共查询到20条相似文献,搜索用时 46 毫秒
1.
Dingsong Feng 《Polymer》2008,49(2):386-393
The convenient synthesis of methoxy-free 1,1-diphenylethylene end-functionalized polyisobutylene (PIB-DPE) has been accomplished by capping living PIB with 1,4-bis(1-phenylethenyl)benzene, followed by hydride transfer reaction with tributylsilane. The proposed method eliminates the need for methylation of the capped living PIB in which large excess of dimethylzinc must be used, resulting in a large amount of inorganic salt contamination. The obtained PIB-DPE was quantitatively lithiated with 1.5-fold excess n-butyllithium in tetrahydrofuran (THF) at room temperature. The methine proton at the chain end remained intact during the lithiation procedure. The resulting macroanion efficiently initiated the polymerization of alkyl methacrylates. Poly(methyl methacrylate) (PMMA)-b-PIB-b-PMMA, poly(2-hydroxyethyl methacrylate) (PHEMA)-b-PIB-b-PHEMA and poly(tert-butyl methacrylate) (PtBMA)-b-PIB-b-PtBMA have been prepared with high blocking efficiency by the proposed methodology. Complete hydrolysis of PtBMA-b-PIB-b-PtBMA into poly(methacrylic acid) (PMAA)-b-PIB-b-PMAA was realized in THF/1,4-dioxane, as confirmed by FTIR, 1H NMR, and DSC analyses. 相似文献
2.
Ordering and microdomain orientation for the films of symmetric polystyrene-b-poly(tert-butyl methacrylate)s (PS-b-PtBMAs) was investigated by in-situ grazing incidence small-angle X-ray scattering (GISAXS) and the electron microscopy. During thermal deprotection at higher temperature (200 °C), functional tert-butyl ester units in the PtBMA block component are integrated into inter- or intra-molecular anhydride linkages. It was observed that this process causes an increase in the Flory-Huggins interaction parameter (χ) between the two block components for disordered PS-b-PtBMA film, leading to a modulated nonequilibrium structure. Interestingly, for lamella-forming PS-b-PtBMA film, a significant chain stretching in lateral direction during thermal deprotection resulted in a characteristic strain-induced perpendicular orientation in the middle of the film confined between two parallel orientations of lamellar microdomains. 相似文献
3.
A series of seven linear homopolymers of poly(methylmethacrylate) ranging from 12,470 to 365,700 g/mol Mw, were utilized to further explore scaling relationships between viscosity and concentration in a good solvent at 25 °C and to investigate the impact of these relationships on fiber formation during electrospinning. For each of the polymers investigated, chain dimensions (hydrodynamic radius and radius of gyration) were measured by dynamic light scattering to determine the critical chain overlap concentration, c*. The experimentally determined c*, was found to be in good agreement with the theoretically determined value that was calculated by the criteria c*∼1/[η], where the intrinsic viscosity was estimated from the Mark-Houwink parameters, K and a (at 25 °C in dimethyl formamide) obtained from the literature. The plot of the zero shear viscosity vs. c/c* distinctly separated into different solution regimes, viz. dilute (c/c*<1), semidilute unentangled (1<c/c*<3) and semidilute entangled (c/c*>3). The crossover between semidilute unentangled and semidilute entangled regimes in the present investigation occurred at c/c*∼3, which, therefore, marked the onset of the critical chain entanglement concentration, ce, according to the procedure utilized by Colby and co-workers [Colby RH, Rubinstein M, Daoud M. J de Phys II 1994;4(8):1299-310. [52]]. Electrospinning of all solutions was carried out at identical conditions to ascertain the effects of solution concentration, molecular weight, molecular weight distribution and viscosity on fiber formation and morphological features of the electrospun material. Only polymer droplets were observed to form from electrospinning of solutions in the dilute concentration regime due to insufficient chain overlap. As the concentration was increased, droplets and beaded fibers were observed in the semidilute unentangled regime; and beaded as well as uniform fibers were observed in the semidilute entangled regime. Uniform fiber formation was observed at c/c*∼6 for all the narrow MWD polymers (Mw of 12,470-205,800 g/mol) but for the relatively broad MWD polymers (Mw of 34,070 and 95,800 g/mol), uniform fibers were not formed until higher concentrations, c/c*∼10, were utilized. Dependence of fiber diameter on concentration and viscosity was also determined, viz. fiber dia∼(c/c*)3.1 and respectively. These scaling relationships were in general agreement with that observed by Mckee et al. [McKee MG, Wilkes GL, Colby RH, Long TE. Macromolecules 2004;37(5):1760-67. [33]]. 相似文献
4.
