Linear PLLA Research Articles

Ring-opening polymerization of emulsion-templated deep eutectic system monomer for macroporous polyesters with controlled degradability.

Biodegradable polyesters with interconnected macroporosity, such as poly(l-lactide) (PLLA) and poly(ε-caprolactone) (PCL), have gained significant importance in the fields of tissue engineering and separation. This study introduces functional macroinitiators, specifically polycaprolactone triol (PCLT) and polyethylene glycol (PEG), both OH-terminated, in the solventless ring-opening polymerization (ROP) of a liquid deep eutectic system monomer (DESm) composed of LLA and CL at a 30 : 70 molar ratio, respectively. The macroinitiators selectively initiate the organocatalyzed ROP of LLA in the DESm during the first polymerization stage, thereby modifying the PLLA architecture. This results in the formation of either branched or linear PLLA copolymers depending on the macroinitiator, PCLT and PEG, respectively. In the second stage, the ROP of the CL, which is a counterpart of the DESm, produces PCL that blends with the previously formed PLLA. The insights gained into the PLLA architectures during the first stage of the DESm ROP, along with the overall molecular weight and hydrophobicity of the resulting PLLA/PCL blend in bulk, were advantageously used to design polymerizable high internal phase emulsions (HIPEs) oil-in-DESm. By incorporating a liquid mixture of DESm and macroinitiators (PCLT or PEG), stable HIPE formulations were achieved. These emulsions sustained the efficient organocatalyzed ROP of the continuous phase at 37 °C with high conversions. The resulting polymer replicas of the HIPEs, characterized by macroporous and interconnected structures, were subjected to a degradation assay in PBS at pH 7.4 and 37 °C and remained mechanically stable for at least 30 days. Notably, they exhibited the capability to sorb crude oil in a proof-of-concept test, with a rate of 2 g g-1. The macroporous and interconnected features of the polyHIPEs, combined with their inherent degradation properties, position them as promising degradable polymeric sorbents for efficient separation of hydrophobic fluids from water.

Hybrid interpenetrating network of polyester coronary stent with tunable biodegradation and mechanical properties

Poly(l-lactide) (PLLA) is an important candidate raw material of the next-generation biodegradable stent for percutaneous coronary intervention, yet how to make a polyester stent with sufficient mechanical strength and relatively fast biodegradation gets to be a dilemma. Herein, we put forward a hybrid interpenetrating network (H-IPN) strategy to resolve this dilemma. As such, we synthesize a multi-functional biodegradable macromer of star-like poly(d,l-lactide-co-ɛ-caprolactone) with six acrylate end groups, and photoinitiate it, after mixing with linear PLLA homopolymer, to trigger the free radical polymerization. The resultant crosslinked polymer blend is different from the classic semi-interpenetrating network, and partial chemical crosslinking occurs between the linear polymer and the macromer network. Combined with the tube blow molding and the postprocessing laser cutting, we fabricate a semi-crosslinked-polyester biodegradable coronary stent composed of H-IPN, which includes a physical network of polyester spherulites and a chemical crosslinking network of copolyester macromers and a part of homopolymers. Compared with the currently main-stream PLLA stent in research, this H-IPN stent realizes a higher and more appropriate biodegradation rate while maintaining sufficient radial strength. A series of polymer chemistry, polymer physics, polymer processing, and in vitro and in vivo biological assessments of medical devices have been made to examine the H-IPN material. The interventional implanting of the H-IPN stent into aorta abdominalis of rabbits and the follow-ups to 12 months have confirmed the safety and effectiveness.

Fabrication of novel flower-bundle microspheres via an inverse-emulsion freezing-phase-separation technology

