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1.
Suspension polymerization expands the study of controlled radical polymerization to high conversions and is known as a method to synthesize polymers with high molecular weights. The radical block copolymerizations of styrene (S) and acrylonitrile (AN) or butyl methacrylate (BUMA) controlled by 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) was performed in an oil/water pressure reactor system at a temperature of 125°C. TEMPO‐terminated styrene homopolymer was employed as macroinitiator. The systems were examined by varying the composition of the monomer mixture at a constant reaction time, as well as by varying the reaction time for a characteristic monomer composition to get all of the possible conversion range. The solubility effects of acrylonitrile in the suspension medium were considered. Furthermore, the yield of the reaction was improved through initiator addition by taking control of the reaction. The polymerizations could proceed under control up to a conversion of 80–90%. By using the copolymerization equations, the solubility of pure acrylonitrile in the suspension medium could be calculated and was found to be 8 wt.‐%.  相似文献   

2.
Poly(L ‐lactide) (PLLA) and poly(3‐hydrobutyrate‐co‐3‐hydroxyvalerate) (PHBV) were blended with poly(butadiene‐co‐acrylonitrile) (NBR). Both PLLA/NBR and PHBV/NBR blends exhibited higher tensile properties as the content of acrylonitrile unit (AN) of NBR increased from 22 to 50 wt %. However, two separate glass transition temperatures (Tg) appeared in PLLA/NBR blends irrespective of the content of NBR, revealing that PLLA was incompatible with NBR. In contrast, a single Tg, which shifted along with the blend composition, was observed for PHBV/NBR50 blends. Moreover NBR50 suppressed the crystallization of PHBV, indicating that PHBV was compatible with NBR50. Decrease of both elongation modulus and stress at maximum load was less significant and increase of elongation at break was more pronounced in PHBV/NBR50 blends than in PLLA/NBR50 blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3508–3513, 2004  相似文献   

3.
In a blend of two immiscible polymers a controlled morphology can be obtained by adding a block or graft copolymer as compatibilizer. In the present work blends of low‐density polyethylene (PE) and polyamide‐6 (PA‐6) were prepared by melt mixing the polymers in a co‐rotating, intermeshing twin‐screw extruder. Poly(ethylene‐graft‐polyethylene oxide) (PE‐PEO), synthesized from poly(ethylene‐co‐acrylic acid) (PEAA) (backbone) and poly(ethylene oxide) monomethyl ether (MPEO) (grafts), was added as compatibilizer. As a comparison, the unmodified backbone polymer, PEAA, was used. The morphology of the blends was studied by scanning electron microscopy (SEM). Melting and crystallization behavior of the blends was investigated by differential scanning calorimetry (DSC) and mechanical properties by tensile testing. The compatibilizing mechanisms were different for the two copolymers, and generated two different blend morphologies. Addition of PE‐PEO gave a material with small, well‐dispersed PA‐spheres having good adhesion to the PE matrix, whereas PEAA generated a morphology characterized by small PA‐spheres agglomerated to larger structures. Both compatibilized PE/PA blends had much improved mechanical properties compared with the uncompatibilized blend, with elongation at break b) increasing up to 200%. Addition of compatibilizer to the PE/PA blends stabilized the morphology towards coalescence and significantly reduced the size of the dispersed phase domains, from an average diameter of 20 μm in the unmodified PE/PA blend to approximately 1 μm in the compatibilized blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2416–2424, 2000  相似文献   

4.
Incorporation of chloramphenicol and captopril into coated and uncoated monofilament sutures was evaluated, as well as the derived bactericide and wound healing effects. To this end, a commercially available suture and an amorphous random copolymer constituted by trimethylene carbonate and lactide units were considered. The suture had a segmented architecture based on polyglycolide hard blocks and a soft block constituted by glycolide, trimethylene carbonate and ε‐caprolactone units. Chloramphenicol was better loaded when the coating copolymer was employed due to its protective effect whereas captopril showed an opposite behavior due to partial solubilization during immersion in the coating bath. Interestingly, the release behavior was very different for the two studied drugs since a significant retention of chloramphenicol was always detected, suggesting the establishment of interactions between drug and copolymers. On the other hand, delivery of captopril showed a typical dose dependent behavior. A low in vitro toxicity of the two drugs was determined considering both epithelial‐like and fibroblast‐like cells. Bactericide effect of chloramphenicol against Gram‐negative and Gram‐positive bacteria was demonstrated at a dose that was non‐toxic for all assayed cells. An accelerating wound healing effect of captopril was also demonstrated for early events. In this case, the use of a coating copolymer was fundamental to avoid cytotoxic effects on highly loaded sutures. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44762.  相似文献   

