Molecular Weight Of Triblock Copolymer Research Articles

Preparation and Characterization of Poly(ethylene glycol)-block-Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-block-Poly(ethylene glycol) Triblock Copolymers

Amphiphilic triblock copolymers, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as a hydrophobic block and poly(ethylene glycol) (PEG) as a hydrophilic block, were successfully synthesized, with an aim to broaden the potential application of PHBV in biomedical areas. Isophorone diisocyanate having two different reactive isocyanate groups was used as the coupling agent. Telechelic hydroxylated PHBV was prepared by alcoholysis reaction, isocyanate modified and finally reacted with PEG. Molecular weight of triblock copolymer increased with the increasing molecular weight of PHBV-diol and PEG. The length of the PHBV block and PEG block had a great influence on the crystallization behavior of the triblock copolymers. Thermal degradation temperature of PHBV segment enhanced greatly. The triblock copolymer showed a tendency toward formation of aggregation in aqueous solution with a critical aggregation concentration of 5.01×10-4 g·L-1, and the rod-shape assembly with a uniform hydrophilic shell might be employed as hydrophobic drug delivery systems.

Simultaneous determination of the styrene unit content and assessment of molecular weight of triblock copolymers in adhesives by a size exclusion chromatography method.

The content of styrene units in nonhydrogenated and hydrogenated styrene-butadiene-styrene and styrene-isoprene-styrene triblock copolymers significantly influences product performance. A size exclusion chromatography method was developed to determine the average styrene content of triblock copolymers blended with tackifier in adhesives. A complete separation of the triblock copolymer from the other additives was realized with size exclusion chromatography. The peak area ratio of the UV and refraction index signals of the copolymers at the same effective elution volume was correlated to the average styrene unit content using nuclear magnetic resonance spectroscopy with commercial copolymers as standards. The obtained calibration curves showed good linearity for both the hydrogenated and nonhydrogenated styrene-butadiene-styrene and styrene-isoprene-styrene triblock copolymers (r=0.974 for styrene contents of 19.3-46.3% for nonhydrogenated ones and r=0.970 for the styrene contents of 23-58.2% for hydrogenated ones). For copolymer blends, the developed method provided more accurate average styrene unit contents than nuclear magnetic resonance spectroscopy provided. These results were validated using two known copolymer blends consisting of either styrene-isoprene-styrene or hydrogenated styrene-butadiene-styrene and a hydrocarbon tackifying resin as well as an unknown adhesive with styrene-butadiene-styrene and an aromatic tackifying resin. The methodology can be readily applied to styrene-containing polymers in blends such as poly(acrylonitrile-butadiene styrene).

Differential analysis on precise determination of molecular weight of triblock copolymer using SEC/MALS and MALDI-TOF MS

Precise determination of the molecular weight of a poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer (PEG-PTHF-PEG) using size-exclusion chromatography/multi-angle laser light scattering (SEC/MALS) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) was carefully investigated. The potential uncertainty factors for both SEC/MALS and MALDI-TOF MS were evaluated using cause-effect diagrams. The consistency of data between the two methods was then assessed by t-test. It was found that the data from SEC/MALS and MALDI-TOF MS were not consistent. For clarifying the differential results, titration was also employed to further measure the molecular weight of triblock copolymer. The result indicated that the data from titration was consistent with that of SEC/MALS, but not consistent with the data from MALDI-TOF MS. The result of MALDI-TOF MS was smaller and showed a deviation of about 10% from the SEC/MALS result. The reason for this difference was then further explored.