• Flower-bundle porous microspheres are prepared by using a four-branched polylactide. • The flower-bundle porous microspheres preserve their crystalline structure during the inverse-emulsion freezing process. • The flower-bundle porous microspheres have good biocompatibility. • The flower-bundle porous microspheres act as cell carriers favor cell affinity. Biodegradable microspheres play great roles in biomedical applications, whereas how to finely adjust their size and morphological microstructure remains a big challenge. Herein, a kind of flower-bundle porous microspheres was developed by using a four-branched polylactide (b-PLLA) via an inverse-emulsion freezing liquid-liquid phase separation technology. The flower-bundle porous microspheres formation mechanism may come from the preservation of its crystalline structure during the cooling process due to the rapid crystallization of b-PLLA, while the linear PLLA (l-PLLA) with slow crystallization capacity tend to form a kind of amorphous dense structure. In contrast to less porous l-PLLA microspheres, b-PLLA microspheres have flower-bundle porous structure and porous interconnectivity, presenting a better cell affinity and proliferation of L929 cells. The special inverse-emulsion freezing liquid-liquid phase separation technology, together with macromolecular architecture adjustability strategy, may offer a new approach to fabricate biodegradable microspheres with size and porous structural tunability for extensive biomedical applications, including drug delivery, tissue engineering and medical cosmetology.

Fabrication of low-density poly(lactic acid) microcellular foam by self-assembly crystallization nucleating agent

In this study, branched PLLA was obtained by mixing linear PLLA with chain extender. And adding different contents of self - assembled nucleating agent to further modify its crystallization properties. The crystallization and rheological properties were tested by POM, DSC and rheometer. It is proved that TMC- 300 was an effective crystallization nucleating agent for branched PLLA, self- assembled fiber could provide large number of crystallization nucleation sites to improve the crystallinity. The appropriate content of TMC- 300 can be self- assembled into fiber network framework to regulate the crystallization behavior of branched PLLA, and to increase storage modulus step by step. It can improve the melt strength of branched PLLA for low- density microcellular foaming at high temperature. The increase in the number of crystallization region and formation of self- assembly network framework can not only provide large number of cell nucleation sites, but also limit the growth of PLLA cells. And low- density microcellular foam with crystallinity of 36.5% was prepared by further synergistic interaction between TMC fiber framework and induced PLLA crystal. Compared with pure branched PLLA, the density of PLLA microcellular foams added with 1wt% TMC is increased by two orders of magnitude, the cell size is reduced to 10 μμm, and the foaming expansion ratio is up to ten- fold at 130 ℃.

Entirely environment-friendly polylactide composites with outstanding heat resistance and superior mechanical performance fabricated by spunbond technology: Exploring the role of nanofibrillated stereocomplex polylactide crystals

This study aims at investigating the manufacturing and characterization of all-polylactide composites prepared by melt spunbond spinning technology. To do so, a series of asymmetric stereocomplex polylactide (SC-PLA) blends (PLLA 95 wt%/PDLA 5 wt%) was melt spun. To examine the impact of molecular structure of PDLA, the blends of linear PLLA, and low and high molecular weight as well as branched PDLAs, were subjected to a single step spunbond process. DSC thermograms of the samples showed two melting temperatures at around 170 °C and 210 °C, which were attributed to the melting of homo and stereocomplex crystals, respectively. The samples were spun at 190 °C, between the homo and stereocomplex crystals' melting temperatures, and at 230 °C, above the stereocomplex crystals' melting temperature. Morphology images showed the formation of fibers in the range of 40–50 μm. Shear rheological measurements revealed that the spun SC-PLA samples had a substantially higher viscosity and storage modulus in the low frequency region, and higher shear thinning behavior, compared to the non-spun samples. Extensional rheology measurements also showed that the spun samples demonstrated strain hardening behavior. Substantial enhancement of rheological properties was noted for the samples containing the branched and high molecular weight PDLA spun at 230 °C. After etching, the spun samples at 190 °C exhibited small spherical crystals with diameters in the range of 80–90 nm, whereas comparatively thin fibers in the size range of 60–70 nm were observed for the samples spun at 230 °C. Remarkable enhancements up to 100% and 60% was noted for the tensile modulus and strength, respectively, of the spun SC-PLA samples. The spun fibers also demonstrated a considerable reduction in boiling water and hot air shrinkage. The distinctive role of nanofibrillated stereocomplex crystals as a rheology modifier and a crystallization nucleating agent makes PLA more sustainable and paves the way for the fabricated all-PLA composites in applications requiring high heat resistance and superior mechanical performance. The present study unequivocally indicates a huge potential for the sustainable entirely all-PLA products manufactured by fiber in fiber and, indeed, unfolds unknown opportunities for PLA-based merchandises in future.

