A theoretical interpretation of free volume at glass transition

We device a relaxed lattice model (RLM) to study the mechanism of glass transition,which unifies the cageeffects from particle-particle interaction and entropy.By analyzing entropy in RLM with considering the influence of interactions on equilibrium,we demonstrate that glass transition is a second-order phase transition.For a perfect onedimensional linked particle system like linear polymer under normal pressure,the free volume at glass transition is rigorously deduced out to be 2.6％,which provides a theoretical basis for the iso-free volume of 2.5％ given by Willian,Landel and Ferry (WLF) equation.Extending to system with dead particles linked with higher dimensions like branched or cross-linked chains under positive or negative pressure,free volume at glass transition is varied,based on which we construct a phase diagram of glass transition in the space of free volume-dead particle-pressure.This demonstrates that free volume is not the single parameter determining glass transition,while either dead particles like cross-linked points or external force fields like pressure can vary free volume at the glass transition.     

芴基聚磷腈微球的制备及其对苯并噁嗪树脂阻燃性能的影响

以六氯环三磷腈(HCCP)和4,4′-(9-芴)二苯酚为原料,通过超声辅助沉淀聚合制备芴基聚磷腈(PZFP)微球,并将其用于双酚A型苯并噁嗪树脂(PBa)的阻燃改性.热重分析仪(TGA)、锥型量热仪(CONE)和动态热机械分析仪(DMA)测试结果表明,PZFP可提高PBa热降解后残留量,并能显著降低热释放速率(HRR),延长点燃时间(TTI),提高火灾性能指数(FPI),起到良好的阻燃作用.其中,PBa/PZFP-10%具有最佳阻燃性能.与纯PBa相比,PBa/PZFP-10%的HRR值由566 k W/m2降低到214 k W/m2,玻璃化转变温度(Tg)和储能模量略有提高.纯PBa和PBa/PZFP-10%的Tg分别为222和226°C.PBa/PZFP-10%复合材料的CONE测试后炭层扫描电镜(SEM)和热重-红外联用(TG-FTIR)结果显示,PZFP在PBa燃烧过程中,可以促进PBa主链和侧基交联成炭,形成外表面致密和内部多孔结构的凝聚相;PZFP本身热解产物部分参与凝聚相形成过程,仍有少量逸到气相中阻碍或终止气相燃烧循环.PZFP在PBa基体中起到凝聚相和气相阻燃机理协同作用.     

聚磷酸铵-苯并噁嗪微胶囊的制备及其对环氧树脂燃烧性能影响

以多聚甲醛、丙烯胺、苯酚为原料,通过Mannich反应合成烯丙基型苯并噁嗪单体(Bala),并通过核磁共振氢谱(~1H-NMR)确定了其化学结构.将Bala在聚磷酸铵(APP)原位开环聚合后,制备APP微胶囊(BMAPP).傅里叶变换红外(FTIR)和静态接触角测试表明,Bala在APP表面成功聚合,并有效提高APP的疏水性,与纯APP相比,BMAPP的接触角从10.8°提高到了71.3°.将BMAPP添加到环氧树脂(EP)中,制备EP/BMAPP复合材料.通过热重分析仪(TGA)、垂直燃烧(UL-94)、极限氧指数(LOI)、锥型量热仪(CONE)和动态热机械分析仪(DMA)对EP和EP/BMAPP的热性能以及燃烧性能进行对比分析.结果显示,10%的BMAPP的成炭效果最佳,有良好的阻燃性能,可使EP的LOI值从22.6%提高到33.6%,并通过UL-94 V-0级,600°C下残炭率达26.3%.同时,BMAPP可大幅度降低EP燃烧过程中烟密度和热释放速率,提高EP的玻璃化转变温度(T_g).BMAPP/EP-10%中,PBala和APP协同后使EP热释放速率峰值(PHRR)由1247 kW·m~(-2)降低到434 kW·m~(-2),生烟速率(SPR)降低67%左右,T_g从169°C提高到了173°C.