L-丙交酯/ε-己内酯共聚物分子链结构非均匀性的研究

利用升温淋洗分级(TREF)和连续自成核退火热分级(SSA)等方法研究了L-丙交酯(LLA)和ε-己内酯(ε-CL)共聚物(PLC)分子链结构的非均匀性.合成了2种不同摩尔比的PLC共聚物,用TREF的方法,将同一个共聚物分级出3个级份.用核磁共振氢谱(1H-NMR)和凝胶渗透色谱(GPC)等方法对每个级份的分子结构进行了表征.结果表明,随着淋洗温度的升高,共聚物级份中的ε-CL单元的含量明显降低,而且级份的数均分子量增大,分子量分布指数降低.在SSA热分级研究中,发现PLC各级份间存在明显的分子链间和分子链内结构上的差异,这种链结构差异使得各个级份表现出不同的熔融行为.     

茂金属聚乙烯的短链支化结构不均匀性研究进展

茂金属支化聚乙烯技术是聚烯烃工业发展史上最重要的技术进展之一,该类产品具有优异的抗穿刺、抗撕裂、抗冲击性质,在薄膜、重包装等领域具有广泛的用途,其力学性能与共聚单体的种类、含量及其在分子链上的分布有密切关系。本文从催化剂活性中心特点和聚合反应工艺条件两方面对聚合物结构的影响出发,阐述了茂金属聚乙烯短链支化结构不均匀性产生的原因,通过核磁共振、升温淋洗分级和热分级等表征支化不均匀性的研究方法,介绍了茂金属支化聚乙烯分子主链上共聚单体的序列结构组成及分布,以及共聚物的结晶性能等方面的差异。     

PP/PB-1釜内合金的升温淋洗分级及级份表征

基于反应器颗粒技术制备的聚丙烯(PP)/聚丁烯-1(PB-1)釜内合金,其结构与组成,特别是嵌段共聚物级份的组成、分布、链序列结构等受两段聚合条件的影响较大。本文采用溶剂抽提法和升温淋洗分级法,对中试合成的两种PP/PB-1釜内合金进行分级,采用示差扫描量热仪(DSC)、高温核磁碳谱(~(13)C-NMR)、高温凝胶渗透色谱仪(GPC)对各级份进行表征,明确了合金的结构、组成及丁烯-丙烯嵌段共聚物(PB-b-PP)级份链序列结构。研究两种釜内合金的组成与力学性能关系,对于聚合工艺的优化及先进聚烯烃材料的开发提供依据。     

基于吸附色谱的分级技术在聚烯烃表征中的应用

聚烯烃树脂具有复杂的化学组成和链结构,液相分级技术是有效识别其精细结构的常用表征手段。相对使用较为广泛的结晶分级技术,高温-温度梯度相互作用色谱技术(HT-TGIC),作为一种最新的分级方法,具有可分析无定形聚烯烃样品的优势,大大拓宽了分级技术在聚烯烃树脂中的应用范围。本文列举了温度梯度相互作用色谱(TGIC)在聚烯烃表征中的典型案列,特别是针对结晶分级技术局限的低结晶度/无定形聚烯烃树脂。基于TGIC与凝胶渗透色谱(GPC)技术的联用分析,揭示了聚烯烃材料链结构的二维信息,为性能优异的新型聚烯烃材料研发与设计提供支撑和指导。     

