Glass Transition Temperature Of Poly Research Articles

Abnormal increase of glass transition temperature of poly(propylene carbonate) modified with rubber particles

AbstractPoly(propylene carbonate) (PPC) modified with CBS‐UFPR rubber particle was used as an example to explore the abnormal increase of glass transition temperature (Tg) of thermoplastics modified with rubber particle. TEM and AFM results showed that CBS‐UFPR was dispersed well in PPC with diameter of about 100 nm. The concentration and size of free‐volume in blends were measured by PALS, which indicated the existence of interfacial interaction between PPC and CBS‐UFRP. A schematic two‐layer model was proposed and the thickness of the interfacial layer was calculated. POLYM. COMPOS. 2012. © 2012 Society of Plastics Engineers

The Role of Amide Groups in Vinyl Monomers Containing Siloxane Groups for Highly Oxygen Permeable Hydrogels

Abstract In order to improve the hydrophilicity of silicone-containing monomers, N-2-(N′,N′-dimethylcarbamoyl)ethyl-N-[3-tris(trimethylsiloxy)silylpropyl]acrylamide (SiDAAA) and N-2-(N′,N′-dimethylcarbamoyl)ethyl-N-{3-[methylbis(trimethylsiloxy)silyl]propyl}acrylamide (SiDAAA2) were designed. Although these two monomers had complicated side chain structures, these showed similar radical polymerizability (from 2.6 × 104 to 3.8 × 104 of Mn, and from 87 to 90% of conversion) as conventional silicone-containing monomer 3-tris(trimethylsiloxy)silylpropyl methacrylate (TRIS) due to the acrylamide backbone. Moreover, the additional amide group in those monomers contributed to improved miscibility during copolymerization with N-(hydroxyethyl)acrylamide (HEAA) and 2-hydroxyethyl methacrylate (HEMA), which was determined by light transmission observation at 88% transmittance using a SiDAAA/HEAA (50/50) hydrogel. In contrast, TRIS/HEAA was not miscible, and TRIS/HEMA (60/40) gave only 26% transmittance. The glass-transition temperatures of poly(SiDAAA) and poly(SiDAAA2) were 61 and 28 °C, which were much higher than that of poly(TRIS) at 0.8 °C. The oxygen permeability of the hydrogels varied with the copolymer composition, mainly due to the siloxanyl group contents. In particular, permeability coefficients of more than 100 Barrer (1 Barrer = 10−11 (cm3 O2) cm cm−2 s−1 mmHg−1) which is sufficient oxygen permeability for corneal safety in the case of contact lens applications, can be obtained at lower than 60% water content. The biocompatibility of these hydrogels is also discussed.

Poly(trimethylene terephthalate‐block‐tetramethylene oxide) elastomer/single‐walled carbon nanotubes nanocomposites: Synthesis, structure, and properties

AbstractNanocomposites based on poly(trimethylene terephthalate)‐block‐poly(tetramethylene oxide) (PTT‐PTMO)‐segmented copolymer and COOH‐functionalized single‐walled carbon nanotubes (SWCNTs) were prepared by in situ polymerization method. The obtained nanocomposites were characterized by thermogravimetric analysis, scanning electron microscopy, differential scanning calorimetry (DSC), DMTA, wide‐angle x‐ray scattering (WAXS), small‐angle X‐ray scattering, and tensile testing. The nanocomposites with low SWCNTs loading (<0.5 wt %) shows uniform dispersion of CNT in polymer matrix. As the SWCNTs loading in the nanocomposites increase, the significant improvement of thermo‐oxidative stability was observed. It was found that the nanocomposites have slightly higher degree of crystallinity (determined by DSC and WAXS) of poly(trimethylene terephthalate) (PTT) hard phase than neat PTT‐PTMO copolymer. The melting point of PTT hard phase and glass transition temperature of poly(tetramethylene oxide)‐rich phase were not affected by the presence of CNTs in polymer matrix. The SWCNTs played a role as nucleating agent in PTT‐PTMO matrix, which led to increase in the crystallization rate. Tensile tests showed that the tensile strength of the nanocomposites with 0.05–0.3 wt % loading of SWCNTs have improved tensile strength in comparison to the neat PTT‐PTMO copolymer without reduction elongation at break. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

