Showing papers in "Journal of Polymer Science Part A in 1968"

Macroreticular resins. III. Formation of macroreticular styrene–divinylbenzene copolymers

Abstract: Experimental evidence is presented that describes the mechanism of formation of macroreticular styrene–divinylbenzene copolymers in which phase separation occurs during a suspension polymerization. The mode of formation of the macroreticular structure is described as a three-stage process in which each droplet of the organic phase behaves as an individual in a bulk polymerization that results in a bead of copolymer. Macroreticular structure formation is described by changes in copolymer swelling ratios, infrared absorption spectra of vinyl groups pendent to the polymeric matrices, surface area, total porosity, and pore-size distribution. The proposed mechanism of formation is also substantiated by electron micrographs of the copolymers during various stages of the copolymerization.

Emulsion polymerization. I. Recalculation and extension of the Smith‐Ewart theory

Abstract: The most important assumptions underlying the Smith-Ewart theory are that the locus of chain propagation is the monomer-swollen latex particle, polymeric chains are initiated by radicals entering from the water phase into the particles, chain termination is an instantaneous reaction between two radicals within one particle, and particles are nucleated by radicals absorbed into monomer-swollen soap micelles. Right or wrong, these and other assumptions used by Smith and Ewart are retained in this paper. The newly derived and experimentally verifiable equations contain only such parameters which can be determined by experiments not involving emulsion polymerization. The proportionality constant between the particle number and the appropriate powers of soap and initiator concentrations is defined in terms of these independent parameters. Absolute rate equations are presented for the intervals before and after the completion of particle nucleation. To calculate these rates it is not necessary to have prior knowledge of the experimental particle number. The conversion at which particle nucleation is complete is calculated. The molecular weight is defined in terms of independent parameters. Predictions are made for the particle size distribution. It is shown that the validity of the theory is confined to specifiable intervals of conversion, to a certain range of monomer/water ratio, and to soap concentrations whose upper and lower limits are given.

Calorimetric investigation of polymerization reactions. I. Diffusion‐controlled polymerization of methyl methacrylate and styrene

Abstract: The rate of bulk polymerization of methyl methacrylate and styrene was determined directly, continuously and over the whole range of conversion with a differential scanning calorimeter (DSC) operated isothermally. At the later stages of the accelerated polymerization of methyl methacrylate, a previously unknown inflection or peak in the rate of polymerization was observed. The variation of the rate after the onset of the gel effect, including this peculiar inflection, was interpreted on the basis of the diffusion behavior of monomer molecules and polymeric radicals in the polymer–monomer system, their diffusion rates being predicted from the free volume theory. The final conversion at which no further polymerization proceeds was determined for both monomers. It was affirmed quantitatively that the final conversion has a close relation with the transition of the polymer–monomer system from a viscous liquid to a glassy state.

Emulsion polymerization. II. Review of experimental data in the context of the revised Smith‐Ewart theory

Abstract: Tables are presented for convenient calculation of the basic parameters of the revised Smith-Ewart theory. For the methyl methacrylate (MMA)/sodium lauryl sulfate (SLS)/K2S2O8, and for the styrene/SLS/K2S2O8 reaction mixtures parameters are presented from which the absolute values of the following quantities can be conveniently calculated for any temperature, soap, and initiator concentration: particle number, particle radius, conversion where particle nucleation stops, rate and molecular weight in interval II, the interval after completion of particle nucleation and before the disappearance of monomer droplets. The theoretical predictions are compared to new experimental data and to those from the literature. The available data confirm the theoretical prediction that particle nucleation stops after a very small amount of polymer is formed, of the order of 0.01 cc. polymer/cc. water in most recipes. The theory and experiments are in good qualitative agreement for the conversion rate prior to completion of particle formation: the conversion rate rises with time and, when particle nucleation stops, it levels off. Excellent quantitative agreement can be obtained between theoretical and experimental particle size values. In the experiments of this laboratory the SLS concentration was varied 60-fold, the K2S2O8 concentration was varied 140-fold and the difference between theoretical and experimental poly(MMA) particle radii was always less than about 20%. Similar good agreement was obtained for polystyrene over the temperature range 30–90°C. Some polystyrene data from the literature with carboxylic soaps give just as good fit as the data with SLS of this laboratory. The predicted proportionality between particle number and the product of 0.6 power of soap concentration and of 0.4 power of initiator concentration was observed for several monomers. The theoretical predictions for the rate and molecular weight obtained in interval II are valid only for relatively low initiator and high soap recipes. For recipes for MMA and styrene the rate data are in good agreement with those calculated from the theory. The theory also correctly predicts the order of magnitude of the experimental molecular weights. For several monomers the rate and molecular weight vary with initiator and soap concentrations in a manner close to theoretical predictions.

