共查询到20条相似文献,搜索用时 62 毫秒
1.
《Journal of polymer science. Part A, Polymer chemistry》2018,56(2):203-212
A series of novel aluminum complexes containing bulky aryl‐β‐ketiminato ligands [ArNCH C10H7C6H5O]Al(CH3)2 ( 3a , Ar = C6F5; 3b , Ar = C6H5; 3c , Ar = 2,6‐iPr2C6H3) have been synthesized in high yields. These complexes were identified by 1H and 13C NMR spectroscopy, elemental analysis, and X‐ray structural analysis. All the aluminum complexes could efficiently catalyze the ROP of ɛ‐caprolactone (ɛ‐CL) and Lactide (LA) in a controlled manner. It was found that the steric effect of the ligand has less effect on the ROP of CL, while the polymerization rate of L‐LA was suppressed significantly. More interestingly, this kind of catalysts can promote the random copolymerization of ɛ‐CL and L‐LA. The transesterification side reaction and the polymer composition could be adjusted by modulating the electronic and steric effects of the ligand. In paticular, compound 3c could produce quasi‐random copolymers without transesterification side reactions, as indicated by both the values of the reactivity ratios of the two monomers (rLA = 1.31; rCL = 0.99) and the similar average lengths of the caproyl and lactidyl sequences (LCL = 2.34; LLA = 2.44). Finally, a drug‐random copolymer conjugates could be easily prepared by using 3c , indicating a potential application of 3c in pharmacutical and biomedical field. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 203–212 相似文献
2.
Brian D. Mullen Chau N. Tang Robson F. Storey 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):1978-1991
The synthesis, characterization, and ring‐opening polymerization of a new cyclic carbonate monomer containing an allyl ester moiety, 5‐methyl‐5‐allyloxycarbonyl‐1,3‐dioxan‐2‐one (MAC), was performed for the first time. MAC was synthesized in five steps in good yield beginning from the starting material, 2,2‐bis(hydroxymethyl)propionic acid. Subsequent polymerization and copolymerizations of the new cyclic carbonate with rac‐lactide (rac‐LA) and ?‐caprolactone (CL) were attempted. Rac‐LA copolymerized well with MAC, but CL copolymerizations produced insoluble products. Oligomeric macroinitiators of MAC and rac‐LA were synthesized from stannous ethoxide, and both macroinitiators were used for the controlled ring‐opening polymerization of rac‐LA. The polymerization kinetics were examined by monitoring the disappearance of the characteristic C? O ring stretch of the monomer at 1240 cm?1 with real‐time in situ Fourier transform infrared spectroscopy. Postpolymerization oxidation reactions were conducted to epoxidize the unsaturated bonds of the MAC‐functionalized polymers. Epoxide‐containing polymers may allow further organic transformations with various nucleophiles, such as amines, alcohols, and carboxylic acids. NMR was used for microstructure identification of the polymers, and size exclusion chromatography and differential scanning calorimetry were used to characterize the new functionalized poly(ester‐carbonates). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1978–1991, 2003 相似文献
3.
Cristiano Egevardt Siddhartha O. K. Giese Alan D. da C. Santos Andersson Barison Eduardo L. de Sá Arion Zandoná Filho Thiago A. da Silva Sônia F. Zawadzki Jaísa F. Soares Giovana G. Nunes 《Journal of polymer science. Part A, Polymer chemistry》2014,52(17):2509-2517
The ionic [Ti3(µ3‐OPri)2(µ‐OPri)3(OPri)6][FeCl4] halo‐alkoxide ( A ) was investigated for its activity towards the bulk polymerization of rac‐lactide (rac‐LA) and ?‐caprolactone (?‐CL) in various temperatures, monomer/ A molar proportions, and reaction times. The reactivity of A in the ring‐opening polymerization (ROP) of both monomers is mainly due to the cationic [Ti3(OPri)11]+ unity and proceeds through the coordination–insertion mechanism. Molecular weights ranging from 6,379 to 13,950 g mol?1 and PDI values varying from 1.22 to 1.52 were obtained. Results of ROP kinetic studies for both ?‐CL and rac‐LA confirm that the reaction rates are first‐order with respect to monomers. The production of poly(?‐caprolactone) shows a higher sensitivity of the reaction rate to temperature, while the polymerization of rac‐LA is slower and more dependent on the thermal stability of the active species during the propagation step. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2509–2517 相似文献
4.
