Functionalization of poly(lactide) with N‐phenyl maleimide using N‐acetoxy‐phthalimide during reactive extrusion

Radical grafting of poly(lactide) (PLA) during postpolymerization reactive extrusion is usually done with peroxide initiation, leading to undesirable side reactions (branching or crosslinking) and to difficulties to control the process parameters as well as the final macromolecular structure. The use of N‐acetoxy‐phthalimide (NAPI) was investigated as an alternative to peroxides for the functionalization in the melt of PLA with N‐phenylmaleimide (PhM) monomer. The use of NAPI was found to lead to similar grafting rates in comparison to peroxides, with a better control of the PLA macromolecular structure, due to the formation of nitroxide radicals that combine with the produced macroradicals. Also, the grafting site on PLA backbone was identified after hydrolysis of grafted PLA. Above an optimal PhM concentration, homopolymerization of the monomer was also highlighted. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 917–928     

Effect of the initial maleic anhydride content on the grafting of maleic anhydride onto isotactic polypropylene

A series of ¹³C‐enriched maleic anhydride grafted isotactic polypropylene samples were prepared in solution at 170 °C by changes in the initial maleic anhydride content. The NMR spectra of the samples showed that the signals of the maleic anhydride attached to the tertiary carbons of the isotactic polypropylene chains increased considerably with increasing maleic anhydride content, whereas the signals of the maleic anhydride on the radical chain ends (with a single bond) arising from β scission did not. On the other hand, the signals of the maleic anhydride on the radical chain ends with double bonds increased markedly with increasing maleic anhydride content, and this suggested that β scission could occur extensively after maleic anhydride was attached to the tertiary carbons. As a result, the molecular weight of the grafted polypropylene decreased significantly with increasing maleic anhydride content in this study. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5529–5534, 2005     

Influence of polypropylene topological structure evolution during melt branching reactive processing on its melt performances

Gel‐free long‐chain‐branched polypropylene (LCBPP) was prepared by the melt radical branching reaction in the presence of peroxide initiator 2,5‐dimethyl‐2,5‐di(tert‐butylperoxy) hexane peroxide, zinc dimethyldithiocarbamate, and trimethylolpropane triacrylate in a torque rheometer. It could be inferred that recombination between PP chains via radical coupled reaction took place and trimethylolpropane triacrylate was grafted onto PP backbone by the torque curves and Fourier transformed infrared spectroscopy results. The presence of long chain branches (LCB) for modified PP was verified by the gel permeation chromatography measurements and vGP plots. On the other hand, it was found that the topological structure of PP chains transformed from linear form to a long star‐like shape during the reaction progress, and the topological structure was directly determined by the radical reaction time. The topological structure of PP would further impact its melt behaviour. After complete melting of raw PP, “sparse and long” LCBPP firstly generated which possessed high melt strength owing to the increasing entanglement of long branching chains. And at the time corresponding to the summit of reaction peak on the torque curve, the modified LCBPP possess the highest melt strength owing to its long star topological structure. While as reaction time was prolonged, severe degradation of the LCBPPs would take place under too long mixing time and “dense and short” branches generated due to the residual radicals, with a sharp decline in melt strength.     

Classification of homogeneous copolymers of propylene and 1‐octene based on comonomer content

The solid‐state structure and properties of homogeneous copolymers of propylene and 1‐octene were examined. Based on the combined observations from melting behavior, dynamic mechanical response, morphology with primarily atomic force microscopy, X‐ray diffraction, and tensile deformation, a classification scheme with four distinct categories is proposed. The homopolymer constitutes Type IV. It is characterized by large α‐positive spherulites with thick lamellae, good lamellar organization, and considerable secondary crystallization. Copolymers with up to 5 mol % octene, with at least 28 wt % crystallinity, are classified as Type III. Like the homopolymer, these copolymers crystallize as α‐positive spherulites, however, they have smaller spherulites and thinner lamellae. Both Type IV and Type III materials exhibit thermoplastic behavior characterized by yielding with formation of a sharp neck, cold drawing, strong strain hardening, and small recovery. Copolymers classified as Type II have between 5 and 10 mol % octene with crystallinity in the range of 15–28%. Type II materials have smaller impinging spherulites and thinner lamellae than Type III copolymers. Moreover, the spherulites are α‐negative, meaning that they exhibit very little crystallographic branching. These copolymers also contain predominately α‐phase crystallinity. The materials in this category have plastomeric behavior. They form a diffuse neck upon yielding and exhibit some recovery. Type I copolymers have more than 10 mol % octene and less than 15% crystallinity. They exhibit a granular texture with the granules often assembled into beaded strings that resemble poorly developed lamellae. Type I copolymers crystallize predominantly in the mesophase. Materials belonging to this class deform with a very diffuse neck and also exhibit some recovery. They are identified as elastoplastomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4357–4370, 2004     

