STUDY ON THE EFFECT OF POLYSTYRENE SULFONIC ACID MACROMOLECULES ON THE POLYMERIZATION OF ACRYLAMIDE

The effect of polystyrene sulfonic acid (PSSA) macromolecules on the polymerization of acrylamide (AM) has been studied. It was found that the rates of polymerization of AM were greatly increased in the presence of PSSA in the polymerization system.The maximum value of the rate of polymerization of AM was obtained when the ratio of [—SO_3H]: [AM] reached 3:1. When the insoluble crosslinked PSSA was used instead of the soluble one, this effect decreased considerably. The interaction between molecules of PSSA and AM was determined by infrared spectroscopy, elementary analysis and X-ray photoelectron spectroscopy. The combination form, —SO_3-NH_3~ CO—, formed between sulfonic group and amide group was found to be existed since the infrared absorption band of —NH_2 shifted from 3400cm~(-1) to 3150 cm~(-1), the binding energy of electron N_(18) changed from 399.7 eV to 401.3 eV, and the atomic ratio of N to S of the products was similar to the ratio of reagents. Based on these experimental results, the mechanism of AM polymerization in the presence of PSSA is proposed. The initial step is the combination of AM with sulfonic group to form —CONH_3~ , then followed by polymerization on the PSSA macromolecule. The role of PSSA on the polymerization of AM is discussed.     

STUDIES ON BIO-ANTIOXIDANTS——PROOXIDATION OF VITAMIN E ON THE AUTOXIDATION OF LINOLEIC ACID IN SODIUM DODECYL SULFATE MICELLES

The reaction of vitamin E (α-tocopherol) with linoleic acid containing peroxidized linoleic acid has been studied. No significant reaction was found in ethanol solution, whereas in sodium dodecyl sulfate micelles vitamin E reacted rapidly with peroxidized linoleic acid, and thereby induced the peroxidation of linoleic acid, leading to oxygen absorption. The reaction kinetics was studied in detail by u. v. spectroscopy, HPLC and ESR spectroscopy. It was found that the main product was α-tocopherone with α-tocopheroxy radical as the reaction intermediate. A mechanism involving two consecutive bimolecular reactions between peroxidized linoleic acid and a-tocopherol and between peroxidized linoleic acid and a-tocopheroxy radical, with rate constant 2.93 and 6.21 mol/L-1s-1 respectively is proposed. The micellar effect on the reaction is discussed.     

AN INVESTIGATION ON KINETICS AND REACTIVE SPECIES IN ANIONIC TELOMERIZATION OF BUTADIENE INITIATED BY n-BUTYLLITHIUM/N, N, N'''', N''''-TETRAMETHYLETHYLENE DIAMINE

The polymerization rate of butadiene in toluene initiated by n-butyllithium and tetramethyl ethy-lene diamine as well as the micro-structure and degree of association of polybutadiene were deter-mined. The effect of TMEDA/n-BuLi (abbr. A/Li) and temperature on the polymerization rate,molecular weight, molecular weight distribution and structure of polybutadiene was investigated. Ac-tivation energy of the propagation reaction and chain transfer reaction, together with the chain trans-fer reaction rate constant were estimated. Kinetic parameters and contribution of different reactivespecies to polymerization rate were calculated by Nonlinear Least-Squares Method. A kinetic equa-tion was proposed. The mechanism of anionic chain transfer reaction was discussed.     

