Jin-Yong Dong

Facile synthesis of chain end functionalized polyethylenes via epoxide ring-opening and thiol–ene addition click chemistry

A wide range of low-molecular-weight, narrow-molecular-weight-distribution chain end functionalized polyethylenes (Cef-PEs), including hydroxyl-, amino-, carboxyl-, sulfo-, chloro-, azide- and trimethoxysilane-terminated polyethylenes, were synthesized under mild conditions via epoxide ring-opening and thiol–ene addition reactions with epoxy- and vinyl-terminated PEs as starting materials, respectively. The selectivities of the functionalizations were excellent. Similarly, amphiphilic polyethylene-block-poly(ethylene glycol) copolymer (PE-b-PEG) was prepared for the first time by simply treating epoxy terminated PE with hydroxyl terminated PEG and potassium hydroxide. A unique combination of primary (hindered-phenol) and secondary (thioester) antioxidants was introduced into the chain end of PE via successive thiol–ene addition and transesterification reactions. All Cef-PEs were characterized unambiguously by NMR, GPC, DSC and FTIR.

Synthesis of low dispersity star-like polyethylene: a combination of click chemistry and a sol–gel process

Low dispersity star-like polyethylene with a “silica” core was synthesized via a simple yet efficient sol–gel process using trimethoxysilane-terminated polyethylene, which was prepared using radical-mediated thiol-ene click chemistry between low molecular weight vinyl-terminated polyethylene and (3-mercaptopropyl)trimethoxysilane.

Fabrication of long chain branched polypropylene using click chemistry

This article presents a new method to produce LCBPP with well-defined structures via Huisgen’s 1,3-dipolar cycloaddition of azide and alkyne (click reaction). Azide-terminated isotactic polypropylene (iPP) (iPP-St-N3) was synthesized via the hydrochlorination and subsequent substitution of the starting styryl-terminated i-PP (i-PP-t-St), which is the product of a metallocene-mediated isospecific propylene polymerization governed by a controlled chain transfer reaction. Alkyne-grafted iPP (iPP-g-≡) can be produced with high efficiency through one-pot esterification and the subsequent amidation of hydroxyl-functionalized iPP. Detailed analysis of the product by 1H NMR, FTIR, DSC, and GPC reveals a clean and clear formation of LCBPP.

Recent key developments in isotactic polypropylene in-reactor alloy and in-reactor nanocomposite technology

Alloying and nanocompositing are two most effective techniques by which isotactic polypropylene (iPP), one of the most promising polymers of the 21st century, can be endowed with high performance for ever-demanding high-end applications. Thanks to the continuous advancement of catalyst technology, the technological trend for iPP alloy and nanocomposite fabrication has been projected to be in-reactor synthesis, the performance and economic advantages of which are beyond doubt. In this paper, we review two recent key developments in the iPP in-reactor alloy and in-reactor nanocomposite technology in our laboratory that will have profound influence on the continuing development of the prestigious iPP modification art. The first is the simultaneous EPR (ethylene-propylene random copolymer) cross-linking chemistry for controlling its physical growth pattern during in-reactor alloying, which helps to remove the compositional cap on EPR that so far greatly limits the iPP in-reactor alloying technique. The second is the nanofiller support fabrication strategy for simultaneously controlling both the phase morphology of the nanofiller dispersion and the polymer particle granule morphology of synthesized nanocomposites, which resolves the critical scale-up issue surrounding the iPP in-reactor nanocompositing technique. Based on these new developments, new advancements of iPP materials are envisaged.

Precision Polyolefin Nanoalloy Polypropylene/Poly(ε-caprolactone).

This communication reports the first example of precision polyolefin nanoalloys where an exotic immiscible polymer is nanometrically dispersed with stability in a polyolefin matrix in a highly controlled mode. Following the preparation of polypropylene/multiwalled carbon nanotubes nanocomposites (PP/MWCNTs) by in situ Ziegler-Natta polymerization, the hydroxyl groups on the surfaces of individual MWCNTs are used to initiate ring-opening polymerization of ε-caprolactone, resulting in PP/poly(ε-caprolactone) (PCL) alloy with PCL grafted on MWCNTs. Upon phase formation, the PP/MWCNTs-g-PCL alloys exhibit a unique PCL dispersion morphology, which is stable and solely governed by PCL molecular weight.

