Structure and properties of highly stereoregular isotactic poly(methyl methacrylate) and syndiotactic poly(methyl methacrylate) blends treated with supercritical CO2

The structure and properties of highly stereoregular isotactic poly(methyl methacrylate) (it-PMMA) and syndiotactic poly(methyl methacrylate) (st-PMMA) blends with crystalline stereocomplex formed by supercritical CO₂ treatment at temperatures ranging from 35 to 130 °C were investigated by means of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and dynamic mechanical analysis (DMA) measurements. The melting temperature, T_m, and the heat of fusion, ΔH_m, had maximum values at about 200 °C and 25 J/g, respectively. The degree of crystallinity evaluated by WAXD ranged in value from 32 to 38%. The fringed-micellar stereocomplex crystallites were formed in case of treatment temperatures below 90 °C, and the orderliness perpendicular to the helix axis of the fringed-micellar crystallites was considered to be increased with increasing treatment temperature. In case of treatment temperature of 130 °C, the fringed-micellar crystallites and the lamellar crystallites with high orderliness parallel to the helix axis coupled with the perpendicular orderliness were formed, and the respective double endothermic peaks, T_m¹ and T_m³, were observed in DSC due to the melting of the two kinds of stereocomplex crystallites. The it-PMMA/st-PMMA blends containing the fringed-micellar crystallites maintained high values of storage modulus, E′, up to higher temperature compared with the amorphous blends. The E′ of the blend treated with CO₂ at 130 °C decreased twice at temperatures corresponding to T_m¹ and T_m³.     

Tacticity dependence of reactivity of stereoregular poly(methyl methacrylate) macromonomers having a methacryloyl function in radical polymerization

Summary Radical polymerizations of highly isotactic (it-) and highly syndiotactic (st-) poly(methyl methacrylate) (PMMA) macromonomers having a methacryloyl function were studied in benzene-d ₆ at 60°C with 2,2′-azobisisobutyronitrile (AIBN). Rate of polymerization (R _p) was determined from the consumption of the macromonomer by means of ¹H NMR spectroscopy. The R _p of the it-PMMA macromonomer was larger than that of the st-PMMA macromonomer. Concentrations of propagating radicals, [M·] , were estimated for the polymerization with di-t-butyl peroxide in benzene under irradiation of light at 30°C. The value of [M · ] for the polymerization of the st-PMMA macromonomer was larger than that for the polymerization of the it-PMMA macromonomer. The results indicated that rate constant of propagation (k _p) for the it-PMMA macromonomer was larger than that for the st-PMMA macromonomer. Received: 14 May 2002 / Accepted: 3 June 2002     

Preparation of highly syndiotactic block copolymers of methyl methacrylate and lauryl methacrylate and their characterization

Summary Highly syndiotactic diblock and triblock copolymers comprising lauryl methacrylate (LMA) and methyl methacrylate (MMA) with narrow molecular weight distributions were prepared by the living anionic polymerization with t-C₄H₉Li/(C₂H₅)₃Al in toluene at low temperature. The block copolymers were soluble in acetone which is a non-solvent for poly(lauryl methacrylate) (PLMA). ¹HNMR and vapor pressure osmometric analyses of the block copolymers indicated the aggregation of the copolymer in acetone through the interaction between PLMA blocks. Stereocomplex formation between the triblock copolymer and isotactic poly(methyl methacrylate) (PMMA) took place more effectively in solution than in the solid state.     

On-line GPC/NMR experiments using the isotactic poly(methyl methacrylate) with well-defined chemical structure

Summary Gel permeation chromatography of. isotactic PMMA has been performed on a Chromatograph linked to a 500 MHz ¹H NMR spectrometer. ¹H NMR spectra of good resolution and high S/N ratio were collected over the entire Chromatographic peak. The Mn of the polymer sample can be directly determined by intensity measurements of the proton signals due to the endgroup and monomeric units, since the polymers used were prepared by the living polymerization initiated by t-C₄H₉MgBr. A good linear relation was obtained between the log(Mn) and elution time.     

FTIR microspectroscopy and DSC analysis of blends of poly(vinylidene fluoride) with isotactic and syndiotactic poly(methyl methacrylate)

Films of blends of poly(vinylidene fluoride) (PVDF) with isotactic and syndiotactic poly(methyl methacrylate) (i-PMMA and s-PMMA), obtained by casting tetrahydrofuran (THF) and dimethyl sulphoxide (DMSO) solutions onto BaF₂ windows, have been investigated by means of FTIR-microspectroscopy (FTIR-M), optical microscopy and differential scanning calorimetry (DSC). The study of the effect of the PMMA tacticity on the intermolecular interaction between the two components, as well as on the structure, morphology and thermal behaviour of these blends, is the object of this paper. On the basis of the major shift of the carbonyl band of i-PMMA in the mixtures, the occurrence of stronger interactions for PVDF/i-PMMA compared with PVDF/s-PMMA blends can be suggested. © 1998 SCI.     

