Bulk Ring-opening Polymerization Research Articles

Modular design of a zwitterionic organocatalyst for bulk ring-opening polymerization of cyclic esters

Zwitterionic organocatalysis in the ring-opening polymerizations of cyclic esters via bifunctional activation of the monomer by Lewis acidic cation and the chain-end by Lewis basic anion of the modular designed phoshonium carboxybetaines.

Room‐Temperature Lewis Acid Organocatalysts for Bulk Ring‐Opening Polymerization of Bis‐Lithium N‐Heterocyclic Carbenes Complexes Activated on ε‐Caprolactone: Synthetic, Experimental, and Density Functional Theory of Mechanistic Studies

AbstractThis work investigates the high catalytic activity of bi‐functional lithium N‐heterocyclic carbene (bisLiNHCs) complexes in bulk ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) monomer at room temperature. The study employs a bulk ROP technique using tetramethylene‐tethered bis[N‐(N′‐alkyl/arylimidazolium)] bishexafluorophosphate (bis[Bim][PF6]), benzyl alcohol (BnOH), and n‐butyl lithium (nBuLi) in molar ratios of 1:2:4. The results show that 1,4‐bisLiNHC (3a) has the highest catalytic capability, producing the highest molecular weight of PCL with acceptable dispersity in only 93 s (59 361 g mol−1, Đ = 1.8). However, longer and aromatic linker chains (3b‐3g) are found to be less effective due to the increased steric effect for complex formation with the monomer, leading to longer reaction times and lower molecular weight PCL with wider dispersity. Additionally, the study conducts a mechanistic analysis using the DFT method with B3LYP (6‐31G(d,p)) as the basis set. The most plausible mechanism proposed involves continuous and coordinated insertion with low energy barriers.

Use of non‐isothermal DSC in comparative studies of tin(II) systems for the ring‐opening polymerization ofd‐lactide

AbstractUnderstanding the kinetics and mechanisms of polymerization, particularly the role of a catalyst or initiator used, allows for the manipulation and control of the fabrication of new materials by the most convenient, straightforward routes. The kinetics of the bulk ring‐opening polymerization (ROP) ofd‐lactide, a useful monomer employed to control the properties of poly(l‐lactide), have been studied herein to identify a relatively quick (1 h), controlled, yet convenient route to moderately high molecular weight poly(d‐lactide). Tin(II) octoate (Sn(Oct)2), Sn(Oct)2/n‐butanol (nBuOH) and liquid tin(II) butoxide (Sn(OnBu)2) as initiating systems were investigated by non‐isothermal differential scanning calorimetry (DSC). Isoconversional methods were employed to determine the activation energy (Ea) for each reaction. The results showed that liquid Sn(OnBu)2was a more efficient initiator than the commonly reported initiating systems of Sn(Oct)2and Sn(Oct)2/nBuOH in terms of producing higher polymerization rates and polymer molecular weights. High‐molecular‐weight poly(d‐lactide) (1.8 × 105 Da) with moderate dispersity (Ð = 1.3) was obtained using 0.1 mol% liquid Sn(OnBu)2as the initiator at 120 °C. This work describes the applications of non‐isothermal DSC and isoconversional methods in comparing the effectiveness of different initiators in the bulk ROP ofd‐lactide for the first time. © 2023 Society of Chemical Industry.

Phosphazene Functionalized Silsesquioxane-Based Porous Polymer as Thermally Stable and Reusable Catalyst for Bulk Ring-Opening Polymerization of ε-Caprolactone.

The bulk ring-opening polymerization (ROP) of ε-caprolactone using phosphazene-containing porous polymeric material (HPCP) has been studied at high reaction temperatures (130-150 °C). HPCP in conjunction with benzyl alcohol as an initiator induced the living ROP of ε-caprolactone, affording polyesters with a controlled molecular weight up to 6000 g mol-1 and moderate polydispersity (Ð~1.5) under optimized conditions ([BnOH]/[CL] = 50; HPCP: 0.63 mM; 150 °C). Poly(ε-caprolactone)s with higher molecular weight (up to Mn = 14,000 g mol-1, Ð~1.9) were obtained at a lower temperature, at 130 °C. Due to its high thermal and chemical stability, HPCP can be reused for at least three consecutive cycles without a significant decrease in the catalyst efficiency. The tentative mechanism of the HPCP-catalyzed ROP of ε-caprolactone, the key stage of which consists of the activation of the initiator through the basic sites of the catalyst, was proposed.

