Synthesis, structure and phase transition property of acrylic acid grafted paraffin

•AA was used to modify paraffin and improve its latent heat capacity effectively.•The composition and sequence structure of the grafted products were characterized.•The mechanism of free radical grafting of AA may be monomeric grafts.•With increasing grafting ratio, the primary structure of grafts varied from B to A.

Polar monomer acrylic acid (AA) was used to modify paraffin in order to improve the latent heat of paraffin as phase change materials. The composition and sequence structure of the grafted products were characterized by FTIR, 13C NMR, 1H NMR and GPC analysis, and the thermal properties of paraffin-g-AA were investigated. It was found that AA was confirmed to be grafted onto the molecular chain of paraffin successfully. The mechanism of free radical grafting of AA may be only monomeric grafts. At low grafting ratio, the structure B can be mainly formed as a result of the radical coupling termination; while at the high grafting ratio, structure A was the primary structure as a result of the radical chain growth process. The number-average molecular weight of the grafted samples increased at first but leveled off with increasing grafting ratio, while the weight-average molecular weight increased gradually. The latent heat capacity of the grafted paraffin can be improved obviously at low grafting ratio due to the formation of structure B.

Graphical abstractPolar monomer acrylic acid (AA) was used to modify paraffin in order to improve the latent heat of paraffin as phase change materials. The composition and sequence structure of the grafted products were characterized, and three types of possible grafted products may be obtained during grafting. The proposed chemical structure of paraffin-g-AA and the calculated chemical shifts of 1H NMR were shown as below:Figure optionsDownload full-size imageDownload as PowerPoint slide