Synthesis,characterization and biocompatibility of novel biodegradable poly[((R)‐3‐hydroxybutyrate)‐block‐(D,L‐lactide)‐block‐(ε‐caprolactone)] triblock copolymers

BACKGROUND: Biodegradable block copolymers have attracted particular attention in both fundamental and applied research because of their unique chain architecture, biodegradability and biocompatibility. Hence, biodegradable poly[((R )‐3 ‐hydroxybutyrate)‐block‐(D ,L ‐lactide)‐block‐(ε‐caprolactone)] (PHB‐PLA‐PCL) triblock copolymers were synthesized, characterized and evaluated for their biocompatibility. RESULTS: The results from nuclear magnetic resonance spectroscopy, gel permeation chromatography and thermogravimetric analysis showed that the novel triblock copolymers were successfully synthesized. Differential scanning calorimetry and wide‐angle X‐ray diffraction showed that the crystallinity of PHB in the copolymers decreased compared with methyl‐PHB (LMPHB) oligomer precursor. Blood compatibility experiments showed that the blood coagulation time became longer accompanied by a reduced number of platelets adhering to films of the copolymers with decreasing PHB content in the triblocks. Murine osteoblast MC3T3‐E1 cells cultured on the triblock copolymer films spread and proliferated significantly better compared with their growth on homopolymers of PHB, PLA and PCL, respectively. CONCLUSION: For the first time, PHB‐PLA‐PCL triblock copolymers were synthesized using low molecular weight LMPHB oligomer as the macroinitiator through ring‐opening polymerization with D ,L ‐lactide and ε‐caprolactone. The triblock copolymers exhibited flexible properties with good biocompatibility; they could be developed into promising biomedical materials for in vivo applications. Copyright © 2008 Society of Chemical Industry     

Synthesis of copolymers of 3-acryloyloxymethyl-3′-methyloxetane and 3-(2-(2-(2-methoxyethylenoxy)ethylenoxy)ethylenoxy)-3′-methyloxetane and their ionic conductivity properties

An oxetane-derived monomer, 3-acryloyloxy-methyl-3′-methyloxetane (AMO) was prepared from the reaction of 3-hydromethyl-3-methyloxetane with acryloyl chloride. The cationic ring-opening copolymerization of AMO with another oxetane-derived monomer, 3-(2-(2-(2-methoxyethylenoxy)ethylenoxy)ethylenoxy)-3′-methyloxetane (MEMO) was conducted in CH₂Cl₂ solution using BF₃ · OEt₂/1,4-butanediol as a co-initiator. The resulting copolymers were characterized by FTIR, ¹H NMR and Gel Permeation Chromatography (GPC) analyses, and it was found that the enchained ratio of AMO in the copolymers is far lower than its feed ratio. They were crosslinked in situ via the radical polymerization of the vinyl group initiated by BPO after doping with lithium trifluoromethanesulfonimide (LiTFSI) to give rise to tough polymeric electrolyte films. The ionic conductivity was measured at varying content of AMO and different concentration of lithium salt LiTFSI by AC impedance, and a maximum ion conductivity of 1.44 × 10⁻⁵ S/cm at 30°C or 1.25 × 10⁻⁴ S/cm at 80°C was attained in the sample PAM 33 at the mole ratio of O: Li = 20. The DSC results indicated that T _g decreases with the increase of the proportion of AMO in the copolymer, well consistent with the ion conductivity trend. The TGA (thermogravimetric analysis) measurement revealed that this kind of copolymer electrolytes is more thermostable than their liquid counterparts. __________ Translated from Transactions of Beijing Institute of Technology, 2006, 26(12): 1098–1103 [译自: 北京理工大学学报]     

Synthesis and properties of 4‐(ω‐methoxyoligodimethylsiloxanyl)butyl maleate: A new surfmer

