Synthesis of Syndiotactic Polystyrene/Atactic Polypropene Block Copolymer in the presnece of Half-sandwich Titanocene Catalysts

Some highly active η~5-pentamethylcyclopentadienyltribenzyloxy titanium complexes [Cp Ti(OBz)_3] activated by modified methylaluminoxane (mMAO) were prepared and used as the catalyst for styrene syndiospecific polymerization and propene atactic polymerization. Styrene could be copolymerized with propene when the propene was prepolymerized for a period, to which styrene and tri-isobutylaluminum (TIBA) were then added. The titled block copolymer together with the related homopolymers was obtained. The copolymerization porducts can be divided into the homopolymers and the copolymer by successive solvent extraction with boiling butanone, heptane and tetrahydrofuran (THF), and each fraction was characterized by ~13C NMR, DSC and WAXD. It was found that aPS and aPP were soluble in boiling butanone and heptane respectively. The block copolymer (sPS-b-aPP) composed of syndiottactic polystyrene segment was soluble in boiling THF and the residue was chiefly sPS.

STUDY ON LIGHTLY SULFONATED SYNDIOTACTIC POLYSTYRENE IONOMERS

Sulfonated syndiotactic polystyrene ionomers (SsPS) with 1.8 mol% degree of sulfonation have been studied. WAXD shows that the crystallinity of SsPS ionomers was decreased with increasing diameter size of the counter ions and sPS > SsPS-H > SsPS-K > SsPS-Zn. Moreover, SsPS ionomers only have alpha crystal form, while original sPS has two crystal forms: alpha and beta crystal form. TGA shows that the thermal stability of SsPS ionomers is higher than that of the original sPS and SsPS-Zn > SsPS-K > SsPS-H. DSC shows that all the glass transition temperatures (T-g) of SsPS ionomers are higher than that of the neat sPS and SsPS-Zn > SsPS-Na > SsPS-K > SsPS-H. However, the melting temperature (T-m) and crystallization peak temperature (T-p) of SsPS ionomers are lower and SsPS-H > SsPS-Zn > SsPS-K > SsPS-Na, while the crystallinity (X-c) of SsPS-Zn is the lowest. Nonisothermal crystallization kinetics shows that the Avrami index of sPS and SsPS-H are both about 4, suggesting the nucleation growth of SsPS-H with lower degree of sulfonation still keeps its three-dimension form. FTIR spectra of SsPS ionomers show a splitting absorption band for asymmetric stretching vibration of sulfonation group. The CH in-plane bending vibration of benzene ring shifted to higher wavenumber and the symmetric stretching vibration of sulfonation group changed slightly with different counter ion neutralized SsPS ionomers.

Multiple Melting Endotherms of Syndiotactic Polystyrene in β Crystalline Form

A series of syndiotactic polystyrene (SPS) samples in β crystalline form were prepared by cooling from the melt at various cooling rates. The effects of cooling rate from the melt, and DSC heating rate on the multiple melting behaviors of β crystals were investigated by differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC), from which the nature.of the multiple melting behavior was ascribed to the occurring of a recrystallization process.

FTIR Spectroscopic Study of Crystallization of Uniaxial Drawn Syndiotactic Polystyrene/Carbon Nanotube Nanocomposite Films

The crystallization of uniaxial hot drawn syndiotactic polystyrene/multi-walled carbon nanotube （sPS/MWCNT） nanocomposite films was studied by FTIR spectroscopy. The effects of MWCNT content, draw ratio and drawing temperature on the sPS crystallinity were investigated. The sPS/MWCMT nanocomposite films show reduced crystallinities with the increase of MWCNT content. In addition, with the increase of draw ratio, both the pure sPS and the sPS/MWCNT nanocomposite drawn films exhibit increased crystallinity. The effect of drawing temperature on the sPS crystallization is complex. In a temperature range of 100―135 °C, the crystallinity decreases with drawing temperature, whereas it increases at 140 °C for both pure sPS and its nanocomposite films.

Synthesis of Syndiotactic Polystyrene with Novel Titanocene Catalysts Activated by Modified Methylaluminoxane

Novel highly active eta(5)-pentamethylcyclopentadienyltribenzyloxy titanium catalyst activated by modified methylaluminoxane (m-MAO) was prepared for styrene syndiospecific polymerization. The influences of the contents of trimethylaluminum (TMA) in m-MAO and external addition of tri-isobutylaluminum (TIBA) on the distribution of the oxidation states of titanium were investigated in detail. The Ti (III) is in favour of styrene syndiospecific polymerization in higher catalytic activity.

