PLLA Segments Research Articles

Effects of the Chiral Interface and Orientation-Dependent Segmental Interactions on Twisting of Self-Assembled Block Copolymers.

The chirality effect on the self-assembly of block copolymers (BCPs) composed of chiral entities, denoted as chiral BCPs (BCPs*), gives rise to the formation of the helical phase (H*) due to intermolecular chiral interactions. The corresponding twisting of self-assembled H* might be initiated from the microphase-separated chiral interface and/or attributed to chiral orientation-dependent segmental interactions. To examine the origins of the twisting mechanisms, a series of polylactide-containing BCPs* with different sequences and molecular weights of chiral block, poly(l-lactide) (PLLA), and achiral block, poly(d,l-lactide) (PLA), were designed for self-assembling. Accordingly, the impact of sequence and length of the blocks on self-assembled BCPs* can be scrutinized. For the ones with the PLLA as a middle block, polystyrene-b-poly(l-lactide)-b-poly(d,l-lactide), the formation of H* can be achieved even with a short PLLA segment. By contrast, the self-assembled morphology of polystyrene-b-poly(d,l-lactide)-b-poly(l-lactide) with the PLA as a middle block is dependent upon the length of the PLA block. On the basis of the self-assembled results, the chirality effect on the self-assembly of BCP* is originated from both the chiral interface and the chiral orientation-dependent segmental interactions. The present work on the study of the formation mechanisms of the H* thus provides insights into the intermolecular chiral interactions from the self-assembly of BCP*.

Preparation, Characterization, and Mechanism for Biodegradable and Biocompatible Polyurethane Shape Memory Elastomers.

Thermally induced shape memory is an attractive feature of certain functional materials. Among the shape memory polymers, shape memory elastomers (SMEs) especially those with biodegradability have great potential in the biomedical field. In this study, we prepared waterborne biodegradable polyurethane SME based on poly(ε-caprolactone) (PCL) oligodiol and poly(l-lactic acid) (PLLA) oligodiol as the mixed soft segments. The ratio of the soft segments in polyurethanes was optimized for shape memory behavior. The thermally induced shape memory mechanism of the series of polyurethanes was clarified using differential scanning calorimeter (DSC), X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS). In particular, the in situ SAXS measurements combined with shape deformation processes were employed to examine the stretch-induced (oriented) crystalline structure of the polyurethanes and to elucidate the unique mechanism for shape memory properties. The polyurethane with optimized PLLA crystalline segments showed a diamond-shape two-dimensional SAXS pattern after being stretched, which gave rise to better shape fixing and shape recovery. The shape memory behavior was further tested in 37 °C water. The biodegradable polyurethane comprising 38 wt % PCL segments and 25 wt % PLLA segments and synthesized at a relatively lower temperature by the waterborne procedure showed ∼100% shape recovery in 37 °C water. The biodegradable polyurethane SME also demonstrated good endothelial cell viability as well as low platelet adhesion/activation. We conclude that the waterborne biodegradable polyurethane SME possesses a unique thermally induced shape memory mechanism and may have potential applications in making shape memory biodegradable stents or scaffolds.

Nucleating agent‐containing P(LLA‐mb‐BSA) multi‐block copolymers with balanced mechanical properties

ABSTRACTIn order to obtain high performance bioplastics and thermoplastic elastomers, P(LLA‐mb‐BSA) multi‐block copolymers containing 30 wt % and 70 wt % soft segment (PLBSA30 and PLBSA70 for short) were synthesized via chain extension and coupling of poly(L‐lactic acid) (PLLA) and poly(butylene succinate‐co‐adipate) (PBSA) prepolymers in the presence of 1% nucleating agent (NA). They were characterized with proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), thermal gravimetric analysis (TGA), transmission electron microscope (TEM), and tensile and impact test. The relatively high molecular weights of (Mn 8200 g/mol and 3100 g/mol for PLLA and PBSA, respectively) the polyester sequences are helpful to improve the PLLA crystallization and the flexibility of the PBSA soft segment. Nucleation effect further accelerates the crystallization of PLLA segment. The synergistic effect of these factors results in good balance between stiffness and toughness. PLBSA30s containing 1% zinc citrate (ZnCC) or talc behave as ultra‐tough bioplastics with ultrahigh impact strength over 50 kJ/m2 and excellent tensile properties. PLBSA70 containing 1% ZnCC possesses elongation at break of 600% and retains high modulus (56 MPa) and strength (16 MPa) and therefore behaves as an excellent thermoplastic elastomer. The excellent and balanced properties would extend the end applications of these PLLA‐based materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44777.

