Living carbocationic polymerization

Mono- and bifunctionaltert-alcohols, i.e., cumyl alcohol (CumOH), 2,4,4-trimethyl-2-pentanol (TMPOH), 2,6-dihydroxy-2,4, 4, 6-tetramethylheptane (TMHDiOH), in conjunction with BCl₃ have been shown to be efficient initiating systems for the living polymerization of isobutylene (IB) in CH₃Cl or CH₂Cl₂ solvents in the –10° to –80°C range. The living nature of the polymerizations was demonstrated by linear M_n versus amount of polyisobutylene (PIB) formed (W_PIB) plots starting at the origin and corresponding horizontal number of PIB moles formed (N) versus W_PIB plots. Quenching with methanol producestert-chlorine terminated PIBs. Quantitative dehydrochlorination of the latter products yields exo-olefin (isopropylidene) end groups. These experiments demonstrate that living carbocationic polymerizations have in fact been conducted in these laboratories long ago (1) without having been recognized as such.     

Living carbocationic polymerization

A new family of initiating systems has been discovered that efficiently induces the truly living polymerization of isobutylene (IB). The initiating systems are complexes of organic tertiary esters e.g., cumyl acetate, 2,4,4-trimethylpentane-2-acetate, with BCl₃. Living polymerizations proceed very rapidly in a variety of solvents, i.e., CH₃Cl, CH₂Cl₂, C₂H₅Cl, and mixtures of chlorinated solvents plus n-hexane, in the range from –10° to –50°C. The living nature of the polymerizations was demonstrated by linear ¯M_n versus W_PIB (g of polymer formed) plots starting at the origin and horizontal N (number of PIB chains) versus W_PIB plots. The DP_n of the products obeys [M_o]/[I_o] where [M_o] and [I_o] are initial monomer and initiator concentrations, respectively. Conversions and initiator efficiencies are 100%. In carefully controlled experiments narrow molecular weight distribution polyisobutylenes (PIB) have been obtained, i.e., M_w/M_n=1.17 – 1.3. A mechanism is outlined that helps rationalize the findings. It is postulated that the living polymerization of IB initiated by organic tertiary ester·BCl₃ complexes most likely proceeds by a two-component group transfer polymerization process.     

Investigation of 1,3,5-tris(2-metoxypropane)benzene/BCl3 initiated living isobutylene polymerization by C13 and B11 NMR spectroscopy

Summary The living carbocationic polymerization of isobutylene initiated by 1,3,5-tris(2-methoxypropane) benzene (TriCumOMe)/BCl₃ system was investigated by C¹³ and B¹¹ NMR spectroscopy. The reaction between the TriCumOMe and BCl₃ at-30°C in CH₂Cl₂ after 15 mins reaction time resulted in 1,3,5-tris(2-chloropropane) benzene (TriCumCl) and methyl-dichloroboronite (BCl₂OMe). The same system in the presence of isobutylene yielded three-arm star, chlorine terminated telechelic polyisobutylene and BCl₂OMe. No counterions, i.e., BCl₃OMe, BCl ₄ , or neutral boron complexes, e.g., TriCumOMe, 3BCl₃ could be detected. The simultaneous measurement of static permittivity (direct monitoring method) showed different reaction rate patterns in the case of AMI method, and when the TriCumOMe+BCl₃ mixture was aged and the polymerization was started by isobutylene.     

Electron pair donors in carbocationic polymerization

Preparatory to a detailed presentation of a large body of accumulated information, representative data have been selected to demonstrate that well-defined narrow molecular weight distribution (MWD) (¯M_w/¯M_n = 1.1) polyisobutylene (PIB) can be readily prepared in the M_n = 1000 – 100,000 range in the presence of certain types of electron pair donors (EDs) under a great variety of conditions. Specifically, many initiating systems, such as dicumyl chloride/BCl₃, dicumyl alcohol/BCl₃, 2-chloro-2,4,4-trimethylpentane/TiCl₄, that induce nonliving polymerizations and/or give relatively broad MWD PIBs, in the presence of suitable EDs, e.g., dimethyl sulfoxide (DMSO), dimethyl acetamide (DMA), give rise to living polymerizations and yield narrow MWD products. Evidently, by the use of select EDs various undesirable side reactions, i.e., uncontrolled initiation, chain transfer, irreversible termination, indanyl end-group formation, etc., that plague carbocationic polymerizations and which therefore yield ill-defined relatively broad MWD products, can be eliminated and well-defined narrow MWD products can be obtained. The addition of EDs to otherwise extremely rapid carbocationic polymerizations results in lower controlled rates. All these observations and beneficial effects can be explained by controlled carbocation stabilization by EDs, a subject that will be explored and discussed in detail in this series of publications.Paper XXV in the series living carbocationic polymerization     

