Incorporation of ? OH groups into PS by copolymerization with hydroxystyrene caused specific OH···O?C interactions with carbonyl groups of PDLLA. PDLLA blends with PSHS16 were completely miscible across the whole composition range, showing a single glass transition. Specific interactions and phase structure were analyzed by FTIR spectroscopy and SEM. DMA around Tg using the WLF theory and Angell's dynamic fragility concept revealed that specific interactions are not acting as other topological constraints (cross‐links, crystalline lamellae, silicate layers), since they rather provide a retardation of segmental dynamics.
For number‐average molecular weight (Mn) below 1 × 104 g mol?1, the comparison of cold crystallization temperature and spherulite growth rate and crystallinity of linear 1‐arm, 2‐arm, and branched 4‐arm poly(L ‐lactide)/poly(D ‐lactide) blends exhibits that the effects of chain directional change and branching significantly disturb stereocomplex crystallization. In contrast, the comparison of glass transition and melting temperatures of linear 1‐arm, 2‐arm, and branched 4‐arm poly(L ‐lactide)/poly(D ‐lactide) blends indicates that the effects of chain directional change and branching insignificantly alter and largely increase the segmental mobility of the blends, respectively, and the crystalline thickness of the blends is determined by Mn per one arm not by Mn and is not affected by the molecular architecture.
Summary: Blends of high molecular weight poly(R‐3‐hydroxybutyrate) (PHB) ( = 352 000 g · mol?1), comprising of either low molecular weight poly(R‐3‐hydroxybutyrate) (D‐PHB) ( = 3 900 g · mol?1) or poly[(R‐3‐hydroxybutyrate)‐co‐(R‐3‐hydroxyvalerate)] (PHBV) ( = 238 000 g · mol?1) with 12 mol‐% hydroxyvalerate (HV) content as a second constituent, were investigated along with the thermal properties and morphologies. After isothermal crystallization, a lowering of the melting temperature of PHB can be observed with increasing content of the second component in the blends. This behavior points towards miscibility of the constituents both in the liquid and the solid state. Crystallization kinetics was studied under isothermal and non‐isothermal conditions. The overall kinetics of isothermal crystallization was analyzed in terms of the Avrami equation. Only one crystallization peak is observed in all cases for the PHB/D‐PHB and PHB/PHBV blends under the conditions studied. This demonstrates co‐crystallization of the constituents. The addition of D‐PHB or PHBV to PHB reduces the rate of crystallization of the blends compared to that of neat PHB. The corresponding activation energies of crystallization also decrease with an increasing concentration of the second constituent. Non‐isothermal crystallization, carried out with different cooling rates held constant, is discussed in terms of a quasi‐isothermal approach. The corresponding rate constants as functions of reciprocal undercooling show Arrhenius‐like behavior in a certain range of temperatures. At sufficiently high undercooling, the rate constants of crystallization for the isothermal process exceed those reflecting non‐isothermal conditions, whereas in the limit of low undercoolings, the rate constants become similar. Ring‐banded morphologies are observed when PHB is in excess. When the respective second component is the major component, fibrous textures of the spherulites develop.
Poly(L ‐lactide) (PLLA) is melt blended with poly(ether urethane) (PEU) based on poly(ethylene glycol) blocks via a chain‐extension reaction by diisocyanate as a chain extender to improve its flexibility without sacrificing comprehensive performance. The elongation at break of the blends with triphenyl phosphate (TPP) as a reactive blending additive is much higher than that without TPP by physical blending. When 10 wt% PEU is blended, the former elongation reaches to 298%, while the latter one is only approximately 20%. The reactive blending forms a PLLA–PEU block copolymer, thus improving their compatibility. When the weight‐average molecular weight (Mw) of PEUs is 18–90 kg mol?1, the effect of Mw is very little on tensile properties of blends. The rheological properties of the blends are modified through the content and molecular weight of PEU. The complex viscosity (η*) of PLLA/PEU blends increases with increasing Mw of PEU. The η* of the PLLA blend containing 5 wt% PEU in Mw 73 kg mol?1 is higher than that of neat PLLA. The water absorption of the PLLA/PEU blends enhances because of the hydrophilicity of PEUs versus neat PLLA.