《Helvetica chimica acta》2017,100(11)
New polynuclear zinc complexes containing tridentate Schiff base ligands were successfully synthesized and fully characterized. The solid‐state structure of the complexes was determined using single crystal X‐ray diffraction. The complexes display a tetranuclear cubane‐like core structure [Zn4O4] and sowed good catalytic activity towards the ring‐opening polymerization (ROP ) of rac‐lactide (rac‐LA ) and ε‐caprolactone (ε‐CL ) under solvent‐free conditions. The polylactic acid (PLA ) obtained from rac‐LA showed isotactic enrichment, as proved by homonuclear decoupled 1H‐NMR analysis. These complexes also showed good activity and superior control towards the ROP of rac‐LA and ε‐CL in the presence of benzyl alcohol as a co‐initiator. Furthermore, kinetic studies demonstrated that the ROP of rac‐LA and ε‐CL has a first order dependence on both monomer (rac‐LA and ε‐CL ) and catalyst concentration. 相似文献
5.
A series of copolymers were prepared by ring-opening polymerization of ?-caprolactone and dl-lactide, using zinc lactate as catalyst. The resulting PCL/PLA copolymers were characterized by various analytical techniques such as NMR, SEC, DSC and X-ray diffraction. The [CL]/[LA] ratios of the copolymers are very close to those in the feed, indicating a good conversion of monomers. The copolymers with CL contents higher than 50% appear semi-crystalline, the crystalline structure being of the PCL-type. Compression moulded polymer films were allowed to degrade in a pH = 7.6 phosphate buffer containing Pseudomonas lipase. Data show that copolymers with CL contents lower than 25% are not degradable and the degradation rate increases with CL content for CL-rich copolymers. Various soluble degradation products are detected in the degradation medium, including CL1 to CL3 and LA1 to LA4 homo-oligomers, and CL2LA1 co-oligomer. The presence of LA homo-oligomers and CL2LA1 co-oligomer suggests that Pseudomonas lipase can not only degrade PCL but also LA short blocks along PCL/PLA copolymer chains. On the other hand, little changes of composition are detected during degradation, in agreement with a surface erosion mechanism as shown by ESEM. 相似文献
6.
Mariagrazia Napoli Rosa Ricciardi Antonia Memoli Pasquale Longo 《Journal of polymer science. Part A, Polymer chemistry》2008,46(4):1476-1487
C2‐symmetric group 4 metallocenes based catalysts (rac‐[CH2(3‐tert‐butyl‐1‐indenyl)2]ZrCl2 (1) , rac‐[CH2(1‐indenyl)2]ZrCl2 (2) and rac‐[CH2(3‐tert‐butyl‐1‐indenyl)2]TiCl2 (3) ) are able to copolymerize styrene and 1,3‐butadiene, to give products with high molecular weight. In agreement with symmetry properties of metallocene precatalysts, styrene homosequences are in isotactic arrangements. Full determination of microstructure of copolymers was obtained by 13C NMR and FTIR analysis and it reveals that insertion of butadiene on styrene chain‐end happens prevailingly with 1,4‐trans configuration. In the butadiene homosequences, using zirconocene‐based catalysts, the 1,4‐trans arrangement is favored over 1,4‐cis, but the latter is prevailing in the presence of titanocene (3) . Diad composition analysis of the copolymers makes possible to estimate the reactivity ratios of copolymerization: zirconocenes (1) and (2) produced copolymers having r1 × r2 = 0.5 and 3.0, respectively (where 1 refers to styrene and 2 to butadiene); while titanocene (3) gave tendencially blocky styrene–butadiene copolymers (r1 × r2 = 8.5). The copolymers do not exhibit crystallinity, even when they contain a high molar fraction of styrene. Probably, comonomer homosequences are too short to crystallize (ns = 16, in the copolymer at highest styrene molar fraction). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1476–1487, 2008 相似文献
7.
