Synthesis Of Dihydroxyalkylpolysiloxanes And Study On Waterborne Polyurethanes Modified With Dihydroxyalkylpolysiloxanes

Due to environmental factors,waterborne polyurethane(WPU)dispersions have been widely used in coatings and adhesives.But compared with solvent-based polyurethane,WPU still has obvious shortcomings in some aspects.After many researches and discussions,WPU can be modified by modification methods to make it have functions that it did not have before.Among them,silicone modified WPU is one of the important modification ideas.Organic silicon materials occupy a unique position in the field of material modification by virtue of their unique and excellent properties.This paper designs and synthesizes four different structures of dihydroxyhydrocarbyl polysiloxanes,and uses two of them with different structures as modifiers to modify the water-based polyurethane and composite the modified water-based polyurethane The performance of the emulsion and its membrane has been studied preliminarily.The ?,?-bis[3-(1-methoxy-2-hydroxypropoxy)propyl]tetramethyldisiloxane(BHTS)and ?,?-bis[3-(1-methoxy-2-hydroxy-propoxy)propyl]capped polysiloxanes(BHTPS)were synthesized by a series of reactions using allyl glycidyl ether,tetramethyldisiloxane and octamethylcyclotetrasiloxane(D4)as raw materials,respectively.The structures of the products of each reaction step were also characterized in detail by infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy.(1,3,5,7-methylpropionate methyl)tetramethylcyclotetrasiloxane(MPTCS)was synthesized from methyl methacrylate,1,3,5,7-tetramethylcyclotetrasiloxane(D4H)and hydroquinone by reaction,and three kinds of ?,?-bis(3-(1-methoxy-2-Hydroxypropoxy)propyl)polymethyl(2-methylpropionate)siloxane(BHPMS)with different molecular weights were prepared by equilibrium reaction with BHTS and MPTCS,and the structure of each product was characterized by infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy,etc.The reaction conditions were optimized.the ?,?-bis(2-methyl-3-hydroxypropyl)tetramethyldisiloxane(BMHTS)was synthesized by a series of reactions using methyl allyl alcohol,hexamethyldisilazane and tetramethyldisiloxane as raw materials.Finally,polysiloxanes with different structures of different molecular weights were prepared by equilibrium reactions of BMHTS with D4 and MPTCS,respectively,and the structures of each product were characterized in detail using the same means.Two different polysiloxane-modified aqueous polyurethanes were prepared from4,4-dicyclohexylmethane diisocyanate(HMDI),polypropylene glycol 2000(PPG-2000),2,2-bis(hydroxymethyl)propionic acid(DMPA),triethylamine(TEA),diethylenetriamine(DETA),and home-made BHTPS and BHPMS.The mechanical properties,thermal stability properties and water resistance of the films after film formation were investigated.The results show that the mechanical properties and water resistance of the waterborne polyurethane modified by polysiloxane have been improved.The elongation at break can reach 1032.90% and 1170.35%,and the water absorption can reach 7.39% and 7.22%,respectively.