Enhancement of ultrasonically initiated emulsion polymerization rate using aliphatic alcohols as hydroxyl radical scavengers

Ultrasonically initiated emulsion polymerization of styrene was carried out in the presence of aliphatic alcohols, e.g. methanol, ethanol, n-pronanol and n-butanol, as volatile hydroxyl radical scavengers. With the addition of methanol, the polymerization rate of styrene increased, while the molecular weight and the average particle size of the produced polystyrene decreased because more radicals were produced in the presence of methanol. This is true also for the other polymerization system using other aliphatic alcohols, such as ethanol, n-pronanol and n-butanol, suggesting that the alcohols enter into cavitation bubbles and further react with hydroxyl radicals (*OH) from the sonolysis of water to produce hydroxyalkyl radicals, so as to reduce the recombination of *H and *OH radicals, therefore more radicals will be present in the systems for initiating polymerization. Obviously, it is an effective way to enhance ultrasonically initiated emulsion polymerization rate of styrene by adding volatile hydroxyl radical scavenger.     

Polystyrene/Fe3O4 magnetic emulsion and nanocomposite prepared by ultrasonically initiated miniemulsion polymerization

Ultrasonically initiated miniemulsion polymerization of styrene in the presence of Fe3O4 nanoparticles was successfully employed to prepare polystyrene (PS)/Fe3O4 magnetic emulsion and nanocomposite. The effects of Fe3O4 nanoparticles on miniemulsion polymerization process, the structure, morphology and properties of PS/Fe3O4 nanocomposite were investigated. The increase in the amount of Fe3O4 nanoparticles drastically increases the polymerization rate due to that Fe3O4 nanoparticles increase the number of radicals and the cavitation bubbles. Polymerization kinetics of ultrasonically initiated miniemulsion polymerization is similar to that of conventional miniemulsion polymerization. PS/Fe3O4 magnetic emulsion consists of two types of particles: latex particles with Fe3O4 nanoparticles and latex particles with no encapsulated Fe3O4 nanoparticles. Fe3O4 nanoparticles lower the molecular weight of PS and broaden the molecular weight and particle size distribution. Thermal stability of PS/Fe3O4 nanocomposite increases with the increase in Fe3O4 content. PS/Fe3O4 emulsion and nanocomposite exhibit magnetic properties. PS/Fe3O4 magnetic particles can be separated from the magnetic emulsion by an external magnetic field and redispersed into the emulsion with agitation.     

Polymerization rate and mechanism of ultrasonically initiated emulsion polymerization of n-butyl acrylate

The factors affecting the induction period and polymerization rate in ultrasonically initiated emulsion polymerization of n-butyl acrylate (BA) were investigated. The induction period takes only an instant in ultrasonically initiated emulsion polymerization of BA without any added initiator by enhancing the N2 flow rate. Increasing temperature, power output and SDS concentration, decreasing the monomer concentration results in further decreasing induction period and enhanced polymerization rate. Under optimized reaction conditions the conversion of BA reaches 92% in 11 min. The polymerization rate can be controlled by varying reaction parameters. The apparatus of ultrasonically initiated semi-continuous and continuous emulsion polymerization were set up and the feasibility was first studied. Based on the experimental results, a free radical polymerization mechanism for ultrasonically initiated emulsion polymerization was proposed, including the sources of the radicals, the process of radical formation, the locus of polymerization and the polymerization process. Compared with conventional emulsion polymerization, where the radicals come from thermal decomposition of a chemical initiator, ultrasonically initiated emulsion polymerization has attractive features such as no need for a chemical initiator, lower reaction temperature, faster polymerization rate, and higher molecular weight of the polymer prepared.     

