PEO分子量对POM/PEO晶/晶共混物溶液结晶的影响

以六氟异丙醇(HFIP)为聚甲醛(POM)与聚氧化乙烯(PEO)的共溶剂,通过溶液结晶研究了PEO分子量对POM/PEO 50/50晶/晶共混物结晶行为及结晶形态的影响。结果表明,PEO分子量越小,POM与PEO在结晶过程中相互干扰越大。当PEO分子量为4×103时,共混物中POM形成部分不完善晶体,出现明显的熔融双峰。SEM结果表明:含不同分子量PEO的共混晶体均无明显相分离,且低分子量PEO的共混物更易形成规整球晶,认为通过溶液结晶,POM/PEO 50/50共混物中POM与PEO形成了晶体相互穿插的结晶结构。     

线形、梳形和星形高分子静态和动态性质的模拟

以梳形高分子为纽带,基于粗粒化分子动力学模拟方法,研究了线形、梳形和星形拓扑结构高分子的静态和动态性质,以揭示稀溶液中高分子链行为与链拓扑结构依赖关系的一般性规律.研究结果表明,随着线形-梳形-星形的链拓扑结构转变,回转半径的标度关系由仅依赖分子聚合度转变为同时依赖链聚合度与臂数或侧链数.分析了星形高分子和梳形高分子的静态和动态性质的特征规律.星形高分子的臂数增加使其尺寸迅速减小,形状则由长椭球形转变为类球形,且扩散系数也随之增加;其均方回转半径(〈R_g〉)和扩散系数(D)与分子聚合度(N)及臂数(f)的标度规律为〈R_g〉~N~(0.581)f~(-0.402),D~N~(-0.763)f~(0.227).梳形高分子的静态与动态性质与分子聚合度及侧链数的依赖关系为〈R_g〉~N~(0.597)f~(-0.212)(每个支化点只有一条侧链)和〈R_g〉~N~(0.599)f~(-0.316)(每个支化点有多条侧链).     

HBPS-PEO多臂星形聚合物电解质的合成及离子导电性的研究

通过叠氮化超支化聚苯乙烯(HBPS-N3)与端炔基聚乙二醇单甲醚(ay-PEO)的点击反应,合成了以超支化聚苯乙烯(HBPS)为核、不同分子量的聚氧化乙烯(PEO)为臂的多臂星形聚合物(HBPS-PEO),并利用ATR-FTIR,1H-NMR,GPC对合成的星形聚合物的结构进行了表征.将该种星形聚合物与双三氟甲基磺酰亚胺锂(LiTFSI)进行复合,制备了星形聚合物为基体的聚合物电解质,通过交流阻抗技术和DSC对该聚合物电解质的离子导电性能及热性能进行了研究.结果表明,星形结构可以在一定程度上抑制结晶的形成,这种新型的星形聚合物电解质的室温电导率明显高于相应的线形聚合物电解质,当n(EO)/n(Li)=40,PEO臂的分子量为1000时,该星形聚合物电解质的离子电导率最高,30℃时为6.7×10-5Scm-1,40℃时可以达到1.2×10-4Scm-1;TGA结果表明,制备的星形聚合物的初始分解温度(Tonset)都高于360℃,具有良好的热稳定性.     

铜离子配位下的聚氧乙烯受限结晶行为研究——缺陷引起的熔点下降

利用铜离子(Cu2+)对聚氧乙烯(PEO)的配位作用所形成的对分子链运动的束缚,研究了链段受限下PEO的结晶和熔融行为.首先利用宽频介电松弛谱(BDS)对受限条件下PEO的松弛行为进行表征,结果表明,加入铜离子后PEO的β-过程和γ-过程的特征松弛时间都变长,说明PEO的链段协同运动和主链扭转运动都变得更加困难;松弛时间为评价受限程度提供了定量的依据.DSC的测试结果表明,受限条件下PEO的玻璃化转变温度(Tg)升高,同时出现冷结晶现象,说明Cu2+配位作用确实对PEO的链段运动产生了束缚作用;同时PEO的结晶度和熔点都随着铜离子含量的提高而降低.WAXD结果表明,CuBr2在共混物中没有发生结晶,同时PEO的晶型没有发生改变.利用AFM进一步研究了PEO/CuBr2共混物薄膜的结晶形貌,发现在不同Cu2+含量的共混物中PEO都形成伸直链晶体,片晶厚度没有变化,说明熔点的降低并非是片晶厚度变化所导致.但是AFM的结果却显示螺位错晶体的数量随着Cu2+含量的提高明显增加.可以认为,在Cu2+配位受限下的PEO体系中,晶体缺陷应是引起熔点下降的主要原因,和金属等其它晶体材料的情况有着类似效应.     

