聚3-羟基丁酸酯从熔体薄膜及溶液中形成的球晶结构及生长机理

研究了聚3-羟基丁酸酯（PHB）分别从熔体薄膜和溶液中结晶时的球晶结构和形态,提出了在两种不同结晶条件下环带球晶的形成机理．当PHB从熔体薄膜中结晶时,由于二维生长的限制,晶体的不连续生长是球晶形成环带结构的主要原因,而当PHB从溶液中结晶时,片晶生长的扭曲取向导致了球晶环带结构的形成．     

聚合物环带球晶的结晶机理

聚合物环带球晶作为一类特殊的球晶结构,其结晶机理一直倍受关注.经过几十年的研究,对于环带球晶形成机理的认识在不断深入,但是仍有许多问题尚未解决.本文总结了常见聚合物环带球晶的分类,综述了国内外在聚合物环带球晶片晶组织形式和片晶扭转机理研究上的主要进展,力图展示聚合物环带球晶研究的整体概况.根据前期研究结果,总结了手性聚...     

液晶聚芳醚酮/含甲基苯侧基聚芳醚酮共混体系的环带球晶

本文通过研究含氯侧基液晶聚芳醚酮/含甲基苯侧基聚芳醚酮共混体系(结晶/非晶)环带球晶的形态演变和发展过程; 利用选择性溶剂刻蚀方法确定共混体系环带球晶的相组成和相结构, 探讨了环带球晶的形成机理.     

聚己内酯/纳米二氧化硅复合体系环带球晶形貌及结晶行为研究

采用溶液浇铸的方法制备了聚己内酯(PCL)/疏水性纳米二氧化硅(R974)复合体系薄膜,利用偏光显微镜、差示扫描量热仪、扫描电镜等研究了R974对PCL环带球晶形貌及结晶行为的影响,并从微观层次探讨了PCL/R974环带球晶可能的形成机理。结果表明,PCL/R974环带球晶是由扭转生长的片晶构成。R974的加入可诱导PCL环带球晶的形成,拓宽环带球晶形成温度。R974含量越高,PCL形成环带温度越低,环带周期越小,环带结构越规整。等温结晶时,R974加入并未改变PCL异相成核机理,但会影响其结晶动力学。当R974含量≤4%(wt)时,其异相成核作用占主导,促进了PCL结晶过程;当R974含量4%(wt)时,其对于球晶生长的阻碍大于异相成核作用,最终抑制了PCL的结晶。     

聚乙二醇-聚L-丙交酯嵌段共聚物结晶形貌研究

用偏光显微镜和原子力显微镜对比研究了PEG-PLLA嵌段共聚物在110℃或120℃等温结晶后的结晶形貌.发现在110℃时只有PEG5000-PLLA2300和PEG5000-PLLA6300在偏光显微镜下呈现环带球晶形貌,在原子力显微镜高度图中显示明显的环带,并具有交替凸凹起伏形貌.而PEG5000-PLLA12000球晶中没有出现环带形貌而是生成了规则的环线.在120℃时,PEG5000-PLLA12000的球晶中才生成了规则的环带图案,原子力显微镜也显示了其球晶具有明显的交替凸凹起伏形貌,说明过冷度直接影响环带球晶的生成.产生周期性凸凹起伏和明暗交替消光是由片晶沿着球晶的半径方向周期性扭转造成的,片晶在凸起部分是Edge-on取向,在凹下部分是Flat-on取向.     

不相容PHBV/PS、PHBV/PMMA结晶/非晶共混体系的结晶行为研究

在不同的共混比例、不同的结晶温度下对不相容PHBV/PS、PHBV/PMMA结晶/非晶共混体系的结晶行为做了系统的研究.研究发现当PHBV含量为75wt%时,共混体系仍然和纯PHBV一样生成环带球晶;而当PHBV含量为50wt%时,共混体系在略低于非晶组分玻璃化转变温度时呈现花瓣状的球晶形貌;当PHBV含量为25wt%时,PHBV/PS体系出现不规则的晶体形貌,而PHBV/PMMA体系在偏光显微镜下没有观察到晶体.在这种不相容共混体系中,非晶组分的分散状态以及共混比例对共混体系中PHBV环带球晶的形成起到决定性的作用,而非晶组分对PHBV球晶的片晶前端生长的影响是形成花瓣状球晶的主要原因.     

