Thermal characterization and thermal degradation of copolyimides containing fluorine and phosphine oxide

A series of copolyimides containing different ratios of fluorine and phosphine oxide were synthesized. The copolymers were characterized with Fourier transform infrared, differential scanning calorimetry, and thermogravimetric analysis measurements. The copolymers were thermally stable up to 700 K and exhibited glass‐transition temperatures in the range of 495–562 K. The glass‐transition temperatures of the copolymers decreased with an increase in the phosphine oxide content. The thermal decomposition behavior of the copolymers was investigated. The copolymers with higher phosphine oxide contents displayed lower onset decomposition temperatures and char yields. A new method involving the multiple‐rate isotemperature was used to define the most possible mechanism [G(α)] for the reactions. The overall kinetic model function of the thermal decomposition of these copolymers obeyed the Avrami–Erofeev model equation, G(α) = [?ln(1 ? α)]^1/m, where α is the conversion degree. The apparent kinetic parameters of the degradation processes were also obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2139–2143, 2005     

The Tg of amorphous linear polyethylene: a torsion braid analysis

Summary The Tg of amorphous linear polyethylene has been studied using torsion braid analysis. 4 transitions are observed: at 150°K, 190°K, 260°K and 370°K. Our results indicate that linear polyethylene has 2 glass transitions, a Tg_(L) at 190°K, corresponding to the truly amorphous polymer and a Tg_(U) at 260°K corresponding to the amorphous regions constrained by crystalline regions.     

Glass transition and exclusion model in crystallization of polyether-polyester block copolymers with amide linkages

Polyether-polyester block copolymers having various polyetheramide contents were synthesized. Single glass transition intermediated in temperature between the glass transition temperatures of polyester and polyetheramide components was found for all of polyether-polyesters. The compositional variation of glass transition exhibited a similar trend to the predicted result of thermodynamic theory for compatible polymer blends. The incompatible pair of homopolyester and homopolyether was forced to be compatible after copolymerization. A modified theoretical prediction for the glass transition of copolymers based on the thermodynamic theory is proposed. Consistent results between theoretical prediction and experimental measurements were found. Unlike homopolyesters, the glass transition temperature of copolymer amorphous domains gradually decreases with crystallization time. An exclusion model for the crystallization of polyester segments in copolymers is proposed. The temperature width of the glass transition increases with crystallization time. The broadening towards the low temperature side in glass transition is interpreted as the evidence of crystallization-induced partial phase separation. Instead of forming macroscopic segregation, the excluded polyether segments resided in-between crystalline polyester lamellae and mix with amorphous polyesters to generate amorphous domains exhibiting concentration gradient along the lamellar basal surface normal. Further increasing the polyetheramide segment content brings the excluded polyetheramide segments to form domains among the crystallized polyester spherulites so as to inhibit the occurrence of spherulitic impingement.     

一种含氟共聚物乳液的制备及其性能

通过制备一种含有全氟壬烯基的含氟共聚物乳液,并考察其性能,研究了含氟单体对共聚物乳液性能的影响。以K2S2O8为引发剂,丙烯酸丁酯(BA)、甲基丙烯酸甲酯(MMA)和全氟壬烯基烯丙基醚(PFNAE)为共聚单体,采用半连续乳液聚合的方法,制备了带蓝色荧光的含氟乳液。用傅里叶红外(FT-IR)、接触角、差示量热扫描(DSC)和热重(TG)分析等手段对制备的PFNAE-BA-MMA共聚物(PBM)结构和性能进行表征。结果表明:引入含氟单体后,聚合物的疏水性、热稳定性、玻璃化温度(Tg)都有提高。水在含氟共聚物上的接触角随含氟单体用量的增加而增大,当PFNAE占单体总质量的25%时,水的接触角为94.9°;当PFNAE占单体总质量的20%时,共聚物在221℃开始分解,429.5℃分解完全,该共聚物Tg为8.5℃。PFNAE-BA-MMA共聚物具有一定的拒水性和良好的热稳定性。     

