Polymerization of polar α-olefin with high activity and high syndiotactic selectivity catalyzed by scandium metal catalyst of fluorene coordination

High functional poly α-olefin can be synthesized from polar α-olefin containing heteroatomic groups by coordination polymerization. These highly functional poly α-olefin materials can obviously improve the non-polar poly α-olefin materials, such as the appearance, printability, adhesion, rheology, compatibility with other polymer materials and blending properties to improve their added value and expand their industrial application range. In this paper, a series of polymer materials with potential application value were prepared with a catalyst of scandium fluorene Flu-Sc(THF)n (CH2SiMe3)2 to achieve high reaction activity (63.1×103g/(molcath)) and high selectivity polymerization (rrrr>99%) of polar α-olefin with different heteroatoms and different chain lengths.


Introduction
Polymer materials are an essential part of modern life.Nowadays polymer materials are mainly prepared by the coordination polymerization of non-polar olefin monomers.However due to the inherent nonpolarity of this kind of material, its practical application is greatly limited, and it is difficult to meet the increasing requirements of people, so people turn their attention to polar olefin polymerization [1][2][3] .The advantage of this kind of polymerization is that the polar groups are directly introduced into the polymer chain, so that the polymer materials meet the requirements of high performance, high function, intelligence, and being green.The natural polarity of the α-olefin polymer makes it possible to achieve good compatibility with other materials, which broadens the application range of materials and meets a variety of needs.Recently, the direct coordination polymerization of polar alpha-olefin has caused a great deal of interest in academic circles [4][5][6] .For instance, Xu et al used a trialkyl rare earth metal catalyst to achieve a variety of polar α-olefin meso-selective polymerization, and prepared the first poly α-olefin with crystallization, but the polymer selectivity is not very good [7] .
In this work, rare earth scandium dialkyl complex with monofluorene coordination is used to achieve high isotropy selective homopolymerization of polar α-olefin with different heteroatoms and different chain lengths (rrrr>99%).On the other hand, polar α-olefin high activity polymerization (63.1×10 3 g/(mol cat h)) is also achieved in the polymerization process.Since the catalyst burst is easily deactivated in air, the preparation of the catalyst and the polymerization of the polar α-olefin with different heteroatoms and different chain lengths are carried out under dry and N 2 -filled conditions.The polar α-olefin monomers [8,9] and Flu-Sc(THF)(CH 2 SiMe 3 ) were prepared according to previous methods [10] (Figures 1 and 2).The rare earth metal catalyst monofluorene scandium was used to polymerize alpha-olefin monomers of different polarities(Figures 3).Through the analysis of the polymerization results, it is found that: (1)  In the polymerization process, compared with the heteroatom oxygen, the activity of the heteroatom sulfur is higher, because the atomic radius S>O, which is more conducive to the interaction between heteroatom and metal (entry 1-2); (2) When the double bond and substituent group are separated by two carbons and methyl groups are substituted on the benzene, the activity of the benzene ring is as follows: para > intersite > ortho.It can be seen that the main effect is steric hindrance, the smaller the size of the polar α-olefin is, the higher the polymerization activity (entry 2-4) will be.(3) When sulfur atoms get more carbon between the double bond, the activity of the double bond decreases, which may be because the steric hindrance becomes larger after coordination (entry 2, entry 5).( 4) Most of the obtained polymers exhibit a high intergauge rrrr>99%.

Discussion
The polymer formed a nearly perfect high syndiotactic structure determined by 13 C NMR spectra, which showed a single peak at 22.5 ppm, indicating high syndiotactic selectivity (Figures 4 and 5).

Conclusion
In this work, rare earth scandium dialkyl-complex with monofluorene coordination is used to achieve a high syndiotactic selective homopolymerization of polar α-olefin with an oxygen and sulfur atoms and with different chain lengths, which shows the highest syndiotactic selectivity (rrrr>99%) achieved so far.It was found that heteroatoms and different chain lengths would affect the polymerization activity, and the polymerization activity was the highest when the heteroatom was a sulfur atom and was separated by two carbon atoms from the double bond.In the following work, we expect to further expand the types of monomers and prepare a series of polymer materials with practical application value.

Figure 2 .
Figure 2. Synthesis of Monomers.Since the catalyst burst is easily deactivated in air, the preparation of the catalyst and the polymerization of the polar α-olefin with different heteroatoms and different chain lengths are carried out under dry and N 2 -filled conditions.The polar α-olefin monomers[8,9] and Flu-Sc(THF)(CH 2 SiMe 3 ) were prepared according to previous methods[10] (Figures1 and 2).