Miniemulsion Polymerization Of Octamethylcyclotetrasiloxane And Study On Copolymerization Modification

Polydimethylsiloxane(PDMS)emulsion,prepared by ring-opening polymerization(ROP)under emulsion conditions with octamethylcyclotetrasiloxane(D4)as the main monomer,can be directly applied as the mold release agent,waterproof agent,waterproof fabric finishing agent,resin modifier and other silicone polymer products with broad application prospects,taking the advantage of its fluid characteristics with water used as medium and relatively green environmental friendly.However,further requirements are still demanded for further improvement:the degradation and bleaching of silicone emulsion during the polymerization should be solved;it is necessary to modify the silicone molecular chain by functional groups which can cross-link or can interact with other polymer matrix;the control on the viscosity or molecular weight in a relatively large range is still in expected.In view of the above problems,in this dissertation,we use D4 as the main silicone monomer to prepare silicone emulsion by miniemulsion polymerization.Systematic studies have been carried out on the effects of different copolymerization modifiers to the stability of the monomer miniemulsion,the silicone polymerization process,the polymer emulsion and the silicone polymer.Further,the core-shell silicone composite emulsion and the self-repairing silicone functional emulsion are also prepared through the combination use on the different polymerization modifiers.The application of the synthesized silicone emulsion in the hydrophobic modification of polymer coating has also been explored.The main contents are as follows:1.Using the main monomer of D4 and dodecylbenzenesulfonic acid(DBSA)as the initiator/anionic surfactant,we prepared the emulsion of PDMS in miniemulsion condition through cationic ROP method.Hydrocyclotetrasiloxane(D4H)was introduced into the system to copolymerize with D4.The composition of the comonomers of D4 and D4H were systematically studied.By tracking the reaction conversion rate,it was found that the addition of D4H could significantly increase the ring opening efficiency of the monomers.The infrared spectra of the polymer showed that silicone polymer emulsions with different contents of Si-H group were successfully prepared through the different addition amount of the comonomer of D4H,whose post crosslinking was also revealed by the same characterization.The prepared H-PDMS emulsion was used as the seed emulsion,and the small molecular silane as the precursor of polysilsesquioxane(PSQ),H-PDMS/PSQ composite emulsion was prepared by sequentially polymerization in emulsion.The composite particles derived in the system were of core-shell structure,which was confirmed by transmission electron microscopy(TEM).2.Using D4 as the starting material,we prepared a mixed monomer system of D4 and bis(heptamethylcyclotetrasiloxane)-ethane(bis-D4).Miniemulsion polymerization method was still applied,with ammonium hydroxide as the initiator,and cetyltrimethylammonium bromide(CTAB)as the surfactant.The silicone emulsion specialized by its internal cross-linked structure was achieved by anionic ROP.The copolymer separated from the emulsion had a heat-induced self-healing function,which was verified in the damage-repair experiment.3.Also using D4 as the main monomer,under the conditions of the above-mentioned miniemulsion cationic ROP,we applied alkoxy silanes,which could condense with silanol groups on the ROP product,to modify the polymerization,and found both the size evolution and the kinetics were altered by the different structures and contents of the small molecular silanes.The structural variables introduced by different silanes modified the produced PDMS with different functional groups,and the viscosities of the polymers also changed in corresponding to the silane contents.Besides,the polymerization as well as the conversion was also improved by the properly addition of silanes.The prepared product was also used for the blending modification on the aqueous coating.The results show that when the copolymerization product is added in an amount of 10%,the hydrophobicity of the film can be significantly improved without affecting the mechanical properties of the film.