Structure and properties of acrylonitrile-[(2-methacryloyloxy)alkoxy]trimethyl silane copolymers

Dielectric, x-ray diffraction, density, thermomechanical, and thermogravimetric studies on polyacrylonitrile (PAN), poly[acrylonitrile-(2 methacryloyloxy)ethoxytrimethylsilane] [poly(AN-2MAETMS)], and poly[acrylonitrile-(2 methacryloyloxy)propoxytrimethylsilene] [poly(AN-2MAPTMS)] copolymers have been carried out for investigating their structure. The glass transition temperature as indicated from the dielectric and thermomechanical analysis data are lower for the copolymers as compared to PAN. Crystallinity is influenced by the introduction of the silylated acrylic comonomer units but the crystalline lattice remains similar to that of PAN. The changes obseved in the various properties of these coplymers clearly suggest a more closely packed structure of poly(AN-2MAETMS) than poly(AN-2MAPTMS), and the uninterrupted PAN sequences are longer in the former. Thermal stability of copolymers has also been investigated.     

一种新型可生物降解聚酯的合成与性能研究

使来源于天然植物的3,4-二羟基肉桂酸(DHCA)和对羟基苯甲酸(HA)进行熔融缩聚,制得了新型聚酯(PDHCA-co-PHA),用核磁共振、傅立叶红外光谱和凝胶渗透色谱对PDHCA-co-PHA的结构与相对分子量进行分析表明,所合成的共聚物结构明确。通过差示扫描量热和X-射线衍射对共聚物的热性能与结晶性能的研究表明,PDHCAc-o-PHA的玻璃化转变温度随着HA投料量的增加而降低;PDHCA-co-PHA为无定形结构聚合物,有利于生物降解。通过三氟乙酸与N,N-二甲基甲酰胺的离子化作用,制备了PDHCAc-o-PHA共聚物微球,微球粒径在1~2μm之间可用于药物负载等领域。     

Fluoroelastomers-dependence of relaxation phenomena on composition

The dynamic-mechanical properties of some fluoroelastomers were determined as a function of composition at low frequency (≈ 1 Hz), by means of a free oscillation torsion pendulum, between −180°C and the softening point. Vinylidenefluoride (VDF)-hexafluoropropene (HFP) copolymers of molar composition 0–39% HFP and terpolymers of VDF and HFP with up to 30mol% tetrafluoroethylene (TFE) and a constant VDF to HFP molar ratio of 3.4 were considered. Two relaxation processes typical of the amorphous phase were found. The first, located at about −87°C, is related to local motions and the transition temperature was found to be independent of composition for copolymers, while it depends on TFE molar content for terpolymers. The second is related to the glass transition and the transition temperature depends on the composition. However, for semicrystalline copolymers the double glass transition phenomenon was observed. When crystallinity goes to zero at about 20 mol% HFP, only one transition is observed. It was also found that ordered structures can take place for terpolymers when TFE molar concentration exceeds 20%. The crystal disorder transition of pure PVDF (75°C) is observed also for low HFP concentrations but the transition temperature is strongly reduced. Analogies between the VDF-HFP and E-P systems are also discussed.     

聚酰胺酯结晶行为研究

利用差式扫描量热法对聚酰胺酯进行结晶行为分析。结果表明:与常规PET相比,聚酰胺酯玻璃化温度、冷结晶温度、熔点、熔融结晶温度均较低,同时其熔融结晶速率也较慢;且随着共聚酯中聚酰胺成分的增加,玻璃化温度、熔点、熔融结晶温度逐渐降低并呈现一定的变化关系;在相同结晶温度下,聚酰胺成分增加,共聚酯半结晶周期t_(1/2)增加,结晶随之变慢。     