Structural evolution of poly(l-lactide) block upon heating of the glassy ABA triblock copolymers containing poly(l-lactide) A blocks

Abstract Two triblock ABA copolymers poly( l -lactide- b -dimethylsiloxane- b - l -lactide) (PLLA- b -PDMS- b -PLLA) and poly( l -lactide- b -ethylene glycol- b - l -lactide) (PLLA- b -PEG- b -PLLA) containing poly( l -lactide) were synthesized by ring opening polymerization of l -lactide using bis(hydroxyalkyl) terminated PDMS and hydroxyl end-capped polyethylene glycol as macroinitiators, respectively. Both the triblock copolymers were melt-quenched to −40 °C to prepare the amorphous samples. The melt morphology of the triblock copolymers was preserved upon cooling the melt to −40 °C. PLLA and PDMS blocks are immiscible in the melt, and the amorphous triblock copolymer shows two distinct glass transition temperatures ( T g ) on heating. On the other hand, PLLA and PEG segments are miscible and the triblock copolymer shows the single T g . Structural evolution of PLLA during heating of the amorphous ABA triblock copolymers has been investigated by measuring the variable temperature small-angle and wide-angle X-ray scattering (SAXS and WAXS) and FTIR spectra. In the case of PLLA- b -PDMS- b -PLLA triblock copolymer (immiscible system), the mesophase of PLLA was found to appear just above the T g of PLLA block (∼45 °C), and on further heating the mesophase changed to the regular α form at around 90 °C. On the other hand, in PLLA- b -PEG- b -PLLA (miscible system), the mesophase of PLLA was found to appear at lower temperature i.e. −20 °C, because of the enhanced molecular mobility of PLLA chains in the presence of PEG. However, irrespective of the mesophase formation temperature, the ordered α form has appeared at around 90 °C. In this way, during heating of the amorphous triblock copolymers, the PLLA block was found to crystallize into the ordered α form always through the mesophase just above the T g of PLLA. These results are helpful in understanding the regularization process of semicrystalline polymers in different environments.

Synthesis of poly(-lactide-co-5-amino-5-methyl-1,3-dioxan-2-ones)[P(L-LA-co-TAc)] containing amino groups via organocatalysis and post-polymerization functionalization

Abstract Poly( l -lactide-co-5-benzyloxycarbonylamino-5-methyl-1,3-dioxan-2-ones) (P(L-LA-co-TMAc)) containing amino groups were synthesized by the ring-opening polymerization of l -lactide(L-LA) and 5-benzyloxycarbonylamino-5-methyl-1,3-dioxan-2-one (TMAc), which was catalysed by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in solution or 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) in bulk. Followed by deprotection under acidic conditions, deprotected copolymer poly( l -lactide-co-5-amino-5-methyl-1,3-dioxan-2-ones)[P(L-LA-co-TAc)] was prepared. Compared to polymerization reactions catalysed by stannous octoate (Sn(Oct)2), a metallic catalyst, organocatalysts showed precise control over the composition and polydispersity index of the copolymers. Proton nuclear magnetic resonance (1H NMR), carbon-13 nuclear magnetic resonance (13C NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) analyses confirmed the polymeric structure and sequence distribution of the product, which indicated that L-LA and TMAc formed random copolymers. Relatively longer PLLA segments were incorporated into the copolymer during the initial polymerization period due to differences in the reactivity of the two monomers, especially in the DBU-catalysed system. And copolymers with gradient property were obtained. The amino bearing deprotected copolymers served as macro-initiator of the subsequent ROP of benzyl- l -glutamate-N-carboxyanhydride(BLG-NCA). Finally, the multi-composite graft copolymer P(L-LA-co-TAc)-g-PBLG was obtained through post-polymerization functionalization.

