When synthesizing thermoplastic polyurethane, what are some ways to improve heat resistance by changing polyols and isocyanates?
Why does heat resistance increase when NPG-based polyols are used?
Dear Donghyeok Im, one way for heat resistance improving is by blending with other polymers such as polyphosphazenes and polyamides. My Regards
Hi ;
In the synthesis of polyurethanes, secondary reactions are very important, especially those of the polymerization of isocyanates (favored by the presence of a basic catalyst). The dimerization of isocyanate can take place at low temperature in the presence of tertiary amines, or even spontaneously, and trimerization occurs at very high temperature and/or in the presence of alkaline salts (potassium or calcium acetate). Isocyanurate nodes are stable up to 270°C and can be seen as a means of increasing resistance to high temperatures. Please see the following document.
With my best regards
Heat resistance of TPU corresponds to the level and strength of intermolecular attractions, primarily hydrogen bonds. Molecules with high hydrogen bonding capability tend to form thermally stable crystals having greater cohesive energies in the hard-segment domains.
Common ways to produce TPU with greater heat stability include:
(1) use of symmetrical diisocyanates (e.g., PPDI, NDI, 1,4-H6XDI) and/or chain extenders, particularly having rigid aromatic backbones;
(2) use of polyol chemistries that promote hydrogen bonding (polyester, polycarbonate in contrast to polyether, hydrocarbons);
(3) introducing of a small level of branching via the allophanate linkages, e.g., by increasing the NCO/OH ratio;
(4) introducing of strong hydrogen bonding urea and/or biuret linkages by replacing diols with diamines as chain extenders;
(5) increasing of the hard segment content, e.g., by reducing MW of polyol or NCO/OH balancing;
(6) use of soft-segment polyols and hard-segment chemistries that promote greater microphase separation (this is often the case why NPG-based polyester polyols improve the thermal resistance of TPU);
(7) and some more to consider.
Hi,
You can refer to this paper also. They have been specially designed for 3D printing.
Regards.
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