Quasiliving Carbocationic Polymerization. IV. Polymerization of p-tert-Butylstyrene

The mechanism of polymerization of p-tert-butylstyrene (ptBuSt) initiated by the cumyl chloride/BCl₃ initiating system in CH₂Cl₂ at -50°C has been investigated. At and below ～0.4 M ptBuSt, quasiliving polymerizations proceed, i.e., initiation is instantaneous, termination is absent or reversible, and chain transfer to monomer can be suppressed or eliminated. In the quasiliving range the M _n versus [ptBuSt]₀ plot is linear and passes through the origin, and a M _w/M _n decreases much below 2.0 with decreasing [ptBuSt]. GPC traces change from broad multimodal to narrow monomodal and the color of polymerization charges change from colorless to golden-yellow with decreasing [ptBuSt]. The effect of temperature jump subsequent to monomer addition has been examined; however, it does not explain the peculiar monomer concentration effect on the mechanism. Changes in the ionicity may be responsible for this phenomenon.     

Quasiliving Carbocationic Poiymerization. III. Quasiliving Polymerization of lsobutylene

The polymerization of isobutylene has been investigated by the use of the steady, slow, continuous monomer addition technique in the presence of a variety of initiating systems, i.e., “H₂O”/TiCl₄, “H₂O”/AlCl₃, C₆H₅C(CH₃)₂Cl/TiCl₄, p-ClCH₂ C₆(CH₃)₄* CH₂Cl/AlCl₃ at -50°C. Quasiliving polymerizations have been obtained with the “H₂O” and C₆H₅(CH₃)₂Cl/TiC1₄ systems in 60/40 v/v n-hexane/methylene chloride solvent mixtures with very slow monomer input. After a brief “flash” polymerization, the M _n of PIB increased linearly with the cumulative amount of monomer added (consumed); however, the number of polymer molecules formed also increased, indicating the presence of chain transfer to monomer. With the “H₂O”/TiCl₄ initiating system, M _n,max was 56,000 and M _w /M _n < 2.0. By the use of the C₆H₅C(CH₃)₂CL/TiCl₄ initiating system, quasiliving polymerization has been achieved and chain transfer could virtually be eliminated.     

Quasiliving Carbocationic Polymerization. VII. Block Polymerization of α-Methylstyrene from Quasiliving Poly(isobutyl Vinyl Ether) Dication

Poly(α-methylstyrene-b-isobutyl vinyl ether-b-α-methylstyrene) triblock polymers have been prepared by blocking α-methyl-styrene (αMeSt) from biheaded quasiliving poly(isobuty1 vinyl ether) (PIBVE) cations generated with the bifunctional p-dicumyl chloride/AgSbF₆ initiating system in methylene chloride solvent at -90°C. The products were fractionated with 2-propanol, a good solvent for PIBVE and a nonsolvent for PaMeSt. The 2-propanol-insoluble fractions had much higher molecular weights (M _n = 30,500–69,100) than the starting PIBVE (M _n =6,600–10,600) and contained 13–29 wt% IBVE together with 87–71 wt% αMeSt units. The 2-propanol-soluble fractions (M _n = 7,300–11,600) contained ～90 wt% IBVE and ～10 wt% αMeSt units.     

Quasiliving Carbocationic Polymerization. XIV. Synthesis of Poly(styrene-b-Isobutylene)

The synthesis of poly(styrene-b-isobutylenes) by the sequential addition of styrene and isobutylene has been accomplished. First a stream of styrene was added to a cumyl chloride/TiCl₄ in nhexane/methylene chloride charge at -50°C under quasiliving conditions. After the polystyrene block has reached a desirable sequence-length (molecular weight), gaseous isobutylene was continuously introduced to the quasiliving polystyrene carbocation until the polyisobutylene block also reached a desirable molecular weight. The M _n versus monomer input plot was uninterrupted and linear over both monomer introduction phases, indicating quasi-living conditions over the entire regime of block copolymer synthesis. The block copolymers have been characterized by selective solvent extraction and GPC, and their compositions determined by ¹H-NMR spectroscopy.     