Anionic reactive maleate with hydrophobic oligosiloxane chain was synthesized to use as a stabilizer in the batch and seeded emulsion polymerization of traditional monomers (acrylates, methacrylates, styrene, etc.). Polymerizable surfactant is obtained in a three‐step synthesis, starting from the anionic polymerization of cyclic siloxanes, followed by the silylation of methanol with the obtained cyclic oligomer, and finishing with the acylation of the linear oligomer by maleic anhydride. The improved technique of the synthesis of 4‐chlorobutoxydimethylchlorosilane, one of the initial substances for obtaining siloxane monomer, was elaborated. The anionic polymerization of octamethylcyclotetrasiloxane using cyclic alkoxysilane was carried out to form siloxane cyclic oligomer for the first time. The chemical structure of the monomer synthesized was confirmed by IR spectroscopy and functional analysis. Critical micelle concentration of the obtained surfactant was measured. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 310–313, 2004     

Polyamides obtained by direct polycondesation of 4‐[4‐[9‐[4‐(4‐aminophenoxy)‐3‐methyl‐phenyl] fluoren‐9‐YL]‐2‐methyl‐phenoxy]aniline with dicarboxylic acids based on a diphenyl‐silane moiety

Polyamides (PAs) containing fluorene, oxyether, and diphenyl‐silane moieties in the repeating unit were synthesized in > 85% yield by direct polycondesation between a diamine and four dicarboxylic acids. Alternatively, one PA was synthesized from an acid dichloride. The diamine 4‐[4‐[9‐[4‐(4‐aminophenoxy)‐3‐methyl‐phenyl]fluoren‐9‐yl]‐2‐methyl‐phenoxy]aniline ( 3 ) was obtained from the corresponding dinitro compound, which was synthesized by nucleophilic aromatic halogen displacement from p‐chloronitrobenzene and 9,9‐bis (4‐hydroxy‐3‐methyl‐phenyl)fluorene ( 1 ). Monomers and polymers were characterized by FTIR and ¹H, ¹³C, and ²⁹Si‐NMR spectroscopy and the results were in agreement with the proposed structures. PAs showed inherent viscosity values between 0.14 and 0.43 dL/g, indicative of low molecular weight species, probably of oligomeric nature. The glass transition temperature (T_g) values were observed in the 188–211°C range by DSC analysis. Thermal decomposition temperature (TDT_10%) values were above 400°C due to the presence of the aromatic rings in the diamine. All PAs showed good transparency in the visible region (>88% at 400 nm) due to the incorporation of the fluorene moiety. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Cyclohexene oxide mid‐chain functional macromonomer of poly(ε‐caprolactone): Synthesis,characterization, and photoinitiated cationic homo‐ and copolymerization

In this study, a novel well‐defined epoxy mid‐chain functional macromonomer of poly(ε‐caprolactone) (PCL) has been synthesized by ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) and epoxidation on workup with 3‐chloroperoxybenzoic acid. The ROP of ε‐CL monomer in bulk at 110°C, by means of a dihydroxy functional initiator namely, 3‐cyclohexene‐1,1‐dimethanol in conjunction with stannous‐2‐ethylhexanoate, (Sn(Oct)₂), yielded a well‐defined PCL with a cyclohexene mid‐chain group. The epoxidation of the cyclohexene (CH) mid‐chain group of PCL was performed using 3‐chloroperoxybenzoic acid. GPC, IR, and ¹H‐NMR analyses revealed that a low‐polydispersity macromonomer of PCL with the desired cyclohexene oxide (CHO) functionality at the mid‐chain was obtained. The photoinduced cationic polymerizations of this macromonomer yielded comb‐shaped and graft copolymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Non‐catalyst synthesis and in vitro drug release property of poly(5,5‐dimethyl‐1,3‐dioxan‐2‐one)‐block‐methoxy poly(ethylene glycol) copolymers

A series of poly(5,5‐dimethyl‐1,3‐dioxan‐2‐one)‐block‐methoxy poly(ethylene glycol) (PDTC‐b‐mPEG) copolymers were synthesized by the ring‐opening polymerization of 5,5‐dimethyl‐1,3‐dioxan‐2‐one (DTC) in bulk, using methoxy poly(ethylene glycol) (mPEG) as initiator without adding any catalysts. The resulting copolymers were characterized by Fourier transform infrared spectra, ¹H NMR and gel permeation chromatography. The influences of some factors such as the DTC/mPEG molar feed ratio, reaction time and reaction temperature on the copolymerization were investigated. The experimental results showed that mPEG could effectively initiate the ring‐opening polymerization of DTC in the absence of catalyst, and that the copolymerization conditions had a significant effect on the molecular weight of PDTC‐b‐mPEG copolymer. In vitro drug release study demonstrated that the amount of indomethacin released from PDTC‐b‐mPEG copolymer decreased with increase in the DTC content in the copolymer. © 2013 Society of Chemical Industry     

