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     

Dielectric properties of stereoregular poly(methyl methacrylates)

To obtain more useful information about the effect of the degree of stereoregularity on the motion of the polymer chain, the dielectric and dilatometric measurements were made for a series of stereoregular poly(methyl methacrylates) (PMMA). The α- and β-absorptions were observed in each sample, of which the dielectric behaviors of the α-process are discussed. The temperature dependence of the relaxation time of the α-process was sufficiently represented by the WLF equation and the resulting values of the parameters f_g and B in the modified WLF equation were found smaller for isotactic-rich PMMA than those values for syndiotactic PMMA. It may be deduced from these results that the chain mobility of the isotactic PMMA is larger than that of the syndiotactic. The dielectric increment of the α-process in the isotactic PMMA is much larger than that in the syndiotactic PMMA, increasing rapidly with temperature, and taking its maximum in the temperature range of 55 to 60°C. The dielectric transition was clearly observed in the case of isotactic-rich PMMA.     

Viscoelastic properties of bis(phenyl)fluorene‐based cardo polymers with different chemical structure

Viscoelastic properties of urethane and ester conjugation cardo polymers that contain fluorene group, 9,9‐bis(4‐(2‐hydroxyethoxy)phenyl)fluorene (BPEF), were investigated. As for the urethane‐type cardo polymers containing BPEF in the main chain, it had a high glass‐transition temperature (T_g), which was observed as the α dispersion on viscoelastic measurement, and its temperature depended on the chemical structure of the spacing unit, such as toluene diisocyanate (TDI), 4,4′‐methylene diphenyl diisocyanate (MDI), methylene dicycloexyl diisocyanate (CMDI), and hexamethylene diisocyanate (HDI). Moreover, the T_g of urethane‐type cardo copolymers with various cardo contents increased with an increase of cardo content. Owing to the increase of T_g of cardo polymers, another molecular motion can be measured at the temperature between the α and β dispersion that was assigned to the molecular motion of urethane conjugation unit around 200 K, and it was referred to as the α_sub dispersion. The peak temperature of the α_sub dispersion was influenced by the chemical structure of the spacing unit, but it did not change for the cardo polymer containing the same spacing unit. Consequently, it was deduced that the α_sub dispersion was originated in the subsegmental molecular motions of the cardo polymers. Ester‐type cardo polymer had higher T_g in comparison with noncardo polymer that consisted of dimethyl groups (BPEP) instead of BPEF as well. The α_sub dispersion was also measured at the temperature between the α and β dispersion, which was assigned to the molecular motion of ester conjugation unit, around 220 K. For ester cardo polymer, the γ dispersion was measured in a low‐temperature region around 140 K, and it was due to a small unit motion in the ester‐type cardo polymers, such as ethoxyl unit, ? C₂H₄O? . Moreover, the intensity of the γ dispersion of noncardo polymer was higher than that of cardo polymer, which means the molecular motion was much restricted by the cardo structure of BPEF. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2259–2268, 2005     

Interpenetrating polymer networks of poly(dimethyl siloxane–urethane) and poly(methyl methacrylate)

Simultaneous IPNs of poly(dimethyl siloxane-urethane) (PDMSU)/poly(methyl methacrylate) (PMMA) and related isomers have been prepared by using new oligomers of bis(β-hydroxyethoxymethyl)poly(dimethyl siloxane)s (PDMS diols) and new crosslinkers biuret triisocyanate (BTI) and tris(β-hydroxylethoxymethyl dimethylsiloxy) phenylsilane (Si-triol). Their phase morphology have been characterized by DSC and SEM. The SEM phase domain size is decreased by increasing crosslink density of the PDMSU network. A single phase IPN of PDMSU/PMMA can be made at an M_c = 1000 and 80 wt % of PDMSU. All of the pseudo- or semi-IPNs and blends of PDMSU and PMMA were phase separated with phase domain sizes ranging from 0.2 to several micrometers. The full IPNs of PDMSU/PMMA have better thermal resistance compared to the blends of linear PDMSU and linear PMMA. © 1993 John Wiley & Sons, Inc.     