Infrared studies of stereoregular polymerization of methyl methacrylate and methacrylonitrile by organometallic compounds

Abstract: Infrared spectra of reaction mixtures of methyl methacrylate or methacrylonitrile with an equimolar amount of organometallic compounds were investigated in relation to the stereoregulating ability of the catalysts in polymerization. It was found that the carbonyl or nitrile stretching frequency correlated with the stereoregularity of polymers prepared with the corresponding catalysts; i.e., the higher the frequency, the higher the isotacticity. From these results a mechanism of isotactic polymer formation was proposed, in which catalyst counterion was located near the carbonyl group in polymer terminal and that of monomer to be reacted, and consequently the isotactic polymerization is facilitated.

Thermogravimetric analysis of cellulose

Abstract: An application of TGA technique to elucidate the chain reaction mechanism of cellulose pyrolysis is discussed. The mathematical expressions for isothermal kinetics are modified for use with temperature-programmed kinetics. It is shown that in temperature-programmed kinetics, the initial reaction should theoretically be a pseudo zero-order type, whereas the latter part should be a pseudo first-order type. Experimental data from the present study and from the literature are in good agreement with the theory. Energies of activation for the initiation and the propagation steps of cellulose pyrolytic reactions are analyzed from TG data. Various cellulose samples, such as adsorbent cotton, vibratory ball-milled absorbent cotton, mercerized commercial yarn, mercerized and treated commercial yarn, dewaxed-kiered cotton, and microcrystalline cellulose are included in this study. A basic problem which is associated with all thermogravimetric kinetic expressions is also discussed.

Quantitative study on hydrogen bonding between urethane compound and ethers by infrared spectroscopy

Abstract: A quantitative infrared spectroscopic study of a model urethane-type compound was carried out in order to obtain basic data on hydrogen bonding in polyurethanes. First, the absolute intensity of free NH groups of N-phenylurethane, which was adopted as the model urethane, was determined by Wilson-Wells' method to be 3.59 × 103l./mole-cm.2. The free NH of this urethane absorbed at 3447 cm.−1, and hydrogen-bonded NH absorbed near 3300 cm.−1. Then, the extents of hydrogen bonding of the urethane at various concentrations were determined, and the hydrogen bonding between the urethane and ethers was studied by using the above-mentioned absolute intensity. For comparison, diphenylamine was also used as proton donor. Di-n-butyl ether and poly-(oxyethylene glycol) were examined and proved to be able to act as proton acceptors. The frequency shifts of NH stretching vibration of diphenylamine and N-phenylurethane caused by hydrogen bonding with di-n-butyl ether were 96 cm.−1 and 150 cm.−1, respectively. The equilibrium constants were 4.8 × 10−1l./mole for the former system 4.6 × 10−1l./mole for the latter.

Thermal decomposition products of polyethylene

Abstract: Decomposition products of polymers have been determined by many investigators, but the results are often conflicting because of difficulties in analyzing a large number of products. A comprehensive analysis of the volatile thermal decomposition products of high-density polyethylene has been made with the latest techniques in gas chromatography. The formation of products is explained on the basis of free-radical mechanism. The predominant process in the formation of volatiles appears to be intramolecular transfer of radicals, in which isomerization by a coiling mechanism plays an important role in determining the relative quantities of each product.

A study of the enzymic degradation of CMC and other cellulose ethers

Abstract: Accelerated enzymic degradation of a series of six sodium carboxymethylcelluloses (CMC) varying in degree of substitution (DS) from 0.41 to 2.45 demonstrated that stability improves with increasing substitution, the DS 2.45 sample being essentially refactory to enzyme attack. The concentration of completely unsubstituted anhydroglucose (AHG) units in these samples, determined by acid hydrolysis followed by a glucose assay, is less at all substitution levels than would be expected from the relative etherification rates of the C2, C3, and C6 hydroxyls reported in the literature. Assuming random distribution of the unsubstituted AHG units, the frequency of single (IU) and multiple adjacent (xU) sequences can be predicted. Consideration of the extent of enzymic degradation, expressed in terms of the decrease in average molecular chain length deduced from [η] measurements, indicated that in CMC chain scission occurs only at xU sites. A limited comparison of the performance of methyl-, hydroxyethyl-, and hydroxypropylcelluloses under identical conditions revealed that, by contrast, in these ethers enzyme-induced chain scission is possible not only at xU but also adjacent to 1U. The hydroxyalkyl and methyl groups appear to offer approximately equivalent protection against enzyme attack.

