Polymerization Of LA Research Articles

Colloidal Characteristics of Poly(L-Lactic Acid)-b-Poly (ε-Caprolactone) Block Copolymer-Based Nanoparticles Obtained by an Emulsification/Evaporation Method.

Poly(L-lactic acid) (PLLA) and poly(ε-caprolactone) (PCL), two biodegradable and biocompatible polymers that are commonly used for biomedical applications, are, respectively, the result of the ring-opening polymerization of LA and ε-CL, cyclic esters, which can be produced according to several mechanisms (cationic, monomer-activated cationic, anionic, and coordination-insertion), except for L-lactide, which is polymerized only by anionic, cationic, or coordination-insertion polymerization. A series of well-defined PLLA-b-PCL block copolymers have been obtained starting from the same PLLA homopolymer, having a molar mass of 2500 g·mol-1, and being synthesized by coordination-insertion in the presence of tin octoate. PCL blocks were obtained via a cationic-activated monomer mechanism to limit transesterification reactions, and their molar masses varied from 1800 to 18,500 g·mol-1. The physicochemical properties of the copolymers were determined by 1H NMR, SEC, and DSC. Moreover, a series of nanoparticles (NPs) were prepared starting from these polyester-based copolymers by an emulsification/evaporation method. The sizes of the obtained NPs varied between 140 and 150 nm, as a function of the molar mass of the copolymers. Monomodal distribution curves with PDI values under 0.1 were obtained by Dynamic Light Scattering (DLS) and their spherical shape was confirmed by TEM. The increase in the temperature from 25 to 37 °C induced only a very slight decrease in the NP sizes. The results obtained in this preliminary study indicate that NPs have a temperature stability, allowing us to consider their use as drug-loaded nanocarriers for biomedical applications.

Lipoic acid/trometamol assembled hydrogel as injectable bandage for hypoxic wound healing at high altitude

To avoid chronic wound formation caused by hypoxia and cold in high-altitude areas, developing an injectable, strongly adhesive hydrogel bandage with controllable oxygen generation and inflammation regulation functions is of great value. Poly(lipoic acid) (PLA)-based adhesives have been well-developed from polymerization of α-Lipoic acid (LA), showing attractive performances including simple preparation, strong adhesion, anti-inflammatory. However, injection of PLA-based adhesives has not been well-practiced because of its high viscosity and strong adhesion. Herein, LA and trometamol are firstly found to rapidly gel into a supramolecular hydrogel within 5 min at room temperature, exhibiting well-performed injectability. Further presence of Ce3+ significantly accelerates this gelation within 2 min. Meanwhile, dopamine (DA) and g-C3N4 nanosheet synergistically endow the injectable hydrogel with photothermal function, which can convert near-infrared-light (NIR) into heat, triggering LA polymerization and achieving post-injection enhancement. In terms of bandage performance after molding, the introduction of Ce3+, DA, and g-C3N4 contributes to the improvement of mechanical and adhesion properties. The injectable hydrogel bandage not only possesses highly tough and adhesive features, but also produces oxygen under NIR irradiation, effectively alleviating wound hypoxia, creating anti-inflammatory microenvironment, and significantly promoting healing of incision in a low-pressure oxygen environment.

Organocatalytic ring-opening polymerization of lactide by bis(thiourea) H-bonding donating cocatalysts with binaphthyl-amine framework

Development of H-bonding organo-catalysts with high catalytic activity and high degree of control is significantly important for the metal-free polyesters that are potentially suitable for biomedical usage. The concomitant use of base and commercially available thiourea generally suffered from prolonged reaction time and resulted in incomplete monomer conversion in some cases. Introducing one or more (thio)urea H-bonding donating arms to the parent thiourea has been proved to be an effective method for substantially increasing the activity of thiourea H-bonding donors. Consequently, we synthesized bis-thioureas derived from binaphthyl-amine bearing different substituents and investigated their catalytic performance in ROPs of lactide in this work. The density functional theory (DFT) calculations suggested that the “activated-thiourea” mode is more preferred for the bis(thiourea) containing binaphthyl-amine framework. The bis(thiourea)/base binary systems could effectively promote the LA polymerization using benzyl alcohol as initiator. The polymerization rates and the degree of control over the polymerization are highly dependent on the structures of the bis(thiourea) and base. Bis(thiourea)/1,5,7-triazabicyclo[4.4.0]dec‑5-ene pairs exhibited highest catalytic activity compared to other bis(thiourea)/base pairs, and the turnover frequency is high up to 1980 h–1 at 75 °C. In addition, the bulky hindrance and axial chirality of the binaphthyl-amine framework could enable stereoselective ROP of rac-LA to produce isotactic-rich and crystalline PLAs at relatively low temperature (0 °C). Mechanistic studies indicated that both enantiomorphic site control (ESC) and chain end control (CEC) concurrently occurred in the rac-LA polymerization catalyzed by bis(thiourea)/base binary systems. This work will inspire future design of H-bonding donors with high catalytic performance.

