PLLA Block Research Articles

Fully biobased biodegradable poly(l‐lactide)‐b‐poly(ethylene brassylate)‐b‐poly(l‐lactide) triblock copolymers: synthesis and investigation of relationship between crystallization morphology and thermal properties

AbstractWell‐defined poly(l‐lactide‐b‐ethylene brassylate‐b‐l‐lactide) (PLLA‐b‐PEB‐b‐PLLA) triblock copolymer was synthesized by using double hydroxyl‐terminated PEBs with different molecular weights. Gel permeation chromatography and NMR characterization were employed to confirm the structure and composition of the triblock copolymers. DSC, wide‐angle X‐ray diffraction, TGA and polarized optical microscopy were also employed to demonstrate the relationship between the composition and properties. According to the DSC curves, the cold crystallization peak vanished gradually with decrease of the PLLA block, illustrating that the relatively smaller content of PLLA may lead to the formation of a deficient PLLA type crystal, leading to a decrease of melting enthalpy and melting temperature. Multi‐step thermal decompositions were determined by TGA, and the PEB unit exhibited much better thermal stability than the PLLA unit. Polarized optical microscopy images of all the triblock samples showed that spherulites which develop radially and with an extinction pattern in the form of a Maltese cross exhibit no ring bond. The growth rate of the spherulites of all triblock samples was investigated. The crystallization capacity of PLLA improved with incorporation of PLLA, which accords with the DSC and wide‐angle X‐ray diffraction results. © 2019 Society of Chemical Industry

Uniform Biodegradable Fiber-Like Micelles and Block Comicelles via "Living" Crystallization-Driven Self-Assembly of Poly(l-lactide) Block Copolymers: The Importance of Reducing Unimer Self-Nucleation via Hydrogen Bond Disruption.

Fiber-like micelles based on biodegradable and biocompatible polymers exhibit considerable promise for applications in nanomedicine, but until recently no convenient methods were available to prepare samples with uniform and controllable dimensions and spatial control of functionality. "Living" crystallization-driven self-assembly (CDSA) is a seeded growth method of growing importance for the preparation of uniform 1D and 2D core-shell nanoparticles from a range of crystallizable polymeric amphiphiles. However, in the case of poly(l-lactide) (PLLA), arguably the most widely utilized biodegradable polymer as the crystallizable core-forming block, the controlled formation of uniform fiber-like structures over a substantial range of lengths by "living" CDSA has been a major challenge. Herein, we demonstrate that via simple modulation of the solvent conditions via the addition of trifluoroethanol (TFE), DMSO, DMF and acetone, uniform fiber-like nanoparticles from PLLA diblock copolymers with controlled lengths up to 1 μm can be prepared. The probable mechanism involves improved unimer solvation by a reduction of hydrogen bonding interactions among PLLA chains. We provide evidence that this minimizes undesirable unimer aggregation which otherwise favors self-nucleation that competes with epitaxial crystallization from seed termini. This approach has also allowed the formation of well-defined segmented block comicelles with PLLA cores via the sequential seeded-growth of PLLA block copolymers with different corona-forming blocks.

Bio-based and Biodegradable Electrospun Fibers Composed of Poly(L-lactide) and Polyamide 4

Novel bio-based and biodegradable block copolymers were synthesized by “click” reaction between poly(L-lactide) (PLLA) and polyamide 4 (PA4). Upon tuning the molar mass of PLLA block, the properties of copolymers and electrospun ultrafine fibers were investigated and compared with those of PLLA and PA4 blends. PLLA and PA4 were found incompatible and formed individual crystalline regions, along with reciprocal inhibition in crystallization. Electrospun fibers were highly hydrophobic, even if hydrophilic PA4 was the rich component. The crystallinity of either PLLA or PA4 decreased after electrospinning and PLLA-rich as-spun fibers were almost amorphous. Immersion tests proved that fibers of block copolymers were relatively homogeneous with micro-phase separation between PLLA and PA4. The fibrous structures of copolymers were different from those of the fibers electrospun from blends, for which sheath-core structure induced by macro-phase separation between homopolymers of PLLA and PA4 was confirmed by TEM, EDS, and XPS.

