PC/PET/EPDM共混体系的结晶与熔融行为

本文用解偏振光法与DSC法分别测定并研究了PC/PET/EPDM共混体系的结晶速度、结晶度、Avrami指数(n)和熔融温度及其影响因素,共混物中PET的结晶速度、结晶度均随PC含量增加而下降;EPDM用量不超过10%时,可提高PET的结晶速度,但不影响结晶度和成核与增长方式,n值不变。当EPDM为5%时,结晶速度呈现极大值。经退火处理的共混物呈现熔融双峰,PC量增加,高温熔融峰略移向高温方向;热处理温度升高或时间延长,则低温熔融峰移向高温方向。     

PBT／PET共混体系非晶区的相容性

利用ＰＢＴ、ＰＥＴ的特性参数，通过不同组份比ＰＢＴ／ＰＥＴ共混体系的混合自由能△Ｇｍ，从理论上预测其相容性。在一定的条件下△Ｇｍ＜０，ＰＢＴ、ＰＥＴ可以相容。对不同组份比共混体系的玻璃化转变过程从分子链段运动的角度进行分析。     

Y-shaped block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide) synthesized by ATRP

Novel Y-shaped block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide),PEG-b-(PNIPAM)_2,were successfully synthesized through atom transfer radical polymerization(ATRP).A difunctional macroinitiator was prepared by esterification of 2,2-dichloroacetyl chloride with poly(ethylene glycol) monomethyl ether(PEG).The copolymers were obtained via the ATRP of N-isopropylacrylamide(NIPAM) at 30℃with CuCl/Me_6TREN as a catalyst system and DMF/H_2O(v/v = 3:1) mixture as solvent.The resulting copo...     

New architectures of poly(ethylene glycol) and poly(methylthiirane) in block copolymers

Two synthetic ways were experimented to prepare new architectures of block copolymers made of poly(ethylene glycol) (PEG) and poly(methylthiirane). The coupling of both blocks conveniently end-capped as well as anionic polymerization of methylthiirane initiated by PEG-thiols gave readily the copolymers. Their characterization by ¹H NMR, SEC and IR confirmed the expected structures.     

Synthesis of poly[arylene ether sulfone-b-vinylidene fluoride] block copolymers

A series of α,ω-dihydroxy polyarylene sulfones (PAES) were synthesized comprising bisphenol A (PAES1, M_n=1800, 4900, and 9500 daltons), 4,4^′-biphenol (PAES2, M_n=4100 daltons), and hexafluorobisphenol A (PAES3, M_n=3300 daltons). These were reacted with α,ω-dibromo poly(vinylidene fluoride) (PVDF, M_n=1200 daltons) prepared by telomerization, to yield block copolymers possessing rigid and flexible segments. Block copolymers were characterized by FTIR, NMR, GPC, DSC, TGA and TEM. In several cases the block copolymers exhibited distinct thermal transitions, i.e. T_m and T_g for PVDF and PAES segments, respectively. Where observable, T_g of PAES domains in the block copolymers occurred at a temperature lower than the corresponding PAES homopolymer due to the flexible nature of the surrounding PVDF domains. Block copolymers exhibited a similar thermal stability to the corresponding PAES homopolymers but higher stability than the PVDF homopolymer, and much higher still than α,ω-dibromo PVDF. TEM analyses indicate that phase separation of PAES and PVDF domains occurs on the nanometer scale.     

The effect of annealing on the subsequent cold crystallization of amorphous poly(ethylene terephthalate)

Amorphous poly(ethylene terephthalate) was annealed at temperatures around the glass transition temperature and then heated up in differential scanning calorimeter at 20 °C min⁻¹. It was found that the annealing favored the subsequent cold crystallization and this effect became stronger with increasing annealing temperature. The experimental results were explained by considering the structural change during the annealing.     

Isothermal crystallization kinetics and melting behaviour of PET/ATO nanocomposites prepared by in situ polymerization

Neat poly(ethylene terephthalate) (PET) and PET/antimony doped tin oxide (ATO) nanocomposites were prepared by in situ polymerization. The study of the isothermal crystallization behaviors of neat PET and PET/ATO nanocomposites was carried out using differential scanning calorimetry (DSC). The crystallization kinetics under isothermal conditions could be described by the Avrami equation. For neat PET and PET/ATO nanocomposites, the Avrami exponent n both decreased with increasing crystallization temperature. In addition, for the same crystallization temperature, the value of n increased with increasing ATO content. These suggested that the crystallization types related to the values of n in the Avrami theory could not be suitable for the crystallization of PET and its nanocomposites. The change of the n values indicated that the addition of ATO resulted in the increase of the crystallizing growth points. That is a heterogeneous nucleating effect of ATO on crystallization of PET. In the DSC scan after isothermal crystallization process, multiple melting behavior was found. And the multiple endotherms could be attributed to melting of the recrystallized materials or the secondary lamellae produced during different crystallization processes. The equilibrium melting temperature of PET in the nanocomposites increased with increasing the ATO content. Surface free energy of PET chain folding for crystallization of PET/ATO nanocomposites was lower than that of neat PET, confirming the heterogeneous nucleation effect of ATO.     

