Low Cyclic Ester Polyester Polyols via Diol Ratio Control
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Solution Overview
Problem
Existing methods for producing polyester polyols based on phthalic anhydride result in undesirably high levels of cyclic esters, which can migrate and are not well understood, particularly when using certain diols like DEG and 1,4-butanediol, posing issues for applications involving indirect food contact.
Innovation Solution
Reacting phthalic anhydride with a diol or diol mixture at a specific molar ratio of 1.1 to 1.4, using diols such as propylene glycol, 1,3-propanediol, neopentyl glycol, and polyethylene glycols with controlled molecular weights, to produce o-phthalate polyester polyols with low cyclic ester content, achieving a hydroxyl value and acid value within specific ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional methods using diols like DEG and 1,4-butanediol are used to produce polyester polyols from phthalic anhydride, then the production process is simple and cost-effective, but the cyclic ester content becomes unacceptably high (3-8 wt.%)
Solution Approach 1:
The patent changes the molecular weight parameter of the diol reactant by selecting from a range of polyethylene glycols (200-600 g/mol) and other specific diols, rather than using conventional DEG or 1,4-butanediol. This parameter change in diol structure fundamentally alters the polymerization pathway to prevent cyclic ester formation while maintaining manufacturing simplicity
Solution Approach 2:
The patent uses commercially available diols with specific molecular weights (PEG-200, PEG-400, PEG-600, propylene glycol, neopentyl glycol) that are inexpensive and readily obtainable, replacing the need for complex purification processes to remove cyclic esters from conventional methods
2Adaptability or versatility
If cyclic esters are present in polyester polyols for food contact applications, then the polyol can be used in packaging adhesives, but the cyclic esters may migrate and cause safety concerns
Solution Approach 1:
The patent converts the potential harm of cyclic ester formation into a benefit by selecting diols whose molecular structure and reactivity characteristics inherently prevent cyclic ester formation during polymerization. The specific diol selection (PEG-200 to PEG-600, propylene glycol, neopentyl glycol) transforms the polymerization pathway to favor linear chain growth over cyclization, eliminating the migration hazard while preserving food contact application suitability
3Ease of operation
If the diol to phthalic anhydride molar ratio is not precisely controlled, then the formulation process is simpler, but the hydroxyl value and acid value become inconsistent affecting product performance
Solution Approach 1:
The patent establishes precise molar ratio ranges (1.05-1.20, preferably 1.10-1.15) as preliminary design parameters for the polymerization reaction. By pre-defining this critical parameter range based on the selected diol type, the formulation process achieves consistent hydroxyl values (18-400 mg KOH/g) and acid values (0.2-5.0 mg KOH/g) without requiring complex real-time adjustments during manufacturing
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
The method effectively reduces cyclic ester content to 1 wt.% or less, enhancing the reactivity and stability of the polyester polyols for applications like polyurethane adhesives and foams, while maintaining mechanical strength and thermal stability, thus addressing migration concerns and improving end-use performance.
Implementation Method 1
reacting phthalic anhydride with a particular diol or diol mixture at a diol to phthalic anhydride molar ratio within the range of 1.1 to 1.4
Data Source
AI summary
A method for producing a polyester polyol is disclosed. The method comprises reacting phthalic anhydride with a diol selected from the group consisting of ethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,6-hexanediol, polyethylene glycols having a number average molecular weight within the range of 200 g/mol to 600 g/mol, and mixtures thereof at a diol to phthalic anhydride molar ratio within the range of 1.1 to 1.6. The resulting o-phthalate polyester polyol has a hydroxyl value in the range of 18 to 400 mg KOH/g, an acid value in the range of 0.2 to 5.0 mg KOH/g, and 1 wt.% or less of cyclic esters.