甲基紫精与醇类间的光诱导电子转移及光催化反应的ESR研究

用ESR方法研究了甲基紫精(MV⁺⁺)与甲醇,乙醇及苄醇等之间的光诱导电子转移和光反应过程.结果发现,甲基紫精存在条件下,某些很稳定的醇类也可以发生光催化分解和光催化氧化的反应,甲基紫精在反应过程中起的是催化剂的作用在无氧条件下,MV⁺⁺/C₂H₅OH体系经UV光照10min后即可观察到很强的MV⁺离子基的信号,表明甲基紫精与乙醇分子之间发生了电子转移;当进行较长时间光辐照,则MV⁺离子基逐步消失而生成H原子和碳中心自由基。在通氧条件下进行光照时,则无MV⁺基信号而产生OOH基和碳中心自由基的信号.当体系中有一定量的水存在时,OOH基减弱而产生·OH基,且随着水量的增加,·OOH基的强度更为减弱直至消失,而同时羟基浓度则大大增加.另一个有趣而重要的现象是,对于MV⁺⁺/苄醇体系,在通氧条件下辐照时可给出很强的超氧阴离子基O₂^-的信号,而MV⁺⁺/甲醇体系可产生较弱的O₂^-信号.但是在无氧时甲基紫精的存在进行光辐照甲醇并不发生反应,而苄醇却可被甲基紫精光催化分解产生很强的苄氧基,羟甲基等自由基.本文详细地研究和讨论了甲基紫精与几种醇之间的光诱导电子转移和相应的均相光催化反应过程的机理.     

Nitroxide-controlled free radical copolymerization of styrene and acrylonitrile monitored by electron spin resonance and fourier transform infrared technique in situ

Nitroxide-mediated homopolymerization of styrene (St) and copolymerization of styrene and acrylonitrile (An) were monitored respectively by electron spin resonance and Fourier transform infrared technique in situ, and the polymerization kinetics was investigated in detail. Homopolymerization of St was well controlled in the presence of 4-hydroxyl-2,2,6,6-tetramethyl-l-piperidinyloxy (HTEMPO, N*) at high temperature. The initiation reactions and polymerization rates were changed by varying initiators, such as benzoyl peroxide (BPO), 2,2-azobis-isobutylonitrile (AIBN) and dicyclohexyl dicarbonate peroxide (DCPO) because of the different half-period values of the initiators. For the St system containing the DCPO with longer half-period value, the reaction rate was enhanced and the final conversion was increased because the larger amount of the DCPO residual released continuously the excess radicals to increase growing radical concentration. But the polydispersity of the resulting polymer became somewhat larger. The copolymerization of St and An with AIBN as initiator in the presence of HTEMPO was also tamed in the living fashion of stable free radical polymerization in the range of the total monomer conversion below 40%. The hydrogen-abstracting effect on the penultimate unit of the primary radicals or growing radical was observed through a copolymerization process. The larger amount of St was combined into the copolymers, leading to an increase of the An contents especially in the latter period of copolymerization, due to the inhibited addition of An on the growing radicals with end An unit. The normal random copolymerization was interrupted, resulting in the different virtual reactivity ratio. The dissociation and combination equilibrium between N* and the different end St and An units on propagating radicals affected the consuming rates of St and An. A possible copolymerization mechanism containing hydrogen-abstracting reaction was suggested.     

Scavenging of OH(*) radicals produced from H(2)O sonolysis with nitrate ions

The scavenging of OH(?) radicals formed during H(2)O sonolysis with nitrate-ions was studied in HNO(3)/NaNO(3) mixture at the constant NO(3)(-) ions concentration ([HNO(3)]+[NaNO(3)])=1 M in Ar atmosphere. Small amounts of N(2)H(5)NO(3) was added to solutions to avoid HNO(2) accumulation due to HNO(3) sonolysis. It was shown that the increase of [H(+)] causes the increase of H(2)O(2) formation rate (W(H(2)O(2)). (W(H(2)O(2)) values reach the plateau at [HNO(3)] approximately 1 M. The (W(H(2)O(2)) ratio in solution with [H(+)]=1 M and pure water was found to be equal to 2.4+/-0.4. It was assumed that (W(H(2)O(2)) increase in nitric acid medium is related to the changing of H(2)O(2) formation mechanism. In pure water H(2)O(2) is formed due to the OH(*) radicals recombination. In HNO(3)+NaNO(3) mixture the mechanism of H(2)O(2) formation consists in conversion of OH(*) radicals to NO(3)(*) radicals followed by NO(3)(*) radicals hydrolysis. Results obtained show that OH(*) radicals recombination mainly occurs in the liquid phase surrounding the cavitating bubble.     

