Study on conformational transition phenomena of poly(methyl methacrylate) in acetonitrile near theta conditions

The coil–globule transition for poly(methyl methacrylate) (PMMA) has been studied in a theta solvent, acetonitrile (Θ = 45 °C). The viscosity of PMMA was measured as a function of temperature in the range 26–55 °C. The contraction and expansion of the molecular chains are determined using the measured viscosity values. The temperature dependence of the intrinsic viscosity can be represented by a master curve in a versus |τ|M _w^1/2 (g^1/2 mol^−1/2) plot, where τ = |T − Θ|/T is the reduced temperature and M_w‐is the weight‐average molecular weight. A universal plot of reduced viscosity versus reduced blob parameter (N/N_c) shows the attainment of the collapsed state below the theta temperature. The dimensions of PMMA in acetonitrile (M_w = 3.15 × 10⁶ g mol⁻¹) decrease to 63 % at 26 °C of those in the unperturbed state. The results in this work are compared with those previously published. © 2000 Society of Chemical Industry     

Viscosity behaviour of poly(ethyl methacrylate) in the ethyl acetate/tert-butanol binary mixture: total and preferential adsorption

The behaviour of poly(ethyl methacrylate) (PEMA) in the ethyl acetate (1)/tert-butanol (2) binary mixture is studied by laser light scattering, differential refractometry and viscometry. Ethyl acetate is a solvent for the polymer and tert-butanol is a precipitant. Preferential adsorption of tert-butanol up to 15% alcohol in the binary mixture is observed, ethyl acetate being preferentially adsorbed in the macromolecular coil at higher percentage of alcohol in the solvent mixture. Total adsorption of PEMA is independent of the amount of tert-butanol in the solvent. Various theoretical expressions for the preferential and total adsorption coefficients are used; their agreement or disagreement with the experimental results is explained on the basis of polymer-solvent interactions.     

Effect of the tacticity of poly(methyl methacrylate) on the phase diagram of its ternary blends

Previously, isotactic and atactic poly(methyl methacrylates) (PMMAs) were found to be miscible with poly(vinyl phenol) (PVPh) and poly(hydroxy ether of bisphenol‐A) (phenoxy) because all the prepared films were transparent and showed composition‐dependent glass transition temperatures (T_g's). However, syndiotactic PMMA was immiscible with PVPh because most of the cast films had two T_g's. On the contrary, syndiotactic PMMA was still miscible with phenoxy. According to our preliminary results, PVPh and phenoxy are not miscible. Also to our knowledge, nobody has reported any results concerning the effect of the tacticity of PMMA on its ternary blend containing PVPh and phenoxy. The miscibility of a ternary blend consisting of PVPh, phenoxy, and tactic PMMA was thus investigated and reported in this article. Calorimetry was used as the principal tool to study miscibility. An approximate phase diagram of the ternary blends containing different tactic PMMA was established, probably for the first time, based on differential scanning calorimetry data. Immiscibility was found in most of the studied ternaries but a slight difference due to the effect of tacticity of PMMA was definitely observed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2720–2726, 2002     

Cosolvency,coil expansion and dimensions of PMMA in mixed solvents

Limiting viscosity numbers ([ν]) and Schulz-Blaschke constants (k_s) of PMMA samples (differing in molecular weight) have been determined at 25°C (as a function of mixed solvent composition) for the following mixtures: acetonitrile+1-butanol, acetonitrile+pentyl acetate, and 1-chlorobutane+pentyl acetate. The first two mixtures are powerful cosolvents of PMMA and the third one is a ‘co-nonsolvent’ of the polymer. The samples are predominantly heterotactic. Their k_s values at θ indicate some association tendency of the polymer. Unperturbed dimensions and coil expansion coefficients have been obtained from [ν], as a function of solvent mixture composition. All the pure liquids are poor or non-solvents of PMMA (at 25°C), but the cosolvent pairs behave as very good solvents for the polymer. The mechanism of such cosolvency is analysed in terms of the different molecular interactions present in these systems.     

Study on polymer solutions in solvent mixtures in the vicinity of the critical point of the solvents: 4. Saturation phenomena

Turbidimetric results have been obtained with the ternary system N,N-dimethylformamide/cyclohexane/polystyrene. The displacement of the heterogeneous region depends on the molecular weight of the polystyrene sample and for each polystyrene sample the displacement changes with the concentration of the polymer. Above a certain molecular weight of the polymer, with a given concentration, the displacement reaches a plateau region. A plateau is also obtained when we change the concentration of the polymer of a given molecular weight. The crossover region, which is determined by the appearance of the plateau region, obeys the scaling laws and is probably the region where the distance between the macromolecular coils is comparable to their diameters.     

