Narrow Molar Mass Distribution Research Articles

Chlorolanthanocene-dialkylmagnesium systems for styrene bulk polymerization and styrene-ethylene block copolymerization

The bulk polymerization of styrene has been investigated at 105°C in the presence of exclusively dialkylmagnesium or combination of chlorolanthanocene and dialkylmagnesium. In the presence of butylethylmagnesium or n,s-dibutylmagnesium, styrene polymerization proceeds via thermal self-initiation, but is accompanied by a reversible transfer to dialkylmagnesiums to yield in turn oligostyrylmagnesium species; the latter are finally hydrolysed to oligostyrenes with Mn = 500–1 500 and Mw/Mn = 2.0–2.8. The analysis of the oligostyrenes by MALDI-TOF mass spectrometry establishes the presence of ethyl and butyl headgroups, consistent with the transfer process. When the dialkylmagnesium is combined with a lanthanocene such as (C5Me5)2NdCl2Li(OEt2)2 (1), an increase in activity is obtained which is ascribed to additional styrene polymerization initiated by in situ generated alkyl(hydride)lanthanocene species. The influence of various reaction parameters on the performance of this system has been investigated. The oligostyrenes (Mn = 500–9 000) produced under optimum conditions have a relatively narrow molar mass distribution (Mw/Mn = 1.20–1.40) which can be explained in terms of an efficient transfer between the chain-growing lanthanide and the oligostyrylmagnesium species. The MALDI-TOF mass spectra of the oligostyrenes produced with various dialkylmagnesium-lanthanocene combinations gives an insight into the initiation mechanism. Finally, the combination of butylethylmagnesium and Cp*2NdCl2Li(OEt2)2 has been used to achieve (styrene-co-ethylene) block copolymers.

Tert-Butyl methacrylate polymerization with tributyltinlithium and tributyltinsodium

tert-Butyl methacrylate was found to polymerize in the presence of tributyltinlithium and tributyltinsodium in benzene at 0°C, resulting in the formation of polymers with narrow molar mass distribution.

Ethylene and propylene polymerizations with the MgCl2-supported tris(acetylacetonato)chromium-diethylaluminium chloride catalyst system

Highly isolactic poly(propylene) with T m = 69.5°C and [mmmm] > 99% in hich selectivity (I.IW 99.9% was prepared with the catalyst system Cr(aca) 3 /MgCl 2 -DEAC. 13 C NMR analysis of low molecular weight isotatic polypropylene indicate that the propylene monomer was inserted in the polymer-metal bond via 1,2-addition selectively. Polymerization activities and isospecificity of the catalyst markedly increase with decreasing Cr content in the catalyst, In ethylene homopolymerization, the Cr(acac) 3 /MgCl 2 catalyst showed almost constant activity for 3 h and produced high molecular weight polyethylene with narrow molar mass distribution.

Chlorolanthanocene-dialkylmagnesium systems for styrene bulk polymerization and styrene-ethylene block copolymerization

The bulk polymerization of styrene has been investigated at 105°C in the presence of exclusively dialkylmagnesium or combination of chlorolanthanocene and dialkylmagnesium. In the presence of butylethylmagnesium or n,s-dibutylmagnesium, styrene polymerization proceeds via thermal self-initiation, but is accompanied by a reversible transfer to dialkylmagnesiums to yield in turn oligostyrylmagnesium species; the latter are finally hydrolysed to oligostyrenes with M n = 300-1500 and M w / M n = 2.0-2.8. The analysis of the oligostyrenes by MALDI-TOF mass spectrometry establishes the presence of ethyl and butyl headgroups. consistent with the transfer process. When the dialkylmagnesium is combined with a lanthanocene such as (C 5 Me 5 ) 2 NdCl 2 Li(OEt 2 ) 2 (1), an increase in activity is obtained which is ascribed to addinonal styrene polymerization initiated by in situ generated alkylthydride)lanthanocene species. The influence of varions reaction parameters on the performance of this system has been investigated. The oligostyrenes (M m = 500-9000) produced under optimum conditions have a relatively narrow molar mass distribution (M w /M n = 1.20-1.40) which can be explained in terms of an efficient transfer between the chain-growing lanthanide and the oligostyrylmagnesium spectes. The MALDI-TOF mass spectra of the oligostyrenes produced with various dialkyimagnesium-lanthanocene combinations gives an insight into the initiation mechanism. Fanally, the combination of butylethylmagnesium and Cp * 2 NdCl 2 Li(OEt 2 ) 2 has been used to achieve (styrene-co-athylene) block copolymers.

