The improved low-temperature elasticity of bio-based polyols is indeed closely related to the design of specific rigid diol structures. This characteristic stems from the synergistic effect of rigid structures and soft-segment phase separation mechanisms, as well as the regulation of chain segment mobility by molecular chain conformation at low temperatures. The molecular structure of bio-based polyols typically includes flexible long chains (such as unsaturated fatty acid chains in vegetable oils) and rigid groups (such as aromatic rings, cyclic structures, or short-chain diol units). The distribution of these two groups within the polyurethane network directly affects the material's low-temperature performance. When rigid diol structures are introduced in appropriate proportions, a microphase-separated structure can be formed in the polymer. The rigid hard segments act as physical crosslinking points, restricting chain slippage, while the flexible soft segments impart elasticity to the material. This structure is particularly important at low temperatures—the rigid hard segments maintain the overall stability of the network, preventing the material from breaking due to low-temperature embrittlement; the flexible soft segments maintain elasticity through micro-Brownian motion of the chains, allowing the material to undergo reversible deformation at low temperatures.
The type of rigid diol structure significantly affects low-temperature elasticity. Taking castor oil-based polyols as an example, the naturally occurring hydroxyl groups in their molecules combine with rigid trimethylene structures to form polyurethane elastomers that possess both flexibility and impact resistance. When rigid diols containing aromatic rings (such as cashew nut shell oil derivatives) are introduced, the π-π conjugation effect of the aromatic rings enhances intermolecular forces, resulting in a more compact arrangement of hard segments and further improving the material's low-temperature tear resistance. Furthermore, the introduction of short-chain diols (such as 1,4-butanediol) can adjust the hard segment spacing, optimize phase separation, and prevent low-temperature embrittlement caused by excessive hard segment aggregation. The key to this structural design lies in balancing the ratio of rigid hard segments to flexible soft segments—too high a hard segment content restricts chain segment movement and reduces elasticity; too high a soft segment content leads to insufficient material strength and an inability to maintain morphological stability at low temperatures.
At low temperatures, the chain segment movement capability of bio-based polyols is significantly affected by the rigid structure. In polyurethanes synthesized from traditional petroleum-based polyols, low temperatures cause soft segments to freeze, leading to a gradual loss of elasticity. However, bio-based polyols with rigid diol structures can have their hard segments act as "physical anchors," limiting excessive slippage of soft segments while providing necessary free volume for segment movement. For example, rigid diols containing cyclic structures (such as isosorbide) can maintain appropriate spacing between segments at low temperatures through the steric hindrance effect of their rigid rings, preventing embrittlement caused by tight molecular chain packing. This structure can also absorb energy through the plastic deformation of hard segments under stress, reducing stress concentration and thus improving the material's low-temperature impact resistance.
The synthesis process of bio-based polyols plays a decisive role in the introduction of the rigid structure. Modification techniques such as transesterification, ozone decomposition, or thiol-double bond click reactions can precisely control the type and content of the rigid diol. For example, trifunctional polyols generated from the ozone decomposition of soybean oil have a more uniform distribution of hydroxyl groups, resulting in a more ordered phase-separated structure when copolymerized with rigid diols. Furthermore, the thiol-double bond click reaction can directionally introduce rigid groups into vegetable oil molecules, avoiding the impact of side reactions on material properties. These process optimizations give bio-based polyols a more significant advantage over traditional petroleum-based polyols in improving low-temperature elasticity.
In practical applications, the improved low-temperature elasticity of bio-based polyols has been widely validated. In the field of cold storage, insulation materials prepared using a combination of bio-based polyols and supercritical CO₂ foaming technology can maintain structural integrity at -40°C, with an impact strength 60% higher than traditional rigid PU foam. In automotive sealing strips, bio-based polyurethane elastomers containing rigid diol structures can still maintain 80% of their room-temperature elasticity at -30°C, meeting the needs of use in extremely cold regions. These examples demonstrate that the design of rigid diol structures has become a key technological path for achieving breakthroughs in the low-temperature performance of bio-based polyols.
From a sustainable development perspective, the improved cryogenic elasticity of bio-based polyols not only addresses the performance limitations of traditional materials in low-temperature environments but also reduces reliance on fossil resources through the use of renewable raw materials. With advancements in gene editing and catalytic conversion technologies, future development of bio-based monomers with specific rigid structures will enable the customization of material cryogenic performance at the molecular level. This synergistic optimization of structure, performance, and sustainability will drive the expansion of bio-based polyol applications in cryogenic fields such as cold chain logistics, polar equipment, and aerospace.
The improved cryogenic elasticity of bio-based polyols is highly dependent on the design of rigid diol structures. Through mechanisms such as controlling phase separation, optimizing chain segment mobility, and enhancing impact resistance, breakthroughs in material performance at low temperatures are achieved. With continuous advancements in synthesis processes and structural design, bio-based polyols will play a more significant role in the field of green materials, providing high-performance and sustainable solutions for cryogenic applications.
