Nanosphere and nanonetwork formations of [60]fullerene-end-capped stereoregular poly(methyl methacrylate)s through stereocomplex formation combined with self-assembly of the fullerenes

We report a novel and versatile method for constructing a supramolecular nanosphere and nanonetwork based on isotactic and syndiotactic C60-end-capped poly(methyl methacrylate)s (it- and st-PMMA-C60's) through their stereocomplex formation combined with self-assembly of the terminal C60. The stereoregular PMMA-C60's with a precisely controlled structure including molecular weight, its distribution, tacticity, and the chain-end structure were synthesized by the stereospecific anionic living polymerizations of methyl methacrylate followed by end-capping with C60, and their structures were proven by size exclusion chromatography, NMR, UV-vis, and MALDI-TOF-MS analyses. The stereoregular PMMA-C60's self-assembled to form a core-shell aggregate with C60 as the core and the PMMA chains as the shell in H2O/CH3CN (1/9, v/v) due to the solvophobic interaction of the C60 units. These it- and st-PMMA-C60 aggregates further supramolecularly assembled through iterative stereocomplex formation into nanonetworks in which the self-assembled C60 clusters were robustly connected with two- and three-dimensional arrangements. In addition, when the it- and st-PMMA-C60's were simultaneously mixed, self-assembly of the C60 units and stereocomplex formation of the it- and st-PMMA chains took place at once, resulting in the formation of uniformly sized spherical nanoparticles with resistance to heat. Similar nanonetwork architectures can be produced using it-PMMA-C60 clusters and st-PMMA prepolymers as the binder.     

Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). V. Kinetics of initial template polymerization

The influence of stereoregular poly(methyl methacrylate) (PMMA) as a polymer matrix on the initial rate of radical polymerization of methyl methacrylate (MMA) has been measured between ?11 and +60°C using a dilatometric technique. Under proper conditions an increase in the relative initial rate of template polymerization with respect to a blank polymerization was observed. Viscometric studies showed that the observed effect could be related to the extent of complex formation between the polymer matrix and the growing chain radical. The initial rate was dependent on tacticity and molecular weight of the matrix polymer, solvent type and polymerization temperature. The accelerating effect was most pronounced (a fivefold increase in rate) at the lowest polymerization temperature with the highest molecular weight isotactic PMMA as a matrix in a solvent like dimethylformamide (DMF), which is known to be a good medium for complex formation between isotactic and syndiotactic PMMA. The acceleration of the polymerization below 25°C appeared to be accompanied by a large decrease in the overall energy and entropy of activation. It is suggested that the observed template effects are mainly due to the stereoselection in the propagation step (lower activation entropy Δ S_p^?) and the hindrance of segmental diffusion in the termination step (higher activation energy Δ E_t^?) of complexed growing chain radicals.     

The effect of molecular properties on the mechanical behaviour of PMMA—IV. The role of chain entanglements in fracture processes

The fracture-toughness—entanglement correlation was shown to be a more fundamental concept than the fracture-toughness—glass transition temperature or the fracture-toughness—solubility-parameter correlations in predicting the effect of molecular weight, molecular weight distribution, stereoregularity and temperature on the fracture behaviour of poly(methyl methacrylate) (PMMA). Morphological study of the fracture surface by scanning electron microscopy (SEM) of high molecular weight PMMA in good and bad solvents and blends of isotactic PMMA and low molecular weight atactic PMMA supports the relationship between molecular entanglements and fracture behaviour. The entanglement network at the crack tip determines whether failure occurs in solvents by rapid stress-cracking or stress-crazing with long-craze growth.     

Effect of Tacticity of Poly(Methyl Methacrylate) on Conductivity of Poly(Ethylene Oxide)-Poly(Methyl Methacrylate) Blend-Based Polymeric Electrolytest

Abstract

Polymer electrolytes based on blends of poly(ethylene oxide) (PEO) with various stereoisomers of poly(methyl methacrylate) (PMMA) were studied by means of impedance spectroscopy and DSC. It was found that isotactic poly(methyl methacrylate) (1PMMA)-based electrolytes exhibit ambient temperature conductivities at least one order of magnitude higher than the electrolytes containing other stereoisomers of PMMA. The highest value of room temperature conductivity equal to 9 × 10^?5 S/cm was measured for a sample containing 30 wt% IPMMA. The effect observed results from the presence of a flexible amorphous phase in PEO-IPMMA blends which is favorable for fast ionic transport. A small increase of ionic conductivity with decreasing molecular weight of the added atactic poly(methyl methacrylate) was also observed.     

