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1.
A well-defined amphiphilic comb-like copolymer of poly(ethylene oxide)(PEO) as main chain and polylactide (PLA) as side chain was successfully prepared via a combination of anionic polymerization and coordination-insertion ring-opening polymerization. The anionic copolymerization of ethylene oxide (EO) and ethoxyethyl glycidyl ether (EEGE) was carried out using potassium 2-(2-methoxyethoxy)ethoxide as initiator, and then ethoxyethyl groups of EEGE units of the copolymers obtained were removed by hydrolysis. Two copolymers of methoxypoly(ethylene oxide-co-glycidol) [mpoly(EO-co-Gly)] were formed with multiple hydroxyl sites (the molar ratio values of Gly to EO in copolymers: 1/10.6 and 1/5.2; Mn: 10,100 and 5,020 respectively), and them were used further to initiate the ring-opening polymerization of lactide in the presence of stannous octoate, and a well-defined comb-like copolymer of PEO as main chain and PLA as side chain was obtained. The intermediate and final products of PEO-g-PLA were characterized by GPC and NMR in detail.  相似文献   

2.
X.Y. Xiong  L.H. Gan 《Polymer》2005,46(6):1841-1850
Poly(lactic acid) (PLA) was successfully grafted to both ends of Pluronic F87 block copolymer (PEO-PPO-PEO) to obtain amphiphilic P(LA-b-EO-b-PO-b-EO-b-LA) block copolymers (PLA-F87-PLA) with short PLA blocks. The block composition and structure of PLA-F87-PLA block copolymers were studied by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetric (DSC) and wide angle X-ray diffraction (WXRD) techniques. The aggregation behavior of PLA-F87-PLA block copolymers in aqueous solutions was studied using the laser light scattering (LLS) technique. Various types of particles consisting of small micelles, medium and large aggregates were observed due to the complex structure of these copolymers. Importantly, PLA-F87-PLA block copolymers retain the thermal responsive behavior found in Pluronic systems. The critical micellization temperatures (CMTs) of PLA-F87-PLA were lower than that of F87 because of increased hydrophobicity introduced by the PLA blocks. A reversible sol-gel transition was observed for the hydrogels formed from PLA6-F87-PLA6 and PLA9-F87-PLA9 block copolymers. Preliminary results from the drug release study using a hydrophilic model drug procain hydrochloride (PrHy) were promising. Constant initial release rate was observed.  相似文献   

3.
A series of ABA type triblock copolymers [Poly(lactide)-block-poly(hexamethylene 2,3-O-isopropylidene tartarate)-block-poly(lactide)] PLA-b-PHIT-b-PLA based on renewable monomers l-tartaric acid and l-lactide have been synthesized and the effect of the PLA chain length on the properties of the triblock copolymers has been systematically investigated. The block nature of the copolymers was established by differential scanning calorimetry (DSC) which showed two glass transition temperatures (Tg) corresponding to PHIT and PLA blocks. Solution cast films of these triblock copolymers turned out to be brittle in nature and to overcome this, ε-caprolactone was copolymerized with l-lactide to generate a separate series of triblock copolymers [PLA-ran-PCL]-b-PHIT-b-[PLA-ran-PCL]. Our study systematically demonstrates that the PLA-to-PCL ratio in the outer block composition influences the mechanical properties via a delayed post-yield stress drop phenomenon. The study further elaborates the time-synchronized strain-field analysis of the novel triblocks to be a convincing approach for the characterization of micro-deformation modes.  相似文献   