Synthesis and characterization of poly(methyl methacrylate) star polymers

Star-branched poly(methyl methacrylate)s (PMMA) were synthesized by linking ‘living’ arms (produced by anionic polymerzation) with ethylene glycol dimethacrylate. Stars having arm molecular weights of 10000 and 40000 and between 4.9 and 18.7 branches were produced. The polymers were characterized using light scattering, size exclusion chromatography, and viscometry. It was found that well-defined PMMA stars were obtained only at the higher (40000) arm molecular weight. The stars prepared using the lower molecular weight (c. 10000) arms contained very high molecular weight gel components.     

Effect of electrical field on dipoles in polymer composites

Orientation of two bipolar compounds embedded in polymer composites was studied. Poly(methyl methacrylate) (PMMA) dissolved in acetone was doped with a cobaltborane derivative of 1,2‐dimethylimidazole and polystyrene (PS) dissolved in toluene was doped with the 3‐(1,2‐dimethyl imidazole)‐borane. To orient the dipoles, the composites were exposed to external electrical field: PMMA composite at the temperature of glass transition (T_g) and PS composite during evaporation of the toluene solvent. The degree of dipole orientation was estimated by the change in relative permittivity (ε) of the resulting composite film. The dependence of the ε on the temperature, frequency, voltage, and dipole concentration was studied. It was found that the dipole's distribution in the composite film was not homogenous. At the T_g, the dipoles in PMMA became oriented by external direct electrical field and the orientation was conserved after cooling to lower temperatures. In a PS‐based composite, the significant permittivity increase was observed already at low‐dopant concentrations. The dipole orientation achieved during solvent evaporation was also permanent and the composite permittivity was an increasing function of the film thickness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 40–45, 2004     

Effects of cononsolvency on preferential adsorption phenomenon in poly(N‐isopropylacrylamide) ternary solutions

In this work, the effect of cononsolvency on the phase transition and preferential adsorption phenomenon behaviors of poly(N‐isopropylacrylamide)/methanol/water ternary solutions was studied. In this cononsolvent system, the , , and χ₁₂ values show a nonlinear behavior and the minimum values of and , while the maximum value of χ₁₂ at ϕ₂ is around 0.7. These facts indicated that one water molecule could directly bond with one methanol molecule to form the H₂O MeOH complex. The H₂O MeOH complex structure was found to remarkably affect the phase transition of poly(N‐isopropylacrylamide) (PNIPAM) in ternary solution. However, at the composition of mixed cononsolvent, ϕ₂ < 0.2, the PNIPAM molecules may preferentially adsorbed pure water molecules; therefore, the LCST decreases slightly with composition of mixed cosolvent and this may be because of the small amount of H₂O MeOH complexes in the mixed cononsolvent. While, at ϕ₂ > 0.7, the PNIPAM molecules may preferentially adsorbed pure methanol molecules. PNIPAM ternary solutions were transparent and no transition occurred in this region. This indicates that the PNIPAM coils exhibited a much‐extended conformation in solutions. In contrast, at 0.2 < ϕ₂ < 0.4 and 0.4 < ϕ₂ < 0.7, PNIPAM molecules preferentially adsorbed water and methanol molecules, respectively, and also adsorbed large amount of H₂O MeOH complexes. In these regions, the clathrate‐like structure around the side chain of PNIPAM molecule became more defected with adsorbing H₂O MeOH complex. Therefore, we considered that the various thermodynamic behaviors between PNIPAM and mixture solvents must be related different preferential adsorption phenomena, which were mainly related to different degrees of polymer–solvent interaction and structures of solvent used. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

苯乙烯-甲基丙烯酸甲酯悬浮-乳液耦合聚合动力学

采用苯乙烯(St)悬浮聚合过程滴加甲基丙烯酸甲酯(MMA)乳液聚合组分,进行悬浮-乳液耦合聚合(SECP), 制备大粒径聚苯乙烯-聚甲基丙烯酸甲酯(PS-PMMA)复合粒子.采用¹H NMR分析方法,讨论了SECP动力学特征.St的SECP聚合速率和转化率与悬浮聚合一致;MMA聚合速率决定于乳胶粒子聚合速度和凝并在悬浮粒子表面的速度,聚合速率比常规乳液聚合速率低.由于凝并在悬浮粒子表面的PMMA乳胶粒子不再有乳液聚合特征,MMA在SECP中转化率低于同条件常规乳液聚合.分别得到乳化剂和引发剂浓度与SECP和普通乳液聚合恒速段聚合速率的关系.     