Elevation of the flow temperature of gels formed by nano fibers of Poly(l-lactic acid) by surface crystallization induced by block copolymers

Block copolymers of poly (l-lactic acid) (PLLA) and polystyrene with different lengths of PLLA blocks entered into the network structures of PLLA gels formed with complex crystals with solvent molecules. The induced changes of the structure and the flow temperature of the gels were investigated to elucidate the mechanism of the block copolymers to elevate the flow temperature. The block copolymer with shorter PLLA blocks elevated the flow temperature of the PLLA gels from 40 °C to 70 °C by immersing in the block copolymer solution with a lower concentration (0.5 wt%). For the block copolymers with longer PLLA blocks, higher concentrations (2.0 wt%) were necessary to elevate the flow temperature to 70 °C, and the flow temperature was elevated to 80 °C by immersing more concentrated solutions (3.0 wt%). This behavior can be explained by assuming that the surface crystallization of PLLA fibers induced by the block copolymers elevated the flow temperature to 70 °C, and the reinforcement of the fibers by spherical structure of the block copolymers elevated the flow temperature to 80 °C, was proposed based on the experimental results.

Bromine-functionalized poly(carbonate-co-lactide)s: Synthesis, characterization and post-polymerization functionalization

The ring-opening copolymerization of lactide with carbonate is an available strategy to incorporate reactive groups to the pendent sites of copolymer for further functional modification. A series of random and block copolymers were synthesized from l-lactide (L-LA) and 2-bromomethyl-2-methyltrimethylene carbonate (BMTC) using dodecanol as initiator and stannous octoate as catalyst. The structures of the copolymers were characterized by nuclear magnetic resonance (1H NMR, 13C NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The composition of the copolymers can be controlled through changing the feed ratios of nBMTC/nL-LA. It was found the random P(BMTC-co-LLA) copolymers had the semicrystalline characteristic due to the relative long block-like segments of PLLA (LL, PLLA = 5.3–7.3) and the polar interactions from bromo groups, but their crystallinity (Xc, PLLA) and melting temperature (Tm, PLLA) decreased when the BMTC content increased. The Xc, PLLA and Tm, PLLA of P(BMTC-b-PLLA) block copolymers were relatively higher than the corresponding random copolymers, and approached gradually to the pure PLLA with the increase of the molecular weight of PLLA block. Finally, the pendent bromo groups of P(BMTC-co-LLA) were easily transformed into azides, which could proceed the azide-alkyne click reaction smoothly and quantitatively at room temperature.

Isodimorphic aliphatic copolyester as midblock of poly(l-lactide)-based triblock copolymers towards largely enhanced impact toughness

Biobased dihydroxy-terminated aliphatic copolyesters were synthesized from melt-polycondensation of 1,6-adipic acid with 1,6-hexanediol and 1,10-decanediol. The isodimorphic behavior of the copolyesters was explored to identify the pseudo-eutectic copolyester, which was selected as macro-initiator for ring opening polymerization of l-lactide to prepare poly(l-lactide)-b-poly(hexamethylene-co-decamethylene adipate)-b-poly(l-lactide) (PLLA-b-PHDA-b-PLLA) triblock copolymers varying PLLA block length. The blocky structure was confirmed by GPC and NMR, and the influence of PLLA block length on physical and mechanical properties was investigated. Impact testing showed that the impressive impact strength was achieved, that is, the values of PLLA10-PHDA-PLLA10 and PLLA20-PHDA-PLLA20 were largely enhanced to 357.2 J/m and 259.6 J/m, respectively, about 9–12 times greater than that of PLLA homopolymer (28.6 J/m). SEM micrographs of impact fractured surface showed that the triblock copolymers underwent a transition from brittle fracture of neat PLLA to ductile fracture, which is attributed to the introduction of flexible aliphatic polyester as middle soft building block of triblcok copolymers. This work demonstrated isodimorphic aliphatic copolyesters as midblock of PLLA-based triblock fully biobased biodegradable copolymers towards highly toughened PLLA material.