Living carbocationic polymerization

Summary Living carbocationic polymerization of styrene (St) has been achieved by the use of the 1(p-methylphenyl)ethyl acetate (pMePhEtOAc)·BCl₃ complex in CH₃Cl solvent at –30°C using both the IMA and AMI techniques. The living nature of the polymerizations has been demonstrated by linear M_n versus W_PSt (weight of polystyrene) plots passing through the origin and horizontal N (moles of PSt) versus W_PSt plots starting at N=I_o (the number of moles of initiator used). The molecular weight distribution MWD of the PSts is broad (M_w/M_n=~5–6) due to slow initiation and/or slow exchange between dormant and active species relative to propagation. The structure of the ester initiator strongly affects the rate and outcome of living polymerization, e.g., cumyl acetate (CumOAc), cumyl propionate (CumOPr), and 2,4,6-trimethylphenylethyl acetate (TMePhEtOAc), do not lead to truly living St polymerizations. The findings with the latter esters is explained in terms of a two path process comprising a slow living polymerization and a faster conventional cationic chain reaction. With phenylethyl acetate (PhEtOAc) living polymerization is achieved, however, initiation (cation generation) is slow. Forced termination by pyridine or methanol, or heating to ambient temperature leads to-CH₂CH(C₆H₅)Cl end groups.     

Retraction of the claim of ring expansion polymerization of isobutylene

Some three years ago in a preliminary report from this laboratory we have proposed that the polymerization of isobutylene (IB) by the -tolyl--valerolactone/BCl₃ initiating system in CH₃Cl or CH₂Cl₂ diluents at-30°C proceeds in a living manner by an unusual ring expansion mechanism and produces macrocyclic polyisobutylenes (PIBs) [1]. Extensive follow-up research confirmed the living nature of the polymerization, however, has failed to confirm the results of a key preliminary experiment upon which the proposition of macrocyclic polymer structure was based. Thus the results of a comparative hydrolysis/GPC experiment carried out with a relatively low molecular weight (Mn=5,400) PIB at -30°C under a blanket of N₂ which gave a lower apparent molecular weight after hydrolysis than the original sample before hhydrolysis, could not be confirmed with higher molecular weight samples, i.e., with Mn=12,000, 17,000 and 30,000. As a consequence we wish to retract our earlier claim in regard to the synthesis of macrocyclic PIBs by certain lactone/BCl₃ initiating systems but maintain that these polymerizations proceed in a living manner and yield asymmetric telechelic PIBs, e.g.,-chloro--carboxyl-PIBs [2].     

Investigation of the mechanism of living cationic polymerization of isobutylene by B11 NMR spectroscopy

Summary The living carbocationic polymerization of isobutylene initiated by tri-cumyl-ether (1)/BCl₃ and tricumyl-acetate(2)/BCl₃ was investigated by B¹¹ NMR spectroscopy in the presence and absence of DMSO. With BCl₃, 1 yields tri-cumyl-chloride and BCl₂OMe due to fast exchange reaction, while 2 forms complexes. If the 1/BCl₃ mixture contains DMSO, well defined complexes can be detected, i.e., DMSO.BCl₃ and BCl₂OMe.DMSO. In the system 2/BCl₃/DMSO neutral complexes with broad NMR signals are formed. In the presence of isobutylene (real polymerization mixture) the same complexes can be detected.     

