Cross-Linked Polypropylene Prepared by PP Copolymers Containing Flexible Styrene Groups

Abstract

This paper discusses an effective method to prepare cross-linked isotactic polypropylene (PP-X) with high purity (almost 100% gel content and no contamination) and high melting temperature and crystallinity. The reaction scheme involves a linear poly(propylene-co-p-(3-butenylstyrene)) copolymer (PP-BSt) containing few pendent styrene groups and the subsequent thermal treatment without any external reagent. The intermediate PP-BSt copolymers were prepared by a specific rac-CH2(3-tert-butyl-Ind)2ZrCl2/MAO catalyst that not only performs iso-specific propylene insertion but also incorporates BSt units with a preferred α-olefin insertion over styrene moiety. The combined features permit the preparation of linear PP-BSt copolymers with high molecular weight and high catalyst activity, without the presence of hydrogen. The resulting PP-BSt copolymers having some flexible pendent styrene moieties are completely soluble in xylene at elevated temperatures, and the solution case films show active cross-linking activity at temperatures >160 °C by engaging in a Diels−Alder [2 + 4] interchain cycloaddition reaction between the pendent styrene units. Evidently, the flexibility of styrene units is important, which enhances the interchain cyclization to form a complete 3-D network, even with a very small amount of BSt units. In contrast, the corresponding poly(propylene-co-p-divinylbenzene) (PP-DVB) prepared by the same metallocene catalyst only shows moderate cross-linking efficiency under similar conditions.

Introduction of reactive functionality by the incorporation of divinylbiphenyl in ethylene copolymerization with styrene or 1‐hexene using aryloxo‐modified half‐titanocenes and MAO catalysts

“…The result thus clearly suggests the successful preparation of the graft polymer by initiating styrene polymerization from the vinyl group in the poly(ethylene‐ co ‐styrene‐ co ‐DVBP). As the above result is only a demonstration for the postmodification, we need to optimize the conditions as well as more applications in more detail (including an introduction of the other functionalities and/or of crosslinking fragments for thermal resistance by thermal treatment). The approach adopted here demonstrates a promising possibility of the precise postmodification.…”

Functionalization of Polypropylene by the Combination of Metallocene Catalysts and Reactive Comonomers

“…We had also studied asymmetric diene comonomers that contain a α‐olefin and a styrenic moiety, as illustrated in Scheme . The objective is to incorporate pending styrene groups into the polyolefin flexible side chains, which are facile for a broad range of reactions, including free radical, cationic, and anionic functionalization and grafting reactions.…”

“…The objective is to incorporate pending styrene groups into the polyolefin flexible side chains, which are facile for a broad range of reactions, including free radical, cationic, and anionic functionalization and grafting reactions. With the versatility of metallocene catalysis, it is possible to select an active site with a specific stereo opening that exhibits selectivity in the α‐olefin enchainment and results in pendent styrene groups, without causing branching and/or cross‐linking side reactions . As shown in Scheme , the pendant styrene groups in the PP copolymer can engage in simple thermal cycloaddition with maleic anhydride to form the MAH‐functionalized PP or between styrene groups (dimmerization) to form cross‐linked PP (x‐PP) under a control manner.…”

“…The rac ‐CH 2 (3‐t‐Butyl‐Ind) 2 ZrCl 2 /MAO was found to be a selective metallocene catalyst for α‐olefin enchainment, without reacting with styrene moiety . All copolymerization reactions between propylene and p ‐(3‐butenylstyrene) ( p ‐BSt) maintained very high catalyst activities, and the resulting PP‐co‐ p ‐BSt copolymers (with up to 8 mol% of p ‐BSt content) were completely soluble in xylene at an elevated temperature.…”

Mechanochemistry: a novel approach to graft polypropylene with dual monomers (PP-g-(MAH-co-St))

“…The grafting technique with reactive monomers onto PP has been widely used in the modification of PP to overcome these problems [3][4][5][6]. Maleic anhydride (MAH) was extensively studied to modify PP in commercial applications due to its unique combination, low cost, high activity, and good processibility [3][4][5][6][7][8][9]. However, it is difficult for the copolymerized MAH to homopolymerize.…”