Synthesis and self‐assembly of amphiphilic star‐block copolymers consisting of polyethylene and poly(ethylene glycol) segments

We report on the synthesis and self‐assembly in water of well‐defined amphiphilic star‐block copolymers with a linear crystalline polyethylene (PE) segment and two or three poly(ethylene glycol) (PEG) segments as the building blocks. Initially, alkynyl‐terminated PE (PE‐?) is synthesized via esterification of pentynoic acid with hydroxyl‐terminated PE, which is prepared using chain shuttling ethylene polymerization with 2,6‐bis[1‐(2,6‐dimethylphenyl) imino ethyl] pyridine iron (II) dichloride/methylaluminoxane/diethyl zinc and subsequent in situ oxidation with oxygen. Then diazido‐ and triazido‐terminated PE (PE‐(N₃)₂ and PE‐(N₃)₃) are obtained by the click reactions between PE‐? and coupling agents containing triazido or tetraazido, respectively. Finally, the three‐arm and four‐arm star‐block copolymers, PE‐b‐(PEG)₂ and PE‐b‐(PEG)₃, are prepared by click reactions between PE‐(N₃)₂ or PE‐(N₃)₃ and alkynyl‐terminated PEG. The self‐assembly of the resultant amphiphilic star‐block copolymers in water was investigated by dynamic light scattering, transmission electron microscopy, and atomic force microscopy. It is found that, in water, a solvent selectively good for PEG blocks; these star‐block copolymer chains could self‐assemble to form platelet‐like micelles with insoluble PE blocks as crystalline core and soluble PEG blocks as shell. The confined crystallization of PE blocks in self‐assembled structure formed in aqueous solution is investigated by differential scanning calorimetry. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Self‐assembled micelles prepared from poly(ɛ‐caprolactone)–poly(ethylene glycol) and poly(ɛ‐caprolactone/glycolide)–poly(ethylene glycol) block copolymers for sustained drug delivery

A series of poly(?‐caprolactone)–poly(ethylene glycol) (PCL‐PEG) and poly(?‐caprolactone/glycolide)–poly(ethylene glycol) [P(CL/GA)‐PEG] diblock copolymers were prepared by ring‐opening polymerization of ?‐caprolactone or a mixture of ?‐caprolactone and glycolide using monomethoxy PEG (mPEG) as macroinitiator and Sn(Oct)₂ as catalyst. The resulting copolymers were characterized using ¹H‐NMR, gel permeation chromatography, differential scanning calorimetry, and wide‐angle X‐ray diffraction. Copolymer micelles were prepared using the nanoprecipitation method. The morphology of the micelles was spherical or worm‐like as revealed by transmission electron microscopy, depending on the copolymer composition and the length of the hydrophobic block. Introduction of the glycolide component, even in small amounts (CL/GA = 10), disrupted the chain structure and led to the formation of spherical micelles. Interestingly, the micelle size decreased with the encapsulation of paclitaxel. Micelles prepared from mPEG5000‐derived copolymers exhibited better drug loading properties and slower drug release than those from mPEG2000‐derived copolymers. Drug release was faster for copolymers with shorter PCL blocks than for those with longer PCL chains. The introduction of glycolide moieties enhanced drug release, but the overall release rate did not exceed 10% in 30 days. In contrast, drug release was enhanced in acidic media. Therefore, these bioresorbable micelles and especially P(CL/GA)‐PEG micelles with excellent stability, high drug loading content, and prolonged drug release could be promising for applications as drug carriers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45732.     

Synthesis of star–comb‐shaped polymer with porphyrin‐core and its self‐assembly behavior study

5,10,15,20‐tetra(4‐hydroxyphenyl)porphyrin (THPP) was synthesized by the condensation of pyrrole with 4‐hydroxybenzaldehyde in the presence of solvent (propionic acid). Subsequently, the resulting THPP was converted to a tetrafunctional star‐shaped macroinitiator (porphyrin‐Br₄) by esterification of it with 2‐bromopropanoyl bromide, and then atom transfer radical polymerization (ATRP) of styrene was conducted at 110°C with CuCl/2,2′‐bipyridine as the catalyst system. The resulting product was reacted with NBS to obtain star‐shaped initiator porphyrin‐(PSt‐Br)₄, which was used the following ATRP of the GMA to synthesize star–comb‐shaped grafted polymer porphyrin‐(PSt‐g‐PGMA)₄. The number molecular weight was 2.3 × 10⁴ g/mol, and the dispersity was narrow (M_w/M_n = 1.32). The structure of the polymers was investigated by NMR, UV–vis, IR, and GPC measurement. The self‐assembly behavior of the polymer porphyrin‐(PSt‐g‐PGMA)₄ was studied by DLS and AFM. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Amphiphilic block copolymer poly(lactic acid)‐block‐(glycidylazide polymer)‐block‐polystyrene: synthesis and self‐assembly

