胶束体系中光敏聚合的研究 Ⅴ.离子型二苯酮在不同离子型胶束中光化学行为

采用水溶性光敏剂——对苯甲酰苄基磺酸钠(BP^-)和对苯甲酰苄基三乙基溴化铵(BP⁺)同二苯酮(BP)进行了对比研究。瞬态和稳态光谱的结果表明:BP⁺,BP^-分别处于十二烷基磺酸钠(SDS)阴离子胶束和十六烷基三甲基溴化铵(CTAB)阳离子胶束的Stern层,它们在匀相和非匀相体系中的光物理和光化学性质与BP相同。测定了它们在不同离子型胶束体系中的光还原反应速度,结果表明,离子型二苯酮BP⁺和BP^-比中性的BP具有更高的反应活性,它们在不同离子型胶束体系中,由于静电相互作用,光还原速度显著不同,在合适的条件下,离子型Bp⁺和BP^-在胶束中的光还原速度比中性BP高几十倍以上。另外对胺的疏水性的影响也进行了考察。     

含氧光敏聚合反应中表面活性剂的催化作用

本文研究了二苯酮/三乙胺/氧体系引发MMA的光聚合反应中烷基铵羧酸盐类(R₁R₂R₃R₄N⁺O^-OCR₅)离子型表面活性剂的催化作用。实验结果表明,聚合速度的大小和表面活性剂的类型,分子结构以及浓度有关。表面活性剂分子对系统中氢过氧化物光敏分解的促进,使聚合反应的量子产率提高了两倍多。     

室温下甲基丙烯酸甲酯原子转移自由基乳液聚合反应研究

以卤化亚铜（CuX）/1,10-邻二氮菲（phen）配合物为催化剂、2-溴代异丁酸 乙酯（EBiB）为引发剂、十二烷基磺酸钠（SLS）为乳化剂,进行了甲基丙烯酸甲 酯（MMA）的原子转移自由基乳液聚合（ATRP）反应。结果表明,与较高温度（70 - 90 ℃）下的聚合反应相比,室温（25 ℃）时聚合反应有更好的可控性,通过 外加钝化剂的复合催化引发体系CuBr/CuBr_2/phen/EBiB或利用CuCl/phen/EBiB催 化引发体系的“卤素交换反应”,可进一步改善聚合反应的可控性。紫外发光谱测 定结果表明,CuBr/phen配合物在MMA相中的分配倾向随着温度的降低而增大,使得 室温下MMA的乳液ATRP保持了较好的可控性和较快的反应速度。     

AIBN/SmCl3/乳酸体系催化甲基丙烯酸甲酯的反向原子转移自由基聚合

利用稀土金属化合物三氯化钐(SmCl3)和二氯化钐(SmCl2)之间的单电子转移反应,以AIBN/SmCl3/乳酸作为反向原子转移自由基聚合(ReverseATRP)的催化体系,成功地实现了甲基丙烯酸甲酯(MMA)的反向ATRP,并考察了温度、溶剂和组分比对聚合反应的影响.MMA在该体系中的聚合反应是一级反应,所得PMMA的分子量与单体转化率成正比,聚合物的分子量分布较窄(Mw/Mn<1.5),具有活性聚合的特征.     

胶束体系中光敏聚合的研究 Ⅶ．微泡水溶液体系中光聚合的研究

研究了在双十六烷基二甲基溴化铵（ＤＣＤＡＢ）形成的微泡溶液中，二苯酮（ＢＰ）／三乙胺（ＴＥＡ）体系的光化学初级反应和引发ＭＭＡ光聚合反应．动力学实验结果表明，ＤＣＤＡＢ微泡对聚合反应有显著的催化作用，使聚合速度提高近４倍左右，其效果和离子型胶束的催化作用结果相近．由ＤＣＤＡＢ微泡中光聚合得到的产物ＰＭＭＡ，具有较高的结构规整性，它的间同和全同结构可达７０％左右．     

胶束中的光物理和光化学过程

一、引言近十几年来化学家们详尽地研究了胶束体系对某些基态有机化学反应速率的影响,发现胶束能显著地提高反应速率,并把这一效应归结为两点:1.胶束能把反应物包围起来,从而增加了反应物的区域浓度,加快了反应速率;2.胶束-水的界面具有一些特殊的性质,例如,离子型胶束表面的区域电场可高达10~6V/cm,这就能大大地影响反应的过渡态,从而影响反应速率。     

