Synthesis and properties of segmented block copolymers based on mixtures of poly(ethylene oxide) and poly(tetramethylene oxide) segments

The synthesis and characterisation of segmented block copolymers based on mixtures of hydrophilic poly(ethylene oxide) and hydrophobic poly(tetramethylene oxide) polyether segments and monodisperse crystallisable bisester tetra-amide segments are reported. The PEO length was varied from 600 to 8000 g/mol and the PTMO length was varied from 650 to 2900 g/mol. The influence of the polyether phase composition on the thermal mechanical and the elastic properties of the resulting copolymers was studied.The use of high melting monodisperse tetra-amide segments resulted in a fast and almost complete crystallisation of the rigid segment. The copolymers had only one polyether glass transition temperature, which suggests that the amorphous polyether segments were homogenously mixed. Thermal analysis of the copolymers showed one polyether melting temperature that was lower than in the case of ideal co-crystallisation between the two polyether segments. However, at PEO or PTMO lengths larger than 2000 g/mol two polyether melting temperatures were observed. The copolymer with the best low temperature properties was based on a mixture of PEO and PTMO segments, both having a molecular weight of 1000 g/mol, at a weight ratio of 30/70.     

Synthesis and micelle formation of triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) in aqueous solution

Amphiphilic triblock copolymers of poly(methyl methacrylate)-b-poly(ethylene oxide)-b-poly(methyl methacrylate) (PMMA-b-PEO-b-PMMA) with well-defined structure were synthesized via atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) initiated by the PEO macroinitiator. The macroinitiator and triblock copolymer with different PMMA and/or PEO block lengths were characterized with ¹H and ¹³C NMR and gel permeation chromatography (GPC). The micelle formed by these triblock copolymers in aqueous solutions was detected by fluorescence excitation and emission spectra of pyrene probe. The critical micelle concentration (CMC) ranged from 0.0019 to 0.016 mg/mL and increased with increasing PMMA block length, while the PEO block length had less effect on the CMC. The partition constant K_v for pyrene in the micelle and in aqueous solution was about 10⁵. The triblock copolymer appeared to form the micelles with hydrophobic PMMA core and hydrophilic PEO loop chain corona. The hydrodynamic radius R_h,app of the micelle measured with dynamic light scattering (DLS) ranged from 17.3 to 24.0 nm and increased with increasing PEO block length to form thicker corona. The spherical shape of the micelle of the triblock copolymers was observed with an atomic force microscope (AFM). Increasing hydrophobic PMMA block length effectively promoted the micelle formation in aqueous solutions, but the micelles were stable even only with short PMMA blocks.     

Synthesis of high‐impact biodegradable multiblock copolymers comprising of poly(butylene succinate) and poly(1,2‐propylene succinate) with hexamethylene diisocyanate as chain extender

Block copolymers demonstrate excellent thermal and mechanical properties superior to their corresponding random copolymers and homopolymers. However, it is difficult to synthesize block copolymers comprising of different polyester segments by copolycondensation due to the serious transesterification reaction. In this study, multiblock copolymers comprising of two different polyester segments, i.e. crystallizable poly(butylene succinate) (PBS) and amorphous poly(1,2‐propylene succinate) (PPSu), were synthesized by chain‐extension with hexamethylene diisocyanate (HDI). Amorphous PPSu segment was incorporated to improve the impact strength of PBS. The copolymers were characterized by GPC, laser light scattering (LLS), NMR, DSC, and mechanical testing. The results of ¹³C NMR spectra suggest that multiblock copolymers with regular sequential structure have been successfully synthesized. The data of DSC and mechanical testing indicate that block copolymers possess excellent thermal and mechanical properties with satisfactory tensile strength and extraordinary impact strength achieving upto 1900% of pure PBS. The influence of PPSu ratio and chain length of both the segments on the thermal and mechanical properties was investigated. The incorporation of an amorphous soft segment PPSu imparts high‐impact resistance to the copolymers without obviously decreasing the melting point (T_m). The favorable mechanical and thermal properties of the copolymers also depend on their regular sequential structure. At the same time, the introduction of amorphous PPSu segment enhances the enzymatic degradation rate of the multiblock copolymers. Copyright © 2009 John Wiley & Sons, Ltd.     

