Thermal and dynamic mechanical properties of microwave and heat‐cured poly(methyl methacrylate) used as dental base material

In this study, the particle size distribution, molecular weight, thermal analysis (TGA) differential scanning calorimetry (DSC) and thermogravimetric analysis, and dynamic mechanical analysis (DMA) of poly(methyl methacrylate) used as dental base material were investigated. The commercial raw material used were prepared for microwave curing, and they were cured by microwave and conventional heat methods. The average particle size of the powder studied (103.1 μm) were much larger than that of the commercial powders (50–78 μm) for conventional curing. The particle size dietribution were almost symmetrical and narrow. The viscosity‐average molecular weight were larger for microwave curing and increased with curing time. The glass transition temperature T_g measured (about 110°C) by DSC increased with curing period in microwave oven. The values of T_g were close to each other for both curing techniques. The degradation temperature range observed by TGA were 200–377°C. The movements of molecular chains in their conformations were studied by DMA in the form of changes in different mechanical properties with temperature. It was shown that crosslinking increased with increase of curing time. The changes were more noticeable in microwave curing compared to conventional heat curing. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2971–2978, 1999     

The effect of layered double hydroxides dispersion on thermal and mechanical properties of poly(vinyl chloride)/poly(methyl methacrylate) blends

Poly(vinyl chloride) (PVC)/layered double hydroxide (LDH) composites and PVC/poly(methyl methacrylate) (PMMA)/LDH composites were prepared via solution intercalation into PVC using both unmodified and organo‐modified LDHs and variable‐molecular‐weight PMMA as additional components. The LDH dispersion was investigated using X‐ray diffraction analysis and electron microscopy in scanning and transmission modes. Spotlight fourier transform infrared (FTIR) chemical imaging analysis was also used to obtain a deeper insight into the dispersion of polymer phases and LDH segregation. Thermal properties were determined using thermogravimetric analysis and differential scanning calorimetry; moreover, a preliminary investigation of mechanical properties in tensile mode and evaluation of the Vicat softening temperature were carried out. The morphological analysis of PVC/LDH and PVC/PMMA/LDH composites evidenced in both cases the presence of disordered micro‐aggregates with loss of the LDH crystallographic symmetry depending on the amount and molecular weight of PMMA. In particular, in the case of PVC/PMMA/LDH composites, the FTIR imaging analysis showed that PMMA mostly segregated in the LDH phase. However, even if the degree of LDH dispersion was not elevated (micro‐aggregates with disordered structures and size ranging from 0.5 up to 11 µm were evidenced), thermal stability and mechanical properties of the composites were improved with a synergic effect of PMMA and LDH. © 2013 Society of Chemical Industry     

Evaluating effects of biobased 2,5‐furandicarboxylate esters as plasticizers on the thermal and mechanical properties of poly (vinyl chloride)

We synthesized 2,5‐furandicarboxylate esters [i.e., dibutylfuran‐2,5‐dicarboxylate, diisoamylfuran‐2,5‐dicarboxylate, and di(2‐ethylhexyl)furan‐2,5‐dicarboxylate] and investigated their potential application as plasticizers of commercial poly(vinyl chloride) (PVC) products. Fourier transform infrared analysis, mechanical tests, scanning electron microscopy investigation, differential scanning calorimetry analysis, dynamic mechanical thermal analysis, thermogravimetric analysis (TGA), melt flow rate (MFR) measurement, and plasticizer migration measurements were used to the evaluate the comprehensive properties of the blended products. The results of the tensile tests demonstrate that the blends exhibited antiplasticization and flexible plastic characteristics at 10 and 50 phr in PVC, respectively. Moreover, flexural and impact test data indicate that the three types of blends exhibited a similar tendency: the hardness decreased continuously as the amount of plasticizer increased. Their morphology indicated that all of the plasticizers had good compatibility with PVC. The resulting glass‐transition temperature of the investigated plasticizers was lower than that of pure PVC, and reduction was largest for the plasticizer with the highest molecular weight. TGA revealed that the thermal degradation of blended polymers occurred in three stages and that all of the blends were stable up to 180°C. Finally, the MFRs of all of the specimens indicated that the addition of a higher concentration of lower molecular weight biobased esters resulted in improved fluidity, but these compounds migrated more easily from the blends. Hence, 2,5‐furandicarboxylic acid derived from biomass has potential as a plasticizer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40938.     

