Is Molecular Weight or Degree of Polymerization a Better Descriptor of Ultrasound-Induced Mechanochemical Transduction?

Simulations are employed to establish the feasibility of achieving controlled/living ethene polymerizations. Such simulations indicate that reversible addition–fragmentation chain transfer (RAFT) agents carrying a fluorine Z group may be suitable to establish control in high-pressure high-temperature ethene polymerizations. Based on these simulations, specific fluorine (F-RAFT) agents have been designed and tested. The initial results are promising and indicate that it may indeed be possible to achieve molecular weight distributions with a polydispersity being significantly lower than that observed in the conventional free radical process. In our initial trials presented here (using the F-RAFT agent isopropylfluorodithioformate), a correlation between the degree of polymerization and conversion can indeed be observed. Both the lowered polydispersity and the linear correlation between molecular weight and conversion indicate that control may in principle be possible.

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Study on MMA and BA Emulsion Copolymerization Using 2,4-Diphenyl-4-methyl-1-pentene as the Irreversible Addition–Fragmentation Chain Transfer Agent

Polymers ◽

10.3390/polym12010080 ◽

2020 ◽

Vol 12 (1) ◽

pp. 80

Author(s):

Zuxin Zhang ◽

Daihui Zhang ◽

Gaowei Fu ◽

Chunpeng Wang ◽

Fuxiang Chu ◽

...

Keyword(s):

Molecular Weight ◽

Tensile Properties ◽

Chain Transfer ◽

Monomer Conversion ◽

Degree Of Polymerization ◽

Polymerization Rate ◽

Chain Transfer Agent ◽

Regulation Mechanism ◽

Transfer Coefficients ◽

Emulsion Copolymerization

As a chain transfer agent, 2,4-diphenyl-4-methyl-1-pentene (αMSD) was first introduced in the emulsion binary copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA) based on an irreversible addition–fragmentation chain transfer (AFCT) mechanism. The effects of αMSD on molecular weight and its distribution, the degree of polymerization, polymerization rate, monomer conversion, particle size, and tensile properties of the formed latexes were systematically investigated. Its potential chain transfer mechanism was also explored according to the 1H NMR analysis. The results showed that the increase in the content of αMSD could lead to a decline in molecular weight, its distribution, and the degree of polymerization. The mass percentage of MMA in the synthesized polymers was also improved as the amounts of αMSD increased. The chain transfer coefficients of αMSD for MMA and BA were 0.62 and 0.47, respectively. The regulation mechanism of αMSD in the emulsion polymerization of acrylates was found to be consistent with Yasummasa’s theory. Additionally, monomer conversion decreased greatly to 47.3% when the concentration of αMSD was higher than 1 wt% due to the extremely low polymerization rate. Moreover, the polymerization rate was also decreased probably due to the desorption and lower reactivity of the regenerative radicals from αMSD. Finally, the tensile properties of the resulting polyacrylate films were significantly affected due to the presence of αMSD.

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Electron Microscope Analysis of the Surface Charge of Human Platelets; Stored and Aggregated by Polymeric Bases

10.1055/s-0039-1689362 ◽

1975 ◽

Author(s):

Y. Taketomi ◽

A. Ihara ◽

A. Kuramoto ◽

H. Uchino

Keyword(s):

Molecular Weight ◽

Sialic Acid ◽

Plasma Membranes ◽

Particle Density ◽

Average Distance ◽

Human Platelets ◽

Degree Of Polymerization ◽

Surface Coat ◽

Cationic Polymers ◽

Neuraminidase Treatment

The stainability of the surface coat of human platelets with positively charged colloidal Thorotrast was studied on the stored and aggregated platelets by some aggregating agents. During storage, the total sialic acid decreased and fell to 65% of initial value on 5th day. The sialic acid released from fresh platelets by neuraminidase treatment was 80% of the total. The density of Thorotrast particles on surface coat did not change during storage up to 7 days. These particles were abolished to some extent from the surface of neuraminidase treated platelets. These particle density did not change significantly in ADP and collagen induced aggregates but decreased in aggregates induced by cationic polymers such as protamine sulfate and polylysine. At the same concentration of polylysines of different degree of polymerization, maximal aggregation was greater with the higher molecular weight. Average distance between the plasma membranes of two adjacent cells in the aggregate was rather wider when the higher molecular weight polylysine was used.