CO2 permeation properties of poly(ethylene oxide)-based segmented block copolymers

This paper discusses the gas permeation properties of poly(ethylene oxide) (PEO)-based segmented block copolymers containing monodisperse amide segments. These monodisperse segments give rise to a well phase-separated morphology, comprising a continuous PEO phase with dispersed crystallised amide segments. The influence of the polyether phase composition and of the temperature on the permeation properties of various gases (i.e., CO₂, N₂, He, CH₄, O₂ and H₂) as well as on the pure gas selectivities were studied in the temperature range of −5 °C to 75 °C. The CO₂ permeability increased strongly with PEO concentration, and this effect could partly be explained by the dispersed hard segment concentration and partly by the changing chain flexibility. By decreasing the PEO melting temperature the low temperature permeabilities were improved. The gas transport values were dependant on both the dispersed hard segment concentration and the polyether segment length (length between crosslinks). The gas selectivities were dependant on the polyether segment length and thus the chain flexibility.     

Synthesis and characterization of biodegradable aliphatic copolyesters with poly(ethylene oxide) soft segments

A series of multiblock poly(ether-ester)s based on poly(butylene succinate) (PBS) as the hard segments and hydrophilic poly(ethylene oxide) (PEO) as the soft segments was synthesized with the aim of developing degradable polymers which could combine the mechanical properties of high performance elastomers with those of flexible plastics. The aliphatic poly(ether-ester)s were synthesized by the catalyzed two-step transesterification reaction of dimethyl succinate, 1,4-butanediol and α,ω-hydroxyl terminated poly(ethylene oxide) (PEO, = 1000 g/mol) in bulk. The content of soft PEO segments in the polymer chains was varied from about 10 to 50 mass%. The effect of the introduction of the soft PEO segments on the structure, thermal and physical properties, as well as on the biodegradation properties was investigated. The composition and structure of these aliphatic segmented copolyesters were determined by ¹H NMR spectroscopy. The molecular weights of the polyesters were verified by gel permeation chromatography (GPC), as well as by viscometry of dilute solutions and polymer melts. The thermal properties were investigated using differential scanning calorimetry (DSC). The degree of crystallinity was determined by means of DSC and wide-angle X-ray scattering. A depression of melting temperature and a reduction of crystallinity of the hard segments with increasing content of PEO segments were observed. Biodegradation of the synthesized copolyesters, estimated in enzymatic degradation tests in phosphate buffer solution with Candida rugosa lipase at 37 °C was compared with hydrolytic degradation in the buffer solution. The weight losses of the samples were in the range from 2 to 10 mass%. GPC analysis confirmed that there were significant changes in molecular weight of copolyesters with higher content of PEO segments, up to 40% of initial values. This leads to conclusion that degradation mechanism of the poly(ether-ester)s based on PEO segments occurs through bulk degradation in addition to surface erosion.     

Block copolymers of poly(ethylene oxide) and poly(vinyl alcohol) synthesized by the RAFT methodology

A methodology for the synthesis of well‐defined poly(ethylene oxide)‐block‐poly(vinyl alcohol) (PEO‐b‐PVA) and PVA‐b‐PEO‐b‐PVA polymers was reported. Novel xanthate end‐functionalized PEOs were synthesized by a series of end‐group transformations. They were then used to mediate the reversible addition–fragmentation chain transfer polymerization of vinyl acetate to obtain well‐defined poly(ethylene oxide)‐b‐poly(vinyl acetate) (PEO‐b‐PVAc) and PVAc‐b‐PEO‐b‐PVAc. When these block copolymers were directly hydrolyzed in methanol solution of sodium hydroxide, polymers with brown color were obtained, which was due to the formation of conjugated unsaturated aldehyde structures. To circumvent these side reactions, the xanthate groups were removed by adding a primary amine before hydrolysis and the products thus obtained were white powders. The polymers were characterized by gel permeation chromatography, ¹H NMR spectroscopy and FT‐IR. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1901–1910, 2009     

Hydrophilic segmented block copolymers based on poly(ethylene oxide) and monodisperse amide segments