Cui Wang Yan Xiao Andreas Heise Meidong Lang 《Journal of polymer science. Part A, Polymer chemistry》2011,49(24):5293-5300
A series of copolymers containing ε‐caprolactone (CL) and 4‐methyl‐ε‐caprolactone (MeCL) were synthesized by ring‐opening polymerization (ROP) using Tin(II) bis(2‐ethylhexanoate)(Sn(Oct)2) or Novozym 435 as catalyst. The molecular structure and weight of copolymers were determined by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC), respectively. Our kinetic study showed that the monomer reactivity ratios for CL (r1) and MeCL (r2) using Sn(Oct)2 as catalyst were estimated to be near unity and r1 × r2 = 1, indicating the random distribution of the monomers in the final copolymer. The results of DSC and XRD consistently indicated that the copolymers were inclined to be amorphous with the increasing of MeCL fraction. Microspheres were prepared from copolymers and characterized by SEM. The preliminary degradability and biocompatibility studies on these copolymers were also assessed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
8.
Noureddine Ajellal Christophe M. Thomas Jean‐François Carpentier 《Journal of polymer science. Part A, Polymer chemistry》2009,47(12):3177-3189
The copolymerization of racemic β‐butyrolactone (rac‐BLMe) with racemic “allyl‐β‐butyrolactone” (rac‐BLallyl) in toluene, catalyzed by the discrete amino‐alkoxy‐bis(phenolate) yttrium‐amido complex 1 , gave new poly(β‐hydroxyalkanoate)s with unsaturated side chains. The poly(BLMe‐co‐BLallyl) copolymers produced have a highly syndiotactic backbone structure (Pr = 0.80–0.84) with a random enchainment of monomer units, as evidenced by 13C NMR, and high molecular weight (Mn up to 58,000 g mol?1) with a narrow polydispersity (Mw/Mn = 1.07–1.37), as determined by GPC. The comonomer incorporation (5–50 mol % rac‐BLallyl) was a linear function of the feed ratio. The pendant vinyl bond of the side‐chains in those poly(BLMe‐co‐BLallyl) copolymers allowed the effective introduction of hydroxy or epoxy groups via dihydroxylation, hydroboration‐oxidation or epoxidation reactions. NMR studies indicated that all of these transformations proceed in an essentially quantitative conversion and do not affect the macromolecular architecture. Some thermal properties (Tm, ΔHm, Tg) of the prepared polymers have been also evaluated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3177–3189, 2009 相似文献
9.
Sarah E. Reybuck Robert M. Waymouth 《Journal of polymer science. Part A, Polymer chemistry》2004,42(13):3323-3331
Ethylene/1‐hexene copolymerizations with disiloxane‐bridged metallocenes, rac‐ and meso‐1,1,3,3‐tetramethyldisiloxanediyl‐bis(1‐indenyl)zirconium dichloride (rac‐ 1 , meso‐ 1 ) activated by modified methylaluminoxane were performed to investigate the influence of conformational dynamics on comonomer selectivity. Although 1H NOESY (nuclear Overhauser and exchange spectroscopy) analysis indicated that the most stable conformation for the meso isomer in solution was that in which both indenes project over the metal coordination site, this isomer showed higher 1‐hexene selectivity in copolymerization (re = 140 ± 30, rh = 0.024 ± 0.004) than the rac isomer with only one indene over the coordination site (re = 240 ± 20, rh = 0.005 ± 0.001). The meso isomer showed high 1‐hexene selectivity, a high product of reactivity ratios (rerh = 3.3 ± 0.5) and produced copolymers that could be separated into fractions with different ethylene content suggesting that the active species exhibited multisite behavior and populated conformations with different comonomer selectivities during the copolymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3323–3331, 2004 相似文献
10.
