Isospecific polymerization of vinyl ethers with titanium catalysts containing modified tridentate anionic donor ligands

Abstract

BACKGROUND: Stereo‐regulated polymerization of vinyl ethers (VEs) assumes significance because of its elegance and the resultant unique polymer properties. Although several Lewis acid catalysts polymerize VEs with good control of molecular weight, achieving stereo‐regularity is quite challenging. There are literature reports of a few catalyst systems capable of producing highly isotactic poly(vinyl ether) (PVE) only at lower temperatures with the polymer becoming atactic with an increase in reaction temperature. Hence innovating new catalyst systems which can produce highly stereo‐regular PVEs with high molecular weight at ambient temperature is quite challenging. RESULTS: We used two different titanium pre‐catalysts (1‐TiCl2 and 2‐TiCl2) for the polymerization of VEs. These pre‐catalysts in combination with methylaluminoxane (MAO)/borate polymerized VEs in higher conversions. Highly isotactic poly(n‐butylvinyl ether) (PBVE; 75% dyad isotactic ratio) was obtained with 1‐TiCl2/MAO at ambient temperature. CONCLUSION: We synthesized unimodal and highly isotactic PBVE with molecular weights of the order of 105 g mol−1 using the non‐metallocene‐type single‐site catalyst system 1‐TiCl2/MAO even at ambient temperature. The symmetry around the metal centre in the pre‐catalyst and the polymerization temperature played a major role in controlling the stereo‐regularization of the olefin inserted. Copyright © 2009 Society of Chemical Industry

Recent Developments on Cationic Polymerization of Vinyl Ethers

“…After that, their group modified the ligand structures to manipulate the steric hindrance and the electronic nature of the metal complexes to control stereoregularity in n -butyl vinyl ether (nBVE) polymerizations. The obtained polymers at or around ambient temperature were highly stereoregular. , In recent years, various endeavors have been undertaken to regulate tacticity in cationic polymerization, resulting in the successful production of stereoregular polymers.…”

“…The obtained polymers at or around ambient temperature were highly stereoregular. 34 , 35 In recent years, various endeavors have been undertaken to regulate tacticity in cationic polymerization, resulting in the successful production of stereoregular polymers.…”

Statistical Copolymers of n-Butyl Vinyl Ether and 2-Chloroethyl Vinyl Ether via Metallocene-Mediated Cationic Polymerization. A Scaffold for the Synthesis of Graft Copolymers

“…PVEs have been polymerized using titanium, zirconium and hafnium complexes by Sudhakar [9] and Masuda [10], however, in these cases polymers of broad molecular distributions and in less than quantitative yields were obtained. Group 4 metallocene and half-metallocene complexes have been employed as homogenous polymerization catalysts in the presence of suitable cocatalysts, resulting in products with unique control over the molecular and structural characteristics [11].…”

Highly Stereoselective Living Polymerization of Vinyl Ethers at Ambient Temperature Mediated by Chiral Titanium Complexes

“…We have already established the ability of aminotriolate-based titanium chlorides with C 3 and pseudo-C s symmetry and modified aminodiolate titanium dichlorides with pseudo-C 2 and pseudo-C s symmetry as effective catalysts for ethylene, a-olefin, [9, 10] and n-butyl vinyl ether (BVE) polymerizations. [11] Literature precedence for the use of titanatranes as olefin polymerization catalysts is very limited. [12] We previously developed a series of titanium precatalysts (Figure 1) for the polymerization of linear a-olefins; [10] [1-TiCl] and [2-TiCl] showed moderate activity whereas [3-TiCl 2 ] and [4-TiCl 2 ] showed very good activity with living behavior.…”

“…These results were supported by our earlier work on BVE polymerization using [N{CH 2 CH(Ph)(Ts)N} 2 TiCl 2 ] and [N{CH 2 CH(Ph)O} 2 TiCl 2 ], which polymerized vinyl ether upon activation with MAO or borate by the carbocationic mechanism. [11] We are further exploring the possibility of copolymerization of vinyl ethers because of the excellent properties of the polymers produced. [14] In summary, stereoregularity during BVE polymerization could be obtained by suitable modification of the parent ligand attached to the metal center and the cocatalyst used.…”