Segmental and secondary dynamics in hydrogen‐bonded poly(4‐vinylphenol)/poly(methyl methacrylate) blends

Broadband dielectric spectroscopy was used to study the segmental (α) and secondary (β) relaxations in hydrogen‐bonded poly(4‐vinylphenol)/poly(methyl methacrylate) (PVPh/PMMA) blends with PVPh concentrations of 20–80% and at temperatures from ?30 to approximately glass‐transition temperature (T_g) + 80 °C. Miscible blends were obtained by solution casting from methyl ethyl ketone solution, as confirmed by single differential scanning calorimetry T_g and single segmental relaxation process for each blend. The β relaxation of PMMA maintains similar characteristics in blends with PVPh, compared with neat PMMA. Its relaxation time and activation energy are nearly the same in all blends. Furthermore, the dielectric relaxation strength of PMMA β process in the blends is proportional to the concentration of PMMA, suggesting that blending and intermolecular hydrogen bonding do not modify the local intramolecular motion. The α process, however, represents the segmental motions of both components and becomes slower with increasing PVPh concentration because of the higher T_g. This leads to well‐defined α and β relaxations in the blends above the corresponding T_g, which cannot be reliably resolved in neat PMMA without ambiguous curve deconvolution. The PMMA β process still follows an Arrhenius temperature dependence above T_g, but with an activation energy larger than that observed below T_g because of increased relaxation amplitude. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3405–3415, 2004     

Miscibility and phase structure of binary blends of polylactide and poly(methyl methacrylate)

Blends of amorphous poly(DL‐lactide) (DL‐PLA) and crystalline poly(L‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were prepared by both solution/precipitation and solution‐casting film methods. The miscibility, crystallization behavior, and component interaction of these blends were examined by differential scanning calorimetry. Only one glass‐transition temperature (T_g) was found in the DL‐PLA/PMMA solution/precipitation blends, indicating miscibility in this system. Two isolated T_g's appeared in the DL‐PLA/PMMA solution‐casting film blends, suggesting two segregated phases in the blend system, but evidence showed that two components were partially miscible. In the PLLA/PMMA blend, the crystallization of PLLA was greatly restricted by amorphous PMMA. Once the thermal history of the blend was destroyed, PLLA and PMMA were miscible. The T_g composition relationship for both DL‐PLA/PMMA and PLLA/PMMA miscible systems obeyed the Gordon–Taylor equation. Experiment results indicated that there is no more favorable trend of DL‐PLA to form miscible blends with PMMA than PLLA when PLLA is in the amorphous state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 23–30, 2003     

Viscoelastic properties and phase behavior of 12‐tert‐butyl ester dendrimer/poly(methyl methacrylate) blends

This study used refractometry, ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and dielectric analysis to assess the viscoelastic properties and phase behavior of blends containing 0–20% (w/w) 12‐tert‐butyl ester dendrimer in poly(methyl methacrylate) (PMMA). Dendritic blends were miscible up through 12%, exhibiting an intermediate glass‐transition temperature (T_g; α) between those of the two pure components. Interactions of PMMA C?O groups and dendrimer N? H groups contributed to miscibility. T_g decreased with increasing dendrimer content before phase separation. The dendrimer exhibited phase separation at 15%, as revealed by Rayleigh scattering in ultraviolet–visible spectra and the emergence of a second T_g in dielectric studies. Before phase separation, clear, secondary β relaxations for PMMA were observed at low frequencies via dielectric analysis. Apparent activation energies were obtained through Arrhenius characterization. A merged αβ process for PMMA occurred at higher frequencies and temperatures in the blends. Dielectric data for the phase‐separated dendrimer relaxation (α_D) in the 20% blend conformed to Williams–Landel–Ferry behavior, which allowed the calculation of the apparent activation energy. The α_D relaxation data, analyzed both before and after treatment with the electric modulus, compared well with neat dendrimer data, which confirmed that this relaxation was due to an isolated dendrimer phase. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1381–1393, 2001     

Structures induced by irradiation of femto-second laser pulse in polymeric materials