Synthesis of triblock copolymer having alternating structures and kinetics study on RAFT‐mediated bulk,miniemulsion and seed miniemulsion polymerizations

We have conducted reversible addition‐fragmentation chain transfer (RAFT) polymerizations of styrene (St) and maleic anhydride (MAh) and n‐butyl acrylate (BA) to produce a well‐defined triblock copolymer having alternating structure, P(St‐alt‐MAh)‐b‐PSt‐b‐PBA, via bulk, miniemulsion and seed miniemulsion polymerizations. The polymerization kinetics and living characters were investigated. The results followed by gel permeation chromatography (GPC) showed that bulk and miniemulsion polymerizations exhibited controlled nature such as narrow polydispersity index (PDI), controlled molecular weight, and first‐order polymerization kinetics, whereas triblock copolymer owned a rather wider PDI. Comparison of GPC RI and UV traces revealed that alternating copolymer and diblock copolymer have a very high percentage of living chains. For seed miniemulsion polymerization, when the molecular weight of triblock copolymer is more than 36,000 g/mol, the formation of homopolymer of BA resulted in broadening of PDI. ¹H NMR method was used to identify the compositions of block copolymers. Differential scanning calorimetry analysis showed that the copolymers exhibited distinct glass temperatures. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Stable free radical polymerization of styrene with 4-sulphonate-2,2,6,6-tetramethylpiperidine-N-oxyl as mediators

The stable free radical polymerizations of styrene were investigated with five 4-sulphonate-2,2,6,6-tetramethylpiperidine-N-oxyl stable radicals as mediators and benzoyl peroxide (BPO) as initiators at 125 °C. The results indicated that the polymerizations proceeded in a “living”/controlled manner, i.e., the polymerization rates were first-order with respect to the monomer concentrations, molecular weights increased linearly with conversions and the molecular weight distributions were relatively low (M _w/M _n = 1.2–1.4), ¹H NMR analysis of the polymer chain-ends and successful chain extensions. The polymerization rates were faster than that of 4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl (OH-TEMPO) mediated ones. The effects of steric interference of different substitute groups at four-position of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), the molar ratios of stable radical to BPO and the temperature on the polymerizations were investigated.     

Direct monitoring of cationic polymerization by temperature,conductivity and permittivity measurements

Summary Direct monitoring of cationic polymerization was accomplished by simultaneous measurement of the average dielectric constant, representing the dipoles, of the conductivity, produced by unpaired ions, and of the temperature, characteristic for reaction rate. The ionogenic equilibria during the living polymerization of isobutylene by 1, 3, 5-tris(2-methoxy-2-propyl)benzen/BCl₃ in CH₂Cl₂ at-25°C were demonstrated. Temperature, resistance and capacitance were measured directly in the reaction mixture by a specially designed instrument.Both the conductivity and the average dielectric constant change characteristically during the living polymerization, indicating the presence and simultaneous change of unpaired ions and strongly polarized species.The differences between the AMI, and the aging technique were demonstrated and explained. In the latter case slow initiation was observed due to the methoxy-chlorine exchange caused by a reaction with BCl₃.The applied direct monitoring method helps to understand the role of polarized and ionic species in polymerizations and related processes.     

Electro‐optical properties of polymer dispersed liquid crystal prepared by successively controlled living radical polymerization

Polymer dispersed liquid crystal (PDLC) films were obtained by successive controlled living radical polymerizations: starting polystyrene (M1) was obtained by reversible addition‐fragmentation polymerization (RAFT), M1 was converted to P‐chloromethylated polystyrene (M2) which was grafted with polystyrene branches by atom transfer radical polymerization (ATRP) to yield RAFT‐initiating graft polymer containing trithiocarbonate moieties in the backbone (M3, RAFT‐active grafted polystyrene), and then PDLC films were prepared by photo‐induced RAFT copolymerization of methyl acrylate with M3 in the presence of a nematic liquid crystal. The electro‐optical properties of the films were investigated for the purpose to apply them to optical devices. Experimental results showed that preferable properties could be acquired by controlling the amount of M3 and the liquid crystal E7 in the polymer matrix of PDLC films. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Bulk polymerization of isobutylene initiated by PVC/SnCl4 systems

Summary It has been surprisingly discovered that an initiator system based on PVC/SUCl₄ produces bulk polymerization of isobutylene even under conditions, when a mixture of isobutylene and SnCl₄, in the absence of a polar medium, does not polymerize. The PVC polymers used were the powders of the commercial suspension PVC Neralit S-652, lower-molecular-weight PVC prepared by extraction of Neralit S-652 with acetone (PVC-AE) and the copolymer of vinyl chloride with 2-chloropropene (VC/2CP). The kinetics of polymerizations were studied dilatometrically at –78°C. It was found that the bulk polymerization of isobutylene proceeds at the boundary between the solid (PVC) and liquid (isobutylene) phase over an unusually long period of time which, depending on the type of PVC used, can last more than 7 days. It followed from the determination of the initial polymerization rate that the activity of the studied types of PVC decreases in the order PVC-AE > VC/2CP PVC.     