Preparation of CO2‐based poly(carbonate‐co‐lactide) with different porphyrin aluminum (III) catalysts

AbstractTwo‐component catalysts composed of tetra (para‐X substituted) phenylporphyrin aluminum (III) chloride, T (p‐X‐P)PAlCl, (where X = H, F, Cl, Br, CH3, OCH3, tert‐butyl), and cocatalyst bis(triphenylphosphine)imminium chloride (PPN+Cl−), could initiate the polymerization of propylene oxide (PO). And they could react with rac‐lactide, (rac‐LA), in the presence of propylene oxide (PO), to yield chains of enriched isotactic polylactide (PLA) with trace polyether segment. Also, these catalysts displayed different catalytic activity in the copolymerization of CO2 and PO, resulting in poly(carbonate‐co‐ether) copolymer with different carbonate unit content (CU%). Further, these catalysts could initiate one‐pot regio‐ and stereo‐ selective terpolymerization of rac‐LA, CO2 and rac‐PO, resulting in multi‐blocky poly(carbonate‐co‐lactide) with trace polyether segment. The structure of the products was verified by 1H NMR, 13C NMR, GPC, and DSC analysis, and it was found that variation of substitution groups in the periphery of porphyrin ligand would affect on the catalytic efficiency of ter‐polymerization, and the relative polymerization reaction ratio of the ring‐opening polymerization of LA (ROP) to the ring‐opening copolymerization of PO and CO2 (ROCOP), resulting in ter‐polymer with different contents of PLA segment and PPC segment. However, H‐T% in polycarbonate unit and Pi% in polylactide unit did not vary much with the change of catalysts.

Natural small molecule-induced polymer hydrogels with inherent antioxidative ability and conductivity for neurogenesis and functional recovery after spinal cord injury

Spinal cord injury (SCI) is a permanent disabling condition of the central nervous system. The secondary oxidative stress and the interruption of nerve electrical signal conduction are the main obstacles in the repair of SCI. Benefiting from the inherent capability for reactive oxygen species (ROS) scavenging by α-lipoic acid (LA) and the therapeutic effect by LiCl as well as conductivity in aqueous solution, we develop advanced hydrogels (poly(lipoic acid-co-sodium lipoate) (PLL) hydrogels) through one-pot ring-opening polymerization of LA in the presence of NaHCO3 for the efficient treatment of SCI. The hydrogels show facile injectability, adequate adhesiveness with tissues, and promising self-healability and can scavenge ROS in vitro and in vivo with high performance. Moreover, in the rat SCI model, PLL hydrogels facilitate electrophysiological signal transduction of nerve fibers at the injury site, regulate oxidative stress and inflammation in situ, and inhibit glial scar formation to promote neural stem cell migration and differentiation into neurons, all of which contribute to fast functional recovery after SCI. As the raw materials are safe and the fabrication process is easily scalable, the developed PLL hydrogels represent a cost-effective strategy for the regeneration of different injured tissues in clinical settings.

Investigating the Ring-Opening Polymerization Activity of Niobium and Tantalum Ethoxides Supported by Phenoxyimine Ligands.

