Synthesis and Characterization of ABBA Block Copolymer of Glycolide and ε-Caprolactone

A biodegradable ABBA block copolymer was synthesized via the ring-opening co-polymerization of ε-Scaprolactone (CL, B) and glycolide (A) by means of step polymerization in the presence of ethylene glycol as an initiator and stannous octanoate as a catalyst at 110 ℃ for 48 h. The molecular length of the PCL prepolymer(BB) could be adjusted by controlling the molar ratio of the ethylene glycol initiator to ε-caprolactone monomer. The structure and the composition of the block copolymer were determined by the weight ratio of the monomer glycolide (A) to PCL pre-polymer(BB). The block copolymers were characterized by ^1H NMR, GPC, DSC and X-ray. The results confirm the successful synthesis of an ABBA block copolymer.     

Homopolymerization and Copolymerization of Adipic Anhydride with ε-Caprolactone Catalyzed by Rare Earth Trisphenolate

The ring-opening polymerization of adipic anhydride and the ring-opening copolymerization of adipic anhydride with ε-caprolactone catalyzed by single component rare earth trisphenolate have been reported. The structure of the copolymer poly（CL-b-AA） has been characterized by SEC, ^1H NMR and DSC.     

AN APPROACH TO SYNTHESIZE POLY(ETHYLENE GLYCOL)-b-POLY(ε-CAPROLACTONE) WITH TERMINAL AMINO GROUP via SCHIFF’S BASE AS AN INITIATOR

A new method to synthesize a degradable terminal amino group-containing copolymer,poly(ethylene glycol)-b- poly(ε-caprolactone)(MPEG-PCL-NH_2),was developed in the following three steps:(1)the ring-opening polymerization (ROP)ofε-caprolactone from the Schiff base prepared from benzatdehyde and ethanolamine(Ph-CH=NCH_2CH_2OH)used as an initiator to obtain heterobifunctional poly(ε-caprolactone)with one terminal Schiff base group and one hydroxyl group (HO-PCL-CH_2CH_2N=CH-Ph);(2)the coupling reaction of two reactive precursors,a hydroxy-terminated HO-PCL- CH_2CH_2N=CH-Ph andα-monocarboxy-ω-monomethoxy poly(ethylene glycol)(CMPEG)to synthesize MPEG-PCL- CH_2CH_2N=CH-Ph;(3)the conversion of the -N=CH-Ph end-group into NH_2 end-group by acidification of acetic acid to obtain MPEG-PCL-NH_2.The structures from the precursors to the terminal amino group-containing copolymer were confirmed by ~1H-NMR and their molecular weights were measured by gel permeation chromatography.The amphiphilic terminal amino group-containing copolymer could self-assemble into micelles in an aqueous system with PCL block as the core and PEG block as the shell.The micelle formation of the terminal amino group-containing block copolymer was studied by fluorescent probe technique and the existence of critical micellar concentration(cmc)confirmed the amphiphilic nature of the resulting copolymer.ESEM and DLS analysis of the micelles revealed a homogeneous spherical morphology and a unimodal size distribution.     

Biodegradable shape memory polyurethanes with controllable trigger temperature

A series of random copolymers(PCLAs) were synthesized by ring-opening polymerization of D,L-lactide(LA)and ε-caprolactone(CL) with different molar ratios. PCLA based polyurethanes(PCLAUs) were obtained by chain-extending of PCLA and polytetramethylene ether(PTMEG) with hexamethylene diisocyanate(HDI). All the PCLAUs exhibit good shape memory properties with high shape fixity ratios above 98% and shape recovery ratios above 82% in the first cycle and 91% in the second cycle. PCLAUs with less CL content show faster recovery speed and PCLAUs with more CL content show higher shape recovery ratio. The trigger temperature can be tuned or controlled around body temperature by adjusting the molar ratio of LA to CL. The PCLAUs have potential applications in implant biomedical devices, especially for minimally invasive deployable devices.     