We investigated the structures induced by irradiation of near-infrared femto-second laser pulse in various polymer materials; olefin gel, acrylic adhesive, poly(ether sulphone) (PES), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and block copolymers of methyl-methacrylate and ethyl acrylate-butyl acrylate. Line irradiation that was performed by scanning laser spots in polymer bulk formed volcano-like upheaval structures on the surfaces of PES, PMMA, and PC, which have relatively high glass-transition temperatures (T_g's); on the other hand, cave or channel structures on the surfaces of olefin gel and acrylic adhesive have low T_g's. For the block copolymers containing both low and high T_g's, aggregation of the submicron scale deposit was induced in the polymer bulk. The submicron scale deposit may be reproduced structures after photodecomposition or photocrosslinking of polymer-chain components induced by multiphoton excitation with femto-second laser irradiation. This deposit aggregation with a stripelike structure had different optical properties from the un-irradiated region. These structures induced by irradiation of femto-second laser pulse might be applicable for optical devices such as diffraction grating and optical guide. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 537–544, 2002; DOI 10.1002/polb.10111     

Influence of sample preparation and processing on observed glass transition temperatures of polymer nanocomposites

Polymer composites composed of poly(methyl methacrylate) (PMMA) and silica (14 nm diameter) have been investigated. The influences of sample preparation and processing have been probed. Two types of sample preparation methods were investigated: (i) solution mixture of PMMA and silica in methyl ethyl ketone and (ii) in situ synthesis of PMMA in the presence of silica. After removing all solvent or monomer, as confirmed using thermogravimetric analysis, and after compression molding, drops in T_g of 5–15 °C were observed for all composites (2–12% w/w silica) and even pure polymer reference samples. However, after additional annealing for 72 h at 140 °C, all previously observed drops in T_g disappeared, and the intrinsic T_g of bulk, pure PMMA was again observed. This is indicative of nonequilibrium trapped voids being present in the as‐molded samples. Field‐emission scanning electron microscopy was used to show well‐dispersed particles, and dynamic mechanical analysis was used to probe the mechanical properties (i.e., storage modulus) of the fully equilibrated composites. Even though no equilibrium T_g changes were observed, the addition of silica to the PMMA matrices was observed to improve the mechanical properties of the glassy polymer host. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2270–2276, 2007     

Viscoelastic characteristics of plasticized cellulose nanocomposites

The plasticization effects of cellulose diacetate composite systems including nanoparticles (montmorillonite, MMT) and plasticizers(diethyl phthalate, DEP) were investigated by the time–temperature superposition technique and viscoelastic modeling. Exhibiting the highest modulus value in the glass state, the viscoelastic modulus of the MMT nanocomposite rapidly decreased above the glass‐transition temperature (T_g). The Arrhenius‐type activation energy of pristine cellulose acetate showed the lowest value of activation energy and both DEP‐plasticized and MMT‐reinforced systems exhibited increased values of activation energy. Although the free volume fraction at the T_g decreased with the plasticizer content, it increased with the incorporation of MMT, seemingly preventing the polymer chains from being arranged in an ordered structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 59–65, 2005     

Preparation,Tg improvement,and thermal stability enhancement mechanism of soluble poly(methyl methacrylate) nanocomposites by incorporating octavinyl polyhedral oligomeric silsesquioxanes

The soluble poly(methyl methacrylate‐co‐octavinyl‐polyhedral oligomeric silsesquioxane) (PMMA–POSS) hybrid nanocomposites with improved T_g and high thermal stability were synthesized by common free radical polymerization and characterized using FTIR, high‐resolution ¹H NMR, ²⁹Si NMR, GPC, DSC, and TGA. The POSS contents in the nanocomposites were determined based on FTIR spectrum, revealing that it can be effectively adjusted by varying the feed ratio of POSS in the hybrid composites. On the basis of the ¹H NMR analysis, the number of the reacted vinyl groups on each POSS molecules was determined to be about 6–8. The DSC and TGA measurements indicated that the hybrid nanocomposites had higher T_g and better thermal properties than the pure PMMA homopolymer. The T_g increase mechanism was investigated using FTIR, displaying that the dipole–dipole interaction between PMMA and POSS also plays very important role to the T_g improvement besides the molecular motion hindrance from the hybrid structure. The thermal stability enhances with increase of POSS content, which is mainly attributed to the incorporation of nanoscale inorganic POSS uniformly dispersed at molecular level. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5308–5317, 2007     