A variety of metal catalysts from around the periodic table have been studied for the ring-opening polymerization (ROP) of cyclic esters. Within this field, group V catalysts have been rarely explored. To better understand the effect the choice of metal and ligand has on ROP activity, a series of 10 niobium and tantalum alkoxide catalysts, supported by a range of phenoxyimine ligands, were synthesized. The electronics and steric bulk of the ligands were varied on the phenoxy group (tBu, Cl, and OMe) and the imine group (Ph; 2,6-diMePh; 2,6-diiPrPh; and 2,4,6-tritBuPh) to probe their effect on the catalyst structure and activity. Catalysts were characterized with 1D, 2D, and variable-temperature NMR techniques to determine their structure in solution. Single crystal X-ray diffraction studies were conducted to establish their solid-state structure. The 10 catalysts are pseudo-octahedral, and each shows ligand coordination through phenoxy-oxygen and imine-nitrogen (O,N). In the case of the o-vanillin ligand set, however, evidence was found for O,O-coordination of the ligand when the steric encumbrance of the imine-nitrogen was increased. Each catalyst was active for the ring-opening polymerization of both rac-lactide (LA) and ε-caprolactone (CL) in the absence of solvent at 140 °C. In the case of CL, the catalysts supported by chloro-containing ligands showed the most polymerization control based on final polymer molecular weight and dispersity. Ligand trends were less clear for the polymerization of LA, though in all cases the catalysts were more controlled than the parent homoleptic alkoxide [M(OEt)5; M = Nb or Ta]. The most promising catalyst in the family was tested for copolymerization activity of LA and CL in one pot. Copolymerization of the two monomers was successful and yielded random poly(caprolactone-co-lactide).

Immortal polymerization of LA: the influence of steric effects, electronic effects and pKaon chain transfer agents

In this paper, we systematically investigated the iROP of l-LA based Ca[N(SiMe3)2]2(THF)2/CTAs binary catalytic systems for the first time. The steric effect, electronic effect and pKa of CTAs all had great influences on the iROP of LA.

Titanium ONN-(phenolate) Alkoxide Complexes: Unique Reaction Kinetics for Ring-Opening Polymerization of Cyclic Esters.

The synthesis, characterization, and polymerization kinetics of four new titanium ONN-(phenolate) alkoxide catalysts were studied. Each catalyst is fluxional at room temperature, suggesting the ligand amine arm may be labile, but adopts a fac geometry in solution at low temperature (223 K) and in the solid state. All catalysts are active for the ring-opening polymerization of both ε-caprolactone (CL) and rac-lactide (LA). GPC analysis indicates that the well-known coordination-insertion mechanism is being followed. However, whereas the typical first-order dependence on monomer concentration is observed in CL, an unexpected zeroth-order dependence is observed with LA. This suggests that, in the case of LA, catalyst saturation occurs and a Michaelis-Menten model can be used to explain the kinetics. An initial mechanism is discussed within this model that proposes CL polymerization proceeds by a 7-coordinate intermediate, whereas LA polymerization adopts a 6-coordinate intermediate, facilitated by the ligand amine arm. Attempts to isolate catalyst-monomer intermediates are ongoing.

Synergistic Catalysis by Brønsted Acid/Carbodicarbene Mimicking Frustrated Lewis Pair-Like Reactivity.

Carbodicarbene (CDC), unique carbenic entities bearing two lone pairs of electrons are well-known for their strong Lewis basicity. We demonstrate herein, upon introducing a weak Brønsted acid benzyl alcohol (BnOH) as a co-modulator, CDC is remolded into a Frustrated Lewis Pair (FLP)-like reactivity. DFT calculation and experimental evidence show BnOH loosely interacting with the binding pocket of CDC via H-bonding and π-π stacking. Four distinct reactions in nature were deployed to demonstrate the viability of proof-of-concept as synergistic FLP/Modulator (CDC/BnOH), demonstrating enhanced catalytic reactivity in cyclotrimerization of isocyanate, polymerization process for L-lactide (LA), methyl methacrylate (MMA) and dehydrosilylation of alcohols. Importantly, the catalytic reactivity of carbodicarbene is uniquely distinct from conventional NHC which relies on only single chemical feature of nucleophilicity. This finding also provides a new spin in diversifying FLP reactivity with co-modulator or co-catalyst.

Syndiotactic PLA from meso-LA polymerization at the Al-chiral complex: a probe of DFT mechanistic insights

The mechanism(s) for the formation of syndiotactic PLA by the ROP of meso-LA by a chiral-Al-complex are disclosed by DFT calculations. The contributions toward stereoselectivity have been analyzed confirming the peculiar chiral recognition for stereocontrolled ROP polymerization.

Use of pyrazoles as ligands greatly enhances the catalytic activity of titanium iso-propoxide for the ring-opening polymerization of l-lactide: a cooperation effect.

Using TiOiPr4 with a pyrazole ligand for one-pot LA polymerization improved catalytic activity compared with using TiOiPr4 only. At 60 °C, TiOiPr4 with furPz exhibited a higher catalytic activity (approximately 3-fold) than TiOiPr4. At room temperature, TiOiPr4 with BuPz exhibited a higher catalytic activity (approximately 17-fold) than TiOiPr4. High molecular mass PLA (MnGPC = 51 100, and Đ = 1.10) could be produced by using TiOiPr4 with furPz in melt polymerization ([TiOiPr4] : [furPz] = 1000 : 1 : 1 at 100 °C, 240 min). The crystal structure of MePz2Ti2OiPr7 revealed the cooperative activation between two Ti atoms during LA polymerization.

