Direct synthesis of potentially biodegradable aromatic–aliphatic thermotropic copolyesters with photocrosslinking properties

ABSTRACT

In this study, aromatic–aliphatic thermotropic copolyesters derived from p-hydroxybenzoic acid, p-hydroxycinnamic acid (HCA), terephthalic acid and polyethylene glycol (PEG) with different molecular weight (200, 400, 600) were directly synthesised via Vilsmeier adduct solution polymerisation method. The structure, thermal behaviour, liquid crystal property, hydrophylicity and photoactivity were investigated by Fourier transform infrared and nuclear magnetic resonance spectroscopy, differential scanning calorimeter, polarised optical microscopy, water contact angle measurement and ultraviolet (UV) spectrophotometer. The PEG incorporation ratio is 0.540–0.691 related to the HCA units, because of its low reactivity. And, the copolyesters have relatively low melting temperatures (96–107°C) and good hydrophylicity (water contact angle value 61.2–75.3°) as compared with wholly aromatic thermotropic copolyester. All of the copolyesters exhibited nematic liquid crystal behaviour and the stable mesophase temperature range was more than 60°C after being melted. The resulted copolyesters had enough thermal stability for melt processing without any degradation. The UV absorption intensities decreased with increased irradiation time, indicating that photocrosslinking occurred.     

Nonisothermal Crystallization Behaviors of Flame-Retardant Copolyester/Montmorillonite Nanocomposites

In order to obtain poly(ethylene terephthalate) (PET) engineering plastics with good flame retardancy, heat resistance, and mechanical properties, a novel phosphorus-containing copolyester (PET-co-DDP)/organo-montmorillonite (OMMT 1%) nanocomposite (PET-co-DDP/OMMT) was prepared by in situ intercalating polymerization. Nonisothermal crystallization kinetics and nanoscale morphology of this composite have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). Based on the results of the nonisothermal crystallization kinetics, the flame-retardant copolyester PET-co-DDP has a lower crystallization rate than pure PET, while PET-co-DDP/OMMT nanocomposite has a higher crystallization rate than pure PET. Based on the Augis and Bennett method, the activation energies for nonisothermal crystallization of pure PET, PET-co-DDP, and PET-co-DDP/OMMT nanocomposite were evaluated as 101, 138, and 76 kJ mol^?1, respectively. All the evidence shows that PET-co-DDP strongly influences the crystallization behavior because of its irregular chain structure, while the addition of nanoscale OMMT to this copolymer can significantly enhance the crystallization rate owing to its remarkable nucleating effect. An understanding of the above crystalline behaviors will be beneficial in preparing PET engineering plastics with good overall comprehensive performance.     

含X-型二维液晶基元和顺式-4,4′-双(4-羟基苯基偶氮)二苯并-14-冠-4冠醚环液晶共聚酯的合成与表征

以4,4′-(α,ω-辛二酰氧)二苯甲酰氯(M1)、2,5-二(对十二烷氧基苯甲酰氧基)对苯二酚(M2)和顺式-4,4′-双(4-羟基苯基偶氮)二苯并-14-冠-4(M3)为单体,通过溶液共缩聚反应,合成了一系列含X-型二维液晶基元和顺式-4,4′-双(4-羟基苯基偶氮)二苯并-14-冠-4冠醚环的主链型液晶共聚酯.单体1(M1)由对羟基苯甲酸和辛二酰氯,通过酯化和取代反应制备,单体2(M2)由2,5-二羟基苯醌和对十二烷氧基苯甲酰氯通过酯化和还原反应制备,单体3(M3)由顺式-二氨基二苯并-14-冠-4和苯酚通过重氮化和偶联反应制备.共聚酯的分子量不高,[η]在0·35~0·25dL/g之间.单体的化学结构通过IR、UV、1H-NMR、MS和元素分析等方法确证.共聚酯的外观为黄色粉状固体,除CP9外,室温下不溶于CHCl3和THF溶剂.共聚酯的性质采用GPC、[η]、DSC、TG、WAXD和POM等方法进行了研究.发现所有的共聚酯加热到各自的熔融温度以上都能形成液晶态,在液晶态可以观察到向列相的丝状织构或纹影织构.共聚酯的熔融温度(Tm)和各向同性温度(Ti)随共聚酯分子中顺式-4,4′-双(4-羟基苯基偶氮)二苯并-14-冠-4用量的改变呈规律性变化.WAXD研究进一步证实了共聚酯的液晶性.     

Effect of association of dicarboxylic acids activated by TsCl/DMF/pyridine upon the copolycondensation with bisphenols

When a mixture of terephthalic acid (TPA) and various dicarboxylic acids was activated by tosyl chloride (TsCl)/dimethyl‐ formamide (DMF)/pyridine (Py), the resulting mixture became dissolved in Py, although the activated TPA was insoluble even at 120 °C. The temperature at which the mixture became soluble was varied with their compositions and the structure of diacids. Mixing the separately activated TPA and isophthalic acid (IPA) also improved the solubility of the activated TPA to some extent. The interesting phenomena were attributed to associations of the activated diacids through the dipole–dipole interactions between the carbonyl groups. The structures of associates were estimated in terms of transition temperatures of the thermotropic IPA/TPA‐methylhydroquinone and IPA/TPA‐chlorohydroquinone copolymers. The transition temperatures were significantly affected by the temperature of polycondensation, the preparative procedures of a mixture of the activated diacids, and several additives. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 196–201, 2001     

