Photoinduced orientation of liquid crystalline copolymer films containing 4-oxybenzoic acid side groups and photo-cross-linkable mesogenic side groups

The cooperative molecular reorientation in methacrylate copolymer films with hexamethylene spacer groups terminated with 4-oxybenzoic acid (BA) and 4-(4-methoxycinnamoyloxy)biphenyl (MCB) in their side chains was investigated by irradiating with linearly polarized ultraviolet light (LPUV) and subsequent annealing. A high degree of cooperative in-plane reorientation of both the BA and MCB groups was obtained when the composition of the BA groups was greater than 50 mol% and hydrogen (H)-bonded LC mesogenic dimers of BA molecules existed. On the other hand, the molecular reorientation was restricted when the BA groups did not form H-bonds. It was clarified that the amount of axis-selectively photoreacted MCB groups and the H-bonds of the BA groups that exhibit a LC nature play important roles in the thermally enhanced molecular reorientation.     

Molecular reorientation behavior of photocrosslinkable liquid-crystalline polymer films containing phenylamide side chains

The cooperative molecular reorientation in methacrylate copolymer films comprising photoreactive 4-(4-methoxycinnamoyloxy)biphenyl and phenylamide in their side chains was investigated by irradiation with linearly polarized ultraviolet light and subsequent annealing. Both cinnamate and phenylamide side groups were miscible in the copolymer composition, and axis-selective photoreaction of the cinnamate groups was observed. Thermally enhanced cooperative in-plane orientation of both side groups was obtained when the irradiated films were annealed in the liquid-crystalline temperature range of the copolymers.     

Esterification of hydroxylated polymers with 2-sulfobenzoic acid cyclic anhydride: A facile approach for the synthesis of near-monodisperse strong acid homopolymers and diblock copolymers

A convenient two-step route was developed to prepare a range of low polydispersity strong acid homopolymers and several examples of well-defined diblock copolymers. Atom transfer radical polymerization (ATRP) of either 2-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate or glycerol monomethacrylate afforded the corresponding near-monodisperse hydroxylated homopolymers, while several diblock copolymer precursors were prepared by either (1) the one-pot ATRP of 2-hydroxypropyl methacrylate and 2-(diethylamino)ethyl methacrylate using sequential monomer addition or (2) the ATRP of either 2-hydroxypropyl methacrylate or glycerol monomethacrylate using a poly(ethylene oxide)-based macro-initiator. Excess 2-sulfobenzoic acid cyclic anhydride was used to fully esterify the hydroxy groups of these homopolymers and diblock copolymers under mild conditions. The resulting zwitterionic diblock copolymers undergo micellar self-assembly on adjusting the pH of the solution, while one of the anionic poly(ethylene oxide)-based diblock copolymers formed colloidal polyelectrolyte complexes in aqueous solution when mixed with a cationic poly(ethylene oxide)-based diblock copolymer.     

Synthesis of amphiphilic diblock copolymers by direct radical polymerization of acrylic acid via DPE method

Amphiphilic diblock copolymers, poly(methyl methacrylate)-b-poly(acrylic acid) (PMMA-b-PAA) was prepared by 1,1-diphenylethene (DPE) method. First, free radical polymerization of methyl methacrylate was carried out with AIBN as initiator in the presence of DPE, giving a DPE-containing PMMA precursor with controlled molecular weight. Amphiphilic diblock copolymer PMMA-b-PAA was then prepared by radical polymerization of acrylic acid (AA) in the presence of PMMA precursor. The formation of PMMA-b-PAA was confirmed by ¹H NMR spectrum and gel permeation chromatography. Transmission electron microscopy and dynamic light scattering were used to detect the self-assembly behavior of the amphiphilic diblock polymers in methanol.     

