Atactic PMMA Research Articles

Effect of Tacticity on London Dispersive Surface Energy, Polar Free Energy and Lewis Acid-Base Surface Energies of Poly Methyl Methacrylate by Inverse Gas Chromatography

This research was devoted to study the effect of the tacticity on the surface physicochemical properties of PMMA. (1) Background: The determination of the surface free energy of polymers is generally carried out by inverse gas chromatography (IGC) at infinite dilution. The dispersive, polar and surface acid-base properties of PMMA at different tacticities were obtained via IGC technique with the help of the net retention time and volume of adsorbed. (2) Methods: The London dispersion equation was used to quantify the polar free energy of adsorption, while the London dispersive surface energy γsd(T) of PMMAs was determined using the thermal model. (3) Results: The results showed non-linear variations of γsd(T) of atactic, isotactic, and syndiotactic PMMAs with three maxima characterizing the three transition temperatures of PMMAs. The obtained values of the enthalpic and entropic Lewis’s acid-base parameters showed that the basicity of the atactic PMMA was about four times larger than its acidity. (4) Conclusions: A large difference in the behavior of the various PMMAs was proven in the different values of the polar acid and base surface energies of the three PMMAs with an important effect of the tacticity of PMMA on its acid-base surface energies.

Aggregation States and Segmental Dynamics of Poly(methyl methacrylate) in Nanofiber Mats

Nanofiber mats composed of polymers, having a large surface-to-volume ratio and high porosity, have been widely applied in the environmental and biomedical fields but fundamental knowledge on the polymer chains in the mats seems to be limited. We here report the aggregation states and segmental dynamics of poly(methyl methacrylate)s (PMMAs) with different stereoregularities in electrospun nanofiber mats. Attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy revealed that, in the case of atactic PMMA (at-PMMA), the population of the trans-trans conformation of the main chain part, which allows carbonyl groups of the side group to interact affirmatively with each other, increased in the electrospun nanofiber mat. On the other hand, in the case of isotactic PMMA (it-PMMA), the skeletal conformation was unchanged even in the nanofiber mat. As a result of the aggregation states of PMMA chains, the glass-transition temperature (Tg) of the electrospun nanofiber mats increased and remained unchanged from the corresponding bulk value for at- and it-PMMA, respectively. These findings should be useful for designing materials and devices composed of electrospun nanofibers.

Green Stereoregular Polymerization of Poly(methyl methacrylate)s Through Vesicular Catalysis

Green Stereoregular Polymerization of Poly(methyl methacrylate)s Through Vesicular Catalysis

Structure, Dynamics, and Apparent Glass Transition of Stereoregular Poly(methyl methacrylate)/Graphene Interfaces through Atomistic Simulations

We provide a detailed investigation of the structure and dynamics of stereoregular poly(methyl methacrylate) (PMMA) chains confined between graphene layers via atomistic molecular dynamics simulations. The density, conformation, and interfacial segmental dynamics of low molecular weight isotactic, syndiotactic, and atactic PMMA chains are examined at various temperatures, ranging from 490 K up to 580 K. For all stereoisomers, a tendency of chains to adsorb on graphene via ester-methyl groups is observed. Compared to other stereoisomers, isotactic chains are stretched and form better organized layers at the interface. Concerning dynamical properties, various dynamical modes of PMMA are studied as a function of distance from graphene as well as over the entire confined system. The interfacial backbone and ester side group motions are restricted, whereas the fast motion of methyl groups remains unaffected. In the temperature range studied here, the interphase thickness remains almost constant; however, the r...