Effect of Composition and Molecular Structure of Poly(l-lactic acid)/Poly(ethylene oxide) Block Copolymers on Micellar Morphology in Aqueous Solution.

The effect of the hydrophobic block length in diblock (PLLA x- b-PEO113, x = 64, 166, 418) and triblock (PLLA y- b-PEO91- b-PLLA y, y = 30, 52, 120) copolymers of l-lactic acid and ethylene oxide on the structure of micelles prepared by dialysis was studied by wide- and small-angle X-ray scattering in dilute aqueous solution, dynamic light scattering, transmission electron microscopy, atomic force microscopy, and force spectroscopy. It was found that the size of the crystalline PLLA core is weakly dependent on the PLLA block length. In addition to individual micelles, a number of their micellar clusters were detected with characteristic distance between adjacent micelle cores decreasing with an increase in PLLA block length. This effect was explained by the change in the conformation of PEO chains forming the micellar corona because of their overcrowding. Force spectroscopy experiments also reveal a more stretched conformation of the PEO chains for the block copolymers with a shorter PLLA block. A model describing the structure of the individual micelles and their clusters was proposed.

Improvement in melt flow property and flexibility of poly(l-lactide)-b-poly(ethylene glycol)-b-poly(l-lactide) by chain extension reaction for potential use as flexible bioplastics

Poly(l-lactide) (PLLA) is a biodegradable bioplastic that has been widely investigated for use instead of petroleum-based plastics. However, its practical applications have been limited by its brittleness. Herein, a high molecular weight triblock copolymer of poly(l-lactide)-b-poly(ethylene glycol)-b-poly(l-lactide) (PLLA-PEG-PLLA) was synthesized by ring-opening polymerization of l-lactide using stannous octoate and PEG as the initiating system. The effect of an epoxy-based chain extender on the thermal properties, melt flow index (MFI), phase morphology and tensile properties of the PLLA-PEG-PLLA were investigated and compared to PLLA homopolymer. Chain-extended PLLA-PEG-PLLA and its films were prepared by reactive melt blending and compression molding, respectively. The flexible PEG blocks significantly improved both crystallization of PLLA blocks and strain at break of PLLA-PEG-PLLA films. The chain extension can decrease MFI of both the PLLA and PLLA-PEG-PLLA but their crystallizabilities were suppressed. All the PLLA-PEG-PLLA films with and without chain extension had no phase separation. The tensile properties of PLLA-PEG-PLLA films increased by the chain extension. The results showed that the chain-extended PLLA-PEG-PLLA have potential for use as highly flexible bioplastics.

Short poly(ethylene glycol) block initiation of poly(l‐lactide) di‐block copolymers: a strategy for tuning the degradation of resorbable devices

AbstractThe current range of medical applications of resorbable polyesters could be hugely expanded if more effective strategies for tailoring degradation rate were available. Block copolymerisation with poly(ethylene glycol) (PEG) has been shown to reduce degradation times; however, to date, this has relied on the addition of PEG to short lengths of polyester. This results in copolymers with high fractions of PEG and low molecular weights, reducing the potential range of applications. Furthermore, there has been no systematic study of the relative lengths of the blocks. In this work, we employed short hydroxyl‐functionalised methoxy‐terminated mPEG to initiate the synthesis of poly(l‐lactide) (PLLA), resulting in controlled di‐block copolymers with short mPEG blocks and long PLLA blocks. A controlled series of polymers was made with PLLA lengths (60 < Mn (kg mol−1) < 200) and mPEG lengths (550 < Mn (g mol−1) < 5000) giving very low mPEG content (0.1–1.5 wt%). We found that, despite the low fraction of mPEG, water uptake and the rate of hydrolytic degradation, k, increased. Significantly, k for the polymers was dependent only on the presence of mPEG, and was little affected by mPEG length or PLLA length in the ranges studied. Moreover, mass loss began in all polymers when Mn of the polymer fell below a threshold of about 20 kg mol−1 and depended on both the initial molecular weight of PLLA and the presence (but not the length) of mPEG. Short‐chain mPEG therefore provides a new route for targeted, temporal control of resorbable polyesters for biomedical devices. © 2018 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Fast Crystallization and Toughening of Poly(L-lactic acid) by Incorporating with Poly(ethylene glycol) as a Middle Block Chain

