloxypropyl groups was considered to successfully proceed.     

Rate Constant of Initiation Reaction in Cationic Polymerization of Vinyl Monomers. I. Polymerization of Styrene Derivatives Catalyzed by Triphenylmethyl Stannic Pentachloride

Abstract

To investigate the method of measurement of the initiation rate constant in cationic polymerization, styrene and α-methylstyrene are polymerized by triphenylmethyl stannic pentachloride (Ph₃CSnCl₅). Adding these monomers to a solution of Ph₃CSnCl₅, the strong absorption of triphenylmethyl cation at 400 to 450 mμ disappears. The rate of disappearance of the absorption at 430 mμ is proportional to the concentration of Ph₃CSnCl₅ and monomer. It is confirmed that this disappearance of the absorption is due to the conversion of triphenyl cation to styryl or α-methylstyryl cation. Therefore, the rate of consumption of triphenylmethyl cation corresponds to that of the addition of triphenylmethyl cation to the olefinic double bond in a monomer, that is, the rate of the initiation reaction. Considering the dissociation constant of Ph₃CSnCl₅, the initiation rate constants of styrene and α-methylstyrene in ethylene chloride solution at 30°C are 11.6 × 10^?2 and 2.85 liters/mole-min, respectively. These values seem to be much smaller than the propagation rate constant of each monomer. However, the effect of polymerization conditions, for example, the kind of a monomer and the polarity of a solvent, on the initiation rate constant is the same as in the propagation reaction. This fact suggests the similarity of a reaction mechanism in both elementary reactions.     

Syntheses and properties of hyperbranched polybenzoxazole by thermal cyclodehydration of hyperbranched poly[o‐(t‐butoxycarbonyl)amide] via A2 + B3 approach

The syntheses and properties of hyperbranched poly(o‐hydroxyamide) [poly(HAB‐BCC)‐ABP], poly[o‐(t‐butoxycarbonyl)amide] [poly(HAB‐BCC)‐ABP‐t‐BOC], and polybenzoxazole [poly(HAB‐cycloBCC)] were examined. Poly(HAB‐BCC)‐ABP was obtained from the polycondensation reaction of 3,3‐dihydroxy‐4,4′‐diaminobiphenyl (HAB) as an A₂‐monomer and 1,3,5‐benzenetricarboxylchloride (BCC) as a B₃‐monomer with 2‐amino‐4‐t‐butylphenol (ABP) in NMP in the presence of pyridine for 24 h. The reaction of poly(HAB‐BCC)‐ABP and di‐t‐buthylcarbonate (DiBOC) was performed to obtain the corresponding poly(HAB‐BCC)‐ABP‐t‐BOC with pendant t‐BOC groups. The thermal cyclodehydration of poly(HAB‐BCC)‐ABP‐t‐BOC was carried out in the film sate at 400 °C, affording the poly(HAB‐cyclo‐BCC) in quantitative yield. Furthermore, the solubilities and thermal properties of these polymers were examined. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3640–3649, 2006     

Synthesis of PEDOT Nanoparticles and Vesicles by Dispersion Polymerization in Alcoholic Media

Summary: The synthesis of PEDOT nanoparticles and vesicles by dispersion polymerization in a methanol/water mixture (3/2, v/v) is reported, using either ammonium persulfate or iron(III) p‐toluenesulfonate as oxidants and α‐EDOT‐PEO as a reactive stabilizer. The influence of the oxidant as well as the α‐EDOT‐PEO molar mass and concentration on the core‐shell particle morphology and conductivity properties have been investigated. PEDOT particles with conductivities up to 1.5 × 10⁻² S · cm⁻¹ have been obtained in high yield.

TEM image of PEDOT vesicles prepared using PEO‐based stabilizers of 25 000 g · mol⁻¹ in water/methanol mixture (2:3 v/v) at room temperature using ammonium persulfate as an oxidant.     

