Copolymerization of bromophenylmaleimide with ethyl or butyl methacrylate

N‐p‐Bromophenylmaleimide (BrPMI) does not polymerize in solution by conventional free radical mechanism. However, it readily polymerized in bulk when mixed with a free radical initiator and heated in a microwave oven for 7–8 min. Copolymerization of ethyl methacrylate or butyl methacrylate with BrPMI was conducted in dioxane. The copolymers were characterized by IR and ¹H NMR spectroscopy and gel permeation chromatography. The monomer reactivity ratios were calculated by a non‐linear least‐square analysis. Thermal analysis indicated a great improvement in thermal stability of the copolymers compared with the methacrylate homopolymers. BrPMI was also polymerized in bulk in the DSC pan, which allowed the calculation of the activation energy of its polymerization. Copyright © 2003 Society of Chemical Industry     

Synthetic hydrogels: 3. Hydroxyalkyl acrylate and methacrylate copolymers: surface and mechanical properties

The surface and mechanical properties of copolymers of hydroxyalkyl acrylates and methacrylates have been examined by a variety of techniques. This work is complementary to earlier parts of this series which describe the effect of copolymer structure on water binding properties. Water structure has been demonstrated to exert a profound effect upon mechanical properties whether measured in compression or in tension. In particular, water that is characterized by differential scanning calorimetry as ‘freezing’ water is observed to have a marked plasticizing effect upon the gel, whereas ‘non-freezing’ water has little such effect. Similarly, the ‘freezing’ water produces a more marked effect on thermally induced transitions. Two distinct transition points are observed as a result of its presence. One corresponds to the freezing point of water and the other to a glass transition temperature, whose value depends upon the proportion of ‘freezing’ or ‘plasticizing’ water in the gel. Several predictive and direct measurement techniques have been used to study the surface properties of the copolymers in both hydrated and dehydrated states. Taken together they have established a sound understanding of the way in which polar and dispersive components of surface free energy vary as a function of copolymer composition and water content. Use of protein adsorption and fibroblast cell interaction techniques demonstrate that biological phenomena respond to changes at a molecular level which current macroscopic surface energy techniques are unable to discern.     

Preparation and characterization of light‐cured methacrylate/montmorillonite nanocomposites

Polymer/clay nanocomposites were prepared from dimethacrylate monomers, commonly used in dental restorative resins, and an organically modified silicate (montmorillonite). The photopolymerization process was hardly affected by the presence of the silicate filler, and thus 2 mm thick samples containing 3 wt% clay were extensively cured. Transmission electron microscopy revealed that the montmorillonite platelets were either intercalated or exfoliated. Nevertheless, for all formulations, intermediate‐sized aggregates of about 1 µm were present and their fraction increased as the amount of filler increased. The presence of the clay was found to have no major effect on the flexural modulus and compressive yield strength of the nanocomposites. Moreover, the water uptake of nanocomposites containing 3 wt% clay was about 10–15% higher than that of unfilled monomers. Modification of the clay surface with alternative organic cations is certainly necessary in order to achieve an optimal dispersion of the clay in the polymer matrix. Copyright © 2010 Society of Chemical Industry     

Blends of amorphous and crystalline polylactides with poly(methyl methacrylate) and poly(methyl acrylate): a miscibility study

Blends of amorphous and crystalline polylactides (PDLA and PLLA) with poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) have been prepared. Thermal behaviour and miscibility of these blends along the entire composition interval were studied by differential scanning calorimetry (d.s.c.). The results were compared with those obtained by dynamic mechanical analysis (DMTA). Only one T_g was found in PDLA/PMA and PDLA/PMMA blends, indicating a high degree of miscibility in both systems. Nevertheless, the PDLA/PMMA blend presented enlargements of the T_g width at high PMMA contents. In this case, additional evidence of complete miscibility was obtained by studying the evolution of the enthalpic recovery peaks which appear after different thermal annealing treatments. When the polylactide used was semicrystalline (PLLA), once the thermal history of the blends had been destroyed, crystallization of PLLA was disturbed in both blends PLLA/PMMA and PLLA/PMA, but in a rather different fashion: in the first case crystallization was almost prevented while in the second one it was favoured. This behaviour was explained in terms of the effect of the higher stiffness as indicated by the value of T_g for PMMA compared to that for PMA.     

Concentration effects in the base-catalyzed hydrolysis of oligo(ethylene glycol)- and amine-containing methacrylic monomers

Concentration effects in the base-catalyzed hydrolysis of water-soluble methacrylates (3-(N,N-dimethylaminoethyl) methacrylate (DMAEMA), 2-hydroxyethyl methacrylate (HEMA) and oligo(ethylene glycol) methacrylates (OEGMAs)) have been studied. These monomers are rapidly hydrolyzed in the presence of bases at the room temperature in dilute aqueous solutions, but the reaction rate decreases sharply in highly concentrated solutions. A clear correlation was found between a form of the viscosity isotherm for DMAEMA solutions and the concentration dependence of the autocatalytic hydrolysis rate which indicates the connection of process kinetics with the structure of solutions. These data should be considered when carrying out homo- and copolymerization of the previously mentioned monomers in aqueous solutions.     