Synthesis and characterization of 4,4′‐diaminodiphenyl methane‐based benzoxazines and their polymers

A series of diamine‐based benzoxazine precursors have been prepared using 4,4′‐diaminodiphenyl methane, formaldehyde, and different phenol derivatives including phenol, p‐cresol, and 2‐naphthol. Their chemical structures were identified by FTIR, ¹H NMR, and elemental analysis. The curing reactions of those precursors were monitored by FTIR and DSC. The obtained materials exhibited higher glass transition temperature and char yields than the corresponding bisphenol‐A based polybenzoxazines. The polybenzoxazine prepared from phenol showed the highest char yields of 65% and thermal stability with 5 and 10% weight‐loss temperatures at 346 and 432°C, respectively. The polybenzoxazine prepared from 2‐naphthol exhibited the highest glass transition temperature at 244°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and characterization of amine‐functionalized amphiphilic block copolymers based on poly(ethylene glycol) and poly(caprolactone)

A series of amine‐functionalized block copolymers, poly(caprolactone)‐block‐poly(ethylene glycol) (PCL‐b‐PEG), were synthesized by ring‐opening bulk polymerization (ROP) of ε‐caprolactone (ε‐CL) initiated through the hydroxyl end of the amino poly(ethylene glycol) (PEG) used as a macroinitiator in the presence of stannous 2‐ethylhexonoate [Sn(Oct)₂]. The polymerization and end functionality of the polymer were studied by different physicochemical techniques (¹H NMR, Fourier transform infrared and X‐ray photoelectron spectroscopy, gel permeation chromatography and thermogravimetric analysis). Thermal, crystalline and mechanical properties of the polymer were thoroughly analyzed using differential scanning calorimetry, wide‐angle X‐ray diffractometry and tensile testing, respectively. The results showed a linear improvement in crystallinity and mechanical properties of the polymer with the content of PEG. Thus the synthesized functional polymers can be used as excellent biomaterials for the delivery of polyanions, as well as macroinitiators for the synthesis of A–B–C‐type block copolymers. Copyright © 2006 Society of Chemical Industry     

AB‐ and ABC‐type di‐ and triblock copolymers of poly[styrene‐block‐(ε‐caprolactone)] and poly[styrene‐block‐(ε‐caprolactone)‐block‐lactide]: synthesis,characterization and thermal studies

Polystyrene terminated with benzyl alcohol units was employed as a macroinitiator for ring‐opening polymerization of ε‐caprolactone and L ‐lactide to yield AB‐ and ABC‐type block copolymers. Even though there are many reports on the diblock copolymers of poly(styrene‐block‐lactide) and poly(styrene‐block‐lactone), this is the first report on the poly(styrene‐block‐lactone‐block‐lactide) triblock copolymer consisting of two semicrystalline and degradable segments. The triblock copolymers exhibited twin melting behavior in differential scanning calorimetry (DSC) analysis with thermal transitions corresponding to each of the lactone and lactide blocks. The block derived from ε‐caprolactone also showed crystallization transitions upon cooling from the melt. In the DSC analysis, one of the triblock copolymers showed an exothermic transition well above the melting temperature upon cooling. Thermogravimetric analysis of these block copolymers showed a two‐step degradation curve for the diblock copolymer and a three‐step degradation for the triblock copolymer with each of the degradation steps associated with each segment of the block copolymers. The present study shows that it is possible to make pure triblock copolymers with two semicrystalline segments which also consist of degradable blocks. Copyright © 2009 Society of Chemical Industry     

Structure and morphology of poly(β‐hydroxybutyrate) synthesized by ring‐opening polymerization of racemic (R,S)‐β‐butyrolactone with distannoxane derivatives