Thermoreversible Supramolecular Polymer Gels via Metal–Ligand Coordination in an Ionic Liquid

Thermoreversible supramolecular polymer gels were prepared via metal–ligand coordination by mixing a poly(4-vinylpyridine)-b-poly(ethyl acrylate)-b-poly(4-vinylpyridine) (P4VP–PEA–P4VP) triblock copolymer and zinc chloride (ZnCl2) in a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imidide. FT-IR spectroscopy revealed metal–ligand coordination between zinc in ZnCl2 and pyridine groups as ligands on P4VP blocks, even in an ionic liquid. Thermoreversible viscoelastic properties between a semisolid (gel-like) state and a liquid-like state were confirmed by temperature-ramp oscillatory shear measurements. It was also revealed that thermoreversibility of supramolecular polymer gels depended strongly on stoichiometry between ligands and metals, where the maximum of storage modulus-loss modulus crossover temperature (Tgel) as an indicator of gelation was achieved when a molar amount of available coordination sites was a certain excessive amount (coordination site/ligand ratio ∼1.6). The molar ratio at the maximum Tgel is nearly independent of the number of ligands per triblock copolymer. On the other hand, the number of ligands per triblock copolymer affected the Tgel, where a larger number of ligands per triblock copolymer gave a higher Tgel, regardless of almost the same molecular weight of triblock copolymers.

Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) triblock copolymer : Synthesis, crystallization behavior and novel morphology

Poly(ethylene glycol)-poly(tetrahydrofuran)-poly(ethylene glycol) (PEG-PTHF-PEG) triblock copolymer was synthesized by ring-opening polymerization of ethylene oxide using sodium alcoholate of PTHF as the macroinitiator. Its crystallization behavior and formation mechanisms of different crystal structures were studied. The study showed that the molecular weight of PEG-PTHF-PEG exhibited a significant effect on its crystallization: that is, with the increase of the copolymer's molecular weight, the crystallizability of PTHF blocks decreased gradually, which led to the transition of copolymer from crystalline-crystalline to crystalline-amorphous. By adjusting the total molecular weight of triblock copolymer, the crystallization process can be effectively controlled, and as a result, different spherulite structures were obtained. Particularly, when PTHF blocks became amorphous, novel double concentric spherulites were observed. The morphological structures were studied by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), polarized optical microscopy (POM), and its crystalline process was investi- gated.

Synthesis of triblock copolymer having alternating structures and kinetics study on RAFT‐mediated bulk, miniemulsion and seed miniemulsion polymerizations

AbstractWe have conducted reversible addition‐fragmentation chain transfer (RAFT) polymerizations of styrene (St) and maleic anhydride (MAh) and n‐butyl acrylate (BA) to produce a well‐defined triblock copolymer having alternating structure, P(St‐alt‐MAh)‐b‐PSt‐b‐PBA, via bulk, miniemulsion and seed miniemulsion polymerizations. The polymerization kinetics and living characters were investigated. The results followed by gel permeation chromatography (GPC) showed that bulk and miniemulsion polymerizations exhibited controlled nature such as narrow polydispersity index (PDI), controlled molecular weight, and first‐order polymerization kinetics, whereas triblock copolymer owned a rather wider PDI. Comparison of GPC RI and UV traces revealed that alternating copolymer and diblock copolymer have a very high percentage of living chains. For seed miniemulsion polymerization, when the molecular weight of triblock copolymer is more than 36,000 g/mol, the formation of homopolymer of BA resulted in broadening of PDI. 1H NMR method was used to identify the compositions of block copolymers. Differential scanning calorimetry analysis showed that the copolymers exhibited distinct glass temperatures. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Synthesis and Characterizations of PLLA/PEG Block Copolymers

Poly(lactic acid-co-ethylene glycol) (PLLA/PEG) copolymers were synthesized and their properties were characterized. The PLLA/PEG/PLLA triblock copolymers were synthesized by ring-opening polymerization from l-lactide (LLA) and PEG macroinitiator. Stannous octoate, Sn(Oct)2 was used as a catalyst. Effects of molecular weight of PEG (600, 2000 and 4000), LLA/OH molar ratios (95:5, 98:2) and a sequence of addition of the reactants on properties of the copolymers were investigated. The triblock copolymers were subsequently used in a production of multiblock copolymers by reacting with a chain-extending agent, hexamethylene diisocyanate (HMDI). Chemical structure and molecular weight of the copolymers were characterized by 1H-NMR, FTIR and GPC. The results showed that molecular weight of triblock copolymers varied from 4,500 to 10,200. After chain extension, multiblock copolymer with molecular weight of 16,490 was produced. Thermal properties of the copolymers were also examined by DSC.