Microhardness-structure correlation of iPP/EPR blends: influence of molecular weight and EPR particle content

The influence of molecular weight on the mechanical properties of isotactic poly(propylene) (iPP) and iPP blended with ethylene-propylene copolymers has been investigated by means of the microhardness technique. The hardness (H) of iPP is shown to slightly decrease with increasing molecular mass, within the range of molecular weights investigated. The H-decrease is correlated to a loss of crystallinity as the average molecular weight increases. On annealing, the mechanical properties are enhanced as a consequence of an increase in both, the degree of crystallinity and the crystalline lamellar thickness. A value of H ^∞ _c for iPP crystals of infinite thickness in the α-form is proposed for the first time. The inclusion of EPR particles in the iPP matrix softens the material. This result could be explained in terms of an increase in the basal surface free energy of the iPP crystals with increasing amount of rubber content. Received: 2 February 1998 Accepted: 11 May 1998     

Effect of carboxyl end groups content on the thermal and electrical properties of poly(propylene terephthalate)

Poly(propylene terephthalate) (PPT) samples with different carboxyl terminal groups content were synthesized in bulk and characterized in terms of chemical structure and molecular weight. The thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. All the polymers under investigation show a good thermal stability, however decreasing with increasing carboxyl terminal groups content. No significant change of the glass transition temperature as well as melting temperature values was found in the samples under investigation; on the contrary, the crystallization rate of PPT was found to be affected by carboxyl terminal groups content, regularly decreasing as the amount of -COOH terminal groups is increased. This trend was interpreted on the basis of the interactions among the terminal groups of the polymeric chains, which determine a decrease in the chain mobility. Direct current (dc) electrical behavior was also investigated. The dc charging/discharging currents and electrical conductivity are studied as a function of temperature, time of applied voltage and amount of -COOH terminal groups. The conductivity values were found to increase as the content of -COOH end groups was increased, due to an increment of amount of ionic charge carriers.     

Effect of Ethylene-Propylene Copolymer Composition on Morphology and Surface Properties of Impact Poly(propylene) Copolymer

Summary: Impact poly(propylene) copolymers (IPC) having various ethylene-propylene rubber (EPR) compositions were prepared using a high activity Ziegler-Natta catalyst. EPR composition was characterized by temperature rising elution fractionation (TREF) analysis and FT-IR spectroscopy. Effect of EPR composition on the morphology and surface properties of IPC was investigated by scanning electron microscopy (SEM), 3D profiler, and gloss meter. Composition and amount of amorphous and crystalline EPR were quantified by TREF and found to be dependent on the ethylene content in EPR. From the SEM result, it was found EPR composition has a strong influence on its shape and size. IPCs containing propylene-rich EPR exhibited a finer dispersion of EPR phase. The surface roughness decreased with decreasing ethylene content in EPR. The comparison of EPR composition and morphology and surface properties exhibited strong correlations.     

Copolymerization of 3‐buten‐1‐ol and propylene with an isospecific zirconocene/methylaluminoxane catalyst

The copolymerization of propylene and 3‐buten‐1‐ol protected with alkylaluminum [trimethylaluminum (TMA) or triisobutylaluminum] was conducted with an isospecific zirconocene catalyst [rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride], combined with methylaluminoxane as a cocatalyst, in the presence of additional TMA or H₂ as the chain‐transfer reagent if necessary. The results indicated that end‐hydroxylated polypropylene was obtained in the presence of the chain‐transfer reagents because of the formation of dormant species after the insertion of the 3‐buten‐1‐ol‐based monomer followed by chain‐transfer reactions. The selectivity of the chain‐transfer reactions was influenced by the alkylaluminum protecting the comonomer and the catalyst structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5600–5607, 2004     

Metalization of polypropylene. I. Synthesis and melt free‐radical grafting of novel maleimides and methacrylates containing chelating moieties

Several chelating monomers with methacrylate and maleimide residues as polymerizable groups and diketone and aspartic acid residues as metal‐bonding groups were synthesized. A long‐chain aliphatic spacer was introduced to increase the solubility of the monomers in the polymer melt and to enhance the compatibility of grafted side chains and homopolymers with polypropylene (PP). PP was functionalized by melt free‐radical grafting, and some properties of the modified polymer were investigated. The grafting of a chelating methacrylic ester by injection molding afforded grafting yields of 30–50%. A comparison with products obtained by the grafting of commercially available acetoacetoxy methyl methacrylate showed the beneficial effect of the aliphatic spacer with respect to the grafting yield as well as the tensile strength and flexural modulus. The grafting of an aspartic acid based maleimide in an extruder afforded grafting yields of 80–95% and a significant increase in the surface wettability, as shown by contact‐angle measurements. A comparative study using samples obtained by the grafting of maleimidobenzoic acid indicated that the homogeneity‐increasing effect of the spacer was neutralized by the detrimental effect of the dicarboxylic chelating group. Nevertheless, the results showed that the maleimides were well suited for grafting by reactive extrusion because of their low susceptibility to homopolymerization under melt‐processing conditions. Preliminary metalization experiments showed the feasibility of plating without the use of corrosive etchants. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3400–3413, 2003     