Thermal and mechanical properties of poly(methyl methacrylate) used as dental base material

The thermal and mechanical properties of poly(methyl methacrylate) prepared at different curing times were studied using DSC, TGA, tensile, and three-point bending test methods. The molecular weights of the polymer samples were determined from the viscosity measurements. The curing time applied for two different commercial materials, manufactured for dental use, ranged from 15 to 180 min. The samples cured for 15 and 20 min were soluble in chloroform completely, but the others were partially soluble. The insoluble fraction increased with curing time but the molecular weight of the soluble fraction remained constant. DSC thermograms showed further curing of the samples cured for 15 and 20 min. After curing for 180 min and/or annealing at room temperature for about 13 months, the samples were completely crosslinked. The characteristic values obtained from the tensile and the three-point bending tests were similar for samples cured at different times. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1409–1417, 1998     

Thermal and mechanical properties of poly(methyl methacrylate) and ethylene vinyl acetate copolymer blends

A series of poly(methyl methacrylate) (PMMA) blends have been prepared with different compositions viz., 5, 10, 15, and 20 wt % ethylene vinyl acetate (EVA) copolymer by melt blending method in Haake Rheocord. The effect of different compositions of EVA on the physico‐mechanical and thermal properties of PMMA and EVA copolymer blends have been studied. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) has been employed to investigate the phase behavior of PMMA/EVA blends from the point of view of component specific interactions, molecular motions and morphology. The resulting morphologies of the various blends also studied by optical microscope. The DSC analysis indicates the phase separation between the PMMA matrix and EVA domains. The impact strength analysis revealed a substantial increase in impact strength from 19 to 32 J/m. The TGA analysis reveals the reduction in onset of thermal degradation temperature of PMMA with increase in EVA component of the blend. The optical microscope photographs have demonstrated the PMMA/EVA system had a microphase separated structure consisting of dispersed EVA domains within a continuous PMMA matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The effects of plasticizers on the dynamic mechanical and thermal properties of poly(lactic acid)

Poly(lactic acid) (PLA) was blended with five plasticizers in a batchwise mixer and pressed into films. The films were analyzed by means of dynamic mechanical analysis and differential scanning calorimetry to investigate the properties of the blends. Triacetine and tributyl citrate proved to be effective as plasticizers when blended with PLA. The glass transition temperature of PLA decreased linearly as the plasticizer content was increased. Both plasticizers were miscible with PLA to an extent of ～ 25 wt %. At this point, the PLA seemed to be saturated with plasticizer and the blends tended to phase separate when more plasticizer was added. There were also signs of phase separation occurring in samples heated at 35, 50, and 80°C, most likely because of the material undergoing crystallization. The presence of the plasticizers induced an increased crystallinity by enhancing the molecular mobility. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1227–1234, 2002     

Synthesis and thermal properties of poly(methyl methacrylate)‐poly(L‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer

Poly(methyl methacrylate)‐poly(L ‐lactic acid)‐poly(methyl methacrylate) tri‐block copolymer was prepared using atom transfer radical polymerization (ATRP). The structure and properties of the copolymer were analyzed using infrared spectroscopy, gel permeation chromatography, nuclear magnetic resonance (¹H‐NMR, ¹³C‐NMR), thermogravimetry, and differential scanning calorimetry. The kinetic plot for the ATRP of methyl methacrylate using poly(L ‐lactic acid) (PLLA) as the initiator shows that the reaction time increases linearly with ln[M]₀/[M]. The results indicate that it is possible to achieve grafted chains with well‐defined molecular weights, and block copolymers with narrowed molecular weight distributions. The thermal stability of PLLA is improved by copolymerization. A new wash‐extraction method for removing copper from the ATRP has also exhibits satisfactory results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

含规整 PMMA支链的 PBA合成及其力学性能

研究了聚甲基丙烯酸甲酯大单体与丙烯酸丁酯在苯中的共聚，该大单体由甲基丙烯酸甲酯在巯基乙酸链转移剂存在下聚合，用甲基烯酸缩不甘油酯封端，研究了共聚速率、大单体相对分子质量、大单体与小单体投料比、引发剂用量、单体浓度及共聚温度对接枝效率及共聚物相对分子质量的影响。用分级沉淀法精制共聚物。用凝胶渗透色谱法、红外光谱法及差示扫描量热法对共聚物进行表征，用蒸汽压式渗透压力计及膜渗透压测定了结构参数，结果表明，平均接枝数随转化率增加而降低，在一定的组成范围内，共聚物呈热塑性弹性体行为。     

