Ring-Opening Polymerization of L-Lactide in Supercritical Chlorodifluoromethane

The ring-opening polymerization of L -lactide initiated by 1-dodecanol/stannous 2-ethylhexanoate (DoOH/Sn(Oct)₂) was carried out in supercritical chlorodifluoromethane at various reaction times, pressures, and temperatures. The monomer conversion increased to ca 70 % on increasing the reaction time to 25 h. The molecular weight of the product also increased to ca 75,000 g/mol over the same period. Increasing the pressure resulted in an accelerated polymerization rate. The pressure-induced increase in the rate of L -LA polymerization can be explained by the formation of chemical bonds in the transition state, which implies the production of a transition state with a lower partial molar volume than the reactants.     

More about the polymerization of lactides in the presence of stannous octoate

The ring-opening polymerization of lactide cyclic monomers in the bulk in the presence of tin(II) 2-ethylhexanoate (stannous octoate or SnOct₂) was reexamined under conditions allowing for the end group characterization of growing chains by high-resolution ¹H-NMR. Data collected for low values of the monomer/initiator (M/I) ratio showed that the DL -lactide ring was opened to yield lactyl octoate-terminated short chains. A cationic-type mechanism involving co-initiation by octanoic acid was proposed to account for experimental findings. The formation of a side product, hydroxytin(II) lactate (HTL), was found which appeared able to initiate lactide polymerization and to yield a high molecular weight PLA50 polymer. However the polymerization with stannous octoate was faster than the HTL one. Anyhow, data suggested that both SnOct₂ and HTL are likely to act simultaneously as initiators during the polymerization of lactides in the presence of SnOct₂. A complete reaction scheme was proposed to account for the presence of the various compounds likely to be formed under these conditions. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3431–3440, 1997     

Ring-Opening Polymerization of the Cyclic Ester Amide Derived from Adipic Anhydride and 1-Amino-6-hexanol in Melt and in Solution

The ring-opening polymerization (ROP) of the cyclic ester amide (cEA) 5 (systematic name, 1-oxa-8-aza-cyclotetradecane-9,14-dione) - prepared from adipic anhydride and 1-amino-6-hexanol - in the melt at 165 °C and in solution at 100 °C and 120 °C with Bu₂Sn(OMe)₂ or Ti(OBu)₄ as initiator yields the alternating poly(ester amide) (PEA) 4 (systematic name, poly(5-(6-oxyhexylcarbamoyl)-pentanoate) with regular microstructure. Kinetic studies for different monomer-to-initiator ratios, different reaction media, initiators and temperatures reveal that the ROP is a first-order reaction with respect to the monomer. Under suitable polymerization conditions termination and transfer reactions are suppressed. The elementary chain growth reaction proceeds by a coordination insertion mechanism in analogy to the polymerization of lactones. By using monohydroxy- and bishydroxy-functional telechelic poly(ethylene oxide) and Sn(octoate)₂ as the initiating system poly(ethylene oxide)-block-poly(ester amide)s and poly(ester amide)-block-poly(ethylene oxide)-block-poly(ester amide)s are obtained. The poly(ester amide) 4 is a semicrystalline material with a melting point of 140 °C, the block copolymers are phase separated systems showing two melting points characteristic for the respective homopolymers.     

A novel catalyst of lanthanum tris(2,6-di-tert-butyl-4-methylphenolate) for ring-opening polymerization of adipic anhydride

Lanthanum tris(2,6-di-tert-butyl-4-methylphenolate) exhibits high catalytic activity toward the ring-opening polymerization of adipic anhydride. Poly(adipic anhydride) (PAA, M_n=1500) was obtained with a conversion of 86.0% within 1 h in methylene chloride at 20 °C. Three melting peaks were found in the DSC curve of the polymer at 51.4, 64.5 and 108.9 °C, respectively.     

