Compatibilized poly(ϵ‐caprolactone)/poly(L‐lactide) blends for biomedical uses

A binary poly(L ‐lactide)/poly(ε‐caprolactone) (PLLA/PCL) (70/30 w/w) blend and a ternary PLLA/PCL/PLLA‐PCL‐PLLA blend of the same composition which contains 4 wt.‐% of a triblock PLLA‐PCL‐PLLA copolyester as compatibilizing agent were prepared by melt mixing at 200°C. Investigation of the thermal and mechanical properties of the blends and scanning electron microscopy of their fracture surfaces showed in the case of the ternary blend a better state of dispersion of PCL in the PLLA matrix and an improved toughness.     

Preparation of methoxy poly(ethylene glycol)/polyester diblock copolymers and examination of the gel‐to‐sol transition

Diblock copolymers consisting of methoxy poly(ethylene glycol) (MPEG) and poly(?‐caprolactone) (PCL), poly(δ‐valerolactone) (PVL), poly(L ‐lactic acid) (PLLA), or poly(lactic‐co‐glycolic acid) (PLGA) as biodegradable polyesters were prepared to examine the phase transition of diblock copolymer solutions. MPEG–PCL and MPEG–PVL diblock copolymers and MPEG–PLLA and MPEG–PLGA diblock copolymers were synthesized by the ring‐opening polymerization of ?‐caprolactone or δ‐valerolactone in the presence of HCl · Et₂O as a monomer activator at room temperature and by the ring‐opening polymerization of L ‐lactide or a mixture of L ‐lactide and glycolide in the presence of stannous octoate at 130 °C, respectively. The synthesized diblock copolymers were characterized with ¹H NMR, IR, and gel permeation chromatography. The phase transitions for diblock copolymer aqueous solutions of various concentrations were explored according to the temperature variation. The diblock copolymer solutions exhibited the phase transition from gel to sol with increasing temperature. As the polyester block length of the diblock copolymers increased, the gel‐to‐sol transition moved to a lower concentration region. The gel‐to‐sol transition showed a dependence on the length of the polyester block segment. According to X‐ray diffraction and differential scanning calorimetry thermal studies, the gel‐to‐sol transition of the diblock copolymer solutions depended on their degrees of crystallinity because water could easily diffuse into amorphous polymers in comparison with polymers with a crystalline structure. The crystallinity markedly depended on both the distinct character and composition of the block segment. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5784–5793, 2004     

Block and random copolymerization of ε‐caprolactone,L‐, and rac‐lactide using titanium complex derived from aminodiol ligand

A series of di‐ and triblock copolymers [poly(L ‐lactide‐b‐ε‐caprolactone), poly(D,L ‐lactide‐b‐ε‐caprolactone), poly(ε‐caprolactone‐b‐L ‐lactide), and poly(ε‐caprolactone‐b‐L ‐lactide‐b‐ε‐caprolactone)] have been synthesized successfully by sequential ring‐opening polymerization of ε‐caprolactone (ε‐CL) and lactide (LA) either by initiating PCL block growth with living PLA chain end or vice versa using titanium complexes supported by aminodiol ligands as initiators. Poly(trimethylene carbonate‐b‐ε‐caprolactone) was also prepared. A series of random copolymers with different comonomer composition were also synthesized in solution and bulk of ε‐CL and D,L ‐lactide. The chemical composition and microstructure of the copolymers suggest a random distribution with short average sequence length of both the LA and ε‐CL. Transesterification reactions played a key role in the redistribution of monomer sequence and the chain microstructures. Differential scanning calorimetry analysis of the copolymer also evidenced the random structure of the copolymer with a unique T_g. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis,crystalline morphologies,self‐assembly,and properties of H‐shaped amphiphilic dually responsive terpolymers