Unperturbed dimension of poly(4-acetoxystyrene) measured in good and theta solvents

In order to obtain the additional data concerning the unperturbed dimension of poly-4-substituted styrene, light scattering measurements are performed on the twenty-two fractions with molecular weight of (0.91–352)·10⁴ of poly(4-acetoxystyrene) in dioxan at 25°C, from which the molecular weight obtained was found easily to be evaluated with the gel permeation chromatography using THF. Phase separation experiments for this polymer indicate that the theta state is attained in isopropyl acetate at 19.7°C and butyl acetate at 26.8°C. By making viscosity measurements at that state, the value of K_Θ is directly evaluated as 5.4·10^?4 dl g^?1. The limiting viscosity number is also obtained in good solvents, THF and dioxan, at 25°C and constants of the Mark-Houwink-Sakurada equation in each solvent are determined. Further, approximately the same K_Θ as above is obtained from these data with the Stockmayer-Fixman plot. The calculated value of steric factor, 2.37, on this polymer may be plausible, compared with those of polyvinylaromatic derivatives.     

拉曼Mapping成像研究聚苯乙烯/聚甲基丙烯酸甲酯共混体系的相态结构

利用拉曼光谱成像技术研究了聚苯乙烯/聚甲基丙烯酸甲酯（PS/PMMA）共混薄膜体系及其增容体系（增容剂为PS-b-PMMA嵌段共聚物）的相态结构及化学成分分布。实验结果表明,拉曼Mapping成像技术不仅可以得到PS/PMMA共混体系化学成分的精确分布图,同时也可以获取共混体系中分散相、界面相和连续相的分子指纹光谱。研究发现,共混体系中分散相和连续相组分分布与体系的组成紧密相关,当PS/PMMA质量比30/70时,分散相为PS,连续相为PMMA;当PS/PMMA质量比为50/50时,分散相为PS,但PS分子链仍存在于PMMA连续相中;当PS/PMMA质量比为70/30时,分散相为PMMA,连续相为PS。当增容剂PS-b-PMMA加入到PS/PMMA共混体系中后,分散相粒径减小、分布更加均匀、共混体系相容性指数（N_c）增大,说明PS/PMMA共混体系由完全不相容体系趋向变成半相容性体系,这是因为增容剂能增加PS和PMMA之间的相互作用,降低了体系的相分离程度,改善了共混体系的相容性。     

Influence of free volume fraction,inter/intramolecular energy ratio,and chain segment density on the Gibbs-DiMarzio theory of the glass transition

Based upon computer analysis, the Gibbs-DiMarzio (G-DM) theory is evaluated for the case of (a) constant V₀ and (b) constant r where V₀ is the fractional free volume at T_g and r is the ratio of the hole (E₀) to the flex (ε) energy. For each respective case, results are presented in a reduced variables format that indicate the extent to which r and V₀ vary at the transition temperature as a function of the reciprocal degree of polymerization (P^?1). To further account for chemical differences that exist among polymers, an index (n) is introduced that ultimately incorporates the effective number average of chain atom segments (x?) per P?. Using these reduced variables plots, the effects of V₀, r, and n are compared with the T_g data for four well-documented polymers. Although the theory adequately describes the PMMA, PS, and PVC data, for PαMS the fit is doubtful. The analysis demonstrates that, in order to maintain V₀ within the range of 0.015–0.045, r must remain within approximately 1.0–1.1. Moreover, under conditions of either constant V₀ or r, other more flexible polymers require that $\text{n?10}$.     

Glass transition and structural relaxation of nano-particle aggregates of atactic poly(methyl methacrylate) formed in microemulsions

Atactic poly(methyl methacrylate) (a-PMMA) nano-particles were prepared in three-component microemulsions using the cationic surfactant cetyltrimethylammonium bromide. To analyze the thermal history, the sub-T_g annealed sample was subsequently measured at a faster heating rate. The a-PMMA prepared in microemulsions shows higher glass transition and higher structural relaxation than those of bulk sample of the same tacticity and the same molecular weight. When the annealing time is longer, additional enthalpy relaxation and glass transition were observed at higher temperatures due to partial self-aggregation of a-PMMA chains, which was proved by spectroscopic studies.     