示差扫描量热法进展及其在高分子表征中的应用

示差扫描量热法(DSC)是表征材料热性能和热反应的一种高效研究工具,具有操作简便、应用广泛、测量值物理意义明确等优点.近年来DSC技术的发展大大拓展了高分子材料表征的测试范围,促进了对高分子物理转变的热力学和动力学的深入研究.温度调制示差扫描量热法(TMDSC)是DSC在20世纪90年代的标志性进展,它在传统DSC的线性升温速率的基础之上引入了调制速率,从而可将总热流信号分解为可逆信号和不可逆信号两部分,并能测量准等温过程的可逆热容.闪速示差扫描量热法(FSC)是DSC技术近年来的创新性发展,它采用体积微小的氮化硅薄膜芯片传感器替代传统DSC的坩埚作为试样容器和控温系统,实现了超快速的升降温扫描速率以及微米尺度上的样品测试,使得对于高分子在扫描过程中的结构重组机制的分析以及对实际的生产加工条件的直接模拟成为可能.本文从热分析基础出发,依次对传统DSC、TMDSC和FSC进行了介绍,内容覆盖其发展历史、方法原理、操作技巧及其在高分子表征中的应用举例,最后对DSC未来的发展和应用进行了展望.本文希望通过综述DSC原理、实验技巧和应用进展,帮助读者加深对DSC这一常用表征技术的理解,进一步拓展DSC表征高分子材料的应用.     

超快扫描量热技术表征高分子结晶动力学

高分子结晶行为是高分子材料加工过程研究的热点,因为高分子组分和加工工艺控制着高分子结晶及其产物性能。差示扫描量热仪(DSC)是研究高分子结晶动力学常规手段。但是,普通DSC所能达到的最快降温速率一般无法抑制较快的样品结晶,结晶行为将在等温结晶动力学测试之前发生,因此可进行等温结晶的研究温度范围局限于较低结晶过冷度的高温区域。近年来,具有超快速升降温扫描速率和精准控温的快速扫描芯片量热仪(FSC,其商业化版本Flash DSC 1)得到了广泛应用。FSC可以抑制高分子样品在升降温过程中的结晶成核,避免对之后的结晶动力学测试产生影响。因此FSC技术将高分子结晶动力学的研究温度区间延伸至具有较大过冷度的低温区,加深了我们对高分子结晶成核机理以及高分子工业加工过程的理解。本文首先介绍了由初级成核方程描述的高分子结晶动力学原理,初级成核自由能位垒(?G~*)和扩散活化能位垒(?U)分别控制了高低温区的结晶动力学。我们还总结了FSC技术的发展,包括氮化硅薄膜芯片技术、快速扫描量热仪、商业化Flash DSC 1在不同高分子结晶熔融行为研究中的应用。然后介绍表征高分子等温结晶动力学的方法,其中包括样品制备、质量估算、消除热历史、临界扫描速率的确定等,并举例介绍FSC在高分子结晶动力学研究中的应用,涵盖高分子总结晶动力学、结晶成核动力学、高分子焓松弛对结晶成核的影响、FSC联用技术等方面。应用举例中对应形貌和结晶信息,分析了通过FSC测试得到的结晶成核动力学特点。另外通过比较不同结构特点的高分子,总结了我们对结晶动力学行为的基本理解。总之,FSC技术是一种能够提供相转变动力学和热力学信息的高效工具,特别是应用于分析只能在快速扫描中得到的样品结构变化信息。同时我们希望本文能够帮助读者考虑超快扫描量热技术在其他材料研究上的应用,包括合金、药物、生物大分子等。     

升温淋洗分级技术在聚乙烯研究中的应用

升温淋洗分级技术是根据结晶性聚合物的结晶度进行分级和表征的一项分析和制备技术，在聚烯烃非均匀性的表征和窄组成分布样品的制备中有重要应用。本文主要介绍升温淋洗分级原理、热力学模型、装置技术特点、分析方法以及在聚乙烯研究中最新应用进展。     