Novel and well‐defined amphiphilic H‐shaped terpolymers poly(L‐lactide)‐block‐(poly(2‐(N,N‐dimethylamino)ethyl methacrylate) ‐block‐)poly(ε‐caprolactone)(‐block‐poly(2‐(N,N‐dimethylamino)ethyl methacrylate)) ‐b‐poly(L‐lactide) (PLLA‐b‐(PDMAEMA‐b‐)PCL(‐b‐PDMAEMA)‐b‐PLLA) were synthesized by the combination of ring‐opening polymerization, atom transfer radical polymerization, and click chemistry. The H‐shaped amphiphilic terpolymers can self‐assemble into spherical nano‐micelles in water. Because of the dually responsive (temperature and pH) properties of PDMAEMA segments, the hydrodynamic radius of the micelles of the H‐shaped terpolymer solution can be adjusted by altering the environmental temperature or pH values. The thermal properties investigation and the crystalline morphology analysis indicate that the branched structure of the H‐shaped terpolymers and the presence of amorphous PDMAEMA segments together led to the obvious decrease of PCL segments and the complete destruction of crystallinity of the PLLA segments in the H‐shaped terpolymers. In addition, the H‐shaped terpolymer film has better hydrophilicity than linear PCL or triblock polymer of PLLA‐b‐(N₃? )PCL(? N₃)‐b‐PLLA, due to the decrease or destruction of the crystallizability of the PCL or PLLA in the H‐shaped terpolymer and the presence of hydrophilic PDMAEMA segments. These unique H‐shaped amphiphilic terpolymers composed of biodegradable and biocompatible PCL and PLLA components and intelligent and biocompatible PDMAEMA component will have the potential applications in biomedical fields. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Characteristics of the biodegradability and physical properties of stereocomplexes between poly(L‐lactide) and poly(D‐lactide) copolymers

Random and block copolymerizations of L ‐ or D ‐lactide with ε‐caprolactone (CL) were performed with a novel anionic initiator, (C₅Me₅)₂SmMe(THF), and they resulted in partial epimerization, generating D ,L ‐ or meso‐lactide polymers with enhanced biodegradability. A blend of PLLA‐r‐PCL [82/18; PLLA = poly(L ‐LA) and PCL = poly(ε‐caprolactone)] and PDLA‐r‐PCL [79/21; PDLA = poly(D ‐LA)] prepared by the solution‐casting method generated a stereocomplex, the melting temperature of which was about 40 °C higher than that of the nonblended copolymers. A blend of PLLA‐b‐PCL (85/15) and PDLA‐b‐PCL (82/18) showed a lower elongation at break and a remarkably higher tensile modulus than stereocomplexes of PLLA‐r‐PCL/PDLA‐r‐PCL and PLLA/PDLA. The biodegradability of a blend of PLLA‐r‐PCL (65/35) and PDLA‐r‐PCL (66/34) with proteinase K was higher than that of PLLA‐b‐PCL (47/53) and PDLA‐b‐PCL (45/55), the degradability of which was higher than that of a PLLA/PDLA blend. A blend film of PLLA‐r‐PDLLA (69/31)/PDLA‐r‐PDLLA (68/32) exhibited higher degradability than a film of PLLA/PDLLA [PDLLA = poly(D ,L ‐LA)]. A stereocomplex of PLLA‐r‐PCL‐r‐PDMO [80/18/2; PDMO = poly(L ‐3,D ,L ‐6‐dimethyl‐2,5‐morpholinedion)] with PDLA‐r‐PCL‐r‐PDMO (81/17/2) showed higher degradability than PLLA‐r‐PDMO (98/2)/PDLA‐r‐PDMO (98/2) and PLLA‐r‐PCL (82/18)/PDLA‐r‐PCL (79/21) blends. The tensile modulus of a blend of PLLA‐r‐PCL‐r‐PDMO and PDLA‐r‐PCL‐r‐PDMO was much higher than that of a blend of PLLA‐r‐PDMO and PDLA‐r‐PDMO. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 438–454, 2005     

