Effect Of Polymer Microstructure Research Articles

Wetting characteristics of polymer adhesives with different chain bending stiffness

Polymer adhesives are widely used in daily applications and in industry owing to their flexibility and overall non-toxicity, particularly in interfacial adhesion. The spreading of polymer adhesives on adherend is one of the essential considerations for the interfacial adhesion of polymer adhesives, which is strongly related to their wetting behaviors. While relationships between polymer microstructure and adhesion have been investigated in previous studies, it remains challenging to unveil the effect of polymer microstructure on wettability. To address this issue, here we utilize coarse-grained molecular dynamics (CGMD) simulations to systematically elucidate how the wettability of a polymer adhesive droplet on a surface depends on bending stiffness. The wetting dynamics and the contact angle are studied to show the evolution of morphology of droplets during the wetting process. The results indicate the wettability is weakened by the increase of bending stiffness of polymer chain. Detailed thermodynamic property analysis is further conducted, revealing that the adhesion between the polymer droplet and substrate deteriorates due to the decline of wettability. Interestingly, we observe such deterioration becomes more significant by both increasing the temperature and decreasing the bending stiffness. Our study sheds light on the dependence of chain bending stiffness and temperature on the wetting behavior of polymer adhesive droplets, and offers insights, which, upon experimental validation can then be used for the design of adhesives or hydrogels.

Effect of polymer microstructure on the docetaxel release and stability of polyurethane formulation

PurSil®AL20 (PUS), a copolymer of 4,4′-dicyclohexylmethane diisocyanate (HMDI), 1,4-butane diol (BD), poly-tetramethylene oxide (PTMO) and poly-dimethyl siloxane (PDMS) was investigated for stability as a vehicle for Docetaxel (DTX) delivery through oesophageal drug eluting stent (DES). On exposure to stability test conditions, it was found that DTX release rate declined at 4 and 40°C. In order to divulge reasons underlying this, changes in DTX solid state as well as PUS microstructure were followed. It was found that re-crystallization of DTX in PDMS rich regions was reducing the drug release at both 4°C and 40°C samples. So far microstructural features have not been correlated with stability and drug release, and in this study we found that at 40°C increase in microstructural domain sizes and the inter-domain distances (from ∼85Å to 129Å) were responsible for hindering the DTX release in addition to DTX re-crystallization.

Effect of Polymer Microstructure on the Nucleation Behavior of Alumina via Atomic Layer Deposition

Atomic layer deposition is a technique that is able to integrate nanoscale inorganic coatings to organic polymers. Through this process a number of different inorganic coating morphologies are able to form during ALD nucleation on a wide variety of polymers. In this work, we provide a systematic analysis of the ALD nucleation characteristics on polymers that have subtle variations in microstructure, such as, the addition of pendant groups or change in length of the polymer repeat unit. Specifically, in situ quartz crystal microgravimetry is employed to understand the nucleation behavior of alumina ALD in a series of poly n-methacrylate and polyester thin films. The work indicates the effect that a subtle change in polymer microstructure has on the properties of the polymer film. The data indicates that the glass transition temperature of the polymer, as influenced by variations in microstructure, has a significant impact on the absorption/desorption characteristics during TMA/water exposures. Through this...

Polyethylene and poly(ethylene-co-1-octadecene) composites with TiO2 based nanoparticles by metallocenic “in situ” polymerization

