STUDY ON THE POLYMERIZATION KINETICS AND STABILITY OF P(UA)/MMA MICROEMULSION

Urethane acrylate anionomer (APUA) as a kind of new type polymerizable emulsifier was synthesized using 2,4-toluene diisocyanate (TDI), polypropylene glycol (PPG), 2-hydroxyethyl methacrylate (HEMA) and dimethylolpropionic acid (DMPA). The critical micelle concentration (CMC) of APUA was measured by the methods of conductance and surface tension. The comparative studies between polymerizable emulsifier AUPA and conventional emulsifier sodium dodecyl sulfate (SDS) were carried out in the emulsion polymerization of methyl methacrylate (MMA). Polymerization kinetics, stability, size and morphology of the latex particles were investigated. It was found that in APUA both water soluble initiator potassium persulfate (KPS) and oil soluble initiator 2,2'-azobisisobutyronitrile (AlBN) can start the reaction of MMA, and the polymerization rate and yield were very high. On using AlBN as an initiator, the conversion-time behavior of MMA with APUA as emulsifier was different to that of SDS as emulsifier, signifying a different nucleation mechanism of the polymer latex particle. The average size of the two kinds of particles is about 50 nm. The particle size decreases with increasing emulsifier concentration. On using KPS as the initiator, APUA as emulsifier, cross-linking hydrogel of PMMA would be formed, but SDS was used as emulsifier and the hydrogel of PMMA was not present.

AROMATIC AND HETEROCYCLIC NITRILES AND THEIR POLYMERS ⅩⅦ. THE POLYMERIZATION KINETICS OF CYANOPYRIDINES AND CHARACTERIZATION OF THE FORMED POLYMER

The polymerization rates of three cyanopyridines catalyzed by cuprous chloride-zinc system are measured, and the structure of the formed polymer is also determined. Compared with aromatic nitrile, cyanopyridines polymerize faster and form polyconjugated polymer with skeleton—（C=N）—;instead of triazine structure. This chain-polymer possesses semiconductive property, and can be converted into conductive material by thermal treatment. In addition, the polymerization kinetics of 3-cyanopyridine catalyzed by 3-cyanopyridinium perchlorate is investigated. It is found that the polymerization rate is directly proportional to the concentrations of monomer and catalyst, and the activation energy of the polymerization is 103.1 KJ/mol.

Polymerization Kinetics and Stabilization Mechanism of the Monodisperse PMMA Microspheres

The effects of the concentration of monomer, crosslinking agent, initiator, stabilizer, and the polarity of medium on the polymerization kinetics were investigated. The results show that the rate of polymerization (Rp) and conversion increased with the increase of monomer concentration from 8% to 15% (total mass); the water content in dispersion medium and the initiator 2, 2′ -azobis (isobutyronitrile) (AIBN) concentration increased as well. Rp and conversion decreases with the increase of PVP when it is low, while it increases when it is high. Moreover, PVP plays an important role in microsphere stabilization. The stabilization mechanism was investigated primarily, which involves both adsorbing mechanism and graft mechanism. Within a certain range of crosslinking degree, Rp and conversion increased with the increase of the crosslinker concentration. The effect can be ignored when crosslinker concentration is above 0.3 % (total mass), and the reason was that the monomer can hardly be diffused into the microsphere phase with a certain degree of crosslinking.

Self-polymerization and co-polymerization kinetics of lead methacrylate

Hydrogen nuclear magnetic resonance(H1-NMR) and X-ray diffractometer(XRD) were used to characterize the molecular and crystal structure of lead methacrylate [Pb(MAA)_(2)] which was produced by the double decomposition reaction of lead oxide and methacrylic acid.Isothermal analysis and Kelen-T(u|")dos(K-T) method were used to study the self-polymerization kinetic and the monomer reactivity ratios of Pb(M A A)_(2) and methyl methacrylate(MMA),respectively.By the ternary polymerization method of bulk casting using MMA,Pb(MAA)_(2) and gadolinium methacrylate(Gd(MAA)_(3)) as monomers,we prepared the plexiglass which have neutron and X-ray protection property.The results show that the polymerization rate(R_(p)) is expressed as Rp=K[M]^(1.02)[I]^(0.37) below the 10% conversion rate at 70℃,where K is the polymerization rate constant.And in the N,N-dimethylformamide(DMF) solution,the activation energy required for Pb(MAA)_(2) to initiate self-polymerization by the free radicals is 74.99 kJ·mol^(-1).The reactivity ratios of r1 [Pb(MAA)_(2)] and r2(MMA) are 3.767 and0.166.As the thickness of the material increases,the X-ray and thermal neutron shielding ability of the plexiglass containing gadolinium and lead is getting better and better.