Synthesis of styryl-capped polypropylene via metallocene-mediated coordination polymerization: Apply to polypropylene macromolecular engineering

In this paper, we review our recent progress in the synthesis and application of styryl-capped polypropylene (PP-t-St), an excellent reactive polyolefin that is both convenient and efficient in synthesis and facile and versatile in application for preparing advanced polypropylene materials via macromolecular engineering. The synthesis of PP-t-St is made possible by a unique chain transfer reaction coordinated by a bis-styrenic molecule, such as 1,4-divinylbenzene (DVB) and 1,2-bis(4-vinylphenyl)ethane (BVPE), and hydrogen in typical C2-symmetric metallocene (e.g.rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2, in association with methylaluminocene, MAO) catalyzed propylene polymerization. The regio-selective 2,1-insertion of the styrenic double bond in DVB or BVPE into the overwhelmingly 1,2-fashioned Zr-PP propagating chain enables substantial dormancy of the catalyst active site, which triggers selective hydrogen chain transfer that, with the formed Zr-H species ultimately saturated by the insertion of propylene monomer, results in an exclusive capping of the afforded PP chains by styryl group at the termination end. With a highly reactive styryl group at chain end, PP-t-St has been used as a facile building block in PP macromolecular engineering together with the employment of state-of-the-art synthetic polymer chemistry to fabricate broad types of new polypropylene architectures.

Dialkylzinc Compounds as Chain Transfer Agents in Ethylene and Propylene Polymerizations Catalyzed by Metallocene Catalysts

Dialkylzinc compounds (ZnR2) with the alkyl groups of different steric hindrance were used as chain transfer agents in ethylene and propylene polymerizations catalyzed by two conventional metallocene catalysts including rac-Et(Ind)2ZrCl2 and rac-Me2Si[2-Me-4-Ph-Ind]2ZrCl2. In general, catalyst activities for ethylene polymerizations are barely affected by chain transfer agents, regardless of the R type; however, there are significant activity reductions in propylene polymerizations when the R in ZnR2 is less hindered, and as R becomes bulkier, catalyst activities are gradually restored. ZnR2 and metallocene catalyst active site tend to form a reversible and catalytically inactive complex, thus the geometry congested ZnR2 would reduce complex formation tendency and hence decreased its negative effect on catalyst activities.

Compatible Polyethylene/Polyvinyl Chloride Particle Hybrids Prepared by in‐situ Polymerization

Polyethylene/polyvinyl chloride (PE/PVC) hybrids were successfully prepared by a polymerization‐filling method. The catalyst for ethylene polymerization was supported on PVC particles, and ethylene was then polymerized in‐situ on the surface of the activated PVC. PVC particles could be well segmented and dispersed during in‐situ polymerization, and the prepared hybrids had an additional tangent peak between the glass transitions of polyethylene and PVC, indicating the formation of a compatible interlayer between nascent polyethylene and PVC during polymerization.

New effort to synthesize star isotactic polypropylene

This study demonstrates an efficient arm-first approach for the synthesis of star isotactic polypropylene (iPP) via two steps. In the first step iPP “arm” containing a methoxysilane-terminal end was prepared via a designed chain-capping reaction in propylene polymerization, and in the second step an acid-catalyzed intermolecular elimination reaction was carried out between methoxysilane groups at these “arm-ends”, finally giving star polymers with iPP as the arm and Si–O–Si cross-linking structure as the core. Moreover, the arm number could be tailored from 3 to 8 by adjusting the star-forming (cross-linking) reaction time. The chemical structures of “arm” and star polymers were monitored by 1H-NMR, and the star-topological structure evolution was investigated via gel permeation chromatography incorporating a light scattering detector (GPC-LS). The star polymers’ absolute molecular weights as well as their dilute solution properties including the intrinsic viscosity ([η]) and the Mark–Houwink exponent (α) were determined by GPC-LS, confirming the successful synthesis of star iPPs.

Comonomer-induced stereo-selectivity enhancement in a c2 -symmetric metallocene-catalyzed propylene polymerization.

Propylene polymerization is carried out with a C 2 -symmetric metallocene catalyst of rac-Et(Ind)2 ZrCl2 /MAO at 40 °C in the presence of a cyclo-triene of trans,trans,cis-1,5,9-cyclododecatriene ((E,E,Z)-CDT). Comonomer incorporations are rather low (<0.10 mol%). However, it is shown for the first time that the comonomer causes a noticeable increase in poly-propylene -isotacticity (>7% in [mmmm]). (E,E,Z)-CDT is speculated to coordinate to the metal center forming comonomer-complexed active sites in charge of the entire polymerization reaction with decreased activity however increased propylene -enantiomorphic selectivity.