Ethylene homopolymer and ethylene-co-1-octadecene copolymers with 0.063 mol/L (LLDPE-1) and 0.38 mol/L (LLDPE-2) were synthesized by a metallocenic catalyst in the presence of titanium dioxide (TiO2) nanoparticles (∼10 nm), producing “in situ” composites. The TiO2 nanoparticles synthesized by the sol–gel method were used either as-synthesized or modified organically on the surface with hexadecyltrimethoxysilane (Mod-TiO2), with a final concentration in the polymers of 3 and 5 wt%. For polymerizations without nanoparticles, the catalytic activity increased with the incorporation of the octadecene as compared with ethylene homopolymerization. Moreover, the surface functionality of nanoparticles and the presence of a comonomer had some influence on the catalytic behavior, resulting in greater activity when Mod-TiO2 was used than that obtained with TiO2 or the pure system when ethylene is homopolymerized. In copolymerization, an effect on the catalytic behavior was not observed. The dispersion of the nanoparticles was studied by transmission electron microscopy (TEM). There was better dispersion when Mod-TiO2Nps were incorporated into PE, although for LLDPE-2/TiO2 nanocomposites the nanoparticles were not well distributed and certain agglomeration zones were mainly observed. Regarding the thermal properties of the composites, the incorporation of the nanoparticles enhanced the thermal stability of the polymers, increasing by ca. 25 °C the maximum decomposition temperature of the matrix as compared with virgin polymers. The final effect of the nanoparticles on the mechanical properties will depend on the matrix used. The addition of TiO2 nanoparticles did not modify the mechanical properties of the PE/TiO2 and LLDPE-1/TiO2 (low octadecene incorporation) matrix, although in polymers with high comonomer incorporation (LLDPE-2/TiO2) an increase of Young's modulus and yield stress by ca. 50% was achieved compares to neat copolymer (LLDPE-2). Our results give relevant information about the effect of polymer microstructure and of the surface functionality of nanoparticles on the catalytic system and on the final properties for in situ composites. The morphology of the nanocomposites was also studied, and it was found that the presence of particles in the PE increased the number of spherulites, therefore the nanoparticles act as nucleating agents. The dynamic–mechanical properties confirm the effect on the mechanical behavior of nanocomposites, that nanoparticles only affect the storage modulus (E′) of the LLDPE-2 matrix.

The Effect of Polymer Microstructure and Thermal Post‐Treatment on Latex‐Based Pressure Sensitive Adhesive Performance

AbstractSummary: Butyl acrylate/acrylic acid/2‐hydroxyl methacrylate (BA/AA/HEMA, weight ratio: 96/2/2) latexes were produced via starved seeded semi‐batch emulsion polymerization. The microstructure of the latex polymers was controlled by varying the amount of chain transfer agent (1‐dodecanethiol). The latexes were characterized for gel content, Mc (molecular weight between two adjacent cross‐linking points), Mw (molecular weight of sol polymers) and Me (molecular weight between entanglements). From these latexes, PSA films were cast, dried, conditioned and then thermally post‐treated at 120 °C to react the carboxyl and hydroxyl groups from the AA and HEMA units. Tack, peel strength and shear strength of the PSA films were then measured. The thermal post‐treatment was shown to be an effective way to improve latex‐based PSA performance. The effectiveness of the post‐treatment was observed to depend on the polymer microstructure (Mc relative to Me relative to Mw) of the untreated latex‐based PSAs and on the gel content.

Effect of composition on the solution rheology of stearyl methacrylate‐co‐styrene‐co‐vinyl pyrrolidinone in paraffinic base oil

