The Influence of Graft Length and Density on Dispersion, Crystallisation and Rheology of Poly(ε-caprolactone)/Silica Nanocomposites

Different techniques of grafting polymer chains to filler surfaces are often employed to compatibilise filler and polymer matrices. In this paper the influence of graft length and graft density on the state of dispersion, crystallisation and rheological properties of poly(ε-caprolactone) (PCL)/silica (SiO2) nanocomposites are reported. Grafted silica nanoparticles were prepared through polymerisation of PCL from the nanoparticle surface. Graft length was controlled by the reaction time, while the grafting density was controlled by the monomer-to-initiator ratio. Grafted nanoparticles were mixed with PCL of different molecular weights and the state of dispersion was assessed. Different matrix-to-graft molecular weight ratios resulted in different states of dispersion. Composites based on the higher molecular weight matrix exhibited small spherical agglomerates while the lower molecular weight matrix revealed more sheet-like microstructures. The state of dispersion was found to be relatively independent of graft length and density. Under quiescent conditions the grafts showed increased nucleation ability in the higher molecular weight PCL, while in the lower molecular weight matrix the effect was less pronounced. Rheological experiments showed an increase in viscosity with increased filler content, which was beneficial for the formation of oriented structures in shear-induced crystallisation.

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Permeability Enhancing and Chemotactic Activities of Lower Molecular Weight Degradation Products of Human Fibrinogen

Thrombosis and Haemostasis ◽

10.1055/s-0038-1650136 ◽

1981 ◽

Vol 45 (01) ◽

pp. 090-094 ◽

Cited By ~ 52

Author(s):

Katsuo Sueishi ◽

Shigeru Nanno ◽

Kenzo Tanaka

Keyword(s):

Molecular Weight ◽

Degradation Products ◽

Electron Microscopic Observation ◽

Chemotactic Activity ◽

Lower Molecular Weight ◽

Electron Microscopic ◽

Human Fibrinogen ◽

Rabbit Skin ◽

Molecular Weights ◽

Active Fragments

SummaryFibrinogen degradation products were investigated for leukocyte chemotactic activity and for enhancement of vascular permeability. Both activities increased progressively with plasmin digestion of fibrinogen. Active fragments were partially purified from 24 hr-plasmin digests. Molecular weights of the permeability increasing and chemotactic activity fractions were 25,000-15,000 and 25,000 respectively. Both fractions had much higher activities than the fragment X, Y, D or E. Electron microscopic observation of the small blood vessels in rabbit skin correlated increased permeability with the formation of characteristic gaps between adjoining endothelial cells and their contraction.These findings suggest that lower molecular weight degradation products of fibrinogen may be influential in contributing to granulocytic infiltration and enhanced permeability in lesions characterized by deposits of fibrin and/or fibrinogen.

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Water vapor induced self-assembly of islands/honeycomb structure by secondary phase separation in polystyrene solution with bimodal molecular weight distribution

10.26434/chemrxiv.14054033.v7 ◽

2021 ◽

Author(s):

Maciej Łojkowski ◽

Adrian Chlanda ◽

Emilia Choińska ◽

Wojciech Swieszkowski

Keyword(s):

Molecular Weight ◽

Phase Separation ◽

Molecular Weight Distribution ◽

Weight Distribution ◽

Self Assembly ◽

Secondary Phase ◽

Honeycomb Structure ◽

Polymer Chains ◽

Molecular Weights ◽

Secondary Phase Separation

The formation of complex structures in thin films is of interest in many fields. Segregation of polymer chains of different molecular weights is a well-known process. However, here, polystyrene with bimodal molecular weight distribution, but no additional chemical modification was used. It was proven that at certain conditions, the phase separation occurred between two fractions of bimodal polystyrene/methyl ethyl ketone solution. The films were prepared by spin-coating, and the segregation between polystyrene phases was investigated by force spectroscopy. Next, water vapour induced secondary phase separation was investigated. The introduction of moist airflow induced the self-assembly of the lower molecular weight into islands and the heavier fraction into a honeycomb. As a result, an easy, fast, and effective method of obtaining island/honeycomb morphologies was demonstrated. The possible mechanisms of the formation of such structures were discussed.