Molecular mobility of poly(methyl methacrylate) glass during uniaxial tensile creep deformation

An optical photobleaching method has been used to measure the segmental dynamics of a poly(methyl methacrylate) (PMMA) glass during uniaxial creep deformation at temperatures between T_g ? 9 K and T_g ? 20 K. Up to 1000‐fold increases in mobility are observed during deformation, supporting the view that enhanced segmental mobility allows flow in polymer glasses. Although the Eyring model describes this mobility enhancement well at low stress, it fails to capture the dramatic mobility enhancement after flow onset, where in addition the shape of the relaxation time distribution narrows significantly. Regions of lower mobility accelerate their dynamics more in response to an external stress than do regions of high mobility. Thus, local environments in the sample become more dynamically homogeneous during flow. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1713–1727, 2009     

Thermal expansion of oriented poly(methyl methacrylate)

The thermal expansivities along (α∥) and perpendicular (α_⊥) to the draw direction of poly(methyl methacrylate) (PMMA) with extrusion draw ratios 1 ≤ λ ≤ 4 have been measured between 150 and 298 K. As λ was increased from 1 to 4, α∥ decreased 2–3 times, whereas α_⊥ increased only 20–35%. The orientation function f calculated from thermal expansivity using the aggregate model is found to change linearly with birefringence, indicating that each property provides a sensitive measure of molecular orientation. For PMMA, however, only thermal expansivity can give an absolute f, with results at 150 K in reasonable agreement with previous studies using other techniques. At higher temperature, i.e., above ambient, PMMA side-group motions are excited, expanding volume, and calculations based on the aggregate model may not be valid.     

Morphological studies of poly(vinylidene fluoride) and its blends with poly(methyl methacrylate)

Both pure poly(vinylidene fluoride) (PVF₂) and its blends with poly(methyl methacrylate) (PMMA) develop a variety of morphologies when they are crystallized above the 420–424 K range. Two populations of spherulites as well as axialitelike growths are observed. Addition of the PMMA lowers the temperature where these new morphologies develop, makes the spherulites more open, causes the banding periodicity to decrease, and increases the number of small, coarse spherulites. These structures melt in three regimes. The highest-melting-point crystals arise only from a solid-solid transformation of the lowest-melting-point ones. This solid-state transition sometimes causes mixed spherulites to be formed in the blends. Electron and wide-angle x-ray diffraction show the lowest-melting-point species to be α crystals, while the other two are γ crystals. The highest-melting-point species, labeled γ′, and the α crystals seem to be more ordered than the other γ crystals.     

STUDIES OF THE CRYSTALLIZATION BEHAVIOR IN THE CRYSTALLINE/AMORPHOUS POLYMER BLENDS: POLY(ETHYLENE OXIDE)/POLY(METHYL METHACRYLATE) AND POLY(ETHYLENE OXIDE)/POLY(VINYL ACETATE)

The crystallization process of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA)and PEO/poly(vinyl acetate) (PVAc) blends has been characterized by Fourier Transform Infrared(FTIR) spectra in conjunction with Differential Scanning Calorimeter (DSC) measurements. Thecrystallinity of PEO varies consistently with PEO content in PEO/PVAc blends and the PEO/PMMAblends containing 50 wt% or less PMMA. For the PEO/PMMA blends containing 60 wt% ormore PMMA, the crystallinity of PEO decreases more than PEO content but develops with crystal-lization time. These results can be explained in terms of difference between the crystallization tem-perature (T_c) and glass transition temperature (T_g) of the blends as a function of content of amorphouscomponent.     

Crystallization of titania ultra-fine particles from peroxotitanic acid in aqueous solution in the present of polymer and incorporation into poly(methyl methacylate) via dispersion in organic solvent

We report a novel strategy for incorporation of titanium dioxide (TiO₂) particles, which were crystallized from peroxotitanic acid in the presence of hydrophilic polymer by hydrothermal treatment in aqueous solution, into poly(methyl methacrylate) (PMMA) via dispersion into chloroform. Dispersion of TiO₂ particles into chloroform was achieved by solvent change from water to chloroform in aid of amphiphilic polymer dispersant, poly(N-vinyl pyrrolidone) (PVP), poly(N-vinyl pyrrolidone-co-methyl methacrylate) (PVP-co-PMMA), poly(N-vinyl pyrrolidone-block-methyl methacrylate) (PVP-b-PMMA) through azeotropical removal of water. Incorporation of TiO₂ particles into PMMA was carried out by a casting process of a mixture of TiO₂ particles dispersed with PVP₁₅₄-b-PMMA₁₅₆ in chloroform and PMMA on a glass substrate. Resultant hybrid film containing TiO₂ less than 10 wt.% showed high transparency in visible region attributable to homogeneous dispersion into PMMA matrix. The refractive index of the hybrid films increased with TiO₂ content and agreed with the calculated values.     