Reile M. Slattery Amanda E. Stahl Kelsey R. Brereton Arnold L. Rheingold David B. Green Joseph M. Fritsch 《Journal of polymer science. Part A, Polymer chemistry》2019,57(1):48-59
Seven magnesium complexes ( 1–7 ) were synthesized by reaction of new ( L 3 ‐H – L 5 ‐H ) and previously reported ketoimine pro‐ligands with dibutyl magnesium and were isolated in 59–70% yields. Complexes 1–7 were characterized fully and consisted of bis‐ligated homoleptic ketoiminates coordinated in distorted octahedral geometry around the magnesium centers. The complexes were investigated for their ability to initiate the ring opening polymerization (ROP) of l ‐lactide (L‐LA) to poly‐lactic acid (PLA) and ?‐caprolactone (?CL) to poly‐caprolactone in the presence of 4‐fluorophenol co‐catalyst. For L‐LA polymerization, complexes containing ligand electron‐donating groups ( 1–5 ) achieved >90% conversion in 2 h at 100 °C, while the presence of CF3 groups in 6 and 7 slowed or resulted in no PLA detected. With ?CL, ROP initiated with 1–7 resulted in lower percentage conversion with similar electronic effects. Moderate molecular weight PLA polymeric material (14.3–21.3 kDa) with low polydispersity index values (1.23–1.56) was obtained, and ROP appeared to be living in nature. Copolymerization of L‐LA and ?CL yielded block copolymers only from the sequential polymerization of ?CL followed by L‐LA and not the reverse sequence of monomers or the simultaneous presence of both monomers. Polymers and copolymers were characterized with NMR, gel permeation chromatography, and differential scanning calorimetry. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 48–59 相似文献
11.
Random propene/4‐methyl‐1‐pentene copolymers synthesized with C2 symmetric highly isospecific metallocenes
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Maria Carmela Sacchi Simona Losio Luigi Fantauzzi Paola Stagnaro Roberto Utzeri Maurizio Galimberti 《Journal of polymer science. Part A, Polymer chemistry》2015,53(22):2575-2585
Propene (P)/4‐methyl‐1‐pentene (Y) copolymers in a wide range of composition were prepared with isospecific single center catalysts, rac‐Et(IndH4)2ZrCl2 ( EBTHI ), rac‐Me2Si(2‐Me‐BenzInd)2ZrCl2 ( MBI ), and rac‐CH2(3‐tBuInd)2ZrCl2 ( TBI ). 13C NMR analysis of copolymers and statistical elaboration of microstructural data at triad level were performed. Unprecedented and surprising results are here reported. Random P/Y copolymers were prepared with the most isospecific catalyst, TBI , that is known to prepare ethene/propene and ethene/4‐methyl‐1‐pentene copolymers with long homosequences of both comonomers, whereas longer homosequences of both comonomers were observed in copolymers from the less enantioselective metallocenes EBTHI and MBI . These findings, which are against what is acknowledged in the field, can pave the way for the preparation on a large scale of random propene‐based copolymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2575–2585 相似文献
12.