Amorphous state transitions in butadiene–acrylonitrile copolymers

Differential thermal analysis, creep measurements, and gas permeation rates are used to confirm the existence of a transition zone in three butadiene acrylonitrile copolymers in a temperature region that starts at roughly 15° to 25°C above the main glass transition temperatures of the copolymers and extends over a broad temperature range. The change appears to be slightly endothermic and softens the copolymers upon heating. It is speculated that the copolymers are in a mesomorphic state above their main glass temperature in which there is either a degree of ordering or a low-grade crystallinity of polybutadiene units along the copolymer chains. It is not until the copolymers are 50° to 75°C above their main glass temperature that they become truly amorphous.     

Copolymerization of norbornene and ethene with homogenous zirconocenes/methylaluminoxane catalysts

The norbornene/ethene copolymerization was investigated by using two C _S-symmetric ([Me₂C(Fluo)(Cp)]ZrCl₂ III, [Ph₂C(Fluo)(Cp)]ZrCl₂ IB) and two C ₂-symmetric ([Me₂Si(Ind)₂]ZrCl₂ I, [Ph₂Si(Ind)₂]ZrCl₂ II) catalysts with methylaluminoxane (MAO) as cocatalyst. This investigation focussed not only on the different polymerization behavior, like catalyst activity, but also considers the material properties of the synthesized copolymers. It was found, that the C _S-symimetric catalysts are very well suitable to yield amorphous copolymers with glass transition temperatures above 180°C and molecular weights >100.000 g/mol. These copolymers could be used as potential starting materials for optical discs and fibers.     

Tg/Tm for unsubstituted polymers

Polymers under discussion can be represented by [CH₂)_nR]_p where R is CH₂, CF₂, O, S or CH = CH; and where n can vary from 0 to ∞. The copolymer, P(ethylene-alt-TFE) is also included. These polymers tend to be highly crystalline with resultant confusion about their Tg and hence their Tg/Tm values and a clarification scheme is proposed in which it is considered that each such polymer has a double glass transition, Tg(L)/f(χ_c), Tg(U) = F(χc); and a sub-glass T<Tg(L) at 0.75 Tg(L), where F(χc) signifies a function of fractional crystallinity, χ_c. T<Tg(L) and Tg(L) increase linearly with Tm. The ratio, Tg(L)/Tm, is therefore, not a constant but is close to 0.5. T<Tg(L)/Tg(L) is also not a constant but is close to 0.75. Tg(U) lies within a wedge whose top and bottom sides increase with Tm. The premelting, intracrystalline transition temperature, Tα_c, is also a linear function of Tm. It is suggested that the scheme outlined above should help to resolve uncertainties in assigning transition temperatures for unsubstituted polymers. The low Tg/Tm values for these polymers is discussed in terms of their small da/dc ratios and small crosssectional areas per chain.     

Temperature effect on the infrared absorption of ferroelectric copolymer poly(vinylidene fluoride‐trifluoroethylene)

The intensity of two infrared absorption bands of annealed ferroelectric copolymers [poly(vinylidene fluoride‐trifluoroethylene)] in the mid‐infrared high‐frequency region was found to be strongly related to the annealing temperature. The vibration modes in the amorphous phase of the copolymers were considered to account for these two bands. On the other hand, the temperature dependence of the absorption spectra of the copolymers in the heating and cooling cycle was investigated. In the vicinity of the Curie transition, the absorption bands associated with the CH₂ vibrations exhibited a shift in frequency. Two bands were identified as shifting to a high frequency, and one band shifted to a low frequency with heating. These three bands were restored to their room‐temperature frequency with cooling. In addition, copolymers of a higher vinylidene fluoride content exhibited a more pronounced thermal hysteresis in terms of a shift in frequency. This was consistent with the electrical behavior of the copolymers. The trends of the frequency shifts suggested that dipole–dipole coupling existed between two adjacent chains in the all‐trans conformation, which originated from the interaction of the CH₂ and CF₂ dipoles. The coupling diminished as the copolymers underwent a change in phase above the transition temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1662–1666, 2005     