Synthesis of ethylene-propylene random copolymers with MgCl2-supported tris(acetylacetonato) chromium-diethylaluminium chloride-ethylbenzoate catalyst system

MgCl 2 -supported Cr(aca) 3 catalyst combined with diethylaluminium chloride (DEAC) was applied to the copolymerization of ethylene and propylene in the presence and absence of ethylbenzoate (EB) as external donor. The productivity was strongly dependent on the isospecificity and Cr content of the catalyst. 13 C NMR and GPC analyses of the resulting copolymers showed that random copolymers were synthesised with narrow molar mass distribution and the enantioselectivity of the catalyst was retained even in the copolymerization

Synthesis of Block Copolymer from Dissimilar Vinyl Monomer by Stable Free Radical Polymerization

Controlled polystyrenes with different molar mass values were synthesized starting from benzoyl peroxide and TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy). The polystyrene homopolymers served as macroinitiators for the block copolymerizations of the dissimilar vinyl monomers butyl methacrylate (BMA), ethyl methacrylate (EMA), methyl methacrylate (MMA), octyl methacrylate (OMA), vinyl acetate (VAc), N,N-dimethylacrylamide (DMA), and 2-(dimethylamino)ethyl acrylate (DAEA). Polystyrene−polymethacrylate diblock copolymers with well-defined structures as well as controlled and narrow molar mass distribution were obtained from the lower-mass polystyrene macroinitiator. Contrary to methacrylates, VAc and DAEA are not readily initiated by the polystyrene macroinitiator. Block copolymer formation was confirmed by 1H NMR and GPC measurements. On the basis of the 1H NMR investigation, there is strong evidence for the presence of TEMPO-terminated copolymers. The TEMPO-mediated polymerization is suitable for the synthe...

Ultrasonic degradation of polystyrene solutions

The degradation of narrow molar mass distribution samples of polystyrene dissolved in toluene when exposed to ultrasound are reported. The change in molar mass on exposure to the ultrasound was monitored by use of gel permeation chromatography and solution viscosity measurements. Dynamic response of the polymer molecules in solution to the ultrasonic perturbation is calculated using a modification of the Wang–Zimm theory. A good correlation between the decrease in the energy absorption predicted by theory and the decrease in the rate of degradation was observed. It is proposed that the degradation process induced by ultrasonic degradation be intimately connected with the viscoelastic response of a polymer molecule in dilute solution and is not just a consequence of the cavitation process.

Cis-Specific Living Polymerization of 1,3-Butadiene Catalyzed by Alkyl and Alkylsilyl Substituted Cyclopentadienyltitanium Trichlorides with MAO

Cis-specific living polymerizations of 1,3-butadiene (BD) catalyzed by the catalyst system composed of C5H4RTiCl3 (4a, R = H; 4b, R = n-butyl; 4c, R = isopropyl; 4d, R = tert-butyl; 4e, R = trimethylsilyl) with methylaluminoxane (MAO) to give polyBDs with narrow molar mass distribution and high cis content are described. Polybutadienes (polyBDs) prepared by the catalyst at −25 °C are monodispersed (Mw/Mn = 1.04−1.05) in all cases. From the comparison with propagation rate constants (kp), the order of polymerization activity was as follows: 4d > 4e > 4c > 4b = 4a. The microstructures of polyBDs were all dominated by the cis configuration. The complex 4d having bulky tert-butyl group showed higher cis specicficity. Both kps and cis specificity in the polymerization of BD were strongly affected by the substituents introduced on the cyclopentadienyl ring.