Self-polymerization and co-polymerization kinetics of gadolinium methacrylate

Gadolinium methacrylate（Gd（MAA）3） was synthesized by using gadolinium oxide and methacrylic acid as the starting materials and its self-polymerization kinetic was studied based on non-isothermal and isothermal analysis. Moreover, the monomer reactivity ratios of methyl methacrylate（MMA） and Gd（MAA）3 were evaluated by using Kelen-Tiidos method. The thermal neutron shielding properties of PMMA and poly（MMA-co-Gd（MAA）3） were calculated by MCNP program. The results show that the selfpolymerization of Gd（MAA）3 can be initiated by thermal and free radical and its activation energy is103.35 kJ/mol or 58.55 kJ/mol correspondingly in the solid state or aqueous solution. The polymerization rate,Rp,under low conversion at 65 ℃ is expressed as Rp = K[M]^（1.05）[I]^（0.60）. The reactivity ratios of r1（MMA） and r2（Gd（MAA）3） are 0.225 and 1.340, respectively. The ability of thermal neutron shielding of poly（MMA-co-Gd（MAA）3） is increased by gadolinium contents and is far better than PMMA.

KINETICS OF VINYL CHLORIDE (CO) POLYMERIZATION AT HIGH CONVERSION

This paper provides a summarized review on the kinetics of vinyl chloride homopolymerization in the absence and presence of chain transfer agents, of VC/DAP(diallyl phthalate) copolymerization with chain extension and/or slightly crosslinking functions, and of vinylidene chloride/VC random copolymerization. Models of rate, degree of polymerization or molecular weight, copolymer composition, gel fraction and crosslinking density were proposed and interpreted mechanistically.

Kinetics of Bulk Polymerization of Octamethylcyclote- trasiloxane

The kinetics of bulk polymerization of octamethylcyclotetrasiloxane under acid circumstance is studied. A kinetic model is put forward and kinetic parameters are obtained through optimization.

Kinetics of Vinyl Chloride Polymerization with Mixture of Initiators

Kinetic models for the rate constants of vinyl chloride polymerization in the presence of initiator mixtures were proposed. They may be used to design the initiator recipes for the vinyl chloride polymerization with uniform rate at different temperatures at which various grades of poly(vinyl chloride) will be prepared.

KINETICS OF POLYMERIZATION OF ACRYLONITRILE INITIATED BY VANADIUM(V)-THIOUREA REDOX SYSTEM

The kinetics of polymerization of acrylonitrile (AN) initiated by quinquevalent vanadium (V^(5+))-thiourea (TU) redox system has been investigated in aqueous nitric acid in the temperature range from 30 to 50℃. The polymerization rate (R_p) can be expressed as follows: In the copolymerization of acryionitrile with methyl acrylate (MA), the reactivity ratios were found to be 1.0 and 1.1, respectively. The experimental observations suggest that the initiating species is probably a complex consisting of a central ion of Lewis acid-VO_2^+ and the ligands of Lewis bases-acrylonitrile, thiourea, and nitrate anions, while the initiating system in lower concentration, the polymerization of acrylonitrile does not occur if the thiourea is acidified prior to its reaction with quinquevalent vanadium. This indicates that the primary radicals (or the monomeric radicals in the present article) are produced by associated thiourea rather than isothlourea.