红外光谱原位跟踪活性自由基聚合反应过程研究

使用新型可插入式红外光谱仪原位检测在4－羟基2，2，6，6－四甲基氧化哌啶醇（HTEMPO）存在下苯乙烯稳定自由基活性均聚合反应和苯乙烯／甲基丙烯酸羟丙酯的共聚合反应以及苯乙烯原子转移活性自由基聚合（ATRP）反应三个过程，分别考虑了它们的反应动力学，并给出了可能的聚合反应机理。研究结果表明，对于均相的苯乙烯（St)均聚合反应和苯乙烯（St)/甲基丙烯酸羟丙酯（HPMA）的自由基共聚合反应体系，聚合反应显示一定的诱导期，与反应体系中存在的HTEMPO捕捉自由基有关，而对于St／HPMA共聚合体系，诱导期更长，这是因为HPMA易和HTEMPO自由基发生氢转移反应，导致游离的HTEMPO浓度升高。最后用红外光谱实时跟踪苯乙烯非均相ATRP过程，发现苯乙烯聚合反应动力学接近于表现零级。因为单体分子在由增长自由基、卤化铜和联二吡啶形成的络合物的界面增长，与单体相内St浓度无关。     

Magnetic interaction in ferrous antimonite, FeSb2O4, and some derivatives

Ferrous antimonite, FeSb(2)O(4), which is isostructural with Pb(3)O(4), and some lead-?and cobalt-doped variants of composition FeSb(1.5)Pb(0.5)O(4) and Co(0.5)Fe(0.5)Sb(1.5)Pb(0.5)O(4) have been examined by (57)Fe and (121)Sb?M?ssbauer spectroscopy. Antimony is present as Sb(3+). The presence of Pb(2+) on the antimony site induces partial oxidation of Fe(2+) to Fe(3+). There is no Verwey-type transition in which electrons are shared between iron in different oxidation states. The quasi-one-dimensional magnetic structure gives rise to situations in which weakly coupled Fe(2+) ions can coexist in a non-magnetic state alongside Fe(3+) ions in a magnetically ordered state.     

Radical generation process studies of the cationic surfactants in ultrasonically irradiated emulsion polymerization

Without any chemical initiators added, ultrasonically irradiated emulsion copolymerization of styrene and a cationic polymerizable surfactant (methacryloxyethyl dodecydimethyl ammonium bromide, C(12)N(+)) was successfully employed to prepare copolymer nanolatexes. Compared with the conventional ionic surfactants, C(12)N(+) has much higher initiation efficiency and C(12)N(+) system exhibits shorter induction period, much higher styrene conversions and polymerization rate R(p) in short reaction time. A radical trapping experiment and gas chromatograph-mass spectrograph analysis proved that under ultrasonic irradiation, C(12)N(+) undergoes bond scission between the two alkyl and ionic group, where both C-N bonds are weak along the chain, thereby producing much more original radicals to initiate the emulsion polymerization.     

N,N,N,N-tetradentate Macrocyclic Ligand Based Selective Fluorescent Sensor for Zinc (II)

N,N,N,N-tetradentate macrocyclic ligand (L) has been synthesized by the condensation of benzil and semicarbazide and characterized. On excitation by light of wavelength 350?nm, L exhibited a fluorescent peak at λ(max)?=?454?nm, which showed ca 6 times enhancement in intensity with a blue shift on interaction with Zn(2+). L has been found to act as a selective fluorescent sensor for zinc(2+) ion over a host of other metal ions such as- Cd(2+), Pb(2+), Hg(2+), Ca(2+), Fe(2+), Na(2+), Co(2+), Mn(2+), Cu(2+) and Ni(2+), in 1:1 CH(3)OH:H(2)O. A 1:1 complex formation between L and Zn(2+) was proved. The enhancement in the fluorescence could be explained on the basis of Photo induced electron transfer (PET) mechanism with log β?=?1.86.     