Polymerization of cyclic iminoethers. V. 1,3-oxazolines with hydroxy-, acetoxy-, and carboxymethyl-alkyl groups in the 2 position and their polymers

Abstract: Oxazolines containing carbomethoxy-, acetoxy-, and hydroxy-alkyl groups on the side chain were prepared and polymerized. The properties of the polymers were investigated.

Thermal reactions of polyacrylonitrile

Abstract: The exothermic process which occurs on heating polyacrylonitrile above 200°C. is studied with a differential scanning calorimeter and by following volatiles production. The process is associated with coloration of the polymer and the production of ammonia. It is not due to chain scission degradation, which occurs in this temperature range and also produces volatiles.

Polymer reactions. IV. Thermal decomposition of polypropylene hydroperoxides

Abstract: The thermal decomposition of polypropylene hydroperoxide (PPH) consists of two consecutive reactions. The initial, faster reaction has rates up to 60 times that of the slower process. The former is largely suppressed by the addition of an excess of 2,6-di-tert-butyl-p-cresol. The course of reaction is the same in either solid state or in solution. The results are consistent with an intramolecular radical-induced mechanism for the initial reaction. This faster reaction consumes about 70–95% of the total hydroperoxides. The decomposition of PPH yields a maximum of about 1.8 radicals. Samples prepared from crystalline and amorphous polypropylenes have identical decomposition kinetics.

Polypyromellitimides: Details of pyrolysis

Abstract: Polyimide films from 4,4′-diaminodiphenyl ether and pyromellitic dianhydride were pyrolyzed at 400–600°C. in non-oxidative systems. Major gaseous products were carbon monoxide and carbon dioxide; hydrogen evolution occurred above 525°C. A mobile n-imide-isoimide equilibrium is in accord with the gas evolution data. Carbon dioxide arises from isoimide decomposition and carbon monoxide arises from the normal imide.

Vinyl polymerization initiated by ceric ion reducing agent systems in sulfuric acid medium

Abstract: Polymerization of the monomers, methyl acrylate (MA) and methyl methacrylate (MMA) was carried out in sulfuric acid medium at 15°C. With the redox initiator system, ceric ammonium sulfate-malonic acid. There was no induction period, and a steady state was attained in a short time. There was found to be no polymerization even after 1 hr. in the absence of the reducing agent R. The initiation was by the radical produced from the Ce 4+ -malonic acid reaction. The rate of monomer disappearance was proportional to [M] 1.5 , [R] 0.5 , and [Ce 4+ ] 0.3-0.5 , and the rate of ceric disappearance was directly proportional to [R] and [Ce 4+ ]. Chain lengths of the polymers were directly proportional to [M] and inversely to [R] ½ and [Ce 4+ ] ½ . The experimental results were explained by a kinetic scheme involving the following steps: (a) oxidation of the substrate to give the primary radical which reacts with Ce 4+ to give the products, (b) initiation by the primary radical, (c) propagation, and (d) termination of the growing polymer radicals by the mutual type. For the polymerization of acrylonitrile (AN) by the redox system, ceric ammonium sulfate-cyclohexanone (CH), in sulfuric acid at 15°C., the scheme was modified to include linear type of termination by Ce 4+ , along with the mutual termination to explain the results especially under conditions with [Ce 4+ ] ≥ [CH].

Polyelectrolytes prepared from perfluoroalkylaryl macromolecules

Abstract: The synthesis of a new generation of high-capacity oxidation-resistant ion-exchange resins and membranes is described which are sulfonic acid polyelectrolytes prepared from high molecular weight poly-α,β,β-trifluorostyrene. The difficult sulfonation of poly-α,β,β-trifluorostyrene is discussed in terms of the finding that this sulfonation must be effected upon an aromatic ring possessing a meta-directing substituent group. The oxidative stability of these new types of perfluoroalkyl aromatic sulfonic acid polyelectrolytes is both demonstrated and described with comparisons to their polystyrenesulfonic acid homologs. The difference in their oxidation–depolymerization stabilities is described in terms of benzylic carbon substituents.