Modeling and Simulation of the Autocatalytic Kinetics of Haemoglobin SS Polymerization: Onset of Polymerization

We report a fresh and simpler approach to the modelling of the kinetics of the polymerization of Hb SS in sickle cell patients that couples the kinetics and the hydrodynamics of blood flow in mechanistic understanding of the process. The well-known two-step autocatalytic reaction scheme was used for the polymerization reaction with the assumption of simpler first-order reaction scheme for each stage. In addition, the forces acting on a particle in motion were also introduced to account for compelling settling of the red cells that lead to vessel occlusion (vaso-occlusion). A first attempt on the prediction of vessel blockage was made using this novel model. The time for the onset of the polymerization reaction was derived from hydrodynamic considerations and kinetics while the kinetic rate constants were obtained from the autocatalytic nature of the reaction. Experimental data for model validation were obtained from recruited SS patients and in vitro data of Hofrichter. Over 100 volunteers were recruited for participation in this work but less than 40% met the inclusion criteria. Participants were of age range 13 - 43 (with a mean of 26 ± 8 years) for SCD patients and 18 - 43 (with a mean of 28 ± 7 years) for control participants. Blood indices and Transcranial Doppler (TCD) test parameters of all participants were the principal parameters used for model validation. Constant k2/k1 ratios was obtained for individual in vivo/in vitro system. This ratio is unique for any individual, independent on protein sequence and also suggests the degree of expression of the symptoms of Sickle Cell Disease (SCD) with higher values reflecting greater propensity to pain crisis. Delay time, tD, was found to have an inverse relationship with the kinetic constant for the residual reaction, k1. Therefore, long delay times calculated, offer insight on why SCD patients are not in perpetual crises because enough time is provided the cells to escape microcirculation while keeping the residual reaction at the minimum. Sensitivity analysis was carried out to obviate the limitations encountered in the course of the work. Results showed the onset of occlusion to be most sensitive to the diameter of the blood vessel.

SIMULTANEOUS POLYMERIZATION AND FORMATION OF POLYPHENYLACETYLENE FILMS BY RARE-EARTH COORDINATION CATALYSIS Ⅳ.KINETICS AND MECHANISM OF POLYMERIZATION

The CO_2 quenching method has been used for the first time to determine the active complex concen- tration in Nd(naph)_3-Al(i-Bu)_3 catalyst system for polymerization of phenylacetylene into polyphenylacetylene(PPA)films.The kinetics and mechanism of this polymerization have been investigated by CO_2 quenching and IR,UV analytical methods.The kinetic equation can be expressed as Rp=k[M][Cp],and the apparent activation energy is about 13.6 kJ/mol.There is self-termination of chain propagating.Models for formation of the active complex and polymerization mechanism are proposed.

STUDIES ON THE KINETICS AND INITIATION MECHANISM OF ACRYLAMIDE POLYMERIZATION USING CERIC/ACETOACETANILIDE SYSTEM AS INITIATOR

It is found that acetoacetanilide possesses very high promoting reactivity towards ceric ion in initiating polymerization of vinyl monomer. The kinetics of acrylamide polymerization and the activation energies were studied. The initiation mechanism of ceric/acetoacetanilide is proposed on the basis of experimental results of FT-IR and ESR.

STUDY ON THE KINETICS OF POLYMERIZATION OF MMA BY COPPER（Ⅱ） CHELATING RESINS

The polymerization of MMA initiated by copper(Ⅱ） chelating resins/CCl4 system was studied.From the kinetic data,the kinetic equation of polymerization can be expressed as Rp=Ke^-56400/RT[MMA]^1.57[CCl4]^m[RESIN-Cu]^0.18 where m:3-4.5,when[CCl4] 0.1-6.93M.The free radical polymerization mechanism is proposed.The primary radicals are formed by the process of complexation-chlorine transformation among the copper(Ⅱ) chelating resin,CCl4 and methacrylate.

Monte Carlo Simulation of Propylene Polymerization (Ⅰ) Effects of Impurity on Propylene Polymerization

A comprehensive mechanism for propylene polymerization was proposed by considering the effects of main impurities in the material on propylene polymerization. According to the proposed mechanism, Monte Carlo simulation was employed to investigate the polymerization kinetics in order to determine the effects of the main impurities on the polymerization. Significant influences of the main impurities on the rate, number-average degree and controlling capability of hydrogen of the polymerization were analyzed.

