共查询到20条相似文献,搜索用时 15 毫秒
1.
《应用有机金属化学》2017,31(9)
Monomeric bis(isopropoxy) titanium complexes LTi(Oi Pr)2 (L = ─ OC6H2–4‐R1–6‐R2–2‐CH2N[(CH2)2N(R3)2]CH2–4‐R4–6‐R5‐C6H2O ─ , R1 = R2 = t Bu, R3 = Et, R4 = R5 = Cl, (L1)Ti(Oi Pr)2; R1 = R2 = Me, R3 = Et, R4 = R5 = Me, (L2)Ti(Oi Pr)2; R1 = R2 = t Bu, R3 = Et, R4 = OMe, R5 = t Bu, (L3)Ti(Oi Pr)2; R1 = R4 = OMe, R3 = Et, R2 = R5 = t Bu, (L4)Ti(Oi Pr)2; R1 = R2 = t Bu, R3 = Me, R4 = OMe, R5 = t Bu, (L5)Ti(Oi Pr)2) supported by amine bis(phenolate) ligands were synthesized and characterized using NMR spectroscopy and elemental analysis. The solid‐state structure of (L3)Ti(Oi Pr)2 was determined using single‐crystal X‐ray diffraction. (L1–5)Ti(Oi Pr)2 were all found to initiate the ring‐opening polymerization of l ‐lactide and rac ‐lactide in a controlled manner at 110–160°C. As shown by kinetic studies, (L1)Ti(Oi Pr)2 polymerized l ‐lactide faster than did (L2–5)Ti(Oi Pr)2. In addition, good number‐average molecular weight and narrow polydispersity index (1.00–1.71) of polymers were also obtained. The microstructure of the polymers and a possible mechanism of coordination–insertion of polymerization were evidenced by MALDI‐TOF and 1H NMR spectra of the polylactides. 相似文献
2.
Ernesto Rufino‐Felipe Nazario Lopez Fabio A. Vengoechea‐Gómez Luis‐Guillermo Guerrero‐Ramírez Miguel‐Ángel Muñoz‐Hernández 《应用有机金属化学》2018,32(6)
A series of Al(III) chloride [LAl‐Cl]; Al(III) alkoxide [LAl‐OR]2; and Zn(II) [LZn]2 complexes with Schiff base ligands were obtained. 1H NMR and X‐ray diffraction studies indicate that [LAl‐Cl] complexes have Cs symmetry and the Al center is penta‐coordinated. The Al(III) alkoxide complex [L5Al‐OiPr]2 is a dimer bridged by OiPr? with the Al center in a distorted octahedral environment. Zn complexes [LZn]2 are double helix dimers with tetra‐coordinated Zn centers. The catalytic activity for the ring‐opening polymerization of rac‐lactide was evaluated. The best activity in this series is shown by the aluminium chloride complex with a flexible three‐carbon bridge; more flexible four‐carbon bridges lower the activity. 相似文献
3.
Yahia Lemmouchi Michael C. Perry Allan J. Amass Khirud Chakraborty Etienne Schacht 《Journal of polymer science. Part A, Polymer chemistry》2007,45(17):3966-3974
Biodegradable star‐shaped poly(ethylene glycol)‐block‐poly(lactide) copolymers were synthesized by ring‐opening polymerization of lactide, using star poly(ethylene glycol) as an initiator and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature. Two series of three‐ and four‐armed PEG‐PLA copolymers were synthesized and characterized by gel permeation chromatography (GPC) as well as 1H and 13C NMR spectroscopy. The polymerization under the used conditions is very fast, yielding copolymers of controlled molecular weight and tailored molecular architecture. The chemical structure of the copolymers investigated by 1H and 13C NMR indicates the formation of block copolymers. The monomodal profile of molecular weight distribution by GPC provided further evidence of controlled and defined star‐shaped copolymers as well as the absence of cyclic oligomeric species. The effects of copolymer composition and lactide stereochemistry on the physical properties were investigated by GPC and differential scanning calorimetry. For the same PLA chain length, the materials obtained in the case of linear copolymers are more viscous, whereas in the case of star copolymer, solid materials are obtained with reduction in their Tg and Tm temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3966–3974, 2007 相似文献
4.
