Molecular Weight and Dispersity Affect Chain Conformation and pH-Response in Weak Polyelectrolyte Brushes

2021 ◽  
Author(s):  
Tzu-Han Li ◽  
Megan L. Robertson ◽  
Jacinta C. Conrad
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Degree Of Polymerization ◽  
Chain Conformation ◽  
Average Degree ◽  
Polyelectrolyte Brushes ◽  
Ph Response ◽  
The Impact

The impact of brush molecular weight distribution on the conformation and response of weak polyacid brushes was investigated. We show that weight-average degree of polymerization (N_w) and dispersity (Ð) alter...

Study on the Molecular Structure and the Performance of PE100 Resin for Tubing

2013 ◽  
Vol 850-851 ◽  
pp. 70-73
Author(s):  
Hua Wang ◽  
Hao Dong Song ◽  
En Guang Zou ◽  
Teng Jie Ge ◽  
Hong Fang
Keyword(s):  
Molecular Structure ◽  
Molecular Weight ◽  
Impact Strength ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Bending Strength ◽  
The Impact

The performance of JHMGC100S, a kind of HDPE for pipe, was studied, and the comparison with other typical PE100 resin in China and abroad was also did. The results show that: the impact strength of JHMGC100S was higher than other samples, and the bending strength was almost the same; the molecular weight distribution was obvious bimodal; the processability of JHMGC100S was good, and the hydrostatic strength of the pipe which was produced by JHMGC100S fulfilled the rule in GB/T 15558.1-2003.

The impact of ionic strength on the molecular weight distribution (MWD) of lignin dissolved during softwood kraft cooking in a flow-through reactor

Holzforschung ◽  
2016 ◽  
Vol 70 (6) ◽  
pp. 495-501 ◽  
Author(s):  
Binh T.T. Dang ◽  
Harald Brelid ◽  
Hans Theliander
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Average Molecular Weight ◽  
Ion Concentration ◽  
Small Scale ◽  
Kraft Cooking ◽  
Flow Through ◽  
Cooking Times ◽  
The Impact

Abstract The molecular weight distribution (MWD) of dissolved lignin as a function of time during kraft cooking of Scots pine (Pinus silvestris L) has been investigated, while the influence of sodium ion concentration ([Na+]) on the MWD was in focus. The kraft cooking was performed in a small scale flow-through reactor and the [Na+] was controlled by the addition of either Na2CO3 or NaCl. Fractions of black liquors (BL) were collected at different cooking times and the lignin was separated from the BL by acidification. The MWD of the dissolved lignin was analyzed by GPC. Results show that the weight average molecular weight (Mw) of dissolved lignin increases gradually as function of cooking time. An increase of [Na+] in the cooking liquor leads to Mw decrement. Findings from cooks with constant and varying [Na+] imply that the retarding effect of an increased [Na+] on delignification is related to the decrease in lignin solubility at higher [Na+].

Controlled/‘living’ polymerization methods

2004 ◽  
Author(s):  
Wayne Hayes ◽  
Steve Rannard
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Chain Transfer ◽  
Living Polymerization ◽  
Degree Of Polymerization ◽  
Polymer Chains ◽  
Chain Growth ◽  
Living Polymerizations ◽  
Living Nature

Chain-growth polymerizations such as free-radical polymerizations are characterized by four key processes:(i) initiation, (ii) propagation, (iii) chain transfer, and (iv) termination. If it is possible to minimize the contribution of chain transfer and termination during the polymerization, it is possible to achieve a level of control over the resulting polymer and achieve a predetermined number average molecular weight and a narrow molecular weight distribution (polydispersity). If such an ideal scenario can be created, the number of polymer chains that are produced is equal to the number of initiator groups; the polymerization will proceed until all of the monomer has been consumed and the polymer chain ends will remain active so that further addition of monomer will lead to continued polymerization. This type of polymerization was termed a ‘living’ polymerization by Szwarc in 1956 and represents one of the ultimate goals of synthetic polymer chemists. Flory determined that in the absence of termination, the number of propagating polymer chains must remain constant and that the rate of polymerization for each growing chain must be equal. In this situation, the number average degree of polymerization (DPn) and hence the molecular weight of the polymer can be predicted by simple consideration of the monomer to initiator ratio (see eqns (1) and (2), respectively). Several key criteria are used to elucidate the ‘living’ nature of a polymerization. For a polymerization to be considered ‘living’, the rate of initiation must exceed the rate of propagation. Therefore, all the propagating polymer chains are formed simultaneously and grow at the same rate. If this situation did not occur, the first chains formed would be longer than those initiated later and the molecular weight distribution of the propagating chains would broaden. In addition, an ideal ‘living’ or ‘immortal’ polymerization must not exhibit any termination of the propagating polymer chains over the lifetime of the reaction. Consequently, ‘living’ polymerizations are characterized by very narrow molecular weight distributions (Mw/Mn < 1.2).