4.
Polymerization of lactide on monomethoxypolyoxyethylene (MPOE), using stannous octoate as a catalyst, was carried out in bulk and in solvent. Polymerization in a solvent permits one to work at a lower temperature and thus to prevent transesterification reactions. The copolymers synthesized in solvent exhibited a lower polydispersity and a polylactic acid (PLA) block longer and closer to the expected one. Therefore, this procedure was used to synthesize a series of diblock copolymers MPOE–D ,L -PLA, keeping the PLA chain constant (45,000 g/mol), the MPOE block increasing from 2000 to 5000, 10,000, 15,000, and 20,000 g/mol. The longer the MPOE chain, the higher the water uptake in the MPOE–PLA films and the lower the glass transition temperature of the copolymers. The synthesized copolymers were used to prepare microspheres by the double-emulsion method. The PLA microspheres possess a smooth surface, whereas those made from copolymers have a rough surface with irregularity increasing with the molecular weight of MPOE. The size of these microspheres depends on the amphiphilic nature of the copolymers, their hydrophilicity, and their intrinsic viscosity in the organic solvent. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1695–1702, 1998  相似文献   

5.
The objective of this work was to determine the compatibilization effect of different concentrations of maleic anhydride (MA) in poly(lactic acid) blended with epoxidized natural rubber (PLA/ENR). ENR-grafted MA [ENR-g-MA] was synthesized using four concentrations of MA: 0.15, 0.30, 0.45, and 0.60 phr. Using an internal mixer, binary (PLA/ENR, PLA/ENR-g-MA) and ternary (PLA/ENR/ENR-g-MA) polymer blends were prepared with a constant rubber content of 10 wt %. ENR impaired the mechanical properties of PLA, perhaps due to the relatively large size of the rubber particles. The compatibilization effect of MA was evaluated from the results of impact strength testing. ENR-g-MA was a toughening agent for PLA when the concentration of MA was in the range of 0.30–0.60 phr. MA increased miscibility between PLA and ENR. This effect was indicated in the blends by reductions in rubber particle size, the glass transition temperature of PLA, and the α-transition temperatures of PLA and ENR. In the binary polymer blends, the MA concentration in ENR-g-MA that produced the optimal mechanical properties of PLA was 0.60 phr. In the ternary blends, mechanical properties of PLA did not improve at any concentration of MA in ENR-g-MA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48297.  相似文献   

6.
Amphiphilic polylactide/poly(ethylene glycol) (PLA–PEG) diblock copolymers with functional groups at the PEG chain ends were synthesized by coupling PLA and PEG homopolymers using different coupling agents. PLA precursors with different endgroups were synthesized by ring‐opening polymerization of l ‐lactide in the presence of different initiators such as octanol, acetic acid or benzoic acid, or water, using non‐toxic zinc lactate as catalyst. The mechanism of the ring‐opening polymerization of lactide initiated by carboxyl groups was investigated and discussed in comparison with the literature. N,N'‐carbonyldiimidazole was used to couple the two hydroxyl groups of PLA and PEG, using 4‐dimethylaminopyridine (DMAP) as catalyst. Dicyclohexylcarbodiimide (DCC) and DMAP were adopted to couple the carboxyl group and the hydroxyl group of PLA and PEG, respectively, while DCC and N‐hydroxysuccinimide were used to connect PLA and PEG by coupling their carboxyl and amine groups. Comparison of different coupling routes shows that the DCC/DMAP one exhibits the highest efficiency. A common tumor targeting ligand, folic acid, was attached to PLA–PEG with hydroxyl endgroups using the DCC/DMAP route. The resulting PLA–PEG copolymers bearing folic acid present great interest for targeted delivery of anti‐cancer drugs. © 2012 Society of Chemical Industry  相似文献   

