Summary: Microwave‐assisted ring‐opening polymerization of ε‐caprolactone in the presence of 1‐butyl‐3‐methylimidazolium tetrafluoroborate ionic liquid using zinc oxide as a catalyst is investigated. By adding 30 wt.‐% ionic liquid, poly(ε‐caprolactone) with a weight‐average molar mass of 28 500 g · mol−1 is obtained at 85 W for 30 min. The results indicate that the polymerization could be efficiently enhanced in the presence of ionic liquids under microwave irradiation because ionic liquids can effectively absorb microwave energy.
Summary: The polymerization of ε‐caprolactone (CL) in the presence of HCl · Et2O by an activated monomer mechanism was performed to synthesize diblock or triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε‐caprolactone) (PCL). The obtained PCLs had molecular weights close to the theoretical values calculated from the CL to PEG molar ratios and exibited monomodal GPC curves. We successfully prepared PEG and PCL block copolymers by a metal‐free method.
The non‐metal catalyzed living ring‐opening polymerisation of ε‐caprolactone by PEG. 相似文献
A facile strategy for synthesis of α‐heterobifunctional polystyrenes is reported. The novel functional polystyrenes have been successfully synthesized via a combination of atom transfer radical polymerization (ATRP) and chemical modification of end‐functional groups. First, ε‐caprolactone end‐capped polystyrenes with controlled molecular weight and low polydispersity were prepared by ATRP of styrene using α‐bromo‐ε‐caprolactone (αBrCL) as an initiator. Then, removal of the terminal bromine atom was performed with iso‐propylbenzene in the presence of CuBr/PMDETA. Finally, ring‐opening modifications of the caprolactone group were carried out with amines, n‐butanol and H2O to produce novel polystyrenes containing two different functional groups at one end.
A new functional lactone, α‐iodo‐ε‐caprolactone (αIεCL), was synthesized from ε‐caprolactone by anionic activation using a non‐nucleophilic strong base (lithium diisopropylamide) followed by an electrophilic substitution with iodine chloride. Ring‐opening (co)polymerizations of the resulting monomer with ε‐caprolactone were carried out using tin 2‐ethylhexanoate as a catalyst in toluene at 100 °C. Homopolymerization of αIεCL was achieved, and poly(αIεCL) was fully characterized by SEC, 1H NMR and elemental analysis. Random copolymerizations of αIεCL with εCL were controlled with experimental molecular weights close to the theoretical values, narrow molecular weight distributions and a good agreement between experimental and theoretical molar compositions of αIεCL.
L,L ‐lactide (LA) and ε‐caprolactone (CL) block copolymers have been prepared by initiating the poly(ε‐caprolactone) (PCL) block growth with living poly(L,L ‐lactide) (PLA*). In the previous attempts to prepare block copolymers this way only random copolyesters were obtained because the PLA* + CL cross‐propagation rate was lower than that of the PLA–CL* + PLA transesterification. The present paper shows that application of Al‐alkoxide active centers that bear bulky diphenolate ligands results in efficient suppression of the transesterification. Thus, the corresponding well‐defined di‐ and triblock copolymers could be prepared.
Summary: An enzymatic one‐pot procedure has been developed for the synthesis of difunctional polyesters containing terminal thiols and acrylates. Candida antarctica lipase B was used as a catalyst for the ring‐opening polymerization of ω‐pentadecalactone. The polymerization was initiated with 6‐mercaptohexanol, then terminated with γ‐thiobutyrolactone or vinyl acrylate to create two types of difunctional polyesters with a very high content of thiol‐thiol or thiol‐acrylate end‐groups.
Films of an α‐cyclodextrin/poly(ε‐caprolactone) inclusion complex have been successfully prepared and show high transparency and heat resistance in comparison to the pure polymer film. The physical properties, such as transparency, mechanical properties, and thermal stability, of the α‐CD‐PCL‐IC films are found to depend on the α‐cyclodextrin‐to‐polymer stoichiometry.