New Approach to the Synthesis of Exfoliated Polymer/Graphite Nanocomposites by Miniemulsion Polymerization Using Functionalized Graphene

A new method is described for the synthesis of exfoliated polymer nanocomposites made with modified graphite oxide (GO) using a miniemulsion polymerization technique. GO was synthesized and then modified with a reactive surfactant, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), which widened the gap between the graphene layers and facilitated monomer intercalation into the GO nanogalleries. The AMPS-modified GO was emulsified in the presence of styrene and butyl acrylate monomers, a surfactant (sodium dodecylbenzenesulfonate), and a hydrophobe (hexadecane). The stable miniemulsions were polymerized to afford encapsulated poly(styrene–butyl acrylate) (poly(S–BA))/GO nanocomposite latex particles. The exfoliated structure of the nanocomposites was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM revealed that graphene oxide nanosheets were largely exfoliated (about 2–5 nm thick) in the resultant films obtained from the synthesized nanocomposite latices. Examination of the nanostructure of the obtained nanocomposites by XRD analysis confirmed the formation of exfoliated graphene oxide nanoplatelets. The thermal stability and mechanical properties of the nanocomposites were evaluated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). TGA showed that all the prepared nanocomposites exhibited enhanced thermal stability relative to the neat poly(S–BA) copolymer. DMA also revealed that the glass transition temperature of poly(S–BA) in the nanocomposites increased significantly in the presence of modified GO relative to pure copolymer. Furthermore, the nanocomposites had improved storage and loss modulus only at relatively high GO content (i.e., 5 and 6 wt % relative to monomer).

Effect of Temperature and Frequency on Dynamic Mechanical Properties of Poly(<i>Methyl Methacrylate</i>)

The temperature sweep tests at defferent frequencies and heating rates, and frequency sweep tests at various temperatures for the samples of poly(methyl methacrylate) are carried out on a dynamic mechanical thermal spectrometer EPLEXOR® 500N-Gabo. The effects of temperature, frequency and heating rate on dynamic mechanical properties of poly(methyl methacrylate) are investigated. The results indicate that the glass transition temperature of poly(methyl methacrylate) increases with increasing frequency from 1 to 100Hz, and increases with increasing heating rate from 3 to 8°C/min as well. The temperature sweep curves at various heating rates suggest that the storage modulus of poly(methyl methacrylate) is non-sensitive at heating rate 3°C/min or 8°C/min, while heating rate is 5°C/min, there exists a critical temperature, within which the storage modulus versus temperature curves depart from each other, and beyond which the curves overlap one another. The glass transition temperature determined by the peak of loss modulus curve is smaller than that defined by the peak of loss tangent. The frequency sweep curves at a constant temperature show that a drop in storage modulus and a peak in loss tangent appear at a certain critical frequency, and the critical frequency increases with increasing temperature. For amorphous polymer, a competitive mechanism between frequency and temperature is observed. Higher temperature accelerates molecular motion, while higher frequency restrains molecular motion, so that the critical frequency corresponding to the peak of loss tangent shifts toward the direction of high temperature.

Poly(ether ether ketone)s and poly(ether ether ketone ketone)s containing cardo decahydronaphthalene groups: Synthesis and characterization

AbstractNew poly(ether ether ketone)s and poly (ether ether ketone ketone)s were synthesized by polycondensation of each of the three bisphenols, viz., 4,4′‐(octahydro‐2(1H)‐naphthylidene)bisphenol, 4,4′‐(octahydro‐2(1H)‐naphthylidene)bis‐3‐methylphenol, and 4,4′‐(octahydro‐2(1H)‐naphthylidene)bis‐3,5‐dimethylphenol with 4,4′‐difluorobenzophenone and 1,3‐bis(4‐fluorobenzoyl)benzene in a mixture of N,N‐dimethylacetamide and toluene [1 : 1 (v/v)] in the presence of anhydrous potassium carbonate. Inherent viscosities of poly(ether ether ketone)s and poly (ether ether ketone ketone)s were in the range 0.32–0.80 dL/g and number‐average molecular weights were in the range 16,100–55,900 g/mol. Poly(ether ether ketone)s and poly(ether ether ketone ketone)s were soluble in organic solvents such as dichloromethane, chloroform, tetrahydrofuran, meta‐cresol, pyridine, and 1‐methyl‐2‐pyrrolidinone at room temperature and could be cast into tough, transparent, and flexible films from their chloroform solutions. Wide angle x‐ray diffraction measurements revealed the amorphous nature of poly(ether ether ketone)s and poly (ether ether ketone ketone)s. The glass transition temperature poly(ether ether ketone)s and poly(ether ether ketone ketone)s were in the range 185–251°C. The temperature at 10% weight loss, determined from thermogravimetric analysis, of poly(ether ether ketone)s and poly(ether ether ketone ketone)s in nitrogen atmosphere was in the range 462–493°C indicating their good thermal stability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Investigation on the Heat Capacity of Water in Poly(Acrylic Acid)/Water Mixtures Through Stepscan Method