The triblock energetic copolymer poly(lactic acid)‐block‐(glycidylazide polymer)‐block‐polystyrene (PLA‐b‐GAP‐b‐PS) was synthesized successfully through atom‐transfer radical polymerization (ATRP) of styrene and ring‐opening polymerization of d,l ‐lactide. The energetic macroinitiator GAP‐Br, which was made from reacting equimolar GAP with α‐bromoisobutyryl bromide, firstly triggered the ATRP of styrene with its bromide group, and then the hydroxyl group on the GAP end of the resulting diblock copolymer participated in the polymerization of lactide in the presence of stannous octoate. The triblock copolymer PLA‐b‐GAP‐b‐PS had a narrow distribution of molecular weight. In the copolymer, the PS block was solvophilic in toluene and improved the stability of the structure, the PLA block was solvophobic in toluene and served as the sacrificial component for the preparation of porous materials, and GAP was the basic and energetic material. The three blocks of the copolymer were fundamentally thermodynamically immiscible, which led to the self‐assembly of the block copolymer in solution. Further studies showed that the concentration and solubility of the copolymer and the polarity of the solvent affected the morphology and size of the micelles generated from the self‐assembly of PLA‐b‐GAP‐b‐PS. The micelles generated in organic solvents at 10 mg mL^?1 copolymer concentration were spherical but became irregular when water was used as a co‐solvent. The spherical micelles self‐assembled in toluene had three distinct layers, with the diameter of the micelles increasing from 60 to 250 nm as the concentration of the copolymer increased from 5 to 15 mg L^?1. © 2017 Society of Chemical Industry     

Poly(ε‐caprolactone)‐graft‐poly(N‐isopropylacrylamide) amphiphilic copolymers prepared by a combination of ring‐opening polymerization and atom transfer radical polymerization: Synthesis,self‐assembly,and thermoresponsive property

Thermoresponsive graft copolymers of ε‐caprolactone and N‐isopropylacrylamide were synthesized by a combination of ring‐opening polymerization and the sequential atom transfer radical polymerization (ATRP). The copolymer composition, chemical structure, and the self‐assembled structure were characterized. The graft length and density of the copolymers were well controlled by varying the feed ratio of monomer to initiator and the fraction of chlorides along PCL backbone, which is acting as the macroinitiator for ATRP. In aqueous solution, PCL‐g‐PNIPAAm can assemble into the spherical micelles which comprise of the biodegradable hydrophobic PCL core and thermoresponsive hydrophilic PNIPAAm corona. The critical micelle concentrations of PCL‐g‐PNIPAAm were determined under the range of 6.4–23.4 mg/L, which increases with the PNIPAAm content increasing. The mean hydrodynamic diameters of PCL‐g‐PNIPAAm micelles depend strongly on the graft length and density of the PNIPAAm segment, allowing to tune the particle size within a wide range. Additionally, the PCL‐g‐PNIPAAm micelles exhibit thermosensitive properties and aggregate when the temperature is above the lower critical solution temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41115.     

Synthesis,self‐assembly,and drug release behavior of star‐shaped poly(ε‐caprolactone)‐b‐poly(ethylene oxide) block copolymer with porphyrin core

A serial of star‐shaped poly(ε‐caprolactone)‐b‐poly(ethylene oxide) (SPPCL‐b‐PEO) block copolymers with porphyrin core were successfully synthesized from ring‐opening polymerization (ROP) of ε‐caprolactone (CL) initiated with porphyrin core, followed by coupling reaction with a hydrophilic polymer poly(ethylene oxide) (PEO) shell. The structure of this novel copolymer were synthesized and thoroughly characterized by Nuclear Magnetic Resonance (NMR), Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FTIR). Notably, the as‐prepared porphyrin‐cored star‐shaped copolymer could self‐assembly into different structures determined by transmission electron microscopy (TEM) and dynamic lighting scattering (DLS), which provides the great potential of using this well‐defined photodynamic therapy material for drug delivery system. Particularly, the doxorubicin‐loaded SPPCL‐b‐PEO nanosphere exhibits property of pH‐induced drug release. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40996.     

