Synthesis and crystalline structure of polyethylene containing 1,3-cylopentane units in the main chain by ring-opening metathesis copolymerization of cycloolefins following hydrogenation reaction

Polyethylene containing 1,3-cyclopentane units in the main chain was synthesized by ring-opening metathesis copolymerization of cyclopentene (CPE) or cyclooctene with norbornene (NB) following hydrogenation reaction. The copolymer with cis-1,3-cyclopentane units was obtained in good yield. The resulting copolymers showed multiple melting points. Temperature-rising elution fractionation of the copolymers elucidated a broad distribution of the copolymer composition. WAXD and FT-IR analyses of the copolymers showed existence of hexagonal crystal in hydrogenated poly(CPE-co-NB).     

A novel amphiphilic AB2 star copolymer synthesized by the combination of ring-opening metathesis polymerization and atom transfer radical polymerization

A new amphiphilic AB₂ star copolymer was synthesized by the combination of ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). Two different routes (methods A and B) were employed firstly to prepare the poly(oxanorbornene)-based monotelechelic polymers as the hydrophobic arm bearing dibromo-ended group via ROMP in the presence of two different terminating agents catalyzed by first generation Grubbs catalyst. The values of capping efficiency (CE) of the polymers were determined by NMR, which were 94% and 67% for methods A and B, respectively. Then, the dibromo-ended ROMP polymers were used as the macroinitiators for ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA) to produce two hydrophilic arms. The prepared amphiphilic AB₂ star copolymers poly(7-oxanorborn-5-ene-exo,exo-2,3-dicarboxylic acid dimethyl ester)-block-bis[poly(2-(dimethylamino)ethyl methacrylate)] (PONBDM_n-b-(PDMAEMA_m)₂) with a fixed chain length of hydrophobic PONBDM and various hydrophilic PDMAEMA chain lengths can self-assemble spontaneously in water to form polymeric micelles, which were characterized by dynamic light scattering, atom force microscopy, and transmission electron microscopy measurements.     

New azo-chromophore-containing multiblock poly(butadiene)s synthesized by the combination of ring-opening metathesis polymerization and click chemistry

A combination of ring-opening metathesis polymerization (ROMP) and click chemistry approach was utilized for the first time in preparation of multiblock copolymers. The dibromo-functionalized telechelic poly(butadiene) (PBD) was synthesized firstly by ROMP of 1,5-cyclooctadiene in the presence of a symmetrical difunctional chain transfer agent and transformed into diazido-telechelic PBD, which was then reacted with a dialkynyl-containing azobenzene chromophore via click reaction, producing novel multiblock PBDs collected by azobenzene groups and newly formed triazole moieties. The monomer and polymer were characterized by IR, UV-vis, LC/MS, and NMR techniques. The produced multiblock copolymers have molecular weights within 13.3 and 57.8 kDa, and their polydispersity indices ranging from 1.98 to 2.38 by gel permeation chromatography measurement. The multiblock PBDs containing azo chromophores and triazole moieties with or without hydrogen-bonding interreaction with 4,4′-dihydroxybiphenyl molecule exhibited different photoisomerization efficiency from trans to cis as observation in UV-vis spectroscopy. The morphologies of multiblock PBDs were also investigated by atom force microscopy.     

A novel shape memory polynorbornene functionalized with poly(?-caprolactone) side chain and cyano group through ring-opening metathesis polymerization

A novel functionalized norbornene-based copolymer with long poly(?-caprolactone) side chain and cyano group was synthesized in the combination of ring-opening polymerization and ring-opening metathesis polymerization, which was characterized by means of ¹H NMR, gel permeation chromatography, thermogravimetry, differential scanning calorimetry, wide-angle X-ray diffraction, and stress-strain measurements. The shape memory effect of the copolymer was evaluated by dynamical mechanical analysis, shape recovery ability, and shape recovery speed. Having the properties of the good shape fixity and the large shape recovery, the functionalized polynorbornene copolymer is expected to use as a potential shape memory material.     

