Synthesis of polypropylene-graft-norbornene by reactive extrusion and its rheological behavior
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Research Letter
Synthesis of polypropylene-graft-norbornene by reactive extrusion and its rheological behavior Zhenghui Li, Lu Chen, and Peijie Yu, School of Materials and Chemical Engineering, Ningbo University of Technology, Ningbo, Zhejiang, China Lingli Zhang, Ningbo College of Health Sciences, Ningbo, Zhejiang, China Hongyu Hu, Xingzhi College Zhejiang Normal University, Jinhua, Zhejiang, China Address all correspondence to Hongyu Hu at [email protected] (Received 5 May 2020; accepted 17 June 2020)
Abstract To overcome the steric effect of norbornene (NB), first-generation Grubbs’ catalyst (GC1) was used as the catalyst to graft NB onto the polypropylene (PP) chain by reactive extrusion. Instead of harsh reaction conditions, such as anhydrous, which was the general method to synthesize NB polymers, this convenient method would be easier to industrialize. The mechanism of grafting was studied by using Fourier Transform InfraRed spectra and differential scanning calorimetry. It was found that GC1 could initiate the ring-opening metathesis polymerization of NB to obtain short NB chain-grafted PP-g-NB. The rheological behavior showed that the grafted NB short chains on PP-g-NB increase the shear thinning of the polymers and decrease the system viscosity.
Introduction Polypropylene (PP) is one of the largest commodity plastic materials benefiting from its relative high tensile strength, low mechanical performance, chemical resistance, and economic benefit. However, some of its properties, such as heat resistance, low melt strength, polarity, and compatibility with other materials, should be improved to expand its application.[1] Functionalized PP by grafting unsaturated monomers onto the PP chain has been prepared successfully by using solution, melt, and solid-state routes. Among them, the melt process has widely been used in the industry owing to its economic and operational advantages.[2,3] Norbornene (NB) is a bicyclic molecule containing a double bond. It can be polymerized by vinyl addition polymerization or ring-opening metathesis polymerization (ROMP),[4,5] which makes it an interesting monomer. ROMP of NB can produce unsaturated rubbery polymers and photolithography materials, which can be used in oil-spill recovery and sound barriers.[6,7] On the other hand, vinyl addition polymerization, which will not destroy NB’s strained bicyclic structure, therefore can impart its rigidity to the polymer chains. Thus, the homo- and co-polymers would have the benefits of high-glass transition temperature (Tg), high thermal stability, low birefringence, and high transparency.[6,8] Thus, NB is an excellent monomer to modify PP or other olefin. However, due to NB’s steric effect, a traditional free radical initiator could not synthesize copolymer of NB and PP. The strategy has been executed by using metal catalyst or coordination catalysts in miniemulsion polymerization, catalytic insertion polymerization, and coordination polymerization.[9] Nomura et al.[10] and
Hasan et al.[11] successfully synthesized NB and ethylene c
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