聚对苯二甲酸1,3-丙二酯的自晶种成核等温结晶动力学

研究了自晶种成核对聚对苯二甲酸1,3-丙二酯(PTT)结晶行为的影响.示差扫描量热结果表明,经过自晶种成核处理后,PTT的结晶温度明显增加.应用Avrami方程分析了PTT等温结晶动力学,Avrami指数n的平均值为3.34,表明初级结晶为三维球晶生长.自晶种成核导致结晶活化能和链折叠功减小,促进PTT的结晶.     

BTDA/m-PDA聚酰亚胺环带球晶形貌与生长影响因素的研究

综述了本课题组BTDA/m-PDA聚酰亚胺环带球晶研究的进展.通过偏光显微镜(PLM),透射电镜(TEM),和原子力显微镜(AFM),研究了球晶中片晶的生长形貌,并探讨了环带形成的机理.考察了环带球晶生长的影响因素,包括:(1)温度:在较低酰亚胺化温度下只能形成不规则的球晶,而在较高温度下形成中心环间距较大的球晶;(2)聚酰胺酸分子量:分子量较低聚酰胺酸不能形成环带球晶;(3)分子链的不对称性:通过不同比例单体共聚发现,分子链上间苯二胺和羰基的不对称性对环带的形成有着决定性的影响;(4)溶剂:随着溶剂含量的增加,环带球晶的环间距增大.     

聚己内酯/硝基纤维素共混体系结晶行为的研究

通过对聚己内酯／硝基纤维素共混体系的热分析、傅立叶变换红外光谱的研究，证实了该共混体系在聚己内酯含量较高时，是一个热力学相容的体系，同时两组分之间存在强的氢键相互作用。在此体系中聚己内酯长成了清晰规整的环带球晶。聚己内酯结晶形态随结晶温度和共混物组成的变化表明，在共混体系中聚己内酯结晶速率与非晶第二组分的扩散速率存在一定的匹配关系，是影响环带球晶形成的重要因素。     

分子端基效应对聚(L-乳酸)球晶环带结构形成的影响

通过活性正离子开环聚合的方法,以苯甲醇或月桂胺引发L-丙交酯聚合合成了一系列分子量可控的聚(L-乳酸)(PLLA).研究发现,端基刚、柔性的变化,改变了PLLA环带球晶的生成条件和环带周期结构,因此可以通过改变端基的结构来调控PLLA所形成的环带结构.分子量相近而端基不同的PLLA,在相同温度下结晶时,刚性引发剂苯甲醇...     

Nonisothermal crystallization kinetics and spherulite morphology of poly(trimethylene terephthalate)

The nonisothermal melt crystallization behavior of poly(trimethylene terephthalate) (PTT) was investigated using the DSC technique. PTT peak exothermic crystallization temperature was found to move to lower temperatures as the cooling rate was increased. The modified Avrami equation exponent, n, was 4 when the cooling rates were between 5 and 15 °C/min, indicating a thermal nucleation and a three-dimensional spherical growth mechanism. When the cooling rate was increased to 25 °C/min, n gradually decreased to near 3, implying the nucleation mechanism changed to an athermal mode. PTT nonisothermal crystallization behavior could also be analyzed using the Ozawa equation and the combined equations of Ozawa and Avrami with very good fit of the data.PTT spherulite morphologies and the sign of the birefringence depended strongly on the spherulite's growth temperature. When the growth temperature was decreased from 222 to 170 °C, the spherulite changed from a saturation-type dendritic morphology to one with a colorful banded texture; the sign of the birefringence also changed in the following order: from a weakly positive spherulite → mixed spherulite → weakly negative spherulite → negative spherulite → positive spherulite → negative spherulite → positive spherulite.     