The heat capacity of poly(acrylic acid)/water mixtures with low water contents were measured by the stepscan differential scanning colorimetry (DSC) method and the Cp of the bound water in the mixtures were obtained based on simple equations with an assumption that the effect of interaction between polymer and water molecules could be ignored. The results indicated that the water decreased the glass transition temperature of poly(acrylic acid) (PAA), evidently as a plasticizer, and PAA/water mixtures were thermodynamically homogeneous blends. It was found that the Cp of nonfreezable water in PAA/water mixtures was higher than those of glassy water and cubic ice. The Cp increased with the water content, showing that average interactions between polymer and water decreased with water content. The Cp of bound water in the mixtures in the liquid state was lower than that of bulk water and also increased with water concentration, since the water molecules’ regular structures were broken. It showed that the Cp of bound water in the mixtures was lower than that of free water. The Cp of glassy water was calculated based on experimental Cp values of the PAA/water mixtures, which provided an easy way to obtain the Cp values of glassy water through a simple experiment. The values, however, were higher than those obtained by other researchers.

Synthesis and characterization of ABA‐type amphiphilic tri‐block copolymers through anionic polymerization using end functionalized poly(ethylene oxide) oligomers

AbstractABA‐type amphiphilic tri‐block copolymers were successfully synthesized from poly(ethylene oxide) derivatives through anionic polymerization. When poly(styrene) anions were reacted with telechelic bromine‐terminated poly(ethylene oxide) (1) in 2:1 mole ratio, poly(styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) tri‐block copolymers were formed. Similarly, stable telechelic carbanion‐terminated poly(ethylene oxide), prepared from 1,1‐diphenylethylene‐terminated poly (ethylene oxide) (2) and sec‐BuLi, was also used to polymerize styrene and methyl methacrylate separately, as a result, poly (styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) and poly (methyl methacrylate)‐b‐poly(ethylene oxide)‐b‐poly(methyl methacrylate) tri‐block copolymers were formed respectively. All these tri‐block copolymers and poly(ethylene oxide) derivatives, 1 and 2, were characterized by spectroscopic, calorimetric, and chromatographic techniques. Theoretical molecular weights of the tri‐block copolymers were found to be similar to the experimental molecular weights, and narrow polydispersity index was observed for all the tri‐block copolymers. Differential scanning calorimetric studies confirmed the presence of glass transition temperatures of poly(ethylene oxide), poly(styrene), and poly(methyl methacrylate) blocks in the tri‐block copolymers. Poly(styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) tri‐block copolymers, prepared from polystyryl anion and 1, were successfully used to prepare micelles, and according to the transmission electron microscopy and dynamic light scattering results, the micelles were spherical in shape with mean average diameter of 106 ± 5 nm. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Highly Reproducible Nanolithography by Dynamic Plough of an Atomic-Force Microscope Tip and Thermal-Annealing Treatment

An approach has been developed to use atomic-force microscope (AFM) to pattern materials at the nanoscale in a controlled manner. By introducing a thermal-annealing process above the glass-transition temperature of poly (methylmethacrylate) (PMMA), the profile of indented nanopatterns has been dramatically improved by abatement of the tip-induced debris. This eliminates the main problem of the previous AFM-based tip-ploughing lithography method, namely the debris formation during the nanoplough and trench refilling by debris. We are able to reproducibly fabricate nanopatterns down to 40 nm. Meanwhile, the AFM-tip lifetime has been increased substantially. In particular, the adhesion between the PMMA layer on the edge of trenches and the substrate is significantly improved to enable reliable pattern transfer into GaAs/AlGaAs heterostructures by wet-chemical etching. Functional nanodevices with a lateral feature size of 100 nm to an etching depth of 70 nm are demonstrated using the method.