Strontium‐based initiator system for ring‐opening polymerization of cyclic esters

An amino isopropoxyl strontium (Sr‐PO) initiator, which was prepared by the reaction of propylene oxide with liquid strontium ammoniate solution, was used to carry out the ring‐opening polymerization (ROP) of cyclic esters to obtain aliphatic polyesters, such as poly(ε‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA). The Sr‐PO initiator demonstrated an effective initiating activity for the ROP of ε‐caprolactone (ε‐CL) and L‐lactide (LLA) under mild conditions and adjusted the molecular weight by the ratio of monomer to Sr‐PO initiator. Block copolymer PCL‐b‐PLLA was prepared by sequential polymerization of ε‐CL and LLA, which was demonstrated by ¹H NMR, ¹³C NMR, and gel permeation chromatography. The chemical structure of Sr‐PO initiator was confirmed by elemental analysis of Sr and N, ¹H NMR analysis of the end groups in ε‐CL oligomer, and Fourier transform infrared (FTIR) spectroscopy. The end groups of PCL were hydroxyl and isopropoxycarbonyl, and FTIR spectroscopy showed the coordination between Sr‐PO initiator and model monomer γ‐butyrolactone. These experimental facts indicated that the ROP of cyclic esters followed a coordination‐insertion mechanism, and cyclic esters exclusively inserted into the Sr–O bond. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1934–1941, 2003     

Nanoindentation of biodegradable cellulose diacetate‐graft‐poly(L‐lactide) copolymers: Effect of molecular composition and thermal aging on mechanical properties

Nanoindentation of cellulose diacetate‐graft‐poly(lactide)s (CDA‐g‐PLLAs) synthesized by ring opening graft copolymerization of L ‐lactide in bulk onto the residual hydroxyl positions on CDA were conducted to investigate the effect of the molecular composition and thermal aging on mechanical properties and creep behavior. Continuous stiffness measurement (CSM) technique was used to obtained hardness and elastic modulus. These material properties were expressed as a mean value from 100 to 300 nm depths and an unloading value at final indentation depth. The hardness and elastic modulus in all CDA‐g‐PLLAs were higher than those in pure CDA, indicating that the introduction of PLLA increases the hardness and elastic modulus. With an increase of crystallinity by thermal aging, the hardness and elastic modulus were increased in both CDA‐g‐PLLA and PLLA. The creep test performed by CSM showed that the creep strain of CDA was decreased by the grafting of PLLA. Thermal aging decreased the creep strain of CDA‐g‐PLLA and PLLA. With an increase of holding time, hardness was decreased, whereas elastic modulus was kept almost constant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1114–1121, 2007     

Toughening modification of PLLA with PCL in the presence of PCL‐b‐PLLA diblock copolymers as compatibilizer

To obtain an effective compatibilizer for the blends of poly(L‐lactide) (PLLA) and poly(ε‐caprolactone) (PCL), the diblock copolymers PCL‐b‐PLLA with different ratios of PCL/PLLA (CL/LA) and different molecular weights (M_n) were synthesized by ring‐opening polymerization (ROP) of L‐lactide with monohydric poly(ε‐caprolactone) (PCL‐OH) as a macro‐initiator. These copolymers were melt blended with PLLA/PCL (80/20) blend at contents between 3.0 and 20 phr (parts per hundred resin), and the effects of added PCL‐b‐PLLA on the mechanical, morphological, rheological, and thermodynamic properties of the PLLA/PCL/PCL‐b‐PLLA blends were investigated. The compatibility between PLLA matrix and PCL phase was enhanced with decreasing in CL/LA ratios or increasing in M_n for the added PCL‐b‐PLLA. Moreover, the crystallinity of PLLA matrix increased because of the added compatibilizers. The PCL‐b‐PLLA with the ratio of CL/LA (50/50) and M_n ≥ 39.0 kg/mol were effective compatibilizers for PLLA/PCL blends. When the content of PCL‐b‐PLLA is greater than or equal to 5 phr, the elongations at break of the PLLA/PCL/PCL‐b‐PLLA blends all reached approximately 180%, about 25 times more than the pristine PLLA/PCL(80/20) blend.     

