Organosilicon Polymers. II. The Open Chain Dimethylsiloxanes with Trimethylsiloxy End Groups<sup>1</sup>

Hunter, M. J.; Warrick, E. L.; Hyde, J.; Currie, Conor

doi:10.1021/ja01215a048

Cited by 87 publications

(27 citation statements)

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“…In addition, a plot of the temperature dependence with respect to io'^ yielded linear relationships with slopes corresponding to E/R, where E is the activation energy and R the gas constant ( Figure 7). The estimated activation energy of approximately 3kcalmol~' was consistent with those associated with dimethylsiloxanes in transport processes such as viscous flow (2.3-3.5 kcal moP') [18][19][20][21][22], and difñision of water (3 kcal mop') [15] and methanol (2-6.5 kcal moP') [23]; in addition, an activation energy of 3kcalmoP' was reported for the self-diffusion of methanol [24].…”

Section: %Rí{=pipq{t)\qo%supporting

confidence: 76%

A generalized cure model for one-part room temperature vulcanizing sealants and adhesives

Buyl¹

2013

Journal of Adhesion Science and Technology

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The cure progression of one-part room temperature vulcanizing (1-RTV) sealants and adhesives is a vital intrinsic material property for their typical end-use applications. Understanding the key factors controlling the cure mechanism becomes more and more important given an ever-increasing demand to improve productivity by allowing assemblies using these materials to move faster through the manufacturing process. For 1-RTV systems, ultimate mechanical and adhesive strengths attain an equilibrium value as their cure proceeds in the presence of atmospheric moisture. A difflision-controlled, moisture-cure mechanism was established for this family of materials about 10 years ago, most definitively by Comyn et al. The depth z of unidirectional cure with time t was derived to be a function of the vapor pressure p of water in the atmosphere in the proximity of the material surface, and two material properties: the permeability P of moisture through the cured layer and the equivalent material volume V reacting with 1 mol of water, and cure time, t, i.e. z = (2VPp t)"^. Hence, the thickness of the cured layer should increase as ?"^. That is, a plot of z vs. t"'^ should yield a straight line where, for a particular RTV material, the magnitude of its slope is a function of the temperature and relative humidity (RH) during cure. This was shown for organic hot-melt adhesives and silicone sealants; validation of the moisture-cure model was demonstrated using gravimetrically based measurements to determine V and P separately. However, a deviation from the moisture-cure model was reported from a study using an alkoxy silicone sealant in geometries requiring deep-section cure and, therefore, longer cure times. An increase in the slope of the z vs. t"'^ plot was observed after a certain time x interval that was a function of cure conditions. The change in cure rate was attributed to the migration of low molar mass crosslinkers and adhesion promoters towards the cure front and the eventual depletion of these species, which compete with the silicone polymer for reacting with the diffusing water It was possible to determine the diffusion coefficient, D, of additives that act as adhesion promoters and crosslinkers in uncured alkoxy silicone sealant. From these studies, the utility of the moisture-cure diffusion model was demonstrated. The variables impacting cure performance are reviewed; and, a generalized form of the model is presented to account for variability in cure rates observed over extended time intervals in assembly geometries requiring deepsection cure. By plotting z as a function of (tp)"'^, data-sets for each material collected at different conditions of temperature and RH merged into a single straight line with a very high coefficient of determination. For end-users of 1-RTV silicone sealants and adhesives, this latter approach provides a material-specific reference line that demonstrates the correspondence between cure time and vapor pressure; i.e. a certain cured depth can be reached at short cure times with a high RH ...

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Section: %Rí{=pipq{t)\qo%supporting

confidence: 76%

A generalized cure model for one-part room temperature vulcanizing sealants and adhesives

Buyl¹

2013

Journal of Adhesion Science and Technology

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“…Indeed, even a superficial overview of the data obtained from previous investigations [3][4][5][6][7][8][9][10][11][12] clearly confirms this expectation, but, surprisingly, it also reveals that rather significant differences exist between the different reports, so that they spread over an unusually large range of values from about 660 (Ref. 9) to almost 1400 (Ref.…”

Section: Ntro Duct10 Nmentioning

confidence: 73%

On the critical molecular chain length of polydimethylsiloxane

Dvornić

Jovanović

Govedarica

1993

J of Applied Polymer Sci

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SYNOPSISBecause a study of the results reported for the chain dimensions of polydimethylsiloxane (PDMS) , critical for the onset of this polymer's non-Newtonian flow behavior, obtained from the viscosity-molecular weight relationships available from the literature, clearly revealed that considerable differences exist between the reported data, a detailed analysis of these data was performed together with an additional examination of 10 new PDMS samples that were selected so as to have molecular weights that would fill the gaps observed in the polymer viscosity-chain length relationship constructed from the accepted literature data. The results obtained were analyzed by using several different procedures integrated into a recently described comparative method that could allow for determination of what is called the most realistic critical value, Zwc. The latter was determined as 930 PDMS main-chain atoms, which corresponds to this polymer's degree of polymerization of 464.5 and the weight-average molecular weight of 34,500. It is not only shown that after elimination of some clearly erroneous data points from the previously reported relationships the obtained critical chain-length values could very well fit the earlier relationships, but also that appropriate "master" relationships were constructed including 48 pairs of the old and 10 pairs of the new data points. It is suggested that this relationship be accepted as the bestfit viscosity-polymer chain-length dependence for PDMS, and it is pointed out that the obtained PDMS critical chain-length value ranks this polymer's macromolecules as the most flexible of the corresponding long-chain molecules presently known. 0 1993

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“…The interpretation of siloxane chemistry in terms of carbon chemistry has met with considerable success in the synthetic fields, but the physical properties often appear anomalous. The major point of difference is summarized in the frequent statement that cohesive or van der Waals forces are reduced by the presence of siloxy (Si0) groups (Wilcock, 1946;Hunter, Warrick, Hyde &Currie, 1946).…”

Section: Introductionmentioning

confidence: 99%

The crystal structure of octamethylspiro [5.5] pentasiloxane: rotation about the ionic silicon–oxygen bond

Roth¹,

Harker²

1948

Acta Cryst

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Organosilicon Polymers. II. The Open Chain Dimethylsiloxanes with Trimethylsiloxy End Groups¹

Cited by 87 publications

References 0 publications

A generalized cure model for one-part room temperature vulcanizing sealants and adhesives

A generalized cure model for one-part room temperature vulcanizing sealants and adhesives

On the critical molecular chain length of polydimethylsiloxane

The crystal structure of octamethylspiro [5.5] pentasiloxane: rotation about the ionic silicon–oxygen bond

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Organosilicon Polymers. II. The Open Chain Dimethylsiloxanes with Trimethylsiloxy End Groups1

Cited by 87 publications

References 0 publications

A generalized cure model for one-part room temperature vulcanizing sealants and adhesives

A generalized cure model for one-part room temperature vulcanizing sealants and adhesives

On the critical molecular chain length of polydimethylsiloxane

The crystal structure of octamethylspiro [5.5] pentasiloxane: rotation about the ionic silicon–oxygen bond

Contact Info

Product

Resources

About

Organosilicon Polymers. II. The Open Chain Dimethylsiloxanes with Trimethylsiloxy End Groups¹