High Molecular Weight Linear Polyethylene Research Articles

Exceptionally high molecular weight linear polyethylene by using N,N,N′‐Co catalysts appended with a N′‐2,6‐bis{di(4‐fluorophenyl)methyl}‐4‐nitrophenyl group

The bis(arylimino)pyridines, 2‐[CMeN{2,6‐{(4‐FC6H4)2CH}2–4‐NO2}]‐6‐(CMeNAr)C5H3N (Ar = 2,6‐Me2C6H3 L1, 2,6‐Et2C6H3 L2, 2,6‐i‐Pr2C6H3 L3, 2,4,6‐Me3C6H2 L4, 2,6‐Et2–4‐MeC6H2 L5), each containing one N′‐2,6‐bis{di(4‐fluorophenyl)methyl}‐4‐nitrophenyl group, have been synthesized by two successive condensation reactions from 2,6‐diacetylpyridine. Their subsequent treatment with anhydrous cobalt (II) chloride gave the corresponding N,N,N′‐CoCl2 chelates, Co1 – Co5, in excellent yield. All five complexes have been characterized by 1H/19F NMR and IR spectroscopy as well as by elemental analysis. In addition, the molecular structures of Co1 and Co3 have been determined and help to emphasize the differences in steric properties imposed by the inequivalent N‐aryl groups; distorted square pyramidal geometries are adopted by each complex. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), precatalyts Co1 – Co5 collectively exhibited very high activities for ethylene polymerization with 2,6‐dimethyl‐substituted Co1 the most active (up to 1.1 × 107 g (PE) mol−1 (Co) h−1); the MAO systems were generally more productive. Linear polyethylenes of exceptionally high molecular weight (Mw up to 1.3 × 106 g mol−1) were obtained in all cases with the range in dispersities exhibited using MAO as co‐catalyst noticeably narrower than with MMAO [Mw/Mn: 3.55–4.77 (Co1 – Co5/MAO) vs. 2.85–12.85 (Co1 – Co5/MMAO)]. Significantly, the molecular weights of the polymers generated using this class of cobalt catalyst are higher than any literature values reported to date using related N,N,N‐bis (arylimino)pyridine‐cobalt catalysts.

Robust Bulky [P,O] Neutral Nickel Catalysts for Copolymerization of Ethylene with Polar Vinyl Monomers

Several nickel complexes bearing sterically bulky phosphino-phenolate ([P,O]) ligands were synthesized and explored as catalysts for olefin (co)polymerization. In the absence of an activator, the complexes showed very high catalytic activities (up to 107 g molNi–1 h–1) for ethylene polymerization even at 90 °C or with the addition of a large amount of a polar additive (such as ethyl alcohol, diethyl ether, acetone, or even water), affording linear polymers with high molecular weights (up to 6.53 × 105). In contrast, most of the previously reported nickel catalysts suffer from severe activity suppression at elevated temperature. It is rare that a catalyst has so many good performances simultaneously, including high catalytic activity, good tolerance for polar groups, strong thermal stability, and yielding high molecular weight linear polyethylene. Most importantly, these bulky nickel complexes used in this study also effectively copolymerized ethylene with challenging polar vinyl monomers, including commer...

Nanocrystal Formation in Aqueous Insertion Polymerization

High molecular weight linear polyethylene, in the form of 7 nm thin single-lamella nanocrystals with a diameter of up to 200 nm, is generated via aqueous catalytic polymerization using the water-soluble catalyst precursor [κ2-N,O-{2,6-(3′,5′-(F3C)2C6H3)2C6H3-N═C(H)-(3,5-I2-2-O-C6H2)}NiCH3{P(3-C6H4SO3Na)3}] (1-TPPTS). Studies under true pressure reactor conditions using a 13C-labeled catalyst precursor 1-13C-TPPTS show that in the first 30 s, 21–28% of the catalyst precursor initiates polymer chains. Catalyst deactivation occurs preferentially by hydrolysis, resulting in the formation of fully saturated polyethylene chains. The catalyst lifetime can be extended for more than 10 h upon addition of weakly coordinating compounds like N,N-dimethylformamide. Alternatively, at strongly basic conditions (pH 12.5) nanoparticle dispersions consisting of polyethylene with molecular weight of up to Mn = 7 × 105 g mol–1 and Mw/Mn = 1.2 are accessible after 60 min polymerization time. “Living”-type polymerization also ...

