MWNTs are modified to possess hydroxy groups and are used as coinitiators to polymerize L ‐lactide by the surface‐initiated ring‐opening polymerization. FT‐IR and TEM observations reveal that the PLLA is covalently attached to the MWNTs (MWNT‐g‐PLLA), and the weight gain as a result of the functionalization is determined by TGA analysis. Two kinds of solvents, namely DMF and toluene, are used to carry out the two series of polymerizations at 140 and 70 °C, respectively, for 2–20 h. The amount of grafted PLLA increases with the reaction time either in DMF or in toluene, but it increases more significantly in DMF at 140 than in toluene at 70 °C, with the reaction time being the same. The grafted PLLA layer on the MWNT is more uniform when the reaction is performed in DMF than in toluene, and some bare surfaces are observed in the TEM image of the MWNT‐g‐PLLA prepared in toluene. The MWNT‐g‐PLLAs are well dispersed in the organic solvents as well as in the PLLA matrix. Incorporation of MWNT‐g‐PLLA greatly improves the tensile modulus and strength without a significant loss of the elongation at break. The specific interaction between the MWNT‐g‐PLLA and the polymer matrix is quantified by way of the Flory‐Huggins interaction parameter, B, which is determined by combining the melting point depression and the binary interaction model.
Graft copolyesters with a PCL backbone and PLLA side chains were successfully prepared in three steps avoiding transesterification. First ε‐caprolactone was polymerised with 1,6‐hexane diol as initiator to obtain hydroxytelechelic oligo(ε‐caprolactone)s. These diols were then subjected—in the second step—to polycondensation with L ‐malic acid yielding in linear poly[oligo(ε‐caprolactone)L ‐malate] having secondary hydroxyl functions in the side chain. For both reactions scandium triflate Sc(OTf)3 was used as a catalyst. In the third step various amounts of L ‐lactide were grafted from the polymer backbone using Zn(oct)2 as catalyst. The successful reaction was confirmed by NMR and SEC (size exclusion chromatography) analysis. Further the thermal properties of the graft copolymers with different graft lengths were determined via differential scanning calorimetry.
The preparation of poly(L ‐lactide) nanoparticles via ring‐opening polymerization (ROP) of L ‐lactide is conducted in non‐aqueous emulsion. In this process, acetonitrile is dispersed in either cyclohexane or n‐hexane as the continuous phase and stabilized by a PI‐b‐PEO, respectively, a PI‐b‐PS copolymer as emulsifier. The air and moisture sensitive N‐heterocyclic carbene 1,3‐bis(2,4,6‐trimethylphenyl)‐2‐ididazolidinylidene (SIMes) catalyzes the polymerization of L ‐lactide at ambient temperatures. Spherical poly(L ‐lactide) nanoparticles with an average diameter of 70 nm and a tunable molecular weight are generated. Hence, the non‐aqueous emulsion technique demonstrates its good applicability toward the generation of well‐defined poly(L ‐lactide) nanoparticles under very mild conditions. 相似文献
Summary: Diblock copolymers, poly(trimethylene oxide)‐block‐poly(styrene)s abbreviated as poly(TMO)‐block‐poly(St), and triblock copolymers, poly(TMO)‐block‐poly(St)‐block‐poly(MMA)s (MMA = methyl methacrylate), with controlled molecular weight and narrow polydispersity have been successively synthesized by a combination of atom transfer radical polymerization (ATRP) and cationic ring‐opening polymerization using the bifunctional initiator, 2‐hydroxylethyl α‐bromoisobutyrate, without intermediate function transformation. The gel permeation chromatography (GPC) and NMR analyses confirmed the structures of di‐ and triblock copolymers obtained.
GPC curves of (a) poly(St); (b) diblock copolymer, poly(St)‐block‐poly(MMA) before precipitation; (c) poly(St)‐block‐poly(MMA) after precipitation in cyclohexane/ethanol (2:1); (d) triblock copolymer, poly(TMO)‐block‐poly(St)‐block‐poly(MMA). 相似文献
Amphiphilic block copolymers possess great potential as biomaterials in drug delivery and gene therapy. Herein, pseudopeptidic‐type diblock copolymer of poly(2‐oxazoline)‐block‐polypeptoid (POx‐b‐POI) is presented and synthesized. Poly[2‐(3‐butenyl)‐2‐oxazoline]‐block‐poly(sarcosine) (PBuOx‐b‐PSar) comprising hydrophobic POx segment bearing alkenyl side chain and hydrophilic POI segment of N‐methyl glycine, viz., sarcosine, is prepared by ring‐opening polymerization (ROP) through a one‐pot and three‐step route. Diphenyl phosphate initiates ROP of BuOx, and then the living chain end of PBuOx is quenched by ammonia to obtain PBuOx‐ammonium phosphate in situ, the active ammonium group initiates ROP of sarcosine N‐carboxy anhydride. PBuOx‐b‐PSar with controlled molecular weights (4.7–10.8 kg mol−1) and narrow dispersities (Ð M 1.15–1.21) are characterized by 1H NMR, 13C NMR, and size‐exclusion chromatography. Dynamic light scattering and transmission electron microscopy analysis reveal that PBuOx‐b‐PSar self‐assembles into nanostructures of average diameter D H of 37–109 nm in aqueous solution. 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide test demonstrates the cytocompatibility (relative cell viability > 80%) of the PBuOx‐b‐PSar. In view of the self‐assembly and biocompatibility, the readily prepared diblock copolymers may hopefully be used in biomedical applications.