Predominantly syndiotactic poly((R,S)‐β‐hydroxybutyrate) (PHB) was synthesized by ring‐opening polymerization of racemic β‐butyrolactone with distannoxane derivatives as catalysts. We have studied the polymerization of (R,S)‐β‐BL using distannoxane derivatives as catalysts and the effects of polymerization time on crude yield and molecular weight of the polymers obtained. Then, a more detailed study of the characterization of polymers obtained using hydroxy‐ and ethoxy‐distannoxanes was performed. ¹³C NMR spectroscopy resolved stereosequences in synthetic PHB at the diad level for the carbonyl carbon and at the triad level for the methylene carbon. These analyses show that distannoxane catalysts produce preferentially syndiotactic polyesters (syndiotactic diads fraction from 0.56 to 0.61). Triad stereosequence distribution of PHB samples agrees favourably with the Bernoullian statistical model of chain‐end control, where ideally Φ = 4(mm) (rr)/(mr + rm)² = 1 for perfect chain‐end control. Polymer samples synthesized from distannoxane catalysts are composed of two distinct transition endotherm components with peak temperatures of approximately 42 °C and 75 °C. The formation of two melting endotherms may be due to the presence of two different crystalline structures. © 2000 Society of Chemical Industry     

Polyethylene‐block‐poly(ε‐caprolactone) diblock copolymers: synthesis and compatibility

A strategy is introduced for the synthesis of polyethylene‐block‐poly(ε‐caprolactone) block copolymers by a combination of coordination polymerization and ring‐opening polymerization. First, end‐hydroxylated polyethylene (PE‐OH) was prepared with a one‐step process through ethylene/3‐buten‐1‐ol copolymerization catalyzed by a vanadium(III) complex bearing a bidentate [N,O] ligand ([PhN?C(CH₃)CHC(Ph)O]VCl₂(THF)₂). The PE‐OH was then used as macroinitiator for ring‐opening polymerization of ε‐caprolactone, leading to the desired nonpolar/polar diblock copolymers. The block structure was confirmed by spectral analysis using ¹H NMR, gel permeation chromatography and differential scanning calorimetry. The unusual topologies of the model copolymers will establish a fundamental understanding for structure–property correlations, e.g. compatibilization, of polymer blends and surface and interface modification of other polymers. © 2014 Society of Chemical Industry     

Synthesis and characterization of novel lipid functionalized poly(ε‐caprolactone)s

A series of novel lipid functionalized poly(ε‐caprolactone)s (PCLs) were synthesized through ROP of ε‐caprolactone in the presence of threo‐9,10‐dihydroxyoctadecanoic acid, synthesized from oleic acid. PCLs with different molecular weights were obtained by controlling the molar ratio of the initiator to the monomer. DSC and XRD analysis indicate that the crystallinity of PCLs decreased when compared to unfunctionalized PCL. The enzymatic degradation study shows that for samples with lower lipid derivatives content, a higher enzymatic degradation rate was observed because the lipase enzymes attack the ester bonds of the polymer; increased lipid content therefore inhibits the action of the lipase enzymes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and properties of polycarbonate copolymers of trimethylene carbonate and 2‐phenyl‐5,5‐bis(hydroxymethyl) trimethylene carbonate

The polycarbonate copolymers poly[trimethylene carbonate‐co‐2‐phenyl‐5,5‐bis(hydroxymethyl) trimethylene carbonate] [P(TMC‐co‐PTC)] were synthesized by the ring‐opening polymerization of trimethylene carbonate (TMC) and 2‐phenyl‐5,5‐bis(hydroxymethyl) trimethylene carbonate (PTC) with tin(II) 2‐ethylhexanoate and aluminum isopropoxide as the catalysts. These copolymers were further reduced by a palladium/carbonate (Pd/C; 10%) catalyst to produce partly deprotected copolymers. These two types of copolymers were characterized by ¹H‐NMR, Fourier transform infrared spectroscopy, UV spectroscopy, gel permeation chromatography, differential scanning calorimetry, and an automatic contact angle meter. The influences of the feed molar ratio of the monomers, the catalyst concentration, the reaction time, and the reaction temperature on the copolymerization process were also studied. The copolymerization of the TMC and PTC monomers was a nonideal copolymerization, and the copolymerization reactivity ratio of TMC was higher than that of PTC. In vitro degradation tests indicated that the partly deprotected copolymers possessed faster degradation rates and more hydrophilicity than the corresponding unreduced copolymers. Moreover, the degradation of these two type copolymers increased when the pH value of the buffer solutions decreased. In vitro drug‐release experiments showed that these two types of copolymers had steady drug‐release rates and good controlled release properties. Moreover, the partly deprotected copolymers had faster drug‐release rates than the corresponding unreduced copolymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of α‐amino acid‐containing polyester: poly[(ε‐caprolactone)‐co‐(serine lactone)]