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Comparison of Electron and Infrared Spectroscopy with Thermal Analysis to Study Molecular Weight Effects in PVC-PMMA Blends

Applied Spectroscopy ◽

10.1366/0003702934334543 ◽

1993 ◽

Vol 47 (10) ◽

pp. 1636-1642 ◽

Cited By ~ 7

Author(s):

Cindy A. Burkhardt ◽

Joseph A. Gardella

Keyword(s):

Thermal Analysis ◽

Molecular Weight ◽

Differential Scanning Calorimetry ◽

Infrared Spectroscopy ◽

Lower Molecular Weight ◽

Scanning Calorimetry ◽

Molecular Weights ◽

Solvent Cast ◽

Pmma Blends

The effects of homopolymer molecular weight on the miscibility of PVC/PMMA solvent cast blends were studied. Two significantly different molecular weights were chosen for each of the homopolymers, and a series of blends was prepared from the four possible homopolymer-homopolymer combinations. Angle-dependent ESCA results suggest that the surfaces of the blends are enriched with PMMA. The extent of this enrichment is dependent on molecular weight, with the most enrichment seen in blends containing the lower-molecular-weight PMMA homopolymer. Differential scanning calorimetry (DSC) results are also presented.

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Statistical Treatments of Rubber Structure

Rubber Chemistry and Technology ◽

10.5254/1.3542244 ◽

1960 ◽

Vol 33 (5) ◽

pp. 1201-1217 ◽

Cited By ~ 4

Author(s):

J. Scanlan ◽

W. F. Watson

Keyword(s):

Molecular Weight ◽

Experimental Testing ◽

Polymer Structure ◽

Polymer Chains ◽

Molecular Weights ◽

Average Value ◽

Physical Form ◽

The Subject ◽

Branched Structures ◽

Mathematical Analyses

Abstract Chemical reactions are random in nature and can therefore be subjected to mathematical analyses based on probability theory. This is a particularly necessary approach to polymer structure in which the effect of chance inherent in the reactions is preserved in physical form and therefore much attention has been given to deductions from such treatments. It is the purpose of this paper to review the results of those investigations which have particular application to rubbery high polymers. Some emphasis will be given to the authors' view that experimental testing of the derived expressions is still far from being satisfactory and that the subject in spite of the effort expended is still only at its beginning. Consideration of details of polymer structure is not merely an academic exercise. The properties of raw rubbers are highly dependent on polymer chain length and for many important ones such as viscosity, either in solution or in the melt, the dependence is not simply linear. Unless linear dependence on the number of molecules and their size does apply, an average value of molecular weight is insufficient to characterize a rubber sample in respect of the property considered and further knowledge of the distribution of molecular weights among the rubber molecules is required. The properties of rubbers are also markedly influenced by the occurrence of branching in the polymer chains; the insolubility and elasticity conferred by vulcanization are the results of the formation of complex branched structures which have been the subjects for statistical treatments.

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The interplay between bi-modal molecular weight distribution in polystyrene and humidity induces self-assembly of biomimetic micropillars/honeycomb morphology in the thin polymer film

10.26434/chemrxiv.14054033.v5 ◽

2021 ◽

Author(s):

Maciej Łojkowski ◽

Adrian Chlanda ◽

Emilia Choińska ◽

Wojciech Swieszkowski

Keyword(s):

Molecular Weight ◽

Molecular Weight Distribution ◽

Weight Distribution ◽

Self Assembly ◽

Phase Segregation ◽

Polymer Chains ◽

Thin Polymer Film ◽

Chemical Compositions ◽

Molecular Weights ◽

The Right

Segregation of polymer chains of different molecular weights is a well-known process. A traditional experimental approach of studying phase segregation in thin films composed of polymer blends with identical chemical compositions but different molecular weights was focused on functionalisation of chemical group or modification of end-group. In this study, however, a different approach was proposed. Polystyrene with bimodal molecular weight distribution, but no additional chemical modification was used. The films were prepared by spin-coating and the segregation between polystyrene phases was investigated by force spectroscopy. The solubility of bimodal polystyrene was explored. At the right molecular weight distribution and soluted in Methyl Ethyl Ketone, the phase segregation occurred. Introduction of moist airflow induced the separation of the lower molecular weight into micropillars and the heavier fraction self-organized into a honeycomb. As a result, an easy, fast, and effective method of obtaining micropillar/honeycomb morphologies was demonstrated. The mechanism of formation of such structures was explained.