新型聚芳醚砜共聚物的制备及其性能

以4,4’-二氯二苯砜、4,4’-二羟基二苯砜和2,4-二羟基二苯砜为单体,通过缩聚合成一系列主链含异构体醚键单元的聚芳醚砜共聚物,利用核磁共振碳谱(13C NMR)、差示扫描量热分析(DSC)和高压毛细管流变仪对产物进行了测试和分析。对比不同产物的熔体黏度、玻璃化转变温度和力学性能,发现随着共聚单元含量的增加,聚芳醚砜共聚物的流动性逐渐提高,玻璃化转变温度逐渐降低,并且屈服点伸长率和缺口冲击强度均逐渐提高。这一结果对实际应用中提高聚芳醚砜树脂流动性和韧性、降低热加工温度等具有重要的指导意义。     

Glass transition of undrawn and drawn copolyetherester thermoplastic elastomers

The phase and deformation behaviour of two types of copolyetheresters (the block copolymers E and P) were studied by means of DSC, dynamic mechanical spectroscopy and X-ray diffraction. The block copolymers E and P based on poly(butylene therephtalate) (PBT) as a hard block have poly(tetramethylene oxide) (PTMO) and triblock copolymer (PEO-PPO-PEO) with a middle poly(propylene oxide) (PPO) block and two end poly(ethylene oxide) (PEO) as a soft block, respectively. The complex investigation shows that the studied copolyetheresters are microphase separated polymer systems in the amorphous matrix of which the PBT crystallites are embedded. The volume fraction of PBT crystallites depends on the block copolymer composition and changes from 5 to 20%. In the amorphous matrix that is the mixed PBT/ the soft block phase the soft block acts as a PBT plasticizer reducing the glass transition temperature of the amorphous mixed phase. The most interesting aspect of the phase behaviour of the copolyetheresters consists in the fact that, in comparison with PTMO, the triblock is characterized by a more pronounced PBT plasticization effect. A special emphasis was placed in this work on the investigation of an increased glass transition temperature of drawn copolyetheresters. It was found that this process depends on the volume fraction of PBT crystallites and chemical structure of the soft blocks. The first factor characterizes the interaction between the amorphous mixed phase and PBT crystallites and, therefore, the higher value of the volume fraction of PBT crystallites the higher is the glass transition temperature of drawn copolyetheresters. The second factor determines the PBT plasticization effect of the soft blocks and a level of the interaction of chains in the amorphous mixed phase. Because of a weaker PBT plasticization effect of PTMO in comparison with that of the triblock, the deformation of the block copolymer E is accompanied by a more pronounced elevation of the glass transition temperature in comparison with the block copolymer P.     

可生物降解聚酯P(ES-co-DGA)和P(BS-co-DGA)的合成及性能比较

通过改变二乙醇酸(DGA)的含量,将其与乙二醇、1,4-丁二醇进行缩聚反应,得到了P(ES-co-DGA)和P(BS-co-DGA)共聚物,采用1H-NMR表征化学结构,并对共聚物的相对分子质量(Mn)、热性能、力学性能、降解性等进行比较研究。结果表明:随着DGA的增加,两种共聚物的熔点(Tm)均呈下降趋势,但P(ES-co-DGA)的玻璃化转变温度(Tg)逐渐升高,P(BS-co-DGA)的Tg却变化不大;所有共聚物的热分解温度(Td)(失重2%)均在300℃左右。当DGA含量为50%时,P(BS-co-DGA)的最大断裂伸长率可达到921%;当DGA含量为20%时,P(ES-co-DGA)的最大断裂伸长率可达到853%。随着DGA的增加,P(BS-co-DGA)的降解速率增大;当DGA含量为10%以上时,P(BS-co-DGA)的降解性能逐渐降低。     