Shear-Induced Crystallization of Star and Linear Poly(L-lactide)s.

The influence of macromolecular architecture on shear-induced crystallization of poly(L-lactide) (PLLA) was studied. To this aim, three star PLLAs, 6-arm with Mw of 120 and 245 kg/mol, 4-arm with Mw of 123 kg/mol, and three linear PLLAs with Mw of 121, 240 and 339 kg/mol, were synthesized and examined. The PLLAs were sheared at 170 and 150 °C, at 5/s, 10/s and 20/s for 20 s, 10 s and 5 s, respectively, and then cooled at 10 or 30 °C/min. Shear-induced crystallization during cooling was followed by a light depolarization method, whereas the crystallized specimens were examined by DSC, 2D-WAXS, 2D-SAXS and SEM. The effect of shear depended on the shearing conditions, cooling rate and polymer molar mass but it was also affected by the macromolecular architecture. The shear-induced crystallization of linear PLLA with Mw of 240 kg/mol was more intense than that of the 6-arm polymer with similar Mw, most possibly due to its higher Mz. However, the influence of shear on the crystallization of the star polymers with Mw close to 120 kg/mol was stronger than on that of their linear analog. This was reflected in higher crystallization temperature, as well as crystallinity achieved during cooling.

The crystallization behavior of poly(l-lactide)/poly(d-lactide) blends: effect of stirring time during solution mixing

Blending of poly(l-lactide) and poly(d-lactide) (PLLA, PDLA) results in the formation of poly(lactide) stereocomplex crystallites (SC). For the preparation method, numerous reports employed solution mixing and stirring to receive a product with uniform performance. However, the effect of stirring time during solution mixing on the subsequent crystallization behavior did not clear yet, and which is important for solution crystallization, casting and spinning. In this paper, linear PLLA and PDLA with various molecular weights were synthesized. The PLLA and PDLA solutions were mixed together and stirred for different times before casting. Results revealed that the structures of PLA SC and homochiral crystallites (HC) did not vary with change in the stirring time. More amount of content of SC with uniform structure and less amount of content of HC were produced in the specimens stirred for longer time. When the specimens crystallized either from the melt or from the melt-quenching, less amount of content of crystallites (total crystallinity of SC and HC) was produced and the melting temperature of SC and HC depressed in the specimens that were stirred for longer time. With the increase in molecular weights, the effect of stirring time on the crystallization behaviors declined. This investigation provides a route to tailor the crystallization behavior of PLLA/PDLA specimens.

다기능기 아민계 개시제를 이용한 Star-Shaped PLLA 벌크와 용액 중합 및 결정성 비교

Poly(L-lactide)(PLLA)의 약물 전달 시스템에서의 낮은 친수성과 높은 결정성을 향상시키기 위하여 2, 3, 4개의 OH기를 가지는 아민계 개시제를 이용하여 star-shaped PLLA를 벌크와 용액 중합으로 합성하였다. Sn(Oct)₂를 중합촉매로 개시제로는 N-butyldiethanolamine, triethanolamine, N,N,N",N"-tetrakis(2-hydroxyethyl)ethylendiamine을 사용하였다. 합성된 고분자는 시차주사열량계, X-선 회절, 편광광학현미경을 통해 결정 형태와 결정 성장 거동을 확인하였다. 벌크 중합으로 합성된 star-shaped PLLA는 선형 PLLA와 비교했을 때 녹는점, 결정성이 낮았으며 결정의 크기가 작으며 결정 성장 속도가 느렸다. 용액 중합으로 합성된 PLLA는 벌크 중합보다 선형 PLLA와 star-shaped PLLA의 녹는점, 결정성, 결정 성장 속도가 차이가 크지 않았다. In this study, star-shaped PLLA was synthesized by using 2, 3 and 4 OH group-contained amine initiators to improve hydrophilicity and to decrease crystallinity of poly(L-lactide) (PLLA) drug delivery system. Tin(II) 2-ethylhexanoate (Sn(Oct)₂) was selected as a polymerization catalyst and N-butyldiethanolamine (NBDA), triethanolamine (TEA), N,N,N",N"-tetrakis(2-hydroxyethyl)ethylendiamine (TEED) were used as initiators. PLLA polymerization was carried out through bulk polymerization and solution polymerization. The synthesized polymers were characterized by differential scanning calorimetry (DSC) and crystal morphology and crystal growth behavior were confirmed by X-ray diffraction (XRD) and polarized optical microscopy (POM). Star-shaped PLLA synthesized by bulk polymerization showed lower melting point and crystallinity, smaller crystal size, and slower crystal growth rate than linear PLLA. The PLLA synthesized by solution polymerization showed no significant difference in melting point, crystallinity, and crystal growth rate between linear PLLA and star-shaped PLLA.

