Grafting of methyl methacrylate (MMA) onto Antheraea assama silk fiber

Graft copolymerization of methyl methacrylate (MMA) onto nonmulberry silk fiber Antheraea assama was investigated in aqueous medium using the KMnO₄–oxalic acid redox system. Grafting (%) was determined as a function of the reaction time, temperature, and monomer and initiator concentrations. The rate of grafting increased progressively with increase of the reaction time up to 4 h and then decreased. The extent of grafting was maximum at 55°C. The extent was also dependent upon monomer and initiator concentrations up to 75.5 × 10^?2 and 6 × 10^?3 M, respectively. The grafted products were evaluated by infrared spectroscopy and their thermal decompositions were studied by TG and DTG techniques in static air at 20°C min^?1 and 30°C min^?1 in the range 30–800°C. The kinetic parameters for ungrafted and grafted fibers were evaluated using the Coats and Redfern method. The grafted products were found to be thermally more stable than were those of the ungrafted fibers. The surface characteristics of the ungrafted and grafted fibers were evaluated by scanning electron microscopy. The water‐retention values (WRVs) of the grafted fibers were in decreasing order with increase in the grafting (%). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2633–2641, 2001     

Molecular weights and molecular weight distribution in phase equilibria of the polystyrene-poly(methyl methacrylate)-toluene system

The composite gel permeation chromatography (GPC) chromatogram of a mixture of polystyrene and poly(methyl methacrylate) has been successfully resolved into its component chromatograms by using a newly developed technique. This technique has made possible the calculation of M _w and M _n values of these polymers in the conjugate phases of the ternary systems with toluene as the solvent. Calculated M _w and M _n values of the two polymers indicated that the larger polystyrene molecules tend to stay in the top polystyrene-rich phase while its smaller molecules tend to stay in the bottom phase to interact with the other polymer. The reverse is true with the poly(methyl methacrylate) molecules. This tendency strongly suggests that interactions among the two polymers were accomplished mainly by their smaller molecules.     

Isotactic copolymerization of methyl methacrylate (MMA) with alkyl acrylates

Summary Copolymerization of methyl methacrylate(MMA) and alkyl acrylates [t-butyl(tBA) and 2-ethylhexyl(OA)] was realized from a short living pre-PMMA. The poly(MMA-co-tBA) and poly(MMA-co-OA) obtained with rac-Me₂Si(Ind)₂ZrMe₂ were characterized as random isotactic copolymers. Whereas, corresponding syndio-rich atactic random copolymers were obtained with Cp₂ZrMe₂.     

Infrared spectroscopy of graft polymers separated from graft copolymers of wool and silk with methyl methacrylate

The HCl- or papain-decomposition residues obtained from reduced wool fibers grafted with 1.5–3.0% methyl methacrylate were extractively fractionated successively with cold acetone, hot acetone, and benzene. Each fraction was examined by infrared spectroscopy. Generally, the 715 cm^?1 spectral band considered to be due to vc-s-c was found in the hot acetone-soluble fraction. It was concluded that the thiol groups on wool keratin provide the main sites of grafting, as might be expected. A similar result was obtained for grafted silk fibroin fibers, the methionine residue being presumed to be related to some of the grafting sites at least. Furthermore, a sort of stereoregularity was observed in some of the graft polymer fractions, isotactic-rich material being obtained in the case of silk fibers. In the range of very low grafting, a stereoregulating effect on the structure of the polymer formed within fibers appears to be present in relation to the grafting or adsorption sites of monomers and the fine structure of fibers.     

甲基丙烯酸甲酯(MMA)吸附剂失活的探析

通过对吸附剂差热-热失重分析(TG-DTA)、红外线光谱(IR)、扫描电镜(SEM)、X射线衍射(XRD)、比表面积和孔结构表征研究,得出结论:甲基丙烯酸甲酯(MMA)中甲酸与吸附剂的碱性中心CaO进行物理-化学吸附,形成甲酸钙堵塞了吸附剂的孔道,致使MMA吸附剂失活。     

Molecular weight fractionation of poly(methyl methacrylate) using Gas Anti-Solvent techniques

The solubility of poly(methyl methacrylate) in acetone, expanded by carbon dioxide, was studied at 20 °C for a variety of molecular weights and architectures. The suitability of the Gas Anti-Solvent method for fractionation of poly(methyl methacrylate) was investigated with positive results. The threshold pressure for precipitation of various monodisperse molecular weights was investigated, and the effectiveness of this technique to fractionate a polymer with a broad molecular weight distribution was evaluated. The pressure required to precipitate polymers was found to be low, generally below 60 bar.     