Rare‐earth‐metal‐initiated polymerizations of (meth)acrylates and block copolymerizations of olefins with polar monomers

The organo‐rare‐earth‐metal‐initiated living polymerization of methyl methacrylate (MMA) was first discovered in 1992 with (C₅Me₅)₂LnR (where R is H or Me and Ln is Sm, Yb, Y, or La) as an initiator. These polymerizations provided highly syndiotactic (>96%) poly(methyl methacrylate) (PMMA) with a high number‐average molecular weight (M_n > 1000 × 10³) and a very narrow molecular weight distribution [weight‐average molecular weight/number‐average molecular weight (M_w/M_n) < 1.04] quantitatively in a short period. Bridged rare‐earth‐metallocene derivatives were used to perform the block copolymerization of ethylene or 1‐hexene with MMA, methyl acrylate, cyclic carbonate, or ?‐caprolactone in a voluntary ratio. Highly isotactic (97%), monodisperse, high molecular weight (M_n > 500 × 10³, M_w/M_n < 1.1) PMMA was first obtained in 1998 with [(Me₃Si)₃C]₂Yb. Stereocomplexes prepared by the mixing of the resulting syndiotactic and isotactic PMMA revealed improved physical properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 1955–1959, 2001     

Synthesis of core/shell structure of glycidyl–functionalized poly(methyl methacrylate) latex nanoparticles via differential microemulsion polymerization

The differential microemulsion polymerization technique was used to synthesize the nanoparticles of glycidyl-functionalized poly(methyl methacrylate) or PMMA via a two-step process, by which the amount of sodium dodecyl sulfate (SDS) surfactant required was 1/217 of the monomer amount by weight and the surfactant/water ratio could be as low as 1/600. These surfactant levels are extremely low in comparison with those used in a conventional microemulsion polymerization system. The glycidyl-functionalized PMMA nanoparticles are composed of nanosized cores of high molecular weight PMMA and nano-thin shells of the random copolymer poly[(methyl methacrylate)-ran-(glycidyl methacrylate)]. The particle sizes were about 50 nm. The ratios of the glycidyl methacrylate in the glycidyl-functionalized PMMA were achieved at about 5–26 wt.%, depending on the reaction conditions. The molecular weight of glycidyl-functionalized PMMA was in the range of about 1 × 10⁶ to 3 × 10⁶ g mol⁻¹. The solid content of glycidyl-functionalized PMMA increased when the amount of added glycidyl methacrylate was increased. The glycidyl-functionalized polymer on the surface of nano-seed PMMA nanoparticles was a random copolymer which was confirmed by ¹H-NMR spectroscopy. The amounts of functionalization were investigated by the titration of the glycidyl functional group. The structure of the glycidyl-functionalized PMMA nanoparticles was investigated by means of TEM. The glycidyl-functionalized PMMA has two regions of T_g which are at around 90 °C and 125 °C, respectively, of which the first one was attributed to the poly[(methyl methacrylate)-ran-(glycidyl methacrylate)] and the second one was due to the PMMA. A core/shell structure of the glycidyl-functionalized PMMA latex nanoparticles was observed.     

RAFT Polymerization: Adding to the Picture

SUMMARY: Factors affecting the choice of RAFT agent [RSC(Z) = S] for a given polymerization are discussed. For polymerization of methyl methacrylate (MMA), tertiary cyanoalkyl trithiocarbonates provide very good control over molecular weight and distribution and polymerizations show little retardation. The secondary trithiocarbonate RAFT agents with R = CHPh(CN) also gives good control but an inhibition period attributed to slow reinitiation is manifest. Radical induced reduction with hypophosphite salts provides a clean and convenient process for removal of thiocarbonylthio end groups of RAFT-synthesized polymers. Two methods providing simultaneous control over stereochemistry and molecular weight distribution of chains formed by radical polymerization are reported. Polymerization of MMA in the presence of scandium triflate provides a more isotactic PMMA. A similar RAFT polymerization with trithiocarbonate RAFT agents also provides control and avoids issues of RAFT agent instability seen with dithiobenzoate RAFT agents in the presence of Lewis acids. RAFT polymerization of tetramethylammonium methacrylate at 45 °C provides a more syndiotactic PMMA of controlled molecular weight and distribution (after methylation; mm:mr:rr 2:21:77 compared to 3:35:62 when formed by bulk polymerization of MMA).     