Reversible Addition-Fragmentation Chain Transfer Polymerization of Methyl Methacrylate in Microemulsion: The Influence of Reaction Conditions on Polymerization

The reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) using cetyltrimethylammonium bromide (CTAB) as surfactant and a difunctional RAFT agent S,S′-bis (α, α′-dimethylacetic acid) trithiocarbonate (BDAT) as chain transfer were conducted in microemulsion. The influence of polymerization temperature and concentration of RAFT agent on the polymerization were investigated, respectively. The results showed that the molecular weight of products increased linearly with conversion, the polydispersity indexes remained low value, and the polymerization processes were totally under control with increasing concentration of RAFT agent, the polymerization behavior exhibited living polymerization characters. In addition, the influence of RAFT concentration on the particle size was investigated by TEM. The results indicated that the particles were highly monodispersed and the particle size increased with increasing concentration of RAFT agent.     

Effect of Some Solvents on the Radical Polymerization of Methyl Methacrylate Studied by Differential Scanning Calorimetry

The course of the isothermal polymerization of methyl methacrylate in different concentrated solutions in toluene, n-butyl acetate, cyclohexanone, and dimethylformamide was measured at four temperatures by differential scanning calorimetry. The conversions at the sharp increase of the reaction rate were found to increase with dilution of the reaction mixture. The polymerization enthalpies and the composite rate constants were calculated. The polymerization enthalpies seem to be solvent independent. The composite rate constants for polymerization in butyl acetate are lower and those for polymerization in toluene are equal to the constants for bulk polymerization. They are independent of the concentration of the reaction system. The constants for polymerization in cyclohexanone and dimethylformamide are, however, concentration dependent. An interrelation between the composite rate constants and solubility parameters of the solvents and methyl methacrylate was found. The relative molecular weight averages decrease with decreasing concentration of the reaction mixture. The MW distributions were very broad.     

Polymerization of propargylamine and 1,1-diethylpropargylamine by transition metal catalysts

Some polyacetylene derivatives containing an amine functional group were prepared by the polymerization of propargylamine (PA) and 1,1-diethylpropargylamine (DEPA) with various transition metal catalysts. In the polymerization of PA, Mo-based catalysts were more effective than that of W-based catalysts, and organoaluminum compounds, especially EtAlCl₂, were found to be very effective cocatalysts. In the polymerization of DEPA, Mo-and W-based catalyst systems showed a similar catalytic activity. The polymerization easily proceeded in polar solvents such as nitrobenzene and DMF as well as nonpolar aromatic solvents such as chlorobenzene, toluene, etc. The resulting poly(PA) and poly(DEPA) were insoluble in organic solvents regardless of polymerization catalysts but the polymers were found to be stable to air oxidation. Thermogravimetric analyses and thermal transitions of poly(PA) and poly(DEPA) were also studied. © 1992 John Wiley & Sons, Inc.     

悬浮聚合制备大粒径磁性聚甲基丙烯酸甲酯微珠: 反应参数对微珠粒径的影响

采用低速搅拌悬浮聚合制得了一系列磁性聚甲基丙烯酸甲酯(PMMA)微珠. 分别以聚乙烯醇(PVA 1788)和碱式碳酸镁作为稳定剂和助分散剂, Fe3O4磁流体为磁性物质, 双甲基丙烯酸甲酯为交联剂. 所有粒子的直径在1～3 mm 范围内, 微球的粒径及其分布可以通过改变聚合反应介质来进行调节. 着重研究了反应体系中电解质的用量、聚合反应温度、水油比、碱式碳酸镁及交联剂的用量等反应参数对微球粒径的影响. 利用振动探针式磁强计(VSM)和原子吸收光谱(AAS)分别对磁性PMMA微珠的超顺磁性和Fe3O4含量进行了表征.     

Melt Polymerization of Adipic Anhydride (Oxepane-2,7-Dione)

Oxepane-2,7-dione (1) was prepared by the reaction of adipic acid and acetic anhydride followed by catalytic depolymerization under vacuum. the ring-opening polymerization of (1) was investigated in the melt, and was studied as a function of polymerization temperature, time and concentration of catalyst (stannous 2-ethylhexanoate). from ¹H-NMR and IR spectra it can be deduced that stannous 2-ethylhexanoate coordinates with the anhydride bond of the ring, and that the resulting species reacts with the monomer by ring-opening of the acyl-oxygen bond. These observations indicate a non-ionic insertion polymerization mechanism at the beginning of the reaction, but after 2 h at 80°C, anhydride exchange appears to be the dominating reaction. Ring-opening melt polymerization of (1) resulted in low molecular weight poly (adipic anhydride).     