Living Carbocationic Polymerization. XLIX. Two-Stage Living Polymerization of Isobutylene to Di-tert-chlorine Telechelic Polyisobutylene

Abstract

A two-stage process was developed for the living polymerization of isobutylene (IB) employing di-tert-alcohol initiators in conjunction with BCl₃ coinitiator in the first or initiation stage, followed by TiCl₄ coinitiator in the second or propagation stage; the process was shown to yield high molecular weight (up to M ⁿ 20,000), narrow molecular weight distribution (MWD) M ^w/M ⁿ = 1.1–1.2) di-tert-chlorine telechelic polyisobutylenes (^tCl-PIB-Cl^t). The initiation stage involves the homogeneous solution living polymerization of IB induced by the di-tert-alcohol/BCl₃ combination in the presence of an electron donor such as N,N-dimethylacetamide in CH₃Cl solvent at ?80°C and proceeds up to M ⁿ < 5000; this is followed by the propagation stage in which TiCl₄ and the bulk of IB plus a sufficient amount of n-C₆H₁₄ are added to the charge to bring the solvent composition to CH₃Cl/n-C₆H₁₄ 60/40 v/v and the living polymerization is continued until high M ⁿ product is obtained. This two-stage process was developed because 1) it employs very inexpensive chemicals; 2) di-tert-alcohol/BCl₃ combinations initiate living IB polymerization in CH₃Cl but the product after reaching M ⁿ ≤ 5000 precipitates out of the CH₃Cl solution, and di-tert-alcohol/BCl₄ combinations do not initiate IB polymerization; and 3) di-tert-alcohol/BCl₃ systems do not initiate (or only very slowly) the living polymerization of IB in CH₃Cl/n-C₆H₁₄ mixtures, whereas similar TiCl₄-based systems do. The polymerization remains living during both stages although the propagating species and solvent polarity are profoundly altered. The livingness of the system has been analyzed by kinetic experiments and the structure of the ^tCl-PIB-Cl^t product by routine spectroscopic means.     

Quasiliving Carbocationic Polymerization. V. Quasiliving Polymerization of lndene

Quasiliving polymerization of indene, i.e., an increase of the molecular weight of polyindenes with the cumulative amount of consumed monomer, has been demonstrated using the “H₂O”/ BCl₃, 2-chloroindene/BCl, “H₂O”/TiCl₄, 2-chloroindene/TiCl₄, and cumyl chloride/TiCl₄ initiating systems in CH₂Cl₂ solvent at -50°C. However, chain transfer operates in every system investigated, and sets a limit to DP _n,max. The efficiency of the 2-chloroindene and cumyl chloride initiators is very low. The behavior of BCl₃ and TiCl₄ coinitiators on the polymerization has also been investigated.     

Preliminary Study of Cationic Copolymerization of α-Methylstyrene and Isobutyl Vinyl Ether. II

α-Methylstyrene (α-MS) and isobutyl vinyl ether (IBVE) were copolymerized by using the H₂O/EtAlCl₂ initiator system and CH₂Cl₂ and CH₃Cl solvent in the temperature range from -30 to -90°C. As compared to homopolymerization of α-MS, both yields and molecular weights are reduced upon addition of small amounts of IBVE to the feed. The reactivity ratios were calculated by the method of Kelen and Tödös as well as the Fineman and Ross method, and the combined effect of change of solvent and temperature on reactivity ratios was determined. Effects of feed composition and temperature on the copolymer yield, composition, and number-average molecular weight M _n were studied in detail. M _n showed a novel exponential dependence on the IBVE concentration in the feed. The overall activation energies of molecular weight were determined from the Arrhenius plots for both homo-and copolymerization systems. Based on these and the yield data, a speculation is made regarding reaction mechanism for molecular weight control. NMR and DTA data are reported, which establish the random nature of the copolymers.     

Quasiliving Carbocationic Polymerization. XIII. Polymerization of 2,4,6-Trimethylstyrene

The polymerization of 2,4,6-trimethylstyrene (vinyl mesitylene) has been investigated, and quasiliving polymerizations have been achieved under a comfortably wide experimental condition range. This monomer is particularly suitable for quasiliving polymerizations because the methyl groups in the 2 and 6 positions prevent chain transfer to monomer involving indanyl-skeleton formation. Quasiliving polymerizations readily occurred by the use of cumyl chloride/TiCl₄ or BCl₃ initiating systems in various n-C₆H₁₄/CH₂Cl₂ mixtures at -50°C. Because indanyl-skeleton formation is impossible, the rate of monomer addition can be safely decreased to very low values without risking chain transfer by intramolecular alkylation.     