The interrelationship between processing conditions, microstructure and mechanical properties for injection moulded rubber-toughened poly(methyl methacrylate) (RTPMMA) samples

The interrelationship between processing conditions, developed microstructure and mechanical properties has been studied for a series of injection moulded rubber-toughened poly(methyl methacrylate) (RTPMMA) samples. A design of experiments (DOE) approach has been adopted to investigate the effect of barrel temperature, mould temperature, screw speed and back pressure on the mechanical properties of the mouldings. The back pressure has been identified as the single most important factor affecting the sample properties. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) have been used to study the relationship between the rubber-toughened microstructure and mechanical properties. SEM has shown that the rubber particles are almost spherical in the central region of the injection-moulded samples, away from the sample surface. AFM topography measurements combined with UFM can reveal the distribution, elongation and orientation of the rubber particles close to the surface of the sample. UFM in particular reveals the core-shell structure of the particles as well as the presence of particles immediately under the surface, invisible by AFM. The particles are elongated in the skin region of the injection moulded samples and well aligned to the melt flow. UFM has shown that samples with different flexural properties exhibit a difference in the number and distribution of rubber particles present in the skin region.     

Synthesis and dielectric properties of poly(methyl methacrylate)–clay nanocomposite materials

Poly(methyl methacrylate) (PMMA)–clay nanocomposite (PCN) materials were synthesized through in situ intercalative polymerization. A cationic surfactant, [2(dimethylamino)ethyl]triphenylphosphonium bromide, was used as an intercalating agent with pristine Na⁺‐montmorillonite (MMT). The synthesized PCN materials were subsequently investigated by a series of characterization techniques, including wide‐angle powder X‐ray diffraction, Fourier transform IR spectroscopy, transmission electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. Compared to pure PMMA, the PCN materials exhibit higher thermal degradation temperatures and glass‐transition temperatures. The dielectric properties of PCN blending with a commercial PMMA material in film form with clay loading from 0.5 to 5.0 wt % were measured under frequencies of 100 Hz–1 MHz at 35–100°C. Significantly depressed dielectric constants and losses were observed for these PCN‐blending materials. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2175–2181, 2005     

The compatibility of poly(methyl methacrylate) and chlorinated polyethylene

The compatibility of poly(methyl methacrylate) with chlorinated polyethylene was studied using differential thermal analysis and dynamic mechanical measurements. For around 50% chlorination of polyethylene they were found to be compatible and show an LCST, but not at 27% chlorination as had previously been thought. The previous results were explained as due to a matching of refractive indices over some temperatures. The compatibility was explained by the heat of mixing which becomes favourable at chlorination levels above approximately 46%.     

Synthesis and properties of poly(methyl methacrylate)/montmorillonite (PMMA/MMT) nanocomposites

PMMA/MMT nanocomposites were successfully synthesized via in situ intercalative polymerization, and characterized by means of wide‐angle X‐ray diffractometry, transmission electron microscopy, thermal gravimetric analysis, dynamic mechanical analysis and Fourier‐transform infrared analysis. The nanocomposites possess partially exfoliated and partially intercalated structure, in which the silicate layers are exfoliated into nanometre secondary particles with thickness of less than 20 nm and uniformly dispersed in the polymer matrix. In comparison with pure PMMA, the thermal stability, glass transition temperature, and mechanical properties of the polymer are notably improved by the presence of the nanometric silicate layers. It was found that part of the PMMA chains in the nanocomposites are well immobilized inside and/or onto the layered silicates and, therefore, the unique properties of the nanocomposites result from the strong interactions between the nanometric silicate layers and the polymer chains. Copyright © 2003 Society of Chemical Industry     

Environmentally friendly plasticizers for poly(vinyl chloride)—Improved mechanical properties and compatibility by using branched poly(butylene adipate) as a polymeric plasticizer

Linear and branched poly(butylene adipate)s (PBA) with molecular weights ranging from 2000 to 10,000 g/mol, and a branching agent content between 0 and 1.8%, were solution cast with poly(vinyl chloride) (PVC) to form 50‐ to 60‐μm thick flexible films. Dry films were analyzed by tensile testing, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and optical microscopy (OM) to study the effects of molecular weight and branching on the plasticizing efficiency of the polyester. PBA formed a semimiscible two‐phase system with PVC, where the amorphous part exhibited a single glass transition temperature. The degree of crystallinity for the polyester, surface composition, and mechanical properties of the films depended on the blend composition, molecular weight, and degree of branching of the polyester. Plasticizing efficiency was improved by higher degree of branching. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2180–2188, 2006     