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THE VISCOSITY – MOLECULAR WEIGHT RELATION FOR POLY-levo-2,3-BUTANEDIYL o-PHTHALATE

Canadian Journal of Research ◽

10.1139/cjr48b-084 ◽

1948 ◽

Vol 26b (12) ◽

pp. 783-797

Author(s):

R. W. Watson ◽

N. H. Grace

Keyword(s):

Molecular Weight ◽

High Purity ◽

Molecular Orientation ◽

Degree Of Polymerization ◽

Solution Viscosity ◽

Dilute Solution ◽

Molecular Weights ◽

Complex Relation ◽

End Group ◽

Long Chain

The inherent viscosities of dilute solutions of acidic polyesters of high purity have been compared with number average molecular weights accurately determined by end-group titration. For unfractionated resins with a degree of polymerization from 2 to 11 [Formula: see text] the viscosity – molecular weight relation is linear in chloroform at 25 °C. Where [Formula: see text], K = 1.923 × 10−5 and β = 0.0176. For fractionated polyesters from DP 5 to 8, K = 1.959 × 10−6 and β = 0.0161. For unfractionated resins with a DP > 11, molecular weights increase more rapidly than inherent viscosities. Above [Formula: see text] for fractionated resins linearity is resumed, and the slope increases. Several attempts have been made to explain this complex relation. Apparently the short chains remain linear, and the formation of anisotropic fibers at a DP close to 100 establishes a degree of molecular orientation in the long-chain superpolyesters. Isomerization of levo-diol to the diastereoisomer during polycondensation is without effect on the dilute solution viscosity of the resulting resin. Preferential degradation of the longer chains is assumed to be partially responsible for the decreasing slope from DP 11 to 65. As yet it has not been possible to assess the roles played by changes in size distribution, and variation in solvation with increasing chain length, but the data point to a curved viscosity – molecular weight relation in chloroform at 25 °C.

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The molecular-weight-dependence of the anti-coagulant activity of heparin

Biochemical Journal ◽

10.1042/bj1750691 ◽

1978 ◽

Vol 175 (2) ◽

pp. 691-701 ◽

Cited By ~ 197

Author(s):

T C Laurent ◽

A Tengblad ◽

L Thunberg ◽

M Höök ◽

U Lindahl

Keyword(s):

Molecular Weight ◽

Binding Sites ◽

Random Distribution ◽

Degree Of Polymerization ◽

Molecular Weight Range ◽

High Affinity ◽

Predicted Probability ◽

Coagulant Activity ◽

The Relationship ◽

Molecular Weight Fractions

It is proposed that the anti-coagulant activity of heparin is related to the probability of finding, in a random distribution of different disaccharides, a dodecasaccharide with the sequence required for binding to antithrombin. It is shown that this probability is a function of the degree of polymerization of heparin. The hypothesis has been been tested with a series of narrow-molecular-weight-range fractions ranging from 5,600 to 36,000. The fractions having mol.wts. below 18,000 (comprising 85% of the original preparation) followed the predicted probability relationship as expressed by the proportion of molecules capable of binding to antithrombin. The probability that any randomly chosen dodecasaccharide sequence in heparin should bind to antithrombin was calculated to 0.022. The fraction with mol.wt. 36,000 contained proteoglycan link-region fragments, which may explain the deviation of the high-molecular-weight fractions from the hypothetical relationship. The relationship between anti-coagulant activity and molecular weight cannot be explained solely on the basis of availability of binding sites for antithrombin. The activity of high-affinity heparin (i.e. molecules containing high-affinity binding sites for antithrombin), determined either by a whole-blood clotting procedure or by thrombin inactivation in the presence of antithrombin, thus remained dependent on molecular weight. Possible explanations of this finding are discussed. One explanation could be a requirement for binding of thrombin to the heparin chain adjacent to antithrombin.