Miscible blends of poly(ethylene oxide) with brush copolymers of poly(vinyl alcohol)‐graft‐poly(l‐lactide)

Even though poly(ethylene oxide) (PEO) is immiscible with both poly(l ‐lactide) (PLLA) and poly(vinyl alcohol) (PVA), this article shows a working route to obtain miscible blends based on these polymers. The miscibility of these polymers has been analyzed using the solubility parameter approach to choose the proper ratios of the constituents of the blend. Then, PVA has been grafted with l ‐lactide (LLA) through ring‐opening polymerization to obtain a poly(vinyl alcohol)‐graft‐poly(l ‐lactide) (PVA‐g‐PLLA) brush copolymer with 82 mol % LLA according to ¹H and ¹³C NMR spectroscopies. PEO has been blended with the PVA‐g‐PLLA brush copolymer and the miscibility of the system has been analyzed by DSC, FTIR, OM, and SEM. The particular architecture of the blends results in DSC traces lacking clearly distinguishable glass transitions that have been explained considering self‐concentration effects (Lodge and McLeish) and the associated concentration fluctuations. Fortunately, the FTIR analysis is conclusive regarding the miscibility and the specific interactions in these systems. Melting point depression analysis suggests that interactions of intermediate strength and PLOM and SEM reveal homogeneous morphologies for the PEO/PVA‐g‐PLLA blends. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1217–1226     

Morphology and dynamics of the poly(ϵ‐caprolactone)‐b‐poly(L‐lactide) diblock copolymer and its inclusion compound with α‐cyclodextrin: A solid‐state 13C NMR study

A biodegradable diblock copolymer of poly(ϵ‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA) was synthesized and characterized. The inclusion compound (IC) of this copolymer with α‐cyclodextrin (α‐CD) was formed and characterized. Wide‐angle X‐ray diffraction showed that in the IC crystals α‐CDs were packed in the channel mode, which isolated and restricted the individual guest copolymer chains to highly extended conformation. Solid‐state ¹³C NMR techniques were used to investigate the morphology and dynamics of both the bulk and α‐CD‐IC isolated PCL‐b‐PLLA chains. The conformation of the PCL blocks isolated within the α‐CD cavities was similar to the crystalline conformation of PCL blocks in the bulk copolymer. Spin–lattice relaxation time (T₁C) measurements revealed a dramatic difference in the mobilities of the semicrystalline bulk copolymer chains and those isolated in the α‐CD‐IC channels. Carbon‐observed proton spin–lattice relaxation in the rotating frame measurements (T_1ρH) showed that the bulk copolymer was phase‐separated, while, in the IC, exchange of proton magnetization through spin‐diffusion between the isolated guest polymer chains and the host α‐CD was not complete. The two‐dimensional solid‐state heteronuclear correlation (HetCor) method was also employed to monitor proton communication in these samples. Intrablock exchange of proton magnetization was observed in both the bulk semicrystalline and IC copolymer samples at short mixing times; however, even at the longest mixing time, interblock proton communication was not observed in either sample. In spite of the physical closeness between the isolated included guest chains and the host α‐CD molecules, efficient proton spin diffusion was not observed between them in the IC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2086–2096, 2005     

Synthesis,characterization, and thermal properties of dendrimer‐star,block‐comb copolymers by ring‐opening polymerization and atom transfer radical polymerization