低密度聚乙烯的升温淋洗分级及链结构研究

采用升温淋洗分级方法对密度相同、熔融指数不同、拉伸强度和断裂伸长率不同、膜的抗冲击强度和抗撕强度有明显差异的2种低密度聚乙烯样品进行了分级,并利用GPC、DSC、SSA、13C-NMR等多种手段对原样和级份进行了链结构表征.由13C-NMR得到样品A和B总的支化含量分别为3.93 mol%,4.82 mol%,都既含有短链支化又含有长链支化;TREF-GPC交叉分级结果可以看出,2个样品的主要分级级份集中在较高温度区域,A样品主要集中于80℃的淋洗温度,分子量集中于3.2×105区域,而B样品主要集中于75℃的淋洗温度,分子量集中于1.8×105区域,样品A具有稍高的分子量且高分子量部分含量较多.由DSC结果得知,样品A的结晶度为34.7%,级份A1~A9的结晶度在26.0%~37.4%;样品B结晶度为34.4%,其级份B1~B9的结晶度在26.2%~34.8%.另外通过热分级结果得出,不管是原样还是各个级份,都具有约10个左右的多重熔融峰,显示出分子链内具有非均匀性,2个样品级份的数均亚甲基序列长度均随着淋洗温度升高而增加,分别为34~86和32~84.此外,讨论了它们的链结构特点以及与性能之间的关系.     

等规聚丙烯/聚丁烯-1釜内合金的结构与性能

高分子材料的组成、 组分分布及链结构与宏观性能紧密相关. 因此, 分析多组分釜内合金材料的链结构特点与性能之间的关系至关重要. 采用升温淋洗分级的方法对两种采用序贯两段聚合原位合成的等规聚丙烯/聚丁烯-1(iPP/iPB)釜内合金在-30 ℃~140 ℃温度范围进行分级, 采用核磁共振波谱仪、 傅里叶变换红外光谱仪、 差示扫描量热仪和凝胶渗透色谱仪等表征了级分的链结构及序列分布、 热行为、 分子量(M_w)及分子量分布(M_w/M_n)等. 结果表明iPP/iPB合金主要由5种级分组成, 高等规聚丁烯(iPB)为主要组分, 同时含有少量的丁烯-丙烯嵌段共聚物(PB-b-PP)和等规聚丙烯(iPP)等. 随淋洗温度升高, PB-b-PP级分中PP嵌段长度逐渐增加, PB嵌段长度逐渐减小; 在相同的淋洗温度, 合金B的嵌段共聚物级分中PP嵌段较长且结晶较完善; 合金B中iPB组分及嵌段共聚物组分含量较高, 使得合金B具有较高的拉伸强度、 弯曲强度、 优异的抗冲击性能、 较高的维卡软化温度及较快的晶型转变速率.     

用TREF方法分离聚烯烃共混物

用ＴＲＥＦ方法分离聚烯烃共混物徐君庭，封麟先，杨士林（浙江大学高分子科学与工程学系，杭州，３１００２７）关键词升温淋洗分级，聚烯烃，共混物升温淋洗分级（ＴＲＥＦ）方法是８０年代发展起来的，它按结晶度将聚合物分级［１］，目前主要用于聚烯烃的分级［２，３...     

Molecular heterogeneity of ethylene‐propylene rubbers: New insights through advanced crystallization‐based and chromatographic techniques

For a long time ethylene‐propylene rubber (EPR) copolymers with high comonomer contents were believed to be amorphous materials with a random copolymer composition. This is not completely correct as has been shown by temperature rising elution fractionation (TREF) combined with differential scanning calorimetry (DSC), crystallization analysis fractionation (CRYSTAF), and high temperature–high‐performance liquid chromatography (HT‐HPLC). When using only conventional crystallization‐based fractionation methods, the comprehensive compositional analysis of EPR copolymers was impossible due to the fact that large fractions of these copolymers do not crystallize under CRYSTAF conditions. In the present work, HT‐HPLC was used for the separation of the EPR copolymers according to their ethylene and propylene distributions along the polymer chains. These investigations showed the existence of long ethylene sequences in the bulk samples which was further confirmed by DSC. The results on the bulk samples prompted us to conduct preparative fractionations of EPR copolymers having varying ethylene contents using TREF. Surprisingly, significant amounts of crystallizing materials were obtained that were analyzed using a multistep protocol. CRYSTAF and DSC analyses of the TREF fractions revealed the presence of components with large crystallizable sequences that had not been detected by the bulk samples analyses. HT‐HPLC provided a comprehensive separation and characterization of both the amorphous and the crystalline TREF fractions. The TREF fractions eluting at higher temperatures showed the presence of ethylene‐rich copolymers and PE homopolymer. In order to obtain additional structural information on the separated fractions, HT‐HPLC was coupled to Fourier transform‐infrared (FT‐IR) spectroscopy. The FT‐IR data confirmed that the TREF fractions were separated according to the ethylene contents of the eluted samples. Preparative TREF analysis together with a combination of various analytical methods proved to be useful tools in understanding the complex molecular composition of these rubber samples. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 863–874     

