Diels-Alder反应可控制备交联等规聚丙烯

交联改性可以提升聚合物材料的机械性能、热稳定性及化学稳定性。 含有蒽基团的高质均分子量等规聚丙烯(iPP)可由配位共聚合反应制得,随后通过双官能的马来酰亚胺试剂与iPP中悬挂蒽基团间的Diels-Alder反应可以成功制备交联的iPP膜材料。 材料的交联度可以通过凝胶重量分析及膜红外分析得出,并由制备过程中交联剂的加入量有效地调控。 通过示差扫描量热仪(DSC)与广角X射线衍射仪(WAXD)表征发现,随交联度增加,交联改性限制了分子链的运动,iPP的结晶度逐渐降低、结晶能力逐渐下降。 对交联材料的动态热机械分析仪(DMA)测试表明,随交联度增加,iPP的损耗模量逐渐降低,材料韧性变差。 交联iPP的T_g逐渐升高,说明材料的耐热性得到提升。 由于交联形成了聚合物链间的交联网络,形成了更多受力点并且限制了聚合物链的自由移动,交联材料的拉伸强度随交联度的升高而增加,而断裂伸长率逐渐下降。

Controlled Preparation of Crosslinked Isotactic Polypropylene via Diels-Alder Reaction

Cross-linking is a commonly used method for polyolefin modification to improve the material's mechanical properties, thermo- and chemical resistance. High molecular mass(M_w) iPPs containing reactive anthracene groups were synthesized by coordination copolymerization. Crosslinked iPP films could be prepared by adding bi-functional N,N'-1,4-phenylene bismaleimide as a crosslinker to react with the pendent anthracene groups during the solvent casting process of the film. The cross-linking degree of the films could be easily tuned by the addition of the crosslinker. Characteristic absorption bands in Fourier transform infrared(FT-IR) spectra of the crosslinked films and gravimetric analysis of the insoluble portion could be used to determine the crosslinking degree. Differential scanning calorimetry(DSC) and wide-angle X-ray diffraction(WAXD) analysis revealed that the crystallinity and crystallization capability of the films decreased followed with the increase of cross-linking degree, which were mainly caused by the restricted chain movement. On the other hand, according to DMA analysis, the loss modulus dropped gradually with the increase of cross-linking degree, indicating the loss of toughness brought by cross-linking. The increased T_g detected from loss angle curves indicated the enhancement of thermoresistance. The tensile stress of the crosslinked iPP films were improved by forming polymer network containing more force bearing point, while the elongation at break dropped drastically because of the chains' poor movability.