Tina M. Ovitt Geoffrey W. Coates 《Journal of polymer science. Part A, Polymer chemistry》2000,38(Z1):4686-4692
The polymerization of racemic lactide with a racemic aluminum alkoxide catalyst is reported. Microstructural analysis of the polymer produced with 1H NMR spectroscopy revealed that an isotactic stereoblock poly(lactic acid) formed, where each enantiomerically pure block contained an average of 11 lactide monomer units. The melting point of this polymer, 179 °C, was higher than that of the enantiomerically pure polymer, consistent with the cocrystallization of the enantiomeric blocks of the polymer. The mechanism of the polymer formation is currently unknown, although a polymer exchange pathway, where living chain ends switch between metal centers to produce diastereomeric active species, is proposed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4686–4692, 2000 相似文献
5.
Cuiping Yu Lifang Zhang Xufeng Ni Zhiquan Shen Kehua Tu 《Journal of polymer science. Part A, Polymer chemistry》2004,42(24):6209-6215
The ring‐opening polymerization of L ‐lactide initiated by single‐component rare‐earth tris(4‐tert‐butylphenolate)s was conducted. The influences of the rare‐earth elements, solvents, temperature, monomer and initiator concentrations, and reaction time on the polymerization were investigated in detail. No racemization was found from 70 to 100 °C under the examined conditions. NMR and differential scanning calorimetry measurements further confirmed that the polymerization occurred without epimerization of the monomer or polymer. A kinetic study indicated that the polymerization rate was first‐order with respect to the monomer and initiator concentrations. The overall activation energy of the ring‐opening polymerization was 79.2 kJ mol?1. 1H NMR data showed that the L ‐lactide monomer inserted into the growing chains with acyl–oxygen bond cleavage. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6209–6215, 2004 相似文献
6.
Kouki Matsubara Chihiro Terata Hiromichi Sekine Kenji Yamatani Tatsuo Harada Kiyoka Eda Misato Dan Yuji Koga Munehisa Yasuniwa 《Journal of polymer science. Part A, Polymer chemistry》2012,50(5):957-966
Ring‐opening polymerization of D,L ‐lactide was stereoselectively achieved using newly designed aluminum alkoxide complexes as initiators. These half‐SALEN aluminum complexes bearing tridentate nonchiral Schiff‐base ligands are racemates, which provide chirality in the aluminum centers, efficiently afforded a stereoblock copolymer of D,L ‐LA. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
7.
Hui‐Ju Chuang Hsiao‐Li Chen Jian‐Li Ye Zn‐Yun Chen Pei‐Ling Huang Tzu‐Ting Liao Tsung‐En Tsai Chu‐Chieh Lin 《Journal of polymer science. Part A, Polymer chemistry》2013,51(3):696-707
A series of magnesium benzylalkoxide complexes, [LnMg(μ‐OBn)]2 ( 1 – 14 ) supported by NNO‐tridentate pyrazolonate ligands with various electron withdrawing‐donating subsituents have been synthesized and characterized. X‐ray crystal structural studies revealed that Complexes 1 – 3 , 5 , 7 , 9 , and 10 are dinuclear bridging through benzylalkoxy oxygen atoms with penta‐coordinated metal centers. All of these complexes acted as efficient initiators for the ring‐opening polymerization of L‐lactide and rac‐lactide. Based on kinetic studies, the activity of these metal complexes is significantly influenced by the electronic effect of the ancillary ligands with the electron‐donating substituents at the phenyl rings enhancing the polymerization rate. In addition, the “living” and “immortal” character of 6 has paved a way to synthesize as much as 40‐fold polymer chains of polylactides with a very narrow polydispersity index in the presence of a small amount of initiator. Among all of magnesium complexes, Complex 6 exhibits the highest stereoselectivity toward ring‐opening polymerization of rac‐lactide with Pr up to 88% in THF at 0 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
8.
D. Mecerreyes R. D. Miller J. L. Hedrick C. Detrembleur R. Jrme 《Journal of polymer science. Part A, Polymer chemistry》2000,38(5):870-875
This article reports the synthesis and copolymerization of 6‐hydroxynon‐8‐enoic acid lactone. The ring‐opening polymerization of this lactone‐type monomer bearing a pendant allyl group led to new homopolymers and random copolymers with ε‐caprolactone and L ,L ‐lactide. The copolymerizations were carried out at 110 °C with Sn(Oct)2 as a catalyst. The introduction of unsaturations into the aliphatic polyester permitted us to carry out different chemical transformations on this family of polymers. For example, this article reports the bromination, epoxidation, and hydrosylilation of the allyl group in the new polyester copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 870–875, 2000 相似文献
9.