Surface characterization of biocompatible polysulfone membranes modified with poly(ethylene glycol) derivatives

Self-transformable and blood compatible devices of sulfonated poly(ethylene glycol) acrylate diblock copolymer (PEG-SO₃A/OA) with hydrophilic and hydrophobic block entrapped to polysulfone membrane surface were investigated in terms of the degree of hydrophilicity. The asymmetric membrane was formed by phase inversion process, and the induced hydrophilicity by reorientation of diblock copolymer at interface was verified with contact angle measurement, electron spectroscopy for chemical analysis (ESCA) depth profiling with ion sputtering and platelet adhesion test. Molecular dynamics (MD) simulations for the interface of hydration layer were also performed with various hydrophilic copolymer densities to gain optimum interfacial structure in information. The dependency of water clustering behavior around diblock copolymers as a hydrophilicity parameter was described in terms of atom-atom radial distribution function (RDF). The results showed that the diblock copolymer entrapped surfaces demonstrated less platelet adhesion than control or copolymers having no hydrophobic blocks. In addition, oxygen composition significantly began to decrease deeper into the membrane, indicating the reorientation of diblock chains. Copolymer entrapped surfaces significantly induced the degree of water clustering, and the resulting equilibrium rearrangement of interfacial structures was distinctly dependent upon the density of copolymer. Taken together, the results show that the novel concept ofin situ self-transformable surface modification strategy was successfully developed for biocompatible ultrathin biomedical membrane device.     

Preparation and characterization of proton‐conducting crosslinked diblock copolymer membranes

The synthesis and properties of crosslinked diblock copolymers for use as proton‐conducting membranes are presented. A polystyrene‐b‐poly(hydroxyl ethyl methacrylate) diblock copolymer at 56 : 44 wt % was sequentially synthesized via atom transfer radical polymerization. The poly(hydroxyl ethyl methacrylate) (PHEMA) block was thermally crosslinked by sulfosuccinic acid (SA) via the esterification reaction between  OH of PHEMA and  COOH of SA. Proton nuclear magnetic resonance and Fourier transfer infrared spectra revealed the successful synthesis of the diblock copolymer and the crosslinking reaction under the thermal condition of 120°C for 1 h. The ion‐exchange capacity continuously increased from 0.25 to 0.98 mequiv/g with increasing SA concentration because of the increasing number of charged groups in the membrane. However, the water uptake increased up to an SA concentration of 7.6 wt %, above which it decreased monotonically (maximum water uptake ∼ 27.6%). The membrane also exhibited a maximum proton conductivity of 0.045 S/cm at an SA concentration of 15.2 wt %. The maximum behavior of the water uptake and proton conductivity with respect to the SA concentration was considered to be due to a competitive effect between the increase of ionic sites and the crosslinking reaction according to the SA concentration. All the membranes were thermally quite stable at least up to 250°C, presumably because of the block‐copolymer‐based, crosslinked structure of the membranes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Synthesis, characterization and evaluation of amphiphilic diblock copolymer emulsifiers based on methoxy hexa(ethylene glycol) methacrylate and benzyl methacrylate

Linear, amphiphilic diblock copolymers based on the nonionic, hydrophilic monomer methoxy hexa(ethylene glycol) methacrylate (HEGMA) and the hydrophobic monomer benzyl methacrylate (BzMA) of different molecular weights and compositions were synthesized by group transfer polymerization. The molecular weights and comonomer compositions of these copolymers were characterized by gel permeation chromatography and proton nuclear magnetic resonance (¹H NMR) spectroscopy, respectively. Dynamic light scattering on aqueous solutions of the diblock copolymers indicated that all the copolymers formed aggregates whose size increased with the % w/w BzMA composition and with the overall molecular weight of the linear chains. Turbidimetry on 1% w/w aqueous copolymer solutions was used to determine the cloud points, which were found to increase with the composition in hydrophilic units and the linear chain molecular weight. After polymer characterization, xylene/water and diazinon (pesticide)/water emulsions were prepared using the above polymers as stabilizers at 1% w/w polymer concentration and at different overall organic phase/water ratios. At an organic phase/water mass ratio of 4/1, the lower molecular weight (2500 and 5000 g mol⁻¹) diblock copolymers provided stable single-phase o/w emulsions, matching the behavior of commercially available hydrophilic Pluronics.     

