Design And Tailoring Of Polyolefin Elastomers

Polyolefin is the the largest polymeric chemical in the world,indispensable to the national economy and daily life.Developing polyolefin thermoplastic elastomers(POE)and other high-performance materials is thus crucial to the progression of the polyolefin industry in China.Precise tailoring the polymer chain structure is an effective way to afford POE with special and value-added properties.Therefore,this project aims to design and manipulate the POE chain structure,and address the demand the clean solar energy demand of long-life photovoltaic cells,starting with the design of POE through the batch and continuous solution polymerization of ethylene,1-octene with 1,9 decadiene,5-vinyl-2-norbornene and 5-ethylidene-2-norbornene.The effects of different polymerization conditions and methods on the POE chain structure and the resulted PV encapsulant performance were investigated.To tailor the composition of olefin copolymers for enhanced temperature resistance and mechanical properties modelguided oligomerization catalyst feeding strategy in ethylene tandem polymerization was employed.It enables the precise synthesis of ethylene/1-hexene copolymers with the same cumulative composition and different copolymer composition distributions;and investigates the regulation of the oligomerization catalyst feeding strategy on the performance of tandem products.Given the lack of high-temperature catalysts for olefin polymerization and the interaction between two catalysts in the tandem polymerization process,covalent organic framework materials(COF)supported polymerization catalysts were used to investigate the influence of the supporting method on the tandem catalytic-polymerization,and to achieve isolation between catalysts through the confinement effect.The main achievements and innovations of this thesis are:(1)Ethylene/1-octene copolymer POE with suspended double bonds for PV cell encapsulation was synthesized.It exhibited a crystallinity of 7.6～26.7%and a melting index of about 20 g/10 min,meeting the PV cell encapsulation requirements.The POE prepared by continuous solution polymerization has a thinner lamellar thickness,a more uniform lamellar distribution and narrower sequence length distribution.(2)The vinyl-containing POE significantly shortened the encapsulation processing time while reducing the amount of curing agents and without the use of curing coagents.The mechanical,optical,electrical,heat and aging resistance properties of the POE samples prepared by inserting the diene monomer 1,9 decadiene into the main chain meet the requirements for industrial use.(3)A synthesis technique based on a model-guided oligomerization catalyst feeding strategy was developed to tailor copolymer composition.A tandem catalyticpolymerization kinetic model was used to guide the stepwise feeding of the oligomerization catalyst to tailor the ethylene/1-hexene copolymer with a cumulative copolymer composition of 5.7 mol%and different composition distributions using ethylene as the sole monomer.The model-guided customized copolymers showed an increase in melting point from 104.5℃ to 121.0℃ and increased tensile strength and elongation at break of 11.8 MPa and 55%,respectively,compared to the copolymers obtained with a single addition of the oligomerization catalyst.(4)Covalent organic framework materials(COF)supported olefin polymerization catalysts were developed.Covalent organic framework materials with hydroxyl groups treated with dry methylaluminoxane(COF@dMAO)were used for in situ supporting of tandem system oligomerization catalysts(SNS-Cr),which effectively suppressed the mutual interference between SNS-Cr and copolymerization catalysts,increased the molecular weight of ethylene/1-hexene copolymers,and had mechanical properties comparable to those of ethylene/1-hexene random copolymers.