Stereocomplex formation in polybutadiene-syndiotactic poly(methyl methacrylate) block copolymers blended with isotactic poly(methyl methacrylate)

Summary The process of stereocomplexation in blends of isotactic poly(methyl methacrylate)s and polybutadiene-syndiotactic poly(methyl methacrylate) diblock copolymers was studied by differential scanning calorimetry as a function of molar mass of the constituents, annealing time and temperature. The amount of complex formed is dependent on these three parameters, while the temperature of decomposition of the complex is only dependent on the annealing temperature. Complex formation can be observed in blends containing a copolymer with a very low molar mass syndiotactic poly(methyl methacrylate) block (Mn=700). In contrast to homopolymer blends, for which two endotherms of decomposition were generally reported, only one endotherm is observed for copolymer-homopolymer blends. This behavior is attributed to the elastomer block.     

NMR-study of structure and dynamics of associates of syndiotactic poly(methyl methacrylate) in toluene

Summary High-resolution ¹H NMR spectra (¹H HR-NMR) of solutions of isotactic (i) and syndiotactic (s) poly(methyl methacrylate) (PMMA) in toluene-d₈ were measured in the concentration range 0.2 to 10% w/v; for solutions of s-PMMA (10% w/v), ¹H NMR spectra with magic angle rotation (MAR-NMR) at various temperatures and ¹³C NMR spectra with strong proton decoupling were also measured. It was found that even in very dilute solutions of s-PMMA in toluene-d₈ a considerable portion (76%) of polymer segments are associated: association is of intramolecular origin and is due to interaction of long syndiotactic sequences. Prom NMR spectra the motion of associated segments appears as isotropic with and effective correlation frequency 10⁶ – 10⁷ Hz. A globular structure of the associates of s-PMMA is proposed.     

Modified frontal polymerization of poly(methyl methacrylate)

In this work, we propose a modified frontal polymerization method to build a uniform reaction front by gradually immersing the reacting mixture in a thermal bath. This scheme allows uniform materials to be obtained with nearly constant molecular weights and polydispersities and a low residual monomer concentration. A comparative study of the molecular weight distributions of poly(methyl methacrylate)s obtained by bulk polymerization, frontal polymerization, and frontal polymerization with the proposed gradual immersion is presented. Samples obtained by these methods show that materials obtained by bulk polymerization and by frontal polymerization are less uniform than those obtained by frontal polymerization with gradual immersion in a thermal bath. The obtained uniformity is directly related to a stabilizing effect of the reaction front by the gradual immersion of the reactor in a constant‐temperature bath and to a reduction in the reaction rate promoted by a moderate transfer agent concentration. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of graft copolymers of methyl methacrylate and poly(n-hexyl isocyanate) macromonomers

Living poly(n-hexyl isocyanate) (PHIC) was deactivated with methacryloyl chloride to produce methacryl-terminated poly(n-hexyl isocyanate) (PHIC-MA) rodlike macromonomers. Radical copolymerization of methyl methacrylate (MMA) with PHIC-MA was performed using 2,2′-azobis(isobutyronitrile) as an initiator in benzene at 60 °C to prepare poly(methyl methacrylate)-graft-poly(n-hexyl isocyanate) (PMMA-graft-PHIC) graft copolymers. The monomer reactivity ratios of MMA (M₁) and PHIC-MA (M₂) were evaluated as r₁=11.5 and r₂=∼0, exhibiting remarkably lower reactivity of PHIC-MA macromonomer than that of common macromonomers. The resultant graft copolymers were characterized using gel permeation chromatography equipped with low-angle laser light-scattering to determine the molecular weights, and equipped with a refractive index detector and an ultraviolet light detector to estimate a PHIC weight fraction of PMMA-graft-PHIC at the ith elution volume of the GPC chromatogram. There are 2-3 PHIC grafts per PMMA molecule, and the PHIC rodlike chains might be difficult to introduce into the PMMA main chains having higher molecular weights. A specific dimension of PMMA-graft-PHIC in solution was discussed in detail.     

