The lower critical solution temperature (LCST) behavior of copolymers of N-isopropylacrylamide (NiPA) and N-isopropylmethacrylamide (NiPMA) in water was studied as a function of the copolymer composition, using a combination of turbidity measurements and differential scanning calorimetry (DSC). The copolymers were prepared by free radical polymerization using N,N-dimethylformamide as a solvent and α,α′-azobis(isobutyronitrile) as an initiator. The copolymer composition was determined by elemental analysis. It was found that the temperature (Tc) at which the copolymer undergoes a phase transition, i.e., LCST, increases linearly with increasing the mole fraction (fm) of NiPMA in the copolymer, within the Tc range from 32?°C (at fm?=?0; NiPA homopolymer) to 42?°C (at fm?=?1; NiPMA homopolymer). Also found from heating DSC thermograms were the linear dependencies of the enthalpy (ΔH) and entropy (ΔS) changes at Tc upon fm. However, the ΔH (5.5?kJ/unit-mol) at fm?=?1 was slightly smaller than that (5.7?kJ/unit-mol) of poly(N-n-propylacrylamide) but considerably smaller than that (7.8?kJ/unit-mol) of poly(N-n-propylmethacrylamide). The same trend was observed in the fm dependence of ΔS. These results were discussed in terms of the structural effects of the NiPMA monomer unit on the heat-induced phase transition in water of poly(NiPA-co-NiPMA)s. It was suggested that a strong interaction of water with the amide group in the NiPMA would raise the transition temperature, but a local dehydration which occurs around the isopropyl side chain would not lead to large changes in the enthalpy and entropy at Tc. 相似文献
Organic–inorganic pentablock copolymers have been synthesized via atom transfer radical polymerization (ATRP) of styrene (St) and vinyl acetate (VAc) monomers at 60 °C using CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine as a catalyst system initiated from boromoalkyl-terminated poly(dimethylsiloxane) (PDMS)/cyclodextrins macroinitiator (Br-PDMS/γ-CD). Br-PDMS-Br was reacted with γ-CD in different conditions with inclusion complexes being characterized through hydrogen nuclear magnetic resonance (1H NMR) and differential scanning calorimetry (DSC). Resulting Br-PDMS-Br/γ-CD inclusion complexes were taken as macroinitiators for ATRP of St and VAc. Well-defined poly(styrene)-b-poly(vinyl acetate)-b-poly(dimethylsiloxane/γ-cyclodextrin)-b-poly(vinyl acetate)-b-poly(styrene) (PSt-b-PVAc-b-PDMS/γ-CD-b-PVAc-b-PSt) pentablock copolymer was characterized by 1H NMR, gel permeation chromatograph (GPC) and DSC. There was a good agreement between the number-average molecular weight calculated from 1H NMR spectra and that of theoretically calculated. Pentablock copolymers consisting of Br-PDMS-Br/γ-CD inclusion complex as central blocks (inorganic block) and PVAc and PSt as terminal blocks were synthesized by this technique. PSt-b-PVAc-b-PDMS/γ-CD-b-PVAc-b-PSt pentablock copolymer can undergo a temperature-induced reversible transition upon heating of the copolymer complex from white complex at 22 °C to green complex in 55 °C which characterized with XRD and 1H NMR. XRD showed a change in crystallinity percent of St peak with changing the temperature which calculated by Origin75 software. 相似文献
The triblock copolymers, poly(styrene-b-isoprene-b-ε-caprolactone)s (PS-b-PI-b-PCL) have been synthesized successfully by combination of anionic polymerization and ring-opening polymerization. Diblock copolymer capped with hydroxyl group, PS-b-PI-OH was synthesized by sequential anionic polymerization of styrene and isoprene and following end-capping reaction of EO, and then it was used as macro initiator in the ring-opening polymerization of CL. The results of DSC and WAXD show big effect of amorphous PS-b-PI on the thermal behaviors of PCL block in the triblock copolymers and the lower degree of crystalline in the triblock copolymer with higher molecular weight of PS-b-PI was observed. The real-time observation on the polarized optical microscopy shows the spherulite growth rates of PCL27, PCL328 and PS-b-PI-b-PCL344 are 0.71, 0.46 and 0.07 μm s−1, respectively. The atomic force microscopy (AFM) images of the PS90-b-PI66-b-PCL28 show the columns morphology formed by it’s self-assembling. 相似文献
A double thermoresponsive ABC-type triblock copolymer(poly(ethyleneglycol)-block-poly(2-(2-methoxyethoxy) ethyl methacrylate)-block-poly(2-(2-methoxy ethoxy) ethyl methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate, PEG-b-PMEO_2MA-b-P(MEO_2MA-co-OEGMA)) was designed and synthesized by reversible additionfragmentation chain transfer polymerization(RAFT). The ABC-type triblock copolymer endowed a thermal-induced twostep phase transition at 29 and 39 °C, corresponding to the thermosensitive properties of PMEO_2 MA and P(MEO_2MA-coOEGMA) segments, respectively. The two-step self-assembly of copolymer solutions was studied by UV transmittance measurement, dynamic light scattering(DLS), transmission electron microscopy(TEM) and so on. The triblock copolymers showed the distinct thermosensitive behavior with respect to transition temperatures, aggregate type and size, which was correlated to the degree of polymerization of thermosensitive blocks and the molar fraction of OEGMA in the P(MEO_2MAco-OEGMA) segments. In addition, micelles could further aggregate to form the hydrogel by the self-associate of PEG chains under the abduction of the concentration and temperature. The transition from sol to gel was investigated by a test tube inverting method and dynamic rheological measurement. 相似文献