Analysis of poly(ethyl methacrylate)s by on-line hyphenation of liquid chromatography at the critical adsorption point and nuclear magnetic resonance spectroscopy

Liquid chromatography at the critical adsorption point (LC CAP) with on-line NMR detection (on-line LC CAP NMR) was utilized for analysis of tacticity distribution of stereo-regular poly(ethyl methacrylate)s (PEMAs). The separation of a model PEMA sample composed of four constituents with similar molar masses (Mw = (14-16) x 10(3) g mol-1) differing in their tacticity (rr triad content = 0, 33, 68, and 89%) was achieved by LC CAP with a mixed eluent composed of acetone, acetone-d6, and cyclohexane. The tacticity composition within each peak eluted from the LC CAP column was directly determined by a 750-MHz 1H NMR spectrometer that was used as a real-time detector in the continuous-flow mode. Tacticity distribution in a particular PEMA sample with mm/mr/rr = 2/45/53 and narrow molar mass distribution of Mw/Mn = 1.05 has been revealed by the LC CAP NMR technique.

Fractionation of Poly(ethylene glycol) by High Osmotic Pressure Chromatography

Poly(ethylene glycol) (PEG) was fractionated by high osmotic pressure chromatography (HOPC) with water and 1,4-dioxane as eluents. Using dimethyloctylchlorosilane (C 8 )-modified controlled-pore glass (CPG) with 1,4-dioxane as eluent, high molar mass (MM) PEG components were fractionated. The average MM of the fractionated PEG samples strongly depends on the eluent and the polarity of column packing materials. PEGs dissolved in water were adsorbed onto the column packing materials more easily compared with 1,4-dioxane. Comparison between simulation and experiments indicated that adsorption of PEG molecules onto the surface of the column packing materials reduces the separation efficiency of HOPC fractionation. By preventing adsorption, PEG components with higher MM and narrow molar mass distribution (MMD) were fractionated even from a commercial PEG with narrow MMD.

Synthesis of new side-group liquid crystalline block copolymers by living anionic polymerization

A new series of AB liquid crystalline (lc) block copolymers was synthesized via living anionic copolymerization of styrene as segment A and 6-[4-(4-cyanophenylazo)phenoxy]hexyl methacrylate (1) as segment B. The copolymers were successfully prepared in quantitative yields and with narrow molar mass distributions. The number-average molar mass of the segments was varied well-defined. The polystyrene block ranged from 3 500 to 7 400 g/mol. The content of the B segment ranged from 1 to 54 wt.-%. Thermotropic phases were detected by differential scanning calorimetry (DSC) for block copolymers with an lc segment of more than 30 wt.-%.

Characterisation of regioselectively functionalized 2,3-O-carboxymethyl cellulose by enzymatic and chemical methods

The determination of the molecular structure of 2,3-O-carboxymethyl cellulose (2,3-O-CMC), prepared via 6-O-(4-monomethoxy)triphenylmethyl cellulose, was carried out in detail by means of enzymatic and chemical methods. The 2,3-O-CMCs had degrees of substitution (DS) in the range of 0.5–1.2 showing a narrow molar mass distribution as revealed by SEC. As a result of an endoglucanase treatment, an intensive depolymerization of the samples occurred which was more pronounced for 2,3-O-CMC with comparatively low DS. All degraded samples could be separated into 18 fractions by preparative SEC and the proportion of each individual repeat unit was analysed by anion exchange chromatography (AEC) following complete hydrolytic chain degradation. The results indicated a homogeneous distribution of the functional groups within the polymer chain. Moreover, it became obvious that a preferred carboxymethylation of O-2 compared with O-3 occurred and that a preferred functionalization of already carboxymethylated units occurred as the reaction progressed. AEC with pulsed amperometric detection, which was used to separate and analyse the differently functionalized repeating units as well as glucose, had to be calibrated. Therefore, a method to determine the response factors of the individual carboxymethylated glucose units was developed using 13C NMR spectroscopic measurements (inverse gated decoupling) of depolymerised 2,3-O-CMC.