Pentamethylcyclopentadienyltitanium aryl(pyridyl)amide complexes: Synthesis, characterization and catalytic performance for olefin polymerization

A series of new half-sandwich pentamethylcyclopentadienyl titanium (IV) aryl(pyridyl)amide complexes, Cp*TiCl2[N(Ar)(2-Py)] [Ar = 2,6-iPr2Ph (1), 2,6-Et2Ph (2), 2,6-Me2Ph (3), 4-MePh (4)], have been synthesized from the reactions of Cp*TiCl3 with the lithium salts of the corresponding aryl(pyridyl)amido ligands in toluene. A byproduct with two aryl(pyridyl)amido ligands, Cp*TiCl[N(4-MePh)(2-Py)]2 (5) was also obtained from the synthetic reaction of complex 4 in a small amount. The new titanium complexes 1–4 were characterized by 1H and 13C NMR and elemental analyses. The molecular structures of complexes 1, 2, 4 and 5 were determined by single-crystal X-ray diffraction analysis. X-ray crystallographic analysis on complexes 1, 2, 4 demonstrates that these complexes possess a relatively crowded hepta-coordinating environment surrounding the central titanium atom. Upon activation with AliBu3 and Ph3CB(C6F5)4, complexes 1–4 exhibited moderate to high catalytic activity for ethylene and propylene polymerization, producing high molecular weight linear polyethylene and atactic polypropylene. It was found that complex 1 shows the highest catalytic activity for ethylene polymerization while complex 4 shows the highest catalytic activity for propylene polymerization among these complexes under similar conditions.

Composites from Aqueous Polyethylene Nanocrystal/Graphene Dispersions

Aqueous high molecular weight linear polyethylene nanocrystal/graphene composite dispersions were produced in situ by ethylene insertion polymerization in water or alternatively via a postpolymerization technique. Graphene was used without any prior compatibilizing surface modification. Remarkably, the Ni(II) salicylaldiminato catalyst employed is polymerization active in the presence of the functional groups of graphene in the absence of any scavengers or activating agents in the aqueous system. The intimate intermixing between the polyethylene nanocrystals and graphene in dispersion enables the formation of a uniformly dispersed graphene framework upon precipitation. Because of the very small size of the polyethylene nanocrystals, no segregation of the graphene on the particle surface is possible. The composites obtained feature a low electrical percolation threshold of the highly dispersed graphene. Commercially available graphene is compared with thermally reduced graphene oxide (TRGO) regarding its d...

Solvent and co-catalyst dependent pyrazolylpyridinamine and pyrazolylpyrroleamine nickel(II) catalyzed oligomerization and polymerization of ethylene

The pyrazolylamine ligands, 2-(3,5-dimethyl-1H-pyrazol-1-yl)-N-(pyridin-2-ylmethyl)ethan-amine (L1a), 2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)-N-(pyridin-2-ylmethyl)ethan-amine (L2a), 2-(3,5-dimethyl-pyrazol-1-yl)-ethyl-(1H-pyrrol-2-ylmethyl)-amine (L3a), 2-(3,5-di-tert-butyl-pyrazol-1-yl)-ethyl-(1H-pyrrol-2-ylmethyl)-amine (L4a), were prepared by reducing the corresponding imine compounds L1–L4. L1a–L4a were then reacted with [NiBr2(DME)] to form the nickel complexes, [NiBr2(L1a)] (1), [NiBr2(L2a)] (2), [NiBr2(L3a)] (3) and [NiBr2(L4a)] (4) in high yields.When activated with aluminum co-catalysts, all four nickel complexes were able to catalyze the oligomerization or polymerization of ethylene; but the products of these reactions were co-catalyst and solvent dependent. With EtAlCl2 as co-catalyst and in toluene, butene and hexene were formed, which subsequently alkylated the solvent selectively to butyl-, dibutyl- and tri-butyltoluene. The same catalysts in chlorobenzene produced butene, hexene and highly branched polyethylene. Changing the co-catalysts to MAO and with toluene as solvent, complexes 2 and 3 catalyzed the polymerization of ethylene to high molecular weight (447,300Da) linear high density polyethylene (ca Tm=135.5°C); with polydispersity indices ranging from 1.63 to 2.51.

