Tuning Melt Strength and Processability of Polyolefins by Addition of a Functionalized Additive Designed via the TEMPO-Driven Thiol-ene Reaction

Abstract

Thiol-ene chemistry with TEMPO as an initiator has been utilized to synthesize a first-generation dendrimer having eight peripheral hydroxyl groups. Long chain branched impact copolymer polypropylene (ICP) and linear low-density polyethylene (LLDPE) were prepared by a postreactor modification process by a meltgrafting dendrimer onto a polyolefin chain using peroxide and maleic anhydride as a co-agent. Long chain branching in ICP controlled the chain scission initiated by peroxide by increasing entanglement, while for LLDPE, it controlled the excessive crosslinking because of peroxide. Neat and modified ICP and LLDPE samples were analyzed by FT-IR, TGA, DSC, HT-GPC, MFI, and parallel-plate rheometry as well as for their melt strength. The presence of long chain branching was mainly confirmed by time−temperature superposition (TTS) analysis obtained using a parallel-plate rheometer. In comparison to neat polymers, modified ICP and LLDPE samples showed higher values of Arrhenius flow activation energy. In the case of ICP, higher processability was observed for a dendrimer-grafted sample, while modified LLDPE samples exhibited higher melt strength as compared to neat polymers. Van Gurp−Palmen plots showed a decrease in phase angle as a function of angular frequency for modified ICP and LLDPE samples, which also confirmed their thermorheological complex behavior.

Improved melt strength and processability of impact copolymer polypropylene by introducing long‐chain branching via reactive extrusion with “ene” functionalized dendrimer

“…It is noteworthy to mention that in our previous work, we concluded that reactive extrusion with G1 enhanced processability while maintaining melt strength as that of neat ICP. [29] In the present work, we observed improved processability as well as melt strength as compared to neat ICP using extended long-chain branching obtained via melt grafting of G2. The prepared samples were also examined for their impact, flexural, and tensile strength, and it was observed that there is no degradation in the bulk mechanical properties of ICP after grafting G2 on polymer chains.…”

“…Precursor generation 1 dendrimer (G1) was synthesized as reported in our previous work. [ 29 ] Carboxyethyl acrylate, free radical initiator Luperox‐101 (luperox), and sodium sulfate were purchased from Sigma Aldrich Chemicals. 1‐Ethyl‐3‐(3‐dimethyl aminopropyl) carbodiimide (EDC) and 4‐dimethyl aminopyridine (DMAP) were supplied from Spectrochem.…”

“…G1 was synthesized by the procedure mentioned in our last published work. [ 29 ] The reaction scheme for the synthesis of G2 has been shown in Scheme 1. G1 (6.8 mmol) was taken in a Schlenk tube and dissolved in around 10 ml of anhydrous THF while purging nitrogen.…”

“…G2 has been synthesized using esterification reaction from its precursor G1, whose synthesis via TEMPO initiated thiol‐ene chemistry and role as an additive in ICP and linear LDPE (LLDPE) has been reported in our previous work. [ 29 ] Dendrimers have a globular and fractal structure with numerous terminal functional groups that can increase their reactivity multifold in the chemical modification process during reactive extrusion. G2 has been prepared to utilize this unique property of dendrimers, by converting terminal eight hydroxyl groups of G1 to respective double bonds.…”

Silica derived from variety of sources and its functionalized forms as an antiblock additive in polypropylene

“…Numerous modifications have been performed with PP, and the new properties achieved have been studied in detail and are well reported. [3][4][5] To improve the properties and to enhance the performance of PP in packaging applications, various fillers 6 and additives are utilized with PP. Resch et al 7 investigated the morphology of different types of PP cast films prepared using different formulations and processing conditions.…”