r - Creating a vector of random samples of variable length

I have an R script where

l2 is an array of all permutations of three letter combinations a-z ie the first values is aaa and the last values is zzz

c <- rpois(n, 5) is a vector of poisson distribution results.

I want to create a data frame that containtns a random number of samples from l2 and concatenates them into a path like this: abc -> vye -> tyb for 3.

df_p <- data.frame('len' = c, 's1' = paste(sample(l2,c), collapse = ' -> '))

I've tried to use the above row to create it, but it returns the same path for every row. The length of this path corresponds to the first value in c.