Polyurethane Prepolymers with Non-Linear Diols for Low Haze
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Solution Overview
Problem
Polyurethane coatings for aerospace applications face challenges in achieving high hard segment content with low haze and high transparency, as increased hard segment content can lead to decreased transparency and flexibility, and existing solutions do not effectively balance these properties.
Innovation Solution
A polyurethane prepolymer system incorporating non-linear short chain diols and soft diisocyanates into the polyurethane backbone, with specific weight percentages and molecular weights, to achieve a hard segment content of at least 50% while maintaining low haze and high optical clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the hard segment content of polyurethane is increased to improve surface adhesion and chemical resistance, then adhesion and chemical resistance are improved, but transparency and elasticity decrease to unacceptable levels
Solution Approach 1:
The patent changes the molecular structure parameters of the diol component from linear to non-linear (branched or cyclic) configuration. This structural parameter change modifies the packing efficiency and hydrogen bonding patterns in the hard segments, allowing high hard segment content (improved adhesion) without the same degree of light scattering (maintained transparency) that would occur with conventional linear diols.
2Strength
If the hard segment content of polyurethane is increased to improve surface adhesion and chemical resistance, then adhesion and chemical resistance are improved, but elasticity and flexibility decrease to unacceptable levels
Solution Approach 1:
The patent modifies the geometric parameters of the diol molecule by introducing non-linear structures (branched or cyclic configurations). This changes the free volume and chain mobility within the polymer matrix, enabling the formation of strong adhesion through high hard segment content while preserving sufficient chain flexibility and elasticity that would be lost with conventional linear diol structures.
3Strength
If linear short chain diols are used to achieve high hard segment content, then adhesion is improved, but haze increases and transparency decreases
Solution Approach 1:
The patent applies asymmetry by replacing symmetric linear diol structures with asymmetric non-linear structures (branched or cyclic). This asymmetry disrupts the regular packing and crystallization of hard segments, reducing light scattering interfaces and thereby decreasing haze while still maintaining the adhesion benefits of high hard segment content.
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 solution enables polyurethane coatings with high hard segment content, low haze, and improved adhesion and flexibility, meeting the demanding performance requirements of aerospace applications by reducing hydrogen bonding and increasing free volume in the polymer matrix.
Implementation Method 1
The hard segment moieties can form hydrogen bonds to produce hard segment domains in a cured polymer network. The formation of hydrogen bonds and the formation of hard segment domains can result in a loss of rotational freedom in the polymer network.
Implementation Method 2
Polyurethanes for these applications can be prepared by reacting diisocyanates, polymeric polyols, and linear short chain diols.
Data Source
AI summary
Polyurethane prepolymers having non-linear short chain diols and/or soft diisocyanates incorporated into the backbone are used to provide cured polyurethane coatings having a high hard segment content and low haze. The polyurethane prepolymers can also be used to improve the dispersion of filler in cured polyurethane compositions having a high filler loading. Cured coatings prepared from the two-part polyurethane systems meet the requirements for aerospace applications.