Anisotropic thermally conductive polymers with dynamic molecular weight, and methods of making the same
Some variations provide an oligomer composition comprising: polarizable first thermotropic liquid-crystal oligomer molecules (preferably urethanes or ureas) containing first triggerable reactive end groups, wherein the first triggerable reactive end groups are selected from the group consisting of hydroxyl, isocyanate, blocked isocyanate, acrylate, epoxide, amine, vinyl, ester, thiol, conjugated diene, substituted alkene, furan, maleimide, anthracene, and combinations thereof, and wherein the polarizable first thermotropic liquid-crystal oligomer molecules are characterized by a weight-average molecular weight from about 200 g/mol to about 10,000 g/mol; optionally, a plurality of polarizable second thermotropic liquid-crystal oligomer molecules containing second triggerable reactive end groups, wherein the second triggerable reactive end groups are capable of reacting with the first triggerable reactive end groups; and optionally, a reactive coupling agent capable of reacting with the first triggerable reactive end groups. Methods are described for converting the oligomer composition into an anisotropic thermally conductive polymer. Many commercial uses are disclosed.
1. An anisotropic thermally conductive polymer composition comprising a plurality of thermotropic liquid-crystal polymer molecules,
wherein said thermotropic liquid-crystal polymer molecules each contain crystalline domains;
wherein said thermotropic liquid-crystal polymer molecules are polarizable;
wherein said thermotropic liquid-crystal polymer molecules are selected from polyurethanes, polyureas, or a combination thereof;
wherein said thermotropic liquid-crystal polymer molecules are characterized by a weight-average molecular weight from about 10 4 g/mol to about 10 7 g/mol;
wherein said thermotropic liquid-crystal polymer molecules are in a nematic phase, a smectic phase, or a combination thereof; and
wherein at least 80% of said crystalline domains are aligned along a crystal axis with a full width at half maximum degree of alignment of 20 degrees or less.
2. The anisotropic thermally conductive polymer composition of claim 1 , wherein said thermotropic liquid-crystal polymer molecules are main-chain liquid-crystal polymer molecules.
3. The anisotropic thermally conductive polymer composition of claim 1 , wherein said crystalline domains contain carbon—carbon double bonds, aromatic rings, hydrogen bonds, or a combination thereof.
4. The anisotropic thermally conductive polymer composition of claim 1 , wherein at least 90% of said crystalline domains are aligned along said crystal axis with said full width at half maximum degree of alignment of 20 degrees or less.
5. The anisotropic thermally conductive polymer composition of claim 1 , wherein said anisotropic thermally conductive polymer composition is in the form of an object with a minimum dimension and a maximum dimension, and wherein the aspect ratio of said maximum dimension to said minimum dimension is selected from 1 to about 100.
6. The anisotropic thermally conductive polymer composition of claim 5 , wherein said object is characterized by thermal conductivity along said minimum dimension that is at least three times greater than thermal conductivity along said maximum dimension.
7. The anisotropic thermally conductive polymer composition of claim 5 , wherein said object is characterized by thermal conductivity along said maximum dimension that is at least three times greater than thermal conductivity along said minimum dimension.
8. The anisotropic thermally conductive polymer composition of 5 , wherein said object is characterized by a coefficient of thermal expansion along said crystal axis that is at least 50% lower compared to an otherwise-equivalent main-chain or side-chain liquid-crystal polymer with no alignment of said crystalline domains.