Four poly(N,N‐dimethylacrylamide)‐block‐poly(L ‐lysine) (PDMAM‐block‐PLL) hybrid diblock copolymers and two PLL homo‐polypeptides are prepared via ROP of ε‐trifluoroacetyl‐L ‐lysine N‐carboxyanhydride initiated by primary amino‐terminated PDMAM and n‐hexylamine respectively. The PLL blocks render the copolymers a multi‐responsive behavior in aqueous solution due to their conformational transitions from random coil to α‐helix with increasing pH, and from α‐helix to β‐sheet upon heating. The random coil‐to‐α‐helix transition is found to depend on the PLL length: the longer the peptide segment, the more readily the transition occurred. The same trend was observed for the α‐helix‐to‐β‐sheet transition, which was found to be inhibited for short polypeptides unless conjugated with the PDMAM block.
PLLA‐MPEG diblock copolymers with a controlled number‐average molar mass ranging from 7 330 to 117 610 g · mol?1 and an L ‐lactide conversion ranging from 65.1 to 97.3% were synthesized effectively in 20 min at 100 °C by MPEG‐initiated ROP of L ‐lactide under microwave irradiation. Prolonged microwave irradiation time led to the degradation of the copolymers because the ROP reaction and the thermal degradation reaction occurred simultaneously at the later stage of the reaction process. The differential scanning calorimetric and thermogravimetric study indicated that higher melting temperatures and thermal stability were obtained for PLLA‐MPEG diblock copolymers with longer PLLA segments.
PLLA/PDLA blends were crystallized between 120 and 195 °C. The stereocomplex spherulites acquired in equimolar and non‐equimolar blends were compared using POM, WAXD, DSC, and AFM. For equimolar blends, stereocomplex crystals show spherulites with positive birefringence, which is ascribed to the existence of domains made up of tangentially oriented lamellae. For PLLA‐rich (or PDLA‐rich) blends, the signs of the birefringence changed from a positive spherulite to a mixed spherulite and then to a negative spherulite. In negative spherulites, most lamellae orient radially. Radial and tangential cracks were observed in equimolar blends when crystallization took place above 175 °C whereas no cracks formed for non‐equimolar blends.
Diblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) were synthesized by the anionic ring‐opening polymerization of propylene oxide (PO), with controlled microwave heating in sealed vessels. A detailed study was carried out to investigate the effects of different parameters on the formation of unwanted byproducts. Parameters that were considered include temperature; the concentration of NaH, monomer and hydroxy groups in the feed; and the polarity of the reaction medium. A continuous decrease of internal pressure during the sealed‐vessel experiment reflected the consumption of PO monomer and the completion of the reaction was confirmed by a drop of the internal pressure to zero when reactions were performed in bulk. The products were characterized by using different chromatographic techniques. A comparison of the reaction times and composition of the polymers prepared by microwave and conductive heating is given.
Equal amounts of poly(L ‐lactide) (PLLA) and poly(D ‐lactide) (PDLA) were mixed with diphenyl ether (DE) at high temperature in DE‐to‐polymer composition from 0 to 80 wt.‐%. Cooling of the ternary mixtures produced white crystallosolvates without deposition of DE. Various analyses revealed that the crystallosolvates consisted of both homo‐chiral (hc) and stereocomplex (sc) crystals of PLLA and PDLA as well as amorphous domains involving DE. The crystallosolvate obtained at a DE content of 80 wt.‐%, comprised only the sc crystals. Atomic force microscopy (AFM) revealed that many granules having a size of 20 nm in diameter were formed from rod‐like hc crystallites and that the DE was slightly phase‐separated to form nano‐sized reservoirs. The stronger sc interaction between the PLLA and PDLA chains excluded DE from the polymer matrix.