The role of zirconium oxide as nano-filler on the conductivity, morphology, and thermal stability of poly(methyl methacrylate)–poly(styrene-co-acrylonitrile)-based plasticized composite solid polymer electrolytes

The plasticized composite solid polymer electrolytes (CSPE) involving polymer blends poly(methyl methacrylate)-poly(styrene-co-acrylonitrile) (PMMA-SAN), plasticizers ethylene carbonate (EC), and propylene carbonate (PC) with lithium triflate (LiCF3SO3) as salt and varying concentration of composite nano-filler zirconium oxide (ZrO2) is prepared by solution casting technique using THF as solvent. The powder X-ray diffraction (XRD) studies reveal amorphous nature of the CSPE samples. Fourier transform infrared (FT-IR) spectroscopy studies reveal interaction of Li+ ion with plasticizers, both C=O and OCH3 group of the PMMA, while nitrile group of SAN is inert. AC impedance and dielectric studies reveal that the ionic conductivity (σ), dielectric constant (e’), and dielectric loss (e”) of the prepared CSPE samples increase with increasing content of ZrO2 nano-filler up to 6 wt% and decrease with further additions. The temperature dependence of ionic conductivity follows Arrhenius relation and indicates ion-hopping mechanism. The sample Z2 (6 wt% ZrO2) with relaxation time τ of 8.13 × 10–7 s possess lowest activation energy (Ea = 0.23 eV) and highest conductivity (2.32 × 10–4 S cm−1) at room temperature. Thermogravimetric analysis (TGA) reveals thermal stability of highest conducting sample Z2 up to 321 °C after complete removal of residual solvent, moisture, and its impurities. Differential scanning calorimetric (DSC) studies reveal absence of glass transition temperature (Tg) corresponding to atactic PMMA for the CSPE Z2, while isotactic PMMA component shows Tg around 70 °C, which is due to increased interaction of filler with PMMA leading to change in its tacticity. Scanning electron microscopy (SEM) analysis reveals blending of PMMA/SAN polymers and lithium triflate salt. The incorporation of nano-filler ZrO2 leads to change in surface topology of polymer matrix. Rough surface of the CSPE Z2 leads to new pathway for ionic conduction leading to maximum ionic conductivity.

Local Structure Contributions to Surface Tension of a Stereoregular Polymer.

We have used all-atom molecular dynamics (MD) simulations to calculate the surface tension of melt poly(methyl methacrylate) (PMMA) as a function of tacticity. Computation of surface tension using the Kirkwood-Buff approach required hundreds of nanoseconds of equilibration. The computed slopes of surface tension versus temperature are in very good agreement with reported experimental values. Using a rigorous treatment of the true interface, which takes into account the molecular roughness, we find that isotactic PMMA, in comparison to syndiotactic and atactic PMMA, shows a larger surface concentration of polar ester-methyl and carbonyl groups on the surface versus nonpolar α-methyl groups. A mechanistic hypothesis based on the helical nature of the isotactic PMMA chains, their relative flexibility, and their reported conformational energies is proposed to explain the trends in composition near the surface. We highlight here how surface composition and surface tension are controlled by both polarity and steric constraints imposed by tacticity.

Tacticity separation of poly(methyl methacrylate) by multidetector thermal field-flow fractionation.

For the first time, thermal field-flow fractionation (ThFFF) has been used for the separation of poly(methyl methacrylate) (PMMA) with regard to molecular microstructure. PMMA exists in three different isomeric forms, namely, isotactic, syndiotactic, and atactic. ThFFF analysis of the different PMMA isomers in tetrahydrofuran, acetonitrile (ACN), and dioxane reveals that isomers with similar molecular weights exhibit different Soret coefficients, and thus different retention times, under identical experimental conditions. Of the three solvents, ACN shows the greatest influence on fractionation of the isomers. The separation according to molecular microstructure is found to be based on the cooperative effects of the normal and thermal diffusion coefficients. Furthermore, it is found that blends of different PMMA isomers with similar molecular weights can be fractionated into their respective isomeric components. The distribution of the isomeric content in an atactic PMMA sample is determined quantitatively by fractionating the sample with ThFFF and subsequently analyzing the fractions by (1)H NMR. The isomeric distributions determined from NMR data correlate well with ThFFF retention data of the samples and thus further highlight the unique fractionating capabilities of ThFFF.

Does Graphene Change Tg of Nanocomposites?

