Copolymerization of propylene with Si-containing α,ω-diolefins: how steric hindrance of diolefins affects long chain branch formation

Abstract

By using pyridylamido-hafnium/[Ph3C][B(C6F5)4]/Al i Bu3 catalytic system, a series of long chain branched isotactic polypropylenes (LCBPPs) were in situ synthesized by copolymerization of propylene with Si-containing monomers 4,4-dimethyl-4-sila-1,6-heptadiene (DMS), 4-methyl-4-phenyl-4-sila-1,6-heptadiene (MPS), 4,4-diphenyl-4-sila-1,6-hepta-diene (DPS), or 4-methyl-4-vinyl-4-sila-1,6-heptadiene (MVS). The effects of the substituent groups on copolymerization behavior and topological structure were further investigated. The substituent groups decreased the cyclization tendency of the diallylsilane, which increased the probability of the insertion of the pendent vinyl groups into other polymer chain. Thus, LCBPPs could be easily prepared under mild conditions by exquisitely controlling comonomer structure and polymerization conditions such as initial concentration of comonomer, the dosage of chain transfer agent (CTA) and reaction time. The presence of LCB structure was confirmed by characterization of SEC equipped with triple detectors, small-amplitude dynamic rheological measurements and uniaxial extension. The introduction of LCBs endowed PP with improved rheological behavior and melt strength, which made the resultant LCBPPs possess potential application in thermal process such as blow molding and foaming. A series of long chain branched isotactic polypropylenes (LCBPPs) were in situ synthesized by copolymerization of propylene with diallylsilanes. The substituent groups can efficiently suppress cyclization of the diolefin and significantly improve LCB formation efficiency during the copolymerization of propylene and diallylsilane.

Long-Chain Branched Polyethylene via Coordinative Tandem Insertion and Chain-Transfer Polymerization Using rac-{EBTHI}ZrCl2/MAO/Al–alkenyl Combinations: An Experimental and Theoretical Study

“…Yet, because of the radical mechanisms involved in these treatments, ample control over LCB formation is rather impossible; hence, polymers with complex structures are obtained in those cases. In-reactor technologies such as copolymerization of ethylene with either in situ-formed or previously isolated macromonomers, , or with a nonconjugated α,ω-diene − have also been developed. Nevertheless, only a limited number of catalyst systems have been shown to efficiently generate and incorporate macromonomers, while the second approach is limited by the rather scarce availability of α,ω-dienes and by the uneven distribution of LCB in the final polymers.…”

Synthesis of Long-Chain Branched Polyolefins by Coordinative Chain Transfer Polymerization

“…LCBs generated via the intermolecular chain transfer process in the radical polymerization of ethylene significantly influence the rheological and mechanical properties, which leads to unique and advantageous properties in LDPEs. − There have been debates and attempts to add LCBs in the coordination polymerization process especially performed using single-site homogeneous catalysts. − A plausible mechanism for LCB generation in the coordination polymerization is the insertion of the polymer chains containing a vinyl end group (−CHCH 2 ) generated via the β-hydride elimination process. However, the main-end groups generated in the ethylene/α-olefin copolymerizations are not the vinyl group; instead, they are the vinylidene (−C­(C)CH 2 ) and/or vinylene (−C­(C)CH−) groups, which are generated via the β-hydride elimination process at the stage of α-olefin insertion.…”

Nonconjugated α,ω-Diolefin/Propylene Copolymerization to Long Chain-Branched Polypropylene by Ziegler–Natta Catalyst: Overcoming Steric Hindrance by Introducing an Extra Electronic Pulling Effect

“…Another synthetic approach to LCB polyolefins is the engagement of nonconjugated α,ω-diolefins as comonomer in olefin polymerization . Released from the requirement of macromonomer intermediate formation, this approach is particularly welcomed in LCB-PP synthesis. − As illustrated in Scheme , with nonconjugation, the two olefin moieties of α,ω-diolefin sequentially follow, in propylene polymerization, a copolymerization path to insert into different PP chains, first with the monomeric α-olefin, then with the intermediate polymeric ω-olefin, forming H-shaped LCB structure. With control of the α,ω-diolefin structure to avoid cyclization and selection of proper catalysts to overcome the high steric hindrance especially in the second step of α,ω-diolefin polymerization (the polymeric ω-olefin polymerization) to form branched structure, a good measure of success has been achieved with the α,ω-diolefin copolymerization chemistry in LCB-PP synthesis.…”

“…For instance, chiral metallocene complexes rac -Me 2 Si­(2-Me-4-Phenyl-Ind) 2 ZrCl 2 /modified methylaluminoxane (MMAO) and rac -Me 2 Si­(2-MeBenz­[e]­Ind) 2 ZrCl 2 /MMAO were combined with high α,ω-diolefins including 1,7-octadiene and 1,9-decadiene in propylene polymerization to synthesize LCB-PP . Nonmetallocene complex dimethylpyridylamido-Hf/[Ph 3 C]­[B­(C 6 H 5 ) 4 ]/Al i Bu 3 was joined by diallylsilanes including 4-methyl-4-vinyl-4-sila-1,6-heptadiene to produce LCB-PP . Chiral metallocene complex rac -Me 2 Si­(2-Me-4-Phenyl-Ind) 2 ZrCl 2 /MAO was also reported to synthesize modified, T-shaped LCB-PP with an exotically structured α,ω-diolefin, p -(3-butenyl)­styrene …”

“…39 Nonmetallocene complex dimethylpyridylamido-Hf/[Ph 3 C][B(C 6 H 5 ) 4 ]/Al i Bu 3 was joined by diallylsilanes including 4-methyl-4-vinyl-4-sila-1,6-heptadiene to produce LCB-PP. 40 Chiral metallocene complex rac-Me 2 Si(2-Me-4-Phenyl-Ind) 2 ZrCl 2 /MAO was also reported to synthesize modified, T-shaped LCB-PP with an exotically structured α,ωdiolefin, p-(3-butenyl)styrene. 41 In modern PP industry, heterogeneous Ziegler−Natta catalysts predominantly in the form of MgCl 2 -supported TiCl 4 adduct (MgCl 2 /TiCl 4 catalysts) are greatly advantageous over metallocene/nonmetallocene catalysts in polymer particle morphology control.…”