The 1 H-NMR spectra analysis of the product corroborates successful synthesis of the polyperoxides (Figure ). The signals at 1.26 and 1.47 ppm are assigned to CH3 protons (signals 1, 2, Figure ) of PM . The peak at 0.97 ppm is attributed to the methyl group of BA (signal 11, Figure , red). The signal at 4.09 ppm is attributed to the methylene group adjacent to the ester moiety in BA (signal 8, Figure , red). Weak and broad peaks that appear in the range 2.2 -3.5 ppm are attributed to signals of MA and methin groups in the polymer backbone, respectively (signals 4, 5 and 7, Figure , both spectra). The peaks at 1.46 and 1.65 ppm are also attributed to signals of BA (signals 10, 9, Figure , red) and methylene group in the polymer backbone (signals 3, 6 Figure ), respectively. At 6.31 ppm a signal is present which belongs to C-H of residual MA monomer. The presence of this residual monomer (approx. 10%) must be kept in mind for the further discussion, as it must be expected to also react during the heat treatment. Table shows the respective values of weight average molar mass (Mw) and dispersity (Ð) of the used polymers, obtained from GPC analysis. Both copolymers were obtained with relatively similar molar mass, ca. 2 * 10 4 kg/mol) and molar mass distribution typical for free radical polymerization (Ð= 1.6 and 2.6 respectively). As was already mentioned before, thermal decomposition of peroxides group leads to formation of free radicals followed by crosslinking via recombination reaction. The main low molecular weight products obtained during this process are acetone and tert-butyl alcohol . The thermal decomposition of the present polyperoxides was analyzed by TGA. The main mass loss was observed from ca. 110 to 200 °C, which is attributed to the decomposition of peroxide moieties (Figure ). According to the suggested decomposition, the main products after full decomposition of present peroxide groups are poly(5-methyl-1-hexen-3-yne-5-ol) or poly(5-methyl-1-hexen-3-yne-5one) (Figure ). Assuming that all peroxides groups decompose and are converted into poly(5methylhept-3-yn-2-one) we can calculate the expected weight loss during peroxide decomposition. For P[PM-co-MA], we expect 74 % residual mass, while 80 % residual mass is expected for P[PM-co-BA-co-MA]. The experimental results give a residual for P[PM-co-MA] of 69 % (137-215 °C) and ca. 71 % (156-203 °C) for P[PM-co-BA-co-MA], respectively (Figure ). Therefore, the mass loss is higher than based on the decomposition of the peroxides within the polymers alone. This may be attributed to other degradation pathways and/or incorrect determination of the peroxide content in the polymers. Following the established mechanism for crosslinking with peroxides, the crosslinking mechanism using polyperoxides should also comprise three main steps (Figure ). Taking into the account the radical nature of the process it is important to note that this scheme can only show a simplified picture of possible events, as radical reactions cannot be considered to be very specific and many side reactions will occur simultaneously, such as radical combination reactions of two small radicals or one macroradical and a small radical that do not lead to crosslinking. From low molar mass peroxides, it is known that the factors which influence crosslinking are crosslinker concentration, temperature and time. Accordingly, we suppose that variation of these parameters allows us to control the crosslinking density and resulting mechanical and swelling properties of the prepared hydrogels. If crosslinking of PEtOx by peroxide copolymers is successful, a covalent network should result, which swells in contact with water or other good solvents. The swelling behavior of hydrogels is one of their most important characteristic and the degree of swelling (SD) correlates with the crosslinking density of the polymer network .