7.
A series of novel degradable triarm poly(propylene oxide)‐block‐polylactide (PPO‐b‐PLA) copolymers was synthesized by ring‐opening polymerization of L ‐lactide (LLA) or D ,L ‐lactide (DLLA) using low unsaturated PPO triols as macromolecular initiator. The chemical structures of the resulting copolymers were characterized by Fourier transform infrared (FTIR), gel permeation chromatography (GPC), and proton nuclear magnetic resonance (1H‐NMR) spectroscopy. Combination of FTIR, GPC, and NMR results confirmed the formation of PPO‐b‐PLA copolymers. One glass transition was observed by differential scanning calorimetry (DSC), suggesting good miscibility between PPO and PLA segments in the copolymers. DSC and wide‐angle X‐ray diffraction demonstrated that PPO‐b‐PLLA copolymers were semicrystalline materials, and the crystallinity increased with increasing the PLLA content. In contrast, PPO‐b‐PDLLA copolymers were totally amorphous. The PPO‐b‐PLA copolymers exhibited improved thermal stability when compared with PPO polyols according to thermogravimetric analysis. The thermal degradation behavior of the copolymers depended on the composition. Polyurethane foams were prepared by crosslinking PPO and PPO‐b‐PLA copolymers using isocyanate. Alkaline degradation of the foams was investigated in 10 wt/vol % NaOH at 80°C. The results show that the novel PPO‐b‐PLA copolymers could be promising as degradable polymeric materials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   

8.
Ring‐opening polymerization of L ‐ or D ‐lactide was realized at 140 °C for a period of 7 days in the presence of dihydroxyl poly(ethylene glycol) (PEG), with M?n = 4000 g mol?1, using zinc lactate as initiator. The resulting poly(L ‐lactide)–PEG–poly(L ‐lactide) and poly(D ‐lactide)–PEG–poly(D ‐lactide) triblock copolymers are water soluble with polylactide (PLA) block length ranging from 11 to 17 units. Both the tube inverting method and rheological measurements were used to evaluate the gelation properties of aqueous solutions containing single copolymers or L /D copolymer pairs. Stereocomplexation between poly(L ‐lactide) and poly(D ‐lactide) blocks is observed for mixed solutions. Hydrogel formation is detected in the case of relatively long PLA blocks (DP PLA = 17), but not for copolymers with shorter PLA blocks (DP PLA = 11–13) due to partial racemization of L ‐lactyl units. Racemization is largely reduced when the reaction time is shortened to 1 day. Under these conditions, DP PLA of 8 is sufficient for the stereocomplexation of PLA–PEG block copolymers, and DP PLA above 10 leads to the formation of hydrogels of PLA–PEG block copolymers. On the other hand, racemization appears as a general phenomenon in the (co)polymerization of L ‐lactide with Zn(Lac)2 as initiator, although it is negligible or undetectable in the case of high molar mass polymers. Therefore, racemization is the limiting factor for the stereocomplexation‐induced gelation of water‐soluble PLA–PEG block copolymers where the PLA block length generally ranges from 10 to 30. Reaction conditions including initiator, time and temperature should be strictly controlled to minimize racemization. Copyright © 2010 Society of Chemical Industry  相似文献   

9.
Melt blending of poly(lactic acid) (PLA) and poly(epichlorohydrin‐co‐ethylene oxide) copolymers (ECO) was performed to improve the toughness and crystallization of PLA. Thermal and scanning electron microscopy analysis indicated that PLA and ECO were not thermodynamically miscible but compatible to some extent. The addition of a small amount of ECO accelerated the crystallization rate and increased the final crystallinity of PLA in the blends. Significant enhancement in toughness and flexibility of PLA were achieved by the incorporation of the ECO elastomer. When 20 wt% ECO added, the impact strength increased from 5 kJ/m2 of neat PLA to 63.9 kJ/m2, and the elongation at break increased from 5% to above 160%. The failure mode changed from brittle fracture of neat PLA to ductile fracture of the blend. Rheological measurement showed that the melt elasticity and viscosity of the blend increased with the concentration of ECO. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.  相似文献   

