Anionic Ring-Opening Reactive Extrusion Polymerization Of 1,3,5-Trimethyl-1,3,5-Tris (3,3,3-trifluoropropyl) Cyclotrisiloxane (D₃F) And Properties Of Poly [Methyl (Trifluoropropyl) Siloxane]

In this work, Firstly, poly[methyl(trifluoropropyl)siloxane] (PMTFPS) was prepared in the mixing chamber of a Haake torque rheometer using sodium silanolate as the initiator, and ethyl acetate (EA) as the polar regulator to simulate reactive extrusion polymerization of 1,3,5-Trimethyl-1,3,5-Tris(3,3,3-trifluoropropyl) Cyclotrisiloxane(D3F).Results showed that when the polymerization was carried out in the presence of 2.74 wt% initiator and 3.21 wt% EA, at 70℃for 4.0 min, the maximum of number average molecular weight (Mn= 2.51×105) of PMTFPS could be obtained with a higher yield (92.7wt%). Meanwhile there was only less than 0.26 wt% of the cyclic by-products in the polymerization system.The maximum of number average molecular weight (Mn= 2.45×105) of PMTFPS was obtained with high yield (89.2wt%) when the polymerization was carried out in the presence of 2.74wt%initiator and 2.38wt% EA at 120℃for 4.0 min. And there was only 0.74 wt% cyclic by-products in the product.That indicated that the back-biting reaction was almost entirely suppressed.Then on the base of anionic bulk ring-opening polymerization of D3F in the Haake torque rheometer, continual and stable reactive extrusion polymerization of D3F was achieved.It showed that the maximum of number average molecular weight (Mn=2.41×105) of PMTFPS could be obtained with the highest yield (90.5wt%),when the feeding rate of D3F was 3.2 kg/h, the feeding rate of initiator was 0.0125 kg/h, the feeding rate of EA was 0.13 kg/h, the screw speed was 25 r/min.Exorbitant feeding volume of EA and reactive temperature will speed up back-biting and depolymerization reaction,leading to decreasing of Mn and yield of PMTFPS with more cyclic by-products.Finally, reactive extrusion anionic bulk ring-opening polymerization of D3F was achieved and acquired PMTFPS of high number average molecular weight (Mn=2.41×105) and narrow molecular weight distribution(D=1.36) with vinyl functional group using tetramethyl ammonium hydroxide as the initiator in the absence of polar regulator.Propertie test showed that prepared fluorosilicon rubber had excellent oil resistance and nice tear strength.Then copolymerization of D3F and octamethyl cyclotetrasilazane(D4) was studied, indicating that random copolymerization in the short time could be achieved through selecting proper polar regulator and reactive conditions.This will provide a conference of reactive extrusion copolymerization of D3F and D4.Investigations of wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) and thermogravimetic analysis (TGA)showed that PMTFPS was low crystallinity and it could be used in a wide range of operational temperatures. Thermogravimetic analysis(TGA) showed that PMTFPS had good thermal stability and thermal degradation temperature was above 400℃as long as (?) reached 0.77×105. The calculated thermal degradation activiation energy of all the samples was about 136 kJ/mol. It was identified by the thermal degradation activiation energy that the degradative mechanism of PMTFPS with different molecular weight was almost alike.