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Moderate Molecular Weights (moderate + molecular_weight)
Selected AbstractsCationic polymerization of L,L -lactideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2010gorzata Ba Abstract Cationic bulk polymerization of L,L- lactide (LA) initiated by trifluromethanesulfonic acid [triflic acid (TfA)] has been studied. At temperatures 120,160 °C, polymerization proceeded to high conversion (>90% within ,8 h) giving polymers with Mn , 2 × 104 and relatively high dispersity. Thermogravimetric analysis of resulting polylactide (PLA) indicated that its thermal stability was considerably higher than the thermal stability of linear PLA of comparable molecular weight obtained with ROH/Sn(Oct)2 initiating system. Also hydrolytic stability of cationically prepared PLA was significantly higher than hydrolytic stability of linear PLA. Because thermal or hydrolytic degradation of PLA starting from end-groups is considerably faster than random chain scission, both thermal and hydrolytic stability depend on molecular weight of the polymer. High thermal and hydrolytic stability, in spite of moderate molecular weight of cationically prepared PLA, indicate that the fraction of end-groups is considerably lower than in linear PLA of comparable molecular weight. According to proposed mechanism of cationic LA polymerization growing macromolecules are fitted with terminal OH and C(O)OSO2CF3 end-groups. The presence of those groups allows efficient end-to-end cyclization. Cyclic nature of resulting PLA explains its higher thermal and hydrolytic stability as compared with linear PLA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2650,2658, 2010 [source] Selective polymerization of functional monomers with Novozym 435JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2007Martijn A. J. Veld Abstract Two novel monomers, ambrettolide epoxide and isopropyl aleuriteate, encompassing functional groups, were obtained in a single step from commercially available materials. Novozym 435 catalyzed ring opening polymerization of ambrettolide epoxide furnished a polymer of Mn = 9.7 kg/mol and PDI = 1.9 while the epoxide groups remained unaffected during the polymerization. Selective polymerization of the primary hydroxyl groups of isopropyl aleuriteate using Novozym 435 was feasible and a polymer with moderate molecular weight (Mn = 5.6 kg/mol, PDI = 3.2) was isolated in moderate yield (43%). Subsequently, copolymerization of isopropyl aleuriteate with ,-CL in different ratios was performed, resulting in soluble, hydroxy functional polymers with good molecular weights (Mn = 10.4,27.2 kg/mol) in good yield (71,78%). The secondary hydroxy groups in the polymer reacted easily with hexyl isocyanate, showing the potential of isopropyl aleuriteate as a comonomer for the synthesis of functional polyesters. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5968,5978, 2007 [source] Shape memory effect of poly(methylene-1,3-cyclopentane) and its copolymer with polyethylenePOLYMER INTERNATIONAL, Issue 4 2002Han Mo Jeong Abstract Poly(methylene-1,3-cyclopentane) (PMCP) cyclopolymerized from 1,5-hexadiene by metallocene catalyst, rac -(ethylenebis(1-indenyl))Zr(N(CH3)2)2 is partially crystalline and has a value of elongation at break of more than 400% in the temperature range 25,85,°C. The shape memory effect of PMCP with moderate molecular weight is enhanced by sequentially polymerized polyethylene segments, the crystalline phase of which seems to strengthen the fixed structure which memorizes the original shape. The glass transition temperature or melting temperature of PMCP can be selectively used as shape recovery temperature when an appropriate deformation temperature is chosen. © 2002 Society of Chemical Industry [source] Ferrocenyl-functionalized long chain branched polydienesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2009Frederik Wurm Abstract A convenient two-step approach for the synthesis of ferrocenyl-functionalized long chain branched polydienes, based on both butadiene and isoprene, respectively, is presented. Classical living anionic polymerization was used to synthesize different ABn type poly(diene) macromonomers with moderate molecular weights between 1700 and 3200 g/mol and narrow polydispersity. Quantitative end-capping with chlorodimethylsilane resulted in the desired ABn macromonomer structures. In the ensuing Pt-catalyzed hydrosilylation polyaddition, branched, functionalized polydienes were obtained by a concurrent ABn + AR type of copolymerization with mono- and difunctional ferrocenyl silanes (fcSiMe2H or fc2SiMeH). Molecular weights of the branched polymers were in the range of 10,000 to 44,000 g/mol (SEC/MALLS). Because of the large number of functional end groups, high loading with ferrocene units up to 63 wt % of ferrocene was achieved. Detailed studies showed full conversion of the functional silanes and incorporation into the branched polymer. Further studies using DSC, TGA, and cyclovoltammetry (CV) measurements have been performed. Electrochemical studies demonstrated different electrochemical properties for fcSiMe2 - and fc2SiMe-units. The CVs of polymers modified with diferrocenylsilane units exhibit the pattern of communicating ferrocenyl sites with two distinct, separate oxidation waves. The polymers were also deposited on an electrode surface and the electrodes investigated via CV, showing formation of electroactive films with promising results for the use of the materials in biosensors. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2518,2529, 2009 [source] Syntheses of cyclic polycarbonates by the direct phosgenation of bisphenol M,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2005Hans R. Kricheldorf Abstract Bisphenol M was subjected to interfacial polycondensations in an NaOH/CH2Cl2 system with triethylamine as a catalyst. Regardless of the catalyst concentration, similar molecular weights were obtained, and matrix-assisted laser desorption/ionization time-of-flight mass spectra exclusively displayed mass peaks of cycles (detectable up to 15,000 Da). With triethyl benzyl ammonium chloride as a catalyst, linear chains became the main products, but the contents of the cycles and the molecular weights strongly increased with higher catalyst/bisphenol ratios. When the pseudo-high-dilution method was applied, both diphosgene and triphosgene yielded cyclic polycarbonates of low or moderate molecular weights. Size exclusion chromatography measurements, evaluated with the triple-detection method, yielded bimodal mass distribution curves with polydispersities of 5,12. Furthermore, a Mark,Houwink equation was elaborated, and it indicated that the hydrodynamic volume of poly(bisphenol M carbonate) was quite similar to that of poly(bisphenol A carbonate)s with similar concentrations of cyclic species. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1248,1254, 2005 [source] Novel, biodegradable, functional poly(ester-carbonate)s by copolymerization of trans -4-hydroxy- L -proline with cyclic carbonate bearing a pendent carboxylic groupJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2004Ren-Shen Lee Abstract Water-soluble poly(ester-carbonate) having pendent amino and carboxylic groups on the main-chain carbon is reported for the first time. This article describes the melt ring-opening/condensation reaction of trans -4-hydroxy- N -benzyloxycarbonyl- L -proline (N -CBz-Hpr) with 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MBC) at a wide range of molar fractions. The influence of reaction conditions such as catalyst concentration, polymerization time, and temperature on the number average molecular weight (Mn) and molecular weight distribution (Mw/Mn) of the copolymers was investigated. The polymerizations were carried out in bulk at 110 °C with 3 wt % stannous octoate as a catalyst for 16 h. The poly(ester-carbonate)s obtained were characterized by Fourier transform infrared spectroscopy, 1H NMR, differential scanning calorimetry, and gel permeation chromatography. The copolymers synthesized exhibited moderate molecular weights (Mn = 6000,14,700 g mol,1) with reasonable molecular weight distributions (Mw/Mn = 1.11,2.23). The values of the glass-transition temperature (Tg) of the copolymers depended on the molar fractions of cyclic carbonate. When the MBC content decreased from 76 to 12 mol %, the Tg increased from 16 to 48 °C. The relationship between the poly(N -CBz-Hpr- co -MBC) Tg and the compositions was in approximation with the Fox equation. In vitro degradation of these poly(N -CBz-Hpr- co -MBC)s was evaluated from weight-loss measurements and the change of Mn and Mw/Mn. Debenzylation of 3 by catalytic hydrogenation led to the corresponding linear poly(ester-carbonate), 4, with pendent amino and carboxylic groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2303,2312, 2004 [source] Synthesis and optical properties of soluble polyethers containing oligophenyl in the main chain and p -styrylbenzene side groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2002Ioakim K. Spiliopoulos Abstract New polyethers containing alternating conjugated segments of p -terphenyl or p -quinquephenyl with p -styrylbenzene side groups and aliphatic spacers were synthesized with pyrylium salts. They had moderate molecular weights, were amorphous, and dissolved in tetrahydrofuran, chloroform, and other common organic solvents. The glass-transition temperatures were 68,82 and 110,153 °C for the polymers that carried p -terphenyl and p -quinquephenyl moieties, respectively. The absorption spectra showed a peak around 325 nm, and the band gaps were 3.27,3.34 eV, which were calculated from the onset absorption in solution. The photoluminescence maxima were at 393,398 nm in solution and 422,449 nm in thin films, indicating that the polymers were violet-blue-emitting materials. The photoluminescence quantum yields in solution were up to 0.25. The polymers displayed both in concentrated solutions and in the solid state intramolecular or intermolecular interactions. The polarity of the solvent influenced the shape of the photoluminescence curve. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 682,693, 2002; DOI 10.1002/pola.10151 [source] Facile synthesis and characterization of hyperbranched poly(aryl ether ketone)s obtained via an A2 + BB,2 approachPOLYMER INTERNATIONAL, Issue 10 2010Xiujie Li Abstract A fast and highly efficient approach for the synthesis of hyperbranched poly(aryl ether ketone)s (HPAEKs) via the polycondensation of A2 and BB,2 monomers is described. Commercially available hydroquinone (HQ, A2 monomer) and easily synthesized 2,4,,6-trifluorobenzophenone (TF, BB,2 monomer) were thermally polycondensed to prepared fluoro- or phenolic-terminated HPAEKs with K2CO3 and Na2CO3 as catalysts. During the reaction, the fluorine at the 4,-position of TF reacts rapidly with the phenolic group of HQ, forming predominantly dimers and some other species. The dimer can be considered as a new AB,2 monomer. Further reactions among molecules AB,2 and AB,2 with some other species result in the formation of HPAEKs. Fourier transform infrared and 1H NMR spectra revealed the structures of the resultant polymers. The degree of branching (DB) of the fluoro-terminated hyperbranched polymers was determined to be in the range 50,57% from 1H NMR spectra, whereas the DB of the phenolic-terminated hyperbranched polymers was determined to be 100%. These hyperbranched polymers exhibit excellent solubility in general organic solvents and possess moderate molecular weights with broad distributions determined using gel permeation chromatography. Moreover, the structure and performance of the HPAEKs can be conveniently regulated by adjusting the type and feed ratio of the two monomers. Copyright © 2010 Society of Chemical Industry [source] | ||||||||||