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Influence of Preparation Method and Molecular parameters on the Rheology of Model PEO/ Laponite Nanocomposites

MRS Proceedings ◽

10.1557/opl.2011.147 ◽

2011 ◽

Vol 1312 ◽

Author(s):

Jesmy Jose ◽

Abakar Adam Omar ◽

Guillaume Brotons ◽

Jean-François Tassin

Keyword(s):

Molecular Weight ◽

Preparation Method ◽

Low Frequency ◽

Elastic Solid ◽

Polymer Chains ◽

Correlation Peak ◽

Preparation Methods ◽

Molecular Weights ◽

Twin Screw ◽

High Concentrations

ABSTRACTModel polymer nanocomposites based on geometrically well defined and protected Laponite particles dispersed in Poly(ethylene oxide) were investigated in order to improve the understanding of the filler dispersion effects on rheology by varying two experimental factors, namely preparation method and PEO matrix molecular weight. Preparation methods are divided into a solution dispersion and a melt dispersion by twin screw extrusion. The linear viscoelastic properties of the samples prepared by solution method revealed an elastic solid like behaviour at Laponite weight fractions as low as 0.1%, dramatically lower than the percolation threshold so far reported for such kind of systems. The sample preparation by melt dispersion, although leading to dispersed particles, does not achieve the same levels of modulus as compared to solution prepared mixtures. We propose a qualitative interpretation of this phenomenon, based on the mixture between a liquid and a dispersed phase of rather solid character. Further experiments using small angle X-ray scattering techniques (SAXS) show that the modulus level is not necessarily related to the height of the correlation peak characteristic of the Laponite stacks. However, for samples prepared with varying PEO matrix molecular weight the fraction of Laponite stacks decreases with increasing PEO molecular weight. The rheology master curve analyses show that confinements of polymer chains arising from high concentrations of particles and high molecular weight matrix chains do not impact the level of the low frequency modulus. However, a slower polymer dynamics, as observed for higher molecular weights, leads to an increase of the modulus at low particle loadings.

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THE BUTYLLITHIUM-INITIATED POLYMERIZATION OF METHYL METHACRYLATE: PART II. MOLECULAR WEIGHT DISTRIBUTIONS

Canadian Journal of Chemistry ◽

10.1139/v63-281 ◽

1963 ◽

Vol 41 (8) ◽

pp. 1905-1910 ◽

Cited By ~ 24

Author(s):

B. J. Cottam ◽

D. M. Wiles ◽

S. Bywater

Keyword(s):

Molecular Weight ◽

Methyl Methacrylate ◽

Proton Magnetic Resonance ◽

Polymer Chains ◽

Double Peak ◽

Molecular Weights ◽

Molecular Weight Distributions ◽

Weight Distributions ◽

Before And After ◽

Made In

Samples of poly (methyl methacrylate) have been made in toluene solution at −30° C with n-butyllithium initiator. Different monomer and initiator concentrations were used to obtain products of different overall molecular weights; polymerization times were varied to achieve partial as well as complete polymerization. The polymer samples were divided into fractions which were examined as to molecular weight and microstructure. It was found that the whole polymers have unusually wide molecular weight distributions which can be attributed to a combination of two narrower distributions, one of which occurs at a low and the other at a higher molecular weight region. This "double peak" phenomenon was observed for polymers at lower conversions as well as for polymers representing complete conversion of monomer. Proton magnetic resonance measurements showed that the degree of isotacticity of various fractions of a whole polymer is not the same at all molecular weights.In one case a second portion of monomer was polymerized after the complete polymerization of a first portion. Comparison of the molecular weight distribution before and after the second addition of methyl methacrylate indicated that polymer chains in all molecular weight regions, above a very low minimum value, are capable of further addition of monomer.