Synthesis and Microphase Separation Behavior of Random,Mixed Cylindrical Brush Copolymers Bearing Polystyrene and Poly(ε-caprolactone) Side Chains

A series of mixed, random cylindrical brush copolymers bearing polystyrene(PS) and poly(ε-caprolactone)(PCL) side chains were synthesized via the combination of ring-opening polymerization(ROP) and atom transfer radical polymerization(ATRP). These novel cylindrical brush copolymers have been characterized by means of nuclear magnetic resonance(NMR) spectroscopy, gel permeation chromatography(GPC) and differential scanning calorimetry(DSC). It was found that the mikto-armed cylindrical brush copolymers were microphase-separated in bulks and that the morphologies were dependent on the mass ratios of PS to PCL side chains. One of the cylindrical brush copolymers was employed to incorporate into epoxy thermoset to investigate effect of the mikto-armed cylindrical brush architecture on the reaction-induced microphase separation behavior. Depending on the concentration of the cylindrical brush in epoxy, the thermosets can display the morphologies with the spherical, worm-like and lamellar PS microdomains dispersing in continuous thermosetting matrices.     

TUNED MECHANICAL PROPERTIES ACHIEVED BY VARYING POLYMER STRUCTURE — KNOWLEDGE THAT GENERATES NEW MATERIALS FOR TISSUE ENGINEERING

By changing both the monomer composition and the polymer structure, we have varied the mechanical properties of resorbable polymers. The polymers were synthesized by ring-opening polymerization using L-lactide （LLA）, ε-caprolactone （εCL）, trimethylene carbonate （TMC） and 1,5-dioxepan-2-one （DXO） as monomers. Well-defined triblock copolymers, microblock copolymers and networks have been evaluated, and comparisons between them show that it is possible to tune the mechanical properties. Triblock copolymers with an amorphous middle block of poly（1,5-dioxepan-2- one） （PDXO） and semi-crystalline end-blocks of poly（ε-caprolactone） （PCL） were stronger and had a higher strain at break than triblock copolymers with poly（L-lactide） （PLLA） as end-blocks. Polymers with both DXO and TMC in the amorphous middle-block and PLLA as end-blocks showed a lower stress at break, but the material gained elasticity, a property which is very valuable in tissue engineering. Mechanical properties of networks, synthesized by a novel method, containing PDXO and PCL are also presented. Although it is difficult to compare them with the uncross-linked polymers, this is an additional way to modify and widen the properties.     

Lanthanum heterocyclic Schiff-base complex initiated ring-opening polymerization of ε-caprolactone

Lanthanum complex supported by the heterocyclic Schiff-base ligand of N-(2-pyridyl)-3,5-di-tert-butyl-salicylaldimine was prepared and employed for the ring-opening polymerization(ROP)ofε-caprolactone(ε-CL).The polymers obtained with this initiator showed a unimodal molecular weight distribution implied that only one active species was present.Mechanism study revealed that the polymerization proceeds via acyl-oxygen bond cleavage.     

Synthesis and characterization of biodegradable amphiphilic PEG-grafted poly(DTC-co-CL)

<正>A novel biodegradable copolymer,poly(5,5-dibromomethyltrimethylene carbonate-co-ε-caprolactone)(poly(DBTC-co-CL)) with pendant bromine groups,was synthesized via ring-opening polymerization(ROP) ofε-caprolactone(CL) and 5,5- dibromomethyltrimethylene carbonate(DBTC) using stannous octoate(Sn(Oct)_2) as catalyst.Then the pendant bromine groups were completely converted into azide form,which permitted"click"reaction with alkyne-terminated polyethylene(A-PEG) by Huisgen 1,3-dipolar cycloadditions preparing biodegradable amphiphilic poly(DTC-co-CL)-g-PEG graft copolymer.The graft copolymer was characterized by nuclear magnetic resonance(NMR) and size-exclusion chromatography(SEC).     

Ring-opening Copolymerization of ε-Caprolactone and δ-Valerolactone Catalyzed by a 2,6-Bis(amino)phenol Zinc Complex

In combination with methyllithium,a 2,6-bis(amino)phenol zinc complex 1 was used in the ring-opening polymerization ofδ-valerolactone in the absence or presence of benzyl alcohol and showed high efficiency,mainly producing cyclic and linear polyvalerolactones,respectively.On the basis of homopolymerization,the ring-opening copolymerization ofε-caprolactone andδ-valerolactone was investigated.The P(CL-co-VL)random copolymers,PCL-b-PVL and PVL-b-PCL diblock copolymers,were prepared by varying the feeding strategy(premixing or sequential feeding).The copolymer composition was adjusted by varying the feeding ratio of two monomers.The structure and thermal properties of obtained polymers were characterized by GPC,1 H-NMR,13 C-NMR,MALDI-TOF mass spectroscopy,and DSC,respectively.     