10.
Zhiguo Hu 《Polymer》2009,50(17):4175-12388
Polylactide (PLA)-based biodegradable and biocompatible amphiphilic block copolymers bearing pendant amino acid residues were synthesized through a relatively easy and efficient way. The composition and structure of these copolymers were characterized by gel permeation chromatography (GPC) and 1H nuclear magnetic resonance (1H NMR) spectroscopy. The self-assembly behavior of the copolymers was investigated by fluorescence (FL), dynamic light scattering (DLS), and transmission electron microscope (TEM). It was shown that aggregates less than 100 nm in average size were formed by these copolymers, which changed from micelles to vesicles with the variation of the block length. In addition, the in vitro cytotoxicity of these copolymers was determined and compared with that of PEO-b-PLA in the presence of Bel-7402 cells. The result suggested that the block copolymers PAGE/cys-b-PLA exhibited better biocompatibility. Therefore, these PLA-based copolymers are expected to find promising applications in drug delivery or tissue engineering.  相似文献   

11.
In order to make poly(lactide) (PLA) suitable for food packaging applications, its toughness must be improved. In this work, the plasticization effectiveness of a low-molecular-weight plasticizer and a triblock copolymer are analyzed. For this purpose, PLA is blended with poly(ethylene glycol) (PEG) and poly(lactide-ethylene glycol-lactide) (LA-EG-LA) triblock copolymer. The obtained results show that copolymers are more effective, reducing the glass transition temperature of PLA. Although PLA/PEG blends have been widely studied in the literature, the barrier character has not been analyzed, which is of paramount importance for packaging applications. Therefore, the permeability to carbon dioxide, oxygen, and water vapor of PLA/PEG blends has been characterized observing an increase with the incorporation of PEG, which is the expected behavior. However, the incorporation of LA-EG-LA copolymers leads to permeability values that are slightly higher, similar, or even lower than PLA. Furthermore, the free volume of the samples has been analyzed in order to gain a deeper insight on the factors affecting the transport properties. Overall, this works aims to provide a better understanding towards the design of biodegradable packaging with improved properties that could be also extended to other biodegradable polymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48868.  相似文献   

12.
Optically pure poly(lactic acid) (PLA) was obtained from lactic acid via purification of the corresponding lactide. The optical purity of PLA was determined using polarimetry and NMR. In the depolymerization process, the effect of the reaction conditions and catalysts on optical purity of the lactide was examined with temperature having a significant effect. In addition, the degree of racemization increased with increasing molecular weight of the oligomeric PLA. The effects of temperature, time, solvent, and stirring speed (RPM) on the lactide purification process were examined in order to improve optical purity. Optical purity was maximized when separation was carried out at 25 °C. The optical purity of PLA was significantly affected by that of lactide used.  相似文献   

13.
Poly(lactic acid)/halloysite nanotube (PLA/HNT) nanocomposites were prepared using melt compounding followed by compression molding. Epoxidized natural rubber (ENR) was used to toughen the PLA nanocomposites. The properties of PLA/HNT nanocomposites were characterized by impact tests, thermal analysis (DSC), morphological analysis (FESEM, TEM), and Fourier transform infrared spectroscopy (FTIR). Water absorption tests were performed at three immersion temperature (30, 40, 50°C). The maximum water absorption (Mm), diffusion coefficient (D), and the activation energy of water diffusion (Ea) were determined. The impact strength of PLA/HNT6 nanocomposites was increased significantly to ~296% by the addition of 15 wt % ENR. The incorporation of HNT and ENR increase its nucleation effect and assist in the crystallization process of PLA. The HNT has good affinity with PLA and ENR, which was revealed by TEM and FTIR. The Mm of PLA was increased in the presence of HNT and ENR. Nevertheless, the D value and the Ea of the PLA nanocomposites were found to be affected by the HNT and ENR contents. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42850.  相似文献   

14.
A series of biodegradable chitosan‐graft‐polylactide (CS‐g‐PLA) copolymers were prepared by grafting of poly(L ‐lactide) (PLLA) or poly(D ‐lactide) (PDLA) precursor to the backbone of chitosan using N,N′‐carbonyldiimidazole as coupling agent. The composition of the copolymers was varied by adjusting the chain length of PLA as well as the ratio of chitosan to PLA. The copolymers synthesized via this ‘graft‐onto’ method present interesting properties as shown by NMR and infrared spectroscopy, gel permeation chromatography and solubility tests. Hydrogels were prepared by mixing water‐soluble CS‐g‐PLLA and CS‐g‐PDLA solutions. Gelation was assigned to stereocomplexation between PLLA and PDLA blocks as evidenced by differential scanning calorimetry and wide‐angle X‐ray diffraction measurements. Thymopentin (TP5) was taken as a model drug to evaluate the potential of these CS‐g‐PLA hydrogels as drug carriers. An initial burst and a final release up to 82% of TP5 were observed from high‐performance liquid chromatography analysis. Copyright © 2011 Society of Chemical Industry  相似文献   

