Molecular Weight Distribution Of Copolymers Research Articles

Methyl methacrylate-styrene copolymers prepared by utilizing the Trommsdorff effect in an inverted two-stage extruder

In this work, the influence of initial viscosity on the Trommsdorff effect was firstly investigated, and it was confirmed that 1000 ± 100 Pa · s of viscosity could be a criterion of the Trommsdorff effect. On this basis, a new inverted two-stage extruder was established, the designed ‘blocking unit’ was introduced to the screw configuration, and then the continuous bulk copolymerization of methyl methacrylate (MMA) and styrene (St) was carried out. The results showed that the blocking unit could effectively enhance the residence time of copolymerization, and make the molecular weight distribution of copolymer more uniform. The position of the Trommsdorff effect in the extruder was then determined by the thermal effect of copolymerization, and the mixed monomers were continuously added to effectively utilize the Trommsdorff effect. As a result, the MMA-St copolymers with high molecular weight and narrow distribution were prepared via reactive extrusion, which possessed higher melt flow rate and better thermal stability than pure-PMMA. The present work provides important reference and guidance for the industrialization of bulk free radical copolymerization via reactive extrusion.

Polymerization with Borane Chemistry. Tributylborane/p-Quinone System as a New Method of Reversible-Deactivation Radical Copolymerization for Styrene and Methyl Acrylate

We report a reversible-deactivation radical copolymerization of styrene and methyl acrylate in the presence of tributylborane and different p-quinones. p-Quinones, such as 1,4-naphthoquinone, 2,3-dimethyl-1,4-benzoquinone, 2,5-ditert-1,4-butylbenzoquinone, and duroquinone, with addition of a catalytic amount of tributylborane, allow for the control over styrene/methyl acrylate copolymerization. The process proceeds in a controlled manner via a reversible homolytic dissociation of the active macromolecules with terminal aryloxyboron-groups. The rate of styrene/methyl acrylate copolymerization depends on the inhibition constants of quinones. The molecular weight and molecular weight distribution of copolymers are directly dependent on the inhibitory abilities of the quinones. 1,4-Naphthoquinone and 2,3-dimethyl-1,4-benzoquinone act as the most effective mediators of chain propagation. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) results showed that the macromolecules contained internal fragments of p-quinone. Also, of the terminal aryloxyboron-groups were detected in the mass spectra. On realization of the “living” mechanism of copolymerization, the structure of copolymers obtained at high conversions can be considered as similar to the gradient structure. Stereo-regularity of the copolymers differed from the conventional radical copolymerization. The glass-transition temperature (Tg) of the gradient copolymer differed from Tg of the random compositional heterogeneous copolymer. The effect of the macromolecular structure on the mechanical properties of the copolymers was studied.

A degradable copolymer of 2-methylene-1,3-dioxepane and vinyl acetate by photo-induced cobalt-mediated radical polymerization

A degradable copolymer of 2-methylene-1,3-dioxepane (MDO) and vinyl acetate (VAc) was synthesized through photo-induced cobalt-mediated radical polymerization under UV irradiation (450 μW cm−2 at 365 nm) at 30 °C by using (2,4,6-trimethylbenzoyl)diphenylphosphine oxide as an initiator and Co(acac)2 as a regulating agent. Living polymerization behavior was proved via pseudo linear kinetics, the molecular weight of the copolymers increasing with conversion, narrow molecular weight distribution of copolymers and successful chain extension. The structure of the copolymer was characterized by NMR and MALDI-TOF MS. The reactivity ratios for MDO and VAc were determined to be rMDO = 0.14 and rVAc = 1.89. It was possible to vary the content of MDO in a wide range of copolymers by changing the feed ratio of VAc and MDO. The glass transition temperature increased gradually with increasing the amount of VAc. Such copolymers were easily degraded no matter in acidic or alkaline solution.