The effect of the addition of graphene on the glass transition temperature (Tg) of polymers was investigated, first with poly(methyl methacrylate) and then with an extensive literature review. Isotactic (i-PMMA) and atactic PMMA (a-PMMA) were blended with pristine graphene (PG) and thermally reduced graphene (TRG). A Tg increase was found for a-PMMA nanocomposites made via in situ polymerization with TRG but not when a-PMMA was solvent blended with TRG. However, a Tg increase was found for TRG solvent blended into i-PMMA and a smaller increase for PG with i-PMMA. Nearly all the increase occurred at the lowest loading, 0.25 wt %, with little change at increased graphene concentration. Tg increases due to interfacial interactions between matrix polymers and fillers. Physical blending such as solvent processes cannot provide enough interaction at the interfaces, whereas chemical blending processes such as in situ polymerization can yield strong covalent bonds. However, i-PMMA molecules can align on graphene sheets at the interface, creating more interaction between i-PMMA and graphene than a-PMMA. Also, the Tg of i-PMMA is 60 °C lower than a-PMMA, meaning that hydrogen bonds are stronger at the lower temperature. The Tg increase of TRG/i-PMMA is higher than that of PG/i-PMMA due to more oxygen functionalities on TRG than on PG to act as interfacial interaction sites. A broad literature survey agrees with our PMMA results. We found no changes in Tg for graphene/polymer nanocomposites synthesized via physical blending processes such as solvent or melt blending, except for blending with strongly polar polymers. In contrast, chemical blending processes such as in situ polymerization or chemically modified fillers yielded significant Tg increases in graphene/polymer nanocomposites.

Chain stiffness and chain conformation of poly(α-methylene-γ-butyrolactone) in dilute solutions

The chain stiffness and local chain conformation of atactic poly(α-methylene-γ-butyrolactone) (PMBL), which is a side chain cyclic structural analog of poly(methyl methacrylate) (PMMA), with a weight-average molecular weight (Mw) ranging from 2.8 × 103 to 2.6 × 106 in N,N-dimethylformamide (DMF) and γ-butyrolactone (GBL) were characterized by size exclusion chromatography with a multi-angle light-scattering detector (SEC-MALS) and synchrotron radiation small-angle X-ray scattering (SAXS). Based on the Kratky-Porod worm-like chain model, the scattering functions and the Mw dependence of z-average root-mean-square radius of gyration <S2>z1/2 yielded the Kuhn segment lengths λ−1, the diameter of the PMBL chains d, and the excluded-volume strengths in DMF and GBL. The local conformation of atactic PMBL in DMF and GBL were slightly larger than those of atactic PMMA, due to the presence of the conformationally rigid lactone ring structure.

New Complex Crystals of Chiral Poly(L -lactic acid) and Different Tactic Poly(methyl methacrylate)

Based on evidence from differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and Fourier-transform infrared (FTIR) spectroscopy, a new stereocomplex crystal (DSC Tm = 175 °C, with WAXD 2θ = 10.0° and 12.5°) is proven for the first time between structurally dissimilar chiral poly(L-lactic acid) (PLLA) and syndiotactic poly(methyl methacrylate) (sPMMA). There is a strong complexing capacity only between low molecular weight PLLA and sPMMA, in miscible state, at specific weight fractions (70:30). The complexing capacity is more significant when the mixtures are melt-crystallized at Tc = 110 °C or lower, and the intensity of this complex can be further enhanced if it is annealed between 100 and 160 °C, below its Tm = 175 °C. The new complex crystal can be formed only between PLLA and sPMMA, but not with isotactic or atactic PMMA.

Macrovoids in solution-cast membranes: Direct probing of systems exhibiting horizontal macrovoid growth

Abstract Macrovoids are defects that are frequently encountered in phase inversion as well as in other solution-cast membranes. Macrovoid formation continues to hold many surprises despite several decades of pertinent studies and frequent claims for definitive answers. We have discovered conditions leading to macrovoid growth parallel to a transparent membrane skin (horizontal macrovoids, HMVs); the benefits from the macrovoid-study point of view are slow growth, easy observation and possibility of designing modes of interference that facilitate the understanding of the parameters that affect the initiation and growth (including orientation) of macrovoids. Our study emphasizes the case of dopes consisting of atactic PMMA dissolved in acetone and solidified in a hexane non-solvent bath but dopes of other polymers also exhibit the same features. While a host of parameters affect the occurrence of HMVs we find that they are ultimately a possible response to the mechanical force field that evolves during progressing solidification of the concentrated polymeric solution; as a result HMVs can occur, under appropriate conditions, regardless if there is phase separation (which leads ultimately to a macroporous bulk membrane microstructure) or not.