5.
Random copolyester namely, poly(ethylene terephthalate‐co‐sebacate) (PETS), with relatively lower molecular weight was first synthesized, and then it was used as a macromonomer to initiate ring‐opening polymerization of l ‐lactide. 1H NMR quantified composition and structure of triblock copolyesters [poly(l ‐lactic acid)‐b‐poly(ethylene terephthalate‐co‐sebacate)‐b‐poly(l ‐lactic acid)] (PLLA‐PETS‐PLLA). Molecular weights of copolyesters were also estimated from NMR spectra, and confirmed by GPC. Copolyesters exhibited different solubilities according to the actual content of PLLA units in the main chain. Copolymerization effected melting behaviors significantly because of the incorporation of PETS and PLLA blocks. Crystalline morphology showed a special pattern for specimen with certain composition. It was obvious that copolyesters with more content of aromatic units of PET exhibited increased values in both of stress and modulus in tensile test. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007  相似文献   

6.
Conventional approaches to toughen thermosets are: (1) the polymerization‐induced phase separation of a rubber or a thermoplastic, or (2) the use of a dispersion of preformed particles in the initial formulation. In the present study it is shown that it is possible to combine both techniques by using graft copolymers with one of the blocks being initially immiscible and the other that phase separates during polymerization. This is illustrated by the use of poly(ethylene‐co‐vinyl acetate)‐graft‐poly(methyl methacrylate) (EVA‐graft‐PMMA) as modifier of an epoxy resin. EVA is initially immiscible and PMMA phase separates during polymerization. Blends of an epoxy monomer based on diglycidylether of bisphenol A (DGEBA, 100 parts by weight), piperidine (5 parts by weight), and PMMA (5 parts by weight), showed the typical polymerization‐induced phase separation of PMMA‐rich domains before gelation of the epoxy network. Replacing PMMA by EVA‐graft‐PMMA (5 parts by weight), yielded stable dispersions of EVA blocks, favoured by the initial solubility of PMMA blocks. Phase separation of PMMA blocks in the course of polymerization led to a dispersion of in situ generated biphasic particles (plausibly composed of EVA cores surrounded by PMMA shells), with average diameters varying from 0.3 to 0.6 µm with the cure temperature. This procedure may be used to generate stable dispersions of biphasic particles for toughening purposes. © 2002 Society of Chemical Industry  相似文献   

7.
The synthesis of two low molecular weight linear unsaturated oligoester precursors, poly(propylene fumarate‐co‐sebacate) (PPFS) and poly(ethylene fumarate‐co‐sebacate) (PEFS), are described. PPFS, PEFS, and poly(ethylene glycol) are then used to prepare poly(propylene fumarate‐co‐sebacate)‐co‐poly(ethylene glycol) (PPFS‐co‐PEG) and poly(ethylene fumarate‐co‐sebacate)‐co‐poly(ethylene glycol) (PEFS‐co‐PEG) block copolymers. The products thus obtained are investigated in terms of the molecular weight, composition, structure, thermal properties, and solubility behavior. A number of design parameters including the molecular weights of PPFS, PEFS, and PEG, the reaction time in the polymer synthesis, and the weight ratio of PEG to PPFS or to PEFS are varied to assess their effects on the product yield and properties. The hydrolytic degradation of PPFS‐co‐PEG and PEFS‐co‐PEG in an isotonic buffer (pH 7.4, 37°C) is investigated, and it is found that the fumarate ester bond cleaves faster than does the sebacate ester bond. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 295–300, 2004  相似文献   

8.
9.
Copolymerization of acrylonitrile (AN) with p‐trimethylsilylstyrene (TMSS) was carried out at 60°C in bulk and in solution in the presence of 2,2′‐azobisisobutyronitrile (AIBN). The reactivity ratios of AN (M1) and TMSS (M2) were determined to be r1 = 0.068 and r2 = 0.309. The effects of the AIBN concentration and that of the chain transfer agent CCl4 on the molecular weights (MWs) of the copolymers were investigated. An increase in the concentrations of AIBN or CCl4 in solution led to a decrease in MW. Poly(AN‐co‐TMSS‐co‐St) was synthesized in solution using AIBN as the initiator. The molar fraction of AN was 0.415, while the molar ratio of TMSS/St varied from 1 : 1 to 1 : 9. The transition temperatures and thermal and thermooxidative stabilities of poly(AN‐co‐TMSS) and poly(AN‐co‐TMSS‐co‐St) were investigated. The differential scanning calorimeter technique was used to determine the compatibility of the poly(AN‐co‐TMSS) and poly(AN‐co‐TMSS‐co‐St) with commercial poly(AN‐co‐St). All the blends show a single glass transition temperature, which indicates the compatibility of the blend components. The surface film morphology of the blends mentioned above was examined by X‐ray photoelectron spectroscopy. The data obtained indicate that the silicon‐containing copolymer is concentrated in the surface layer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1920–1928, 2000  相似文献   