Co(acac)2 mediated controlled radical copolymerization of vinyl acetate and methyl acrylate initiated by benzoyl peroxide

Cobalt mediated radical copolymerization of vinyl acetate (VAc) and methyl acrylate (MA) was successfully performed in the presence of cobalt(II) acetylacetonate (Co(acac)2), dimethylformamide (DMF) and benzoyl peroxide (BPO) as catalyst, cobalt coordinating agent and initiator, respectively, at 45°C. The individual monomer conversion and comonomer composition of copolymers were determined by 1H NMR spectroscopy. Molecular weight (Mn) and its distribution (Mw/Mn) were analyzed by GPC technique. The time dependence of ln[M]0/[M], the variation of molecular weight with respect to the conversion, and molecular weight distribution of copolymers were studied to evaluate controlled characteristics of copolymerization. It was found that Co(acac)2 successfully mediated the radical copolymerization of VAc and MA. Moreover, copolymer molecular weight and copolymerization rate increased with increasing initial MA ratio. The spectroscopy analysis revealed VAc content in the copolymer increased with conversion regardless of VAc initial ratio, indicating a gradient sequence distribution of the copolymer.

비닐리덴 플루오라이드와 헥사플루오르프로필렌 공중합체의 합성

Polyvinylidene fluoride (PVDF) and its copolymer with hexafluoropropylene (HFP) were successfully prepared from free radical solution polymerizations using diisopropyl peroxidicarbonate (DIPPDC) in the presence of 1,1,2-trichlorotrifluoroethane (R-113). The reactivity ratios of VDF and HFP were estimated as and . This result indicates that HFP cannot undergo self propagation. The weight-average molecular weight and molecular weight distribution of copolymers were found to decrease with increasing HFP content. The melting temperature of copolymers linearly decreased with the increase of HFP content because of the introduction of HFP. Moreover, no melting peak was observed for the copolymers with high HFP content. The glass transition temperature of copolymers gradually increased with the increase of HFP content due to the restricted flexibility of the polymer chains.

Unexpected Consequences of Block Polydispersity on the Self-Assembly of ABA Triblock Copolymers

Controlled/"living" polymerizations and tandem polymerization methodologies offer enticing opportunities to enchain a wide variety of monomers into new, functional block copolymer materials with unusual physical properties. However, the use of these synthetic methods often introduces nontrivial molecular weight polydispersities, a type of chain length heterogeneity, into one or more of the copolymer blocks. While the self-assembly behavior of monodisperse AB diblock and ABA triblock copolymers is both experimentally and theoretically well understood, the effects of broadening the copolymer molecular weight distribution on block copolymer phase behavior are less well-explored. We report the melt-phase self-assembly behavior of SBS triblock copolymers (S = poly(styrene) and B = poly(1,4-butadiene)) comprised of a broad polydispersity B block (M(w)/M(n) = 1.73-2.00) flanked by relatively narrow dispersity S blocks (M(w)/M(n) = 1.09-1.36), in order to identify the effects of chain length heterogeneity on block copolymer self-assembly. Based on synchrotron small-angle X-ray scattering and transmission electron microscopy analyses of seventeen SBS triblock copolymers with poly(1,4-butadiene) volume fractions 0.27 ≤ f(B) ≤ 0.82, we demonstrate that polydisperse SBS triblock copolymers self-assemble into periodic structures with unexpectedly enhanced stabilities that greatly exceed those of equivalent monodisperse copolymers. The unprecedented stabilities of these polydisperse microphase separated melts are discussed in the context of a complete morphology diagram for this system, which demonstrates that narrow dispersity copolymers are not required for periodic nanoscale assembly.