Study on processing of ultrahigh molecular weight polyethylene/polypropylene blends

The processing of ultrahigh molecular weight polyethylene (UHMWPE) by the addition of polypropylene (PP) and high‐density polyethylene (HDPE) was investigated. The results show that the addition of PP improves the processability of UHMWPE more effectively than does the addition of HDPE. UHMWPE/PP blends can be effectively processed with a twin‐roller and general single‐screw extruder. In the extrusion of UHMWPE/PP blends, PP is enriched at the surface of the blend adjacent to the barrel wall, thus increasing the frictional force on the wall; the conveyance of the solid down to the channel can then be carried out. The melt pool against the active flight flank exerts a considerable pressure on the UHMWPE powder in the passive flight flank, which overcomes the hard compaction of UHMWPE. The PP penetrates into the gaps between the particles, acting as a heat‐transfer agent and adhesive, thus enhancing the heat‐transfer ability in the material. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 977–985, 2004     

Preparation and properties of cyclopentadiene-containing monomer modified polydicyclopentadiene

A series of 1,4-dicyclopentadienylmethyl benzene (DMB) enhanced polydicyclopentadiene (DMB/polyDCPD blends) and 2,2′-dicyclopentadienyl ether (DCPE) toughened polyDCPD (DCPE/polyDCPD blends) were prepared via the ring-opening metathesis polymerisation (ROMP). The curing behaviour, thermal and mechanical properties were investigated. Differential scanning calorimetry (DSC) investigations of the DMB/polyDCPD blends showed the samples exhibited similar singular exothermic peak, and the exothermic peak of blends shifted to a higher temperature direction compared with the unfilled polyDCPD. However, the exothermic peak of the DCPE/polyDCPD blends presented two exothermic peaks. Dynamic mechanical analysis (DMA) measurements exhibited that the glassy modulus was enhanced as the DMB content increased. Thermal performance of DMB/polyDCPD has been enhanced with an increasing amount of DMB which was investigated by thermo gravimetric analysis (TGA) measurements. Whereas, the thermal stabilities of the DCPE/polyDCPD blends have been weakened with an increasing amount of DCPE. Moreover, the toughness of the DCPE/polyDCPD blends displayed a maximum performance at 60 wt% loading of DCPE.     

Fully-reversible and semi-reversible coordinative chain transfer polymerizations of 1,3-butadiene with neodymium-based catalytic systems

Coordinative chain transfer polymerization (CCTP) of 1,3-butadiene was assessed by employing several traditional Ziegler–Natta type Nd-based catalytic systems. Both the types of alkylaluminum as CTA and chloride donor as third component significantly affected the chain transfer characteristic of the CCTP systems. Among the catalytic systems examined, Nd(OiPr)₃/Al(iBu)₂H/Me₂SiCl₂ and Nd(OiPr)₃/Al(iBu)₂H/Al₂Et₃Cl₃ systems exhibited the highest catalytic efficiency, yielding 6–10 polymer chains per Nd atom in the presence of 20 equiv. CTA. Kinetic examination revealed that Nd(OiPr)₃/Al(iBu)₂H/Me₂SiCl₂ and Nd(OiPr)₃/Al(iBu)₂H/Al₂Et₃Cl₃ catalytic systems proceeded with fully- and semi-reversible chain transfer reactions, respectively. Quantitative formation of polymers was observed in each step of the 1,3-butadiene seeding polymerization, indicating the living mode of the two catalytic systems. Moreover, the triblock copolymers, PBD-b-PIP-b-PBD and PBD-b-PIP-b-PCL, were successfully synthesized with Nd(OiPr)₃/Al(iBu)₂H/Me₂SiCl₂ catalytic system.     