Microfluidic-assisted nanoprecipitation of (PEGylated) poly (d,l-lactic acid-co-caprolactone): Effect of macromolecular and microfluidic parameters on particle size and paclitaxel encapsulation

In this work we evaluate the effect of polymer composition and architecture of (PEGylated) polyesters on particle size and paclitaxel (PTX) loading for particles manufactured via microfluidic-assisted, continuous-flow nanoprecipitation using two microfluidic chips with different geometries and mixing principles.We have prepared poly (d,l-lactic acid-co-caprolactone) (PLCL) from ring-opening polymerization (ROP) of LA and CL mixtures and different (macro) initiators (namely, 1-dodecanol, a MeO-PEG-OH, and a 4-armed star PEG-OH), rendering polyesters that vary in monomer composition (i.e. LA/CL ratios) and architecture (i.e. linear vs 4-armed star). Continuous-flow nanoprecipitation was assayed using two microfluidic chips: a cross-flow chip with a X-shaped mixing junction (2D laminar flow focusing) and a micromixer featuring a Y-shaped mixing junction and a split and recombine path (2D laminar flow focusing convinced with stream lamination for faster mixing). Nanoparticle formulations were produced with Z-average sizes in the range of 30–160 nm, although size selectivity could be seen for different polymer/chip combinations; for instance, smaller particles were obtained with Y-shaped micromixer (30–120 nm), specially for the PEGylated polyesters (30–50 nm), whereas the cross-flow chip systematically produced larger particles (80–160 nm). Loading of the anti-cancer drug paclitaxel (PTX) was also heavily influenced not only by the nature of the polyester, but also by the geometry of the microfluidic chip; higher drug loadings were obtained with the cross-flow reactor and the star block copolymers. Finally, decreasing the LA/CL ratio generally had a positive effect on drug loading.

Effect of Star-shaped chain architectures on the polylactide stereocomplex crystallization behaviors

Linear and star-shaped polylactides (PLA) with similar molecular weights of each arm are synthesized via ring-opening polymerization of LA with 3-butyn-1-ol and pentaerythritol as initiators, respectively. By solution blending of equivalent mass of poly(L-lactic acid)s (PLLAs) and poly(D-lactic acid)s (PDLAs), perfect PLA stereocomplexes (scPLAs) are prepared and confirmed by WAXD and FTIR analysis. Effect of chain architectures on stereocomplex crystallization is investigated by studying the non-isothermal and isothermal crystallization of linear and star-shaped polylactide stereocomplexes. In dynamic DSC and POM test, star-shaped PLLA (4sPLLA)/PDLA and PLLA/star-shaped PDLA (4sPDLA) stereocomplexes reach rapid crystallization and higher crystallinity due to larger spherulite density of star-shaped chain and excellent chain mobility of linear chain. In isothermal crystallization test, much faster crystallization and less crystallization half-time is obtained with the increase of star-shaped chain. Meanwhile, 4sPLLA/PDLA and PLLA/4sPDLA are found to have the highest crystallinity, suggesting limitation of too much star-shaped chain for 4sPLLA/4sPDLA and restriction of linear chain in nucleation capacity for PLLA/PDLA. The results reveal that star-shaped chain has an important influence on the crystallization of scPLAs.

Improving the Ring‐opening Polymerization of l‐Lactide Using n‐Butyl Lithium with Various Bidentate Ligands

A series of bidentate ligands were examined to improve the catalytic activity of l ‐lactide (LA) polymerization by using n‐butyl lithium and BnOH. For LA polymerization, n‐butyl lithium with tetraisopropyl methylenebis(phosphonate) (L8 ) showed the greatest catalytic activity but with poor controllability of the polymer molecular weight. The polydispersity indices (PDIs) could be improved without BnOH addition, but Mn GPC was much different from the Mn Cal . 1H NMR spectra confirmed that the cyclized PLA was obtained, thus implying that active chain‐end mechanisms were operative in LA polymerization.