Poly(acrylonitrile) ultrafiltration membranes. I. Polymer‐salt‐solvent interactions

Fourier transform infrared spectroscopy was used to study the interactions among LiCl, ZnCl₂, and AlCl₃ with N,N‐dimethylformamide (DMF) and poly(acrylonitrile) (PAN). It was observed that all three salts complex with DMF as well as PAN. The strength of the cation interaction with the >C?O oxygen of DMF was found to be higher than that with the ? CN group of PAN. The >C?O stretching frequency of DMF with ZnCl₂ was red shifted, indicating stronger complex formation compared with other two cations. With the addition of salt, the salt–DMF pseudo solvent was found to become a θ solvent for PAN compared with neat DMF. This change in PAN solvation power was primarily the result of DMF–salt complexation. As a result of the complexation, Mark‐Houwink constant a, was found to reduce from 0.75 (for pure DMF) to ～0.6 for DMF–salt solvents, indicating decreased PAN chain expansion. Comparison of intrinsic viscosity [η] values indicated that addition of salts to PAN–DMF solutions resulted in: (i) decrease in the DMF solvation power, which causes less expanded polymer coils, and (ii) increased interpolymer chain entanglements via salt‐promoted chain association. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2061–2073, 2005     

Theory of Shear‐Thickening in Transient Networks of Associating Polymers

Summary: Shear‐thickening phenomena observed in thermo‐reversible gels of telechelic associating polymers are theoretically studied on the basis of the transient network model. Non‐linear tension due to over‐stretching of the middle chain leads to thickening, if the coupling constant g of the end‐chain dissociation rate to the middle chain tension fulfills a certain condition. We give the condition for thickening in terms of the molecular parameters.

The thickening phase diagram: The region below each curve leads to thickening, whereas the region above the curve causes thinning for each molecular weight.     

Poly(ethylene terephthalate) copolymers containing nitroterephthalic units. I. Synthesis and characterization

The synthesis, microstructure, and thermal behavior of a series of poly(ethylene terephthalate) (PET) copolymers containing nitroterephthalic units are described. These novel copolyesters were synthesized by transesterification followed by melt copolycondensation of dimethyl terephthalate and dimethyl nitroterephthalate mixtures with ethylene glycol. The molar ratio of the two comonomers in the feed varied from 95/5 to 25/75. Furthermore, PET and poly(ethylene nitroterephthalate) homopolymers were synthesized with the same method and comparatively studied. Copolyester compositions were practically the same as in the feed, and weight‐average molecular weights ranged from 10,000 to 60,000. The two monomeric units were randomly distributed along the polymer chain, and the experimentally determined average sequence lengths were in accordance with ideal copolycondensation statistics. Melting temperatures and enthalpies of the copolyesters decreased with increasing content in nitroterephthalic units, and they all showed a single glass‐transition temperature superior to that of PET. They appeared to be stable up to 300 °C, and thermal degradation occurred in two well‐differentiated steps. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3761–3770, 2000     

Polymerization of propene by post-metallocene catalysts

In the last few years several non-metallocene catalysts have been disclosed as efficient catalysts for the stereospecific polymerization of propene. In this paper we summarize some recent literature data and some new results concerning the stereochemical mechanism of propene polymerization promoted by late transition metal systems and group 4 metal bis(phenoxyimine) systems. NMR analysis of the fine structure of the polymers obtained, in some cases using isotopically enriched reagents, provides valuable information on the regiochemistry and stereochemistry of the polymerization.     

溶液法星型聚乳酸的合成与表征

探讨了采用辛酸亚锡为催化剂,多元醇及多元酸为引发剂,以溶液法制备星型聚乳酸的可行性,研究了不同引发剂对产物分子量的影响.采用核磁共振及DSC对产物进行了表征,结果表明:以溶液法合成星型聚乳酸是可行的,但与丙交酯开环聚合制备星型聚乳酸的方法相比,溶液法在产物结构和分子量控制上并不十分有效,由于反应受到多官能团核引发剂空间位阻和反应概率的影响,聚乳酸产物的结构除星型结构外也同时存在大量的线型结构.