Edward D. Cross Laura E. N. Allan Andreas Decken Michael P. Shaver 《Journal of polymer science. Part A, Polymer chemistry》2013,51(5):1137-1146
Aluminum‐based salen and salan complexes mediate the ring‐opening polymerization (ROP) of rac‐β‐butyrolactone (β‐BL), rac‐lactide, and ε‐caprolactone. Al‐salen and Al‐salan complexes exhibit excellent control over the ROP of rac‐β‐butyrolactone, yielding atactic poly(3‐hydroxybutyrate) (PHB) with narrow PDIs of <1.15 for Al‐salen and <1.05 for Al‐salan. Kinetic studies reveal pseudo‐first‐order polymerization kinetics and a linear relationship between molecular weight and percent conversion. These complexes also mediate the immortal ROP of rac‐β‐BL and rac‐lactide, through the addition of excess benzyl alcohol of up to 50 mol eq., with excellent control observed. A novel methyl/adamantyl‐substituted Al‐salen system further improves control over the ROP of rac‐lactide and rac‐β‐BL, yielding atactic PHB and highly isotactic poly(lactic acid) (Pm = 0.88). Control over the copolymerization of rac‐lactide and rac‐β‐BL was also achieved, yielding poly(lactic acid)‐co‐poly(3‐hydroxybutyrate) with narrow PDIs of <1.10. 1H NMR spectra of the copolymers indicate a strong bias for the insertion of rac‐lactide over rac‐β‐BL. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
13.
Controlled ring‐opening polymerization of l‐lactide and ε‐caprolactone catalyzed by aluminum‐based Lewis pairs or Lewis acid alone
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yuushou Nakayama Shunsuke Kosaka Kentaro Yamaguchi Gentaro Yamazaki Ryo Tanaka Takeshi Shiono 《Journal of polymer science. Part A, Polymer chemistry》2017,55(2):297-303
Ring‐opening polymerization of cyclic esters was studied using catalysts composed of bulky Lewis acids (LA) and Lewis bases (LB). Controlled polymerization of l ‐lactide (l ‐Lac) was proceeded by Al(C6F5)3·THF in combination with trimesitylphosphine (Mes3P) or triphenylphosphine (Ph3P) using BnOH as an initiator to produce poly(l ‐Lac) with narrow molecular weight distribution (MWD; Mw/Mn = 1.1). Both the LA and the LB were indispensable to promote the polymerization. The molecular weights of the resulting poly(l ‐Lac)s were controlled by the feed monomer to initiator ratio. ε‐Caprolactone (CL) was rapidly polymerized by Al(C6F5)3·THF with or without Mes3P, although the resulting polymer had rather broad MWD (Mw/Mn = 1.7). The CL polymerization by Al(C6F5)3·THF alone at r.t. gave poly(CL) with relatively narrow MWD (Mw/Mn = 1.2). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 297–303 相似文献
14.
Deivasagayam Dakshinamoorthy Frédéric Peruch 《Journal of polymer science. Part A, Polymer chemistry》2012,50(11):2161-2171
A series of di‐ and triblock copolymers [poly(L ‐lactide‐b‐ε‐caprolactone), poly(D,L ‐lactide‐b‐ε‐caprolactone), poly(ε‐caprolactone‐b‐L ‐lactide), and poly(ε‐caprolactone‐b‐L ‐lactide‐b‐ε‐caprolactone)] have been synthesized successfully by sequential ring‐opening polymerization of ε‐caprolactone (ε‐CL) and lactide (LA) either by initiating PCL block growth with living PLA chain end or vice versa using titanium complexes supported by aminodiol ligands as initiators. Poly(trimethylene carbonate‐b‐ε‐caprolactone) was also prepared. A series of random copolymers with different comonomer composition were also synthesized in solution and bulk of ε‐CL and D,L ‐lactide. The chemical composition and microstructure of the copolymers suggest a random distribution with short average sequence length of both the LA and ε‐CL. Transesterification reactions played a key role in the redistribution of monomer sequence and the chain microstructures. Differential scanning calorimetry analysis of the copolymer also evidenced the random structure of the copolymer with a unique Tg. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
15.
