Radical polymerization of a trimer of methyl acrylate as polymerizable α-substituted acrylate

The radical polymerization of a trimer of methyl acrylate was investigated in relation to the steric hindrance-assisted polymerization of an α-(substituted methyl)acrylic ester. The trimer can also be regarded as a model of the unsaturated end group formed by the addition-fragmentation chain transfer of methyl α-(bromomethyl)acrylate during methyl acrylate polymerization. The trimer polymerizes slowly to a low-molecular-weight polymer at 30–60°C, and electron spin resonance (ESR) quantification of the propagating radical of the trimer allowed the determination of the absolute rate constants of propagation (k_p) and termination (k_t). The k_p and k_t values for the trimer indicate slow propagation and slow termination of polymerizable acrylates bearing a bulky α-substituent. In conformity with a higher reactivity of the trimer of methyl acrylate than the corresponding trimer of methyl methacrylate, poly(methyl acrylate) bearing an unsaturated end group, which is produced by the polymerization of methyl acrylate in the presence of methyl α-(bromomethyl)acrylate, was confirmed to copolymerize with methyl acrylate to yield a branched homopolymer.     

Role of bulky α-substituent in free-radical polymerization and copolymerization of methyl α-(alkoxymethyl)acrylates

Methyl α-(alkoxymethyl)acrylates were prepared from methyl α-(bromomethyl)acrylate in 80–90% yield. The monomers homopolymerize fast to yield low-molecular-weight polymers. The monomers bearing a linear alkoxymethyl group except for the ethoxymethyl group are characterized by a relatively low ceiling temperature. The rate constants for propagation k_p and termination k_t of methyl α-(butoxymethyl)acrylate were evaluated to be k_p = 298 dm³ · mol^?1 · s^?1 and k_t = 8 · 10⁶ dm³ · mol^?1 · s^?1 at 60°C, respectively. The α-(alkoxymethyl)acrylates are more reactive than methyl methacrylate toward polystyrene radical, except for the α-(dodecyloxymethyl)acrylate which is slightly less reactive, indicating that an increase in the reactivity by the electron-withdrawing character of the alkoxy group prevails over the steric hindrance against addition of the polymer radical, except for the large dodecyloxymethyl group.     

Rate constants for elementary reactions of the radical polymerization of methyl 2-(benzyloxymethyl)acrylate as polymerizable acrylate bearing large substitutents

Methyl 2-(benzyloxymethyl)acrylate (MBZMA) which was synthesized by reaction of methyl 2-(bromomethyl)acrylate with benzyl alcohol was radically homo- and copolymerized. MBZMA polymerized as fast as methyl methacrylate despite of the presence of a large 2-substituent. The absolute rate constants for propagation and termination were evaluated from the direct determination of the steady state concentration of the propagating radical by electron spin resonance spectroscopy at 60°C: k_p = 182 dm³ · mol^?1 · s^?1 and k_t = 1,6 · 10⁶ dm³ · mol^?1 · s^?1. It was deduced from the magnitude of the rate constants that the balance of the slow propagation and termination allows the formation of a polymer. Evaluation of the cross-propagation rate constants in the copolymerization with styrene revealed that primarily the steric effect of the benzyloxymethyl group reduced the reactivity of the polymer radical and that the electronwithdrawing character of the 2-substituent prevailing the steric effect enhanced the monomer reactivity toward the polystyrene radical.     

Morphology and rheology of poly(methyl methacrylate)‐block‐poly(isooctyl acrylate)‐block‐poly(methyl methacrylate) triblock copolymers,and potential as thermoplastic elastomers

The phase morphology and rheological properties of a series of poly(methyl methacrylate)‐block‐poly(isooctyl acrylate)‐block‐poly(methyl methacrylate) triblock copolymers (MIM) have been studied. These copolymers have well‐defined molecular structures, with a molecular weight (MW) of poly(methyl methacrylate) (PMMA) in the range of 3 500–50 000 and MW of poly(isooctyl acrylate) (PIOA) ranging from 100 000 to 140 000. Atomic force microscopy with phase detection imaging has shown a two‐phase morphology for all the MIM copolymers. The typical spherical, cylindrical, and lamellar phase morphologies have been observed depending on the copolymer composition. MIM consisting of very short PMMA end blocks (MW 3 500–5 000) behave as thermoplastic elastomers (TPEs), with however an upper‐service temperature higher than the traditional polystyrene‐block‐polyisoprene‐block‐polystyrene TPEs (Kraton D1107). A higher processing temperature is also noted, consistent with the higher viscosity of PMMA compared to PS.     