Relationship between structure and dielectric behavior of stereoregular poly(methyl methacrylate) in the glassy state

In order to elucidate the relationship between dielectric behavior and structure in solid polymers, we studied the dielectric relaxation of stereoregular poly(methyl methacrylate) (PMMA) in the glassy state. Assuming that the extremes of molecular structure are attained in the crystal and in solution, the most probable conformation of the main chain in the glassy state is estimated for isotactic and syndiotactic PMMA in terms of conformational analysis, the unperturbed mean-square end-to-end distance in solution, and the NMR second moment in the glassy state. Under the assumption that the molecular structure varies in a limited range near the most probable conformation and that the α-methyl group rotates freely, the energy barrier for the rotation of the side group is calculated. With the calculated energy barrier, the dielectric relaxation due to the side group is interpreted fairly satisfactorily by the barrier theory of Hoffman and Lauritzen, although the width of the relaxation curve is not. The experimental result that the loss peak of syndiotactic PMMA is located at higher temperature than that of isotactic PMMA is interpreted qualitatively in terms of different conformations for the syndiotactic and isotactic chains.     

Hindered lithium dialkylamide initiators for the living anionic polymerization of methacrylic esters

Lithium diisopropylamide is an efficient initiator for the anionic polymerization of methyl methacrylate in polar solvents at –78°C. Predictable molecular weights based on the initiator concentration were obtained, yields were quantitative, and molecular weight distributions were relatively narrow (<1.30). The presence of an amino end group and confirmation of the initiation mechanism were confirmed by potentiometric titration using HClO₄. Number-average molecular weights determined by titration agreed well with values determined by SEC. Other lithium dialkylamides that contain larger alkyl groups such as lithium diisobutylamide were less efficient initiators. This was attributed to the more nucleophilic anion due to less steric hindrance near the nitrogen atom. Molecular weight distributions were significantly broadened (>2.0), and molecular weight control was not achieved. However, polymer yields were quantitative. In all cases, PMMA stereochemistry was indicative of a solvent-separated lithium counterion, and triad compositions were identical to organolithium initiated homopolymers, i.e., 78% syndiotactic, 20% heterotactic, and 2% isotactic. © 1994 John Wiley & Sons, Inc.     

Inhibition by red phosphorus of unimolecular thermal chain-scission in poly(methyl methacrylate): Investigation by NMR,FT-IR and laser desorption/fourier transform mass spectroscopy

The reaction of red phosphorus with poly(methyl methacrylate) under pyrolysis conditions was investigated with a number of physical techniques. A random methyl methacrylate/cyclic anhydride copolymer is formed from atatic PMMA, whereas a random methyl methacrylate/methacrylic acid copolymer is obtained with isotactic PMMA. The backbones of both these copolymers are more stable toward depolymerization than that of PMMA. The flame-retardant activity of red phosphorus with PMMA may arise in part from stabilization of the polymer toward depolymerization via modification of the sidechains.     

聚甲基丙烯酸甲酯辐射裂解和消旋的空间立构效应

本文研究了三种不同空间立构聚甲基丙烯酸甲酯的辐射效应,提出裂解过程是一种裂解与重合的动态平衡过程。分子量降低和消旋作用对温度的依赖性,是由于分子运动和笼罩效应以及重合的空间位阻效应所致。辐照温度愈高,裂解产额愈大。相同条件下辐照,全同立构比无规立构试样的裂解产额更大。 全同立构聚甲基丙烯酸甲酯辐照后,不仅分子链断裂,而且空间立构也发生很大变化。随着辐照剂量的增加,全同立构含量逐渐减少,而无规立构含量和间同立构含量却逐渐增加。     