Design,Synthesis and Characterization of A Novel Cationic Polymer Poly(lactic acid-b-L-lysine)

A novel biodegradable block copolymer poly(lactic acid-b-lysine) (PLA-b-PLL) has been synthesized and characterized in this study. This product was synthesized via a five-step reaction: Synthesis of hydroxyl-tailed poly(lactic acid) (PLA) by the ring-opening polymerization (ROP) of D,L-lactide in the presence of stannous octoate (Sn(OCt)₂) as initiator; coupling N-t-butoxycarbonyl-L-phenylalanine to hydroxyl-tailed PLA using dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP); the amino-tailed PLA was obtained through de-protection of the Boc-protective group in trifluoroacetic acid (TFA) solution; and then ring-opening polymerization of N ^ε -(Z)-lysine-N-carboxyanhydride (NCA) using the amino-tailed PLA as macro-initiator; finally removal of the Cbz-protective group of PLA-b-poly(N ^ε -(Z)-L-lysine) (PLA-b-PLL(Z) in a mixed hydrobromic acid/acetic acid solution to give the target copolymer. The characterization of this copolymer and its precursors were performed by ¹H-NMR, FTIR and GPC. The block copolymer PLA-b-PLL, combining the characteristics of an aliphatic polyester and poly(amino acids), could be of potential interest in a variety of medical applications, such as the fields of targeted drug delivery and gene delivery systems.     

Melt block copolymerization of ϵ-caprolactone and L-lactide

AB block copolymers of ϵ-caprolactone and (L )-lactide could be prepared by ring-opening polymerization in the melt at 110°C using stannous octoate as a catalyst and ethanol as an initiator provided ϵ-caprolactone was polymerized first. Ethanol initiated the polymerization of ϵ-caprolactone producing a polymer with ϵ-caprolactone derived hydroxyl end groups which after addition of L -lactide in the second step of the polymerization initiated the ring-opening copolymerization of L -lactide. The number-average molecular weights of the poly(ϵ-caprolactone) blocks varied from 1.5 to 5.2 × 10³, while those of the poly(L -lactide) blocks ranged from 17.4 to 49.7 × 10³. The polydispersities of the block copolymers varied from 1.16 to 1.27. The number-average molecular weights of the polymers were controlled by the monomer/hydroxyl group ratio, and were independent on the monomer/stannous octoate ratio within the range of experimental conditions studied. When L -lactide was polymerized first, followed by copolymerization of ϵ-caprolactone, random copolymers were obtained. The formation of random copolymers was attributed to the occurrence of transesterification reactions. These side reactions were caused by the ϵ-caprolactone derived hydroxyl end groups generated during the copolymerization of ϵ-caprolactone with pre-polymers of L -lactide. The polymerization proceeds through an ester alcoholysis reaction mechanism, in which the stannous octoate activated ester groups of the monomers react with hydroxyl groups. © 1997 John Wiley & Sons, Inc.     

Homopolymerization and Copolymerization of Adipic Anhydride with ε-Caprolactone Catalyzed by Rare Earth Trisphenolate

The ring-opening polymerization of adipic anhydride and the ring-opening copolymerization of adipic anhydride with ε-caprolactone catalyzed by single component rare earth trisphenolate have been reported. The structure of the copolymer poly（CL-b-AA） has been characterized by SEC, ^1H NMR and DSC.     

Synthesis and structural analysis of functionalized poly (ϵ‐caprolactone)‐based three‐arm star polymers

Hydroxyl‐functionalized three‐arm poly(?‐caprolactone)s (PGCL‐OHs) were synthesized by the ring‐opening polymerization of ?‐caprolactone in the presence of glycerol (as the core) and stannous octoate. The effect of the feed ratio of ?‐caprolactone to glycerol on the ring‐opening polymerization was studied. These three‐arm PGCL‐OHs were then converted into double‐bond‐functionalized three‐arm poly(?‐caprolactone)s (PGCL‐Mas) by the reaction of PGCL‐OH with maleic anhydride in the melt at 130 °C. The quantitative conversion of hydroxyl functionality was achieved at a low molecular weight. The resulting PGCL‐OH and PGCL‐Ma were characterized with gel permeation chromatography, Fourier transform infrared, ¹H NMR, ¹³C NMR, and differential scanning calorimetry. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1127–1141, 2002     

Synthesis and characterization of biodegradable poly(ester anhydride) based on ε‐caprolactone and adipic anhydride initiated by potassium poly(ethylene glycol)ate