A Highly Active and Selective Zirconium-Based Catalyst System for the Industrial Production of Poly(lactic acid).

The biodegradable, aliphatic polyester poly(lactic acid), PLA, is a leading bio-based alternative to petrochemical-derived plastic materials across a range of applications. Widely reported in the available literature as a benchmark for PLA production via the bulk ring-opening polymerization of lactides is the use of divalent tin catalysts, and particularly tin(II) bis(2-ethylhexanoate). We present an alternative zirconium-based system that combines an inexpensive Group IV metal with the robustness, high activity, control, and designed compatibility with existing facilities and processes, that are required for industrial use. We have carried out a comprehensive kinetic study and applied a combined experimental and theoretical approach to understanding the mechanism by which the polymerization of lactide proceeds in the presence of this system. In the laboratory-scale (20 g) polymerization of recrystallized racemic d,l-lactide (rac-lactide), we have measured catalyst turnover frequencies up to at least 56,000 h-1, and confirmed the reported protocols' resistance toward undesirable epimerization, transesterification, and chain scission processes, deleterious to the properties of the polymer product. Further optimization and scale-up under industrial conditions have confirmed the relevance of the catalytic protocol to the commercial production of melt-polymerized PLA. We were able to undertake the efficient preparation of high-molecular-weight PLA on the 500-2000 g scale, via the selective and well-controlled polymerization of commercial polymer-grade l-lactide under challenging, industrially relevant conditions, and at metal concentrations as low as 8-12 ppm Zr by weight ([Zr] = 1.3 × 10-3 to 1.9 × 10-3 mol %). Under those conditions, a catalyst turnover number of at least 60,000 was attained, and the activity of the catalyst was comparable to that of tin(II) bis(2-ethylhexanoate).

Aluminum Salen Complexes Modified with Unsaturated Alcohol: Synthesis, Characterization, and Their Activity towards Ring-Opening Polymerization of ε-Caprolactone and D,L-Lactide.

A highly efficient one-step approach to the macromonomer synthesis using modified aluminum complexes as catalysts of ring-opening polymerization (ROP) of ε-caprolactone and D,L-lactide was developed. The syntheses, structures, and catalytic activities of a wide range of aluminum salen complexes, 3a-c, functionalized with unsaturated alcohol (HO(CH2)4OCH=CH2) are reported. X-Ray diffraction studies revealed a tetragonal pyramidal structure for 3c. Among the complexes 3a-c, the highest activity in bulk ROP of ε-caprolactone and D,L-lactide was displayed by 3b, affording polyesters with controlled molecular weights at low monomer to initiator ratios (Mn up to 15,000 g mol-1), relatively high polydispersities (Ð~1.8) and high number-average functionalities (Fn up to 85%).

Scalable and Degradable Dextrin-Based Elastomers for Wearable Touch Sensing.

Elastomer-based wearables can improve people's lives; however, frictional wear caused by manipulation may pose significant concerns regarding their durability and sustainability. To address the aforementioned issue, a new class of advanced scalable supersoft elastic transparent material (ASSETm) is reported, which offers a unique combination of scalability (20 g scale), stretchability (up to 235%), and enzymatic degradability (up to 65% in 30 days). The key feature of our design is to render native dextrin hydrophobic, which turns it into a macroinitiator for bulk ring-opening polymerization. Based on ASSETm, a self-powered touch sensor (ASSETm-TS) for touch sensing and non-contact approaching detection, possessing excellent electrical potential (up to 65 V) and rapid response time (60 ms), is fabricated. This work is a step toward developing sustainable soft electronic systems, and ASSETm's tunability enables further improvement of electrical outputs, enhancing human-interactive applications.