Novel polyesters, poly[(ε‐caprolactone)‐co‐(N‐trityl‐L ‐serine‐β‐lactone)]s, were prepared by copolymerizing ε‐caprolactone (CL) with N‐trityl‐L ‐serine‐β‐lactone (TSL) using ZnEt₂ as the catalyst. The number‐average molecular weights were determined which ranged from 2.7 × 10⁴ to 4.9 × 10⁴ Da with dispersity values ranging from 1.6 to 1.8. The structures of the copolymers were investigated by means of ¹H NMR, ¹³C NMR and infrared spectroscopies, thermogravimetric analysis and differential scanning calorimetry. The results indicated that CL and TSL monomer units were randomly distributed within the copolymer backbone structures and the ratios of TSL to CL in the copolymers were close to those in the feeds. After removal of the trityl group under mild condition, a new polyester with side amino groups provided by serine units was obtained. L929 cell culturing test indicated good biocompatibility of the polyester with or without protective groups. © 2012 Society of Chemical Industry     

Curing behaviors and thermal properties of benzoxazine and N,N′‐(2, 2, 4‐trimethylhexane‐1, 6‐diyl) dimaleimide blend

A blend of bisphenol‐A based benzoxazine (BA‐a)/N, N′‐(2, 2, 4‐Trimethylhexane‐1, 6‐diyl) dimaleimide (TBMI) with the ratio of 1:1 was prepared and its curing behaviors were studied by differential scanning calorimetry (DSC), Fourier Transform Infrared (FTIR). The curing mechanism was proposed based on the semiquantitative analysis from FTIR spectra. The model compound was used to study the catalysis effect of BA‐a on the curing reaction of TBMI. It was found the curing reactions of BA‐a and TBMI not only proceeded simultaneously, but their coreactions also occurred. The research further indicated that negative oxygen ions from ring opening of benzoxazine mainly promoted the polymerization of maleimide groups, even though the amine group of benzoxazine had a positive effect on the reaction of maleimide groups. Besides, BA‐a and TBMI blends showed improved thermal properties based on the results from DMA and TGA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Amphiphilic diblock copolymers poly(2‐hydroxyethylmethacrylate)‐b‐(N‐phenylmaleimide) and poly(2‐hydroxyethylmethacrylate)‐b‐(styrene) using the macroinitiator poly(HEMA)‐Cl by ATRP: Preparation,characterization, and thermal properties

In recent years, much attention has been given to the development of specialty polymers from useful materials. In this context, amphiphilic block copolymers were prepared by atom transfer radical polymerization (ATRP) of N‐phenylmaleimide (N‐PhMI) or styrene using a poly(2‐hydroxyethylmethacrylate)‐Cl macroinitiator/CuBr/bipyridine initiating system. The macroinitiator P(HEMA)‐Cl was directly prepared in toluene by reverse ATRP using BPO/FeCl₃ 6 H₂O/PPh₃ as initiating system. The microstructure of the block copolymers were characterized using FTIR, ¹H‐NMR, ¹³C‐NMR spectroscopic techniques and scanning electron microscopy (SEM). The thermal behavior was studied by differential scanning calorimetry (DSC), and thermogravimetry (TG). The theoretical number average molecular weight (M_n,th) was calculated from the feed capacity. The microphotographs of the film's surfaces show that the film's top surfaces were generally smooth. The TDT of the block copolymer P(HEMA)₈₀‐b‐P(N‐PhMI)₂₀ and P(HEMA)₉₀‐b‐P(St)₁₀ of about 290°C was also lower than that found for the macroi′nitiator poly(HEMA)‐Cl. The block copolymers exhibited only one T_g before thermal decomposition, which could be attributed to the low molar content of the N‐PhMI or St blocks respectively. This result also indicates that the phase behavior of the copolymers is predominately determined by the HEMA block. The curves reveal that the polymers show phase transition behavior of amorphous polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Molecular simulation of the glass transition and proton conductivity of 2,2′‐benzidinedisulfonic acid and 4,4′‐diaminodiphenylether‐2,2′‐disulfonic acid‐based copolyimides as polyelectrolytes for fuel cell applications