High molecular weight poly(L-lactic acid)-poly(ethylene glycol)-poly(L-lactic acid) (PLLA–PEG–PLLA; PLGL) triblock copolymers with various lengths of the PLLA blocks were synthesized by ringopening polymerization of L-lactide. The amorphous and crystalline PLLA and PLGL films were prepared by hot pressing with different temperature treatments. PLLA and PEG blocks exhibited good miscibility in the amorphous PLGL samples, while phase separation occurred in the crystalline ones. The flexible PEG blocks not only accelerated the crystallization rate of PLLA but also greatly improve its flexibility. The crystallization time of PLGL copolymers shorten to less than 5 min and copolymers showed much better flexibility than neat PLLA, the maximum fracture strain reached about 600% for amorphous sample. The processing time of PLLA was greatly shortened and the brittleness of material was improved.

How the Complex Interplay between Different Blocks Determines the Isothermal Crystallization Kinetics of Triple-Crystalline PEO-b-PCL-b-PLLA Triblock Terpolymers

PEO-b-PCL-b-PLLA triblock terpolymers are fascinating triple-crystalline materials. In this work, the isothermal crystallization kinetics of these terpolymers evaluated by differential scanning calorimetry (DSC) is presented for the first time and compared to analogous PCL-b-PLLA diblock copolymers and to PLLA, PCL, and PEO homopolymers. The results are complemented by in situ SAXS/WAXS synchrotron experiments. One-, two-, and three-step crystallization protocols were employed to study the crystallization kinetics of the blocks. At PLLA block crystallization temperatures, both PCL and PEO molten chains caused a strong plasticizing effect on the PLLA block crystallization, and the overall crystallization rate of the PLLA block in the terpolymers was higher than that in the PLLA-b-PCL diblock copolymers. In the case of the PCL block, the crystallization was followed after PLLA was fully crystallized (two-step crystallization). A nucleating effect induced by the previously formed PLLA crystals was observed. ...

On the enhancement of thermo-mechanical properties of poly(L-lactide) by solid-state extrusion for biodegradable spinal fixation devices

Poly(L-lactide) (PLLA) has been receiving attention as a material for bone fixation devices because of its good biocompatibility and biodegradability. However, its mechanical properties are weaker than those of natural bone. Interestingly, solid-state extrusion can enhance the mechanical properties by orienting the polymer chains, and molecular weight is one of the key factors in this process. In this study, we optimized the heating conditions for vacuum compression molding to make a PLLA block for the solid-state extrusion process. We confirmed that the molecular weight of the material decreased with increasing heating temperature and time. In the case of a low molecular weight such as 120 kDa, the heating temperature and time were optimized to 190 oC and 90 min, respectively. Moreover, we fabricated a plate, a rod, and a square pole of PLLA by solid-state extrusion for the development of a bone plate, a screw, and an interbody cage. PLLA plates having various molecular weights (150-250 kDa) were extruded to various draw ratios to investigate the effect of molecular weight on the solid-state extrusion process. The mechanical properties such as flexure stress and flexure modulus increased with increasing draw ratio, which in turn increased with increasing molecular weight of the polymer. In addition, we determined that the crystallinity of PLLA dramatically increased when the draw ratio was more than 4. In addition, the orientation of the crystals by solid-state extrusion was confirmed by using X-ray diffraction, and the orientation effect increased with increasing draw ratio of the extruded PLLA. PLLA plates made by solid-state extrusion could be manufactured into bone plates. Furthermore, we fabricated a PLLA rod by solid-state extrusion and vacuum compression molding. The flexural properties of the extruded rod were better than those of the molded rod. We could, therefore, fabricate a screw using the extruded PLLA rod. Finally, interbody cages were made by using poly(L,D/L-lactide) (PLDLLA), PLLA of various molecular weights (150-250 kDa), and PLLA enhanced by solid-state extrusion. The results of the compression tests indicated that PLLA was generally stronger than PLDLLA and that the extruded PLLA had the best mechanical properties. Consequently, it is possible to successfully manufacture biodegradable spinal fixation devices, including plates, screws, and interbody cages, by solidstate extrusion. Moreover, their mechanical properties could be improved by increasing the draw ratio and molecular weight.