Stress-induced Solid-Solid Crystal Transition in Trans-1,4-polyisoprene

The polymorphic transition of trans-1,4-polyisoprene(TPI) during stretching was investigated by in situ wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The influences of the initial structure, stretching temperature, and strain rate on the contents of different crystal modifications(α, β) were explored. The results confirm that the α-β transition occurs during stretching of TPI that only contains αcrystal(α-TPI). When the stress is relaxed, the β crystal formed during stretching remains, which indicates that the transition is irreversible. On the other hand, stretching of TPI that only contains β crystal(β-TPI) results in orientated β crystal. No β-α transition occurs during stretching. The different structures of stretched α-TPI and β-TPI exclude the previously proposed "melting-recrystallization mechanism". The α-β transition depends significantly on temperature and strain rate, indicating the transition is governed both by thermodynamics and kinetics. Our results support a solid-solid transition mechanism rather than a melting-recrystallization mechanism. The irreversible nature of the transition is attributed to the metastability of the β phase in the unstretched state. Different from the "β phases" that appear in polymers with stress-induced reversible transitions, e.g. poly(butylene terephthalate) and poly(butylene succinate), the stability of β phase in TPI is high that can be long-lived.The strain rate dependence of α-β transition hinders the determination of critical stress for the transition. It further indicates that the local stress within the sample is more heterogeneous at higher strain rates.     

GROUP TRANSFER POLYMERIZATION OF ETHYL ACRYLATE WITH LEWIS ACID CATALYST

This paper reports the kinetics of group transfer polymerization (GTP)of ethyl acrylate (EA)with zinc iodide catalyst in 1,2-dichloroethane using dimethyl ketene methyl trimethylsilyl acetal (MTS) as initiator at 0℃and above 0℃. The amount of catalyst used was studied. When zinc iodide catalyst used is more than 10mol% relative to monomer, the rate of polymerization is proportional to the concentration of monomer, whereas zinc iodide catalyst used is less than 10 mol% of the monomer, the rate of polymerization is independent of the monomer concentration.In the GTP of EA an induction period was observed when the zinc iodide contents are less than l0mol%. If the reaction temperature is over 0℃, living species become unstable and diminish, leading to incomplete monomer conversion. The reaction curves equations are obtained. The polymers have narrow molecular weight distributions which are not changed as decreasing zinc iodide contents. The polydispersity is about 1.2.     

In-situ copolymerization of aniline with alkyl amine by APS： Kinetics and application

The kinetic study of in-situ eopolymerization of aniline with o- and p-methylaniline by ammonium persulfate （APS） has been carried out. UV-vis spectroscopic method was used to investigate the course of copolymerization. Structural characterization was studied by PT-IR spectral analysis. The electronic spectra of the copolymers poly（aniline-co-p-toluidine） and poly（aniline-co-o- toluidine） show blue shift. The shift has been observed in the bands corresponding to π→π^＊ transition as well as in the exciton transition. The increase in absorbance recorded during the reaction for different concentration of aniline, o- and p-toluidine at various intervals of time of polymerization reaction indicates a growth in the polymer formation. The resulting first-order rate constant was used to calculate the rate of copolymer formation using the rate equation -d[A]/dt = kc^n.     

KINETICS AND MECHANISM OF PHOTOINDUCED POLYMERIZATION BY α,α-DIMETHOXY-α-PHENYL ACETOPHENONE

α,α-dimethoxy-α-Phenyl acetophenone (DMPA) is an efficient and thermally stable photoinitiator. Here its spectral characteristics in the transient state were shown. The transient species were identified as a benzoyl radical and a dimethoxyi benzyl radical that played a primary initiation role in polymerization. The kinetics and mechanism of the bulk polymerization of MMA were investigated. The exponent of DMPA concentration and k_p/k_1~(1/2) value were found to be 0.5 and 0.066 mol(-1/2)l~(1/2)s~(-1/2), respectively. The existence of oxygen led to obtain the polymer with higher molecular weight, which can be attributed to the occurrence of the subsequent polymerization induced by active polymer end group. In the photocrosslinking reaction, the dependence of DMPA content on initial rate has been found. A principal reason is that the sample contained higher percentage of DMPA has higher light-absorbed efficiency. In solid film, higher concentration of DMPA is permitted to be used because there is little excited state self-quenching effect in the rigid medium.     