含环糊精链节的拓扑高分子

星形、超支化、树枝状、刷状等具有支化拓扑结构的高分子通常具有不同于直链结构高分子的优异性能。将有客体包合功能的环糊精与其结合构筑环糊精拓扑高分子体系,有望在分子识别、基因传输、药控释放等领域得到应用。本文根据高分子拓扑形态的不同,从星形、超支化、树枝状以及其他拓扑形态环糊精聚合物的合成及自组装构筑等方面进行了总结和评述,并在此基础上展望了基于环糊精的拓扑高分子的研究方向和发展趋势。     

聚氧化乙烯受限态下等温结晶动力学的高速扫描量热研究

利用高速扫描量热仪(FSC)研究聚氧化乙烯(PEO)样品在三维受限小液滴中的等温结晶过程,获得了样品从玻璃化转变温度至熔点温度整个区间的等温结晶动力学. PEO本体样品由于异相成核作用明显,以5×104 K/s的速率降温依然无法抑制其在降温过程中的成核过程,而通过PEO薄膜去润湿获得的小液滴则可在1×104 K/s升降温速率下获得完全无序态的样品.对本体PEO和去润湿得到的PEO液滴样品进行不同温度的等温结晶实验,通过对比PEO受限前后等温结晶动力学的变化发现,相对于PEO本体样品,液滴样品的结晶速率在整个等温温度区间均有所下降.在高温异相成核控制区,当PEO样品受限成为多个比本体样品直径小10倍左右的小液滴后,每个液滴内异相成核位点数减少或缺失,从而导致整体总结晶速率降低;而低温均相成核控制区,由于PEO样品的独特性,异相成核对其成核过程仍然有一定的影响,受限成液滴后此影响消失,同时链段扩散晶体生长过程受到尺寸效应的限制,也在一定程度上影响了PEO的总结晶速率.     

温敏星形树枝化聚合物的制备及表征

通过两步可逆-加成断裂链转移(RAFT)聚合反应制备了双嵌段树枝化共聚物PPDSn-b-PG1m,以此嵌段共聚物为臂,进一步以1,2-乙二硫醇为交联剂通过二硫键与巯基的交换反应实现核交联,采用"先臂后核"法设计制备了系列以烷氧醚树枝化聚合物为臂的温敏星形树枝化聚合物PPDSn-b-PG1m-SS.采用1H-NMR、GPC对目标星形树枝化聚合物的结构和分子量进行了分析表征;利用变温UV-Vis光谱和原子力显微镜等分别考察了目标星形树枝化聚合物水溶液的温敏行为及其分子形貌特征.结果表明,该类星形树枝化聚合物具有与母体树枝化聚合物类似的优异温敏行为(相转变温度~36?C),其单分子尺寸较大,且随着臂长的不同在底物上分别呈现出明显的星状或球状形貌.     

三(2,6-二叔丁基-4-甲基苯氧基)镧配合物催化合成星形聚己内酯

分别以三乙醇胺和四乙醇乙二胺为引发剂,用三(2,6-二叔丁基-4-甲基苯氧基)镧(La(DBMP)3)作催化剂,催化ε-己内酯开环聚合,制备了三臂和四臂星形聚己内酯.通过1HNMR表征了聚合物的星形结构以及分子量.研究表明,每一个催化剂分子可与多个引发剂分子作用,当三乙醇胺与La(DBMP)3的摩尔比值为1.7～6.4时,均可制得纯净的三臂星形聚己内酯.通过调节ε-己内酯与多元醇的摩尔比值,可以改变星形聚己内酯的分子量,实现聚合产物分子量可控.     

