Crystal-amorphous interphases in binary polymer blends that are miscible in the melts but phase separate due to crystallization of one polymer have been investigated theoretically by employing lattice models and experimentally by dielectric spectroscopy measurements. Theory predicts the extent of tight adjacent re-entry to depend strongly on the energy Eq disfavoring the tight-fold conformations and to increase slightly with favorable interaction energy - χAB in the blends. The interfacial region of varying composition is predicted to depend strongly on χAB, with the interfacial thickness varying with the reciprocal of |χAB|1/2. Therefore, in the limit χAB → 0 the amorphous polymer, which is miscible in the melt, is predicted to be completely excluded from the interlamellar region, in agreement with experimental results. Dielectric relaxation experiments on semicrystalline blends of poly(vinylidene fluoride) (PVDF) with poly(methyl methacrylate) (PMMA) or poly(vinyl pyrrolidone) (PVP) show the existence of nearly pure PVDF interphase which is not penetrated by PMMA or PVP, despite their strongly favorable interactions with PVDF. These experimental results are discussed and compared with theoretical predictions. 相似文献
The electric field poling process of free-standing films of poly(methyl methacrylate) (PMMA) matrix doped with the nonlinear
optical compound 4-(dimethylamino)-4'-nitrostilbene (DMANS) was investigated by molecular simulation methods. The influence
of the vacuum/bulk interfacial regions on static and dynamic properties, including the glass transition temperature Tg and the field-induced chromophore reorientation, was studied by employing films of three different thicknesses and by comparison
with previous work on the bulk system. The interfacial region, defined as the region, where the local density increases from
zero to the bulk density, is about 2 nm wide, independent of the film thickness. Tg decreases with decreasing film thickness, in accord with previous experimental work and theoretical predictions. The resistance
against field-induced chromophore reorientation in the liquid state is found to increase strongly with the film thickness. 相似文献
ABSTRACTHerein, the polar anchoring energy coefficient (Aθ) of nematic liquid crystal (NLC) was examined for high-density polymer brushes via capacitance measurements. The Aθ is 10?4 J m?2 for the brushes of poly(methyl methacrylate), poly(ethyl methacrylate) and poly(styrene). The value decreases to 10?5 J m?2 for poly(n-butyl methacrylate) and poly(hexyl methacrylate) with lower glass transition temperatures. However, each polymer brush displays a constant Aθ value over a temperature range of ?15°C to 90°C, which is hardly affected by the graft density and brush thickness. At 25°C, Aθ is 10 times greater than the corresponding azimuthal anchoring energy coefficient (Aφ); therefore, NLCs on polymer brushes can be preferentially aligned along the in-plane component of the applied field. 相似文献
The photochromic effect has been investigated for three compounds of the benzospiran group dissolved in amorphous polymers: poly(methyl methacrylate), poly(n-butyl methacrylate), poly(vinyl acetate), and poly(vinyl n-butyrate). The kinetics of the thermal bleaching reaction above Tg of the matrix follow a first-order equation due to the averaging of free volume distribution related to the diffusion of segments in viscoelastic state. A more complex mechanism of decolorization below Tg has been considered from the point of view of unequal, discrete distribution of environments in which the photochromic molecules exist in the glassy matrix. A change of the activation energy and the mechanism of color decay on passing through Tg is not a rule (PVB), which shows, that for a polymer having long, flexible chains, secondary glass transition phenomena play a decisive role. In the case of glassy polymers (PMMA), the photochromic effect of benzospirans may be employed to determine Tβ. It seems, that in addition to steric restrictions for trans–cis isomerization in the decolorization process one must consider the interactions of photochromic molecules with the matrix as well as their chemical nature. 相似文献
The synthesis and second harmonic coefficients, d3,1 and d3,3 as well as the related susceptibilities χ(2)zzz of five series of (NLO-dye methacrylate)-(methyl methacrylate) copolymers were investigated. The NLO-chromophores bound covalently to the polymer backbone were 5-(2,2-dicyanovinyl)-or 4-(2-cyano-2-methoxycarbonyl)vinyl-1-piperidino-2-thiophene (P1 and P2), 4-nitro-4′-alkoxy-stilbene (P3), 4-nitro-3′-methoxy-4′-alkoxystilbene (P4) and 4-nitro-4′-alkoxy-α-cyano stilbene (P5). The second order nonlinear optical properties of corona-poled aligned thin polymer films, using a needle electrode in order to induce noncentrosymmetry, were evaluated. Nonlinear susceptibilities, χ(2)zzz, of the films were derived from the analysis of full-angle Maker fringe patterns at 1064 nm, χ(2)zzz values as high as 1.98×10−7 esu for P2 copolymers and of 1.19×10−7 esu for P3 copolymers could be achieved. 相似文献
Isotactic and syndiotactic living polymerizations of methacrylates with t-C4H9MgBr and t-C4H9Li-R3Al (Al/Li≥2), respectively, were utilized to prepare highly stereoregular block and random copolymers, stereoblock PMMAs, highly branched star polymers with stereoregular arms, stereoregular PMMA macromonomers with methacryloyl functions and stereoregular comblike and graft polymers derived therefrom. A combination of t-C4H9Li and bis(2,6-di-t-butylphenoxy) methylaluminum was found to be an efficient initiator for heterotactic living polymerization of methacrylates in toluene at −78°C; e.g. ethyl methacrylate gave a polymer with mr content of 87%. Polymerization of triphenylmefhyl crotonate (TrC) with fluorenyllithium (FILi)/N,N,N′,N′-tetramethylethylenediamine in toluene at −78°C gave a threodiisotactic polymer with narrow MWD, whose stereochemistry was confirmed from the x-ray analysis of the pentamer of methyl crotonate (MeC) derived from the TrC pentamer and 1H NMR spectral comparison of the pentamer and the poly(MeC). The poly(TrC) prepared with FILi/(S,S)-(+)-2,3-dimethoxy-1,4-bis(dimethylamino) butane also gave a threodiisotactic polymer which showed optical activity due to the one-handed helix. Polymerization of t-butyl crotonate was also discussed in some detail. 相似文献
New water‐soluble block copolymers of 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO2MA), oligo(ethylene glycol) methacrylate (OEGMA), and N‐(3‐(dimethylamino) propyl) methacrylamide (DMAPMA) (poly(OEGMA‐co‐MEO2MA)‐b‐poly(DMAPMA)) were prepared via sequential reversible addition‐fragmentation chain transfer (RAFT) polymerization. Selective quaternization of poly(DMAPMA) block gives poly(OEGMA‐co‐MEO2MA)‐b‐poly((3‐[N‐(3‐methacrylamidopropyl)‐N,N‐dimethyl]ammoniopropane sulfonate)‐co‐N‐(3‐(dimethylamino) propyl) methacrylamide), such block copolymer exhibits double thermo‐responsive behavior in water, poly(MEO2MA‐co‐OEGMA) block shows a lower critical solution temperature (LCST), and poly((3‐[N‐(3‐methacrylamidopropyl)‐N,N‐dimethyl]ammoniopropane sulfonate)‐co‐N‐(3‐(dimethylamino) propyl) methacrylamide) block shows a upper critical solution temperature (UCST). Both of LCST and UCST can be controlled: LCST could be tuned by the fraction of OEGMA units in poly(OEGMA‐co‐MEO2MA), and UCST was found to be dependent on the degree of quaternization (DQ).