Side-chain crystallinity,heat of melting,and thermal transitions in poly[N-(10-n-alkyloxycarbonyl-n-decyl)maleimides] (PEMI)

The heat of melting, the melting temperature T_m, and the sub-T_g transition temperature have been studied from –120°C to above T_m in a series of 11 poly[N-(10-n-alkyloxycarbonyl-n-decyl)]-maleimides (PEMI). Side-chains from ethyl to n-docosyl with n even have been included. The contribution to the heat of melting per methylene group shows that the hexagonal paraffin crystal modification is present in these poly(N-maleimides), in agreement with x-ray data for the same compounds. The enthalpy data show that only a part of the outer methylene groups are present in the crystalline aggregates. Furthermore, DSC traces exhibit a typical distribution of crystallite sizes, which become narrower as the side-chains become longer. The critical chain length needed to form a stable nucleus includes nine methylene groups in the outer part of the n-alkyl side-chain. The influence of the side-chain length and crystallinity on the γ-transition temperature of these polymers was also investigated. In the range where these polymers are essentially amorphous the sub-T_g transition temperature decreases continuously as the number of methylene groups in the side-chain increases. This transition is attributed to internal motion within the external side-group without any interaction with the main chain. This is presumably made possibly by the partial rotation of the oxycarbonyl group. We suggest that this transition is similar to the well known γ transition which has been attributed to various segmental motions in all ethylene copolymers and in all homopolymers containing a determined number of? CH₂? units in the main-chain or in the side-chain. Estimates based on the chemical structure, yield a value for the γ transition of ? CH₂? similar to that measured by other methods in polyethylene and related materials.     

Glass transition and polymer dynamics in silver/poly(methyl methacrylate) nanocomposites

Dynamic mechanical–thermal analysis (DMTA), differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) and, mainly, broadband dielectric relaxation spectroscopy (DRS) were employed to investigate in detail glass transition and polymer dynamics in silver/poly(methyl methacrylate) (Ag/PMMA) nanocomposites. The nanocomposites were prepared by radical polymerization of MMA in the presence of surface modified Ag nanoparticles with a mean diameter of 5.6 nm dispersed in chloroform. The fraction of Ag nanoparticles in the final materials was varied between 0 and 0.5 wt%, the latter corresponding to 0.055 vol%. The results show that the nanoparticles have practically no effect on the time scale of the secondary β and γ relaxations, whereas the magnitude of both increases slightly but systematically with increasing filler content. The segmental α relaxation, associated with the glass transition, becomes systematically faster and stronger in the nanocomposites. The glass transition temperature T_g decreases with increasing filler content of the nanocomposites up to about 10 °C, in good correlation by the four techniques employed. Finally, the elastic modulus decreases slightly but systematically in the nanocomposites, both in the glassy and in the rubbery state. The results are explained in terms of plasticization of the PMMA matrix, due to constraints imposed to packing of the chains by the Ag nanoparticles, and at the same time, of the absence of strong polymer–filler interactions, due to the surface modification of the Ag nanoparticles by oleylamine at the stage of preparation.     

Catalytic effect of dimethyl sulfoxide in the Cu(0)/tris(2‐dimethylaminoethyl)amine‐catalyzed living radical polymerization of methyl methacrylate at 0–90 °C initiated with CH3CHClI as a model compound for α,ω‐di(iodo)poly(vinyl chloride) chain ends

A variety of conditions, including catalysts [CuCl, CuI, Cu₂O, and Cu(0)], ligands [2,2′‐bipyridine (bpy), tris(2‐dimethylaminoethyl)amine (Me₆‐TREN), polyethyleneimine, and hexamethyl triethylenetetramine], initiators [CH₃CHClI, CH₂I₂, CHI₃, and F(CF₂)₈I], solvents [diphenyl ether, toluene, tetrahydrofuran, dimethyl sulfoxide (DMSO), dimethylformamide, ethylene carbonate, dimethylacetamide, and cyclohexanone], and temperatures [90, 25, and 0 °C] were studied to assess previous methods for poly(methyl methacrylate)‐b‐poly(vinyl chloride)‐b‐poly(methyl methacrylate) (PMMA‐b‐PVC‐b‐PMMA) synthesis by the living radical block copolymerization of methyl methacrylate (MMA) initiated with α,ω‐di(iodo)poly(vinyl chloride). CH₃CHClI was used as a model for α,ω‐di(iodo)poly(vinyl chloride) employed as a macroinitiator in the living radical block copolymerization of MMA. Two groups of methods evolved. The first involved CuCl/bpy or Me₆‐TREN at 90 °C, whereas the second involved Cu(0)/Me₆‐TREN in DMSO at 25 or 0 °C. Related ligands were used in both methods. The highest initiator efficiency and rate of polymerization were obtained with Cu(0)/Me₆‐TREN in DMSO at 25 °C. This demonstrated that the ultrafast block copolymerization reported previously is the most efficient with respect to the rate of polymerization and precision of the PMMA‐b‐PVC‐b‐PMMA architecture. Moreover, Cu(0)/Me₆‐TREN‐catalyzed polymerization exhibits an external first order of reaction in DMSO, and so this solvent has a catalytic effect in this living radical polymerization (LRP). This polymerization can be performed between 90 and 0 °C and provides access to controlled poly(methyl methacrylate) tacticity by LRP and block copolymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1935–1947, 2005     