Inhibited transesterification of PET/PBT blends filled with silica nanoparticles during melt processing

The blends of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) undergo transesterification reactions between PET and PBT during melt processing. In this research, PET/PBT transesterification has been investigated in the presence of nano-fillers, including pure SiO₂ and silane-coupling-agent-modified SiO₂. The results show that the incorporation of SiO₂ nanoparticles inhibits PET/PBT transesterification, and the influence of pure SiO₂ is higher than modified SiO₂. The inhibition of SiO₂ on transesterification is explained by the fact that the hydroxyl end groups of PET and PBT react with the surface hydroxyl groups of SiO₂ before transesterification due to the high activity of surface hydroxyl groups of SiO₂, and the reduction of hydroxyl end groups of PET and PBT leads to the inhibition of transesterification between PET and PBT. This has been demonstrated by the experimental data of TGA, FTIR, and XPS. And the reactivity of hydroxyl end groups of PBT is higher than that of PET.     

PET/PEN/DBS共混体系结构与形貌的研究

共混是改善聚合物性能的一种简单而又行之有效的方法,PET和PEN均为结晶性聚酯,由于PEN合成原料的影响,致使PEN的价格较高,但性能比PET优良,通过二者的共混,既可以提高PET的性能,又可以降低PEN成本,有关PET／PEN共混体系的研究已引起人们的关注,而对于共混体系结晶形态和结晶条件的研究较少,由于成核剂能够提高结晶速率,减小球晶尺寸,因此本文对PET／PEN／DBS共混体系中,组分组成的影响及不同结晶条件下共混物的结晶形貌进行研究。     

Polycaprolactone–poly(ethylene glycol) block copolymer,I: synthesis and degradability in vitro

A new type of biodegradable polymer material, poly(caprolactone)–poly(ethylene glycol) block copolymer (PCL-b-PEG), was synthesized by means of direct copolycondensation of ε-caprolactone with poly(ethylene glycol) in the presence of a Ti(OBu)₄ catalyst. The degradability of the polycaprolactone was improved by introducing a PEG component into it. The degradation of PCL-b-PEG copolymer increase with a decreasing crystallinity of the copolymer, and can be controlled by adjusting the component ratio of the copolymer.     

增容剂对聚对苯二甲酸乙二酯/聚丙烯共混体系结构流变学的影响

采用马来酸酐接枝聚丙烯(PP-g-MAH)对聚丙烯/聚对苯二甲酸乙二酯(PP/PET)共混体系进行增容,研究了增容前后复合体系的相形态和流变行为的变化.结果表明,共混体系中当PP组分为分散相时,增容剂能够显著减小PP液滴尺寸,使其形状松弛时间减小,变形与破裂的剪切敏感性降低;当共混体系两组分配比处于临界相反转点周围时,增容剂则会导致其内部部分双连续与“海-岛”结构共存的复杂相形态消失,低频区模量频率依赖性的增加表明体系内部界面结合程度的增加;而当共混体系中的PET组分为分散相时,增容剂的引入对体系结构流变学影响较小,表明增容效果不大.     

PBT／PET共混体系的熔融行为

用差示扫描量热法（ＤＳＣ）考察了ＰＢＴ／ＰＥＴ共混体系的结晶熔融行为，在共混体系中两组份的结晶熔上均随着含量的减小而下降，熔点下降既有形结构变化因素，又有因两组份相容而引起的热力学因素。熔融热焓△Ｈｍ的变化与两组份结晶熔点的变化有相似的规律。这些结果说明在共混体系中ＰＥＴ、ＰＢＴ两组份在结晶一熔融过程中存在相互协同作用，同时也说明ＰＢＴ、ＰＥＴ两组份是晶相分离的，而非晶区是相混容的。     

PET分子量对PET/PC共混体系高压结晶行为的影响

以往高压合成的聚合物伸直链晶体尺寸较小且合成时间过长,不能满足单晶应用的要求。加入10wt%PC于不同分子量的PET中,采用自制高压装置,制备共混体系,用WAXD,SEM,DSC等表征手段,研究了PET/PC共混体系在高压下的结晶行为。研究结果表明:通过PET/PC体系在高压下化学反应诱导的自组装,不同分子量PET的PET/PC共混体系均在较短的时间内生成了尺寸较大的聚酯伸直链晶体,对应于三斜晶系,其中PET/PC体系最适于大尺寸伸直链晶体的合成,仅需6hr时间即生成PE需200hr方可合成的40μm厚度的伸直链晶体。同时提出了PET1/PC体系中伸直链晶体高温下缺陷自我修复模型。     

聚对苯二甲酸丁二酯/聚对苯二甲酸乙二酯固态缩聚的研究

研究了聚对苯二甲酸丁二酯(PBT)/聚对苯二甲酸乙二酯(PET)共混物的固态缩聚反应,从反应动力学过程的测定结果,表明与纯PET或PBT不同,其反应速度较快,并呈超加和的相对分子质量(以特性粘数[η]表征)增长。从反应发生在液相的基本观点出发,说明温度、共混等使液相增多,将加速反应的进行,加上共混物之间的相互缩聚和酯交换,生成嵌段共聚物的结果,导致超加和效应。     

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.     