A combination of anionic polymerization, atom transfer radical polymerization (ATRP) and ??click?? chemistry was used to construct trishydrophilic ABC triblock terpolymers composed of a pH-sensitive A block, a water-soluble B block and two different thermo-sensitive C blocks without any block sequence limitation problems. First, an azido end-functionalized poly(2-vinylpyridine)-block-poly(ethylene oxide) (P2VP-b-PEO-N3) diblock copolymer was synthesized by anionic polymerization. In a second step, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(oligo(ethylene glycol) methacrylate) (POEGMA) were synthesized via ATRP using an alkyne functionalized initiator. The resulting polymers were attached to the P2VP-b-PEO-N3 diblock copolymer using the 1,3-dipolar Huisgen cycloaddition (??click?? chemistry). For the ??click?? step, P2VP-b-PEO-N3 diblock copolymers with either an azidoacetyl or a 2-azidoisobutyryl group were tested. In the latter case, however, a side reaction involving the cleavage of the formed ??click?? product via nucleophilic substitution occurred, preventing a permanent attachment of PDMAEMA or POEGMA to the P2VP-b-PEO-N3 diblock copolymer. Finally, P2VP-b-PEO-b-POEGMA (with POEGMA=P(MEO2MA-co-MEO8.5MA)) and P2VP-b-PEO-b-PDMAEMA triblock terpolymers were successfully synthesized and used to construct stimuli-responsive hydrogels. A concentrated solution of P2VP56-b-PEO370-b-P[(MEO2MA)89-co-(MEO8.5MA)7] showed a gel?Csol?Cgel transition at pH?7 upon temperature increase, whereas in the case of P2VP56-b-PEO370-b-PDMAEMA70, a gel?Csol or a weak gel?Cstrong gel transition was observed, depending on the applied pH. Finally, the addition of trivalent hexacyanocobaltate(III) ions to the P2VP56-b-PEO370-b-PDMAEMA70 solution induced an upper critical solution temperature for the PDMAEMA block, which led to gel formation. This allows for the construction of light-sensitive hydrogels, utilizing the photo-aquation of hexacyanocobaltate(III) ions. 相似文献
Nitroxide-mediated polymerization (NMP) was used to polymerize methacrylate-functionalized polyhedral oligomeric silsesquioxane, POSSMA, in a controlled manner with bio-based C13 methacrylate (C13MA) to improve the thermal stability of the latter by copolymerization (using 10 mol% acrylonitrile controlling comonomer). Kinetic experiments (80–110 °C) revealed the relatively low ceiling temperature of POSSMA (135 °C). Synthesis of poly(POSSMA-co-AN) with fAN,0 = 0.10 at 90 °C resulted in low dispersity (1.16) and relatively high conversion (~50%) after 3 hr in 50 wt% toluene. Assuming binary statistical copolymerizations, POSSMA was slightly less reactive than C13MA toward the propagating species (rPOSSMA = 0.91 ± 0.07 and rC13MA = 1.94 ± 0.13). Incorporating POSSMA up to 68 mol% improved decomposition temperature of C13MA-based copolymers from 190 to 262 °C. Chain end fidelity of POSSMA-rich compositions was confirmed by subsequent chain extensions to make block and gradient copolymers. Differential scanning calorimetry revealed multiple transition temperatures in block copolymers, suggesting microphase separation. Powder X-ray diffraction confirmed crystalline domains ~30 nm in POSSMA-rich statistical copolymers while transmission electron microscopy revealed weakly ordered lamellar morphology for poly(C13MA-co-AN)-b-(POSSMA-co-AN) block copolymer at a smaller length scale. Oscillatory shear measurements of block copolymers indicated primarily viscous character below 200 s−1 but crossover above this frequency, indicating POSS–POSS interactions were increasing the elasticity of the block copolymers. 相似文献
The stimuli-responsive copolymers with poly(ethylene oxide) (PEO) as side chain were prepared by free-radical copolymerization of methacrylamide end-capped PEO macromonomer and 4-vinylpyridine (4VP). Phase transition behavior of these copolymers of poly(4-vinylpyridine)-g-poly(ethylene oxide) (P4VP-g-PEO) was investigated as a function of polymer concentration, temperature, pH and ionic strength by monitoring the turbidity of the polymer solutions. The copolymers displayed sharp response to temperature and pH. The LCST of P4VP-g-PEO copolymer increased with the increase of PEO content and decreased with increasing pH due to the deprotonation of the pyridine ring, indicating well-tunable LCST. In addition, the LCST of P4VP-g-PEO9 presented a unique phase transition behavior with varying salt concentration, showing a minimum with 1 M NaCl solution at pH 6.0. 相似文献
Poly(N‐isopropylacrylamide)‐block‐poly(l ‐lactic acid)‐block‐poly(N‐isopropylacrylamide) (PNIPAAM‐b‐PLLA‐b‐PNIPAAM) and PNIPAAM‐b‐PDLA‐b‐PNIPAAM triblock copolymers with varying polylactic acid (PLA) lengths are synthesized using a combination of ring‐opening polymerization and atom‐transfer radical polymerization. Results of 1H NMR and gel permeation chromatography analyses show that the copolymers have a well‐defined triblock structure and the PLA segment lengths can be readily controlled with monomer feed ratio. Stereocomplexation between the enantiomeric PLA segments is confirmed with differential scanning calorimetry and wide‐angle X‐ray scattering. Dynamic light scattering experiments show that (1) the LCST of PNIPAAM in water could be tailored from 32 °C up to 38.5 °C by increasing the length of PLA segments and mixing copolymers of similar molecular weight with enantiomeric PLA segments to induce stereocomplexation, and (2) the LCST of each mixed copolymer system could be tailored within a 2–3 °C range of body temperature by manipulating the ratio of the enantiomeric copolymers in solution.