聚左旋乳酸/聚氧化乙烯共混物的拉伸行为及结构转变

采用熔融共混方法制备了聚左旋乳酸(PLLA)和超高分子量聚氧化乙烯(PEO)共混物, 通过差示扫描量热(DSC)、 扫描电子显微镜(SEM)和二维广角X射线散射(2D-WAXS)等方法系统研究了PEO的加入对不同温度下PLLA拉伸行为及拉伸过程中微观结构变化的影响. 结果表明, PLLA/PEO共混物为非均相体系, PEO粒子均匀分布在PLLA中形成两相结构. PEO的加入能够显著降低PLLA的玻璃化转变温度(T_g), 在25～60 ℃范围内显著提高PLLA的拉伸性能. 在60 ℃拉伸时, PEO的加入提高了PLLA在拉伸过程中的结晶和形变能力. 在80 ℃拉伸时, 共混物的拉伸断裂伸长率下降, 但共混物的结晶速度仍高于纯PLLA样品.     

一组线型聚苯乙烯和星形支化聚苯乙烯的凝胶色谱与热场流分级方法的比较

本文应用热场流分级方法,在两种不同的场强下(△T=30℃、△T=50℃),测试了一系列窄分布聚苯乙烯标样和星形支化聚苯乙烯的淋出体积V_r和分子量M的依赖关系。星形支化物的臂数不同,但臂的分子量相同,上述样品进行了GPC测试,实验表明,由TFFF得到的支化的与线型聚苯乙烯在V_r～M关系上的差别大于GPC的结果,表明链结构对扩散系数的影响大于对分子体积的影响。     

Langmuir and Langmuir-Blodgett films of poly(ethylene oxide)-b-poly(epsilon-caprolactone) star-shaped block copolymers

Self-assembly of poly(ethylene oxide)-block-poly(epsilon-caprolactone) five-arm stars (PEO-b-PCL) was studied at the air/water (A/W) interface. The block copolymers consist of a hydrophilic PEO core with hydrophobic PCL chains at the star periphery. All the polymers have the same number of ethylene oxide repeat units (9 per arm), and the number of epsilon-caprolactone repeat units ranges from 0 to 18 per arm. The Langmuir monolayers were analyzed by surface pressure/mean molecular area isotherms, compression-expansion hysteresis experiments, and isobaric relaxation measurements, and the Langmuir-Blodgett (LB) films' morphologies were investigated by atomic force microscopy (AFM). PCL homopolymers crystallize directly at the A/W interface in a narrow surface pressure range (11-15 mN/m). In the same pressure region, the star-shaped block copolymers undergo a phase transition corresponding to the collapse and the crystallization of the PCL chains as shown by the presence of a pseudoplateau in the isotherms. The LB films were prepared by transferring the Langmuir monolayers onto mica substrates at various surface pressures. AFM imaging confirmed the formation of PCL crystals in the LB monolayers of the PCL homopolymers and of the copolymers, but also showed that the PCL segments can undergo additional crystallization after monolayer transfer during water evaporation. The PCL crystal morphologies were also strongly influenced by the surface pressure and by the PEO segments.     

Effects of multi-arm structure on crystallization and biodegradation of star-shaped poly(epsilon-caprolactone)

Star-shaped PCL with one to five arms were synthesized by ROP. They have the same crystal structure as linear PCL, indicating that the central cores are located in amorphous regions. The influence of arm length and number on crystallization and melting behavior were studied by DSC, POM, and through the Avrami equation. A model is proposed to analyze the enzymatic degradation process of star-shaped polymers. The multi-arm structure and the limitation of the central cores on the chain mobility of each arm are considered to be the primary factors influencing the characteristic crystallization and enzymatic degradation behavior of star-shaped PCLs.     

