Flow Accelerates Interfacial Coupling Reactions

Abstract

Reactive coupling of functional polymer chains has been reported to be 3 orders of magnitude slower at static interfaces than under mixing conditions, and the reaction rates under mixing are close to the rates measured in homogeneous melts [Jeon et al. Prog. Polym. Sci. 2005, 30, 939]. However, due to the complexity of interfacial area generation during mixing, it was difficult to isolate the effects of flow on reaction kinetics. In this paper, a reactive multilayer system was created to explore this issue. A 640-layer polystyrene (PS)/poly(methyl methacrylate) (PMMA) sample was fabricated with a multilayer coextruder. Each component contained 10 wt % functional polymer, an amine-terminal PS (PS-NH 2 ), and an anthracence-labeled anhydride-terminal PMMA (PMMA-anh-anth), respectively. Coupling reactions between PS-NH 2 /PMMA-anh-anth occurred during extrusion. The reaction conversion was measured with size exclusion chromatography, and interfacial morphology was monitored with both scanning and transmission electron microscopy. It was found that a significant amount of PS-b-PMMA copolymer formed during coextrusion, such that the interfaces of the extrudate were almost completely saturated with the block copolymers formed in situ. The coupling reaction of PS-NH 2 /PMMA-anh-anth under coextrusion was as rapid as that under mixing and was up to 1000 times faster than that under quiescent annealing. Subsequent steady shear of the multilayer samples further increased the reaction conversion significantly but destroyed the layer structure. Micelles and swollen micelles were formed under shear. Dynamic shear did not promote any further reaction due to the already high interfacial coverage for the extrudate. In contrast, for a simple laminated bilayer sample with nearly zero interfacial coverage, reactive coupling was promoted significantly by dynamic shear as evidenced by interfacial roughening. We speculate that the high surface energy of the functional chain ends causes them to be depleted near the interface, leading to very slow coupling under quiescent conditions. Moreover, the diffusion of polymer chains very close to the surface has been reported to be much slower than in bulk. Under coextrusion or mixing, external flow increased the functional group concentration in the interfaces, restoring reaction rates to the level expected under homogeneous conditions. The uniformity of block copolymer formation across the coextruded sample argues that extensional deformation is more important than shear in accelerating coupling.

Flow accelerates adhesion between functional polyethylene and polyurethane

“…As shown in Figures 8a, b, coextrusion accelerates the coupling reaction for all types of functional PEs. Similar phenomena were found in the literature where the coupling reaction between an amine-terminal polystyrene (PS-NH 2 ) and an anhydride-terminal polymethyl methacrylate (PMMA-anh) bilayer took about 1 h for the interface to be saturated with block copolymers, whereas when these two polymers were melt blended 11,28 or multilayer coextruded, 8 it took less than 1 min (i.e., about two orders of magnitude faster compared to quiescent annealing). For the coextrusion experiments reported here, the reaction acceleration occurs during laminar flow without mixing.…”

“…Therefore, the reaction rate between two immiscible reactive polymers in a molten interface was significantly higher than that of small molecule analogues in solution. Zhang et al 8 and Feng and Hu 28 also observed similar phenomena. This is not surprising considering increased collision probability originating from longer relaxation time of reactive polymer chains holding functional groups at the interface.…”

Forced assembly by multilayer coextrusion to create oriented graphene reinforced polymer nanocomposites

“…It has been suggested that the interface can be improved by the use of block copolymer compatibilizers to prevent delamination in this system [34,48].…”

“…Fig. 8 1 We note that a significant spontaneous delamination between the PMMA and PS layers occurred after two months of the samples sitting at ambient conditions in the lab, apparently due to the low interfacial adhesion between the immiscible PS and PMMA layers [34]. presents the T g corrected reinforcements of flow and transverse directions.…”

Adhesion between polyethylenes and different types of polypropylenes

“…A detailed description of the co-extrusion line can be found in the literature. 3,[6][7][8][9] On the basis of the continuity equation, melt velocity in the co-extrusion dies can be deduced from the chill-roll speed and film thickness. At a total flow rate of 38.4 cm 3 min À1 as determined from gear-pump rotation rate, the residence time of the interface traveling at equal flow rates was determined to be 9-13 s by using the method described by Song et al 3 Upon exiting the die land, bilayer films were drawn by stainless steel rolls chilled at 4 1C.…”