Scalable and Room-Temperature Ring-Opening Polymerization of ε-Caprolactone Catalyzed by Active Lithium Tetramethylene-Tethered Bis[N-(N'-butylimidazol-2-ylidene)] N-Heterocyclic Carbene as a Lewis Acid Organocatalyst.

The Lewis acid organocatalytic system of lithium tetramethylene-tethered bis[N-(N'-butylimidazol-2-ylidene)] N-heterocyclic carbene (1,4-bisNHC) including lithium benzyloxide and benzyl alcohol has been successfully utilized in the ring-opening polymerization (ROP) of ε-caprolactone (CL) for the first time. The catalytic performance of this organic catalyst in the synthesis of high-molecular-weight polymers was investigated via bulk polymerization using different combinations of tetramethylene-tethered bis[N-(N'-butylimidazolium)] hexafluorophosphate (1,4-bis[Bim][PF6]), benzyl alcohol (BnOH), and n-butyl lithium (nBuLi) ([1,4-bis[Bim][PF6]]/[BnOH]/[nBuLi]) with the molar ratios of 0:2:2, 1:1:3, 1:2:3, and 1:2:4. The results showed that the molar ratio of 1:2:3 efficiently and rapidly initiated the bulk ROP of CL at room temperature with a high molar ratio of CL to 1,4-bis[Bim][PF6] of 3000/1 and produced the highest number of average-molecular-weight (Mn) poly(ε-caprolactone) (103,057 g mol-1) with the dispersity (D̵) and %conversion of 1.73 and 98% in a short period of time (152 s). From comparative studies, the relative polymerization rates of the bulk ROP of CL with different [1,4-bis[Bim][PF6]]/[BnOH]/[nBuLi] molar ratios was determined in the following order: 1:2:4 > 1:1:3 > 1:2:3 > 0:2:2. For mechanistic investigation, the bulk ROP mechanism of CL with our organic catalyst was proposed through the intramolecular bis-lithium-carbene interaction pathway for 1,4-bisNHC1,1,3, 1,4-bisNHC1,2,3, and 1,4-bisNHC1,2,4 systems.

Long-term in vivo degradation behavior of poly(trimethylene carbonate-co-2, 2′-dimethyltrimethylene carbonate)

Poly(trimethylene carbonate-co-2, 2′-dimethyltrimethylene carbonate) P(TMC-co-DTC) copolymers with different molecular weights or molar ratios were prepared by bulk ring-opening polymerization (ROP) of trimethylene carbonate (TMC) and 2, 2′-dimethyltrimethylene carbonate (DTC). The in vivo degradation behavior of the resulting copolymers of 2 mm diameter was subsequently investigated by implanting the samples subcutaneously in the back of rats. The data showed that the sample's mass loss was reduced, and the form-stability was enhanced with the increase of DTC segments content in the copolymer while increasing the molecular weight could accelerate the degradation rate and improve the form-stability of the copolymers. Among them, the samples containing 25 mol% DTC segments with a molecular weight of 205 kDa achieved the highest mass loss of 26.1% and maintained good form-stability after 35 weeks of implantation. In particular, implants with high DTC segments amount of 75 mol% (molecular weight of 208 kDa) maintained excellent form-stability and a low mass loss of 4.8% during the implantation cycle and exhibited some properties different from the other groups. Further experimental results showed that the content of DTC segments increased from 74.4% to 77.3%, and the crystallinity of the copolymer transformed to semi-crystalline state also increased from 61.4% to 76.4% during the degradation. The Tg, Tm and hardness of the degraded polymers were correspondingly improved. In addition, the degradation mechanism of surface erosion in vivo of the resulting P(TMC-co-DTC) copolymers were verified. This work provides a promising class of candidate carrier materials for the application of long-acting drug delivery systems through a detailed study of the in vivo degradation behavior of P(TMC-co-DTC) copolymers.

Development and Characterization of PEGylated Fatty Acid-Block-Poly(ε-caprolactone) Novel Block Copolymers and Their Self-Assembled Nanostructures for Ocular Delivery of Cyclosporine A.