微波液相放电等离子体发射光谱研究

液相放电能够产生各种活性物质,其中羟基自由基(OH),氢自由基(H)被认为是引发液相化学反应的主要活性物种,但由于其活性强寿命短的特点,测量比较困难,由于缺少标准样品,定量测量更为困难。用光学方法测量自由基是一种直接测量方法,其特点是瞬时在线测量,能立即获得数据,进行时间和空间分布测量。为了研究微波水中放电产生的自由基特性,利用发射光谱诊断技术对微波水中放电产生的活性物质进行了在线检测,考察了微波功率、反应器内部压强对OH自由基相对光谱强度的影响,并观测了等离子体中OH自由基强度的空间分布;同时,估算了微波液相等离子体中的电子激发温度。实验结果表明,微波水中放电可以产生大量的OH,H,O自由基,其中OH自由基的相对光谱强度最强,并随微波功率的增加呈现明显上升的趋势,随反应器内部压强的增大而迅速减弱;以OH为主的自由基主要产生于电极尖端附近。微波液相等离子体的电子激发温度约为0.33×104 K。     

Sonochemical degradation of chlorophenols in water

Sonochemical degradation of dilute aqueous solutions of 2-, 3- and 4-chlorophenol and pentachlorophenol has been investigated under air or argon atmosphere. The degradation follows first-order kinetics in the initial state with rates in the range 4.5-6.6 microM min-1 under air and 6.0-7.2 microM min-1 under argon at a concentration of 100 microM of chlorophenols. The rate of OH radical formation from water is 19.8 microM min-1 under argon and 14.7 microM min-1 under air in the same sonolysis conditions. The sonolysis of chlorophenols is effectively inhibited, but not completely, by the addition of t-BuOH, which is known to be an efficient OH radical scavenger in aqueous sonolysis. This suggests that the main degradation of chlorophenols proceeds via reaction with OH radicals; a thermal reaction also occurs, although its contribution is small. The addition of appropriate amounts of Fe(II) ions accelerates the degradation. This is probably due to the regeneration of OH radicals from hydrogen peroxide, which would be formed from recombination of OH radicals and which may contribute a little to the degradation. The ability to inhibit bacterial multiplication of pentachlorophenol decreases with ultrasonic irradiation.     

CuO/Cu2(OH)3Cl的制备及其光催化降解染料光谱性能研究

以CuCl2和NaOH为原料、微波液相加热法制得CuO/Cu2(OH)3Cl粉体作为光催化剂,XRD和FTIR进行了表征.用光度分析法测定了不同光源、溶液的酸度、催化剂的用量、光照时间等条件对染料脱色率的影响.结果表明,用太阳光作为光源照射4h,溶液的酸度为pH8,CuO/Cu3(OH)3 Cl的用量为40 mg/50 mL,氨基黑、靛蓝二磺酸钠等染料脱色率达到90%以上.加入Fe3 ,H2O2等其他物质可提高染料的脱色率.通过红外光谱和紫外光谱分析,表明染料分子在催化剂和光照条件下发生了降解.     

Infinite period and Hopf bifurcations for the pH-regulated oscillations in a semibatch reactor (H(2)O(2)-Cu(2+)-S(2)O(2-) (3)-NaOH system)