Segmented block copolymers based on poly(ethylene oxide) (PEO) flexible segments and monodisperse crystallizable bisester tetra‐amide segments were made via a polycondensation reaction. The molecular weight of the PEO segments varied from 600 to 4600 g/mol and a bisester tetra‐amide segment (T6T6T) based on dimethyl terephthalate (T) and hexamethylenediamine (6) was used. The resulting copolymers were melt‐processable and transparent. The crystallinity of the copolymers was investigated by differential scanning calorimetry (DSC) and Fourier Transform infrared (FTIR). The thermal properties were studied by DSC, temperature modulated synchrotron small angle X‐ray scattering (SAXS), and dynamic mechanical analysis (DMA). The elastic properties were evaluated by compression set (CS) test. The crystallinity of the T6T6T segments in the copolymers was high (>84%) and the crystallization fast due to the use of monodisperse tetra‐amide segments. DMA experiments showed that the materials had a low T_g, a broad and almost temperature independent rubbery plateau and a sharp flow temperature. With increasing PEO length both the PEO melting temperature and the PEO crystallinity increased. When the PEO segment length was longer than 2000 g/mol the PEO melting temperature was above room temperature and this resulted in a higher modulus and in higher compression set values at room temperature. The properties of PEO‐T6T6T copolymers were compared with similar poly(propylene oxide) and poly(tetramethylene oxide) copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4522–4535, 2007     

Synthesis of four‐armed poly(ε‐caprolactone)‐block‐poly(ethylene oxide) by diethylzinc catalyst

Biodegradable, amphiphilic, four‐armed poly(?‐caprolactone)‐block‐poly(ethylene oxide) (PCL‐b‐PEO) copolymers were synthesized by ring‐opening polymerization of ethylene oxide in the presence of four‐armed poly(?‐caprolactone) (PCL) with terminal OH groups with diethylzinc (ZnEt₂) as a catalyst. The chemical structure of PCL‐b‐PEO copolymer was confirmed by ¹H NMR and ¹³C NMR. The hydroxyl end groups of the four‐armed PCL were successfully substituted by PEO blocks in the copolymer. The monomodal profile of molecular weight distribution by gel permeation chromatography provided further evidence for the four‐armed architecture of the copolymer. Physicochemical properties of the four‐armed block copolymers differed from their starting four‐armed PCL precursor. The melting points were between those of PCL precursor and linear poly(ethylene glycol). The length of the outer PEO blocks exhibited an obvious effect on the crystallizability of the block copolymer. The degree of swelling of the four‐armed block copolymer increased with PEO length and PEO content. The micelle formation of the four‐armed block copolymer was examined by a fluorescent probe technique, and the existence of the critical micelle concentration (cmc) confirmed the amphiphilic nature of the resulting copolymer. The cmc value increased with increasing PEO length. The absolute cmc values were higher than those for linear amphiphilic block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 950–959, 2004     

Effect of small amount of poly(ethylene naphthalate) on isothermal crystallization and spherulitic morphology of poly(trimethylene terephthalate)

The effect of a small amount of poly(ethylene naphthalate) (PEN) in its blends with poly(trimethylene terephthalate) (PTT) on isothermal melt-crystallization kinetics and spherulitic morphology of the blends was thoroughly investigated. The maximum PEN content in the blends was 9 wt%. Due to the single composition-dependent glass transition temperature (T_g) that was observed for each blend, these blends appeared to be miscible in the amorphous state. After isothermal crystallization from the melt state, the neat PTT and its blends with PEN exhibited either double or triple melting endotherms. The triple endothermic peaks were observed in both the neat PTT and the blends when being crystallized at crystallization temperatures (T_c) of less than or equal to 195 °C. The equilibrium melting temperature () for the neat PTT was determined based on the linear Hoffman–Weeks extrapolative method to be 248 °C. Such values for the blends were found to decrease with the addition and increasing amount of PEN. Both the neat PTT and the blends were isothermally crystallized over the T_c range of 190–205 °C. At a given T_c, the 97PTT/3PEN blend exhibited a half-time of crystallization (t_0.5) value that was lower, while it exhibited reciprocal half-time (), Avrami rate constant (K_A), and spherulitic growth rate (G) values that were greater, than those of the neat PTT. With further increase in the PEN content, the t_0.5 value increased, while the , K_A, and G values decreased. Analysis of the G values based on the Lauritzen–Hoffman's (LH) secondary nucleation theory showed that the neat PTT and the 91PTT/9PEN blend exhibited a regime II→III transition at 194 °C (467.2 K), while no regime transition was observed for the other two blends. The lateral and the fold surface free energies (σ and σ_e) and the work of chain folding (q) for the neat PTT and the blends were 19.4, 30.2–46.3 erg cm⁻², and 2.4–3.6 kcal mol⁻¹, respectively. Lastly, the effect of both the T_c and the PEN content on morphology and texture of the PTT spherulites was also investigated and the results showed that the texture of the spherulites became coarser with increasing T_c and PEN content.     