SOLID PHASE TRANSITION OF SYNDIOTACTIC POLYSTYRENE IN SUPERCRITICAL CO_2

Solid phase transition of the a form crystals to the 3 form crystals in syndiotactic polystyrene (sPS) samples has occurred in supercritical CO2. This transformation is different from those detected under other conditions. The effects of some factors (e.g. time, temperature, and pressure) on the solid phase transformation of sPS in supercritical CO2 were analyzed in detail. Experimental results show that longer time, higher temperature or higher pressure favors the transformation of the a form crystals to the beta form crystals.

The Phase Transition of Syndiotactic Polystyrene Induced by Electrostatic Field

The crystal structure and morphology of syndiotactic polystyrene (sPS) melt crystallized in various electrostatic fields have been investigated by using wide angle X ray diffraction (WAXD), differential scanning calorimeter (DSC) and scanning electron microscope (SEM). WAXD and DSC analyses show that sPS is gradually transformed from α phase to β phase with increase of electrostatic intensity. The SEM observations indicate that the morphology of sPS micro crystals is strongly dependent on electrostatic intensity applied to the sample during solidification. The variation of the micro crystals orientation from disordered lamellae to ordered lamellare have been observed with increase of electrostatic intensity.

Effects of Ligands in Novel Non-titanocene on Syndiotactic Polymerization of Styrene

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Synthesis of polystyrene-styrene/butadiene diblock copolymers via reversible addition-fragmentation chain transfer miniemulsion polymerization

Polystyrene-styrene/butadiene diblock copolymers were synthesized via reversible addition-fragmentation chain transfer （RAFT） miniemulsion polymerization.During the polymerization process,the molecular weight distribution was narrow and the numerical molecular weight of the copolymers increased with increasing conversion of monomers,which was close to the theoretical.FT-IR and ^1H NMR results indicated that the microstructure of the polymer was mainly 1,4-trans-butadiene with small amount of 1,2-units,and composition in the copolymers was obtained.

Equilibrium Crystallization Temperature of Syndiotactic Polystyrene γ Form

The crystallization behavior of syndiotactic polystyrene（s PS） γ form undergoing annealing at various temperatures was investigated using the thermodynamic phase diagram based on Strobl＇s crystallization theory. On the basis of the differential scanning calorimetric results, it was observed that γ form melt-recrystallization occurred at a higher temperature with the increasing lamellar thickness, which resulted from the pre-annealing at the elevating temperature after acetone induced crystallization. Further temperature dependent small-angle X-ray scattering（SAXS） measurement revealed the evolution of the γ form lamellae upon heating until phase transition, involving three different regimes： lamellae stable region（25-90 °C）, melt-recrystallization region（90-185 °C） and pre-phase transition region（185-195 °C）. As a result, recrystallization line, equilibrium recrystallization line and melting line were developed for the s PS γ form crystallization process. Since the melt of γ form involved a γ-to-α/β form phase transition, the melting line was also denoted as the phase transition line in this special case. Therefore, the equilibrium crystallization temperature and melting（phase transition） temperatures were determined at around 390 and 220 °C on the basis of the thermodynamic phase diagram of the s PS γ form.

THE MORPHOLOGY AND STRUCTURE OF ETHYLCYANOETHYL CELLULOSE IN STYRENE AND POLYSTYRENE

Ethyl-cyanoethyl cellulose ((E-CE)C)/styrene solution could form anisotropic system when the concentration was high enough. The (E-CE)C/polystyrene(PS)multiphase polymer could be obtained by radical polymerization of the styrene in the solution. The (E-CE)C/PS multiphase polymer maintained both the crystalline structure of the (E-CE)C and the amorphous structure of the PS. In the multiphase polymer produced from the isotropic solution, however, the (E-CE)C formed spherulites and spread in the PS amorphous phase. While, in the multiphase polymer produced from the anisotropic solution, the (E-CE)formed cylinderic crystalline aggregates. Moreover, the ordered lamellar texture was also observed in the multiphase polymer produced from the anisotropic solution.