Blends of linear and peroxide‐modified branched polylactide for extrusion coating

The purpose of the present work was to improve melt rheological properties of linear poly(L‐lactide) (PLLA) by melt blending with peroxide‐modified branched PLLA for extrusion coating. Peroxide‐modified PLLA, ie, PLLA melt extruded with 0.3 wt% of tert‐Butyl‐peroxybenzoate (TBPB); 2,5‐dimethyl‐2,5‐(tert‐butylperoxy)‐hexane (Lupersol 101 [LOL1]); and benzoyl peroxide was added to linear PLLA in ratios of 5, 15, and 30 wt%. All blends showed increased zero shear viscosity, elastic feature (storage modulus, decreased tan delta), and shear sensitivity. The blends' properties were mostly dependent on the peroxide applied for the modification and, to some extent, on the amount of added peroxide‐modified PLLA. Rheological models suggest that all blend compositions are mainly immiscible. Thermal properties were unchanged; all materials remained amorphous, though the enthalpy of cold crystallization was slightly increased. Extrusion coating on paperboard was conducted with PLLA and peroxide‐modified PLLA blends (90:10). All blends were processable; however, only that made with 2,5‐dimethyl‐2,5‐(tert‐butylperoxy)‐hexane (LOL1) afforded a smooth high‐quality coating surface with improved line speed. Adhesion levels between fibre and plastic and heat seal performance were marginally reduced compared with pure PLLA (3051D). The water vapour transmission measurements with 2,5‐dimethyl‐2,5‐(tert‐butylperoxy)‐hexane (LOL1) showed acceptable water transmission levels, being only slightly higher than for neat PLLA coating.

Stereocomplex Crystallization of Star-Shaped Four-Armed Stereo Diblock Poly(lactide) from the Melt: Effects of Incorporated Linear One-Armed Poly(l-lactide) or Poly(d-lactide).

Star-shaped four-armed stereo diblock poly(lactide) (4-LD) and linear one-armed PLLA or PDLA (1-L or 1-D) having a molecular weight similar to that of 4-LD [higher molecular weight 1-L(H) or 1-D(H)] and that of one block of 4-LD [lower molecular weight 1-L(L) or 1-D(L)] were synthesized, and the effects of incorporated 1-L or 1-D on the isothermal and nonisothermal crystallization of 4-LD blends from the melt were investigated. Solely stereocomplex crystallites were formed in unblended 4-LD and 4-LD blends incorporated with 1-L or 1-D during isothermal and nonisothermal crystallization. Incorporated 1-L or 1-D increased normalized stereocomplex crystallinity and accelerated cold nonisothermal crystallization and isothermal crystallization. The accelerating effect became higher with decreasing the molecular weight of 1-L or 1-D. The crystalline growth mechanism was not altered by the incorporation of 1-L and 1-D, whereas the crystalline growth geometry changed from line to sphere or circle, depending on the type of sample and Tc. The difference in crystallization half time and cold crystallization temperature between 4-LD/1-L(H) and 4-LD/1-D(H) blends or 4-LD/1-L(L) and 4-LD/1-D(L) blends was explained by the difference in radial growth rate and spherulite density, which was further discussed considering the non-interpenetrating and interpenetrating models.

Competitive Stereocomplexation and Homocrystallization Behaviors in the Poly(lactide) Blends of PLLA and PDLA-PEG-PDLA with Controlled Block Length.

