Ethylene-Styrene Copolymers by ansa-Zirconocene- and half-Titanocene-Based Catalysts: Composition, Stereoregularity, and Crystallinity Vincenzo Venditto,* Giancarlo De Tullio, Lorella Izzo, and Leone Oliva Dipartimento di Chimica, Universita ` di Salerno, I-84081 Baronissi (SA), Italy Received December 31, 1997 Revised Manuscript Received March 23, 1998 Introduction Copolymerization of ethylene with styrene has been recently achieved using a variety of homogeneous Zie- gler-Natta catalysts. 1 The presence of a tertiary carbon atom in the styrene units of these copolymers makes stereoregularity possible, but in most of those copoly- mers previously described the stereoregularity, if present, was not satisfactorily defined. Kakugo et al. 1b and, more recently, some of us 2 reported the synthesis of stereo- regular, possibly isotactic, ethylene-styrene copolymers. At high styrene content these macromolecules show an alternating structure, due to the absence of styrene- styrene sequences. 2 The X-ray spectra of these high styrene content, crystalline copolymers exhibit patterns which are different from those of polyethylene and polystyrene. 1b,2 In this paper ethylene-styrene copoly- mers obtained with stereospecific and nonstereospecific catalysts are compared with respect to their crystal- lization behavior. Results and Discussion A series of atactic ethylene-styrene (E-S) copolymers have been synthesized with cyclopentadienyltitanium trichloride (CpTiCl 3 ) activated with methylalumoxane (MAO). The E-S copolymer was isolated from the reaction products by extraction with boiling benzene. 1a,h Alternatively, E-S copolymers with stereoregular alternating sequences have been prepared using the rac- (ethylene)bis(1-indenyl)zirconium dichloride (rac-EBI- ZrCl 2 )/MAO catalyst system; 2 with this catalyst, the copolymer is the only reaction product. All the E-S copolymers samples have been analyzed by 13 C NMR. The spectra of copolymers obtained in the presence of the stereospecific and nonstereospecific catalysts are reported in Figure 1. In the samples obtained with the zirconocene-based catalyst (Figure 1a), the signals assigned to the S  carbon (around 23,5 ppm) are not split, which suggests the presence of stereoregular alternating sequences in accordance to refs 1b,g and 3. However, in the spectra of the copoly- mers obtained with CpTiCl 3 (Figure 1b) the S  carbon resonance is split. From the relative intensity of the resonances, the composition of the copolymers and the average length of the methylene sequences can be determined using previously reported relationships. 4 The results of these calculations are reported in Table 1. The styrene content ranges from 12 to 44%; however, one must keep in mind that with these catalysts styrene-styrene insertion is forbidden, and as a consequence, the theo- retical upper limit for the styrene content is 50%. All the copolymers have been also analyzed by wide- angle X-ray scattering. A series of diffractograms of E-S copolymers with increasing styrene content are reported in Figure 2, and for comparison, the diffrac- togram of a sample of high-density polyethylene (HDPE) is also included. At low styrene content (Figure 2b,c) the diffraction patterns, irrespective of the catalyst stereospecificity, are very similar to that of the HDPE (Figure 2a) in accordance with the findings of Kressler et al. 5 Figure 1. 13 C NMR spectra of the aliphatic region: (a) stereoregular E-S sample with 44% styrene molar content (HMDS scale); (b) nonstereoregular E-S sample with 34% styrene molar content. Table 1. Styrene Content, Average Length of Methylene Sequences and DSC Endothermic Peaks of the E-S Copolymers sample catalyst % styrene (mol) L h CH2 mp, °C 1 CpTiCl3 12 16.5 122 2 CpTiCl3 15 11.7 110 3 CpTiCl3 33 5.1 a 4 CpTiCl3 34 5.3 a 5 Et(Ind)2ZrCl2 13 16.2 85-125 b 6 Et(Ind)2ZrCl2 13 14.4 80-125 b 7 Et(Ind)2ZrCl2 15 12.0 75-125 b 8 Et(Ind)2ZrCl2 18 10.4 45-130 b 9 Et(Ind)2ZrCl2 28 6.1 40-80 b 10 Et(Ind)2ZrCl2 32 5.9 60-100 b 11 Et(Ind)2ZrCl2 37 5.1 128 12 Et(Ind)2ZrCl2 37 4.6 128 13 Et(Ind)2ZrCl2 44 3.7 145 a No DSC peaks. b Wide transition range, probably due to the contemporary presence of the crystalline polyethylene homose- quences and of the alternating sequences. 4027 Macromolecules 1998, 31, 4027-4029 S0024-9297(97)01908-6 CCC: $15.00 © 1998 American Chemical Society Published on Web 05/23/1998