Novel and well‐defined dendrimer‐star, block‐comb polymers were successfully achieved by the combination of living ring‐opening polymerization and atom transfer radical polymerization on the basis of a dendrimer polyester. Star‐shaped dendrimer poly(?‐caprolactone)s were synthesized by the bulk polymerization of ?‐caprolactone with a dendrimer initiator and tin 2‐ethylhexanoate as a catalyst. The molecular weights of the dendrimer poly(?‐caprolactone)s increased linearly with an increase in the monomer. The dendrimer poly(?‐caprolactone)s were converted into macroinitiators via esterification with 2‐bromopropionyl bromide. The star‐block copolymer dendrimer poly(?‐caprolactone)‐block‐poly(2‐hydroxyethyl methacrylate) was obtained by the atom transfer radical polymerization of 2‐hydroxyethyl methacrylate. The molecular weights of these copolymers were adjusted by the variation of the monomer conversion. Then, dendrimer‐star, block‐comb copolymers were prepared with poly(L ‐lactide) blocks grafted from poly(2‐hydroxyethyl methacrylate) blocks by the ring‐opening polymerization of L ‐lactide. The unique and well‐defined structure of these copolymers presented thermal properties that were different from those of linear poly(?‐caprolactone). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6575–6586, 2006     

Poly(caprolactone‐co‐lactide)/perfluoropolyether block copolymers: Synthesis,thermal, and surface characterization

Poly[(caprolactone‐co‐lactide)‐b‐perfluoropolyether‐b‐(caprolactone‐co‐lactide)] copolymers (TXCLLA) were prepared by ring‐opening polymerization of D ,L ‐dilactide (LA2) and caprolactone (CL) in the presence of α,ω‐hydroxy terminated perfluoropolyether (Fomblin Z‐DOL TX) as macroinitiator and tin(II) 2‐ethylexanoate as catalyst. ¹H NMR analysis showed that LA2 is initially incorporated into the copolymer preferentially with respect to CL. A blocky structure of the polyester segment was also indicated by the sequence distribution analysis of the monomeric units. Differential scanning calorimetry analysis showed the compatibility between poly(lactide) (PLA) and poly(caprolactone) (PCL) blocks inside the amorphous phase with glass‐transition temperature values increasing from ?60 to ?15 °C by increasing the PLA content. Copolymers with high average length of CL blocks were semicrystalline with a melting temperature ranging from +35 to +47 °C. Surface analysis showed a high surface activity of TXCLLA copolymers with values of surface tension independent from the PLA/PCL content and very close to those of pure TX. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3588–3599, 2005     

Porous Biodegradable Polyesters, 3. Preparation of Porous Poly(ε‐caprolactone) Films from Blends by Selective Enzymatic Removal of Poly(L‐lactide)

Porous poly(ε‐caprolactone) (PCL) films were prepared by the removal of poly(L ‐lactide) (PLLA) from phase‐separated PLLA/PCL blend films using the selective Proteinase K™‐catalyzed hydrolysis of PLLA and subsequent elution of its water‐soluble oligomers and monomer into the surrounding hydrolysis media. Polarimetry, gravimetry, and differential scanning calorimetry (DSC) confirmed the complete removal of PLLA molecules from the blend films within 5 d of the Proteinase K‐catalyzed hydrolysis and therefore the formation of porous PCL films when the initial PLLA content [X_PLLA(0)(w/w) = PLLA/(PCL + PLLA)] of the blend films was in the range 0.3–0.5. The fragmentation of the blend film with X_PLLA(0) = 0.7 occurred when the Proteinase K‐catalyzed hydrolysis was continued for longer than 5 d. These findings exhibited that both the PLLA‐rich and PCL‐rich phases were continuous in the blend films for X_PLLA(0) ranges of 0.3–0.7 and of 0.3–0.5, respectively, and that the PCL‐rich phase became dispersed when X_PLLA(0) was increased to 0.7. The dependence of enzymatic hydrolysis rate on X_PLLA(0) strongly suggests that the Proteinase K‐catalyzed hydrolysis of the blend films occurs at the interfaces of PLLA‐rich and PCL‐rich phases as well as at the film surfaces.     

