Types of Polysiloxanes - The Polysiloxanes - page 42

lattice is employed, and kink translocations are introduced to speed up
the computations. Similarly, Monte Carlo simulations have been used to
calculate dimensions of ring polymers 294-296 and excluded volume effects
in semiflexible ring polymers. 297 Monte Carlo simulations have also been
used to characterize stiffening transitions in semiflexible cyclics. 298 Mo-
lecular dynamics simulations have given interesting information on both
static 299-300 and dynamic properties 299-301 of cyclic polymers. A self-
consistent field theory for Gaussian ring polymers is also available. 302 Di-
mensional analyses using a scaling model have been used to describe
cyclic molecules in general, including those of PDMS. 303 Finally, simula-
tions have been carried out on the cyclization of α,ω-telechelic chains. 304

3.5.3 Comparisons Between Polysiloxane Cyclics and Polysiloxane
Linear Chains

There have been many comparisons of cyclic polysiloxanes with the corre-
sponding linear chains of the same molecular weight. Table 3.3 provides

Table 3.3. COMPARISONS BETWEEN CYCLIC POLYSILOX ANES AND LINEAR
POLYSILOX ANES OF THE SAME MOLECULAR WEIGHT

Value of property for
cyclics relative to linears Reference Property Polymer

Intrinsic
viscosities

Poly(dimethylsiloxane) Lower

347-348

Gel permeation
chromatography

“ Both gave sharp

fractions

349-350

Chain dimensions “ Lower

351

Bulk viscosities “ Higher at low M, but

lower at high M

352

Diffusion
coefficients

“ Higher

353-356

Effects of heat “ Both show bond

interchanges

357-358

Second virial
coefficients

“ Lower

359

Radii of gyration
(Monte Carlo)

“ Lower

360

Ellipsoidal shapes
(Monte Carlo)

“ Lower asymmetry

361

( continued )