We show that small quantities of 1,3:2,4‐di(4‐chlorobenzylidene) sorbitol dispersed in poly(ε‐caprolactone) provide a very effective self‐assembling nanoscale framework which, with a flow field, yields extremely high levels of polymer crystal orientation. During modest shear flow of the polymer melt, the additive forms highly extended nano‐particles which adopt a preferred alignment with respect to the flow field. On cooling, polymer crystallisation is directed by these particles. This chloro substituted dibenzylidene sorbitol is considerably more effective at directing the crystal growth of poly(ε‐caprolactone) than the unsubstituted compound.
Summary: A protection‐graft‐deprotection method was developed to prepare chitosan‐g‐polycaprolactone graft copolymers, during which the ring‐opening copolymerization of ε‐caprolactone onto phthaloylchitosan (PHCS) happened without any additional catalysis. The intermediate PHCS was introduced primarily to protect the active amino group of chitosan. After controlled experiments, the phthalimido compound was proposed to be a novel kind of organic catalyst for the ring‐opening polymerization of caprolactone monomers, while the hydroxyl group acted as an initiator. Hence, in this graft system, PHCS was endowed with both self‐catalysis and self‐initiation at the same time, and the PCL side chains grew from the hydroxyl groups of the chitosan backbone.
Summary: The use of microwave heating in polymer science is a rapidly growing field of research leading to faster and cleaner polymerization procedures. However, the majority of the investigations are performed at small scales (≈1 mL), which is far away from potential commercial applications of microwave‐assisted polymerizations. In addition, it has been shown in organic chemistry that microwave‐assisted reaction protocols can be directly scaled without the need for process optimization. In this contribution, we have investigated the direct scaling of microwave‐assisted polymerization procedures under pressure conditions using the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline as the model system. This polymerization was performed at scales ranging from 4.0 mmol (1 mL) to 1.0 mol (250 mL) in different microwave synthesizers covering both monomode and multimode devices.
Scale‐up of microwave‐assisted polymerizations in batch mode: the cationic ring‐opening polymerization of 2 ethyl‐2‐oxazoline. 相似文献
A novel method is described for transforming an anionic polymerization process into a cationic polymerization process assisted by organosilyl groups. The reaction of the p‐tolyldimethylsilyl end group of polystyrene and trifluoromethanesulfonic acid produced a silyl triflate end group that served as a macroinitiator for the living cationic polymerization of isobutyl vinyl ether. The Si O linkage in the block copolymers underwent specific cleavage by reaction with tetrabutylammonium fluoride.
New amphiphilic graft copolymers that have a poly(ε‐caprolactone) (PCL) biodegradable hydrophobic backbone and poly(4‐vinylpyridine) (P4VP) or poly(2‐(N,N‐dimethylamino)ethyl methacrylate) (PDMAEMA) hydrophilic side chains have been prepared by anionic polymerization of the corresponding 4VP and DMAEMA monomers using a PCL‐based macropolycarbanion as initiator. The water solubility of these amphiphilic copolymers is improved by quaternization, which leads to fully water‐soluble cationic copolymers that give micellar aggregates in deionized water with diameters ranging from 65 to 125 nm. In addition, to improve the hydrophilicity of PCL‐g‐P4VP, grafting of poly(ethylene glycol) (PEG) segments has been carried out to give a water‐soluble double grafted PCL‐g‐(P4VP;PEG) terpolymer.
This communication reports the first example of precision polyolefin nanoalloys where an exotic immiscible polymer is nanometrically dispersed with stability in a polyolefin matrix in a highly controlled mode. Following the preparation of polypropylene/multiwalled carbon nanotubes nanocomposites (PP/MWCNTs) by in situ Ziegler‐Natta polymerization, the hydroxyl groups on the surfaces of individual MWCNTs are used to initiate ring‐opening polymerization of ε‐caprolactone, resulting in PP/poly(ε‐caprolactone) (PCL) alloy with PCL grafted on MWCNTs. Upon phase formation, the PP/MWCNTs‐g‐PCL alloys exhibit a unique PCL dispersion morphology, which is stable and solely governed by PCL molecular weight.