Micro- and nanostructures of polylactide stereocomplexes and their biomedical applications

The discovery of stereocomplexation, secondary interaction between enantiomeric poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) provides a method for the creation of novel biomaterials with distinctive chemical and physical stability. Stereocomplexation opens a new way for the preparation of diverse micro- and nanostructures such as uniform microspheres, hollow particles, micelles, nanocrystals, nanofibres, nanotubes and polymerosomes. Herein, we describe the design of stereocomplex assemblies for specific applications and methods for their preparation. This review focuses primarily on the use of stereocomplex assemblies in biomedical applications due to the improved stability and physicochemical properties in comparison to enantiomeric polylactides. To make the polylactide stereocomplexes soluble in water and, as a consequence, to improve compatibility with the human body, various amphiphilic copolymers with PLLA and PDLA enantiomeric segments can be prepared. Stereocomplexation can facilitate their self-assembly into micro- and nanoparticles, stabilize the particle size and morphology and can also have an influence on the in vivo degradation rate and cytotoxicity of these materials. Stimuli-responsiveness in stereocomplex assemblies can be achieved by copolymerization of lactide with, for example, thermoresponsive N-isopropylacrylamide or amino acids with pH-sensitive pendant groups. Stereocomplex micro- and nanoparticles are used for encapsulation of various bioactive compounds: anticancer drugs, antibiotics and proteins. Finally, examples of materials in which high thermal and mechanical stabilities delivered as a result of stereocomplexation play a crucial role, i.e. hydrogels, nanofibres, microcellular foams and artificial skin, are described. The preparation of biomaterials and biomedical systems based on polylactide stereocomplex assemblies opens new opportunities in this field. © 2015 Society of Chemical Industry

Synthesis and properties of Poly(L-lactide)-Poly(ɛ-caprolactone) multiblock copolymers by the self-polycondensation of diblock macromonomers

Poly(L-lactide) (PLLA)–poly(ɛ-caprolactone) (PCL) multiblock copolymers (MBCs) were synthesized by the self-polycondensation of PLLA–PCL diblock copolymers. We synthesized three types of MBCs with degrees of polymerization of the lactide–caprolactone segments of 12–15 (MBC1), 24–26 (MBC2) and 49–50 (MBC3) to investigate the effect of the segment length on the properties. The strict control over the terminal functional groups of the diblock copolymers resulted in the formation of high-molecular weight MBCs (Mw=(2.4–4.9) × 105 g mol−1). Differential scanning calorimetry (DSC) measurements suggest the phase mixing of PLLA and PCL segments in amorphous region and that the MBCs contain PCL-rich regions, the extent of which is influenced by the segment length. The X-ray diffraction patterns of the MBCs contain diffraction peaks originating from lactide segment crystals. High moduli (95–43 MPa) and elongation at break (~500%) were observed for all the MBC films. The MBCs hydrolyzed slowly in comparison with PLLA, and the hydrophilic porous films of MBC2 were obtained. To estimate their potential as adhesion barrier films, the hydrophilic porous MBC films were implanted onto the abdominal side walls of rats. The MBC films effectively prevented the adhesion at the target site, but intermediate adhesion was observed at the suture site where the MBC film was fixed. Poly(L-lactide)–poly(ɛ-caprolactone) multiblock copolymers (MBCs) were synthesized by self-polycondensation of diblock copolymers. Strict control of the terminal functional groups of the diblock copolymers resulted in the formation of high-molecular-weight MBCs (Mw=2.4–4.9 × 105 g mol−1).

Hydrolytic degradation of cellulose-graft-poly(l-lactide) copolymers

A series of cellulose-g-poly(l-lactide) (cellulose-g-PLLA) copolymers with 30.65–85.21 % PLLA weight content and the molar substitution of PLLA (MSPLLA) from 0.99 to 12.73 were synthesized via the homogeneous graft-from reaction in 1-allyl-3-methylimidazolium chloride (AmimCl) with 4-dimethylaminopyridine (DMAP) acting as the catalyst. In common organic solvents, the solubility of obtained graft copolymers was better than cellulose and strongly depended on the MSPLLA. The hydrolytic degradation of cellulose-g-PLLA copolymers was investigated in phosphate buffered solution (PBS, pH 7.4) at 37 °C. Interestingly, it was found that, when the MSPLLA was below 8.83, the hydrolytic degradation rate of cellulose-g-PLLA copolymers was obviously faster than that of both pristine cellulose and PLLA. Moreover, as the MSPLLA decreased, the cellulose-g-PLLA copolymers showed a more rapid weight loss, due to its higher hydrophilicity. Both XPS and 1H NMR analyses demonstrated the degradation occurred mainly at PLLA segments. The morphological observations indicated that, during the hydrolytic degradation, the graft copolymers firstly experienced a surface erosion process, and then the bulk erosion happened.

