CO2 based polycarbonate hard segment enables polyurethane foam to maintain 54% compression modulus at 70 ℃

Research background and material design

The performance of polyurethane foam usually depends on the regulation of soft and hard segment structure. A recent study published in the Journal of Applied Polymer Science used CO2 derived triblock copolymer polyols to synthesize networked polyurethane foam, in which the hard segment is poly (cyclohexene carbonate) (PCHC) and the soft segment is polycaprolactone (PCL), forming a PCHC-b-PCL-b-PCHC structure, with CO2 derived components accounting for 16 wt%. The glass transition temperature (Tg) of PCHC is 104 ℃, which is the first report of polyurethane foam containing polyol segments with Tg higher than 100 ℃.

The study adjusted the viscosity of the system by adding low viscosity PCL homopolymer polyols, which kept the polyols liquid at room temperature and facilitated foaming processing.

. PCHC content varies from 0 to 15 wt%, which is used to systematically investigate the influence of hard segment content on the structure and properties of foam.

Change in structure and performance

With the introduction of PCHC segments, the density of foam increases, the cell size decreases and the distribution is more uniform. When the PCHC content increased from 0 to 15 wt%, the crystallinity of PCL decreased from 29% to 5%, indicating that the hard segment has a significant inhibitory effect on the crystallization of the soft segment. The mechanical properties show significant temperature dependent differences. Compared with foam without PCHC, the compression modulus and 25% strain compression strength of 15 wt% PCHC foam at room temperature decreased by about 40%; But under the condition of 70 ℃ and disappearance of crystallinity, its compressive modulus increased by five times and compressive strength increased by 210%. More importantly, 15 wt% PCHC foam still retains 54% of the room temperature compression modulus at 70 ℃, while foam without PCHC only retains 7%. This means that the compression performance of foam containing PCHC is far from sensitive to temperature changes.

Enlightenment for polymer additives and rubber industry

Although this research focuses on polyurethane foam, its structure-activity relationship on hard segment Tg, soft segment crystallization and high temperature modulus retention has reference value for tire and rubber formula design. In rubber systems, reinforcing fillers such as white carbon black affect modulus and heat generation through filler rubber interactions, while anti-aging agents and antioxidants are used to suppress performance degradation caused by thermal oxidative aging. This study suggests that by introducing high Tg segments or regulating the crystallization of soft segments, high-temperature dimensional stability can be improved without relying on a significant increase in crosslinking density in traditional vulcanization systems.

For foam rubber or sponge rubber products, the uniformity of foam pores and high-temperature compression permanent deformation are key indicators.

. The smaller and more uniform pores and high temperature modulus retention brought by PCHC segments provide a reference path for the molecular design of heat-resistant foamed elastomers. In addition, CO2 derived PCHC as a polyol component also echoes the tire and rubber industry’s focus on sustainable raw materials. However, this study is aimed at polyurethane foam system, and whether its conclusions can be directly transferred to the vulcanization system and filler network of diene rubber still needs further verification.

Research core data: the retention rate of compression modulus of 15 wt% PCHC foam at 70 ℃ is 54%, and that of foam without PCHC is 7%; The compressive modulus at 70 ℃ increased by five times, and the compressive strength increased by 210%.

Information source:Polyurethane Foams From a Triblock Copolymer Polyol With CO2‐Derived, High‐Tg Polycarbonate Segments， Organized by Herun Chemical.