Photocurable Nitric Oxide-Releasing Copolyester for the 3D Printing of Bioresorbable Vascular Stents

The design of bioresorbable vascular stents (BVS) capable of releasing nitric oxide (NO) at the implant site may enable BVS to mimic the antiplatelet, antiproliferative, and pro-endothelial actions of NO, overcoming complications of BVS such as late thrombosis and restenosis. In this study, the fabrication of BVS composed of methacrylated poly(dodecanediol citrate-co-dodecanediol S-nitroso-mercaptosuccinate) (mP(DC-co-DMSNO)), a novel elastomeric, bioabsorbable, and photocurable copolyester, containing covalently bound S-nitrosothiol groups in the carbon backbone of the polymer, is reported. The mP(DC-co-DMSNO) stents are manufactured via photoinduced 3D printing and allow deployment via a self-expansion process from a balloon catheter. After deployment, hydration of the stents triggers the release of NO, which is maintained during the slow hydrolysis of the polymer. Real-time NO release measurements show that by varying the copolyester composition and the strut geometry of the mP(DC-co-DMSNO) stents, it is possible to modulate their NO release rate in the range of 30–52 pmol min⁻¹ cm⁻². Preliminary biological assays in cell culture show that endothelial cells adhere to the surface of the stents and that NO release favors their endothelization. Thus, mP(DC-co-DMSNO) may emerge as a new platform for the fabrication of advanced BVS.     

Orientation and mechanical properties of PBT and its blends with a liquid-crystalline copolyester

Blends of poly (butylene terephthalate) (PBT) and a liquid-crystalline copolyester (60 mol % poly(p-hydroxy benzoic acid)/40 mol % polyethylene terephthalate) (LCP) were prepared in the melt state. The investigation of mechanical properties indicated that, for the processing conditions used, neither the addition of up to 30 wt % LCP to PBT nor the cooling history affected significantly the tensile modulus E. For oriented specimens, a marked improvement of E was obtained for all the blends, and increased with the LCP content. This improvement was more marked for slowly cooled samples. X-ray diffraction was used to quantify the orientation of the crystalline PBT and liquid-crystalline LCP phases. It was shown that neither the thermal history nor the presence of up to 30 wt % LCP affected the orientation behavior of the PBT crystalline phase. For the LCP phase, measurements were not possible for concentrations lower than 10 wt %, and were more difficult and less precise than for PBT. Nevertheless, it was possible to show that a better orientation was obtained for the slowly cooled samples and for higher concentrations of LCP in the blends. This correlated with the enhancement of mechanical properties observed for the oriented samples.     

Miscibility of a polyarylate with a liquid crystalline copolyester

The miscibility has been investigated for binary blends of a polyarylate (PAr) with a liquid crystalline copolyester of p-hydroxybenzoate and ethylene terephthalate units in a 6/4 molar ratio (PET/PHB). The binary blends were prepared by solution precipitation. The transitions of the PET/PHB have been measured with a rheometrics dynamic spectrometer. The phases in blends have been studied with a differential scanning calorimeter, by ther-mogravimetry and with a polarizing optical microscope. The blends exhibit two glass transitions (T_gs) over the composition range 10–90 wt %. The amorphous PET phase from the PET-PHB is found to be partially miscible with PAr, which leads to a decrease of the PAr T_g. The amount of this partially miscible portion of PET has been estimated by the Couch-man equation. On heat treatment of the blends at 250 to 300°C, transesterficiation takes place, as judged by the shift of the higher of the two T_gs. © 1993 John Wiley & Sons, Inc.     

Morphology of poly(butylene terephthalate)–poly(ethylene terephthalate‐co‐isophthalate‐co‐sebacate) segmented copolyesters

Segmented copolyesters, namely, poly(butylene terephthalate)–poly(ethylene terephthalate‐co‐isophthalate‐co‐sebacate) (PBT‐PETIS), were synthesized with the melting transesterification processing in vacuo condition involving bulk polyester produced on a large scale (PBT) and ternary amorphous random copolyester (PETIS). Investigations on the morphology of segmented copolyesters were undertaken. The two‐phase morphology model was confirmed by transmission electron microscopy and dynamic mechanical thermal analysis. One of the phases was composed of crystallizable PBT, and the other was a homogeneous mixture of PETIS and noncrystallizable PBT. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2257–2263, 2003     

Thermotropic liquid crystalline polymers with low thermal transitions. II. Low melting thermotropic liquid crystalline homo- and co-polyesters

Thermotropic liquid crystalline (TLC) polymers with low melt transitions are useful for imaging technologies. This is the first report describing thermotropic liquid crystalline copolyesters of low melt transitions comprised of a mesogen with up to three different spacer moieties. We have noted that the smectic mesophase range decreased with increasing amounts of different spacer moieties, without altering the isotropic transition and thereby leading to a broader nematic range. © 1995 John Wiley & Sons, Inc.     

对羟基苯甲酸与对苯二甲酸乙二酯的共聚物研究

对羟基苯甲酸与对苯二甲酸乙二酯的共聚物研究张广利，阎丰琪，李勇，王震，潘景岐，张鸿志（北京大学化学系北京１００８７１）关键词液晶共聚酯，ＰＥＴ／ＰＨＢ共聚脂，序列分布Ｊａｃｂｏｎ和ＫｕｈｆｕＪ’ｌ于７０年代报道了对羟基苯甲酸（ＰＨＢ）一对苯二甲酸乙二...