Quasiliving Carbocationic Polymerization. II. The Discovery: The α-Methylstyrene System

A detailed analysis of elementary reactions of carbocationic polymerization culminated in the prediction and subsequent experimental demonstration of quasiliving polymerization. Quasiliving polymers are formed in a system provided that the process of chain termination and chain transfer to monomer are absent or reversible, i.e., the propagating ability of the chain end is maintained throughout the experiment, and the molecular weight increases in proportion to the cumulative amount of monomer added. The chain end can be active (carbocation) or dormant (reactivable polymeric olefin or cation source). Chain transfer is suppressed by keeping the monomer concentration low. Quasiliving polymerizations are maintained by continuous slow feeding of dilute monomer to a charge containing the initiating or propagating species (quasiliving polymerization technique). A comprehensive kinetic scheme has been developed that describes quasiliving polymerization in quantitative terms. Quasiliving polymerization was demonstrated experimentally in the “H₂O”/BCl₃/α-methylstyrene and cumyl chloride/BCl₃/α-methylstyrene systems. M _n versus monomer input plots are linear over wide ranges, indicating quasiliving conditions, and poly(α-methylstyrenes) with M _n > 2 × 10⁵ have been obtained, Molecular weight distributions were found progressively to narrow and dispersion ratios M _w/M _n to decrease.     

Living Carbocationic Polymerization. XXIII. Analysis of Slow Initiation in Living Isobutylene Polymerization

The aim of this research was to develop a quantitative treatment of the consequences of relatively slow initiation on M _n and N (the number of molecules formed, W_p/M _n , where W_p =weight of polymer formed) in living carbocationic polymerizations, particularly for the case of the incremental monomer addition (IMA) technique. This has been achieved by analysis of the effect of initiator efficiency (I_eff (%) = 100N/[I ₀], where [I ₀] = initiator input) on M _n versus W_p , and N versus W_p plots. Three types of systems have been discerned: 1) I_eff equal to 100%; 2) I_eff constant but less than 100%; and 3) I_eff less than 100% but increasing with increasing number of monomer increments j by the IMA technique. Thus conditions can be found under which slowly initiating systems yield close to “ideal” product, i.e., one with M _n = [M₀ ]/[I₀ ] and narrow molecular weight distribution (M _w /M _n ≈ 1.1). The corresponding equations and plots can be used to diagnose the mechanism. Subsequently, this quantitative analysis was used to describe a novel living system, trans‐2,5‐diacetoxy‐2,5‐dimethyl‐3‐hexene (DiOAcDMH₆)/BCI₃/isobutylene/CH₃CI. This system produces linear t‐chlorine‐telechelic polyisobutylenes under homogeneous conditions. Surprisingly, cationation seems to be rate determining. This conclusion is illustrated by chemical equations.     

Molecular Weight and Functionality Determination of Polyisobutylenes Containing Tertiary Chlorine Chain Ends by Thermal Dehydrochlorination

A sensitive thermal dehvdrochlorination method has been used to determine quantitatively the HCl arising from -CH₂C(CH₃)₂Cl endgroups in polyisobutylenes synthesized by BCb as the co-initiator. Quantitative endgroup analyses provided number-average molecular weights, M _n and functionality, F _n. Select M _n data obtained by this endgroup analysis is in agreement with those obtained by osmometry, GPC, and NMR techniques; indeed, M _n's obtained by this dehydrochlorination technique appears to be more accurate (2-3% error) than conventional methods (～5-10% error). The rate of HCl loss from -CH₂C(CH₃)₂Cl termini is first order in HCl with an ΔE_a of 19.1 kcal/mol in the 170-200°C range. This relatively low activation energy is most likely due to internal strain in the -CH₂C(CH₃)₂CH₂C(CH₃)₂Cl endgroup. These studies quantitatively substantiate earlier conclusions in regard to the mechanism of endgroup formation in BC13 coinitiated isobutylene polymerization.     

Kinetics of the Photopolymerization of Vinyl Monomers by Bis(Isopropylxanthogen) Disulfide. Design of Block Copolymers

Bis(isopropylxanthogen) disulfide (BX) has been used as a photoinitiator with various vinyl monomers at 30°C. The kinetics of polymerization of styrene (St) and methyl methacrylate (MMA) at 30°C were studied for various concentrations of monomer and initiator. The observed deviations in polymerization rate from simple kinetic theory could be explained in terms of primary radical termination. The fraction of primary radical terminating chains was obtained as a function of various concentrations. The ratio of the rate constants for chain initiation and chain termination by a primary radical was determined to be 3.34 ± 10⁷ for St and 2.60 ± 10⁷ for MMA. The number-average degree of polymerization (DP _n) of polymers obtained by photopolym-erization with BX was found to increase linearly with conversion. However, the DP _n extrapolated to zero conversion was in good agreement with that calculated on the basis of the kinetic scheme. It was found that BX had interesting properties for the design of block copolymers, i.e., BX acts as a terminator and a chain transfer agent as well as an initiator in these polymerizations. The polymers obtained with BX contained two reactive isopropyl xanthate groups bonded at their chain ends, which could also act as macrophotoinitiators.     

