发泡材料是一种良好的绝热材料，但是不透光的特性限制了它的很多应用。减小发泡材料的孔径至<40纳米或更小，有望赋予发泡材料透明和超绝热的特性，从而引发许多新的科学概念和实际应用。针对目前CO2发泡制备纳米发泡材料存在的一些瓶颈，如孔径不够小、孔隙率低、不透光、表面含致密层和过渡层、操作条件苛刻（超高压、低温）等，本申请提出一种解决这些问题的新思路，即通过调控聚合物的组成，调控发泡基体的玻璃化转变温度和CO2吸附能力，提出逐步升温多步发泡和在基体表面覆盖聚合物膜的方法，并结合原位小角X-ray散射研究CO2发泡过程孔结构的演变规律，有望创建一种在温和CO2吸附条件下制备高透明性（透光度>80%）、高孔隙率（>80%）、超绝热发泡材料的新技术，并揭示透明发泡材料的制备机理和孔径调控机制。该方法有望低操作成本制备高透明性、超绝热发泡材料，可应用于窗户玻璃的隔热材料等领域，具有巨大的的潜在商业价值。

Adding transparency function can significantly expand the applications of polymer foams in various areas, for example, as thermal insulating window films to save a substantial amount of building energy every year because the majority of energy loss in a building goes through windows. Fabrication of polymer foams using CO2 foaming is a low-cost and efficient way. However, it is a formidable challenge to develop highly transparent polymer foams as the pore size of the foams should be typically smaller than ~20 nm. There are several problems regarding nanofoams prepared by CO2 foaming, such as too large pore size, low porosity, low transparency or completely opaque, containing nonporous outer layer and transition layer, prepared under harsh operating conditions (extremely high pressure, low temperature for CO2 absorption) etc. To address these issues, new strategies are proposed: firstly, high Tg polynorbornene is selected as the matrix and the composition of the polynorbornene is tuned by copolymerization of varied amount of CO2-philic fluorinated norbornene monomers to increase the absorption of CO2 in the polymer matrix even under mild CO2 saturation conditions, resulting in great increase of the nucleation rate during foaming, which is beneficial for reducing the pore size (<20 nm) of the foams for highly transparent nanofoams. Secondly, a multi-step foaming method that foaming under gradually increased foaming temperature is proposed to increase the porosity of the nanofoams while inhibiting the severe coalescence of the bubbles during the bubble growth process. To prevent the polymer nanofoams from generating nonporous outer layer and transition layer, PDMS films are proposed to cover on the surface of the polymer matrix to prevent the CO2 from directly diffusing out to the air. Besides, the in-situ small angle X-ray scattering (SAXS) is proposed to characterize the pore structure evolution of the nanofoams for the whole foaming process and reveal the mechanism for fabricating nanofoams with ultra-small pore size. . These proposed strategies enable fabricating highly transparent and high porosity polymer nanofoam with super thermal insulating property under mild operating conditions and reveal the mechanism of fabricating nanofoams by CO2 foaming, which may significantly extend the applications of polymer foams in various areas.