Oxidative polymerization of hydroquinone using deoxycholic acid supramolecular template

Polyhydroquinone (PHQ) is a redox-active polymer with quinone/hydroquinone redox active units in the main chain and may have potential applications as a mediator in biosensors and biofuel cells. By the oxidative polymerization of hydroquinone (HQ), PHQ can be easily synthesized, but the reaction lacks control over the structure of the product. Deoxycholic acid (DCA) was introduced as a supramolecular template to control the reaction. The reaction rate is 14 times of that in deionized water and twice of that in buffer. The DCA template increases not only the reaction rate, but also the molecular weight of the polymer obtained. The template effect of DCA was attributed to the supramolecular assemblies of DCA formed in the solution. Cyclic voltammetry study indicated the resulting PHQ was redox-active. While the supramolecular assemblies of DCA provided a template for the oxidative polymerization of HQ, the protons released as a by-product of the oxidative polymerization of HQ in turn enhanced the self-assembly of DCA. As a result, DCA microfibers form and separate out of the solution.     

THE PROCESS OF THE EMULSIFIER-FREE POLYMERIZATION IN THE PRESENCE OF BARIUM SULFATE POWDER

The process of emulsifier-free copolymerization of the Styrene-Butyl Acrylate-K_sS_sO_s-water in thepresence of Barium Sulfate(BS)powder was investigated under varied conditions within the range of BSpowder quantity,initiator concentration and reaction temperature.Experimental results showed thatthe rate of polymerization is proportional to 0.3-power of the BS quantity and 1.3-power of theinitiator concentration.There is a linear relationship of 2/3-power for the conversion and time.Aprocess for the polymerization is propose to explain the experimental results.     

THE EFFECT OF POLAR ADDITIVES ON THE γ RADIATION INDUCED POLYMERIZATION OF STYRENE*

The γ induced polymerization of styrene in the presence of polar additives such as tributylphosphate, triethyl amine and ethanol was studied at dose rate of 5.0×10~(17) eV/ml. min. The re-sult shows that radiation induced polymerization of styrene was sensitized by the three kinds ofadditives at the approximate same rate and the experimental results were in agreement with thetheoretical calculation of WAS equation. The cause of sensitization is due to the proton transfer.     

Synthesis of α-Bromine- Terminated Polystyrene Macroinitiator and Its Initiation of MMA Polymerization by ATRP

In the present paper the synthesis of block copolymers via the transformation from living anionic polymerization (LAP) to atom transfer radical polymerization (ATRP) was described. Α-Bromine-terminated polystyrenes(PStBr) in the LAP step was prepared by using n-BuLi as initiator, tetrahydrofuran (THF) as the activator, α-methylstyrene (α-MeSt) as the capping group and liquid bromine (Br2) as the bromating agent. The effects of reaction conditions such as the amounts of α-MeSt, THF, and Br2 as well as molecular weight of polystyrene on the bromating efficiency (BE) and coupling extent (CE) were examined. The present results show that the yield of PStBr obtained was more than 93.8% and the coupling reaction was substantially absent. PStBr was further used as the macroinitiator in the polymerization of methyl-methacrylate(MMA) in the presence of copper(Ⅰ) halogen and 2,2-bipyridine(bpy) complexes. It was found that the molecular weight of the resulted PSt-b-PMMA increased linearly with the increase of the conversion of MMA and the polydispersity was 1.2-1.6. The structures of PStBr and P(St-b-MMA) were characterized by 1H NMR spectra.     

A DYNAMIC MECHANICAL ANALYSIS STUDY OF THE TRANSITION BEHAVIOUR OF I-PP/EPDM BLENDS

The transition behaviour of the blends of isotactic polypropylene (i-PP) with ethylene-propylene terpolymer (EPDM) containing 42 wt% propylene was investigated by dynamic mechanical analysis technique (DMA). Owing to its high propylene content, EPDM is compatible with i-PP to some degree. The interaction between the two components was strengthened. As expected, for partially compatible system the glass transition temperature of i-PP in the blends shifted to lower temperature. It was found that there existed two transitions, αEPDM and βEPDM, for the EPDM used in this work. The former was considered to be the glass transition of the random chain segments of EPDM, while the latter the local motion of the long ethylene sequences in EPDM. The unusual transition behaviour of αEPDM in the blends was explained in terms of the greater thermal expansion of EPDM and the compatibility of the two components. On the other hand, the βEPDM changed with the composition of the blends in a regular manner.     