Self-Assembled Ferrimagnet−Polymer Composites for Magnetic Recording Media

A self-assembled magnetic recording medium was created using colloidal ferrimagnetic building blocks. Monodisperse cobalt ferrite nanoparticles (CoFe(2)O(4)) were synthesized using solution-based methods and then stabilized in solution using the amphiphilic diblock copolymer, poly(acrylic acid)-b-poly(styrene) (PAA-PS). The acid groups of the acrylate block bound the polymer to the nanoparticle surface via multivalent interactions, while the styrene block afforded the magnetic nanoparticle--polymer complex solubility in organic solvents. Moreover, the diblock copolymer improved the colloidal stability of the ferrimagnetic CoFe(2)O(4) nanoparticles by reducing the strong interparticle magnetic interactions, which typically caused the ferrimagnetic nanoparticles to irreversibly aggregate. The nanoparticle--polymer complex was spin-coated onto a silicon substrate to afford self-organized thin film arrays, with the interparticle spacing determined by the molecular weight of the diblock copolymer. The thin film composite was also exposed to an external magnetic field while simultaneously heated above the glass transition temperature of poly(styrene) to allow the nanoparticles to physically rotate to align their easy axes with the direction of the magnetic field. In order to demonstrate that this self-assembled ferrimagnet--polymer composite was suitable as a magnetic recording media, read/write cycles were demonstrated using a contact magnetic tester. This work provides a simple route to synthesizing stabilized ferrimagnetic nanocrystals that are suitable for developing magnetic recording media.

Synthesis and characterization of polyhedral oligomeric silsesquioxane (POSS) with multifunctional benzoxazine groups through click chemistry

We prepared a new class of polybenzoxazine-POSS nanocomposites with network structures through thermal curing of multifunctional benzoxazine groups of POSS (OBZ-POSS), which was synthesized from octa-azido functionalized POSS (OVBN3-POSS) with 3,4-dihydro-3-(prop-2-ynyl)-2H-benzoxazine (P-pa) via a click reaction. Incorporation of the silsesquioxane core into the polybenzoxazine matrix could significantly enhance the thermal stability of these hybrid materials. For these nanocomposites, the POSS nanoparticles in the hybrids were improved their thermal properties with 2,2-bis(3,4-dihydro-3-methyl-2H-1,3-benzoxazine)propane (BA-m) and P-pa polybenzoxazine, analyzed via TGA analyses. In addition, the incorporation of the POSS led to the formation of an inorganic protective layer on the nanocomposite’s surface. Contact angle data provided positive evidence to back up this hypothesis that the incorporation of the POSS units would decrease the surface energy property. In addition, the low glass transition temperature of poly(4-vinyl pyridine) and polycarbonate thin films, which lack liquid resistance, could possess low surface free energy after modification with OBZ-POSS due to low temperature curing of this new compound.

Poly(amideimide)s containing pendant pentadecyl chains: Synthesis and characterization

A new aromatic diacylhydrazide monomer viz., 4-[4′-(hydrazinocarbonyl)phenoxy]-2- pentadecylbenzohydrazide was synthesized starting from cardanol, which in turn is obtainable from cashew nut shell liquid – a renewable resource material. A series of new poly(amideimide)s containing flexibilizing ether linkages and pendant pentadecyl chains was synthesized from 4-[4′-(hydrazinocarbonyl)phenoxy]-2-pentadecylbenzohydrazide and commercially available aromatic dianhydrides, viz., benzene-1,2,4,5-tetracarboxylic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, benzophenone-3,3′,4,4′-tetracarboxylic dianhydride, 4,4′-oxydiphthalic anhydride and 4,4′-(hexafluoro isopropylidene)diphthalic anhydride by a two-step solution polycondensation in N,N-dimethylacetamide via the poly(hydrazide acid) intermediate. Inherent viscosities of poly(amideimide)s were in the range 0.60–0.64 dL/g in N,N-dimethylacetamide at 30 ± 0.1 °C. Poly(amideimide)s could be solution cast into tough, transparent and flexible films from their N,N-dimethylacetamide solutions. The solubility of poly(amideimide)s was significantly improved by incorporation of pendant pentadecyl chains and were found to be soluble in N,N-dimethylacetamide, 1-methyl-2-pyrrolidinone, pyridine and m-cresol at room temperature or upon heating. Wide angle X-ray diffraction patterns of poly(amideimide)s revealed a broad halo at around 2 θ = ∼19° suggesting that polymers were amorphous in nature. In the small-angle region, diffuse to sharp reflections of a typically layered structure resulting from the packing of pentadecyl side chains were observed. The temperature at 10% weight loss ( T 10), determined by TGA in nitrogen atmosphere, of poly(amideimide)s was in the range of 388–410 °C indicating their good thermal stability. Glass transition temperatures of poly(amideimide)s were in the range 162–198 °C. It was observed that the plasticization effect of attached pentadecyl side chains induced the depression of T g .

