Weekly topic: 5 Wealth points for correct answers, 2 Wealth points for participation； Question 228
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Judgment: The degree of swelling of cross-linked polymers depends partly on the degree of cross-linking; as the degree of cross-linking increases, the degree of swelling decreases. ( ) —————————————————— Please note: We will close this thread after 24 hours, and at that time we will announce the best reply (the best assistance), as well as the answer and explanation. Attraction Reward: If you post a topic in this section within two days to provide a detailed explanation or discussion of the knowledge points related to this question, please reply or leave a comment in this post to inform us, and we will have a moderator grant you +Attraction. It is not allowed to simply copy and paste; original content is preferred, with at least some organization by the user along with personal insights.
The degree of swelling of cross-linked polymers depends partly on the degree of cross-linking; as the degree of cross-linking increases, the degree of swelling decreases. (Correct)
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The degree of swelling of cross-linked polymers depends partly on the degree of cross-linking; as the degree of cross-linking increases, the degree of swelling decreases. Cross-linked polymers cannot dissolve in solvents, but they can swell to a certain extent; the degree of swelling depends on the degree of cross-linking of the polymer. When a cross-linked polymer comes into contact with a solvent, since the molecular segments between the cross-linking points are still relatively long and thus possess considerable flexibility, solvent molecules can easily penetrate into the polymer, causing the three-dimensional molecular network to expand and its volume to increase. However, the stretching of the molecular chains between the cross-linking points leads to a decrease in the conformational entropy of the network; as a result, the network exerts an elastic contracting force that causes it to shrink, thereby preventing solvent molecules from entering the network. When these two opposing effects cancel each other out, the system reaches a state of swelling equilibrium, and the volume of the swollen substance no longer changes. As the degree of crosslinking in the polymer increases, the chain segment length decreases, the flexibility of the molecular network diminishes, and accordingly the swelling degree of the polymer decreases; as a result, experimental errors also increase. When highly cross-linked polymers come into contact with a solvent, the molecular segments between the cross-linking points are very short and no longer flexible; as a result, solvent molecules find it difficult to penetrate into this rigid molecular network. Therefore, highly cross-linked polymers do not even swell in a solvent. On the contrary, if the degree of crosslinking is too low, the free ends present in the molecular network do not contribute to swelling, resulting in a significant deviation from theory. Moreover, polymers with too low a degree of crosslinking contain components that can dissolve in solvents; upon swelling in such solvents, they form sols with very low strength, which poses many difficulties for measurement and also leads to substantial experimental errors. Therefore, the swelling equilibrium method is only suitable for determining the degree of crosslinking in moderately crosslinked polymers.
The degree of swelling of cross-linked polymers depends partly on the degree of cross-linking; as the degree of cross-linking increases, the degree of swelling decreases. ( Right )
The degree of swelling of cross-linked polymers depends partly on the degree of cross-linking; as the degree of cross-linking increases, the degree of swelling decreases. ( Right )
The degree of swelling of cross-linked polymers depends partly on the degree of cross-linking; as the degree of cross-linking increases, the degree of swelling decreases. ( Right )