“LIVING”POLYMERIZATION OF BUTADIENE BY RARE EARTH COORDINATION CATALYST

In this paper, the kinetic method was used to study the polymerization of butadiene initiated by NdCl_3·3i-PrOH-AlEt_3 catalyst system, at-70, -30 and 0℃. Results obtained indicated that there are no both reactions of detectable transfer limiting molecular weight of polymers and irreversible termination with deactivation of propagation centers. It was found that polymers produced had narrow molecular weight distributions (MWD) and extremely high cis-1,4 content, and that the living chain had a very long lifetime. Block copolymers of butadiene and isoprene were prepared and characterized by means of GPC, ~(13)C NMR, and IR. It was fully proved that the polymerization of butadiene initiated by the rare earth catalyst under these conditions had a living polymerization nature.     

SYNTHESIS OF TRIBLOCK COPOLYMERS OF STYRENE AND ISOPRENE BY A NITROXIDE-MEDIATED LIVING FREE RADICAL POLYMERIZATION

The controlled free radical polymerization of styrene and isoprene initiated with benzoyl peroxide (BPO) in the presence of 2,2,6,6-tetramethyl piperidine-N-oxyl (TEMPO) at 125 ℃ were performed. The obtained polyisoprene and polystyrene homopolymers served as macroinitiators for block copolymerization of isoprene and styrene to synthesize poly(styrene-b-isoprene) and poly(isoprene-b-styrene) diblock copolymers. Diblock copolymers with well-defined structures as well as controlled and narrow molecular weight distribution wereobtained from the lower-mass polystyrene and polyisoprene homopolymers. These copolymers were found to be active as macroinitiators in the synthesis of the poly(styrene-b-isoprene-b-styrene) and poly(isoprene-b-styrene-b-isoprene) triblock copolymers. 1H-NMR spectroscopy and gel permeation chromatography (GPC) were used for the investigation of polymer strucmre, molecular weight and polydispersity (PD).     

SYNTHESIS AND POLYMERIZATION OF OLIGO (OXYETHYLENE) MACROMONOMER

This paper reports the synthesis of methoxyoligo (oxyethylene) methacrylate (MEO_n , n is the repeating unit number of (CH_2CH_2O) in the macromonomer), and its polymerization in different solvents. MEO_n is prepared through such two independent reactions as (1) anionic polymerization of oxirane initiated by potassium alkoxide and (2) end-capping of methoxy oligo(oxyethylene) by methacrylic group. The n value can be conveniently controlled over the range of 5 ～30 by varying the molar ratio of oxirane to initiator and the molecular weight distribution of MEO_n be narrowed by increasing reaction time only in step (1). MEO_n thus obtained shows a rapid polymerization in water and benzene respectively, and both give water-soluble polymers as long as suitable conditions are used.     

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.     

PLASMA POLYMERIZATION OF HEXAMETHYLCYCLOTRISILOXANE

In a capacitively coupled RF discharge system with external electrodes ,hexamethyicyclotrisiloxane was polymerized, and the effects of discharge power and plasma gas on polymer deposition rate were studied. The polymer structures and properties were studied by IR spectroscopy, XPS measurement, PGC/MS combined technique, TG analysis and contact angle measuring. The results showed that the polymers prepared in H_2 or O_2 have higher C/Si ratio in comparison with those prepared in inert gases. PGC/MS results revealed the existence of many short carbon chains in the polymer structure .TG analysis suggested that the polymers prepared in the inert gas would possess better thermal stabilities.     

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.     

KINETICS OF VINYL CHLORIDE (CO) POLYMERIZATION AT HIGH CONVERSION

This paper provides a summarized review on the kinetics of vinyl chloride homopolymerization inthe absence and presence of chain transfer agents, of VC/DAP(diallyl phthalate) copolymerization with chainextension 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 andcrosslinking density were proposed and interpreted mechanistically.     

CHANGES OF STRUCTURE AND PROPERTIES OF POLY (ETHYLENE TEREPHTHALATE) CAUSED BY IN-SITU POLYMERIZATION OF PYRROLE

Conductive polymer composites based on crystalline polymer matrix have been prepared by using an in-situ polymerization process of pyrrole in amorphous poly (ethylene terephthalate) (PET) film. The DSC and WAXD measurement and SEM observation show that liquid-induced crystallization of PET matrix has occurred during the preparation of composite films. Depending upon the equilibrium degree of swelling and crystallinity, the limited depth of penetration of pyrrole molecules results in a skin-core structure of the composite film. The skin layer containing charge transfer intercalated polypyrrole has a surface resistance of 3.5×10~4 Ω. Rigid and heat-resistant polypyrrole molecules formed in PET film increase the tensile modulus and, especially, the rigidity of PET at elevated temperatures. However, they decrease the tensile strength and elongation at break, and impair the thermal ductility of PET.     