Novel biodegradable poly(ester anhydride) block copolymers based on ε‐caprolactone (ε‐CL) and adipic anhydride (AA) were prepared by sequential polymerization. ε‐CL was first initiated by potassium poly(ethylene glycol)ate and polymerized into active chains (PCL‐O^?K⁺), which were then used to initiate the ring‐opening polymerization of AA. The effects of the AA feed ratio, solvent polarity, monomer concentration, and temperature on sequential polymerization were investigated. The copolymers, obtained under different conditions, were characterized by Fourier transform infrared, ¹H NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). The GPC results showed that the weight‐average molecular weights of the block copolymers were approximately 6.0 × 10⁴. The DSC results indicated the immiscibility of the two components. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1511–1520, 2003     

Functional and highly porous scaffolds for biomedical applications

Highly porous functional scaffolds were obtained from linear and cross-linked multifunctional poly(ε-caprolactone) and poly(L-lactide). The polymers were synthesized by ring-opening polymerization of ε-caprolactone and L-lactide using poly(but-2-ene-1,4-diyl malonate) (PBM) as macroinitiator and stannous 2-ethylhexanoate. The presence of a double bond in each repeating unit of PBM enabled cross-linking of both scaffolds and films. Soft and flexible scaffolds were created from cross-linked PBM. The mechanical properties of scaffolds and films were evaluated under cyclic conditions, with a focus on the compositions and molecular weights. It was obvious that PBM in the polymers and its cross-linking ability resulted in tunable material characteristics, including an increased ability to recover after repeated loading.     

Ring-opening polymerization of macrocyclic aryl ether ketone oligomers containing the 1,2-dibenzoylbenzene moiety

Facile ring-opening polymerization of cyclic aryl ether oligomers containing the 1,2-dibenzoylbenzene moiety to form high molecular weight linear polymers in the presence of a nucleophilic initiator is described. The polymerization can be initiated in the melt in the presence of a nucleophilic initiator such as potassium carbonate, cesium fluoride, and alkali phenoxides. Various alkali phenoxides were investigated as potential nucleophilic initiators. The polymerization reaction rate in the melt increases in the order of K⁺ > Na⁺ > Cs⁺, and in the order of ⁻OPhPhO⁻ > PhO⁻ > PhOPhO⁻ > PhPhO⁻. However, the polymerization in an aprotic dipolar solvent is faster in the presence of cesium phenoxide than in the presence of potassium phenoxide. Polymerization of the cyclic oligomers in solution demonstrates that the ring-opening polymerization proceeds via a chain-growth mechanism and involves a transetherification reaction between linear and cyclic aryl ether oligomers. The ring-chain equilibrium is much more favorable towards linear polymers. Since little or no ring strain exists in the cyclic system, the transetherification reactions are indiscriminate with regards to cyclic or linear chains and the interchain equilibration is also a facile process during polymerization. This intermolecular transetherification has been demonstrated by using low molecular weight aryl ethers to control the molecular weight of the polymer formed via ring-opening polymerization. © 1996 John Wiley & Sons, Inc.     

Synthesis of polyamides by the polyaddition of bisimidazoline with dicarboxylic acids

N,N′-Dipropionylethylenediamine was synthesized by the ring-opening addition reaction of 2-ethyl-2-imidazoline with propionic acid at 220°C. By applying this reaction to polymerization, polyamides were synthesized by the ring-opening polyaddition reaction at 220°C. of 1,4-bis(imidazoline-2-yl)butane with adipic acid, succinic acid, sebacic acid, and terephthalic acid. The reaction product of 1,4-bis(imidazoline-2-yl)butane with adipic acid, which was proposed to be nylon 26, was compared with an authentic sample of nylon 26 and shown to possess a very similar infrared spectrum and melting point.     

Synthesis and characterization of 1,3-bis(2-hydroxyethoxy) benzene based saturated and unsaturated polyesters

Polyesterification of adipic acid and maleic anhydride with 1,3-bis(2-hydroxyethoxy)benzene (HER) in the presence of toluene-4-sulphonic acid was carried out using melt condensation technique. The structural characterization of the synthesized polyesters had been carried out using Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR) spectroscopic methods. The thermal properties of the polyesters were studied using differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The activation energies for the thermal degradation of the polyesters were calculated by the method of Dharwadkar and Kharkhanavala and discussed. The char residue value at 600 °C indicated maleic anhydride based polyester is thermally more stable compared to the adipic acid based polyester. The mechanism of degradation of these polyesters is discussed.     