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Poly(glycolide) multi-arm star polymers: Improved solubility via limited arm length

Beilstein Journal of Organic Chemistry ◽

10.3762/bjoc.6.67 ◽

2010 ◽

Vol 6 ◽

Cited By ~ 13

Author(s):

Florian K Wolf ◽

Anna M Fischer ◽

Holger Frey

Keyword(s):

Molecular Weight ◽

Ring Opening ◽

Biomedical Applications ◽

Weight Control ◽

Glycolic Acid ◽

Polymer Melt ◽

Degree Of Polymerization ◽

Star Block Copolymers ◽

Grafting From ◽

Low Solubility

Due to the low solubility of poly(glycolic acid) (PGA), its use is generally limited to the synthesis of random copolyesters with other hydroxy acids, such as lactic acid, or to applications that permit direct processing from the polymer melt. Insolubility is generally observed for PGA when the degree of polymerization exceeds 20. Here we present a strategy that allows the preparation of PGA-based multi-arm structures which significantly exceed the molecular weight of processable oligomeric linear PGA (<1000 g/mol). This was achieved by the use of a multifunctional hyperbranched polyglycerol (PG) macroinitiator and the tin(II)-2-ethylhexanoate catalyzed ring-opening polymerization of glycolide in the melt. With this strategy it is possible to combine high molecular weight with good molecular weight control (up to 16,000 g/mol, PDI = 1.4–1.7), resulting in PGA multi-arm star block copolymers containing more than 90 wt % GA. The successful linkage of PGA arms and PG core via this core first/grafting from strategy was confirmed by detailed NMR and SEC characterization. Various PG/glycolide ratios were employed to vary the length of the PGA arms. Besides fluorinated solvents, the materials were soluble in DMF and DMSO up to an average arm length of 12 glycolic acid units. Reduction in the T g and the melting temperature compared to the homopolymer PGA should lead to simplified processing conditions. The findings contribute to broadening the range of biomedical applications of PGA.

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METAL OXIDE TRIALKYLSILYLOXIDE POLYMERS (POLYTRIALKYLSILOXANOMETALLOXANES): PART I. TITANIUM OXIDE TRIMETHYLSILYLOXIDE POLYMERS

Canadian Journal of Chemistry ◽

10.1139/v63-089 ◽

1963 ◽

Vol 41 (3) ◽

pp. 629-635 ◽

Cited By ~ 13

Author(s):

D. C. Bradley ◽

C. Prevedorou-Demas

Keyword(s):

Molecular Weight ◽

Metal Oxide ◽

Titanium Oxide ◽

Degree Of Polymerization ◽

Average Degree ◽

Degree Of Hydrolysis ◽

Controlled Conditions

Tetrakis-(trimethylsilyloxy)-titanium Ti(OSiMe3)4 has been hydrolyzed under controlled conditions in dioxane. The initial products of hydrolysis undergo facile disproportionation, e.g. 3Ti2O(OSiMe3)6 → 4Ti(OSiMe3)4 + polymeric Ti2O3(OSiMe3)2. Molecular weight determinations were made on the titanium oxide trimethylsilyloxide polymers (polytrimethylsiloxanotitanoxanes) obtained by thermal disproportionation. Structures have been suggested for the polymers on the basis of the variation of number-average degree of polymerization with the degree of hydrolysis.

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Getting Graft Cellulose Copolymers and Acrylic Monomers

International Journal of Recent Technology and Engineering - 2 ◽

10.35940/ijrte.d6816.118419 ◽

2019 ◽

Vol 8 (4) ◽

pp. 719-723 ◽

Cited By ~ 2

Keyword(s):