悬浮聚合法制取不同分子量级别的聚甲基丙烯酸甲酯

采用粉状MgCO3 作为分散剂 ,悬浮聚合制取了分子量从 2 4× 10 4 ～ 2 5 4× 10 4 的聚甲基丙烯酸甲酯。考察了温度、引发剂种类和浓度、分子量调节剂、转化率对聚合物分子量的影响规律 ,用粘度法测量了聚合物聚甲基丙烯酸甲酯 (PMMA)的分子量。结果表明 :温度的升高、引发剂浓度的增大、分子量调节剂的加入都会导致分子量的减小 ,随着转化率的提高 ,聚合物的分子量增大。在同等条件下 ,引发剂过氧化苯甲酰 (BPO)聚合所得的分子量较偶氮二异丁腈 (AIBN)高。通过实验 ,得到了满足作者需求的分子量 (96× 10 4 ～ 10 0× 10 4 )的聚合物的聚合条件为 :分散剂MgCO3 用量 1% ,单体∶水相 =1∶2 5 (质量比 ) ,引发剂BPO浓度 0 5 % ,反应温度 70℃ ,反应时间 3h。     

Rate constants during the hydrolysis of syndiotactic poly(methyl methacrylate) with base

A procedure is presented for the determination of rate constants for the reaction of triads during the reaction on polymers and the method applied to the base hydrolysis of syndiotactic methyl methacrylate/methacrylic acid copolymers.     

Relative rate constants during the acidic hydrolysis of syndiotactic poly(methyl methacrylate)

The relative rates during acidic hydrolysis of triads of monomer units in syndiotactic methyl methacrylate/methacrylic acid copolymers in aqueous solution at different degrees of neutralization have been studied by proton n.m.r. Relative rate constants were determined by application of a graphical method to experimental and computer simulated relative rates of triads.     

Sorption of water vapour by atactic and isotactic poly (methyl methacrylate)

For the purpose of studying the relation between the stereoregularity and the sorption properties of atactic (a-PMMA) and isotactic (i-PMMA) poly(methyl methacrylate) samples, the isotherms for the sorption of water vapour by these polymers were determined. The glass transition temperatures, T_g and the densities of both PMMA samples were also measured under different conditions of moisture content. The amount of water vapour sorbed by i-PMMA was found, in this study, to be greater than that by a-PMMA. This is rather peculiar when we consider that the former has a high crystallinity (76%) and the latter is non-crystalline in nature. It was concluded that water vapour is sorbed by a-PMMA by a mechanism whereby the water molecules sorbed, fill pre-existing sites (polar groups) and spaces occupied by microvoids or free volumes in the polymer without causing any swelling in the latter; and that the extra sorption of water vapour by i-PMMA was due to a mechanism by which the water molecules sorbed cause the polymer to swell, and thus increase its sorption capacity.     

Preparation and characterization of poly(methyl methacrylate) beads

The phase behavior of Poly(ethylene terephthalate)/Poly(ethylene‐2,6‐naphthalate)/Poly(ethylene terephthalate‐co‐ethylene‐2,6‐naphthalate) (PET/PEN/P(ET‐co‐EN)) ternary blends in molten state was evaluated from differential scanning calorimetry (DSC) and NMR results as well as optical microscopic observations. Copolymer of ethylene terephthalate and ethylene‐2,6‐naphthalate was prepared by a condensation polymerization, which was a random copolymer with an intrinsic viscosity (IV) of 0.3 dL/g. The phase diagram of the ternary blends revealed that the miscibility of ternary blends in molten state was dependent on the fraction of P(ET‐co‐EN) in the blends and holding time of the blends at high temperatures above 280°C. With increase in the holding time, the fraction of copolymer in the blends necessary to induce the immiscible to miscible transition decreased. For the blends with longer holding time at 280°C, the phase diagram in molten state was irreversible against the temperature, although a reversibility was found for the blends with short holding time of 1 min at 280°C. The irreversibility of phase behavior was not explained simply by the increase of copolymer content produced during heat treatment. Complex irreversible physical and chemical interactions between components and change of phase structure of the blend in the molten state might influence on the irreversibility. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of polyaniline coated poly(methyl methacrylate) microsphere by graft polymerization and its electrorheology

Monodisperse acrylic microspheres (diameter 9.2 μm) (An-PGMA) with aniline moieties on the surface were initially prepared by a seeded emulsion method, and then composite particles (PA-PGMA) possessing polyaniline (PANI) shell were prepared via an in situ polymerization of aniline using An-PGMA particles as a core material inducing grafting polymerization of aniline. The PANI layer was found to be formed on the An-PGMA surface from the microscopic image, ¹³C FT-NMR and TGA of the PA-PGMA particles. Suspension of the PA-PGMA particle dispersed in silicone oil showed typical electrorheological (ER) characteristics under external electric fields.     

