A Novel Approach for Investigation of Chain Transfer Events by Pulsed Laser Polymerization

Pulsed laser polymerization (PLP) with subsequent analysis of molecular mass distribution (MMD) is used to determine the rate coefficient of chain transfer to an agent A, k_trA, by varying pulse repetition rate such that the contributions of PLP‐induced and chain‐transfer‐induced peaks to the MMD change to a significant extent. It is shown by simulation that the relative heights of these peaks may be used to estimate k_trA. The method is applied to evaluation of the rate coefficient of chain transfer to dodecyl mercaptan with butyl methacrylate polymerizations at ?11, 0, 20 and 40 °C. The Arrhenius parameters for this coefficient are determined to be: A(k_trA) = (2.2 ± 0.6) × 10⁶ L · mol^?1 · s^?1 and E_a(k_trA) = (22.1 ± 0.7) kJ · mol^?1.

     

Poly(neopentylene carbonate) Hyperstars

Summary: Branched aliphatic polycarbonates were synthesized by ring opening polymerization of 5,5‐dimethyl‐1,3‐dioxane‐2‐one (NPC) initiated from polyfunctional alcohols and a commercial hyperbranched polyester (BOLTORN®). Polymerizations in the presence of fumaric acid under bulk conditions allowed high conversion (80%) without gelation. The synthesis of polymers with long chain branches was confirmed by size exclusion chromatography and universal calibration. The Mark–Houwink exponent decreased, indicating an increased density, while increasing the number of arms. The star polymers with up to four arms showed thermal properties T_g (20–30 °C) and T_m (100–110 °C) similar to linear PNPC.

Boltorn? hyperbranched polymer with radial polycarbonate grafts.     

Xanthate‐Mediated Controlled Radical Polymerization of N‐Vinylcarbazole

Summary: Well‐defined poly(N‐vinylcarbazole) [poly(NVC)] was synthesized by macromolecular design via interchange of the xanthates (MADIX)/reversible addition‐fragmentation chain transfer (RAFT) polymerization. The homopolymers with controlled molecular weights ( = 3 000–48 000) and low polydispersities indices ( = 1.15–1.20) were obtained by the polymerization of NVC with AIBN in the presence of O‐ethyl‐S‐(1‐phenylethyl) dithiocarbonate as a xanthate‐type chain transfer agent (CTA). Good control of the polymerization was confirmed by the linear first‐order kinetic plot, the molecular weight controlled by the monomer/CTA molar ratio, linear increase in the molecular weight with the conversion, and the ability to extend the chains by the second addition of the monomer.

Radical polymerization of NVC in the presence of CTA and plot of number‐average molecular weight (circles) and polydispersity (squares) as a function of conversion.     

Nitroxide‐Mediated Radical Polymerization of N‐tert‐Butylacrylamide

The nitroxide‐mediated polymerization of N‐tert‐butylacrylamide (TBAM) in DMF at 120 °C using SG1/DEPN and AIBN has been investigated. Linear growth in number‐average molecular weight ( ) versus conversion and narrow molecular weight distributions (MWDs) with high livingness were obtained up to ≈8 000 g · mol^?1. For higher molecular weights, the MWDs gradually became broader with low molecular weight tailing, and deviated downwards from theoretical values. Quantitative analyses of MWDs, along with specifically designed conventional radical polymerizations at 120 °C, were consistent with chain transfer to monomer limiting the attainable . This finding can be equally applied to existing literature polymerizations of TBAM.

     

Self‐Assembly of Carbon Nanotubes Modified by Amphiphilic Block Polymers in Selective Solvent

Block copolymers of polystyrene and poly(tert‐butyl methyacrylate) were prepared by ATRP. Halogen atoms at the chain ends were transformed into azide groups to obtain  N₃ terminated block copolymers, which were connected to the surface of multi‐walled carbon nanotubes (MWNTs) by reacting  N₃ with MWNT's surface. Amphiphilic diblock copolymer modified MWNTs were obtained after PtBMA blocks were hydrolyzed to polymethyacrylic acid (PMAA). Results showed that the amphiphilic diblock copolymer was grafted onto MWNTs by covalent bonds. TEM showed that they formed self‐assembly structures by hydrophilic/hydrophobic interaction in good solvents. As the block length of PMAA increased, the self‐assembly structures of amphiphilic MWNTs became increasingly ordered and uniform.

