Novel Ethylene-siloxane Copolymers Synthesis And Lubrication

Polyolefin is the most widely used general plastics due to its low price and comprehensive performance.However,because of the lack of functional groups,traditional polyolefin products are difficult to meet the increasingly diverse performance requirements.Therefore,the functionalization of polyolefin has great research significance and extensive industrial impact.Silicone is composed of a Si-O backbone and two methyl attached to each silicon atom,thus it has organic-inorganic dual nature.Silicone has excellent molecular chain flexibility,low surface tension and good thermal stability,but its mechanical properties and compatibility with carbon-based materials are poor.If we combine polyolefin with silicone by designing and synthesizing their block or graft copolymers,their advantages such as good mechanical properties,great compatibility with carbon-based materials,excellent chain flexibility and low surface tension could be effectively integrated.Those copolymers are particularly suitable for the composite lubricant of polyolefin processing.This work firstly designed and synthesized three novel ethylene-siloxane copolymers,including silicone-containing ethylene copolymers,polydimethylsiloxane-g-polyethylene copolymers and polyethylene-b-polyhybridsiloxane-b-polyethylene copolymers.Then the copolymers were used as composite lubricant of HDPE processing.The effects of different copolymer structures on the bulk and surface properties of HDPE were systematically examined.The major achievements of this thesis include:(1)A novel type of silicone-containing macromonomer(007)with low polarity was designed and synthesized.Through the copolymerization of ethylene with 007 macromonomer,silicone-containing ethylene copolymer(E-co-007)was successfully prepared.Two catalyst systems-rac-EtInd2ZrCl2/MAO and VCl3(THF)3/Et2AlCl were studied.It was found that the catalyst deactivation of 007 was much lower than that of other kinds of silicone macromonomers.With the increase of 007 addition amount from 80 mmol/L to 280 mmol/L,the comonomer incorporation increased from 1.7 mol%to 5.6 mol%,the weight average molecular weight(Mw)of E-co-OO7 decreased from 22700 g/mol to 10700 g/mol,the molecular weight distribution index(PDI)decreased from 2.6 to 1.7.The thermal analysis showed that with the increase of 007 incorporation,the glass transition temperature of E-co-OO7 became lower(-76.1?-64.0 ?),and the crystallizability of E-co-OO7 became poorer.(2)Novel polydimethylsiloxane-g-polyethylene copolymer(PDMS-g-PE)was synthesized through hydrosilylation reaction of polydimethylhydrogensiloxane with vinyl terminated polyethylene(vPE).With the increase of hydrogen content in polydimethylhydrogensiloxane,the grafted PE branches became more,the molecular weight of PDMS-g-PE became larger(MW was 69800?82900 g/mol,PDI was 2.8?4),the silicone content in PDMS-g-PE became lower(27?46 wt%).The thermal analysis showed that the glass transition temperature of PDMS-g-PE were very low(-124.5?-118.2?).With the decrease of silicone content in PDMS-g-PE,the glass transition temperature of PDMS-g-PE became higher,the crystallizability of PDMS-g-PE became stronger.(3)A series of polyhybridsiloxane(PHSX)with different siloxane chain lengths and similar molecular weights were prepared.By hydrosilylation reaction of PHSX with vPE,novel polyethylene-b-polyhybridsiloxane-b-polyethylene copolymer(PE-b-PHSX-b-PE)was synthesized.The MW of PE-b-PHSX-b-PE were 16100?18700 g/mol,PDI was 1.5?1.7,silicone content was 21?48 wt%.The thermal analysis indicated that with the increase of siloxane chain length in PE-b-PHSX-b-PE,the glass transition temperature of PE-b-PHSX-b-PE became lower(-120.5?-89.0?),the crystallizability of PE-b-PHSX-b-PE became poorer.Phase morphology showed that after annealing,the surface and bulk morphology of copolymer showed lamellar phase separation.(4)The above ethylene-siloxane copolymers were used as composite lubricants for HDPE processing.The results demonstrated that adding small amounts(2%,5%or 10%)of ethylene-siloxane copolymers to HDPE improved the flowability,decreased the elasticity modulus and tensile strength,increased the elongation at break,partly enhanced the notched impact strength,and decreased the surface tension,coefficient of friction and specific wear rate.The block copolymer PE-b-PHSX15-b-PE with longest siloxane segment had best internal and external lubricantion.Compared with HDPE control,the melt flow rate(2.53 g/10min)of the blends(adding 5%PE-b-PHSX15-b-PE)was 81%higher,the water contact angle(106°)was 18%higher,the coefficient of friction(0.047)was 35%lower and thespecific wear rate(5.2×10-3 mm3/Nm)was 53%lower.Compared to conventional lubricants(siloxane masterbatch or polyethylene wax),ethylene-siloxane copolymers had comprehensive advantages in internal and external lubrication,mechanical properties,and thermal stability.