POSS-enhanced shape-memory copolymer of polynorbornene derivate and polycyclooctene through ring-opening metathesis polymerization

A copolymer consisting of polycyclooctene (PCOE) and poly(5-norbornene-exo,exo-2,3-dicarboxylic anhydride) (PNBEDCA) was firstly synthesized through ring-opening metathesis polymerization, and then the obtained copolymer P(COE-co-NBEDCA) was readily modified by grafting reaction of NBEDCA units with polyhedral oligomeric silsesquioxanes (POSS) to afford a novel functionalized copolymer P(COE-co-NBEDCA-g-POSS), in which carboxyl and POSS as side chains attached to polynorbornene backbones. The copolymers were characterized by means of thermogravimetry, wide-angle X-ray diffraction, and stress–strain measurements. The shape memory effect of the copolymer was evaluated by dynamical mechanical analysis and shape recovery speed. Having the properties of the good shape fixity and the large shape recovery, the POSS-enhanced copolymer is expected to use as a potential shape memory material.     

Kinetic study on reversible addition-fragmentation chain transfer (RAFT) process for block and random copolymerizations of styrene and methyl methacrylate

The degenerative (exchange) chain transfer constant C_ex was determined for the dithioacetate-mediated living radical block and random copolymerizations of styrene (St) and methyl methacrylate (MMA) at 40 °C. The addition of the polystyrene (PSt) radical to a polymer-dithioacetate adduct (P-X) to form the intermediate radical (PSt-(X)-P) was (about twice) faster than that of the poly(methyl methacrylate) (PMMA) radical to form the intermediate radical PMMA-(X)-P. The fragmentation (release) of the PMMA radical from the PSt-(X)-PMMA intermediate formed at the initiating stage of block copolymerization was much (about 100 times) faster than the release of the PSt radical, explaining why the block copolymerization of MMA from a PSt-dithiocarbonate adduct is not so satisfactory as that of St from a PMMA-dithiocarbonate adduct. In the random copolymerization, there was implicit penultimate unit effect on the exchange chain transfer process, which appeared in the addition process but not in the fragmentation process.     

Synthesis and characterization of side chain polymer with helical PLLA segments containing mesogenic end group

Series of mesogenic biphenol derivatives HO6OPPOn (n = 4,6,8) were prepared by asymmetric reaction and purified. Then HOLAxO6OPPOn were prepared with controlled molecular weights by adjusting the feed ratios of HO6OPPOn, SnOct₂ catalyst and LLA by Ring-Opening Polymerization. P-AOLAxO6OPPOn materials were obtained in high yields by the free radical polymerization of polymerizable macromonomers of AOLAxO6OPPOn synthesized by esterization of HOLAxO6OPPOn with acrylic acid in the presence of DCC/DMAP. Their molecular weights were characterized by ¹H NMR and GPC. Differential Scanning Calorimeter method and Polarized Optical Microscopy method were used to study their thermal behaviors. Both AOLAxO6OPPOn and P-AOLAxO6OPPOn materials are found to form LCs with increased T_g, T_m and T_i with longer O-LLA segment length. Polymerization of AOLAxO6OPPOn also resulted in the increase of T_g, T_m and T_i. X-ray diffraction measurements revealed the presence of smectic phase in these materials. The O-LLA segments are in helical structure from CD spectra and this makes the resulting polymer materials good candidate of optical materials for huge optical rotation power.     

Novel fluorescent polynorbornenes with multi-functional armed structure by using highly stable block macroinitiators via a combination of living ring-opening metathesis polymerization and atom transfer radical polymerization