Graft copolymerization of methyl methacrylate (MMA) onto silk using potassium peroxydiphosphate–cysteine (PP–Cys) redox system

Poly(methyl methacrylate) has been grafted onto mulberry silk in an aqueous medium by using potassium peroxydiphosphate–cysteine (PP–Cys) redox initiator. Various effects upon grafting such as concentration of cysteine, concentration of peroxydiphosphate, concentration of monomer, concentration of sulfuric acid, and temperature were studied. At a low range of cysteine concentration (6.25 × 10^?4 mol/L), the rate of polymerization R_p (%/s) is proportional to cysteine concentration and the exponent is calculated to be 0.8. The monomer exponent is calculated to be unity up to the concentration of 65.72 × 10^?2 mol/L. From the Arrhenius plot of log R_p vs. 1/T (T = absolute temperature) the overall activation energy is computed to be 15.19 kcal/mol. A suitable kinetic path has been pictured and a rate expression has been derived.     

Synthesis of polymer gel electrolyte with high molecular weight poly(methyl methacrylate)-clay nanocomposite

Polymer nanocomposite gel electrolytes consisting of high molecular weight poly(methyl methacrylate) PMMA-clay nanocomposite, ethylene carbonate (EC)/propylene carbonate (PC) as plasticizer, and LiClO₄ electrolyte are reported. Montmorillonite clay was ion exchanged with a zwitterionic surfactant (octadecyl dimethyl betaine) and dispersed in methyl methacrylate, which was then polymerized to synthesize PMMA-clay nanocomposites. The nanocomposite was dissolved in a mixture of EC/PC with LiClO₄, heated and pressed to obtain polymer gel electrolyte. X-ray diffraction (XRD) of the gels indicated intercalated clay structure with d-spacings of 2.85 and 1.40 nm. In the gel containing plasticizer, the clay galleries shrink suggesting intercalation rather than partial exfoliation observed in the PMMA-clay nanocomposite. Ionic conductivity varied slightly and exhibited a maximum value of 8 × 10⁻⁴ S/cm at clay content of 1.5 wt.%. The activation energy was determined by modeling the conductivity with a Vogel-Tamman-Fulcher expression. The clay layers are primarily trapped inside the polymer matrix. Consequently, the polymer does not interact significantly with LiClO₄ electrolyte as shown by FTIR. The presence of the clay increased the glass transition temperature (Tg) of the gel as determined by differential scanning calorimetry. The PMMA nanocomposite gel electrolyte shows a stable lithium interfacial resistance over time, which is a key factor for use in electrochemical applications.     

Effect of molecular weight distribution on fatigue crack propagation in poly(methyl methacrylate)

It is well established that both molecular weight (M) and its distribution (MD) affect many polymer properties such as mechanical behavior. Thus studies have shown that fatigue life is enhanced by increases in M. Research here has shown that with notched specimens fatigue crack propagation (FCP) rates are dramatically decreased by increasing M, even when the M is high enough that the static fraeture energy has essentially reached its asymptotic limit. In this study, specimens of poly(methyl methacrylate) containing either high- or low-M tails were prepared and characterized. The earlier finding that FCP rates are inversely related to average M was confirmed, but specific effects of M distribution were observed. At constant Mⁿ, a low-M tail had little effect on FCP resistance, while a high-M tail improved FCP resistance of polymers whose average M was too low for effective entanglements. Thus with high-M tails, it was possible to test specimens whose average M's were too low to permit machining. It is proposed that the effects noted are due to relative stabilization or destabilization of crazes ahead of the crack.     

Molecular weight and molecular weight distribution from dynamic measurements of polymer melts

A method for determining the molecular weight distribution (MWD) of a polymer melt has been developed using the dynamic elastic modulus (G'), plateau modulus (G), and zero shear complex viscosity (η). The cumulative MWD was found to be proportional to a plot of (G'/G)^0.5 vs. measurement frequency (ω). Frequency (ω) was found to be inversely proportional to (MW)^3.4, as expected. Results were scaled to absolute values using the empirical relationship η ∝ (M?_w)^3.4, where M?_w is the weight-average MW. M?_w, M?_n (number-average MW) and M?_w/M?_n calculated from melt measurements were found to agree with size exclusion chromatography usually well within 10 percent for broad and bimodal distribution samples. M?_w/M?_n tended to be approximately 20 percent higher for narrow distribution samples (M?_w/M?_n < 1.2) because we did not account for a finite distribution of relaxation times from a collection of monodisperse polymer chains. We also did not account for the plasticizing effect of short chains mixed with long ones which caused peak positions to be closer together for Theological vs, size exclusive chromatography (SEC) determinations of MW for bimodal distribution blends.     