Calibration curve establishment and fractionation temperature selection of polyethylene for preparative temperature rising elution fractionation

A series of copolymers of ethylene with 1-hexene synthesized using a metallocene catalyst are selected and mixed. The blend is fractionated via preparative temperature rising elution fractionation(P-TREF). All fractions are characterized via high-temperature gel permeation chromatography(GPC), 13 C nuclear magnetic resonance spectroscopy(13C-NMR), and differential scanning calorimetry(DSC). The changes in the DSC melting peak temperatures of the fractions from P-TREF as a function of elution temperature are almost linear, thereby providing a reference through which the elution temperature of TREF experiments could be selected. Moreover, the standard calibration curve(ethylene/1-hexene) of P-TREF is established, which relates to the degree of short-chain branching of the fractions. The standard calibration curve of P-TREF is beneficial to study on the complicated branching structure of polyethylene. A convenient method for selecting the fractionation temperature for TREF experiments is elaborated. The polyethylene sample is fractionated via successive self-nucleation and annealing(SSA) thermal fractionation. A multiple-melting endotherm is obtained through the final DSC heating scan for the sample after SSA thermal fractionation. A series of fractionation temperatures are then selected through the relationship between the DSC melting peak temperature and TREF elution temperature.     

Combination of TREF, high-temperature HPLC, FTIR and HPer DSC for the comprehensive analysis of complex polypropylene copolymers

A novel, powerful analytical technique, preparative temperature rising elution fractionation (prep TREF)/high-temperature (HT)-HPLC/Fourier transform infrared spectroscopy (FTIR)/high-performance differential scanning calorimetry (HPer DSC)), has been introduced to study the correlation between the polymer chain microstructure and the thermal behaviour of various components in a complex impact polypropylene copolymer (IPC). For the comprehensive analysis of this complex material, in a first step, prep TREF is used to produce less complex but still heterogeneous fractions. These chemically heterogeneous fractions are completely separated by using a highly selective chromatographic separation method—high-temperature solvent gradient HPLC. The detailed structural and thermal analysis of the HPLC fractions was conducted by offline coupling of HT-HPLC with FTIR spectroscopy and a novel DSC method—HPer DSC. Three chemically different components were identified in the mid-elution temperature TREF fractions. For the first component, identified as isotactic polypropylene homopolymer by FTIR, the macromolecular chain length is found to be an important factor affecting the melting and crystallisation behaviour. The second component relates to ethylene–propylene copolymer molecules with varying ethylene monomer distributions and propylene tacticity distributions. For the polyethylene component (last eluting component in all semi-crystalline TREF fractions), it was found that branching produced defects in the long crystallisable ethylene sequences that affected the thermal properties. The different species exhibit distinctively different melting and crystallisation behaviour, as documented by HPer DSC. Using this novel approach of hyphenated techniques, the chain structure and melting and crystallisation behaviour of different components in a complex copolymer were investigated systematically.

Crystallization Elution Fractionation of LLDPEs Made with Metallocene Catalysts

Summary: Temperature rising elution fractionation (TREF) and crystallization analysis fractionation (CRYSTAF) fractionate semicrystalline polymers according to their crystallizabilities from dilute solution and have been widely used to measure the CCD of LLDPE. A new fractionation technique, known as crystallization elution fractionation (CEF), has been developed recently. The main difference between CEF and TREF and CRYSTAF is that the crystallization cycle in CEF is performed dynamically under solvent flow in a long column that contains an inert support material. In this paper, several metallocene-LLDPE resins have been analyzed by CEF to investigate the effect of cooling cycle parameters, comonomer fraction, polymer molecular weight, and blend cocrystallization on the fractionation. This new technique can be used to obtain CCDs with better resolution and in shorter times than TREF and CRYSTAF.     