聚(对苯二甲酸-1,3-丁二醇酯/对苯二甲酸-1,4-丁二醇酯)/PEG嵌段共聚物的合成及性能研究

用熔融缩聚法合成了一系列聚(对苯二甲酸-1,3-丁二醇酯/对苯二甲酸-1,4-丁二醇酯)/聚乙二醇的嵌段共聚物。用FT-IR,1H-NMR,DSC,TGA,水降解测试等方法表征了材料的结构与性能。FT-IR和1H-NMR分析表明合成得到的共聚物为预期产物;DSC分析显示,共聚聚酯随着1,3-丁二醇在共聚物中比例的增大,熔点(Tm)逐渐降低,由158.24℃下降至104.19℃,玻璃化温度(Tg)逐渐升高,由4.86℃升至24.56℃,合成得到的共聚酯趋向于无定形态;TGA分析表明1,3-丁二醇在共聚酯中比例增大会使聚酯的热稳定性下降,但合成得到的共聚酯依然具有较好的热稳定性,初始分解温度大于310℃,不需要在反应过程中添加热稳定剂;水降解测试结果表明共聚物随1,3-丁二醇比例的增加,降解速率大幅提升。     

环烯烃共聚物——一种新型的非结晶热塑性塑料

以环戊二烯或环戊二烯衍生物为原料制备的环烯共聚物是一类集高透明度、高玻璃化转变温度、低双折射率、低吸水性、耐化学性和耐高温度等诸多优点为一体的非结晶热塑性塑料。     

Self‐complementary multiple hydrogen bonding interactions increase the glass transition temperatures to supramolecular poly(methyl methacrylate) copolymers

We have prepared a series of poly(methyl methacrylate) (PMMA)‐based copolymers through free radical copolymerization of methyl methacrylate in the presence of 2‐ureido‐4[1H]‐pyrimidinone methyl methacrylate (UPyMA). The glass transition temperature was increased with the increase of UPyMA contents in PMMA copolymers due to strong self‐complementary multiple hydrogen bonding interactions of UPy moiety. The Fourier transform infrared and solid‐state NMR spectroscopic analyses provided positive evidence for the presence of multiple hydrogen bonds interaction of UPy moiety. Furthermore, the proton spin‐lattice relaxation time in the rotating frame [T_1ρ(H)] for the PMMA copolymers had a single value that was less than pure PMMA, indicating the smaller domain sizes in PMMA copolymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Multiple glass transitions in butadiene-acrylonitrile copolymers

The second order transition temperatures (Tg) have been determined for a range of compositions of polybutadiene-acrylonitrile copolymers. It was found that copolymers having more than 36 percent acrylonitrile had a single Tg while copolymers with less than 36 percent acrylonitrile had two main Tg's. The analyses were carried out with differential thermal analysis (DTA). The two Tg's are interpreted as the result of incompatible phases which differ in BD and VCN ratio. The presence of two phases is discussed in terms of polymerization conditions and molecular structure.     

Microindentation studies at the near surface of glassy polymers: Influence of molecular weight

The viscoelastic‐plastic properties of various amorphous, glassy polymers [polystyrene (PS), poly(styrene‐acrylonitrile) copolymer (SAN), poly(methyl methacrylate) (PMMA), poly(vinyl chloride) (PVC), polycarbonate (PC)] in the micron and submicron range were investigated by means of load‐displacement analysis from depth‐sensing experiments. Hardness and Young's modulus values decrease rapidly with increasing depth up to a few microns. New data on the glass transition temperature correlation with microhardness are presented. The influence of annealing below the glass transition temperature upon the microhardness for various glassy polymers is pointed out. For PS, the influence of the molecular weight variation and molecular weight distribution on the microhardness is reported. Results are discussed on the basis of an entanglement network model, recently developed to explain the fine structure of crazes in amorphous polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1951–1956, 2004