Summary: A new photoluminescent poly(arylene ethynylene) containing 1,3,5‐triazine units was prepared by polycondensation between 2,4‐diphenyl‐6‐N,N‐bis(4‐bromophenyl)amino‐1,3,5‐triazine and 1,4‐didodecyloxy‐2,5‐diethynylbenzene using Pd(PPh3)4 and CuI as the catalysts in the presence of triethylamine. The polymer showed good solubility in common organic solvents and had a number average molecular weight, , of 3 400, and a weight average molecular weight, , of 8 100. In toluene the polymer exhibited an intrinsic viscosity [η] of 0.11 dL · g?1 at 30 °C. The polymer showed photoluminescence (PL) with emission peaks at 479 nm in CHCl3 and at 509 nm in the solid state; quantum yield of the PL in CHCl3 was 21%. Electrochemical reduction (or n‐doping) of the polymer started at about ?2.05 V versus Ag/AgNO3 and gave a peak at ?2.30 V versus Ag/AgNO3.
The 1,2,3‐triazine unit‐containing poly(arylene ethynylene) (PATZ) polymer synthesized and investigated here. 相似文献
Summary: Thermal characterizations were performed to further discern the miscibility and qualitative interactions in blends of isotactic polystyrene (iPS) and poly(cyclohexyl methacrylate) (PCHMA). A method based on the enthalpy relaxation of the blends was used to overcome the difficulty or ambiguity in resolving closely‐spaced glass transitions of these two constituent polymers. Interactions between the blend components were further estimated by two additional methods: the blend's glass transition temperature (Tg) and the melting point depression. The blend's Tg method yielded a χ12 value ranging from ?0.0016 (i.e., almost 0) to ?1.98 (with the values depending on the amorphous PCHMA contents in the blends) in the temperature range of 95–110 °C, whereas the melting point depression led to χ12 = ?0.039 at 240 °C. The interaction parameters obtained from these two methods are negative, confirming the miscibility with weak interactions. The results of these alternative thermal characterizations further clarified that the iPS/PCHMA blends, whose Tg's are too close to allow the use of conventional Tg criteria, are indeed completely miscible.
Specific heat increment (ΔCP) at Tg for the iPS/PCHMA blends. 相似文献
New hydrophilic networks combining poly(ethylene glycol) (PEG) and β‐cyclodextrin (β‐CD) have been prepared. Both components are linked by reacting PEG chains previously end‐capped with isocyanate groups and β‐CD, forming urethane links. Networks of molar compositions (β‐CD/PEG) ranging from 1/4 to 1/14, and with four different molar masses (400, 600, 900, and 1 350 g · mol?1) of the end‐capped PEG precursor have been synthesized. The networks have good thermal stability and low glass transition temperatures. Crystallinity has only been detected for the two higher molar mass PEG precursors. The swelling properties of these hydrogels depend on the chain lengths of the PEG precursor and also on the temperatures.
Poly(norbornene)s with pendant imidazolium moieties and three different counter anions, i.e. poly[exo,endo‐5‐norbornene‐2‐yl‐carboxyethyl‐3‐ethylimidazolium bis(trifluoromethyl‐sulfonyl)imide], poly(exo,endo‐5‐norbornene‐2‐yl‐carboxyethyl‐3‐ethylimidazolium tetrafluoroborate), and poly(exo,endo‐5‐norbornene‐2‐yl‐carboxyethyl‐3‐ethylimidazolium hexafluorophosphate) were prepared via ROMP using ionic liquids as the reaction medium. The ionic polymers possessed in the range 8.1–44 × 103 and ionic conductivity up to 1.13 × 10−5 and 1.44 × 10−4 S · cm−1 at 20 and 50 °C, respectively. The solubility of the new polymeric ionic liquids, their thermal stability and their glass transition temperatures were investigated in detail. Ionic conductivities were found to depend on the nature of the counter‐anion and on the polymers' glass transition temperature rather than its molecular weight.