Analysis of poly(bisphenol A carbonate) by size exclusion chromatography/matrix-assisted laser desorption/ionization. 2. self-association due to phenol end groups

We report here a case of apparent failure of the size exclusion chromatography/matrix-assisted laser desorption/ionization (SEC/MALDI) method to provide polymer fractions with narrow molar mass distribution, showing that intermolecular chain association is responsible for this phenomenon. Poly(bisphenol A carbonate) (PC) chains terminated with hydroxyl groups undergo self-association by hydrogen bonding, providing macromolecular aggregates with higher hydrodynamic volume. These aggregates are eluted through SEC columns at the same volume as higher molar mass chains, which remain non-associated. Thus, self-association affects negatively the SEC fractionation experiments, and even the sharpest SEC fractions contain a heterogeneous mixture of PC chains of different size. When the off-line SEC/MALDI procedure is applied, the SEC fraction is diluted in the matrix which, being a dissociating medium (carboxylic acid) for hydrogen-bonded aggregates, suppresses the chains' self-association. Therefore, the MALDI spectra of these PC fractions indicate a polydisperse character, with irregular bimodal distributions of peaks. As a consequence, in the presence of chain association, the SEC/MALDI method for the calculation of molar masses of polymers cannot be directly applied. In the present case we have found that, under opportune experimental conditions, self-association in polycarbonates can be avoided, so that nearly monodisperse SEC fractions can be obtained and the SEC/MALDI method can be applied. Our results also show that MALDI is a very sensitive technique for the detection of association of polymers in dilute solutions. Copyright 1999 John Wiley & Sons, Ltd.

Comparative thermoanalytical investigation of the cross-linking behaviour of three different paraffin waxes in the presence of potassium persulphate

The cross-linking of three different paraffin waxes – a hard oxidised wax, a medium wax, and a hard wax with narrow molar mass distribution – in the presence of potassium persulphate (PPS) was investigated thermoanalytically. DSC and TG curves for untreated waxes and waxes treated with different amounts of PPS were obtained and the observations were compared with gel content data obtained through gravimetric analysis. Although initial indications were that cross-linking did occur, reheat curves of wax/PPS mixtures as well as gel content data showed that no cross-linking occurred. It was, however, found that PPS most probably decomposed into KHSO 4 and that this decomposition gave rise to functionalisation of the waxes.

Comparative thermoanalytical investigation of the cross-linking behaviour of three different paraffin waxes in the presence of dicumyl peroxide

The cross-linking of three different paraffin waxes – a hard oxidized wax, a medium wax, and a hard wax with narrow molar mass distribution – in the presence of dicumyl peroxide (DCP) was investigated thermoanalytically. DSC and TG curves for untreated waxes and waxes treated with different amounts of DCP were obtained and the observations were compared with gel content data obtained through gravimetric analysis. It was found that all three waxes cross-linked in the presence of DCP, with the extent of cross-linking increasing with increasing DCP : wax ratio. It was also clear that the higher melting fractions of the different waxes preferably cross-linked. From the gel content data it seems as if the oxidized and higher molar mass waxes tend to cross-link at a faster rate.

Diblock and triblock functional copolymers by controlled radical polymerization

Controlled polystyrenes with different molar mass values were synthesized starting from benzoyl peroxide and TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy). The polystyrene homopolymers served as initiators for the block copolymerization of phthalimide methylstyrene (PIMS) to synthesize polystyrene-b-poly(PIMS) diblock copolymers. Diblock copolymers with well defined structures as well as controlled and narrow molar mass distribution were obtained from the lower-mass polystyrene homopolymers. The lower-mass copolymers were found to be active as initiators in the synthesis of the polystyrene-b-poly(PIMS)-b-polystyrene triblock copolymers. In each reaction step, the effects of conversion and reaction time on the molar mass characteristics of the prepared block copolymers were investigated. The diblock and triblock copolymers were modified using hydrazine as the reagent in order to obtain the corresponding functional amino block copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1237–1244, 1999