Miscibility of mixed stereoregular PMMA/PVCN monolayers at the air/water interface

AbstractThe mixed monolayer behavior of stereoregular poly(methyl methacrylate) (PMMA) and poly(vinyl cinnamate) (PVCN) was investigated from the measurements of surface pressure–area per molecule (π–A) isotherms at three different temperatures of 25 ± 1, 32.5 ± 1, and 40 ± 1°C. The miscibility and nonideality of the mixed monolayers were examined by calculating the excess area as a function of composition. Positive and negative deviations from ideality were observed. Negative deviations were observed mostly in syndiotactic PMMA (sPMMA) and PVCN blends suggesting the existence of favorable interactions. However, positive deviations in most isotactic PMMA (iPMMA) and PVCN blends indicated that the existence of unfavorable interactions. Atactic PMMA and PVCN blends demonstrated intermediate deviation behavior to sPMMA and iPMMA blends. On the basis of the results of π–A isotherms, the monolayer miscibility between PMMA and PVCN was in the majority not in agreement with the studies on the same blends in the bulk state. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Anionic polymerization of MMA and renewable methylene butyrolactones by resorbable potassium salts

AbstractThree resorbable potassium salts of hydride (K[H]), enolate Me2CC(OiPr)OK (K[E]), and allyl K[1,3‐(SiMe3)2C3H3] (K[A]) have been investigated for controlled anionic polymerization of methyl methacrylate (MMA) and its cyclic analogs, naturally renewable methylene butyrolactones including α‐methylene‐γ‐butyrolactone (MBL) and γ‐methyl‐α‐methylene‐γ‐butyrolactone (MMBL). When used alone at ambient temperature in toluene, these salts exhibit no (K[H]) to low (K[A]) to modest (K[E]) polymerization activity. Mixing of K[H] and Al(C6F5)3 leads to the formation of an “ate” complex, K+[HAl(C6F5)3]−, which has been structurally characterized by X‐ray diffraction; this complex has a high polymerization activity producing atactic PMMA, but addition of another equiv of Al(C6F5)3 further enhances both the rate and the efficiency of the polymerization, now producing syndiotactic PMMA with a narrow molecular weight (MW) distribution of 1.04. The K[H]/2Al(C6F5)3 system also exhibits high activity for polymerization of (M)MBL. In sharp contrast, addition of Al(C6F5)3 to K[A] shuts down the polymerization at various temperatures. The most active, controlled, and syndioselective polymerization system in this series is K[E]/2Al(C6F5)3. Accordingly, the polymerization control and kinetics of this most effective system have been examined in more detail. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Atomistic simulations of isotactic and atactic poly(methyl methacrylate) melts: exploring the backbone conformational space

Molecular dynamics simulations were performed separately on an isotactic poly(methyl methacrylate) (PMMA) melt and on an atactic PMMA melt. These simulations allow for a detailed atomistic exploration of the conformational space about the polymers' backbone at a temperature above the glass transition for both polymers, which is experimentally difficult to accomplish. In agreement with previous experimental and theoretical studies, we found the trans–trans backbone conformation to be the most energetically stable, followed by the trans–gauche conformations. Unique in this study is the ability to attribute how the underlying meso and racemic diad pairs contribute to the overall backbone population. Additional simulations were performed on methyl methacrylate, the compound that forms PMMA through radical reactions. These latter simulations help to validate our recently created force field for use in condensed-phase simulations.