Synthesis and physicochemical characterization of amphiphilic block copolymer self‐aggregates formed by poly(ethylene glycol)‐block‐poly(ϵ‐caprolactone)

Diblock copolymers with different poly(ε‐caprolactone) (PCL) block lengths were synthesized by ring‐opening polymerization of ε‐caprolactone in the presence of monomethoxy poly(ethylene glycol) (mPEG‐OH, MW 2000) as initiator. The self‐aggregation behaviors and microscopic characteristics of the diblock copolymer self‐aggregates, prepared by the diafiltration method, were investigated by using ¹H NMR, dynamic light scattering (DLS), and fluorescence spectroscopy. The PEG–PCL block copolymers formed the self‐aggregate in an aqueous environment by intra‐ and/or intermolecular association between hydrophobic PCL chains. The critical aggregation concentrations of the block copolymer self‐aggregate became lower with increasing hydrophobic PCL block length. On the other hand, reverse trends of mean hydrodynamic diameters were measured by DLS owing to the increasing bulkiness of the hydrophobic chains and hydrophobic interaction between the PCL microdomains. The partition equilibrium constants (K_v) of pyrene, measured by fluorescence spectroscopy, revealed that the inner core hydrophobicity of the nanoparticles increased with increasing PCL chain length. The aggregation number of PCL chain per one hydrophobic microdomain, investigated by the fluorescence quenching method using cetylpyridinium chloride as a quencher, revealed that 4–20 block copolymer chains were needed to form a hydrophobic microdomain, depending on PCL block length. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3520–3527, 2006     

Vesicular and micellar self‐assembly of stimuli‐responsive poly(N‐isopropyl acrylamide‐b‐9‐anthracene methyl methacrylate) amphiphilic diblock copolymers

Dually responsive amphiphilic diblock copolymers consisting of hydrophilic poly(N‐isopropyl acrylamide) [poly(NIPAAm)] and hydrophobic poly(9‐anthracene methyl methacrylate) were synthesized by reversible addition fragmentation chain‐transfer (RAFT) polymerization with 3‐(benzyl sulfanyl thiocarbonyl sulfanyl) propionic acid as a chain‐transfer agent. In the first step, the poly(NIPAAm) chain was grown to make a macro‐RAFT agent, and in the second step, the chain was extended by hydrophobic 9‐anthryl methyl methacrylate to yield amphiphilic poly(N‐isopropyl acrylamide‐b‐9‐anthracene methyl methacrylate) block copolymers. The formation of copolymers with three different hydrophobic block lengths and a fixed hydrophilic block was confirmed from their molecular weights. The self‐assembly of these copolymers was studied through the determination of the lower critical solution temperature and critical micelle concentration of the copolymers in aqueous solution. The self‐assembled block copolymers displayed vesicular morphology in the case of the small hydrophobic chain, but the morphology gradually turned into a micellar type when the hydrophobic chain length was increased. The variations in the length and chemical composition of the blocks allowed the tuning of the block copolymer responsiveness toward both the pH and temperature. The resulting self‐assembled structures underwent thermally induced and pH‐induced morphological transitions from vesicles to micelles and vice versa in aqueous solution. These dually responsive amphiphilic diblock copolymers have potential applications in the encapsulation of both hydrophobic and hydrophilic drug molecules, as evidenced from the dye encapsulation studies. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46474.     