磷酸三苯酯对PBT／PET共混体系结晶行为的影响

用广角Ｘ－角线衍射法和差法扫描量热法研究了磷酸三苯酯对ＰＢＴ／ＰＥＴ共混体系结晶行为影响，结果表明：ＴＰＰＷ作为该共混体系的稳定剂，只能延长在熔融状态下酯交换反应发生的时间，ＴＰＰ含量一定时，熔融时间增加，ＰＢＴ，ＰＥＴ之间的酯交换反应同样会发生，不同熔融时间，就要求ＴＰＰ的用量也不相同。ＴＰＰ在ＰＢＴ／ＰＥＴ共混体系中没有结晶成核剂的作用，它也不改变ＰＢＴ，ＰＥＴ的结晶结构。     

Shape memory effects of poly(ethylene terephthalate-co-ethylene succinate) random copolymers

Random copolymers based on terephthalate acid, succinic acid and ethylene glycol, with thermally induced shape memory, were synthesized via melt polycondensation. The chemical structures of these poly(ethylene terephthalate-co-ethylene succinate) copolymers (PET-co-ES) were ascertained by ¹H NMR spectroscopy. The thermal and viscoelastic characteristics of these copolymers were studied in terms of the succinic acid content using differential scanning calorimetry and dynamic mechanical analysis. The shape memory effects of the copolymers were examined using the strain test. The experimental results suggested that all copolymers exhibited shape memory above the glass transition temperature and that the highest shape recovery rate was 90%. The shape recovery rates of all test samples declined with the number of cycles. This decrease in the shape recovery rate may result from the change in the degree of polymer orientation and/or crystallinity during repeated testing.     

Synthesis and MALDI-TOF-MS of PS-PMA and PMA-PS block copolymers

The synthesis of well-defined block copolymers from styrene and methyl acrylate via ATRP is discussed in this contribution. Kinetic studies on these block copolymerizations as well as characterization studies were performed to investigate the monomer composition in the respective PS and PMA blocks. MALDI-TOF-MS was performed to clarify the exact number of repeating units of each block and the total number of units in the block copolymer. Block copolymers up to 22 kDa could be analyzed by MALDI-TOF-MS, whereby polymers with PMA as first block showed a large second distribution corresponding to PMA homopolymers. However, SEC demonstrated that only a small amount of homopolymer was present indicating that care needs to be taken with interpreting MALDI-TOF-MS data, which is a qualitative rather than a quantitative technique.     

A comparative study on transreactions induced phase changes in blends of poly(trimethylene terephthalate) and poly(ethylene naphthalate) upon annealing

By using wide-angle X-ray diffraction (WAXD), thermal analysis, scanning and optical microscopy, and nuclear magnetic resonance (NMR) analyses, this study has demonstrated that blends of two semicrystalline polyesters, poly(trimethylene terephthalate) and poly(ethylene naphthalate) (PTT/PEN), were initially immiscible in as-blended state. The process of blend phase/morphology changes upon extended heating/annealing at elevated temperatures was monitored and probed. With reactions induced at heating/annealing at high temperatures (300°C) for long enough times, the original two phases quickly merged into a single phase. NMR analyses have shown that the products of the transreactions are identified as the random copolyesters (termed as EN-TT). From the NMR results, statistical analyses revealed that the average sequence lengths decreased upon heating, and the degree of chain randomness increased with time of heating at the fixed temperature. Upon extended heating, all PTT and PEN chains could be fully transformed into random copolymers of higher randomness with only a single but amorphous phase. Results are compared to another blend system comprised of PEN and a homologous polyester, PPT, of different structure. Influence of polyester structure on transreactions and phase homogenization process is analyzed.     

Segmented block copolymers of poly(ethylene glycol) and poly(ethylene terephthalate)

A new series of segmented copolymers were synthesized from poly(ethylene terephthalate) (PET) oligomers and poly(ethylene glycol) (PEG) by a two‐step solution polymerization reaction. PET oligomers were obtained by glycolysis depolymerization. Structural features were defined by infrared and nuclear magnetic resonance (NMR) spectroscopy. The copolymer composition was calculated via ¹H NMR spectroscopy. The content of soft PEG segments was higher than that of hard PET segments. A single glass‐transition temperature was detected for all the synthesized segmented copolymers. This observation was found to be independent of the initial PET‐to‐PEG molar ratio. The molar masses of the copolymers were determined by gel permeation chromatography (GPC). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4448–4457, 2004