Synthesis and characterization of four- and six-arm star-shaped poly(ε-caprolactone)-b-poly(N-vinylcaprolactam): Micellar and core degradation studies

Star-shaped copolymers with four and six poly(ε-caprolactone)-block-poly(N-vinylcaprolactam) (S(PCL-b-PNVCL)) arms were successfully synthesized by combining ring opening polymerization (ROP) of ε-caprolactone (CL) and reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylcaprolactam (NVCL). The resulting star copolymers were characterized using ¹H NMR, GPC and UV–vis. The numbers of arms in the star-shaped PCL-b-PNVCL block copolymers were demonstrated using degradation studies under acidic conditions, and the individual PNVCL chains were characterized by GPC and ¹H NMR. In aqueous solution, star-shaped PCL-b-PNVCL block copolymers self-assembled into large aggregates or micelles with sizes varying from 54 to 300 nm, depending on the molecular weight of the copolymer and the relative lengths of the hydrophobic and hydrophilic segments. Micelles were characterized by atomic force microscopy (AFM), dynamic light scattering (DLS) and scanning electron microscopy (SEM).     

Synthesis, characterization and thermal properties of hexaarmed star-shaped poly(ε-caprolactone)-b-poly(d,l-lactide-co-glycolide) initiated with hydroxyl-terminated cyclotriphosphazene

Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene was prepared by the reaction of hexachlorocycltriphosphaneze with the sodium salt of 4-hydroxybenzaldehyde and subsequent reduction of aldehyde groups to alcohol groups by using sodium borohydride. Hexaarmed star-shaped hydroxyl-terminated poly(ε-caprolactone) (PCL) were successfully synthesized via ring-opening polymerization of ε-caprolactone (CL) with the above hydroxyl-terminated cyclotriphosphazene initiator and stannous octoate catalyst in bulk. The number-average molecular weight of PCL linearly increased with the molar ratio of monomer to initiator. The star-shaped PCL with hydroxy end groups could be used as a macroinitiator for block copolymerization with d,l-lactide (d,l-LA) and glycolide (GA) using stannous octoate catalyst. IR, ¹H NMR and GPC analysis showed the star-block copolymers were successfully synthesized and the molecular weights and the unit composition of the star-shaped block copolymers were controlled by the molar ratios of d,l-LA and GA monomers to CL. The copolymer presented a two-phase structure, namely, PCL crystalline and d,l-LAGA amorphous domains, which made the copolymer different from linear PCL and star-shaped PCL in crystallinity and thermal behaviors.     

Synthesis,characterization of star-shaped copolymers of <Emphasis Type="SmallCaps">l</Emphasis>-lactide and epoxidized soybean oil

Biodegradable star-shaped PLLA–ESO copolymers were synthesized by the bulk copolymerization of l-lactide (l-LA) and epoxidized soybean oil (ESO) with stannous octanoate as the catalyst. Effects of molar ratios of monomer to catalyst, and various amounts of ESO on copolymerization were studied. The resulting copolymers were characterized by FTIR, ¹H NMR, GPC, etc., which confirmed the successful synthesis of star-shaped copolymers of l-LA and ESO. The thermal and mechanical properties of samples were also investigated by means of DSC, TGA and tensile testing. The results showed that the PLLA–ESO copolymers possed lower glass transition temperature, melting point, crystallinity, and maximum decomposition temperature than those of neat polylactide. Tensile testing demonstrated that PLLA–ESO copolymer had better ductility than linear PLLA. It was also found that the amount of catalyst almost had no influence on the weight average molecular weight of PLLA–ESO copolymers, but which could be controlled by variation of molar ratios of l-LA to ESO.     

