新型线状-树枝状两亲嵌段共聚物的合成

本文设计合成了一系列由不同链长的聚丙烯酸(PAA)为亲水嵌段和不同代数聚苄醚树枝体(Dendr.PBE)为疏水嵌段的杂化共聚物(PAA-Dendr.PBE)。     

Temperature-triggered reversible micellar self-assembly of linear-dendritic block copolymers

Polymeric micelles based on a thermoresponsive linear-dendritic block copolymer were completely disrupted into unimers upon cooling the solution to a temperature below its LCST and reversibly regenerated upon heating again.     

Liquid crystal polymers containing permanent dipole azobenzene chromophores

Three photochromic monomers containing a permanent dipole photochromic azobenzene group spaced from the methacryloyl moiety by a polymethylene segment were synthesized in three steps starting from 4-cyanoaniline. The monomers were homopolymerized and copolymerized with an optically active monomer, (-)-menthyl methacrylate, in the presence of AIBN as a radical initiator. Structurally similar amphiphilic polymers were obtained by homopolymerization of analogous methacrylates in which oligo(oxyethylene) segments replaced the polymethylene spacers. The polymeric materials, having a molar content of photochromic units between 5 and 100% and molecular weights of about 15,000, were characterized by thermal analysis, X-ray diffraction, 1D and 2D NMR. Mobility and photochromic properties in solution were also investigated.     

Solution behavior of linear-dendritic rod diblock copolymers in methanol

The solution behavior of spherical dendrimers as well as hybrid-linear dendritic diblock copolymers has been extensively studied, and the size, shape, and ability of these polymers to encapsulate small molecules have led to their comparison with traditional micelles. We have recently reported the synthesis of a new dendritic copolymer architecture, the linear-dendritic rod diblock copolymer, and in this work, we examine the solution behavior of these unique polymers in methanol at 25 degrees C, using dynamic light scattering and intrinsic viscosity measurements. The diblock copolymers consist of a linear poly(ethylene oxide)-poly(ethylene imine) diblock copolymer backbone around which poly(amido amine) branches have been divergently synthesized from the poly(ethylene imine) block. The hydrodynamic radii and the viscometric radii of the polymers were found to increase slowly with increasing generation up to generation 3.5; however, after generation 3.5, the radii were found to increase very rapidly. This increase can be explained by an elongation of the dendritic block into a more rodlike configuration and a corresponding breakdown of the spherical approximation used to calculate the radii. The intrinsic viscosity of the amine and ester terminated polymers was found to follow two very different trends at low generation; however, at higher generations, they followed similar, yet slightly different, curves with the values for the amine terminated polymers only a little larger than those of the ester terminated polymers. At low generations, the chemistry of the end groups and its interaction with the solvent were found to be more important, whereas at higher generations, the highly branched nature of the dendritic block was the more important factor. For the ester terminated polymers, a maximum in the intrinsic viscosity occurred at generation 1.5. Since this maximum occurred at a much lower generation number than is traditionally seen for spherical dendrimers, new scaling relations for the intrinsic viscosity of dendritic rod polymers were developed and were found to support this observation. A minimum in the intrinsic viscosity was also observed at generation 3.5 for the ester terminated polymers and a minimum or leveling off in the intrinsic viscosity at generation 4.0 was found for the amine terminated polymers, which can be attributed to the transitioning of the polymers to a more elongated, rodlike shape and the increased influence of the shape factor on the intrinsic viscosity.     

Synthesis and polymerization of amphiphilic methacrylates containing permanent dipole azobenzene chromophores