Substrate-Dependent Features of Polyethylene Oxide (Peo) Adsorption from Aqueous Solution: Competitive Adsorption Versus Surface Relaxations

1994 ◽  
Vol 366 ◽  
Author(s):  
M. M. Santore ◽  
V. A. Rebar
Keyword(s):  
Aqueous Solution ◽  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Polyethylene Oxide ◽  
Weight Distribution ◽  
Adsorption Process ◽  
Polymer Concentration ◽  
Hydroxyethyl Cellulose ◽  
Total Internal Reflectance ◽  
The Impact

ABSTRACTThis work employed total internal reflectance fluorescence (TIRF) to examine the adsorption kinetics of polyethylene oxide (PEO) on silica from aqueous solution in controlled shearing flow. Studies with PEO, fluorescently labeled such that TIRF tracked the chain number on the surface, exhibited an overshoot in the early stages of adsorption. This overshoot was not seen with other polymers such as polyvinyl alcohol, and hydroxyethyl cellulose, possibly because these other polymers were labeled such that TIRF measured the interfacial mass. Indeed, reflectometry studies of PEO adsorption, sensitive to interfacial mass, showed no overshoot. This suggests that the overshoot results from the selectivity of the surface for high molecular weight populations within a polydisperse sample. Initially short chains adsorb because they diffuse to the surface quickly. At longer times, higher molecular weight chains reach the surface and replace the short chains. This evolution occurs as the mass coverage increases (according to reflectivity) but the number of adsorbed chains, and hence the TIRF signal decrease at long times. A study of the impact of the molecular weight distribution confirmed this hypothesis.Several complications to the molecular weight selectivity hypothesis, however, arose: First, the same PEO samples which overshot during adsorption on silica showed no overshoot on a polystyrene substrate. This suggested that the ability to overshoot was governed by the substratesegment interactions, even though the molecular weight distribution within the sample determined the overshoot shape. Further, the effect of transport conditions (wall shear rate, bulk polymer concentration) were not completely consistent with the molecular weight competition hypothesis, which was based on surface-solution equilibrium, taking into account transport-limited rates of adsorption. Finally certain runs, where the adsorption process was interrupted by solvent flow and later allowed to proceed, never reached the full coverage seen for uninterrupted runs. Hence, the surface coverage and possibly the chain configurations can depend on the history of the adsorption process, a feature which points to surface relaxations and non-equilibrium structures.

Production of hemicellulose oligomers from softwood chips using autohydrolysis followed by an enzymatic post-hydrolysis

Holzforschung ◽  
2017 ◽  
Vol 71 (7-8) ◽  
pp. 575-581 ◽  
Author(s):  
Vivien Deloule ◽  
Christine Chirat ◽  
Claire Boisset ◽  
Bertrand Toussaint ◽  
Jadwiga Chroboczek
Keyword(s):  
Molecular Weight ◽  
Chemical Composition ◽  
Enzymatic Hydrolysis ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Value Added ◽  
Degree Of Polymerization ◽  
Water Soluble ◽  
Time Parameters ◽  
Temperature Time

AbstractIn the context of value added valorization of hemicelluloses (HCs), their soft extraction by autohydrolysis (AH) of softwood (SW) chips has been optimized via the temperature/time parameters (170°C/2 h, 170°C/1 h and 150°C/1 h). Two enzyme mixtures containing mainly a glucanase and a mannanase were used to decrease the degree of polymerization (DP) of the extracted HCs. Hydrolysates containing HCs were analyzed in terms of monomers and oligomers, molecular weight distribution (MWD) and chemical composition. The MW was strongly dependent on AH conditions: most of the water-soluble HCs with 1800 Da MW were obtained at 150°C/1 h. The parameters 170°C/2 h gave rise to MWs<1800 Da. Enzymatic hydrolysis (EH) reduced efficiently the DP of HCs, and the glucosidase was more efficient than the mannanase, but the former also hydrolyzed more oligomers into their monomeric components.

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