Low aqueous solubility and membrane permeability of some drugs are considered major limitations for their use in clinical practice. Polymeric micelles are one of the potential nano-drug delivery systems that were found to ameliorate the low aqueous solubility of hydrophobic drugs. The main objective of this study was to develop and characterize a novel copolymer based on poly (ethylene glycol) stearate (Myrj™)-block-poly(ε-caprolactone) (Myrj-b-PCL) and evaluate its potential as a nanosystem for ocular delivery of cyclosporine A (CyA). Myrj-b-PCL copolymer with various PCL/Myrj ratios were synthesized via ring-opening bulk polymerization of ε-caprolactone using Myrj (Myrj S40 or Myrj S100), as initiators and stannous octoate as a catalyst. The synthesized copolymers were characterized using 1H NMR, GPC, FTIR, XRD, and DSC. The co-solvent evaporation method was used to prepare CyA-loaded Myrj-b-PCL micelles. The prepared micelles were characterized for their size, polydispersity, and CMC using the dynamic light scattering (DLS) technique. The results from the spectroscopic and thermal analyses confirmed the successful synthesis of the copolymers. Transmission electron microscopy (TEM) images of the prepared micelles showed spherical shapes with diameters in the nano range (<200 nm). Ex vivo corneal permeation study showed sustained release of CyA from the developed Myrj S100-b-PCL micelles. In vivo ocular irritation study (Draize test) showed that CyA-loaded Myrj S100-b-PCL88 was well tolerated in the rabbit eye. Our results point to a great potential of Myrj S100-b-PCL as an ocular drug delivery system.

Ring‐opening polymerization of 1,4‐oxathian‐2‐one and its copolymerization with δ‐valerolactone

AbstractMonomer 1,4‐oxathian‐2‐one (OX) was synthesized by a one pot two‐step method, and it was oxidized to the sulfone ester monomer, 1,4‐oxathian‐2‐one‐4,4‐dioxide (OX‐SO2). Three organic catalysts, 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD), 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), and diphenyl phosphate (DPP) were screened for the ring‐opening polymerization (ROP) of OX in dichloromethane at 30°C. It was found that OX has a high polymerizability, the TBD‐catalyzed ROP is very fast but with serious side reactions, the DBU‐catalyzed ROP is moderately controlled, and the DPP‐catalyzed ROP is well controlled until the polymerization reach equilibrium. Bulk ROP of OX‐SO2 was achieved with stannous octoate ((Sn[Oct]2) at 130°C. Poly(OX) is a semicrystalline polyester (Tm = 40‐60°C, Tg = −39.6°C), while Poly(OX‐SO2) is a highly crystalline polyester(Tg = 55°C, Tm = 211°C with decomposition). Kinetics experiments of OX and δ‐valerolactone (VL) revealed that VL polymerized faster than OX with DPP as the catalyst. Thermodynamic parameters of the ROP of OX and VL under identical conditions were measured; the ROP of OX is thermodynamically more favorable than that of VL. A series of random copolymers of OX and VL was prepared using TBD as the catalyst and confirmed that the in‐chain heteroatom greatly affected the crystallization of the copolymers.

Metal-free, in bulk synthesis of highly hydrophilic polyester bearing pyrrolidone pendants and its diblock copolymers with UCST-type phase transition in water

Aliphatic polyesters are readily degradable, highly hydrophobic and lack of functionality. In contrast, polyvinylpyrrolidone (PVP), a vinyl-based polymer, exhibits excellent water solubility owning to its highly hydrophilic pyrrolidone (Py) pendant groups but suffers from degradation issues due to stable C-C bonds in its backbones. Functionalizing polyester with pyrrolidone pendant groups leads to a new type of polymer that is highly hydrophilic and hydrolytically labile at the same time. Well defined functional polyesters can be obtained via controlled ring opening polymerization (ROP) of functional lactone monomers. Functionalization of δ-valerolactone with Py groups is realized by thiol-ene click ligation and subsequent oxidation to afford functional lactone (pyvl). Bulky pendant groups, Py, on lactone rings impede ROP of the functionalized lactones. It is found that strong Brønsted superacid, trifluoromethanesulfonic acid (HOTf), can promote bulk ROP of pyvl at 120 °C and that control of the polymerization can be moderately improved in the presence of diphenylphosphate (DPP) under these conditions. Well defined functional polyesters, poly(pyvl)s, are found to be highly hydrophilic and hydrolytically labile. Surprisingly, its amphiphilic block copolymers such as poly(pyvl)20-b-PCL60 exhibit sharp and concentration-independent UCST type phase transition at around 35 °C in pure water.