New amphiphilic photochromic methacrylates with the structures of 4‐[ω‐methacryloyloxyoligo(ethyleneglycol)]‐4′‐cyanoazobenzene (MEn) and 4‐methacryloyloxy‐4′‐{2‐cyano‐3‐oxy‐3‐[ω‐methoxyoligo(ethyleneglycol)]prop‐1‐en‐1‐yl}azobenzene (MEnMe) and oligo(oxyethylene) segments of different lengths were synthesized. These methacrylates were characterized by the presence of permanent dipole azobenzene chromophores and hydrophilic oligo (oxyethylene) segments. The methacrylates were obtained with six‐step and five‐step synthetic sequences, respectively, in 12–47% overall yields. The radical polymerization of the MEn monomers afforded a 50% yield of the corresponding polymers as orange solids with a number‐average molecular weight of about 40 kD. No solid polymer was obtained from the radical polymerization of the MEnME compounds. Two‐dimensional NMR spectra allowed the unequivocal assignment of the NMR signals and demonstrated a significant contribution of internal charge transfer to the electronic distribution of the azobenzene chromophore. Relaxation time measurements confirmed that the flexible polyether segment effectively decoupled photochromic groups from the polymer backbone. Optical microscopy, differential scanning calorimetry analysis, and X‐ray diffraction data demonstrated the presence of interdigitated smectic mesophases. The stability of mesophases showed a significant dependence on the chemical structure of the analyzed compounds. The glass‐transition temperatures of the polymers were rather low because of the plasticizing effect of the spacers. The monomers and polymers were used for the deposition of Langmuir films and Langmuir–Blodgett–Kuhn multilayers. A strong influence of the macromolecular structure on the film properties was observed. The photoresponsive properties of monomers and polymers were investigated with irradiation at different wavelengths. Isomerization kinetics were independent of both molecular weight and spacer length. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2957–2977, 2001     

Stimuli-responsive supramolecular assemblies of linear-dendritic copolymers

With the goal of developing a pH-responsive micelle system, linear-dendritic block copolymers comprising poly(ethylene oxide) and either a polylysine or polyester dendron were prepared and hydrophobic groups were attached to the dendrimer periphery by highly acid-sensitive cyclic acetals. These copolymers were designed to form stable micelles in aqueous solution at neutral pH but to disintegrate into unimers at mildly acidic pH following loss of the hydrophobic groups upon acetal hydrolysis. Micelle formation was demonstrated by encapsulation of the fluorescent probe Nile Red, and the micelle sizes were determined by dynamic light scattering. The structure of the dendrimer block, its generation, and the synthetic method for linking the acetal groups to its periphery all had an influence on the critical micelle concentration and the micelle size. The rate of hydrolysis of the acetals at the micelle core was measured for each system at pH 7.4 and pH 5, and it was found that all systems were stable at neutral pH but underwent significant hydrolysis at pH 5 over several hours. The rate of hydrolysis at pH 5 was dependent on the structure of the copolymer, most notably the hydrophobicity of the core-forming block. To demonstrate the potential of these systems for controlled release, the release of Nile Red as a "model payload" was examined. At pH 7.4, the fluorescence of micelle-encapsulated Nile Red was relatively constant, indicating it was retained in the micelle, while at pH 5, the fluorescence decreased, consistent with its release into the aqueous environment. The rate of release was strongly correlated with the rate of acetal hydrolysis and was therefore controlled by the chemical structure of the copolymer. The mechanism of Nile Red release was investigated by monitoring the change in size of the micelles over time at acidic pH. Dynamic light scattering measurement showed a size decrease over time, eventually reaching the size of a unimer, thus providing evidence for the proposed micelle disintegration.     

Photoinduced chirality in achiral liquid crystalline polymethacrylates containing bisazobenzene and azobenzene chromophores

One new liquid crystalline polymer containing bisazobenzene, poly[4-{(2-methacryloyloxyethyl)oxy}-4′-(4-nitrophenylazo)azobenzene] (PM2BAN), and two liquid crystalline polymers containing azobenzenes with spacers of two and six methylene units, poly[(4-(4′-nitrophenylazo)phenyloxy)x-methylene methacrylate] (PMxAN, x = 2, 6), were synthesized and characterized. The level and rate of photoinduced chirality were studied in films of the achiral polymers by irradiation with one handed circularly polarized light (CPL) at 442 nm. The results of circular dichroism (CD) suggest that left-CPL induces left helical arrangements of the polymers and right-CPL reverses the resulting arrangements into right helices. Photoinduced chirality in film of PM2BAN is increased with the increase of irradiation time. However, the level and rate of photoinduced chirality in film of PM2BAN are lower than those in films of PMxAN (x = 2, 6) at similar irradiation time. Compared with PM2AN, photoinduced CD values are higher in PM6AN. The results are discussed in terms of interactions between azobenzene chromophores and circularly polarized light.     