Effect of Star-shaped chain architectures on the polylactide stereocomplex crystallization behaviors

Linear and star-shaped polylactides (PLA) with similar molecular weights of each arm are synthesized via ring-opening polymerization of LA with 3-butyn-l-ol and pentaerythritol as initiators,respectively.By solution blending of equivalent mass of poly(L-lactic acid)s (PLLAs) and poly(D-lactic acid)s (PDLAs),perfect PLA stereocomplexes (scPLAs) are prepared and confirmed by WAXD and FTIR analysis.Effect of chain architectures on stereocomplex crystallization is investigated by studying the non-isothermal and isothermal crystallization of linear and star-shaped polylactide stereocomplexes.In dynamic DSC and POM test,star-shaped PLLA (4sPLLA)/PDLA and PLLA/star-shaped PDLA (4sPDLA) stereocomplexes reach rapid crystallization and higher crystallinity due to larger spherulite density of star-shaped chain and excellent chain mobility of linear chain.In isothermal crystallization test,much faster crystallization and less crystallization half-time is obtained with the increase of star-shaped chain.Meanwhile,4sPLLA/PDLA and PLLA/4sPDLA are found to have the highest crystallinity,suggesting limitation of too much star-shaped chain for 4sPLLA/4sPDLA and restriction of linear chain in nucleation capacity for PLLA/PDLA.The results reveal that star-shaped chain has an important influence on the crystallization of scPLAs.     

The combination of fluctuation-assisted crystallization and interface-assisted crystallization in a crystalline/crystalline blend of poly(ethylene oxide) and poly(ε-caprolactone)

The nucleation and crystallization of poly(ethylene oxide) (PEO) and poly(ε-caprolactone) (PCL) in the PEO/PCL blends have been investigated by means of optical microscopy (OM) and differential scanning calorimetry (DSC). During the isothermal or nonisothermal crystallization process, when the adjacent PEO is in the molten state, PCL nucleation preferentially occurs at the PEO and PCL interface; after the crystallization of the adjacent PEO, much more PCL nuclei form on the surface of the PEO crystal. However, PEO crystallizes normally and no interfacial nucleation occurs in the blend. The concentration fluctuation caused by liquid–liquid phase separation (LLPS) induces the motion of PEO and PCL chains through interdiffusion and possible orientation of chain segments. The oriented PEO chain segments can assist PCL nucleation, and the heterogeneous nucleation ability of PEO increases with the orientation of PEO chains. Oriented PCL chain segments have no heterogeneous nucleation ability on PEO. It is postulated that the interfacial nucleation of PCL in the PEO/PCL blend follows the combination of “fluctuation-assisted crystallization” and “interface-assisted crystallization” mechanisms.

原子力显微镜针尖诱导聚氧乙烯熔体结晶的研究

原子力显微镜(AFM)是研究高分子结晶行为的一种重要实验手段.在使用AFM原位观察高分子结晶时,为保证能真实地反映结晶过程,一个必须注意的问题是要避免AFM针尖的影响.与此同时,人们考察了在AFM扫描时针尖诱导高分子结晶成核的情况.若使用AFM接触模式(contactmode),扫描时容易造     

Molecular and hydrodynamic characteristics of star-shaped polystyrenes with one or two fullerene (C<Subscript>60</Subscript>) molecules as a branching center

The molecular properties of regular star-shaped polystyrenes with different numbers of arms (6, 12, and 22) and different structures of the branching center (one or two covalently bonded fullerene C60 molecules) are studied by static light scattering; translational diffusion; and viscometry in toluene, THF, and chloroform. The lengths of the arms for the studied polymer stars are found to be the same. (The molecular mass of the arm is 8.1 × 10³.) The molecular mass and hydrodynamic sizes of macromolecules are estimated. It is shown that the conformational and hydrodynamic characteristics of polymer stars remain practically unchanged on passage from THF to chloroform. Compared to the linear analog, star-shaped fullerene-containing PSs are characterized by a higher density of the molecular coil. The shape of their macromolecules differs insignificantly from spherical, in consistence with theoretical predictions for polymer stars with relatively short arms.     