ACPMA/BPO引发甲基丙烯酸甲酯聚合及其动力学

以4,4′-偶氮二[4-氰基戊酰(对-二甲氨基)苯胺](ACPMA)/过氧化二苯甲酰(BPO)为氧化还原引发体系,研究了甲基丙烯酸甲酯(MMA)在N,N-二甲基甲酰胺(DMF)中的聚合及其动力学行为.考察了聚合反应温度、单体浓度、ACPMA浓度和BPO浓度对聚合反应速率和聚合物分子量的影响,测定了反应级数和聚合反应的活化能.结果表明,在一定范围内,聚合反应速率随单体浓度增大、ACPMA浓度增大、BPO浓度增大和反应温度的升高而增大;聚合物分子量随单体浓度的增大而增大,随ACPMA浓度的增大、BPO浓度增大和反应温度的升高而降低.该体系具有氧化还原引发体系的特征,其引发MMA的聚合速率方程为Rp=K[ACPMA]0.57     

采用ATRP合成天然橡胶接枝共聚物——Ⅲ.NR-g-PMMA的制备

N-溴代丁二酰亚胺与天然橡胶(NR)反应合成了大分子引发剂——溴代天然橡胶[NR-Br(1)].通过原子转移自由基聚合(ATRP),以CuBr/PMDTA为催化体系,1引发甲基丙烯酸甲酯(MMA)接枝共聚制得新型天然橡胶-g-聚甲基丙烯酸甲酯[NR-g-PMMA(2)],其结构经1H NMR和IR表征.初步聚合反应动力学研究结果表明,NBS与NR在高温下反应容易伴随双键加成和环化反应,于室温反应所得1具有较高的引发活性;接枝聚合符合一级动力学反应,即2的分子量随MMA单体转化率的提高而增加.     

(7-N,N-二甲氨基)香豆素基-3-甲酸乙酯/二芳基碘鎓盐光敏引发聚合反应体系

本工作合成了(7-N,N-二甲氨基)香豆素基-3-甲酸乙酯(EDACF)光敏剂。在光作用下,激发态的EDACF分子与二芳基碘盐OPPIP分子之间发生电子转移反应,伴随发生EDACF的褪色反应和OPPIP的光解反应,后者生成具有引发活性的芳基自由基。由于EDACF具有CT态特性,使得它与OPPIP之间的光电子转移反应速度随着溶剂极性增加明显减慢。EDACF/OPPIP体系可有效地引发MMA聚合反应,聚合反应动力学方程为R_p=K[OPPIP]^0.47[EDACF]^0.42[MMA]^0.98.     

MA7iBu-POSS与MMA本体聚合反应动力学及竞聚率研究

为研究POSS参与聚合反应的反应动力学,以MA~(7iBu)-POSS和MMA的本体聚合反应为研究对象,采用称重法测定转化率,得到转化率曲线以及各单体用量对反应速率的影响。结果得出:反应速率随着温度和引发剂浓度的增加而增加,随MMA质量的增加而降低,而MA~(7iBu)-POSS对反应速率的影响是先增大后减小,且存在一个拐点A。另外,得到聚合反应的活化能Ea=87.297kJ/mol;反应级数(引发剂)i=0.617,当MA~(7iBu)-POSS的浓度C_N小于0.1239mol/L,MA~(7iBu)-POSS的反应级数n=0.217,当C_N大于0.1239mol/L,n=-0.202;同时,得出竞聚率r_1(MMA)=1.212,r_2(MA~(7iBu)-POSS)=0.567,由此得出,MMA的自聚大于共聚,MA~(7iBu)-POSS的共聚大于自聚,二者在聚合物中的分布情况为无规分布。     

Revisit to the formation mechanism of exfoliated montmorillonite/PMMA nanocomposite latex through soap‐free emulsion polymerization

Soap‐free emulsion polymerization of methyl methacrylate (MMA) in the aqueous suspension of montmorillonite (MMT) was able to fabricate the exfoliated MMT/PMMA nanocomposite latex. Because neither MMA nor substantial quantity of potassium persulfide (KPS) initiator could be individually absorbed into the interlayer region of MMT, the polymerizing ionic radicals in water phase were considered as a major component to diffuse into the gallery of MMT. They have been observed to organize into disk‐like micelles in the interlayer regions to exfoliate MMT. The diffusion of the polymerizing ionic radicals was further supported by using sodium dodecyl sulfate (SDS) surfactant as a model compound to diffuse into the gallery of MMT. The exfoliation of MMT was almost completed before micellization stage was over. After exfoliation, the disk‐like micelles became a polymerization loci for monomers. Because the disk‐like micelles in numbers were substantially over the commonly formed spherical micelles in the typical soap‐free emulsion polymerization, the conversion rate of MMA to MMT/PMMA nanocomposite latex was faster. Based on the above experimental observation, a justified exfoliation mechanism of MMT was proposed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 459–466, 2009     

PHOTOPOLYMERIZATION IN THE MICELLAR SYSTEMSⅡ THE CATALYSIS OF PKT FUNCTIONAL MICELLE*

A kind of cationic compounds, having benzophenone end group and various length chain (PKT) (BP-CH_2N+R_2R'·X~-, R&R' different chain iength alkyl group) were used as photosensitizers. Various BP/TEA systems have been used for study, The efficiency of MMA photopolymerization initiated by them shows PKT>BP in homogeneous water solution and PKT> BP/CTAB in micellar water solution. The results obtained indicate that catalytic effects of PKT type functional micelles are far greater than that of common micelle with the enhancement of polymerization rate over 10 times compared with BP in water solution. The catalytic role, reaction character of PKT, effect of counter ions and retarding effect of oxygen have also been discussed.     