Transition behaviour of polyurethane-poly(methyl methacrylate) interpenetrating polymer networks

The transition behaviour of polyurethane-poly(methyl methacrylate) interpenetrating polymer networks (PUR/PAc IPN's) was studied by means of differential scanning calorimetry (d.s.c.), dynamic mechanical spectroscopy (d.m.s.) and thermally stimulated depolarization (t.s.d.). Instead of a sharp discontinuity in heat capacity, as for the individual networks, a very broad change is observed by calorimetry and some intermediate changes in heat capacity appear too. D.m.s. yields only two peaks which show a marked inward shift, with an important damping and broadening, as compared to the individual networks. Some preliminary results obtained by t.s.d. confirm these findings. It can be concluded that PUR/PAc IPN's are phase separated, but that the mutual miscibility of both components is enhanced by the special mode of combining them, namely interpenetration. When the second component is not crosslinked, phases appear to be less entangled. Previous results on physical and mechanical properties corroborate these conclusions.     

Stereo-regulated methyl methacrylate (MMA) polymerization catalyzed by asymmetric Salen-type Schiff-base Cu(II) complexes

A series of mononuclear asymmetric Salen-type Schiff-base complexes [Cu(Lⁿ)] (n = 1–5, 1–5) were obtained by the Cu(II)-templated approach in the presence of one of five salicylaldehyde derivatives, respectively. These complexes could effectively catalyze the metal-coordinative polymerization of MMA for the formation of the syndio-enriched PMMAs (poly(methyl methacrylates)) in the presence of AIBN, where the Cu(II)-to-chelate-plane distances are positively relative to the catalytic activity. Moreover, the introduction of the encumbering substituent ortho to the phenoxide ring of the ligands plays a much more important and influential role on the tacticity and chain-growth of the obtained PMMAs than the variation of reaction conditions under the controllable polymerization.     

Analysis of methyl methacrylate adhesive (MMA) relaxation with non-linear stress–strain dependence

One of the problems regarding high strength and stiffness adhesive connections is the concentration of stresses on the edges of the bond. The use of adhesives characterized by high strength but also greater flexibility would avoid this effect and prevent brittle failure. Therefore, the results of a series of laboratory tests are presented in the paper for a semi-rigid methyl methacrylate adhesive (MMA). The research included quasi-static tensile and relaxation tests of the adhesive at a temperature of 23 °C and 50% humidity. Based on the test results, the complex characteristics of the viscoelastic material parameters of the adhesive for different stress levels were determined. The Maxwell model was used to describe the material model of the adhesive during relaxation, for which Prony series were calculated. The work also indicates the approach to numerical modelling using the Finite Element Method (FEM) for selected adhesive, ensuring good convergence of results in the elastic work of the material. Numerical analyses were performed in the ABAQUS software, using material models such as hyperfoam and viscoelasticity. Finally, the relaxation function values obtained during the laboratory tests and numerical analyses were compared and a forecast for longer term function values was presented. The presented results can be used for numerical analysis of adhesive joints with the use of a selected methacrylate adhesive, in the scope of the elastic range subjected to short- or long-term loads.     

Molecular weight distribution of products of free radical nonisothermal polymerization with gel effect. Simulation for polymerization of poly(methyl methacrylate)

A gel effect model for the free radical polymerization of PMMA under nonisothermal conditions has been used to simulate the profiles of various system parameters, such as temperature, initiator concentration and conversion. Cumulative molecular weight and instantaneous radical molecular weight profiles for processes with greatly different histories have been computed using the method of moments. Continuous approximation of the discrete variable, degree of polymerization, renders the transformation of a large set of ordinary equations for species conservation into partial differential equations. The resulting radical and dead polymer molecular weight distributions give averages consistent with those found by the method of moments. Basic rules of thumb correlating the product molecular weights with the governing process parameters have been established based on simulations applicable to either plug flow or well-stirred batch reactors.     

Grafting of methyl methacrylate onto Antheraea pernyi silk fiber with the assistance of supercritical CO2

Graft copolymerization of methyl methacrylate (MMA) onto Antheraea pernyi silk fibers, initiated by benzoyl peroxide in the supercritical CO₂ was investigated. The grafting degree was determined as a function of impregnating pressure, impregnating time, monomer concentration, initiator concentration, and reaction time. The structural properties of MMA‐grafted fiber were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. Grafted MMA was chemically bonded and/or physically adhered to the surfaces of the fibers. The grafted silk fibers exhibited two steps of weight loss according to the characteristic of each component as demonstrated by the thermogravimetric analysis. The water‐retention values indicated that the hydrophobic nature of the fibers was improved. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1299–1305, 2006     

Molecular weight variations in perylene‐doped poly(methyl methacrylate) for luminescent solar concentrators

