Phase‐transition characteristics of amphiphilic poly(2‐ethyl‐2‐oxazoline)/poly(ε‐caprolactone) block copolymers in aqueous solutions

Amphiphilic diblock and triblock copolymers of various block compositions based on hydrophilic poly(2‐ethyl‐2‐oxazoline) (PEtOz) and hydrophobic poly(ε‐caprolactone) were synthesized. The micelle formation of these block copolymers in aqueous media was confirmed by a fluorescence technique and dynamic light scattering. The critical micelle concentrations ranged from 35.5 to 4.6 mg/L for diblock copolymers and 4.7 to 9.0 mg/L for triblock copolymers, depending on the block composition. The phase‐transition behaviors of the block copolymers in concentrated aqueous solutions were investigated. When the temperature was increased, aqueous solutions of diblock and triblock copolymers exhibited gel–sol transition and precipitation, both of which were thermally reversible. The gel–sol transition‐ and precipitation temperatures were manipulated by adjustment of the block composition. As the hydrophobic portion of block copolymers became higher, a larger gel region was generated. In the presence of sodium chloride, the phase transitions were shifted to a lower temperature level. Sodium thiocyanate displaced the gel region and precipitation temperatures to a higher temperature level. The low molecular weight saccharides, such as glucose and maltose, contributed to the shift of phase‐transition temperatures to a lower temperature level, where glucose was more effective than maltose in lowering the gel–sol transition temperatures. The malonic acid that formed hydrogen bonds with the PEtOz shell of micelles was effective in lowering phase‐transition temperatures to 1.0M, above which concentration the block copolymer solutions formed complex precipitates. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2400–2408, 2000     

低温溶液缩聚合成聚芳醚酮酮的研究

低温溶液缩聚合成聚芳醚酮酮的研究宋才生，蔡明中，周丽云（江西师范大学化学系南昌３３００２７）关键词低温溶液缩聚，付一克或化反应，聚芳醚酮酮，二苯醚聚芳醚酮酮（ＰＥＫＫ）是一种新型的热塑性耐热高分子材料，具有优异的机械力学性能，耐溶剂抗化学腐蚀性能，抗...     

Synthesis and characterization of temperature-sensitive cellulose-graft-poly(N-isopropylacrylamide) copolymers

A new series of cellulose-graft-poly(N-isopropylacrylamide)(cellulose-g-PNIPAM) copolymers were prepared by atom transfer radical polymerization(ATRP) of N-isopropylacrylamide monomers from a cellulose-based macro-initiator, which was homogeneously synthesized in an ionic liquid 1-allyl-3-methylimidazolium chloride(Amim Cl). The composition of cellulose-g-PNIPAM copolymers could be adjusted by altering the feeding ratio and reaction time. The resultant copolymers with relatively high content of PNIPAM segments(molar substitution of PNIPAM ? 18.3) were soluble in water at room temperature. Aqueous solutions of cellulose-g-PNIPAM copolymers exhibited clear temperature-sensitive behavior, and their sol-to-gel phase transition properties were investigated by dynamic light scattering(DLS) and UV measurements. Compared with pure PNIPAM, the cellulose-g-PNIPAM copolymers possessed higher lower critical solution temperatures(LCST) in a range from 36.9 ?C to 40.8 ?C, which are close to normal human body temperature, and could be tuned by adjusting the content of PNIPAM segments in copolymers. Spherical structure of cellulose-g-PNIPAM copolymers formed at temperatures above LCST and its morphology was observed by TEM and SEM. These novel cellulose-g-PNIPAM copolymers may be attractive substrates for some biomedical applications, such as drug release and tissue engineering.     