Phase behavior and properties of poly(methyl methacrylate)/poly(vinyl acetate) blends prepared via in situ polymerization

Polymer blends composed of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) were prepared via radical-initiated polymerization of methyl methacrylate (MMA) in the presence of PVAc. Differential scanning calorimetry and dynamic mechanical analysis were employed to investigate the miscibility and phase behavior of the blends. The PMMA/PVAc blends of in situ polymerization were found to be phase separated and exhibited a two-phase structure, although some chain transferring reaction between the components occurred. The phase separation resulted from the solvent effect of MMA during the in situ polymerization, which was confirmed by the investigation of phase behavior based on solution cast blending. Solubility analysis of the polymerized blends indicated that some chain transferring reaction between the components occurred during the polymerization. An abrupt increase in gel content from 21.2 to 72.4 wt % was observed when the inclusion of PVAc increased from 30 to 40 wt %, and the gel component consisted of the component polymers as shown by infrared spectroscopy studies. The thermogravimetric analysis study indicated that the inclusion of a small amount of PVAc gives rise to a marked stabilization effect on the thermal stability. The PMMA/PVAc blends exhibited increased notched impact properties with the inclusion of 5 wt % PVAc. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 675–684, 1998     

Effect of vitrification pressure on radius of gyration,specific heat and density of amorphous polymers

The effects of vitrification pressure (to 500 MPa) and temperature (to 180°C) on the radius of gyration (as determined by small-angle neutron scattering), specific heat, and density were measured for polystyrene and poly(methyl methacrylate). The radius of gyration increased slightly (5 × 10^?3/°C) in both polymers; this increase is near the experimental uncertainty in the measurements. The small observed values are due to either small intrinsic effects of temperature or pressure on the conformation or competing effects of temperature and pressure. Density and specific heat showed changes which have been observed before and are attributed to intermolecular factors.     

Simulation of viscoelastic behavior of glassy polymers

The frequency master curves of thermoset and thermoplastic glassy polymers were determined by dynamic mechanical analysis, and the results were simulated by sinusoidal response of the standard viscoelastic model. The elastic and viscous elements of the model were determined and correlated with structure of glassy polymers. The advantage of this viscoelastic approach in toughening studies of polymers was discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 971–982, 1997     

Probing the structure of polymer blends by vibrational spectroscopy: the case of poly(ethylene oxide) and poly(methyl methacrylate) blends

The blends of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) are prepared in the form of thin films from solution casting. The Fourier transform infrared spectra of the blends are recorded in the spectral range 400–4000 cm^?1. The spectra are analysed using various recent techniques of vibrational spectroscopy. It is concluded that upon blending PEO takes preferentially a planar zig-zag structure. Furthermore the intermolecular interactions between the molecules of PEO and PMMA in blends are very weak and their compatibility as blends is more ‘physical’ than ‘chemical’. Further, on the basis of the atomic charges transferred from model molecules it is seen that the blending is preferred with isotactic PMMA when compared to syndiotactic PMMA.     

Effect of tacticity of poly(methyl methacrylate) on the miscibility with poly(vinyl pyrrolidone)

Isotactic, atactic, and syndiotactic poly(methyl methacrylates) (PMMA) (designated iPMMA, aPMMA, and sPMMA) with approximately the same molecular weight were mixed separately with poly(vinyl pyrrolidone) (PVP) primarily in chloroform to make three polymer blend systems. Differential scanning calorimetry (DSC) was used to study the miscibility of these blends. The results showed that the tacticity of PMMA has a definite impact on its miscibility with PVP. The aPMMA/PVP and sPMMA/PVP blends were found to be miscible because all the prepared films showed composition-dependent glass-transition temperatures (T_g). The glass-transition temperatures of the aPMMA/PVP blends are equal to or lower than weight average and can be qualitatively described by the Gordon–Taylor equation. The glass-transition temperatures of the other miscible blends (i.e., sPMMA/PVP blends) are mostly higher than weight average and can be approximately fitted by the simplified Kwei equation. The iPMMA/PVP blends were found to be immiscible or partially miscible based on the observation of two glass-transition temperatures. The immiscibility is probably attributable to a stronger interaction among isotactic MMA segments because its ordination and molecular packing contribute to form a rigid domain. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3190–3197, 2001     

Apparent specific volumes of polymers in dilute solutions

New results obtained on various polymers in solvents of differing molecular size and polarity confirm the dependence of their apparent specific volume ø₂ on polymer molecular weight and solvent molar volume. Existing models are discussed and a new model is proposed which assumes that ø₂ essentially depends on α, the expansion coefficient of the macromolecular coil, through the variation of the conformer sequence length in the chain. Some technical problems encountered with the vibrating tube densimeter are discussed.