Flow-induced crystallization precursor structure in high molecular weight isotactic polypropylene (HMW-iPP)/low molecular weight linear low density polyethylene (LMW-LLDPE) binary blends

The formation of initial crystallization precursor induced by flow was investigated by synchrotron-based wide- and small-angle X-ray scattering techniques (WAXS/SAXS), using polymer blends consisting of high molecular weight isotactic polypropylene (HMW-iPP) and low molecular weight linear low density polyethylene (LMW-LLDPE) as model systems. LMW-LLDPE, the dominant component, served as the amorphous matrix. Crystallization behavior of the blends with three different HMW-iPP concentrations, i.e., 3, 6 and 9 wt%, were examined at temperatures higher than the blends' cloud points, in a time-resolved manner. It was found that the formation of a flow-induced precursor of crystallization was strongly influenced by the concentration of HMW-iPP in the blends. The blend with low HMW-iPP content (3 wt%) was not able to form a shear-induced crystalline structure. As the concentration of HMW-iPP increased, crystallization kinetics, crystallinity, and lamellar orientation were greatly enhanced.

Synthesis and olefin polymerization activity of (quinolin-8-ylamino)phenolate and (quinolin-8-ylamido)phenolate Group 4 metal complexes

New Zr and Hf complexes bearing either a tridentate monoanionic 2- tert-butyl-6-[(quinolin-8-ylamino)methyl]phenolate [N,N,O −] or a dianionic 2- tert-butyl-6-[(quinolin-8 ylamido)methyl]phenolate [N,N −,O −] ligand have been synthesized and characterized. The geometries of the zirconium complexes have been studied using DFT methods. The complexes were tested as catalysts in the polymerization of ethylene and α-olefins after activation with methylalumoxane, resulting in the production, with moderate activities, of high molecular weight linear polyethylene and prevailingly isotactic polypropylene, poly(1-butene), poly(1-pentene) and poly(1-hexene). The content of isotactic pentads of these poly(α-olefins) increases while the size of the monomer increases, ranging between 50% for polypropylene and 99% for poly(1-hexene).

Self-Assembled Tetranuclear Palladium Catalysts That Produce High Molecular Weight Linear Polyethylene

The phosphine-bis-arenesulfonate ligand PPh(2-SO(3)Li-4-Me-Ph)(2) (Li(2)[OPO]) coordinates as a kappa(2)-P,O chelator in Li[(Li-OPO)PdMe(Cl)] (2a) and (Li-OPO)PdMe(L) (L = pyridine (2b); MeOH (2d); 4-(5-nonyl)pyridine) (py', 3)). 2a reacts with AgPF(6) to form {(Li-OPO)PdMe}(n) (2c). Photolysis of 2d yields {(OPO)Pd}(2) (5) in which the [OPO](2-) ligand coordinates as a kappa(3)-O,P,O pincer. 3 self-assembles into a tetramer in which four (Li-OPO)PdMe(py') units are linked by Li-O bonds that form a central Li(4)S(4)O(12) cage. The Pd centers are equivalent but are spatially separated into two identical pairs. The Pd-Pd distance within each pair is 6.04 A. IR data (upsilon(ArSO(3)(-)) region) suggest that the solid state structures of 2a-c are similar to that of 3. 3 reacts with the cryptand Krypt211 to form [Li(Krypt211)][(OPO)PdMe(py')] (4). 3 is in equilibrium with a monomeric (Li-OPO)PdMe(py') species (3') in solution. 2a-c and 3 produce polyethylene (PE) with high molecular weight and a broad molecular weight distribution, characteristic of multisite catalysis. Under conditions where the tetrameric structure remains substantially intact, the PE contains a substantial high molecular weight fraction, while, under conditions where fragmentation is more extensive, the PE contains a large low molecular weight fraction. These results suggest that the tetrameric assembly gives rise to the high molecular weight polymer. In contrast, the monomeric complex 4, which contains a free pendant sulfonate group that can bind to Pd, oligomerizes ethylene to a Schultz-Flory distribution of C(4)-C(18) oligomers.

Early Transition Metal Complexes Bearing a C-Capped Tris(phenolate) Ligand Incorporating a Pendant Imine Arm: Synthesis, Structure, and Ethylene Polymerization Behavior