Integrating highly efficient luminescent dyes into poly(methyl methacrylate) matrices with well‐defined parameters, such as degree of polymerization and dispersity, is a key step in the development of emerging technologies such as fiber‐based solar collectors, sensors, contactless coupling devices and integrated light sources. In this work, four perylene‐based fluorescent dyes, perylene from Sigma‐Aldrich, Lumogen F Yellow 083 from BASF, Perylene Orange from TCI and Lumogen F Red 300 from BASF, were polymerized in bulk with methyl methacrylate. The molecular weight distribution was controlled by the ratio between the chain transfer agent and initiator and was measured by size exclusion chromatography. A dopant‐dependent increase in the degree of polymerization, in which the dye causes a drop in the concentration of active growing polymer chains, was observed. Spectroscopic online monitoring of the process in transmission mode confirmed this observation and indicated the formation of stable perylene radicals during the polymerization. Comparative experiments with fluorescent (metal) organic dyes did not show a similar effect. Fitting models for the dye‐dependent molecular weights for Lumogen Yellow and Lumogen Red are proposed. © 2018 Society of Chemical Industry     

Comparison of the phase behaviour of the liquid-crystalline polymer/poly(methyl methacrylate) and poly(vinyl acetate)/poly(methyl methacrylate) blends

The phase behaviour of blends of a liquid-crystalline polymer (LCP) and poly(methyl methacrylate) (PMMA), as well as the phase state of blends of PMMA and poly(vinyl acetate) (PVA) has been investigated using light scattering and phase-contrast optical microscopy. The blends of LCP and PMMA have been obtained by coagulation from ternary solutions. The cloud point curves were determined. It was established that both pairs demix upon heating, ie have an LCST. In the region of intermediate composition, the phase separation proceeds according to a spinodal mechanism; however for LCP/PMMA blends, the decomposition proceeds according to a non-linear regime from the very onset. In the region of small amounts of LCP, the phase separation follows a mechanism of nucleation and growth. For PMMA/PVA blends, the spinodal decomposition proceeds according to a linear regime, in spite of the molecular mobility that PVA chains develop at lower temperatures. Only after prolonged heat treatment does the process transit to a non-linear regime. The data show a similarity between the phase behaviour of blends of liquid-crystalline and of flexible amorphous polymers. The distinction consists of the absence of a linear regime of decomposition for LCP-PMMA blends. © 1999 Society of Chemical Industry     

Highly syndiotactic poly(methyl methacrylate) with narrow molecular weight distribution formed by tert-butyllithium-trialkylaluminium in toluene

Summary Polymerization of MMA with t-C₄H₉Li in toluene in the presence of trialkylaluminum(alkyl=methyl, ethyl, butyl, isobutyl, and octyl) was examined at various Al/Li ratios. Triethyl-, tributyl and trioctylaluminums worked quite effectively in the polymerization to give highly syndiotactic PMMA with narrow molecular weight distribution (MWD) at the Al/Li ratio of 3 and higher than 3. The highest syndiotacticity of 96% was attained with t-C₄H₉Li/(n-C₈H₁₇)₃Al (1/3) at –93°C. The polymerization was initiated by t-C₄H₉ anion and proceeded in a living manner. The structure of the syndiotactic PMMA is chemically identical to that of isotactic PMMA prepared with t-C₄H₉MgBr. Consequently, highly isotactic and syndiotactic PMMAs with narrow MWD and with the same chemical structure from -end to -end were obtained.     

Influence of molecular weight on the fracture of poly(methyl methacrylate) (PMMA)

A model is proposed to explain the dependence of fracture parameters on the molecular weight of glassy polymers. The model assumes that the fracture event occurs in two stages; the first involves the orientation of polymer chain segments between entanglement points and the second, the fracture itself. A value has been calculated, (～0.6J m^?2), for the fracture surface energy corresponding to the lower critical molecular weight between entanglements, M=M_e. Allowing for the simplifying assumptions made in its derivation, this value is in good agreement with that found experimentally. It is proposed that, after the chain segments between entanglements crossing a plane have been fully extended, two possible mechanisms are involved; chain ‘pull-out’ up to a maximum governed by the time scale of the local fracture event, or chain scission. Using the concept of a reptating chain it is proposed that above M ～2 M_e there is a relationship between the fracture energy (γ) and the molecular weight of the form γ∝ ∝M² up to a critical value of M, above which γ is constant. It has been shown that there is some agreement with experimental relationships determined independently.     

Graft copolymerization of methyl methacrylate (MMA) on hydrazine treated oxycellulose in limited aqueous system

Graft copolymerization of methyl methacrylate (MMA) on oxycellulose modified with hydrazine treatment was studied in a limited aqueous system using K₂S₂O₂ as the initiator. Hydrazine modified oxycellulose prepared from oxycellulose corresponding to low degrees of oxidation (copper nos. 2–6) produced the best grafting effects. Grafting parameters under different sets of conditions were studied and compared and the mechanism of graft copolymerization discussed.