NMR evidence of the block structure of poly(methyl methacrylate)-block-poly(ethyl acrylate) prepared by group transfer polymerization

The structure of poly(methyl methacrylate)-block-poly(ethyl acrylate) prepared by group transfer polymerization was studied by ¹H and ¹³C 1 D and 2D NMR methods including SINEPT, COSY, LR H-H-C RELAY and COLOC using model homopolymers of methyl methacrylate (MMA) and ethyl acrylate (EA) of a length equal to that of the blocks and prepared under the same conditions. The ¹H and ¹³C spectra of the copolymer are shown to be a superposition of the respective spectra of the homopolymers, with the exception that the copolymer lacks the terminal group present in the MMA homopolymer and the initiating group of the EA polymer. Moreover, a new minor signal is found in the CH₂ region of the copolymer which is shown to belong to the link of the blocks. The existence of a direct link between the blocks is further supported by the results of 1D and 2D coherence transfer methods, especially, those using the newly modified DS INEPT and H-C-C RELAY pulse sequences.     

High resolution NMR studies on sequence distribution of vinylidene chloride copolymers

Sequence distributions of several radical copolymers of vinylidene chloride were examined by NMR spectroscopy, including methyl methacrylate, benzyl methacrylate, methaeryloyl chloride, methyl acrylate, α-methylstyrene, styrene, and vinyl acetate as comonomers. Except for the α-methylstyrene and styrene systems, some of the diad, triad, and tetrad sequences were observed in the CH₂ and αCH₃ resonances and are discussed in the light of the usual copolymerization theory.     

Controlled Polymerization Under 60Co γ‐Irradiation in the Presence of Dithiobenzoic Acid

The polymerization of methyl acrylate and styrene was carried out under ⁶⁰Co γ‐irradiation in the presence of dithiobenzoic acid (DTBA) and the kinetics of the polymerization of methyl acrylate was studied. The polymerizations are of a controlled free radical character. The molecular weight of the polymers increases with increasing monomer conversion, and the polydispersities of polystyrene and poly(methyl acrylate) are less than 1.4.     

Solution properties of copolymer of p-chlorostyrene and methyl methacrylate

The monomer reactivity ratios in the free radical copolymerization of methyl methacrylate and p-chlorostyrene were obtained and an azeotropic copolymer containing the 0.484 mole fraction of methyl methacrylate was prepared. The copolymer was fractionated into nine fractions, which on the basis of their chlorine content and specific refractive index increments, were found to be homogeneous in their chemical composition. The solution behaviour of these fractions was examined by viscosity, osmotic pressure and light-scattering techniques. The weight-average molecular weights obtained in dioxane, chloroform and 78:22 v/v mixture of trans-decalin and trichloro ethylene (Θ solvent at 22.3°C) were found to be identical but those obtained from benzene were as much as 80% higher, depending on the molecular weight. The data were treated by the method of STOCKMAYER and BENOIT and the deviation and square-deviation of the chemical composition was obtained as zero and proportional to M^1.5, respectively. The value of exponent “a” in the KUHN -HOUWINK equation[η] = KM^a obtained by use of the number-average molecular weight and corrected weight-average molecular weight, was identical but the apparent weight-average molecular weights obtained in benzene gave a low value of “a” confirming the applicability of the STOCKMAYER-BENOIT relationships. The value of the constant K obtained for the copolymer in the theta solvent was 6.4·10^?4 compared with 4.9·10^?4 and 5.0·10^?4 obtained for poly(methyl methacrylate) and poly-p-chlorostyrene, respectively, indicating a 10% higher dimension for the copolymer.     

Block copolymers by sequential group transfer polymerization: poly(methyl methacrylate)-block-poly(2-ethylhexyl acrylate) and poly(methyl methacrylate)-block-poly(tert-butyl acrylate)

Poly(methyl methacrylate)-block-poly(2-ethylhexyl acrylate) (PMMA-block-PEHA) and poly(methyl methacrylate)-block-poly(tert-butyl acrylate) with a methacrylate/acrylate unit ratio of 1:1 and 1:3, 16000 < M _n < 44000 and 1,9 < M _w/M _n < 2,5, were prepared by sequential group transfer polymerization using (1-methoxy-2-methyl-1-propenyloxy)trimethylsilane as initiator and tetrabutylammonium fluoride monohydrate as a catalyst in tetrahydrofuran at ?30°C, PMMA being the first block. The increase in M _n during the successive addition of monomers is linearly dependent on the (co)polymer yield and size-exclusion chromatography (SEC) curves are shifted towards higher molecular weights in comparison with PMMA macroinitiators. The block structure of the copolymers was also proven by extraction experiments. The presence of homopolymers in the copolymers was not detected. When the former copolymer is prepared in a reverse way (PEHA segment being the first), the MMA polymerization ceases at ≈ 43–45% conversion.     