Kinetic Modeling of Ring Opening Polymerization of Lactones under Microwave Irradiation

AbstractA kinetic study on the mathematical modeling of polymerization rate and molar mass development in the ring opening bulk polymerization (ROP) of lactones under microwave irradiation (MI), for the production of biodegradable green polymers used in the biomedical sector, is presented. Two modeling approaches, one based on calculation of average properties using a self‐developed code based on the method of moments, and the other one providing calculation of full molar mass distributions with the aid of the Predici software are contrasted. The observed enhancement on polymerization rate under MI is captured well by using a non‐thermal microwave effect modeling approach, namely, a microwave‐enhanced propagation model. The proposed approach is validated with available experimental data for ROP of ε‐caprolactone, a monomer which can be obtained from biomasses, using benzyl alcohol (BzOH) and stannous octoate (SnOc)2 as initiator and catalyst, respectively, at 150 °C. Seven case studies are analyzed, including ROPs carried out under both conventional heating (CH) and MI. The effect of initiator and alcohol initial concentrations on polymerization rate and molar mass distributions is analyzed. The advantages of using MI in ROP are assessed.

Controlling the switching temperature of biodegradable shape memory polymers composed of stereocomplex polylactide / poly(d,l-lactide-co-ε-caprolactone) blends

We synthesized new biodegradable shape-memory polymers (SMPs) by blending synthesized poly(d,l-lactide-co-ε-caprolactone) (PLCL) and stereocomplex polylactide (sc-PLA) to be used as biomaterials for medical devices. PLCL copolymers (Mn ∼80,000) with various monomer ratios (LA:CL) were synthesized by the bulk ring-opening polymerization. The glass transition temperature of the resulting PLCL copolymers could be well controlled from −3 °C to 60 °C, agreeing well with the values by the Gordon-Taylor equation, confirming the homogeneous random distribution of LA and CL monomers in the synthesized PLCL. The synthesized PLCL and sc-PLA were eventually blended for the fabrication of biodegradable SMPS. The PLCL/sc-PLA blend samples possessed the sc-PLA crystallinity of ∼13%, which effectively worked as crosslinkings, exhibiting shape-memory behavior with various switching temperatures (30.5°C–62 °C) and shape-recovery ratios realized by adjusting the CL ratio of the PLCL copolymers: a lower CL ratio resulted in a higher switching temperature and a higher shape-recovery ratio.

Stereoretention in the Bulk ROP of l-Lactide Guided by a Thermally Stable Organocatalyst.

Polylactide (PLA) has emerged as one of the most promising bio-based alternatives to petroleum-based plastics, mainly because it can be produced from the fermentation of naturally occurring sugars and because it can be industrially compostable. In spite of these benefits, the industrial ring-opening polymerization (ROP) of l-lactide (L-LA) still requires the use of highly active and thermally stable metal-based catalysts, which have raised some environmental concerns. While the excellent balance between activity and functional group compatibility of organic acid catalysts makes them some of the most suitable catalysts for the metal-free ROP of L-LA, the majority of these acids are highly volatile and subject to decomposition at high temperature, which limits their use under industrially relevant conditions. In this work we exploit the use of a nonstoichiometric acid–base organocatalyst to promote the solvent-free and metal-free ROP of L-LA at elevated temperatures in the absence of epimerization and transesterification. To do so, a stable acidic complex was prepared by mixing 4-(dimethylamino)pyridine (DMAP) with 2 equiv of methanesulfonic acid (MSA). Both experimental and computational results indicate that DMAP:MSA (1:2) not only is highly thermally stable but also promotes the retention of stereoregularity during the polymerization of L-LA, leading to PLLA with a molar mass of up to 40 kg mol–1 and a chiral purity in excess of 98%. This result provides a new feature to exploit in organocatalyzed polymerization and in the design of new catalysts to facilitate the path to market.

