Full Monomer Conversion Research Articles

Photoinduced Acrylate Polymerization: Unexpected Reduction in Chain Branching.

The branching stemming from midchain radical formation in n-butyl acrylate polymerization is investigated via melt-state (13) C NMR measurements. The dependence of the degree of branching (DB) on the monomer conversion of the system is examined for photoinduced polymerizations, revealing a steady increase in branching with conversion. For polymerization at moderate light intensities, an increase in branching from 0.03% to 0.37% is observed for polymerizations at 60 °C, which is fivefold below the level of branching observed in thermally initiated polymerizations under otherwise identical reaction conditions. The reason for this overall reduction in branching remains momentarily unclear; yet, a strong dependence of branching on light intensity is observed. While polymerization under a 1 W LED lamp results at almost full monomer conversion in branching degrees of 0.22%, polymerization under a 400 W lamp yields 1.81% of chain branches.

Living Anionic Polymerization in Continuous Flow: Facilitated Synthesis of High-Molecular Weight Poly(2-vinylpyridine) and Polystyrene

We describe the living anionic polymerization of 2-vinylpyridine (2VP) and styrene (S) in continuous flow, comparing two micromixing devices with different mixing principles. The use of a continuous flow setup reduces the experimental effort for living anionic polymerizations significantly, compared to a conventional batch system. By adjusting the ratio of the flow rates of the monomer and initiator solutions a variety of different molecular weights can be rapidly synthesized within several minutes, using one setup. Additionally, a comparison of the influence of the two different mixing devices—an interdigital micromixer (SIMM-V2) leading to laminar mixing and a tangential four-way jet mixing device leading to a turbulent mixing pattern—has been achieved. Both setups allow living anionic polymerization in polar solvents at room temperature with full monomer conversion within seconds and yield polymers with narrowly distributed molecular weights. A maximum Mn of approximately 149,000 g mol–1 (PS-9, PDI = 1.04) for PS and 96,000 g mol–1 for P2VP (P2VP-15, PDI = 1.05) was obtained. Clearly, the turbulent four-way jet mixing device led to lower polydispersity than the laminar mixing device. All polymers were characterized by 1H NMR spectroscopy and size exclusion chromatography (SEC).

Pushing the Limit of the RAFT Process: Multiblock Copolymers by One-Pot Rapid Multiple Chain Extensions at Full Monomer Conversion

We describe an optimized method to prepare multiblock copolymers. The approach is based on our previously reported use of reversible addition–fragmentation chain transfer (RAFT) polymerization, which here has been optimized into a fast, versatile, efficient, and scalable process. The one-pot, multistep sequential polymerization proceeds in water, to quantitative yields (>99%) for each monomer addition, thus circumventing requirements for intermediate purification, in 2 h of polymerization per block. The optimization of the process is initially demonstrated via the synthesis of a model decablock homopolymer (10 blocks) of 4-acryloylmorpholine with an average degree of polymerization of 10 for each block (Đ = 1.15 and livingness >93% for the final polymer). Both the potential and the limitations of this approach are illustrated by the synthesis of more complex high-order multiblock copolymers: a dodecablock copolymer (12 blocks with 4 different acrylamide monomers) with an average degree of polymerization of 10 for each block and two higher molecular weight pentablock copolymers (5 blocks with 3 different acrylamide monomers) with an average degree of polymerization of 100 per block.

Exploitation of the Degenerative Transfer Mechanism in RAFT Polymerization for Synthesis of Polymer of High Livingness at Full Monomer Conversion

We report the synthesis by the reversible addition–fragmentation chain transfer process of well-defined decablock polymers with a final dispersity as low as 1.15 and a fraction of living chain as high as 97% after 10 successful block extensions, each taken to >99% monomer conversion. By using model decablock homopolymers of poly(N,N-dimethylacrylamide) and poly(4-acryloylmorpholine) of relatively low DP (10 units per block in average), we describe the theoretical and experimental considerations required to access high-order multiblock copolymers with excellent control over molecular weight distributions and high livingness.