Ultrasonic Solution Degradations of Polystyrene and Substituted Polystyrenes in Tetrahydrofuran as Solvent

Abstract

Ultrasonic (70 W, 20 kHz) solution (2% THF) degradations of polystyrene (PS), poly(α-methylstyrene) (PαMeS), poly(p-isopropyl α-methylstyrene) (PpiPrαMeS), poly(p-chlorostyrene) (PpCIS), poly(p-bromostyrene) (PpBrS), and poly(p-methoxystyrene) (PpOMeS) have been carried out in tetrahydrofuran at 27° C. The average number of chain scissions S (where S = [(M _n)₀/(M _n)_t] - 1), computed from the overall values of [(M _n)₀ and (M _n)_t, were found to be different from those of S' (where S' = α([(M _n)₀/(M _n)_t] - 1)) based on the component (only that part of the polymer which is involved in degradation) data of the weight fraction (α), (M _n)₀, and (M _n)_t), S' for polystyrene and substituted polystyrene follows the order PS gt; PpCIS gt; PpiPrαMeS gt; PpBrS gt; PpOMeS gt; PαMeS. In the case of PS where degradations were also carried out at -20°C, lowering of the temperature increased the weight fraction of polymer degraded as well as S. Based on the viscosity and GPC data, it is concluded that the ultrasonic solution degradation of PS does not lead to branched polymers.     

Crystallizable Polyphenylacetylene-Preparation and Solution Properties

The molecular weight distribution (MWD) of crystallizable polyphenylacetylene prepared near room temperature in the presence of ferric acetylacetonate and triethylaluminum was determined through use of fractions characterized by vapor pressure osmometry and gel permeation chromatography (GPC). The number- and weight-average molecular weights (M _n and M _w) are both less than the molecular weight corresponding to the maximum of the weight distribution function, which lacks a high molecular weight tail. M _wandM _n is less than is consistent with models allowing for chain termination characteristic of vinyl polymers. GPC elution volumes are much less than those characteristic of polystyrene of similar molecular weight, and the Mark-Houwink exponent is high (2.4 for M _v 4800 to 6800). These data indicate more rodlike behavior than for polystyrene of equivalent molecular weight. The MWD and other data suggest intramolecular chain termination, possibly associated with the molecule's tendency to form paramagnetic defect states.     

Living Carbocationic Polymerization. Li. Living Carbocationic Copolymerization of Indene and p-Methylstyrene. 1. Demonstration of the Living and Random Copolymerization of Indene and p-Methylstyrene

Abstract

The living carbocationic polymerization and copolymerization of indene (Ind) and p-methylstyrene (pMeSt) have been investigated by the use of the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ and the 2-chloro-2-propylbenzene (cumyl chloride, CumCl)/BCl₃ initiating systems in the presence of triethylamine (Et₃N) as electron donor and CH₃Cl or CH₃Cl/QH14 mixed solvents at ?80°C. The TMPCl/TiCl₄ initiating system gives essentially living copolymerization with slow initiation up to M _n ≈ 20,000. The CumCl/BCl₃ initiating system also induces living Ind homopolymerization up to at least M _n ≈ 13,000. The homopolymerization of pMeSt with the latter initiating system, however, is not living as it shows evidence for a large amount of chain transfer. Thus, with the CumCl/BCl₃ combination a small amount of chain transfer has apparently been observed in the presence of 50% of pMeSt in the charge. Reactivity ratio studies, fractionation, ¹H- and ¹³C-NMR spectroscopy, and glass transition temperature (T_g ) investigations indicate that virtually random Ind-co-pMeSt copolymers of M _n ≈ 20,000 can be obtained under suitable conditions. The T_g of the copolymers can be controlled between ≈115°C (the T_g of PpMeSt) and ≈194°C (the T_g of PInd) by the relative composition of the two monomers in the charge.     

