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Novel Polyethylene-based Block & Graft Copolymes: Synthesis And Characterization

Posted on:2017-05-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z X XuFull Text:PDF
GTID:1221330482476467Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
Polyolefins are widely used in industrial and agricultural production and people’s life due to their excellent mechanical properties and superior processability as well as abundant resource and low cost. However, the profits of production of general polyolefin resins are getting lower along with the high maturity of the industrialization of polyolefins. In addition, the emergence of new application fields urgently calls for more sophisticated requirements on the performance of polyolefin, the traditional products of which cannot meet the growing demand of various applications. Therefore, currently the development of novel polyolefin materials with high performance and high added value is imperative. On the basis of the original excellent properties of polyolefins, the functionalization of polyolefins can not only make up for the inherent defects of nonpolar polyolefin materials and endow them with new and special functions, but also can improve the performance of polyolefins and other polymers, thus expanding the application fields of polyolefins.Aiming at the controlled preparation of novel functional polyethylene-based block and graft copolymers, the well-defined polyethylene-b-polydimethylsiloxane (PE-b-PDMS) diblock copolymers, polyethylene-b-polyurethane-b-polyethylene (PE-b-PU-b-PE) triblock copolymers and polynorbornene-g-polyethylene (PNB-g-PE) graft copolymers were synthesized in this thesis and the application of block copolymers as compatibilizers in polyolefin blends were also investigated. The following four parts are included:(1) Synthesis and characterization of end-functionalized polyethylenes via the combination of coordination polymerization and radical initiated thiol-ene click chemistry. In the presence of dried methylaluminoxane (dMAO), a phenoxycyclopentylimine ligated zirconium complex (PTFI), bis[N-(3-tert-butylsalicylidene)cyclopentyl aminato]zirconium(IV) dichloride, was used as the precatalyst for the preparation of vinyl end-terminated polyethylenes (PE-ene) under 1 atm of ethylene pressure. The molecular weight (940~1840 g/mol) of PE-ene gradually decreased along with the increase of reaction temperature from 10 to 55℃, while the corresponding molecular weight distribution substantially remained unchanged (2.2~2.4). The crystallinities of the obtained linear PE-ene products ranged in 70~81% with high melting temperature (126.1~128.3℃) and the chain end functionality of PE-ene was found to be nearly 100%. The thiol-ene click reactions subsequently took place between PE-ene and 3-mercaptopropionic acid to afford the carboxyl-terminated polyethylenes (PE-COOH). The click reaction was optimized by varying the reaction conditions, such as temperature, reaction time, type of solvent, amount of initiator and ratio of thiol/double bond. The PE-ene could be converted into PE-COOH quantitatively under the optimized conditions. In addition, the hydroxyl-terminated polyethylenes (PE-OH) with nearly 100% end-functionality were also obtained through the thiol-ene click reactions between PE-ene and 2-mercaptoethanol.(2) Synthesis and characterization of PE-b-PDMS diblock copolymers. The PE-b-PDMS diblock copolymers were prepared through the esterification reactions between monohydroxy-terminated poly(dimethylsiloxane) (PDMS-OH) and PE-COOH. The diblock copolymers had the Mn in the range of 5870 to 6800 g/mol with the mass fraction of PDMS segment ranging from 72.5% to 83.1%. Moreover, the PE-b-PDMS diblock copolymers have been evaluated as compatibilizers in the blends of high-density polyethylene (HDPE) and silicone oil. The mechanical properties demonstrated that the compatibilized blends with low loading concentration of PE-b-PDMS (HDPE/silicon oil/PE-b-PDMS=100/3/1) displayed the significant improvements in modulus of elasticity (increased from 1476 MPa to 2210 MPa) and elongation at break (increased from 65% to 455%) as compared to the uncompatibilized binary blends.(3) Synthesis and characterization of PE-b-PU-b-PE triblock copolymers. The PE-b-PU-b-PE triblock copolymers were produced by the coupling reaction between polyurethane prepolymer (OCN-PU-NCO) with PE-OH and well characterized. The chain lengths of both PE and PU segments could be well controlled (Mn=7950~ 9580 g/mol, PDI=2.0~2.4, wPE=20.3%~39.5%). The thermal analysis indicated that the large amorphous PU phase could perturb the crystallinity of PE segments and the thermal stability of EUE triblock copolymers increased along with the increase in PE weight fraction. The TEM micrographs of EUE triblock polymers showed an apparent micro-phase separation. Additionally, the PE-b-PU-b-PE triblock copolymers have been evaluated as compatibilizers in the polymer blends of HDPE and TPU. The research results showed that the compatibility of the immiscible blends was enhanced greatly after the addition of EUE triblock copolymers.(4) Synthesis and characterization of PNB-g-PE graft copolymers. The macromonomer (PE-NB) was firstly prepared via the esterification reaction between norbornene-6-carbonyl chloride and PE-OH. Both random and block PNB-g-PE graft copolymers were produced by ring-opening metathesis polymerization (ROMP) of norbornene with PE-NB in the presence of Grubbs’ 2st generation catalyst and well characterized. The conversion of monomers was found to be nearly 100% in random copolymerization and the random graft products were obtained with the Mn of 17.9~ 31.4 kg/mol and relatively narrow molecular weight distribution (2.1~2.6). The mass fraction of PE in random copolymers ranged from 4.6% to 16.8%. However, the conversion of macromonomer reached about 80% in block copolymerizaiton. Due to the steric hindrance, the crystallinity of the graft copolymer was slightly lower than the corresponding PE precursor.
Keywords/Search Tags:polyethylene, thiol-ene click chemistry, block copolymers, graft copolymers, ROMP
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