“Tree‐shaped” copolymers constituted by an m‐PEG trunk and poly(L ‐lactide) or poly(D ,L ‐lactide) branches were obtained. The m‐PEG was functionalized at the terminal chain with two (G1) and four (G2) hydroxyl groups, then reacted with Al(CH3)3 to produce aluminum alkoxide species, active as initiators in the ROP of L‐ or D ,L‐ lactide. Copolymers were characterized by 1H and 13C NMR, GPC and DSC, and compared with analogous linear copolymers. Characterization of a low‐molecular‐weight G1 copolymer confirmed the architecture. GPC curves showed monomodal and narrow molecular weight distribution for all the samples, while the melting points of the copolymers seemed more correlated to the architecture than to the composition.
The amphiphilic triblock copolymer PLA‐b‐PLL‐b‐MPEG is prepared in three steps through acylation coupling between the terminal amino groups of PLA‐b‐PZLL‐NH2 and carboxyl‐terminal MPEG, followed by the deprotection of amines. The block copolymers are characterized via FT‐IR, 1H NMR, DSC, GPC, and TEM. TEM analysis shows that the triblock polymers can form polymeric micelles in aqueous solution with a homogeneous spherical morphology. The cytotoxicity assay indicates that the final triblock polymer micelles after deprotection show low cytotoxicity against Bel7402 human hepatoma cells. MPEG and PLL were introduced into the main chain of PLA affording a kind of ideal bioabsorbable polymer materials, which is expected to be useful in drug and gene delivery.
Summary: Both intercalated and exfoliated poly(L ,L ‐lactide) (P(L ,L ‐LA)/organomodified montmorillonite nanocomposites were synthesized by in situ ring‐opening polymerization of L ,L ‐lactide, in bulk, directly in the presence of the nanofiller. Intercalation of polyester chains was found to appear even for natural unmodified montmorillonite‐Na+, while exfoliation occurred when the aluminosilicate layers were modified by ammonium cations bearing primary hydroxyl groups. Clay delamination was effectively triggered by the grafting reaction of the growing PLA chains onto the hydroxyl groups. Aluminium triisopropoxide, triethylaluminium, and stannous octoate, as initiating or co‐initiating species, were compared in terms of polymerization control. The influence of nanoclay content (from 1 to 10 wt.‐% in inorganics) on morphology and thermal behavior was also studied. In parallel, a highly filled nanocomposite (called masterbatch), prepared by in situ polymerization, was dispersed into a (plasticized) preformed polylactide matrix in the molten state, to reach a better clay delamination than that obtained by direct melt blending. Finally, L ,L ‐lactide and α,ω‐dihydroxylated poly(ethylene glycol) (PEG 1000) were copolymerized in presence of clay in order to study the behavior of the resulting triblocks towards nanocomposite formation.
Significant exfoliation of clay platelets has been achieved in a commercial polylactide matrix using a “masterbatch” process (white arrows). 相似文献
Ring‐opening polymerization of D ,L ‐lactide is critically reevaluated under both microwave dielectric heating and conventional conduction/convection heating in order to probe the nonexistence of “nonthermal” microwave effects. All experiments are conducted in toluene by resorting to a fiber‐optic sensor that allows for accurate internal reaction temperature measurements. For a given temperature, the results obtained either with a “temperature control” microwave heating mode or with a “power control” procedure can well be reproduced through conventional thermal heating. Microwave irradiation does not induce any alteration of the polymerization kinetics or “livingness”, clearly demonstrating the absence of any specific “nonthermal” effect in the microwave‐assisted process. 相似文献
Summary: A series of PCL‐b‐PVPh diblock copolymers were prepared through combinations of ring‐opening and atom‐transfer radical polymerizations of ε‐caprolactone and 4‐acetoxystyrene, and subsequent selective hydrolysis of the acetyl protective group. This PCL‐b‐PVPh diblock copolymer shows a single glass transition temperature over the entire composition range, indicating that this copolymer is able to form a miscible amorphous phase due to the formation of intermolecular hydrogen bonding between the hydroxyl of PVPh and the carbonyl of PCL. In addition, DSC analyses also indicated that the PCL‐b‐PVPh diblock copolymers have higher glass transition temperatures than their corresponding PCL/PVPh blends. FT‐IR was used to study the hydrogen‐bonding interaction between the PVPh hydroxyl group and the PCL carbonyl group at various compositions.