Novel organosoluble fluorescent polynorbornenes with multi-functional armed structure were designed and prepared by using highly stable block macroinitiators via a combination of living ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). A bromo-containing functional norbornene (NBMBr) was prepared from the Diels-Alder reaction of cyclopentadiene and allyl bromide. The diblock copolymer of 5-(N-carbazolyl methyl)bicycle[2.2.1]hept-2-ene (CbzNB) and NBMBr was successfully prepared using living ROMP and used as a novel macroinitiator [poly(CbzNB-b-NBMBr)] for ATRP. Carbazoyl-containing multi-functional armed copolymer with poly(methyl methacrylate) (PMMA) was prepared by using poly(CbzNB-b-NBMBr) as a macroinitiator for ATRP. Strong fluorescence emissions (370-450 nm) were observed in the low excimer-forming multi-functional armed fluorescent polynorbornenes. The fact is that low excimer-forming carbazole-containing polymeric compound would apparently be favorable in photoconductive materials. The multi-functional armed structure make this compound an attractive candidate for applications as multi-modified hole transport materials in molecular electronic devices. Multi-modification could be further considered to be carried out by using such a functional bromo group at the end of multi-arms.     

Triple-detector GPC characterization and processing behavior of long-chain-branched polyethylene prepared by solution polymerization with constrained geometry catalyst

Fourteen long-chain branched (LCB) polyethylene (PE) samples were prepared by a constrained geometry catalyst. The PE samples had average branching frequencies of 0.06-0.98 branches per polymer chain, as determined by the nuclear magnetic resonance spectroscopy (¹³C NMR). These samples, as well as five linear PEs were characterized using a gel permeation chromatography (GPC) coupled with online three-angle laser light scattering (LS), differential refractive index (DRI), and viscosity (CV) detectors. The root mean-square radius of gyration intrinsic viscosity ([η]), and molecular mass (M) of the PEs were measured for each elution fraction. Based on the comparison of the long-chain branching (LCB) PEs with their linear counterparts and the Zimm-Stockmayer equation, the distributions of long-chain branch frequency (LCBF) and density (LCBD) as function of molecular mass were estimated. It was found that although the LCBF increased with the increase of molecular mass, the LCBD showed a maximum value in the medium molecular mass range for most of the PE samples. The average LCBD data from the GPC analysis were in good agreement with the ¹³C NMR measurements. The rheological properties and processing behavior of these samples were also assessed. While the long chain branching showed significant effects on the modulus and viscosity, it did not improve the processing. Compared to linear PE, polymer melt flow instabilities such as sharkskin, stick-slip and gross melt fracture developed in extrusion of LCB PEs occurred at lower wall shear stresses and apparent shear rates.     

Reversible chain transfer catalyzed polymerization (RTCP): A new class of living radical polymerization

This article introduces the new family of living radical polymerizations with germanium (Ge), tin (Sn), phosphorus (P), and nitrogen (N) catalysts which we recently developed. The polymerizations are based on a new reversible activation mechanism, Reversible chain Transfer (RT) catalysis. Low-polydispersity polymers are obtained in the homopolymerizations and random and block copolymerizations of styrene, methyl methacrylate, and functional methacrylates. The background, performance, and kinetic features of the polymerizations are described. Attractive features of the catalysts include their high reactivity, low toxicity (Ge, P, and N), low cost (P and N), and ease of handling (robustness).     

SEC-MALS method for the determination of long-chain branching and long-chain branching distribution in polyethylene

This paper systematically describes a LCB determination method that can quantify both LCB content and LCB distribution across the molecular weight distribution in polyethylene homopolymers as well as copolymers. Coupling size-exclusion chromatography with multi-angle light scattering (SEC-MALS), this method quantifies molecular weights (MW) and radii of gyration (R_g) simultaneously. The number of LCB per molecule and LCB frequency as a function of MW can be calculated by comparing R_g of a branched polymer with that of a linear control at the same MW using the Zimm-Stockmayer approach. Because the presence of short-chain branching in copolymers results in changes in R_g of the copolymers, their LCB contents cannot be obtained before the short-chain branching (SCB) effect is corrected. Using well-characterized linear PE copolymers as standards, an empirical method is successfully established in this paper to correct the SCB effect. Consequently, this method can be applied to determine LCB in PE copolymers as well. Some practical aspects, such as the selection of formalism for data processing, the LCB detection sensitivity and precision, and long-term reproducibility of this method are also discussed. Finally, examples are given to demonstrate how this method is applied to determine LCB and LCB distribution in practical PE homopolymers and copolymers.     