Stereocomplex poly(lactide) (PLA) was obtained by solution blending of linear PLLA and PDLA-PEG-PDLA. Effects of the L/D ratios, PEG block, and PDLA block on stereocomplexation of the blends are systemically discussed. The full stereocomplex PLA can be acquired by solution blending when L/D ratios are in the range of 7/3–5/5. The experiment results demonstrated that the stereocomplex degree of PLLA/PDLA-PEG-PDLA prepared by melt blending was closely related to the PEG block and PDLA block. POM results indicated that the blends with high L/D ratio showed large disordered spherulites, and the typical Maltese cross pattern was observed as the L/D ratios decreased. The results of PEG block on the stereocomplexation of PLLA/PDLA-PEG-PDLA revealed that the PEG blocks possessed two sides: accelerating agent for the mobility of polymer chains and decreasing nucleation capacity due to their diluting effect. The effect of PDLA block on the stereocomplexation of the blends was also well investigated. The results showed that the crystallization of sc-crystallites and hc-crystallites in the PLLA/PDLA-PEG4k-PDLA blends with different PDLA blocks presents an obvious competition relationship, and this is not beneficial to the formation of sc-crystallites with increasing PDLA block. The melting behavior of PLLA/PDLA-PEG4k-PDLA with different PDLA blocks after isothermal crystallization showed that the blends could achieve full stereocomplex when the crystallization temperature exceeded 160 °C, and a crystallite with high perfection could be formed as the crystallization temperature increased. This study systemically investigated the effects of the L/D ratios, PEG block, PDLA block, and crystallization conditions on stereocomplex crystallization of PLLA/PDLA-PEG-PDLA blends, which can provide potential approaches to control the microstructure and physical performances of PLLA/PDLA-PEG-PDLA blends.

Uniaxial stretching behavior of polylactide with long chain branching

The investigation about the uniaxial stretching behavior of fully crystallized poly(L-lactide)s (PLLA) containing long chain branching (LCB) is carried out by two dimensional wide angle X-ray scattering (2D-WAXS) and differential scanning calorimetry (DSC). The controlled sample is the linear PLLA containing nucleating agents which owns the similar degree of crystallinity and crystalline morphologies as that of PLLA LCB. The results show that much more chain entanglements in the amorphous area of PLLA LCB make the LCB sample be able to bear much larger stress and then reach larger elongation when it breaks. Although the original lamellae are more difficult to be damaged in PLLA LCB due to the more chain entanglements compared with linear PLLA, the final crystal orientation is much better for it. The higher melting point indicates that the extended chain crystals in this stretched LCB sample are more perfect, especially at high drawing temperature. The original topological structure of chains is supposed to be the governing factor which determines the different evolution of crystalline structures under strain.

Synthesis of multi-arm poly(l-lactide) and its modification on linear polylactide

Multi-arm poly(l-lactide)s (PLLAs) were prepared by using alcohols with different numbers of hydroxyl groups as initiator and Sn(Oct)2 as catalyst. The structure and composition was confirmed by NMR and GPC analysis. A series of blends of PLLA/multi-arm PLLA were prepared by melt-mixing. Several techniques were applied to investigate the effects of multi-arm PLLA on the melt rheology, crystallization, thermal stability, morphology and mechanical properties of the linear PLLA. Multi-arm PLLA enhanced crystallization rate of PLLA as a nucleating agent. Rheological analysis showed that the viscosity of PLLA at low frequencies increased after addition of multi-arm PLLA. In addition, the tensile strength was increased with the increase of multi-arm PLLA and can achieve a maximum. FE-SEM measurements revealed that the surface of blends was homogenous, indicating good compatibility between PLLA and multi-arm PLLA. The results had an important guiding role in PLA modification, which provided an opportunity for generating new PLA blending systems with enhanced properties.