FT‐IR spectra in the 1 680–1 780 cm?1 for PCL‐b‐PVPh copolymers with various PVPh contents. 相似文献
The ring‐opening polymerization (ROP) of trimethylene carbonate (TMC) initiated by a monoalcohol and catalyzed by CH3SO3H is investigated, in an effort to reveal extra features of the known activated monomer/active chain‐end (AM/ACE) combined mechanism. Size‐exclusion chromatography (SEC) profiles obtained with high‐molar‐mass samples show a poly(trimethylene carbonate) (PTMC) fraction generated by AM/ACE with a molar mass that is exactly twice that of the PTMC fraction coming from pure AM. Conversely, PTMC prepared with a diol is perfectly unimodal and keeps its molar mass dispersity below 1.1. This suggests that the side AM/ACE mechanism may be a bidirectional AM mechanism, and that PTMC with a narrow unimodal molar‐mass distribution can be obtained easily from a diol regardless of this side propagation. 相似文献
Copolymerization represents a modular synthetic strategy toward optochemical sensors by disassembling small molecule probes and recombining them to screen various fluorophore‐quencher combinations, instead of synthesizing individual sensor molecules. To demonstrate this, a polymerizable, fluorescent 1,6,7,12‐tetrachloroperylene‐3,4:9,10‐bis(dicarboximide) derivative with a norbornene ester side chain is prepared and copolymerized with a tertiary‐amine‐bearing monomer, as well as an oligo‐glycol‐bearing monomer, via ring‐opening metathesis polymerization (ROMP). In this manner, water‐soluble optical pH sensor polymers (with apparent pka values of 6.4–7) are obtained. The effect of the macromolecular architecture on the sensing performance is evaluated, whereby a diblock copolymer structure made of an oligoglycol segment and a segment containing the secondary amine and the fluorescent moiety is identified as being most favorable for pH sensing. Similarly, profluorescent polymers are obtained by employing nitroxides instead of secondary amines, which allows detection of ascorbic acid (with a detection limit of 0.1 × 10?3m ) in water.
Comb‐like copolymers based on a polyolefin backbone of poly(10‐undecene‐1‐ol) (PUol) with poly(ε‐caprolactone) (PCL) side chains are synthesized in two steps. After synthesis of PUol by metallocene‐catalyzed polymerization, the side‐chain hydroxyl functionalities of this polar polyolefin are used as an initiator for the ring‐opening polymerization (ROP) of ε‐caprolactone (CL). In this context, copolymers with different lengths of PCL grafts are prepared. The chemical structure and the composition of the synthesized copolymers are characterized by 1H and 13C NMR spectroscopy. It is shown that the hydroxyl end groups of PUol act effectively as initiating sites for the CL ROP. Size‐exclusion chromatography (SEC) measurements confirm the absence of non‐attached PCL and the expected increase in molar mass after grafting. The thermal and decomposition behaviors are investigated by DSC and thermogravimetric analysis (TGA). The effect of the length of the PCL grafts on the crystallization behavior of the comb‐like copolymers is investigated by DSC and wide‐angle X‐ray scattering (WAXS).
A series of long‐chain branched poly(d‐/l ‐lactide)s is synthesized in a two‐step protocol by (1) ring‐opening polymerization of lactide and (2) subsequent condensation of the preformed AB2 macromonomers promoted by different coupling reagents. The linear AB2 macromonomers are prepared by Sn(Oct)2‐catalyzed ROP of D ‐ and L ‐lactide with 2,2‐bis(hydroxymethyl)butyric acid (BHB) as an initiator. Optimization of the polymerization conditions allows for the preparation of well‐defined macromonomers (Mw/Mn = 1.09–1.30) with adjustable molecular weights (760–7200 g mol?1). The two‐step approach of the synthesis comprises as well the coupling of these AB2 macromonomers and hence allows precise control over the lactide chain length between the branching units in contrast to a random polycondensation. 相似文献
Macromonomers have been extensively used, as well defined building blocks for various macromolecular architectures via anionic, ROMP and free radical homo‐ or copolymerization processes. The purpose of the present work was to examine the homopolymerization and copolymerization of ω‐allyl, ω‐undecenyl and ω‐vinylbenzyl polystyrene (PS) macromonomers, in the presence of early or late transition metal catalysts. The influence of several parameters (type of catalytic system, nature of polymerizable end‐group and molar mass of the macromonomer) on the homopolymerization was first investigated. Whereas ω‐allyl or ω‐undecenyl PS macromonomers were not very reactive in homopolymerization whatever the catalyst, ω‐vinylbenzyl PS macromonomers gave interesting results with CpTiCl3/MAO and Cp*TiCl3/MAO. The copolymerization of these macromonomers with ethylene was also studied in the presence of the following palladium catalyst: [(ArN?C(Me)? C(Me)?NAr)Pd(CH2)3(COOMe)]+BAr4′?(VERSIPOL?) (Ar = 2,6‐iPr2–C6H3 and Ar′ = 3,5‐(CF3)2? C6H3). ω‐vinylbenzyl PS macromonomers could not be incorporated into poly(ethylene) chains. On the contrary, the incorporation of ω‐allyl PS macromonomers was achieved. Moreover, for macromonomers containing an alkyl spacer between the allylic unit and the PS chain, the incorporation rate, the copolymerization yield and the molar masses of the copolymers were increased, giving access to a new type of graft copolymer structure.