Phase transition of aqueous solutions of poly(N,N-diethylacrylamide-co-acrylic acid) by differential scanning calorimetric and spectrophotometric methods

 The phase transition of aqueous solutions of poly(N,N-diethylacrylamide-co-acrylic acid) (DEAAm–AA) is studied by differential scanning calorimetry (DSC) and UV–vis spectrophotometry. The copolymer aqueous solutions are shown to have well-defined lower critical solution temperatures (LCSTs). The LCST values obtained from the maximum of the first derivatives of the DSC and optical transition curves agree well. DSC can be used to measure the phase-transition temperature of more dilute polymer solutions. On increasing the AA composition in the copolymers, the LCST values of the copolymer increase, then decrease at higher AA composition. For the aqueous solution of the copolymers, the transition curve obtained by the spectrophotometric method is highly wavelength dependent. The LCST values are found to be concentration-dependent. The changes in the heat of the phase transition of the copolymer solutions measured from DSC are lower than that of the homopolymer PDEAAm solution. This is consistent with the suggestion that the polymer chains of the copolymers collapsed only partially at temperatures above the LCST. The added salt (sodium chloride) decreases the transition temperature of the polymer solution. Received: 14 November 2000 Accepted: 15 January 2001     

Synthesis of poly(aryl ether ketone)s containing diphenyl moieties by electrophilic Friedel–Crafts solution polycondensation

A new monomer, 4,4′‐bis(4‐phenoxybenzoyl)diphenyl (BPOBDP), was prepared by Friedel–Crafts reaction of 4‐bromobenzoyl chloride and diphenyl, followed by condensation with potassium phenoxide. Novel poly(ether ketone ketone) (PEKK)/poly(ether ketone diphenyl ketone ether ketone ketone) (PEKDKEKK) copolymers were synthesized by electrophilic Friedel–Crafts solution copolycondensation of isophthaloyl chloride (IPC) with a mixture of diphenyl ether (DPE) and BPOBDP, in the presence of anhydrous aluminum chloride and N‐methyl‐pyrrolidone (NMP) in 1,2‐dichloroethane (DCE). The copolymers obtained were characterized by various analytical techniques such as FT‐IR, DSC, TGA, and wide‐angle X‐ray diffraction (WAXD). The results showed that the resulting copolymers exhibited excellent thermal stability due to the existence of diphenyl moieties in the main chain. The glass transition temperatures are above 152°C, the melting temperatures are above 276°C, and the temperatures at a 5% weight loss are above 548°C in nitrogen. The copolymers with 50–70 mol% BPOBDP had tensile strengths of 101.5–102.7 MPa, Young's moduli of 3.23–3.41 GPa, and elongations at break of 12–17%. All these copolymers were semicrystalline and insoluble in organic solvents. Copyright © 2008 John Wiley & Sons, Ltd.     

Sequence Distribution-Glass Transition Effects. II. Alkyl Methacrylate/Vinyl Chloride Copolymers

The glass transition temperatures of cyclized and un-cyciized alkyl methacrylate/vinyl chloride copolymers have been measured and found to differ from values predicted using conventional glass transition prediction relationships. An additive relationship was developed that relates the sequence distribution of the copolymer to the polymer glass transition temperature. Using this relationship, good agreement between experimental and sequence distribution predicted glass transitions was found.     

Synthesis and gelation properties of PEG-PLA-PEG triblock copolymers obtained by coupling monohydroxylated PEG-PLA with adipoyl chloride

Ring-opening polymerization of D,L-lactide was carried out in the presence of monohydroxylated poly(ethylene glycol) (PEG) with Mn of 2000 and 5000, using zinc powder as catalyst. The resulting PEG-b-polylactide (PEG-PLA) diblocks with various ethylene oxide/lactyl (EO/LA) ratios were coupled with adipoyl chloride to yield PEG-PLA-PEG triblock copolymers. N-Dimethylaminopyridine (DMAP) was used as catalyst. The obtained PEG-PLA-PEG triblock copolymers were characterized by various analytical techniques such as IR, 1H NMR, size exclusion chromatography, X-ray diffraction, and differential scanning calorimetry. Data showed that all the copolymers were semicrystalline with the PEG-type crystalline structure, the crystallinity decreasing with increasing PLA block length. Bioresorbable hydrogels were prepared from the water-soluble triblock copolymers. Rheological measurements showed a gel-sol transition with increasing temperature and gelation was found to be thermoreversible. The copolymer solution behaves like a viscoelastic liquid above the gel point and like a viscoelastic solid below the gel point. The critical gelation concentration, the gel-sol transition temperature at a given concentration, and corresponding moduli depend on both the EO/LA ratio and the molecular weight of the copolymers. It is assumed that gelation results from interactions between PEG blocks at low temperatures and that these interactions are disrupted as the temperature is elevated. The shrinking of PEG blocks with increasing temperature seems to be in agreement with the variation of the gel-sol transition temperatures.     