Dynamic behavior of the pH-regulated oscillations has been studied for the hydrogen peroxide oxidation of thiosulfate ions in the presence of trace amounts of copper(II) ions in a semibatch reactor. A solution of 0.08 M Na(2)S(2)O(3) and 0.112 M NaOH was flowed at 0.160 mL/min into 300 mL of solution containing the H(2)O(2) and Cu(2+) in a vessel. There exists a critical value of the H(2)O(2) or Cu(2+) concentrations below which the system does not oscillate. The oscillations appear due to an infinite period bifurcation at low initial concentrations of the H(2)O(2). The initial concentration of Cu(2+) may be considered as a bifurcation parameter in this case. Increase of the initial hydrogen peroxide concentration causes the pH-regulated oscillations through a nondegenerate supercritical Hopf bifurcation. The classification of bifurcations is based on the analysis of the behavior of oscillation amplitude and period at different initial concentrations of the H(2)O(2) and Cu(2+). Our results show a possibility to distinguish different scenarios for the appearance of transient oscillations in semibatch experiments. (c) 1996 American Institute of Physics.     

Radical graft polymerization from carbon whisker initiated by peroxyester groups introduced onto the surface

The radical graft polymerization of vinyl monomers onto carbon whiskers, i.e. vapor grown carbon fibers, initiated by tert-butyl peroxyester groups that are introduced onto the surface was investigated. The introduction of tert-butyl peroxyester groups onto the carbon whisker surface was achieved by the reaction of acyl chloride groups on the surface with tert-butyl hydroperoxide. The carbon whisker having acyl chloride groups was prepared by the following three methods: (1) reaction of surface carboxyl groups with thionyl chloride, (2) reaction of surface phenolic hydroxyl groups with succinyl dichloride, and (3) reaction of surface phenolic hydroxyl groups with phthaloyl dichloride. The carbon whiskers having tert-butyl peroxyester groups prepared from these three methods were abbreviated as CW-POE 1, 2, and 3, respectively. The peroxyester group content of CW-POE 1, 2, and 3 was determined to be 0.06, 0.05, and 0.17 mmol/g, respectively. It was found that the radical polymerization of vinyl monomers such as methyl methacrylate, styrene, and N-vinylcarbazole was successfully initiated in the presence of CW-POE 2 and 3, and the corresponding polymers were grafted onto the surface. However, CW-POE 1 failed to initiate the radical graft polymerization, because surface phenyl radicals formed by the thermal decomposition of the tert-butyl peroxyester groups are stabilized by the aromatic rings of the carbon whisker surface.     

Mechanism and kinetics of the atmospheric degradation of 2-formylcinnamaldehyde with O3 and hydroxyl OH radicals – a theoretical study

In the present investigation, the reaction mechanism and kinetics of 2-formylcinnamaldehyde (2-FC) with O₃ and hydroxyl OH radicals were studied. The reaction of 2-FC with O₃ radical are initiated by the formation of primary ozonide, whereas the reaction of 2-FC with the hydroxyl OH radical are initiated by two different ways: (1). H-atom abstraction by hydroxyl OH radical from the –CHO and –CH = CHCHO group of 2-FC (2). Hydroxyl OH addition to the –CH = CHCHO group to the ring-opened 2-FC. These reactions lead to the formation of an alkyl radical. The reaction pathways corresponding to the reactions between 2-FC with O₃ and hydroxyl OH radicals have been analysed using density functionals of B3LYP and M06-2X level of methods with the 6-31+G(d,p) basis set. Single-point energy calculations for the most favourable reactive species are determined by B3LYP/6-311++G(d,p) and CCSD(T)/6-31+G(d,p) levels of theory. From the obtained results, the hydroxyl OH addition at C8 position of 2-FC are most favourable than the C9 position of 2-FC. The subsequent reactions of the alkyl radicals, formed from the hydroxyl OH addition at C8 position, are analysed in detail. The individual and overall rate constant for the most favourable reactions are calculated by canonical variational transition theory with small-curvature tunnelling corrections over the temperature range of 278–350 K. The calculated theoretical rate constants are in good agreement with the available experimental data. The Arrhenius plot of the rate constants with the temperature are fitted and the atmospheric lifetimes of the 2-FC with hydroxyl OH radical reaction in the troposphere calculate for the first time, which can be applied to the study on the atmospheric implications. The condensed Fukui function has been verified for the most favourable reaction sites. This study can be regarded as an attempt to investigate the O₃-initiated and hydroxyl OH-initiated reaction mechanisms of 2-FC in the atmosphere.     

