Chain conformation and compatibility in polymer blends. A small-angle X-ray scattering study of the system poly(propylene glycol)-poly(methyl methacrylate)

The thermodynamic compatibility of dilute, solid solutions of poly(propylene glycol) (PPG) (mass-average molar mass M?_w = 3900 g/mol) in poly(methyl methacrylate) (PMMA) (M?_w = 550000 g/mol) was investigated by means of small-angle X-ray scattering. The results of the analysis show that PPG is molecularly dispersed in the solid, amorphous matrix of PMMA, and that the molecules display the typical statistical coil macroconformation of polymers in dilute, liquid solution, whereby the numerical value of the second virial coefficient seems to point to the unperturbed nature of the coils. This behaviour, consistent with the concept of “interpenetration of segments”, is in total agreement with the experimentally measured compositional variation of the glass transition temperature of the blends.     

Effect of polyfunctional chain transfer agents on the molecular weight distribution in free-radical polymerization, 3 Polymerization of methyl methacrylate in the presence of polyfunctional chain transfer agents

Polymerization of methyl methacrylate was carried out in the presence of polyfunctional chain transfer agents: 1,6-hexanedithiol, trimethylolpropane^b tris(mercaptoglycolate) and pentaerythritol tetrakis(3-mercaptopropionate). The theoretical results reported in the preceding papers are completely confirmed: the experimental values of the dispersion index (D = M?_w/M?_n) are 1.62 for f = 2, 1.39 for f = 3 and 1.28 for f = 4. In the case of bifunctional transfer agents the molecular weights calculated are in very good agreement with those obtained by size exclusion chromatography. The formation of star-shaped macromolecules was confirmed by cleavage of the C? S? C bonds. The number-average molecular weight decreases and the dispersion index is approximately equal to 2 after exposure to UV rays. The phenomenon of “pseudo-living” polymerization in the presence of polyfunctional chain transfer agents is also discussed.     

Graft copolymerization of methyl methacrylate by lithium diisopropylamide-treated poly(vinyl propionate)

The anionic grafting of methyl methacrylate (MMA) onto poly(vinyl propionate) (PVPr) was achieved after treatment of the latter with lithium diisopropylamide (LDA). The percentage of grafting of the polymer was between 120 and 730%, no homopolymers being obtained. The degree of lithiation was determined to be 26 mol-% with respect to monomer units by means of deuterolysis. The hydrolysis of the graft copolymers results in the side-chain polymers (PMMA) and poly(vinyl alcohol) (PVA). The average number of branches in the graft copolymer increases from 1 to 7 with increasing percentage of grafting. M?_w/M?_n of the side chain poymer is between 2,0 and 6,7. The low reactivity of the lithium sites may be caused by aggregation of enolates, leading of the broadening of the molecular weight distribution.     

Block copolymers by transformation of living anionic polymerization into controlled/“living” atom transfer radical polymerization

A method for the transformation of living anionic polymerization (LAP) to controlled/“living” atom transfer radical polymerization (ATRP) is reported and utilized for the preparation of block copolymers. The macroinitiators, polystyrene and polystyrene-block-polyisoprene containing the 2-bromoisobutyryl end group (PS-Br, M_n = 12 200, M_w/M_n = 1.04; PS-b-PIP-Br, M_n = 16 800, M_w/M_n = 1.03), were prepared by LAP of styrene and styrene/isoprene, correspondingly, and suitable termination agents. These compounds were used as macroinitiators for controlled/“living” ATRP to prepare block copolymers with methyl acrylate (PS-b-PMA), butyl acrylate (PS-b-PBA), methyl methacrylate (PS-b-PMMA), a mixture of styrene and acrylonitrile (PS-b-P(S-r-AN)) and also chain extension with styrene (PS-b-PS and PS-b-PIP-b-PS). The block copolymers were characterized by means of size exclusion chromatography, ¹H NMR and FT-IR spectroscopy.     