The glass transition temperatures (T_gs) and proton conductivities of polyimides synthesized from naphthalene‐1,4,5,8‐tetracarboxylic dianhydride (NTDA), 2,2′‐benzidinedisulfonic acid (BDSA), 4,4′‐diaminodiphenylether‐2,2′‐disulfonic acid (ODADS), and non‐sulfonated diamine monomers have been predicted using molecular dynamics simulations. The specific volumes for two dry and four hydrated NTDA‐based polyimides were plotted versus temperatures above and below T_gs to obtain the glass transition temperatures. The simulation results suggest that the ODADS‐based polyimide membranes exhibit lower T_gs and thus better mechanical properties than the BDSA‐based polyimides, which may be attributed to the high mobility of backbones of ODADS as supported by the vectorial autocorrelation function (VACF) results of this study. In addition, comparison of the simulated T_gs for the dry and hydrated ODADS‐based polyimides has shown that water content in polyimides can affect their T_gs. The proton conductivities of a representative polyimide in both dry and hydrated conditions have been obtained from molecular dynamics simulations of the proton and hydronium ion diffusion. The simulated conductivity for the hydrated NTDA‐ODADS/BAPB cell is in reasonable agreement with the experimental value obtained from the AC impedance method. The relationship between the chemical composition, chain flexibility, and the glass transition and proton conduction of these NTDA‐based polyimides was explored on the basis of VACF and pair correlation function analysis. Copyright © 2006 Society of Chemical Industry     

Poly(ε‐caprolactone)‐grafted acetylated anhydroglucose oligomer by ring‐opening polymerization—Synthesis and characterization

A novel acetylated anhydroglucose oligomer (AGU‐oligomer), prepared by acid catalyzed transglycosidation of potato starch triacetate and ethylene glycol, was used as a multifunctional coinitiator for the ring‐opening polymerization of ε‐caprolactone (ε‐CL). The polymers were synthesized using different weight ratios of the starting materials and were characterized by NMR, SEC, and MALLS. The results confirmed the expected P(AGU/CL) polymer structure, namely a ‘comb‐like’ graft‐copolymer having the AGU oligomer as backbone with PCL grafts of variable chain lengths (L_CL = 4–21). Thermal and mechanical properties of graft‐copolymers with different ε‐CL block lengths were examined. By changing the graft length, crystallinity was controlled and amorphous polymers were obtained with AGU‐oligomer contents higher than 50 wt %. The tensile properties varied with the composition and a copolymer having 40 wt % of AGU‐oligomer behaved like soft elastomer, showing high elongation at break. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1633–1641, 2006     

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     

Synthesis and characterization of new biodegradable comb‐dendritic triblock copolymers

A series of well‐defined dumbbell‐shaped triblock copolymers consisting of linear poly(ethylene glycol) (PEG) and comb‐like poly(ε‐caprolactone) (PCL) with varied PCL arm lengths have been synthesized via the sequential preparation of different generation terminal dendronized PEG and ring‐opening polymerization of ε‐caprolactone. The copolymers were characterized using Fourier transform infrared, ¹H NMR and ¹³C NMR spectroscopy and gel permeation chromatography. Differential scanning calorimetry was performed to measure the glass transition temperature, melting point and degree of crystallinity and the PEG segment and PCL segment crystallization temperatures. The crystallization of the copolymers was also studied using X‐ray diffraction. The dumbbell‐shaped copolymers were further used to construct microspheres using a double emulsion method. Scanning electron microscopy and dynamic light scattering results showed the size of the microspheres was about 2 to 4 µm and the size distribution was quite narrow. Copyright © 2012 Society of Chemical Industry