Reversible addition fragmentation chain transfer polymerization of 3-[tris(trimethylsilyloxy) silyl] propyl methacrylate

Reversible addition fragmentation chain transfer (RAFT) bulk polymerizations of 3-[tris(trimethylsilyloxy)silyl] propyl methacrylate (TRIS) have been carried out at 60 °C, employing cumyl dithiobenzoate (CDB) and 2-cyanoprop-2-yl dithiobenzoate (CPDB) as mediating agents at concentrations ranging from 5.0×10⁻³ to 2.0×10⁻² mol l⁻¹. The monomer conversion vs. time evolution was followed via dilatometry and ¹H NMR spectroscopy. The CDB mediated polymerization displays RAFT agent concentration dependent inhibition and rate retardation phenomena, whereas the CPDB mediated polymerization process is less susceptible to rate retardation and inhibition effects. The different behavior of CDB and CPDB in TRIS polymerization is most likely due to the increased stability of the intermediate macroRAFT radicals in the CDB mediated process. The generated RAFT polymers were analyzed via size exclusion chromatography indicating linear macromolecular growth with respect to monomer conversion and low polydispersities (PDI<1.15) up to high monomer to polymer conversion (>90%).     

Ultradrawing behavior of one- and two-stage drawn gel films of ultrahigh molecular weight polyethylene and low molecular weight polyethylene blends

The ultradrawing behavior of gel films of plain ultrahigh molecular weight polyethylene (UHMWPE) and UHMWPE/low molecular weight polyethylene (LMWPE) blends was investigated using one- and two-stage drawing processes. The drawability of these gel films were found to depend significantly on the temperatures used in the one- and two-stage drawing processes. The critical draw ratio (λ_c) of each gel film prepared near its critical concentration was found to approach a maximum value, when the gel film was drawn at an “optimum” temperature ranging from 95 to 105°C. At each drawing temperature, the one-stage drawn gel films exhibited an abrupt change in their birefringence and thermal properties as their draw ratios reached about 40. In contrast, the critical draw ratios of the two-stage drawn gel films can be further improved to be higher than those of the corresponding single-stage drawn gel films, in which the two-stage drawn gel films were drawn at another “optimum” temperature in the second drawing stage after they had been drawn at 95°C to a draw ratio of 40 in the first drawing stage. These interesting phenomena were investigated in terms of the reduced viscosities of the solutions, thermal analysis, birefringence, and tensile properties of the drawn and undrawn gel films. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 149–159, 1998     

Synthesis of thermoresponsive block and graft copolymers via the combination of living cationic polymerization and RAFT polymerization using a vinyl ether-type RAFT agent

A novel vinyl ether-type RAFT agent, benzyl 2-(vinyloxy)ethyl carbonotrithioate (BVCT) was synthesized for various block copolymers via the combination of living cationic polymerization of vinyl ethers and reversible addition−fragmentation chain transfer (RAFT) polymerization. The novel BVCT–trifluoroacetic acid adduct play an important role to produce well-defined block copolymers, which is both as a cationogen under EtAlCl₂ initiation system in the presence of ethyl acetate for living cationic polymerization and a RAFT agent for blocks by RAFT polymerization. The resulting polymer, poly(vinyl ether)s, by living cationic polymerization had a high number average α-end functionality (≥0.9) as determined by both ¹H NMR and MALDI-TOF-MS spectrometry. In addition, this poly(vinyl ether)s worked well as a macromolecular chain transfer agent for RAFT polymerization. The RAFT polymerization of radically polymerizable monomers was conducted in toluene using 2,2′-azobis(isobutyronitrile) at 70 °C. For example, a double thermoresponsive block copolymer (MOVE₆₁-b-NIPAM₁₅₀) consisting of 2-methoxyethyl vinyl ether (MOVE) and N-isopropylacrylamide (NIPAM) was prepared via the combination of living cationic polymerization and RAFT polymerization. The block copolymer reversibly formed and deformed micellar assemblies above the phase separation temperature (T_ps) of poly(NIPAM) block in water. This BVCT is not only functioned as an initiator, but also acted as a monomer. When BVCT was copolymerized with MOVE by living cationic polymerization, followed by graft copolymerization with NIPAM via RAFT polymerization, well-defined graft copolymers (MOVE_n-co-BVCT_m)-g-NIPAM_x (n = 62–73, m = 1–9, x = 19–214) were successfully obtained. However, no micelle formed in water above T_ps of poly(NIPAM) graft chain unlike the case of block copolymers.     