Aqueous Dispersion Polymerization: A New Paradigm for in Situ Block Copolymer Self-Assembly in Concentrated Solution

Reversible addition-fragmentation chain transfer polymerization has been utilized to polymerize 2-hydroxypropyl methacrylate (HPMA) using a water-soluble macromolecular chain transfer agent based on poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC). A detailed phase diagram has been elucidated for this aqueous dispersion polymerization formulation that reliably predicts the precise block compositions associated with well-defined particle morphologies (i.e., pure phases). Unlike the ad hoc approaches described in the literature, this strategy enables the facile, efficient, and reproducible preparation of diblock copolymer spheres, worms, or vesicles directly in concentrated aqueous solution. Chain extension of the highly hydrated zwitterionic PMPC block with HPMA in water at 70 °C produces a hydrophobic poly(2-hydroxypropyl methacrylate) (PHPMA) block, which drives in situ self-assembly to form well-defined diblock copolymer spheres, worms, or vesicles. The final particle morphology obtained at full monomer conversion is dictated by (i) the target degree of polymerization of the PHPMA block and (ii) the total solids concentration at which the HPMA polymerization is conducted. Moreover, if the targeted diblock copolymer composition corresponds to vesicle phase space at full monomer conversion, the in situ particle morphology evolves from spheres to worms to vesicles during the in situ polymerization of HPMA. In the case of PMPC(25)-PHPMA(400) particles, this systematic approach allows the direct, reproducible, and highly efficient preparation of either block copolymer vesicles at up to 25% solids or well-defined worms at 16-25% solids in aqueous solution.

Optimization of N-carboxyanhydride (NCA) polymerization by variation of reaction temperature and pressure

Several new methods for the controlled ring-opening polymerization of N-carboxyanhydrides (NCA ROP) have been established in the recent past, all of which based on the normal amine mechanism. In this paper the optimal NAM polymerization conditions were investigated combining the high-vacuum and the low-temperature for the NCAs of γ-benzyl-L-glutamate (BLG), Ne-benzyloxycarbonyl-L-lysine (ZLL), L-alanine (Ala), β-benzyl-L-aspartate (BLA), O-benzyl-L-serine (BLS), and O-benzyl-L-threonine (BLT). The polymerizations were followed by FTIR, size exclusion chromatography (SEC) and MALDI-ToF-MS to provide information of the monomer conversion, polymer molecular weight and chain composition as a function of pressure and temperature. It was found that the studied NCAs could be divided into two groups: in the first group monomers of BLG, ZLL and Ala polymerized considerably faster when a lower pressure of 1 × 10−5 bar was applied. MALDI-ToF-MS analysis confirmed that the formation of side products for these monomers mostly started after full monomer conversion. The second group of monomers, i.e. BLA, BLS and BLT, polymerized considerably slower than the first group and no effect was observed from the lower pressure. On the other hand, the number of side reactions was significant at 20 °C, so that the polymerizations for the latter monomers should preferably be done at 0 °C. By combining both methods, multiblock polypeptides were synthesized including a tetrablock of PBLG-b-PAla-b-PZLL-b-PBLA with a polydispersity of 1.3.

Kinetics and mechanism of cyclic esters polymerization initiated with covalent metal carboxylates, 5

Ring-opening polymerizations of ε-caprolactone (CL) and L,L-dilactide (LA) initiated by tin(II) octoate (Sn(Oct)2) and zinc octoate (Zn(Oct)2) and co-initiated with butyl alcohol (BuOH) carried out in tetrahydrofuran as a solvent at 80 °C were studied. By means of MALDI-TOF mass spectrometry, the formation of several populations of polyester macromolecules bearing various end-groups was revealed, namely for poly(ε-caprolactone) (PCL): BuO(O)CPCLOH (A), BuO(O)CPCLOct (B), HO(O)CPCLOH (C), HO(O)CPCLOct (D), and PCL cyclics (E), and for poly(L-lactide) (PLA): BuO(O)CPLAOH (A′), BuO(O)CPLAOct (B′), HO(O)CPLAOH (C′), and HO(O)CPLAOct (D′) (where Bu = C4H9 and Oct = O(O)CCH(C2H5)C4H9). In these polymerizations the end-groups in the originally formed macromolecules change slowly with time. In the LA/Sn(Oct)2/BuOH system at the beginning of polymerization almost exclusively macromolecules of the structure A′ are formed and then structures B′, C′, and D′ start to appear, however, after a period more than 300 times (at 80 °C) longer than that required for full monomer conversion, these macromolecules give exclusively esterified B′ and D′ chains. With Zn(Oct)2/BuOH all of these processes are much slower and less selective. Dependencies of mass fraction of macromolecules with various end-groups on time in L,L-dilactide polymerization initiated with Sn(Oct)2/BuOH system. Symbols ▵, ▴, ○, • correspond to PLA populations A′, B′, C′, and D′.