Hybrid Copolymerization via the Combination of Proton Transfer and Ring-opening Polymerization

Phosphazene base,t-BuP2,was employed to catalyze the proton transfer polymerization(PTP)of 2-hydroxyethyl acrylate(HEA),and PTP was further combined with ring-opening polymerization(ROP)to exploit a new type of hybrid copolymerization.The studies on homopolymerization showed that t-BuP2 was a particularly efficient catalyst for the polymerization of HEA at room temperature,giving an excellent monomer conversion.Throughout the polymerization,transesterification reactions were unavoidable,which increased the randomness in the structures of the resulting polymers.The studies on copolymerization showed that t-BuP2 could simultaneously catalyze the hybrid copolymerization via the combination of PTP and ROP at 25°C.During copolymerization,HEA not only provided hydroxyl groups to initiate the ROP ofε-caprolactone(CL)but also participated in the polymerization as a monomer for PTP.The copolymer composition was approximately equal to the feed ratio,demonstrating the possibility to adjust the polymeric structure by simply changing the monomer feed ratio.This copolymerization reaction provides a simple method for synthesizing degradable functional copolymers from commercially available materials.Hence,it is important not only in polymer chemistry but also in environmental and biomedical engineering.     

Multiarm Star Poly(ε-caprolactone) with Hyperbranched Polyamidoamine as Core Capable of Selective Accommodating Cationic or Anionic Guests

Hyperbranched polyamidoamines(HPAs) were directly employed as macroinitiators to initiate the Sn(Oct)2 catalyzed ring-opening polymerization of ε-caprolactone(CL), resulting in multiarm star copolymers with poly(ε-caprolactone)(PCL) as shells and HPA as core(HPA-b-PCL). From 1H-NMR characterization it was deduced that both the primary amines and the secondary amide groups of HPAs could initiate the CL polymerization, and the initiation efficiency increased when more CL monomers were fed. The average arm-numbers of the obtained stars were in the range of 115-353. Differential scanning calorimetry measurements demonstrated that the melting and crystallization temperatures, fusion and crystallization enthalpy and the degree of crystallinity of the star polymers increased as the PCL arm length increased. HPAb-PCL stars could be used as nanocarriers to efficiently accommodate anionic dyes at acidic condition, while load cationic dyes at basic condition. Compared with the dye-loading behavior of multiarm star PCL with the neutral hyperbranched polyglycerol as core, it was deduced that HPA-b-PCL nanocarriers accommodated anionic dyes using the HPA core, while loaded cationic dyes using both the HPA core and the PCL shell. Dynamic light scattering analyses also supported such deduction. Furthermore, HPA-b-PCL nanocarriers could selectively load the anionic Eosin Y or the cationic methylene blue from their mixture at p H = 6 or 9, respectively, realizing their separation.     

Preparation of polymer brushes on attapulgite surfaces via a combination of CROP and click reaction

<正>In this work,by a combination of controlled ring-opening polymerization(CROP) and click reaction,we reported a facile and useful method to synthesize linear poly(ε-caprolactone) at attapulgite nanocomposites with well-defined structures.For this,first, the chlorine terminated attapulgite was prepared by the self-assembly of 3-chloropropyltrimethoxysiIane from the surfaces of attapulgite.And then,the terminal chlorines of modified attapulgite were substituted with azido groups.As the second step,linear propargyl-terminated poly(ε-caprolactone)(PCLs) with different molecular weights were synthesized by the CROP ofε-CL monomer in toluene with Sn(Oct)_2 as a catalyst and propargyl alcohol as an initiator.Finally,the azido-terminated attapulgites were reacted with propargyl-terminated PCLs via the click reactions.     