KINETIC STUDY OF THE POLYCONDENSATION OF 9-AMINO-NONANOIC ACID

9-Amino-nonaneic acid was polycondensed in boiling paraffin hydrocarbon medium, the water formed during the reaction was immediately carried away by the vapor of the medium. By using this technique, polycondensation ran very rapidly, and within 15 min. the extent of reaction (p) reached more than 95%, and after 3 hrs., p surpassed 99%. The number average molecular weight was higher than 40,000. These have never been reached as reported in literature.Because p can be pushed to over 99%, it is possible to study the complete course of polycondensation reactions. It was found that the reaction followed second order from the beginning up to p around 99%. Beyond this, the system became so viscous that a viscosity factor should be considered. This caused the reaction to be changed to third order.     

THE OVERALL KINETICS OF FREE RADICAL (CO)POLYMERIZATION WITH HIGHLY DIFFUSION CONTROLLED TERMINATION

The overall reaction rate kinetics of polymerization of diethyleneglycol dimethacrylate and copolymerization of it with styrene in bulk and in the presence of inert diluents were investigated. Theresults indicated that these reactions can be treated as free radical polymerization with highly diffu-sion controlled termination reaction in which the termination rate constant is an empirically derivedfunction of monomer conversion: K_t=K_(to)(1-c ln[M]/ [M_0])~(-1) in which K_(to) is the initial terminationrate constant and c is a factor related to the magnitude of diffusion co?re The following equationof monomer conversion as a function of time could then be derived: U=1-exp {1/c [1-(1+ckt/2)~2]}in which k=K_P(R_i/2K_(to))~(1/2) and t is the time of reaction. Excellent agreement between the theoreticaland experimental overall reaction kinetic curves was obtained. The equation is valid for crosslinkingand noncrosslinking free radical polymerizations in which the self-acceleration effcct is effective fromthe very beginning of the reaction. The equation can be expressed in a more generally applicableform: U=1--exp{1/e[1--(1+?t/n)~n] in which n≥0.     

Effect of Temperature-responsive Solution Behavior of PNIPAM-bPPEOMA-b-PNIPAM on Its Inclusion Complexation with α-Cyclodextrin

The effect of temperature-responsive solution behavior of PNIPAM-b-PPEOMA-b-PNIPAM on its inclusion complexation with α-cyclodextrin was studied. The triblock polymer was prepared by reversible addition-fragmentation chain transfer(RAFT) polymerization and formed inclusion complexes(ICs) after selective threading of the PEO segment of the triblock polymer through the cavities of α-CD units. For comparison, PPEOMA homopolymer was prepared and the inclusion complexation with α-CD was also studied. The ICs were prepared with α-CD when the polymer was in different conformations by changing the temperature, and the formed ICs were characterized by XRD, 1H-NMR, TGA and DSC. The solutions of the ICs show temperature-responsive clear/turbid transition or fluidic emulsion/gel transition depending on the concentration of the α-CD added, and the stoichiometry determined by 1H-NMR and TGA indicates that the stoichiometry of EO to α-CD of the resulted ICs increases with increasing of temperature.     

Ligand Steric Effects on Naphthyl-α-diimine Nickel Catalyzed α-Olefin Polymerization

Naphthyl-α-diimine nickel complexes with systematically varied ligand sterics, activated by modified methylaluminoxane(MMAO), were tested in the polymerization of higher α-olefin(1-hexene, 1-decene and 1-hexadecene) under suitable conditions. The polymerization results indicated the possibility of precise microstructure control, depending on catalyst structure, polymerization temperature, monomer concentration and types of monomers, which in turn strongly affects the resultant polymer properties. Naphthyl-α-diimine nickel complex bearing chiral bulky sec-phenethyl groups in the o-naphthyl position showed good catalytic activity, and resulted in branched polymers(42-88/1000 C) with high molecular weights(M_n:(4.3-15.2) × 10~4 g·mol~(-1)) and narrow molecular weight distribution(M_w/M_n = 1.13-1.29, RT), which suggested a living polymerization. The increasing steric hindrance of catalyst leads to enhance insertion for 2,1-insertion of α-olefin and the chain-walking reaction.     