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Organic–inorganic nanocomposites for shape memory effects

High Performance Polymers ◽

10.1177/0954008311424319 ◽

2011 ◽

Vol 23 (7) ◽

pp. 518-525 ◽

Cited By ~ 5

Author(s):

Cha Young Bae ◽

Hong Chae Park ◽

Byung Kyu Kim

Keyword(s):

Sol Gel ◽

Silica Particles ◽

Polymer Chains ◽

Silica Nanocomposites ◽

Molecular Weights ◽

Reinforcing Fillers ◽

Shape Memory Effects ◽

Cross Links ◽

Inorganic Nanocomposites ◽

Shape Fixity

Polyurethane (PU)–silica nanocomposites were synthesized by sol–gel reactions between the surface silanol groups of fumed silica and 3-aminopropyltriethoxysilane (APTES) terminated PU with a broad range of silica contents (1–5%) with two different molecular weights of PU. It was found that the silica particles that were incorporated into the polymer chains were well dispersed in the PU matrix and acted as multifunctional cross-links and reinforcing fillers; in addition, the silica particles augmented the initial and rubbery moduli, yield, and break strengths, as well as the glass transition temperature. Moreover, 98–99% shape fixity and shape recovery with minimum cyclic hysteresis were obtained with only 1% silica particle loading.

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Influence of Thermal Treatment on the Molecular Weights of Polyhydroxyalkanoate Containing 3-Hydroxyhexanoate

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.812.250 ◽

2013 ◽

Vol 812 ◽

pp. 250-253 ◽

Cited By ~ 3

Author(s):

Yoga Sugama Salim ◽

Chin Han Chan ◽

Kumar Sudesh ◽

Seng Neon Gan

Keyword(s):

Molecular Weight ◽

Thermal Treatment ◽

Gel Permeation Chromatography ◽

Polymer Processing ◽

Polymer Chains ◽

Molecular Weights ◽

Gel Permeation ◽

Ftir Spectrometer ◽

Major Reduction ◽

End Group

With blooming interests in the research of biodegradable polyesters produced from microorganisms as well as polymer processing and technology, this study is intended to reveal the influence of thermal treatment on the molecular weight of poly (3-hydroxybutyrate-co-3 mol% 3-hydroxyhexanoate)/P(3HB-co-3 mol% 3HHx), a copolymer of polyhydroxyalkanoates (PHA). P(3HB-co-3 mol% 3HHx) was thermally treated using Differential Scanning Calorimeter and analyzed using Gel Permeation Chromatography and Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) spectrometer. Results from gel permeation chromatography suggest a major reduction of molecular weight up to 50 % when P(3HB-co-3 mol% 3HHx) is exposed to 180 °C for 30 mins. The half-time degradation of P(3HB-co-3 mol% 3HHx) treated at 170 °C and 180 °C is 14.1 and 9.9 mins, respectively. FTIR spectroscopy shows an increase absorbance intensity of P(3HB-co-3 mol% 3HHx) after thermal treatment, indicating a formation of more alkenyl and carboxylic end-group in polymer chains due to random chain scissions.

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Exploiting the Interplay Between Bi-Modal Molecular Weight Distribution in Polystyrene and Humidity to Induce Self-Assembly of Biomimetic Micropillars/honeycomb Morphology in Thin Polymer Film

10.26434/chemrxiv.14054033.v1 ◽

2021 ◽

Author(s):

Maciej Łojkowski ◽

Adrian Chlanda ◽

Emilia Choińska ◽

Wojciech Swieszkowski

Keyword(s):

Molecular Weight ◽

Molecular Weight Distribution ◽

Weight Distribution ◽

Self Assembly ◽

Spin Coating ◽

Phase Segregation ◽

Polymer Chains ◽

Thin Polymer Film ◽

Chemical Compositions ◽

Molecular Weights

Segregation of polymer chains of different molecular weights is a well-known process. For many years, it was assumed that this process occurs over long-time intervals. On the contrary, solvent evaporation during spin-coating is very fast. A traditional experimental approach of studying phase segregation of thin films composed of polymer blends with identical chemical compositions but different molecular weights, was focused on functionalization of chemical group or modification of end-group. In this study however, a different approach was proposed, in which polystyrene with a bimodal molecular weight distribution but no additional chemical modification was implemented in order to examine and analyze its phase segregation. By doing this, we have presented an easy, fast, effective and fully controlled method of obtaining biomimetic micropillar/honeycomb morphologies. In addition, the evaporation rate during spin-coating and the viscosity of a solution with a bimodal molecular weight distribution was described.

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