Copolymers of nylon 266 and nylon 66: Synthesis and characterization

Copolymers of nylon 266 and nylon 66 were prepared by interfacial polymerization of N-glycyl hexanediamine and hexanediamine with adipoyl chloride. According to the results of intrinsic viscosity measurements and GPC analysis, the molecular weights of the copolymers were relatively high. The structure of the copolymers was confirmed by FTIR, and the compositions were determined by ¹H-NMR spectroscopy. The copolymers have similar solubility features as nylon 66. Both melting and glass transition temperatures showed a minimum at around 20–30% nylon 66 content. The copolymers are semicrystalline. Copolymers with lower T_m could be melt-spun into fibers without appreciable thermal degradation. © 1993 John Wiley & Sons, Inc.     

Studies on copolymers of vinyl chloride with diethyl fumarate,isobutylene and vinyl bromide,as models of PVC with chain irregularities—II The influence of copolymerization on the tacticity of PVC sequences: The influence f copolymerization on the tacticity of PVC sequences

Copolymers of vinyl chloride (> 90%) with diethyl fumarate, isobutylene and vinyl bromide, prepared at temperatures between +25 and ?30°, were used to determine the influence of the copolymerization on the tacticity of polyvinyl chloride sequences in the copolymers. The tacticity appeared to decrease in proportion as the comonomer content increases, this effect being different for the three kinds of copolymers. The results are discussed by taking into consideration the comonomer volume, the Arrhenius plots and the sequence distribution in copolymers after calculation of the number of alternances per 100 monomer units.     

Direct polyesterification by use of phosphorus oxychloride and LiCl in pyridine

The reaction of the N-phosphonium salt of pyridine derived from phosphorus oxychloride in pyridine was successfully used for the preparation of aromatic polyesters with high molecular weight when carried out in the presence of lithium chloride. In the copolycondensations of isophthalic and terephthalic acid with diphenols, the mode of reaction with the diacids was expected to produce several types of the diacid activated intermediates, which might control the sequences of the diacids in the copolymers. The possible variation of the sequences was studied in terms of the mode and copolymer properties such as glass transition temperatures and liquid crystalline transition temperatures. Competitive model reactions were carried out to discuss these relationships. © 1993 John Wiley & Sons, Inc.     

Grafting polymerization of styrene onto alternating terpolymers based on chlorotrifluoroethylene,hexafluoropropylene, and vinyl ethers,and their modification into ionomers bearing ammonium side‐groups

The grafting polymerization of styrene initiated by the alkyl chloride groups of poly(CTFE‐alt‐VE) and poly[(CTFE‐alt‐VE)‐co‐(HFP‐alt‐VE] copolymers (where CTFE, HFP, and VE stand for chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), and vinyl ether (VE), respectively) followed by the chemical modification of the polystyrene grafts are presented. First, the fluorinated alternating copolymers were produced by radical copolymerization of CTFE (with HFP) and VE. Second, atom transfer radical polymerization enabled the grafting polymerization of styrene in the presence of the poly(CTFE‐alt‐VE)‐macroinitiator using the alkyl chloride group of CTFE as the initiation site. Kinetics of the styrene polymerization indicated that such a grafting had a certain controlled character. For the first time, grafting of polystyrene onto alternating fluorinated copolymers has been achieved. Differential scanning calorimetry thermograms of these graft copolymers exhibited two glass transition temperatures assigned to both amorphous domains of the polymeric fluorobackbone (ranging from ?20 to +56 °C) and the polystyrene grafts (ca. 95 °C). The thermostability of these copolymers increased on grafting. Thermal degradation temperatures at 5% weight loss were ranging from 193 to 305 °C when the polystyrene content varied from 81 to 27%. Third, chloromethylation of the polystyrene grafts followed by the cationization of the chloromethyl dangling groups led to original ammonium‐containing graft copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Thermal degradation of graft copolymers of PVC prepared by mastication with styrene and methyl methacrylate,and of further PVC mixtures and vinyl chloride copolymers