两亲性六臂星型端氨基PEG-PLGA的合成、表征及胶束化行为

采用本体开环聚合法,以乙交酯(GA)和DL-丙交酯(DLA)为原料,肌醇为引发剂,合成了一系列不同分子量的六臂星型聚乳酸聚乙醇酸(PLGA)(6-s-PLGA50,6-s-PLGA100,6-s-PLGA200,其中50,100,200为原料与引发剂的摩尔比),采用羧基化反应对其端基进行羧化处理.以聚乙二醇4000(PEG4000)为原料用对甲苯磺酰化法得到sTO-PEG-OTs,再进行氨解得到双端氨基PEG(H2N-PEG-NH2).末端羧基6-s-PLGAx通过N-环己基碳二亚胺(DCC)缩合反应与双端氨基PEG连接得到两亲性星型六臂结构的聚合物(6-s-PLGAx-PEG-NH2).分别用核磁共振氢谱法(1H NMR)、凝胶排阻色谱法(GPC)及差示热量热分析法(DSC)等手段对6-s-PLGAx和6-s-PLGAx-PEG-NH2进行了表征.以6-s-PLGA100-PEG-NH2聚合物为例,自组装得到空白的纳米粒子,并用透射电子显微镜法(TEM)和动态光散射法(DLS)考察了粒子的表面形态以及粒径分布特征,用1H NMR分析了胶束的"核-壳"结构.用噻唑蓝四氮唑溴化物(MTT)比色法探讨了该两亲性材料的体外细胞毒性.研究结果表明,合成了不同分子量的两亲性六臂星型端氨基PEG-PLGA,该两亲性聚合物可自组装形成纳米胶束,粒径范围在40～60 nm,与PLGA相比体外细胞毒性无显著性差异.     

Convenient approach to novel functional substituted and branched poly(silylenemethylenes)

Novel poly(silylenemethylenes) have been prepared by the ring-opening polymerization of 1,3-disilacyclobutanes followed by a protodesilylation reaction with triflic acid. The silicon–aryl bond cleavage could be controlled by using different leaving groups, for instance phenyl- and para-anisyl substituents. The reactions of the triflate derivatives with organomagnesium compounds, LiAlH₄, amines, or alcohols gave functional substituted poly(silylenemethylenes). Hydrosilylation reactions or reductive coupling with potassium–graphite led to organosilicon network–polymers, which may serve as suitable precursors for silicon carbide and Si/C/N-based materials. The structures of the polymers were identified by NMR spectroscopy (²⁹Si, ¹³C, ¹H). © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 725–735, 1998     

四臂星形嵌段共聚物s-PDLLA-b-PEG的合成

季戊四醇与D,L-丙交酯开环聚合制得末端为羟基的四臂星形聚乳酸(s-PDLLA);s-PDLLA与羧基封端的聚乙二醇单甲醚(CT-mPEG)完成酯化反应,合成了以季戊四醇为核,以聚乳酸为内部嵌段、聚乙二醇为外部嵌段的四臂星形聚(D,L-乳酸)-聚乙二醇嵌段共聚物(s-PDLLA-b-PEG),其结构经1H NMR,IR和GPC表征。     

Synthesis, characterization and degradability of the comb-type poly(4-hydroxyl-ε-caprolactone-co-ε-caprolactone)-g-poly(l-lactide)