10.
The heterofunctional condensation of 1,3‐dichloro‐1,3‐disila‐1,3‐diphenyl‐2‐oxaindane with dihydroxydiphenylsilane at various ratios of initial compounds in the presence of amines was carried out, and α,ω‐dihydroxy(1,3‐disila‐1,3‐diphenyl‐2‐oxaindane)‐diphenylsiloxane oligomers with various degrees of condensation were obtained. Corresponding block copolymers were obtained by heterofunctional polycondensation of synthesized α,ω‐dihydroxy(1,3‐disila‐1,3‐diphenyl‐2‐oxaindane)‐diphenylsiloxane oligomers with α,ω‐dichlorodimethylsiloxanes in the presence of amines. Thermogravimetry, gel permeation chromatography, differential scanning calorimetry, and wide‐angle X‐ray analysis were carried out on the synthesized block coplymers. Differential scanning calorimetry and wide‐angle X‐ray studies of these copolymers showed that their properties were determined by the ratio of the lengths of the flexible linear poly(dimethylsiloxane) and rigid poly(1,3‐disila‐1,3‐diphenyl‐2‐oxaindane)‐diphenylsiloxane fragments in the main macromolecular chain. Two‐phase systems were obtained with specific flexible and rigid fragment length values in synthesized block copolymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3462–3467, 2006  相似文献   

11.
The complexation behavior between poly(styrene‐co‐methacrylic acid) of different compositions (SMA‐12 or SMA‐29) and poly(styrene‐co‐4‐vinylpyridine) (S4VP‐6 or S4VP‐15) was studied by viscometry and differential scanning calorimetry using tetrahydrofuran (THF) and butan‐2‐one as solvents. This complexation is attributed to the presence of strong intermolecular interactions between the different polymer chains by hydrogen bonding. A single glass‐transition temperature, intermediate between those of the two pure copolymers SMA‐29 and S4VP‐15, was obtained with each composition of the mixture when THF or butan‐2‐one is used as a common solvent. The obtained results showed that the formation of such complexes depends strongly on the nature of the solvent and the contents of the interacting species. The complex formation is inhibited in THF because of the important ability of this latter to interact with the SMA. A quantitative analysis of the interactions between the constituents of these blends was carried out by FTIR spectroscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 806–811, 2005  相似文献   

12.
The copolymer poly(vinylidene fluoride)‐graft‐poly(4‐vinylpyridine) (PVDF‐g‐P4VP) was prepared through the graft copolymerization of poly(vinylidene fluoride) with 4‐vinylpyridine. Through the blending of the PVDF‐g‐P4VP copolymer with poly(N‐isopropylacrylamide) (PNIPAm) in an N‐methyl‐2‐pyrrolidone solution, PVDF‐g‐P4VP/PNIPAm membranes were fabricated by phase inversion in aqueous media. Elemental analyses indicated that the blend concentration of PNIPAm in the blend membranes increased with an increase in the blend ratio used in the casting solution. Scanning electron microscopy revealed that the membrane surface tended to corrugate at a low PNIPAm concentration and transformed into a smooth morphology at a high PNIPAm concentration. The surface morphology and pore size distribution of the microfiltration membranes could be regulated by the blend concentration of the casting solution, temperature, pH, and ionic strength of the coagulation bath. X‐ray photoelectron spectroscopy revealed a significant enrichment of PNIPAm on the membrane surface. The flux of aqueous solutions through the blend membranes exhibited a pH‐ and temperature‐dependent behavior. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4089–4097, 2006  相似文献   