Visible Light–Induced RAFT Polymerization of Methacrylate with 4‐(N,N‐diphenylamino)benzaldehyde as Organophotoredox Catalyst and the Effect of Temperature on the Polymerization

With UV–vis absorption in the range of 270–435 nm, 4‐(N,N‐diphenylamino)benzaldehyde (DPAB) takes efficient photoreduction quench with 4‐cynao‐4‐(phenylcarbonothioylthio)pentanoic acid (CTP). The polymerization rates of methyl methacrylate (MMA) are 0.019, 0.056, and 0.102 h^?1 at 33, 40, and 50 °C, respectively, in the presence of DPAB and CTP under visible‐light irradiation. Dark reaction produces no PMMA at 50 °C for 120 h. The living feature is demonstrated by linearly increasing M_n with the monomer conversions and narrow polydispersity index (PDI), chain extension, and block polymerizations with benzyl methacrylate (BnMA) and poly(ethylene glycol) monomethyl ether methacrylate (PEGMA). With PMMA‐CTP (M_n = 6800, PDI = 1.17), chain extension gives PMMA with M_n = 15 900 and PDI = 1.15. With PMMA‐CTP (M_n = 6000, PDI = 1.21) as macro‐RAFT, PMMA‐b‐PBnMA of M_n = 12 600 (PDI = 1.44) and M_n = 18 500 (PDI = 1.31) are prepared. These results support that there is a positive synergistic effect between polymerization temperature and visible‐light irradiation on the photo‐RAFT without losing the living features.     

Viscosity-molecular weight relationships for low molecular weight polymers. II. Poly(vinyl acetate) and poly(methyl methacrylate)

[η]/M?_n relationships at 25°C. have been found for low molecular weight fractions of poly(vinyl acetate) (PV Ac) in chlorobenzene and poly(methyl methacrylate) (PMMA) in toluene. The PMMA used contains about 75% of syndiotactic form. Due to the difficulties of PMMA fractionation, the constants in the equation [η] = K M? refer to an average degree of polydispersity equal to M?_w/M?_n = 1.2. For both PVAc and PMMA there is a range of molecular weight where a = 0.5; in these ranges [η] is practically indistinguishable from [η]Θ.     

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.     

Neodymium(III) tert‐Butoxide‐Dialkylmagnesium,a New Initiator System for Syndiotactic Polymerization of Methyl Methacrylate

The polymerization of methyl methacrylate (MMA) in toluene at 0°C using combinations of dihexylmagnesium (Hex₂Mg) with various metal tert‐butoxides as initiators has been studied. Purely anionic initiator systems based on alkali metal salts allow complete conversion of MMA within 1 h to yield either highly isotactic PMMA (LiOt‐Bu/MgR₂ = 5, M̄_n = 61 000, M̄_w/M̄_n = 1.95, 84% mm) or narrow polydispersity atactic PMMA (NaOt‐Bu/MgR₂ = 20, M̄_n = 39 000 and M̄_w/M̄_n = 1.18). The combination of Hex₂Mg with Nd₃(Ot‐Bu)₉(THF)₂ (Nd/Mg = 5–10) affords a novel initiator system that gives in 40–63% yield syndiotactic‐rich PMMA (M̄_n = 50–90 000, M̄_w/M̄_n = 1.06–1.12, 76–79% rr) with low initiation efficiency. In this case, characteristics of the polymers and polymerization reactivity data are consistent with the in situ generation of an alkylneodymium species.     

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.     

“Living” free radical ring‐opening polymerization of 2‐methylene‐4‐phenyl‐1,3‐dioxolane by atom transfer radical polymerization

The “living” free radical ring‐opening polymerization of 2‐methylene‐4‐phenyl‐1,3‐dioxolane (MPDO) in the presence of ethyl α‐bromobutyrate/CuBr/2,2′‐bipyridine at various temperatures has been investigated. In comparison with the conventional ring‐opening polymerization of MPDO, a lower content of ring‐opened unit in the polymer was found. The results of ln[M]₀/[M]) against polymerization time, (M_n)_th and (M_n)_NMR vs conversion, and GPC of the polymers are strongly indicative of the “living” polymerization process. Initiator efficiency was measured. The mechanism of polymerization, and the effect of pyridine on the polymerization mechanism were discussed.     