Microwave‐assisted synthesis of star‐shaped poly(ε‐caprolactone)‐block‐poly(L‐lactide) copolymers and the crystalline morphologies

A monomode microwave reactor was used for the synthesis of designed star‐shaped polymers, which were based on dipentaerythritol with six crystallizable arms of poly(ε‐caprolactone)‐b‐poly(L ‐lactide) (PCL‐b‐PLLA) copolymer via a two‐step ring‐opening polymerization (ROP). The effects of irradiation conditions on the molecular weight were studied. Microwave heating accelerated the ROP of CL and LLA, compared with the conventional heating method. The resultant hexa‐armed polymers were fully characterized by means of FTIR, ¹H NMR spectrum, and GPC. The investigation of thermal properties and crystalline behaviors indicated that the crystalline behaviors of polymers were largely depended on the macromolecular architecture and the length of the block chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis of biodegradable thermoplastic elastomers from ε‐caprolactone and lactide

This article reports the synthesis and the properties of novel thermoplastic elastomers of A‐B‐A type triblock copolymer structure, where the hard segment A is poly(l ‐lactide) (PLLA) and the soft segment B is poly(ε‐caprolactone‐stat‐d ,l ‐lactide) (P(CL‐stat‐DLLA)). The P(CL‐stat‐DLLA) block with DLLA content of 30 mol % was applied because of its amorphous nature and low glass transition temperature (T_g = approximately ?40 °C). Successive polymerization of l ‐lactide afforded PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLAs, which exhibited melting temperature (T_m = approximately 150 °C) for the crystalline PLLA segments and still low T_g (approximately ?30 °C) of the soft segments. The triblock copolymers showed very high elongation at break up to approximately 2800% and elastic properties. The corresponding d ‐triblock copolymers, PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLAs (PDLA = poly(d ‐lactide)) were also prepared with the same procedure using d ‐lactide in place of l ‐lactide. When the PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLA was blended with PDLA‐block‐P(CL‐stat‐DLLA)‐block‐PDLA, stereocomplex crystals were formed to enhance their T_m as well as tensile properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 489–495     

Methylated and pegylated PLA–PCL–PLA block copolymers via the chemical modification of di‐hydroxy PCL combined with the ring opening polymerization of lactide

Methylated and pegylated poly(lactide)‐block‐poly(ε‐caprolactone)‐block‐poly(lactide) copolymers, PLA–P(CL‐co‐CLCH₃)–PLA and PLA–P(CL‐co‐CLPEG)–PLA, were prepared in three steps: combining the formation of carbanion‐bearing dihydroxylated‐PCL, the coupling of iodomethane or bromoacetylated α‐hydroxyl‐ω‐methoxy‐poly(ethylene glycol) onto the carbanionic PCL, and finally the ring opening polymerization of DL ‐lactide initiated by the preformed grafted diOH‐PCL copolymers. The resulting block copolymers exhibited lower crystallinity, melting temperature, and hydrophobicity with respect to the original PCL. Degradation of the grafted copolymers was investigated in the presence of Pseudomonas cepacia lipase and compared with that of the triblock copolymer precursor. It is shown that the presence of the grafted substituents affected the enzymatic degradation of PCL segments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4196–4205, 2005     

Synthesis of PCL‐branched P(MMA‐co‐HEMA) to toughen electrospun PLLA fiber membrane

Electrospun biodegradable fiber mesh is a promising alternative scaffold for delivering progenitor cells for repairing damaged or diseased tissue, but its cripple mechanical stability has not met the requirement of tissue engineering yet. In this work, the well‐defined poly(ε‐caprolactone)‐branched poly(methyl methacrylate‐co‐hydroxyethylmethacrylate) (PCL‐PMH) has been successfully synthesized to toughen electrospun poly(l ‐lactide) (PLLA) fiber membrane. Characterization of the obtained nanofibrous meshes indicates that PCL‐PMH and PLLA can be well blended to make smooth fibers, and fibrous diameter vary little with blending PCL‐PMH. The aggregation state of two macromolecules is closely correlated with blend ratio, molecular structure, and molecular weight of PCL‐PMH, and only when PCL‐PMH and PLLA form good interfacial adhesion can PMH give full play to its potential for toughening the fiber membrane. The tensile strength and elongation at break of the blend are 6.20 MPa and 63.40% under the optimal conditions, respectively, and it also exhibits the representative feature of toughness materials. The blending fiber membrane is as no cytotoxic as original PLLA. This work will provide a new way for toughness of electrospun fiber membrane in practice.     

