In the present study, poly(N-vinylcaprolactam)s (PVCaps) as potent kinetic hydrate inhibitors (KHIs) were synthesized to unveil their effect on the structure I (sI) and structure II (sII) hydrate nucleation and growth rate. With the aim of enhancing the KHI performance of PVCap, 3-mercaptopropionic acid, mercaptoacetic acid, and L-cysteine as chain transfer agents (CTAs) were applied to produce polymers with different end groups. The synthesized polymers were evaluated in methane-water system and methane-THF-water system. All of the modified PVCaps outperformed the non-modified PVCap in terms of cloud point temperature (Tcl) and decreasing both sI and sII hydrate growth rate. The most effective PVCap to reduce the sI growth rate was mercaptoacetic acid-modified PVCap, while mercaptopropionic acid-modified PVCap was the strongest to slow down the sII growth rate. Furthermore, the synthesized polymers acted better than commercial Luvicap EG and PVP to retard the induction time in a way that the relative inhibition power (RIP) value for PVCap was 1.5 times greater than the RIP when Luvicap EG was used, also the maximum subcooling that synthesized PVCap could tolerated, was 2.7 and 1.5 K greater than that of PVP and Luvicap EG, respectively. Besides, it was found that a blend of PVCap (MWav = 4308 g/mol) with a higher molecular weight PVCap (6900 g/mol) had the best performance to increase the RIP values to 4.07 and 22.87 on sI and sII hydrate, respectively.

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