Flash memory effects based on styrene/maleimiade copolymers with pendant azobenzene chromophores

Two styrene/maleimiade copolymers with pendant azobenzene chromophores, poly(styrene-1-(4-phenylazo-phenyl)-pyrrole-2,5-dione) (PS-DP) and poly((4-vinyl-benzyl)-9H-carbazole-1-(4-phenylazo-phenyl)-pyrrole-2,5-dione) (PVCz-DP), were synthesized. The polymeric memory devices based on each of the two polymer films (ITO/Polymer/Al) show similar rewritable flash memory behaviors but different transition voltages. By introduction of carbazole groups in the polymer side chains, the voltage difference from OFF to ON state of ITO/PVCz-DP/Al is reduced obviously in comparison with that of ITO/PS-DP/Al, which is beneficial to the protection of devices. Both ITO/PS-DP/Al and ITO/PVCz-DP/Al show high stability under a constant stress or continuous read pulses voltage of 1.0 V. The memory mechanism is governed by space-charge limited conduction (SCLC) on the basis of the I–V curves of these fabricated memory devices. With excellent flash memory characteristics and simple processability, the memory devices fabricated with these two styrene/maleimiade copolymers have potential applications for the future electronic memory devices.     

Synthesis and chiroptical properties of optically active polymer liquid crystals containing azobenzene chromophores

A series of optically active methacrylic homopolymers, poly[(4‐{4′‐[(S)‐2‐methyl‐1‐butyloxycarbonyl]phenylazo}phenoxyl)x‐methylene methacrylate] (x = 0, 2, 6, or 11), were synthesized. The structures of the polymers were characterized by IR, ¹H NMR, UV, differential scanning calorimetry, and gel permeation chromatography. The chiroptical properties of the polymers in films were investigated with circular dichroism (CD) measurements. The CD and UV spectra of the films suggested that CD absorptions occurred in the films of the polymers with long spacers (x = 6 or 11) but not in the films of the polymers with short spacers (x = 0 or 2). After irradiation with linearly polarized light at 442 nm, the CD values were amplified in all the polymeric films. The amplificatory values of the CD bands in the absorption region (260–360 nm) of azobenzene chromophores suggested that the spacer length had an effect on both the transfer of chirality and photoinduced chirality in the polymeric films. The largest level of photoinduced chirality was induced in the polymer containing six methylene units. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3210–3219, 2006     

Polyisobutylene containing organic/inorganic hybrid block copolymers and their crystalline behavior

Block copolymer comprising of polyisobutylene (PIB) soft segment and poly(3‐(3,5,7,9,11,13,15‐heptaisobutyl‐pentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]‐octasiloxane‐1‐yl)propyl methacrylate) (PMAPOSS) hard segment was synthesized by combination of living carbocationic and reversible addition‐fragmentation chain transfer (RAFT) polymerizations. Block copolymers were characterized by ¹H and ²⁹Si NMR spectroscopy, FT‐IR study, energy dispersive X‐ray spectroscopy (EDX), and gel permeation chromatography (GPC). The EDX, combined with scanning electron microscopy (SEM) was employed for determination of elemental composition. Thermal transition and degradation behaviors were confirmed by differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA), respectively. Although both the PIB and MAPOSS homopolymers are amorphous in nature, in their block copolymers the PMAPOSS domain showed crystalline behavior, as confirmed from wide‐angle X‐ray scattering (WAXS) technique, DSC studies and polarized optical microscopy (POM). Interestingly, crystalline melting temperatures (T_m) can be tuned by changing the PIB to PMAPOSS block length ratios. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1125–1133     

Synthesis and characterization of luminescent copolymers containing iminodibenzyl and divinylbenzene chromophores