Glass‐transition temperatures of nanostructured amorphous bulk polymers and their blends

Nanostructured amorphous bulk polymer samples were produced by processing them with small molecule hosts. Urea (U) and gamma‐cyclodextrin (γ‐CD) were utilized to form crystalline inclusion compounds (ICs) with low and high molecular weight as‐received (asr‐) poly(vinyl acetate) (PVAc), poly(methyl methacrylate) (PMMA), and their blends as included guests. Upon careful removal of the host crystalline U and γ‐CD lattices, nanostructured coalesced (c‐) bulk PVAc, PMMA, and PVAc/PMMA blend samples were obtained, and their glass‐transition temperatures, T_gs, measured. In addition, non‐stoichiometric (n‐s)‐IC samples of each were formed with γ‐CD as the host. The T_gs of the un‐threaded, un‐included portions of their chains were observed as a function of their degree of inclusion. In all the cases, these nanostructured PVAc and PMMA samples exhibited T_gs elevated above those of their as‐received and solution‐cast samples. Based on their comparison, several conclusions were reached concerning how their molecular weights, the organization of chains in their coalesced samples, and the degree of constraint experienced by un‐included portions of their chains in (n‐s)‐γ‐CD‐IC samples with different stoichiometries affect their chain mobilities and resultant T_gs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1041–1050     

Gamma-ray response of a clear,crosslinked PMMA dosimeter,Radix W

Radix W, a clear poly(methyl-methacrylate) (PMMA) dosimeter was developed with improved properties compared to the conventional clear PMMA dosimeter, Radix RN15. PMMA with a glass transition temperature (T_g) higher than 120 °C was selected making it possible to measure doses in a wide range of 1 to 150 kGy. Dose rates of 2.5–10 kGy/h were tested and did not affect significantly the dose response. The influence of irradiation temperature was reduced compared with Radix RN15.     

Effects of molecular mass and surface treatment on adsorbed poly(methyl methacrylate) on silica

The behavior of relatively monodisperse adsorbed poly(methyl methacrylate) (PMMA) samples, from 19 to 587 kDa on silica, was studied using modulated differential scanning calorimetry and FTIR. On untreated Cab? O? Sil silica, the glass transition temperatures (T_gs) were higher (by around 30 °C), and the transitions were significantly broader (by a factor of 5–6) than those for the corresponding bulk samples. While the T_gs for the bulk polymers showed the expected dependence on molecular mass, the polymers on untreated silica showed little dependence, i.e., at the same adsorbed amounts, the glass transitions were very similar. The FTIR spectra of the adsorbed PMMA (on untreated silica) showed the presence of at least two resonances, one for the bound (hydrogen bonded to surface silanols) and another for free carbonyls. Fitting of the spectra allowed the estimation of the bound fractions of carbonyls that were dependent on the adsorbed amount, but not molecular mass. On Cab? O? Sil treated with hexamethyldisilizane (HMDS), the adsorbed PMMA exhibited glass transition behavior with little molecular‐mass dependence; the T_gs for the different PMMA samples were very similar to those of the high‐molecular mass bulk polymer, but with additional broadening of about a factor of 2. FTIR spectra for the PMMA samples on the treated silica did not show significant amounts of any of the hydrogen‐bonded carbonyl groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 649–658, 2008     

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 (T_g) when the film thickness is less than ～60 nm, whereas more model atactic PMMA shows an increased T_g 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 T_g compared with the initial PMMA fraction. The extracted sample exhibits initially a slight decrease in T_g as the film thickness is reduced below ～60 nm, but then T_g 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 T_g of polymer thin films that exist in the literature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Influence of interaction between poly(methyl methacrylate) and clay on the properties of nanocomposites prepared by a heterocoagulation method

To have a better insight into the effect of interaction between polymer matrix and clay on the properties of nanocomposite, poly(methyl methacrylate)/clay nanocomposites were prepared by a heterocoagulation method. Using a reactive cationic emulsifier, methacryloyloxyethyltrimethyl ammonium chloride (METAC), a strong polymer–clay interaction was obtained with the advantage of keeping a consistent polymer matrix property. X‐ray diffraction and transmission electronic microscopy indicated an exfoliated structure in nanocomposites. The glass transition temperature (T_g) of the nanocomposites was measured by DSC and DMA. The DMA results showed that with a strong interaction, PMMA–METAC nanocomposite showed a 20 °C enhancement in glass transition temperature (T_g), whereas a slight increase in T_g was observed for PMMA–cetyl trimethylammonium bromide (CTAB)/clay nanocomposite with a weak interaction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 733–738, 2010     

