Conformation of Cyclics and Linear Chain Polymers in Bulk by SANS

Abstract

Small-angle neutron scattering (SANS) has been used to investigate the conformation of linear and cyclic poly(dimethylsiloxane)s (PDMS) in chemically identical, undiluted blends. SANS measurements have been carried out on (1) linear hydrogenous (H) mixed with linear deuterated (D) PDMS and (2) cyclic H mixed with cyclic D PDMS. The conformational behavior of the cyclic and linear polymers is studied over a wide range of molar mass and composition. Isotopic blends of linear PDMS are shown to adopt conformations that agree well with theoretical predictions for Gaussian random-coil polymers and confirm previous SANS studies. As expected for chains obeying Gaussian statistics, the mean radii of gyration, R g, scale with the weight-average molar mass as Rg ∝ Mw 0.5 . A detailed study of H/D cyclic PDMS mixtures is presented, and we demonstrate that, since Rg ∝ Mw 0.4 , highly flexible cyclic polymers in the melt adopt an even more compact conformation than that of unperturbed rings. This behavior confirms previous predictions based on computer simulations and theoretical studies. The results are in excellent agreement with computer simulations and theoretical predictions reported in the literature.

Cyclic polymers: Synthetic strategies and physical properties

“…299 Therefore, the T g s of the cyclic species were higher than those of the linear analogues for M n s < 10 kDa. These findings were in agreement with the aforementioned properties of other cyclic polymers, [62][63][64][65][66]253,274 but surprisingly the T g s of cyclic oligosiloxanes (M n s < 4 kDa) increased above T g 1.…”

“…299 When samples with masses above the critical entanglement molecular weight (M e ) were included, 293 the extent of entanglements was surprisingly quite similar for cyclic and linear PDMS. Information about segmental mobility and diffusion was derived from Raman spectroscopy 295 from dielectric relaxation 296,297 and from spin-spin relaxation measurements.…”

“…298 Finally, a SANS study of conformations of cyclic and linear PDMS in bulk should be mentioned. 299 Blends of protonated and deuterated cyclic PDMSs and also blends of protonated and deuterated linear PDMS were studied. It was found that the radius of gyration of the linear chain R gl varies with molar mass (M w ) according to eq 8, whereas eq 9 was found for cyclic PDMSs.…”

Monte Carlo simulation of a single ring among linear chains: Structural and dynamic heterogeneity

“…With the same BFM, Suzuki et al 23 simulated ring polymers with N Ring as large as 1000 and concluded that v is bracketed by 1 / 3 Յ v Ͻ 0.365. Experimentally, at least two different values of v for ring polymers in melt have been reported: 0.42 by Arrighi et al 8 and 0.34 by Takano, 10 both from neutron scattering data.…”

“…The diffusion mechanism of rings has been suggested theoretically as amoebalike motion: they thrust and pull on unentangled loops. 1,2 For ring polymers in bulk, in spite of extensive work using experiments, [3][4][5][6][7][8][9][10] theories, [11][12][13][14] and simulations, [15][16][17][18][19][20][21][22][23] many controversies still remain.…”