Synthesis and characterization of star-shaped block copolymer of poly-(?-caprolactone) and poly(ethyl ethylene phosphate) as drug carrier

A series of novel 4-arm biodegradable star block copolymers of poly(?-caprolactone) and poly(ethyl ethylene phosphate) were synthesized via ring-opening polymerization of 2-ethoxy-2-oxo-1,3,2-dioxaphospholane using hydroxyl terminated 4-arm star-shaped poly(?-caprolactone) and stannous octoate co-initiation system. Gel permeation chromatography (GPC), NMR and FT-IR were used to demonstrate the structure and analyze their compositions. The self-assembly behavior of these star-shaped copolymers in aqueous solution was studied by ¹H NMR and fluorescence technique, and the results indicated those copolymers formed nanoparticles in aqueous solution with hydrophobic poly(?-caprolactone) core and hydrophilic poly(ethyl ethylene phosphate) shell. The critical micelle concentration was relative to the length of poly(?-caprolactone) and poly(ethyl ethylene phosphate) block. Paclitaxel was encapsulated in the micelles and the release behavior demonstrated that a longer hydrophobic block resulted in slightly slower release rate from the micelles. These copolymer micelles were biocompatible and potential as drug-delivery vehicles for pharmaceutical application.     

两亲性苯乙烯嵌段共聚物的合成及结构表征

以α,α'-二甲基-α-乙酸-三硫代碳酸酯(BDATC)为链转移剂,采用可逆-加成-断裂链转移(RAFT)自由基聚合方法合成了末端带有—COOH官能团的两亲性嵌段共聚物聚苯乙烯-b-聚甲基丙烯酸聚乙二醇单甲醚-b-聚苯乙烯(PSt-b-POEOMA-b-PSt),这种含有亲水性端基的嵌段共聚物可以自组装成核-壳结构的纳米微粒,用于载药高分子的模板研究。利用FTIR、1HNMR、GPC对产物结构进行表征,用热失重(TG)和差示扫描量热(DSC)的方法研究了3种不同比例的嵌段共聚物的热性能。实验结果表明,通过RAFT聚合方法得到了所设计的嵌段共聚物,相对分子质量(简称分子量,下同)分布1.35左右;嵌段共聚物的热稳定性较好,通过玻璃化转变温度(Tg)的变化推测出嵌段共聚物中两种嵌段比例对两嵌段相容性的影响。     

Synthesis and characterization of poly(ϵ‐caprolactone)‐b‐poly(ethylene glycol) block copolymers prepared by a salicylaldimine‐aluminum complex

A series of poly(?‐caprolactone)‐b‐poly(ethylene glycol) (PCL‐b‐PEG) block copolymers with different molecular weights were synthesized with a salicylaldimine‐aluminum complex in the presence of monomethoxy poly(ethylene glycol). The block copolymers were characterized by ¹H NMR, GPC, WAXD, and DSC. The ¹H NMR and GPC results verify the block structure and narrow molecular weight distribution of the block copolymers. WAXD and DSC results show that crystallization behavior of the block copolymers varies with the composition. When the PCL block is extremely short, only the PEG block is crystallizable. With further increase in the length of the PCL block, both blocks can crystallize. The PCL crystallizes prior to the PEG block and has a stronger suppression effect on crystallization of the PEG block, while the PEG block only exerts a relatively weak adverse effect on crystallization of the PCL block. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis,characterization, and hydrolytic degradation of biodegradable poly(ether ester)‐urethane copolymers based on ε‐caprolactone and poly(ethylene glycol)

In this article, a new kind of biodegradable poly(ε‐caprolactone)‐poly(ethylene glycol)‐poly(ε‐caprolactone)‐based polyurethane (PCEC‐U) copolymers were successfully synthesized by melt‐polycondensation method from ε‐caprolactone (ε‐CL), poly(ethylene glycol) (PEG), 1,4‐butanediol (BD), and isophorone diisocyanate (IPDI). The obtained copolymers were characterized by ¹H‐nuclear magnetic resonance (¹H‐NMR), FTIR, and gel permeation chromatography (GPC). Thermal properties of PCEC‐U copolymers were studied by DSC and TGA/DTG under nitrogen atmosphere. Water absorption and hydrolytic degradation behavior of these copolymers were also investigated. Hydrolytic degradation behavior was studied by weight loss method. ¹H‐NMR and GPC were also used to characterize the hydrolytic degradation behavior of PCEC‐U copolymers. The molecular weight of PCL block and PEG block in soft segment and the content of hard segment strongly affected the water absorption and hydrolytic degradation behavior of PCEC‐U copolymers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Crystallization behavior of biodegradable amphiphilic poly(ethylene glycol)‐poly(L‐lactide) block copolymers