Stereocomplex formation of isotactic poly(methyl methacrylate) with a wide variety of syndiotactic polymethacrylates

Syndiotactic (st–) polymers of methacrylates with primary and secondary ester groups, prepared by the syndiotactic-specific living polymerization with t-C₄H₉Li/R₃Al, were found to form stereocomplexes with isotactic (it–) poly(methyl methacrylate) (PMMA) by annealing in the solid state or by mixing in certain solvents such as acetone and toluene. Melting points of the complexes depend on the structure of the ester group and can be changed in a wide range of temperature. st–Polymers of tertiary esters did not form the complex. Effects of anneal conditions, molecular weight, and tacticity on the melting point of the complex were studied in some detail for the combination of st–poly(benzyl methacrylate) and it–PMMA. st–Random copolymers of MMA with several alkyl methacrylates also formed stereocomplexes with it–PMMA, whose melting point could be changed continuously by changing the composition in a certain range of temperature. st–Block copolymers of PMMA and poly(benzyl methacrylate) formed stereocomplexes with it–PMMA which showed two melting points, provided the block lengths are long enough for the two types of the com plexes to form independently. Stereoblock PMMA, it–PMMA–block–st–PMMA, and stereoblock copolymer, it–PMMA–block–st–poly(butyl methacrylate), were found to form stereocomplexes more easily than the corresponding mixtures. The stereoregular uniform PMMAs were used for elucidating the process of stereocomplex formation and its stoichiometry by means of gelpermeation chromatography (GPC). The preliminary results clearly indicated that the complexation occurs mainly in 1:1 stoichiometry in the beginning, while a small fraction of 1:2 (it–: st–) complex was also formed concomitantly. By similar GPC experiments using a series of uniform PMMAs, the minimum length of PMMA chains for the complex formation was found to be in the range of degrees of polymerization from 42 to 46.     

Synthesis and characterization of poly(phenylene oxide) graft copolymers by atom transfer radical polymerizations

A series of comb-like poly(phenylene oxide)s (PPO) graft copolymers with controlled grafting density and length of grafts were synthesized by atom transfer radical polymerization (ATRP). The α-bromo-poly(2,6-dimethyl-1,4-phenylene oxide)s (BPPO) were used as macroinitiators to polymerize vinyl monomers and the graft copolymers carrying polystyrene (PS), poly(p-acetoxystyrene) (PAS), and poly(methyl methacrylate) (PMMA) as side chains were synthesized and characterized by NMR, FTIR, GPC, DSC and TGA. The composition-dependent glass-transition temperatures (T_g) of PPO-g-PS exhibited good correlation with theoretical curve in Couchman equations except for the cases of low PS content (<40 mol%) copolymers in which a positive deviation was observed due to enhanced molecular interactions. The increase in monomer/initiator ratio led to the increase of degree of polymerization and the decrease of polydispersity. Despite the immiscibility nature between PPO and PMMA, the PPO-g-PMMA exhibited enhanced compatibilization as apparent single T_g in a wide temperature window throughout various compositions revealing an efficient segmental mixing on a molecular scale due to grafting structure.     

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     

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     

Mass spectroscopy and SEC of SRM 1487, a low molecular weight poly(methyl methacrylate) standard

Matrix Assisted Laser Desorption Ionization (MALDI) Time of Flight (TOF) Mass Spectrometry (MS) was used to study the molecular weight distribution (MWD) and the number of α-methyl styrene (α-MeSty) repeat units in SRM 1487, a narrow MWD poly(methyl methacrylate) (PMMA) standard reference material of about 6300 g/mol, which was initiated with α-MeSty. It was found that each PMMA polymer chain had from zero to seven α-MeStys per chain. The MWD of the polymer chains containing a fixed number of α-MeStys was obtained. The MWD, M_w, and the average number of α-MeSty at a given molecular weight from MALDI TOF MS compare well with those obtained from more traditional methods such as ultracentrifugation and Size Exclusion Chromatography (SEC). The implications of the number of α-MeStys per chain is discussed in terms of the chemistry of anionic polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2409–2419, 1997     