Formation mechanism of conducting polypyrrole nanotubes in reverse micelle systems

Polypyrrole (PPy) nanotubes were readily fabricated through chemical oxidation polymerization in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse (water-in-oil) emulsions. The reverse cylindrical micelle phase was characterized, and the key factors affecting the formation of PPy nanotubes were systematically inspected. AOT reverse cylindrical micelles were prepared via a cooperative interaction between an aqueous FeCl3 solution and AOT in an apolar solvent. In the H2O/FeCl3/AOT/apolar solvent system, the aqueous FeCl3 solution played a role in increasing the ionic strength and decreasing the second critical micelle concentration of AOT. As a result, AOT reverse cylindrical micelles could be spontaneously formed in an apolar solvent. In addition, iron cations were adsorbed to the anionic AOT headgroups that were capable of extracting metal cations from the aqueous core. Under these conditions, the addition of pyrrole monomer resulted in the chemical oxidation polymerization of the corresponding monomer at the surface of AOT reverse cylindrical micelles, followed by the formation of tubular PPy nanostructures. In a typical composition (74.0 wt % hexane, 22.4 wt % AOT, and 3.6 wt % aqueous FeCl3 solution at 15 degrees C), the average diameter of PPy nanotubes was approximately 94 nm and their length was more than 2 mum. The PPy nanotube dimensions were affected by synthetic variables such as the weight ratio of aqueous FeCl3 solution/AOT, type of apolar solvent, and reaction temperature. Moreover, the relationship between the diameter and the conductivity of the nanotubes was investigated.     

Miscibility of dodecyltrimethylammonium bromide and dodecyltrimethylammonium chloride in surface-adsorbed film and micelle

Surface tension of aqueous solutions of mixtures of dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) has been measured and analyzed by using thermodynamic relations. The adsorbed film has been found to contain more DTAB molecules than the solution. The shape formed by the curves of the total molality at constant surface tension against the solution and surface compositions indicates the ideal mixing of the DTAB and DTAC molecules in the adsorbed film. Micellar composition has been estimated at the critical micelle concentration (CMC). The micelles have been found to be richer in DTAB than the solution, but poorer in DTAB than the adsorbed film at the CMC. The DTAB and DTAC molecules have been shown to mix ideally in the micelles. From the comparison with the results on the system of decylammonium bromide and decylammonium chloride, it has been concluded that, on the mixing of surfactants differing only in counter ions, the adsorbed film is influenced more significantly by the ionic head group of the surfactant than the micelle.     

Liquid solubilization dynamics: Oleic acid in bile salt

The solubilization dynamics of oleic acid by aqueous sodium taurodeoxycholate solutions at 37°C does not conform to previous resistance in series models involving diffusion and interfacial steps. This is especially true as the ionic strength of the aqueous solution is increased by adding NaCl or by increasing the taurodeoxycholate concentration above 2%. Experiments conducted with a liquid/liquid stirred cell show that as the ionic strength is increased, the flux of oleic acid into the aqueous solution exceeds a reasonable value for the diffusion limit, assuming that oleic acid diffuses only in mixed micelles, and that the flux becomes independent of flow at these high ionic strengths. Two alternative models for the solubilization process are proposed. One involves a rapid exchange of oleic acid between mixed micelles and oleic acid free micelles in parallel with mixed micelle diffusion; and the second involves formation of a small emulsion droplet at the interface, which contains significantly more oleic acid than a mixed micelle, and which rapidly dissolves into micellar solution as the droplet leaves the interface.     

Conventional synthesis of amphiphilic block copolymer utilized for polymeric micelle by mechanochemical solid-state polymerization

The first example is presented here of an amiphiphilic block copolymer synthesized by mechanochemical solid-state polymerization and used to form polymeric micelles. A model amphiphilic block copolymer was synthesized first, possessing galactose as a hydrophilic side chain and theophylline as a hydrophobic side chain, by mechanochemical solid-state polymerization. The resulting copolymer had a narrow molecular weight distribution. Polymeric micelle formation was subsequently carried out with the copolymer by a dialysis method. To gain insight into the physicochemical properties of the polymeric micelle, dynamic light scattering (DLS) measurements were performed. A narrow distribution of diameters was observed in the polymeric micelle solution, and these micelles were disrupted by the addition of sodium dodecyl sulfate (SDS). It was also confirmed by DLS measurements that the polymeric micelles were spherical. These results suggested that the block copolymer synthesized by mechanochemical solid-state polymerization was as suitable for the preparation of polymeric micelles as materials obtained by living polymerization.     