Study of the nature of radical polymerization of methyl methacrylate with “aged” chromium(II) acetate/benzoyl peroxide

The polymerization of methyl methacrylate (MMA) in DMF with “aged” chromium (II) acetate (Cr(Ac₂)) and benzoyl peroxide (BPO), previously formulated as a living radical polymerization, was investigated. The reaction between Cr(Ac)₂ and BPO gives besides N-methylformamidomethyl benzoate ( 3 ) the N-methylformamidomethylchromium(III) cation ( 6 ) as intermediate, which itself may react with BPO with the formation of additional free radicals as compared with the thermolysis of BPO. Thus, the polymerization of MMA in this system could be shown to be a normal radical one with free and uncomplexed radicals. The increase of the degree of polymerization with aging and monomer conversion is explained by the decreasing rate of the radical forming reactions and the onset of the gel effect.     

Étude viscosimétrique du système ternaire polystyrène/poly(méthacrylate de méthyle)/p-xylène

Some theoretical considerations and experimental results are presented on the limiting viscosity number of polystyrene, (PS), dissolved in a mixture of poly(methyl methacrylate), (PMMA), and p-xylene, and of PMMA in a mixture of PS and p-xylene. At relatively low concentration, this problem can be treated using the classical formalism of dilute solutions, introducing in addition a new parameter b_AB characterizing the interactions between the polymers A and B. The quantitative use of this apparently simple method involves some difficulties owing to the fact that terms of higher order have to be taken into account even at moderate concentrations. The results can be explained by a decrease of the polymer dimensions which is more pronounced when the “solvent polymer” is of low molecular weight. At higher concentration, there is a critical point which seems to appear when the total volume of the two polymers is equal to the volume of the solution.     

Initiating Mechanism of the Anionic Polymerization of Methacrylates with t‐BuOK and the Synthesis of ABA Type Triblock Copolymers

Using potassium tert‐butoxide (t‐BuOK) as initiator, anionic polymerization and copolymerization of the methacrylate monomers are carried out in tetrahydrofuran at 0 °C or above. The polymers are characterized by gel permeation chromatography (GPC), proton nuclear magnetic resonance (¹H‐NMR), Fourier transform infrared (FTIR), and dynamic mechanical analyzer (DMA). There is a critical concentration of the active species in t‐BuOK, above which no matter how much more t‐BuOK is added, it has no initiation activity. Among the active species of t‐BuOK, the main part possesses large average vibration distance between anion–cation pairs, which can initiate all methacrylate monomers in this study. While another part of the active species possesses the small average vibration distance, which can only initiate the polymerization of methyl methacrylate at slow rate. It provides an supporting evidence for the “channel idea” proposed previously. Finally, poly(methyl methacrylate)‐b‐poly(lauryl methacrylate)‐b‐poly(methyl methacrylate) (PMMA‐b‐PLMA‐b‐PMMA) three‐block copolymer is synthesized. This study paves the way for the synthesis of thermoplastic elastomers with full polar monomers and full saturated chains by anionic polymerization.     

Fourier transform infrared spectroscopic study of polyacetylene, 1. Spectral assignment and characteristics of Z/E (“cis”/“trans”) geometric isomers

An FTIR spectroscopic study was carried out for rare-earth polyacetylenes

1 IUPAC name: poly(vinylene).

(PA) containing both Z (“cis”) and E (“trans”)

2 We distinguish formally between configurations (Z, E = “cis”, “trans”) and conformations (cis, trans), though in the case of poly(vinylene) the physical quality is virtually the same.

geometric isomers. Spectral assignments were made by the study of PA samples with different Z/E ratios and by referring to the known assignment of the IR spectrum of PA obtained with Ti(OC₄H₉)₄·Al(C₂H₅)₃. The conjugation effect of Z or E ? CH?CH? sequences and their length distribution in PA are investigated by spectral subtraction and peak separation. It is shown that the frequency of v(CH) (out-of-plane deformation) is located in the regions 741 to 747 cm^?1 and 940 to 1014 cm^?1 for Z- and E-PA, respectively, depending on the conjugation length. At the beginning of thermal isomerization of Z-PA, long Z sequences are interrupted quite frequently; this causes a shift of v(CH) towards higher frequencies. In high E-PA obtained by thermal isomerization of Z-PA, uninterrupted long E sequences persist. This demonstrates that a crosslinking reaction between PA chains is not conspicuous during the thermal isomerization process.     