Model experiments for a molecular understanding of polymer crystallization

Time‐resolved real‐space observations of morphology and pattern formation resulting from crystallization of ultrathin films of low‐molecular‐weight poly(ethylene oxide) (PEO) or diblock copolymers containing PEO shed light on the mechanisms of how polymer crystals are formed. We used simple but restricted geometries like thin films of controlled thickness or confinement resulting from block copolymer mesotructures. Under such conditions, we were able to relate the observed morphology and its temporal evolution directly to molecular processes and the kinetics of crystal growth. We demonstrate that changes in the morphology with time are due to different thermal histories and are the consequence of the mestable nature of polymer crystals. Information about the nucleation process was obtained by examining crystal formation in 12‐nm small spherical cells of a block copolymer mesostructure. We discuss the advantages of thin‐film studies for a better understanding of polymer crystallization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1869–1877, 2003     

Structural features of star-shaped fullerene (C60)-containing polystyrenes: Neutron scattering experiments

Structural features of star-shaped polyprotostyrene and polydeuterostyrene containing fullerene C₆₀ as a branching center have been studied by small-angle neutron scattering in benzene solutions. The results are compared with the corresponding characteristics of linear PSs, the molecular mass of which is equal to the molecular mass of one star arm in star-shaped macromolecules. The molecular masses of star-shaped polymers are estimated, and their branching center is shown to be hexafunctional. At relatively low concentrations of starshaped polymers in solutions, one can observe excluded volume effects, which are related by the presence of regions with higher densities at the center of a macromolecule. Using the Fourier transform of the scattering cross section, three-dimensional correlation functions are obtained, and the regular structure of stars is proved. Conclusions about the local correlations of units within one star arm and averaged correlations between units of neighboring arms within a given star are derived. An analysis of three-dimensional correlations shows that the centers of mass of all star arms are directed along orthogonal axes passing through the C₆₀ branching center of a star-shaped macromolecule.     

Synthesis and characterisation of star-shaped liquid crystalline polymer with a POSS core

The star-shaped POSS-graft-LCP with POSS as the core and liquid crystal polymer, poly{6-(4?-octyloxyphenyl-4″-benzoyl)hexyl acrylate}, as arms was prepared by atom transfer radical polymerisation technique using octa(3-chloropropyl) polyhedral oligomeric silsesquioxane [POSS-(CH₂CH₂CH₂Cl)₈] as initiator. For comparison, the linear liquid crystal polymer, poly{6-(4?-octyloxyphenyl-4″-benzoyl)hexyl acrylate} (LLCP), was obtained by conventional radical polymerisation. Both liquid crystal polymers were characterised by FT-IR, ¹H NMR, ¹³C NMR, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, polarised optical microscopy and X-ray diffraction analysis. The liquid crystal phase behaviour research demonstrated that both liquid crystal polymers were reversible thermotropic nematic liquid crystal materials. The number of polymerisation degree of every arm attached on POSS in POSS-graft-LCP impacted greatly on the liquid crystal properties and only a small one was necessary for it to exhibit a broad liquid crystal range. Results further demonstrated that the special star-shaped topology of POSS and the eight arms attached helped POSS-graft-LCP form and stabilise liquid crystal phase easily. This research may further expand the way to star-shaped LCPs by employing a variety of (meth)acrylate and other vinyl liquid crystalline monomers.     

Crystallization behavior of disproportionately high and low molecular weight PEO blends

The crystallization behavior of PEOs with molecular weight of 1 Ok and 200k as well as their blends was studied in details. The results show that the lower molecular weight PEO crystallizes with faster crystallization rate as judged from a shorter time for completing the crystallization. On the other hand, the higher molecular weight PEO crystallizes at relatively higher temperature, indicating an early start of crystallization compared with the lower molecular weight one. The blends of these two PEOs with different blend ratios always cocrystallize during the cooling processes. It is confirmed that mixing of the 10k PEO with the 200k one is in favor of the crystallization of the system. This is not only demonstrated by the early start of the crystallization at higher crystallization temperature, and also a faster crystal growth of the blend with respect to the 200k PEO. The crystallization of the blends at higher temperature is caused by an early start of nucleation and an increment of nucleus density. This may originate from the density fluctuation of the blend and a reduction in energy barrier for nucleation. Moreover, it is found that the crystallinity of the 1 Ok PEO rich blends increases with increasing concentration of the 10k PEO. This is caused by the solvent effect of the 10k PEO toward the 200k PEO. On the other hand, the crystallinity of the 30/70 （10k/200k） PEO blend is decreased a little bit. This may be a balanced result of the improved crystallization of the 200k PEO at the expense of the high crystallization ability of the 1 Ok PEO.