Der 331

Hexamethylene diisocyanate (HDI, AR) and triethylenetetramine (TETA) were purchased from Aladdin Industrial Corporation (Shanghai, China) and used as received. PTMG (PTMG-650 and PTMG-2000, whose average molecular weight is 650 and 2000 g/mol, respectively), PPG (PPG400, whose average molecular weight is 400 g/mol.), N,N-dimethylformamide (DMF, AR) and acetone (AR) were purchased from Aladdin Industrial Corporation and dried by 3A molecular sieves for one week. Organic tin (Thermolite 890) was obtained from PMC Group (Beijing, China) and used as received. Bisphenol-A epoxy resin whose epoxide equivalent is about 189g/mol (DER331), was purchased from DOW (Zhangjiagang, China) and used as received.

The epoxy resin used (DER 331, Dow Chemical Company, Midland, MI, USA) is a commercial diglycidyl ether of bisphenol-A (DGEBA), with an epoxy equivalent in the range 182–192 g/eq and a viscosity in the range 11,000–14,000 mPa·s. The hyperbranched polymers used are polyethyleneimines (HBPEI) of different molecular weights, provided by the BASF Chemical Company (Florham Park, NJ, USA) with tradenames: Lupasol^® FG, referred to here as PEI800 and with a molecular weight of 800 g/mol and viscosity at 20 °C in the range 800–5000 mPa·s; and Lupasol^® WF, referred to here as PEI25000 and with a molecular weight of 25,000 g/mol and viscosity at 50 °C in the range 13,000–18,000 mPa·s. Before performing any experiments, the samples were previously preconditioned at 100 °C for 30 min in order to remove any moisture content in the samples. The chemical structure of the hyperbranched polymer was shown above in Figure 1. The characteristics of the HBPEI samples for the amine ratio, equivalent H mass, equivalent N mass, and degree of branching are listed in Table 6.