Impact of low-molecular mass components (oligomers) on the glass transition in thin films of poly(methyl methacrylate)

Commercial polydisperse atactic poly(methyl methacrylate) (PMMA) exhibits a decreased glass transition temperature (Tg) when the film thickness is less than ∼60 nm, whereas more model atactic PMMA shows an increased Tg in thin films supported on clean silicon wafers. NMR indicates no difference in tacticity, so the divergent thin film behavior appears related to the relative distribution of molecular mass. Extraction of some low molecular weight PMMA components from the commercial sample results in a significant modification of the thin film Tg compared with the initial PMMA fraction. The extracted sample exhibits initially a slight decrease in Tg as the film thickness is reduced below ∼60 nm, but then Tg appears to increase for films thinner than 20 nm. These results illustrate the sensitivity of polymer thin film properties to low-molecular mass components and could explain some of the contradictory reports on the Tg of polymer thin films that exist in the literature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Miscibility induced by confinement in mixed monolayer films

Both poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) are known to be immiscible with poly(styrene). PMMA is found to be miscible with poly(ethylene oxide). Therefore, PMMA is predicted by the mean field theory to be immiscible with poly(styrene-b-ethylene oxide) (PS-b-PEO) in the bulk state. The miscibility of PMMA with PS-b-PEO may be different in the two-dimensional state. The mixed monolayer behavior of stereoregular (including isotactic, atactic and syndiotactic) PMMA and PS-b-PEO was investigated in this article on the basis of the measurements of surface pressure–area per molecule ( π– A) isotherms at three different temperatures. The miscibility and nonideality of the mixed monolayers were examined by calculating the excess area as a function of composition. Mostly negative deviations from ideality were observed in the mixed monolayers at 25 °C and 32.5 °C. This is likely because of favorable interaction between PMMA and PEO. However, positive deviations occurred at 32.5 °C and 40 °C with atactic PMMA (or syndiotactic PMMA) mixed monolayers. With confinement in the two-dimensional state, the miscibility between PMMA and PS-b-PEO was greatly improved in comparison with the bulk state.

Cluster SIMS depth profiling of stereo‐specific PMMA thin films on Si

AbstractCluster SIMS, employing an SF5+ polyatomic primary ion sputter source, in conjunction with a Bi3+ analysis source, was utilized to depth profile through poly(methylmethacrylate) (PMMA) thin films (approximately 140 nm) of variable tacticity. The damage characteristics of the stereospecific PMMA films under SF5+ bombardment were measured as a function of temperature in the range of − 75 °C–150 °C. On average, the isotactic PMMA exhibited the least amount of damage accumulation as compared to syndiotactic and atactic PMMA, with increased signal constancy as a function of SF5+ dose and sharper PMMA/Si interface widths in the temperature range of 0 °C–80 °C. These improvements in sputter properties were attributed to steric hindrances along the side‐chain moieties in isotactic PMMA, causing increased strain along the main‐chain backbone, and consequently increasing the likelihood of main‐chain scission. Similar to previous studies, − 75 °C yielded the most ideal depth profiles for all tacticities, exhibiting the least amount of damage accumulation in the form of characteristic signal loss and interfacial broadening. There were also significant improvements in the damage characteristics at higher temperatures as compared to 25 °C. However, other interfacial artifacts started to appear at or near the glass transition temperature (Tg) of the various polymers, indicative of increased interfacial damage at these higher temperatures. Published in 2010 by John Wiley &amp; Sons, Ltd.

Coordination polymerization of renewable butyrolactone-based vinyl monomers by lanthanide and early metal catalysts

This contribution reports the first study of coordination-addition polymerization of renewable butyrolactone-based vinyl monomers, MBL (alpha-methylene-gamma-butyrolactone) and MMBL (gamma-methyl-alpha-methylene-gamma-butyrolactone), using neutral lanthanocene(II), non-lanthanocene(III), and cationic group 4 metallocene catalysts. The samarocene(II) catalyst, Cp*(2)Sm(THF)(2), promotes a rapid, efficient, and controlled polymerization of MBL and MMBL in DMF at ambient temperature, exhibiting a high TOF of 3000 h(-1), typically near quantitative initiator efficiency, and the ability to control the polymer MW. The resulting atactic PMBL and PMMBL have high T(g)'s of 194 degrees C and 227 degrees C, respectively; when compared to atactic PMMA having comparable MW, the T(g) and onset decomposition temperatures of the PMMBL produced are substantially higher (by approximately 120 degrees C and 40 degrees C, respectively). Owing to the living/controlled characteristics of this polymerization, well-defined random and block copolymers of MBL with MMA and MMBL can be readily synthesized. Results of the kinetic and polymerization studies indicate that the true active species is the trivalent samarocene centers attached to the single growing polymer chain, derived presumably from a redox-then-radical-coupling process. In comparison, the polymerizations by non-lanthanocene(III) silylamides, Ln[N(SiMe(3))(2)](3) (Ln = La, Nd, Sm, Er), and by cationic group 4 metallocene and half-metallocene catalysts incorporating C(2) and C(s) symmetric ligands are much slower and less effective. Catalytic polymerization of MBL by Cp*(2)Sm(THF)(2) has also been realized in the presence of an enolizable organo acid as a suitable chain transfer agent.