Poly(ω-pentadecalactone)-b-poly(l-lactide) Block Copolymers via Organic-Catalyzed Ring Opening Polymerization and Potential Applications

Poly(pentadecalactone)-b-poly(l-lactide) (PPDL-b-PLLA) diblock copolymers were prepared via the organic catalyzed ring-opening polymerization (ROP) of l-lactide (l-LA) from PPDL macroinitiators using either 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). Synthesis of PLLA blocks targeting degrees of polymerization (DP) up to 500 were found to yield diblock copolymers with crystalline PPDL and PLLA segments when TBD was used as the catalyst. The synthesis was further improved in a one-pot, two-step process using the same TBD catalyst for the synthesis of both segments. The application of these diblock copolymers as a compatibilizing agents resulted in homogenization of a biobased PLLA/poly(ω-hydroxytetradecanoate) (90:10) blend upon a melt-process, yielding enhanced material properties.

Synthesis of biodegradable thermoplastic elastomers from ε‐caprolactone and lactide

ABSTRACTThis 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 (Tg = approximately −40 °C). Successive polymerization of l‐lactide afforded PLLA‐block‐P(CL‐stat‐DLLA)‐block‐PLLAs, which exhibited melting temperature (Tm = approximately 150 °C) for the crystalline PLLA segments and still low Tg (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 Tm as well as tensile properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 489–495

Solvent-induced crystallization behaviors of PLLA ultrathin films investigated by RAIR spectroscopy and AFM measurements.

The crystallization of poly(L-lactide acid) (PLLA) ultrathin films induced by different solvents was investigated using reflection-absorption infrared (RAIR) spectroscopy and atomic force microscopy (AFM). Irregular PLLA dendrite lamellae grew in the flat-on orientation with dichloromethane solvent before being redissolved after longer induction times owing to the strong interaction between the PLLA segments and solvent molecules. Faster formation of PLLA spherulites was induced with acetone than with dichloromethane, and these remained unchanged with increasing induction time because of the polarity difference between the PLLA segments and acetone molecules. PLLA ultrathin films could not be induced to crystallize using chloroform because of the very strong interactions between the chloroform (CHCl3) molecules and PLLA amorphous chains, which caused the CHCl3 solvent molecules to rapidly permeate the PLLA random coils and dissolve the amorphous chains. These phenomena are attributed to solvent-specific competition between solvent-induced crystallization and dissolution effects in PLLA ultrathin films, which ultimately leads to the higher degree of crystallinity obtained with acetone than with dichloromethane.

Long terminal linear alkyl group as internal crystallization accelerating moiety of poly(l-lactide)

Poly(l-lactide) (PLLA) polymers having terminal n-alkyl groups with a wide variety of lengths (C0–C22) were synthesized by ring-opening polymerization of l-lactide in the presence of coinitiators of l-lactic acid (C0), 1-hexanol (C6), 1-dodecanol (C12), and 1-docosanol (C22) and their segmental mobility and non-isothermal and isothermal crystallization behavior were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffractometry (WAXD). Glass transition and cold crystallization temperatures of melt-quenched samples during heating decreased with an increase in the length of terminal n-alkyl groups. The enhanced PLLA segmental mobility and hydrophobic interaction-based accelerated PLLA nucleation by the presence of terminal long n-alkyl groups should have caused the accelerated non-isothermal and isothermal crystallization of PLLA segments traced by cold crystallization temperature during heating and by radial growth rate of spherulites, respectively. The crystallization accelerating effect became higher with the length of terminal n-alkyl groups. The effects of the length of terminal n-alkyl group on the crystalline growth mechanism of PLLA at the lowest crystallizable temperature was insignificant, whereas the effects of the length of terminal n-alkyl group on the nucleation mechanism of PLLA chains were significant and insignificant for PLLA having Mn of 6–7 × 103 of 2 × 104 g mol−1, respectively. WAXD measurements revealed that the transition crystallization temperature at which crystalline modification changes from δ-form to α-form was affected by the length of terminal n-alkyl group for PLLA having Mn of 6–7 × 103 g mol−1, but was not altered by the length of terminal n-alkyl group for PLLA having Mn of 2 × 104 g mol−1.