Graft copolymers prepared by mastication of PVC in the presence of styrene or of a styrene/ methyl methacrylate mixture, have been studied by thermogravimetry, estimation of hydrogen chloride, thermal volatilization analysis, and flash pyrolysis/g.l.c. The degradation behaviour of PVC/ polystyrene mixtures, vinyl chloride/styrene random copolymers, a random copolymer of methyl methacrylate and styrene, and PVC/poly-α-methylstyrene mixtures has also been studied. The graft copolymers resemble the PVC/methacrylate graft copolymers previously studied in showing retardation of the dehydrochlorination reaction, but contrast with them in yielding chain fragments but no monomer during HCl production. Some stabilization of the second component at higher temperatures is also found. PVC/polystyrene mixtures behave in the same way as the corresponding graft copolymers, but vinyl chloride/styrene copolymers show reduced stability towards both dehydrochlorination and monomer production compared with the homopolymers. PVC/poly-α-methylstyrene mixtures yield some monomer concurrently with HCl loss, and display marked retardation of the latter reaction. Stabilization of the second polymer at higher temperatures is again observed. Many of these results add further strong support to the view that chlorine atoms are involved as chain carriers in the thermal dehydrochlorination of PVC.     

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...     

Ultrastructure studies of polystyrene-based side-chain liquid-crystalline copolymers containing charge transfer groups

A series of new side-chain liquid-crystalline copolymers has been prepared, and the thermal properties of the individual copolymers have been determined. These copolymers are derived from atactic polystyrene and contain both 4-methoxyazobenzene and 4-nitroazobenzene mesogens; these are linked through octyl spacers to the polystyrene backbone. All the copolymers exhibit a smectic phase that has been assigned smectic A on the basis of polarizing microscopy and x-ray diffraction studies. The glass transition temperatures of the polymers exhibit a linear dependence on composition, whereas the clearing temperatures and the associated entropies show significant deviations from such behavior. The smecticisotropic transition temperatures of the copolymers are higher than those of the composition-weighted averages for the corresponding homopolymers, whereas the entropies of transition are lower than expected. X-ray diffraction studies of fiber samples revealed that the director of the mesophase is oriented perpendicular to the fiber axis. The liquid-crystalline polystyrene containing 25 mol % nitro-substituted mesogen shows an unusual S_A-phase WAXS pattern. The copolymers were investigated further by ¹³C CP/MAS NMR spectroscopy, and the observed changes in the spectra are analyzed in terms of chemical composition and local electronic environment. The application of the interrupted decoupling technique revealed that the spacer contains a number of gauche defects. These observations lead us to suggest possible microstructural arrangements in the smectic phase. © 1993 John Wiley & Sons, Inc.     

The effect of copolymerization on transition temperatures of polymeric materials

The relationship between transition temperatures and copolymer composition was studied by DSC. Three types of copolymers were studied: styrene-acrylonitrile (SAN), vinyl chloride-vinyl acetate (VC-VA), and ethylene vinyl acetate (EVA). SAN's and VC-VA's are amorphous copolymers, whereas EVA's are semi-crystalline copolymers. The variation of the glass transitions and the crystalline melting are discussed in this study.     

Synthesis and characterization of novel aromatic poly(imide–benzoxazole) copolymers

New poly(imide–benzoxazole) copolymers were prepared directly from a dianhydride, a diacid chloride, and a bis(o‐diaminophenol) monomer in a two‐step method. In the first step, poly(amic acid–hydroxyamide) precursors were synthesized by low‐temperature solution polymerization in an organic solvent. Subsequently, the thermal cyclodehydration of the poly(amic acid–hydroxyamide) precursors at 350 °C produced the corresponding poly(imide–benzoxazole) copolymers. The inherent viscosities of the precursor polymers were around 0.19–0.33 dL/g. The cyclized poly(imide–benzoxazole) copolymers had glass‐transition temperatures in the range of 331–377 °C. The 5% weight loss temperatures ranged from 524 to 535 °C in nitrogen and from 500 to 514 °C in air. The poly(imide–benzoxazole) copolymers were amorphous, as evidenced by the wide‐angle X‐ray diffraction measurements. The structures of the precursor copolymers and the fully cyclized copolymers were characterized by Fourier transform infrared, ¹H NMR, and elemental analysis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6020–6027, 2005     