15.
Fang Yuan  Hong Pan  Fa Cheng  Yu Chen  Shi-Chun Jiang 《Polymer》2012,53(11):2175-2182
Ethyl cellulose (EC), lactide (LA) and branching comonomer 2,2-bis(hydroxymethyl) butyric acid (BHB) were copolymerized in xylene using Sn(Oct)2 as catalyst. Catalyst amount and polymerization temperature were optimized for the effective introduction of certain amount of branched polylactide (PLA) into the side chains of comb-like copolymers having EC backbone. The characterization of the obtained copolymers by GPC and 1H NMR demonstrated that the influence of polymerization temperature in the range of 110–150 °C on the efficient incorporation of branching units was not pronounced, whereas high amount of catalyst was the key point. The content of branching units in the copolymers could be enhanced by increasing the feed amount of BHB monomer. A plausible mechanism for the polymerization was proposed according to the model experiments. Compared with the comb-like copolymers with merely linear PLA side chains, the ones bearing both branched and linear PLA side chains had the following characters: (1) better solubility in the polar solvent of ethanol; (2) much faster hydrolysis degradation. These characters became more pronounced when the content of branching units in the side chains increased.  相似文献   

16.
The aim of this study was to investigate influences of three different ethylene copolymers on the toughness and other properties of very brittle biopolymer PLA (polylactide). For this aim, PLA was melt blended by twin-screw extruder with various amounts of ethylene vinyl acetate (EVA), ethylene-methyl-acrylate (EMA) and ethylene-n-butyl acrylate-glycidyl-methacrylate (EBA-GMA). SEM and DSC analyses indicated that these ethylene copolymers were thermodynamically immiscible with phase separation in the form of 1–5?µm sized round domains in the PLA matrix. Rubber toughening mechanisms of EVA, EMA and EBA-GMA were very effective to improve ductility and toughness of PLA significantly. Depending on the type and content of the ethylene copolymers, the highest increases in % elongation at break, Charpy impact toughness and GIC fracture toughness values of PLA were as much as 160, 320 and 158%, respectively. Although there were no detrimental effects of using EVA, EMA and EBA-GMA on the thermal properties of PLA, they resulted in certain level of reductions in stiffness, strength and hardness values.  相似文献   

17.
The present study reports on the development of binary blends consisting of bio-based high-density polyethylene (bio-HDPE) with polylactide (PLA), in the 5–20 wt % range, prepared by melt compounding and then shaped into pieces by injection molding. In order to enhance the miscibility between the green polyolefin and the biopolyester, different reactive compatibilizers were added during the melt-blending process, namely polyethylene-grafted maleic anhydride (PE-g-MA), poly(ethylene-co-glycidyl methacrylate) (PE-co-GMA), maleinized linseed oil (MLO), and a combination of MLO with dicumyl peroxide (DCP). Among the tested compatibilizers, the dual addition of MLO and DCP provided the binary blend pieces with the most balanced mechanical performance in terms of rigidity and impact strength as well as the highest thermal stability. The fracture surface of the binary blend piece processed with MLO and DCP revealed the formation of a continuous structure in which the dispersed PLA phase was nearly no discerned in the bio-HDPE matrix. The resultant miscibility improvement was ascribed to both the high solubility and plasticizing effect of MLO on the PLA phase as well as the crosslinking effect of DCP on both biopolymers. The latter effect was particularly related to the formation of macroradicals of each biopolymer that, thereafter, led to the in situ formation of bio-HDPE-co-PLA copolymers and also to the development of a partially crosslinked network in the binary blend. As a result, cost-effective and fully bio-based polymer pieces with improved mechanical strength, high toughness, and enhanced thermal resistance were obtained. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47396.  相似文献   

