The role of entanglements in network formation in unsaturated low density polyethylene

Smedberg, A.; Hjertberg, Thomas; Gustafsson, Bill

doi:10.1016/j.polymer.2004.05.005

Cited by 31 publications

(21 citation statements)

References 26 publications

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“…4 Equation (1) was also used because it implies the fewest assumptions, and because the contribution of entanglements to the modulus is difficult to quantify. 4,7,8 The values obtained were consistent with what might be expected from the model polymer. 1…”

Section: Dynamic Mechanical Thermal Analysis (Dmta)supporting

confidence: 86%

Mechanical property changes and degradation during accelerated weathering of polyester-urethane coatings

Skaja

Fernando

Croll

2006

J Coat. Technol. Res.

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Chemical changes, measured using spectroscopy, and crosslink density, measured by mechanical thermal analysis, were determined during accelerated weathering on a model polyester-urethane coating of known composition. The tensile modulus, measured above the glass transition temperature, and thus the crosslink density, decreased with exposure, as expected from the chemical changes. However, the tensile modulus, measured at room temperature, increased with exposure. Physical aging of the polymer network was found to occur concurrently with photodegradation and accounts for much of the increase in room temperature modulus. Increased hydrogen bonding in the increasingly oxidized polyesterurethane may also contribute to the increase in modulus at room temperature. Both physical and chemical changes must be determined if changes, and rates of change, in performance due to weathering are to be understood. C oatings are used in many applications and environments where high levels of durability are required. Often, the requirements include maintenance of appearance, barrier properties, toughness, etc. during exposure to natural weathering, which includes solar ultraviolet radiation, heat, moisture, and pollutants. In many cases, the lifetime of the coating is determined by a change in appearance, but crucial equipment may rely on the protective properties of the coating. However, understanding the relationship between coating composition and how it changes during exposure and how that is related to macroscopic end-use properties remains a fertile field of research. Many protective attributes of a coating can be related to its mechanical integrity, e.g., chemical and corrosion protection depend crucially on whether a coating remains intact and continuous during service. Cracks or adhesion failures due to in-service stresses immediately define the useful service life of a coating. These macroscopic failures are the accumulations of, or initiated by, the erosion processes that result from chemical changes during degradation.Understanding how the mechanical integrity of a coating, or any construction material, changes under exposure is very important. However, mechanical measurements, while relating closely to end-use and service life, are not directly linked to the chemical changes in the material and, thus, how the environment affects a polymer. It is necessary to examine the chemical changes, relate those to changes in the polymer network, and include any other physical changes that occur before understanding the important factors that determine the macroscopic mechanical properties of a coating.There has been a great deal of excellent basic work done in determining the chemical changes that occur during degradation of a particular coating's chemistry. Unfortunately, further progress towards connecting that information with macroscopic properties has often been hindered by examining commercial polymers that are undisclosed complex mixtures of functionality and composition. This work examines model polyester-urethane systems...

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Section: Dynamic Mechanical Thermal Analysis (Dmta)supporting

confidence: 86%

Mechanical property changes and degradation during accelerated weathering of polyester-urethane coatings

Skaja

Fernando

Croll

2006

J Coat. Technol. Res.

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“…). The network density was then calculated based on the molecular weight between crosslinks M c according to the affine network model, which is applicable to elastomers:

M_{c} = {(\frac{2}{M_{n}} + \frac{σ}{ρRT (λ_{hot} - λ_{hot}^{- 2})})}^{- 1}

where M n is the number‐average molecular weight (we used the M n ~ 12 kg mol −1 of p(E‐ stat‐ GMA 8 ) for all calculations), ρ is the density of LDPE at 200 °C (0.754 g cm −3 ), R is the universal gas constant, T is the temperature at which the hot set measurement was carried out, i.e. 200 °C, σ is the true stress and λ hot = ( ε hot + 100%)/100 % = L hot / L 0 is the hot set extension relative to the initial length L 0 at 200 °C.…”

Section: Resultsmentioning

confidence: 99%

“…5). The network density was then calculated based on the molecular weight between crosslinks M c according to the affine network model, which is applicable to elastomers: 30,31…”

Section: Resultsmentioning

confidence: 99%

Click chemistry‐type crosslinking of a low‐conductivity polyethylene copolymer ternary blend for power cable insulation

Mauri

Hofmann

Gómez-Heincke

et al. 2020

Polymer International

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High‐voltage direct‐current power cables are vital for the efficient transport of electricity derived from renewable sources of energy. The most widely used material for high‐voltage power cable insulation – low‐density polyethylene (LDPE) – is usually crosslinked with peroxides, a process that releases unwanted by‐products. Hence, by‐product‐free crosslinking concepts that mitigate the associated increase in electrical conductivity are in high demand. Click chemistry‐type crosslinking of polyethylene copolymer mixtures that contain glycidyl methacrylate and acrylic acid co‐monomers is a promising alternative, provided that the curing reaction can be controlled. Here, we demonstrate that the rate of the curing reaction can be adjusted by tuning the number of epoxy and carboxyl groups. Both dilution of copolymer mixtures with neat LDPE and the selection of copolymers with a lower co‐monomer content have an equivalent effect on the curing speed. Ternary blends that contain 50 wt% of neat LDPE feature an extended extrusion window of up to 170 °C. Instead, at 200 °C rapid curing is possible, leading to thermosets with a low direct‐current electrical conductivity of about 10−16 S cm−1 at an electric field of 20 kV mm−1 and 70 °C. The conductivity of the blends explored here is comparable to or even lower than values measured for both ultraclean LDPE and a peroxide‐cured commercial crosslinked polyethylene grade. Hence, click chemistry curing represents a promising alternative to radical crosslinking with peroxides. © 2019 Society of Chemical Industry

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“…A number of authors have examined the effect of entanglements on networks 32–34. It is generally accepted that both crosslink points and entanglements, which are trapped during curing, contribute to the elastic moduli of networks 35.…”

Section: Introductionmentioning

confidence: 99%

Novel Michael Addition Networks Containing Poly(propylene glycol) Telechelic Oligomers

Mather

Miller

Long

2006

Macro Chemistry & Physics

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Summary: Poly(propylene glycol) oligomers with molecular weights ranging from 1 000 to 8 000 g · mol−1 were end‐functionalized with acetoacetate groups and subsequently crosslinked using carbon‐Michael addition with PEG diacrylate. Gel fraction analysis, DMA, TGA, tensile, and swelling measurements were utilized to characterize the networks. The thermomechanical properties of the networks were analyzed with respect to the molecular weight between crosslink points (Mc) and the critical molecular weight for entanglement (Me). Sampling experiments during crosslinking revealed the evolution of molecular weight with time and monomer conversion. Kinetic analyses of the Michael additions were performed using 1H NMR spectroscopy, and the influence of basic catalyst and concentration was elucidated.Synthesis of acetoacetate networks from acetoacetate‐functionalized PPG using DBU as a basic catalyst.magnified imageSynthesis of acetoacetate networks from acetoacetate‐functionalized PPG using DBU as a basic catalyst.

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The role of entanglements in network formation in unsaturated low density polyethylene

Cited by 31 publications

References 26 publications

Mechanical property changes and degradation during accelerated weathering of polyester-urethane coatings

Mechanical property changes and degradation during accelerated weathering of polyester-urethane coatings

Click chemistry‐type crosslinking of a low‐conductivity polyethylene copolymer ternary blend for power cable insulation

Novel Michael Addition Networks Containing Poly(propylene glycol) Telechelic Oligomers

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