Rheology and crystallization behavior of asymmetric PLLA/PDLA blends based on linear PLLA and PDLA with different structures

In this study, several asymmetric poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) blends were prepared by adding small amounts of PDLA with different structures into linear PLLA matrix. The effect of PDLA on rheological behavior, crystallization behavior, nucleation efficiency and spherulite growth of PLLA was investigated. Rheological results indicated that PLLA/PDLA blends showed solid-like viscoelastic behavior at low temperature (<200°C), and the cross-linking density of PLLA/PDLA melt at 180°C followed the order: PLLA/6PDLA > PLLA/L-PDLA > PLLA/3PDLA > PLLA/4PDLA. No-isotherm and isotherm crystallization results indicated that the crystallization capacity of PLLA/PDLA blends was strongly related to the PDLA structure, crystallization temperature and thermal treatment temperature. Furthermore, the dimension of crystal growth during isotherm crystallization presented the obvious dependent on the PDLA structure. The nucleation efficiency of sc-crystallites in the blends and spherulite density during isothermal crystallization were also studied. Nucleation efficiency of sc-crystallites in the PLLA/S-PDLA blends showed the obvious dependent on thermal treatment temperature with respect to PLLA/L-PDLA, and nucleation efficiency sc-crystallites in the PLLA/S-PDLA blends first decreased and then increased as the thermal treatment temperature increased. Spherulite density of PLLA/PDLA blends was also related to thermal treatment temperature and the PDLA structure. This study has discussed the temperature dependence of the stereocomplex networks between PLLA and PDLA with different structure, and then its consequential influence on rheology and crystallization capacity of PLLA, which would provide the theoretical direction for PLA processing. Copyright © 2016 John Wiley & Sons, Ltd.

Multi‐arm star polymers of lactide obtained in melt in the presence of hyperbranched oligoglycerols

AbstractMulti‐arm star poly(l‐lactide) (PLLA) was synthesized in bulk, via ring‐opening polymerization of l‐lactide initiated by: trimethylolpropane, pentaerythritol, dipentaerythritol, myo‐inositol and hyperbranched polyglycerols. The synthesis was carried out on a laboratory scale and also in a model research installation equipped with a 2 L polymerization reactor. Matrix‐assisted laser desorption ionization time‐of‐flight analysis of the products synthesized in the presence of simple polyols and tin 2‐ethylhexanoate revealed that the reactions were not entirely selective and the final products were a mixture of multi‐arm star, linear and cyclic PLLA. The reactions co‐initiated by polyglycerols (PGs) led to polymer mixtures with molar masses in the range 13.5–102 kg mol−1 and intrinsic viscosity significantly lower than that of linear PLLA with the same molar mass. In order to obtain more hydrophobic PG initiator, a suitable method of modification of PG structure was developed. The PG and modified PG branching agents were used to prepare multi‐arm star PLLA in the model semi‐technical installation. Molar masses of the resulting polymers were in the range 169–249 kg mol−1 and exhibited much lower intrinsic viscosity than the linear homologue. The rheological properties of synthesized materials with commercial PLLA blends as well as thermal and mechanical properties were analysed. © 2016 Society of Chemical Industry

Formation, structure and promoting crystallization capacity of stereocomplex crystallite network in the poly(lactide) blends based on linear PLLA and PDLA with different structures

A series of asymmetric PLLA/PDLA blends based on linear PLLA and PDLA (linear PDLA and star-shaped PDLA) were prepared by solution blending, and stereocomplex crystallites (sc-crystallites) were formed between PLLA and various PDLA due to strong hydrogen bonding. Rheological results indicated that the melt strength of PLLA was improved due to the network structure of sc-crystallites in the PLLA melt. The effect of PDLA on rheological behavior of the melt decreased in the following order: 6PDLA > L-PDLA > 3PDLA > 4PDLA. Dissolution experiment revealed that the formed network structure could be formed by interparticle polymer chains or branched points. Nonisothermal and isothermal crystallization showed that the promoting crystallization of sc-crystallites for PLLA was closely related to thermal treatment temperature, crystallization temperature and the structure of PDLA, and the PDLA structure could change the pattern of crystal growth during isothermal crystallization. Nucleation efficiency of sc-crystallites during non-isothermal crystallization decreased with increasing of arm numbers of PDLA. POM results also demonstrated that the nucleation and spherulite growth during isothermal crystallization were affected by the PDLA structure. This study has systemically investigated the effects of the PDLA structure on rheology and crystallization capacity of asymmetric PLLA/PDLA blends, which would provide potential approaches to control the microstructure and physical performances of PLLA/PDLA blends.

Catechin-Modified Polylactide Stereocomplex at Chain End Improved Antibiobacterial Property.

