Novel Si-Based Chain Transfer Agents for LDPE Molecular Architecture Control

Abstract

In this work, we present a new class of silane chain-transfer agents (CTAs) for the molecular weight and the molecular weight distribution control during the production of low-density polyethylene (LDPE). These silanes exhibit a wide range of chain-transfer propensity as measured by their C_s values (the ratio of the rate coefficient for hydrogen abstraction and ethylene propagation, k_h/k_p) with the best performers being tris(trimethylsilyl)silane (C_s = 16.0) and trimethylsilylsilane (C_s = 15.7). Density functional theory (DFT) calculations were used to estimate the C_s values. The quantum chemical calculations were validated by pilot-plant experiments for triethylsilane (C_s = 0.22) and tris(trimethylsilyl)silane (C_s = 36.5). Given the expected variability in the pilot-plant data, an excellent agreement between theory and experiment was achieved. Furthermore, a model utilizing the DFT calculated Mulliken charge on the silicon atom to predict the C_s value was developed to facilitate silane screening in the future.