Fully bio‐based poly(ɛ‐capolactone)/poly(lactide) alternating multiblock supramolecular polymers: Synthesis, crystallization behavior, and properties

ABSTRACTSupramolecular poly(ɛ‐capolactone)/poly(lactide) alternating multiblock copolymers were prepared by UPy‐functionalized poly(lactide)‐b‐poly(ɛ‐capolactone)‐b‐poly(lactide) copolymers. The prepared supramolecular polymers (SMPs) exhibit the characteristic properties of thermoplastic elastomers. The stereo multiblock SMPs (sc‐SMPs) were formed by blending UPy‐functionalized poly(l‐lactide)‐b‐PCL‐b‐poly(l‐lactide) (l‐SMPs) and UPy‐functionalized poly(d‐lactide)‐b‐PCL‐b‐poly(d‐lactide) (d‐SMPs) due to stereocomplexation of the PLLA and PDLA blocks. Sc‐SMPs with low content of d‐SMPs (≤20%) are transparent, elastic solids, while those having high d‐SMPs content are opaque, brittle solids. The effects of l‐SMPs/d‐SMPs mixing ratios on thermal, crystallization behaviors, crystal structure, mechanical and hydrophilic properties of sc‐SMPs were deeply investigated. The incorporation of UPy groups depresses the crystallization of polymer, and the stereocomplex formation accelerates the crystallization rate. The used initiator functionalized polyhedral oligomeric silsesquioxanes causes a different effect on the crystallization of PLA and PCL blocks. The tensile strength and elongation at break of ld/dd‐SMPs (d represents the initiator diethylene glycol) are significantly larger than that of lp/dp‐SMPs (p represents the initiator polyhedral oligomeric silsesquioxanes), and their heat resistance and hydrophilicity can be also modulated by the l‐SMPs/d‐SMPs mixing ratios and the different initiators. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45575.

Thermal Annealing to Modulate the Shape Memory Behavior of a Biobased and Biocompatible Triblock Copolymer Scaffold in the Human Body Temperature Range.

A biodegradable and biocompatible electrospun scaffold with shape memory behavior in the physiological temperature range is here presented. It was obtained starting from a specifically designed, biobased PLLA-based triblock copolymer, where the central block is poly(propylene azelate-co-propylene sebacate) (P(PAz60PSeb40)) random copolymer. Shape memory properties are determined by the contemporary presence of the low melting crystals of the P(PAz60PSeb40) block, acting as switching segment, and of the high melting crystal phase of PLLA blocks, acting as physical network. It is demonstrated that a straightforward annealing process applied to the crystal phase of the switching element gives the possibility to tune the shape recovery temperature from about 25 to 50 °C, without the need of varying the copolymer's chemical structure. The thermal annealing approach here presented can be thus considered a powerful strategy for "ad hoc" programming the same material for applications requiring different recovery temperatures. Fibroblast culture experiments demonstrated scaffold biocompatibility.

Preparation of Cellulose Nanocrystal-Reinforced Poly(lactic acid) Nanocomposites through Noncovalent Modification with PLLA-Based Surfactants.

Cellulose nanocrystal (CNC)-reinforced poly(lactic acid) (PLA) nanocomposites were prepared by twin-screw extrusion followed by injection-molding using a masterbatch approach. Noncovalent modification of CNCs was performed with two different poly(l-lactide) (PLLA)-based surfactants to improve the filler/matrix compatibility. They both have a PLLA block that is expected to improve the compatibility with the PLA matrix and differ by the polar head. It consists of either a poly(ethylene glycol) (PEG) block (PEG-b-PLLA) or an imidazolium group (Im-PLLA), that is able to interact with the surface of the CNCs. The morphological, structural, thermal, rheological, and mechanical properties of the nanocomposites were investigated. The different modes of interaction of the polar head of the surfactant lead to different properties. However, the global decrease in the molecular weight of PLA, induced by the short PLLA blocks from the surfactants and the possible degradation during melt processing, results in a plasticization effect and impacts the crystallization of the matrix.