FOURIER TRANSFORM INFRARED SPECTROSCOPIC STUDY OF EFFECT OF LANTHANIDE IONS ON PHOSPHOLIPID MULTIBILAYERS

The molecular interactions between Nd~(3+), Gd~(3+)and Yb~(3+) and DPPC in multibilayer have been studied by Fourier transform infrared spectroscopy. The results show that incorporations of the lanthanide ions considerably shift the gel to liquid-crystal phase transition to higher temperatures. The incorporations of Gd~(3+) and Yb~(3+) obviously reduce the cooperations of the transition. The phosphate region of the spectra indicates that the Ln~(3+) binding to DPPC forms DPPC-Ln~(3+)complex and the Lna~(3+)binding is not dependent on the phase state of DPPC. The C-H stretching region of the spectra suggests that the incorporation of Ln~(3+)increases the conformational order of DPPC both in gel and in liquid-crystal phase as a result of the reduction of gauche rotamers.     

PHOTOSENSITIVITY OF Ce (Ⅳ) INITIATED METHYL ACRYLATE POLYMERIZATION

The influences of UV light irradiation (313 nm) and diffused daylight on the polymerization of methyl acrylate initiated by the ceric ammonium nitrate without any reducing agent have been studied both in aqueous nitric acid and in pure water. The rate of polymerization was found to be accelerated and the overall activation energy and the induction time were found to be decreased sharply by the UV light irradiation. Under UV light, the rate of polymerization is 8 times as high as the rate in dark. The rate of polymerization was found to attain a maximum with the increase of nitric acid concentration and the rate of polymerization became less sensitive to UV light in the presence of nitric acid whereas the induction period reduced outstandingly. Based on the experimental results, the mechanism is proposed.     

DEPENDENCE OF ACRYLONITRILE POLYMERIZATION KINETICS ON THE COMPOSITION OF POLYAMIDOXIME-THIOUREA SYSTEM

The polymerization of acrylonitrile (AN) initiated by polypropylene based-polyamidoxime (PPAO)-thiourea (TU) system was investigated at [TU]/[PPAO]>0.5 molar ratio. It shows that the variation of the concentrations of PPAO, thiourea and nitric acid does not exert an observable influence on the reaction rate. The overall rate of polymerization (R_p) isR_p = 2.07e~(-7,800/RT)[ AN]~(2.0)The zero order dependence on PPAO and thiourea concentrations and the lowest value of the collision frequence factor were considered to be a feature of the primary radical termination.     

A comprehensive Monte Carlo simulation of styrene atom transfer radical polymerization

<正>An optimized and high-performance Monte Carlo simulation is developed to take thorough account of four different cases of termination in styrene ATRP.According to the simulation results,the bimolecular termination rate constant sharply drops throughout the polymerization when either chain-length dependency of termination rate constant,gel effect,or both together is applied to the simulation.In addition,as expected,the initiator is quickly decomposed at the early stages of the polymerization.The concentration of the catalyst in lower oxidation state decreases at first and then plateaus at higher conversion;furthermore,the steady concentration of M_t~nY/L in the polymerization is the highest when the chain-length-dependent diffusion-controlled termination rate constant is employed in the simulation.The rates of deactivation and chain end degradation reactions are also smaller in this case.Therefore,the fraction of dormant chains is higher throughout the reaction and consequently the portion of dead polymers decreases.Besides,molecular weight increases linearly with conversion;however,when neither gel effect nor chain-length dependency of termination rate constant is considered,the molecular weight deviates from linearity at the end of the reaction.The peak of chain length distribution shifts toward higher molecular weight too during the reaction.Finally,the molecular weight distribution broadens at higher conversion;however, the chain length distribution of polymers produced under conditions of applying chain-length-dependent diffusion-controlled termination rate constant is narrower.