Polymer conformation and NMR chemical shifts, 9. Poly(α-methylene-γ-butyrolactone)

The conformational energies of poly(α-methylene-γ-butyrolactone) are calculated and compared with those of poly(methyl methacrylate). In spite of the structural resemblance of these two polymers, the patterns of the energy contour maps are clearly distinguishable from each other; the energy barriers between rotational isomeric states are appreciably higher in the former than in the latter polymer. The calculation indicates large non-bonded interactions between the protons in one lactone ring and those in the adjacent lactone rings. The broad NMR spectrum of poly(α-methylene-γ-butyrolactone) apparently reflects its rigid conformational structure. ¹H and ¹³C NMR chemical shifts are calculated by theoretical shielding calculations based on conformational analysis. Much lower magnetic field resonances of the O? CH₂ and α-CH₂ carbons in poly(α-methylene-γ-butyrolactone) as compared with those of the O? CH₃ and α-CH₃ carbons in poly(methyl methacrylate) are well reproduced by the calculation. The shift to lower magnetic field is mainly attributed to paramagnetic shielding derived from the interaction between O? CH₂ carbon and α-CH₂ carbon. Tacticity- and conformation-dependent ¹H and ¹³C NMR chemical shifts of poly(α-methylene-γ-butyrolactone) are well interpreted on the basis of the conformational analysis.     

Simple Photochemical Route to Block Copolymers via Two‐Step Sequential Type II Photoinitiation

A simple method for the preparation of block copolymers by a two‐step sequential Type II photoinitiation is described. In the first step, amine functionalized poly(methyl methacrylate) (PMMA‐N(Et)₂) is prepared by photopolymerization of methyl methacrylate at λ = 350 nm using benzophenone and triethyl amine as photosensitizer and hydrogen donor, respectively. Subsequent benzophenone‐sensitized photopolymerization of tert‐butyl acrylate using PMMA‐N(Et)₂ as hydrogen donor yielded poly(methyl methacrylate)‐block‐poly(tert‐butyl acrylate). The obtained hydrophobic block copolymer is readily converted to amphiphilic polymer by hydrolysis of the tert‐butyl ester moieties of the block copolymer as demonstrated by contact angle measurements. All polymers are characterized by NMR, Fourier transform infrared and UV–vis spectroscopies, and differential scanning calorimetry (DSC) thermal analyses.     

Stereoregularity of poly(methyl vinyl ketone) and poly(isopropenyl methyl ketone) determined by 13C NMR spectroscopy

¹³C NMR spectra of poly(methyl vinyl ketone)s (PMVK) and poly(isopropenyl methyl ketone)s (PIPMK) obtained by radical and anionic catalysts were measured. The ¹³C resonances of the CH₂ carbon of PMVK were tentatively assigned to diad tacticities. The spectra of carbonyl carbon and methyl carbon of the CH₃CO group of PIPMK were assigned to pentad and triad tacticities, respectively. It is shown that radically obtained PMVK and PIPMK have atactic and syndiotactic-rich structure, respectively. The stereoregularity of radically obtained PIPMK obeys Bernoullian statistics, while that of anionically obtained PIPMK conforms to first-order Markov statistics.     

Preparation and polymerization behavior of 2-[2,2,2-tris-(alkoxycarbonyl)ethyl]acrylic ester as a sterically congested monomer