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
10.
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
11.
Ring‐opening polymerization and block copolymerization of L‐lactide with divalent samarocene complex
Dongmei Cui Tao Tang Wuguo Bi Jianhua Cheng Wenqi Chen Baotong Huang 《Journal of polymer science. Part A, Polymer chemistry》2003,41(17):2667-2675
Divalent samarocene complex [(C5H9C5H4)2Sm(tetrahydrofuran)2] was prepared and characterized and used to catalyze the ring‐opening polymerization of L ‐lactide (L‐LA) and copolymerization of L‐LA with caprolactone (CL). Several factors affecting monomer conversion and molecular weight of polymer, such as polymerization time, temperature, monomer/catalyst ratio, and solvent, were examined. The results indicated that polymerization was rapid, with monomer conversions reaching 100% within 1 h, and the conformation of L‐LA was retained. The structure of the block copolymer of CL/L‐LA was characterized by NMR and differential scanning calorimetry. The morphological changes during crystallization of poly(caprolactone) (PCL)‐b‐P(L‐LA) copolymer were monitored with real‐time hot‐stage atomic force microscopy (AFM). The effect of temperature on the morphological change and crystallization behavior of PCL‐b‐P(L‐LA) copolymer was demonstrated through AFM observation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2667–2675, 2003 相似文献
12.
Jamie M. Messman Robson F. Storey 《Journal of polymer science. Part A, Polymer chemistry》2004,42(24):6238-6247
Polymerization rates were proportional to initial Sn(Oct)2 concentration at low [Sn(Oct)2]0/[PrOH]0 values, but began to level off at higher values. When [Sn(Oct)2]0/[PrOH]0 was significantly greater than unity, the opposite behavior occurred. Tin(II) alkoxide concentration became limited by the initial PrOH concentration and independent of initial Sn(Oct)2 concentration. Addition of 2‐ethylhexanoic acid caused polymerization rate retardation, without affecting molecular weight. A control polymerization was conducted in the absence of PrOH. The molecular weight of the resulting polymer was consistent with the measured water content (3.7 wt % by Karl Fisher titration) of the as‐received Sn(Oct)2. The polymerization rate in the absence of PrOH was slow, and this suggested that water is less efficient than an alcohol in creating polymerization‐active stannyl ether bonds. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6238–6247, 2004 相似文献
13.
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
14.
《应用有机金属化学》2017,31(12)
Zinc complexes supported by tertiary 1,3,5‐triazapenta‐1,3‐dienate ligand (L1) and N ‐benzoyl‐N′ ‐arylbenzamidinate [aryl =2,6‐diisopropylphenyl (L2), phenyl (L3)] ligands have been synthesized and characterized. The reaction of L1H with ZnEt2 affords a mononuclear zinc complex [L1ZnEt] ( 1 ) in good yield. Tetra nuclear zinc complex [(L1)2Zn4O(OAc)4] ( 2 ) is prepared by treating L1H with one equivalent of Zn(OAc)2 in toluene. Further, dinuclear zinc complexes [L2ZnEt]2 ( 3 ) and [L3ZnEt]2 ( 4 ) are obtained in good yields from L2H and L3H with ZnEt2 in toluene respectively. The complexes 1–4 have been characterized by 1H/13C NMR spectroscopy and single crystal X‐ray diffraction studies. All of the complexes have been explored for their catalytic activity toward the ring‐opening polymerization (ROP) of ε ‐caprolactone. It has been found that complex 1 is an active catalyst for the polymerization of ε ‐caprolactone in presence of a cocatalyst benzyl alcohol (BnOH). While complex 2 is as active as 1 there is no need for a cocatalyst for the polymerization to proceed. Dinuclear zinc complexes 3 and 4 show very high activity for the ROP of ε ‐caprolactone (CL) and rac ‐lactide (LA) without requiring a cocatalyst. The resultant polymers are found to have very high molecular weight (M n = 296 X 103 g mol−1) and relatively narrow polydispersity index compared to 1 and 2 . 相似文献
15.
