Significant thermal property and hydrogen bonding strength increase in poly(vinylphenol-co-vinylpyrrolidone) copolymer

A series of poly(vinylphenol-co-vinylpyrrolidone) (PVPh-co-PVP) copolymers were prepared by free radical copolymerization of acetoxystyrene with vinylpyrrolidone (PAS-co-PVP), followed by selective removal of the acetyl protective group. These copolymers were investigated by solid state nuclear magnetic resonance (NMR) and thermal gravimetric analyzer (TGA) to compare with previous results on differential scanning calorimetry (DSC) and Fourier-Transform infrared spectroscopy (FTIR) analyses. The spin-lattice relaxation time in the rotating frame (T1ρ(H)) of the PVPh-co-PVP is greater than the corresponding PVPh/PVP blend, indicating that the polymer mobility is more restricted and high rigid character of the former. At the same time, the thermal decomposition temperature of homopolymer, copolymer and polymer blend is the order of PVPh-co-PVP copolymer>PVPh/PVP blend>pure PVP homopolymer>PAS-co-PVP copolymer and this order is consistent with previous studies on DSC, FTIR and NMR analyses. In order to understand the mechanism of significant glass transition temperature increase of the PVPh-co-PVP copolymer, the degree of hydrolysis was controlled by varying time of reaction of the PAS-co-PVP copolymer.