Relative rate constants during the hydrolysis of syndiotactic poly(methyl methacrylate) with base

The relative rates of appearance and disappearance of triads of monomer units during the hydrolysis of syndiotactic methyl methacrylate/methacrylic acid copolymers in aqueous solution with excess base are studied by proton n.m.r. The relative rate constants are determined from these data using a graphical method. The measured relative rates and rate constants are consistent with a mechanism wherein COO^? retards the attack of OH^?. There is, however, a mechanism change indicated on consumption of OH^? during hydrolysis. The COOH which are then formed apparently participate in an intramolecular mechanism. The change of mechanism is accompanied by a change in copolymer statistics, i.e. from alternation tendency to block character. The lack of temperature dependence of the relative rate constants during the hydrolysis with OH^? as the active species leads to the conclusion that enthalpies of activation are equal for the three reacting triads. Thus the differences found between the relative rate constants are entropic in origin.     

Synthesis and structure of the poly(methyl methacrylate) microlatex

Microemulsion polymerization is a new approach for preparing nanosize polymer materials. In this article, a nanosize poly(methyl methacrylate) (PMMA) was prepared by a novel microemulsion polymerization. The kinetics of the polymerization and the effects of the temperature, the monomer, and emulsifier/water ratio on the polymerization were investigated by means of the conversion, the transmittance, and the refractive index measurements. The structure of the obtained PMMA microlatex was studied through transmission electron microscopy (TEM), nuclear magnetic resonance (¹H‐NMR), and differential scanning calorimetry (DSC). The results show that the polymerization exhibits typical kinetic characteristics of a microemulsion polymerization, i.e., there only exists two rate stages: a stage of increasing rate, and a stage of decreasing rate, and no constant rate stage is observed during the polymerization. The obtained PMMA microparticles are very uniform, regular, and small, being about 17–33 nm in the number‐average diameter. The polymer has higher molecular weight (1.71 × 10⁶ viscosity average molecular weight), higher tacticity (51% syndiotacticity), and higher glass transition temperature (127°C), much different from the commercial PMMA. Experimentally, a stable and transparent PMMA microlatex with higher polymer content (30–40 wt %), lower weight ratio of emulsifier to water (E/W ≤ 0.03) and emulsifier to monomer (E/M ≤ 0.05) as well as smaller particle size (d_p < 40 nm), has been prepared, which is very important for the industrialization of the microemulsion polymerization technique. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2839–2844, 2002     

Emulsion polymerization of methyl methacrylate using poly(methyl methacrylate-co-2-hydroxypropyl methacrylate)-graft-polyoxyethylene as the stabilizer

This study involved the use of an amphipathic graft copolymer, poly(methyl methacrylate-co-2-hydroxypropyl methacrylate)–graft–polyoxyethylene, as a stabilizer in the emulsion polymerization of methyl methacrylate. The stabilizing effectiveness of this graft copolymer was studied as a function of its chemical structure. It was found that the stabilizing effectiveness of the graft copolymer was independent of the molecular weight of the backbone within the investigated range of 4 × 10³ g/mol to 2 × 10⁴ g/mol. In all cases, stable emulsion polymerizations of methyl methacrylate were observed. Effective stabilization also occurred when the graft moieties possessed a molecular weight of either 2 × 10³ g/mol or 5 × 10³ g/mol. However, the stabilizing effectiveness was found to be dependent on the amount of polyoxyethylene (POE) contained in the graft copolymer. In this case, graft copolymers possessing 67% by weight POE were poor stabilizers, but ones with 85% POE were very good stabilizers. Moreover, the graft copolymers were found to be superior stabilizers as compared to POE homopolymers.     

Constrained shrinkage of highly oriented poly(methyl methacrylate) fibers

Constrained shrinkage of fibers is the primary method used to examine orientation in amorphous materials. During the test, fibers are constrained, heated, and the stress that develops is measured as a function of time and temperature. This article describes an apparatus developed to measure that stress and a series of experiments for melt‐spun poly(methyl methacrylate) fibers fabricated under three conditions: (1) constant viscosity, (2) increasing temperature, and (3) increasing draw velocity. Results show that both the rates of rise and the decay of the fiber shrinkage stress have an Arrhenius relationship with temperature. Fibers fabricated at a constant viscosity have the same maximum shrinkage stress and rate of stress decay. As the processing temperature decreases or as draw velocity increases, for other parameters held constant, the maximum shrinkage stress increases. The rate of stress rise increases with decreasing processing temperature or increasing draw velocity. Maximum shrinkage stress also increases with increasing molecular orientation when measured by a different test, free heat‐induced shrinkage of the fibers. However, it was not possible to correlate both of these results to rubber elasticity theory attributed to the high degree of orientation present in the fibers and high polydispersity in the starting material. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4047–4056, 2004