Characterization of polypropylene�Cpolyethylene blends by temperature rising elution and crystallization analysis fractionation

The introduction of single-site catalysts in the polyolefins industry opens new routes to design resins with improved performance through multicatalyst-multireactor processes. Physical combination of various polyolefin types in a secondary extrusion process is also a common practice to achieve new products with improved properties. The new resins have complex structures, especially in terms of composition distribution, and their characterization is not always an easy task. Techniques like temperature rising elution fractionation (TREF) or crystallization analysis fractionation (CRYSTAF) are currently used to characterize the composition distribution of these resins. It has been shown that certain combinations of polyolefins may result in equivocal results if only TREF or CRYSTAF is used separately for their characterization.     

Updated “Onion Skin” Model for Temperature Rising Elution Fractionation

Recent developments on the temperature rising elution fractionation (TREF) technique, understanding the impact strength of polyethylene blends based on their chemical structure, as well as ongoing discussions on REACH legislation regarding the oligomer fraction of polymers, are all reasons for better comprehension of the separation mechanism in TREF. To achieve this goal, two carefully chosen blends of linear metallocene polyethylene were analyzed by TREF over a large domain of crystallization rates. The results allowed updating the “onion skin” model for the crystallization kinetics during the cooling step of TREF. The advantages and limitations of the TREF technique for different applications are discussed.     

Advanced Characterization of Propylene-Based Copolymers and Olefin Block Copolymers

Summary: The newly developed interactive separation of polyolefins by high temperature liquid chromatography (HTLC) provides new information about the chemical composition distribution of polyolefin elastomers. The technique has the advantage of being quantitative in its separation, and has high resolution for the separation of polyolefins by their chemical composition without influence by cocrystallization. Chemical composition distributions can be determined for individual polymers and blends which contain the full range of comonomer typically present in polyethylene and poylypropylene homopolymers, semi-crystalline copolymers, and amorphous copolymers. HTLC analysis in combination with the other fractionation techniques, such as DSC, TREF, NMR, and xylene fractionation, can be used to estimate the amount of olefin block copolymer present in a block composite produced by chain shuttling catalysis.     

Short Chain Branches Distribution Characterization of Ethylene/1-Hexene Copolymers by Using TREF + 13C-NMR and TREF + SC Methods

Summary: Short chain branches distribution (SCBD) is the key factor for high density polyethylene (HDPE) pipe materials to achieve their excellent performance for long term (50 years) applications. However, the precise SCBD characterization of these HDPE materials with relatively low content of comonomer incorporation still remained as a challenge in this field. In this work, two characterization methods, namely temperature rising elution fractionation (TREF) cross step crystallization (SC) (TREF + SC) and TREF cross ¹³C-NMR (TREF + ¹³C-NMR), have been respectively used to qualitatively and quantitatively investigate the SCBD for two HDPE pipe materials (PE-1 and PE-2 with different long term performances) with small amount of 1-hexene incorporation prepared from SiO₂-supported silyl chromate catalyst system (S-2 catalyst) during UNIPOL gas phase polymerization. The comparison of SCBD between the two samples showed that: although short chain branches of PE-2 with good performance were less than those of PE-1 with bad performance, PE-2 showed less comonomer incorporation on the low crystallinity and low molecular weight (MW) fractions keeping even higher comonomer incorporation on the high crystallinity and high MW parts compared with PE-1. This difference on the SCBD for PE-1 and PE-2 was thought to be the key factor which is responsible for their great difference on environment slow crack resistance (ESCR). Moreover, TREF + SC method further reflected the intra- and inter-molecular heterogeneities of each fraction from the two HDPE samples through the lamella thickness distribution compared with TREF + ¹³C-NMR.