稀土硫化物：e–己内酯开环聚合新催化剂

The ring-opening polymerization （ROP） of ε-caprolactone （ε-CL） using lanthanide thiolate complexes [（CH3CsH4）2Sm（μ-SPh）（THF）]2 （1） and Sm（SPh）3（HMPA）3 （2） as initiators has been investigated for the first time. Both of 1 and 2 were found to be highly efficient initiators for the ROP of ε-CL. The poly（ε-caprolactone） （PCL） with molecular weight Mn up to 1.97 ×10^5 and relatively narrow molecular weight distributions （1.20〈MW/Mn〈 2.00） have been obtained in high yield in the temperature range of 35-65℃. According to the polymer yield, 2 showed much higher activity than 1. However, the number-average molecular weight of PCL obtained with 2 was much lower than with 1. The possible polymerization mechanism of the ε-CL polymerization has been proposed based on the results of the end group analysis of the ε-CL oligomer.     

Confined lamella formation in crystalline-crystalline poly(ethylene oxide)-b-poly(ɛ-caprolactone) diblock copolymers

The real time and in situ investigation of the crystallization process and structure transitions of asymmetric crystalline-crystalline diblock copolymers from the melt was performed with synchrotron simultaneous SAXS/WAXS. The asymmetric poly(ethylene oxide)-b-poly(ε-caprolactone) diblock copolymers were chosen for the present study. It was shown that the short blocks crystallized later than the long blocks and final lamellar structure was formed in all of the asymmetric diblock copolymers. The final lamellar structure was confirmed by AFM observation. The SAXS data were analyzed with different methods for the early stage of the crystallization. The Guinier plots indicated that there were no isolated domains formed before the formation of lamellae in the asymmetric diblock copolymers during the crystallization process. Debye-Bueche plots implied the formation of correlated domains during crystallization.     

Synthesis of novel biodegradable poly(ethylene glycol) analogue:Water-soluble aliphatic polyester with pendant oligo(ethylene glycol) chains

A novel poly(ethylene glycol)(PEG) analogue composed of aliphatic polyester backbone and pendant oligo(ethylene glycol) short chains is reported.The PEG analogue is a copolymer synthesized by ring-opening alternating copolymerization of succinic anhydride with 2-((2-(2-metho xyethoxy)ethoxy)methyl)oxirane.The structure of the copolymer was confirmed by ~1H NMR spectrum.The effects of the monomer feed ratio on the copolymerization were studied and the polymerization mechanism was given.The PEG analogue di...     

PREPARATION AND CHARACTERIZATION OF INCLUSION COMPLEXES OF TWO-ARM LINEAR AND FOUR-ARM STAR-SHAPED POLY（ε-CAPROLACTONE）S WITH α-CYCLODEXTRIN

Both four-ann star-shaped poly（ε-caprolactone） （4sPCL） and two-ann linear PCL （2LPCL） were synthesized and their inclusion complexation with α-cyclodextrin （α-CD） were studied. The inclusion complexes （ICs） formed between the PCL polymers and α-CD were characterized by ^1H-NMR, DSC, TGA, WAXD, and FT-1R, respectively. Both branch ann number and molecular weight of the PCL polymers have apparent effect on the stoichiometry （CL：CD, mol：mol） of these ICs. All these analytical results indicate that the branch arms of the PCL polymers are incorporated into the hydrophobic α-CD cavities and their original crystalline properties are completely suppressed. Moreover, the inclusion complexation between two-ann linear or four-ann star-shaped PCL polymers and α-CD not only enhances the thermal stability of the guest PCL polymers but also improves that of α-CD.     

Synthesis of Syndiotactic Polystyrene/Atactic Polypropene Block Copolymer in the presnece of Half-sandwich Titanocene Catalysts

Some highly active η5-pentamethylcyclopentadienyltribenzyloxy titanium complexes [Cp*Ti(Obz)3] activated by modified methylaluminoxane (mMAO) were prepared and used as the catalyst for styrene syndiospecific polymerization and propene atactic polymerization. Styrene could be copolymerized with propene when the propene was prepolymerized for a period, to which styrene and tri-isobutylaluminum (TIBA) were then added. The titled block copolymer together with the related homopolymers was obtained. The copolymerization porducts can be divided into the homopolymers and the copolymer by successive solvent extraction with boiling butanone, heptane and tetrahydrofuran (THF), and each fraction was characterized by 13C NMR, DSC and WAXD. It was found that aPS and aPP were soluble in boiling butanone and heptane respectively. The block copolymer (sPS-b-aPP) composed of syndiotactic polystyrene segment was soluble in boiling THF and the residue was chiefly sPS.     

