Aliphatic Polyester Molecular Weight Control via Static Mixing
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Solution Overview
Problem
Conventional methods for producing high molecular weight aliphatic polyesters face challenges such as reduced accuracy in controlling molecular weight, gelation, and the formation of fish eyes due to evaporation of diisocyanate at high temperatures, leading to insufficient mixing and reaction inefficiencies.
Innovation Solution
A method involving quantitative injection and continuous mixing of diisocyanate into an aliphatic polyester prepolymer at a temperature above its melting point, followed by a coupling reaction using a static mixer and additional mixing tank with specific stirring blades, to prevent evaporation and ensure uniform mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If diisocyanate is added to aliphatic polyester prepolymer at high temperature (not lower than melting point) to increase molecular weight, then molecular weight increases, but diisocyanate evaporates due to high temperature causing reduced accuracy in controlling molecular weight and formation of gelation and fish eyes
Solution Approach 1:
The patent applies preliminary action by pre-cooling the diisocyanate to a temperature below its melting point before injection, and by maintaining the prepolymer temperature within a specific range (10-50°C above melting point) before adding the diisocyanate. This preliminary temperature control prevents evaporation during the addition process, ensuring accurate molecular weight control and preventing gelation and fish eyes.
2Quantity of substance
If diisocyanate is added at high temperature to increase molecular weight, then molecular weight increases, but mixing uniformity deteriorates leading to gelation and fish eyes
Solution Approach 1:
The patent applies preliminary action by pre-cooling the diisocyanate to below its melting point before injection, ensuring it remains in a controlled state during addition. This preliminary temperature control prevents premature reaction and ensures uniform mixing, eliminating gelation and fish eyes while achieving the desired molecular weight increase.
3Device complexity
If conventional stirring blades are used in polymerization apparatus, then apparatus complexity remains low, but surface area of reactants cannot be sufficiently renewed leading to insufficient reaction
Solution Approach 1:
The patent applies dynamics by introducing a static mixer that creates turbulent flow and continuously renews the surface area of reactants during the coupling reaction. This dynamic mixing approach significantly improves reaction efficiency and molecular weight control without requiring complex moving stirring mechanisms, maintaining apparatus simplicity while enhancing productivity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively produces high-quality aliphatic polyesters with increased molecular weight, reduced gelation, and improved control over melt-flow rate, ensuring high-quality polymer production with minimal defects.
Implementation Method 1
quantitatively and continuously mixing the diisocyanate-containing aliphatic polyester prepolymer obtained at step (i) by a static mixer
Implementation Method 2
reacting the aliphatic polyester prepolymer with the diisocyanate in the coupling reaction tank
Data Source
AI summary
The problem to be solved by the present invention is to provide a method for continuously and effectively producing an aliphatic polyester having an increased molecular weight which prevents evaporation of diisocyanate at the step of mixing the diisocyanate with the aliphatic polyester prepolymer in a molten state at a temperature not lower than the melting point of the prepolymer and enables uniform mixing of the diisocyanate with the aliphatic polyester prepolymer. In order to solve this problem, the present invention provides a method for producing an aliphatic polyester having an increased molecular weight comprising the steps of:(i) quantitatively injecting a diisocyanate into an aliphatic polyester prepolymer which has a number average molecular weight of 5000 or higher and has terminal hydroxyl groups and in which at least one acid component is a succinic acid compound, in a molten state at a temperature not lower than the melting point thereof, whereinthe amount of diisocyanate is equivalent to between one tenth and two times the amount of the hydroxyl groups in the aliphatic polyester prepolymer,(ii) quantitatively and continuously mixing the diisocyanate-containing aliphatic polyester prepolymer obtained at step (i) by a static mixer, discharging same from the static mixer, and then supplying same to a coupling reaction tank, and(iii) reacting the aliphatic polyester prepolymer with the diisocyanate in the coupling reaction tank.