ANALYSIS OF CROSS-LINK STRUCTURE OF POLYB UTADIENE LATEX BY PULSED NMR

H-1 pulsed NMR measurements were carried out for three systems: i) cis -polybutadine samples cross-linked by sulfur at different degrees, ii) emulsion-polymerized polybutadiene samples obtained by the additon of a chain transfer agent, and iii) emulsion-polymerized polybutadiene s amples at different monomer conversions. Cross-link spacing (M-c) for samples i), determined by the pulsed NMR method by the use of the Schn eider theory, was compared with the results obtained by equilibrium sw elling and extensional experiments. Good correlation was obtained betw een them for the cross-linked samples (M-c<10000), while agreement bet ween them was poor for loosely cross-linked samples (M-c>10000). Cross -link parameters which characterize the cross-link such as M-c, dangli ng chain fraction (F-b), spin-spin relaxation time (T-2), and correlat ion time (tau) for systems i) and ii) showed the similar tendency with the gel content. However, M-c values for samples ii) were smaller tha n those of samples i). This might be caused by the difference in the m echanism of cross-link formation between samples i) and samples ii). N etworks in samples iii) were formed at a certain polymerization degree independent of a chain transfer agent. The cross-link formation proce eded continuously during the entire emulsion polymerization. A small a mount of intramolecular cross-link was obseved in this emulsion-polyme rization, as found in other emulsion-polymerization systems.