Aggregation work at polydisperse micellization: ideal solution and "dressed micelle" models comparing to molecular dynamics simulations

General thermodynamic relations for the work of polydisperse micelle formation in the model of ideal solution of molecular aggregates in nonionic surfactant solution and the model of "dressed micelles" in ionic solution have been considered. In particular, the dependence of the aggregation work on the total concentration of nonionic surfactant has been analyzed. The analogous dependence for the work of formation of ionic aggregates has been examined with regard to existence of two variables of a state of an ionic aggregate, the aggregation numbers of surface active ions and counterions. To verify the thermodynamic models, the molecular dynamics simulations of micellization in nonionic and ionic surfactant solutions at two total surfactant concentrations have been performed. It was shown that for nonionic surfactants, even at relatively high total surfactant concentrations, the shape and behavior of the work of polydisperse micelle formation found within the model of the ideal solution at different total surfactant concentrations agrees fairly well with the numerical experiment. For ionic surfactant solutions, the numerical results indicate a strong screening of ionic aggregates by the bound counterions. This fact as well as independence of the coefficient in the law of mass action for ionic aggregates on total surfactant concentration and predictable behavior of the "waterfall" lines of surfaces of the aggregation work upholds the model of "dressed" ionic aggregates.     

Zeta potential of dodecyltrimethylammonium hydroxide micelles in water

 The electrophoretical mobility of dodecyltrimethyl-ammonium hydroxide micelles has been measured at two different concentrations giving values similar to that determined in other surfac-tants. There is a good agreement between micelle ionization degrees computed from zeta potential measurements and those from ion-selective electrodes experiments. This demonstrates that electrophoresis experiments may be replaced by the simpler ion-selective electrode measurements to determine micelle surface potential. It has also been concluded that ion-selective electrodes detect only the non-micellised ions, that only free ions contribute to the intermicellar solution ionic strength, and micelles do not affect the result, and that the dependence of the electrophoretic mobility on the soap concentration is due to the reduction of the micelle net charge when the ionic strength of the intermicellar solution arises. Received: 2 December 1996 Accepted: 24 February 1997     

Bioinspired core‐crosslinked micelles from thymine‐functionalized amphiphilic block copolymers: Hydrogen bonding and photo‐crosslinking study

Bioinspired core‐bound polymeric micelles, based on hydrogen bonding and photo‐crosslinking, of thymine have been prepared from poly(vinylbenzylthymine)‐b‐poly(vinylbenzyltriethylammonium chloride). The amphiphilic block copolymer was synthesized by 2,2‐tetramethylpiperidin‐1‐oxyl‐mediated living radical polymerization in water/ethylene glycol solution. Micelle characterization and critical micelle concentration measurements demonstrated that the hydrogen bonding of the attached thymine units stabilizes the micelles. Further, core‐crosslinked polymeric micelles were formed by ultraviolet (UV) radiation showing that the stability of the micelle could be controlled by the UV crosslinking of the attached thymines. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Micellization and reversible pH-sensitive phase transfer of the hyperbranched multiarm PEI-PBLG Copolymer

A novel, hyperbranched, amphiphilic multiarm biodegradable polyethylenimine-poly(gamma-benzyl-L-glutamate) (PEI-PBLG) copolymer was prepared by the ring-opening polymerization of gamma-benzyl-L-glutamate-N-carboxyanhydride (BLG-NCA) with hyperbranched PEI as a macroinitiator. The copolymer could self-assemble into core-shell micelles in aqueous solution with highly hydrophobic micelle cores. As the PBLG content was increased, the size of the micelles increased and the critical micelle concentration (CMC) decreased. The surface of the micelles had a positive zeta potential. The cationic micelles were capable of complexing with plasmid DNA (pDNA), which could be released subsequently by treatment with polyanions. The PEI-PBLG copolymer formed unimolecular micelles in chloroform solution. The pH-sensitive phase-transfer behavior exhibited two critical pH points for triggering the encapsulation and release of guest molecules. Both the encapsulation and release processes were rapid and reversible. Under strong acidic or alkaline conditions, the release process became partially or completely irreversible. Thus, this copolymer system should be an attractive candidate for a gene- or drug-delivery system in aqueous media and could provide the phase-transfer carriers between water and organic media.