Synthesis of Ethylene-co-Norbornene Polymers Promoted by MAO Free Catalysts Based on Group 4 Dicarbollide Complexes

Crystalline Ethylene−Norbornene Copolymers: Plastic Crystals from Macromolecules

“…The presence of three-dimensional order ("crystallinity") in samples of ethylene-norbornene (E-N) copolymers [8][9][10][11] has been related to an alternating sequence of the comonomers along the polymer chains and a regular succession of configurations of stereoisomeric centers in the norbornene units (stereoregularity). 9 The X-ray diffraction patterns of E-N copolymers, prepared with various metallorganic catalysts, with norbornene contents in the range 40-50 mol %, show a very intense peak with a maximum at 2 sin θ/λ ) 0.186 Å -1 (2θ ) 16.7°for Cu KR radiation).…”

“…The profile of Figure 1b corresponds to a sample reported in the literature, 8 whereas the profiles of parts c, d, and e of Figure 1 correspond to three samples A, B, and C, respectively, prepared in our laboratories with different catalysts. 11,12 It is apparent form Figure 1 that the diffraction peak at 2θ ) 16.7°may be more or less sharp depending on the sample. The width at halfheight of this peak is, indeed, rather large (∆(2θ) ) 4.5°) in the case of the diffraction profile of sample C (Figure 1e) and similar to that of the halo observed in the X-ray diffraction profile of liquid norbornadiene (Figure 1f), or quite small, ∆(2θ) ) 1.6°, 1.7°, and 2.4°in the case of samples of parts b, c, and d of Figure 1, respectively.…”

“…Sample A is an alternating copolymer with a [meso]/[racemic] ratio 1.1/ 1, whereas sample B is an alternating copolymer with prevailingly meso configurations, that is, basically isotactic. 11,12 Conformational energy calculations performed on the portion of the E-N copolymer chain of Figure 2 (N-E-N sequence) have shown that low-energy conformations are possible for either meso or racemic diads. Wide energy minima have been obtained for values of the torsion angles (defined in Figure 2) θ 1 ) -θ 3 ) 177°, θ 2 ) -174°, θ 4 ) 0°for the meso diad of Figure 2B and θ 1 ) θ 3 ) 174°, θ 2 ) -172°, θ 4 ) 0°for the racemic diad of Figure 2C.…”

“…The presence of three-dimensional order (“crystallinity”) in samples of ethylene−norbornene (E−N) copolymers − has been related to an alternating sequence of the comonomers along the polymer chains and a regular succession of configurations of stereoisomeric centers in the norbornene units (stereoregularity) …”

“…The [ meso ]/[ racemic ] ratio may be different depending on the copolymer sample, according to the catalyst and the method of preparation. Sample A is an alternating copolymer with a [ meso ]/[ racemic ] ratio 1.1/1, whereas sample B is an alternating copolymer with prevailingly meso configurations, that is, basically isotactic. ,

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