Photodegradation of polyethylene film

Abstract: A structure occurs in radical-polymerized polyethylene which leads to formation of a triene on ultraviolet radiation. An inhibition of oxidative processes is observed while the triene or its precursor are being consumed. Subsequent formation of oxygenated products—hydroxyl, carbonyl, and carboxyl—is well behaved and arises from short wavelenght light. A crosslinking reaction is initiated by light of ∼4000 A wavelength.

Study of the substitution pattern of hydroxyethylcellulose and its relationship to enzymic degradation

Abstract: The concentration of completely unsubstituted anhydroglucose (AHG) units in hydroxyethylcellulose (HEC) at varying average number of moles of substituent (MS) is in accord with a reaction rate ratio of 3:1:10:10 for the etherification of the C2, C3, C6, and side chain hydroxyls. Assuming random substitution along the cellulose chain at these relative reaction rates, the degree of substitution (DS), average poly(ethylene oxide) side-chain length, and probably frequency of isolated and multiple adjacent unsubstituted AHG units have been projected as functions of MS. Such estimates of DS and side-chain length compare favorably with actual measurements made on a variety of samples by other investigators below a substitution level of 2.0 MS. Reducing end, intrinsic viscosity, and ultracentrifuge data on enzymically hydrolyzed HEC's varying from 1.9 to 3.7 in MS indicate resistance to chain scission is a function of substitution, best expressed in terms of a proposed substitution index, the percentage of substituted AHG units. The rate of chain scission under carefully controlled conditions is initially rapid, tapering to a very slow, essentially steady level. On relating the frequency of chain breaks to the predicted substitution pattern of these samples, this behavior is interpreted to mean that scission occurs relatively rapidly at multiple contiguous unsubstituted sequences, but much more slowly adjacent to isolated unsubstituted AHG units. A possible mechanism of enzyme attack, correlating molecular chain breaks with glucose released, has been developed.

Determination of concentration of propagating species in cationic polymerization of tetrahydrofuran

Abstract: A spectroscopic method is described for the determination of the concentration of propagating species, [P*], in the polymerization of tetrahydrofuran catalyzed by a mixture of AlEt3−H2O (1:0.5) and epichlorohydrin. A phenyl ether group was introduced at the polymer chain end by the quantitative reaction of the propagating species with excess sodium phenoxide. From the amount of phenyl ether groups in the polymer and of the remaining sodium phenoxide, [P*] was determined by means of ultraviolet spectroscopy. The [P*] value so determined was found to be in good agreement with that calculated from the amount and molecular weight of polymer based on a stepwise addition mechanism without chain transfer or termination. The present method of [P*] determination was employed to examine the course of polymerization. It has now been found that [P*] increases progressively during an induction period and remains unchanged in the subsequent period of polymerization.

Polymerization and copolymerization studies on vinyl fluoride

Abstract: The polymerization of vinyl fluoride has been studied in the temperature range of 0–50°C. with the aid of different types of initiators. Ziegler-Natta systems based on vanadyl acetylacetonate and AIR(OR)Cl compounds showed good activity. Enhanced reaction rates and higher polymerization degrees were achieved with boron alkyls (and, to a lesser degree, Cd, Zn, and Be alkyls) activated by oxygen. With either types of initiator, the main features and the kinetic parameters of the polymerization were determined. In all cases, the polymerization is considered to be of the free-radical type, though some properties (crystallinity, melting temperature) of the polymer are shown to be markedly improved over the previously described high-pressure polymer. This is chiefly ascribed to an improved degree of chemical regularity of the chains. The copolymerization of vinyl fluoride in the presence of the cited initiators was studied with a number of monomers. The values of the copolymerization parameters allow us to obtain Q (0.010 ± 0.005) and e (−0.8±0.2) values and to discuss the reactivity of vinyl fluoride in radical chain propagation.