The high‐pressure melt‐crystallization behaviors of poly(p‐phenylene sulfide) (PPS) were investigated using WAXD, DSC, TEM and SEM. PPS extended‐chain crystals with c‐axis thickness exceeding 4.5 µm were formed at high pressure. The DSC results showed that the melting temperature and melting enthalpy of high‐pressure crystallized PPS samples were up to 327.53 °C and 94.96 J · g?1, respectively, which were higher than the values of ideal PPS perfect crystals used by some researchers, and the melting enthalpy of the samples fluctuated regularly during the thickening growth of the PPS crystals. Other characteristic morphologies obtained at high pressure, i.e. spherulites and rod‐like crystals, were also presented with the SEM measurements.
Summary: Analysis was made of the crystallization of the PET blocks in PET/PC copolymers as a function of the block length, varying from = 5300 to 17100 g · mol?1 (Xn PET = 28–89, PET monomeric sequences). Analysis was also made of a series of PET homopolymers with the same values. The copolymers were found to crystallize at a slower rate, with lower crystallinity and lower crystal perfection, than the homopolymers and secondary crystallization does not take place, unlike with PET homopolymers. However the crystallization mechanism is the same. The plot of the crystallization rate versus Xn PET shows that the homopolymers have a maximum crystallization rate at Xn PET ? 50 ( ? 10000 g · mol?1), whereas the crystallization rate for copolymers continuously increases with the increment of Xn PET (see Figure). The decrement of the crystallization rate for homopolymers with higher than 10000 g · mol?1 has been interpreted as due to the effect of the high melt viscosity. For copolymers with long PET blocks, instead, a phase separation is likely and improves the PET reptation and fold, causing an increment in crystallization rate. Block size and miscibility between the components are therefore the key parameters in understanding the crystallization process in PET/PC block copolymers.
Summary: The novel asymmetric ansa‐complexes [1‐(9‐η5‐fluorenyl)‐2‐(2,5,7‐trimethyl‐indenyl)ethane]hafnium dichloride ( 7a ) and [1‐(9‐η5‐fluorenyl)‐2‐(2,4,6‐trimethyl‐indenyl)ethane]hafnium dichloride ( 7b ) were prepared and used as catalysts for propylene homopolymerization reactions after in situ activation. The synthetic route allows to separate the 4,6‐ and 5,7‐substituted ligand isomers before the complexation step. The orientation of the methyl groups to the “front” (4,6) or to the “back” (5,7) of the tetrahedral hafnocene dichloride species influences their performances in polymerization reactions. Whereas hafnocene ( 7b ) which bears trimethyl substitution at 2,4,6‐positions of the indenyl moiety exhibits only moderate activity, the 2,5,7‐trimethyl substituted structure ( 7a ) produces isotactic poly(propylene)s with high molecular weights (up to = 9.0 × 105 g · mol?1) and high activities [up to 3.2 × 105 kg of PP (mol Hf × h)?1]. A comparative analysis of polymerization data and mechanical behavior of 7a , and previously reported 6,7‐indenyl substituted complex 6b are reported.
Typical stress‐strain curves of different types of poly(propylene)s. 相似文献
Poly(3‐hexylthiophene)‐block‐poly(tetrahydrofuran) was synthesized by cationic ring‐opening polymerization of tetrahydrofuran (THF) using a poly(3‐hexylthiophene) macroinitiator. Poly(3‐hexylthiophene) macroinitiator used for the ring‐opening polymerization of THF was synthesized by reacting the hydroxypropyl end‐group with trifluoromethanesulfonic anhydride in the presence of 2,6‐di‐tert‐butylpyridine. 1H NMR spectroscopy and SEC data confirmed the formation of the di‐block copolymers. Field‐effect mobility of poly(3‐hexylthiophene)‐block‐poly(tetrahydrofuran) was measured in a thin‐film transistor configuration and was found to be 0.009 cm2 · V?1 · s?1.