Triblock copolymers: synthesis, characterization, and delivery of a model protein

The purpose of this study was to synthesize and characterize biodegradable and thermosensitive triblock copolymers for delivering protein at controlled rate in biologically active form for longer duration of time. A series of thermosensitive triblock copolymers with different block lengths (PLGA–PEG–PLGA) were synthesized by ring-opening polymerization of d, l-lactide and glycolide with polyethylene glycol (PEG) in the presence of stannous octoate. Compositions and molecular weight of triblock copolymers were characterized by 1H NMR spectrometry and gel permeation chromatography, respectively. A single test-tube inverting method was employed to determine the sol–gel transition temperature. Lysozyme was used as a model protein. Lysozyme solution formulation was prepared with different triblock copolymers for in vitro release. Lysozyme concentration and its biological activity in the released sample were determined using a standard MicroBCA method and bacterial cell lysis method, respectively. The effects of varying block lengths and concentrations of copolymers on the in vitro release of lysozyme were evaluated. The release profiles from formulations showed a higher initial release followed by slower release up to 4 weeks. Increasing the block lengths of copolymers decreased burst release of lysozyme from 41.2 ± 5.4% to 16.1 ± 3.9%. Increasing copolymer concentrations decreased the drug release. Lysozyme in the 4 weeks released samples retained most of its biological activity (>80%). It is feasible to deliver protein in biologically active form for longer duration by varying block lengths and concentrations of triblock copolymers.

Synthesis of ABA triblock copolymer of poly(potassium acrylate-styrene-potassium acrylate) by atom transfer radical polymerization and the self-assembly in selective solvents

A series of well-defined ABA triblock copolymers of poly(methyl acrylate)-polystyrene-poly(methyl acrylate) (PMA- b-PS- b-PMA) with different molecular weights were synthesized using Cl-PS-Cl as macroinitiator, CuCl/ N, N, N′, N″, N″-pentamethyldiethylenetriamine (PMDETA) as catalyst system via atom transfer radical polymerization (ATRP). Amphiphilic triblock copolymer poly(potassium acrylate)-polystyrene-poly(potassium acrylate) (PKAA- b-PS- b-PKAA) was obtained by hydrolyzing PMA- b-PS- b-PMA. The self-assembly behavior of the triblock copolymers in organic solutions, which is a good solvent for the PS block and in aqueous solutions, which is a good solvent for the PKAA blocks was studied by high performance particle sizer (HPPS). The results showed that the Z-average size of the micelles obviously increases with increase in molecular weight of triblock copolymers, and the micelles in organic solutions are relatively more stable than in aqueous solutions. The effect of the length of PS block on the Z-average size of the micelles is more obvious in organic solution than in aqueous solution. The morphology of triblock copolymers PKAA- b-PS- b-PKAA in aqueous solution, which is a nearly ‘pearl-necklace’-like shape, was examined by transmission electron microscopy (TEM) at room temperature.

Synthesis and properties of novel biodegradable triblock copolymers of poly(5-methyl-5-methoxycarbonyl-1,3-dioxan-2-one) and poly(ethylene glycol)

Novel biodegradable triblock copolymers of poly(5-methyl-5-methoxycarbonyl-1,3-dioxan-2-one) (PMMTC) with poly(ethylene glycol) (PEG), PMMTC-b-PEG-b-PMMTC, were synthesized by the ring-opening polymerization of MMTC in bulk, using the dihydroxyl PEG as initiator and Sn(Oct)2 as catalyst. The triblock copolymers with different compositions were characterized by IR and 1H NMR, their molecular weight was measured by gel permeation chromatography (GPC). The results showed that the molecular weight of triblock copolymers increased either with the increase of the molar ratio of MMTC in feed while the PEG chain length kept constant, or by lengthening the backbone chain of PEG block with the same ratio of MMTC in feed. The hydrophilicity of copolymers was greatly improved by incorporation of PEG block into polycarbonate. The in vitro hydrolytic/enzymatic degradation and controlled drug release properties of the triblock copolymers were also investigated.