Methyl 2-[2,2,2-tris(methoxycarbonyl)ethyl]acrylate and methyl 2-[2,2,2-tris(ethoxycarbonyl)ethyl]acrylate [M(TE)EA] were synthesized for the first time by the reaction of methyl 2-(bromomethyl)acrylate with the corresponding tris(alkoxycarbonyl)methane in the presence of triethylamine at room temperature in 90 and 89% yields, respectively. Attempted homopolymerization of these particular acrylates did hardly occur. However, the radical produced by attack of the primary radical from 2,2′-azo-2,4,4-trimethylpentane at the β-carbon of M(TE)EA was detected via its 5-line ESR spectrum, and a similar spectrum was observed using tert-butyl peroxide as initiator. These findings imply that persistency of the adduct radical of M(TE)EA suppresses further propagation to high molecular weight polymer. Steric congestion of the adduct radical was shown by ESR spectral change at different temperatures. Copolymerization of M(TE)EA with methyl methacrylate proceeded at a slow rate and yielded products containing only 1,7–2,7 units of M(TE)EA per polymer chain irrespective of comonomer composition. When the content of M(TE)EA was lower than 10 mol-% in the monomer mixtures of M(TE)EA with styrene and methyl acrylate, copolymers whose molecular weights decreased with an increase in M(TE)EA content in monomer mixture were obtained. The copolymerization rates were also reduced considerably with increasing content of M(TE)EA in the feed.     

Synthesis of Riboflavin‐Based Macromolecules through Low ppm ATRP in Aqueous Media

A vitamin‐B₂‐based macroinitiator is prepared by esterification of riboflavin with 2‐bromoisobutyryl bromide. Following the “core first” methodology, “phoenix”‐shape (co)polymers with a polar riboflavin core and either a hydrophobic (poly(n‐butyl acrylate) or poly(methyl methacrylate)) or hydrophilic (poly(N‐isopropylacrylamide)‐block‐poly(oligo(ethylene glycol) acrylate) or poly(N‐isopropylacrylamide)‐block‐poly(2‐hydroxyethyl acrylate)) tails are synthesized via low ppm atom transfer radical polymerization procedures. Polymers have predetermined molecular weights and a low dispersity (Ð < 1.2). ¹H NMR analysis confirms the successful formation of targeted (co)polymers with the preserved riboflavin functionality.     

Über die radikalpolymerisation einiger monomerer in dimethylformamid

The polymerization of acrylonitrile, methyl acrylate, methyl methacrylate, α-chloromethyl acrylate and α-bromo methyl acrylate in dimethylformamide has been investigated using α.α′-azobisisobutyronitrile as initiator. The following relations have been derived at 60°C: for methyl acrylate v = 15.15·10^?4·[I]^0.5·[M], for methyl methacrylate v = 3.46·10^?4·[I]^0.5·[M], for α-chloro methyl acrylate v = 5.25·10^?4·[I]^0.5·[M], and for α-bromo methyl acrylate v = 4.12·10^?4·[I]^0.5·[M]. It has been found that (k_p/k_t^0.5)₆₀ is 14.4·10^?2 for α-chloro methyl acrylate and 12.15·10^?2 for α-bromo methyl acrylate. The relation between the kinetic data obtained and the HAMMETT σ_p constants has been discussed for the substituents in α-position to the double bond which are considered to be the characteristic parameters for the chemical structure of the monomers.     

Influence of thionoesters on the degree of polymerization of styrene,methyl acrylate,methyl methacrylate and vinyl acetate

The aromatic thionoester 3 (benzyl thionobenzoate) was an effective chain transfer agent in polymerizations of styrene (C_x = 1,0) and methyl acrylate (C_x = 1,2) at 60°C. This activity was close to the ideal for obtaining narrow molecular-weight distributions in batch polymerizations. The thionoester 3 showed no activity in polymerizations of methyl methacrylate, but was too reactive to be useful in vinyl acetate polymerizations. Ring-substituted thionoesters 9-11 and 14 and ¹H NMR spectroscopy of the resulting polymers were used to establish the type and quantity of end-groups. The thionoester 12 was used to produce low-molecular-weight polystyrene that was terminated at one end with a hydroxy group and at the other end by a thioloester moiety.     

Mechanical shear degradation of polymers in solution by turbulent flow, 3. The influence of chemical constitution and thermodynamic quality of the solvent on shear degradation