     

Solvent Effects,Diffusion Control and Mechanistic Aspects of Catalytic Chain Transfer Polymerization

In the catalytic chain transfer polymerization of methyl methacrylate, butyl methacrylate and 2‐ethylhexyl methacrylate in toluene, it was found that the chain transfer constants (C_T) were independent of solvent concentration and therefore of solution viscosity, and did not differ from the bulk polymerization values. For a diffusion controlled system, theoretical calculations predict an increase in C_T when the solution viscosity is lowered. This points at a non‐diffusion controlled catalytic chain transfer step. These results were obtained when the solvent was thoroughly purified using a Grubbs‐type set‐up, whereas a large reduction in C_T was found in unpurified solvent. Similar results were obtained for butyl acetate. Therefore it is concluded that the decrease of C_T in non‐purified solvents is not related to the solvent itself, but to solvent impurities. Further we found that methyl methacrylate ended radicals do not covalently bind to the cobalt complex, in contrast to styrene and acrylate ended radicals.

Chain transfer constant for the CCT polymerization of 2‐ethylhexyl methacrylate in toluene, and predictions for diffusion controlled systems.     

Double‐Gyroid Morphology of a Polystyrene‐block‐Poly(ferrocenylethylmethylsilane) Diblock Copolymer: A Route to Ordered Bicontinuous Nanoscale Architectures

A polystyrene‐block‐poly(ferrocenylethylmethylsilane) diblock copolymer, displaying a double‐gyroid morphology when self‐assembled in the solid state, has been prepared with a PFEMS volume fraction ?_PFEMS = 0.39 and a total molecular weight of 64 000 Da by sequential living anionic polymerisation. A block copolymer with a metal‐containing block with iron and silicon in the main chain was selected due to its plasma etch resistance compared to the organic block. Self‐assembly of the diblock copolymer in the bulk showed a stable, double‐gyroid morphology as characterised by TEM. SAXS confirmed that the structure belonged to the Ia d space group.

     

Critically Evaluated Rate Coefficients for Free‐Radical Polymerization, 4

Propagation rate coefficients, k_p, which have been previously reported by several groups for free‐radical bulk polymerizations of cyclohexyl methacrylate (CHMA), glycidyl methacrylate (GMA), benzyl methacrylate (BzMA), and isobornyl methacrylate (iBoMA) are critically evaluated. All data were determined by the combination of pulsed‐laser polymerization (PLP) and subsequent polymer analysis by size‐exclusion chromatography (SEC). This so‐called PLP‐SEC technique has been recommended as the method of choice for the determination of k_p by the IUPAC Working Party on Modeling of Polymerisation Kinetics and Processes. The present data fulfill consistency criteria and the agreement among the data from different laboratories is remarkable. The values for CHMA, GMA, and BzMA are therefore recommended as constituting benchmark data sets for each monomer. The data for iBoMA are also considered reliable, but since SEC calibration was established only by a single group, the data are not considered as a benchmark data set. All k_p data for each monomer are best fitted by the following Arrhenius relations: CHMA: , GMA: , BzMA: , iBoMA: . Rather remarkably, for the methacrylates under investigation, the k_p values are all very similar. Thus, all data can be fitted well by a single Arrhenius relation resulting in a pre‐exponential factor of 4.24 × 10⁶ L · mol^?1 · s^?1 and an activation energy of 21.9 kJ · mol^?1. All activation parameters refer to bulk polymerizations at ambient pressure and temperatures below 100 °C. Joint confidence intervals are also provided, enabling values and uncertainties for k_p to be estimated at any temperature.

95% joint confidence intervals for Arrhenius parameters A and E_A for cyclohexyl (CHMA), glycidyl (GMA), benzyl (BzMA), and isobornyl (iBoMA) methacrylate; for details see text.     