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 asRp = Ke-56400/RT[MMA]1.57[CCl4]m[RESIN-Cu]0.18where 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.     

POLYMERIZATION OF ETHYLENE WITH UNSYMMETRIC 2,6-BIS(IMINO)PYRIDINE IRON(Ⅱ)COMPLEX

An unsymmetric 2,6-bis(imino)pyridine iron(II) complex 1' was synthesized. The relationship between catalyststructure and its activity in ethylene polymerization is discussed. The kinetic behavior of ethylene polymerization and theeffects of polymerization conditions such as temperature, aluminum/iron molar ratio on the activity of catalyst and thecharacteristics of polyethylene were reported. The unsymmetric catalyst 1' has a good catalytic performance of 3.47×10~6 gPE·mol~(-1)·Fe·h~(-1) at 40℃ with aluminum/iron molar ratio = 2500. A dependence of catalyst activity on themethylaluminoxane (MAO) concentration and reaction temperature was found. The molecular weight (MW) of polyethylenewith broad dispersity is about 10~4-10~5 g/mol. The melting temperature and branching of polyethylenes vary with changingreaction temperature and aluminum/iron molar ratio.     

KINETICS OF SUSPENDED EMULSION POLYMERIZATION OF METHYL METHACRYLATE

The kinetics of suspended emulsion polymerization of methyl methacrylate (MMA), in which water acted as the dispersed phase and the mixture of MMA and cyclohexane as the continuous phase, was investigated. It showed that the initial polymerization rate (Rp0) and steady-state polymerization rate (Rp) were proportional to the mass ratio between water and oil phase, and increased as the polymerization temperature, the potassium persulphate concentration ([I]) and the Tween20 emulsifier concentration ([S]) increased. The relationships between the polymerization rate and [I] and [S] were obtained as follows: Rp0 ∝ [I]0.73[S]0.32 and Rp ∝ [I]0.71[S]0.23. The above exponents were close to those obtained from normal MMA emulsion polymerization. It also showed that the average molecular weight of the resulting poly(methyl methacrylate) decreased as the polymerization temperature, [I] and [S] increased. Thus, MMA suspended emulsion polymerization could be considered as a combination of many miniature emulsion polymerizations proceeding in water drops and obeyed the classical kinetics of MMA emulsion polymerization.     

STRUCTURE AND PROPERTIES OF POLY (N-VINYLCARBAZOLE) OBTAINED VIA ASYMMETRICALLY STEREOSELECTIVE POLYMERIZATION

The structure and properties of poly(N-vinylcarbazole) (PVCZ) obtainedvia asymmetrically stereoselective polymerization have been studied by using ~1HNMRspectra, UV spectra, DSC analysis and GPC. The steric microstructure i.e. the contentof isotactic sequences was found to be increased by using AIBN to (-)Sp~+(+)CSA~- asthe initiators or catalysts and the mole extinction coefficient to be decreased. Bimodalmolecular weight distribution (MWD)s of the obtained PVCZs were caused by two propa-gating species of the free ions and the ion-pairs associated with the organic salts duringpolymerization.     

CARBON FILMS PREPARED BY PLASMA POLYMERIZATION OF NATURAL GAS(Ⅱ)MECHANICAL PROPERTIES OF CARBON FILMS

Mechanical properties of carbon films deposited by plasma polymerization on different sub-strates were studied.Film hardness was measured to be approximately 20GPa.Adhesive scratch testsfound the critical load L,at which film failure occurred,of the films on silicon,glass,hard magneticrecording disc were 28,45 and 18N,respectively.No definite value was detected for the film on bear-ing steel substrate.Tribological study suggests that the friction coefficient of the films was in the rangeof 0.1—0.3.The wear rate of the carbon film was 1-2 orders of magnitude lower than that of thesubstrates.Micrographs of the wear tracks and the magnitude of the wear coefficients indicate that thelikely wear mechanism is the threebody abrasive wear.Films with stable low friction coefficient andsuperior wear resistance were obtained on silicon and steel substrates.     

SYNTHESIS, CHARACTERIZATION AND RING-OPENING POLYMERIZATION OF CYCLIC (ARYLENE PHOSPHONATE) OLIGOMERS

INTRODUCTIONThe use of cyclic oligomers as macrocyclic precursors for the preparation of high performance polymers byring-opening polymerization (ROP) has sparked much interest in recent years. It could produce a revolutionarychange in the preparation of advanced composite materials, and is of great importance in the polymerizationprocess yielding polymers such as the reinforced reactive injection model (RRIM) and the resin transfer model(RTM) etc. Within the last 10 years, the synthes…     

