聚醚醚酮酮强电场下的熔融结晶

聚醚醚酮酮 (PEEKK)是在聚醚醚酮 (PEEK)基础上开发成功的一种新型特种工程塑料 ,由于酮基与醚基比例的提高 ,其耐热等级比 PEEK提高了近 2 0℃ . Zimmermann等 [1] 首先报道了 PEEKK的晶体结构 ,同 PEEK类似 ,也为正交晶系 ,Pbcn空间群 .众所周知 ,结晶聚合物材料的产品性能与其结晶条件密切相关 .我们先后对 PEEKK的等温及非等温熔融与冷结晶动力学 [2 ,3] ,晶胞参数及结晶度随结晶温度变化关系 [4 ] ,拉伸诱变多晶型5,6] ,溶剂诱变多晶型进行了研究 [7] .但电场效应对聚合物结晶的影响尚罕见报道 [8] .本文对 PEEKK强电场…     

聚对苯二甲酸乙二醇酯/聚乙二醇醚插层嵌段共聚物的结晶性能

合成了不同用量、不同分子量的聚乙二醇醚(PEG)或聚丁二醇醚(PTMC)与聚对苯二甲酸乙二醇酯(PET)/蒙脱土(MMT)的嵌段共聚物。研究了MMT在共聚物中的分散状态及PEG或PTMG对PET/MMT插层聚合物结晶性能的影响。结果表明,MMT在共聚物中以纳米尺寸分散;加入PEG或PTMG增强了聚酯链段的柔顺性,使共聚物熔体降温过程的结晶温度提高,冷结晶温度降低,即插层嵌段共聚物的结晶速率提高;在合成的共聚物中,分子量为2000,用量为DMT的6%的PEG对插层共聚物结晶速率的促进作用最大     

TIME-TEMPERATURE-MISCIBILITY AND MORPHOLOGY OF POLYOLEFIN BLENDS

Miscibility and crystallization have been studied for polypropylene-polyethylene and polyethylene-polyethyleneblends. In the case of the polypropylene blends the composition of interest is 20% polypropylene. At this composition thepolypropylene has been found to be soluble in linear low density polyethylene but insoluble in high, low and very lowdensity polyethylenes. The miscibility has been concluded from the crystallization kinetics and polarised optical microscopywith a hot stage. Polyethylene-polyethylene blends have been formed from polymers with similar average branching contentbut where they have different melting temperatures. Important consequences are to introduce long branches into apolyethylene that only has short branches, and to modify the morphology of a polyethylenes so that haze, gloss and strainhardening are improved. Polyethylene blends must be developed after careful consideration of the branch content anddistribution within each of the constituents. It is not sufficient to simply blend polyethylenes, with the desired range ofproperties, without regard to the miscibility of the blend composition.     

四乙基溴化铵-氟化物复合模板剂合成β沸石(Ⅱ)--β沸石晶化过程研究

采用FT-IR,XRD,SEM,TG,ICP-AES等技术研究了四乙基溴化铵(TEABr)-氟化物复合模板剂体系合成β沸石的晶化过程.发现本体系β沸石的合成遵循液相转变机理,在诱导期向生长期转变的转折点存在过渡态,氟离子对过渡态的形成和转变起到重要作用.在诱导期初期固相是富铝的,但晶体生长期固相硅铝比基本不变,表明硅铝同步进人骨架.     

高分子液晶态有序性对其结晶过程的影响

采用退偏振光强度法、ＳＡＬＳ和ＰＯＭ测定了高分子液晶态有序微区结构随体系温度变化的规律,并用ＤＳＣ法研究具有不同有序微区结构尺寸的液晶态的结晶过程．结果发现,高分子液晶态有序性或有序微区结构是随着体系退火温度和时间的变化而变化．同时从相应的不同有序性为起始态进行结晶时,其结晶速率明显不同．并讨论了高分子液晶态的结晶机理     

链缠结对高聚物热转变行为的影响

用冷冻升华方法,由等规聚苯乙烯、聚环氧乙烷的稀溶液制备单链、寡链附聚粒子．附聚粒子的热分析表明,冷结晶温度降低、结晶速度加快、晶体增厚明显．这些结果是因为附聚粒子没有或有很少链间缠结．附聚粒子形成较小尺寸的晶体,因而熔点较低,相应的热结晶温度移向低温．在平衡熔点以上放置短时间,链相互贯穿、缠结,又回复到本体的熔融、结晶行为     

分子动力学方法研究单链聚乙烯的结晶过程

用分子动力学方法（ＭＤ）研究了单链聚乙烯在不同温度（１００Ｋ、２００Ｋ、３００Ｋ、４００Ｋ、５００Ｋ）下的结晶过程,并用能量和结构参数进行了描述．结果表明伸直分子链的结晶过程都经历了三个阶段,首先是伸直链的卷曲与聚集,然后通过链段的排列形成规整的片晶结构,最后是结晶形成的片晶在结构与能量上的涨落变化。研究表明,结晶温度越高,分子链的内聚速度越快．研究发现,分子链在内聚阶段经历一个局部凝聚的中间状态,在结晶温度很低（１００Ｋ）时,局部凝聚的结构是有序的．而在５００Ｋ时,该结构为无规线团．结晶温度的差异,一般来说,将导致得到的片晶厚度的不同．对于模拟的单链,随着结晶温度的降低而形成了较厚的片晶．该行为与聚乙烯本体结晶中片晶厚度对结晶温度的依赖性相反．在有序化阶段和之后的片晶调整运动阶段,分子链线团的回转半径基本保持不变．这与宏观多链体系的结果相同．另外,在模拟中发现,尺寸微小的单链聚乙烯晶片的扭转运动     

Pd—B／SiO2非晶态合金的晶化过程及其催化加氢活性的研究

用Ｒａｍａｎ,ＸＲＤ,ＳＥＭ等技术,研究了Ｐｄ－Ｂ／ＳｉＯ２非晶态合金的晶化过程及其对催化活性的影响。研究发现,Ｐｄ＾２＋能高度分散在ＳｉＯ２载体上,并与载体发生作用,但Ｐｄ－Ｂ合金在载体上形成颗粒微细的原子簇,温度低于６７３Ｋ时,这些原子簇在ＳｉＯ２载体上呈非晶态结构,并随着温度的增加而发生团聚。     

Stochastic birth-and-growth processes modelling crystallization of polymers with spatially heterogeneous parameters

The morphology of a crystalline polymeric material is characterized by the crystallization process, which occurs during the solidification from the liquid state. This process includes a stochastic birth process (nucleation) and the growth of crystals. From a mathematical point of view, the nucleation process is a marked point process with a stochastic intensity depending on the history of the proceses of birth and growth. Here we consider an extension of the classical Avrami–Kolmogorov model to the case of space-time heterogeneous kinetic parameters. Concepts from stochastic geometry are used, which include the so called causal cone. The Markov property of the process is also analysed.     

Preparation of LiTi2(PO4)3 by the Solgel Method and Investigation of Its Formation Process*

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