Synthesis of azobenzene‐containing side chain liquid crystalline diblock copolymers using RAFT polymerization and photo‐responsive behavior

Well‐defined azobenzene‐containing side chain liquid crystalline diblock copolymers composed of poly[6‐[4‐(4‐methoxyphenylazo)phenoxy]hexyl methacrylate] (PAzoMA) and poly(glycidyl methacrylate) (PGMA) were synthesized by a two‐step reversible addition–fragmentation chain transfer polymerization (RAFT). The thermal liquid‐crystalline phase behavior of the PGMA‐b‐PAzoMA diblock copolymers in bulk were measured by differential scanning calorimetry (DSC) and polarized light microscopy (POM). The synthesized diblock copolymers exhibited a smectic and nematic liquid crystalline phase over a relatively wide temperature range. With increasing the weight fraction of the PAzoMA block, the phase transition temperatures, and corresponding enthalpy changes increased. Atomic force microscope (AFM) measurements confirmed the formation of the microphase separation in PGMA‐b‐PAzoMA diblock copolymer thin films and the microphase separation became more obvious after cross‐linking the PGMA block. The photochemical transition behavior of the PGMA‐b‐PAzoMA diblock copolymers in solution and in thin films were investigated by UV–vis spectrometry. It was found that the trans–cis isomerization of diblock copolymers was slower than that of the corresponding PAzoMA homopolymer and the photoisomerization rates decreased with increasing either the length of PAzoMA block or PGMA block. The photo‐induced isomerization in solid films was quite different with that in CHCl₃ solution due to the aggregation of the azobenzene chromophore. The cross‐linking structures severely suppressed the photoisomerization of azobenzene chromophore. These results may provide guidelines for the design of effective photo‐responsive anisotropic materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2165–2175, 2013     

Microphase separation behavior on the surfaces of poly(dimethylsiloxane)‐block‐poly(2,2,3,3,4,4,4‐heptafluorobutyl methacrylate) diblock copolymer coatings

Microphase separation behavior on the surfaces of poly(dimethylsiloxane)‐block‐poly(2,2,3,3,4,4,4‐heptafluorobutyl methacrylate) (PDMS‐b‐PHFBMA) diblock copolymer coatings was investigated. The PDMS‐b‐PHFBMA diblock copolymers were successfully synthesized via atom transfer radical polymerization (ATRP). The chemical structure of the copolymers was characterized by nuclear magnetic resonance and Fourier transform infrared spectroscopy. Surface composition was studied by X‐ray photoelectron spectroscopy. Copolymer microstructure was investigated by atomic force microscopy. The microstructure observations show that well‐organized phase‐separated surfaces consist of hydrophobic domain from PDMS segments and more hydrophobic domain from PHFBMA segments in the copolymers. The increase in the PHFBMA content can strengthen the microphase separation behavior in the PDMS‐b‐PHFBMA diblock copolymers. And the increase in the annealing temperature can also strengthen the microphase separation behavior in the PDMS‐b‐PHFBMA diblock copolymers. Moreover, Flory‐Huggins thermodynamic theory was preliminarily used to explain the microphase separation behavior in the PDMS‐b‐PHFBMA diblock copolymers.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of novel rod–coil diblock copolymers of poly(methyl methacrylate) and liquid crystalline segments of poly(2,5‐bis[(4‐methoxyphenyl)oxycarbonyl] styrene)