A novel initiating system for ring‐opening polymerization of ε‐caprolactone: Synthesis of triarm star‐shaped poly(ε‐caprolactone)

The rare earth compound, scandium trifluoromethanesulfonate [Sc(OTf)₃], has been used as a water‐tolerant catalyst for the synthesis of star‐shaped poly(ε‐caprolactone)s (SPCLs) with trimethylol propane as trifunctional initiator in solvent at 40°C. Triarm SPCLs have been successfully prepared. The molar mass of SPCLs were determined by end‐group ¹H NMR analyses, which could be well controlled by the molar ratio of the monomer to the initiator, and were independent of the amount of Sc(OTf)₃ used. Differential scanning calorimetry analyses suggested that the maximal melting point, the cold crystallization temperature, and the degree of crystallinities of SPCLs increased with the increasing of the molar mass and were lower than the linear poly(ε‐caprolactone) (LPCL) with similar molar mass. Furthermore, polarized optical microscopy indicated that LPCL showed fast crystallization rate and good spherulitic morphology with apparent Maltese cross pattern, whereas SPCLs exhibit much lower crystallization rate and poor spherulitic morphology. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Controllable self‐assembly of polystyrene‐block‐poly(2‐vinylpyridine)

Block copolymers can form various ordered structures by self‐assembly, and their composites with inorganic materials may give surprising properties. This review summarizes recent developments in the preparation, mechanism and application of various types of self‐assembly of polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP). The focus of the review is on how to control the self‐assembly of the dynamic and ordered structure of PS‐b‐P2VP based materials by applying effective factors such as thermal annealing, solvent annealing, block composition and blending. Moreover, the combination of the self‐assembly of PS‐b‐P2VP and various nanoparticles, with potentials in drug delivery, sensors and catalysis, is highlighted. © 2018 Society of Chemical Industry     

Atomic force microscopy study of self‐assembly behaviors of hydrophobic poly(n‐butyl methacrylate)‐block‐polydimethylsiloxane‐block‐poly(n‐butyl methacrylate) ABA triblock copolymers

Poly(n‐butyl methacrylate)‐block‐polydimethylsiloxane‐block‐poly(n‐butyl methacrylate) (PBMA‐block‐PDMS‐block‐PBMA) ABA triblock copolymers were synthesized successfully via atom‐transfer radical polymerization using PDMS as macroinitiator. The effects of PDMS content and substrate nature on self‐assembly behaviors of PBMA‐block‐PDMS‐block‐PBMAs were systematically studied using atomic force microscopy. Two series of triblock copolymers with different molecular weights and compositions, i.e. PBMA‐block‐PDMSA12‐block‐PBMAs and PBMA‐block‐PDMSA21‐block‐PBMAs, were used, where the latter were of a higher PDMS content than the former. On silicon wafer, it was found that only spherical structures formed after annealing films spin‐coated from chloroform solutions of PBMA‐block‐PDMSA12‐block‐PBMAs. In contrast, films of PBMA‐block‐PDMSA21‐block‐PBMAs formed semi‐continuous structures. On mica wafer, it was found that ordered cylindrical pores formed after annealing films spin‐coated from chloroform solutions of PBMA‐block‐PDMSA12‐block‐PBMAs. In contrast, films of PBMA‐block‐PDMSA21‐block‐PBMAs formed isolated cylinders or worm‐like morphologies. Copyright © 2011 Society of Chemical Industry     

Synthesis,characterization and crosslinking of functional star‐shaped poly(ε‐caprolactone)

Star‐shaped low molecular weight poly(ε‐caprolactone)s (PCLs) were synthesized and functionalized with crosslinkable terminal groups for subsequent crosslinking. The ε‐caprolactone (CL) prepolymers were polymerized by ring‐opening in the presence of polyglycerine (PGL) as an initiator (1, 3 and 5 mol%) and Sn(II)2‐ethylhexanoate as a catalyst. Characterization of the prepolymer by ¹³C/¹H nuclear magnetic resonance (NMR) spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) revealed a six‐armed star‐shaped structure for the prepolymer with the molecular weight controlled by the ratio of PGL and CL. Functionalization of the hydroxyl‐terminated prepolymer was carried out with maleic or itaconic anhydride. In both cases, the characterization of the functionalized prepolymer showed that the hydroxyl groups were completely substituted. The functionalized PCLs were successfully crosslinked through the reaction of double bonds. The crosslinking was induced either thermally with organic peroxide or photochemically with a photosensitive initiator. Characterization of the crosslinked PCLs by Soxhlet extraction, DSC and FTIR showed that the itaconic double bond was much more reactive in thermal crosslinking than the maleic double bond. Thus, the crosslinked prepolymers that were functionalized with itaconic double bonds achieved a gel content of about 90%. A gel content of 100% was achieved with several compositions where crosslinking agents were employed. © 2002 Society of Chemical Industry     

