Crystallization of Coagent-Modified Polypropylene: Effect of Polymer Architecture and Cross-Linked Nanoparticles

Abstract

Linear isotactic polypropylene (PP) was chemically modified by solvent-free, peroxide-initiated grafting of trimethylolpropane trimethacrylate and triallyl trimesate. The resulting coagent-modified PP materials possessed bimodal molecular weight and branching distributions, whose populations varied with coagent structure. In addition to changing polymer chain architecture, these chemical modifications generated a small amount of well-dispersed, coagent-derived nanoparticles. When compared with the parent material and PP samples treated with peroxide alone, coagent-modified materials demonstrated significantly higher crystallization temperatures and crystallization rates, as well as a finer spherulitic structure. The importance of a particle-induced, heterogeneous nucleation mechanism is confirmed by comparative analysis of a long-chain branched PP derivative synthesized by homogeneous silane grafting and moisture curing chemistry. Crystallization studies show that whereas branching has a moderate effect on crystallization kinetics, heterogeneous nucleation effects dominate the crystallization of coagent-modified PP materials.

Transition from microcellular to nanocellular PLA foams by controlling viscosity, branching and crystallization

“…Reaction of PLA1 with DCP and TAM resulted in a product having comparable M w with PLA1/GMA and PLA2 (Figure 2 and Table 1). This material showed deviations from the M-H plot, pronounced bimodality in the molar mass distribution, and enhanced shear thinning, which has been commonly reported in polyolefins branched following this method, and is attributed to the presence of a highly branched population (Figure 10 a and b) [42][43][44].…”

Comprehensively improved mechanical properties of silane crosslinked polypropylene/ethylene propylene diene monomer elastomer blends

“…The crystallinity ( X c ) of silane crosslinked PP/EPDM blends decreases with the concentration of EPDM increasing, indicating that EPDM has a negative effect on the crystallization of PP and the incorporation of EPDM hinders the movement and rearrangement of PP chains. The crystallization peak temperatures ( T c ) and initial crystallization temperatures ( T i ) of SC7030 are higher than those of 7030, demonstrating that branching and crosslinking increase obviously the heterogeneous nucleation density and accelerate the crystallization of PP matrix . Furthermore, T c and T i of silane crosslinked PP/EPDM blends decrease gradually with EPDM content increasing, suggesting that excessive EPDM and high crosslinking degree retard the diffusion and packing of PP chains into crystal lattices.…”

A DSC study of polypropylene chain branching effects on structure formation under rapid cooling and reheating from the amorphous glass

“…LCB PPs made by a radical‐grafting technique usually contain a small cross‐linked fraction, a chemical gel, nonsoluble in boiling xylene 74 . To determine this gel content, we placed 1 g of the LCB PP samples in a porous stainless steel pouch and dissolved the sample with boiling xylene under reflux for 5 h. We then rinsed the insoluble matter retained in the pouch with fresh xylene for another 30 minutes.…”

“…Most authors explain the LCB PP α‐nucleation effect via melt structure, by the chain immobilization by entanglents 68,70 . Alternatively, the cross‐linked fraction formed by extensive branching may act as athermal permanent nuclei 74 …”

“…68,70 Alternatively, the cross-linked fraction formed by extensive branching may act as athermal permanent nuclei. 74 However, the LCB PP α-nucleation effect is regardless of whether the production route has formed a cross-linked fraction. 68,73 Moreover, LCB PP crystallization changes by melt-processing history, 29 and finally, it also exists for other polymers like for branched polylactide.…”