Dilution effects on dimethylsiloxane ring-chain equilibria

Carmichael, Jack B.; Gordon, David; Isackson, Frank J.

doi:10.1021/j100866a006

Cited by 31 publications

(13 citation statements)

References 3 publications

(4 reference statements)

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“…120,121 At 100% conversion, a clean TCP should yield the same mixture of cyclic products as an equilibration of a cyclic monomer or oligomer as exemplarily illustrated for poly(dimethyl siloxane)s in Scheme 47. Equilibrations of polysiloxanes and cyclosiloxanes were intensively studied by several research groups [169][170][171][172][173][174][175][176][177][178][179][180][181][182][183][184][185][186][187] either promoted by heating [169][170][171][172] or by strong protic acids or by potassium silanolates. The main purpose of those studies was determination of frequency distribution (or weight fraction) of the individual cyclic oligomers in correlation with the Jacobson-Stockmayer theory of TCP.…”

Section: Ring-ring Equilibrationmentioning

confidence: 99%

Cyclic polymers: Synthetic strategies and physical properties

Kricheldorf

2009

J. Polym. Sci. A Polym. Chem.

396

442

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Syntheses of cyclic polymers including cyclic homopolymers, cyclic block copolymers, sun-shaped polymers, and tadpole polymers are discussed on the basis of a differentiation between synthetic methods and synthetic strategies (e.g., polycondensation, ring-ring equilibration, or ring-expansion polymerization). Furthermore, all synthetic methods are classified as kinetically or thermodynamically controlled reactions. Characteristic properties of cyclic polymers such as smaller hydrodynamic volume, lower melt viscosities, and higher thermostabilities are compared to the properties of their linear counterparts. Furthermore, the nanophase separation of cyclic diblock copolymers is discussed.

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Section: Ring-ring Equilibrationmentioning

confidence: 99%

Cyclic polymers: Synthetic strategies and physical properties

Kricheldorf

2009

J. Polym. Sci. A Polym. Chem.

396

442

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“…At 100% conversion, a clean TCP should yield the same mixture of cyclic products as an equilibration of a cyclic monomer or oligomer as exemplarily illustrated for poly(dimethyl siloxane)s in Scheme . Equilibrations of polysiloxanes and cyclosiloxanes were intensively studied by several research groups169–187 either promoted by heating169–172 or by strong protic acids or by potassium silanolates. The main purpose of those studies was determination of frequency distribution (or weight fraction) of the individual cyclic oligomers in correlation with the Jacobson‐Stockmayer theory of TCP 120, 121.…”

Section: Ring–ring Equilibrationmentioning

confidence: 99%

Distinct topography of erosion and new bone formation in achilles tendon enthesitis: Implications for understanding the link between inflammation and bone formation in spondylarthritis

McGonagle¹,

Wakefield²,

Tan³

et al. 2008

Arthritis & Rheumatism

112

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Objective. This study combined ultrasonography of the Achilles tendon enthesis at different stages of spondylarthritis (SpA) with microanatomic studies of normal cadaveric entheses, with the aim of exploring the relationship between bone erosion and new bone formation in enthesitis.Methods. Thirty-seven patients with SpA and Achilles tendon enthesitis (20 with early SpA and 17 with chronic SpA) and 10 normal control subjects underwent ultrasound scanning. The presence of bone erosion and spur formation was recorded at 3 sites: the proximal and distal halves of the enthesis and the adjacent calcaneal superior tuberosity. Parallel histologic analysis was performed on cadaveric Achilles tendon entheses to determine whether regional variations in bone density and trabecular architecture in relation to fibrocartilage distribution are related to disease patterns.Results. Bone erosion in patients with early SpA occurred at either the proximal insertion or the superior tuberosity (11 of 20 patients; P < 0.001 versus distal enthesis). Very small spurs, which were present almost exclusively at the distal enthesis, were evident in patients with early SpA and in normal control subjects. However, large spurs were evident distally only in patients with chronic SpA (9 of 17 patients, compared with none of 20 patients with early SpA; P < 0.0001). Histologic studies showed that aged normal individuals had small spurs at the corresponding location. The bone-to-marrow ratio was also significantly lower in the regions prone to erosions (P < 0.05).Conclusion. Bone erosion in association with Achilles tendon enthesitis in SpA is anatomically uncoupled from bone formation-the 2 processes are topographically and temporally distinct. We thus conclude that disease patterns in SpA are related to normal enthesis structure and biomechanics.

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“…They result from the hydrolytic polycondensation of dimethyl dichlorosilane or from the equilibration of poly(dimethyl siloxane)s. D 3 is the thermodynamically least stable and most reactive cyclosiloxane, and detailed studies of its cationic polymerization were published. [1][2][3] Numerous studies deal with the acidic [4][5][6][7][8][9][10][11][12][13][14] or basic equilibration [15][16][17][18][19][20][21][22][23][24][25] of D 4 . Concentrated sulfuric acid and triflic acid were the most widely used acidic catalysts but SbCl 5 [4] or the combination of FeCl 3 and HCl [12] were also applied.…”

Section: Introductionmentioning

confidence: 99%

Polymerization of Cyclosiloxanes by Means of Triflic Acid and Metal Triflates

Yashiro

Kricheldorf

Schwarz

2010

Macro Chemistry & Physics

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Hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5) were equilibrated with potassium tert‐butoxide or triflic acid in bulk at 100 °C to elaborate the 1H NMR and 13C NMR spectra, SEC elution curve, and MALDI‐TOF (MT) mass spectrum of a fully equilibrated poly(dimethylsiloxane). Surprisingly, triflic acid did not effect complete equilibration (even after 360 h), seemingly because cleavage of Si–C bonds eliminates the acidic proton. Large amounts of D4 and D5 together with small amount of D6 were formed in the early stage of the polymerization in contrast to potassium alkoxide‐catalyzed polymerizations. The usefulness of numerous metal triflates as polymerization catalysts of D3 was explored, and only the most acidic ones were active. Bismuth and hafnium triflate catalyzed a polymerization mechanism similar to that of triflic acid but were more active despite their poor solubility. BiCl3 and HfCl4 were considerably less reactive and the polymerization kinetics were quite different from those of the metal triflate catalyzed polymerizations. The decisive role of acidic protons was revealed by addition of a proton scavenger. Bismuth triflate proved to be an interesting and useful catalyst because it combines the highest activity with poor solubility and low toxicity.magnified image

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Dilution effects on dimethylsiloxane ring-chain equilibria

Cited by 31 publications

References 3 publications

Cyclic polymers: Synthetic strategies and physical properties

Cyclic polymers: Synthetic strategies and physical properties

Distinct topography of erosion and new bone formation in achilles tendon enthesitis: Implications for understanding the link between inflammation and bone formation in spondylarthritis

Polymerization of Cyclosiloxanes by Means of Triflic Acid and Metal Triflates

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