疏水缔合聚合物重均分子量的测定

The Determination of Weight-average Molecular Weight of Hydrophobically Associated Water-soluble Polymers

采用毛细管法和荧光探针法研究了疏水缔合聚合物在不同甲酰胺浓度和盐浓度的溶剂中的特性黏数和疏水缔合作用强度.找到可以消除缔合作用和聚电解质效应的溶剂条件,用静态光散射法测定疏水缔合聚合物的重均分子量.结果表明,NaCl能够有效的屏蔽聚电解质效应,但是不能消除缔合作用,而且由于NaCl增加了溶液的极性,会进一步促进疏水缔合作用,疏水缔合聚合物以聚集体形态存在溶液中,因此,在NaCl溶剂中测得的疏水缔合聚合物的重均分子量不是真实分子量;而甲酰胺可以完全破坏疏水缔合作用,使聚合物分子以单分子态分散在溶液中,进而测得疏水缔合聚合物的真实分子量.当溶剂中的NaCl浓度为0.2 mol/L、甲酰胺体积分数为50%时,可准确测定疏水缔合聚合物的重均分子量.当缔合作用消除后再改变甲酰胺浓度,测得的重均分子量不再变化;聚电解质效应消除后,盐离子浓度的变化不会再改变测得的重均分子量结果.

Intrinsic viscosity and strength of hydrophobic association of hydrophobically associated water- soluble polymers （HAWSP） were investigated in different solvents containing formamide and salt, through the capillary tube method and fluorescence probe technique. Weight-average molecular weight of HAWSP was measured by static light scattering method under suitable solvent conditions that could eliminate the hydrophobic association and polyeleetrolyte effect. The experimental results showed that NaC1 had the capability of eliminating the polyelectrolyte effect, but NaC1 can not destroy hydrophobic association. And NaC1 promoted hydrophobic interaction because of increasing the polarity of HAWSP solutions. Macromoleeular aggregation would be greater at higher levels of hydrophobe, which explains the observed rise in molecular weight. As a result, the weight-average molecular weight of HAWSP measured in NaC1 solvent was not the real molecular weight. However,hydrophobie association can be completely destroyed by formamide. Moleculars of HAWSP dispersed in the formamide solvent, and real molecular weight of HAWSP can be measured. The results showed that weight-average molecular weight of HAWSP can be measured accurately in 50% formamide solvent with 0.2 mol/L NaC1. When hydrophobic association was eliminated completely, the values of weight- average molecular weight were identical with increasing formamide concentration; when the polyelectrolyte effect was removed, altering the salt concentration would not change the results of weight-average molecular weight.