Employing (half‐)titanocene complexes as initiators for the synthesis of end‐functionalized polylactides by coordination polymerization

Abstract

Seven (half‐)titanocene alkoxide complexes, [Cp2TiCl(OEt)], [Cp2TiCl(O‐2‐Bu)], [Cp2TiCl(OCH2CF2CF2H)], [CpTiCl2(OEt)], [CpTiCl2(O‐(S)‐2‐Bu)], [CpTiCl2(OCH2CF3)], and [Cp2TiCl(OCH2CF3)], were synthesized and employed in lactide coordination polymerization. These organotitanium (IV) compounds proved to be very efficient initiators for the ring‐opening polymerization of enantiomeric l‐lactide and racemic mixture of rac‐lactide, leading to end‐functionalized polymers. Kinetic studies illustrated that these compounds produce well‐defined polymers in a controlled manner. This was further demonstrated by synthesizing poly(l‐lactide‐b‐hexyl isocyanate) diblock copolymer. The effect of the alkoxy end groups on the thermal behavior of the polymers was also studied by thermogravimetric analysis and differential scanning calorimetry. The polymers were characterized using size exclusion chromatography and proton nuclear magnetic resonance spectroscopy. The optical properties of the diblock copolymer were also investigated. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2192–2202

Synthesis and characterization of statistical and block copolymers of n‐hexyl isocyanate and 2‐chloroethyl isocyanate via coordination polymerization

“…TGA was employed to study the thermal stability of all the products. The kinetics of thermal decomposition of the homopolymers and the statistical copolymers, were also investigated by conducting TGA and DTG measurements under different heating rates (3,5,7,10,15, and 20 C/ min). TGA and DTG thermograms of the homopolymer PClEtIC, the statistical copolymer S50/50 and the block copolymers are presented in Figures 12-14.…”

Radical and Ring-Opening Polymerizations with Aryl-Substituted Methylene-Bridged Titanium Bisphenolates

“…Likewise, Cp and substituted Cp Ti alkyl/aryloxides including (RCp)TiCl 2 -OMe, 88a IndTiCl 2 -OMe, 88b Cp*Ti(O-C(CH 3 ) 2 -R) 3 , 89 CpTi( i OPr) 3 , 71 Cp 2 TiCl-OR, and CpTiCl 2 - 90 as well as Te(4-Me-6-t Bu-C 6 H 2 -O-) 2 TiCp*Cl 81b and 2,2′-CH 2 (4-Me-6-t Bu-C 6 H 2 -O-) 2 Ti(RCp)Cl (R = H, Me 5 /Cp*, Si(CH 3 ) 2 -Cl), 91a were employed in ROPs and coordination polymerizations, whereas substituted chiral ((R*Cp)Ti(OR) 3 , (R*Cp)Ti(OR) 2 Cl, and (R*Cp)Ti(OR)-Cl 2 ) 92 ular R = polystyrene or polynorbornene were only evaluated for α-olefins. 93 Here, both experimental data and modeling 94 indicate that in homoleptic alkoxide systems, the initiator efficiency (IE, the fraction of initiator molecules that actually initiate the polymerization) decreases with increasing steric crowding, i.e., Ti(O n Pr) 4 > Ti(O n Bu) 4 > Ti(2-ethylhexyloxide) 4 > Ti(O t Bu) 4 .…”

“…Likewise, Cp and substituted Cp Ti alkyl/aryloxides including (RCp)­TiCl 2 -OMe, IndTiCl 2 -OMe, Cp*Ti­(O-C­(CH 3 ) 2 -R) 3 , CpTi­( i OPr) 3 , Cp 2 TiCl-OR, and CpTiCl 2 -OR (R = -CH 2 -CH 3 , -CH 2 -CH­(OH)-CH 2 -CH 3 , -CH 2 -CF 3 , -CH 2 -CF 2 -CF 2 H), as well as Te­(4-Me-6- t Bu-C 6 H 2 -O-) 2 TiCp*Cl and 2,2′-CH 2 (4-Me-6- t Bu-C 6 H 2 -O-) 2 Ti­(RCp)Cl (R = H, Me 5 /Cp*, Si­(CH 3 ) 2 -Cl), were employed in ROPs and coordination polymerizations, whereas substituted chiral ((R*Cp)­Ti­(OR) 3 , (R*Cp)­Ti­(OR) 2 Cl, and (R*Cp)­Ti­(OR)­Cl 2 ) alkyl/aryloxides were tested in the stereospecific polymerization of lactides. Cp*Me 2 Ti-OR with macromolecular R = polystyrene or polynorbornene were only evaluated for α-olefins …”

“…Thus, we anticipate that many L n TiCl/OR precursor complexes currently used in coordination polymerizations and other reactions − ,− may show promise in CRPs and LROPs in conjunction with Zn, epoxides, or other initiators. Indeed, while typical L n TiCl m systems may require the conversion of the Cl to an OR ligand to initiate LROP, the reaction of L n Ti­(III) • radicals with epoxides or aldehydes provides well-defined Ti alkoxides that accordingly afford more well-defined polymers vs metal alkoxide aggregates.…”

Poly{dl‐lactide‐b‐[oligo(ethylene glycol) methyl ether (meth)acrylate)]} block copolymers. Synthesis, characterization, micellization behavior in aqueous solutions and encapsulation of model hydrophobic compounds

“…The biodegradation (hydrolysis) of these materials in physiological medium produces the nontoxic lactic acid, which participates in the Krebs cycle and is eliminated by the human body as water and carbon dioxide eventually. [5] Ring opening polymerization (ROP) of lactides using specific metal complexes [6] or organic catalysts [7] with (macro) initiators leads to the preparation of well-defined (co)polymers. One of the most studied systems by our team [8][9][10][11][12] and others [13][14][15][16][17] is stannous octoate Sn(oct) 2 /alcohol, which was also employed in this study.…”