Mechanical shear degradation of polyisobutylene, polystyrene, poly(vinyl chloride), poly(methyl methacrylate), poly(decyl methacrylate), poly(methyl acrylate), and 1,4-polybutadiene in dilute solutions of tetrahydrofuran (THF) are studied under turbulent flow conditions through a capillary, in order to study the effect of the chemical constitution on shear degradation. In addition the influence of solvent quality on shear degradation is investigated. The changes of the molecular weight distribution curves were followed by gel permeation chromatography (GPC), in order to determine the degradation constants k_i for the corresponding molecular weight distribution fractions M?_i. GPC calibration via the concept of universal calibration, Mark-Houwink relations for polyisobutylene, poly(methyl methacrylate), poly(methyl acrylate), 1,4-polybutadiene, and poly(dimethylsiloxane) in THF as solvent had to be established for this purpose. Substantial differences in the rate constants k_i were observed as a function of M?_i, whereas a master curve resulted for all polymers except 1,4-polybutadiene when k_i was plotted against the number of main chain carbon atoms n?_i for each molecular weight M?_i. From this the shear degradation of C? C single bond polymers can be represented by k_i = C · n?, C being independent of the chemical nature of the C? C single bond polymer, and a varying from 1,7 to 2,6. This means that in addition to the shape of the deformed macromolecule to be degraded not only its hydrodynamic volume (in rest) but also its chain length plays an important role. As to the influence of solvent quality, the degradation constants were found to increase with decreasing solvating power of the solvent. Mechanical shear degradation of the type discussed here takes place in drag reduction by polymers.     

Poly(methyl methacrylate)-block-poly(ethyl acrylate) by group transfer polymerization: synthesis and structural characterization

Poly(methyl methacrylate)-block-poly(ethyl acrylate) (PMMA-block-PEA) was synthesized by sequential group transfer polymerization (GTP) in tetrahydrofuran at ?30°C using (1-methoxy-2-methyl-1-propenyloxy)trimethylsilane (MTS) as an initiator and tetrabutylammonium fluoride monohydrate (TBAF · H₂O) as a catalyst. First, the PMMA macroinitiator was prepared in situ in quantitative conversion and its lifetime was at least 15 min. In the second step, an equimolar amount of ethyl acrylate was polymerized with a conversion of 67–88% and PMMA-block-PEA with number-average molecular weight 5000 < M?_n < 11 500 and polydispersity 1,4 < M?_w/M?_n < 2,1 was obtained. The number of chains almost does not change during the polymerization and the initiating efficiency of MTS was in both steps ca. 0,65–0,80. The diblock structure of the copolymer was confirmed by the ¹³C NMR spectrometric direct proof of the bond-linking of both blocks and by comparing the DSC behaviour of the copolymer with that of the corresponding blend of the homopolymers. No contamination of the block copolymer with the homopolymers was detected by the analytical methods used for the structural characterizations.     

Thermal degradation of copolymers of methyl methacrylate and n-butyl acrylate. I. Thermal analysis

By means of thermal volatilisation analysis (TVA) the principal features of the thermal degradation of a series of copolymers of methyl methacrylate and n-butyl acrylate covering the entire composition range have been revealed. The degradation which is initiated in poly(methyl methacrylate) at unsaturated chain terminal structures is progressively suppressed by increasing concentrations of copolymerised n-butyl acrylate while the degradation initiated by random chain scission moves to higher temperatures. It is clear from the TVA thermograms that the products of degradation consist of a complex mixture of gases and liquids and a viscous oily fraction. Energies of activation have been derived from thermal gravimetric analysis thermograms by the method of COATS and REDFERN. The increase with increasing n-butyl acrylate content of the copolymer has been associated with the greater heat of polymerisation of n-butyl acrylate compared with methyl methacrylate.     

Copolymerization of ethene with methyl acrylate and ethyl 10-undecenoate using a cationic palladium diimine catalyst

The cationic palladium catalyst [(ArN=C(Me)C(Me)N=Ar)Pd(CH₃)(NC—CH₃)]⁺BAr'₄^- (Ar = 2,6-C₆H₃(CH(CH₃)₂); Ar' = 3,5-C₆H₃(CF₃)₂) (DMPN/borate) was applied in ethene homopolymerization as well as ethene copolymerization with polar monomers such as methyl acrylate and ethyl 10-undecenoate. Both ethene homo- and copolymerization afforded amorphous, branched polyethenes with glass temperatures around –65°C and very similar high degree of branching (105 branched C/1000C), which was independent of temperature and ethene pressure. Copolymerization with polar comonomers gave polyethylene containing both alkyl and ester-functional alkyl side chains. The ratio of both types of short chain branches was influenced by the feed concentration of polar monomer. In the presence of sterically hindered phenols (e. g., 2,6-di-tert-butyl-4-methylphenol (BHT)) and tetramethylpiperidine-N-oxyl radical (TEMPO) acrylate homopolymerization was prevented. BHT addition promoted both catalyst activity and methyl acrylate incorporation significantly. Polymerization reaction, polymer microstructures and polymer properties of polar and non-polar branched polyethenes were investigated.