Controlled reduction of polypropylene isotacticity and crystallinity by epimerization during reactive processing

Amorphous and low crystallinity polypropylenes were produced by reactive processing of commercial isotactic polypropylenes in the presence of a peroxide (2,5‐dimethyl‐2,5‐di(tert‐butylperoxy)hexane) and N‐bromosuccinimide. Characterization of the modified polypropylene microstructures using ¹³C NMR spectroscopy revealed that crystallinity loss is correlated with the epimerization of numerous methynes randomly along the polymer backbone, leading to decreasing isotacticities ([mmmm]) and average isotactic block lengths. Moreover, degradation usually induced by peroxide was shown to be comparatively limited in additional presence of N‐bromosuccinimide. This fast and easy process therefore allows the production of polypropylene plastomers and elastomers with controlled and homogeneous crystallinities and isotacticities, and relatively low molecular weight distributions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4505–4518, 2009     

Synthesis and characterization of polypropylene-based block copolymers possessing polar segments via controlled radical polymerization

A new method to prepare the polypropylene (PP) macroinitiator for controlled radical polymerization was described. Bromination of terminally-unsaturated PP was carried out by using N-bromosuccinimide and 2,2′-azobis(isobutyronitrile) to give a brominated PP (PP-Br), that has allylic bromide moieties at or near the chain ends. Thus, the obtained PP-Br was successfully used as a macroinitiator for radical polymerization of styrene, methyl methacrylate, and n-butyl acrylate using a copper catalyst system. From ¹H NMR analysis, it was confirmed that the chain extension polymerization was certainly initiated from allylic bromide moieties with high efficiency, leading to the PP-based block copolymers linking the polar segment. From differential scanning calorimetry, it was observed that peak melting temperature of block copolymers was higher than that of PP-Br and the obtained PP-PS block copolymers with different compositions of each segment demonstrated the unique morphological features due to the microphase separation between both segments. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 812–823, 2009     

Influence of the graphite type on the synthesis of polypropylene/graphene nanocomposites

In this work, the synthesis of polypropylene (PP)/graphene nanosheet (GNS) nanocomposites by in situ polymerization using metallocene catalysts was studied. Initial reactions were performed using rac‐Et(Ind)₂ZrCl₂ and rac‐Me₂Si(Ind)₂ZrCl₂ catalysts to select the best one to obtain good molecular weight, thermal properties, and tacticity. Subsequently, PP nanocomposites with different loadings of GNS were obtained. GNS from two different sources [Graphite Nacional (GN) and Graphite Aldrich (GA)] have been used, and the differences between the obtained nanocomposites were evaluated. The GNS and nanocomposites were studied by scanning electronic microcopy, transmission electronic microcopy, and X‐ray diffraction. They showed that the GN nanosheets had lower crystal size and diameter than the GA nanosheets and dispersed better in the PP matrix. Differential scanning calorimetry analyses of both types of nanocomposites showed an increase in the crystallization temperature with increasing graphite loading. The polymeric materials were also characterized by GPC, thermogravimetric analysis, and ¹³C NMR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Derivatization of propene/methyloctadiene copolymers: A flexible approach to side‐chain‐functionalized polypropenes

The copolymerization of propene with 7‐methyl‐1,6‐octadiene (MOD) catalyzed by Cp*TiMe₃/B(C₆F₅)₃ ( A ) and rac‐C₂H₄(Ind)₂ZrCl₂/methylaluminoxane ( B ) in toluene under 1 bar propene gave copolymers with unsaturated side chains. Under these conditions, catalyst A produced copolymers with an atactic backbone structure of type 1 , with 3.5–19.6 mol % MOD incorporation and weight‐average molecular weight = 0.7–2.7 × 10⁵. Using catalyst B , copolymers 2 with 0.4–3.8 mol % MOD incorporation were prepared. The comonomer incorporation was a linear function of the feed ratio. The titanium catalyst A had a significantly higher affinity for MOD than the sterically more hindered zirconocene B . Postpolymerization modification of the side‐chain C?C bond allowed the facile introduction of a wide variety of functional groups. Epoxidation and especially ozonolysis of the C?C bond, to give ? CHO and ? COOH functionalized copolymers, proved to be very facile routes to functionalized polypropenes. According to monitoring by NMR, most of these transformations proceed in an essentially quantitative conversion. As an example of potential applications of such polymers, polypropenes with covalently attached dyes were prepared that are suitable for blending. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1484–1497, 2002     

