壳聚糖大分子链的形态调控及其在微悬浮聚合中的分散稳定作用

以易去除可回用的壳聚糖(CS)为分散剂,通过微悬浮聚合制备微米级的软硬质聚合物胶粒.考察不同酸碱度下水相介质中CS大分子链的质子化程度、亲疏水性和形态结构,及其对油水界面处CS存在形态的影响,进而评估其对剪切均质化所制单体液滴的分散稳定作用.发现通过调节体系pH值可较容易地控制CS大分子链的质子化程度、亲疏水性以及在单体液滴表面的吸附效率和铺展程度,进而可在弱酸性环境下调控微悬浮聚合体系中CS的分散能力和稳定效果.特别是当pH值在6.0左右时,CS大分子链质子化程度和亲疏水性适中,链内易形成具有一定内聚密度的高分子链收缩构象、链间易形成由多根CS链缠结而成的疏松聚集状态.在此状态下的CS链对苯丙单体液滴具有较强的分散能力和稳定作用,因而通过微悬浮聚合可制得形态结构规整、分散状态良好的聚合物粒子.进一步与微悬浮聚合常用的无机粉末类和高分子类分散剂进行应用效果比较,发现CS具有形态调控性好、分散稳定效率高、易去除能回用、特别适合制备软质微米胶粒等优点,是一种有别于无机粉末类和高分子类分散剂的新型微悬浮聚合分散剂.

Conformation Regulation of Chitosan Macromolecular Chain and Its Dispersing and Stabilizing Effects in Micro-suspension Polymerization

With easily removed and reused chitosan (CS) as dispersant,a series of micron-sized hard or soft polymer particles were prepared via micro-suspension polymerization.The protonation degree,hydrophilic-hydrophobic property,conformation of the CS macromolecular chains in aqueous medium at different pH and their influences on the form of the CS presence at the oil water interface were studied.The dispersion and stabilization effect of the CS chains on the monomer droplets in shear homogenization and polymerization processes were explored.It was found that,the protonation degree and hydrophilic-hydrophobic property of the CS chains can be easily controlled by adjusting the pH of the aqueous medium.And the adsorption efficiency and spreading degree of the CS chains on the monomer droplet surface can be adjusted in a wide range.All of them can be used to improve the dispersion ability and stabilizing effect of the CS chains in the micro-suspension polymerization system.Especially,when the pH of CS aqueous solution is near 6.0,the protonation degree and hydrophilic-hydrophobic property of the CS chains are suitable to form a shrinkage CS chain conformation with a certain cohesive density,and an entanglement structure consisted of a few entangled CS chains.Under this state,the monomer droplets can be well dispersed and stabilized by these CS chains,and thus a series of polymer particles with smaller particle size,narrower size distribution,regular morphology and good dispersion can be easily obtained.Comparing with inorganic powder and water-soluble polymer dispersants commonly used in micro-suspension polymerization system,this CS dispersant has many advantages,such as recyclability,better dispersion stability,higher dispersion efficiency,and excellent chain conformation controllability.CS is particularly suitable to prepare micron-sized soft particles of polymers with low Tg,and is expected to replace part of the dispersants currently used in micro-suspension polymerization.