Ethylene Polymerization with “Constrained‐Geometry” Titanium Catalysts over Borate‐Modified Silica Supports

Two different mesoporous silica materials, Sylopol® 948 and MPS5, were used as substrates for the preparation of silica‐bound trityl tris(pentafluorophenyl)borate activators. The borate‐modified silica supports, B‐Sylopol and B‐MPS5, were characterized by solid‐state NMR spectroscopy and ICP mass spectrometry, and applied as activators for slurry polymerization of ethylene using “constrained‐geometry” titanium complexes of the formula Ti(η⁵ : η¹‐C₅Me₄SiMe₂NR)X₂ (R = Me, ⁱPr, ^tBu; X = Me, Bz, Cl) in the presence of triisobutylaluminium (TIBA). The activity of the B‐Sylopol system was higher than that of the corresponding homogeneous catalysts Ti(η⁵ : η¹‐C₅Me₄SiMe₂NR)X₂/Ph₃C⁺ [B(C₆F₅)₄]^–, whereas that of the B‐MPS5 system was lower. These supported catalysts produced polyethylenes with higher molecular weights (M̄_w in the range of 10⁶), narrower molecular weight distributions (M̄_w/M̄_n = 1.5–2.3) and higher bulk densities (up to 0.4 g/cm³) compared to those of polyethylenes obtained with the homogeneous system. The resulting polyethylenes were found to replicate the shapes of the supported borate activators. Fine polyethylene particles due to the cracking of the support were observed with the B‐Sylopol system, while well‐shaped polyethylene spheres were formed with the B‐MPS5 system.     

The effect of TMEDA on the kinetics of the anionic polymerization of methyl methacrylate in tetrahydrofuran using lithium as counterion

The kinetics of the anionic polymerization of methyl methacrylate in presence of N,N,N ′,N ′‐tetramethylethylenediamine (TMEDA) in THF are investigated using 1,1‐diphenyl‐hexyllithium as initiator in a temperature range between –20°C and 0°C in a flow‐tube reactor. The rate constants of propagation determined in the presence of TMEDA are compared to those obtained in the absence of a chelating agent. For propagation, the reaction order with respect to active centers is found to be 0.5 in both cases which indicates that the chelation of the lithium cation does not effectively perturb the aggregation of the enolate ion pair. Both the rate constants of propagation via non‐aggregated ion pairs, k_±, and the equilibrium constants of aggregation, K_A, are not significantly affected by TMEDA. The rate constants of termination in absence and presence of TMEDA are also comparable. Thus, it is concluded that TMEDA is not a better ligand for lithium ester enolates than THF. Even the addition of a cyclic tertiary polyamine (“crown amine”) such as 1,4,8,11‐tetramethyltetraazacyclotetradecane, does not lead to a significant change in the propagation rate constant, however, no termination is observed at –20°C. Extrapolation of the observed rate constants at two temperatures gives estimates for the equilibrium constants of aggregation, K_A, and the corresponding enthalpy and entropy. It is shown, that aggregation of PMMA‐Li in THF is an endothermic, entropy‐driven process (ΔH_A; ΔS_A > 0), similar to the dimer‐tetramer equilibrium of model ester enolates.     

