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

Abstract

Polyolefins (POs) are the most abundant polymers. However, synthesis of PO-based block copolymers has only rarely been achieved. We aimed to synthesize various PO-based block copolymers by coordinative chain transfer polymerization (CCTP) followed by anionic polymerization in one-pot via conversion of the CCTP product (polyolefinyl)2Zn to polyolefinyl-Li. The addition of 2 equiv t-BuLi to (1-octyl)2Zn (a model compound of (polyolefinyl)2Zn) and selective removal or decomposition of (tBu)2Zn by evacuation or heating at 130 °C afforded 1-octyl-Li. Attempts to convert (polyolefinyl)2Zn to polyolefinyl-Li were unsuccessful. However, polystyrene (PS) chains were efficiently grown from (polyolefinyl)2Zn; the addition of styrene monomers after treatment with t-BuLi and pentamethyldiethylenetriamine (PMDTA) in the presence of residual olefin monomers afforded PO-block-PSs. Organolithium species that might be generated in the pot of t-BuLi, PMDTA, and olefin monomers, i.e., [Me2NCH2CH2N(Me)CH2CH2N(Me)CH2Li, Me2NCH2CH2N(Me)Li·(PMDTA), pentylallyl-Li⋅(PMDTA)], as well as PhLi⋅(PMDTA), were screened as initiators to grow PS chains from (1-hexyl)2Zn, as well as from (polyolefinyl)2Zn. Pentylallyl-Li⋅(PMDTA) was the best initiator. The Mn values increased substantially after the styrene polymerization with some generation of homo-PSs (27–29%). The Mn values of the extracted homo-PS suggested that PS chains were grown mainly from polyolefinyl groups in [(polyolefinyl)2(pentylallyl)Zn]−[Li⋅(PMDTA)]+ formed by pentylallyl-Li⋅(PMDTA) acting onto (polyolefinyl)2Zn.

Styrene Moiety-Carrying Diorganozinc Compound Preparation for Polystyrene-Poly(ethylene-co-1-hexene)-Polystyrene Triblock Copolymer Production

“…These chains are ended with styrene moieties at one end and anchored to Zn atoms at the other end. An anionic initiator pentylallyl-Li·(PMDTA) (2.50 mmol) and styrene monomer (80–110 g) were sequentially fed in one-pot to allow the growth of PS chains from not only the Zn–C sites but also the styrene moieties . Using this procedure, we prepared triblock copolymer PS- block -poly­(ethylene- co -1-hexene)- block -PS (SEHS) on a 300-g scale.…”

“…Dispersity of PO chains generated during CCTP step was acceptably narrow considering the value observed for the sample produced in a continuous pilot plant with the same pyridylamido Hf catalyst ( M w / M n 1.9 vs 1.7) . Dispersity of the PS chains generated during anionic polymerization step was also acceptably narrow considering the value observed for the PS samples prepared during styrene polymerization performed with pentylallyl-Li·(PMDTA) initiator in the presence of (hexyl) 2 Zn ( M w / M n 1.56 vs 1.30) . It might be intrinsically impossible to make the dispersity of SEHS as narrow as that of the commercial-grade SEBS ( M w / M n 1.8 vs 1.1), even though M w value of SEHS was made close to that of the commercial-grade SEBS (161 kDa vs 139 kDa).…”

“…CCTP is a matured technology that is actively used in olefin polymerization reactions requiring precise architectural design and end-group functionalization. − CCTP was eventually used in the industry for the production of olefin block copolymers composed of hard crystalline and soft rubbery PO blocks. − The best-reported catalyst for CCTP is the pyridylamido Hf complex, with which the β-elimination process and thus the formation of PO chains not attached to Zn sites can be inhibited. − We found an anionic initiator that allowed PS chain growth from diorganozinc compounds. When styrene polymerization was performed in the presence of diorganozinc compounds and special organolithium compounds [e.g., pentylallyl-Li·(PMDTA) or Me 3 SiCH 2 –Li·(PMDTA), where PMDTA is pentamethyldiethylenetriamine, i.e., Me 2 NCH 2 CH 2 N­(Me)­CH 2 CH 2 NMe 2 ] in methylcyclohexane, PS chains could efficiently be grown from the diorganozinc compounds …”

Preparation of Pyridylamido Hafnium Complexes for Coordinative Chain Transfer Polymerization

“…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].…”

Design of selective divalent chain transfer agents for coordinative chain transfer polymerization of ethylene and its copolymerization with butadiene

“…As a controlled polymerization technique, CCTP potentially allows the production of end-functional polyolefins, 17–19 telechelic polyethylenes, 20,21 and block copolymers. 22–27 Employing a polymetalated CTA based on zinc, Lee and coll. took the advantage of CCTP to control the copolymerization of ethylene with propylene using a pyridylamido hafnium complex.…”