Using different type of initiators, the antibacterial moieties are introduced at the chain end of poly(L,L-lactide) (PLLA) and poly(D,D-lactide) (PDLA), and the thermal properties are simultaneously improved using the stereocomplex approach. The physical interaction of polymers and antibacterial compounds is investigated. The double bonds at the chain end are utilized for the interaction of silver ion; however, the silver ions are not detected after stereocomplexation of PLLA and PDLA. On the other hand, catechin (CT) is selected as an initiator precursor of lactide polymerization, protecting the phenolic hydroxyl groups. The linear PLLA and PDLA are obtained by the initiator, resulting in CT conjugated PLAs at the chain end groups after deprotection of phenolic hydroxyl groups. The antibacterial properties are determined by proliferation tests of staphylococcus aureus. The results suggest that the antibacterial properties of CT modified PLAs are derived from the original CT parts.

Hydrogel formation by the ‘topological conversion’ of cyclic PLA–PEO block copolymers

An amphiphilic cyclic block copolymer consisting of poly(L- or D-lactide) and poly(ethylene oxide), that is, PLLA–PEO or PDLA–PEO, was synthesized from its corresponding linear triblock precursor, PLLA–PEO–PLLA or PDLA–PEO–PDLA, respectively, with alkenyl end groups. A mixture of the micellar dispersions of linear PLLA–PEO–PLLA and linear PDLA–PEO–PDLA formed a gel upon heating, whereas a mixture of the cyclic counterparts did not undergo this phase transition. These results suggest that the gelation behavior is directed by the topology of the polymer components. Furthermore, cyclic PLLA–PEO and cyclic PDLA–PEO block copolymers incorporating photocleavable o-nitrobenzyl units were synthesized. A mixture of the micellar dispersions of these block copolymers formed a gel upon ultraviolet irradiation via the ‘topological conversion’. A mixture of the micellar dispersions of linear PLLA–PEO–PLLA and linear PDLA–PEO–PDLA block copolymers formed a gel upon heating, whereas a mixture of the cyclic counterparts did not undergo this phase transition. These results suggest that the gelation behavior is directed by the topology of the polymer components. Furthermore, cyclic PLLA–PEO and cyclic PDLA–PEO block copolymers incorporating photocleavable o-nitrobenzyl units were synthesized. A mixture of the micellar dispersions of these block copolymers formed a gel upon ultraviolet (UV) irradiation via the ‘topological conversion’.

Combination of lignin and l-lactide towards grafted copolymers from lignocellulosic butanol residue

A series of BBL-graft-poly (l-lactide) copolymers were synthesized via ring-opening polymerization (ROP) of l-lactide (l-LA) with a biobutanol lignin (BBL) initiator and a triazabicyclodecene (TBD) catalyst under free-solvent at 135°C. By manipulating the mass ratio of BBL/LLA, BBL-g-PLLA copolymers with tunable number⿿average molecular weight (Mn) (2544⿿7033gmol⿿1) were obtained. The chemical structure of PLLA chains was identifiable by FT-IR, 1H NMR and 13C NMR spectroscopies, in combination with UV⿿vis spectra to provide support for the existence of the BBL in the copolymer. This provided solid evidence for the successful synthesis of BBL-g-PLLA copolymer. The thermal properties and surface characterization of BBL-g-PLLA copolymers were different from those of linear PLLA. Furthermore, the BBL-g-PLLA copolymer film showed good absorption capacity in the UV region and high transparency in the visible light region, which was expected to find significant applications in UV-protective coating film.

Synthesis and Characterization of Linear and Tri-Block PLLA–PEG–PLLA Blends

ABSTRACTThis study was conducted to synthesize poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) triblock copolymer (PEGLA) with different poly(L-lactide) block length, and explore its applicability in a blend with linear poly(L-lactide) (3051D NatureWorks) with the intention of improving heat seal and adhesion properties at extrusion coating on paperboard. Poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) was obtained by ring opening polymerization of L-lactide using poly(ethylene glycol) (molecular weight 6000 g mol−1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy. The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology and differential scanning calorimeter. All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat poly(L-lactide), while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan δ). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.