Thermoset Polymers with Tunable CTE via Molecular Isomerization
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Solution Overview
Problem
Thermoset polymers often experience significant thermal expansion mismatch with other materials in composites, leading to internal stresses and potential device failure, and current solutions requiring high loadings of inorganic fillers to achieve tunable coefficients of thermal expansion (CTE) are limited in temperature range and hinder material processing.
Innovation Solution
Incorporation of thermally contractile units such as disubstituted-dibenzocyclooctane (DBCO) into thermoset polymers, which undergo reversible twist-boat to chair isomerization, reducing the coefficient of thermal expansion (CTE) to near zero ppm/°C without the need for fillers, by manipulating molecular volume with temperature-dependent isomerization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inorganic fillers are incorporated to reduce CTE, then the coefficient of thermal expansion is reduced, but the material processing is hindered and the useful temperature range is limited to sub-ambient temperatures
Solution Approach 1:
The patent extracts the CTE-reducing function from inorganic fillers and transfers it to organic molecular units (dibenzocyclooctane, dibenzocycloheptane, stilbene, azobenzene) that undergo thermal isomerization. This eliminates the need for filler incorporation, enabling proper material processing while achieving low CTE values without temperature limitations
Solution Approach 2:
The patent changes the fundamental mechanism from physical filler incorporation to chemical isomerization of molecular units. The molecular units undergo reversible twist-boat to chair isomerization with temperature, dynamically adjusting molecular volume to compensate for thermal expansion and achieve low CTE across a wide temperature range
2Reliability
If inorganic fillers are used to achieve low CTE, then the CTE is reduced, but the service life is reduced due to processing limitations
Solution Approach 1:
By removing inorganic fillers and using organic isomerizing units, the patent eliminates processing limitations that would otherwise reduce service life, while maintaining CTE matching capability across the full service temperature range
Solution Approach 2:
The patent creates a composite-like effect at the molecular level by incorporating multiple isomerizing units with different transition temperatures into the polymer network, enabling CTE control across a broad temperature range throughout the service life
3Reliability
If high loadings of inorganic fillers are used to significantly reduce CTE values, then the CTE is reduced, but the mechanical performance is dramatically altered
Solution Approach 1:
The patent changes from high filler loading (80-90 wt%) to low concentration organic molecular units incorporated into the polymer network, achieving CTE control while preserving the inherent mechanical properties of the base polymer matrix
Solution Approach 2:
The patent introduces CTE-control functionality at the molecular level within the polymer network rather than as separate filler particles, maintaining homogeneous material properties and avoiding the mechanical performance degradation associated with high filler loading
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 approach results in thermoset materials with highly reversible thermal expansion and contraction behavior, achieving low CTE values and maintaining material integrity across a wide temperature range, enhancing the reliability and service life of composite components.
Implementation Method 1
curatives comprising thermally contractile units that undergo a reversible twist-boat to chair isomerization upon heating accompanied by a change in molecular volume
Data Source
AI summary
Curatives and their resulting thermosets and other crosslinked polymers can reduce thermal expansion mismatch between an encapsulant and objects that are encapsulated. This can be accomplished by incorporating a negative CTE moiety into the thermoset resin or polymer backbone. The negative CTE moiety can be a thermal contractile unit that shrinks as a result of thermally induced conversion from a twist-boat to chair or cis/trans isomerization upon heating. Beyond CTE matching, other potential uses for these crosslinked polymers and thermosets include passive energy generation, energy absorption at high strain rates, mechanophores, actuators, and piezoelectric applications.