Synthesis of polypropylene graft copolymers by the combination of a polypropylene copolymer containing pendant vinylbenzene groups and atom transfer radical polymerization

This article discusses a facile and inexpensive reaction process for preparing polypropylene‐based graft copolymers containing an isotactic polypropylene (i‐PP) main chain and several functional polymer side chains. The chemistry involves an i‐PP polymer precursor containing several pendant vinylbenzene groups, which is prepared through the Ziegler–Natta copolymerization of propylene and 1,4‐divinylbenzene mediated by an isospecific MgCl₂‐supported TiCl₄ catalyst. The selective monoenchainment of 1,4‐divinylbenzene comonomers results in pendant vinylbenzene groups quantitatively transformed into benzyl halides by hydrochlorination. In the presence of CuCl/pentamethyldiethylenetriamine, the in situ formed, multifunctional, polymeric atom transfer radical polymerization initiators carry out graft‐from polymerization through controlled radical polymerization. Some i‐PP‐based graft copolymers, including poly(propylene‐g‐methyl methacrylate) and poly(propylene‐g‐styrene), have been prepared with controlled compositions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 429–437, 2005     

Surface-grafting onto aramid powder: reaction of acyl chloride groups on the surface with functional polymers having terminal hydroxyl or amino groups

The surface-grafting of polymers onto aramid, poly(p-phenylene terephthalamide), powder surface by the reaction of acyl chloride groups on the surface with functional polymers having terminal hydroxyl and amino groups was investigated. The introduction of acyl chloride groups onto the aramid powder surface was achieved by the reaction of the aramid powder with adipoyl dichloride: the acyl chloride group content of the surface was estimated to be 1.14 mmol/g (0.17 mmol/m²) by elemental analysis. It was found that by the reaction of acyl chloride groups on the surface with functional polymers, such as terminal diol-type poly(propylene oxide) (PPG) and terminal diamine-type poly(dimethylsiloxane) (SDA), these polymers were grafted onto the aramid powder surface; the percentage of surface grafting of PPG and SDA onto the aramid powder was 16.7 and 22.4%, respectively. The thermogravimetric curve of PPG surface-grafted aramid powder exhibited an initial weight loss at about 250°C and a second weight loss at about 500°C. This indicated that the grafting of PPG is limited to the powder surface. The wettability of the aramid powder surface turned from hydrophobic to hydrophilic by the surface-grafting of PPG onto the surface.     

Melt‐extensional properties and orientation behaviors of polypropylene‐layered silicate nanocomposites

Polypropylene‐layered silicate nanocomposites consisting of three components—pure polypropylene, maleated polypropylene, and organically modified silicate—were prepared by the melt‐intercalation method to investigate melt‐extensional properties such as melt strength, neck‐in test, and orientation behavior. The nanocomposites showed an enhanced tensile modulus, enhanced storage modulus, much enhanced melt tension, and reduced neck‐in during the melt processing as compared with neat polymer. The uniaxial drawing induced the silicate surface to align parallel to the sheet surface. The c and a* axes of the polypropylene crystals were bimodally oriented to the flow direction, and the b axes were oriented to the thickness direction. The bimodal orientation of the polypropylene crystal was enhanced with the concentration of silicates. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 158–167, 2005     

Isotactic Poly(propylene)/Monoalkylimidazolium‐Modified Montmorillonite Nanocomposites: Preparation by Intercalative Polymerization and Thermal Stability Study

Summary: Poly(propylene)/monoalkylimidazolium‐modified montmorillonite (PP/IMMT) nanocomposites were prepared by in situ intercalative polymerization of propylene with TiCl₄/MgCl₂/MMT catalyst. The PP synthesized possessed high isotacticity and molecular weight. Both wide‐angle X‐ray diffraction (XRD) and transmission electron microscopy (TEM) examinations evidenced the nanocomposite formation with exfoliated MMT homogeneously distributed in the PP matrix. A thermal stability study revealed that the nanocomposites possess good thermal stability.

X‐ray diffraction patterns of PP/IMMT (MMT = 2.2 wt.‐%) nanocomposite before and after processing.     

Prediction of yield and long‐term failure of oriented polypropylene: Kinetics and anisotropy

The time‐dependent yield and failure behavior of off‐axis loaded uniaxially oriented polypropylene tape is investigated. The yield and failure behavior is described with an anisotropic viscoplastic model. A viscoplastic flow rule is used with an equivalent stress, based on Hill's anisotropic yield criterion, and the Eyring flow theory combined with a critical equivalent strain definition. This model is based on factorization of the rate and draw ratio dependence and is capable of quantitatively predicting the rate, angle and draw ratio dependence of the yield stress as well as time‐to‐failure in various off‐axis tensile loading conditions characterized solely from the transverse direction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2026–2035, 2009