Copolymerization of ethylene with α‐olefins over supported titanium–magnesium catalysts. I. Effect of polymerization duration on comonomer content and the molecular weight distribution of copolymers

AbstractThe data on the effect of polymerization duration on molecular weight (MW), molecular weight distribution (MWD), and content of α‐olefin were obtained for ethylene/1‐hexene copolymers produced on a supported titanium–magnesium catalyst (TMC) upon polymerization in the absence and presence of hydrogen. An increase in MW, narrowing of the MWD, and a decrease in 1‐hexene content in the copolymer takes place with increasing polymerization duration. It was shown by molecular weight fractionation of copolymers obtained at different polymerization duration followed by analysis of narrow fractions to determine the butyl branching content that the decrease comonomer content in copolymers with increasing polymerization duration is accounted for by the decrease in the share of low molecular weight fractions with an increased butyl branch content. These data, in combination with the data concerning the narrowing of the MWD of copolymers and the decrease in activity with polymerization duration allow arriving at conclusion that active sites producing low molecular weight polymer with an increased butyl branching content is predominantly deactivated with polymerization. Active sites producing high molecular weight polymer has a low ability to copolymerize ethylene with α‐olefins; however, these sites show higher stability during copolymerization. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis and Spectroscopic Studies of DGEBA–Grafted Polyaniline

N-grafted polyaniline with diglycidyl ether bisphenol A (DGEBA) was synthesized via anionic copolymerization technique. Metalation reaction was performed to cause grafting to occur between DGEBA with emeraldine salt polyaniline (PANI-ES) and leucoemeraldine base polyaniline (PANI-LEB), respectively. Fourier transform infrared (FTIR), 13C-nuclear magnetic resonance (NMR), and 1H-NMR spectroscopies and gel permeation chromatography (GPC) were performed to characterize the PANI-EB-g-DGEBA and PANI-ES-g-DGEBA copolymers. The gel content of the resultant copolymers was determined by Soxhlet extraction. Results of spectroscopic studies showed that grafting took place together with the side reaction, cross-linking, and DGEBA homopolymerization. Oxidation states of PANI were found to influence the gel content and molecular weight distribution of copolymers produced.

Effect of monomer composition on apparent chain transfer coefficient in reversible addition fragmentation transfer (RAFT) copolymerization

The effects of monomer composition on the apparent chain transfer coefficient (〈Ctr〉) in reversible addition fragmentation transfer (RAFT) copolymerization were investigated. The studied RAFT systems included methyl methacrylate (MMA)/butyl acrylate (BA) mediated by 1-phenylethyl phenyldithioacetate (PEPDTA) (i.e. MMA/BA–PEPDTA), MMA/BA by 2-cyanoprop-2-yl dithiobenzoate (i.e. MMA/BA–CPDTB), and styrene (St)/BA by benzyl dithioisobutyrate (i.e. St/BA–BDTiB). The R groups of the RAFT agents were first converted to the corresponding copolymer oligomers having the same composition to facilitate the measurement of the main RAFT equilibrium transfer coefficients. It was found that there exist minimum values in the 〈Ctr〉∼f1 curves in MMA/BA–CPDTB and St/BA–BDTiB at f1=0.75 and 0.25, respectively. The apparent transfer coefficients of the copolymerization systems within some composition range were lower than their homopolymerization values. The lower 〈Ctr〉 values resulted in broader copolymer molecular weight distributions. The composition dependence of 〈Ctr〉 was determined by the comonomer reactivity ratios and the Z group functionality of the RAFT agent. The experimental data could be well described by a simple equation derived from the terminal model:〈Ctr〉=〈ktr〉〈kp〉=ψ1r1f1Ctr,11+r2f2Ctr,21r1f12+r2f22+2f1f2+ψ2r1f1Ctr,12+r2f2Ctr,22r1f12+r2f22+2f1f2.