Polylactones. 16. Cationic Polymerization of Trimethylene Carbonate and Other Cyclic Carbonates

1,3-Dioxanone-2 (trimethylene carbonate) was polymerized by use of methyl triflate or triethyloxonium fluoborate under various reaction conditions. Chloroform, 1,2-dichloroethane, and nitrobenzene were used as solvents; the temperature was varied between 25 and 50°C; and the monomer/initiator ratio between 50 and 400. However, inherent viscosities above 0.29 dL/g ( M _n > 6000) were never obtained, owing to side reactions such as backbiting and formation of ether groups. IR and ¹H-NMR spectroscopy revealed that the polymerization mechanism agrees with that of the cationic polymerization of lactones in that propagation involves cleavage of the alkyl-oxygen bond. The active cationic chain end and the dead methylcarbonate end groups were identified by means of ¹H-NMR spectra. A reaction mechanism for the formation of ether groups is discussed. Furthermore, ¹H-NMR spectroscopy indicated that ethylene carbonate and biphenyl-2,2′-carbonate do not react with methyl triflate at 20, 60, or even 100°C.     

New Interpretations: Molecular Weight Averages for a Polymer

The statement is often made in the polymer literature, without proof, that M _z ≤ M _w ≤ M _n, where M _z, M _w, and M _n are the z-, z weight-, and number-average molecular weights respectively. Four proofs of a generalization of these inequalities are given. It is shown that a higher-order molecular weight average is larger than a lower-order one, regardless of the form of the molecular weight distributions, except for the case when all the molecules have the same molecular weight. A brief discussion of the viscosity-average molecular weight is also included.     

Synthesis of Block Copolymers of Styrene with <Emphasis Type="Italic">D</Emphasis>,<Emphasis Type="Italic">L</Emphasis>-Lactide by the Sequential Controlled Cationic Polymerization and Ring-Opening Anionic Polymerization

The cationic polymerization of styrene initiated by the system 2-chloro-2-phenylpropane–TiCl₄–pyridine is studied in a mixture CH₂Cl₂–n-hexane at a temperature of –80°С. It is shown that under these conditions polymerization occurs via the living mechanism at [monomer]: [initiator] ≤ 100. The method of preparing polystyrenes with terminal primary hydroxyl groups (M_n = 4000–10000 g/mol) by the sequential controlled cationic polymerization of styrene and the in situ alkylation of 4-phenoxy-1-butanol by polystyrene macrocations is proposed. The resulting functionalized polystyrenes are used as macroinitiators of anionic-coordination ring-opening polymerization of D,L-lactide in the presence of tin bis(2-ethyl hexanoate) [Sn(Oct)₂] in toluene at 80°С. Copolymers polystyrene-block-poly(D,L-lactide) with the controlled length of the poly(D,L-lactide) block (M_n = 10000–17000 g/mol) and a relatively low molecular-weight distribution (M_w/M_n = 1.6–1.8) are synthesized. Formation of the block copolymers is confirmed by ¹Н NMR spectroscopy, gel-permeation chromatography, and atomic force microscopy.     

Characterization of Copolymers and Polymer Mixtures by Gel Permeation Chromatography

Abstract

Estimation of molecular weights from GPC data is complicated when the polymer sample consists of a mixture of homopolymers or of statistical copolymers with nonuniform compositions. This is because sizes of solvated polymer coils depend on solvent interaction with both the homo-and hetero-units of the copolymers and because the extent of solvation of different homopolymers can differ. The overall degree of solvation may change effectively with composition and use of a single “average” set of Mark-Houwink constants in calibration procedures will then produce false molecular weight data from the GPC data. A new molecular weight average, M _x, is defined to overcome this problem. This average can be determined from the GPC chromatogram and intrinsic viscosity of the sample in the GPC solvent. Mark-Houwink coefficients are not needed. M _x lies between M _w and M _z.     

Copolymers from Castor Oil Prepolymers (COP). 2. Copolymerization of Styrene with COP

A study of copolymerization of castor oil prepolymers (COP) with styrene has been made at 75°C using benzoyl peroxide as initiator. It has been found that good yields of copolymers (high molecular weight M _n = 123,989) are obtained at a low concentration of COP. With an increasing concentration of COP in the binary mixture, copolymers with decreasing molecular weight are obtained. This is explained as due to presence of a high percentage of oxygen (from COP) in the system which is acting as a chain transfer agent.