Stereoregular uniform polymers

Progress in stereospecific living polymerizations of methacrylate monomers and the concept and realization of “uniform polymers” and “uniform polymer architectures” are described, with particular emphasis on the fusion of polymer synthesis and characterization and their interactive stimulation, which are inevitable not only for the formation of polymers with highly controlled structures but also for the development of polymer characterization, thereby bringing about the spiral progress of both fields. First, three types of stereospecific living polymerizations are described, including formation of 100% isotactic poly(methyl methacrylate) (PMMA), 98% syndiotactic PMMA, and 96% heterotactic PMMA. Supercritical fluid chromatography (SFC) has proven useful for isolating uniform polymers from these stereoregular PMMAs with narrow molecular weight distributions. Living nature of these stereospecific polymerizations is further utilized for the synthesis of end‐functionalized stereoregular polymers, which are separated into uniform end‐functionalized polymers and used to construct more elaborated uniform polymer architectures such as stereoblock, star, and comb polymers. The uniform polymers have proven quite useful for the studies on the relationship between structures and properties such as glass transition temperature, melting temperature, and solution viscosity. In addition to this, stereoregular uniform polymers are particularly important to understand stereocomplex formation between isotactic and syndiotactic uniform PMMAs. On‐line GPC/NMR measurement at 750 MHz and −15°C in acetone/acetone‐d₆ allowed definitive determination of the compositions of the complexed species and noncomplexed species separately, but not in average. Also interesting is the stereocomplex formation of uniform stereoblock PMMA, where intramolecular complexation in addition to an intermolecular complexation was distinctively observed by GPC analysis in acetone. Uniform star and comb PMMAs were also prepared and found useful to discuss the effect of branching on the solution viscosity. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 245–260, 1999     

Postulation of the mechanism of the selective synthesis of isotactic poly(methyl methacrylate) catalysed by [Zr[(Cp)(Ind)CMe2](Me)(thf)](BPh4): a Hartree-Fock, MP2 and density functional study

The bridged. C1-symmetric, single-component zirconocene [Zr((Cp)(Ind)CMe2](Me)(thf)](BPh4) (Ind = indenyl, Cp = cyclopentadienyl) polymerises methyl methacrylate (MMA) selectively to isotactic poly(methyl methacrylate) (PMMA) without further cocatalysts or activators. To elucidate the stereoselective steps of the polymerisation of MMA by using this catalyst we studied the propagation steps occurring with the derivative [Zr[(Cp)(Ind)CH2][-O-C(OMe)=C(Me)(Et)](MMA)]+ by ab initio calculations at the Hartree-Fock(HF) level of theory. After the initiation step, which consumes the first two MMA molecules, each new catalytic cycle begins with the stereoselective addition of a new MMA molecule at the indenyl side of the zirconocene fragment. At the same time the enolate ring undergoes a stereoselective in-plane ring shift to the side opposite to the indenyl ring. These findings are used to postulate a mechanism for the polymerisation that explains the stereoselective synthesis of isotactic PMMA.     

Solid matrix polymerization and stereoisomeric complexes of poly(methyl methacrylate)

The polymerization of methyl methacrylate within solid matrices of stereoregular poly(methyl methacrylate) has been studied by proton NMR and wide angle X-ray diffraction. The semi-crystalline isotactic (i-) PMMA matrix was synthesized in the laboratory by anionic polymerization initiated by phenylmagnesium bromide, and the syndiotactic (s-) PMMA matrix was synthesized through a Ziegler–Natta reaction. Matrix polymerization of the monomer was initiated through the redox activation of benzoyl peroxide with N,N-dimethyl-p-toluidine. NMR measurements of triad distributions in matrix-polymerized chains suggest that the well-known stereospecific replica polymerization in PMMA (syndiotactic sequences promote isotactic sequences and vice versa) plays only a limited role in the systems studied. Experimental results indicate that chains grown within the i-PMMA or s-PMMA solid matrices have greater degrees of configurational disorder. The greater concentration of atactic triads in these chains could be the result of limited free volume or steric effects during polymerization in a highly condensed environment. X-ray diffraction studies of solution cast blends of isotactic PMMA and PMMA with conventional tacticity reveal some crystallinity with a structure characteristic of the stereocomplex formed by isotactic and syndiotactic PMMA from suitable solvents. Evidence was obtained for the presence of this complex in solidified mixtures of the i-PMMA solid matrix and liquid monomer. This observation is an example of special intermolecular structures that can form under conditions of in situ growth of chains within a pre-polymerized matrix.     

The Formation of Ordered Nanoholes in Binary,Chemically Similar,Symmetric Diblock Copolymer Blend Films

Summary: Binary symmetric diblock copolymer blends, that is, low‐molecular‐weight poly(styrene‐block‐methyl methacrylate) (PS‐b‐PMMA) and high‐molecular‐weight poly(styrene‐block‐methacrylate) (PS‐b‐PMA), self‐assemble on silicon substrates to form structures with highly ordered nanoholes in thin films. As a result of the chemically similar structure of the PMA and the PMMA block, the PMMA chain penetrates through the large PMA block that absorbs preferentially on the polar silicon substrate. This results in the formation of nanoholes in the PS continuous matrix.