Analysis of molecular weight distributions of styrene‐methyl methacrylate copolymers using size exclusion chromatography data

AbstractSize exclusion chromatography (SEC) is a common method for the determination of molecular weight distributions (MWD) of polymers. Using appropriate normalization procedures, MWD data may be put in a form suitable for the description by different theoretical distribution functions. In this paper such a procedure is described and applied to a model system. Statistical copolymers of styrene and methyl methacrylate (SMMA) of different compositions were synthesized by radical copolymerization in a batch isothermal reactor with toluene as solvent and azobisisobutyronitrile as initiator. Copolymer MWDs were obtained by SEC and average copolymer composition by elemental analysis. MWDs of SMMA copolymers were correlated with the lognormal, Flory, Schulz, and Tung theoretical function. The best match between experimental and calculated data was obtained by the Schulz distribution. The α‐parameter of Schulz's function was related to the average molecular weight and showed its maximum at the midpoint of the copolymer composition range, in connection with the observed minimal copolymerization rate. The variation of the b‐parameter was found to be less pronounced; the parameter was related to the polydispersity index. This feature indicated that there was no significant change in the copolymerization reaction mechanism throughout the entire copolymer composition range.

Synthesis and characterization of propylene-?-olefin random copolymers with isotactic propylene sequence. II. Propylene-hexene-1 random copolymers

A series of novel hexene-1–propylene random copolymers with isotactic sequence of propylene was synthesized with a MgCl2-supported Cr(acac)3 catalyst. The molecular weight distribution of copolymers and homopolymers was considerably narrower than that of typical polyolefins produced by heterogeneous Ziegler–Natta catalysts. The crystallizability of the copolymers having a propylene-unit content of more than 50 mol % drastically decreased with decreasing propylene-unit content, and the copolymers with a propylene content of less than 50 mol % were completely amorphous. In the present novel type of random copolymers with crystallizable and noncrystallizable units, a single glass transition was observed between pure polypropylene and polyhexene-1, and a major component was found to govern the final morphology and the mechanical characteristics. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2949–2954, 2004

Effects of TMA and MAO on Ethylene–Propylene Copolymer Using Supported Zirconocene Catalysts

Copolymerization of ethylene and propylene was carried out in the presence of rac-ethylenebis(indenyl)zirconium dichloride (Et[Ind]2ZrCl2) with SiO2 as the support for the catalyst. The effect of trimethylaluminum (TMA) and methylaluminoxane (MAO) was investigated using two methods of providing a supported system i.e., in situ supported system and a preformed supported system. Catalyst activity increased with increasing the [Al]TMA/[Zr] ratio to a maxima whereafter an adverse effect was observed in both the in situ and preformed supported system, while activity continuously increased with the increase of the [Al]MAO/[Zr] ratio. With respect to the molecular weight of the copolymers, an increase of TMA in the system reduced Mw only slightly, while an increase in MAO appeared to have no effect. This suggested that chain transfer to alkylaluminum is not the major chain transfer reaction for this copolymerization system. The molecular weight distribution of copolymer obtained for these supported systems is higher than for the copolymer normally produced from the corresponding homogeneous system. These supported systems might yield plural active species. Copolymers produced have ethylene incorporation close to the ethylene molar feed ratio with random distribution of comonomer insertion. A very low level of the PPP triad was observed. The amount of Al loaded on silica depended linearly with [Al]MAO added, whereas almost all the loaded Zr were immobilized on the support. From SEM-EDX analysis, Al was well dispersed on the silica support, no effect of zirconocene catalyst loaded on the Al distribution was observed at the reaction condition used. In ethylene/propylene copolymer produced, Al was detected throughout the particles supporting the possibility of catalyst fragmentation mechanism.

Control of copolymer hydrodynamic volume distribution in a semibatch free radical copolymerization process

In copolymerization processes, molecular weight averages and copolymer composition are commonly used as property indices for reactor control purposes. In general, it is difficult to measure the molecular weight distribution of copolymer accurately by gel permeation chromatography (GPC) because there is no unique relationship between chain length and hydrodynamic volume for a copolymer with a heterogeneity in the composition distribution. In this paper, the hydrodynamic volume distribution is used as a primary control objective in a semibatch free radical copolymerization process. The hydrodynamic volume distribution of copolymer is modeled by computing the weight fraction of polymers over a number of hydrodynamic volume intervals. Then the target hydrodynamic volume distribution is obtained by designing optimal reactor operating policy. Both copolymer composition and the entire hydrodynamic volume distribution are controlled by adding reactants as a function of time. A numerical simulation example is presented for a styrene–methyl methacrylate copolymerization process to illustrate the proposed method.