AbstractThe rheological behavior of dilute and semi‐dilute solutions of stearyl methacrylate‐co‐styrene‐co‐vinyl pyrrolidinone copolymers (SMA‐S‐VP) was investigated over a wide range of temperatures (20–140°C) under steady shear (0.1–5000 s−1) and dynamic conditions (0.01–500 rad/s). The solvent used was polyalpha olefin, PAO4 (C20‐C40 fraction), a fully synthetic paraffinic oil normally used as base oil for lubricant oil formulations. The investigation focuses on the effect of the polar comonomer segment content, of the copolymer, on the viscosity‐temperature relationship of the solution. This information provides insight into the effect of polymer microstructure on the viscosity index (VI) behavior of the lubricant. Copolymers with different ratios of stearyl methacrylate, styrene and vinyl pyrrolidinone were synthesized by solution radical polymerization. The microstructure and molecular weight of the copolymers were evaluated by nuclear magnetic resonance spectroscopy (NMR). The molecular weight and polydispersity of the polymers were determined using GPC. The polymer solutions exhibit non‐Newtonian behavior, which is more evident at lower temperatures and higher concentrations. The temperature‐concentration superposition principle developed by Ferry (1) was applied to steady shear data and the resulting master curve was fitted to the Carreau model. A modified Fedors equation for intrinsic viscosity calculation, at low and moderate polymer solution concentrations, was used. The results confirm that the viscosity index improver properties (VII) of the copolymer are superior when the VP content is low. The polymer‐solvent interactions and solvency power of PAO4 were analyzed using an Arrhenius expression. The results show that at low VP content, PAO4 is a better solvent for the copolymer. Polym. Eng. Sci. 44:736–748, 2004. © 2004 Society of Plastics Engineers.

Synthesis, Thermal and Mechanical Properties of Poly(methylphenylsilmethylene)s

The synthesis, thermal and mechanical properties of poly(methylphenylsilylmethylene)s (PMPSMs) were investigated focusing on the effect of polymer microstructure on these properties. Stereoisomers of 1,3-dimethyl-1,3-diphenyl-1,3-disilacyclobutane were used as monomers to provide a series of PMPSMs having different molecular weights and tacticities. The monomers easily underwent bulk polymerization without catalyst as well as catalytic polymerization in the presence of Pt or Rh compounds to give high molecular weight PMPSMs. It is suggested by the 13C NMR analysis that the stereochemical configuration of the starting material may be retained during polymerization. 13C NMR spectrometry was also utilized to calculate the meso dyad content (Xm) which is regarded as a measure of the polymer tacticity. According to the relationship between Xm and the glass transition temperatures (Tgs) of PMPSMs, Tgs tend to decrease with increasing Xms. PMPSM showed the excellent thermostability represented in terms of the 5%...

Effect of polymer microstructure on solubility characteristics and interactions

The effect of polymer microstructure on the solubility characteristics and propensity for interactions of polybutadiene (PBD) has been studied by means of the general solvation equation using data reported by Alessi et al. An increase in the vinyl content from 8% to 69% did not affect the propensity of PBD to interact with π and n electron pairs and with dipolar — polarisable probes. In contrast, the hydrogen-bond basicity decreased due to steric hindrance from the alkene side group.

Effect of polymer microstructure on methyl group torsional vibrations

Fundamental torsional frequencies of methyl groups have been measured with neutron incoherent inelastic scattering for isotactic poly(methyl methacrylate)-COOCD 3, and heterotactic, syndiotactic and head-to-head isomers of poly(α-methylstyrene). The measurements confirm that the spectrum of isotactic PMMA differs considerably from the syndiotactic polymer in the region of the fundamental vibration, but no difference is found for the two stereoregular forms of poly(α-methylstyrene). However, the torsional frequency of the methyl group in the head-to-head configuration of α-methylstyrene lies at lower wavenumbers than that observed in the head-to-tail.

Pyrolysis-Gas Chromatography of Polyolefins

Parameters affecting the reproducibility of pyrolysis results have been examined; it was concluded that the Curie point pyrolyser should give the most reliable results. Such a pyrolyser was used to pyrolyse twenty polyolefins at temperatures in the range 480–770°C and the products of pyrolysis analysed by gas chromatography. Different classes of polyolefins produced characteristic pyrolysis patterns at any temperature in the range. However, the choice of pyrolysis temperature was found to be of major importance if homopolymers having very similar properties were to be unequivocally identified. The effect of polymer microstructure upon pyrolysis products was investigated by pyrolysing polyolefins having known degrees and types of branching, and unsaturation; here, results at the pyrolysis temperature of 480°C provided most information since higher temperatures caused greater fragmentation which tended to mask small differences in polymer microstructure.