An atomic force microscopy image of the thin film obtained from the blend of low‐molecular‐weight PS‐b‐PMMA and high‐molecular‐weight PS‐b‐PMA. The regular array of nanoholes in the films surface is clearly visible.     

Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). IV. Influence of solvent type

Methyl methacrylate (MMA) was polymerized by radical initiation at 25°C or 35°C in various solvents in the presence of stereoregular poly(methyl methacrylate) (PMMA). The occurrence of stereospecific replica polymerization appeared to be related to the capability of stereoassociation of isotactic and syndiotactic PMMA. The solvents can be roughly divided into three types. Type A solvents are polar solvents, which promote stereoassociation resulting in gelation and precipitation. Examples are dimethylformamide, dimethyl sulfoxide, and acetone. Type B solvents are nonpolar aromatic solvents like benzene and toluene, wherein stereoassociation is weaker but still leads to gelation. Type C solvents are very good solvents, in which stereoassociation does not occur. Chloroform and dichloromethane belong to this class. In solvents of type A as well as type B, polymerization in the presence of i-PMMA as a polymer matrix was syndiospecific. However, in the presence of s-PMMA as a polymer matrix the polymerization was isospecific only in type A solvents. The syndiotactic or isotactic triad contents of the polymer formed could be as high as ca. 90% at low conversions. In solvents of type C, polymerization in the presence of stereoregular PMMA proceeds according to a normal radical mechanism. Syndiotacticity was always less than 70%. Stereocomplexes formed in situ during replica polymerization were partly crystalline as detected by x-ray diffraction. The highest crystallinity was detected in those formed in type A solvents.     

Changes in post-source decay fragmentation behavior of poly(methyl methacrylate) polymers with increasing molecular weight studied by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

In order to investigate the systematic changes in fragmentation behavior of poly(methyl methacrylate) (PMMA) with increasing molecular weight, alkali-metal cationized PMMA 20-mer, 60-mer and 100-mer were selected for post-source decay (PSD) fragmentation study by matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry. PMMA polymers were cationized with lithium, potassium and cesium cations to explore the influence of the cation size on the fragmentation behavior of the polymers. All PMMA polymers could be fragmented by MALDI-PSD and fragmentation of the MALDI ionized synthetic polymer of molecular weight 10 kDa is reported here for the first time. It was shown that an increasing molecular weight of the PMMA chain required an increase in the size of the cation to improve the intensity and the number of the fragments in the PSD spectrum. Some instrumental parameters had to be optimized prior to a successful PSD analysis of the largest PMMA polymers.     

Composition and origin of trace elements in fog water studied by INAA

Characterization of dilute solution of gamma-irradiated polymethyl methacrylate (PMMA) in acetone has been carried out. The polymer sample in form of natural beads was administered a gamma-ray dose of 30 kGy by a cobalt-60 radiationsource. Various types of viscosities, viscosity average molecular weight, shape and size of irradiated PMMA and its two fractions were calculated. The results were compared with those for unirradiated PMMA. Degradation of PMMA as a result of irradiation has been observed.     

活性自由基聚合法制备以C60封端的聚苯乙烯

通过活性自由基聚合的方法制备了以２,２,６,６－四甲基－４－羟基呱啶氮氧自由基（ＴＥＭＰＯＬ）封端的聚苯乙烯大分子,实验结果证明该反应体系是一个典型的活性自由基聚合体系,同时研究了ＴＥＭＰＯＬ／ＡＩＢＮ的比例及ＡＩＢＮ的含量对聚合反应的影响。用以ＴＥＭＰＯＬ封端的聚苯乙烯和Ｃ６０反应,制得了Ｃ６０的聚苯乙烯高分子衍生物,紫外和ＧＰＣ结果均证明Ｃ６０已连接到聚苯乙烯的长链上,ＧＰＣ的结果还证明,Ｃ６     

Synthesis of high molecular weight poly(methyl methacrylate) microspheres by suspension polymerization in the presence of silver nanoparticles

To prepare high molecular weight (HMW) poly(methyl methacrylate) (PMMA)/silver microspheres, methyl methacrylate was suspension-polymerized in the presence of silver nanoparticles using a low-temperature initiator at different conditions. The rate of conversion was increased with increasing initiator concentration. In the case of adding silver nanoparticles, the rate of polymerization decreased slightly. High monomer conversion (about 95%) was obtained in spite of low polymerization temperature of 30 °C. Under controlled conditions, PMMA/silver microspheres with various viscosity-average degree of polymerization (6,000–37,000) were prepared.