ATRP of 2‐(N,N‐dimethylamino)ethyl acrylate (DMAEA) was investigated using CuBr or CuCl with different multidentate ligands. The catalyst was found active for DMAEA polymerization when ligated with tris[2‐(N,N‐dimethylamino)ethyl]amine. Good control over molecular weight was achieved, but quaternization of the terminal monomeric/polymeric tertiary amine by the C Br group of polyDMAEA caused chain termination. Using a chloride‐based system helped to suppress chain termination. Amphiphilic poly(methyl acrylate)‐block‐polyDMAEA was synthesized using polyMA as a macroinitiator.
Molecular weights and polydispersities of polyDMAEA versus DMAEA conversion for different catalyst systems. 相似文献
PCL/clay nanocomposites were prepared by microwave‐assisted in situ ROP of ε‐caprolactone in the presence of either unmodified clay (Cloisite® Na+) or clay modified by quaternary ammonium cations containing hydroxyl groups (Cloisite 30B). This PCL showed significantly improved monomer conversion and molecular weight compared with that produced by conventional heating. An intercalated structure was observed for the PCL/Cloisite Na+ nanocomposites, while a predominantly exfoliated structure was observed for the PCL/Cloisite 30B nanocomposites. Microwave irradiation proved to be an effective and efficient method for the preparation of PCL/clay nanocomposites.
A series of π‐conjugated polymers linked by benzocarborane (1,2‐(buta‐1′,3′‐diene‐1′,4′‐diyl)‐1,2‐dicarbadodecaborane) were synthesized via Sonogashira–Hagihara polycondensation reaction. The opened molecular structure of diiodo monomer containing benzocarborane resulted in fast polymerization and high molecular weights. The obtained polymers were fully characterized by 1H, 13C, and 11B NMR spectroscopies. UV‐vis absorption and photoluminescence studies revealed the acceptor‐profile of benzocarborane. Unlike the polymers linked by o‐carborane, these polymers exhibited strong luminescence in the solution state, presumably because the inductive effect of carborane is dominant, rather than cage‐π interactions.
Summary: Novel alternating polyketone‐based polymers bearing pendant saccharide units that are accessible by polymerization catalysis are presented. The materials were synthesized by polymerization of carbon monoxide and α‐olefins containing protected glucose or N‐acetyl glucosamine residues. The dicationic PdII bis(phoshine) complex [Pd(dppp)(NCCH3)2](BF4)2 was used as a catalyst precursor. An O‐deacetylation of the copolymers afforded materials with amphiphilic character.
Structure of the poly(1,4‐ketone) copolymers synthesized here. 相似文献
Summary: This work reports a new type of poly(ε‐caprolactone) (PCL) robust hollow sphere with controllable biodegradability, produced by grafting PCL shells from the surface of silica sphere cores and removing the template cores. Bis(ε‐caprolactone‐4‐yl) (BCY) composed of two ε‐caprolactone molecules was used as the crosslinker, which not only greatly strengthened the PCL hollow spheres but also brought hardly any non‐biodegradable component into the system. Solubility experiments and biodegradation tests show that the crosslinked PCL hollow spheres were robust both in water and acetone, and were completely biodegradable with characteristics of controllable biodegradability according to the content of the BCY. The Rhodamine release test indicated that the release rate of encapsulated drugs in the PCL hollow spheres was controlled by diffusion and the biodegradability of the PCL molecules, and the latter mechanism will dominate when more enzymes are involved.
Reaction scheme for synthesis of linear and crosslinked hollow poly(ε‐caprolactone) spheres. 相似文献
Sixteen parallel polymerization reactions of 2‐ethyl‐2‐oxazoline have been performed at different temperatures in an automated synthesizer that allowed individual heating of each reactor. During the reactions samples were taken automatically, which were characterized by means of both online GPC and offline GC, in order to optimize the reaction temperature and to determine the activation energy of the polymerization.
The synthesis of poly(β‐alanine) by Candida antarctica lipase B immobilized as novozyme 435 catalyzed ring‐opening of 2‐azetidinone is reported. After removal of cyclic side products and low molecular weight species pure linear poly(β‐alanine) is obtained. The formation of the polymer is confirmed with 1H NMR spectroscopy and MALDI‐TOF mass spectrometry. The average degree of polymerization of the obtained polymer is limited to = 8 by its solubility in the reaction medium. Control experiments with β‐alanine as a substrate confirmed that the ring structure of the 2‐azetidinone is necessary to obtain the polymer.