Emulsion polymerization. III. Theoretical prediction of the effects of slow termination rate within latex particles

Abstract: The Smith-Ewart theory predicts that there is an interval during an isothermal homopolymerization when the conversion varies linearly with time. This prediction rests on the assumptions that, during this interval II, the particle number is constant, the monomer concentration in the particles is constant, and the termination rate within the particles is instantaneous, so that the average number of radicals per particle Q is half. In this paper this latter assumption is abandoned. If the termination rate is slow, two or more radicals can coexist in a particle. The termination rate within a particle becomes a function of the particle size because of the decreased probability that two radicals meet for termination in a given time when the volume in which these radicals are located increases. It follows that with increasing conversion the termination rate decreases. Stockmayer's calculations based on this model neglected the variation of particle volume with time, and it was assumed that a steady state of radical concentration in particles exists. In the present calculations these restrictive assumptions were not used. Stockmayer calculated only how Q should vary with conversion. In the present paper several experimentally verifiable consequences of the model are shown. The new calculations show that the interval II conversion-time curve can be represented by the formula At2 + Bt, where B is the Smith-Ewart rate and is proportional to the particle number and the parameter A is independent of the particle number and depends mainly on initiation and termination rates. From A and B and propagation and termination rate constants can be calculated. With the aid of parameters A and B the conversion dependence of molecular weight and of Q can also be predicted for interval II. In the theoretical calculations the distribution of radicals among particles is established. It is shown that for a given value of Q this distribution is unique, independent of the experimental conditions leading to this Q. This distribution was derived solely from kinetic considerations and is analogous to the statistical Poisson distribution. With increasing Q, i.e., with increasing conversion, this distribution broadens. Since each particle grows proportionally to the number of radicals in it, particles must grow at greatly varying rates if there is broad distribution of radicals among them. It follows that the particle size distribution has to broaden with increasing conversion, contrary to predictions based upon the Smith-Ewart model. At present it is not yet possible to predict quantitatively the shape of the conversion-time curve in interval III, the interval following the disappearance of monomer droplets. The reason for this is that the functional dependence of the termination rate constant upon monomer concentration in the particles is not known. However, once the conversion-time curve is experimentally determined, it is possible to calculate from it the interval III values of Q and of molecular weight.

Ordered structures of styrene-butadiene block copolymers in the solid state

Abstract: Several narrow molecular weight distribution block copolymers were prepared by a two-stage anionic polymerization technique. Films cast from these solutions were studied by electron microscopy. Replicas showed that the film surfaces were composed of layered structures with various orientations. Micrographs of ultrathin sections of stained films demonstrate that layered structure occur throughout the film. The widths of the copolymer layer spacings increase with increasing molecular weight and agree quite well with the calculated values.

Morphology of nascent polyolefins prepared by Ziegler‐Natta catalysis

Abstract: The morphology of nascent (i.e., as-polymerized) Ziegler-Natta polymers was studied by optical and electron microscopy and x-ray and electron diffraction. Observations were made on six polyolefins: polyethylene, polybutene, polypropylene, polystyrene, poly-4-methylpentene-1, and polyisoprene. These polymers were synthesized by using conventional techniques by polymerizing the undiluted monomer or monomer–diluent mixtures with a preformed heterogeneous catalyst obtained by reacting a titanium halide and aluminium alkyl. After the reactions were terminated the polymers were subjected to suitable purification treatments and stored in the wet state. Observations in the optical microscope revealed that, in most cases, the polymers is formed as discrete hollow particles with a fibrous texture, but in a few instances, depending upon experimental conditions, it could also form as fibrous sheets or webs. More detailed observations in the electron microscope showed that the polymer is composed of a profusion of fibrils 200–1000 A. in width and of indefinite length. The fibrils themselves have a fine structure as indicated by the presences of lamellae running prependicular to their length. Various interpretations of this appaerent structure are discussed. The x-ray and electron diffraction studies show that the molecular chain axis is oriented prependicular, or nearly so, to the plane of fibril lamellae and suggest that the molecules are folded within the lamellae in a manner analogous to conventional polymer single crystals. As fibril formation is observed under most conditions of polymerization it is considered to be basic to the mechanism of Ziegler-Natta catalysis. It is proposed that the fibrils are formed by the crystallization of polymer chains growing from the active sites on the catalyst surface. The process is likened to root growth in whiskers, new materials being added at the base or root. The detailed mechanism of fibril formation and of the organization of the fibrils into larger structural formations are obscure, but several possibilities are discussed.