Synthesis and characterization of poly(ethylene oxide)/polylactide/poly(ethylene oxide) triblock copolymer

Poly(ethylene oxide/polylactide/poly(ethylene oxide) (PEO/PL/PEO) triblock copolymers, in which each block is connected by an ester bond, were synthesized by a coupling reaction between PL and PEO. Hydroxyl‐terminated PLs with various molecular weights were synthesized and used as hard segments. Hydroxyl‐terminated PEOs were converted to the corresponding acid halides via their acid group and used as a soft segment. Triblock copolymers were identified by Fourier transform infrared spectroscopy, ¹H NMR, and gel permeation chromatography. Differential scanning calorimetry (DSC) and X‐ray diffractometry of PEO/PL/PEO triblock copolymers suggested that PL and PEO blocks were phase‐separated and that the crystallization behavior of the PL block was markedly affected by the presence of the PEO block. PEO/PL/PEO triblock copolymers with PEO 0.75k had two exothermic peaks (by DSC), and both peaks were related to the crystallization of PL. According to thermogravimetric analysis, PEO/PL/PEO triblock copolymer showed a higher thermal stability than PL or PEO. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2545–2555, 2002     

Synthesis,physical properties and enzymatic degradation of bio-based poly(butylene adipate-co-butylene furandicarboxylate) copolyesters

A series of bio-based poly(butylene adipate-co-butylene furandicarboxylate) (PBAFs) copolyesters were synthesized from 2,5-furandicarboxylic acid (FDCA), adipic acid (AA), and 1,4-butanediol (BDO) through a two-step polycondensation reaction. The copolyesters were characterized by ¹H NMR, GPC, DSC, XRD and tensile tests, and their enzymatic degradation behaviors were also investigated. They were random copolymers whose composition was well controlled and the weight average molecular weight (M_w) ranged from 54,100 to 76,800 g/mol. By combining the results of DSC and XRD, with increasing FDCA content, PBAFs changed from semi-crystalline polymers to nearly amorphous polymers, then to semi-crystalline polymers again. Specifically, the crystallizability and melting temperature (T_m) decreased with FDCA content 0–50 mol%, but rose again at FDCA content 75–100 mol%. And, the glass transition temperature (T_g) increased continuously with increasing FDCA content. Consequently, the tensile modulus and strength decreased but the ultimate elongation increased at lower FDCA content (0–50 mol%), which were converse at higher FDCA content (75–100 mol%). Especially, the P(BA-40 mol% BF) shows outstanding elasticity and rebound resilience. In addition, the influences of FDCA content on the enzymatic degradation by lipase from porcine pancreas were studied in terms of the weight loss and morphological change. At FDCA content of 0–50 mol%, the copolyesters showed biodegradability but only the degradation rate of P(BA-10 mol% BF) was faster than PBA. When the FDCA content were 75–100 mol%, they were actually un-degradable. Thus, depending on their composition, PBAFs might find applications from biodegradable elastomers to thermoplastics.     