Sarah El Habnouni Sébastien Blanquer Vincent Darcos Jean Coudane 《Journal of polymer science. Part A, Polymer chemistry》2009,47(22):6104-6115
A novel method is proposed to access to new poly(α‐amino‐ε‐caprolactone‐co‐ε‐caprolactone) using poly(α‐iodo‐ε‐caprolactone‐co‐ε‐caprolactone) as polymeric substrate. First, ring‐opening (co)polymerizations of α‐iodo‐ε‐caprolactone (αIεCL) with ε‐caprolactone (εCL) are performed using tin 2‐ethylhexanoate (Sn(Oct)2) as catalyst. (Co)polymers are fully characterized by 1H NMR, 13C NMR, FTIR, SEC, DSC, and TGA. Then, these iodinated polyesters are used as polymeric substrates to access to poly(α‐amino‐ε‐caprolactone‐co‐ε‐caprolactone) by two different strategies. The first one is the reaction of poly(αIεCL‐co‐εCL) with ammonia, the second one is the reduction of poly(αN3εCL‐co‐εCL) by hydrogenolysis. This poly(α‐amino‐ε‐caprolactone‐co‐ε‐caprolactone) (FαNH2εCL < 0.1) opens the way to new cationic and water‐soluble PCL‐based degradable polyesters. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6104–6115, 2009 相似文献
16.
Ilaria D'auria Mina Mazzeo Daniela Pappalardo Marina Lamberti Claudio Pellecchia 《Journal of polymer science. Part A, Polymer chemistry》2011,49(2):403-413
Phosphido‐diphosphine Group 3 metal complexes 1–4 [(o‐C6H4PR2)2P‐M(CH2SiMe3)2; R = Ph, 1 : M = Y, 2 : M = Sc; R = iPr, 3 : M = Y, 4 : M = Sc] are very efficient catalysts for the ring‐opening polymerization (ROP) of cyclic esters such as ε‐caprolactone (ε‐CL), L ‐lactide, and δ‐valerolactone under mild polymerization conditions. In the ROP of ε‐CL, complexes 1–4 promote quantitative conversion of high amount of monomer (up to 3000 equiv) with very high turnover frequencies (TOF) (~4 × 104 molCL/molI h) showing a catalytic activity among the highest reported in the literature. The immortal and living ROP of ε‐CL and L ‐lactide is feasible by combining complexes 1–4 with 5 equiv of 2‐propanol. Polymers with controlled molecular parameters (Mn, end groups) and low polydispersities (Mw/Mn = 1.05–1.09) are formed as a result of fast alkoxide/alcohol exchange. In the ROP of δ‐valerolactone, complexes 1–4 showed the same activity observed for lactide (L ‐ and D ,L ‐lactide) producing high molecular weight polymers with narrow distribution of molar masses. Complexes 1–4 also promote the ROP of rac‐β butyrolactone affording atactic low molecular weight poly(hydroxybutyrate) bearing unsaturated end groups probably generated by elimination reactions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
17.
A “Mitsubishi emblem” tetrauclear aluminum complex containing two unsymmetric N2O2‐ligands and a symmetric NO3‐ligand as initiator for polymerization of rac‐lactide
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Minggang Hu Fugui Wang Fuzhong Han Qigang Deng Wenhui Ma Hailong Yan Guohua Dong Weiming Song 《Journal of polymer science. Part A, Polymer chemistry》2017,55(12):2084-2091
A novel hydroxy‐, methoxy‐, and phenoxy‐bridge “Mitsubishi emblem” tetranuclear aluminum complex ( 1 ) is synthesized from an unsymmetric amine‐pyridine‐bis(phenol) N2O2‐ligand (H2L1) and a symmetric amine‐tris(phenol) NO3‐ligand (H2L2). Two same configuration chiral nitrogen atoms are formed in the tetranuclear Al complex upon coordination of the unsymmetric tertiary amine ligand to central Al. Complex 1 initiates controlled ring‐opening polymerization (ROP) of rac‐lactide and afford polylactide (PLA) with narrow molecular weight distributions (Mw/Mn = 1.05–1.19). The analysis of 1H NMR spectra of the oligomer indicates that the methoxy group is the initiating group and the ring‐opening polymerization of lactide follows a coordination‐insertion mechanism. The Homonuclear decoupled 1H NMR spectroscopy suggests the isotactic‐rich chains is preferentially formed in PLA. The study on kinetics of the ROP of lactide reveals the homopropagation rate is higher than the cross‐propagation rate, which is in agreement with the observed isotactic selectivity in the ROP of rac‐lactide. The stereochemistry of the polymerization was also supported by activation parameters. The introduction of unsymmetric ligand H2L1 has an effect on stereoslectivity of polymerization. This result may be of interest for the design of multinuclear metal complex catalysts containing functionalized ligands. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2084–2091 相似文献
18.
