Study on Chain-Extension of Ester

With the increase of molecular weight, the properties of polyester increase its mechanical properties such as yield stress, tensile strength, and flexural modulus. Usually the viscosity average molecular weight of polyester is expressed by intrinsic viscosity. The methods for producing high-weight polyester include melt polycondensation, solid-phase polycondensation and chain extension method.

The representative method of chemical chain extension is the use of chain extenders. Chain extenders refer to certain compounds used to increase the relative molecular weight of polymers in a short period of time. They are usually a bifunctional compound that easily reacts with the groups at the ends of the two polymer chains. The principle of the chain extender is: the prepolymer contains hydroxyl end groups and carboxyl end groups, and the substance with high reactivity to these two groups is used as the chain extender to double the molecular weight of the polyester and obtain high characteristics. The add amount of chain extender is very small, and the general mass is about 1%.

The chain extension reaction of polyester can be carried out on an extruder or on a medium-sized rheometer. The extruder integrates chain extension and extrusion processing into one step. It has the advantages of short cycle, simple operation and high economic efficiency. In the past few years, the research on the chain extension reaction has mostly focused on the extruder. The reason why the viscosity of the polyester is significantly increased by the addition of a chain extender is that the functional group of the chain extender and the polyester first undergo a coupling reaction, which increases the average molecular weight; further reactions may produce branching reactions, which significantly increase the viscosity.