Copolymerization Propagation Kinetics of Styrene and Methyl MethacrylateRevisited. 1. Pulsed Laser Polymerization Study

A comprehensive set of propagation rate coefficients for styrene−methyl methacrylate bulk copolymerization has been obtained from pulsed laser polymerization experiments performed over a range of temperatures (18−57 °C). The copolymer molecular weight distributions were analyzed using size exclusion chromatography with on-line low-angle laser-light scattering (LALLS) and differential viscometry (DV) detectors. The molecular weight data obtained using these absolute detection methods were compared with data obtained by assuming the copolymer hydrodynamic volumes (HDVs) can be described by a weighted average of the homopolymer HDVs. The analyses via these three different approaches yielded virtually identical molecular weight data, validating previous work on this copolymerization system. The precision of the data obtained from LALLS and DV was worse than that obtained from the HDV-weighted approach. However, the errors in the molecular weight data from DV and LALLS analyses are believed to be a more correct representation of the true errors in the molecular weight measurement. A strategy for reducing the effect of the molecular weight errors in the k̄p measurements, via the selection of slow laser flashing rates, is presented.

Macromolecular Engineering of Lactones and Lactides. 24. Controlled Synthesis of (R,S)-β-Butyrolactone-b-ε-Caprolactone Block Copolymers by Anionic and Coordination Polymerization

Block copolymers of (R,S)-β-butyrolactone and ε-caprolactone have been synthesized by combining the anionic polymerization of the first monomer with the coordinative ring-opening polymerization of the second one. The copolymerization yield is close to 100% and the final molecular weight of each sequence can be predicted from the initial monomer-to-initiator molar ratio. The molecular weight distribution of copolymers obtained is quite narrow (Mw/Mn ≤ 1.3). According to NMR and DSC analysis, the polybutyrolactone block is atactic and totally amorphous, in contrast to the polycaprolactone block which is semicrystalline. A partial miscibility of the two blocks in the amorphous phase has however been detected. Thermal and enzymatic degradations of the block copolymers have been investigated. The enzymatic degradation rate promoted by the lipase form Rhizopus arrhizus strongly depends on the copolyester composition and increases with the β-butyrolactone content.

Ethylene-propylene copolymers by a supported Ziegler-Natta catalyst based on TiCl4/MgCl2

Ethylene-propylene copolymers have been prepared by using Ziegler-Natta catalysts based on TiCl4, MgCl2, PCl3 and (n-Bu)3PO4. The catalysts TiCl4/MgCl2PCl3 and TiCl4/MgCl2/(n-Bu)3PO4 were prepared by reacting TiCl4 with pretreated MgCl2. The support was prepared by ball milling of MgCl2 with varied amounts of PC13 or (n-Bu)3PO4. The addition of PCl3 has remarkably increased the MgCl2 surface area in comparison with (n-Bu)3PO4. The effects of PCl3 and (n-Bu)3PO4 on ethylene homopolymerization, ethylene-propylene copolymerization and on copolymer properties were evaluated. The catalyst system containing PCl3 permitted to synthesize propylene-ethylene copolymers with up to 75 % (w/w) of propylene and provided control of copolymer crystallinity. The reduction of the copolymer molecular weight distribution suggested that PCl3 acted as an internal donor, poisoning some active catalytic sites.