Reaction-induced miscibility in blends comprised of bisphenol-A polycarbonate and poly(trimethylene terephthalate)

The inherent miscibility and effects of reaction-induced changes on the phase behaviour of blends of poly(trimethylene terephthalate) (PTT) with bisphenol-A polycarbonate (PC) were studied. The as-prepared (solution-cast) blends exhibited two well-spaced and separated glass transition temperatures (T_gs) and a heterogeneous phase-separated morphology, indicating an immiscible system. However, after annealing at high temperature (at 260 °C), the blends original two T_gs merged into one single T_g, and the annealed blends exhibited a homogeneous morphology, and turned from having a semicrystalline into having an amorphous nature upon extended annealing. The annealing-induced changes of phase behaviour in the blends were analyzed. The homogenization process of the blends upon heating is attributed to chemical transreactions between the PTT and PC chain segments, as evidenced with FT-IR characterization. The IR result showed a new aryl C-O vibration peak at 1,070 cm^–1 for the annealed blends, which is characteristic of an aromatic polyester structure formed from exchange reactions between PTT and PC. The transreactions between PTT and PC led to a random copolymer comprised of PC/PTT segments, which is believed to serve as a compatibilizer at the beginning stage of transreactions, but at later stage, the random copolymer became the main species of blends and turned to a homogeneous and amorphous phase.     

Synthesis,characterization, effect of architecture on crystallization,and spherulitic growth of poly(L‐lactide)‐b‐poly(ethylene oxide) copolymers with different branch arms

Well‐defined poly(L ‐lactide)‐b‐poly(ethylene oxide) (PLLA‐b‐PEO) copolymers with different branch arms were synthesized via the controlled ring‐opening polymerization of L ‐lactide followed by a coupling reaction with carboxyl‐terminated poly(ethylene oxide) (PEO); these copolymers included both star‐shaped copolymers having four arms (4sPLLA‐b‐PEO) and six arms (6sPLLA‐b‐PEO) and linear analogues having one arm (LPLLA‐b‐PEO) and two arms (2LPLLA‐b‐PEO). The maximal melting point, cold‐crystallization temperature, and degree of crystallinity (X_c) of the poly(L ‐lactide) (PLLA) block within PLLA‐b‐PEO decreased as the branch arm number increased, whereas X_c of the PEO block within the copolymers inversely increased. This was mainly attributed to the relatively decreasing arm length ratio of PLLA to PEO, which resulted in various PLLA crystallization effects restricting the PEO block. These results indicated that both the PLLA and PEO blocks within the block copolymers mutually influenced each other, and the crystallization of both the PLLA and PEO blocks within the PLLA‐b‐PEO copolymers could be adjusted through both the branch arm number and the arm length of each block. Moreover, the spherulitic growth rate (G) decreased as the branch arm number increased: G_{6sPLLA‐b‐PEO} < G_{4sPLLA‐b‐PEO} < G_{2LPLLA‐b‐PEO} < G_{LPLLA‐b‐PEO}. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2034–2044, 2006     

Molecular weight effect on the complexation of poly(methacrylic acid) and poly(ethylene oxide) as studied by high-resolution solid-state C NMR spectroscopy

Complexes of poly(methacrylic acid) (PMAA) and poly(ethylene oxide) (PEO) with different PEO molecular weight were studied by solid-state high-resolution ¹³C NMR spectroscopy, with the emphasis on the PEO molecular weight effect on inter-polymer interaction, morphology and molecular motion. It is found that the crystalline phase of PEO is completely destroyed in the complex. The results of ¹H transverse relaxation times and ¹³C spin-lattice relaxation times indicate that the chain mobility of both PEO and PMAA are greatly restricted by inter-molecular hydrogen-bonding interactions, especially when the molecular weight of PEO is 1500. The bulk structures of the complexes are found to be closely dependent on the molecular weight of PEO. The fraction of “free” PEO segments without forming hydrogen-bonds with PMAA increases with increasing PEO molecular weight.     

Transreactions in poly trimethylene terephthalate/bisphenol-A polycarbonate (PC) blends analysed by pressure-volume-temperature measurements

The effect of annealing on the miscibility and thermal properties of poly trimethylene terephthalate (PTT)/bisphenol-A polycarbonate (PC) blends was examined using pressure-volume-temperature (PVT) measurements. The PTT/PC blends were thermally annealed at 260 °C for different times to induce various extents of transesterification reactions between the two polymers. The non-annealed blends are immiscible and exhibit the thermal properties of the blend components. Upon annealing, the original semi-crystalline morphology transforms to an increasingly amorphous nature. PVT and WAXS analysis confirmed that the PTT/PC blends completely lost their crystallinity when annealed at 260 °C for a period of 120 min or longer, indicating the formation of random co-polyesters due to chemical transreactions between the PTT and PC. The further increase in the specific volume with annealing time also indicates that after reaching a completely amorphous co-polymer the transesterification continuous until a fully random copolymer is formed.     