PREPARATION AND CHARACTERIZATION OF INCLUSION COMPLEXES OF TWO-ARM LINEAR AND FOUR-ARM STAR-SHAPED POLY(ε-CAPROLACTONE)S WITH α-CYCLODEXTRIN

Both four-arm star-shaped poly(ε-caprolactone) (4sPCL) and two-arm linear PCL (2LPCL) were synthesized and their inclusion complexation with α-cyclodextrin (α-CD) were studied. The inclusion complexes (ICs) formed between the PCL polymers and α-CD were characterized by 1H-NMR, DSC, TGA, WAXD, and FT-IR, respectively. Both branch arm number and molecular weight of the PCL polymers have apparent effect on the stoichiometry (CL:CD, mol:mol) of these ICs. All these analytical results indicate that the branch arms of the PCL polymers are incorporated into the hydrophobicα-CD cavities and their original crystalline properties are completely suppressed. Moreover, the inclusion complexation between two-arm linear or four-arm star-shaped PCL polymers and α-CD not only enhances the thermal stability of the guest PCL polymers but also improves that of α-CD.     

Solution Crystallization Behavior of Linear and Star-shaped Poly(ethylene glycol)-b-Poly(ε-caprolactone) Block Copolymers简

Lamellar crystals of diblock, triblock and four-arm poly（ethylene glycol）-b-poly（ε-caprolactone） （PEG-b-PCL） crystalline-crystalline copolymers were successfully obtained from their solution. Morphology and structure of lamellar crystals of crystalline-crystalline copotymers were investigated using tapping-mode atomic force microscopy （AFM） and selected area electron diffraction （SAED）. All of these samples showed the truncated-lozenge multilayer basal shapes with central screw dislocation or central stack, which were all obtained simultaneously from the oil bath. The diffraction pattern of PEG block lamellar crystal is attributed to the （120） diffracting planes and the pattern of PCL block lamellar crystal is attributed to the （1 I0） diffracting planes and （200） diffracting planes according to the SAED results. Four （110） crystal growth planes and two （200） crystal growth planes are discovered for the PCL blocks, but the （120） crystal growth planes of PEG blocks are hided in the figure of AFM. The crystalline structure of the four-arm copolymers （FA） is more disorder and confused than that of the diblock （DI） copolymer and the striated fold surface structures of lamellar crystals of four-arm copolymers （FA） are smoother than these of linear analogues, owing to the confused crystallization of blocks caused by the mutual restriction of blocks and the hindrance of the dendritic cores. In addition, the aspect ratio of FA is greater than that of the others. It is hypothesized that there are two reasons for the change of aspect ratios. First, the （200） diffracting planes of PCL crystals grew slowly compared to their （110） diffracting planes because of difference in the energy barrier. Secondly, edge dislocations on the （200） diffracting planes are also responsible for the variation of the aspect ratio. Consequently, the crystalline defects are augmented by the competing blocks crystallized simultaneously and the hindrance of the dendritic cores.     

Dual thermal- and pH-responsive polypeptide-based hydrogels

Smart hydrogels have received increasing attention for their great potential for the applications in many fields. Herein, we report a facile approach to prepare a class of dual-responsive hydrogels assembled from synthetic statistical/block thermal-responsive copoly(L-glutamate)s copolymerized with poly(ethylene glycol), which were prepared by ring-opening polymerization(ROP) and post-modification strategy. The incorporation of oligo(ethylene glycol)(OEG) and glutamic acid residues offers the gels with thermal-and p H-responsive properties simultaneously. We have systematically studied the influence of both temperature and p H on the gelation behaviors of these copolymers. It is found that the increase of glutamic acid content and solution p H values can significantly suppress the gelation ability of the samples. Circular dichroism(CD) results show that the α-helix conformation appears to be the dominant secondary conformation. More interestingly, the gelation property of the block copolymer with statistical thermal-responsive copoly(L-glutamate)s shows greater dependence on p H as compared to that with block segments due to the distinct morphology of the self-assemblies. The obtained hydrogels exhibit p H-dependent and thermal-responsive gelation behaviors, which enable them as an ideal smart hydrogel system for biomedical applications.