Kosuke Makiguchi Seiya Kikuchi Toshifumi Satoh Toyoji Kakuchi 《Journal of polymer science. Part A, Polymer chemistry》2013,51(11):2455-2463
The ring‐opening polymerization (ROP) of cyclic esters, such as ε‐caprolactone, 1,5‐dioxepan‐2‐one, and racemic lactide using the combination of 3‐phenyl‐1‐propanol as the initiator and triflimide (HNTf2) as the catalyst at room temperature with the [monomer]0/[initiator]0 ratio of 50/1 was investigated. The polymerizations homogeneously proceeded to afford poly(ε‐caprolactone) (PCL), poly(1,5‐dioxepan‐2‐one) (PDXO), and polylactide (PLA) with controlled molecular weights and narrow polydispersity indices. The molecular weight determined from an 1H NMR analysis (PCL, Mn,NMR = 5380; PDXO, Mn,NMR = 5820; PLA, Mn,NMR = 6490) showed good agreement with the calculated values. The 1H NMR and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry analyses strongly indicated that the obtained compounds were the desired polyesters. The kinetic measurements confirmed the controlled/living nature for the HNTf2‐catalyzed ROP of cyclic esters. A series of functional alcohols, such as propargyl alcohol, 6‐azido‐1‐hexanol, N‐(2‐hydroxyethyl)maleimide, 5‐hexen‐1‐ol, and 2‐hydroxyethyl methacrylate, successfully produced end‐functionalized polyesters. In addition, poly(ethylene glycol)‐block‐polyester, poly(δ‐valerolactone)‐block‐poly(ε‐caprolactone), and poly(ε‐caprolactone)‐block‐polylactide were synthesized using the HNTf2‐catalyzed ROP. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2455–2463 相似文献
16.
Kyeong Pang Richard Kotek Alan Tonelli 《Journal of polymer science. Part A, Polymer chemistry》2006,44(23):6801-6809
Poly(trimethylene terephthalate) (PTT) was prepared by the ring‐opening polymerization of its cyclic dimer. Antimony(III) oxide, titanium(IV) butoxide, dibutyltin oxide, and titanium(IV) isopropoxide were used as catalysts. Among the catalysts, titanium(IV) butoxide was the most effective for the same reaction conditions. A weight‐average molecular weight of 63,500 g/mol was obtained from ring‐opening poly merization at 265 °C for 2 h in the presence of 0.5 mol % titanium(IV) butoxide. The PTTs obtained from the polymerization catalyzed with increasing amounts of antimony(III) oxide showed increasing weight‐average molecular weights and reaction conversions. When 1 mol % antimony(III) oxide was used, the weight‐average molecular weight was 32,000 g/mol and the conversion was 82% after 1 h of polymerization at 265 °C. In the case of the polymer catalyzed by titanium(IV) butoxide under the same conditions, the weight‐average molecular weight and conversion were 40,000 g/mol and 77% when 0.25 mol % was used, whereas 0.5 mol % catalyst produced a weight‐average molecular weight of 27,000 g/mol and a conversion of 95%. To get an acceptable molecular weight and relatively high reaction conversion, a catalyst concentration of at least 0.5 mol % was found to be necessary, in contrast to conventional condensation polymerizations, which require only about one‐tenth of this amount of the catalyst. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6801–6809, 2006 相似文献
17.
Antonella Silvestri Fabia Grisi Stefano Milione 《Journal of polymer science. Part A, Polymer chemistry》2010,48(16):3632-3639
The alcoholysis of the heteroscorpionate methyl aluminum complex (bpzmp)AlMe2 ( 1 ) (bpzmp = 2,4‐di‐tert‐butyl‐6‐(bis‐(3,5‐dimethylpyrazol‐1‐yl)methyl)phenoxo), promoted both by phenol and isopropanol, has been investigated. The reaction of 1 with phenol afforded the dimeric mono(phenoxo) derivative 2 , whereas the alcoholysis of 1 with the less acidic isopropanol involved the coordinated heteroscorpionate ligand and led to the tetrahedral complex 3 in which the aluminum atom is surrounded by one κ2‐N,O? coordinated bpzmp ligand and one η1‐O? coordinated ppzmp ligand (ppzmp = 2,4‐di‐tert‐butyl‐6‐(i‐propoxy‐(3,5‐dimethylpyrazol‐1‐yl)methyl)phenoxo). Complexes 1 – 3 have been tested in the ring opening polymerization (ROP) of L ‐lactide. The dimeric mono(phenoxo) derivative 2 was inactive in the ROP of L ‐lactide. Quite surprisingly, complex 3 was found to be active in ROP of L ‐ and rac‐lactide, showing a good molar‐mass control. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3632–3639, 2010 相似文献
18.