Poly(l-lactic acid)-block-poly(butylene succinate-co-butylene adipate) Multiblock Copolymers: From Synthesis to Thermo-Mechanical Properties

Multiblock copolymers poly(l-lactic acid)-block-poly(butylene succinate-co-butylene adipate)s (abbr. P(LLA-mb-BSA)s) are synthesized via a polycondensation/chain extension/coupling method using binary chain extenders. A poly(l-lactic acid) (PLLA) prepolymer synthesized via direct melt polycondensation of l-lactic acid is rapidly chain extended with a bis (2-oxazoline) to form hydroxyl terminated dimer, and the dimer is then chain extended/coupled with a hydroxyl terminated poly(butylene succinate-co-butylene adipate) (PBSA) prepolymer by a diisocyanate. The microstructure is characterized with GPC, 1H NMR and FTIR, and the thermo-mechanical properties are investigated with DSC, TGA, DMA, tensile, and impact testing. In the copolymers, the PLLA hard segments are crystallizable and the PBSA soft segments are amorphous, and only melting of PLLA segment was detected. Two independent glass transitions corresponding to both segments are observed, suggesting incompatibility between the two kinds of segments. The tensile modulus and strength decrease while the elongation at break and impact strength increase with increasing the weight percentage of PBSA segment (ϕw,PBSA). The mechanical properties can be tuned in wide range by ϕw,PBSA, from toughened thermoplastics with excellent tensile modulus, strength and impact strength to thermoplastic elastomers with high elongation at break.

Dendritic Crystallization of Poly(l-lactide)/poly(d-lactide) Stereocomplexes in Ultrathin Films

Ultrathin films (12–125 nm) of poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blends of different compositions have been crystallized between 180 and 210 °C, i.e., above the melting point of each polymer crystallized separately. The overall crystal shape depends on the temperature, film thickness and ratio of the two polyenantiomers in the blends. In nonequimolar blends, lamellae show curvatures, and the sense of the curvature is determined by the chirality of the polyenantiomer in excess, blend ratio, film thickness, crystallization temperature and lamellar orientation (flat-on or edge-on). The curvature of the stereocomplex lamellae is ascribed to the unequal amount of PLLA and PDLA segments at the crystal growth front, creating an unbalanced mechanical stress at the chain folding surfaces which can be released by a curvature of the growth tip.

Chiral poly(l-lactic acid) driven helical self-assembly of oligo(p-phenylenevinylene)

The synthesis and self-assembly of a series of copolyesters incorporating varying mol ratios of an achiral oligo(p-phenylenevinylene) (OPV) into the backbone of a chiral poly(L-lactic acid) (PLLA) via high temperature solution blending is reported. The polymers were characterized by 1H NMR spectroscopy and size exclusion chromatography (SEC) and their bulk properties were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WXRD). The DSC and WXRD analyses confirmed the crystallinity and π–π stacking of the OPV units in the PLLA–OPV copolyester. Absorption, emission and lifetime-decay studies showed that the OPV chromophore was highly aggregated in the solid state. The solid powder samples of the copolyesters exhibited an intense, red shifted aggregate emission beyond 470 nm. Circular dichroism (CD) spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies revealed that the PLLA–OPV copolyester formed a self-assembled architecture, in which the helical organization of the achiral OPV segments was dictated by the chiral PLLA segments. The observed CD signal and AFM image accounted for the right-handed helical self-assembly of the OPV chromophore in the solid state. These results confirmed the effect of the chiral PLLA segment on tuning the OPV chromophore packing and supramolecular chirality in molecular aggregates. The methodology illustrated here provides opportunities for the design of a new class of hierarchical, self-assembled architectures, based on organic π-conjugated materials and the manipulation of their optical properties.