Diblock and triblock copolymers of t-butyl methacrylate (tBMA) with 2-ethylhexyl methacrylate (EHMA) and n-hexyl methacrylate were prepared via alkyl lithium initiation and sequential addition techniques in THF at ?78°C. The tBMA blocks were quantiatively and selectively hydrolyzed to afford poly(methacrylic acid) (PMAA) blocks which were then neutralized with alkali metal bases to form block ionomers. The unhydrolyzed copolymers had a phase mixed morphology as evidenced by thermal analysis while the hydrolyzed and neutralized polymers were multiphase materials. The carboxylic acid and ioncontaning triblock copolymers formed gels in nonpolar solvents which could be disrupted by the addition of polar additives. Certain carboxylic acid and ioncontaining EHMA/tBMA diblock copolymers also showed this behavior. The triblock ionomers did not show thermoplastic flow prior to degradation, except at the lowest ionic content studied (2%). 相似文献
5.
A series of linear and star-shaped poly(l-lactide)s (PLA's) have been prepared by living polymerization of l,l-dilactide (LA) and analyzed by liquid chromatography at critical conditions (LC-CC). For the analysis of the PLA's LC-CC conditions have been used corresponding to silica gel as the stationary phase and a mixture of 1,4-dioxane/n-hexane (56.25/43.75 by vol%) at 50 °C as the mobile phase. At the critical point of adsorption, a series of linear C4H9-PLA-OH's having molar masses (Mn) in the range from 2.3×103 to 7.4×104, prepared by ring-opening polymerization of LA initiated with Sn(OC4H9)2 (THF, 80 °C), showed no dependence of the elution volumes on molar mass. In subsequent experiments, star-shaped PLA's bearing various numbers of PLA-OH arms (R-(PLA-OH)x) have been prepared in a controlled synthesis starting from various polyols (R-(OH)x) containing exclusively primary hydroxyl groups: diethyleneglycol (x=2), trimethylolpropane (x=3), di(trimethylolpropane) (x=4), dipentaerithritol (x=6), and poly(3-ethyl-3-hydroxymethyloxetane) (〈x〉=13.4) and LA monomer. As coinitiator/catalyst tin(II) octoate (Sn(Oct)2) has been used (bulk polymerization, 120 °C). 1H NMR analysis of the resulting star-shaped polymers revealed that all OH-groups in the polyols started growth of the PLA chains. The series of star-shaped PLA's have been analyzed by LC-CC as well as by two-dimensional (2D) chromatography (i.e. LC-CC versus size exclusion chromatography (SEC)) with regard to possible structural imperfections. It has been shown, that the LC-CC elution volumes of the resulting R-(PLA-OH)x increase with the number of PLA-OH arms, allowing discrimination of the individual R-(PLA-OH)x's in their mixture. An exponential increase of the retention volume as a function of the number of arms has been found. Eventually, LC-CC measurements of the elution volumes carried out for acetylated star-shaped PLA's (R(PLA-OOCCH3)x) have shown that for the interactions of the R-(PLA-OH)x macromolecules with the column packing the hydroxyl end-groups are mostly responsible. 相似文献
6.