Diblock and triblock functional copolymers by controlled radical polymerization

Controlled polystyrenes with different molar mass values were synthesized starting from benzoyl peroxide and TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy). The polystyrene homopolymers served as initiators for the block copolymerization of phthalimide methylstyrene (PIMS) to synthesize polystyrene-b-poly(PIMS) diblock copolymers. Diblock copolymers with well defined structures as well as controlled and narrow molar mass distribution were obtained from the lower-mass polystyrene homopolymers. The lower-mass copolymers were found to be active as initiators in the synthesis of the polystyrene-b-poly(PIMS)-b-polystyrene triblock copolymers. In each reaction step, the effects of conversion and reaction time on the molar mass characteristics of the prepared block copolymers were investigated. The diblock and triblock copolymers were modified using hydrazine as the reagent in order to obtain the corresponding functional amino block copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1237–1244, 1999

LIVING CARBOCATIONIC OLIGOMERIZATION OF ISOBUTYLENE BY TERTIARY ALCOHOL/BCl3/1-METHYL- 2-PYRROLIDINONE INITIATING SYSTEMS. KINETIC STUDY

Low molar mass ( n < 4000 g.mol), narrow molar mass distribution ( w/ n =1.1–1.3) linear α-(tert-butyl) ω-(tert-chloro) and α-cumyl ω-(tert-chloro) oligoisobutylenes (PIBs) were synthesized using two initiating systems: 2,4,4-trimethyl-pentan-2-ol (TMPOH)/BCl3/−40°C and 2-phenylpropan-2-ol (CumOH)/-BCl3/−70°C in the presence of an efficient electron-pair donor (ED),1-methyl-2-pyrrolidinone (NMP) in methyl chloride. The kinetics of oligomerization were investigated. In these two systems, similar polymerization mechanisms were observed with, nevertheless, a slight difference of growing species behavior in the early polymerization steps. The initiation and propagation rate constants were determined; their values are low showing that the addition of NMP to these initiating systems leads to controlled carbocationic polymerizations. Moreover, the living character of the polymerization was demonstrated.

Universal Supercritical Binary Mixture for Polymer Fractionation

Supercritical fluids are well known for their efficiency to fractionate polymers as a function of their molar mass, their architecture and their chemical composition, in the case of copolymers. We have used a supercritical solvent mixture, made of CO2 and ethanol, to fractionate poly(ethylene oxide) (PEO) and polystyrene (PS). This mixture which can solubilize both polar (PEO) and nonpolar (PS) polymers, allows the obtention of a narrow molar mass distribution with possibility to select the molar mass value and the molar mass distribution of the extracted sample. The purification of a binary mixture of star and linear PEO has been also performed.

Polymerization of olefins with a novel dinuclearansa-zirconocene catalyst having a biphenyl bridge

Both the rac- and meso-dinuclear ansa-zirconocene catalysts (μ-C12H8{[SiPh(Ind)2]ZrCl2}2) were prepared by a coupling reaction between 2 equiv of diindenylphenylchlorosilane (rac- and meso-isomers) and 1 equiv of p-dilithiobiphenyl in diethyl ether at −80°C, followed by a successive reaction with ZrCl4 · 2THF in THF at −78°C. Polymerizations of ethene and propene were conducted in a 1 dm3 high-pressure glass reactor equipped with a mechanical stirrer at 60, 80, 100, 120, and 150°C using methylalumoxane (MAO) as cocatalyst and toluene or decahydronaphthalene as the solvent. Copolymerization of ethene and 1-octene was also checked in brief. For ethene polymerization, the meso-catalyst was found to be more active, which displayed an extremely high activity to give linear polyethene with a high molecular weight and a narrow molar mass distribution (MMD). The apparent activity increased monotonously with rising polymerization temperature from 60°C up to 150°C, indicating that the active species are stable even at a high temperature. On the other hand, both the rac- and meso-catalysts showed very poor activities for propene polymerization. However, copolymerization of ethene and 1-octene proceeded at a high speed. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2269–2274, 1998