Effect of coal ash on hydrazine degradation under stirring and ultrasonic irradiation conditions

The degradation of hydrazine (N(2)H(4)) with concentrations of 0.1-5.0 mmol/L was investigated as a function of amount of coal ash (0.0-5.0 wt%) under the stirring (300 rpm) and ultrasonic irradiation (200 kHz, 200 W) conditions. It was found that the rate of decrease in the hydrazine concentration depended upon an amount of coal ash under the stirring and ultrasonic irradiation condition. It was considered under the stirring condition that hydrazine was adsorbed and degraded partly on coal ash. Furthermore, the sonochemically formed OH radicals were more effective in the hydrazine degradation than stirring condition in the presence of an intermediate amount of coal ash (0.6-2.4 wt%), whereas the effect of OH radicals disappeared in the presence of coal ash more than 2.4 wt%.     

Theoretical study on the mechanism of the reaction of FOX-7 with OH and NO2 radicals: bimolecular reactions with low barrier during the decomposition of FOX-7

The decomposition of 1,1-diamino-2,2-dinitroethene (FOX-7) attracts great interests, while the studies on bimolecular reactions during the decomposition of FOX-7 are scarce. This study for the first time investigated the bimolecular reactions of OH and NO₂ radicals, which are pyrolysis products of ammonium perchlorate (an efficient oxidant usually used in solid propellant), with FOX-7 by computational chemistry methods. The molecular geometries and energies were calculated using the (U)B3LYP/6-31++G(d,p) method. The rate constants of the reactions were calculated by canonical variational transition state theory. We found three mechanisms (H-abstraction, OH addition to C and N atom) for the reaction of OH + FOX-7 and two mechanisms (O abstraction and H abstraction) for the reaction of NO₂ + FOX-7. OH radical can abstract H atom or add to C atom of FOX-7 with barriers near to zero, which means OH radical can effectively degrade FOX-7. The O abstraction channel of the reaction of NO₂ + FOX-7 results in the formation of NO₃ radical, which has never been detected experimentally during the decomposition of FOX-7.     

Sonocatalytic facilitation of hydroxyl radical generation in the presence of TiO2

The generation of hydroxyl (OH) radicals was investigated during ultrasonic irradiation and in the presence of TiO(2). The effect of TiO(2) on an ultrasonic system's oxidation power was evaluated by examining the oxidation of salicylic acid. The generation of the salicylic acid derivatives, 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA, was measured by high-performance liquid chromatography coupled with electrochemical detection under different experimental conditions. The presence of TiO(2) enhanced the generation of DHBA during ultrasonic irradiation, thus indicating a higher oxidation power in the ultrasonic system. Al(2)O(3) also increased the generation of DHBA during irradiation; however, the effect of TiO(2) was found to be higher than that of Al(2)O(3). The addition of OH radical scavengers such as dimethylsulfoxide (DMSO), methanol and mannitol significantly suppressed the production of DHBA, and DMSO was found to have the highest suppressive effect among all scavengers. The effects of dissolved gases on the generation of OH radicals were further studied, and their power was found to be in the order Xe > Ar > O(2) > N(2). The degassing of the irradiation solution completely suppressed the generation of OH radicals. These results indicate that the presence of TiO(2) accelerates the generation of OH radicals during ultrasonic irradiation, and that the process may be mediated through the induction of cavitation bubbles in irradiating solutions.     

氧原子和甲基自由基反应机理的理论研究

用分子轨道从头算和密度泛函理论（DFT）中的B3LYP方法以及适中基组6－311＋G（2df,2p)对氧原子与甲基CH3反应进行了系统的研究。计算给出了通道上各斑点物种的构型参数、振动频率和能量。结果表明：CH2OH比CH3O稳定,能量约低26．63kJ/mol,且生成氢和甲醛为其最主要反应通道。