Uma Chatterjee 《Polymer》2005,46(5):1575-1582
ATRP of several methacrylates viz. methyl methacrylate (MMA), ethyl methacrylate (EMA), n-butyl methacrylate (nBMA), t-butyl methacrylate (tBMA), benzyl methacrylate (BzMA) and (N,N-dimethylamino)ethyl methacrylate (DMAEMA) has been studied in neat as well as aqueous (up to 12 vol% water) acetone at 35 °C using CuCl/bipyridine (bpy) catalyst and ethyl 2-bromoisobutyrate as the initiator. Addition of water significantly enhances the rate of polymerization without losing control. Unlike CuCl/bpy the CuBr/bpy catalyst gives poor control which is attributed to the lower solubility and consequent heterogeneity in the latter case. Of the other ligands used with the CuCl catalyst viz. o-phenanthroline (o-phen), 1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA), 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA), Me6TREN only o-phen offers reasonably good control. The CuCl/bpy catalyst system has been used also in preparing some di- and tri-block copolymers with reasonably low polydispersity index (PDI) at ambient temperature (35 °C) using aqueous acetone as the solvent. The following block copolymers have been prepared PMMA-tBMA, PMMA-b-tBMA-b-MMA, PMMA-DMAEMA, by this method. 相似文献
7.
The dynamic behaviors of potato amylopectin and waxy corn amylopectin in semidilute solution were investigated by laser light scattering and viscometer. For potato amylopectin with relatively smaller molecular weight, only pure diffusion motion of amylopectin was found by LLS in dilute regime. When the concentration was above the critical overlapping concentration (C∗), three relaxation modes were found. The line-width of fast mode (Γf) had a q2 dependence, where q is the scattering vector, and the correlative length (〈ξh〉) could be scaled to concentration (C) as 〈ξh〉 ∼ C−0.79±0.1 when C > 2%. This mode was attributed to the cooperative relaxation motion of the “blobs” in the transient network. The line-width of slow relaxation mode (Γs) could be scaled with q as Γs∼qαs, αs varying from 2.0 to 2.66 as the concentration increased. The relaxation time of slow relaxation mode (τs) had a C1.8±0.1 dependence. This mode was originated from the association of the amylopectin. The medium mode was found when C > 4%. The line-width of medium relaxation mode (Γm) could be scaled to q as Γm∼qαm, αm varying from 2.7 to 2.5 with the increasing concentration. The relaxation time of medium relaxation mode (τm) had C0.7±0.1 dependence. The relative intensity contribution of the medium relaxation mode decreased with a rise in the concentration. This mode was attributed to the thermally agitated density fluctuation in semidilute solution induced by heterogeneities of the transient network. For waxy corn amylopectin with relatively huge molecular weight (∼108 g/mol), only the internal motion of the single amylopectin molecule was found in dilute regime when qRg ≥ 2, where Rg is the gyration radius of amylopectin. It was also found that there were three relaxation modes in semidilute solution of waxy corn amylopectin. The fast relaxation mode was found to be caused first by the internal motion of the single amylopectin molecule, and then, with the increasing concentration, by the cooperative motion of the transient network. The medium and slow relaxations for waxy corn amylopectin have the same physical origin as those for potato amylopectin. However, the C dependence and the q dependence of the medium and slow relaxation times for waxy corn amylopectin were different from those for potato amylopectin. This was attributed to the strong dynamic coupling effect in semidilute solution of the waxy corn amylopectin. The concentration dependence of the viscosity of amylopectin in semidilute solution indicated that the topological entanglement of amylopectin was weak due to the highly branching. 相似文献
8.
Hongwei Chen 《Polymer》2008,49(8):2095-2098
Polystyrene-block-poly(4-vinylpyridine) (PS-b-PVP) forms hairy micelles with PVP and long PS block as the core and corona in toluene, respectively. Diffusion of the micelles in solution in the presence of poly(methyl methacrylate) (PMMA) or polystyrene homopolymer (h-PS), from dilute to semidilute, has been investigated by laser light scattering (LLS). Our results indicate the micelles only exhibit translational diffusion with characteristic Γ = Dq2 in PMMA dilute and semidilute solutions, where Γ, D and q are characteristic line width, translational diffusion coefficient and scattering vector, respectively. PMMA concentration dependence of D reveals that the micelle diffusion follows a “stretched exponential” scaling law, similar to that of a hard sphere in the presence of matrix polymer. This is because the PS corona is incompatible with PMMA and no entanglement between them occurs. In contrast, in h-PS solution, due to the overlap and entanglement between the PS corona and h-PS matrix, the micelles exhibit diffusion with characteristic of Γ ∝ qα, where α = 2-2.6. For the same matrix polymer concentration, the micelles exhibit a faster diffusion in PMMA solution than that in h-PS solution, especially in semidilute solutions. The fact further indicates that the overlap and entanglement between the corona and h-PS matrix restrict the micelle motion. 相似文献
9.