An Amylose‐Poly(l‐lactide) Inclusion Supramolecular Polymer: Enzymatic Synthesis by Means of Vine‐Twining Polymerization Using a Primer–Guest Conjugate

An inclusion supramolecular polymer composed of amylose and poly(l‐lactide) (PLLA) is successfully synthesized by phosphorylase‐catalyzed enzymatic polymerization using a malto­heptaose‐functionalized poly(l‐lactide) (G7‐PLLA) as a primer–guest conjugate substrate according to vine‐twining polymerization. The product forms a polymeric continuum of an inclusion complex in which PLLA is included by an amylose chain enzymatically elongated from the other G7‐PLLA. The product is characterized by powder X‐ray diffraction, 1H NMR spectroscopy, and gel‐permeation chromatography measurements. The analytical results indicate that such an inclusion supramolecular polymer is efficiently produced, even under the low concentration of the guest polymer, PLLA, owing to the high local concentration of PLLA segments in the present system because G7‐PLLA forms aggregates 50–110 nm in diameter in aqueous media. image

Relatively Short Poly(D‐lactide) Segments as Intra‐Crystallization‐Accelerating Moieties in Stereo Diblock Poly(lactide)s

The homo‐crystallization of stereo diblock poly(lactide)s with high number‐average molecular weight () values of ca. 105 g mol−1 is accelerated by the incorporated relatively short poly(D‐lactide) (PDLA) segments with = 2.0–7.7 × 103 g mol−1 during heating and PDLA segments with = 3.5 and 7.7 × 103 g mol−1 during cooling. The relatively short PDLA segments linked to PLLA segments, which have sufficient lengths to form stereocomplex crystallites, are very effective to shorten a crystallization timeand to increase the productivity and thermal stability.

Synthesis, Self‐Assembly, and Properties of Homoarm and Heteroarm Star‐Shaped Inorganic–Organic Hybrid Polymers with a POSS Core

AbstractNovel homoarm and heteroarm star‐shaped inorganic–organic hybrid polymers with a polyhedral oligomeric silsesquioxane (POSS) core are prepared via click chemistry of azide POSS [POSS‐(N3)8], alkynyl poly(L‐lactide) (PLLA), and alkynyl poly(ethylene oxide) (PEO). The melting and crystallization behaviors of the polymers can be adjusted by altering the PLLA to PEO ratio. The hybrid polymers reveal unique crystalline morphology due to the influence of the star‐shaped structure and the mutual influence of PLLA and PEO. The hybrid polymers show different thermostabilities, owing to the different compositions of the polymers. The hydrophilicity can be adjusted by alternating the composition of the PLLA and PEO segments. In addition, the sizes of the polymer micelles change with the change of the ratio of PLLA and PEO arms in the hybrid polymers.magnified image

Studies on the degradation of poly(L-lactide-r-trimethene carbonate) copolymers

Biodegradable poly(L-lactide-r-trimethene carbonate) copolymers (P(LLA-co-TMC)) with different compositions were synthesized. The degradation of the copolymers was carried out in phosphate buffer saline solutions (pH = 7.4) at 37 °C. The compositions, structure and properties of the copolymers in degradation were characterized with 1H-NMR, DSC, XRD, GPC, and SEM. The weight loss of the P(LLA-co-TMC) 50/50 was much faster than that of P(LLA-co-TMC) 85/15 and PLLA homopolymer. Interestingly, though the molecular weight of the compolymers decreased greatly during degradation, the compositions were rarely varied. After long time degradation, the PLLA segments were induced to crystallize in the P(LLA-co-TMC) 85/15 copolymer. The SEM observation of the surface and cross-section of P(LLA-co-TMC) 85/15 copolymer films found it was similar to the bulk degradation of PLLA homopolymer.

Tunable Mesoporous Lamellar Silicas Prepared Using Poly(ethylene oxide-<I>b</I>-L-lactide) and Poly(ethylene-<I>b</I>-ethylene oxide-<I>b</I>-L-lactide) Block Copolymers as Templates

In this study, we synthesized poly(ethylene oxide-b-L-lactide) (PEO-PLLA) diblock copolymers and poly(ethylene-b-ethylene oxide-b-L-lactide) (PE-PEO-PLLA) triblock terpolymers as templates for the preparation of mesoporous lamellar silicas, possessing single, bimodal, or trimodal pore size distributions, through an evaporation-induced self-assembly (EISA) approach. As templates, we synthesized the diblock copolymers EO114LLA26 and EO114LLA130 and the triblock terpolymers E13EO42LLA26 and E13EO42LLA35 using simple ring-opening polymerization. Small-angle X-ray scattering, transmission electron microscopy, and N2 sorption measurements revealed that the mesoporous silicas displayed the morphologies of either lamellar silica walls featuring a distribution of many short cylindrical mesopores or pure lamellar structures. The morphology was greatly affected by the nature of the template (diblock or triblock copolymer) and the molecular weight of the PLLA segment in the block copolymer.