Influence of Reaction Conditions on Degree of Branching in Hyperbranched Aliphatic Polyethers from 3-Ethyl-3-(hydroxymethyl)oxetane

The cationic ring-opening polymerization of 3-ethyl-3-(hydroxymethyl)oxetane to form hyperbranched polyethers has been studied. The polymerizations have been performed in bulk using sulfonium salt initiators. To produce polymers of different degrees of branching, the reaction conditions (reaction temperature and initiator) have been varied. Polymerizations have also been performed in the presence of a trifunctional core molecule, trimethylolpropane. The conversion of monomer turned out to be the main factor determining the degree of branching in the resulting polymer. Polymers with degrees of branching ranging from 0.15 to 0.41 were synthesized. When 3-ethyl-3-(hydroxymethyl)oxetane was polymerized by slow addition of monomer to a core molecule, a lower degree of branching was obtained compared to the one-step synthesis with full conversion of monomer. The polydispersity was generally slightly lower when a core molecule was used than in the one-step homopolymerization of 3-ethyl-3-(hydroxymethyl)oxetane.

On the steady-state approximation in thermal free radical frontal polymerization

Frontal polymerization is a process in which a spatially localized reaction zone propagates into a monomer converting it into a polymer. We formulate a mathematical model of thermal free radical frontal polymerization involving a five-species reaction mechanism and justify its reduction to a four-species problem by combining the concentrations of two kinds of radicals, primary radicals and polymer radicals. We study the simplified problem both numerically and analytically, and determine such important characteristics of the process as the propagation speed of the wave, the final temperature in the system, and the spatial distributions of all the species in the wave. We perform the analyses with the steady-state approximation (SSA) and without it, and reveal where the SSA solution breaks down. Specifically, the non-SSA solution predicts full monomer conversion and an adiabatic final system temperature, whereas the SSA solution predicts a less-than-adiabatic final temperature and incomplete conversion.

Mechanism of Anionic Polymerization of (Meth)acrylates in the Presence of Aluminum Alkyls, 6. Polymerization of Primary and Tertiary Acrylates

The kinetics of the polymerization of n-butyl acrylate initiated by lithiated ester enolates in the presence of aluminum alkyls was investigated in toluene and in toluene/Lewis base mixed solvents at −78 °C. In pure toluene, curved time−conversion plots, incomplete monomer conversion, and broad molecular weight distributions (Mw/Mn ≈ 2) are observedin the absence of aluminum alkyls the molecular weight distributions are significantly broader (Mw/Mn > 14). High monomer conversions and narrower molecular weight distributions (Mw/Mn ≈ 1.5) are obtained when using Lewis bases (e.g., methyl pivalate) as cosolvents. The polymerization of tert-butyl acrylate rapidly reaches full monomer conversion with rather broad molecular weight distributions (Mw/Mn ≈ 2); the addition of a Lewis base, however, does not have a pronounced effect on these values.

Cationic polymerization of siloxanes kinetically controlled oligomerization in hexamethylcyclotrisiloxane – linear dimethylsiloxane systems

AbstractThe kinetically controlled distribution of linear oligomers in the cationic solution polymerization of hexamethylcyclotrisiloxane (D3) in the presence of hexamethyldisiloxane (MM), octamethyltrisiloxane (MDM), and decamethyltetrasiloxane (MD2M) as molecular chain stoppers was investigated by gas chromatography. At an early stage of the process the distribution was practically unaffected by consecutive reactions involving original stable products of oligomerization, which renders the distribution an important tool in the studies of the mechanism of cationic polymerization of siloxanes. Triple pattern distribution (the excess of every third homologue of the MDnM series) is observed even at nearly full monomer conversion. The distribution of this excess oligomers at low monomer conversion is highly specific as the amounts of each subsequent homologue is decreased by a constant factor. The factor is related to the relative reactivity of the siloxane bonds in the chain stopper and in the monomer. In principle, the results agree with the chain mechanism of polymerization involving kinetic chain transfer to the molecular chain stopper.Studies of the kinetically controlled distribution of linear oligomers in the oligomerization involving a chain stopper of unsymmetrical structure with respect to the reacting siloxane bond allow to determine the specificity of the combination of stopper fragments with a linear molecule. Low specificity showed by MDM constitutes evidence against the mechanism involving a silicenium ion intermediate.