Poly(tert‐butyl methacrylate) [P(tBMA)] star polymers were synthesized by copolymerization of p(tBMA) macroinitiator with ethylene glycol dimethacrylate via atom transfer radical polymerization method. P(tBMA) stars had a narrow molecular weight distribution (Mw/Mn = 1.06–1.15). The ratio of radius of gyration to hydrodynamic radius RG/RH, which indicates inner segment density, was in the range 1.16–1.22 in tetrahydrofuran (THF) (arm number f = 25–142). These stars behaved not as hard spheres but as soft spheres in THF. Poly(methacrylic acid) stars were obtained by the hydrolysis of P(tBMA) arms. We investigated the conformation of star polyelectrolyte as a function of pH and ionic strength by means of dynamic light scattering (DLS). The hydrodynamic diameter increased gradually from 18.8 to 48.3 nm as a function of the solution pH. In addition, we compared experimental results with theoretical models for star polyelectrolytes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
10.
The effects of strontium doping on the structural properties and magnetic ordering of Nd1?xSrxFeO3 orthoferrite system have been studied by employing macroscopic and microscopic structural techniques like X-ray diffraction, scanning electron microscopy and 57Fe Mössbauer spectroscopy. X-ray diffraction confirmed that single phase materials have been synthesized. It has been observed that orthorhombic distortion, density and porosity have decreased; whereas, grain size, tolerance factor and symmetry have increased with increase in the strontium concentration. Mössbauer results showed an increase in the Fe4+/Fe3+ ratio, sagging and local octahedral distortions while decrease in the magnetic ordering with increase in the strontium content. The origin behind anomalous octahedral distortions in this system has been attributed to the decrease in the oxidation state and mismatch in the ionic radii of A-site cations and increase in the concentration of Fe4+, due to Sr2+ doping at Nd3+ sites. The collapse of magnetic ordering has been ascribed to the weakening of super-exchange interactions, dilution of strong long range magnetic sub-lattice of high spin Fe3+ (five unpaired electrons) by relatively lower spin of high spin Fe4+ (four unpaired electrons) and increase in the spin–spin relaxation frequency. 相似文献
11.
Niti Sunsandee Natchanun Leepipatpiboon Prakorn Ramakul 《Korean Journal of Chemical Engineering》2013,30(6):1312-1320
The enantioselective separation of levocetirizine via a hollow fiber supported liquid membrane was examined. O,O′-dibenzoyl-(2R,3R)-tartaric acid ((?)-DBTA) diluted in 1-decanol was used as a chiral selector extractant. The influence of concentrations of feed and stripping phases, and extractant concentration in the membrane phase, was also investigated. A mathematical model focusing on the extraction side of the liquid membrane system was presented to predict the concentration of levocetirizine at different times. The extraction and recovery of levocetirizine from feed phase were 75.00% and 72.00%, respectively. The mass transfer coefficients at aqueous feed boundary layer (k f ) and the organic liquid membrane phase (k m ) were calculated as 2.41×102 and 1.89×102 cm/s, respectively. The validity of the developed model was evaluated through a comparison with experimental data, and good agreement was obtained. 相似文献
12.