The ligand 3-[2,2'-methylenebis(4,6-di- tert-butylphenol)-5- tert-butylsalicylidene-(2,6-diisopropyl)phenylimine] (L(1)H 3) was reacted with MCl 4 (M = Ti, Zr) or MCl 5 (M = Nb, Ta) to give complexes of the type [MCl 2(L(1)H 2) 2] (M = Ti (1); Zr (2)), [NbCl 3( L (1)H)] (3), or [TaCl 4(L(1)H 2)] (4), respectively. Single crystal X-ray diffraction of 1- 4 revealed common "iminium" species resulting in zwitterionic complexes. Reaction of [V(N p-tol)(O n-Pr) 3] with L (1)H3 afforded [{(VN p-tol)(L(1)H)} 2(mu-O n-Pr)2] (5), and a second complex [(VO) 2(mu-O)(L(3)H) 2] (6)(L(3)H being derived from 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene- p-tolylimine]). The condensation reaction between 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butyl-2-hydroxybenzaldehyde] (L(0)H 3) and o-phenylenediamine (1,2-diaminobenzene) afforded two products: a pseudo-16-membered hydrogen bonded macrocyclic structure {1,2-bis-3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-benzyldiimine]} (L(5)H6), or the benzimidazolyl bearing ligand (L(6)H 3). The reaction of L (5)H6 or L(6)H 3 with [VO(O n-Pr) 3] under varying conditions produced the complexes [(VO)(L(5)H 4)] (7), [(VO) 2(L(5)H)] (8), or [VO(L(6)H 2) 2] (9). L (0)H 3 was reacted with a number of anilines to give the proligands {3-[2,2'-methylenebis(4,6-di- tert-butylphenol)-5-tert-butylsalicylidene-R-imine]}, where R = NC 6H 5 (L(2)H3), NC 6H 4-Me (L(3)H 3), and NC 6H 2-Me 3 (L(4)H 3). Reactions of these ligands with [VO(O n-Pr) 3] formed bischelating complexes of the form [(VO)(L(2-4)H 2)2] (10, 11, and 12, respectively). The reaction of L (1)H 3 with trimethylaluminum led to a bis-aluminum complex {(AlMe 2)[AlMe(NCMe)] L (1)} (13). The ability of complexes 1-12 to polymerize ethylene in the presence of an organoaluminum cocatalyst was investigated. Procatalysts 1 and 2 were found to produce negligible activities in the presence of dimethylaluminum chloride (DMAC) and the reactivator ethyltrichloroacetate (ETA), whereas 3 and 4 were found to be completely inactive for polymerization using a variety of different organoaluminum cocatalysts. Using the combination of DMAC and ETA, complexes 5-12 were found to be highly active catalysts; in all cases, the polymer formed was of high molecular weight linear polyethylene.

Comparison of olefin polymerization behavior of sterically crowded tris(pyrazolyl)borate group 4 metal complexes

The ethylene polymerization and ethylene/α-olefin copolymerization behavior of the sterically crowded tris(pyrazolyl)borate group 4 metal complexes Tp Ms*TiCl 3 ( 1, Tp Ms* = HB(3-mesitylpyrazolyl) 2(5-mesitylpyrazolyl) −), {K[Tp Ms*TiCl 3]} 2 ( 2), Tp Ms*TiCl 2(O-2,4,6- tBu 3-Ph) ( 3), Tp Ms*ZrCl 3 ( 4), Tp MsZrCl 3 ( 5, Tp Ms = HB(3-mesitylpyrazolyl) 3 −), and Tp Ms*HfCl 3 ( 6) were studied with dried-MAO activation in toluene solution. These catalysts all produce very high molecular weight ( M v > 10 6) linear polyethylene. Zirconium catalyst 5 excels in productivity in ethylene homopolymerization and ethylene/1-hexene copolymerization, molecular weight, and hexene incorporation ability. Catalyst 5 produces moderately alternating ethylene/1-hexene copolymer (41 mol% hexene) with ultra-high molecular weight ( M w = 1.3 × 10 6), narrow molecular weight distribution ( M w/ M n = 2.2) and narrow composition distribution with high efficiency.

Highly Active Half-Metallocene Chromium(III) Catalysts for Ethylene Polymerization Activated by Trialkylaluminum

Highly active half-metallocene type chromium(III) catalysts for ethylene polymerization have been developed. High molecular weight linear polyethylene (Mn > 1 000 000 g/mol) was produced by these catalysts in the presence of a relatively small amount of AlR3 (25 equiv).