Jian‐Bing Zeng Madhusudhan Srinivansan Yi‐Dong Li Ramani Narayan Yu‐Zhong Wang 《Journal of polymer science. Part A, Polymer chemistry》2010,48(24):5885-5890
Ring‐opening polymerization of 1,4‐dioxan‐2‐one in bulk was initiated by three titanium alkoxides, titanium dichlorodiisopropoxide (TiCl2(OiPr)2), titanium chlorotriisopropoxide (TiCl(OiPr)3), and titanium tetraisopropoxide (Ti(OiPr)4). The results indicate that the polymerization rate increased with number of OiPr groups in the initiator. High conversion of monomer (90%) and high molecular weight (11.9 × 104 g/mol) of resulting polymer can be achieved in only 5 min at 60 °C with Ti(OiPr)4 as an initiator. Analysis on nuclear magnetic resonance (NMR) spectra suggests the initiating sites for TiCl2(OiPr)2, TiCl(OiPr)3, and Ti(OiPr)4 to be 1.9, 2.6, and 3.8, respectively. Coordination‐insertion mechanism for the polymerization via cleavage of the acyl–oxygen bonds of the monomer was proved by NMR investigation. Kinetic studies indicate that polymerization initiated by Ti(OiPr)4 followed a first‐order kinetics, with an apparent activation energy of 33.7 kJ/mol. It is noteworthy that this value is significantly lower than earlier reported values with other catalysts, namely La(OiPr)3 (50.5 kJ/mol) and Sn(Oct)2 (71.8 kJ/mol), which makes it an attractive catalyst for reactive extrusion polymerization. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
19.
Catherine Lefay David Glé Marion Rollet Jérôme Mazzolini Denis Bertin Stéphane Viel Christina Schmid Christophe Boisson Franck D'Agosto Didier Gigmes Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2011,49(3):803-813
Poly(styrene) macromercaptanes (Mn = 1900, 3600, and 6100 g mol?1, PDI ≈ 1.2) derived from thiocarbonyl thio capped polymers prepared via reversible addition fragmentation chain transfer polymerization were employed to initiate the ring opening polymerization (ROP) of D ,L ‐lactide under conditions of organo‐catalyis employing 4,4‐dimethylaminopyridine. Poly(styrene)‐block‐poly(lactide) polymers of number average molecular weights up to 25,000 g mol?1 (PDI ≈ 1.2 to 1.6) were obtained and characterized via multiple detection size exclusion chromatography (SEC) using refractive index as well as UV detection. In addition, diffusion ordered nuclear magnetic resonance and liquid chromatography at critical conditions (of both polystyrene as well as poly(lactide) were employed to assess the copolymers' structure. Furthermore, it was demonstrated that polyethylenes capped with a thiol moiety can also be readily chain extended in a ROP employing D ,L ‐lactide, evidenced via NMR and high temperature SEC. This study indicates that the direct use of macromercaptantes is indeed a methodology to switch from a radical to a ROP process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
20.
Scott J. Moravek Jamie M. Messman Robson F. Storey 《Journal of polymer science. Part A, Polymer chemistry》2009,47(3):797-803
rac‐Lactide polymerization kinetics in THF at 72 °C were monitored in real‐time using mid‐infrared ATR‐FTIR spectroscopy, with diamond composite insertion probe and light conduit technology. Monomer concentration as a function of time was acquired using the 1240 cm?1 resonance associated with the ? CO? O? C? stretch. Polymerizations were initiated with either n‐propanol (PrOH), ethylene glycol (EG), trimethylol propane (TMP), or pentaerythritol (PENTA) with the coinitiator stannous octoate (Sn(Oct)2). Polymerizations were found to be reversible at high monomer conversions, with a residual monomer concentration at 72 °C (345 K) of 0.081 M. The polymerizations were internally first‐order with respect to monomer, indicating a constant concentration of propagating centers. For a typical reaction with [rac‐LA]0 = 1.0 M, [PENTA]0 = 1.3 × 10?2 M, and [Sn(Oct)2] = 2.5 × 10?2 M, the first‐order rate constant, kapp was measured as 1.8 × 10?4 s?1. First‐order rate constants were determined to be independent of polymer architecture (i.e., initiator functionality) and proportional to [Sn(Oct)2] for [Sn(Oct)2]0/[ROH]0 ? 1, where [ROH]0 represents the initial concentration of initiating hydroxyl groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 797–803, 2009 相似文献