《Chemical engineering journal (Lausanne, Switzerland : 1996)》2002,85(2-3):265-272
The facilitated transport of copper(II) from nitrate/nitric acid media through a flat-sheet supported liquid membrane (FSSLM) is investigated, using the commercially available oxime Acorga M5640 as ionophore, as a function of hydrodynamic conditions, concentration of copper (7.9×10−5 to 1.3×10−3 M) and H+ (pH 1.0–2.0) and ionic strength in the feed solution, carrier concentration (5–40% v/v) in the membrane and support characteristics. The performance of the system is also compared using various diluents for the organic phase and against other available oxime extractants (MOC-55TD, LIX 860 and LIX 622). A model is presented that describes the transport mechanism, consisting of diffusion through a feed side aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of carrier and its metal complex through the organic membrane. The organic membrane diffusional resistance (Δo) and aqueous diffusional resistance (Δa) were calculated from the proposed model, and their values were 7.6×106 and 273 s/cm, respectively. It was observed that the copper flux across the membrane tends to reach a plateau at high concentration of copper or a low concentration of H+ owing to carrier saturation within the membrane, and leads to a diffusion-controlled process. The values of the apparent diffusion coefficient (Doa) and limiting metal flux (Jlim) were calculated from the limiting conditions and found to be 2.0×10−8 cm2/s and 2.3×10−11 mol/cm2 s, respectively. The values of the bulk diffusion coefficient (Do,b) and diffusion coefficient (Do) calculated from the model were 5.9×10−9 and 1.6×10−9 cm2/s, respectively. The polymeric microporous solid support, Durapore GVHP 04700, was selected throughout the study as it gave the best performance. 相似文献
13.
Yuxia Lv Jin Wu Jinming Zhang Yanhua Niu Chen-Yang Liu Jiasong He Jun Zhang 《Polymer》2012,53(12):2524-2531
Rheological properties of cellulose dissolved in two ionic liquids (ILs), 1-allyl-3-methylimidazolium chloride (AmimCl) and 1-butyl-3-methylimidazolium chloride (BmimCl), with co-solvent dimethylsulfoxide (DMSO), are studied in the concentration range of cellulose from 0.070 to 6.0 wt%. The viscosities of ILs are exponentially decreased by adding DMSO in the concentration range of 0–100 wt%. The co-solvent DMSO decreases the monomer friction coefficient in cellulose solutions and has no significant change for the entanglement state of cellulose, thus results in the reduced solution viscosity, shortened relaxation time and unchanged moduli of the cross-over point. For cellulose solutions, dilute regime, semidilute unentangled regime and semidilute entangled regime were determined by steady shear experiments. In semidilute entangled regime, the specific viscosities ηsp, relaxation time τ, and plateau modulus GN, exhibit concentration dependences as ηsp ~ C4.4, τ ~ C2.2, andGN ~ C1.9, respectively, in AmimCl-DMSO (80/20 w/w); and ηsp ~ C4.3, τ ~ C2.0, and GN ~ C2.1, respectively, in BmimCl–DMSO (80/20 w/w). Therefore, the rheological properties of cellulose/IL/DMSO solutions are approximately of IL-independence in this study. The dependence of ηsp upon cellulose concentration shows that the IL–DMSO mixture is more like a θ solvent for cellulose, and the thermodynamic properties of IL–DMSO mixtures are similar with those of ILs for cellulose at 25 °C. The conformation of cellulose in ILs would not be changed with the addition of DMSO not only in the dilute regime but also in the entanglement regime. 相似文献
14.
Jeff P. Kalish 《Polymer》2011,52(15):3431-13841
Simulations in conjunction with Raman scattering were performed to determine the conformational distortion of the α′ form of poly(lactic acid) (PLA). Based on packing constraints of an overall helical structure, the chain conformation can only be approximated by slight deviations from a tg’t chain conformation. Models were generated with different types of random departures from the expected dihedral angles. Raman active vibrations in the 700 cm−1 region that are sensitive to changes in chain conformation were analyzed. The model that showed the best fit to the experimental data contains a majority (80%) of tg’t-103 sequences with randomly distributed tg’t-31 units. Departure of the O-Cα dihedral angle was also proved. The mechanism of order formation was established. As PLA chains crystallize at low temperatures, only the α′ phase with a disordered helix can be formed which at elevated temperatures can transform to the more ordered α phase. The conformation distortion is then due to the inability for some chains to complete the transition to 103 helicity, thus resulting in the formation of the distorted α′ structure. 相似文献
15.