New conjugated copolymers containing alternating N‐hexyl‐3,8‐iminodibenzyl and divinylbenzene chromophores {poly(N‐hexyl‐3,8‐iminodibenzyl‐1,2‐ethenylene‐2,5‐dihexyloxy‐1,4‐phenylene‐1,2‐ethenylene) ( P1 ) and poly[N‐hexyl‐3,8‐iminodibenzyl‐2,5‐bis(hexyloxy)cyanoterephthalidene] ( P2 )} were synthesized according to Wittig and Knoevenagel polymerization. A copolymer containing alternating carbazole and divinylbenzene derivatives {poly[9‐(2‐ethylhexyl)‐3,6‐carbazole‐1,2‐ethenylene‐2,5‐dihexyloxy‐1,4‐phenylene‐1,2‐ethenylene] ( P3 )} was also synthesized for comparison. The copolymers were soluble in common organic solvents such as tetrahydrofuran and toluene. Absorption and photoluminescence measurements revealed that cyano substitution at the vinylene moiety in P2 brought about a significant bathochromic shift and led to an electroluminescence color change from green to orange. The band edge energies of the copolymers were estimated from cyclic voltammograms and optical band gaps. P1 and P3 showed similar highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, indicating that the electron‐donating abilities of the iminodibenzyl and carbazole chromophores were comparable. However, compared with those of P1 and P3 , the HOMO and LUMO levels of P2 were greatly reduced because of conjugating and electron‐withdrawing CN groups. The threshold electric field of an Al/ P1 /ITO glass single‐layer light‐emitting diode was approximately 10 × 10⁵ V/cm, whereas those for P2 and P3 were 7.5 and 16 × 10⁵ V/cm, respectively. The electroluminescence emission maxima of P1–P3 were 498, 514, and 559 nm, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3847–3857, 2002     

Two-photon degradable supramolecular assemblies of linear-dendritic copolymers

Micelles of dendritic-linear copolymers have been developed to release a payload after infrared stimulus.     

Review of the recent progress in photoresponsive molecularly imprinted polymers containing azobenzene chromophores

Photoresponsive molecularly imprinted polymers (PMIPs) containing azobenzene have received wide research attention in recent years and made notable achievements. This article reviews the recent developments on PMIPs containing azobenzene. Topics include the following: (i) brief introduction of azobenzene, molecularly imprinted polymers, and PMIPs containing azobenzene; (ii) progress in functional monomers, cross-linkers, and polymerization conditions; (iii) preparation methods, properties, applications, as well as advantages and disadvantages of conventional PMIPs; (iv) substrate, preparation method, and applications of photoresponsive surface molecularly imprinted polymers; and (v) some perspectives for further development of PMIPs containing azobenzene.     

Photochromic LC copolymers containing azobenzene and crown‐ether groups

An approach for the creation of a novel family of multifunctional crown‐ether‐containing comb‐shaped copolyacrylates consisting of chromophoric (azobenzene), ionophoric (crown‐ether), and mesogenic groups in the same macromolecule was developed. Phase behavior of the copolymers was studied, and correlation between their molecular structure and thermal properties was established. The increase of crown‐ether‐containing groups' concentration up to 26 mol % leads to disruption of nematic order and formation of amorphous phase. Influence of copolymers complexation with potassium perchlorate on mesomorphic properties of such systems was investigated. It was shown that complexation leads to decrease in mesophase thermostability due to the significant reducing of the side group anisometry by perchlorate counter ion. The comparative investigations of photooptical properties and photoorientation processes of copolymers and their complexes were also performed. An essential difference in kinetics of photooptical behavior was revealed; the bulky crown‐ether substituents decrease rotational mobility and prevent photoorientation process of azobenzene fragments diminishing photoinduced orientation and order parameter. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6532–6541, 2008     

Effects of stereocomplexation on the physicochemical behavior of PLA/PEG block copolymers in aqueous solution

A series of polylactide/poly(ethylene glycol) (PLA/PEG) block copolymers were synthesized by ring‐opening polymerization of L ‐ or D ‐lactide in the presence of mono‐ or di‐hydroxyl PEG. The effects of stereocomplexation on the physicochemical behavior of PLA/PEG copolymers in aqueous solution were investigated by varying the degree of stereocomplexation or PLLA/PEG to PDLA/PEG ratio. In mixture solutions of insoluble and soluble copolymers, stereocomplexation strongly affects the solubility of the copolymers. In mixture solutions of soluble copolymers, both the size and aggregation number (N_agg) of the aggregates vary as a function of the degree of stereocomplexation. It is suggested that the size variation of the aggregates with increasing the degree of stereocomplexation is dependent on N_agg changes which are determined by two effects: the self‐adjusting of the aggregates so as to minimize the free energy and thus to increase the N_agg, and the kinetics of aggregation which tend to form more aggregates and thus to decrease the N_agg. Combination of the two opposite effects well explains the diverse variations of N_agg and size of the aggregates as a function of the degree of stereocomplexation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012