18.
In this study, stereocomplexed poly(lactide) (PLA) was investigated by blending linear poly(l ‐lactide) (PLLA) and tri‐block copolymer poly(d ‐lactide) ? (polyethylene glycol) ? poly(d ‐lactide) (PDLA‐PEG‐PDLA). Synthesized PDLA‐PEG‐PDLA tri‐block copolymers with different PEG and PDLA segment lengths were studied and their influences on the degree of sterecomplexation and non‐isothermal crystallization behaviour of the PLLA/PDLA‐PEG‐PDLA blend were examined in detail by DSC, XRD and polarized optical microscopy. A full stereocomplexation between PLLA and PDLA‐PEG4k‐PDLA200 could be formed when the L/D ratio ranged from 7/3 to 5/5 without the presence of PLA homocrystals. The segmental mobility and length of both PEG and PDLA are the dominating factors in the critical D/L ratio to achieve full stereocomplexation and also for nucleation and spherulite growth during the non‐isothermal crystallization process. For fixed PEG segmental length, the stereocomplexed PLA formed showed first an increasing and then a decreasing melting temperature with increasing PDLA segments due to their intrinsic stiff mobility. Furthermore, the effect of PEG segmental mobility on PLA stereocomplexation was investigated. The results clearly showed that the crystallization temperature and melting temperature of stereocomplexed‐PLA kept increasing with increasing PEG segmental length, which was due to PEG soft mobility in the tri‐block copolymers. However, PEG was not favourable for nucleation but could facilitate the spherulite growth rate. Both the PDLA and PEG segmental lengths in the tri‐block copolymers affect the crystallinity of stereocomplexed‐PLA and the stereocomplexation formation process; they have a different influence on blends prepared by solution casting or the melting method. © 2015 Society of Chemical Industry  相似文献   

19.
Biodegradable poly[(2‐methacryloyloxyethyl phosphorylcholine)‐block‐(D ,L ‐lactide)] (PMPC‐b‐PLA) diblock copolymers with various hydrophilic PMPC weight fractions (fPC) will spontaneously self‐assemble into well‐defined vesicles and large compound micelles (LCMs) in water. Transmission electron microscopy, scanning electron microscopy, dynamic light scattering and fluorescence microscopy were used to observe their aggregate morphologies. The degradation of the LCMs was investigated and the loss of molecular weight of PLA blocks was confirmed using 1H NMR analysis. The hydrolysis of PLA increases fPC and consequently shifts the preferred morphology from LCMs to vesicles. Such degradation‐induced morphological transitions mean that the biocompatible and biodegradable LCMs have great application potential in drug delivery. Copyright © 2010 Society of Chemical Industry  相似文献   

20.
Biocomposites from poly(lactic acid) (PLA) and grape pomace (GP) were created via injection molding to examine the effects of GP in a PLA matrix. To optimize the mechanical performance the biocomposites were compatibilized with maleic anhydride grafted PLA (MA-g-PLA). The objective of this work was to create a model that could accurately predict the mechanical properties of GP/PLA biocomposites. A region of feasibility for the biocomposites was determined using a statistical design of experiments. Linear regression was used to model the mechanical performance and predicted results with an error of 10% for both tensile and flexural strength and 16% for impact strength. The model was verified with a biocomposite of PLA/GP/MA-g-PLA with a ratio of 62/36/2. This biocomposite had a tensile strength, flexural modulus, and impact strength of 25.8 MPa, 40.0 MPa, and 18.4 J/m, respectively. It was found that a linear model can accurately predict the mechanical properties of PLA/GP/MA-g-PLA biocomposites.  相似文献   

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