Thermally stable polymers from 1,4,5,8‐naphthalenetetracarboxylic acid and aromatic tetraamines

Abstract: Polycondensations of 1,4,5,8-naphthalenetetracarboxylic acid (NTCA) with both 3,3′-diaminobenzidine (DAB) and 1,2,4,5-tetraaminobenzene tetrahydrochloride (TAB) in polyphosphoric acid (PPA) were found to produce soluble polymers which exhibit excellent thermal stabilities. Polymer structures were deduced from infrared, thermal, and elemental analyses of model compounds and polymers. Polymer derived from TAB had a ladder-type structure. Polymers with solution viscosities near 1 or above (determined in H2SO4) were obtained from polymerizations near 200°C., and analysis showed these to possess a very high degree of completely cyclized benzimidazobenzophenanthroline structure. Less vigorous reaction conditions gave polymers with lower solution viscosities which appeared to be less highly cyclized. Low-viscosity polymer was also prepared from DAB and NTCA by solid-phase polycondensation. Some advancements in the solution viscosities of polymers synthesized from DAB in PPA were caused by second staging in the solid phase.

Light-scattering study of polyacrylonitrile solution

Abstract: Light-scattering measurements of polyacrylonitrile (PAN) prepared by aqueous suspension polymerization and solution polymerization were made in both dimethylformamide (DMF) and γ-butyrolactone (γ-BL). The following relations between the intrinsic viscosity [η] (in deciliters per gram) and the weight-average molecular weight were obtained: [η] = 3.35 × 10−4 Mw0.72 (in DMF at 30°C.) and [η] = 4.00 × 10−4 Mw0.69 (in γ-BL at 30°C.). The relation in DMF is in agreement with the results of many other researchers, but differs from the results of Bisschops et al. and Peebles. Analysis of the results by the recent viscosity theory reported by Inagaki et al. indicates that the steric factor σ is 2.17 on PAN in both DMF and γ-BL. It is found that the root-mean-square radius of gyration of the chain measured by light scattering 〈S2〉w1/2 (LS) is in good agreement with the root-mean-square radius of gyration of the chain calculated by using the viscosity theory of Inagaki et al. 〈S2〉w1/2 (vis) in both DMF and γ-BL. Relations between the root-mean-square radius of gyration of the chain (in Angstroms) in DMF and γ-BL and the molecular weight were obtained: 〈S2〉w1/2 = 7.94 × 10−2 Mw0.66 (in DMF) and 〈S2〉w1/2 = 2.19 × 10−1 Mw0.57 (in γ-BL). From the estimation of the second virial coefficient A2 and the value of B obtained from viscosity theory, it is found that DMF is a better solvent than γ-BL.

Emulsion polymerization. IV. Experimental verification of the theory based on slow termination rate within latex particles

Abstract: A large body of data shows that the time dependence of conversion fits the equation P = At2 + Bt in the interval where, according to the Smith-Ewart model, the relationship should be linear. For latexes of very small particle size the Smith-Ewart linear relationship (P = Bt) is often observed, and for latexes of very large particle size the conversion was found to be proportional to t2. The experimental value of parameter B was in good agreement with independent theoretical predictions. From A and B the ratio between termination and propagation constants was calculated and was in the 5–200 range. Independent estimates of this ratio give the same order of magnitude. These independent estimates are from the literature and are obtained from the increase in conversion rate at catalyst post-addition during emulsion polymerization or from emulsion polymerization initiated by intermittent irradiation or from homogeneous polymerization in the presence of inert polymers of high viscosity. The conversion–time curves describing the whole conversion process generally have sigmoid shape. The molecular weight is often found to pass through a maximum as the conversion increases. In one experiment this maximum coincided with the calculated maximum in the average number of radicals per particle Q. The variation of experimental molecular weights with conversion accurately followed the theoretical predictions. The deviation from the Smith-Ewart model was often significant. The value of Q was not 0.5, as the Smith-Ewart model requires it to be, but often reached values much larger, as large as 10. The particle size distribution broadened with increasing conversion and became increasingly skew. Numerous data taken from the literature are in good quantitative or qualitative agreement with the theory proposed in Part III and for these data the observed deviations from the Smith-Ewart theory are readily explainable. The new data obtained with styrene, n-butyl methacrylate, and methyl methacrylate are also in quantitative agreement with the new theory. One experiment involving methyl methacrylate is analyzed in great detail. The variation of time, of Q, of molecular weight, of average particle size, and of particle size distribution with conversion are reported. The molecular weight distribution is also calculated from the conversion dependence of molecular weight.