Design and Development of D‒α‒Tocopheryl Polyethylene Glycol Succinate‒block‒Poly(ε-Caprolactone) (TPGS-b-PCL) Nanocarriers for Solubilization and Controlled Release of Paclitaxel.

The objective of this study was to synthesize and characterize a set of biodegradable block copolymers based on TPGS-block-poly(ε-caprolactone) (TPGS-b-PCL) and to assess their self-assembled structures as a nanodelivery system for paclitaxel (PAX). The conjugation of PCL to TPGS was hypothesized to increase the stability and the drug solubilization characteristics of TPGS micelles. TPGS-b-PCL copolymer with various PCL/TPGS ratios were synthesized via ring opening bulk polymerization of ε-caprolactone using TPGS, with different molecular weights of PEG (1–5 kDa), as initiators and stannous octoate as a catalyst. The synthesized copolymers were characterized using 1H NMR, GPC, FTIR, XRD, and DSC. Assembly of block copolymers was achieved via the cosolvent evaporation method. The self-assembled structures were characterized for their size, polydispersity, and CMC using dynamic light scattering (DLS) technique. The results from the spectroscopic and thermal analyses confirmed the successful synthesis of the copolymers. Only copolymers that consisted of TPGS with PEG molecular weights ≥ 2000 Da were able to self-assemble and form nanocarriers of ≤200 nm in diameter. Moreover, TPGS2000-b-PCL4000, TPGS3500-b-PCL7000, and TPGS5000-b-PCL15000 micelles enhanced the aqueous solubility of PAX from 0.3 µg/mL up to 88.4 ug/mL in TPGS5000-b-PCL15000. Of the abovementioned micellar formulations, TPGS5000-b-PCL15000 showed the slowest in vitro release of PAX. Specifically, the PAX-loaded TPGS5000-b-PCL15000 micellar formulation showed less than 10% drug release within the first 12 h, and around 36% cumulative drug release within 72 h compared to 61% and 100% PAX release, respectively, from the commercially available formulation (Ebetaxel®) at the same time points. Our results point to a great potential for TPGS-b-PCL micelles to efficiently solubilize and control the release of PAX.

Prefunctionalised PLGA microparticles with dimethylaminoethyl moieties promote surface cell adhesion at physiological condition

Synthetic hydrolytically degradable polyesters have seen widespread translation into a variety of clinical and biomedical settings; finding use as cell culture systems, drug delivery systems, tissue repair scaffolds, and medical devices. This success is owed in part due to their biocompatible nature and tuneable degradation profile. However, the lack of adhesion moieties limits the capacity of the polyesters to interact with cellular material and as such hampers their effectiveness within these applications. Several physical and chemical post-modification techniques have been developed to insert adhesion moieties; however, the nature of these methods remains complex and troublesome for translational medicine. To combat this flaw, we present a novel prefunctionalization method for the generation of poly (lactic-co-glycolic acid) PLGA microparticles with integrated adhesion moieties as a proof-of-principle. This strategy promotes surface cell adhesion at physiological conditions without the requirement for further post-modification. The basis of the prefunctionalization method was to utilise the 2-2-dimethylaminoethanol as an initiator in a standard bulk Ring Opening Polymerization process to obtain PLGADMAE polymers. The resultant polymers were subsequently used in the fabrication of the microparticles, via membrane emulsion. This process allowed control over the morphology and size distribution of the microparticles. The surface cell adhesive properties of the new PLGADMAE microparticles were investigated via co-culture with Adipose-Derived Stem Cells. Scanning Electron Microscopy showed that the new PLGADMAE microparticles readily promote adhesion of the ADSCs at physiological conditions. LDH and LIVE/DEAD assays demonstrated that the surface functionalised PLGADMAE microparticles maintained a low toxicity profile compared to the unmodified PLGA microparticles. Both thermogravimetric and differential scanning calorimetric analysis confirmed that the bulk properties of the polymer remained unchanged compared to the control PLGA. Gel Permeation Chromatography and Scanning Electron Microscopy imaging showed that the degradation profile of the new PLGADMAE was enhanced compared to that of standard PLGA polymers. This novel prefunctionalization strategy eliminates the need for post-modification and could evolve rapidly to develop biodegradable biomaterials with enhanced cell adhesion and tuneable surface chemistry to allow greater control and/or maintain interaction with living cells and tissues. The implication of this new approach would be far reaching in the field of cell delivery, cell expansion, tissue engineering and regenerative medicine.