Biodegradable thermogel as culture matrix of bone marrow mesenchymal stem cells for potential cartilage tissue engineering

Poly(lactide-co-glycolide)-poly(ethylene glycol)-poly(lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymer was synthesized through the ring-opening polymerization of LA and GA with PEG as macroinitiator and stannous octoate as catalyst. The amphiphilic copolymer self-assembled into micelles in aqueous solutions, and formed hydrogels as the increase of temperature at relatively high concentrations (> 15 wt%). The favorable degradability of the hydrogel was confirmed by in vitro and in vivo degradation experiments. The good cellular and tissular compatibilities of the thermogel were demonstrated. The excellent adhesion and proliferation of bone marrow mesenchymal stem cells endowed PLGA-PEG-PLGA thermogelling hydrogel with fascinating prospect for cartilage tissue engineering.

Facile synthesis of thiol-functionalized amphiphilic polylactide–methacrylic diblock copolymers

Biodegradable amphiphilic diblock copolymers based on an aliphatic ester block and various hydrophilic methacrylic monomers were synthesized using a novel hydroxyl-functionalized trithiocarbonate-based chain transfer agent. One protocol involved the one-pot simultaneous ring-opening polymerization (ROP) of the biodegradable monomer (3S)-cis-3,6-dimethyl-1,4-dioxane-2,5-dione (L-lactide, LA) and reversible addition–fragmentation chain transfer (RAFT) polymerization of 2-(dimethylamino)ethyl methacrylate (DMA) or oligo(ethylene glycol) methacrylate (OEGMA) monomer, with 4-dimethylaminopyridine being used as the ROP catalyst and 2,2′-azobis(isobutyronitrile) as the initiator for the RAFT polymerization. Alternatively, a two-step protocol involving the initial polymerization of LA followed by the polymerization of DMA, glycerol monomethacrylate or 2-(methacryloyloxy)ethyl phosphorylcholine using 4,4′-azobis(4-cyanovaleric acid) as a RAFT initiator was also explored. Using a solvent switch processing step, these amphiphilic diblock copolymers self-assemble in dilute aqueous solution. Their self-assembly provides various copolymer morphologies depending on the block compositions, as judged by transmission electron microscopy and dynamic light scattering. Two novel disulfide-functionalized PLA-branched block copolymers were also synthesized using simultaneous ROP of LA and RAFT copolymerization of OEGMA or DMA with a disulfide-based dimethacrylate. The disulfide bonds were reductively cleaved using tributyl phosphine to generate reactive thiol groups. Thiol–ene chemistry was utilized for further derivatization with thiol-based biologically important molecules and heavy metals for tissue engineering or bioimaging applications, respectively.

Single-site bismuth alkoxide catalysts for the ring-opening polymerization of lactide

Salen bismuth alkoxides, where the salen ligand contains 2,4-di-tert-butylphenoxy groups and one of ethylene, cyclohexane or ortho-phenyl as a backbone have been prepared from reactions involving Bi[N(SiMe₃)₂]₃ and the free salen ligand followed by alcoholysis (ButOH, PriOH and 2,6-But₂C₆H₃OH). The molecular structures of the salen ligand with the cyclohexyl back-bone have been determined for the complexes salenBiCl and salenBiOC₆H₃-2,6-But₂. The chloro compound is a dimer with chloride bridges while the phenoxide is monomeric with an unusually distorted five-coordinate geometry. The phenoxide and tert-butoxide complexes have been employed in the ring-opening polymerization of lactides (L- and rac-) to give polylactides, PLAs. With rac-LA heterotactic PLA is formed preferentially, Pr = ~0.9, in dichloromethane or toluene at room temperature. The reaction is first order in [Bi] and is notably faster than most aluminum and zinc initiators as well as tin(II) octanoate. These results are discussed in terms of a recent report on the polymerization of LA by Peptobismol® and bismuth subsalicylate.

Lactic acid- and carbonate-based crosslinked polymeric micelles for drug delivery