Liquid crystalline diblock copolymers with different molecular weights and low polydispersities were synthesized by atom transfer radical polymerization of methyl methacrylate (MMA) and 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene (MPCS) monomers. The block architecture (coil‐conformation of MMA segment and rigid‐rod of MPCS segment) of the copolymer was experimentally confirmed by a combination of ¹H nuclear magnetic resonance and gel permeation chromatograph techniques. The liquid crystalline behaviour of the copolymer was studied using differential scanning calorimetry and polarized optical microscope. It was found that the liquid crystalline behaviour was dependent on the number average molecular weight of the rigid segment. Only those copolymers with M_n(GPC) of the rigid block above 9200 g mol^?1 could form liquid crystalline phases higher than the glass transition temperature of the rigid block. The random copolymers MPCS‐co‐MMA were also synthesized by conventional free radical polymerization. The molar content of MPCS in MPCS‐co‐MMA had to be higher than 71% to maintain liquid crystalline behaviour. © 2003 Society of Chemical Industry     

Photoinduced molecular reorientation in photoreactive liquid crystalline copolymers in a phase retarder application

Polymethacrylate copolymers, which have hexamethylene spacer groups terminated with 4-methoxyphenyl-4′-oxycinnamate (MPC) and 4-oxybenzoic acid (BA) in the side chain, were synthesized. Thin films underwent thermally enhanced photoinduced cooperative molecular reorientation using linearly polarized ultraviolet (LPUV) light and subsequent annealing. Moreover, low exposure energy (4-80 mJ cm⁻²) and annealing temperature (<140 °C) provided sufficient cooperative molecular reorientation of both side groups with a large reorientational order (S > 0.5). Tuning the copolymer composition adjusted the birefringence (?n) of homogeneously reoriented films between 0.10 and 0.22 at 517 nm. Finally, a phase retarder (?nd = 130 nm) using an oriented copolymer on a triacetylcellulose (TAC) film substrate, which exhibited a thermal stability up to 140 °C, was fabricated.     

含氟嵌段丙烯酸酯聚合物/环氧树脂自分层涂料的制备与性能

利用引发剂连续再生催化剂原子转移自由基聚合(ICAR-ATRP)合成了一系列结构可控的含有含氟丙烯酸酯和甲基丙烯酸缩水甘油酯(GMA)的两嵌段丙烯酸酯聚合物,即聚(甲基丙烯酸丁酯-co-甲基丙烯酸缩水甘油酯)-b-聚甲基丙烯酸十二氟庚酯[P(BMA-co-GMA)-b-PDFHMA,BGF]。将嵌段聚合物与环氧树脂混合制备自分层涂料。傅里叶变换红外光谱(FT-IR)和扫描电子显微镜-能谱分析仪(SEM-EDS)测试表明,当两嵌段聚合物中P(BMA)-co-GMA与PDFHMA的相对分子质量分别为5 300和2 300、GMA结构单元相对分子质量占总相对分子质量的20%,且BGF用量为10%时,漆膜固化过程中含氟嵌段聚合物可以部分迁移到漆膜表面,共混漆膜氟元素自迁移效果较好,表层氟含量达到20%以上,且增加含氟树脂中GMA含量时漆膜氟元素迁移效果下降;耐紫外老化性测试结果表明,含氟树脂的加入使得漆膜的光泽保持率更好,耐黄变性变化不大;水接触角和耐盐雾性测试结果表明,相对纯环氧树脂,加入10%含氟嵌段聚合物使漆膜的水接触角均提高到了100°以上,自分层漆膜的耐盐雾性都有一定提高,可以有效防止漆膜的起泡。嵌段聚合物的加入量低于4%时,对漆膜的基本力学性能没有影响,但光泽有一定下降。     

Synthesis and characterization of perfluorocyclobutyl aryl ether-based amphiphilic diblock copolymer