Direct Synthesis of Controlled Poly(styrene‐co‐acrylic acid)s of Various Compositions by Nitroxide‐Mediated Random Copolymerization

Styrene and acrylic acid were copolymerized under controlled conditions, in 1,4‐dioxane solution at 120 °C and 2 bar, using an alkoxyamine initiator based on the N‐tert‐butyl‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl) nitroxide, SG1. A broad composition range from 90/10 to 10/90 was investigated. With slightly different initiator concentrations and a similar initial proportion of free SG1 (4.5 mol‐% with respect to the initiator) the polymerizations exhibited very similar rates, irrespective of the proportion of acrylic acid in the comonomer mixture (80% conversion within 8 h). In all cases, the copolymers presented number average molar masses, , that increased linearly with overall monomer conversion, and polydispersity indexes that ranged between 1.2 and 1.4. Moreover, followed the calculated values, based on the initial concentrations of monomers and initiator. The variation in the initiator concentration allowed to target various molar masses, but some limitation appeared at low initiator concentration owing to chain transfer to 1,4‐dioxane. From the kinetic data, the reactivity ratios were determined: r_A = 0.27 ± 0.07 for acrylic acid and r_S = 0.72 ± 0.04 for styrene. Depending on the initial comonomer composition, chains exhibited no or small composition drift, and hence a slightly pronounced gradient structure.

Reactivity ratios for acrylic acid and styrene.     

Radical Polymerization of MMA Co‐initiated by 2‐Phenyloxazoline

The subject of this work is the study of a new type of radical polymerization that occurs at elevated temperatures (80–100 °C) in mixtures of acrylates or (meth)acrylates and imine baes (IBA polymerization). The radical character of this polymerization is proven by the determination of copolymerization ratios and the reaction kinetics. On the basis of these facts and the hypothesis that the vinyl monomer acts as a co‐initiator, calculations reveal the concentration of the initiating species to be very low (K_eq < 10^?6). Furthermore, the choice of the reaction medium plays a crucial role on reaction kinetics and the average molecular weight of the resulting polymer. In combination with computational methodologies on the initiation, the multistep nature of this reaction is indicated.

     

Anionic Copolymerization of 5‐(N,N‐Dialkylamino)isoprenes

Summary: The anionic copolymerization of various 5‐(N,N‐dialkylamino)isoprenes initiated by sec‐butyllithium in hexane is investigated. The bulkiness of the alkyl side chains has a strong influence on the copolymerization behavior, monomer reactivity decreasing in the order of alkyl groups methyl > ethyl ≈ propyl > isopropyl. Polymer structures vary from nearly block over tapered and gradient to random, depending on the relative reactivities of comonomers. Since the basicity of the tertiary amino groups depends on the nature of the alkyl groups, it is possible to vary the basicity along the polymer backbone by a suitable choice of the comonomers. Copolymerization kinetics do not seem to follow first‐ or second‐order with respect to monomer conversion and they cannot be described using the terminal model.

General structure of obtained polymers.     

Polystyrene with Improved Chain‐End Functionality and Higher Molecular Weight by ARGET ATRP

The bromine chain‐end functionality of polystyrene (PSt) prepared by activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) was analyzed using 500 MHz ¹H nuclear magnetic resonance (NMR). Bulk polymerization of styrene (St) was carried out with 50 ppm of copper in the presence of tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) ligand and tin(II) 2‐ethylhexanoate [Sn(EH)₂] reducing agent at 90 °C. Due to the use of a low concentration of an active Cu/ligand catalyst complex, it was possible to significantly decrease the occurrence of catalyst‐based side reactions (β‐H elimination). As a result, compared to PSt prepared via normal ATRP, PSt with improved chain‐end functionality was obtained. For example, at 92% monomer conversion in normal ATRP only 48% of chains retained chain‐end functionality, whereas 87% of the chains in an ARGET ATRP still contained halogen functionality. PSt with controlled molecular weight ( = 11 600 g · mol^?1, = 9 600 g · mol^?1) and narrow molecular weight distribution ( = 1.14) was prepared under these conditions. In addition, as a result of decreased frequency of side reactions in ARGET ATRP, PSt with relatively high molecular weight was successfully prepared ( = 185 000 g · mol^?1, = 1.35).