Poly(ethylene glycol)‐poly(L ‐lactide) diblock and triblock copolymers were prepared by ring‐opening polymerization of L ‐lactide with poly(ethylene glycol) methyl ether or with poly(ethylene glycol) in the presence of stannous octoate. Molecular weight, thermal properties, and crystalline structure of block copolymers were analyzed by ¹H‐NMR, FTIR, GPC, DSC, and wide‐angle X‐ray diffraction (WAXD). The composition of the block copolymer was found to be comparable to those of the reactants. Each block of the PEG–PLLA copolymer was phase separated at room temperature, as determined by DSC and WAXD. For the asymmetric block copolymers, the crystallization of one block influenced much the crystalline structure of the other block that was chemically connected to it. Time‐resolved WAXD analyses also showed the crystallization of the PLLA block became retarded due to the presence of the PEG block. According to the biodegradability test using the activated sludge, PEG–PLLA block copolymer degraded much faster than PLLA homopolymers of the same molecular weight. © 1999 John Wiley amp; Sons, Inc. J Appl Polym Sci 72: 341–348, 1999     

Synthesis and characterization of diblock copolymers based on crystallizable poly(ε-caprolactone) and mesogen-jacketed liquid crystalline polymer block

Diblock copolymers comprising crystallizable poly(ε-caprolactone) and poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) were synthesized by ring-opening polymerization of ε-caprolactone and subsequent atom transfer radical polymerization (ATRP) of MPCS. The molecular structure of the copolymers was confirmed by ¹H NMR spectroscopy and GPC. Kinetic study of ATRP showed that the polymerization proceeded in a controlled way up to high conversions. Three series of diblock copolymers were obtained with relatively narrow polydispersity indices (PDI≤1.11) and PCL blocks of 8000, 12,900, and 22,800 molecular weights, respectively. The existence of microphase separation was identified by differential scanning calorimetry (DSC) and directly observed through transmission electron microscopy (TEM). The melting behavior of PCL block was significantly affected by the length of PCL block and composition of PMPCS. The thermotropic liquid crystalline behavior was examined by polarized optical microscopy (POM) and DSC. The result showed that the diblock copolymer exhibited liquid crystalline behavior when the degree of polymerization (DP) of PMPCS block was not less than 44.     

Synthesis of poly(ethylene glycol-b-styrene) block copolymers by reverse atom transfer radical polymerization

Reverse atom transfer radical polymerization (RATRP) of styrene (S) was carried out in bulk using polyazoester prepared by the reaction of polyethylene glycol with molecular weight of 3000 and 4,4′-azobis(4-cyanopentanoyl chloride) as initiator and CuCl₂/2,2′-bipyridine (bpy) catalyst system to yield poly(ethylene glycol-b-styrene) block copolymer. The block copolymers were characterized ¹H NMR, FT-IR spectroscopy and GPC. The ¹H NMR, and FT-IR spectra showed that formation of poly(ethylene glycol-b-styrene) block copolymer. The polydispersities of block copolymers were observed between from 1.49 and 1.98 GPC measurements.     

ROP和ATRP法制备具有核壳结构的温敏性纳米胶束的研究

结合活性开环聚合(ROP)和原子转移自由基聚合(ATRP)方法,制备了以POSS-OH为核引发剂、PCL为核和PNIPAM为壳的X聚合物纳米胶束。借助GPC,IR,NMR,TEM,UV和DLS对聚合物的分子量、结构、形貌和温敏性进行了分析。结果表明,成功合成了星型嵌段共聚物;当POSS-OH的质量一定时,可以通过[CL]控制POSS-PCL的分子量;纳米胶束具有较为规整的球形和粒径分布均一;纳米胶束具有明显的温敏性与宽的相转变温度。     

Aliphatic tertiary amine mediated synthesis of highly branched polylactide copolymers

