Synthesis and properties of branched poly(ethylene oxybenzoate)s
The synthesis and properties meta and para poly(ethylene oxybenzoate)s, two semi-crystalline polymers, are reported. It is found that by copolymerising equimolar quantities of meta and para monomers amorphous polymers are produced which are significantly more soluble than their respective homopolymers. The effects of introducing an AB(_2) branching agent (A) into p-PEOB are also considered. It is found that the relationship between Tg and molecular weight does not vary significantly with the extent of branching. Using the data obtained from DSC experiments, a linear relationship between the melting temperature and the branching composition of p-PEOB is reported up to a critical value of 12.5mole% of A, above which materials are amorphous and chloroform soluble. A general technique for measuring number average molecular weight of branched materials, using (^1)H NMR end group counting, is described. This is used successfully in the analysis of p-PEOB copolymers with less than 15mole% branching. Molecular weights of the amorphous materials, i.e. with extents of branching in excess of 12.5mole%, are measured using conventional GPC with respect to linear polystyrene equivalents. Relationships between the extent of branching, log Mw and log [n] in chloroform, appear to be linear for amorphous copolymers with branching compositions of between 20mole% and 100mole%. A detailed analysis of carbonyl signals in (^13)C NMR spectra of these materials is reported, which provides evidence that the copolymerisations are statistical and not selective.