Rheology and Foaming of Long-Chain Branched Ethylene-Tetrafluoroethylene Copolymer and Its Blends

The long-chain branched ethylene-tetrafluoroethylene copolymer (B-ETFE) was synthesized by radical polymerization using ethylene, tetrafluoroethylene, termonomer, and a very small amount of divinyl monomer. We studied melt rheology under shear and elongational flow, and foamability for B-ETFE, comparing with conventional linear ETFE. Addition of a small amount of the divinyl monomer had a considerable impact on the melt rheology of ETFE and its blends. The observed non-linear elongational behavior and emergence of long relaxation time components can be explained by long-chain branching in the modified ETFE. B-ETFE and its blends showed excellent foaming processability: uniform and smaller cell sizes and much higher cell number densities than those of linear ETFE. To the best of our knowledge, this is the first report of the enhancement of the melt rheology of ETFE from the viewpoint of modification of its molecular architecture.

Neutron scattering from equilibrium-swollen networks

Small-angle neutron scattering measurements were performed on end-linked poly (dimethylsiloxane) (PDMS) networks swollen to equilibrium with d-benzene. Comparison was made with equivalent concentration PDMS solutions. Equilibrium-swollen networks consistently displayed a linear scattering regime at low q followed by a good-solvent-like scaling regime at high q in agreement with the predictions of the Gel Tensile Blob (GTB) model. Data are fit using the unified function modified for the GTB model (3-parameter fit). Equilibrium-swollen networks display a base structural size, the gel tensile-blob size, xi, that was found to be independent of the molecular weight between crosslinks for the series of molecular weights studied, consistent with the predictions of the model. The length of the extended tensile structure, L, can be larger than the length of the fully extended network strand. The predicted scaling relationship for L, L approximately Q(1/2)N(avg), where N(avg) = (1/fN(c)(2) + 1/4N(e)(2), Q is the equilibrium swelling ratio, N(c) is the molecular weight between crosslinks, N(e) is the entanglement molecular weight and f is the crosslink functionality is in agreement with experimental results for the networks studied.