Synthesis,characterization, and micellization of PCL‐g‐PEG copolymers by combination of ROP and “Click” chemistry via “Graft onto” method

Biodegradable and biocompatible PCL‐g‐PEG amphiphilic graft copolymers were prepared by combination of ROP and “click” chemistry via “graft onto” method under mild conditions. First, chloro‐functionalized poly(ε‐caprolactone) (PCL‐Cl) was synthesized by the ring‐opening copolymerization of ε‐caprolactone (CL) and α‐chloro‐ε‐caprolactone (CCL) employing scandium triflate as high‐efficient catalyst with near 100% monomer conversion. Second, the chloro groups of PCL‐Cl were quantitatively converted into azide form by NaN₃. Finally, copper(I)‐catalyzed cycloaddition reaction was carried out between azide‐functionalized PCL (PCL‐N₃) and alkyne‐terminated poly(ethylene glycol) (A‐PEG) to give PCL‐g‐PEG amphiphilic graft copolymers. The composition and the graft architecture of the copolymers were characterized by ¹H NMR, FTIR, and GPC analyses. These amphiphilic graft copolymers could self‐assemble into sphere‐like aggregates in aqueous solution with diverse diameters, which decreased with the increasing of grafting density. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A new class of biodegradable hydrogels stereocomplexed by enantiomeric oligo(lactide) side chains of poly(HEMA‐g‐OLA)s

Two enantiomeric amphiphilic graft copolymers consisting of water soluble poly(2‐hydroxyethyl methacrylate) (HEMA) and biodegradable oligo(L ‐lactide) (OLLA) or oligo(D ‐lactide) (ODLA) were synthesized by free radical copolymerization. HEMA‐OL(D)LA macromonomers were synthesized by ring opening polymerization of L ‐ or D ‐lactide. Both HEMA‐OLA macromonomers and graft copolymers were characterized by NMR spectroscopy and gel permeation chromatography. Graft copolymers and their stereocomplexes were analyzed by wide angle X‐ray diffraction and differential scanning calorimetry (DSC). Due to the formation of stereocomplex crosslinks between poly(HEMA) main chains, amphiphilic, biodegradable hydrogels prepared by blending of two enantiomeric poly(HEMA‐g‐OLLA) and poly(HEMA‐g‐ODLA) degraded more slowly in phosphate buffered saline than individual optically pure poly‐(HEMA‐g‐OL(D)LA).     

Polyethylene‐poly(L‐lactide) diblock copolymers: Synthesis and compatibilization of poly(L‐lactide)/polyethylene blends

A model polyethylene‐poly(L ‐lactide) diblock copolymer (PE‐b‐PLLA) was synthesized using hydroxyl‐terminated PE (PE‐OH) as a macroinitiator for the ring‐opening polymerization of L ‐lactide. Binary blends, which contained poly(L ‐lactide) (PLLA) and very low‐density polyethylene (LDPE), and ternary blends, which contained PLLA, LDPE, and PE‐b‐PLLA, were prepared by solution blending followed by precipitation and compression molding. Particle size analysis and scanning electron microscopy results showed that the particle size and distribution of the LDPE dispersed in the PLLA matrix was sharply decreased upon the addition of PE‐b‐PLLA. The tensile and Izod impact testing results on the ternary blends showed significantly improved toughness as compared to the PLLA homopolymer or the corresponding PLLA/LDPE binary blends. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2755–2766, 2001