Study on the PMMA/GO nanocomposites with good thermal stability prepared by in situ Pickering emulsion polymerization

Graphene oxide (GO) is used as a stabilizer in the Pickering emulsion polymerization of methyl methacrylate (MMA) to prepare PMMA/GO nanocomposites. Transmission electron microscope studies of the emulsion polymerization products showed that the average diameter of nanocomposite particles was about 150 nm, the transparent GO flakes covered the surface of the particles, and were well dispersed in polymer matrix. The influence of GO on the thermal stability of PMMA was investigated by thermogravimetry analysis and differential scanning calorimetry. The results showed that the thermal stability and the glass transition temperature (T _g) of PMMA/GO nanocomposites were improved obviously compared with PMMA. The apparent activation energy (E _a) for the degradation process of PMMA/GO nanocomposites was evaluated by Kissinger method, which indicated that their E _a s were much higher than those of PMMA both in nitrogen and air atmosphere.     

Structure and properties of poly(methyl methacrylate) particles prepared by a modified microemulsion polymerization

Nanoscale poly(methyl methacrylate) (PMMA) particles were prepared by modified microemulsion polymerization. Different from particles made by traditional microemulsion polymerization, the particles prepared by modified microemulsion polymerization were multichain systems. PMMA samples, whether prepared by the traditional procedure or the modified procedure, had glass-transition temperatures (T_g's) greater than 120 °C and were rich in syndiotactic content (55–61% rr). After the samples were dissolved in CHCl₃, there were decreases in the T_g values for the polymers prepared by the traditional procedure and those prepared by the modified process. However, a more evident T_g decrease was observed in the former than in the latter; still, for both, T_g was greater than 120 °C. Polarizing optical microscopy and wide-angle X-ray diffraction indicated that some ordered regions formed in the particles prepared by modified microemulsion polymerization. The addition of a chain-transfer agent resulted in a decrease in both the syndiotacticity and T_g through decreasing polymer molecular weight. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 733–741, 2004     

Glass Transition Temperature Improvement for Polychloroprene by One-Step ATRP Reaction

Polymethyl methacrylate (PMMA) polymer chains were grafted on neoprene W (NW) by a one-step ATRP reaction. The thermal properties of the products were analyzed by DSC. Improvement of T _g was a result of the PMMA grafted chains. Also, the melting point (T _m ) changed from 42°C for NW to 142°C for modified NW. Using different solvents for the resulting copolymers, aggregates were obtained. Phase separation was influenced by the grafting degree of PMMA and the employed solvent. The copolymers were analyzed by GPC, FT-IR, DSC, and SEM.     

Structure–property relationships in modified natural rubber latexes grafted with methyl methacrylate and vinyl neo‐decanoate

A series of modified natural rubber latexes (NRLs) grafted with poly(methyl methacrylate) (PMMA) were prepared by seeded emulsion polymerization with NRL as the seed polymer. Two different redox systems, cumene hydroperoxide (CHP)/tetraethylene pentamine (TEPA) and tert‐butyl hydroperoxide (t‐BHP)/TEPA, were used to initiate polymerization, and phase mixing was promoted by the addition of vinyl neo‐decanoate (VneoD). The CHP/TEPA system was more efficient than t‐BHP/TEPA for the grafting of secondary polymers in modified natural rubber (NR). The enhanced phase mixing in the presence of VneoD was attributed to the solubility parameter of the VneoD‐rich methyl methacrylate–VneoD copolymer formed late in the reaction, lying between that of PMMA and NR, and the extent to which this polymer was grafted to the NR backbone. The viscoelastic properties of the polymers were investigated as a function of composition, temperature, and frequency; changes in viscoelastic behavior consistent with the presence of a high‐T_g PMMA phase (where T_g is the glass‐transition temperature) were observed. This suggested a degree of phase mixing that increased with increasing VneoD content and increasing flux of oxygen‐centered radicals within the NR particles. More phase mixing resulted in poorer film formation, which was consistent with the localization of a high‐T_g secondary polymer phase near the particle surface. The apparent concentration of PMMA near the surface of the particles was also observed with transmission electron microscopy. The localization of PMMA near the particle surfaces was consistent with the presumed locus of radical generation in these systems: the redox couple used to initiate the polymerization consisted of an oil‐soluble hydroperoxide and a water‐soluble amine that reacted predominantly at the water/particle interface. The viscoelastic properties of the modified NRLs that were prepared suggest that these synthetic procedures provide a means of controlling phase mixing and branching, such as for improving the suitability of these modified rubbers in pressure‐sensitive‐adhesive formulations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 809–822, 2002; DOI 10.1002/pola.10165     

