Found these mentioned in a footnote in Skarsaune & Hvalvik's Jewish Believers in Jesus (amazon.com); this is the proverbial "note to myself" so I can dig the references out again:

Kenneth Berding, Polycarp and Paul: An Analysis of Their Literary and Theological Relationship in Light of Polycarp's Use of Biblical and Extra-Biblical Literature (amazon.com) (VCSup 62; Leiden: Brill, 2002)

Paul Hartog, Polycarp and the New Testament: The Occasion, Rhetoric, Theme and Unity of the Epistle to the Philippians and its Allusions to New Testament Literature (amazon.com) (WUNT 2.134; Tübingen: J.C.B. Mohr, 2002)

That is all.