Kinetics of group transfer polymerization of tert-butyl methacrylate in tetrahydrofuran

The reaction kinetics for the group transfer polymerization (GTP) of tert-butyl methacrylate (TBMA) using a silyl ketene acetal initiator and a nucleophilic catalyst are investigated. The reaction is shown to be of first order in both monomer and catalyst concentrations. The “livingness” of this system appears to be influenced by the reaction temperature. At temperatures above ?20°C, deactivation is observed, with its severity increasing with increasing temperature. This deactivation is attributed to a depletion of catalyst by side reactions. It was demonstrated that reactivation is made possible by the addition of more catalyst. This result is in contrast to the anionic polymerization of TBMA, where no deactivation was observed even at ambient temperature. At temperatures below ?20°C no deactivation is observed; however, at these temperatures, the reactions manifest induction periods with lengths increasing with decreasing temperature. The rate constants are lower than those for the GTP of methyl methacrylate (MMA) by a factor of 1,5 to 2. The following Arrhenius parameters were obtained for the propagation rate constants: activation energy, E_a = (19,₁ ± 3) kJ/mol, preexponential factor, log₁₀ A = (7,0₅ ± 0,3). These values are comparable with those obtained for MMA. The molecular weight distributions are similar to those obtained in the GTP of MMA, i.e. the ratio of weight-to number-average molecular weights is rather high for low monomer conversions and narrows to M?_w/M?_n ≥ 1,3 for full conversion. This is attributed to the rates of the catalyst exchange equilibrium.     

Cationic copolymerization of norbornadiene with styrene by AlEtCl2/tert-butyl chloride catalyst system, 2. Effect of polymerization conditions on “crosslinking” and “polymer linking” reactions

The cationic copolymerization of norbornadiene (NBD) and styrene (St) was carried out with the AlEtCl₂/tert-butyl chloride catalyst system under various conditions. Detailed analyses were focused on the effect of reaction conditions on the two types of intermolecular reactions, that is, the “crosslinking” reaction to form an insoluble polymer and the “polymer linking” reaction to form a soluble polymer with a molecular weight higher than that of the non-crosslinked polymer. The two types of crosslinking processes can explain the unique dependency of the polymer solubility on the NBD/St feed ratio. The “polymer linking” reaction is initiated after complete consumption of the monomers and is strongly affected by the polymerization conditions. For example, longer polymerization time, lower temperature, an initial monomer concentration [M]₀ around 1,0–1,5 mol/L, a [t-BuCl]₀/[AlEtCl₂]₀ ratio around 0,75–1,0 and increasing [AlEtCl₂]₀ are the factors that facilitate the “polymer linking”.     

Towards the control of the reactivity in high temperature bulk anionic polymerization of styrene, 1. Influence of n,s-dibutylmagnesium on the reactivity of polystyryllithium species

The influence of n,s-dibutylmagnesium on the kinetics of styrene polymerization initiated by s-butyllithium was investigated in cyclohexane at 50°C. The presence of n,s-dibutylmagnesium, in molar ratios ranging from 0 to 20 with respect to polystyryllithium, leads to a drastic and continuous reduction of the reactivity of the propagating species. The living character of the polymerization, especially the control of the molar mass is preserved over the entire range studied. The experimental molar masses are in agreement with the formation of one polystyrene chain per lithium and 0.5 to 0.8 chains per magnesium atom, indicating that both alkyllithium and dialkylmagnesium species are involved in the polymerization process through the formation of “ate” complexes. The UV-visible study of the PSLi/n,s-dibutylmagnesium systems shows that several types of “ate” complexes with different stoichiometry are formed depending on the proportion of the two metal derivatives.     

Free radical “grafting from” hyperbranched polyesters based on polymeric azo initiators

Aromatic and aliphatic hyperbranched polyesters were prepared by AB₂ polycondensation process. The highly branched, functional structure of these polymers leads to excellent solubility in combination with low solution viscosities. Varied numbers of the functional groups of the hyperbranched structures were modified with azo functions which are able to initiate free radical polymerization. An increase in temperature in the presence of the vinyl monomers methyl methacrylate (MMA), butyl methacrylate (BMA), styrene (S), or acrylamide (AA) results in “grafting from” the hyperbranched structure. Using this method several graft products were synthesized with variations in structure, number, and size of the graft arms. Gel-permeation chromatography (GPC) with universal calibration and viscosity measurements indicate a strong influence of the hyperbranched core on the properties of the graft product. It was possible to control the phase behavior of the graft products from two phases to homogeneous by the ratio hyperbranched polyester: grafted monomer. The film forming properties which are very poor for unmodified hyperbranched polyester were improved by grafting with linear polymer chains.