Leaching of styrene and other aromatic compounds in drinking water from PS bottles

Bottled water may not be safer, or healthier, than tap water. The present studies have proved that styrene and some other aromatic compounds leach continuously from polystyrene （PS） bottles used locally for packaging. Water sapmles in contact with PS were extracted by a preconcentration technique called as ＂purge and trap＂ and analysed by gas chromatograph-mass spectrometer （GC/MS）. Eleven aromatic compounds were identified in these studies. Maximum concentration of styrene in PS bottles was 29.5 μg/L. Apart from styrene, ethyl benzene, toluene and benzene were also quantified but their concentrations were much less than WHO guide line values. All other compounds were in traces. Quality of plastic and storage time were the major factor in leaching of styrene. Concentration of styrene was increased to 69.53 μg/L after one-year storage. In Styrofoam and PS cups studies, hot water was found to be contaminated with styrene and other aromatic compounds. It was observed that temperature played a major role in the leaching of styrene monomer from Styrofoam cups. Paper cups were found to be safe for hot drinks.

SYNDIOSPECIFIC POLYMERIZATION OF STYRENE WITH MULTI-NUCLEAR TITANIUM COMPLEXES

Two multi-nuclear titanium complexes [Ti（η^5-Cp^＊）Cl（μ-O）]3 （1） and [（η^5-Cp^＊TiCl）（μ-O）2（η^5-Cp^＊Ti）2（μ- O）（μ-O）2]2Ti （Cp^＊ = C5Me5） （2） have been investigated as the precatalysts for syndiospecific polymerization of styrene. In the presence of modified methylaluminoxane （MMAO） as a cocatalyst, complexes 1 and 2 display much higher catalytic activities towards styrene polymerization, and produce the higher molecular weight polystyrenes with higher syndiotacticities and melting temperatures （Tm） than the mother complex Cp^＊TiCl3 does when the polymerization temperature is above 70℃ and the Al/Ti molar ratio is in the low range especially.

SYNTHESIS AND CHARACTERIZATION OF FOUR-ARMED BLOCK POLY(STYRENE-b-p-NITROPHENYL METHACRYLATE)PREPARED BY THE ATRP METHOD

A novel tetrafunctional initiator, C [CH_2O (CH_2)_3 OOCCH(Br)CH_3]_4 (1), was synthesized through the reaction oftetraol with α-bromopropionyl chloride, and then was used as initiator of atom transfer radical polymerization (ATRP) in thepreparation of 4-armed polystyrene (PSt) with narrow polydispersity. The structure, molecular weight and molecular weightdistribution (MWD) of each arm were studied by ~1H-NMR and GPC data of hydrolyzed products of the 4-armed PSt. TheATRP of St using 1/CuBr/bpy as initiator system is of 'living' character based on the following evidence: narrow MWD,constant concentration of chain radical during the polymerization, control of molecular weight by the molar ratio of monomerconsumed to 1. The 4-armed poly(St-b-p-nitrophenyl methacrylate) [poly(St-b-NPMA)] was prepared by the ATRP ofNPMA using 4-armed PSt with terminal bromine as the initiator, and characterized by FT-IR, ~1H-NMR spectra and GPCcurves. The micelles with PSt as core, and PNPMA as shell were formed by dropping DMSO into a solution of 4-armedpoly(St-b-NPMA) in DMF, as proved by laser light scatter (LLS) method.

SYNDIOSPECIFIC POLYMERIZATION OF STYRENE WITH Ar[O,O/NH]Cp ~*TiCl ACTIVATED WITH MMAO

A series of titanium complexes Ar[O,E]Cp~*TiCl(Cp~*=C_5Me_5,Ar=1,2-phenylene,E=NH(1a);Ar=1,2- phenylene,E=O(1b);Ar=2.2'-diphenylene,E=O(1c);Ar=2,2'-dinaphthalene,E=O(1d)) has been prepared by the reaction of corresponding phenol derivatives with Cp~*TiCl_3 in the presence of excessive triethylamine.Under the conditions of low Al/Ti molar ratio(e.g.500) and high reaction temperatures(>70℃),all the titanium complexes display higher catalytic activities towards the syndiospecific polymerization of styrene,in t...

Synthesis and Characterization of p-[Perfluoro-1-(2-fluorosulfonylethoxy)]ethylated Polystyrene

A new fluorinated polystyrene bearing a p substituted perfluoro[1 (2 fluorosulfonylethoxy)]ethyl group was synthesized via one electron oxidation of polystyrene by perfluoro[2 (2 fluorosulfonyl ethoxy)]propionyl peroxide at different peroxide to polystyrene molar ratios. The yield of perfluoroalkylation decreases with the increase of the reactant molar ratio. The modified polymer has been characterized by various techniques: the ring pefluoro[1 (2 fluorosulfonylethoxy)]ethylation has been proved by FT IR and 19 F NMR; the X ray photoelectron spectra (XPS) show the maximum binding energy of F 1s , O 1s , C 1s (two kinds of carbon atoms, namely C H and C F) and S 2p , respectively; desulfonylation of the fluorinated polystyrene appearing at 217 ℃ has been found by its thermogravimetric analysis (TGA). The determinations of contact angle, refractive index and glass transition temperature of the modified polymer have disclosed that when the contact angle increases with the increase of the molar ratio, the refractive index and glass transition temperature decrease. The polydispersity values indicate that the degradation of the polymer chains did not occur during the reaction.

