Crystallinity of bottlebrush polymers due to side chain crystallization has been considered to be related to the length of the side chains only under the assumption of complete participation of crystallization by all side chains. Recent experimental results revealed that in poly( n -alkyl methacrylate)s a fraction of side chains could not crystallize due to constraints imposed by the trapped main chain entanglements and required expansion of main chain-main chain distance. This result renders the original simplified consideration of the origin of crystallinity in bottlebrush polymers questionable. In this work, we introduce a new parameter f c , the fraction of crystallizable side chains, to better describe the crystallinity of bottlebrush polymers. A linear relationship between the melting enthalpy and the number of alkyl groups in side chains for bottlebrush polymers reported repeatedly indicates that f c remains essentially unchanged when bottlebrush polymers had the same main chain structure and grafting degree but different side chain lengths. The slope of the above-mentioned linear relationship is thus \(\Delta H_{\text{CH}_2}\times f_{c}\) , where \(\Delta H_{\text{CH}_2}\) stands for the melting enthalpy of one mole alkyl group packed into the crystal. With a known value of f c , it is possible to estimate the value of \(\Delta H_{\text{CH}_2}\) . In case of poly( n -alkyl methacrylate)s, we estimated \(\Delta H_{\text{CH}_2}\) of hexagonal crystal being at most 5.74 kJ/mol with the knowledge of possibly smallest f c of 0.67 obtained from small angle X-ray scattering data. Therefore, the crystallinity of bottlebrush polymer would be calculated based on the equation \(X_{\rm{c}}=f_{\rm{c}}\times\frac{N_{\rm{c}}}{N}\) with N and N c being the number of alkyl groups in a side chain and those packed in the crystalline structure, respectively. Both chemical structure and grafting degree of bottlebrush polymers affect f c .
A series of nanoencapsulated phase change materials with n-tetradecane as the core material and melamine–urea–formaldehyde (MUF)–TiO 2 composite as the shell material was developed using a two-step method. Sol-gel and blending modification methods were respectively utilized after the in situ polymerization. The physical, chemical, and thermal properties of the nanoencapsulated phase change material (NEPCM) samples were characterized. Furthermore, a comprehensive performance evaluation system was established based on the efficacy coefficient method. The results indicated that the average diameter of the nanocapsules was significantly increased by the sol-gel modification and was slightly influenced by the blending method. All NEPCMs exhibited high chemical and thermal stability. The NEPCMs modified by the sol-gel method (C 14 @MUF–TiO 2 -S1) exhibited the best performance in terms of the encapsulation ratio, melting enthalpy , and onset decomposition temperature , which were 68.6%, 156.2 J·g -1 , and 155.36 °C, respectively. C 14 @MUF–TiO 2 -S2 exhibited the lowest mass loss of 44.2% at 100 h. For the blending method, C 14 @MUF–TiO 2 -B1 had the highest yield of 53.87%. The thermal conductivity of C 14 @MUF–TiO 2 -B3 increased up to 88.15% compared with the unmodified NEPCMs. Therefore, modification by the sol-gel method with 2.2 g TiO 2 sol had the highest total efficacy coefficient of 0.843 among the samples.
Summary Microencapsulated phase change materials (MEPCMs) have attracted extensive attention due to their ability to encapsulate and protect core materials. Herein, this paper presents the successful preparation of an environmentally friendly bio-based polyurethane (PU) by utilizing soy polyols as raw material and utilizing it innovatively to achieve the microencapsulation of phase change materials (PCMs). The surface morphology, thermal properties, particle size and particle size distribution of MEPCMs were comprehensively characterized and analyzed. Especially, a systematic study was conducted on MEPCMs in terms of their structure and properties, depending on different preparation conditions. According to the results, microcapsules obtained with a core-shell ratio of 1:1 and mechanical stirring speed of 300 rpm display good spherical shape, smooth surface, and narrow particle size distribution. Moreover, the melting enthalpy of microcapsules can reach 91.4 J/g when the core material content is 48.4%. Moreover, compared to pure paraffin, the prepared microcapsules have superior thermal stability and high reliability, which shows promising energy storage efficiency of 91.5% even after 50 hot-cold cycles.
危险品化学品经营许可证（带存储）