Calculating molecular weight distributions in emulsion polymerization under conditions of diffusion limited chain transfer

When highly reactive chain transfer agents with low water solubilities (e.g., long chain thiols) are used in emulsion polymerizations, transport of the chain transfer agent (CTA) from the monomer droplets to the polymer particles can become diffusion limited. Consequently, the concentration of CTA in the particles is lower than expected, resulting in apparent transfer constants that can be much lower than the actual transfer constants obtained from studies with homogeneous systems such as bulk or solution. Furthermore, molecular weights will be greater than those obtained in homogeneous systems with the same overall concentration of CTA. There are currently no techniques or methodologies available for predicting molecular weight distributions when the transport of CTA is diffusion limited. Apparent transfer constants may be used but they are typically restricted to a given system and operating conditions. In this work, we describe how the actual CTA concentration in the polymer particles can be estimated through analysis of instantaneous molecular weight distributions. This information is then used to calculate the cumulative molecular weight distribution during the polymerization. Comparisons with experimental molecular weight distributions validate the essential correctness of the approach, but also highlight potential problems. The extension of the approach to online applications is discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 217–227, 2000     

Modeling and theoretical development in controlled radical polymerization

Controlled radical polymerization (CRP) systems have gained increasing interests for the past two decades. Numerous publications may be found in the literature reporting experimental and modeling work on various CRP processes, including their use in surface modification through grafting. Knowledge of underlying mechanism behind polymerization systems is valuable for product design and process optimization. This information may be obtained through the combination of modeling and experimental studies. In this review, published studies on kinetic and stochastic based modeling for CRP systems are summarized. Their relevance in model discrimination of proposed mechanisms is discussed. This review also includes various parameter estimation studies, that is crucial to obtain accurate simulation predictions. Existing issues on the fundamental mechanism in CRP processes are also addressed.     

Synthesis of a water-soluble chain transfer agent and its application in gel dispersions

Pre-crosslinked gel particles, colloidal dispersion gels, and polymer microspheres are often used as profile-controlling and flooding agents to displace residual crude oil from formations. The preparation process of these profile-controlling and flooding agents is complicated. In order to simplify the preparation steps, a water-soluble chain transfer (RAFT) agent, S,S′-bis(2-propionic acid) trithiocarbonate (PATTC), was synthesized, and then, hydrogel dispersions were prepared by one-pot RAFT polymerization. The structure of PATTC was confirmed by infrared spectroscopy and nuclear magnetic resonance. The effects of reaction conditions on the viscosity and viscosity-average molecular weight of hydrogel dispersions were explored, the rheology, viscoelasticity, particle size, temperature responsiveness, and salinity responsiveness of hydrogel dispersions were measured, and the seepage properties of hydrogel dispersions in porous medium were analyzed. The results show that at higher shear rates, the polyacrylamide gel dispersions exhibited Newtonian fluid characteristics. Viscoelasticity tests further confirmed that the polyacrylamide gel dispersions were successfully synthesized. The particle size of the hydrogel dispersions is 1–75 μm, its viscosity is less affected by temperature and salinity, and its residual resistance coefficient is higher than that of the polyacrylamide solution under similar apparent viscosity.