Properties of ethylene-propylene copolymers synthesized by a supported Ziegler-Natta catalyst based on TiCl 4/MgCl 2/PCl 3

Enthylene-propylene copolymers were synthesized through Ziegler-Natta catalysts based on TiCl 4, MgCl 2 and PCl 3. The catalyst system TiCl 4/MgCl 2/PCl 3 was prepared by impregnating the support, obtained by ball milling of MgCl 2 with varied amounts of PCl 3, with TiCl 4. The addition of PCl 3 has, remarkably, increased MgCl 2 surface area and, according to plasma spectrometry data, promoted the PCl 3 incorporation in the catalyst. The effect of PCl 3 on the ethylene homopolymerization, ethylene-propylene copolymerization and on the copolymer properties was studied. The employed catalyst system produced propylene-ethylene copolymers up to 75% (w/w) of propylene. The reduction on the copolymer molecular weight distribution suggested the PCl 3 acted as an internal donor, poisoning some catalytic active sites. The effect of Al Ti ratio on the copolymer structures was investigated. Low ratio caused increase of propylene incorporation in the copolymer and high Al Ti ratio promoted overreduction of titanium as shown by EEE triad content. The reactivity ratio data indicated the ethylene-propylene copolymerization present a tendency to produce block copolymers.

An algorithm for determination of the copolymer molecular weight distribution by Markov chain simulation

AbstractA simple and general algorithm, convenient for computer implementation, for calculation of the copolymer molecular weight distribution (MWD), its moments, copolymer composition, etc. from standard data has been developed describing copolymerization as a Markovian process. The algorithm is applicable for simulations of multimonomer copolymerization with monomolecular, bimolecular and mixed termination. It can be used for calculating the MWD of copolymers prepared under non‐stationary conditions. Explicit formulae have been derived for the above parameters. They are exact even for low‐molecular‐weight oligomers. The calculation procedure involves nothing but plain matrix operations as matrix multiplication and inversion. For high‐molecular‐weight copolymers, even simpler dependencies that resemble those used for homopolymers can be used. A very simple numerical test has been proposed for checking their correctness.

Effects of removing THF from the titanium trichloride(AA)/magnesium chloride/THF catalyst system on the ethylene-propylene copolymerization mechanism

TiCl3(AA)/MgCldTHF (T3ME) catalyst was prepared by reacting TiC13(AA) and MgClz in a solution of tetrahydrofuran (THF), and THF was removed from T3ME by diethylaluminum chloride to make four different catalysts with different THF contents (T3MED2, T3MED4, T3MED8, T3MED12). The investigation through XRD and ESR indicated that the removal of THF resulted in a change of the state of the Ti3+ species, isolated Ti3+ species for TBME, T3MED2, and T3MED4 catalysts, and multinuclear Ti3+ species for T3MED12 and TiCldAA) catalysts. The l3C NMR study showed that the microstructure of ethylene-propylene copolymers strongly depended upon the nature of Ti3+. The activity and stereospec- ificity for homopolymerization depended on the THF content of the catalyst, and the molecular weight distribution of copolymer became broader with THF removal. Multinuclear Ti3+ species increased the relative reactivity of propylene in the copolymerization, and isolated Ti3+ species with vacancies favored the random insertion of propylene in the ethylene main chain.

Characterization of random copolymers by size exclusion chromatography with a light scattering detector

Measurement of the molecular weight and molecular-weight distribution of copolymers by size exclusion chromatography (s.e.c.) can be difficult because of the lack of appropriate samples for calibration of the column. Comparison of copolymers of varying composition is even more problematic. The recent development of light scattering detectors for s.e.c. permits direct measurement of the molecular weight as the polymer elutes from the column, so that no calibration is necessary. A series of six copolymers of poly(4-(acetoxymethyl)styrene- co-4-(t-butyloxycarbonyloxy)styrene) have been measured, ranging in composition from 5 to 100 mol% of the poly(4-(acetoxymethyl)styrene). The differential refractive index increment varied linearly with composition. The weight-average molecular weights ( M w) determined by s.e.c. with the light scattering detector agree well with those determined with light scattering alone. Application of the technique to copolymers is discussed.