Thermal Decomposition and Glass Transition Temperature of Poly(methyl Methacrylate) and Poly(isobutyl Methacrylate)

Abstract

The thermal decomposition and the glass transition temperatures of poly(methyl methacrylate) (PMMA) and poly(isobutyl methacrylate) (PiBuMA) were studied with a differential scanning calorimeter (DSC). The undecomposed and decomposed polymers were analyzed by gel permeation chromatography (GPC) for molecular weight distributions and by DSC for changes in the thermal properties and glass transition temperatures, T. In the isothermal decomposition of PMMA and PiBuMA, depolymerization reactions exclusively are operative. During low temperature decompositions, longer PMMA chains depolymerize first. These are followed by the shorter chains. In the case of PiBuMA, the shorter chains depolymerize first. Some of these undergo chain recombinations to yield very high molecular weight products. For identical values of weight loss, the respective decomposition temperatures for PiBuMA are 40 to 70 K lower than those for PMMA. The activation energies of decomposition (42 kJ/mol for PMMA and 67 kJ/mol for PiBuMA) have been found to be lower than those reported in the literature. Although T_g∞ of PiBuMA (331 K) agrees well with the literature value (326 K), T_g∞ of atactic PMMA (394 K) is higher than the reported value (378 K).     

Characterization and degradation of the poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymer

Poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymers (PSXE-g-PMMA) were prepared by condensation reaction of poly(methylphenylsiloxane)-containing epoxy resin (PSXE) with carboxyl-terminated poly(methyl methacrylate) (PMMA), and they were characterized by gel permeation chromatography (GPC), infrared (IR), and ²⁹Si and ¹³C nuclear magnetic resonance (NMR). The microstructure of the PSXE-g-PMMA graft copolymer was investigated by proton spin–spin relaxation T₂ measurements. The thermal stability and apparent activation energy for thermal degradation of these copolymers were studied by thermogravimetry and compared with unmodified PMMA. The incorporation of poly(methylphenylsiloxane) segments in graft copolymers improved thermal stability of PMMA and enhanced the activation energy for thermal degradation of PMMA. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2521–2530, 1998     

Depression of the glass transition temperature of poly(methyl methacrylate) by plasticizers: Conformity with free volume theory

Mixtures of poly(methyl methacrylate) (PMMA) and plasticizer were made by γ-irradiation of mixtures of methyl methacrylate with diethyl phthalate or with dioctyl phthalate. The glass transition temperature T_g was determined by differential scanning calorimetry. Plots of T_g versus volume fraction of PMMA were found to conform to the simple free volume theory of Kelley and Bueche, using physical property values either reported in the literature or else calculated by Bondi's procedures.     

Poly(methyl methacrylate)/Methacryl-POSS Nanocomposites with Excellent Thermal Properties

Poly(methyl methacrylate) (PMMA) nanocomposites containing (methacryloxy)propyl polyhedral oligomeric silsesquioxane (methacryl‐POSS) were prepared by bulk‐polymerization process. The structures of the products were characterized by FTIR, solid‐state NMR, TEM, XRD, DSC, TGA, XPS and UV‐Vis spectra. The hybrid materials were found to be largely homogeneous. DSC and TGA results indicate that the thermal properties of PMMA nanocomposites are significantly improved. The glass transition temperature (T_g) and thermal decomposition temperature (T_dec) of the nanocomposites increased by 58 and 110°C, respectively. The bulk hybrid material maintains excellent optical transparency in visible region.