Predicting the effect of dissolved carbon dioxide on the glass transition temperature of poly(acrylic acid)

AbstractThe morphology and size of poly(acrylic acid) (PAA) particles produced by precipitation polymerization in supercritical CO2 (scCO2) depends on the glass transition temperature (Tg) of the polymer at reaction conditions. In this study, the use of the Sanchez–Lacombe equation of state (SL‐EOS), in conjunction with Chow's equation, to predict the effect of CO2 pressure on the Tg of PAA was evaluated. Characteristic parameters for PAA were determined by fitting density data. Characteristic parameters for CO2 were determined by fitting density data in the supercritical region. When the SL‐EOS was used in a purely predictive mode, with a binary interaction parameter (ψ) of 1, the solubility of CO2 in PAA was underestimated and Tg was overestimated, although the trend of Tg with CO2 pressure was captured. When was determined by fitting the SL‐EOS to the measured sorption of scCO2 in PAA, the calculated Tg's agreed very well with measured values. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

9,10-Diphenylanthracene-containing poly(arylene ether sulfone)s with improved glass transition temperature and photocrosslinking properties

In this study, novel poly(arylene ether sulfone)s containing 9,10-diphenylanthracene units were synthesized and their thermal and optical properties were investigated. This new bisphenol monomer, 9,10-bis(4-hydroxyphenyl)anthracene, was facially synthesized in two steps and showed similar reactivity for SNAr reactions as other bisphenol monomers, such as bisphenol A. The introduction of an anthracene unit to poly(arylene ether sulfone)s can obviously improve glass transition temperature and retain good solubility and high decomposition temperatures. The glass transition temperature of poly(arylene ether sulfone) reached up to 265 °C when the bisphenol A was entirely substituted by bis(4-hydroxyphenol)anthracene. These polymers are soluble in chloroform, N,N-dimethylformamide and N-methyl-2-pyrrolodone and can be film-formed through spin-coating. Interestingly, anthracene units endowed these polymers with photocrosslinkable properties and further improved their thermal stability.

Tack and viscoelastic properties of an acrylic block copolymer/tackifier system

The role of tackifier in a pressure sensitive adhesive tape was investigated. For this purpose, a model pressure sensitive adhesive was prepared using an acrylic block copolymer consisting of poly(methyl methacrylate) and poly(butyl acrylate) as base polymer and a tackifier. The poly(butyl acrylate) oligomer was also used as a diluent to compare the effect on the adhesion properties. Tack was measured using a rolling tack tester in wide temperature and rolling rate ranges, and the master curve was made in accordance with the time–temperature superposition law. The tack increased and the failure mode varied from cohesive failure to interfacial failure with an increase in the rolling rate. The tack was higher in the tackifier added system than in the oligomer added system. From a dynamic mechanical analysis, the modulus at high temperature decreased by the addition of both tackifier and oligomer, however, the glass transition temperature of poly(butyl acrylate) and the modulus at low temperature increased only by the addition of tackifier. The dynamic viscoelastic properties were measured in wide temperature and frequency ranges, and the master curve was also made. The viscoelastic properties varied in the order of viscosity, rubbery and glassy with an increase in the deformation rate. It was clarified that the tack value and the failure mode were strongly dependent upon the viscoelastic properties of adhesive. Both tackifier and oligomer improves the mobility of base polymer, whereas, only tackifier increases the cohesive strength of base polymer.