Influence of miscible and immiscible sequences of poly(D-lactide) copolymers on the competition of stereocomplex- and homo-crystallization in poly(L-lactide) blends

A high molecular weight (HMw) PLLA has been blended with a low molecular weight (LMw) PDLA and its two types diblock copolymers (PEG-b-PDLA and PDMS-b-PDLA), respectively, to investigate the stereocomplex (sc) and homochiral (hc) crystallization behaviors. The miscible PEG and immiscible PDMS segments with comparable molecular weight were introduced into PDLA by bulk ring-opening polymerization method. Compared to PLLA/PDLA, the introduction of both sequences could inhibit the crystallization kinetics of sc and hc crystallites of the blends due to the dilution effect of LMw segments. The formation of sc crystallites is prior to its hc counterparts. The shorter induction period of hc crystallites of PLLA/PEG-b-PDLA blend indicates that the miscible PEG segments could promote the mobility of PLLA chains. Due to the involving of PEG chains, the spherulite exhibits coarsen and irregular texture and its lamellae show sparse string-like structure. The microphase separation between PLA and PDMS segments as evidenced by SAXS results in the increased sc nuclei and different growth mode of hc crystallites. The phase separated microdomains weakened the competition between sc and hc crystallites, and the former acts as a template for repeated assembly of the latter. X-ray analysis also reveal that sc crystallites possess much thicker lamellar thickness than hc crystallites in PLLA/PDLA and PLLA/PEG-b-PDLA blends.

Synthesis of bio-based poly limonene oxide with green catalyst

In the present work, the polymerization of limonene oxide (LO) catalyzed by Maghnite H+ (Mag- H+) is investigated. Mag-H+ is Algerian montmorillonite sheet silicate clay exchanged with protons. The poly limonene oxide (PLO) is obtained by cationic ring opening polymerization in bulk and with solvent. The effect of the reaction time, the temperature and the amount of catalyst are studied and discussed in order to find the optimal reactions conditions. The polymerization in solution at 0 °C with 5% by weight of catalyst leads to the best yield 61.34% for a reaction time of 1h. The structure of the obtained products is characterized by XRD, 1H-NMR, 13C-RMN, ATR-FTIR, DSC and TGA.

Eco-friendly synthesis of biodegradable poly(ε-caprolactone) using L-lactic and glycolic acids as organic initiator

Biodegradable poly(e-caprolactone) (PCL) was successfully synthesized by the green polymerization process that was conducted in the absence of heavy metal catalyst and toxic solvent. L-Lactic (LLA) and glycolic acids (GA) were utilized as green initiator for the bulk ring-opening polymerization (ROP) of e-caprolactone (e-CL). These organic initiators could produce PCL with number average molecular weight (Mn) in the range of 8.46 × 103–1.98 × 104 g/mol and molecular weight distribution (MWD) of 1.71–1.81. GA could produce higher molecular weight PCL than LLA under identical synthesis condition. The catalytic performance of these initiators in the ROP of e-CL was completely investigated by the non-isothermal differential scanning calorimetry (DSC). From non-isothermal DSC kinetics analysis, the reactivity of GA was higher than LLA in the bulk ROP of e-CL as supported by the lower values of activation energy (Ea) and frequency factor (A) of GA than LLA initiator. The polymerization mechanism for the ROP of e-CL initiated by LLA and GA was proposed through the activated monomer mechanism.