水性聚氨酯乳化过程中相转变的研究

本文合成了单官能团小分子物质封端的脂肪族水性聚氨酯预聚物 ,通过考察预聚物加水乳化过程中粘度及电导率的变化 ,研究了其相转变行为 .实验结果表明 ,随着软段分子量升高 ,体系的相转变点后延 ;聚酯体系的相转变比聚醚体系的相转变发生得早 ;[NCO]/ [OH]值越接近 1,体系的粘度就越高 ,相转变发生所需的水含量也越高 ;羧基含量及中和度也会对分散体系的相转变产生影响 .通过选择合适的条件 ,可以实现对乳化过程的优化

INVESTIGATION ON THE PHASE INVERSION BEHAVIOR OF WATERBORNE POLYURETHANE DURING EMULSIFICATION PROCESS

Several aliphatic waterborne polyurethane prepolymers are prepared from isophorone diisocyanate,dimethylolpropanic acid, poly(butylene adipate) (PBA) and polypropylene glyco (PPG).The prepolymers are blocked with 2 methoxyethanol,followed by neutralization pendant carboxyl by triethylamine,then diluted to 50?wt% with methyl ethyl ketone,emulsified by adding deionized water under constant agitation.The principle of emulsification is explained.The aggregated structure of prepolymers in organic solvent is discussed.The prepolymer molecules with ionic groups can form segment microionic lattices.The emulsification process and phase inversion are characterized by using the variation of viscosity and conductivity.The emulsification process includes the dissociation of the segment microionic lattices and the aggregation of the hydrophobic segments.The inversion process can be clearly divided into three regions depending upon the variation of viscosity and conductivity.The experimental results show that several factors can affect the phase inversion heavily,including the molecular weight and type of soft segments,the [NCO]/[OH] ratio,carboxyl content and neutralization degree.With the increasing of the molecular weight of soft segment,the phase inversion delays.In addition,the phase inversion of PBA based prepolymer occurs earlier than that of PPG based prepolymer,while their soft segment molecular weights are equal.High [NCO]/[OH] ratio not only decreases the viscosity of both prepolymer solution and emulsification system,but also makes phase inversion occur earlier.With the increasing of carboxyl content,the phase inversion occurs early.In the meantime appropriate carboxyl content can decrease the viscosity of phase inversion point and lead to easy phase inversion.The decrease of neutralization degree can contribute to low viscosity and early phase inversion.Selecting appropriate conditions can optimize the emulsification process.