Thermal analysis of water in reinforced plasma-polymerised poly(2-hydroxyethyl acrylate) hydrogels

• Thermal analysis of water was determined in reinforced plPHEA and bulk PHEA.
• Less undercooling of water crystallisation was observed in plPHEA than in bulk PHEA.
• Water crystallises much faster in plPHEA than in bulk PHEA.
• All the melting peaks of water in bulk PHEA and plPHEA are around 0 °C as free water.
• Much less water is segregated from plPHEA than from bulk PHEA.

Thermal analysis of water in reinforce hydrogels of plasma-polymerised poly(2-hydroxyethyl acrylate) (plPHEA) grafted onto macroporous poly(methyl methacrylate) (PMMA) are explained in a simple thermodynamic framework based on the transition diagram. Water in bulk PHEA was also analysed for comparison with plPHEA. These two hydrophilic polymers were prepared with a broad range of water mass fractions from 0.05 to 0.72. Thermal transition diagrams of water/PHEA and water/plPHEA were determined showing less undercooling of water crystallisation in plPHEA than in PHEA. Kinetics of water crystallisation for high and low water contents were studied in both hydrophilic systems following several thermal treatments. Water crystallises much faster in plPHEA than in PHEA for high water contents. For low water contents, crystallisation becomes possible holding at −30 °C for some time due to water segregation in both PHEA systems. However, much less water is segregated from the water/plPHEA mixture due to the influence of the hydrophobic component.

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