Our objective was to synthesize and evaluate lactic acid- and carbonate-based biodegradable core- and core-co- rona crosslinkable copolymers for anticancer drug delivery. Methoxy poly(ethylene glycol)-b-poly(carbonate-co-lactide-co- 5-methyl-5-allyloxycarbonyl-1,3-dioxane-2-one) (mPEG-b-P(CB- co-LA-co-MAC)) and methoxy poly(ethylene glycol)-b-poly(acry- loyl carbonate)-b-poly(carbonate-co-lactide) (mPEG-b-PMAC-b- P(CB-co-LA)) copolymers were synthesized by ring-opening polymerization of LA, CB, and MAC using mPEG as an macroi- nitiator and 1,8-diazabicycloundec-7-ene as a catalyst. These amphiphilic copolymers which exhibited low polydispersity and critical micelle concentration values (0.8-1 mg/L) were used to prepare micelles with or without drug and stabilized by crosslinking via radical polymerization of double bonds introduced in the core and interface to improve stability. mPEG114-b-P(CB8-co-LA35-co-MAC2.5) had a higher drug encap- sulation efficiency (78.72% 6 0.15%) compared to mPEG114-b- PMAC2.5-b-P(CB9-co-LA39) (20.29% 6 0.11%). 1 H NMR and IR spectroscopy confirmed successful crosslinking (� 70%) while light scattering and transmission electron microscopy were used to determine micelle size and morphology. Crosslinked micelles demonstrated enhanced stability against extensive dilution with aqueous solvents and in the presence of physio- logical simulating serum concentration. Furthermore, bicaluta- mide-loaded crosslinked micelles were more potent compared to non-crosslinked micelles in inhibiting LNCaP cell prolifera- tion irrespective of polymer type. Finally, these results suggest crosslinked micelles to be promising drug delivery vehicles for chemotherapy. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000-000, 2012

Effect of Biodegradable Cross-Linkers on the Properties of the Novel Poly(NIPAAm) Hydrogels

In this article, a series of biodegradable cross-linkers, [poly(d,l-lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(d,l- lactide-co-glycolide), (PLGA-PEG-PLGA), diacrylate] (LGE dA) with different molar ratios of d,l-lactide (LA)/glycolide (GA) in PLGA, were prepared from the corresponding PLGA-PEG-PLGA diol (LGE diol) triblock copolymers and then acrylated with acryloyl chloride. The LGE diols were synthesized through ring-opening polymerization of LA and GA using PEG as an initiator and stannous octoate [Sn(Oct)2] as a catalyst in advance. A series of novel thermosensitive and biodegradable hydrogels were then prepared from N-isopropyl acrylamide (NIPAAm) and LGE dA as a cross-linker. The effect of different molar ratios of LA/GA in PLGA on the swelling ratio and physical properties of the poly(NIPAAm) hydrogels were investigated. The results showed that the swelling ratios of the poly(NIPAAm) hydrogels in deionized water decreased with increasing cross-linker content and increased with increasing GA content in the hydrogel. The compressive modulus and cross-linking density of the hydrogels also increased with an increase in the cross-linker content and molar ratio of LA/GA in the present hydrogel. The hydrogels can be degraded about 60% for the NL50 series of gels, but for NL78 about 53% can be degradable in 1-month biodegradable experiment. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E633–E650, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21307

Amphiphilic multiarm star polylactide with hyperbranched polyethylenimine as core: A systematic reinvestigation

The Sn(Oct)2 catalyzed polymerization condition of l-lactide (LLA) and racemic lactide (r-LA) using hyperbranched polyethylenimine (PEI) as the macroinitiator was optimized. Multiarm star polymers bearing PEI core and well-controlled poly(l-lactide) (PLLA) or poly(racemic lactide) (PDLLA) arms were successfully prepared under the optimized condition, including: (1) high concentration of Sn(Oct)2 catalyst was required; (2) with respect to the polymerization of r-LA, the optimal temperature was in the range of 115–130 °C; (3) as for the polymerization of LLA, the optimal temperature was only around 130 °C. Model experiments demonstrated that secondary amine could also effectively initiate the Sn(Oct)2 catalyzed polymerization of LA under the optimized condition, however, its initiation efficiency was usually a little less than 100%, unlike the primary amine and hydroxyl initiators. The results of Gel Permeation Chromatography demonstrated that the obtained multiarm star polymers with PDLLA arms had narrower dispersities than those with PLLA arms. Thermal analyses demonstrated that raising the arm numbers of the stars impaired their thermal stability a little. Stars with PDLLA arm were amorphous. The glass transition temperature of all the PDLLA-based polymers was similar and had no obvious relationship with the arm length, arm number and the molecular architecture. The crystallizability of star polymers with PLLA arm was weaker than that of linear PLLA, and only star polymers with long PLLA arm showed obvious crystallization. The guest encapsulation and release properties of the obtained star polymers were also investigated. It was found that their guest encapsulation capacity had correlation with the PLA arm length, the PEI core size and the degree of quaternization of PEI core, but had no relationship with the type of the PLA arm (PDLLA or PLLA). Whereas the guest release rate was strongly affected by the arm type.