In the Sn(Oct)₂ catalyzed bulk copolymerization of l-lactide (LLA) and a large amount of branching comonomer 2,2-bis(hydroxymethyl)butyric acid (BHB) (LLA/BHB/Sn(Oct)₂ ratio is 5:1:0.05, 135 °C), low molecular weight of copolymers with inhomogeneous structure were generated. MALDI-TOF mass spectrum demonstrated that the lower molar mass fraction was dominated with the BHB homo-polycondensation products; whereas the higher molar mass fraction was mainly composed of linear chains of poly(l-lactide) (PLLA) bearing one BHB unit. The addition of aliphatic tertiary amine to this polymerization system could effectively enhance the molecular weight of the obtained copolymers, whereas, aromatic tertiary amines and aliphatic primary and secondary ones were not so effective. The obtained PLLA copolymers were characterized by GPC, ¹H NMR, ¹³C NMR and MALDI-TOF MS, which verified that they were composed of LLA and BHB units and had the highly branched structure. The degree of branching was about 0.23–0.30. Thermal analyses by TGA and DSC demonstrated that the resulting highly branched PLLA copolymers were amorphous. Compared with linear PLLA, the highly branched PLLA copolymers were thermally more stable and had lower T_g. The mechanism of aliphatic tertiary amine mediated synthesis of medium molecular weight of highly branched PLLA copolymers was proposed.     

Synthesis and Characterization of Polystyrene-b-Poly(4-vinyl pyridine) Block Copolymers by Atom Transfer Radical Polymerization

We aimed at the synthesis of well-define PS-b-P4VP by using atom transfer radical polymerization in two-step process. First, polystyrenes with benzyl bromide end group (PS-Br; by ATRP) were prepared as macroinitiator for the next ATRP of 4-vinyl pyridine and characterized these polymers from ¹H-NMR and MALDI-TOF. Comparing with MALDI-TOF-MS, ¹H-NMR and GPC analyses, this indicates that the formation of the block copolymer can be observed. During the polymerizations, molecular weight distribution and kinetics have been evaluated from GPC traces and ¹H-NMR analyses. We further characterized the thermal properties of these block polymers by DSC and TGA. DSC measurement on the PS-b-P4VP block copolymers exhibited two glass transitions, indicating that the resulting block copolymers are phase separated. Two maxima differential peaks were observed on the TGA trace for the PS-b-P4VP block copolymers might be assigned to the decomposition of the P4VP blocks at 380 ^○C and the PS blocks at higher temperature.     

Synthesis, characterization and properties of chitosan modified with poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers

Synthesis of poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers is discussed herein. Siloxane prepolymer was first prepared via acid-catalyzed ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) to form polydimethylsiloxane (PDMS) prepolymers. It was subsequently functionalized with hydroxy functional groups at both terminals. The hydroxy-terminated PDMS can readily react with acid-terminated poly(ethylene glycol) (PEG diacid) to give PEG-PDMS block copolymers without using any solvent. The PEG diacid was prepared from hydroxy-terminated PEG through the ring-opening reaction of succinic anhydride. Their chemical structures and molecular weights were characterized using ¹H NMR, FTIR and GPC, and thermal properties were determined by DSC. The PEG-PDMS copolymer was incorporated into chitosan in order that PDMS provided surface modification and PEG provided good water swelling properties to chitosan. Critical surface energy and swelling behavior of the modified chitosan as a function of the copolymer compositions and contents were investigated.     

Atom-Transfer Radical Polymerization to Synthesize Novel Liquid Crystalline Diblock Copolymers with Polystyrene and Mesogen-jacketed Liquid Crystal Polymer Segments

The synthesis of a series of new rod-coil diblock copolymers with different molecular weights and low polydispersity was achieved by atom transfer radical polymerization. The block architecture (coil-conformation of styrene segment and rigid-rod conformation of 2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene segment) of the diblock copolymers was experimentally confirmed by proton nuclear magnetic resonance (¹H NMR) and differential scanning calorimetry (DSC). The liquid crystalline behavior of the copolymers was studied using DSC and a polarized optical microscope (POM). It was found that the liquid crystalline behavior was dependent on the molecular-weight of the rigid segment. Only those copolymers with M _n of the rigid block beyond 9,300 g/mol could form liquid crystalline phases above the glass transition temperature of the rigid block.     