SYNTHESIS OF POLY(METHYL METHACRYLATE)-graft-POLYSTYRENE BY ATOM TRANSFER RADICAL POLYMERIZATION

The radical copolymerization of methyl methacrylate and 2-hydroxyethyl methacrylate was carried out via atomtransfer radical polymerization (ATRP) initiated by ethyl 2-bromoisobutyrate and catalyzed by CuBr/2,2'-bipyridinecomplex. This polymerization proceeds in a living fashion with controlled molecular weight and low polydispersity. Theobtained copolymer was esterified with 2-bromoisobutylryl bromide yielding a macroinitiator, poly(methyl methacrylate-co-2-hydroxyethyl methacrylate-co-2-(2-bromoisobutyryloxy)ethyl methacrylate), and its structure was characterized by ~1H-NMR. This macroinitiator was used for ATRP of styrene to synthesize poly(methyl methacrylate)-graft-polystyrene. Themolecular weight of graft copolymer increased with the monomer conversion, and the polydispersity remained relatively low.The individual grafted polystyrene chains were cleaved from the macroinitiator backbone by hydrolysis and the hydrolyzed product was characterized by ~1H-NMR and GPC.     

INDUCTION—POLYMERIZATION OF PREPARING POLYMERS OF REGULAR STRUCTURE

Induction-Polymerization is a novel method for preparing polymers of regular structure. In the presence of a special macromolecular compound, monomer molecules are aggregeted regularly around one or more growth points and polymerized to polymer of regular structure. Regularity of structure of the polyacrylamide prepared by this means has been verified with electron diffractograms, DSC curve and IR spectrum of the polymer.     

POLYMERIZATION OF METHYL METHACRYLATE CHIRAL LIGANDS

Methyl methacrylate was anionically polymerized in the presence of chiral ligands, e. g. (+)-DDB and (-)-Sp. The polymers thus formed were optically inactive due to the instability of the helical chain for the less bulky ester group. Isotactic poly(methyl methacrylate) was given when (+)-DDB was used, whereas, a syndiotactic polymer was formed in the presence of (-)-Sp. Accordingly, two different propagation mechanisms were postulated.     

SYNTHESIS AND POLYMERIZATION OF BISPHENYLENE ORTHOCARBONATE

Bisphenylene orthocarbonate (Ⅱ) was synthesized by the reaction of dicopper catecholate with carbon tetrachloride, and underwent cationic ring-opening polymerization with the introduction of phenyl group into the main chain. The obtained polymer with ester and ether group was verified by IR and ~1H NMR spectra. Based on the analysis of the polymer structures, the polymerization mechanism was proposed. Its T_m and T_(?) are 254℃and 160℃respectively. No decomposition of the polymer was observed below 320℃. The volume expansion property of the monomer during polymerization was studied by measuring the density difference between Ⅰand its polymer at various temperatures.     

DOPING LEVEL INCREASE OF POLY(3-METHYLTHIOPHENE)FILM DURING ELECTROCHEMICAL POLYMERIZATION PROCESS

The Raman spectra of poly(3-methylthiophene) (PMeT) films with different thicknesses, which have beenelectrochemically deposited on a flat stainless steel electrode surface by direct oxidation of 3-methylthiophene in borontrifluoride diethyl etherate (BFEE) at a constant applied potential of 1.38 V (versus SCE), have been investigated byexcitation with a 633-nm laser beam. The spectroscopic results demonstrated that the doping level of PMeT film wasincreasing during film growth. This finding was also confirmed by electrochemical examination. Moreover, the Raman bandsassigned to radical cations and dications in doped PMeT films were found approximately at 1420 and 1400 cm~(-1),respectively. Radical cations and dications coexist on the backbone of PMeT as conductive species and their concentrationsincrease with the increase of doping level. Successive cyclic voltammetry was proved to be an effective approach toimproving the doping level of as-grown thin compact PMeT film.     

PREPARATION OF NOVEL POLYETHYLENE-graft-POLY(4-VINYLPYRIDINE)-SUPPORTED METALLOCENE CATALYSTS FOR ETHYLENE POLYMERIZATION

Polyethylene (PE) grafting 4-vinylpyridine copolymers has been produced as powders of different rushes by theirradiation method. After treatment with methylaluminoxane (MAO), the copolymers were used as supports for Cp_2ZrCl_2catalyst Results of X-ray photoelectron spectroscopy, Fourier transforms infrared spectroscopy, ultraviolet spectroscopy andscanning electron microscope measurements show that the catalytic sites have been linked through MAO on the PE-graft-4-vinylpyridine (PEVP). The percentages of grafting 4-vinylpyridine and supported Cp_2ZrCl_2 depend on the size ofpolyethylene powder. The smaller the polyethylene powder, the more percent of 4-vinylpyridine groups and Cp_2ZrCl_2 existon the polyethylene chains, and the PEVP-supported catalyst has a relatively high activity for ethylene polymerization.