Polyethers with phosphate pendant groups by monomer activated anionic ring opening polymerization: Syntheses,characterization and their lithium-ion conductivities

This paper describes the preparations and lithium-ion conductivities of various solid polymer electrolytes for potential use in high-energy density lithium-ion batteries. The ring opening polymerization of epoxides (M1–M6), catalyzed by Zn(II), Cu(II) and Cd(II) complexes in the presence of tetrabutylammonium bromide (TBAB), yielded polyethers (P1–P6) in which phosphates were attached as pendant groups. A reaction condition where Zn(II) catalyst used slightly excess to TBAB increased the polymerization rate remarkably and yielded the polyethers with higher molar masses in a short time. These polymerizations proceeded following a “monomer activated anionic ring opening polymerization” mechanism. These living like polymerizations also progressed according to “formation of polymer chain per initiator” model. The solid-state lithium-ion conductivities of these polymers were examined using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The conductivity of one of the solid polymer electrolytes with 40 wt% of LiTFSI was 5.2 × 10⁻⁵ S cm⁻¹ at room temperature and 2.9 × 10⁻⁴ S cm⁻¹ at 80 °C.     

Photo-induced living/controlled surface radical grafting polymerization and its application in fabricating 3-D micro-architectures on the surface of flat/particulate organic substrates

This feature article covers the fundamental chemistry and applications of photo-induced living surface grafting polymerization. The mechanism of activation of inert alkyl C-H bonds of polymer substrates, the structures of the active free radical and reversible dormant species, the modes of the grafting chain growth (including linear, branched and cross-linked variants), and the role of spatial effect are discussed. Two technologies, i.e., 1-step and 2-step processes, their features and applications in fabricating polymer brushes with precisely controlled patterns, desired functions, branched and block grafting chains on planar substrates, and polymer lamination are presented. The fabrication of 3-dimensional covalently bonded polymer particles, such as nano-sized polymer particle monolayers (with uniform and bimodal distributions), discrete solid and hollow polymer particles of micrometer size, and multilayer polymer particles on polymeric substrates are also introduced. In the last part, the application of photo-induced living surface grafting polymerization in non-planar surface modifications, such as the preparation of core-shell polymer particles, Janus particles and cross-linked hydrogels with hairy polymer chains is summarized.     

The polymerization of alkyl substituted acetylenes using metal halide based initiators: The bulky substituent effect

Summary The polymerization of 1-hexyne, 3,3-dimethyl-1-butyne, 2-hexyne and 1-chloro-1-hexyne by using metal halide based initiators was studied. By analogy with ionic ring opening polymerization systems, living acetylene polymerizations resulted when backbiting and interchain reactions were suppressed, i.e., k_tr, k_t=0. Large acetylenic substituents suppress the formation of cis-cisoidal propagating chains and subsequently eliminate backbiting reactions and also propagating carbene interchain reactions. Possible explanations for differences in polymer dispersities which result under different reaction conditions were also provided.     

RAFT (Reversible addition–fragmentation chain transfer) crosslinking (co)polymerization of multi‐olefinic monomers to form polymer networks

The use of reversible addition–fragmentation chain transfer (RAFT) crosslinking (co)polymerization of multi‐olefinic monomers to produce three‐dimensional polymer networks is reviewed. We give specific attention to differences between RAFT and conventional processes, differences between RAFT and other forms of reversible deactivation radical polymerization (such as atom transfer radical and nitroxide‐mediated polymerizations) and the dependence of the polymerization process and network properties on RAFT agent structure. This knowledge is important in network optimization for applications as dynamic covalent polymers (in self‐healing polymers), as porous polymer monoliths or gels (used as chromatographic media, flow reactors, controlled release media, drug delivery vehicles and in molecular imprinting) and as coatings. © 2014 Society of Chemical Industry     

