Peroxide-Mediated Alkyl–Alkyl Coupling of Dialkylzinc: A Useful Tool for Synthesis of ABA-Type Olefin Triblock Copolymers

Abstract

A practical and simple method for the preparation of ABA-type olefin triblock copolymers, e.g., PE-b-poly­(ethylene-co-propylene)-b-PE, has been described. The performance of the so-called “coordinative chain transfer polymerization” (CCTP) by sequential feed of ethylene and ethylene/propylene mixed gas generated a Zn-bound diblock copolymer (i.e., (PE-b-poly­(ethylene-co-propylene)­yl)2Zn). Treatment of the Zn-bound diblock copolymer with lauroyl peroxide (CH3(CH2)10C­(O)­O-OC­(O)­(CH2)10CH3) led to a C­(sp3)–C­(sp3) coupling reaction between the two diblock chains bound on the zinc site and an ABA-type olefin triblock copolymer, PE-b-poly­(ethylene-co-propylene)-b-PE, was formed. Upon the treatment with lauroyl peroxide, the number-average molecular weight increased by 1.5–1.7 times. The occurrence of the coupling reaction was verified using a model compound, (Oct)2Zn. The ABA-type triblock copolymer exhibited thermoplastic elastomeric properties and dramatically improved mechanical properties (twice the tensile strength and 10-fold increase in the elongation at break) as compared to the diblock congener.

Polystyrene Chain Growth Initiated from Dialkylzinc for Synthesis of Polyolefin-Polystyrene Block Copolymers

“…The gel permeation chromatography (GPC) data were obtained in 1,2,4-trichlorobenzene at 160 • C using a PL-GPC 220 system equipped with an RI detector and two columns [PLgel mixed-B 7.5 × 300 mm from Varian (Polymer Lab)]. (1-Octyl) 2 Zn and (1-hexyl) 2 Zn were prepared and purified as described in the literature [26]. n-BuLi and sec-BuLi were used as neat oils, while t-BuLi as solid after removing the solvent inside the glove box.…”

“…Moreover, 1 is capable of incorporating a significant amount of α-olefins in an ethylene/α-olefin copolymerization [47]. A minimal amount of MMAO (50 µmol-Al) had to be fed, in addition to the CTA (1-hexyl)2Zn (100 or 200 µmol-Al), to realize the full activity of 1, even though PO chain growth from some Al-sites was unavoidable [26,48,49]. The generated (polyolefinyl)2Zn was treated with t- In contrast, we found that (tBu) 2 Zn was decomposed at 130 • C, and a black solid precipitated when a solution of (tBu) 2 Zn in decane was heated at 130 • C. Isobutene and H 2 signals were detected in the 1 H NMR spectrum when the reaction was performed in a sealed tube in toluene-d 8 (Scheme 2b).…”

“…Moreover, 1 is capable of incorporating a significant amount of α-olefins in an ethylene/α-olefin copolymerization [47]. A minimal amount of MMAO (50 µmol-Al) had to be fed, in addition to the CTA (1-hexyl) 2 Zn (100 or 200 µmol-Al), to realize the full activity of 1, even though PO chain growth from some Al-sites was unavoidable [26,48,49]. The generated (polyolefinyl) 2 Zn was treated with t-BuLi (…”

“…Therefore, it is possible to grow PO chains with a varying ethylene/αolefin composition either, by the sequential variation of ethylene/α-olefin feed ratio or by employing a dual catalytic system with distinctly different monomer reactivities. Thus, we can successfully produce diblock and multiblock copolymers composed of hard crystalline, and soft rubbery PO blocks [22][23][24][25][26].…”

Preparation of Pyridylamido Hafnium Complexes for Coordinative Chain Transfer Polymerization

“…In CCTP performed with I, PO chains are generated as a form of (polyolefinyl) 2 Zn with a rather narrow molecular-weight distribution (M w /M n ≈ 1.7) and with negligible formation of PO chains not attached to Zn sites, owing to a feature of I ensuring the rapid alkyl exchange process and the absence of the β-elimination process [16,18]. Due to these characteristics, it is possible to grow PO chains with variation of ethylene/α-olefin composition, either by sequential variation of the ethylene/α-olefin feed ratio or by means of a dual catalytic system with distinctly different monomer reactivity, enabling commercial production of olefin block copolymers composed of hard crystalline and soft rubbery PO blocks [19][20][21][22][23]. A method has also been developed to grow polystyrene (PS) chains further from the CCTP product (polyolefinyl) 2 Zn, thereby allowing for the synthesis of commercially relevant PO-block-PS and PS-block-PO-block-PS via one-pot synthesis [14,[24][25][26][27].…”