Chain-length and tacticity effects on the conformational behavior of MMA-oligomer thin films on an Au (111) substrate

Abstract Chain-length and tacticity effects on the conformational behavior, including density distributions and conformations, of MMA-oligomer thin films deposited on an Au (1 1 1) substrate at room temperature were investigated using molecular dynamics (MD) simulations. Three kinds of MMA-oligomer thin film with the oligomers containing m repeat units with m = 5, 10, and 20, respectively, were selected to examine the chain-length effects. Three types of MMA-oligomer thin film (made of isotactic, syndiotactic, and atactic PMMA isomers, respectively) were utilized to inspect the tacticity effects. For ease of investigation, the thin film was divided into three regions (the contact, the bulk, and the surface regions) according to the through-thickness distribution of density of the thin film. For short-chain thin films (with m = 5 and 10), the density distribution had a remarkable peak in the contact region of the thin film. The density peak, however, was not evident for the long-chain thin film (with m = 20). Regarding tacticity, the isotactic thin films had a prominent peak density in the contact region as compared with the syndiotactic and atactic thin films. Moreover, the MMA oligomers were found to exhibit a flattened conformation parallel to the Au substrate in the contact region and a slightly flattened conformation in the surface region for both the short-chain and the long-chain thin films. The flattened conformation remained in the bulk region of the long-chain thin film. However, it was not present in the bulk region of the short-chain thin film, which had a randomly orientated conformation–a characteristic similar to bulk MMA. It was also observed that the tacticity of the MMA-oligomer thin films did not have obvious effects on the conformations of the thin films for both the short-chain and the long-chain cases.

A Polymer Platform Composed of Structurally Well-defined Stereocomplex Structures for Efficient Enzymatic Reactions

Previously we reported that p-galactosidase immobilized on the structurally well-defined poly(methyl methacrylate) (PMMA) stereocomplex films fabricated by layer-by-layer (LbL) assembly of isotactic (it) and syndiotactic (st) PMMAs on solid substrates were highly active when compared to the enzyme immobilized on the single-component films, and that a slight difference of polymer surface structures strongly affects activities of immobilized enzymes, even though polymers have the same chemical component (Chem. Mater., 19, 2174-2179 (2007)). In this paper, we demonstrated activities of other enzymes immobilized on the PMMA films. Activities of immobilized alkaline phosphatase (ALP) were measured by following hydrolysis rate of fluorescence substrate 4-methylumbelliferyl phosphate (4-MUP). Initial velocity of ALP hydrolysis reaction immobilized on the complex film was approximately 2-fold faster than those on the single-component it-PMMA and atactic (at) PMMA films. Michaelis-Menten analyses revealed that catalytic efficiency (kcat/Km) of ALP was strongly dependent on conformational regulation of PMMA chains at film surfaces. Quartz crystal microbalance (QCM) analyses revealed that immobilization amount of ALP on the complex was greater than those on the single-component films. Similar dependencies were also observed in the case of cellulases that degrade polymeric cellulose under acidic condition. Secondary structural analyses using an attenuated total reflection infrared (ATR-IR) spectroscopy revealed that structural denaturation of the enzyme after immobilization processes was well-suppressed on the complex film, although the enzymes on the single-component PMMA films were relatively denatured. We propose here that PMMA stereocomplex films are a generally convenient platform for immobilization of functional proteins and could be used under various conditions without loss of their activities.