TERMINATION AND TRANSFER OF THE CHAIN RADICALS IN THE POLYMERIZATION OF ACRYLONITRILE INITIATED BY VANADIUM(V)-THIOUREA REDOX SYSTEM

The dependence of the molecular weights on the concentration of reactants in the polymerization of acrylonitrile initiated by vanadium (V)-thiourea redox system has been investigated. It was found that the molecular weights of the polymer change nonlinearly with increasing concentrations of nitric acid and thiourea. Probably, the composition of the complexes exert a great influence on the chain initiation and termination. The reaction of 'complextermination' gives rise to the decrease of the molecular weights markedly while the concentrations of thiourea and vanadium (V)in the range from one to three molar ratios.

Polymerization of Methyl Acrylate with Nd-Al-α,α'-Dipyridyl Catalyst System

The polymerization of methyl acrylate (MA) with Nd(naph) 3 Al( i Bu) 3 α,α′ dipyridyl catalyst was studied. The molecular weight and its distribution were determined by gel penetration chromatography. Kinetic studies show that the MA polymerization rate is the first order with respect to monomer concentration. The apparent activation energy of MA polymerization is 49 34 kJ·mol -1 .

MECHANISM FOR THE INITIATION OF ACRYLONITRILE POLYMERIZATION BY POLYPROPYLENE-BASED POLYAMIDOXIME-THIOUREA COMBINATION

Polymerization of acrylonitrile (AN) in aqueous nitric acid initiated by polypropylene-based polyamidoxime (PPAO)-thiourea (TU) combination has been investigated. The overall rate of polymerization (R_p) under the conditions of [TU]/[PPAO]<0.5 molar ratio isThe molecular weights of the polymers were found to be inversely proportional to 3/2-power of nitric acid concentration and 1-power of thiourea concentration. In addition, it is independent with the concentrations of monomer and PPAO, and decreases with increasing temperature.On the basis of these experimental results, a coordination-proton transfer mechanism for the initiation was proposed and discussed.

RADICAL POLYMERIZATION OF N, N-DI(2-2'-METHYL-ACRYLOYLOXY-PROPYL)-PARA-TOLUIDINE FUNCTIONAL MONOMER

Functional monomer (MP)_2PT having tertiary aromatic amino group was systhesized from the reaction of N, N-di (2-hydroxypropyl)-p-toluidine with 2-methyl acryloyl chloride. In the presence of organic peroxide, the radical polymerization of (MP)_2PT in toluene took place. The kinetics of (MP)_2PT polymerization and the ESR spectra of LPO-(MP)2PT-MNP systems were determined respectively.

KINETIC STUDY ON PHOTOISOMERIZATION OF AN AZO-CONTAINING POLYMER AT THE AIR-WATER INTERFACE USING A IANGMUIR TROUGH

Photoisomerization of a new polymer: monoesters of polymaleic acid containing naphthalene-azo-anthraquinone groups in side chains at the air-water interface of a Langmuir trough wan detected by recording the development of surface pressure with time. This process wan found to be a first-order reaction and complete within several minutes.

Modulation of polymerization rate of N-carboxyanhydrides in a biphasic system

The recent advances in accelerated polymerization of N-carboxyanhydrides (NCAs) offer an effective strategy to simplify the preparation of polypeptide materials. However, the fine-tuning of polymerization kinetics, which is critical to differentiate the main polymerization and the side reactions, remains largely unexplored. Herein we report the modulation of polymerization rate of NCA in a water/oil biphasic system. By altering the aqueous pH, the initial location of the initiators, and the pK_(a) of initiating amines, we observed the change in polymerization time from several minutes to a few hours. Due to the high interfacial activity and low pKa value, controlled polymerization was observed from multi-amine initiators even if they were initially located in the aqueous phase. This work not only improves our understanding on the biphasic polymerization mechanism, but also facilitates preparation of versatile polypeptide materials.