     

ATRP of Allyl Methacrylate with Alkyl Methacrylates – Crosslinking of Poly(methacrylate)s with Allyl Ester Side Groups

Summary: Random copolymers of methyl methacrylate (MMA), butyl methacrylate (BMA) and allyl methacrylate (AMA) were prepared via atom transfer radical polymerization (ATRP). AMA is a bifunctional monomer with two double bonds of different reactivity: a highly reactive methacrylate double bond and an allyl ester double bond of lower reactivity. In order to obtain linear polymers with pendant allyl ester groups, the copolymerization conditions have to be optimized with respect to the concentration of AMA, the catalyst system applied – especially the ligand – and the temperature. By means of kinetic studies the reaction parameters for a controlled polymerization were determined. The results obtained show that the higher the temperature and the amount of AMA is the higher is the probability of irregular chain growth and side reactions induced by the pendant allyl ester groups such as hydrogen abstraction from the allyl position or radical addition to the allyl ester double bond. The random copolymers were photochemically crosslinked by using 2,2‐dimethoxy‐2‐phenylacetophenone as photoinitiator. The thermal properties of linear and crosslinked polymers were determined. The glass transition temperatures of both show no significant difference at low AMA content and thus low crosslinking densities.

GPC eluograms of MMA/BMA (70:30) copolymers with 5 mol‐% AMA at different conversions.     

Control of the radical polymerization by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl and its sodium salt

The control of the radical polymerization of styrene by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl is reported here in bulk at 90 °C, 120 °C and in miniemulsion. Similarly, the control by its sodium complex is reported in bulk at 90 °C.

M _n vs. conversion for 3 , 3Na , and TEMPO.     

Controlled Radical Polymerization of Vaporized Vinyl Monomers on Solid Surfaces under UV Irradiation

Summary: In order to prepare well‐defined polymers on solid surfaces in the gas phase, a gas phase‐assisted surface polymerization (GASP) of vinyl monomers was carried out on solid surfaces pre‐coated with a photoiniferter, 2‐cyanoprop‐2‐yl N,N′‐dimethyldithiocarbamate, under UV irradiation. The GASP of methyl methacrylate (MMA) resulted in the formation of polymer on the surfaces and showed a proportional relationship between and polymer yield. Consecutive copolymerization of MMA and styrene led to the formation of a block copolymer, which was confirmed by a selective solvent fractionation method. These results demonstrate that controlled radical polymerization of vaporized monomer occurred on the solid surfaces.

Expected mechanism of GASP under UV irradiation.     

Synthesis and Characterization of Amphiphilic Poly(ethylene oxide)‐block‐poly(hexyl methacrylate) Copolymers

We describe the preparation of amphiphilic diblock copolymers made of poly(ethylene oxide) (PEO) and poly(hexyl methacrylate) (PHMA) synthesized by anionic polymerization of ethylene oxide and subsequent atom transfer radical polymerization (ATRP) of hexyl methacrylate (HMA). The first block, PEO, is prepared by anionic polymerization of ethylene oxide in tetrahydrofuran. End capping is achieved by treatment of living PEO chain ends with 2‐bromoisobutyryl bromide to yield a macroinitiator for ATRP. The second block is added by polymerization of HMA, using the PEO macroinitiator in the presence of dibromobis(triphenylphosphine) nickel(II), NiBr₂(PPh₃)₂, as the catalyst. Kinetics studies reveal absence of termination consistent with controlled polymerization of HMA. GPC data show low polydispersities of the corresponding diblock copolymers. The microdomain structure of selected PEO‐block‐PHMA block copolymers is investigated by small angle X‐ray scattering experiments, revealing behavior expected from known diblock copolymer phase diagrams.

SAXS diffractograms of PEO‐block‐PHMA diblock copolymers with 16, 44, 68 wt.‐% PEO showing spherical (A), cylindrical (B), and lamellae (C) morphologies, respectively.     