Poly(l-lactide-b-butylene succinate-b-l-lactide) triblock copolymer: A multi-functional additive for PLA/PBS blend with a key performance on film clarity

Blending of poly(butylene succinate) (PBS) with poly(lactic acid) (PLA) is an effective way to fine tune PLA brittleness. However, the immiscibility between these two polymers leads to product defects in terms of strength and clarity. The present work proposes a simple triblock copolymer, i.e. poly(l-lactide-b-butylene succinate-b-l-lactide) (PLLA-b-PBS-b-PLLA), as a multi-functional additive, i.e. compatibilizer, plasticizer, and nucleating agent for improving the PLA/PBS blend. Based on a critical content of PLA/PBS (at 80/20 wt%) which gives the opaque film, an addition of PLLA-b-PBS-b-PLLA induces drastic changes in crystallization behavior and mechanical properties. The ratio between PLLA and PBS block length, and the amount are the factors to fine tune the PLA/PBS blend. The PLLA40-b-PBS28-b-PLLA40 at 3 phr is an optimal condition to tune the blends with the decreases in glass transition temperature (Tg) (from ∼50 °C to ∼20 °C) as well as an increase in the elongation at break (for two-fold). At that time, the rapid co-crystallization of PBS and PLA in the blend as seen from the small and homogeneously dispersed spherulite results in a key performance to enhance the clarity of the blend film. The present work demonstrates how the block copolymer of PLA and PBS performs its multi-function for miscibility, toughness, and clarity of PLA/PBS blends.

Homo- and Stereocomplex Crystallization of Star-Shaped Four-Armed Stereo Diblock Copolymers of Crystalline and Amorphous Poly(lactide)s: Effects of Incorporation and Position of Amorphous Blocks.

Star-shaped four-armed stereo diblock copolymers with an amorphous poly(dl-lactide) (PDLLA) core and a crystalline poly(l-lactide) (PLLA) or poly(d-lactide) (PDLA) shell (4-DL-L and 4-DL-D) and with a crystalline PLLA or PDLA core and amorphous PDLLA shell (4-L-DL and 4-D-DL) copolymers were synthesized. The effects of incorporation and position of amorphous PDLLA blocks on homo- and stereocomplex (SC) crystallization behavior of unblended copolymers and their blends (4-DL-L/4-DL-D and 4-L-DL/4-D-DL) were investigated during isothermal crystallization from the melt and DSC heating. The incorporated amorphous PDLLA blocks disturbed the SC crystallization and orientation of SC lamellae in the copolymer blends as well as homocrystallization and orientation of homocrystalline lamellae in the unblended copolymers compared to those reported for four-armed PLLA/four-armed PDLA homopolymer blends or four-armed PLLA homopolymers, irrespective of the position of amorphous PDLLA blocks. The disturbance effect was stronger for the amorphous PDLLA shell than for the amorphous PDLLA core. The crystallizability was higher for SC crystallites in the copolymer blends than for homocrystallites in the unblended copolymers, irrespective of the position of amorphous PDLLA blocks. SC crystallization in the copolymer blends disclaimed the positional effects of crystalline PLLA and PDLA blocks and amorphous PDLLA blocks on spherulite growth rate and crystallinity.

