# Functionalized Polypropylene Copolymers as Multisubstrate Hot-Melt Adhesives

## TL;DR

This paper introduces new amine-modified polypropylene copolymers that work well as adhesives for both steel and plastic surfaces.

## Contribution

The study presents a novel method to create functionalized polypropylenes with enhanced multisubstrate adhesion.

## Key findings

- PP EAE and PP DEOA showed the highest adhesive strength to steel, with 16.8 MPa and 17.4 MPa, respectively.
- PP DEOA demonstrated a 252-fold improvement in adhesion compared to unmodified PP.
- PP DEA and PP EAE exhibited optimal performance with failure by stock break, indicating strong adhesion.

## Abstract

Amine-modified polypropylenes
(PP

R
, R = NH­(Et)2 (DEA);
NH­(Et)­(CH2CH2OH) (EAE); NH­(CH2CH2OH)2 (DEOA))
have been prepared via a two-step synthesis and display enhanced adhesive
performance with respect to both steel and polypropylene (PP) substrates.
PP typically displays poor adhesion to polar substrates, which consequently
restricts its utility as a hot-melt adhesive (HMA). Solvent-free,
quantitative postmodification of poly­(propylene)-co-(11-bromo-1-undecene) (range of comonomer incorporations (3–9
mol %)) with secondary amines yielded amine-modified PPs: PP

DEA
, PP

EAE
, and PP

DEOA
. Rheological
and FT-IR characterization identified the presence of a PP-based supramolecular
hydrogen bonding network. (Co)­polymers were evaluated as HMAs by lap
shear strength between steel–steel and steel–plastic
substrates. PP

EAE
and PP

DEOA
both excelled as HMAs between steel,
recording the largest mean adhesive forces of 16.8 and 17.4 MPa, respectively; PP

DEOA
displayed a 252-fold increase
vs PP and comparable adhesive strengths to conventional
structural adhesives. The adhesive failure mode in multisubstrate
adhesion was found to be a function of interfacial effects, depending
on the relative ability of the HMAs to bind to the polar steel surface
and diffuse into the plastic substrate. PP

DEA
and PP

EAE
were
found to be optimal in this case with failure by stock break indicative
of adhesion greater than the tensile strength of the substrate and
consequently appropriate for the application. The unique properties
of these bifunctional materials highlight the versatility of the relatively
limited application of functionalized PPs to date. This study now
allows further sets of functionalized PPs to be readily prepared to
meet a diverse array of multisubstrate adhesive requirements.