Thermosensitive self‐assembly micelles from A2BA2‐type poly(N‐isopropyl acrylamide)2‐b‐Poly(lactic acid)‐b‐Poly(N‐isopropyl acrylamide)2 four‐armed star block copolymers and their applications as drug carriers

A novel A₂BA₂‐type thermosensitive four‐armed star block copolymer, poly(N‐isopropyl acrylamide)₂‐b‐poly(lactic acid)‐b‐poly(N‐isopropyl acrylamide)₂, was synthesized by atom transfer radical polymerization and characterized by ¹H‐NMR, Fourier transform infrared spectroscopy, and size exclusion chromatography. The copolymers can self‐assemble into nanoscale spherical core–shell micelles. Dynamic light scattering, surface tension, and ultraviolet–visible determination revealed that the micelles had hydrodynamic diameters (D_h) below 200 nm, critical micelle concentrations from 50 to 55 mg/L, ζ potentials from ?7 to ?19 mV, and cloud points (CPs) of 34–36°C, depending on the [Monomer]/[Macroinitiator] ratios. The CPs and ζ potential absolute values were slightly decreased in simulated physiological media, whereas D_h increased somewhat. The hydrophobic camptothecin (CPT) was entrapped in polymer micelles to investigate the thermo‐induced drug release. The stability of the CPT‐loaded micelles was evaluated by changes in the CPT contents loaded in the micelles and micellar sizes. The MTT cell viability was used to validate the biocompatibility of the developed copolymer micelle aggregates. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4137–4146, 2013     

Synthesis and characterization of star‐shaped poly(ethylene glycol)‐block‐poly(L‐lactic acid) copolymers by melt polycondensation

Compared with linear diblock or triblock poly(ethylene glycol)‐block‐poly(L ‐lactic acid) copolymer (PEG‐b‐PLLA), star‐shaped PEG‐b‐PLLA (sPEG‐b‐PLLA) copolymers exhibit smaller hydrodynamic radius and lower viscosity and are expected to display peculiar morphologies, thermal properties, and degradation profiles. Compared with the synthesis routine of PEG‐b‐PLLA form lactide and PEG, the traditional synthesis routine from LA and PEG were suffered by the low reaction efficiency, low purity, lower molecular weight, and wide molecular weight distribution. In this article, multiarm sPEG‐b‐PLLA copolymer was prepared from multiarm sPEG and L ‐lactic acid (LLA using an improved method of melt polycondensation, in which two types of sPEG, that is, sPEG₁ (four arm, Mn = 4300) and sPEG₂ (three arm, Mn = 3200) were chosen as the core. It was found the molecular weight of sPEG‐b‐PLLA could be strongly affected by the purity of LLA and sPEGs, and the purification technology of vacuum dewater and vacuum distillation could help to remove most of the impurities in commercial available LLA. The polymers, including sPEG and sPEG‐b‐PLLA with varied core (sPEG₁ and sPEG₂) and LLA/sPEG feeding ratios, were characterized and confirmed by ¹H‐NMR and ¹³C‐NMR spectroscopy, Fourier transform infrared spectroscopy (FT‐IR) and gel permeation chromatography, which showed that the terminal hydroxyl group in each arm of sPEGs had reacted with LLA to form sPEG‐b‐PLLA copolymers with fairly narrow molecular weight distribution. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Construct biomimetic giant vesicles via self‐assembly of poly(2‐methacryloyloxyethyl phosphorylcholine)‐block‐poly(D,L‐lactide)

The poly(2‐methacryloyloxyethyl phosphorylcholine)‐block‐poly(D ,L ‐lactide) (PMPC‐b‐PLA) was specially designed to develop biomimetic giant vesicles (GVs) and giant large compound vesicles via a simple spontaneous assemble in aqueous solution. The weight fraction of the hydrophilic PMPC block (f_PC) was proved to play an important role in the size and morphology control of the self‐assembled aggregates. The GVs with controlled micrometer size and biomimetic PMPC corona have great potential as artificial cell models. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of poly[(decanoic acid)‐block‐styrene] diblock copolymers and their self‐assembly behavior in aqueous medium