Molecular Weight ◽

Graft Copolymerization ◽

Spectroscopic Studies ◽

Degree Of Polymerization ◽

Potassium Persulfate ◽

Water Soluble ◽

Active Centers ◽

Solvent Absorption ◽

Adsorption Interaction ◽

Acrylic Monomers

Graft copolymers of acrylic monomers with cotton cellulose were obtained. The dependence of the degree and efficiency of grafting of acrylic acid and methyl methacrylate to cellulose on the concentration of monomer and initiator was investigated. Pre-adsorption of the initiator in the macromolecules of cellulose leads to an increase in the efficiency of the grafting. The efficiency of grafting is higher in those systems in which the initiator used is insoluble in the monomer solvent. Absorption of cellulose with an aqueous solution of the initiator - potassium persulfate, followed by removal of water was done. The advantage of using a water-soluble initiator is that during subsequent processing with a solution of monomer in an organic solvent, the desorption of the active centers does not occur. An increase in the concentration of theinitiator leads to an increase in the degree of grafting, a slight increase in the efficiency of the grafting, a significant decrease in the degree of polymerization and the molecular weight of the graft chains. In a heterogeneous process, an increase in the efficiency of grafting with an increase in the concentration of theinitiator is promoted by the additional adsorption interaction of the initiator molecules with the surface of cellulose. With an increase in the concentration of monomers, the overall degree of conversion slightly increases, the efficiency of grafting slightly decreases, the degree of grafting and the molecular weight of the graft chains increase significantly. The mechanism of graft copolymerization was investigated by comparative analysis of the IR and PMR spectra of cellulose, potassium persulfate, acrylic monomers and products of their interaction. Due to the results of spectroscopic studies, a scheme of graft copolymerization reactions has been proposed. The active centers of graft copolymerization are formed as a result of the reductive interaction of potassium persulfate, water and cellulose macromolecules.

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Tuning the Properties of High Molecular Weight Chitosans to Develop Full Water Solubility Within a Wide pH Range

10.26434/chemrxiv.11854293.v1 ◽

2020 ◽

Author(s):

Anderson Fiamingo ◽

Sergio Paulo Campana Filho ◽

Osvaldo Novais Oliveira Junior

Keyword(s):

Molecular Weight ◽

Biomedical Applications ◽

Random Distribution ◽

Water Solubility ◽

Aqueous Media ◽

Degree Of Polymerization ◽

Molecular Weights ◽

H Nmr ◽

Wide Ph Range ◽

Ph Range

The preparation of chitosans soluble in physiological conditions has been sought for years, but so far solubility in non-acidic aqueous media has only been achieved at the expense of lowering chitosan molecular weight. In this work, we applied the multistep ultrasound-assisted deacetylation process (USAD process) to β-chitin and obtained extensively deacetylated chitosans with high molecular weights (Mw ≥ 1,000,000 g mol-1). The homogeneous N-acetylation of a chitosan sample resulting from three consecutive USAD procedures allowed us to produce chitosans with a high weight average degree of polymerization (DPw ≈ 6,000) and tunable degrees of acetylation (DA from 5 to 80%). N-acetylation was carried out under mild conditions to minimize depolymerization, while preserving a predominantly random distribution of 2-amino-2-deoxy-D-glucopyanose (GlcN) and 2-acetamido-2-deoxy-D-glucopyanose (GlcNAc) units. This close to random distribution, inferred with deconvolution of nuclear magnetic resonance (1H NMR) spectra, is considered as responsible for the solubility within a wide pH range. Two of the highly N-acetylated chitosans (DA ≈ 60 % and ≈ 70 %) exhibited full water solubility even at neutral pH, which can expand the biomedical applications of chitosans.

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Assessing wood pulp reactivity through its rheological behavior under dissolution

Cellulose ◽

10.1007/s10570-019-02750-0 ◽

2019 ◽

Vol 26 (18) ◽

pp. 9877-9888

Author(s):

Sara Ceccherini ◽

Thad Maloney

Keyword(s):

Molecular Weight ◽

Water Retention ◽

Wood Pulp ◽

Degree Of Polymerization ◽

Cellulose Dissolution ◽

Water Retention Value ◽

Cellulosic Fibers ◽

Measurement Protocol ◽

Convenient Approach ◽

Viscose Process

Abstract Recent years have witnessed an increasing interest in man-made cellulosic fibers, whose production generally requires cellulose dissolution and regeneration. Cellulosic fibers are difficult to dissolve. Thus, the recalcitrance of wood pulp can be an estimate of its reactivity. Pulp reactivity is usually assessed via complex and time-consuming laboratory simulations of the viscose process. This study proposes a faster and more convenient approach. The dissolution-based torque reactivity (DTR) test measures the evolution of the rheological properties of a pulp suspension under dissolution in cupriethylenediamine. Reactivity is quantified in terms of initial dissolution rates (IDR) and dissolution times (DT). This study describes the measurement protocol for the DTR test and its application to some commercial pulps and a series of pulps hornified to different extents. The IDR and DT values were compared with other pulp features, including degree of polymerization, molecular weight distribution, specific surface area and water retention value. The DTR test proved to be reasonably precise and fast to carry out. Graphic abstract

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