PLLA/PDLA blends were crystallized between 120 and 195 °C. The stereocomplex spherulites acquired in equimolar and non‐equimolar blends were compared using POM, WAXD, DSC, and AFM. For equimolar blends, stereocomplex crystals show spherulites with positive birefringence, which is ascribed to the existence of domains made up of tangentially oriented lamellae. For PLLA‐rich (or PDLA‐rich) blends, the signs of the birefringence changed from a positive spherulite to a mixed spherulite and then to a negative spherulite. In negative spherulites, most lamellae orient radially. Radial and tangential cracks were observed in equimolar blends when crystallization took place above 175 °C whereas no cracks formed for non‐equimolar blends.
CROP has been used to synthesize well‐defined POXZ with a monofunctional (iodomethane) or a bifunctional (1,3‐diiodopropane) initiator. POXZ has been functionalized with an azido group at one (α‐azido‐POXZ, = 3.58 × 103 g · mol?1) or both ends (α,ω‐azido‐POXZ, = 6.21 × 103 g · mol?1) of the macromolecular chain. The Huisgen 1,3‐dipolar cycloaddition has been investigated between azido‐POXZ and a terminal alkyne on a small or larger molecule (PEG). In each case, the click reaction has been successful and quantitative. In this way, different telechelic polymers (polymers bearing different functions such as acrylate, epoxide, or carboxylic acid) and block copolymers of POXZ and PEG have been prepared. The polymers have been characterized by means of FTIR, 1H NMR, and SEC.
Summary: Polybenzoxazine (PBA‐a)/poly(ε‐caprolactone) (PCL) blends were prepared by an in situ curing reaction of benzoxazine (BA‐a) in the presence of PCL. Before curing, the benzoxazine (BA‐a)/PCL blends are miscible, which was evidenced by the behaviors of single and composition‐dependant glass transition temperature and equilibrium melting point depression. However, the phase separation induced by polymerization was observed after curing at elevated temperature. It was expected that after curing, the PBA‐a/PCL blends would be miscible since the phenolic hydroxyls in the PBA‐a molecular backbone have the potential to form intermolecular hydrogen‐bonding interactions with the carbonyls of PCL and thus would fulfil the miscibility of the blends. The resulting morphology of the blends prompted an investigation of the status of association between PBA‐a and PCL under the curing conditions. Although Fourier‐transform infrared spectroscopy (FT‐IR) showed that there were intermolecular hydrogen‐bonding interactions between PBA‐a and PCL at room temperature, especially for the PCL‐rich blends, the results of variable temperature FT‐IR spectroscopy by the model compound indicate that the phenolic hydroxyl groups could not form efficient intermolecular hydrogen‐bonding interactions at elevated temperatures, i.e., the phenolic hydroxyl groups existed mainly in the non‐associated form in the system during curing. The results are valuable to understand the effect of curing temperature on the resulting morphology of the thermosetting blends.
SEM micrograph of the dichloromethane‐etched fracture surface of a 90:10 PBA‐a/PCL blend showing a heterogeneous morphology. 相似文献
Crystallization kinetics of the biodegradable and fast crystallizing poly(butylene succinate) is studied, under both isothermal and non‐isothermal conditions. For the isothermal process at temperatures from 75 to 95 °C it is found that the Avrami model successfully describes the transformation kinetics. The non‐isothermal crystallization data obtained at a wide range of cooling rates from 0.1 to 20 °C · min?1 are treated with several models, which include the modified Avrami, the Ozawa, the combined Avrami‐Ozawa, and the Tobin model. The Lauritzen‐Hoffman parameters are estimated from isothermal and non‐isothermal differential scanning calorimetry data, using different approximations for the growth rate and from the effective activation energy equation proposed by Vyazovkin and Sbirrazzuoli. The multiple‐melting behavior has been interpreted in the context of the melting–recrystallization–remelting phenomena.