13.
Deformation mechanisms in postfractured high‐thermal‐resistant poly(acrylonitrile‐butadiene‐styrene) (ABS) were investigated using transmission electron microscopy (TEM) and small‐angle X‐ray scattering (SAXS). Although crazes were clearly identified by TEM, they were not detectable by SAXS. This was possibly due to a short distance between sample and imaging plate in the SAXS set‐up and invisibility of craze fibril scattering from the postfractured samples. A rhomboid‐shaped SAXS pattern was obtained from ABS samples with high ductility but with no crazes shown in the TEM micrographs. It is believed that the rhomboid‐shaped SAXS pattern was generated from matrix shear yielding. The results show that a combination of TEM and SAXS enable us to distinguish crazing and shear yielding in the postfractured ABS. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1316–1321, 2001  相似文献   

14.
A series of temperature‐ and pH‐responsive hydrogels were prepared from acrylic acid (AAc), acrylamide (AAm), oligo(ethylene glycol)monoacrylate (OEGMA), and oligo(ethylene glycol)diacrylate by varying the AAc:AAm molar ratio and the OEGMA content. Phase‐transition temperatures and swelling ratios of the obtained poly(AAc‐co‐AAm)‐graft‐OEG gels were measured as a function of temperature and pH. At pH < 5, the obvious transition temperatures ranging from 5 to 35°C were obtained as the AAc : AAm molar ratio was varied. The highest transition temperature was obtained at the AAc : AAm ratios of 5 : 5 and 6 : 4, and the sharp transition curves were observed at the AAc : AAm ratios from 5 : 5 to 8 : 2. The transition temperature further increased with increasing OEGMA content. It was suggested that OEG graft chains with a large mobility played an important role for the formation of hydrogen bonding in the hydrogels. The gels prepared here showed obvious reproducibility of the phase transition in response to temperature changes, which suggests the feasibility of their practical applications. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 798–805, 2001  相似文献   

15.
The hydrolytic condensation of 1,3‐dichloro‐1,3‐disila‐1,3‐diphenyl‐2‐oxaindane under neutral conditions produced α'ω‐dihydroxy‐1,3‐disila‐1,3‐diphenyl‐2‐oxaindane (polymerization degree ≈ 4). The homofunctional condensation of α'ω‐dihydroxy‐1,3‐disila‐1,3‐diphenyl‐2‐oxaindane in a toluene solution and in the presence of activated carbon was performed, and dihydroxy‐containing oligomers with various degrees of condensation were obtained. Through the heterofunctional condensation of dihydroxy‐containing oligomers with α'ω‐dichlorodimethylsiloxanes in the presence of amines, corresponding block copolymers were obtained. Gel permeation chromatography, differential scanning calorimetry, thermomechanical analysis, thermogravimetry, and wide‐angle roentgenography investigations were carried out. Differential scanning calorimetry and roentgenography studies of the block copolymers showed that their properties were determined by the ratio of the lengths of the flexible and linear poly(dimethylsiloxane) and rigid poly(1,3‐disila‐1,3‐diphenyl‐2‐oxaindane) fragments in the macromolecular chain. At definite values of the lengths of the flexible and rigid fragments, a microheterogeneous structure was observed in the synthesized block copolymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1409–1417, 2002; DOI 10.1002/app.10335  相似文献   

16.
The effect of poly(D ,L ‐lactide‐copara‐dioxanone) (PLADO) as the compatibilizer on the properties of the blend of poly(para‐dioxanone) (PPDO) and poly(D ,L ‐lactide) (PDLLA) has been investigated. The 80/20 PPDO/PDLLA blends containing from 1% to 10% of random copolymer PLADO were prepared by solution coprecipitation. The PLADO component played a very important role in determining morphology, thermal, mechanical, and hydrophilic properties of the blends. Addition of PLADO into the blends could enhance the compatibility between dispersed PDLLA phase and PPDO matrix; the boundary between the two phases became unclear and even the smallest holes were not detected. On the other hand, the position of the Tg was composition dependent; when 5% PLADO was added into blend, the Tg distance between PPDO and PDLLA was shortened. The blends with various contents of compatibilizer had better mechanical properties compared with simple PPDO/PDLLA binary polymer blend, and such characteristics further improved as adding 5% random copolymers. The maximum observed tensile strength was 29.05 MPa for the compatibilized PPDO/PDLLA blend with 5% PLADO, whereas tensile strength of the uncompatibilized PPDO/PDLLA blend was 14.03 MPa, which was the lowest tensile strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   

