Albert Barnes on 2 Timothy 4:12

And Tychicus. See Acts 20:4. In Eph 6:21, Paul calls him "a beloved brother, and faithful minister in the Lord." But it may be asked, why he did not retain him with him, or why should he have sent him away, and then call Timothy to him? The probability is, that he had sent him before he had seen reason to apprehend that he would be put to death; and now, feeling the need of a friend to be with him, he sent to Timothy, rather than to him, because Tychicus had been employed to perform some service which he could not well leave, and because Paul wished to give some special instructions to Timothy before he died.

Have I sent to Ephesus. Why, is not certainly known. Comp. Intro paragraph 2.

(a) "Tychius" Tit 3:12