Diblock copolymers, poly[(10‐hydroxydecanoic acid)‐block‐styrene] (PHDA‐b‐PSt), were synthesized by combining enzymatic condensation polymerization of HDA and atom transfer radical polymerization (ATRP) as of St PHDA was first obtained via enzymatic condensation polymerization catalyzed by Novozyme‐435. Subsequently, one terminus of the PHDA chains was modified by reaction with α‐bromopropionyl bromide and the other terminus was protected by chlorotrimethylsilane. The resulting monofunctional macroinitiator was used subsequently in ATRP of St using CuCl/2,2′‐bipyridine as the catalyst system to afford diblock copolymers including biodegradable PHDA blocks and well‐defined PSt blocks. Polymeric nanospheres were prepared by self‐assembly of the PHDA‐b‐PSt diblock copolymers in aqueous medium. Copyright © 2008 Society of Chemical Industry     

Synthesis of star‐shaped poly(ϵ‐caprolactone) by samarium‐based tetrafunctional initiator and its dilute‐solution properties

An in situ–generated tetrafunctional samarium enolate from the reduction of 1,1,1,1‐tetra(2‐bromoisobutyryloxymethyl)methane with divalent samarium complexes [Sm(PPh₂)₂ and SmI₂] in tetrahydrofuran has proven to initiate the ring‐opening polymerization of ?‐caprolactone (CL) giving star‐shaped aliphatic polyesters. The polymerization proceeded with quantitative conversions at room temperature in 2 h and exhibited good controllability of the molecular weight of polymer. The resulting four‐armed poly(?‐caprolactone) (PCL) was fractionated, and the dilute‐solution properties of the fractions were studied in tetrahydrofuran and toluene at 30°C. The Mark–Houwink relations for these solvents were [η] = 2.73 × 10^?2M_w^0.74 and [η] = 1.97 × 10^?2M_w^0.75, respectively. In addition, the unperturbed dimensions of the star‐shaped PCL systems were also evaluated, and a significant solvent effect was observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 175–182, 2006     

α‐cyclodextrin assisted self‐assembly of poly(ethylene glycol)‐block‐poly(N‐isopropylacrylamide) in aqueous media

Poly(ethylene glycol)‐block‐poly(N‐isopropylacrylamide) (PEG‐b‐PNIPAM) block copolymers were synthesized by atom transfer radical polymerization, and the α‐cyclodextrin (α‐CD) induced self‐assembly characteristics of the system were elucidated. Below the lower critical solution temperature (LCST) of PNIPAM, CD threaded onto the PEG segments and induced micellization to form rod‐shaped nanostructures comprising of a PEG/α‐CD condensed phase and a PNIPAM shell. Increasing the temperature of system above the LCST caused the PNIPAM segments to collapse, which resulted in the dethreading of the CD. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis of star‐shaped poly(ε‐caprolactone)‐b‐poly(L‐lactide) copolymers: From star architectures to crystalline morphologies

Hexa‐armed star‐shaped poly(ε‐caprolactone)‐block‐poly(L ‐lactide) (6sPCL‐b‐PLLA) with dipentaerythritol core were synthesized by a two‐step ring‐opening polymerization. GPC and ¹H NMR data demonstrate that the polymerization courses are under control. The molecular weight of 6sPCLs and 6sPCL‐b‐PLLAs increases with increasing molar ratio of monomer to initiator, and the molecular weight distribution is in the range of 1.03–1.10. The investigation of the melting and crystallization demonstrated that the values of crystallization temperature (T_c), melting temperature (T_m), and the degree of crystallinity (X_c) of PLLA blocks are increased with the chain length increase of PLLA in the 6sPCL‐b‐PLLA copolymers. On the contrary, the crystallization of PCL blocks dominates when the chain length of PLLA is too short. According to the results of polarized optical micrographs, both the spherulitic growth rate (G) and the spherulitic morphology are affected by the macromolecular architecture and the length of the block chains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Self‐assembly and degradation of poly[(2‐methacryloyloxyethyl phosphorylcholine)‐block‐(D,L‐lactide)] diblock copolymers: large compound micelles to vesicles

Biodegradable poly[(2‐methacryloyloxyethyl phosphorylcholine)‐block‐(D ,L ‐lactide)] (PMPC‐b‐PLA) diblock copolymers with various hydrophilic PMPC weight fractions (f_PC) 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 f_PC 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