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     

Interface and mechanical properties of poly(methyl methacrylate)–fiber composites

Long‐fiber pellets were made by an in situ pultrusion process. Fiber‐reinforced composites were prepared by an injection‐molding process and an extrusion/injection‐molding method with pellets, respectively. SEM observations showed that the strong interface was maintained during the injection process for low shearing forces, although polymer adhesion to the fiber surface was completely delaminated in the process of extrusion/injection molding for very high shearing forces. Enhanced adhesion of composites promoted substantial improvement of mechanical properties compared to those with poor adhesion. However, the enhanced adhesion between the fiber and the matrix also sacrificed the impact resistance properties. Longer fibers substantially enhanced the properties of composites. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2478–2483, 2004     

Evaluation of the effects of biobased plasticizers on the thermal and mechanical properties of poly(vinyl chloride)

Blends were prepared of poly(vinyl chloride) (PVC) with four different plasticizers; esters of aconitic, citric, and phthalic acids; and other ingredients used in commercial flexible PVC products. The thermal and mechanical properties of the fresh products and of the products after 6 months of aging were measured. Young's modulus of the PVC blends was reduced about 10‐fold by an increase in the plasticizer level from 15 to 30 phr from the semirigid to the flexible range according to the ASTM classification, but a 40‐phr level was required for PVC to retain its flexibility beyond 6 months. At the 40‐phr level, tributyl aconitate performed better than diisononyl phthalate (DINP) or tributyl citrate, in terms of lowering Young's modulus, both in the fresh materials and those aged for 6 months. The effects of the four plasticizers on the glass‐transition temperature (T_g) were similar, with T_g close to ambient temperature at the 30‐ and 40‐phr levels in freshly prepared samples and at 40–60°C in those aged for 6 months. The thermal stability of the PVC plasticized with DINP was superior among the group. Overall, tributyl aconitate appeared to be a good candidate for use in consumer products where the alleged toxicity of DINP may be an issue. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1366–1373, 2006     

Mechanical properties of soft liner–poly(methyl methacrylate)‐based denture material

In this study, the mechanical properties of two different permanent soft lining materials and their bonding to poly(methyl methacrylate) (PMMA) were compared. Both of the soft liners were heat‐cured commercial materials. The polymerization was carried out by conventional methods suggested by manufacturer, and the curing was done at the temperature of boiling water for 5, 15, 25, and 35 min. The sample groups were tested in the computer‐aided tensile‐testing machine at a rate of 2 mm/min. The slow rate helps the collection of more and more reliable data. At this time, the stress–strain curves were used to calculate ultimate tensile strength, elastic modulus, resilience, and toughness. The measurements were carried for PMMA, Molloplast B, Flexor, and a combination of PMMA/soft liner. After introducing the soft lining material on PMMA of the same thickness, the new material structure was more elastic than the original PMMA. Flexor showed adhesive failure at studied curing periods, but Molloplast B gave larger tear strength values and cohesive rather than adhesive failure at the 25‐min and 35‐min curing times. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 467–474, 2002     

表面修饰氧化石墨烯纳米带增强PMMA的研究

以多壁碳纳米管(MWNTs)为原料,使用纵向氧化切割法制备了氧化石墨烯纳米带(GONR),通过物理吸附作用制备了聚醚型苯并咪唑(OPBI)非共价修饰GONR(FGONR)。采用溶液浇注法制得了聚丙烯酸甲酯(PMMA)/FGONR复合材料薄膜,对FGONR及其PMMA复合材料的结构与性能进行了研究,同时对比了以MWNTs,GONR,OPBI改性MWNTs(FCNTs)增强的PMMA复合材料的力学性能。结果表明:OPBI成功地物理吸附到GONR的表面,且FGONR在PMMA中具有良好的分散性能;在PMMA/FGONR复合材料中,当FGONR的质量分数为0.5%时,复合材料的拉伸强度达到49.50 MPa,杨氏模量达到2.27 GPa,其增强效果比MWNTs,GONR,FCNTs的要好,FGONR有望作为制备高性能复合材料的一种良好的纳米填料。     

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