Final Polymer Molecular Weight Research Articles

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).

Enzymatic Poly(octamethylene suberate) Synthesis by a Two-Step Polymerization Method Based on the New Greener Polymer-5B Technology

Here, we report a new two-step enzymatic polymerization strategy for the synthesis of poly(octamethylene suberate) (POS) using an immobilized Pseudozyma antarctica lipase B (IMM-PBLI). The strategy overcomes the lack of enzymatic POS synthesis in solvent-free systems and increases the final polymer molecular weight. In the first step, the direct polycondensation of suberic acid and 1,8-octanediol was catalyzed by IMM-PBLI at 45 °C, leading to the production of prepolymers with molecular weights (MWs) of 2800, 3400, and 4900 g mol−1 after 8 h in miniemulsion, water, and an organic solvent (cyclohexane: tetrahydrofuran 5:1 v/v), respectively. In the second polymerization step, wet prepolymers were incubated at 60 or 80 °C, at atmospheric pressure, in the presence of IMM-PBLI, and without stirring. The final POS polymers showed a significant increase in MW to 5000, 5800, and 19,800 g mol−1 (previously synthesized in miniemulsion, water, or organic solvent, respectively). FTIR analysis of the final polymers confirmed the successful POS synthesis and a high degree of monomer conversion. This innovative two-step polymerization strategy opens up a new opportunity for implementing greener and more environmentally friendly processes for synthesizing biodegradable polyesters.

Efficient Design to Monitor the Site‐specific Sustained Release of a Non‐Emissive Anticancer Drug

A pH-responsive smart nanocarrier with significant components was synthesized by conjugating the non-emissive anticancer drug methyl orange and polyethylene glycol derived folate moiety to the backbone of polynorbornene. Complete synthesis procedure and characterization methods of three monomers included in the work: norbornene-derived Chlorambucil (Monomer 1), norbornene grafted with polyethylene glycol, and folic acid (Monomer 2) and norbornene attached methyl orange (Monomer 3) connected to the norbornene backbone through ester linkage were clearly discussed. Finally, the random copolymer CHO PEG FOL METH was synthesized by ring-opening metathesis polymerization (ROMP) using Grubbs' second-generation catalyst. Advanced polymer chromatography (APC) was used to find the final polymer's molecular weight and polydispersity index (PDI). Dynamic light scattering, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were utilized to explore the prodrug's size and morphology. Release experiments of the anticancer drug, Chlorambucil and the coloring agent, methyl orange, were performed at different pH and time. Cell viability assay was carried out for determining the rate of survived cells, followed by the treatment of our final polymer named CHO PEG FOL METH.

New thermoplastic elastomer triblock copolymer of PLLA for cardiovascular tissue engineering: Annealing as efficient tool to tailor the solid-state properties

A new high molecular weight aliphatic copolyester of PLLA characterized by a ABA triblock architecture was successfully synthesized by ring opening polymerization, using as initiator a low molecular weight hydroxyl terminated random copolymer of PBS, poly(butylene/triethylene succinate). To increase the final polymer molecular weight, thus ensuring both good processability and mechanical properties, chain extension reaction has been performed with hexamethylene diisocyanate (HDI) as chain extender. All the synthetic steps have been carried out in solvent-free conditions. Specifically, the A block consists of LLA sequences, whereas the B one is an aliphatic biodegradable and biocompatible random copolyester of poly(butylene succinate) containing “PEG-like” moiety. The so-obtained material was first characterized by the molecular point of view and then, prior to further characterization, subjected to two different annealing treatments. Annealing revealed to be an efficient tool to control the kind and amount of crystalline phase developed by the material, as confirmed by WAXS structural analysis, and to tailor the mechanical properties, typical of thermoplastic elastomers. Thermal treatment was found to affect also the mechanism of polymer degradation under physiological conditions. Last, but not least, in order to explore the possible use of such new PLLA-based copolymer in vascular tissue engineering, preliminary biocompatibility tests, using endothelial cells, were carried out.

