Maria Rosário Ribeiro

Homo- and copolymerisation of norbornene and styrene with nickel bis(acetyl acetonate)/methylaluminoxane system

Abstract The homo and copolymerisations of norbornene and styrene with nickel bis(acetyl acetonate)/methylaluminoxane system were systematically investigated. This catalytic system shows a high activity towards homopolymerisation of both norbornene and styrene. For random copolymerisation, an increase in the initial styrene feed content leads to a gradual loss of activity relative to norbornene homopolymerisation. On the other hand, a drastic loss of activity, relative to styrene homopolymerisation, was found for very low norbornene feed contents. These results are qualitatively interpreted using the trigger coordination mechanism proposed by Ystenes. The structural characterisation of the polymers showed that norbornene polymerisation occurs via a 2,3 addition mechanism and that true copolymers are formed by random copolymerisation. At low styrene feed contents, only isolated styrene units or very short styrene sequences are present in the resulting copolymer. At higher styrene feed contents, short polystyrene sequences with more than eight styrene units may be formed. Determination of the reactivity ratios shows a much higher reactivity for norbornene (rnorbornene=17.8 and rstyrene=0.16). Size exclusion chromatography measurements have shown that polynorbornenes possess high molecular weights. Relatively low molecular weights were observed for homopolystyrene and copolymers.

Improved adhesion of polyethylene by copolymerisation of ethylene with polar monomers

Abstract The inertness of polyethylene restricts its compatibility with other materials. Thus, the adhesion between polyethylene and various substrates usually requires surface pretreatments on the polyolefin in order to obtain satisfactory results. One different approach is the production of ethylene copolymers with small amounts of polar comonomers that can act as adhesion promoters. Using metallocene based catalysts, ethylene copolymers with 10-undecenoic acid (UA) and with 5,7-dimethylocta-1,6-diene (5,7DMO) were synthesised. The adhesion strengths of the copolymers in direct tension were measured. The obtained results show that UA/ethylene and 5,7DMO/ethylene copolymers exhibit higher adhesion strengths with increasing comonomer contents. UA/ethylene copolymers are more effective in improving adhesion properties than 5,7DMO/ethylene copolymers. This difference is easily understandable on the basis of the polarities of both comonomers.

Transition Metal Complexes as Catalysts for the Homo‐ and Copolymerisation of Olefins and Non‐Conjugated Dienes

The copolymerisation of ethylene with 5,7-dimethylocta-1,6-diene (5,7-DMO) was conducted in the presence of a series of catalytic systems, based on different transition metal derivatives associated with methylaluminoxane (MAO): a metallocene-based catalyst, Cp2ZrCl2(1); a constrained geometry catalyst (Me4Cp)SiMe2(N-tert-Bu)TiCl2 (2); an iron-based catalyst, [(ArN=C(Me))2C5H3N]FeCl2(3); and a Brookhart-type catalyst [Ar—N=C(An)C(An)=N—Ar]NiBr2 (Ar = 2-C6H4(t-Bu)) (4). The metallocene catalyst (1) and the constrained geometry catalyst (2) are able to incorporate 5,7-dimethylocta-1,6-diene (5,7-DMO) into polyethylene chains. Although (2) shows lower overall activities than Cp2ZrCl2, similar 5,7-DMO incorporation levels are obtained for much lower diene concentrations in the feed. The characteristics of the copolymers obtained with the two catalysts are compared. The iron catalyst (3) can only homopolymerise ethylene. However, the presence of 5,7-DMO in the feed does not significantly affect the polymerisation activity. On the contrary, with the Brookhart system (4), the presence of 5,7-DMO as well as any of the tested dienes (5-ethylidene-2-norbornene, 7-methyl-1,6-octadiene and 1,5-hexadiene) completely inhibits the polymerisation of olefins. A tentative mechanism, based on the chain migration mechanism proposed by Brookhart is suggested for the deactivation of the Ni catalyst.

Metallocene-catalysed copolymerisation of ethylene with 10-undecenoic acid : The effect of experimental conditions

The copolymerisation of ethylene with 10-undecenoic acid (UA) using the metallocene catalyst system Cp 2 -ZrCl 2 /MAO was achieved. A reaction between the comonomer and MAO, prior to the copolymerisation, was used in order to protect, to some extent, the carboxylic group. The degree of MAO protection was found to be dependent on the Al/UA ratio used in the precontact mixture. The interaction between the two compounds was investigated by means of NMR spectroscopy. The influences of comonomer concentration in feed, Al/Zr moleratio and polymerisation temperature on the copolymerisations, were investigated with respect to catalyst activity and to UA incorporation. Higher concentrations of UA in feed favour the incorporation rate but decrease the activity. The Al/Zr more ratio shows a strong influence on activity, but not on the comonomer incorporation. Both the polymerisation activity and the UA incorporation rate present an optimal polymerisation temperature of around 40°C. DSC characterisation shows a decrease in the melting temperature of the polymers for increasing UA incorporations. Bimodal melting peaks, representative of polymer inhomogeneity, were observed for the highest UA incorporations.

Addition polymerisation of 5-vinyl-2-norbornene with nickel bis(acetyl acetonate)/methylaluminoxane system

Abstract Poly(5-vinyl-2-norbornene) was synthesised using the nickel bis(acetyl acetonate)/methylaluminoxane (Ni(acac) 2 /MAO) catalytic system. The polymerisation activity is low and depends strongly on temperature. The low reactivity of 5-vinyl-2-norbornene monomer results from both chelating effects and increased steric hindrance of the bulky monomer and the growing chain, which will account for low complexation and insertion rates. Fourier transform infrared spectroscopy (FTIR) characterisation has shown that polymerisation occurred mainly via addition polymerisation of the more strained endocyclic vinylene bond leaving the less strained exocyclic vinyl bond free.

[(η5-C5Me4)SiMe2(NtertBu)]TiCl2 as Pre-Catalyst for the Copolymerisation of Ethylene with 5,7-Dimethylocta-1,6-diene and with 3,7-Dimethylocta-1,6-diene

[(η 5 -C 5 Me 4 )SiMe 2 (NtertBu)]TiCl 2 was used as catalyst in the presence of methylaluminoxane (MAO) for the copolymerisation of ethylene with 5,7-dimethylocta-1,6-diene (5,7-DMO) and with 3,7-dimethylocta-1,6- diene (3,7-DMO), two linear non-conjugated dienes readily available from terpene feedstock. The effects of reaction temperature, Al/Ti mole ratio and diene concentration in feed on the polymerisation activity and on the incorporation rates of the diene were investigated. The structure of the polymer and the distribution of the comonomer along the chains were investigated through NMR and DSC.