The novel comb-type biodegradable graft copolymers based on ε-caprolactone and l-lactide were synthesized. Firstly, 2-oxepane-1,5-dione (OPD) was synthesized by the Baeyer-Villiger oxidation of 1,4-cyclohexanedione, and was subsequently copolymerized with ε-caprolactone (CL) to produce poly(2-oxepane-1,5-dione-co-ε-caprolactone) (POCL) catalyzed by stannous(II) 2-ethylhexanoate in toluene. Then, POCL was converted into poly(4-hydroxyl-ε-caprolactone-co-ε-caprolactone) (PHCL) using sodium borohydride as reductant. Finally, poly(4-hydroxyl-ε-caprolactone-co-ε-caprolactone)-g-poly(l-lactide) (PHCL-g-PLLA) were prepared successfully by bulk ring-opening polymerization of l-lactide using PHCL as a macro-initiator. All the copolymers have been characterized by ¹H and ¹³C NMR, DSC, and GPC. Compared with the random copolymer of poly(CL-co-LA), the elongation is highly increased. And the thermal analysis showed that the crystallization rate of the PCL backbone in the graft copolymers was greatly reduced compared to the PCL homopolymer. The hydrolytic degradation of the copolymer was much faster in a phosphate buffer (pH = 7.4) at 37 °C, which is confirmed by the weight loss and change of intrinsic viscosity.     

Preparation and characterization of biodegradable poly(trimethylenecarbonate‐ε‐caprolactone)‐block‐poly(p‐dioxanone) copolymers

A series of poly(trimethylenecarbonate‐ε‐caprolactone)‐block‐poly(p‐dioxanone) copolymers were prepared with varying feed rations by using two step polymerization reactions. Poly(trimethylenecarbonate)(ε‐caprolactone) random copolymer was synthesized with stannous‐2‐ethylhexanoate and followed by adding p‐dioxanone monomer as the other block. The ring opening polymerization was carried out at high temperature and long reaction time to get high molecular weight polymers. The monofilament fibers were obtained using conventional melting spun methods. The copolymers were identified by ¹H and ¹³C NMR spectroscopy and gel permeation chromatography (GPC). The physicochemical properties, such as viscosity, molecular weight, melting point, glass transition temperature, and crystallinity, were studied. The hydrolytic degradation of copolymers was studied in a phosphate buffer solution, pH = 7.2, 37 °C, and a biological absorbable test was performed in rats. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2790–2799, 2005     

Synthesis and characterization of biodegradable poly(L-aspartic acid-co-PEG)

The melt polycondensation reaction of the prepolymer prepared from N-(benzyloxycarbonyl)-L -aspartic acid anhydride (N-CBz-L -aspartic acid anhydride) and low molecular weight poly(ethylene glycol) (PEG) using titanium isopropoxide (TIP) as a catalyst produced the new biodegradable poly(L -aspartic acid-co-PEG). This new copolymer had pendant amine functional groups along the polymer backbone chain. The optimal reaction conditions for the preparation of the prepolymer were obtained by using a 0.12 mol % of p-toluenesulfonic acid with PEG 200 for 48 h. The weight-average molecular weight of the prepolymer increased from 1,290 to 31,700 upon melt polycondensation for 6 h at 130°C under vacuum using 0.5 wt % TIP as a catalyst. The synthesized monomer, prepolymer, and copolymer were characterized by FTIR, ¹H- and ¹³C-NMR, and UV spectrophotometers. Thermal properties of the prepolymer and the protected copolymer were measured by DSC. The glass transition temperature (T_g) of the prepolymer shifted to a significantly higher temperature with increasing molecular weight via melt polycondensation reaction, and no melting temperature was observed. The in vitro hydrolytic degradation of these poly(L -aspartic acid-co-PEG) was measured in terms of molecular weight loss at different times and pHs at 37°C. This pH-dependent molecular weight loss was due to a simple hydrolysis of the backbone ester linkages and was characterized by more rapid rates of hydrolysis at an alkaline pH. These new biodegradable poly(L -aspartic acid-co-PEG)s may have potential applications in the biomedical field. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2949–2959, 1998     

Synthesis of functional polycarbonates by lipase-catalyzed ring-opening polymerization

Poly(5-benzyloxy-trimethylene carbonate) (PBTMC), a new functional polycarbonate was synthesized by enzymatic ring-opening polymerization in bulk at 150°C using Porcine pancreas lipase (PPL) or Candida rugosa lipase (CL) as catalyst. Influences of different polymerization conditions such as the source of enzyme, enzyme concentration and polymerization time on the molecular weight and yield were studied. The results showed that PPL exhibited higher activity than CL. Both higher molecular weight(Mn, 18953) and yield(98%) could be obtained by the use of PPL as catalyst. ¹H NMR spectrum showed no decarboxylation occurrence during the ring-opening polymerization.