Lateral habits of single crystals of metallocene-catalyzed low molecular weight short chain branched polyethylene from the melt

The lateral habits of low molecular weight short chain branched polyethylene single crystals from the melt were studied. Three crystallization temperatures (102, 104 and 106°C) were selected for single crystal growth. It was found that the lateral habits of single crystals were asymmetric at all the crystallization temperatures selected. The electron diffraction patterns and tilting series experiments evidenced that there existed chain tilting in all the lamellae. It was the chain tilting that lead to the asymmetry of the growth rate and of lateral habits of the single crystals about the b-axis. The lateral habits substantially changed from the growth at 102°C where the truncated lozenge single crystals formed with straight (110) faces to the growth at 104°C where the lenticular single crystals appeared. This change occurred at 20°C lower than that in a low molecular weight linear polyethylene with the same molecular weight. Furthermore, kinetics theory analysis evidenced that the change of lateral habits from truncated lozenge to lenticular shape resulted from the transition of growth regime. The results were the same as that of high molecular weight linear polyethylene but different to that of low molecular weight linear polyethylene. It may be attributed by the existence of short branched chains.

Supported transition metal complexes for ethylene polymerization

This paper describes the preparation of some active organometallic species derived from nickel, titanium and zirconium fixed on the surface of different supports and their behaviour for the catalytic polymerization of ethylene. In the case of nickel, the transition metal species were attached to crosslinked polystyrene resins through a carbon atom of the P O chelate ligand. The formation of high molecular weight linear polyethylene is discussed in comparison to homogeneous analogs giving oligomeric products under the same conditions. Titanium containing species on the MgCl 2 surface are obtained by coprecipitating the metals from solution of their alcoholates or carboxylates. These species are shown to be sensitive to the presence of carboxylate ligands which affect the catalytic process. Finally biscyclopendienyl dichloro or dimethyl zirconium have been supported on modified HY zeolite to give catalysts showing the same activity as the homogeneous analogs but higher stability during the polymerization reactions. General aspects deriving from these results are discussed with reference to the possibility of improving the design of well defined physically heterogeneous catalysts.

Iso-specific Ziegler-Natta polymerization of .alpha.-olefins with a single-component organoyttrium catalyst

The synthesis of a sterically tailored ligand array (M)_2((C_5H_2-2-Si(CH_3)_3-4-C(CH_3)_3)S_2i(CH_3)_2](M_2Bp) (M = Li, 16; K, 19) is described. Transmetallation of Li_2Bp with YCl_3(THF)_3 affords exclusively the C_2 symmetric product rac-[BpY(µ_2-Cl)_2Li(THF)_2], 20. A X-ray crystal structure of 20 has been determined; triclinic, P1, a= 13.110 (8), b = 17.163 (15), c = 20.623 (14) A, α = 104.02 (7), β = 99.38 (5), γ = 100.24 (6)° , Z = 4, R = 0.056. Transmetallation of K_2Bp with YCl_3(THF)_3 affords the halide free complex rac-BpYCl, 23. The corresponding rac-BpLaCl, 28, is prepared in an anlogous manner. In all cases the achiral meso isomer is not obtained since only for the racemic isomers are the unfavorable steric interactions between the Si(CH3)_3 groups in the narrow portion of the [Cp-M'-Cp] wedge avoided. Alkylation of 20 or 23 with LiCH(Si(CH_3)_3)_2 affords rac-BpYCH(Si(CH_3)_3)_2, 26 in good yield. Alkylation of 28 with LiCH(Si(CH_3)_3)_2 affords rac-BpLaCH(Si(CH_3)_3)_2 29. Hydrogenation of 26 cleanly affords the bridging hydride species [BpY(µ_2-H)]_2, 27, as the homochiral (R,R) and (S,S) dimeric pairs. 26 is an efficient initiator for the polymerization of ethylene to high molecular weight linear polyethylene. 27 catalyzes the polymerization of propylene (25% v/v in methylcyclohexane) and neat samples of 1-butene, 1-pentene, 1-hexene to moderately high molecular weight polymers: polypropylene (M_n = 4,200, PDI 2.32, T_m 157 °C); poly-1-butene (M_n = 8,500, PDI 3.44, T_m 105 °C); poly-1-pentene (M_n = 20,000, PDI 1.99, T_m 73 °C); poly-1-hexene (M_n = 24,000, PDI 1.75, T_m < 25 °C). ^(13)C NMR spectra at the pentad analysis level indicates that the degree of isotacticity is 99% mmmm for all polymer samples. 27 is the first single component iso-specific α-olefin polymerization catalyst. The presumed origins of the high isospecificity are presented.