Perfluorocyclobutyl aryl ether-based amphiphilic diblock copolymer containing hydrophilic poly(ethylene glycol) segment was synthesized by atom transfer radical polymerization (ATRP). Perfluorocyclobutyl-containing methacrylate-based monomer, 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate, was prepared firstly, which can be polymerized by ATRP in a controlled way to obtain well-defined homopolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.30). The molecular weights increased linearly with the conversions of monomer and the apparent polymerization rate exhibited first-order relation with respect to the concentration of monomer. ATRP of 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate was initiated by PEG-based macroinitiators with different molecular weights to obtain amphiphilic diblock copolymers with narrow molecular weight distributions (M_w/M_n < 1.35) and the number of perfluorocyclobutyl linkage can be tuned by the feed ratio and the conversion of the fluorine-containing methacrylate monomer. The critical micelle concentrations of these amphiphilic diblock copolymers in water and brine were determined by fluorescence probe technique. The morphologies of the micelles were found to be spheres by TEM.     

Preparation of amphiphilic PS-b-PMAA diblock copolymer by means of atom transfer radical polymerization

Amphiphilic diblock copolymers of polystyrene-b-poly(methacrylic acid) were synthesized by means of atom transfer radical polymerization. First, the polystyrene with a bromine atom at the chain end (PS-Br) was prepared using styrene as the monomer, 1-bromoethyl benzene as the initiator, and CuCl/2,2′-bipyridyl (bpy) as the catalyst ([1-bromoethyl benzene]/[CuCl]/[bpy] = 1:1:3). The polymerization was well controlled. Second, the diblock copolymer of polystyrene-b-poly(tert-butyl methacrylate) was synthesized also by atom transfer radical polymerization using PS-Br as the macro-initiator, CuCl/bpy as the catalyst, and tert-butyl methacrylate (tBMA) as the monomer. Finally, the amphiphilic diblock copolymer, PS-b-PMAA, was obtained by hydrolysis of PS-b-PtBMA under the acid condition. The molecular weight and the structure of aforementioned copolymers were characterized with gel permeation chromatography, infrared, and nuclear magnetic resonance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2381–2386, 2001     

Synthesis and characterization of pH/temperature-sensitive block copolymers via atom transfer radical polymerization

In order to prepare well-defined pH-sensitive block copolymers with a narrow molecular weight distribution (MWD), we synthesized a pH-sensitive block copolymer via atom transfer radical polymerization (ATRP) of sulfamethazine methacrylate monomer (SM) and amphiphilic diblock copolymers by the ring-opening polymerization of d,l-lactide/?-caprolactone (LA/CL), and their sol-gel phase transition was investigated. SM, which is a derivative of sulfonamide, was used as a pH responsive moiety, while PCLA-PEG-PCLA was used as a biodegradable, as well as a temperature sensitive one, amphiphilic triblock copolymer. The pentablock copolymer, OSM-PCLA-PEG-PCLA-OSM, was synthesized using Br-PCLA-PEG-PCLA-Br as an ATRP macroinitiator. The number average molecular weights of SM were controlled by adjusting the monomer/initiator feed ratio. The macroinitiator was synthesized by the coupling of 2-bromoisobutyryl bromide with PCLA-PEG-PCLA in the presence of triethyl amine catalyst in dichloromethane. The resultant block copolymer shows a narrow polydispersity. The block copolymer solution shows a sol-gel transition in response to a slight pH change in the range of 7.2-8.0. Gel permeation chromatography (GPC) and NMR were used for the characterization of the polymers that were synthesized.     

Synthesis and characterization of temperature and pH-responsive pentablock copolymers

A family of amphiphilic ABCBA pentablock copolymers based on commercially available Pluronic^® F127 block copolymers and various amine containing methacrylate monomers was synthesized via Cu(I) mediated controlled radical polymerization. The block architecture and chemical composition of the pentablock copolymers were engineered to exhibit both temperature and pH responsive self-assembly by exploiting the lower critical solution temperature of the poly(ethylene oxide)/poly(propylene oxide) blocks and the polycationic property of the poly(amine methacrylate) blocks, respectively. In aqueous solutions, the pentablock copolymers formed temperature and pH-responsive micelles. Concentrated aqueous solutions of the copolymer formed a pH-responsive, thermoreversible gel phase. The controlled radical synthesis route yielded well-defined copolymers with narrow molecular weight distributions with the benefit of mild reaction conditions. Small angle X-ray scattering, laser light scattering, cryogenic transmission electron microscopy and dynamic mechanical analysis have been used to characterize the self-assembled structures of the micellar solution and gel phases of the aqueous copolymer system. These copolymers have potential applications in controlled drug delivery and non-viral gene therapy due to their tunable phase behavior and biocompatibility.     