A simple and versatile method for the synthesis of soluble C_(60)-based polystyrene derivatives

A new simple and useful method for the synthesis of soluble C60-styrene copolymer is demonstrated. Covalent attachment of C60 onto the polystyrene backbone has been confirmed by UV-VIS absorption spectra, 13C NMR and SEM.

DMAO-activated Rare-earth Metal Catalysts for Styrene and Its Derivative Polymerization

The catalytic performa nee of rare-earth metal dialkyl complexes in combi nation with DMAO(dry methylalumi no xane)is explored.In the presence of 60 equivalents of DMAO,the half-sandwich complex(C_(13)H_(8)CH_(2)Ph)Sc(CH_(2)SiMe_(3))_(2)(THF)(1)is inert for styrene polymerization,but(C_(5)Me_(4)Ph)Sc(CH_(2)C_(6)H_(4)NMe_(2)-o)_(2)(2)con verts 18% styre ne into syn diotactic polystyrene.Under the same conditi ons,the con strained-geometry configuration sandium complex(C13H8CH2Py)Sc(CH_(2)SiMe_(3))_(2)(3a)displays extremely high catalytic activity(>6420 kg·mol_(sc)^(-1)h^(-1))and perfect syndiospecific(rrrr>99%)for styrene polymerization,while its lutetium(3b)and yttrium(3c)analogues are nearly inactive.Although the binary catalytic system 3a/DMAO exhibits very low activity for 4-methoxystyrene polymerization,it is an efficient catalyst for the syndioselective polymerization of other styrene derivatives such as 2-methoxystyrene,4-methylthiostyrene,4-fluorostyrene,4-dimethylhydrosilylstyrene,alkyne-susbstituted styrenes and 4-methylstyrene.In addition,the binary system 3a/DMAO can copolymerize ethylene and styrene to give alternating copolymers with a single glass tran sition at 80℃ and 0.4 MPa ethylene pressures.By in creasing styrene feed amount from 20 mmol to 60 mmol,the styre ne con tent slight in creases from 48.2 mol% to 53.8 mol%,but the polymerizatio n activity is obviously promoted from 240 kg·mol_(Sc)^(-1)·h^(-1) to 532 kg·mol_(sc)^(-1)·h^(-1).

Substituent Effects of Pyridyl-methylene Cyclopentadienyl Rare-earth Metal Complexes on Styrene Polymerization

Salt metathesis reactions between pyridyl-methylene-cyclopentadienyl lithium salt and LnCl_3 followed by the addition of two equivalents of LiCH_2SiMe_3 afforded a series of constrained-geometry-configuration rare-earth metal bis(alkyl) complexes(Cp′CH_2-Py)Ln(CH_2SiMe_3)_2(THF)_n(Py = C_5H_4N, Cp′ = C_5H_4(Cp), Ln = Sc, n = 0(1); Cp′ = C_9H_6(Ind), Ln = Sc, n = 0(2); Cp′ = 3-Me_3Si-C_9H_5(3-Me_3Si-Ind), Ln = Sc, n = 0(3a), Ln = Lu(3b), Y(3c), n = 1; Cp′ = 2,7-(~tBu)_2C_(13)H_8(2,7-(~tBu)_2-Flu), Ln = Sc(4 a), n = 0, Ln = Lu(4b),Y(4c), n = 1) in moderate to good yields, which were characterized by NMR spectroscopy and single-crystal X-ray diffraction(for complex 3a). In the presence of [Ph_3C][B(C_6F_5)_4] and Al^iBu_3, these complexes displayed different performances towards styrene polymerization. Rare-earth metal bis(alkyl) precursors bearing Cp, Ind, and 3-Me_3Si-Ind segments exhibited very low catalytic activity to afford syndiotactic polystyrene. All electron-donating t Bu substituted complexes 4 a, 4 b, and 4 c showed very high activity and perfect syndiotactivity(rrrr > 99%), producing high molecular weight polystyrene(up to 54.1 × 10~4) with relatively narrow molecular distribution(PDI = 1.28-2.49).