Poly(arylene ether oxadiazole) telechelics with fluorine and hydroxyl end groups were synthesized by nucleophilic substitution polymerizations of 2,5‐bis(4‐fluorophenyl)‐1,3,4‐oxadiazole monomer with bishydroxy compounds containing ? C(CH3)2, ? C(CF3)2 and ? SO2? groups. Fluorotelechelics were obtained with about 3 repeating units (molecular weight about 2 000 g · mol?1) using a rather excess (100 mol‐%) of bis(fluorophenyl) oxadiazole compound. On the other hand, hydroxytelechelics were synthesized with about 9 repeating units (molecular weight about 5 000 g · mol?1) using a small excess of bishydroxy compound (monomer molar ratio of 0.93). Sulfonated poly(arylene ether oxadiazole) hydroxytelechelics were also synthesized using sulfonated and unsulfonated bishydroxy compounds. All sulfonated hydroxytelechelics were partially water soluble, even when only 40 mol‐% of sulfonated monomers was used. The number of repeating units of hydroxytelechelics increased up to 12 (molecular weight about 9 000 g · mol?1) using sulfonated monomers, probably because of the higher reactivity of sulfonated phenoxide. The molecular weights estimated by 1H NMR were in agreement to the results obtained by SEC. The telechelics can be used as precursor for the synthesis of block copolymer.
The melting behavior, crystal structure, and spherulitic morphology of melt‐crystallized poly(butylene adipate) (PBA) at a temperature range from 25 to 35 °C have been investigated by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD) and optical microscopy. Two distinct melting behaviors with double peaks have been observed after melt‐crystallizing at different temperatures. X‐ray analysis proves that these two behaviors arise from two forms of PBA crystal structures. The β‐form crystals are formed at temperatures below 31 °C, while the α‐form crystals are formed above 29 °C. When the crystallization temperature is 30 ± 1 °C, a mixture of α‐form and β‐form crystals has been formed. The influences of annealing treatment and sample preparation method on the two forms of PBA crystal structures have been discussed. The results indicate that the low temperature‐formed β‐form crystals are very sensitive to the preparation conditions.
The melting curves at different heating rates for poly(butylene adipate) after melt‐crystallized at 25 °C and 33 °C, respectively. 相似文献
Poly(ethylene azelate) (PEAz) was synthesized and its melting behavior was studied with DSC and Step Scan DSC. The equilibrium melting point of PEAz was found 62 °C and the heat of fusion of 100% crystalline polymer was estimated at 160 J · g?1. Polarized light microscopy showed mixed birefringence. From isothermal crystallization DSC study, after self‐nucleation, crystallization rates were estimated. The Lauritzen–Hoffman plots showed crystallization regime I to II and II to III transition at 34 and 19 °C respectively. Non‐isothermal crystallization was studied. The activation energy was calculated applying the isoconversional method of Friedman. Chemical hydrolysis of PEAz was very slow, while enzymatic hydrolysis showed comparable rates with PCL.
A modular synthesis of short chain length and medium chain length poly(3‐hydroxyalkanoate)s‐b‐poly(ethylene glycol) (PHAs‐b‐PEG) diblock copolymers is described. First, length‐controlled oligomers of hydrophobic poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBHV), poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHHx), and poly(3‐hydroxyoctanoate‐co‐hydroxyhexanoate) (PHOHHx) containing a carboxylic acid end group were obtained by thermal treatment, with molar masses ranging from 3 800 to 15 000 g · mol?1. After quantitative functionalization with propargylamine, ligation with azide‐terminated poly(ethylene glycol) of 5 000 g · mol?1 was accomplished using the copper (I) catalyzed azide alkyne cycloaddition (CuAAC). Well‐defined diblock copolymers were obtained up to 93% yield, with molar masses ranging from 9 900 to 23 100 g · mol?1. All products were fully characterized using 1H NMR, COSY, SEC, TGA, and DSC.