Methoxy poly(ethylene glycol)-b-poly(valerolactone) diblock polymeric micelles for enhanced encapsulation and protection of camptothecin

Amphiphilic block copolymers, methoxy poly(ethylene glycol)-b-poly(valerolactone) (mPEG-b-PVL), were synthesized via ring opening polymerization of δ-valerolactone in the presence of methoxy poly(ethylene glycol) (mPEG). The copolymers form micelle-like nanoparticles by their amphiphilic characteristics and their structures were examined by Nuclear Magnetic Resonance (NMR). The sizes of nanoparticles ranged from 60 to 120 nm as measured by dynamic light scattering detection, and were larger with higher molecular weight of the copolymers. The Critical Micelle Concentration (CMC) of these nanoparticles in water decreased with increasing molecular weight of hydrophobic segment. Stability analysis showed that the micellar solutions maintain their sizes at 37 °C for six weeks without aggregation or dissociation. The lyophilization method was better than the evaporation method when camptothecin (CPT) was incorporated to the micelles. The former method yielded higher CPT loading efficiency and lower aggregation. The loading efficiency of CPT could be more than 96% and a steady release rate of CPT was kept for twenty six days. Moreover, the mPEG-b-PVL polymeric micelles offered good protection of CPT lactone form at 37 °C for sixteen days. The copolymers showed no cytotoxicity towards L929 mouse muscular cells when incubated for one day. Taken together, the mPEG-b-PVL copolymer has potential to be used for the delivery of CPT or other similar drugs.     

Model block–graft copolymer via anionic living polymerization: Preparation and characterization of polystyrene-block-[poly(p-hydroxystyrene)-graft-poly(ethylene oxide)]-block-polystyrene

A model graft copolymer in which position of graft points was set to the center of a backbone molecule was prepared via anionic living polymerization. Polystyrene-block-poly(p-tert-butoxystyrene)-block-polystyrene (PSt-b-PBSt-b-PSt) was prepared by three-stage sequential addition. The tert-butyl group was removed from PBSt by hydrogen bromide to yield PSt-b-PHSt-b-PSt, having a poly(p-hydroxystyrene) (PHSt) block. The hydroxyl group of PHSt was reacted with dimeric potassium dianions of 1, 1-diphenylethylene (DPE-K) or cumyl potassium (cumyl K) to yield the corresponding macromolecular initiators of PSt-b-PHSt⁻K⁺-b-PSt containing the potassium alkoxide ion of PHSt. The newly formed alkoxide groups and remaining initiators of DPE-K or cumyl K are capable of initiating the additionally introduced ethylene oxide (EO). Thus, two block–graft copolymers of polystyrene-block-[poly(p-hydroxystyrene)-graft-poly(ethylene oxide)]-block-polystyrene (PSt-b-(PHSt-g-PEO)-b-PSt) were prepared by a “grafting from” process (backbone initiation). A PSt-b-PHSt-b-PSt backbone (M_n = 1.7₅ × 10⁵ by osmometry and M_w/M_n = 1.0₈ by GPC), and two PSt-b-(PHSt-g-PEO)-b-PSt block–graft copolymers (M_n = 2.4₅ × 10⁵ by osmometry and M_w/M_n < 1.1₀ by GPC) had narrow molecular weight distributions. A relationship between nonquantitative metallation and spacing of the graft points on a backbone molecule was discussed in detail. Two benzene-cast films formed clear microphase-separated structures of lamellar structure. The dependence of composition on the morphology of the block–graft copolymers was found to differ from that of common block copolymers. A degree of crystallinity of PEO segment and lamellar thickness of PEO phase serving as graft molecule were also found to differ from those of homo PEO and/or PEO segment in common block copolymer. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3021–3034, 1998     

Synthesis and characterization of well‐defined ABC 3‐Miktoarm star‐shaped terpolymers based on poly(styrene), poly(ethylene oxide), and poly(ϵ‐caprolactone) by combination of the “living” anionic polymerization with the ring‐opening polymerization