Solid‐phase grafting of a soft vinyl monomer, butyl methylacrylate (BMA), onto polypropylene (PP) matrixes with 2,2′‐azobisisobutyronitrile (AIBN) as initiator was carried out to enhance the polarity of polymer. Soft vinyl monomer was a novel notion in grafting modification of PP. Effects of swell time, BMA concentration, AIBN concentration, grafting reaction time, and temperature on grafting percentage (Gp) and grafting efficiency (Ge) were examined. The optimal conditions of grafting reaction were obtained: swell time of 60 min, BMA concentration of 6 wt %, AIBN concentration of 0.05 wt %, reaction temperature of 85°C, and reaction time of 2 h. The grafting samples were investigated by such characterization techniques as Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and scanning electron microscope (SEM) analysis. FTIR results indicated that BMA was actually grafted onto PP backbone. TGA results showed that the decomposition temperature increases with addition of BMA into PP backbone. SEM results indicated that the surfaces of PP‐g‐BMA had a markedly bumpy texture, whereas the pure PP surface was very smooth. Water contact angle results showed that the polarity and hydrophilicity of PP were improved effectively. Compared with the traditional monomer MAH, Gp, and Ge, melt flow rate and mechanical property results all indicated that the soft vinyl monomer had a many advantages in the modification of PP. In the end, the mechanism of solid grafting was discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
16.
《Ceramics International》2015,41(4):5705-5712
Ce substituted Bi1−xCexFeO3 (x=0.03, 0.05, 0.07 and 0.10) nanoparticles were prepared by a tartaric acid based sol–gel route. X-ray diffraction patterns and Raman spectra revealed a structural phase transition from rhombohedral to orthorhombic phase for x=0.10 sample. Room temperature magnetic measurements showed weak ferromagnetic ordering and enhancement in magnetization with increasing Ce concentration. The improved magnetic properties due to the breaking of spin cycloid with Ce substitution have been observed from electron spin resonance (ESR) study. The measured g-values for all samples are greater than 2 and the ESR lines shift towards higher g-value with increasing Ce concentration, indicating ferromagnetic nature of these samples. UV–visible diffuse reflectance spectra showed a sharp absorption in the visible region with two d–d and three charge transfer (C-T) transitions. Prominent red shift in the band gap indicates a significant change in the band structure of the doped nanoparticles. 相似文献
17.
L. Cossignani L. Giua G. Lombardi M. S. Simonetti P. Damiani F. Blasi 《Journal of the American Oil Chemists' Society》2013,90(3):327-335
Nutritional supplements containing conjugated linoleic acid (CLA) isomers, widely used to improve body composition and inhibit fat storage, should be thoroughly analyzed, as CLA effects are isomer specific. In this research, an improvement of silver-ion high performance liquid chromatography (Ag+-HPLC) was obtained by using a single-column instead of the most commonly used multi-columns. To develop the procedure, a standard CLA mixture has been derivatized with different chain length alcohols (from methanol to hexanol). Hexyl CLA showed better separation between CLA isomer pairs, in particular the resolution of the t10,c12: c9,t11 pair increased from 0.3 (methyl esters) to 0.8 (hexyl esters). Therefore, the CLA isomer composition of some commercial CLA products was determined by Ag+-HPLC analysis of hexyl esters. The main isomers in all supplements turned out to be c9,t11-CLA and t10,c12-CLA, the most anti-adipogenic isomer. t8,c10- and c11,t13-CLA were not detected. The nutritional supplements were also analyzed by high resolution gas chromatography of methyl esters to evaluate the fatty acid % composition and total CLA % content. The total CLA ranged from 79.4 to 94.4 %, and the t,t isomer from 1.4 to 7.3 %. 相似文献
18.