Morphological changes of BTDA/m‐PDA polyimide banded spherulites: The effect of solvent on banding

BTDA/m‐PDA polyimide banded spherulites with different band spacing were observed in the same sandwiched film. Atom force microscopy (AFM) analysis suggested that the banded structure was caused by periodic twisting of radial grown lamella bundles. Based on polarizing light microscopy (PLM) and AFM observation, it was found that spherulites grown near the center of the film exhibited bigger band spacing and consisted of wider lamellae compared with those grown near the fringe, which was suggested to be caused by different solvent amount during imidization and crystallization: the more solvent existed, the wider the lamella would grow and the bigger the band spacing would be. It was further proved by changing the film thickness and PAA solution concentration. SEM observation showed that when crystallized in the solution, the lamella became ultra thick and straight, and formed small particles. Powder X‐ray diffraction revealed that crystal structures of the banded spherulite and the small particle were identical or at least very similar. Another solvent with lower boiling point was used in sample preparation, however, under the same preparation conditions, the grown features of banded spherulites did not change. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 659–667, 2008     

Isothermal and Non-Isothermal Crystallization Kinetics and Morphology of Poly(trimethylene terephthalate)/Multiwalled Carbon Nanotube Composites

Summary: Multiwalled carbon nanotubes (MWCNTs) synthesized using chemical vapor deposition method were dispersed in poly(trimethylene terephthalate) (PTT, Mv = 88,000) by melt compounding technique using DMS microcompounder. The nanocomposites consisting of varying amounts of MWCNTs were characterized by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of carbon nanotubes on the crystallization behavior (under isothermal and non isothermal crystallization conditions) of PTT was studied using DSC. The presence of carbon nanotubes didn't show any significant effect on crystallization temperature of PTT matrix under non-isothermal conditions. Crystallization studies under isothermal conditions were carried out at different temperatures i.e 185, 190, 195 and 200 °C. Complete crystallization was observed within 60 sec at 185 °C whereas at 200 °C, longer time was required for complete crystallization. Crystal growth was also investigated using hot stage polarizing microscope (PLM). The effect of annealing time at 200 °C was investigated in the presence as well as in the absence of varying amounts of MWCNTs. Spherulitic growth was seen and the spherulite size in all the samples increased with annealing time. Morphological characterization using SEM and TEM showed a uniform dispersion of MWCNTs and poor compatibility with PTT matrix.     

Lamellar orientation in thin films of symmetric semicrytalline polystyrene-b-poly(ethylene-co-butene) block copolymers: effects of molar mass, temperature of solvent evaporation, and annealing

Orientation of the lamellar microdomains in thin films of three symmetric polystyrene-b-poly(ethylene-co-butylene) block copolymers (S65E155, S156E358, and S199E452) on mica was investigated via atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS). The results show that lamellar orientation in the SxEy block copolymers greatly depends on the molar mass of the block copolymers, the temperature of solvent evaporation, and annealing. The nascent thin film of the low molar mass block copolymer, S65E155, shows a multilayered structure parallel to the mica surface with the PS block at both polymer/mica and polymer/air interfaces, but the high molar mass block copolymers, S156E358 and S199E452, exhibit a structure with lamellar microdomains perpendicular to the mica surface. When the solvent is evaporated at a lower temperature, the crystallization rate is fast and a two-dimensional spherulite structure with the lamellar microdomains perpendicular to the mica surface is observed. Annealing of all the thin films with lamellar microdomains perpendicular to the mica surface leads to morphological transformation into a multilayered structure parallel to the mica surface. In all SxEy thin films on mica, the stems of PE crystals are always perpendicular to the interface between the lamellar PE and PS microdomains. A mechanism is proposed for the formation of different microdomain orientations in the thin films of semicrystalline block copolymers. When the thin film is prepared from a homogeneous solution, microdomains perpendicular to the substrate surface are formed rapidly for strongly segregated block copolymers or at a lower crystallization temperature and kinetically trapped by the strong segregation strength or solidification of crystallization, while for weakly segregated block copolymers or at slower crystallization rate, the orientation of the microdomains is dominated by surface selectivity.     

Morphologies and enzymatic degradability of melt-crystallized poly(3-hydroxybutyric acid-Co-6-hydroxyhexanoic acid)

The films of poly[(R)-3-hydroxybutyric acid-co-10mol% 6-hydroxy-hexanoic acid] (P[(R)-3HB-co-6HH]) were prepared by melt-crystallized method at various crystallization temperatures. The morphologies and properties of melt-crystallized films were characterized by means of x-ray diffraction, differential scanning calorimetry, optical microscopy, and scanning electron microscopy. All of the melt-crystallized films showed the banded spherulite morphology. The enzymatic degradation of melt-crystallized films was carried out at 37 °C in an aqueous solution (pH 7.4) of PHB depolymerase from Alcaligenes faecalis. The rate of enzymatic erosion was strongly dependent on the crystallinity of films, and the highest rate was as large as 2.15 mg·h⁻¹·cm⁻². After enzymatic degradation, the banded morphology of P[(R)-3HB-co-6HH] spherulites was visible, suggesting that PHB depolymerase predominantly hydrolyzes polymer chains on the edges of crystalline lamellar stacks.     