Insights into the Ring‐Expansion Polymerization of Thiiranes with 2,4‐Thiazolidinedione

The behavior of the ring‐expansion homopolymerization of 2 (phenoxymethyl)thiirane (PMT) and propylene sulfide (PS), respectively, with thiazolidine‐2,4‐dione (TZD) as a cyclic initiator is investigated. The polymerizations show steadily growing molar masses with increasing monomer conversions. In addition, reversible merging reactions between rings are observed, with up to six merged macrocycles formed. The degree of merging is strongly dependent on the initial monomer concentration, whereas temperature has only a small impact. Under optimized conditions, ring‐poly(PMT) polymer with values of M _n up to 50 250 g mol^?1 and dispersities down to 1.11 can be synthesized. DSC and ESI‐MS measurements of the novel ring‐poly(PS) prove the formation of ring polymer having topological purity above 95%.

     

MADIX Polymerization of Captodative Ethyl α‐Acetoxyacrylate with Acrylate Monomers

Summary: MADIX homopolymerization of a captodative monomer, ethyl‐α‐acetoxyacrylate (EAA) was investigated using AIBN as an initiator and O‐ethyl‐S‐(1‐methoxycarbonyl)ethyl dithiocarbonate as a transfer agent at 70 °C in a mixture of iPrOH and H₂O. The experimental results revealed that this transfer agent had no effect on the polymerization reaction when compared with a free radical polymerization. Copolymerization of ethyl‐α‐acetoxyacrylate, with different acrylic monomers, such as butyl acrylate (BuA), acrylic acid, N,N‐(dimethylamino)ethyl acrylate and N,N‐dimethyl acrylamide, was then studied by MADIX polymerization using the same transfer agent. All the prepared copolymers were characterized by ¹H NMR and size exclusion chromatography, and the obtained results were in accordance with theoretical predictions regarding molecular weight and copolymer composition. Futhermore, the living character of the polymerization has been checked by the chain extension of poly(EAA‐stat‐BuA) with vinyl acetate (Vac) which led to poly(EAA‐stat‐BuA)‐block‐poly(VAc).

     

Reverse Atom Transfer Radical Polymerization of Methyl Methacrylate using a New Catalyst,Copper(II) N,N′‐Butyldithiocarbamate

Summary: The homogeneous bulk reverse ATRP using AIBN/Cu(SC(S)N(C₄H₉)₂)₂/bpy as the initiating system has been successfully carried out for methyl methacrylate. Well‐controlled polymerizations with low polydispersities ( = 1.10–1.30) have been achieved. The revised number‐average molecular weights ( 's) increased linearly with monomer conversion and were close to the values. The polymerization rate followed the first‐order kinetics in monomer, while it is about 2.0 order in initiator concentration and 1.15 order in Cu(II) concentration. The k values for the homogeneous bulk reverse ATRP of MMA initiated by AIBN/Cu(SC(S)N(C₄H₉)₂)₂/bpy (1:2:6) at 80, 90, 100 and 110 °C were 0.402 × 10^?4, 1.021 × 10^?4, 2.952 × 10^?4, and 3.687 × 10^?4 (s^?1), respectively. On the basis of the Arrhenius plot, the apparent activation energy was calculated to be ΔE = 87.1 kJ/mol. The obtained PMMA was functionalized with an ultraviolet light sensitive ω‐SC(S)N(C₄H₉)₂ group characterized by means of ¹H NMR spectroscopy, and which was also proved by its chain extension with fresh MMA under UV‐light irradiation at room temperature. A polymerization mechanism for this novel initiation system is proposed.

Dependence of and on the monomer conversion for the homogeneous bulk reverse ATRP of MMA at different concentration of catalyst.     

Synthesis and Characterization of New Acrylate and Methacrylate Monomers with Pendant Pyridine Groups

To overcome some drawbacks of polyvinylpyridines, new monomers of acrylate and methacrylate type with pendant pyridine groups i.e., 4‐(3‐methacryloylpropyl)pyridine 1a and 4‐(3‐acryloylpropyl)pyridine 1b were successfully prepared, although it turned out to be challenging work to synthesize the acrylate monomer 1b . First polymerization studies showed that the new monomers could be polymerized easily by atom transfer radical polymerization (ATRP). The new polymers show excellent characteristics, such as very good solubility, low glass‐transition temperature, and easy quaternization.

Design and structure of new monomers 1a and 1b .