Fabrice Stassin Robert Jrme 《Journal of polymer science. Part A, Polymer chemistry》2005,43(13):2777-2789
Ring‐opening polymerization (ROP) of (L,L)‐lactide (LA) has been initiated by dibutyltin dimethoxide in supercritical carbon dioxide (sc CO2). Polymerization is controlled and proceeds at quasi the same rate as in toluene, which indicates that the reactivity of the propagating species is not impaired by parasitic carbonation reaction. Random copolymerization of LA with ?‐caprolactone (CL) has also been studied in sc CO2, and the reactivity ratios have been determined as 5.8 ± 0.5 for LA and 0.7 ± 0.25 for CL. These values have to be compared to 0.7 ± 0.25 for LA and 0.15 ± 0.05 for CL in toluene. Good control on ROP of CL and LA in sc CO2 has been confirmed by the successful synthesis of diblock copolymers by sequential polymerization of CL and LA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2777‐2789, 2005 相似文献
19.
Hanneke M. L. Lambermont‐Thijs Mark J. H. C. Jochems Richard Hoogenboom Ulrich S. Schubert 《Journal of polymer science. Part A, Polymer chemistry》2009,47(23):6433-6440
In this study, the structure–property relationships for a series of statistical 2‐nonyl‐2‐oxazoline (NonOx) and 2‐phenyl‐2‐oxazoline (PhOx) copolymers were investigated for the first time. The copolymerization kinetics were studied and the reactivity ratios were calculated to be rNonOx = 7.1 ± 1.4 and rPhOx = 0.02 ± 0.1 revealing the formation of gradient copolymers. The synthesis of a systematical series of NonOx–PhOx copolymers is described, whereby the amount of NonOx was increased in steps of 10 mol %. The thermal and surface properties were investigated for this series of well‐defined copolymers. The thermal properties revealed a linear decrease in glass transition temperature for copolymers containing up to 39 wt % NonOx. Furthermore, the melting temperature of the copolymers containing 0 to 55 wt % PhOx linearly decreased most likely due to disturbance of the NonOx crystalline domains by incorporation of PhOx in the NonOx part of the copolymer. The surface energies of spincoated polymer films revealed a strong decrease in surface energy upon incorporation of NonOx in the copolymers due to strong phase separation between NonOx and PhOx allowing the NonOx chains to orient to the surface. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6433–6440, 2009 相似文献
20.
Zhiqiang Jiang Yujing You Qun Gu Jianyuan Hao Xianmo Deng 《Macromolecular rapid communications》2008,29(14):1264-1268
Amphiphilic poly[(ε‐caprolactone)‐co‐glycolide]‐block‐poly(ethylene glycol)‐block‐poly[(ε‐caprolactone)‐co‐glycolide) [P(CL‐GL)‐PEG‐P(CL‐GL)] triblock copolymers with different average lengths of caproyl sequences (LCL) were synthesized by ring‐opening polymerization at different temperatures. A 25% aqueous solution of the copolymer with LCL = 11.0 formed a gel, owing to strong crystallinity‐induced hydrophobicity at low temperature, and underwent a gel‐sol transition (UCST behavior) when the temperature was increased to 40 °C. In contrast, the solution of copolymer with LCL = 6.7 underwent a sol‐gel transition (LCST behavior) due to micelle aggregation. However, a clear sol‐turbid sol phase transition was observed for the copolymer with more random microstructures (LCL = 5.2).