Study On Anionic Bulk Ring-opening Mechanism And Reactive Processing Polymerization Of 1,3,5-Tris (Trifluoropropylmethyl) Cyclotrisiloxane

Poly[methyl (3,3,3-trifluoropropyl) siloxane] (PMTFPS) was synthesized using 1,3,5-tris (trifluoropropylmethyl) cyclotrisiloxane (F3) as monomer and sodium silanolate as initiator in a mixing chamber of a haake torque rheometer and in a co-rotating close intermeshing twin-screw extruder, resepctively. The anionic bulk ring-opening mechanism of F3 and the reactive processing polymerization were studied.Firstly, the sodium silanolate initiator was synthesized using F3 as monomer and sodium hydroxide (NaOH) as initiator and was characterized by gel permeation chromatography (GPC), fourier transform infrared spectrometer (FT-IR),1H nuclear magnetic resonance (1H-NMR) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS).The results showed that the initiator is structure on the silicon atoms and oxygen atoms of a main chain, and the hydroxide radical and Na ion of the end groups, which consisted of most of sodium silanolate with low molecular weight and a small quantity of macrocyclosiloxane. The optimal preparation conditions for sodium silanolate initiator was determined at 120℃by 30 min of polymerization between F3 and NaOH with the weight ratio of 100:2.PMTFPS with high molecular weight were prepared by the initiator with the effective storage time less than 48 h.Secondly, the kinetics of F3 anionic bulk ring-opening polymerization was studied at different reaction temperatures using sodium silanolate as initiator. The investigation of the polymerization meachanism showed the polymerization rate was proportionsl to the monomer concentration and the apparent activation energy (Ea) was 34.29 kJ·mol-1. The linear polymers with high molecular weights and yield are synthesized in a reactor. The polymer was not the end group of hydroxide radical by the analysis of FT-IR spectra and 1H-NMR. The effects of the initiator content, reaction temperature and time on the molecular weight and its distribution of PMTFPS were investigated.The results showed that the molecular weight of PMTFPS firstly increased and then decreased.Howerver, the molecular weight distribution of PMTFPS became broader. PMTFPS with the maximal molecular weight (Mn=4.57×105) and narrow molecular weight distribution (MWD=1.39) was obtained at 120℃by 40 min of polymerization in the presence of 0.21 wt% initiator. The molecular weight of PMTFPS decreased and its molecular weight distribution increased with the further increase of the initiator content, reaction temperature and time due to the chain depropagation. It was confirmed that there exists an unfavorable equilibrium reaction between linear polymers and cyclosiloxane during the anionic bulk ring-opening polymerization of F3.In addition, the anionic bulk ring-opening of F3 was performed for 15 min at gradient temperature-elevating from 130℃to 140℃,resulting in the formation of PMTFPS with Mn=5.43×105 and yield= 95.9 wt%. The analysis of differential scanning calorimetry (DSC), thermogravimetic analysis (TGA) indicated that PMTFPS could be used in a wide range of operational temperatures. The investigation of the thermal degradation kinetics showed that PMTFPS with different molecular weights were degraded by an approach.In order to accelerate the anionic ring-opening polymerization of F3 and simulate the preparation process of PMTFPS in a twin-screw extrude, the preparation of PMTFPS in a haake torque rheometer was carried out using sodium silanolate as initiator, dimethyl sulfoxide (DMSO) or ethyl acetate (EA) as promoters. PMTFPS was a linear polymer with the hydroxide radical as the end group by the analysis of FT-IR spectra and 1H-NMR. Effects of the promoter concentration, the initiator content, the reaction temperature and time on the molecular weight and yield of PMTFPS were discussed. The results showed that there existed a complete equilibrium and the molecular weight and yield of PMTFPS firstly increased and then decreased with the increase of the promoter concentration, the initiator content, the reaction temperature and time. For DMSO promoter system, the maximal molecular weight and yield of PMTFPS were obtained in the presence of 0.017 mol·L-1 DMSO at 100℃by 2.5 min of polymerization. For EA promoter system, the maximal molecular weight and yield of PMTFPS were obtained in the presence of 0.45 mol·L-1 EA at 70℃by 4.0 min of polymerization. The molecular weights of PMTFPS didn’t be affected by the rotation rate higher than 30 rpm for the both promoters system.Moreover, the oligomers and cyclic by-products for EA promoter system were less than those for DMSO promoter system by the investigation of MALDI-TOF-MS.The ratio of cis-F3 and trans-F3 had remarkable effect on the crystallinity of PMTFPS.The analysis of wide angle x-ray diffraction (WAXD) showed that PMTFPS was a semi-crystalline polymer at the ratio of 35:65 of cis-F3 and trans-F3. Moreover, PMTFPS with different molecular weight were also degraded by an approach according to the analysis method of Ozawa-Flynn-Wall (OFW).Finally, PMTFPS was prepared by reactive extrusion of the anionic bulk ring-opening of F3 based on the preparation of PMTFPS in the Haake rheometer when DMSO or EA was used as promoters, respectively. Effect of F3 throughput, DMSO or EA throughput, initiator throughput and rotation rate on the molecular weight and yield of PMTFPS were investigated. The results showed that the maximal molecular weight and yield of PMTFPS were obtained for EA promoter system at the rotation rate of 25 rpm in the presence of 3.2 kg·h-1 F3 and 0.13 kg·h-1 EA throughputs, where the molecular weight and yield of PMTFPS were respectively 2.41×105 and 90.5 wt%. As the zones reactive temperature increased further, the molecular weight and yield of PMTFPS were reduced for the serious chain depropagation. The contents cyclic by-products increased with increasing EA throughput by the analysis of MALDI-TOF-MS. Moreover, the continuous reactive extrusion process was stable by the investigation of the yields of PMTFPS sampled at different extrusion time. It would be favor of the continuous preparation of PMTFPS by reactive extrusion bulk polymerization in the future.The analysis of WAXD and DSC showed that the crystallinity of PMTFPS obtained in a twin-screw extruder was lower than that prepared in Haake rheometer. The anslysis of Freeman-Carroll equations showed that the thermal decomposition kinetics model of PMTFPS accorded with quasi-first order dynamic equations.