Self‐assembled nanostructures: preparation,characterization, thermal,optical and morphological characteristics of amphiphilic diblock copolymers based on poly(2‐hydroxyethyl methacrylate‐block‐N‐phenylmaleimide)

A series of well‐defined amphiphilic poly[(2‐hydroxyethyl methacrylate)‐block‐(N‐phenylmaleimide)] diblock copolymers containing hydrophilic and hydrophobic blocks of different lengths were synthesized by atom transfer radical polymerization. The properties of the diblock copolymers and their ability to form large compound spherical micelles are described. Their optical, morphological and thermal properties and self‐assembled structure were also investigated. The chemical structure and composition of these copolymers have been characterized by elemental analysis, Fourier transform infrared, ¹H NMR, UV–visible and fluorescence spectroscopy, and size exclusion chromatography. Furthermore, the self‐assembly behavior of these copolymers was investigated by transmission electron microscopy and dynamic light scattering, which indicated that the amphiphilic diblock copolymer can self‐assemble into micelles, depending on the length of both blocks in the copolymers. These diblock copolymers gave rise to a variety of microstructures, from spherical micelles, hexagonal cylinders to lamellar phases. © 2013 Society of Chemical Industry     

四官能度过氧化物JWEB50引发的PS-b-PMMA合成与表征

引言嵌段共聚物是具有两种或两种以上不同链段的聚合物,不同链段间存在的化学键限制了聚合物的相分离程度,易形成微相分离结构[1],而嵌段共聚物能作为聚合物共混体系的相容剂,只需加入少量     

Effect of acrylic diblock copolymer upon interfacial adhesion

The preparation and adhesion properties of poly(methyl methacrylate–butyl acrylate)[P(MMA-b-BA)] diblock copolymers have been studied. Block copolymers were analyzed by ¹H-NMR, DSC, and SEC, and confirm the synthesis of diblock copolymers, using the iniferter route. Investigation of peel strength in laminate joints, reinforced with various block copolymers, suggests that adhesion depends on both molecular weight and composition. When the copolymer contains mainly PMMA block, molecular weight has a marked effect, with adhesion being enhanced at higher copolymer molecular weight. For other PBA/PMMA compositions, no reinforcement was seen, irrespective of molecular weight. © 1996 John Wiley & Sons, Inc.     

Sustained release of ibuprofen from polymeric micelles with a high loading capacity of ibuprofen in media simulating gastrointestinal tract fluids

Amphiphilic diblock copolymers with poly(ethylene glycol) as the hydrophilic block and a random copolymer of n-butyl methacrylate or styrene and (N,N-diethylamino)ethyl methacrylate as the hydrophobic block were prepared by atom transfer radical polymerization (ATRP). Ibuprofen, a model drug that contains a carboxylic group and hydrophobic moiety, was loaded into micelles formed from the amphiphilic diblock copolymers by a combination of ionic interaction and hydrophobic effect. The loading capacity of ibuprofen in the micelles reached 60%. Loaded ibuprofen was released in a sustained fashion into media simulating gastric fluid (pH 1.6, 2 h), small intestinal fluid (pH 7.4, 4 h), and colon fluid (pH 6.7, 18 h). Simulating the case of oral administration at 2 doses per day, loaded ibuprofen was released almost linearly against time after the second dose in media simulating human gastrointestinal tract fluids.