Enzymatic ring opening polymerization of ω-pentadecalactone using supercritical carbon dioxide

ω-pentadecalactone, a cyclic macrolactone can be polymerized by enzymatic ring opening polymerization (e-ROP). The resulting polyester, poly(ω-pentadecalactone) has mechanical and biocompatibility properties that make it desirable for biomedical uses, especially for bone and cartilage tissue regeneration. Conventional synthesis of poly(ω-pentadecalactone) involves acid or metal catalysts and organic solvents such as toluene that can leave toxic residuals in obtained material. In this work, e-ROP of ω-pentadecalactone was performed using supercritical carbon dioxide (scCO2) as solvent, a co-solvent and Novozym 435 lipase as catalyst. Different polymerization conditions were tested to obtain high molecular weight polyesters. Reactions conducted using only scCO2 as solvent showed yields around 60wt% and molecular weights up to 33,000g/mol. Higher molecular weights were obtained when a co-solvent was used. The results also showed a strong influence of water content on enzyme and monomer concentration in reaction medium over the final polymer molecular weight and reaction yield.

Reversible addition-fragmentation chain transfer polymerization in microemulsion

This tutorial review first details the uncontrolled microemulsion polymerization mechanism, and the RAFT polymerization mechanism to provide the necessary background for examining the RAFT microemulsion polymerization mechanism. The effect of the chain transfer agent per micelle ratio and the chain transfer agent aqueous solubility on the RAFT microemulsion polymerization kinetics, polymer molecular weight and polydispersity, and polymer nanoparticle size are discussed with a focus on oil-in-water microemulsions. Modeling of RAFT microemulsion polymerization kinetics and the resulting final polymer molecular weight are presented to assist with the analysis of observed experimental trends. Lastly, the current significance of RAFT microemulsion polymerization and the future directions are discussed.

Regulation of initiation and polymer molecular weightof cis-1,4-polyisoprene synthesized in vitro by particlesisolated from Parthenium argentatum (Gray)

Parthenium argentatum is a prime candidate for development as a new crop for theproduction of natural rubber (cis-1,4-polyisoprene). The rubber obtained from P. argentatum iscomparable in molecular weight (and quality) to that obtained from Hevea brasiliensis (Mr ca.106 Da), which is currently the sole commercial source of natural rubber. Most of the 2500rubber-producing plant species known make much lower molecular weight rubber, although theregulation of polymer molecular weight is not understood. In the experiments reported here,we investigated the regulation of rubber biosynthesis and polymer molecular weight usingpurified, enzymatically-active rubber particles isolated from P. argentatum, under variousconcentrations of the allylic diphosphate (allylic-PP) rubber molecule initiators farnesyldiphosphate (FPP, a 15-carbon molecule), or geranyl diphosphate (GPP, a 10-carbon molecule)and the elongation substrate isopentenyl diphosphate (IPP). Our results show that the rates ofboth rubber molecule initiation and polymerization, and the final polymer molecular weight,were greatly affected by the concentration of initiator and IPP. Increasing allylic-PP initiatorconcentrations caused an increase in the amount of rubber synthesized and the number ofmolecules initiated but a decrease in the mean polymer molecular weight; increasing IPPconcentrations increased the amount of rubber and the mean polymer molecular weight. Atidentical substrate concentrations of IPP and allylic-PP, GPP initiated about one third of therubber polymers initiated by FPP but incorporated about two thirds the amount of IPP, comparedto FPP. Consequently, while the amount of rubber synthesized in the presence of GPP was lessthan with FPP, the rubber polymers synthesized with GPP initiator were, on average, about twicethe molecular weight of those with FPP.

Kinetics of the reaction between alkaline sulfides and aryl dichlorides — model study on 4‐chloro‐ and 4,4′‐dichlorobenzophenones

AbstractThe kinetics of the reaction between alkaline sulfides and halogenated aromatic monomers was studied using lithium sulfide and 4‐chlorobenzophenone (1a) and 4,4′‐dichlorobenzophenone (1b) as models. The release of H2S from reaction medium and the possible formation of a compound between sulfide and N‐methyl‐2‐pyrrolidone (NMP) during the preliminary dehydration step are key steps of the reaction. The reaction proceeds following two successive kinetic regimes: a first one where rapid second‐order reactions of sulfide and thiolate with 1a or 1b take place, and a second one where the slow release of sulfide from the compound formed during dehydration is rate determining and therefore governs the molecular weight of final polymer. A good agreement was found between theoretical curves calculated from this kinetic scheme and experimental data, indicating a polymerization mechanism based on an SNAr reaction mechanism.