Accelerant‐promoted free radical polymerization of methacrylates by stabilized nitroxide unimolecular initiators: synthesis and characterization

BACKGROUND: This investigation evaluates the effectiveness of initiator adducts for living and controlled polymerization of methacrylates, crosslinking of dimethacrylates and thermal stabilities of the resulting polymers. Adducts of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy with benzoyl peroxide and with azobisisobutyronitrile were prepared and evaluated as stabilized unimolecular initiators for the free radical polymerization of methacrylate monomers using sulfuric acid as catalyst. The monomers used were methyl methacrylate, triethylene glycol dimethacrylate (TEGDMA) and ethoxylated bisphenol A dimethacrylate (EBPADMA). RESULTS: Successful polymerization was achieved at 70 and 130 °C with reaction times ranging from 45 min to 120 h. The dispersity (D) of poly(methyl methacrylate) (PMMA) was 1.09–1.28. The livingness and extent of control over polymerization were confirmed with plots of M_n evolution as a function of monomer conversion and of the first‐order kinetics. The glass transition temperature (T_g) for PMMA was 123–128 °C. The degradation temperature (T_d) for PMMA was 350–410 °C. T_d for poly(TEGMA) was 250–310 °C and for poly(EBPADMA) was 320–390 °C. CONCLUSION: The initiators are suitable for free radical living and controlled polymerization of methacrylates and dimethacrylates under mild thermal and acid‐catalyzed conditions, yielding medium to high molecular weight polymers with low dispersity, high crosslinking and good thermal stability. Copyright © 2008 Society of Chemical Industry     

Surface fatigue of brittle polymers in rolling line contact

The two-disc machine was used to study surface fatigue in polymethylmethacrylate (PMMA) specimens in rolling line contact. A notch was introduced to the specimen to study the crack growth rate. The form of damage in PMMA disc ranges from the appearance of small cracks on the contact path, leading to the formation of pits and initiation, growth and failure of crazes. A degree of sliding was introduced into the contact between the two discs to study the effect of the tangential force on surface fatigue and crack propagation. The creation of crazes was observed in both rolling and rolling/sliding configurations, but the time of initiation, the appearance, their size and the time to failure were different. An optical microscope and SEM were used to study the morphology of the failure produced. The growth rate in the artificially induced crack was monitored and appeared to be stable with an initial burst of crack extension.     

Synthesis and nonlinear optical properties of PMMA copolymers having novel benzoxazole chromophores attached with various electron-withdrawing groups

For improvements of thermal stability and nonlinear optical (NLO) activity of chromophores, we newly synthesized a series of NLO chromophores incorporating aromatic benzoxazole unit as a π-conjugated bridge with various electron-withdrawing groups, such as nitrophenyl, nitrothiophene, nitrofuran, dicyanovinylphenyl, and nitrophenylethenyl group. Polymethylmethacrylate copolymers (PMBz) containing these benzoxazole chromophores were synthesized and their properties were investigated by thermogravimetry and ultraviolet-visible spectroscopy. The PMBz copolymers exhibited better thermal and ultraviolet stabilities than the corresponding copolymer with general stilbene chromophores (PMSt). Moreover, temporal stability of nonlinear optical coefficient (d₃₃) of PMBz copolymer increased in comparison with that of PMSt. The copolymer with benzoxazole–nitrothiophene chromophores had the largest d₃₃ value of 153 pm/V (at 1.064 mm) and nonresonant d₃₃ calculated by the two-level model was 21.3 pm/V.     

Miscibility and surface crystal morphology of blends containing poly(vinylidene fluoride) by atomic force microscopy

The miscibility and surface crystalline structure of blends containing poly(vinylidene fluoride) (PVDF) composed of and γ phases were investigated by atomic force microscopy (AFM) and differential scanning calorimeter (d.s.c.) measurements. It was found that the surface crystalline phase of PVDF and the degree of surface enrichment of a lower surface free energy component in a blend might strongly be affected by the magnitude of the intermolecular interaction, even though the blend is miscible. Also, the segmental interaction parameters was determined by combining the T_m depression of PVDF in a blend and the binary interaction model. According to the binary interaction model, the introduction of a carboxyl group for miscible [poly(methyl methacrylate)/PVDF] and [poly(vinyl acetate)/PVDF] blends decreased their miscibility.     

聚丙烯酸高级酯煤油溶液的流动行为

本文制备了一系列高分子量的聚丙烯酸和甲基丙烯酸高级酯,研究了这些聚合物的分子量及其分布,侧基大小和溶液浓度对煤油溶液的流变性、减阻性和抗剪切性的影响。实验证明,这些高级酯煤油溶液都是假塑性流体,流动行为可用幂律描述:τ=k_γ~n;溶液的湍流摩擦系数(f)、雷诺数(R_e)和减阻触发时的雷诺数(R_(eo))之间的关系为:(?)。发现减阻百分率(DR)先随壁切应力(τ_w)增大而增加,超过一定的壁切应力(τ_(wm))后,DR 逐渐下降。DR 随分子量增大而增大,当分子量超过一定值后,DR 达到一个极限值(DR_m)而不再增大。DR_m 随浓度增加而增加。τ_(wm)基本上与浓度无关。在低速下,分子量分布较宽的样品具有较高的 DR 值。在湍流中,聚合物的抗剪切性随侧基增大和溶液浓度的提高而增强。