Optimizing nitroxide-mediated miniemulsion polymerization processes

Living/controlled radical polymerizations provide significant advantages in the control of polymer resin microstructure compared to conventional radical polymerization. Advances in our ability to tailor polymer microstructure will enable improvements in coatings properties and possible new applications of coating technologies. Adapting living radical polymerizations to heterogeneous media such as aqueous-based miniemulsion polymerization presents several challenges related to maintaining the livingness (the fraction of chains that are still “living” at the end of polymerization) of the polymer chains and also developing a commercially viable process. We have studied the nitroxide-mediated polymerization of styrene in miniemulsion, with the intent of maintaining a high degree of livingness by balancing the rates of biradical termination and disproportionation. We can now achieve >95% monomer conversion in less than three hours, while maintaining polydispersities ∼1.3. Monomer conversion can be dramatically increased from about 60–95% by changing the concentration of sodium dodecylbenzenesulfonate (SDBS) surfactant. Conversions in Dowfax 8390 stabilized miniemulsions showed no comparable dependency. Reasons for this potentially commercially important effect are under investigation.     

Semibatch styrene suspension polymerization processes

Emulsion and suspension polymerization processes have widely been studied for more than 40 years. Although both polymerization processes are performed in heterogeneous media, each one presents its own typical characteristics, such as the particle size distribution, molecular weight distribution, polymer particle nucleation rate, and polymerization rate. In this study, semibatch styrene suspension polymerizations were carried out with feed compositions typical of emulsion processes. The initial reactor charge resembled the recipe of standard styrene suspension polymerizations, and the emulsion polymerization constituents were added during the batch. The influence of the moment at which the emulsion feed was started on the course of the polymerization and the effects of the feed on the polymer properties were analyzed. The polymer particle morphology and the average molecular weights changed very significantly with the emulsion feed time, and the changes could lead to the production of broad molecular weight distributions. Core–shell polymer particles could also be obtained, with the core being formed of polymer particles originating from the suspension polymerization process and the shell being formed of polymer particles originating from the emulsion polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3021–3038, 2003     

Controlled free‐radical polymerization of vinyl chloride

Owing to the importance of poly(vinyl chloride) (PVC) as the second‐largest plastic in volume after the polyolefins and above styrene polymers, the control of the free‐radical polymerization of vinyl chloride (VC) is of high industrial and academic interest. But still the term “controlled” polymerization is not yet clearly defined. Often it is used for quasi‐living polymerizations with equilibrium reactions in the initiation and/or termination step or for the control of the molecular weight distribution (MWD), but it can also be applied to several structural aspects such as stereochemistry, branching, or special technical properties. In the present article, the control of chain growth and chain transfer is discussed. It has been well known for many years that the propagation step in the VC polymerization is terminated to a large degree by the rather frequent and temperature‐dependent chain transfer of the growing macromolecules to the monomer. Therefore, the degree of polymerization is strongly governed by the polymerization temperature. However, this transfer step does not result in a controlled or a narrow MWD. By means of free‐radical nitroxide‐mediated polymerization of VC in suspension, PVC with a narrower MWD can be obtained also at higher polymerization temperatures. The resulting PVC with nitroxide end groups can act as a macro‐initiator for various monomers, resulting in two‐block copolymers, which are, e.g., interesting compatibilizers in blends with PVC. J. VINYL ADDIT. TECHNOL., 11:86–90, 2005. © 2005 Society of Plastics Engineers     

Radical polymerization of styrene initiate with a new multifunctional iniferter

Summary A new multi-functional iniferter with photo-induced and thermal dissociation group in one molecule, diethyl 2,3-dicyano-2,3-di(p-N,N-diethyldithiocarbamylmethyl)phenylsuccinate(DDDCS), was successfully synthesized. The bulk polymerizations of styrene (St) with DDDCS were studied. The initiation can take place either under UV light irradiation by the reversible C-S bonds dissociation of DDDCS or under heating by the reversible hexa-substituted C-C bond thermally dissociation. The polymerizations have "living" polymerization characteristics under both cases, i.e., the yield and the molecular weight of the resulting polymer increased linearly with increasing reaction time, and the resultant polymers can act as macroiniferter for preparing block copolymer. Received: 5 December 1999/Revised version: 17 January 2000/Accepted: 21 January 2000