聚对苯二甲酸乙二酯结晶过程中的反常行为

聚合物的结晶是高分子链由无序转变为在三维空间中有规则排列的过程。实现转变的外界条件主要是温度和时间。近年来,人们借助偏光显微镜法(PLM)、小角激光光散射法(SALS)等研究聚对苯二甲酸乙二酯(PET)的结晶形态已有不少报导。     

Surface and interior views on origins of two types of banded spherulites in poly(nonamethylene terephthalate)

Top-surface and three-dimensional views of Type-1 and Type-2 of ring-banded spherulites in poly(nonamethylene terephthalate) (PNT) in thicker bulk crystallized on a nucleating potassium bromide (KBr) substrate were examined using various microscopy techniques: scanning electron microscopy (SEM), polarized-optical microscopy (POM), and atomic-force microscopy (AFM). In PNT crystallized at higher crystallization temperature (T(c)) with heterogeneous nucleating substrate, typically two types of ring-banded spherulites are present that differ significantly in patterns and ring spacings: Type-1 Type-2 (single- and double-ring-banded spherulites). Three-dimensional view on fractured spherulites in bulk PNT samples reveals that the single-ring-banded spherulite (Type-1) tends to be well-rounded spheres as they are nucleated homogeneously from bulk; the double-ring-banded spherulite (Type-2) is concentric hemisphere or truncated sphere shells owing to be nucleated from bottom. With confined thickness of films, the 3-D hemispheres in PNT may become truncated into multi-shell annular cones or arcs when thickness or growth is restricted. Based on the top-surface vs. interior views of banded lamellar assembly, origins and inner structures of dual types of ring bands in PNT were examined in greater details.     

PTT/PET共混体系晶体形态与结晶性能的研究

用差示扫描量热仪(DSC)、广角X射线衍射(WAXD)和正交偏光显微镜研究了聚对苯二甲酸丙二酯(PTT)和聚对苯二甲酸乙二酯(PET)共混体系的晶体形态与结晶性能.结果表明,共混体系结晶性能与PTT的含量有关.PET的加入,使共混体系的球晶尺寸减小.球晶完善性降低.当PTT含量为40wt%～60wt%时,共混物分别出现了双重熔融峰和双重结晶峰.双重熔融峰是加热过程中熔融重结晶造成的,双重结晶峰说明不完善的晶体产生的次级结晶.     

Crystal structure and thermal behavior of cold-crystallized poly(trimethylene terephthalate)

The structure and thermal behavior of cold-crystallized poly(trimethylene terephthalate) (PTT) are revealed in detail by DSC, AFM, TEM, and WAXD as well as in situ FTIR and SAXS techniques. There is no effect of crystallization temperature and initial state on the crystal modification, yet the morphology is strongly affected by these two factors. First, the small rod-like lamellae for PTT are obtained during the cold crystallization instead of the spherulites formed in the melt crystallization. Second, the edge-on lamellar orientation in thin films is identified during the cold crystallization. The thickness and the lateral width of rod-like lamellae get larger and larger with increasing crystallization temperature. Thin lamellar crystals assemble randomly when the cold-crystallization temperature is lower, while lamellar stacks composed of thicker lamellae are observed when the PTT was annealed at elevated temperature. Moreover, for the cold-crystallized PTT, the final melting temperature does not vary with the crystallization temperature. This phenomenon is explained by the structural improvement during the heating process. For the cold-crystallized PTT sample at lower temperature, three transitions occur when it is heated again: the relaxation of the rigid amorphous phase, the reorganization of molecules in the intermediate phase, and then the melt–recrystallization behavior. Those transitions finally lead to thicker lamellae besides a higher crystallinity before the final fusion. Therefore, the final melting peak of these lamellae is at the same temperature.