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Mixtures of butyl rubber with polyisobutylene (molecular weights 0.055 and 2.3 × 106) up to 50% by weight were crosslinked by sulfur, leaving the polyisobutylene molecules free to reptate in the butyl rubber network. Linear viscoelastic properties were measured in shear creep for periods up to 5 × 105 sec at 25°C and oscillating shear deformations from 0.1 to 3 Hz, at temperatures from 2 to 63°C. Comparison with the properties of a butyl rubber crosslinked without polyisobutylene showed contributions to creep and mechanical loss attributable to the reptating species. Comparison with the properties of polyisobutylene (higher molecular weight) showed that the relaxation times associated with the reptating species in the upper part of the terminal zone are the same for different polyisobutylene contents (25% and 50%) and for 100% polyisobutylene in which no permanent network is present; their contributions to modulus appear to be proportional to the volume fraction of polyisobutylene to a power of about 2/3. The time required in stress relaxation for the portion of the modulus attributable to the reptating species to decay to half its plateau value is, based on the two molecular weights employed, proportional to the polyisobutylene molecular weight to the third power. The magnitude of the associated mechanical loss and its location on the frequency scale can thus be controlled independently.

The preparation and characterization of randomly cross-linked polybutadiene (PB) networks containing unattached PB chains are presented. These were used as model systems for the experimental study of the dynamics of linear chains trapped in networks, which is the basic model of the reptationin-a-tube model of Doi and Edwards. The preparation consists of the conversion at random of a small fraction of the PB chains' double bonds into epoxide groups and in the subsequent selective use of these as cross-linking centers in the presence of unmodified PB chains; these last remain chemically unattached to the network. The selectivity of the cross-linking reaction was examined by swelling-extraction of networks containing known fractions of relatively short "monodisperse" unattached chains. The polymeric phase composition of the networks with unattached chains (nuc) was tested by glass transition temperature measurements. Dynamic-mechanical measurements were shown to be sensitive to the polymer-phase composition of nuc, as well. The dynamics of the linear PB chains in the melts and in the networks was studied by dynamic-mechanical measurements. The experimental results for the longest relaxation time τ L were compared with the predictions of the reptation-in-a-tube model with and without chain-end effects. Within experimental accuracy, the obtained scaling of τL relative to the chain mass M (up to 9 × 10 5 g/mol) is the same in both media: τL ∼ M x with x ) 3.35 ((0.10 as against x ) (3 from the pure reptationin-a-tube model; correcting for chain-end effects in the form of contour length fluctuation, results in a good description of the experimental data for the τLs of unattached chains. τL for the chains trapped in networks were found to be 1.9-3.2 times longer than the τL of the respective melts. Data on 14 PB prepared by anionic polymerization and covering the range of weight average molar masses 1.0 × 10 4 to 1.5 × 10 6 g/mol are presented. IntroductionRubber networks with unattached chains 1-7 are ideally one-phase, two-component systems; the first component is one macroscopic molecule (the network) and the second consists of linear chains "dissolved" into the network. The materials (with or without phase separation) are also classified in the literature as "semiinterpenetrating networks" (sIPN). 8 Because the short time dynamics (glass and transition regions 1 ) of a rubber network is essentially the same as that of a high polymer melt, 1 the rubber networks containing small concentrations of unattached chains permit one to study the dynamics of almost isolated chains in the rubber plateau and the terminal zones. 1 Therefore, these systems can be used to test the predictions of one-chain theoretical models (specifically the reptation-in-a-tube model 9-12 ) and as references for the study of polymer melts. On the other hand, the same systems are well-fitted for the investigation of the longtime (eventually equilibrium) properties of rubber networks as depending on the degree of cross-linking. The analysis of the con...

Mixtures of crosslinkable ethylene–propylene terpolymer with saturated ethylene–propylene copolymer (molecular weights 3.6, 16.7, and 45 × 104) containing up to 50% by weight of copolymer were crosslinked by sulfur, leaving the saturated copolymer unattached and free to reptate in the terpolymer network. Stress relaxation in small simple elongations (stretch ratio about 1.15) and dynamic Young's modulus at frequencies from 3.5 to 110 Hz were measured at temperatures from 10 to 50°C. Comparison with the properties of the terpolymer crosslinked without added copolymer showed contributions to stress relaxation and mechanical loss attributable to the unattached species. The time required in stress relaxation for the portion of the modulus attributable to the unattached species to decay to half its plateau value, t1/2, is approximately proportional to the 3.5 power of the molecular weight; t1/2 appears to be slightly smaller for networks containing 50% than for those containing 25% unattached component.

The spectrum of the Rayleigh line in the light scattered from dilute solutions of polystyrene in 2-butanone at 25" has been measured for four samples ranging in molecular weight from about 8.7 X lo5 to 5 X IO7. All spectra were fit fairly well by single least-squares Lorentzians, although small deviations from the least-squares Lorentzians were noticeable at high molecular weights. The spectral breadth increased more rapidly than in proportion to the square of the scattering vector ~2 for the high molecular weight samples. This result is attributed to simultaneous effects of polydispersity and intramolecular motion. Calculations based on theory by Pecora and Tagami for the effect of intramolecular motion show that only small deviations of the spectral shape from a single Lorentzian are to be expected. although significant increases in the spectral breadth beyond that predicted from proportionality to K~ may be observed. The data are in accord with these predictions. The calculations and experimental results given establish guidelines for predicting when effects of polydispersity and intramolecular motion can influence measurement of translational diffusion coefficients for high molecular weight randomcoil polymers, and they also allow specification of the restricted conditions where semiquantitative information concerning intramolecular motion may be obtained from Rayleigh line spectroscopy.ccording to theory,l-3 the Rayleigh line in the spectrum