Easily grafted polyurethanes with reactive main chain functional groups. Synthesis,characterization, and antithrombogenicity of poly(ethylene glycol)-grafted poly(urethanes)

A novel synthesis of poly(ethylene glycol) (PEG)-grafted poly(urethanes) (PURs) is described based on a precursor PUR containing free amino groups in the main chain. Three different poly(urethane) backbones were prepared: a homopoly(urethane) comprised of N-Bocdiethanolamine (BDA) and 4,4′-methylenebis(phenyl isocyanate) (MDI), a copoly(urethane) (COPUR) consisting of BDA, N-benzyldiethanolamine and MDI, and a poly(urethane urea) (PUU) that was prepared from BDA, MDI, and ethylenediamine as the chain extender. The M_n of these poly(urethanes) ranged from 32,000 to 72,000 g/mol. PEG (750, 1,900, and 5,000 g/mol) was grafted onto the boc-deprotected poly(urethanes) via the chloroformate. Films of the polymers were spin cast from dilute solutions, annealed, and the surfaces analyzed by goniometry. Water contact angle data indicates increasing PEG surface coverage of the poly(urethanes) with increasing PEG molecular weight. Reorientation of the polymer films is evidenced by contact angle hysteresis. Polymer thrombogenicity, which was studied using blood perfusion experiments, shows that COPUR-g-PEG5000 and PUU-g-PEG5000 exhibit very little platelet adhesion. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3441–3448, 1999     

Synthesis of amphiphilic copolymer brushes possessing alternating poly(methyl methacrylate) and poly(N‐isopropylacrylamide) grafts via a combination of ATRP and click chemistry

We report on the synthesis of well‐defined amphiphilic copolymer brushes possessing alternating poly(methyl methacrylate) and poly(N‐isopropylacrylamide) grafts, poly(PMMA‐alt‐PNIPAM), via a combination of atom transfer radical polymerization (ATRP) and click reaction (Scheme 1 ). Firstly, the alternating copolymerization of N‐[2‐(2‐bromoisobutyryloxy)ethyl]maleimide (BIBEMI) with 4‐vinylbenzyl azide (VBA) affords poly(BIBEMI‐alt‐VBA). Bearing bromine and azide moieties arranged in an alternating manner, multifunctional poly(BIBEMI‐alt‐VBA) is capable of initiating ATRP and participating in click reaction. The subsequent ATRP of methyl methacrylate (MMA) using poly(BIBEMI‐alt‐VBA) as the macroinitiator leads to poly(PMMA‐alt‐VBA) copolymer brush. Finally, amphiphilic poly(PMMA‐alt‐PNIPAM) copolymer brush bearing alternating PMMA and PNIPAM grafts is synthesized via the click reaction of poly(PMMA‐alt‐VBA) with an excess of alkynyl‐terminated PNIPAM (alkynyl‐PNIPAM). The click coupling efficiency of PNIPAM grafts is determined to be ～80%. Differential scanning calorimetry (DSC) analysis of poly(PMMA‐alt‐PNIPAM) reveals two glass transition temperatures (T_g). In aqueous solution, poly(PMMA‐alt‐PNIPAM) supramolecularly self‐assembles into spherical micelles consisting of PMMA cores and thermoresponsive PNIPAM coronas, which were characterized via a combination of temperature‐dependent optical transmittance, micro‐differential scanning calorimetry (micro‐DSC), dynamic and static laser light scattering (LLS), and transmission electron microscopy (TEM). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2608–2619, 2009     

Non-Isothermal Crystallization of Poly (vinylidene fluoride)/Poly (methyl methacrylate)/Cellulose Nanocrystal Nanocomposites

Poly (vinylidiene fluoride) (PVDF)/poly (methyl methacrylate) (PMMA)/cellulose nanocrystal (CNC) nanocomposites were prepared by solution blending. Non-isothermal crystallization of PVDF/PMMA (70/30) blend and its composites was investigated using differential scanning calorimetry. It was found that the addition of CNCs played a positive role in both the crystallization rate and crystallization percentage. The addition of CNCs increased the initial crystallization temperature, peak crystallization temperature, and crystalline enthalpy. The Avrami index indicated that CNCs did not change the crystallization mechanism; while other parameters derived from Jeziorny theory and Mo's method, including Z _c , F(t), and α, further verified the positive role played by CNCs.