17.
Surfactant‐free nanoparticles of poly(DL ‐lactide‐co‐glycolide) (PLGA) nanoparticles were prepared with or without poly(L ‐lactide)‐poly(ethylene oxide) (LE) diblock copolymer (abbreviated as PLGA/LE and PLGA nanoparticles) by dialysis method. LE diblock copolymer was used to make PLGA nanoparticles to alternate conventional surfactant. The size of PLGA and PLGA/LE nanoparticles was 295.3 ± 171.3 and 307.6 ± 27.2 nm, respectively, suggesting LE diblock copolymer might be coated onto the surface of nanoparticles. Observation of scanning electron microscope (SEM) showed that PLGA/LE nanoparticles have spherical shapes ranging ~ 200–500 nm. In 1H‐NMR study, characteristic peaks of the methyl protons of PLGA disappeared in D2O, whereas characteristic peaks of the methyl proton of both PEG and PLGA were shown in both CDCl3 and D2O, indicating that LE diblock copolymer coated on the surface of the PLGA nanoparticles. The higher the initial content of drug, the higher the drug contents and the lower the loading efficiency. PLGA/LE nanoparticles at higher drug contents resulted in slower adriamycin·HCl (ADR) release rate than that of lower drug contents. Also, slower release rate of ADR was achieved by entrapped into the PLGA/LE nanoparticles, whereas LE polymeric micelles showed rapid ADR release. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1116–1123, 2003  相似文献   

18.
The thermal degradation of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB‐HV)] was studied using thermogravimetry (TG). In the thermal degradation of PHB, the temperature at the onset of weight loss (To) was derived by To = 0.97B + 259, where B represents the heating rate (°C/min). The temperature at which the weight loss rate was maximum (Tp) was Tp = 1.07B + 273, and the final temperature (Tf) at which degradation was completed was Tf = 1.10B + 280. The percentage of the weight loss at temperature Tp (Cp) was 69 ± 1% whereas the percentage of the weight loss at temperature Tf (Cf) was 96 ± 1%. In the thermal degradation of P(HB‐HV) (7:3), To = 0.98B + 262, Tp = 1.00B + 278, and Tf = 1.12B + 285. The values of Cp and Cf were 62 ± 7 and 93 ± 1%, respectively. The derivative thermogravimetric (DTG) curves of PHB confirmed only one weight loss step change because the polymer mainly consisted of the HB monomer only. The DTG curves of P(HB‐HV), however, suggested multiple weight loss step changes; this was probably due to the different evaporation rates of the two monomers. The incorporation of 10 and 30 mol % of the HV component into the polyester increased the various thermal temperatures (To, Tp, andTf) by 7–12°C (measured at B = 20°C/min). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2237–2244, 2001  相似文献   

19.
Current supervised approaches, such as classification and regression methodologies, are strongly focused on optimizing estimation accuracy metrics, leaving the interpretation of the results produced as a secondary concern. However, in the analysis of complex systems, one of the main interests is precisely the induction of relevant associations, to understand or clarify the way the system operates. Two related frameworks for addressing supervised learning problems (classification and regression) are presented, that incorporate interpretational‐oriented analysis features right from the onset of the analysis. These features constrain the predictive space, in order to introduce interpretable elements in the final model. Interestingly, such constraints do not usually compromise the methods' performance, when compared to their unconstrained versions. The frameworks, called network‐induced classification (NI‐C), and network‐induced regression (NI‐R), share a common methodological backbone, and are described in detail, as well as applied to real‐world case studies. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1570–1587, 2013  相似文献   

20.
Various (R)‐ and (S)‐C‐allylglycine derivatives were synthesized by means of an auxiliary controlled diastereoselective aza‐Claisen rearrangement. Starting from (S)‐configured auxiliaries derived from optically active proline, an aza‐Claisen rearrangement enabled us to synthesize α(R)‐configured γ,δ‐unsaturated amides. Since (R)‐allylglycine derivatives could be directly generated by reacting N‐allylproline derivatives and various protected glycine fluorides, the corresponding (S)‐enantiomers were built‐up via an initial α‐chloroacetyl chloride rearrangement and a subsequent chloride azide substitution with complete inversion of the configuration. High diastereoselectivities were obtained (>15 : 1). The auxiliary could be efficiently removed by organolithium reactions of the amides furnishing α‐amino ketones. Another allyllithium addition allowed us to introduce a second allyl chain with high diastereoselectivity. Final ring closures by means of metatheses using Grubbs' (I) catalyst gave raise to the formation of enantiopure phenanthridines and cyclohexenes displaying defined substitution patterns ready for alkaloid total syntheses.  相似文献   

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