Effect of acrylic diblock copolymer upon interfacial adhesion

The preparation and adhesion properties of poly(methyl methacrylate–butyl acrylate)[P(MMA-b-BA)] diblock copolymers have been studied. Block copolymers were analyzed by ¹H-NMR, DSC, and SEC, and confirm the synthesis of diblock copolymers, using the iniferter route. Investigation of peel strength in laminate joints, reinforced with various block copolymers, suggests that adhesion depends on both molecular weight and composition. When the copolymer contains mainly PMMA block, molecular weight has a marked effect, with adhesion being enhanced at higher copolymer molecular weight. For other PBA/PMMA compositions, no reinforcement was seen, irrespective of molecular weight. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of star-shaped block copolymers with polyhedral oligomeric silsesquioxane (POSS)core via ATRP

Star-shaped PMMA-b-PS block copolymers with POSS core were prepared by atom transfer radical polymerization of St using star-shaped POSS/PMMA-Cl as a macroinitiator in presence of CuCl, 2,2,-bipyridine, toluene at 110 °C. The core-first method, which used an active multifunctional core to initiate the growth of polymer chains, was applicable to making star-shaped block copolymers with POSS core. The structure of hybrid star-shaped PMMA-b-PS block copolymers was characterized by GPC and ¹H NMR, respectively.     

Synthesis and characterization of biodegradable amphiphilic triblock copolymers methoxy-poly(ethylene glycol)-b-poly(L-lysine)-b-poly(L-lactic acid)

Starting from MPEG-NH₂, a series of amphiphilic triblock copolymers MPEG-b-PLL-b-PLA were synthesized through PEG-NH₂-initiated ring-open polymerization of N ^ε-benzyloxycarbonyl-L-lysine, followed by acylation coupling between the amino-terminated MPEG-b-PZLL-NH₂ and carboxyl-terminal PLA and the deprotection of amines. The block copolymers were characterized by FT-IR, ¹H NMR, GPC, DSC and TEM. The copolymer functional groups, molecular and block structures were verified by FT-IR, ¹H NMR and DSC, respectively. The GPC results indicate that the chain lengths of each block can be controlled by varying the feed ratios of the monomer and initiator, providing the polymer samples with a narrow molecular weight distribution (M _w /M _n = 1.10 ~ 1.25). The TEM analysis shows that the triblock polymers can self-assemble into polymeric micelles in aqueous solution with spherical morphology. The cell-cytotoxicity assay indicates that the triblock polymers show no obvious cytotoxicity against Bel7402 human hepatoma cells.     

苯乙烯-丁二烯-苯乙烯-甲基丙烯酸酯嵌段共聚物的合成与表征

用正丁基锂为引发剂,环已烷和四氢呋喃为混合溶剂,以苯乙烯、丁二烯、甲基丙烯酸酯为单体,按阴离子顺序加料方法合成了聚苯乙烯-丁二烯-苯乙烯-甲基丙烯酸酯嵌段共聚物,共聚物经GPC、IR、DSC、TEM等测试方法表征。结果表明,在30 ℃左右、1,1-二苯基乙烯(DPE)戴帽和LiCl配合的条件下,合成了窄分布(MWD<1.3)聚苯乙烯-丁二烯-苯乙烯-甲基丙烯酸酯嵌段共聚物,成功地在SBS中引入了一小段极性链段。     

Syntheses and Properties of Novel Copolymers of Polylactide and Aliphatic Polycarbonate Based on Ketal-Protected Dihydroxyacetone

The novel random copolymers of L-LA and 2, 2-ethylenedioxy-1, 3-propanediol carbonate (EOPDC) were synthesized in bulk using Sn(Oct)₂ as a catalyst. The poly(EOPDC -co- L-LA)s obtained were characterized by FT IR, ¹H NMR, ¹³C NMR, GPC and DSC. The copolymers were obtained with yield of 87.9–95.6%. The number average molecular weight of the copolymer is 1.85–6.18 × 10⁴ with a polydispersity of 1.41–1.73. The properties of the copolymer including the enzymatic degradation by proteinase K and drug-controlled release property were also investigated. The results show that the degradation rate of the copolymers increases with increasing LA content in the copolymers.