Synthesis, swelling, degradation and cytocompatibility of crosslinked PLLA-PEG-PLLA networks with short PLLA blocks

A series of triblock macromonomers with the general structure PLAa-PEGb-PLAa with acrylate end-groups and very short segments of PLA have been synthesized and characterized for potential use in the treatment of periodontitis. In the proposed application aqueous solutions of the triblock macromonomers would be injected into the pockets formed around the teeth and then crosslinked via photo-induced free radical polymerization to form drug-laden hydrogels. One of the macromonomers with the structure PLA4-PEG45-PLA4 showed optimum properties for the proposed application and was chosen for a more detailed study. In the study, the nature of the hydrogels formed by the macromonomer and by its copolymerization with PEG16 diacrylate has been investigated, along with its swelling and degradation in PBS at 37°C and pH 7.4. The hydrogels swell to equilibrium in water or PBS within approximately 5h, with swelling ratios in the range 4.5–3.5 and penetrant diffusion coefficients 1.5–2.4×106cm2s−1in PBS, depending on the PLA4-PEG45-PLA4 macromonomer content over the range 1.00–0.80wt fraction. The swollen hydrogels have an open pore structure, with the diameter of the largest pores in excess of 25μm. A detailed spectroscopic study confirmed that degradation in PBS proceeds as expected via hydrolysis of the lactide segments, and the polymer matrix completely dissolves after ≈22 days. The potential for control of degradation kinetics using the comacromonomer composition was also demonstrated. The cytotoxicity towards fibroblasts and osteoblasts, two important cell types involved in tissue repair and bone regeneration, has also been thoroughly evaluated. The hydrogels, and the products of hydrolytic degradation, were found to be non-cytotoxic towards these particular cells.

PLLA Crystallization in Linear AB and BAB Copolymers ofl-Lactide and 2-Dimethylaminoethyl Methacrylate

Well-defined poly(l-lactide-b-2-dimethylaminoethyl methacrylate) (PLLA-b-PDMAEMA) linear AB block copolymers and BAB block copolymers with PLLA as the central block (PDMAEMA-b-PLLA-b-PDMAEMA) were synthesized by combined ring-opening polymerization and atom transfer radical polymerization. Molar masses of the PLLA block vary from 13K to 19K and the PDMAEMA block from 5K to 35K. Thermal properties, morphology, and crystallization kinetics of the copolymers were analyzed for crystallization conducted in the bulk, in thick and thin films, and in solution as well as for a limited number of stereocomplexes of diblock and triblock copolymers with poly(d-lactide) in thin films and of partially quaternized diblock copolymers. In the bulk, it is shown that crystallization rates are reduced and morphologies disordered when adding a PDMAEMA block to PLLA; these tendencies are more pronounced in the triblock compared to diblock copolymers of the same PDMAEMA content. Usually, G, the local growth rate, and K, the over...

Synthesis and self-assembly of amphiphilic and biocompatible poly(vinyl alcohol)-block-poly(l-lactide) copolymer

Abstract Well-defined amphiphilic and biocompatible poly(vinyl alcohol)- block -poly( l -lactide) copolymers (PVA- b -PLLA) were synthesized by the combination of reversible addition-fragmentation chain transfer (RAFT), ring opening polymerization (ROP), and click chemistry. First, an innovative azide-functionalized xanthate mediated chain transfer agent (CTA) [S-(3-azidopropyl propanamide)-( O -butyl xanthate)] was synthesized and used for vinyl acetate (VAc) polymerization through RAFT. Then, azide-terminated poly(vinyl acetate) (azide-PVAc) was converted to the corresponding azide-terminated poly(vinyl alcohol) (azide-PVA) through hydrolysis. Alkyne-terminated poly ( l -lactide) (alkyne-PLLA) was synthesized via ROP using a bifunctional initiator, having an alkyne and a hydroxyl group. Finally, azide-PVA and alkyne-PLLA were coupled by 1,3 cycloaddition click reaction to get PVA- b -PLLA. Synthesized azide-PVAc, azide-PVA, alkyne-PLLA and PVA- b -PLLA were characterized by size exclusion chromatography and 1 H NMR spectroscopy. The self-assembly of PVA- b -PLLA in water was investigated by transmission electron microscope, atomic force microscopy, dynamic light scattering and 1 H NMR spectroscopy. Spherical micelles in water were clearly observed. The critical micelle concentration of PVA- b -PLLA in water was determined by fluorescence spectroscopy, and it was decreased with increasing the molecular weight of PLLA block. PVA- b -PLLA exhibited low cytotoxicity which could be used in biomedical application.