Viscoelasticity of some crosslinked polymers

Abstract

Taking, as the samples for investigation, filaments of viscose rayon (60% crystallinity) and acetate rayon (54% acetyl) both crosslinked to various extents by tetramethylenebisethylene urea and tetramethylenediisocyanate urea as the crosslinking agents, the dynamic and transient moduli, E′, G1, G2, the internal friction, Q−1, and the apparent activation energy for relaxation of segment, ΔU, were measured and the results were considered in their relation to the degree of crosslinking. From the results, the following conclusions were made: (1) When crosslinking is caused by long molecular chains of the crosslinking agents between the nearest neighboring molecules, the intermolecular spaces are widened to some extent and the restraint of segmental motion due to the dipole interaction of the strong polar hydroxyl groups is partly relieved so that the decreases in ΔU, E′, G1, and G2 are rather caused by a small amount of the crosslinking agents; for example, while the values of ΔU and E′, for the original viscose rayon not crosslinked are 230 kcal./mole and 2.0 × 1011 dynes/cm.2, respectively, they both decrease with an increase in degree of crosslinking and each shows a minimum (ΔU = 95 kcal./mole, E′ = 0.9 × 1011 dynes/cm.2) at the amount of bound nitrogen N = 0.73%. When the crosslinking proceeds further, the primary crosslinking effect makes its appearance so that ΔU, E′, G1, and G2 begin to rise with an increase in degree of crosslinking. (2) Due to the strong solvating or plasticizing effects, the water molecules absorbed bring about a strong decrease in the apparent activation energy; ΔU = 90 kcal./mole at 80% RH, 200 kcal./mole at 66% RH, and 210 kcal./mole at 55% RH for viscose rayon.

Microcalorimetric Study of Thermal Cooperative Transitions in Poly(N-vinylcaprolactam) Hydrogels

“…Recently, a new type of nonionic hydrogel, namely, chemically cross-linked poly-(N-vinylcaprolactam) (PVCa), was synthesized that undergoes the collapse transition under heating. 24 Critical phenomena associated with the volume phase transition in acrylamide and NIPA gels were studied by friction measurements, 25 dynamic light scattering, 26 and small-angle neutron scattering. 27 The last method is highly informative as it allows one to detect in detail spatial inhomogeneity of polymer chains in the gels.…”

A new hydrogel system undergoing a volume phase transition upon heating

“…Eq. (3), (4), and (7) - (9) with T t , D t H and n as adjustable parameters were used to fit the two-state model to the experimental excess heat capacity function for the volume phase transition of the PDADMA-Cl/SDS gel. In the case of the three-state model the fitting was performed by Eq.…”

“…This effect can be tackled rather simply from theoretical 3) and experimental points of view. Experimental studies involve such advanced and informative approaches as friction measurements 4) , dynamic light scattering 5) , small angle neutron scattering 6,7) , and microcalorimetry 8,9) . However, the number of systems capable of a thermotropic collapse was, until recently, strongly limited.…”

Kinetics of water flow through a polymer gel

“…The second process is the convective flow of the water through the polymer network [4,5,6]. When the water flows in the gel, it experiences the hydrodynamic friction from the polymer network, at the same time, the polymer network of gel is deformed from the initial configuration by the drag force of the water.…”

“…The collective diffusion coefficient of polymer gels has been extensively measured by quasi-elastic light scattering [22,23]. The friction coefficient between the polymer network of gel and the water has been measured by flowing the water through the gel [4,5,6].…”