Conductive polyethylene-carbon black composites by elongational-flow injection molding Part 3. Study of the structure and morphology

The morphology and structure of high molecular weight linear polyethylene (M w 450000) filled with carbon black and processed using molds that introduce an elongational flow component during injection molding has been examined using electron microscopy and x-ray diffraction techniques. The study of fracture surfaces reveals the display of shish-kebabs oriented along the injection direction with segregated longitudinal channels of carbon black particles. Molecular and lamellar changes in orientation are, furthermore, studied across the thickness of the moldings. It is shown that addition of carbon black particles to injection-molded polyethylene induces significant changes in lamellar orientation. Thus, while lamellar overgrowth proceeds perpendicular to the fiber axes within carbon free channels, lamellae grow randomly within carbon-enriched regions where flow is less pronounced.

Uniaxial tensile creep behaviour of ultra high molecular weight linear polyethylene

The present paper examines the room temperature constant-load uniaxial tensile creep response of two ultra high molecular weight linear polyethylene (UHMW LPE) materials and compares it with that of a normal molecular weight linear polyethylene (NMW LPE). It was found that at all stress levels examined, the magnitude of creep deformation is significantly higher in UHMW LPE than in NMW LPE. Possible reasons for this behaviour are explored. Potential techniques for improving the tensile creep behaviour (i.e. decreasing the creep deformation) of LPE are discussed.

The Structure of High Molecular Weight Linear Polyethylene Injection Moulded at High Pressures

Abstract High density polyethylene with a low melt flow index (0.1 g/10 min) was injection moulded at pressures ranging from 100 to 500 MPa. The tensile modulus and strength in the flow direction increased substantially with the injection pressure. Three regions are characteristic of the specimens produced; a thin layer near the surface, a transition layer beneath the skin, and a core. DSC, wide angle X-ray scattering (WAXS), scanning and transmission electron microscopy were used to study the structure of the different layers. It was concluded that the skin was slightly oriented containing primarily chain-folded lamellae; the transition layer had a fibre texture and was oriented in the flow direction; the orientation of the core was similar to that of the transition layer but contained extended chain-morphologies similar to those found by Porter et al. in capillary extruded specimens. The composite structure gives rise to the improvement of mechanical properties and the increase in modulus is due to the ...

Thermal decomposition and volatilization of poly(α‐olefins)

AbstractThe thermal decomposition of normal alkanes and linear poly(α‐olefins) was found to occur predominately by random scissions, followed by volatilization into an open system. To show these processes the fragment distribution from high molecular weight linear polyethylene (fragments to C55), n‐alkanes, polypropylene, and polyisobutylene (fragments to C60) are reported and discussed in depth. Based on the results, a mechanism of random scissions followed by volatilization is postulated for polyethylene and n‐alkanes as well as for polyisobutylene and polypropylene. Polystyrene is shown not to follow the same mechanism, for little evidence for fragments above trimers was found. In addition, temperature rise–time measurements at the pyrolyzer probe are reported and explained.

Polyethylene networks crosslinked in solution: Preparation, elastic behavior, and oriented crystallization. I. Crosslinking in solution

AbstractA study has been made of the crosslinking of linear polyethylene in solution. Networks containing a low number of trapped entanglements and elastically ineffective chain ends were prepared by crosslinking high molecular weight linear polyethylene in 1,2,4‐trichlorobenzene solutions with dicumyl peroxide at 120°C. No syneresis was observed during crosslinking except at high peroxide concentrations. The networks were characterized by swelling measurements, infrared spectroscopy, and differential scanning calorimetry. The crosslinking efficiency, calculated from swelling, was found to be proportional to the square of the polymer volume fraction. The proportionality constant was 0.8, indicating close to unit efficiency for undiluted polymer.Chemical modification of the polyethylene chains by attachment of peroxide and solvent fragments was of the order of one foreign unit per elastically active network chain, depending on peroxide and polymer concentration. Sol–gel analysis indicated that no chain scission occurred. These results are shown to be consistent with a “cage” mechanism for crosslinking. The possible topological consequence of this mechanism, preferential crosslinking of entanglements, is discussed. The concentration of trapped entanglements was also found to be proportional to the square of the polymer volume fraction. The proportionality constant corresponds to a molecular weight between entanglements of 4000 for the undiluted polymer, which is close to the value of 4200 found for networks prepared from the undiluted polymer. Since the results obtained are based mainly on the use of the swelling equation, different aspects of the applicability of this equation for the evaluation of the crosslinking process are discussed. As regards the reference dimensions, which should be known for a quantitative application of the elastic theory, the results strongly support the use of the dimensions of the network chains after completion of crosslinking.