Surface Trimer Removal of Polyester Fibers by Ozone Treatment

The oxidative ozone treatment of poly (ethylene terephthalate) fibers after dyeing was recently proposed as a novel afterclearing method. High fastness properties, energy and time savings, and environmental benefits were reported by the ozone treatment compared to the conventional reduction clearing. This study investigated the efficiency of the ozone treatment afterclearing process on the surface trimer removal of poly(ethylene terephthalate) fibers. Results indicated similar cyclic trimer [(GT)3] removal rates after 1 min ozone treatment when compared to the conventional reduction clearing; the removal rates increased at 3 min ozone treatment time. The migration rate of the cyclic trimers [(GT)3] out of the fibers was also investigated as a function of temperature and a sudden increase was observed after second glass transition temperature of poly (ethylene terephthalate) fibers rather than a linear increase.

Note on the glass transition temperature of Poly(vinylphenol)

Critical overview of literature data on the glass transition temperature T g of poly(4-vinylphenol) PVPh revealed a large scatter of values ranging between 53 and 194 °C, which can only partially be attributed to molecular-mass effect. The reason could be seen in residual moisture and/or solvent in samples subjected to insufficient or even no drying. Based on selected two thirds of literature data, a regression equation is proposed for the dependence of T g on 1/ M n. Two samples of commercial PVPh ( M n 11,500; M w 22,100) and ( M n 19,700; M w 40,900) were studied by DSC, ATR-FTIR, and SEC methods. A procedure of preparing well defined samples is proposed: PVPh vacuum-dried at 140 °C for 24 h is dissolved in tetrahydrofuran and precipitated in hexane. The precipitate is vacuum-dried at 40 °C for 24 h, weighed into a pierced DSC pan. After final vacuum drying at 140 °C for 24 h, the sample is analyzed. The PVPh samples treated in this way showed T g of 175.0 °C and 179.6 °C, respectively.

Radical Polymerization of Novel N-Substituted-N-vinylacetamides and Regulated Polymer Structures by Bulky Substituents and Menthol Coordination

N-(p-Methoxybenzyl)-N-vinylacetamide (1), N-(3,3-diphenylpropyl)-N-vinylacetamide (2), and N-(3-phenylpropyl)-N-vinylacetamide (3) were synthesized as novel N-substituted-N-vinylacetamides to investigate polymerizabilities and stereochemistries on polymer main chains by introducing bulky substituents. Polymer was not obtained from 1 with a radical method; however, 2 and 3 gave rise to hexane-insoluble polymers during bulk polymerization with 14% and 84% yields, respectively, implying that alkyl spacers were necessary between amide and phenyl groups. When 3 was polymerized with menthol at 0 °C, both 1H NMR and 13C NMR spectroscopies demonstrated sharper spectral patterns than those of poly(3) obtained at 60 °C. Since menthol coordinates with 3 at room temperature as shown by 1H NMR spectroscopy, combinations of additive coordination and substituent bulkiness would be effective approaches to produce regulated polymer structures. Glass transition temperatures of poly(3)s also varied from 54 to 67 °C, dependi...

Nanoscale mechanical measurement determination of the glass transition temperature of poly(lactic acid)/everolimus coated stents in air and dissolution media

Localized atomic force microscopy (AFM) force analysis on poly(lactic acid) (PLA) and poly(lactic acid)/everolimus coated stents has been performed under ambient conditions. Similar Young's modulus were derived from both PLA and PLA/everolimus stent surface, namely 2.25 ± 0.46 and 2.04 ± 0.39 GPa, respectively, indicating that the drug, everolimus does not significantly effect the mechanical properties of PLA up to a 1:1 (w/w) drug loading. Temperature controlled force measurements on PLA only coated stents in air and in a 1% Triton surfactant solution allowed the glass transition temperature ( T g) of the polymer to be determined. A significant drop of the Young's modulus in solution was observed at 36 °C, suggests that in vivo the T g of the polymer is below body temperature. The possible consequences on drug release and the mechanisms by which this may occur are considered.

High glass transition temperatures of poly(methyl methacrylate) prepared by free radical initiators

PMMA samples were prepared with different free radical initiators, and it was found that samples from tert-butyloxy radicals have a higher Tg. The viscosity–molecular weight study showed that the PMMA with lower Tg has higher viscosity than that of the PMMA with higher Tg when they have the same molecular weight. This indicated that when MMA is polymerized with tert-butyloxy radicals some branched polymers were produced, which resulted in the decreased segmental mobility of the polymer chain and an increased Tg.