Performance of Liquid Benzoxazine-PEG Blend Resin Systems for Potential Industrial Composites Processing

The manufacturing of technology and materials based on benzoxazine resin is limited by melt or solvent-based processing in which benzoxazine monomer is either dissolved in a solvent or melted to transfer onto fiberglass or carbon fiber. Solvent based processing depends on the use of organic solvents which impart health and financial risks. Benzoxazine monomer also suffers from high curing temperatures where the benzoxazine polymerizes to form structures with desirable mechanical and thermal properties. Non-flammable liquid benzoxazine resin with low curing temperatures are attractive for their exclusion of organic solvents and ease of processing. In this study three series of blends containing bisphenol A benzoxazine (BO) monomer were prepared with two poly(ethylene glycol) (PEG) polymers: poly(ethylene glycol) methyl ether (mPEGOH) or poly(ethylene glycol) methyl ether tosylate (mPEGOTs). The cure and crystallinity of the blends were studied with differential scanning calorimetry (DSC). From the cure studies a suppression of the max and onset cure temperatures were observed in the blends with mPEGOTs. The crystallinity study examines the percent of PEG that crystallizes and separates from the bulk of the sample. The crystallinity study revealed the miscibility of the PEG in BO up to 40 % weight loading in the case of the mPEGOH. In the case of the mPEGOTs blends a larger miscibility range was found. Images generated with scanning electron microscopy (SEM) of cured samples from the mPEGOH series revealed void content after extraction of free PEG. When mPEGOTs blends were studied the PEG was not easily extracted which suggests a molecular composite formed. The presence of the suspected catalyst, p-toluenesulfonic acid, was determined with thermogravimetric analysis in series with mass spectrometry or Fourier transform infrared spectroscopy (TGA-MS and TGA-FTIR). The structural property relationships for molecular weights 2000, 900, and 500 Da PEG components will be discussed.