A series of well‐defined ABC 3‐Miktoarm star‐shaped terpolymers [Poly(styrene)‐Poly(ethylene oxide)‐Poly(ε‐caprolactone)](PS‐PEO‐PCL) with different molecular weight was synthesized by combination of the “living” anionic polymerization with the ring‐opening polymerization (ROP) using macro‐initiator strategy. Firstly, the “living” poly(styryl)lithium (PS^?Li⁺) species were capped by 1‐ethoxyethyl glycidyl ether(EEGE) quantitatively and the PS‐EEGE with an active and an ethoxyethyl‐protected hydroxyl group at the same end was obtained. Then, using PS‐EEGE and diphenylmethylpotassium (DPMK) as coinitiator, the diblock copolymers of (PS‐b‐PEO)_p with the ethoxyethyl‐protected hydroxyl group at the junction point were achieved by the ROP of EO and the subsequent termination with bromoethane. The diblock copolymers of (PS‐b‐PEO)_d with the active hydroxyl group at the junction point were recovered via the cleavage of ethoxyethyl group on (PS‐b‐PEO)_p by acidolysis and saponification successively. Finally, the copolymers (PS‐b‐PEO)_d served as the macro‐initiator for ROP of ε‐CL in the presence of tin(II)‐bis(2‐ethylhexanoate)(Sn(Oct)₂) and the star(PS‐PEO‐PCL) terpolymers were obtained. The target terpolymers and the intermediates were well characterized by ¹H‐NMR, MALDI‐TOF MS, FTIR, and SEC. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1136–1150, 2008     

Synthesis,morphology, and nonisothermal crystallization behavior of poly(trimethylene terephthalate)/poly(propylene glycol) segmented random copolymers

Poly(trimethylene terephthalate)/poly(propylene glycol) (PTT/PPG) segmented random copolymers were synthesized by melt copolycondensation. The weight fraction of PPG blocks was ranged from 12.1 to 33.4 wt%, which was confirmed by ¹H NMR spectroscopy. The result of wide‐angle X‐ray diffractometer indicated that all copolymers had the same crystal structure of PTT homopolymer at room temperature. At a determined crystallization temperature, ring‐banded spherulites could be observed in all copolymers samples, and the band spacing increased with the increase of PPG content. Morphologies of copolymers after nonisothermal crystallization process were strongly depended on the cooling rate. Well‐defined ring‐banded spherulites can be observed only at moderate cooling (20°C/min), while it was really hard to be observed at too low (2.5°C/min) or too high (by air‐quenching) cooling rate. Moreover, the size of spherulites decreased with the increase of cooling rate. Finally, different nonisothermal crystallization kinetics were adopt to analyze this copolymer system, and only the Mo method was suitable to describe this copolymer system. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation and characterization of biodegradable nanoparticles based on amphiphilic poly(3-hydroxybutyrate)-poly(ethylene glycol)-poly(3-hydroxybutyrate) triblock copolymer

Amphiphilic triblock copolymers of poly(3-hydroxybutyrate)-poly(ethylene glycol)-poly(3-hydroxybutyrate) (PHB-PEG-PHB) were directly synthesized by the ring-opening copolymerization of β-butyrolactone monomer using PEG as macroinitiator. Their structure, thermal properties and crystallization were investigated by ¹H NMR, differential scanning calorimetry (DSC) and X-ray diffraction. It was found that both PHB and PEG blocks were miscible. With the increase in the PHB block length, the triblock copolymers became amorphous because amorphous PHB block remarkably depressed the crystallization of the PEG block. Biodegradable nanoparticles with core-shell structure were prepared in aqueous solution from the amphiphilic triblock copolymers, and characterized by ¹H NMR, SEM and fluorescence. The hydrophobic PHB segments formed the central solid-like core, and stabilized by the hydrophilic PEG block. The nanoparticle size was close related to the initial concentrations of the nanoparticle dispersions and the compositions of the triblock copolymers. Moreover, the PHB-PEG-PHB nanoparticles also showed good drug loading properties, which suggested that they were very suitable as delivery vehicles for hydrophobic drugs.