Dongrui Wang 《Polymer》2009,50(2):418-508
In this work, a series of amphiphilic diblock copolymers bearing strong push-pull type azo chromophores was synthesized through post-polymerization azo-coupling reaction scheme. The copolymers (P(CNAZOm-b-MAAn)), composed of 2-(N-ethyl-N-(4-(4′-cyanophenylazo)-phenyl)amino)ethyl methacrylate (CNAZO) and methacrylic acid (MAA) blocks, were obtained through four-step reactions. Firstly, precursor diblock copolymers (P(EMAm-b-tBMAn)) were obtained through sequential two-stage ATRP reactions of 2-(N-ethyl-N-phenylamino)ethyl methacrylate (EMA) and tert-butyl methacrylate (tBMA). Then, 4-amino-4′-cyanoazobenzene chromophores were introduced by azo-coupling reaction of P(EMAm-b-tBMAn) with diazonium salt of 4-aminobenzonitrile. Finally, P(CNAZOm-b-MAAn) was obtained through selective hydrolysis of the tert-butyl ester linkages in the tBMA blocks. Three block copolymers with the same CNAZO block length (m = 100) and different MAA block lengths (n = 5, 13, 23) were prepared by this method. The polymer and copolymers prepared in the process were characterized by GPC, 1H NMR, UV-vis, DSC and TGA measurements. Results show that P(CNAZOm-b-MAAn) forms spherical micellar aggregates by gradually increasing the water content in THF/H2O mixtures. The diameters of the spherical aggregates are related to the composition of the block copolymers and the water-adding rate. The block copolymer with larger molecular weight of the hydrophilic MAA block forms the aggregates with the smaller average size. The increase of the water-adding rate also shows an effect to reduce the diameters. Upon irradiation with a linearly polarized Ar+ laser beam, the spherical aggregates can be elongated in the light polarization direction. The deformation degree shows an almost linear dependence on the light irradiation time in the testing period. The deformed aggregates can recover the original spherical shape after thermal annealing at a temperature above Tg of the block copolymer. 相似文献
19.
Jeffrey Pyun Krzysztof MatyjaszewskiGyeong-Man Kim Seung B Chun Patrick T Mather 《Polymer》2003,44(9):2739-2750
The synthesis and characterization of POSS containing ABA triblock copolymers is reported. The use of atom transfer radical polymerization (ATRP) enabled the preparation of well-defined model copolymers possessing a rubbery poly(n-butyl acrylate)(pBA) middle segment and glassy poly(3-(3,5,7,9,11,13,15-heptaisobutyl-pentacyclo[9.5.1.13,9.15,15.17,13]-octasiloxane-1-yl)propyl methacrylate(p(MA-POSS)) outer segments. By tuning the relative composition and degree of polymerization (DP) of the two segments, phase separated microstructures were formed in thin films of the copolymer. Specifically, dynamic mechanical analysis and transmission electron microscopy (TEM) observations reveal that for a small molar ratio of p(MA-POSS)/pBA (DP=6/481/6) no evidence of microphase separation is evident while a large ratio (10/201/10) reveals strong microphase separation. Surprisingly, the microphase-separated material exhibits a tensile modulus larger than expected (ca. 2×108 Pa) for a continuous rubber phase for temperatures between a pBA-related Tg and a softening point for the p(MA-POSS)-rich phase. Transmission electron microscopy (TEM) images with selective staining for POSS revealed the formation of a morphology consisting of pBA cylinders in a continuous p(MA-POSS) phase. Thermal studies have revealed the existence of two clear glass transitions in the microphase-separated system with strong physical aging evident for annealing temperatures near the Tg of the higher Tg phase (p(MA-POSS). The observed aging is reflected in wide-angle X-ray scattering as the strengthening of a low-angle POSS-dominated scattering peak, suggesting some level of ordering during physical aging. The Tg of the POSS-rich phase observed in the microphase separated triblock copolymer was nearly 25 °C higher than that of a POSS-homopolymer of the same molecular weight, suggesting a strong confinement-based enhancement of Tg in this system. 相似文献
20.
Grzegorz Lapienis 《Polymer》2009,50(1):77-84
The introduction of methacrylic, carboxylic and phosphate functional groups on the core and at the end of the poly(ethylene oxide) (PEO) arms in the PEO star-shaped polymers is described. In the polyglycidol (PGL) star-shaped polymers phosphate groups were attached to the PGL arms as side groups. Polymers were characterized by NMR and SEC analysis with triple detection. The conversion of the unsubstituted star-shaped polymers into functionalized has been confirmed by 1H and 13C NMR spectra. The influence of the length of arms, their structure and the presence of functional groups on melting (Tm) and crystallization (Tc) temperatures and the degree of crystallinity (Xc) by differential scanning calorimetry (DSC) has been studied. 相似文献