The copolymerization reaction of butadiene and styrene copolymers prepared by anionic living polymerization using an initiator composed of alkyl aluminum, n‐butyl lithium, and barium alkoxide is studied using a kinetic model that considers the reactivity of active sites to be different; this assumption is justified by the varying geometric configurations. With the first‐order Markov model, the expressions for the fraction of active sites and dyad distribution are obtained. The rate constants are determined by fitting to the conversion and Bernoulli dyad data using the nonlinear least squares method. The conversion and dyad sequence distribution are correctly predicted, and the experimental results indicate that the microstructure and sequence distribution do not change with the conversion and temperature.
Summary: Fully linear polyethylene‐based latexes have been prepared by the hydrogenation of polybuta‐1,4‐diene dispersions. The latter were synthesized via dispersion ring‐opening metathesis polymerization of cycloocta‐1,5‐diene, and hydrogenated using RuCl2(PPh3)3 as catalyst, without any further treatment. A high hydrogenation efficiency was achieved as demonstrated by different techniques including DSC, and 1H NMR and FT‐IR spectroscopy. The hydrogenation process could be carried out without detrimental effect on particle size and colloidal stability as evidenced by optical microscopy and light scattering analysis.
Optical microscopy photograph of a polybutadiene‐based dispersion after hydrogenation. No change in size is observed. 相似文献
A low-molecular-weight liquid polybutadiene (LPB) is employed as the sole co-stabilizer in miniemulsion polymerization of styrene in present work. Results indicate that the LPB can be used as an effective co-stabilizer to retard the diffusional degradation of monomer droplets in miniemulsion system and get stable miniemulsions. When the miniemulsions were initiated, particle formation occurred predominantly by monomer droplet nucleation. Moreover, the effects of various reaction parameters on the polymerization kinetics and the nucleation mechanisms were also investigated. These parameters include the level of LPB ([LPB]) and the concentrations of SDS ([SDS]) and potassium persulfate ([KPS]). It is shown that the polymerization rate indicates little dependence on [LPB], while increases with increasing [SDS] and [KPS]. Competition between droplet nucleation and homogeneous nucleation occur in the course of polymerization, but droplet nucleation becomes more important by increasing [LPB] or decreasing [SDS]. Furthermore, the result that the particle size is rather insensitive to changes in [KPS] provides the most compelling evidence for the dominant droplet nucleation. 相似文献
The damage such as microcracks limits the application of hydroxy-terminated polybutadiene (HTPB) elastomer. Here, hydroxy-carboxy-terminated polybutadiene (HCTPB) and Fe3+ selected to facilitate ionic bonds (COO−⋯Fe3+) formation is proposed as a strategy to alleviate the intrinsic self-healing problem for HTPB elastomer. In typical HTPB polyurethane elastomer, the elongation at break is 997.3% while the tensile strength is 1.83 MPa, the damage cannot repair by intrinsic covalent or non-covalent, resulting in permanent damage. In contrast, HCTPB is able to offer COO−, entailing a COO−⋯Fe3+ ionic bonds. Incorporated 6 wt% HCTPB and Fe3+ into the HTPB elastomer elevates the tensile strength to 5.2 MPa, reducing the elongation at break in 877.8%. HCTPB and Fe3+ enhance the self-repair rate reaches up to 92% after repairing at 80 °C for 10 h after cutting for HTPB elastomer. This strategy has immediate implications for using COO−⋯Fe3+ ionic bonds to improve the performance of HTPB polyurethane elastomer devices. 相似文献