Thermotropic copolyesters prepared by solution polycondensation with TsCl/DMF/pyridine condensing agent

When mixtures of terephthalic acid (TPA) and 1,6-naphthalenedicarboxylic acid (NDC) or 4,4′-dicarboxydiphenylether (DCDPE), TPA, and isophthalic acid (IPA) were reacted in pyridine (Py) with Tosyl chloride (TsCl)/DMF/Py to activate the diacids, the reaction mixture was soluble in Py, despite each of the separately activated diacids being insoluble. The solubility of the activated diacids was examined at a variety of acid compositions and temperatures. It was expected that a competitive reaction among the diacids with an aromatic diol in solution might be different from those in the melt, resulting in a different distribution of the acids in the copolymers. The TPA/NDC-phenylhydroquinone and DCDPE/TPA/IPA-chlorohydroquinone copolymers were prepared in solution using TsCl/DMF/Py as the condensing agent and the transition temperatures of these liquid crystalline copolyesters were compared to those obtained by melt copolycondensation. A practical depression of the transition temperature by the solution polycondensation was observed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3710–3714, 1999     

Synthesis and Properties of Poly （aryl ether ketone） Copolymers Containing 2,7-Naphthalene Moieties

IntroductionPoly(aryl ether ketone)s are high performance en-gineering plastics with outstanding physical,chemical,thermal and mechanical properties and have been ap-plied to the aerospace industry,the electronic industry,the automobile industry,the petro…     

Glass transition temperature of low molecular weight styrene–isoprene block copolymers

Different series of poly(styrene–isoprene) diblock and poly(styrene–isoprene–styrene) triblock copolymers were prepared. In each series, the low molecular weight polystyrene block was kept constant, and the molecular weight of the polyisoprene block varied. The glass transition behavior of these polymers was studied and their glass transition temperatures compared with those of the random copolymers of styrene and isoprene. It is concluded that some low molecular weight styrene-isoprene block copolymers form a single phase. Krause's thermodynamic treatment of phase separation in block copolymers was applied to the data. One arrives at a polystyrene–polyisoprene interaction parameter χ1,2 ≈ 0.1. The experimental and theoretical limitations of this result are discussed.     

Thermoresponsive hydrogels from symmetrical triblock copolymers poly(styrene-block-(methoxy diethylene glycol acrylate)-block-styrene)

A series of symmetrical, thermo-responsive triblock copolymers was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization, and studied in aqueous solution with respect to their ability to form hydrogels. Triblock copolymers were composed of two identical, permanently hydrophobic outer blocks, made of low molar mass polystyrene, and of a hydrophilic inner block of variable length, consisting of poly(methoxy diethylene glycol acrylate) PMDEGA. The polymers exhibited a LCST-type phase transition in the range of 20-40 °C, which markedly depended on molar mass and concentration. Accordingly, the triblock copolymers behaved as amphiphiles at low temperatures, but became water-insoluble at high temperatures. The temperature dependent self-assembly of the amphiphilic block copolymers in aqueous solution was studied by turbidimetry and rheology at concentrations up to 30 wt %, to elucidate the impact of the inner thermoresponsive block on the gel properties. Additionally, small-angle X-ray scattering (SAXS) was performed to access the structural changes in the gel with temperature. For all polymers a gel phase was obtained at low temperatures, which underwent a gel-sol transition at intermediate temperatures, well below the cloud point where phase separation occurred. With increasing length of the PMDEGA inner block, the gel-sol transition shifts to markedly lower concentrations, as well as to higher transition temperatures. For the longest PMDEGA block studied (DP(n) about 450), gels had already formed at 3.5 wt % at low temperatures. The gel-sol transition of the hydrogels and the LCST-type phase transition of the hydrophilic inner block were found to be independent of each other.